Water and Carbon feedbacks: How Soil Moisture dynamics shape Gross Primary Productivity across Brazil's contrasting Biomes?

Gross primary production (GPP) constitutes a fundamental component of terrestrial carbon sequestration, underpinning climate equilibrium and the provision of ecosystem services. Among various environmental factors influencing GPP, soil moisture (SM) is critical for the regulation of stomatal conductance and photosynthetic processes. In light of climate change and intensive land use, understanding the impact of soil moisture on plant productivity across diverse Brazilian biomes and ecosystems is of strategic significance. This study conducts a distributed analysis examining the relationship between soil moisture and GPP within six major Brazilian biomes: Amazon, Cerrado, Caatinga, Atlantic Forest, Pampa, and Pantanal. The methodology integrates spatio-temporal remote sensing and reanalysis data for GPP and soil moisture to generate response curves of GPP to soil moisture variations. Random sampling points were established throughout all Brazilian biomes, with GPP and SM time series extracted from the FLUXCOM-X and ERA5 datasets, respectively. Daily means for both variables were calculated for the observational period, and results were evaluated via biome-specific scatter plots. The analysis enabled the identification of areas susceptible to water stress as well as those with acclimatization potential, thereby informing improvements in climate modeling and land use strategies. Distinct patterns emerged among the Brazilian biomes; most exhibited a positive correlation between GPP and SM, except for the Pampa biome in southern Brazil, which is predominantly characterized by open fields and grasslands. Notably, the Amazon and Cerrado displayed contrasting hysteresis patterns in the GPP-SM relationship over the years. In the Amazon, GPP increases during spring and summer at a greater rate than its decline during fall and winter, whereas in the Cerrado, the increase in GPP is more gradual during spring and summer and declines more sharply in fall and winter. Consequently, seasonal responses to water availability vary significantly among the principal Brazilian biomes.