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Changing precipitation patterns are predicted to alter ecosystem structure and function with potential carbon cycle feedbacks to climate change. Influenced by both land and sea, salt marshes are unique ecosystems and their productivity and respiration responses to precipitation change differ from those observed in terrestrial ecosystems. How salt marsh greenhouse gas fluxes and sediment microbial communities will respond to climate-induced precipitation changes is largely unknown. We conducted 1-year precipitation manipulation experiments in the Spartina patens (high marsh) zone of two salt marshes and quantified ecosystem functions at both and microbial community structure at one. Precipitation treatments (doubled rainfall, extreme drought, and seasonal intensification) had a significant, although transient, impact on porewater salinity following storms at both sites, but most site conditions (nutrient concentrations, sediment moisture, and temperature) were unaffected. Extreme drought led to a subtle change in microbial community structure, but most ecosystem functions (primary productivity, litter decomposition, and greenhouse gas fluxes) were not affected by precipitation changes. The absence of ecosystem function change indicates functional redundancy (under extreme drought) and resistance (under doubled precipitation and seasonal intensification) exist in the microbial community. Our findings demonstrate that salt marsh ecosystems can maintain function (including ecosystem services like carbon sequestration) under even the most extreme precipitation change scenarios, due to resistance, resilience, and functional redundancy in the underlying microbial community.

Plain Language Summary Precipitation change, especially the intensification of precipitation events (e.g., longer droughts and stronger storms) is an important aspect of human-caused global climate change. Salt marshes are important hotspots for carbon sequestration, so if precipitation changes alter the microbial processes that drive carbon burial and greenhouse gas emissions in salt marshes, there could be an important feedback to the climate system. How salt marsh greenhouse gas fluxes and sediment microbial communities will respond to precipitation changes is largely unknown, so we conducted 1-year precipitation experiments in two salt marshes. We found that precipitation treatments (doubled rainfall, extreme drought, and seasonal intensification) had a significant impact on porewater salinity following storms, and one of the precipitation treatments (extreme drought) led to a subtle change in microbial community structure. However, ecosystem functions including greenhouse gas fluxes were not affected by any precipitation changes, regardless of changes to the microbial community. Our findings demonstrate that salt marsh ecosystems can maintain their functions (including valuable ecosystem services like carbon sequestration) under even the most extreme precipitation change scenarios, due to the stability of the underlying microbial community.