不同水分条件下杨树-玉米复合系统凋落物分解特性

为探讨水分变化对农林复合生态系统凋落物分解特性的影响，以河西走廊杨树（Populus）-玉米（Zea mays）凋落物为研究对象，设置正常水分（9200 m³/hm²，对照），轻度干旱胁迫（减少15%，7800 m³/hm²），中度干旱胁迫（减少30%，6400 m³/hm²）3种不同水分处理条件，采用分解袋法研究了不同水分条件下杨树叶和玉米秸秆的质量残留率、分解速率和养分含量变化特征。结果表明：（1）随着干旱胁迫的加剧，两种凋落物的质量残留率均增加，而分解速率降低。经过164 d的分解后，杨树叶和玉米秸秆的质量残留率分别为70.43%-77.49%、63.55%-68.29%。分析表明：水分和时间对各类型凋落物的质量残留率均有极显著的影响（P<0.001），但二者的交互作用不显著（P>0.05）；干旱胁迫显著降低了玉米秸秆的分解速率，但杨树叶的分解速率却只是在中度干旱胁迫下显著降低（P<0.05）。对于不同类型凋落物而言，分解速率表现为玉米秸秆>杨树叶。（2）两种类型凋落物的氮（N）残留率在分解过程中表现为降低的趋势，但随着干旱程度的加大，N的残留率增加，表明水分抑制了N的释放过程。分解164d后，同一类型凋落物不同水分条件下的N残留率均存在显著差异。对于同一水分条件下不同凋落物而言，玉米秸秆的N残留率最低，而杨树叶最高。总的来说，水分降低对干旱区农林复合系统内凋落物的分解和氮元素含量具有显著的抑制作用。

Litter decomposition characteristics of poplar-maize agroforestry system under different water conditions

Litter decomposition plays an important role in the carbon budget and nutrient cycling in terrestrial ecosystems, but the decomposition process and decomposition rate of litters were affected by environmental factors, especially the water condition. However, little attention has been paid to the effect of changing water condition at litter decomposition for the maize-poplar system in arid regions. Here the litters of poplar leaves and maize straws in the Hexi Corridor were selected as research objects, and there were three water treatments including normal water (9200 m³/hm², CK), mild drought stress (irrigation reduced by 15%, 7800 m³/hm²), moderate drought stress(irrigation reduced by 30%, 6400 m³/hm²), which were designed in our experiment. The mass remaining, decomposition rate and nitrogen content for poplar leaves and maize straws were measured and analyzed under different water conditions using decomposing bag method, meanwhile the effects of water changes on the decomposition characteristics of two litter types were analyzed. The results showed that:(1) the mass remaining for two litter types were increasing with increasing drought stress, but the decomposition rates were decreasing. After 164 days of decomposition, the mass remaining for poplar leaves and maize straws litter were 70.43%-77.49%, 63.55%-68.29% under three water conditions, respectively. The analysis indicated that water and time extremely significant affected the mass remaining (P<0.001), but their interactive effects on mass remaining were not significant (P>0.05). Drought stress significantly reduced the decompoation rate of maize straws, but it was only significantly decreased under moderate drought stress for poplar leaves. For the different litter types, the decomposition rate of maize straw was higher than that of poplar leaf. (2) The N remaining of two litter types was decreasing trends in the decomposition process under three water conditions, this showed that the N remaining presented releasing mode in the study period, but the N remaining was increasing with increasing drought stress, it indicated that water reducing significantly inhibited the release process of N for the two litter types. After 164 days of decomposition, the N remaining had significant difference under three water conditions for the same litter, and the decomposition time also extremely significant affected N remaining, but the two interaction has no significant effect on N remaining. For the different litter types, the N remaining for maize straws was minimum and it was maximum for poplar leaves in the same water condition, this showed the N release of poplar leaf was greater than that of maize straw. As a whole, water reducing significantly inhibited the litter decomposition and N release for the two litter types in the agroforestry system in the arid region.