Interannual and Seasonal Variations in Ecosystem Transpiration and Water Use Efficiency in a Tropical Rainforest

Abstract

Warmer and drier climates over Amazonia have been predicted for the next century with expected changes in regional water and carbon cycles. We examined the impact of interannual and seasonal variations in climate conditions on ecosystem-level evapotranspiration (ET) and water use efficiency (WUE) to determine key climatic drivers and anticipate the response of these ecosystems to climate change. We used daily climate and eddyflux data recorded at the Guyaflux site in French Guiana from 2004 to 2014. ET and WUE exhibited weak interannual variability. The main climatic driver of ET and WUE was global radiation (Rg), but relative extractable water (REW) and soil temperature (Ts) did also contribute. At the seasonal scale, ET and WUE showed a modal pattern driven by Rg, with maximum values for ET in July and August and for WUE at the beginning of the year. By removing radiation effects during water depleted periods, we showed that soil water stress strongly reduced ET. In contrast, drought conditions enhanced radiation-normalized WUE in almost all the years, suggesting that the lack of soil water had a more severe effect on ecosystem evapotranspiration than on photosynthesis. Our results are of major concern for tropical ecosystem modeling because they suggest that under future climate conditions, tropical forest ecosystems will be able to simultaneously adjust CO2 and H2O fluxes. Yet, for tropical forests under future conditions, the direction of change in WUE at the ecosystem scale is hard to predict, since the impact of radiation on WUE is counterbalanced by adjustments to soil water limitations. Developing mechanistic models that fully integrate the processes associated with CO2 and H2O flux control should help researchers understand and simulate future functional adjustments in these ecosystems.

Scaling Up Sap Flow Measurements from the Stem Scale to the Individual Scale for Multibranched Caragana Korshinskii on the Chinese Loess Plateau

“…These results suggest quite different controls of environmental factors on SF. In our study, VPD and ET0 were the two main meteorological factors affecting SF, which were similar to those of other studies [11,44]. Our data indicated that VPD, VT, and ET0 explained more of the variations in SF than T and PAR, and VPD was more closely correlated with SF than PAR and T. Plant transpiration becomes stronger with increasing VPD levels, which also has a direct influence on stem SF.…”

“…The observed poor correlation between SF and SWC suggests that SWC in the 0-180 cm soil depth range was not a limiting factor on SF. It also could be attributed to that fact that C. korshinskii used SWC from the soil layer that is deeper than 180 cm [44]; however, this was not monitored in our study. Further study is justified to clarify the correlation between SF and deep SWC in both dry and rainy seasons.…”

Disentangling Drought and Nutrient Effects on Soil Carbon Dioxide and Methane Fluxes in a Tropical Forest

“…The study was conducted in French Guiana, South America, at the Paracou research station ( Figure 1A, 05 • 16 ′ 54 ′′ N, 52 • 54 ′ 44 ′′ W). Decadal average annual rainfall at the study site was 3,102 mm ± 70 mm and average annual air temperature was 25.7 • C ± 0.1 • C (from 2004 to 2014, Aguilos et al, 2019). The tropical wet climate of French Guiana is highly seasonal due to the north/south movement of the Inter-Tropical Convergence Zone.…”

“…This zone brings heavy rains from December to July (wet season, with precipitation between 300 and 500 mm mo −1 ) and a long dry season from mid-August to mid-November. Precipitation during the dry period is typically <100 mm mo −1 (Aguilos et al, 2019). Soils at Paracou are predominantly schist soils with veins of pegmatite along a Precambrian metamorphic formation called the Bonidoro series (Sabatier et al, 1997).…”

Response of Ecosystem Water Use Efficiency to Drought over China during 1982–2015: Spatiotemporal Variability and Resilience

“…Water use efficiency (WUE) is a widely accepted parameter in describing carbon-water flux coupling between terrestrial ecosystems and the atmosphere and linking biological (e.g., vegetation transpiration and photosynthesis) and physical (e.g., soil evaporation) processes [12,13]. It reflects how much water is consumed by an ecosystem while it obtains carbon unit, which can be quantified as the ratio of carbon uptake (measured by GPP-gross primary productivity, NPP-net primary productivity or NEP-net ecosystem productivity) and water consumption (measured by ET-evapotranspiration or precipitation) [14][15][16].…”