Manipulative experiments demonstrate how long-term soil moisture changes alter controls of plant water use

• Published in: Environmental and experimental botany Vol. 152; no. C; pp. 19 - 27
• Main Authors: Grossiord, Charlotte, Sevanto, Sanna, Limousin, Jean-Marc, Meir, Patrick, Mencuccini, Maurizio, Pangle, Robert E., Pockman, William T., Salmon, Yann, Zweifel, Roman, McDowell, Nate G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01.08.2018; Elsevier
• Subjects: Acclimation; Climate change; Drought; environmental factors; evaporative demand; forest types; Irrigation; plant available water; sap flow; Sap flux; transpiration; trees; Vapor pressure deficit; Water use; Climate change; Irrigation; LAI; REW; Sap flux; Water use; VPD; Drought; FD; Vapor pressure deficit; Acclimation
• ISSN: 0098-8472; 1873-7307
• DOI: 10.1016/j.envexpbot.2017.12.010

•How long-term soil moisture change affects the sensitivity of transpiration to environmental variability is unknown.•Exposure to long-term soil moisture reduction decreased sap flux sensitivity to VPD and REW.•Long-term irrigation increased sap flux sensitivity to VPD and REW but at highly water-limited sites only.•Relative sensitivity is generalizable across forest types suggesting common adjustment mechanisms to soil moisture status. Tree transpiration depends on biotic and abiotic factors that might change in the future, including precipitation and soil moisture status. Although short-term sap flux responses to soil moisture and evaporative demand have been the subject of attention before, the relative sensitivity of sap flux to these two factors under long-term changes in soil moisture conditions has rarely been determined experimentally. We tested how long-term artificial change in soil moisture affects the sensitivity of tree-level sap flux to daily atmospheric vapor pressure deficit (VPD) and soil moisture variations, and the generality of these effects across forest types and environments using four manipulative sites in mature forests. Exposure to relatively long-term (two to six years) soil moisture reduction decreases tree sap flux sensitivity to daily VPD and relative extractable water (REW) variations, leading to lower sap flux even under high soil moisture and optimal VPD. Inversely, trees subjected to long-term irrigation showed a significant increase in their sensitivity to daily VPD and REW, but only at the most water-limited site. The ratio between the relative change in soil moisture manipulation and the relative change in sap flux sensitivity to VPD and REW variations was similar across sites suggesting common adjustment mechanisms to long-term soil moisture status across environments for evergreen tree species. Overall, our results show that long-term changes in soil water availability, and subsequent adjustments to these novel conditions, could play a critical and increasingly important role in controlling forest water use in the future.