川南天然常绿阔叶林人工更新后土壤碳库和氮库对氮沉降的响应

Subtropical evergreen broadleaved forest is a world precious vegetation type, which plays an important and unsubstitutable role in environment protection, world carbon cycle balance maintenance and other ecological service functions. Atmospheric nitrogen deposition is continuously increasing due to human activities, and has many deep effects on forest ecosystem. The previous studies on the effects of nitrogen deposition on soil carbon and nitrogen fractions were not systematic, and could not quantify the contribution of litter and fine root decomposition to soil carbon and nitrogen fractions, and as well as the leakage and transference of carbon and nitrogen fractions in soil, thus the accurate estimation of the effects of nitrogen deposition on soil carbon and nitrogen fractions was confined. The methods of field investigation, soil column culture and 15N isotopic technique were used to systematically study the effects of nitrogen deposition on soil carbon and nitrogen fractions content, greenhouse gas emission, formation and decomposition of litter and fine root under natural evergreen broadleaved forest and Sassafras tzumu, Cryptomeria fortunei and Metasequoia glyptostroboides plantations in Southern Sichuan Province. This study may contribute in: 1) estimating the carbon and nitrogen import (nitrogen deposition, carbon and nitrogen of litter and fine root) and export (water soluble carbon and nitrogen and greenhouse gas emission) in soil; 2) firstly discovering the contribution of litter and fine root decomposition to soil carbon and nitrogen fractions, and as well as the leakage and transference of carbon and nitrogen fractions in soil.

亚热带常绿阔叶林是世界上罕见的植被类型，对保护环境、维持全球性碳循环平衡和其它生态服务功能具有不可替代的极重要的地位和作用。由于人类活动导致大气氮沉降输入持续升高，这必将从多方面对森林生态系统产生深远影响。过去有关氮沉降对土壤碳氮组分影响的研究缺乏系统性，且不能量化枯落物和细根分解对土壤碳氮组分的贡献及碳氮组分在土中的淋溶与转化，从而制约氮沉降对土壤碳库和氮库影响的准确评估。为此，本项目拟采用野外定位研究和室内土柱培养相结合，并运用15N同位素技术，系统研究氮沉降对川南天然常绿阔叶林及其人工更新形成的檫木林、柳杉林和水杉林土壤碳氮组分含量、温室气体排放、枯落物和细根形成与分解的影响。这一研究将：1)有助于估算土壤碳氮输入(氮沉降、枯落物和细根碳氮)与输出(水溶性碳氮渗漏及温室气体排放)；2)有望首次揭示枯落物和细根分解对碳氮组分含量的贡献及土壤碳氮组分在土中的淋溶与转化规律。

亚热带常绿阔叶林是世界上罕见的植被类型，对保护环境、维持全球性碳循环平衡和其它生态服务功能具有不可替代的极重要的地位和作用。由于人类活动导致大气氮沉降输入持续升高，这必将从多方面对森林生态系统产生深远影响。天然林更新为人工林后土壤持水性能、抗蚀性、肥力、碳氮组分含量、枯落物归还量和细根生物量降低。大气氮沉降在一定范围内能够增加枯落物的归还量、细根生物量，促进枯落物分解和细根周转，从而提高土壤养分、酶活性、微生物数量及各碳氮组分含量。但过高的氮沉降对枯落物和细根分解具有一定的抑制作用。