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The Tibetan Plateau, housing 20% of China's wetlands, plays a vital role in the regional carbon cycle. Examining the phenological dynamics of wetland vegetation in response to climate change is crucial for understanding its impact on the ecosystem. Despite this importance, the specific effects of climate change on wetland vegetation phenology in this region remain uncertain. In this study, we investigated the influence of climate change on the end of the growing season (EOS) of marsh wetland vegetation across the Tibetan Plateau, utilizing satellite‐derived Normalized Difference Vegetation Index (NDVI) data and observational climate data. We observed that the regionally averaged EOS of marsh vegetation across the Tibetan Plateau was significantly (p <.05) delayed by 4.10 days/decade from 2001 to 2020. Warming preseason temperatures were found to be the primary driver behind the delay in the EOS of marsh vegetation, whereas preseason cumulative precipitation showed no significant impact. Interestingly, the responses of EOS to climate change varied spatially across the plateau, indicating a regulatory role for hydrological conditions in marsh phenology. In the humid and cold central regions, preseason daytime warming significantly delayed the EOS. However, areas with lower soil moisture exhibited a weaker or reversed delay effect, suggesting complex interplays between temperature, soil moisture, and EOS. Notably, in the arid southwestern regions of the plateau, increased preseason rainfall directly delayed the EOS, while higher daytime temperatures advanced it. Our results emphasize the critical role of hydrological conditions, specifically soil moisture, in shaping marsh EOS responses in different regions. Our findings underscore the need to incorporate hydrological factors into terrestrial ecosystem models, particularly in cold and dry regions, for accurate predictions of marsh vegetation phenological responses to climate change. This understanding is vital for informed conservation and management strategies in the face of current and future climate challenges. [ABSTRACT FROM AUTHOR]

• A paired waterlogging-control system was established to evaluate effects of sea‐level rise on BSi and BSiOC accumulations. • Sea‐level rise significantly reduced BSi and BSiOC densities, particularly in the salt marsh dominated by the Phragmites australis. • Although sea‐level rise increased SOC content, it generally decreased soil BSiOC content and its contribution to total SOC. • The depleted BSi and BSiOC stocks was attributed to increased anaerobiosis, higher salinity and pH, and higher soil erosion. The fate of soil biogenic silica (BSi) in coastal salt marshes is of global importance because of its role in providing both available silicon (Si) for the growth of plants and diatoms and in sequestering carbon (C) (blue C) in soils and sediments. However, the accumulation of BSi and BSi-occluded C (BSiOC) under different vegetation habitats in coastal ecosystems, particularly in response to relative sea‐level rise (RSLR), remains poorly understood. Here we established a paired waterlogging-control system and collected the soil samples under both waterlogged and non-waterlogged conditions from three vegetation habitats (single Phragmites australis , a mixture of P. australis and Suaeda salsa , and single S. salsa) corresponding to a gradient of distance from the coastline in three independent salt marshes. Our findings indicated that RSLR decreased average BSi content, especially in the 0–20 cm soil layer of the single P. australis and the mixed P. australis and S. salsa community. Although RSLR increased soil organic C (SOC) content, it generally decreased soil BSiOC content and its contribution to SOC. Consequently, RSLR resulted in lower soil BSi and BSiOC densities, particularly in the salt marsh dominated by the Si accumulator P. australis. Here, BSi and BSiOC densities at depths of 0–80 cm decreased by an average of 19% and 18% following waterlogging, respectively. The BSi pool was dominated by phytoliths in non-waterlogged soils, while both diatoms and phytoliths were present in soils subjected to RSLR. Soil physicochemical properties including SOC, electrical conductivity and dissolved Si were influenced by RSLR. These factors, along with erosion were suggested as key influencers for BSi and its C sequestration in coastal salt marshes. Our results provide a scientific basis for elucidating biogeochemical Si cycles and predicting changes in BSiOC sequestration to optimize its storage. [ABSTRACT FROM AUTHOR]