Soil moisture thresholds explain a shift from light-limited to water-limited sap velocity in the Central Amazon during the 2015–16 El Niño drought. (1st June 2022)

• Record Type: Journal Article
• Authors: Meng, Lin; Chambers, Jeffrey; Koven, Charles; Pastorello, Gilberto; Gimenez, Bruno; Jardine, Kolby; Tang, Yao; McDowell, Nate; Negron-Juarez, Robinson; Longo, Marcos; Araujo, Alessandro; Tomasella, Javier; Fontes, Clarissa; Mohan, Midhun; Higuchi, Niro
• Is Part Of: Environmental research letters. Volume 17:Number 6(2022)
• Publication Date: 2022-06-01
• Subjects: drought -- tropical forests -- water cycle -- soil moisture -- evapotranspiration; Environmental sciences -- Periodicals; Human ecology -- Research -- Periodicals; Environmental health -- Periodicals; 333.7
• DOI: 10.1088/1748-9326/ac6f6d
• Languages: English
• ISSNs: 1748-9326

Abstract

Abstract: Transpiration is often considered to be light- but not water-limited in humid tropical rainforests due to abundant soil water, even during the dry seasons. The record-breaking 2015–16 El Niño drought provided a unique opportunity to examine whether transpiration is constrained by water under severe lack of rainfall. We measured sap velocity, soil water content, and meteorological variables in an old-growth upland forest in the Central Amazon throughout the 2015–16 drought. We found a rapid decline in sap velocity (−38 ± 21%, mean ± SD.) and in its temporal variability (−88%) during the drought compared to the wet season. Such changes were accompanied by a marked decline in soil moisture and an increase in temperature and vapor pressure deficit. Sap velocity was largely limited by net radiation during the wet and normal dry seasons; however, it shifted to be primarily limited by soil moisture during the drought. The threshold in which sap velocity became dominated by soil moisture was at 0.33 m 3 m −3 (around −150 kPa in soil matric potential), below which sap velocity dropped steeply. Our study provides evidence for a soil water threshold on transpiration in a moist tropical forest, suggesting a shift from light limitation to water limitation under future climate characterized by increased temperature and an increased frequency, intensity, duration and extent of extreme drought events.