Abstract
Both low soil water content (SWC) and high atmospheric dryness (vapor pressure deficit, VPD) can negatively affect terrestrial gross primary production (GPP). The sensitivity of GPP to soil versus atmospheric dryness is difficult to disentangle, however, because of their covariation. Using global eddy-covariance observations, here we show that a decrease in SWC is not universally associated with GPP reduction. GPP increases in response to decreasing SWC when SWC is high and decreases only when SWC is below a threshold. By contrast, the sensitivity of GPP to an increase of VPD is always negative across the full SWC range. We further find canopy conductance decreases with increasing VPD (irrespective of SWC), and with decreasing SWC on drier soils. Maximum photosynthetic assimilation rate has negative sensitivity to VPD, and a positive sensitivity to decreasing SWC when SWC is high. Earth System Models underestimate the negative effect of VPD and the positive effect of SWC on GPP such that they should underestimate the GPP reduction due to increasing VPD in future climates.
Abstract from the paper’s OpenAlex record; open copy licensed cc-by. Read at the source ↗
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Claims 9
Claim · model-written summary
GPP increased as soil water content declined from high levels.
Not reportedTaxon
Verbatim
e0“GPP increases in response to decreasing SWC when SWC is high”
Claim · model-written summary
GPP declined with lower soil water only below a threshold.
Not reportedTaxon
Verbatim
e0“GPP increases in response to decreasing SWC when SWC is high and decreases only when SWC is below a threshold”
Claim · model-written summary
Increasing VPD negatively affected GPP throughout the soil-water range.
Not reportedTaxon
Verbatim
e0“the sensitivity of GPP to an increase of VPD is always negative across the full SWC range.”
Claim · model-written summary
Canopy conductance declined as VPD increased regardless of SWC.
- Treatment
- increasing VPDe0
- Outcome
- canopy conductancee0
- Direction
- decreasese0
- Qualifier
- irrespective of SWCe0
Not reportedTaxon
Verbatim
e0“canopy conductance decreases with increasing VPD (irrespective of SWC)”
Claim · model-written summary
Canopy conductance declined with decreasing SWC on drier soils.
Not reportedTaxon
Verbatim
e0“canopy conductance decreases with increasing VPD (irrespective of SWC), and with decreasing SWC on drier soils”
Claim · model-written summary
Maximum assimilation rate had negative sensitivity to VPD.
Not reportedTaxon
Verbatim
e0“Maximum photosynthetic assimilation rate has negative sensitivity to VPD”
Claim · model-written summary
Maximum assimilation rate had positive sensitivity to decreasing SWC when SWC was high.
- Treatment
- decreasing SWCe0
- Outcome
- Maximum photosynthetic assimilation ratee0
- Direction
- positivee0
- Qualifier
- when SWC is highe0
Not reportedTaxon
Verbatim
e0“Maximum photosynthetic assimilation rate has negative sensitivity to VPD, and a positive sensitivity to decreasing SWC when SWC is high”
Claim · model-written summary
Earth System Models underestimated the negative VPD effect on GPP.
Not reportedTaxon
Verbatim
e0“Earth System Models underestimate the negative effect of VPD and the positive effect of SWC on GPP”
Claim · model-written summary
Earth System Models underestimated the positive SWC effect on GPP.
Not reportedTaxon
Verbatim
e0“Earth System Models underestimate the negative effect of VPD and the positive effect of SWC on GPP”