中国生态农业学报(中英文)

Analysis of historical characteristics of phosphorus nutrient flow in food chain in Changchun area

ZHANG Xiaomeng, WANG Yin, YAN Li, FENG Guozhong, GAO Qiang

2017, 25(8): 1099-1105. doi: 10.13930/j.cnki.cjea.170125

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Abstract:
Phosphorus is an important element of life, whose cycle and transformation are critical in the food chain. With statistical and literature data, the trends and characteristics of phosphorus flow in the food chain in Changchun area were investigated for the period 1993-2013 using the NUFER (Nutrient flows in Food chain, Environment and Resources use) model. The study determined the existing problems, put forward strategies and provided examples of optimal management of phosphorus in the food chain. The results showed that total input of phosphorus in the food chain system in Changchun area increased from 32.6 Gg in 1993 to 113.9 Gg in 2013. In food production, phosphorus flow in animal-derived food increased from 0.7 Gg in 1993 to 2.7 Gg in 2013, and that of plant-derived food dropped from 16.1 Gg in 1993 to 15.7 Gg in 2013. In food consumption, phosphorus flow rate in animal-derived food increased from 0.5 Gg in 1993 to 1.1 Gg in 2013, and phosphorus flow in plant-derived food dropped from 5.0 Gg in 1993 to 4.4 Gg in 2013. In the last two decades, phosphorus accumulation in the form of waste in the food chain increased by 15%, while phosphorus loss via runoff, leaching and erosion increased by 17.6 Gg. Up till 2013, the rate of phosphorus loss in the food chain was 20.2%. The trend in phosphorus use efficiency in various paths of the food chain decreased, in which the phosphorus utilization rate by animals/crops decreased from 94.2%/4.1% to 49.3%/3.8%, respectively. Phosphorus use efficiency in the whole food chain decreased by 20.3%. At the same time, the recycling efficiency of phosphorus gradually reduced. In the last two decades, phosphorus flow of food chain in Changchun area followed the path of "high input, high accumulation, high loss, low efficiency and low recycle". Therefore, it was important to control phosphorus input, reduce phosphorus loss, increase phosphorus recycling in waste and enhance the rate of phosphorus use efficiency in Changchun area.

Effect of straw mulching on soil respiration and its' temperature sensitivity under different crop rotation systems

DING Ruixia, WANG Weiyu, ZHANG Qing

2017, 25(8): 1106-1118. doi: 10.13930/j.cnki.cjea.170078

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Abstract:
Soil respiration is the second largest source of terrestrial carbon (C) flux between the atmosphere and the terrestrial ecosystems. It is critical for regulating global soil C dynamics. As soil temperature and soil moisture would exert stronger effects on soil respiration in the future, a thorough understanding of the response of soil microbes to temperature change can provide a novel method of studying the effects of drought on soil respiration and of predicting drought-induced changes in future terrestrial C cycle. Temperature sensitivity of soil respiration can explain the relationship between soil respiration and soil temperature. The objective of this study was to explore the effects of straw mulch on the linkages between the changes in soil respiration and temperature. The study aimed to lay the basis of C cycle process in agro-ecosystems in Yangling, Shaanxi province. To that end, a 2-year field experiment (October 2012 to September 2014) was conducted to study the linkages under different crop rotation systems. It included two treatments of no straw (NS) and straw mulch (SM) in winter wheat-summer maize rotation and winter wheat-summer soybean rotation systems. Soil respiration rate, temperature, and moisture were analyzed under different crop rotation systems. In addition, the Q₁₀ (with Q₁₀ value as the multiplier in determining soil respiration rate after temperature increase of 10 ℃) was used to determine the effect of soil temperature change on soil respiration. It was noted that SM significantly (P < 0.05) increased soil respiration rate during crop growth period. Mean soil respiration rate and cumulative soil respiration during crop growth period significantly increased under straw mulch (P < 0.01). The order of mean soil respiration rate under various crops was as follows: maize (3.401-4.810 μmol·m^-2·s^-1) > soybean (3.390-3.762 μmol·m^-2·s^-1) > wheat (2.673-3.141 μmol·m^-2·s^-1). Then the order of cumulative soil respiration among different rotations was as follows: wheat-maize[34.68-40.81 t(CO₂)·hm^-2] > wheat-soybean[30.04-33.86 t(CO₂)·hm^-2]. In addition, soil temperature varied significantly (P < 0.05) among different crops. Particularly, soil temperature under wheat-maize rotation system was higher than that under wheat-soybean rotation system during the growth stage of wheat. Soil temperature at 5 cm soil depth in maize field was higher than that in soybean field during the summer of 2014. It was noted that SM treatment was a major regulator of soil temperature — significantly increasing it in winter and then significantly decreasing it in spring and summer. Moreover, mean soil moisture content in the 0-30 cm soil layer was significantly higher under SM treatment than under NS treatment during the dry season. Further, mean soil moisture content in the 0-30 cm layer during wheat growth period varied significantly among different crop rotation systems, which was associated with root characteristics under crop rotation. The mean soil moisture content for the 0-30 cm soil layer during maize growth period was significantly higher than that during soybean growth period. Soil temperature at the 5-10 cm soil layer was positively correlated with soil respiration. However, soil moisture at the 0-30 cm soil layer was not significantly correlated with soil respiration. Changes in soil temperature at 5 and 10 cm soil depths were respectively 64.6%-67.3% and 51.5%-59.6% explained by the variance in soil respiration. In this study, Q₁₀ varied within 1.70-2.01 across different crop rotation systems and was significantly higher under wheat-maize than wheat-soybean rotation system. In addition, Q₁₀ was significantly higher under SM treatment than under NS treatment. Therefore, SM treatment was more advantageous in terms of the ability to effectively reduce temperature sensitivity of soil respiration and to accurately predict soil moisture and soil heat conditions.

Effect of long-term fertilization on soil aggregate formation in greenhouse and farmland conditions in the North China Plain

LIU Zhe, SUN Zenghui, LYU Yizhong

2017, 25(8): 1119-1128. doi: 10.13930/j.cnki.cjea.161060

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Abstract:
The status of soil aggregates is an important soil physical property and the amount of soil aggregates is a critical index for measuring and evaluating soil fertility. Organic fertilizer application is an essential measure for improving soil organic carbon (SOC) content, promoting soil aggregate formation and improving soil structure. A long-term experiment was conducted in greenhouse soil and in farmland soil under three fertilizer treatments in Quzhou County in the North China Plain in order to investigate the effects of different modes of fertilization on the content, distribution and stability of soil water-stable aggregates using the wet-sieving method under different land use types. Results indicated that continuous organic matter application (OM) significantly decreased soil bulk density and significantly increased soil organic matter content, compared with chemical fertilizer application (NP) and mixed organic manure with chemical fertilizer treatment (NPM) in both greenhouse and farmland soils (P < 0.05). This effect was obviously for the 0-10 cm soil layer. The bulk density of the 0-10 cm soil layer under greenhouse conditions with organic fertilize application treatment was 1.17 g·cm^-3, which decreased respectively by 12.0% and 8.6% compared with those under chemical fertilizer and mixed organic manure with chemical fertilizer treatments. The content of organic matter in the 0-10 cm soil layer of greenhouse with organic fertilize application treatment was 54.81 g·kg^-1, which increased respectively by 104.8% and 35.7% compared with those under chemical fertilizer and mixed organic manure with chemical fertilizer treatments. Also the bulk density of soil in the 0-10 cm layer of farmland with organic fertilize application was 1.19 g·cm^-3, which decreased respectively by 8.5% and 7.0% compared with those under chemical fertilizer and mixed organic manure with chemical fertilizer treatments. The contents of farmland organic matter in the 0-10 cm soil layer with organic fertilize application was 22.67 g·kg^-1, which increased respectively by 23.1% and 15.0% compared with those under chemical fertilizer and mixed organic manure with chemical fertilizer treatments. The mean weight diameter (MWD) and geometric mean diameter (GMD) of water-stable aggregates of both greenhouse and farmland soils changed in the following order: OM > NPM > NP. Fractal dimension (D) of water-stable aggregates under OM treatment was lowest while that under NP treatment was highest. Treatments with OM significantly decreased D value in the 0-20 cm soil layer, which effect was most obvious for the 0-10 cm soil layer where soil structure improvement was also very obvious. Compared with farmland soil, changes of soil stability indexes and the effects of aggregate structure were more obvious for greenhouse soil. The most significant correlation was between soil organic matter content and the content of > 0.25 mm soil aggregates, which indicated that the more soil organic matter, the greater stability the soil structure. In conclusion, the application of organic matter not only increased the content of soil organic matter and available nutrients, but also promoted the formation of macro-aggregates and improved aggregate stability. It was an effective measure to improve the stability of farmland soil, which also was good for sustaining soil development, especially for soils under greenhouse conditions in the North China Plain.

Assessment of rural landscape scenario visualization using visual indicators of ecological significance

ZHANG Xiaotong, LIU Wenping, XIAO He, ZHANG Qian, YU Zhenrong

2017, 25(8): 1129-1138. doi: 10.13930/j.cnki.cjea.170032

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Abstract:
It is important to determine the scenario for the identification and summarization of variation patterns, approaches and key elements of future landscape. Landscapes can be simulated by increasing and decreasing some key elements in the classical trial and error method. However, few studies used ecological visual indicators in the simulation of rural landscape development scenarios. Thus in this study, 5 visual landscape indicators of ecological significance (complexity, nature, openness, coherence and imaging) were used to assess rural visual landscape scenarios at village level. These indicators were analyzed in scenario visualization by both expert judgment and objective analysis in GIS. Using both subjective and objective criteria, 4 landscape scenarios were designed — real traditional, ecological protection, agriculture production and leisure tourism. The 4 scenarios were assessed by 46 local peoples, 46 nearby stakeholders and 37 undergraduates/graduates majored in landscape. In the case study, some relations came out certain. Most of the participants had less interest in agriculture production landscape. The participants living close to local locations had more interest in leisure tourism landscape and less interest in ecological protection landscape. The choices were sometimes different between aesthetic judgment toward scenarios only and rational thinking. The background of individuals was a key factor for the differences in subjective judgment towards landscape. The study, based on ecological significance, explored the factors of rural landscape preferences of different stakeholders using visual indication to build a reference for future conditions of rural landscape visualization. In this study, the scenario visualization based on visual indicators with ecological significance was used to effectively determine the changes in rural landscapes. 1) The evaluation process was both objective and subjective because of the visual standard was developed by the difference between landscape supply from objective field mapping and landscape demand from subjective requirements of different stakeholders. However, this was not an absolute value compared with the reference value. 2) 5 visual indicators of ecological significance were used in the evaluation of both landscape supply and demand. 3) The relationship between subjective and objective in terms of visual indicators of ecological significance was a scientifically reasonable basis for visualization of rural landscape scenarios. It was more directly related to management of rural landscape resources in government decision-making departments.

Effects of reduced nitrogen application and intercropping on sweet corn AMF colonization, soybean nodulation and nitrogen and phosphorus absorption

ZHOU Xianyu, TANG Yiling, WANG Zhiguo, WANG Jianwu

2017, 25(8): 1139-1146. doi: 10.13930/j.cnki.cjea.170050

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Abstract:
In order to explore a sustainable pattern of sweet corn production in South China, a field experiment was carried out in Guangzhou over the period of 4 growing seasons—autumn of 2014, spring and autumn of 2015 and spring of 2016. The study investigated the effects of 2 N fertilizer levels[300 kg·hm^-2 (N1, reduced N dose) and 360 kg·hm^-2 (N2, conventional N dose)] and 4 planting patterns[sweet corn/vegetable soybean intercropping with 2:3 (S2B3) and 2:4 (S2B4) line ratios, sole sweet corn (SS) and sole soybean (SB)] on yield of sweet corn and soybean, degree of arbuscular mycorrhizal fungi (AMF) colonization of sweet corn and soybean rhizobia. The results showed that the yield of sweet corn under reduced N application and intercropping treatment was significantly higher than that under monoculture. In spring of 2016, nodule number of soybean under S2B3-N1 treatment was significantly higher than that under S2B3-N2 treatment. In the 4 seasons of the experiment, dry weight of soybean nodule was not affected by reduced N application and intercropping. In 2015, N content and biomass of sweet corn were significantly higher than those under monoculture, regardless of the N application level. In 2015, AMF infection rate of sweet corn under reduced N-intercropping treatment was significantly higher than that under conventional N treatment. In autumn of 2015, phosphorus content of sweet corn under reduced N and intercropping treatment was significantly higher than that under monoculture. In conclusion, the reduction of N input and intercropping with soybean significantly improved N and phosphorus contents, rate of AMF infection, biomass and yield of sweet corn. Intercropping with soybean under reduced chemical N input maintained high yield, increased resource utilization efficiency of sweet corn, and thus it was a practicable pattern for sustainable sweet corn production in southern China.

Characteristics of NO₃^- absorption and utilization in Malus hupehensis Rehd. seedlings under different phosphorus levels

PENG Ling, ZHU Zhanling, CHEN Qian, JI Mengmeng, CHEN Ru, GE Shunfeng, JIANG Yuanmao

2017, 25(8): 1147-1153. doi: 10.13930/j.cnki.cjea.170145

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In recent years, excessive application of nitrogen and phosphate fertilizers has not only wasted fertilizer, but also brought a high potential risk of environmental pollution. In addition, an unreasonable fertilization over the long-term has damaged the physical and chemical properties of soil, including soil porosity and nutrients contents. Therefore, it is crucial for sustainable fruit tree production to promote scientific utilization of nutrient, increase fertilizer utilization rate, reduce eluviation, volatilization and loss of nitrogen. In order to determine the key factors influencing nitrogen utilization ratio under different phosphorus levels, ¹⁵N-labeled tracer and non-invasive micro-test techniques were used to investigate NO₃^- absorption and utilization in Malus hupehensis Rehd. seedlings under different phosphorus levels (0 mmol·L^-1, 1.0 mmol·L^-1, 2.0 mmol·L^-1, 3.0 mmol·L^-1, 4.0 mmol·L^-1, 6.0 mmol·L^-1, 8.0 mmol·L^-1, 12.0 mmol·L^-1, 16.0 mmol·L^-1 H₂PO₄^-). The study aimed to increase nitrogen fertilizer utilization and reduce nitrogen fertilizer loss, which could provide theoretical basis for scientific and efficient utilization of phosphate fertilizer in apple orchard. The results showed that root length, root surface area and root tip quantity were lower in seedlings under phosphorus deficiency (0-1.0 mmol·L^-1). With the addition of 2.0-4.0 mmol·L^-1 of phosphorus, the biomass of single plant, root length, root surface area and root tip quantity increased over seedlings under other treatments. Also root growth was restrained in seedlings under excess phosphorus (6.0-16.0 mmol·L^-1). The absorption of NO₃^- in M. hupehensis seedlings was significantly different under different phosphorus levels. The non-invasive micro-test technique showed significant absorption of NO₃^- by M. hupehensis seedlings under 3.0-6.0 mmol·L^-1 phosphorus with the highest rate of absorption under 3.0 mmol·L^-1 treatment. While 0-2 mmol·L^-1 and 8.0-16.0 mmol·L^-1 phosphorus applications showed efflux effect of NO₃^-by M. hupehensis seedlings. With the addition of phosphorus, Ndff (percent of nitrogen derived from fertilizer) and nitrogen utilization efficiency initially increased and then decreased. The highest nitrogen use efficiency (42.24%) was observed under the phosphorus treatment of 4.0 mmol·L^-1. Then there was a significant reduction under phosphorus application in excess of 4.0 mmol·L^-1 treatments. Leaf nitrate reductase activity was very low under phosphorus deficiency, but it had significantly higher levels under 1.0-3.0 mmol·L^-1 phosphorus application. There was a marked decrease in leaf nitrate reductase activity when the phosphorus concentration exceeded 4.0 mmol·L^-1. In conclusion, phosphorus level had significant effect on NO₃^- absorption and utilization by M. hupehensis seedlings. Root growth and nitrogen absorption increased with appropriate phosphorus application. With phosphorus overdose, root growth and nitrate reductase activity decreased significantly. This resulted in a decrease in the absorption and utilization of nitrogen. The analysis showed that 3.0-4.0 mmol·L^-1 of phosphorus was beneficial to the efficient growth of M. hupehensis seedlings, nitrogen absorption and utilization.

Effect of combined application of biochar and N-fertilizer on yield and C:N:P ratio of spring wheat

NAN Xuejun, CAI Liqun, WU Jun, LIU Xiaoning, GAO Zhiqiang, Stephen Yeboah, ZHANG Renzhi

2017, 25(8): 1154-1162. doi: 10.13930/j.cnki.cjea.161184

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Carbon (C), nitrogen (N) and phosphorus (P) are the 3 main elements existing in living organisms. It has long been known that C:N:P stoichiometry of consumers and their resources affect both the structure and function of the food web that eventually influence broad-scale processes such as global carbon cycles. The balance of these nutrients can influence plant growth and its stoichiometry in ecosystems. Wheat is one of the most important food crops and wheat production affects global food security. The combined application of biochar and N fertilizer has been reported to be a beneficial agronomic measure, and noted to affect grain yield and C:N:P allocation patterns in wheat. In addition, the study of different N fertilizer and biochar on wheat yield, C, N and P contents and their ratio have been closely linked with nutrient limitation and rational fertilization. In this study, we explored the yield and C, N and P contents and their ratios of wheat under different N-fertilizer and biochar treatments (50 kg·hm^-2 N-fertilizer, 100 kg·hm^-2 N-fertilizer, biochar, biochar combined with 50 kg·hm^-2 N-fertilizer, biochar combined with 100 kg·hm^-2 N-fertilizer and no N-fertilizer or biochar as control). The results showed that different treatments significantly increased wheat straw and grain yield, compared with that of control treatment. Except for the single biochar application, other treatments increased N contents of wheat organs. Biochar combined with different doses of N-fertilizer significantly increased C and P contents of both wheat stem and grain. Biochar combined with 50 kg·hm^-2 N-fertilizer significantly decreased leaf C:N and C:P ratios. Then biochar combined with 100 kg·hm^-2 N-fertilizer significantly reduced stem C:N, C:P and N:P ratios and grain C:N and C:P ratios. In terms of nutrient limitation, N:P ratio in wheat leaf in the study area was 18-23, wheat may be limited by P element. Biochar combined with N-fertilizer significantly increased wheat yield and CNP nutrient contents. At the same time, it decreased wheat C:N, C:P and N:P ratios. From the above, the comprehensive performance of biochar plus 100 kg·hm^-2 N-fertilizer was the best pattern to enhance wheat productivity.

Effect of low iron stress on root growth and iron uptake and utilization of different maize cultivars at seedling stage

LONG Wenjing, GU Tao, WAN Nianxin, PENG Baiyu, KONG Fanlei, YUAN Jichao

2017, 25(8): 1163-1172. doi: 10.13930/j.cnki.cjea.170082

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Iron, as a mineral element necessary for plant growth, has a significant effect on chlorophyll synthesis, REDOX reaction, plant photosynthesis, respiration, and substance/energy metabolism. Low content of effective iron in soil can easily cause iron deficiency (chlorosis) in maize planted in calcareous soils of arid/semi-arid regions. The study of the ability/mechanism of maize to resist low iron stress is critical for solving chlorosis due to iron deficiency. In order to determine the mechanism of resistant maize cultivars to low iron stress at seedling stage, 'Zhenghong 2' (resistant to low iron) and 'Chuandan 418' (sensitive to low iron) were selected for the study. For genetic improvement of the maize varieties resistant to low iron stress, three-leaf maize seedlings were treated with different levels of iron solution with severe (10 μmol·L^-1), medium (30 μmol·L^-1), light (50 μmol·L^-1) iron stress and control (100 μmol·L^-1). Analysis of low iron stress for different maize varieties to low iron showed that the low iron stress had significant effects on root growth and iron uptake of maize seedlings after 14 and 28 days of treatments. As iron concentration decreased, root length, root volume, root vitality, dry matter, iron content, iron accumulation and relative absorption capacity of maize seedlings significantly dropped. However, iron treatment increased root-washing mugineic acid, iron distribution in aboveground parts and iron physiological efficiency of the seedlings. This was one of the most important physiological mechanisms of maize adaptation to low iron stress. Although iron accumulation had significant positive correlation with iron absorption ability of maize, iron absorption capacity under moderate and severe low iron stress in maize cultivars with different low iron resistances were not significant. Thus the difference in iron absorption ability was not the main cause of high iron accumulation in 'Zhenghong 2'. Iron accumulation was also significantly positively correlated with root length, root volume, root dry weight and root activity. Compared with 'Chuandan 418' low iron resistant variety 'Zhenghong 2' had longer root length, larger root volume, heavier root dry weight, higher root vitality and higher iron accumulation. There was a positive correlation between mugineic acid and iron distribution in stems and leaves of maize seedlings. Also a positive correlation was observed between iron physiology efficiency and iron distribution in stems and leaves of maize seedlings. The enhancement of root secretion of mugineic acid improved iron allocation rate in the shoot system of maize so as to improve the efficiency of iron physiology. The rate of increase in mugineic acid was higher for 'Zhenghong 2' under moderate and severe low iron stress and that was the main reason for the high iron physiological efficiency.

Effect of biological disinfestation on soil improvement, Ralstonia solanacearum suppression and tomato growth

WU Chaorong, HUANG Fei, GAO Yang, MAO Yihang, CAI Kunzheng

2017, 25(8): 1173-1180. doi: 10.13930/j.cnki.cjea.170029

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Abstract:
Soil-borne diseases and soil degradation caused by continuous cropping or monoculture restrain the sustainable development of agriculture. Chemical soil fumigation is the most popular method used to control soil-borne diseases in terms of cost and efficacy, but its negative impact on the environment raises a significant concern. Biological soil disinfestation (adding organic materials in soil and mulching for certain time, BSD) is widely used as alternative improvement of degraded soils and in preventing the occurrence of soil-borne diseases. To solve the problems associated with continuous cropping and the soil degradation caused by the intensification of monoculture, the effects of BSD on soil properties, bacterial wilt control and tomato growth were determined in soil incubation and field experiments. There were four treatments in the experiment — the control (CK), BSD with 2% rice bran, wheat bran and tea seed bran. The results showed that different BSD treatments had no significant effect on soil total P and K content, but significantly increased soil temperature, pH, electric conductivity and contents of organic matter, total N, available N and available K. Contrarily BSD treatments significantly reduced soil Eh and the amount of Ralstonia solanacearum in the soil by 97.27%-99.14%. BSD treatments reduced the incidence of bacterial wilt by 29.41%-42.65%, which in turn enhanced tomato plant resistance against the disease. In addition, BSD significantly increased chlorophyll fluorescence parameter F_v/F_m of tomato leaves, but it had no significant effect on net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO₂ concentration. BSD treatments increased tomato yield by 41.41%-56.25%, and the ratio of sugar to acid and soluble sugar content of tomato fruits. Among different organic materials, BSD with wheat bran had the best effect in terms of soil improvement, yield increase and bacterial wilt suppression. In summary, the potential of BSD was promising for the improvement of soil, prevention and control of soil-borne bacterial wilt disease and promotion of tomato growth. Thus BSD was critical for a non-chemical disinfection of cultivated soils.

Analysis of photosynthetic and fluorescence characteristics of low-light tolerant genotype potato under shade condition

LI Caibin, GUO Huachun

2017, 25(8): 1181-1189. doi: 10.13930/j.cnki.cjea.170177

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With constant development of potato cultivation in winter agriculture fields in south China and in relay-intercropping systems in recent years, low light stress has been becoming the emerging limitation to potato development in these regions and it has increasingly gained considerable research attention. In order to explore the effects of low light stress on photosynthetic and chlorophyll fluorescent characteristics along with the distribution of absorbed light energy of low-light tolerant genotype potato, a field experiment was conducted with low-light sensitive potato cultivar 'Lishu 6' and low-light tolerant potato cultivar 'Zhongshu 20'. The experiment consisted of a shade treatment using black net that can filter 70% of sunlight (T) and then a light treatment with full natural sunlight (CK) after seed emergence. The variations in photosynthesis, light and CO₂ response curves, light induced curve and chlorophyll fluorescence parameters of the different potato genotypes following 30 days of shade treatment were measured. The results following the shade treatment were as follows: 1) the net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), maximum net photosynthetic rate (P_max), light saturation point (LSP) and light compensation point (LCP) under T were significantly lower than those under CK. While P_n, P_max and LSP of 'Zhongshu 20' potato cultivar were relatively higher than those of 'Lishu 6' potato cultivar, LCP and dark respiration rate (R_d) of 'Zhongshu 20' potato cultivar were lower than those of 'Lishu 6' potato cultivar. 2) The parameters of CO₂ response curve were not significantly different between the shade and control treatments, but 'Zhongshu 20' potato cultivar had higher maximum carboxylation rate (V_cmax), higher maximum electron transportation rate (J_max) and lower CO₂ compensation point (CCP) than 'Lishu 6' potato cultivar. 3) Potato cultivar 'Zhongshu 20' reacted quicker to high introduction rate and performed better in terms of photosynthetic capacity than potato cultivar 'Lishu 6'. 4) Compared with the control (CK), the increases of initial fluorescence (F_o), maximum fluorescence (F_m) and maximum photochemical quantum efficiency (F_v/F_m) were significantly higher in T treatments. Also reductions in actual photochemical quantum efficiency of PSⅡ(ΔF/F_m'), apparent electron transfer rate (ETR) and photochemical quenching coefficient (qP) were significantly higher in T treatments. Furthermore, there was an increasing trend in non photochemical quenching coefficient (NPQ). 5) Compared with the control, the ratios of non-photochemical dissipation (Ф_NPQ) and fluorescence dissipation (Ф_{f, d}) pathways increased remarkably under shade treatment. The ratio of photochemical quenching pathway (Ф_PS_Ⅱ) decreased significantly, making Ф_NPQ as the main pathway of dissipation. After shade treatment, the low-light tolerant potato genotype 'Zhongshu 20' overall performance for NPQ and Ф_NPQ was higher than the low-light sensitive potato genotype 'Lishu 6', suggesting that 'Zhongshu 20' cultivar had more stronger photosynthetic apparatus protective capability. The above comprehensive analysis indicated that low-light tolerance genotype potatoes had relatively higher P_n, lower LCP and CCP, faster light induced reaction rate and higher non-photochemical dissipation capacity under shade conditions compared with that of low-light sensitive potato cultivar.

Hydraulic characteristics of Lycium barbarum L. seedlings under drought stress and re-watering conditions

XU Shengrong, ZHANG Enhe, MA Ruili, WANG Qi, LIU Qinglin, WU Rui

2017, 25(8): 1190-1197. doi: 10.13930/j.cnki.cjea.161081

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Lycium barbarum L. is the main commercial crop across the arid lands in northwestern China, which is drought resistant with various functions, such as soil improvement, soil fertility enhancement. To determine water transport characteristics and increase the potential for agricultural productivity of L. barbarum, we conducted a pot experiment at the agricultural demonstration site in Gulang, Gansu Province (37.09°N, 102.79°E). The experiment consisted of 3 treatments — normal water application (N), moderate drought (M) and severe drought (S). The hydraulics characteristics of the canopy and root, photosynthetic rate (P_n) and stomatal conductance (G_s) were monitored in 2-year-old seedlings of 'Ningqi 1', 'Ningqi 5' and 'Mengqi 1' varieties of L. barbarum during drought stress. The effect of re-watering after drought stress on the hydraulics characteristics of the shoot system was determined in the study. The results showed that hydraulic conductance of canopy, shoot and root gradually declined with increasing drought stress. Also hydraulic conductance of the plant decreased with increasing degree of drought stress and the ratio of root to plant (R_root/R_plant) hydraulic conductance resistance increased the most in 'Ningqi 5'. It was also noted that the canopy equation of xylem embolism vulnerability curve in L. barbarum seedlings and xylem water potential loss of hydraulic conductance was 50% in 'Ningqi 1', significant higher than those in 'Ningqi 5' and 'Mengqi 1'. Also there was a statistically significant correlation (P < 0.05) among specific hydraulic conductance of leaf (K_{l, leaf}) and stomatal conductance (G_s) as well as photosynthetic rate (P_n) of leaf of L. barbarum. The growth of plants after drought stress was largely determined by the ability of root system to absorb water following re-watering after 4 days of drought stress. The recovery of hydraulic conductance was fastest with the most obvious compensation effect of water transportation for 'Mengqi 1' and the slowest hydraulic conductance recovery for 'Ningqi 5'. The results suggested that drought-tolerate characteristics was associated with hydraulic conductance in L. barbarum. Hydraulic sensitivity of root to drought stress reflected a continuous capacity of plant to resist drought. The ability of the root system to recover from drought stress and compensation effect was critical for plant soil water utilization under adverse conditions. It was important to regulate the hydraulic conductance of roots for improvement of soil water use efficiency.

Effect of Bt gene insertion on growth, physiology and gene expression of phosphorus transporter gene of corn after arbuscular mycorrhizal fungi colonization

ZHONG Wang, ZENG Huilan, WANG Jianwu

2017, 25(8): 1198-1205. doi: 10.13930/j.cnki.cjea.170065

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Bt (Bacillus thuringiensis)-corn root can exudate insecticide active Bt protein and persistent toxin in soils which can affect symbiotic relationship between corn and arbuscular mycorrhizal fungi (AMF). In this paper, two Bt-corn varieties '5422Bt1' (Bt11) and '5422CBCL' (Mon810), and one conventional corn variety '5422' were used to explore the difference between Bt and non-Bt varieties with Funneliformis mosseae inoculation and non-inoculation treatments. The colonization of AMF, phosphorus transporter gene expression, growth and nutrients contents were measured after 50 d and 80 d of inoculation. The results showed that AMF colonization of Bt-corn varieties '5422Bt1' and '5422CBCL' were significantly higher than that of the conventional variety '5422' at 50 d and 80 d after treatment, which increased by 13.54% and 11.24% at 50 d and then by 9.83% and 6.70% at 80 d, respectively. There was no significant difference in phosphorus transporter gene expression between inoculation and non-inoculation for Bt-corn varieties at 50 d. The height of '5422' under inoculation treatment was significantly higher than that of '5422Bt1' and '5422CBCL' at 50 d. Dry weight of '5422Bt1' under inoculation treatment was significantly higher than that of '5422CBCL' at 50 d. The root length, root surface and root volume of '5422Bt1' were significantly higher than those of '5422' and '5422CBCL' under non-inoculation treatments at 80 d. Bt gene insertion affected nitrogen concentration of the two Bt-corn varieties ('5422Bt1'and '5422CBCL') at the two sampling times. As compared with conventional corn variety, the two Bt-corn varieties needed more nitrogen and phosphorus to synthetize Bt protein. There were significant differences among the responses of three corn varieties to AMF inoculation. F. mosseae inoculation significantly increased nitrogen absorption of'5422Bt1' and '5422CBCL' at the two sampling times (50 d and 80 d). In conclusion, the effect of Bt-gene insertion and AMF inoculation on growth and nutrient utilization of Bt-corn was mainly dependent on its transformation event.

Effect of leaf area index change on evapotranspiration and water yield in northern China

LIU Yibo, HU Zhenghua, LI Qi, ZHANG Xuesong, ZHANG Qi

2017, 25(8): 1206-1215. doi: 10.13930/j.cnki.cjea.170103

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Abstract:
There has been growing evidence that leaf area index (LAI) has changed in many parts of northern China, including northeast (NER), north (NR), northwest (NWR) and Huanghuaihai (HHH) regions. Changes in LAI can alter hydrologic cycle by regulating matter and energy cycles. However, the effects of the changes in LAI, particularly for afforestation/reforestation, on the hydrologic cycle have remained controversial. Better understanding on how the changes in LAI affect evapotranspiration (ET) and water yield has implications for ecohydrology, and regional and national afforestation/reforestation policies. In this study, we used satellite-derived LAI dataset and process-based ecosystem model (Boreal Ecosystem Production Simulator, BEPS) to examine how changes in LAI affect annual ET and water yield in northern China during the period 2000-2014. Firstly, LAI dataset was used to assess linear trends in LAI per pixel. Secondly, increasing and decreasing trends in LAI were removed on per-pixel basis by detrending LAI. Thirdly, we used the BEPS model along with the original and detrended LAI datasets to conduct two model simulations — one with original LAI (i.e., with increasing and decreasing trends in LAI) and one with detrended LAI (i.e., without trends in LAI). Finally, the two model simulations were conducted to assess the effects of increasing and decreasing LAI on terrestrial ET and water yield in northern China. Results showed significant trends in LAI for 20.2% of area of northern China, with increases and decreases in area accounted for 18.8% and 5.5%, respectively. Annual mean LAI averaged at the regional scale significantly increased for NR (0.001 4 a^-1, P < 0.05) and NWR (0.004 7 a^-1, P < 0.001). Temporal trends in LAI were not significant for NER and HHH. Two model simulations driven by original and detrended LAI, respectively, showed that the effects of the changes in LAI on terrestrial ET and water yield varied with spatial scale. At pixel scale, an increase in LAI increased annual ET but decreased water yield or weakened increase in water yield. However, a decrease in LAI decreased ET and increased water yield or weakened decrease in water yield. At regional scale, increase in LAI had positive effects on annual ET, but negative effects on water yield. Annual ET averaged at regional scale significantly increased in NR (3.5 mm·a^-1, P < 0.000 1) and NWR (2.1 mm·a^-1, P < 0.05). The difference in annual ET between the two simulations exhibited significant increase in the trends in all the 4 regions. Difference in water yield between the simulations with original and detrended LAI had decreasing trends for NWR (-0.95 mm·a^-1, P < 0.000 1), NER and NR (-0.38 mm·a^-1, P < 0.000 1) and for HHH (-0.11 mm·a^-1, P < 0.001). Future studies on the effects of the changes in LAI on hydrological cycle should account for feedbacks of the changes in ET and other biophysical properties (e.g., albedo) to the climate. Given the negative effects of increasing LAI on water yield and the water crisis in northern China, afforestation efforts should perhaps focus on southern China.

Using remote sensing to extract and correct irrigation data during early cotton growth stage

LIU Huanjun, MENG Linghua, QIU Zhengchao, ZHANG Xinle, YIN Jixian, XU Mengyuan, YU Wei, XIE Yahui

2017, 25(8): 1216-1223. doi: 10.13930/j.cnki.cjea.170118

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Abstract:
Vegetation index is affected by background soil, especially in the early stage of crop growth. When vegetation cover is low, the effect of background soil is very obvious. In order to improve the precision of remote sensing (RS) monitoring on crop growth in the early growth stage, it is necessary to eliminate the effect of background soil moisture due to irrigation on normalized difference vegetation index (NDVI). Agricultural irrigation districts have failed to develop an effective method to eliminate difference in NDVI change, which has in turn hindered efforts to limit the effect of irrigation on NDVI. Thus, in order to increase the accuracy of RS monitoring of crop growth at early stage, this study explored the effects of difference in soil moisture information between irrigated and non-irrigated cotton field on NDVI. Two cotton plots in San Joaquin Valley in California (US) were selected as the research area. Day of Year (DOY) 174 was determined as the critical phase at early growth stage of cotton for the extract of irrigation data through band reflectance, NDVI analysis of cotton field for 2002. Based on RS images, NDVI, normalized difference water index (NDWI), soil adjusted vegetation index (SAVI) and modified soil adjusted vegetation index (MSAVI) of irrigated and non-irrigated pixels were calculated. Also the relationships between NDWI and different vegetation indexes (VIs) were analyzed, and the two methods[the standard deviation of the NDWI method (STD_WI) and irrigation line extraction method (based on relationship between NDVI and NDWI of irrigation and non-irrigation pixels, IR_L)] were used to extract the irrigation data. Then the accuracies of different methods were compared to determine the optimum extraction method of irrigation information. The IR_L method was next used to extract irrigation data and correct the NDVI of irrigation pixels in the early stage of cotton to improve monitoring accuracy of cotton growth. The results showed that difference in NDVI between irrigation and non-irrigation pixels was as high as 12% in the early growth of cotton. There was an extremely significant linear correlation between NDVI and NDWI of both irrigation and non-irrigation pixels, with coefficients of determination greater than 0.80. Compared with STD_WI method, IR_L method had a higher accuracy and with a precision greater than 88%. Through IR_L model correction, the accuracy of irrigation linear regression model was as high as 0.95. With this, correction effect of irrigation was obvious and the difference in NDVI between irrigated and non-irrigated pixels dropped to 2%. Thus in this study, NDVI with irrigation data was corrected, the effect of irrigation on NDVI eliminated while the effect of background soil moisture reduced. Finally, the study reflected the true vegetation data, obtained accurate remote sensing monitoring of cotton growth at the early growth stage and provided convenient monitoring method of crop growth via remote sensing. Moreover, it promoted accurate irrigation towards saving water resources.

Hyperspectral estimation of rice pigment content based on band depth analysis and BP neural network

ZHENG Wen, MING Jin, YANG Mengke, ZHOU Siwei, WANG Shanqin

2017, 25(8): 1224-1235. doi: 10.13930/j.cnki.cjea.170112

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Abstract:
The estimation accuracy of plant pigment content is low under higher pigment content since conventional vegetation indices tend to be less sensitive to the variance of pigment content. In order to improve estimation accuracy of rice carotenoid and chlorophyll contents with canopy reflectance during all growth stage, we explore the feasibility and effectiveness of combining the band depth analysis (BDA) and back propagation (BP) neural network to solve the problem of vegetation index saturation. With canopy hyperspectral data (400-750 nm), four band indices — band depth (BD), band depth ratio (BDR), normalized band depth index (NBDI) and band depth normalized to band area (BNA) — were calculated via continuum removal processing. Principal component analysis (PCA) was used to reduce the dimensions of hyperspectral data, and determined 10 principle components, which were introduced into BP neutral network as input variables. In the study, canopy hyperspectral reflectance and pigment content measurements were conducted in Meichuan Town of Hubei Province, China. Eight treatments of nitrogen fertilization (0, 45, 82.5, 127.5, 165, 210, 247.5 and 292.5 kg·hm^-2) were applied to generate various indices of vegetation and pigment content. Linear and nonlinear regression models were used to quantitatively analyze the vegetation indices and measured pigment content. In addition, coefficient of determination (R²) and root mean square error (RMSE) were used to evaluate the models. All the hyperspectral indices were comparatively analyzed. As a result, BDA showed the differences in spectral absorption characteristics and revealed more potential information to enhance spectral difference. The estimation model combined band index BD and BP had the highest estimation accuracy for carotenoid content in rice leaves, with R² = 0.61 and RMSE = 0.128 mg·g^-1; while the estimation model combined band index BNA and BP had the highest estimation accuracy for chlorophyll content in rice leaves, with R² = 0.73 and RMSE = 0.343 mg·g^-1. Further comparison between BDA & BP models with the best regression model for vegetation index indicated that BP neutral network model based on BDA provided a better solution to saturation problem and a higher estimation precision of rice leaf pigment content.

Sources, migration and transformation of nitrate in Fuhe River and Baiyangdian Lake, China

LIANG Huiya, ZHAI Deqin, KONG Xiaole, YUAN Ruiqiang, WANG Shiqin

2017, 25(8): 1236-1244. doi: 10.13930/j.cnki.cjea.161187

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Abstract:
The increasing urban sewage discharges have severely threatened the quality of surface water. Baiyangdian is the largest freshwater lake in the North China Plain, which plays a critical role in flood control, micro-climate regulation, improvement of ecological environment and development of aquaculture and tourism in the region. However, with rapid economic development and population growth in recent years, its' pollutant load has increased rapidly. Also eutrophication of water body caused by high nitrate concentration has created a significant problem. Excessive nitrate in water not only causes eutrophication, but also threatens human health. Therefore, the investigation of the sources of nitrate pollution and transformation in Fuhe River-Baiyangdian Lake area is important in order to provide a reference for the management of eutrophication and water quality. For the period 2008-2016, the variation in hydrochemical type as well as sources of nitrate in Fuhe River and Baiyangdian Lake surface water systems were investigated by the combined use of hydrochemistry with isotopes (d²H, d¹⁸O and d¹⁵N). The environmental behavior of NO₃^- along the river was evaluated using Cl^- as the standard reference to estimate the dilution and mix of different waters in the study area. 1) If variation in measured NO₃^- was similar to calculated NO₃^-, then it implied that dilution and mix effects were the controlling factors for the change in NO₃^- in the river. 2) If the measured NO₃^- was smaller than calculated NO₃^-, it implied that apart from dilution and mixing, other processes such as biochemical reactions influenced the change in NO₃^-. 3) If also measured NO₃^- was larger than calculated NO₃^-, it implied that there was excess NO₃^- entering the river compared with Cl^-. The results showed that in September 2008, NO₃-d¹⁵N in Fuhe River was higher than 10‰, with a range of 2.07‰-18.49‰ in July 2014. Domestic waste water from nearby villages was the dominant source of nitrate in Fuhe River. However, in June 2009, the range of NO₃-d¹⁵N was -3.7‰-4‰ and discharge of industrial waste water had a significant impact on nitrate concentration in the river in June 2009. In Baiyangdian Lake, the ranges of NO₃-d¹⁵N for September 2008 and July 2014 were 5.8‰-11.7‰ and 3.31‰-12.53‰, respectively. However, the range of NO₃-d¹⁵N for June 2009 was -3.8‰-0.7‰. Domestic and industrial waste water in Fuhe River were the main source of nitrate pollution in Baiyangdian Lake. For 2008-2014, the proportion of Cl^- and SO₄^2-decreased gradually and the discharge of industrial wastewater and domestic sewage was controlled. In 2009, NO₃^- concentration in industrial waste water exceeded 50 mg·L^-1. Then in 2014 and 2016, NO₃^- concentration fell below the standard. The spatial variation in nitrate concentration along the river was mainly affected by dilution, extra input of sewage and denitrification. In June 2011, the variation in nitrate concentration along the river was mainly affected by extra input of sewage. In June 2009, July 2014 and June 2016, denitrification impacted the decrease in concentration of nitrate in Fuhe River when dissolved oxygen (DO) was less than 2 mg·L^-1.

2017 Vol. 25, No. 8