秦岭弃耕地植被演替导致的凋落叶质量改变对土壤有机碳组分的影响

Litter is the main input of soil organic carbon (SOC)in terrestrial ecosystem, and its quanlity may affect SOC by regulating microbial metabolism and chemical transformations during humification. In the present project, we will identify the responses of SOC to the changes in leaf-litter quality as a consequence of secondary vegetation succession following agricultural abandonment in the Qinling Mountains. Based on our previous works such as vegetation succession, litter quality and decomposition, we will select three main situations resulted from different quality leaf-litter input during vegetation succession as the follows: 1) dominant species shift in different successional stages, 2) the same species occuring at different successional stages may preduce different quality leaf-litter, 3) mixing leaf-litter materials which includes different diversity levels both in litter species richness and functional traits of leaves (relevant to decomposition rate), may lead to litter quality change. Soils with different litter treatments will be incubated in artificial climate chests. Soil respiration, soil microbial biomass, soil enzyme activity, total SOC and SOC fractions, including microbial biomass carbon, dissolved organic carbon, labile organic carbon, recalcitrant organic carbon, light- and heavy fraction carbon, and their associations with the initial chemical quality traits of litter will be examined. Meanwhile, we will identify the mechanism of SOC fractions in response to leaf-litter quality by analyszing the carbon input (i.e.,litter), release (i.e., respiration) and dynamics in soil (i.e., SOC fractions).This project will yield insight into the mechanism of soil carbon sequestration associated with vegetation succession.

凋落物是陆地生态系统土壤有机碳（SOC）的主要输入源，凋落物质量可能影响微生物代谢、腐殖化过程中的化学转化等进而对SOC产生影响。本项目在前期已完成的秦岭弃耕地植物群落调查、植被演替分析、凋落叶质量及分解等工作的基础上，针对弃耕地植被次生演替导致的凋落叶质量改变（即演替过程中优势种替代、同种植物不同演替阶段凋落叶质量的差异、植物物种多样性和叶功能性状多样性变化），通过添加不同质量凋落叶的控制实验，揭示凋落叶质量的改变对SOC组分（包括土壤微生物量碳、溶解性有机碳、活性有机碳、惰性有机碳、轻组和重组有机碳）的影响，进而从碳输入（凋落叶）、碳释放（土壤呼吸）及土壤碳变化（SOC组分含量及官能团信息）着手，结合土壤微生物及土壤酶活性的分析，揭示SOC组分对输入不同质量凋落叶的响应机理。本研究有望从凋落叶质量这一视角，加深对弃耕地植被演替过程中SOC积累机制的理解。

本项目针对弃耕地植被次生演替导致的凋落叶质量（quality）改变，通过不同质量凋落叶分解的控制实验，探讨凋落叶质量的改变对土壤有机碳（SOC）组分的影响。从碳输入、碳释放及土壤碳变化着手，揭示SOC组分对输入不同质量凋落叶的响应机理。本项目按照任务书的安排，完成了预定目标。主要研究结论如下：.（1）凋落物木质素含量、土壤惰性有机碳（RC）含量均随弃耕地的弃耕年限增加而升高，凋落叶木质素含量与土壤惰性有机碳含量存在显著正相关。说明随着弃耕地植被演替，植被产生的凋落物中难分解成分含量提高；弃耕地恢复过程中土壤RC含量的增加与植被凋落物中难分解组分含量的提高有关。.（2）凋落物分解过程中，草本、灌木、乔木凋落物凋落物的碳含量均呈现下降的趋势。分解一年后，草本、灌木、乔木凋落物的碳释放量分别为82.4%、76.3%、70.3%。凋落物的碳释放量随着样地年限的增加呈显著下降趋势，说明随着弃耕地植被演替，凋落物的碳释放速率减慢。主要原因是随着植被由草本阶段演替到乔木阶段，凋落物的化学品质发生改变从而导致凋落物可分解性下降。.（3）凋落物类型（即草本、灌木、乔木凋落物）对土壤SOC含量、SOC含量的增量有显著影响。不过，对于惰性有机碳和土壤可溶性碳（DOC），添加乔木凋落物、添加灌木凋落物、添加草本凋落物处理下的差异并不显著。凋落物类型对DOC官能团特征（芳香性、分子量和疏水性）产生显著影响。.（4）凋落物物种丰富度对呼吸速率（土壤+凋落物）有显著影响，呼吸速率随着凋落物物种数的增加显著升高。凋落物的物种组成对凋落物的分解速率有显著影响，但凋落物的物种丰富度对凋落物的分解速率没有显著影响。凋落物的木质素含量是影响分解速率的最主要参数。凋落物分解210天、365天，木质素含量能分别解释分解速率49.5%、25.6%的变异。在整体上，凋落物残留量的观测值显著高于基于单个种估算的期望值，说明凋落物混合对凋落物的分解速率产生了非加和效应（non-additive effect）。.（5）分解前期（0-210天），凋落物的物种组成对残留凋落物的DOC浓度和DOC量均有显著影响，但凋落物的物种丰富度对残留凋落物的DOC浓度和DOC量均没有显著影响。凋落物混合对残留凋落物DOC浓度和DOC量的影响表现为加和效应。