Disentangling the effects of vapor pressure deficit on northern terrestrial vegetation productivity

来自 <https://www.science.org/doi/10.1126/sciadv.adf3166>

解开水汽压亏缺对北方陆地植被生产力的影响

来自 <https://www.science.org/doi/10.1126/sciadv.adf3166>

## Intro:

1. Backgrounds:

• The impact of atmospheric vapor pressure deficit (VPD) on plant photosynthesis has long been acknowledged, but large interactions with air temperature (T) and soil moisture (SM) still hinder a complete understanding of the influence of VPD on vegetation production across various climate zones.
• Considering the likely increase in VPD under global warming, VPD will play an increasing role in controlling global ecosystem, carbon, and water exchanges.
• Changes in VPD can be caused by moisture content in the air and air temperature (T): Evapotranspiration is controlled by soil moisture (SM) among other factors, providing an important source of atmospheric moisture.
• A question that remains open is to what extent vegetation productivity at the regional scale and in different climate zones is influenced by VPD. The difficulty in answering this question lies in the fact that VPD is closely coupled to T and SM, which also have strong influences on terrestrial vegetation productivity.

1. Research:

• Analyzed the independent effects of VPD on vegetation productivity over the Northern Hemisphere (NH) after excluding the effects caused by T and SM.
• First used ridge regression analysis to eliminate the interactions between VPD and T or SM and assessed the response of vegetation productivity to VPD at the interannual scale using growing-season mean values.
• Then applied a structural equation model with the partial least square (PLS-SEM) algorithm to disentangle the direct effect of VPD on vegetation from the indirect effects of T or SM on vegetation via VPD.

## Results:

1. The independent effects of VPD on vegetation productivity

The independent effect refers to the impact of an independent variable on the dependent variable after excluding confounding effects of other independent variables.

1. The role of VPD in vegetation production

In the real world, however, VPD is considered the middle variable of T or SM variations affecting vegetation productivity. For example, rising T could lead to higher VPD and thereby further limit plant photosynthesis. In addition, when soil becomes wetter, the increasing evaporation reduces VPD and further promotes plant transpiration and photosynthesis.

1. The threshold of VPD sensitivities of vegetation productivity

The shift from a positive to a negative influence of VPD on productivity indicates that there is a VPD threshold that determines the direction of the effect of VPD on vegetation productivity.