光照在极端干旱区凋落物分解中的作用

Litter decomposition in terrestrial ecosystems is one of the most important ecosystem processes，which plays a critical role in regulating and balance carbon, nitrogen and mineral nutrient cycling and in energy flow. The regulation mechanism of litter decomposition is extremely complex, involving physical, chemical and biological processes, however, it can be summarized as biological factors and non-biological factors. In most ecosystems, biological processes, such as microorganisms carry out mineralization of soil organic matter, plays an important role in the litter decomposition. In arid region, however, rainfall is scarce, solar radiation, especially the intense radiation of ultraviolet, plays more important role in the litter decomposition..At present, the result of photo-degradation on litter decomposition is controversial in some reports. At the same time, research of photo-degradation on plant litter decomposition is relatively lack at extreme arid region. The result of the litter decomposition is great uncertainty in arid and semi-arid ecosystems that was caused by underestimation of litter photo-degradation. Thus, more research project should be carried out in arid regions to obtain certainly and accurately research results. The research results have been proved that the photodegradation caused by ultraviolet radiation is an important driving factor in litter decomposition. Some studies have also indirectly confirmed the effect of photodegradation by ultraviolet-b. However, in most studies, there is no evidence of direct photochemical production of litter decomposition in photodegradation. To reveal the effects of litter photodegradation, the absence of the photochemical production evidence chain is very inconvenient, as well as inconvenient to explain related research results qualitatively. Focusing on above problems, it is important to study the influence of photodegradation on litter decomposition in extreme regions, to accurate identification of photodegradation's contribution to the litter decomposition, and to determine photochemical constituents of litter decomposition. The results will helpful to reveal direct photochemical production in litter decomposition and to illuminate the main factor affecting the litter decomposition process in different ecological systems. Therefore, it would be have important practical significance and scientific values in this project.

在大多数生态系统中，生物过程，例如微生物对土壤有机质的矿化，在凋落物的分解中具有重要作用。然而，在干旱地区，降水稀少。光照，特别是干旱地区强烈的紫外线辐射，在凋落物分解中具有重要作用。目前光照对凋落物分解影响的研究还存在争议。极端干旱地区相关研究也较为少见。对光照引起的凋落物分解估计的不足，可能是造成干旱生态系统凋落物分解研究结果存在较大的不确定性的重要原因。已有的研究结果证实，紫外线辐射引起的光降解是凋落物分解的重要驱动因素。一些研究也间接证实了UV-B的光降解效应。但多数研究中，试验缺乏光降解效应直接产物的证据。产物证据链的缺失对于揭示凋落物的光降解效应，以及相关研究结果的定性阐述带来了很大的不便。针对上述问题，研究光照在极端干旱区凋落物分解中的作用，准确辨识光照对凋落物分解的贡献，揭示干旱区凋落物分解的光化学物质成分，对于确定不同生态系统影响凋落物分解的主要成因具有的重要科学意义。

大多数生态系统中，生物过程在凋落物的分解中具有重要作用。然而，在干旱地区，降水稀少，光照强烈，微生物活动微弱，光照在凋落物的分解中具有重要作用。但目前对于光照是否直接影响凋落物的分解还存在争议。一些研究认为光照直接造成了凋落物的分解，但也有研究认为光照影响其它环境因素造成了凋落物分解的辩护。目前多数光凋落物分解研究中，试验缺乏光降解效应直接产物的证据。产物证据链的缺失对于揭示凋落物的光降解效应，以及相关研究结果的定性阐述带来了很大的不便。针对上述问题，项目选择塔克拉玛干沙漠南缘极端干旱地区，通过自然光照与遮挡、紫外光遮蔽与光化学产物分析等不同实验设计，研究光照在极端干旱区凋落物分解中的作用，揭示干旱区凋落物分解的光化学物质成分，辨识光照对凋落物分解的贡献，阐明光照对干旱区凋落物的分解是否具有直接和主要的作用。项目的研究表明，光照条件下凋落物的质量损失率显著高于黑暗条件和遮挡紫外线条件，例如分解6个月后，花花柴的质量损失为：光照45.43%、遮UV20.03%，黑暗20.06%，差异显著(P＜0.05)。凋落物的光照分解常数k显著高于遮UV和黑暗处理，但遮UV和黑暗条件下的凋落物分解常数k之间的差异不显著。对光化学分解产物的研究表明，地表2cm深度土壤中的过氧化氢的含量显著高于其他深度的土壤过氧化氢含量，且差异达到极显著水平(P<0.01)。0.5cm和5cm深度以下的土壤中过氧化氢含量接近为较少。0.5cm深度的土壤中羟基自由基含量高于2cm及以下的土壤中的羟基自由基含量，且差异达到极显著水平。野外实验也显示土壤表层凋落物的分解速度显著高于土壤深层和不接触土壤的凋落物。以上研究表明，在极端干旱地区，光照确实能够直接影响植物凋落物的分解，土壤是光照产生直接分解作用的重要媒介，光照下的土壤中产生了羟基自由基和过氧化氢，光照和非光照环境，凋落物分解有显著的差异。