模拟增温和降水增加对东北典型针阔混交林土壤氮转化的影响

Global climate change has profound effects on biogeochemical processes in forest ecosystems. Warming and precipitation change highly influence soil nitrogen transformations, the key process of forest N cycling. Experimental manipulations of warming and precipitation change in situ are powerful tools that allow for the mechanistic understanding of responses, and elucidation of feedbacks of ecosystems to global climate change. However, experiments of warming and precipitation increase have rarely been conducted in temperate forests in northeastern China, and studies concerning on responses of soil N transformations to warming and precipitation increase in situ are rather lacking. Here, this project will select a temperate coniferous and broad-leaved mixed forest in northeastern China to establish experimental treatments including control (no treatment), soil warming (+2℃ above ambient) by infrared radiator, water addition (ambient +30% of average growing season ambient) and soil warming plus water addition. By applying 15N pool dilution method and in situ 15N labelling technique, the objectives are: 1) to reveal responses of rates of soil nitrogen mineralization and nitrification, dynamics of different nitrogen pools (soil, plants and microbes), and leaching losses of various N forms to warming and precipitation increase; 2) to improve the mechanistic understanding of responses and feedbacks of soil N transformations to global change. This project will help to evaluate characteristics of temperate forest nitrogen cycling and feedbacks to climate change and to reduce uncertainties in modelling and predicting the responses of temperate forest ecosystem under future global climate change scenarios, which is also fundamental for efficient forest management.

全球气候变化将对森林生态系统土壤氮转化过程产生深刻影响。气候模型预估我国东北森林生态系统未来会呈现温度升高和降水增加的趋势。然而，野外原位模拟增温和降水增加实验研究在我国东北温带森林相对匮乏，有关土壤氮转化过程对增温和降水增加交互作用的响应研究尤其不足。因此，本项目拟以我国东北典型温带森林生态系统——针阔混交林为研究对象，通过野外红外辐射器增温和水分添加模拟增温和降水增加，采用15N同位素标记技术，结合野外定位监测和室内培养实验，系统研究土壤氮矿化硝化作用速率，土壤、植物及微生物氮库的变化，以及土壤不同形态氮淋失，旨在揭示森林生态系统关键土壤氮转化过程响应温度升高和降水增加变化的驱动机制，有助于评估温度升高和降水增加情景下我国东北温带森林生态系统氮循环特点及其反馈机制，减少模型模拟和预测全球温带森林对全球变化的响应的不确定性，为科学经营和管理森林生态系统提供理论依据和实践基础。

全球气候变化将对森林生态系统土壤氮转化过程产生深刻影响，气候模型预估我国东北森林生态系统未来会呈现温度升高的趋势。野外原位模拟增温实验研究我国东北温带森林生态系统土壤氮转化过程对增温的响应尤其不足。鉴于此，本项目以我国东北针阔混交林为研究对象，通过野外红外辐射器增温，采用15N同位素标记技术，结合野外定位监测和室内培养实验，系统研究土壤氮矿化硝化作用速率，土壤不同形态氮淋失，以及氮在凋落物、土壤和植物氮库的分配和去向，旨在揭示温度升高对森林生态系统关键土壤氮转化过程的影响。结果表明：1）红外辐射增温能使表层土壤稳定升温2℃，但降低了表层土壤含水量；2）增温处理改变了表层土壤无机氮含量，尤其在生长季末期提高了土壤硝态氮含量；增温在生长季初期显著降低了土壤淋溶水中硝态氮的含量，增加了铵态氮的含量；3）增温降低了不同土层氮转化速率，尤其在深层土壤，增温显著降低了土壤矿化和硝化速率；4）增温降低了植物和土壤中氮回收率，降低了氮在植物和土壤中的分配和去向，增加了森林生态系统氮的淋溶迁出。本项目有助于评估气候变暖情景下我国东北温带森林生态系统氮循环特点及其反馈机制，减少模型模拟和预测全球温带森林对全球变化的响应的不确定性，为科学经营和管理森林生态系统提供理论依据和实践基础。