Wetlands store a substantial amount of soil organic carbon (SOC), and their response to climate warming is critical for predicating global carbon (C) cycling in future climate change. To understand whether warming causes substantial C loss in wetland soils, a 6-year microcosm experiment was carried out to examine the impact of rising temperature (3–5 °C) on SOC and its two fractions (labile versus recalcitrant) in six types of wetland soils with varied nutrient status. Warming decreased SOC contents in nutrient-enriched soils by invoking a large loss in recalcitrant organic C fractions, while in nutrient-poor soils SOC loss was limited by substrate limitation. With low temperature ranges in the winter (1–10 °C), warming increased the microbial capacity for recalcitrant organic C acquisition greater than that for labile organic C fractions. A relatively higher cross-site contribution of fungi in warmed soils as one strategy of microbial acclimation to rising temperature implies an adjustment of microbial C utilization patterns, leading to substantial C loss in wetland soils. In order to maintain the functional roles of wetlands for C sequestration, our results further suggested that more attention should be paid to nutrient-enriched wetlands in future climate warming scenarios.
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