摘要
研究大气氮沉降对青藏高原高寒草甸土壤CH4吸收的影响,对于揭示氮素调节土壤CH4吸收的机制和评价氮沉降增加背景下大气CH4收支平衡至关重要。通过构建多形态、低剂量的增氮控制试验,测定土壤CH4净交换通量和相关土壤理化性质,分析高寒草甸土壤CH4通量变化特征及其主要驱动因子。研究结果表明:自然状态下高寒草甸土壤是大气CH4汇,CH4平均吸收量为(35.40±1.92)μg.m-.2h-1。土壤CH4吸收主要受水分驱动,其次为土壤NH+4-N和NO-3-N含量。NH+4-N抑制CH4吸收,NO-3-N促进CH4吸收;不同剂量氮素输入对土壤CH4吸收影响也不尽相同,低氮处理促进土壤CH4吸收,而中氮和高氮处理抑制土壤CH4吸收。结果显示青藏高原高寒草甸土壤是重要的大气CH4汇,在未来大气氮沉降加倍的情景下CH4汇功能增强,但当氮沉降量增加两倍以上时CH4汇功能将会减弱。
The increase in atmospheric nitrogen（N） deposition caused by human activities significantly changes carbon cycling and the carbon budget in terrestrial ecosystems.Unsaturated soil is a unique biological methane（CH4） sink,accounting for about 5% of all atmospheric CH4 absorption.Alpine meadow is a typical N-limited ecosystem in which the soil microorganisms and plants have adapted to the N poor environment so that long-term slow N input will change the carbon cycle process,structure and function of this fragile ecosystem.Therefore,it is crucial and helpful to explore the mechanisms responsible for the responses of soil CH4 uptake to exogenous N input.In 2007,a multi-form,low-level N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station on the Qinghai-Tibetan Plateau.Three N fertilizers;NH4Cl,（NH4）2SO4,and KNO3 were added at four rates;control（0 kgN · hm^-2 · a^-1）,low N（10 kgN · hm^-2 · a^-1）,medium N（20 kgN · hm^-2 · a^-1）,and high N（40 kgN · hm^-2 · a^-1）.Each N treatment contained three replicates,making a total of 36 plots.During the growing season（May to October）,soil CH4 fluxes were monitored weekly by the static chamber-gas chromatograph technique.Simultaneously to the soil CH4 flux measurements,soil temperature and soil moisture were also recorded at 10 cm depth.In addition,the soil ammonium,nitrate and dissolved organic carbon contents as well as the pH were measured monthly to examine the key driving factors of soil CH4 uptake.The results showed that：（1） N addition significantly changed the soil moisture content.Both low and high levels of N addition tended to consume soil moisture,whereas a medium level of N input was favorable to maintaining soil moisture,which mainly depended on the soil moisture balance of precipitation,soil evaporation and plant transpiration.（2） N addition significantly changed soil NH4^＋-N,but did not affect the soil NO3^--N pool.As the most vulnerable part of the ecosystem to a change in N forms,plants preferentially absorbed NO3^--N rather than NH4^＋-N and added NO3^--N was absorbed more strongly by plants than NH4^＋-N.Therefore,accumulation of soil NH4^＋-N caused by N addition was more significant than that of soil NO3^--N.Nitrogen addition did not significantly decrease the soil pH values.（3） Soil-dissolved organic carbon strongly fluctuated within the growing season.After accumulating over the non-growing season,dissolved organic carbon content was at a maximum in May,and then continued to decrease until October because of microbial consumption.（4） Soil CH4 uptake was mainly driven by soil moisture,followed by soil NH4^＋-N and NO3^--N contents.Ammonium fertilizer addition inhibited soil CH4 uptake,where as nitrate fertilizer promoted it.This research suggests that alpine meadow soils are an atmospheric CH4 sink and that N addition can significantly affect CH4 uptake in the short term.Low N addition can promote CH4 uptake from alpine meadow soil,while medium and high N deposition inhibits CH4 uptake and decreases the atmospheric CH4 sink.The critical level of atmospheric N deposition is about 20 kgN/hm^2·a if the ambient N deposition rate is considered.
出处
《生态学报》
CAS
CSCD
北大核心
2013年第13期4101-4110,共10页
Acta Ecologica Sinica
基金
国家自然科学基金(31070435
41071166
31130009)
中国科学院知识创新工程重要方向项目(Y225017EA2)
国家重点基础研究发展计划项目(2010CB833502
2010CB833501)
中国科学院地理科学与资源研究所"秉维"优秀青年人才基金(2011RC202)
中国科学院战略性先导科技专项(XDA05050600)资助
关键词
大气氮沉降
CH4吸收
土壤氮素
驱动因子
高寒草甸
atmospheric nitrogen deposition
Methane flux
Soil nitrogen
Controlling factors
Alpine meadow
