1982-2018年青藏高原水分利用效率变化及归因分析

Variation in ecosystem water use efficiency and its attribution analysis during 1982-2018 in Qingzang Plateau

水分利用效率(WUE)是衡量地表生态系统碳水耦合的重要指标。青藏高原是我国重要的生态屏障,其生态系统对全球变化响应敏感,开展青藏高原WUE研究有利于深入理解高寒生态系统碳水循环的过程和机制,对指导植被生态建设具有重要意义。该研究基于GLASS遥感数据、气象数据和植被类型数据,对1982-2018年期间青藏高原WUE的时空变化格局及其对温度、降水量、太阳辐射、饱和水汽压差、CO_(2)浓度以及叶面积指数的响应进行了分析,并进一步揭示了植被类型间的差异。结果表明:(1)青藏高原WUE总体呈现由东南向西北递减的空间分布格局,多年平均值约为1.64 g C·kg^(-1)。WUE在不同植被类型间差异明显,森林最高,高寒荒漠最低,高寒草甸高于高寒草原。(2)青藏高原WUE主要呈现增加趋势,除森林和栽培植被外,其他植被类型WUE均显著增加,总初级生产力主导了研究区77.84%面积的WUE变化。(3)叶面积指数和CO_(2)浓度主导了青藏高原WUE的变化,且均为正向效应。而饱和水汽压差的升高对高寒草原、高山植被、栽培植被以及高寒荒漠的WUE有抑制作用。

Aims Water use efficiency(WUE)is a crucial parameter reflecting the coupling of carbon and water cycles in terrestrial ecosystems.Qingzang Plateau(QP)is the ecological barrier of China and its accommodated ecosystem is extremely sensitive to global change.Revealing the ecosystem WUE pattern and the driving forces is critical for improving our understanding on the process and mechanism of carbon and water cycles in the alpine ecosystem of the QP,which are the basis for vegetation conservation and restoration.Methods Using the Global Land Surface Satellite(GLASS)data,meteorological data and vegetation type data,the spatio-temporal changes of WUE and their responses to temperature,precipitation,solar radiation,vapor pressure deficit(VPD),CO_(2)concentration and leaf area index(LAI)during 1982-2018 over the QP were analyzed in this study.The trend magnitude and the influencing factors on WUE were further compared among vegetation types.Important findings(1)The WUE decreases gradually from southeast to northwest on the QP,with an overall annual mean value of 1.64 g C·kg^(-1).Evident differences in WUE are observed among vegetation types,with the highest value in forest and the lowest value in alpine desert.In addition,the WUE in alpine meadow is higher than that in alpine steppe.(2)The QP is prevailed by an increasing trend in WUE.Significantly increasing trends are observed in all vegetation types except for forest and cultural vegetation.Meanwhile,the variation of WUE is dominated by ecosystem gross primary productivity over 77.84%of the study area.(3)The WUE variation is mainly regulated by LAI and CO_(2)concentration on the QP,and these two factors both cause positive effects on WUE.Increasing VPD inhibits WUE in alpine steppe,alpine vegetation,cultural vegetation and alpine desert.