温度变化对干旱区盐渍土壤作物根际碳氮损失的研究

Agricultural soils in Xinjiang region are strongly degraded by salinization and desertification. Salinization and alkalization have a broad range of negative consequences for crops, soil microorganisms, and affect nutrient cycling, water conservation and greenhouse gas emissions. This is especially important considering raising temperatures as they accelerate all negative effects of salinization and alkalization, especially in the rhizosphere of dominant crops. Application of carbon and nitrogen isotopes helps to disentangle and to quantify the element cycles in soil as well as their losses to the atmosphere. The project consists of 3 workpackages including 1) laboratory incubation of soil with plant studies (CO2 emission, nitrogen leaching NH4+, NO3-, DOC, DIC, MBC, MBN), 2) labeling of plants in 14CO2 atmosphere and addition of 13C labeled glucose to soil with 15NO3-, 15NH4+, Glycine-15N; 14C, 13C and 15N will be traced in plant roots, soil, aboveground biomass, 3) field experiments with different fertilization levels and analyzing the soil C, N, MBC, MBC, enzyme activities, water budget, plant biomass in different soil layers and growth periods. All the soil parameters will be measured by root-free soil and rhizosphere separately. Morphology (plant height, leaf length, width) and physiological indexes (chlorophyll content, soluble protein content, leaf area, aboveground biomass, root length, root activity) will be measured in all treatments. All studies will be done on saline and alkaline soils (pH 8, 9, 10) dominating in Xinjiang region and depending on temperature (15℃, 25℃, 35℃). Losses of C and N will be measured in laboratory under field conditions. Based on the combination of laboratory and field experiments with application of C and N isotopes, we will quantify the C and N losses and the responsible mechanisms in the rhizosphere of the main crops by land used and temperature increase in arid land.

干旱地区农业土壤盐渍化问题严重。此项目着重考虑温度对盐渍土壤作物根际C, N的影响并使用碳氮同位素来揭示并量化土壤中的相关元素循环。实验采用新疆地区不同盐碱水平土壤( pH 8, 9, 10) 并于不同温度 (15℃, 25℃, 35℃)下进行。本实验由3部分组成。其包括1）室内非标记实验（测定CO2排放, 土壤碳氮及微生物量碳氮）2）标记实验（加入14CO2或13CO2气体；在土壤中加入13C，14C标记的葡萄糖与15NO3，15NH4+，glycine-15N；14C，13C和15N将在植物根、土壤、地上生物量中测定）3）田间试验(不同施肥水平下测定CO2,N2O,土壤碳氮、微生物量碳氮、酶、土壤水分以及不同生长期的生物量)。其中相应指标将在无根土和根际土分别测定。通过室内实验和田间试验相结合，并应用碳氮同位素技术，定量分析模拟农业土地利用和温度升高对干旱区作物根际碳氮流失的影响。

由于耕地退化和气候变化的影响，为了追踪量化盐碱地的碳氮损失，我们开展了一系列的室内外实验。研究了长期施肥对土壤化学性质的影响；设计了有关不同水肥，不同水肥与有机肥配施的小区实验，进行了控制条件下的室内土壤碳循环实验；研究了不同田间管理下的温室气体排放与土壤碳氮运移循环过程，评估了区域碳平衡与农业可持续发展。我们的研究得出1）土壤对CO2的吸收是半荒漠和荒漠地区碳吸收的重要途径。通过计算得出，在农业田间管理中，用于盐渍土的冬灌和春灌使得由土壤水带走的碳量为0.2 gC m-2yr-1；2）新疆干旱区盐碱土中进行玉米秸秆（茎和叶）还田可以储存约0.1~1.7 kg ha-1yr-1C；3）驱动秸秆分解的微生物主要是原本的叶际微生物群落而不是土壤微生物群落，在秸秆分解过程中叶际微生物群落并未向土壤微生物群落转变；3）土壤CO2被部分的发现固定于可溶性有机碳中。相对于灭菌实验，非灭菌实验中微生物在土壤碳酸钙表面的生长减少了土壤碳酸钙的重结晶。土壤通气状况的下降，也使得重结晶的土壤碳酸钙大大的减少。影响土壤CO2浓度的多种因素（微生物和土壤根的呼吸，土壤含水量等）也是影响土壤碳酸钙的重结晶和的碳酸钙成土过程的主要因素；4）中水肥处理(230 kg N ha-1,475 mm)是盐碱土的最佳田间管理模式,可保持充足的产量和较低的GHGI；5）塔里木河流域盐碱土脆弱生态系统有N2O排放风险,在农业施肥管理中应该尤其得到关注；6）生物炭配合平衡施肥能够实现低碳可持续的农业生产； 7）减施化肥和将矿物肥料与粪肥结合起来是避免农业土壤恶化和增加土壤碳汇的最佳途径；8）提出了一种基于土壤类型的光谱定量反演模型的构建方法及其对不同盐度和各种性质的盐渍土的适用性；9）计算塔里木河流域的20年土壤碳库变化，得出塔里木河流成为碳源（-9.83Tg）；10）利用遥感、气候、经济和社会发展数据追踪了塔里木河流域脆弱生态系统20年来的农业发展，为生态问题和潜在的侵蚀土壤类型，提供了可持续农业发展策略。