典型红砂-珍珠荒漠灌丛群落碳通量对降水量变化的响应及其机制

Precipitation in desert regions will change significantly in the future under the climate change backgroud. This will induce far-reaching effects on the carbon cycle of arid regions which is driven by precipitation primarily. To ascertain the characteristics of the effects and related mechanisms is a hotspot in global change research, and is a key scientific issue in deep insight of response and acclimation of carbon balance in desert regions with global climate change. The Reaumuria soongorica-Salsola passerina shurb community is most representative and most widely distributed in typical temperate desert. In this study, controlling experiments of precipitation performed in field and laboratory were performed, and static chamber and eddy covariance technique were adopted to study the response of carbon fluxes of Reaumuria soongorica-Salsola passerina shurb community of the typical temperate desert vegetation in the southeast edge of the Tengger Desert. In the field and laboratory experiments, the precipitation will be controlled in three scenarios: natural precipitation, increasing and decreasing respectively the precipitation. By the experiments, the response of carbon fluxes (soil respiration, autotrophic respiration, heterotrophic respiration, community respiration and gross primary productivity) to the precipitation variations will be determined, and the contribution rate of these carbon fluxes in net ecosystem exchange (NEE) will be determined also. The response mechanisms of C fluxes in desert shurb communities to precipitation variations will be revealed, based on a comprehensive analysis on the synergetic changes of the key biotic factors and abiotic factors with the key process of C exchange caused by variation of precipitation, and on the interrelationship between the carbon exchange process and key biotic factors and abiotic factors. The achievement of this study will provide a reference for predicting the carbon budget changes in desert ecosystem of China under the background of global climate change.

气候变化背景下，地球中纬度荒漠区降水特征将发生显著变化，这势必会对受降水驱动的荒漠区碳循环产生深远的影响。如何揭示这种影响的特征及其机制，是深刻理解荒漠区碳平衡对降水变化的响应与适应迫切需要解决的重要科学问题。本项目拟以我国典型温带荒漠分布最为广泛和最具有代表性的红砂-珍珠灌丛群落为研究对象，通过改进的自动控制降水野外模拟试验和室内模拟试验，采用静态箱法和涡度相关法，量化描述红砂-珍珠群落碳交换过程对降水量变化响应规律；区分并量化碳通量主要组分（土壤呼吸、自养呼吸、异养呼吸、群落系统呼吸和总初级生产力）对降水量变化的响应规律，及其主要组分对群落净交换量（NEE）的贡献率；综合分析碳通量各组分、关键生物和非生物因子对降水量变化的协同响应及其相互关系，初步揭示红砂-珍珠群落碳通量对降水量变化的响应机制。为准确评估和预测全球气候变化背景下我国荒漠生态系统碳收支提供参考。

降水是受水分制约型的荒漠生态系统碳交换过程和碳收支平衡的主要驱动因子。如何揭示这种影响的特征及其机制，仍是尚待解决的重要科学问题。本研究通过增减降水和人工模拟降水试验，量化描述了碳通量对降水事件的响应规律；估算了降水量变化对碳收支的影响，综合分析碳通量、生物和非生物因子对降水量变化的协同响应及其相互关系。主要研究结论：（1）降水事件尺度上，小于3mm的降降水事件对总初级生产力(GEP)无明显影响，而大于3mm的降水事件会显著增加GEP，即固碳速率对降水事件的响应响应阈值约为3mm；碳排放速度对降水事件响应过程相对于碳输入速率更为敏感，对降水事件无阈值要求。小降水事件（小于3mm）增加碳排放速率而对于碳输入无明显影响，最终导致荒漠生态系统净碳排放，碳源效应增强；大降水事件同时增加了碳排放和输入速率，但最终表现为净碳固定增加，碳汇效应增加。（2）季节和年际尺度上，增加和减少降水分别提高和降低了荒漠净碳吸收，但减少降水相对于增加降水对碳收支的影响程度更大，并且这种改变效应随着降水变化持续年限增加而呈增强趋势。。降水量变化持续3年后，仅提高了生物碳库储量，但对土壤碳库影响不大。（3）降水对碳通量的影响机制上，降水事件尺度上，降水量变化导致的土壤水热变化是影响碳通量变化的主要原因；生长季或年际尺度上，降水变化引起的土壤土热、养分和植物群落生物量特征的协同变化是降水变化对碳通量（或碳收支）影响的主要原因，且土壤水分是主导环境因子，各环境因子作用排序为（土壤水分>草本层平均高度>草本株密度>灌木新生枝长度>土壤有机质含量）。本研究有助于深刻理解荒漠生态系统碳收支对降水变化的响应机制，为准确评估和预测全球气候变化背景下我国荒漠生态系统碳收支提供依据。