利用单体化合物的碳同位素揭示植物凋落物降解机制

Plant litter and soil organic matter represent the largest carbon pool affecting the short-term global cycle. The decomposition of litter makes this terrestrial pool a source of atmospheric CO2. The components in litter are not equal in a sense how easily they can be assimilated by soil microbes: carbon sub-pools of high-quality are readily biologically utilized but those of low-quality are not. In the meantime, the different carbon sub-pools of a certain quality often have a distinct isotopic signature, and thus qualification of the sizes as well as the isotopic changes of these carbon pools provides insights to the response of individual carbon pools to changes of environmental conditons such as temperature and humidity, etc. In addition to the change of d13C of bulk matter of litter residue, the sub-pools of different quality also experienced evolution of carbon pool size and isotope signature during decomposition. ..We plan to perform a series of litterbag and incubation experiments,in order to investigate the litter decomposition, the evolution of sub-pools of different quality in litter and their individual carbon isotope ratios, including bulk organic matter, chemical components (such as amino acids, cellulose, lipids, lignin, etc) and compound-specific biomarkers (such as long chain n-alkanes, alkanols, fatty acids etc), as well as their responses to different climate regimes. The systematic study will enable use to better understand the carbon isotope fractionation in sub-pools due to preferential decomposition, and gain insight into the mechanism of decomposition rate and evolution with time, and establish their responses to temperature and humidity variations, which will help predict the short-term effect on the carbon pool due to global climate change.

植物凋落物(litter)和土壤有机质代表着影响短期全球碳循环中的最大碳库，其分解产生的CO2在全球陆地碳循环中起到非常重要的作用。凋落物中不同化学组成的碳库在生物利用上是不同的，存在着选择性分解，对气候条件（温度和湿度等）的反应也不同。同时其不同有机质组成部分的d13C值也是不一样的。除了总有机质的碳量和d13C随时间变化外，不同的化学组成部分的碳库和它们的d13C在降解过程中也同样要经历着不同的变化。本课题旨在系统性地研究凋落物在土壤表层的降解、不同质量碳库的化学组成和同位素组成的演变，包括总有机质、不同的化学组分（如氨基酸、脂类化合物、纤维素、木质素等）和生物标志物单体的碳同位素变化（如长链烷烃、脂肪醇、脂肪酸等等）。研究优先性分解引起的同位素分馏，探讨降解机制，建立它们和植物类型和气候因素（温度、湿度等）的联系，帮助我们预测由于全球气候变化而对于碳库的短期效应。

植物凋落物(litter)和土壤有机质代表着影响短期全球碳循环中的最大碳库，其不同化学组成的碳库在生物利用上是不同的，存在着选择性分解，对气候条件（温度和湿度等）的反应也不同。我们收集不同的植物叶片，涵盖了不同的植物类型（草本/木本，C3/C4）。放置于南到广东湛江、北至吉林白城、西到宁夏中卫、东到江苏南京等覆盖了不同的气候带，用于研究不同气候条件下凋落物分解速率和对碳同位素分馏的影响；实验室里通过培养箱实验进行验证。. 凋落物除了提供碳以外，也向土壤提供了氮。凋落物产生的氨基酸除了自己矿化（氨化、硝化等)以外，也会影响到土壤里的氮循环。我们选择了丙氨酸和蛋氨酸，利用氮同位素对它们在60%和90%含水量条件下酸性土壤里对硝酸根、铵根和N2O的激发效应。. 在港湾沉积物里面的凋落物分解产物的生物标志物和碳同位素可以用来指示海水的侵入程度。我们对新洋港的沉积物、河水过滤物、沿岸的植被进行了生物标志物和同位素分析。结果表明植物凋落物生物标志物和碳同位素的结合可以被用来指示海水的入侵程度。