念青唐古拉山南坡高寒草甸生产力对温度和降水变化的敏感性及其海拔分异

目前人们仍不清楚不同海拔高寒草地植被生长对气候变化的敏感性差异及其与最适宜海拔分布中心的关系。利用西藏当雄县念青唐古拉山南坡7个海拔梯度固定样地的高山嵩草草甸地上净初级生产力(ANPP)观测数据(2009—2013),建立了ANPP与同期遥感植被指数(MODIS NDVI)的线性回归方程。基于长时间序列的NDVI数据,利用建立的回归方程估算了研究区2000—2013年的ANPP。结合沿海拔梯度的HOBO气象站数据(2006—2013)及当雄县气象站数据(2000—2013),分析了2000—2013年该地区高寒草甸ANPP对降水和温度变化的敏感性及其随海拔的变化规律。结果表明:(1)多年平均ANPP随海拔的变化均表现为先增加后降低的单峰分布格局,最大值出现在海拔4893—4942 m,说明在海拔梯度上存在一个最适宜高寒草甸植被生长的分布中心;(2)ANPP与生长季降水量(GSP)呈正相关关系,与生长季平均气温(GST)呈负相关关系,其相关斜率的绝对值(指示ANPP的降水敏感性和温度敏感性大小)与ANPP的海拔格局具有相反的变化趋势,即在最适宜高寒草甸植被生长的海拔分布中心附近,ANPP对降水和温度变化的敏感性最低,而在远离该分布中心的较高和较低海拔,ANPP对降水和温度变化的敏感性则相对较大。研究明确了高寒草甸ANPP对降水和温度变化的敏感性随海拔的分异性及其与高寒草甸最适宜海拔分布中心的关系,这有助于理解沿海拔梯度不同水热组合环境下高寒生态系统对未来气候变化的响应模式。

Altitudinal variations in the sensitivity of alpine meadow productivity to temperature and precipitation changes along the southern slope of Nyainqentanglha Mountains

It remains unclear whether and how the sensitivity of alpine plant growth to climate change may vary with distance away from the altitudinal distribution center of a vegetation type. On the basis of measurements of aboveground net primary productivity (ANPP) in an alpine Kobresia meadow across 7 altitudes along the southern slope of Nyainqentanglha Mountains in Tibet during 2009-2013, we established a linear regression model between ground ANPP and satellite vegetation index (MODIS NDVI). Using the long time-series MODIS NDVI data, we then applied the established model to estimate ANPP in the study area during 2000-2013. In combination with climatic data obtained from altitudinal HOBO weather stations (2006-2013) and Damxung weather station (2000-2013), we aimed to clarify the altitudinal pattern in the sensitivity of ANPP to changes in temperature and precipitation in alpine meadows. A unimodal pattern in multi-year mean ANPP was observed along the altitudes; ANPP increased with increasing altitude up to 4893-4942 m and then decreased, demonstrating the altitudinal distribution center of the alpine meadow at mid-altitude. ANPP was positively correlated with growing season precipitation but negatively correlated with growing season mean air-temperature during 2000-2013. The absolute values of the linear regression slopes (referred to as the sensitivity of ANPP to changes in precipitation and temperature) showed a pattern opposite to the change in ANPP along the altitudes. The precipitation and temperature sensitivities of ANPP were the lowest around the distribution center but higher at lower or higher altitudes with distance away from the distribution center. In conclusion, our data identified the altitudinal pattern in sensitivity of alpine meadow ANPP to climate change with a link to the altitudinal distribution center of the alpine meadow. Such knowledge is important for understanding the response of alpine meadow ecosystems to future climate change in different environments along an altitudinal gradient.