增温对亚热带格氏栲天然林凋落物可溶性有机质数量和结构的影响

Effects of warming on quantity and structure of litter-derived dissolved organic matter in subtropical natural Castanopsis kawakamii forests

凋落物层淋溶析出的可溶性有机质(DOM)是土壤DOM的重要来源,其对气候变暖的响应会影响土壤碳排放和氮周转等森林碳氮循环过程。本研究以格氏栲天然林为对象,依托野外增温实验平台,原位收集凋落物层淋溶析出液,结合紫外可见光谱和荧光光谱分析,探究增温对亚热带常绿阔叶林凋落物层DOM数量和化学组成的影响。结果表明:凋落物层可溶性有机碳和可溶性有机氮含量呈现明显的月变化特征,峰值出现在4月,月均值分别为1.02和0.15 g·m^(-2)。同时,凋落物层DOM具有较高的荧光指数和较低的自生源指数,表明凋落物层DOM主要以微生物来源为主,微生物可利用性较低。凋落物层DOM的主要成分包括类腐殖质酸组分和类色氨酸组分。增温未显著影响凋落物层DOM的含量、芳香性、疏水性、分子量大小、荧光指数、自生源指数和腐殖化指数,表明温度升高未改变DOM的数量和化学组成。增温也未显著影响凋落物层DOM主要成分的相对贡献率,表明温度变化未影响微生物降解作用。总的来说,增温未显著改变亚热带格氏栲天然林凋落物层淋溶液的DOM数量和结构,温度变化对凋落物层DOM向土壤输入的影响较为微弱。

Litter-derived dissolved organic matter(DOM)is an important source of soil DOM,and the response of which to climate warming may change forest soil carbon and nitrogen dynamics,such as soil carbon and nitrogen mineralization.In this study,we conducted a field manipulative warming experiment in natural Castanopsis kawakamii forests.Combined with litter leaching solution collected in the field and ultraviolet-visible and three-dimensional fluorescence spectroscopy analyses,we explored the effects of warming on the content and structure of litter-derived DOM in subtropical evergreen broad-leaved forests.The results showed that litter-derived dissolved organic carbon and nitrogen content exhibited monthly dynamics,with the peak(in April)and the mean monthly content being 1.02 and 0.15 g·m^(-2),respectively.Litter-derived DOM had higher fluorescence index and lower biological index,indicating the microbial-origin of DOM from litter.The litter DOM mainly included humic-like fractions and tryptophan-like substances.Warming did not affect the content,aromaticity,hydrophobicity,molecular weight,fluorescence index,biological index and humification index of DOM,suggesting neutral effect of warming on the quantity and structure of litter DOM.Warming also did not affect the relative contribution of main components in DOM,indicating that the temperature variation exerted no effects on microbial degradation.In summary,warming did not change the quantity and quality of litter-derived DOM in subtropical evergreen broadleaved forests,indicating warming had little effect on litter-derived DOM input to soil.