Hydrology mediates salt marsh belowground biomass response to warming

Abstract Salt marshes provide vital ecosystem services, including coastal protection and carbon sequestration. Roots play a key role in delivering these ecosystem services, as they stabilize soils and contribute to organic carbon accumulation. This study examines the impact of an experimental 3°C temperature increase in a temperate salt marsh on belowground biomass dynamics across three elevation zones (pioneer zone, low marsh, and high marsh) and two temperature treatments (ambient, + 3°C) over a period of 3 yr (2019–2021). The elevation zones reflect different hydrological conditions. We found minimal effects of warming on belowground biomass, except in the high marsh during 2019, where drought and warming caused a shift to deeper rooting depths (− 53 ± 19% in the upper soil depth, + 272 ± 129% in the lower soil depth). Overall, root biomass was lowest in the high marsh (72.0 ± 94.5 g m −2 ) and highest in the low marsh (360.2 ± 174.7 g m −2 ), followed by the pioneer zone (218.7 ± 233.8 g m −2 ). In all years, root biomass peaked in summer (248.5 ± 235.5 g m −2 ) after rising from spring (181.4 ± 183.4 g m −2 ) and declining in autumn (216.5 ± 209.4 g m −2 ). Our findings suggest that a temperature increase of + 3°C above ambient temperatures has a marginal impact on root biomass dynamics, indicating that soil‐stabilizing functions and belowground contributions to carbon sequestration may remain intact under global warming. Moreover, interactions between tidal regime and interannual precipitation patterns seem to play a more important role for root biomass variations.