第七届青年地学论坛

Global warming caused increasing drought stress in terrestrial, including enhanced atmospheric vapor pressure deficit (VPD) and reduced soil water content (SWC). Midday depression that plants close stomata to reduce water loss at noon time is one of the strategies for species adaption to the drought stress. However, the intensity and variation of midday depression in large-scale and further influence on community productivity have not yet been quantified. Here, based on 103 FLUXNET sites around the world, we found that increased VPD and reduced SWC significantly suppressed daily gross primary photosynthesis (GPP) and its distribution at noon and afternoon times, while enhanced the distribution at morning time, consistently in forest, grassland, shrubland and wetland biomes and most sites. This suggests that increasing drought stress widely enhanced the intensity of community level midday depression. Meanwhile, the effect of raising VPD was stronger than that of reducing SWC. Moreover, mean noon GPP proportion was strongly reduced while mean morning GPP proportion was enhanced when moving from mesic to xeric sites. In the xeric sites, GPP proportions at morning, noon and afternoon times were all largely affected by changing SWC relative to the mesic sites, while the influence of VPD on noon GPP proportion raised from mesic to xeric sites, but with no significant site difference for VPD effects on GPP proportions at morning and afternoon times.
 

soil water content, vapor pressure deficit, adaption, FLUXNET, morning time