2022年夏季长江流域破纪录的高温干旱事件导致了植被光合作用显著下降

Unprecedented decline in photosynthesis caused by summer 2022 record-breaking compound drought-heatwave over Yangtze River Basin

2022年夏季,一场破纪录的高温干旱席卷了长江流域,造成了自2000年以来7~9月最严重的高温、水汽压差增强和土壤湿度减少,但此次事件对陆地生态系统及其碳通量的影响尚不清楚.利用最新的多源数据,本研究及时评估了其对植被绿度和光合作用的影响.结果表明,这一复合极端事件导致长江流域植被绿度和光合作用普遍减少,特别是重庆和湖南的植被NDVI、总初级生产力(GPP)和近红外反射率(NIRv)分别下降了5%~8%、12%和11%.整个长江流域平均NDVI下降了0.04(5.16%),总GPP下降了84.50 Tg C(7.46%)和NIRv下降了0.01(7.43%),是自2000年以来夏季最大的降幅.将长江流域区分为森林、灌木和农田3种主要植被类型,平均NDVI在农田地区下降最强,而光合作用在森林地区降幅最大.另外,研究发现除了农田NDVI的减少主要是高温胁迫引起,其他植被类型NDVI的减少和所有植被类型光合能力的下降主要是由增加的VPD导致.而随着全球变暖复合极端气候事件的强度和频率增加,其将潜在增加长江流域生态系统的脆弱性,并严重威胁其固碳能力.

The frequency and intensity of droughts and hot extremes have increased due to anthropogenic greenhouse gas emissions[1].Drought and heat are major abiotic stresses on terrestrial ecosystems,which can greatly influence the regional carbon cycling[2–6].Specifically,these weather extremes can inhibit gross primary productivity(GPP)[2,6,7],increase tree mortality[8],induce losses of above-ground biomass[9],and promote wildfires[10].The severe drought and heat in 2003,for instance,reduced GPP over Europe by about 30%,which caused a strong anomalous carbon source to the atmosphere(about 0.5 Pg C a^(-1)),offsetting the net ecosystem carbon sequestration for the previous four years[2].However,the impact of drought and heat on terrestrial carbon cycling can be different over different geographical regions and seasons,which is closely related to differences in the vegetation composition,phenological stage and preconditioning effects of past disturbance legacies[4].An extensive and in-depth understanding of the impact of drought and heat worldwide is important in understanding the variations in global and regional carbon cycling.