Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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Quantifying contributions of slaking and mechanical breakdown of soil aggregates to splash erosion for different soils from the Loess plateau of China
No full textThe information of aggregate disintegration mechanisms during splash erosion is scant. This study was conducted to quantify contributions of the mechanisms of aggregate disintegration to splash erosion. Six soils with five soil textures were used. Soil aggregate stability was determined by the Le Bissonnais (LB) method. Deionized water was used to simulate the combined effect of slaking and mechanical disaggregation, while ethanol was used to estimate the sole contribution of the mechanical breakdown. Simulated rainfall with intensity of 60 mm h(-1) was applied at five fall heights (0.5 m, 1 m, 1.5 m, 2 m and 2.5 m) to achieve different levels of rainfall kinetic energy. The results indicated that slaking caused the most severe aggregate breakdown, and followed by mechanical breakdown, while chemical dispersion in slow wetting with deionized water was the weakest breakdown mechanism. The splash erosion rates due to the effects of slaking and mechanical breakdown increased with an increase in rainfall kinetic energy. The contributions of the slaking (mechanical breakdown) to splash erosion decreased (increased) as rainfall kinetic energy increased. The contribution of mechanical breakdown had a power function relation with rainfall kinetic energy, and had the most significant correlation with RSI (relative slaking index)/RMI (relative mechanical breakdown index). A power and a linear function could be used to describe the relationships between the contributions of mechanical breakdown with rainfall kinetic energy and RSI/RMI, respectively, which could be used to estimate the contribution of mechanical breakdown. The results of this research would be helpful to improving the soil erosion prediction models
Early-spring soil warming partially offsets the enhancement of alpine grassland aboveground productivity induced by warmer growing seasons on the Qinghai-Tibetan Plateau
No full textAims The response of vegetation productivity to global warming is becoming a worldwide concern. While most reports on responses to warming trends are based on measured increases in air temperature, few studies have evaluated long-term variation in soil temperature and its impacts on vegetation productivity. Such impacts are especially important for high-latitude or high-altitude regions, where low temperature is recognized as the most critical limitation for plant growth. Methods We used Partial Least Squares regression to correlate long-term aboveground net primary productivity (ANPP) data of an alpine grassland on the Qinghai-Tibetan Plateau with daily air and soil temperatures during 1997-2011. We also analyzed temporal trends for air temperature and soil temperature at different depths. Results Soil temperatures have steadily increased at a rate of 0.4-0.9 degrees C per decade, whereas air temperatures showed no significant trend between 1997 and 2011. While temperature increases during the growing season (May-August) promoted aboveground productivity, warming before the growing season (March-April) had a negative effect on productivity. The negative effect was amplified in the soil layers, especially at 15 cm depth, where variation in aboveground productivity was dominated by early-spring soil warming, rather than by increasing temperature during the growing season. Conclusions Future warming, especially in winter and spring, may further reduce soil water availability in early spring, which may slow down or even reverse the increases in grassland aboveground productivity that have widely been reported on the Qinghai-Tibetan Plateau
Enhanced iron(III) reduction following amendment of paddy soils with biochar and glucose modified biochar
No full textAlthough biochar application to paddy fields has been widely studied, its effects on Fe(III) reduction have not yet been investigated. Paddy soil slurry and soil microbial inoculation incubation were conducted with unmodified biochar (UMB) or glucose-modified biochar (GMB) additions at different particle sizes. The Fe(II) concentration and pH value were determined regularly, and Fe(III) reducing capacity (FeRC) was evaluated by modeling. Fe(III) reduction potential (a) was increased by 0-1.96 mg g(-1) in response to UMBs addition, and a more remarkable increase in a was related to the decrease of particle size. The dissolved organic carbon of UMBs was responsible for the majority of the biochar reducing capacity. UMBs addition increased the contribution of free Fe and nitrate nitrogen to FeRC, while it decreased that of available phosphorus. Moreover, GMBs led to greater promotion of FeRC than the corresponding UMBs, with an increase in a of 2.9-16% in soil slurry and reduction rate of 13-35% in microbial inoculation incubation. The maximum Fe(III) reduction rate (V-max) with GMBs addition was faster or invariable than UMBs, while the time to V-max (T (Vmax)) was shorter or stable. The effect of GMBs on Fe(III) reduction was less sensitive as GMB particle size increased. Compared with UMBs addition, pH declined remarkably in response to GMBs. These findings suggest that GMBs can effectively stimulate Fe(III) reduction in paddy fields, while simultaneously alleviating the pH increase usually caused by pristine biochar application
Allocation pattern and accumulation potential of carbon stock in natural spruce forests in northwest China
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Background: The spruce forests are dominant communities in northwest China,
and play a key role in national carbon budgets. However, the patterns of carbon
stock distribution and accumulation potential across stand ages are poorly
documented.
Methods: We investigated the carbon stocks in biomass and soil in the natural
spruce forests in the region by surveys on 39 plots. Biomass of tree components were
estimated using allometric equations previously established based on tree height
and diameter at breast height, while biomass in understory (shrub and herb) and
forest floor were determined by total harvesting method. Fine root biomass was
estimated by soil coring technique. Carbon stocks in various biomass components
and soil (0–100 cm) were estimated by analyzing the carbon content of each
component.
Results: The results showed that carbon stock in these forest ecosystems can be as
high as 510.1 t ha-1, with an average of 449.4 t ha-1. Carbon stock ranged from
28.1 to 93.9 t ha-1 and from 0.6 to 8.7 t ha-1 with stand ages in trees and deadwoods,
respectively. The proportion of shrubs, herbs, fine roots, litter and deadwoods
ranged from 0.1% to 1% of the total ecosystem carbon, and was age-independent.
Fine roots and deadwood which contribute to about 2% of the biomass carbon
should be attached considerable weight in the investigation of natural forests.
Soil carbon stock did not show a changing trend with stand age, ranging from
254.2 to 420.0 t ha-1 with an average of 358.7 t ha-1. The average value of carbon
sequestration potential for these forests was estimated as 29.4 t ha-1, with the lower
aged ones being the dominant contributor. The maximum carbon sequestration rate
was 2.47 t ha-1 year-1 appearing in the growth stage of 37–56 years.
Conclusion: The carbon stock in biomass was the major contributor to the
increment of carbon stock in ecosystems. Stand age is not a good predictor of soil carbon stocks and accurate evaluation of the soil carbon dynamics thus requireslong-term monitoring in situ. The results not only revealed carbon stock status and dynamics in these natural forests but were helpful to understand the role of Natural Forest Protection project in forest carbon sequestration as well.</div
干旱下氮素营养对不同穗型小麦苗期耐旱性的影响机制
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水分短缺和土壤贫瘠是限制我国北方植物生长和发育的两个重要的环境因
素，水分和养分既有各自的特殊作用，又互相作用，影响着作物的产量和品质。
本文以两种不同品系小麦（多穗型品种西农 979 和大穗型品种 2036））作为研究
材料，采用人工控制实验方法，分别从小麦根系活力、叶片光合、叶绿素荧光、
活性氧代谢以及抗氧化物质代谢调控等方面，研究了不同水分和养分处理下两个
小麦品种的生理响应及其调控机制，揭示了小麦幼苗耐旱性机理及氮素对缓解干
旱的生理调控机制，可为小麦利用自身的营养遗传特征挖掘其吸收、利用氮素的
生理潜力提供理论依据。获得的主要研究结果如下：
（1）水分与氮素存在着明显的互作效应，重度干旱胁迫和低氮处理都会降
低小麦的生物量、根系总吸收面积、活跃吸收面积、根系活力、氮含量和植株的
氮素积累量，且低氮处理增加了根长和根冠比。相比于低氮和中氮处理，高氮处
理下西农 979 的根系总吸收面积、活跃吸收面积和根系活力显著提高，且分别比
大穗小麦 2036 提高了 11%、14%和 27%。西农 979 植株氮素积累量在中氮和高
氮处理之间无显著差异，但中氮处理下西农 979 的植株氮素积累量比大穗小麦
2036 提高了 13%~62%。低氮处理下，小麦根冠比（R/S）随干旱胁迫程度的增
加而略有增加，其中在高氮处理和中度干旱胁迫下根-冠比表现为最小。相关分
析结果表明，小麦根系的活跃吸收面积、根系活力与植株氮素积累量呈极显著的
正相关关系（P<0.01），和根冠比呈极显著的负相关关系（P<0.01）。在轻度干旱
胁迫下，增加氮素供给能有效提高西农 979 的根系吸收面积和根系活力，但是过
量的氮素供给不利于大穗小麦 2036 根系的生长，表明不同穗型小麦的根系活力
和生长对不同水氮耦合的响应是不同的。通过适宜的水氮耦合调控，有利于良好
小麦根系形态的构建与根系活力的提高，从而提高小麦根系对水分和养分的吸收
能力。
（2）干旱胁迫显著降低了小麦的净光合速率（Pn）、蒸腾速率（Tr）和气孔
导度（Gs），但提高了瞬时水分利用效率（WUE）。此外，干旱胁迫同样导致了
小麦叶片的光化学猝灭系数（QP）、最大光化学效率（Fv/Fm）、光系统Ⅱ（ΦPSⅡ）
的量子产量和表观光合电子传递速率（ETR）的下降，但在氮素（N）的供给有
效缓解了小麦因干旱胁迫导致的光合效率的下降。在干旱胁迫下，氮素供应的适度增加能够减轻光抑制作用从而提高小麦的光合效率，最终提高小麦的抗旱性；
但过量的氮素供应对植物抗旱性的提高并没有显著性作用，甚至对植物的生长产
生了不利的影响。在低氮处理下，西农 979 比大穗小麦 2036 具有更强的抗旱性。
（3）在同样的干旱胁迫条件下，耐旱性品种西农 979 具有较高的抗氧化和
活性氧调控能力。随着氮素浓度的提高，小麦体内活性氧表现出下降的趋势。干
旱胁迫下大穗小麦 2036 根系中的活性氧和膜脂过氧化产物（MDA）都高于西农
979。此外，干旱胁迫下，氮素供应增加能够提高小麦植株中超氧化物歧化酶
（SOD）和酚过氧化物酶（POD）的活性以及抗氧化剂抗坏血酸（ASA）和谷胱
甘肽（GSH）的含量，尤其是在轻度干旱胁迫下，保护酶活性的显著升高有利于
活性氧的清除。低氮处理下，西农 979 小麦的 POD 和过氧化氢酶（CAT）活性
均高于大穗小麦 2036，抗氧化剂 GSH 的含量也较高，表明在相同的干旱胁迫条
件下，耐旱性品种西农 979 具有较高的抗氧化和活性氧调控能力，此外，西农
979 在低氮处理下适应性也比大穗小麦 2036 更强。在没有受到干旱胁迫时，适
量的氮素供给增加可以提高叶片中抗氧化酶的活性；而在遭受干旱胁迫时，适量
氮素供给的增加能够提高酶活性，表明适当的增加氮素供给可以缓解干旱胁迫，
减轻自由基对细胞的伤害。
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侵蚀环境中土壤微生物群落变化特征
No full text土壤微生物作为陆地生物圈的主要组分，驱动土壤有机碳矿化并调节土壤CO2通量，对土壤环境的变化有很强的敏感性。土壤微生物受到土壤温度、土壤水分和有机物质的深刻影响，而这些因素在侵蚀环境中发生强烈的分异。不同的侵蚀环境对土壤微生物的形成和稳定具有显著不同的影响，从而造成土壤微生物及其所调控的土壤碳动态截然不同的响应。加强不同侵蚀环境中土壤微生物的研究对准确理解和估算陆地生态系统CO2通量变化特征及其对变化环境的响应具有重要意义。
黄土区地形破碎，坡地分布广泛，土壤侵蚀强烈。径流和泥沙强烈地影响着侵蚀坡面土壤理化和微生物变化特征；侵蚀发生后发生土壤剖面倒转，出露的亚表土遗留在侵蚀区和沉积区的表面，使得原来掩埋在地下的土壤微生物曝露在自然环境中而发生强烈的变化；植被恢复措施也强烈地影响着水、热、泥沙、有机物在坡面的分布，进而影响着土壤微生物。本研究以长武站为依托，在典型侵蚀发生和治理的王东沟小流域内设置三个试验：1）径流小区试验：包括陡坡坡面上、中、下三个坡位，比较侵蚀坡面上不同坡位土壤微生物群落的变化特征；2）植被措施试验：比较侧柏林地和白羊草地两个半干旱区典型植被恢复措施对侵蚀坡面上土壤微生物群落的影响；3）模拟土层试验：比较对照和出露两个剖面，模拟底土出露对不同土层（表土：0–20 cm、亚表土：20–60 cm和深层土：60–100 cm）土壤微生物群落的影响。围绕土壤微生物开展以下三个方面的研究：1）描述不同侵蚀条件（陡坡坡位、植被措施及底土出露）下土壤微生物群落的变化特征；2）识别侵蚀条件下土壤微生物群落变化的影响因素；3）构建侵蚀环境中微生物群落与土壤呼吸的关联。测定指标包括土壤微生物多样性、群落组成、酶活性、土壤呼吸及其温度敏感性（Q10）、土壤碳氮组分、根系生物量和土壤温度、土壤水分等。
主要结果如下：
1）细菌多样性在中坡位和下坡位显著高于上坡位，而真菌多样性在坡位间无显著差异。细菌β-变形菌纲（贫养菌）在中坡位和下坡位分别比上坡位减少25.3%和20.7%，而酸杆菌纲（富养菌）增加31.5%和35.8%。真菌群落组成由上坡位的以伞菌纲（贫养菌）为主（相对丰度23.7%）变为下坡位的以被孢霉目（富养菌）为主（相对丰度35.3%）。β-葡萄糖苷酶活性沿坡位向下降低，β-木糖苷酶和纤维二糖水解酶活性在中坡位提高，全部酶活性在下坡位最低。土壤水分、根系生物量及碳氮底物是坡位间土壤微生物群落差异的影响因素。
2）不同坡位细菌多样性（香农指数）在上坡位林地显著大于草地，在中坡位二者接近，在下坡位草地显著大于林地。草地变形菌门在各坡位均显著高于林地（15.0%，18.7%和9.7%）；草地酸杆菌在上中坡位低于林地（31.1%和29.6%），而在下坡位无显著差异。β-葡萄糖苷酶活性在上坡位草地大于林地，而在中坡位和下坡位都表现为林地大于草地；纤维二糖水解酶活性在上坡位林草地一致，在中坡位草地大于林地，而在下坡位林地大于草地。土壤温度和碳氮底物是影响林草地之间土壤微生物群落差异的主要因素。
3）与原位相比，底土出露之后细菌群落主要表现为相对丰度的变化，真菌群落几乎无显著差异，且不同土层之间细菌群落的响应随土层深度而增加。出露土壤与原位土壤之间细菌群落组成在表层无显著差异；亚表土和深层土出露之后变形菌和放线菌内的富养群组增加，而贫养的热孢菌和硝化螺旋菌群组降低。细菌多样性在深层土显著增加，细菌群落结构在深层土达到差异显著。土层出露增加了亚表土β-木糖苷酶和纤维二糖水解酶活性和深层土β-葡萄糖苷酶活性。土壤矿质氮（亚表土）、矿质氮和DOC（深层土）是影响出露土壤和原位土壤间细菌群落组成差异的主要因素。
4）侵蚀坡面上沿着坡面向下，草地土壤呼吸显著增加了49.1%，Q10降低了13.2%。土壤呼吸与细菌丰富度和多样性呈显著正相关，而Q10与富养菌（酸杆菌纲、被孢霉目）负相关，与贫养菌（变形菌纲、伞菌目）正相关。侧柏林地和白羊草地虽然具有不同的侵蚀强度，但具有类似的呼吸和Q10。NO3-N与鞘氨醇单孢菌、芽球菌属、红色杆菌属呈正相关，且与Q10呈正相关；同时，NO3-N与红色杆菌属及纤维二糖水解酶活性呈正相关，且与草地土壤呼吸正相关，与Q10负相关。由于较少的微生物数量、较低的酶活性，底土出露之后的亚表土和深层土具有相对于表土显著降低的土壤呼吸（38.5%和33.9%）及Q10（21.8%和24.1%）。变形菌、放线菌、子囊菌中的富养菌群（芽球菌、微小杆菌和突脐蠕孢属、Pyrenochaetopsis属）直接与土壤呼吸和Q10正相关，而这些菌又都与参与碳循环的酶活性正相关。
主要结论:
1）陡坡不同坡位微生物群落组成由上坡位贫养菌为主转变为下坡位富养菌为主。相比侵蚀较弱的草地，较强侵蚀条件下林地微生物群落的空间变异较弱，富养菌更少，贫养菌更多。
2）相比真菌群落，细菌群落受土层出露的影响较大，这可能是由于真菌群落自身的内稳态机制。相比对照土壤，出露之后的土层具有更多的富养细菌，且侵蚀强度越大对微生物的影响越大。
3）通常富养微生物与较高的呼吸速率和较低的温度敏感性成正相关，而贫养微生物与较低的土壤呼吸速率和较高的温度敏感性成正相关。
上述结果对深入理解不同侵蚀环境下土壤微生物变化的影响机制以及准确估算区域CO2通量变化具有重要意义。<br /
硫化氢在植物中的生理功能及作用机制
No full text硫化氢(H2S)是继一氧化氮(NO)和一氧化碳(CO)之后第3个气体信号分子, 在植物体内参与许多重要的生理活动, 能 够促进植物光合作用和有机物的积累, 缓解各种生物和非生物胁迫并促进植物生长发育。该文综述了植物体内H2S的物理 化学性质、产生机制、主要生理功能和作用机制以及与其它信号分子的互作关系, 并展望了H2S信号分子的研究前景。</p
Drip irrigation with film mulch improves soil alkaline phosphatase and phosphorus uptake
No full textPhosphorus (P) is essential for various metabolic activities in plants and plays an extremely important role in crop development, yield and quality. Organic P fertilizers can provide sustainable P and maintain agroecosystem health; however, the uptake of soil organic P by plants is significantly influenced by soil phosphatase activities. The objective of this study was to quantify the effects of different layout measures (film covering, drip irrigation line density, and irrigation lower limits) in drip irrigation with film mulch on the soil phosphatase activity, culturable microorganism populations and crop growth and yield in a greenhouse. The results show that the greatest levels of soil alkaline phosphatase activity were observed with an irrigation lower limit of 80%, a field capacity of 50%, and film mulch covering but were relatively insensitive to the drip irrigation line density. Soil alkaline phosphatase activity was also significantly correlated with the root growth and culturable microbial populations. Specifically, soil alkaline phosphatase activity was positively correlated with the actinomycete population and root activity but negatively correlated with root volume and root area. These results can be used to improve crop production in greenhouse conditions in China. (C) 2017 Published by Elsevier B.V
Impacts of natural polymer derivative neutral polysaccharide Jag S and cationic hydroxypropyl polysaccharide Jag C162 on rainfall infiltration on an experimental loess hillslope
No full textDeveloping effective measures to improve soil structure and increase soil infiltration in the Loess Plateau located in arid and semiarid areas is important for soil and water conservation. Simulated rainfall experiments were conducted to determine the effects of two new natural polymer derivatives, namely neutral polysaccharide (Jag S) and cationic hydroxypropyl polysaccharide (Jag C162), on rainfall infiltration and their underlying mechanisms. The proportions of different sizes of water-stable soil aggregates were analyzed after spraying four different concentrations (0, 1, 3, and 5 g m(-2)) of Jag S and Jag C162 under rainfall intensities of 1, 1.5, and 2 mm min(-1) and a slope gradient of 15 degrees. Treatments with Jag S and Jag C162 significantly improved the rainfall infiltration rates (IRs) compared with the control. Moreover, applying 1 and 3 g m(-2) Jag S effectively increased the IRs by 22.81% and 13.69%, respectively. Treatment with Jag C162 also increased the rainfall IRs by 39.47%, 46.59%, and 46.50%. Furthermore, the content of >0.25 mm water-stable soil aggregates increased from 27.19% to 90.42% before rainfall and from 9% to 50% after rainfall. Compared with Jag C 162, treatment with Jag S was less effective on improving rainfall infiltration and aggregate content. In particularly, application of 5 g m(-2) Jag S improved the soil aggregate content but weakened rainfall infiltration because of the higher viscidity and consistency of the Jag S solution. Overall, spraying appropriate amounts of Jag C162 and Jag S on the loess slope surface can increase the water-stable soil aggregate content, resulting in improved rainfall infiltration and reduced soil erosion. Thus, application of two new natural polymer derivatives is a possible alternative conservation practice in the Loess Plateau
Soil Moisture Availability at Early Growth Stages Strongly Affected Root Growth of Bothriochloa ischaemum When Mixed With Lespedeza davurica
No full textRainfall is the main resource of soil moisture in the semiarid areas, and the altered rainfall pattern would greatly affect plant growth and development. Root morphological traits are critical for plant adaptation to changeable soil moisture. This study aimed to clarify how root morphological traits of Bothriochloa ischaemum (a C-4 herbaceous species) and Lespedeza davurica (a C-3 leguminous species) in response to variable soil moisture in their mixtures. The two species were co-cultivated in pots at seven mixture ratios under three soil water regimes [80% (HW), 60% (MW), and 40% (LW) of soil moisture field capacity (FC)]. At the jointing, flowering, and filling stages of B. ischaemum, the LW and MW treatments were rewatered to MW or HW, respectively. At the end of growth season, root morphological traits of two species were evaluated. Results showed that the root morphological response of B. ischaemum was more sensitive than that of L. davurica under rewatering. The total root length (TRL) and root surface area (RSA) of both species increased as their mixture ratio decreased, which suggested that mixed plantation of the two species would be beneficial for their own root growth. Among all treatments, the increase of root biomass (RB), TRL, and RSA reached the highest levels when soil water content increased from 40 to 80% FC at the jointing stage. Our results implied that species-specific response in root morphological traits to alternated rainfall pattern would greatly affect community structure, and large rainfall occurring at early growth stages would greatly increase their root growth in the semiarid environments