藏北高原高寒草甸生产力对不同幅度增温的响应

摘要

为了探讨植被指数、地上生物量和总初级生产力对增温的响应是否会随着增温幅度而发生变化,2013年6月底在藏北高原高寒草甸进行了两个梯度的野外增温试验.2013-2014年的生长季节(6-9月)利用农业多光谱相机获取归一化植被指数(normalized difference vegetation index,NDVI)、归一化绿波段差值植被指数(normalized green difference vegetation index,GNDVI)和土壤调节植被指数(soil adjusted vegetation index,SAVI)三种植被指数.基于NDVI和气象数据模拟了地上生物量(aboveground plant biomass,AGB)和总初级生产力(gross primary production,GPP).结果表明:1、2013-2014年低幅度和高幅度的增温分别显著增加了空气温度(air temperature,Ta)1.54℃和4℃,同时分别显著增加了饱和水汽压亏缺(vapor pressure deficit,VPD) 0.13和0.31 kPa;2、在三个增温处理间,GNDVI,AGB和ANPP并没有显著差异;3、高幅度的增温显著减少了23.3％(-0.06)的NDVI,而较低增温幅度并没有影响NDVI.低幅度和高幅度增温分别显著减少了19％(-0.04)和27.4％(-0.05)的SAVI,同时分别减少了24.2％(0.21 g Cm-2d-1)和44％(0.39 C m-2 d-1)的GPP.低幅度和高幅度增温两处理间的平均NDVI,SAVI和GPP并无显著差异;4、增温引起的NDVI,GNDVI,SAVI,AGB,ANPP和GPP的绝对变化量与增温引起的土壤和空气温度的绝对变化量呈不显著相关.因此,在藏北高寒草甸,生产力和植被指数对增温的响应与增温幅度并不呈简单线性变化趋势,这可能归因于较高的增温导致了更高的干旱,进而抑制了温度升高对高寒草甸植被的生长.%In order to understand whether or not the response of vegetation indices and biomass production to warming varies with warming magnitude,an experiment of field warming at two magnitudes was conducted in an alpine meadow on the northern Tibetan Plateau beginning in late June,2013.The normalized difference vegetation index (NDVI),green normalized difference vegetation index (GNDVI) and soil adjusted vegetation index (SAVI) data were obtained using a Tetracam Agricultural Digital Camera in 2013--2014.The gross primary production (GPP) and aboveground plant biomass (AGB) were modeled using the surface measured NDVI and climatic data during the growing seasons (i.e.June-September) in 2013-2014.Both low and high warming significantly increased air temperature by 1.54 and 4.00C,respectively,and significantly increased vapor pressure deficit by 0.13 and 0.31 kPa,respectively,in 2013-2014.There were no significant differences of GNDVI,AGB and ANPP among the three warming treatments.The high warming significantly reduced average NDVI by 23.3％ (-0.06),while the low warming did not affect average NDVI.The low and high warming significantly decreased average SAVI by 19.0％ (-0.04) and 27.4％ (-0.05),respectively,and average GPP by 24.2％ (i.e.0.21 g C m-2 d-1) and 44.0％ (i.e.0.39 g C m-2 d-1),respectively.However,the differences of the average NDVI,SAVI,and GPP between low and high warming were negligible.Our findings suggest that a greater drying may dampen the effect of a higher warming on vegetation indices and biomass production in alpine meadow on the northem Tibetan Plateau.