Ecosystem Carbon Flux Responses to Local Climate and Management in Irrigated Vineyards

Agricultural ecosystems are receiving increasing attention as potential natural climate solutions. High-value perennial crops, including wine grapes, have unique structural and management characteristics that present opportunities for carbon sequestration. Evaluating the climate adaptation and mitigation potential of vineyards requires information on ecosystem-scale carbon and water fluxes and their response to climate and management. Here we evaluate multi-year eddy covariance observations from the Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project to examine how management and local climate impact carbon and water fluxes in California vineyards. Across 9 sites spanning 3 American Viticultural Area regions, annual net ecosystem exchange (NEE) of CO2 ranged from -230 to -722 g C m-2 due to differences in vineyard variety, management, and climate. Collocated measurements of vegetation greenness and soil moisture revealed that temporal dynamics in NEE were driven by changes in vine and cover crop phenology, light availability, and soil moisture. At all sites, growing cover crops supported carbon uptake during the spring, except immediately after mowing. We further examined cover crop contributions to carbon fluxes using paired flux towers and found that vineyards with cover had 90 g C m-2 greater springtime carbon uptake (-NEE) than those with bare interrow spaces. We also evaluated flux responses to re-grafting, in which the existing mature scion was replaced with a new variety, and found significant reductions in evapotranspiration and NEE in the first year after re-grafting. Soil moisture measurements along a vine-interrow gradient showed that drip irrigation concentrated soil moisture near vine roots, which likely supported photosynthesis while suppressing soil respiration from dry interrow spaces. Cumulative evapotranspiration was a strong predictor of site differences in ecosystem photosynthesis and NEE, illustrating strong carbon-water coupling in irrigated vineyards. These results indicate that cover crop and efficient irrigation practices contribute to net carbon uptake in vineyards and may help inform carbon budgets for irrigated woody perennials in California.