Year: 2025
Type: preprint
Abstract: Texas experienced a severe drought in 2022-2023, the largest since 2012. Here we describe the divergent responses in the ecosystem gas exchange and carbon allocation, as affected by lagged effects caused by the 2-year lifetime of the needles. Even though the drought was more severe in the second year, some physiological responses were stronger, whereas others were weaker compared to the first year. This study was conducted in a shortleaf pine forest in east Texas, USA (US-CRK Ameriflux site). Ecosystem level CO 2 exchange was measured using eddy covariance (with associated micrometeorological systems) at 43 m height. Soil CO 2 efflux (R s ) was measured using survey chambers (LI-8100) and partitioned to its autotrophic (R s-a ) and heterotrophic fraction (R s-h ). Fine roots and aboveground growth were also measured during the 2023 drought to estimate biomass production (BP). Annual net ecosystem exchange of CO 2 was 28 g C m -2 year -1 in 2022 and -81 g C m -2 year -1 in 2023, indicating greater assimilation in 2023. However, gross primary productivity (GPP) and ecosystem respiration (R e ) decreased in 2023 by 20% and 24% respectively, while R s increased by 23% primarily due to the increase in R s-a . Environmental drivers like air temperature, soil temperature, soil water content and precipitation were similar among years, but vapor pressure deficit (VPD) and canopy conductance (gs) varied. Higher canopy conductance and lower VPD in spring 2022 correlated with higher monthly fluxes of GPP and BP whereas higher VPD and lower canopy conductance in late summer 2023 correlated with decreased GPP and BP. Both aboveground (20 to -30 g C m -2 month -1 ) and belowground (22 to 2 g C m -2 month -1 ) monthly production decreased as the drought progressed in 2023. The sensitivity of gs to VPD increased during peak drought months in both years, but was insignificant in pre-drought months in 2023, possibly due to adaptive changes in the leaf traits. These findings highlight that the changes in C dynamics during drought period are mediated by canopy conductance of ecosystem which is in turn driven by VPD.
Institutions: Texas A&M University, Fujian Normal University
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDGs: Climate action, Life on land
Open Access status: gold
OpenAlex ID: W4413527276