保水剂（SAP）是一种应用较为广泛的化学节水材料，能够促进土壤水分增加，改善土壤结构，但 是在频繁干湿交替的环境中，保水剂的长效性及其有效性的影响因素尚不明确。本研究中，土壤中混施不 同用量的保水剂（0%，0.1%，0.2%和0.3%），研究在连续三次失水-复水条件下（T1、T2和T3），保 水剂对土壤结构和水分物理性质的影响效应。结果表明，当土壤处于轻度干旱（T2）和充分灌溉（T3）时， 用量为0.2%和0.3%的保水剂可以提高土壤的供水能力；但在重度干旱（T1）条件下，保水剂反而会降低 土壤的供水能力；且这种变化趋势与保水剂用量呈负相关。保水剂与土壤中的Si-O-Si键、-OH，以及不同 的结晶二氧化硅等矿物胶体之间的物理吸附和化学作用是直接导致干湿交替条件下保水剂持水性能降低的 重要因素之一。与对照相比，保水剂处理组的土壤液相比显著增加了8.8%~202.7%，T1和T2处理尤为明 显，引起土壤气相比显著降低。经历反复的干湿交替过程，尤其当保水剂用量较大时，保水剂处理组会显 著增加>0.25 mm的土壤团聚体和水稳性大团聚体（R_0.25）的含量，减低<0.053 mm的土壤团聚体含量。 保水剂处理组平均重量直径（MWD）和几何平均直径（GMD）的增加，以及分形维数（D）和不稳定团粒 指数（E_LT）数值的下降，说明保水剂可以大幅改善土壤结构的稳定性。综合分析认为，土壤团聚体的分 布和结构稳定性，以及土壤供水能力的改善与保水剂用量、土壤水分状况，以及保水剂和土壤颗粒之间的 相互作用密切相关。

The irrigation method used in winter wheat fields affects micro-environment factors, such as relative humidity (RH) within canopy, soil temperature, topsoil bulk density, soil matric potential, and soil nutrients, and these changes may affect plant root growth. An experiment was carried out to explore the effects of irrigation method on micro-environments and root distribution in a winter wheat field in the 2007–2008 and 2008–2009 growing seasons. The results showed that border irrigation (BI), sprinkler irrigation (SI), and surface drip irrigation (SDI) had no significant effects on soil temperature. Topsoil bulk density, RH within the canopy, soil available N distribution, and soil matric potential were significantly affected by the three treatments. The change in soil matric potential was the key reason for the altered root profile distribution patterns. Additionally, more fine roots were produced in the BI treatment when soil water content was low and topsoil bulk density was high. Root growth was most stimulated in the top soil layers and inhibited in the deep layers in the SDI treatment, followed by SI and BI, which was due to the different water application frequencies. As a result, the root profile distribution differed, depending on the irrigation method used. The root distribution pattern changes could be described by the power level variation in the exponential function. A good knowledge of root distribution patterns is important when attempting to model water and nutrient movements and when studying soil-plant interactions.

Climate change is recognized to increase the frequency and severity of extreme temperature events. At flowering and grain filling stages, risk of high temperature stress (HTS) on rice might increase, and lead to declining grain yields. A regulated cabinet experiment was carried out to investigate effects of high temperature stress on rice growth at flowering and grainfilling stages. Results showed that no obvious decrease pattern in net photosynthesis appeared along with the temperature rising, but the dry matter allocation in leaf, leaf sheath, culm, and panicle all changed. Dry weight of panicle decreased, and ratio of straw to total above ground crop dry weight increased 6-34% from CK, which might have great effects on carbon cycling and green house gas emission. Grain yield decreased significantly across all treatments on average from 15 to 73%. Occurrence of HTS at flowering stage showed more serious influence on grain yield than at grain filling stage. High temperature stress showed negative effects on harvest index. It might be helpful to provide valuable information for crop simulation models to capture the effects of high temperature stress on rice, and evaluate the high temperature risk.