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Background and aims: In recent decades, temperate herbaceous wetlands have been widely experiencing shrub encroachment. By now, little has been known about whether such alteration in plant community would generate updated soil organic carbon (SOC) conservation strategies, and thus alter SOC dynamics. Methods: To assess the temporal dynamics of SOC stock and fractions after shrub encroachment into temperate herbaceous wetlands, we measured floor litter mass, fine root biomass, and SOC stock and fractions (i.e. labile C pool I, labile C pool II, and recalcitrant C pool) across the 0–50 cm soil profile in the open wetlands and shrub islands (Betula fruticose and Salix floderusii) with different basal diameter sizes (small, 10 ~ 15 cm; medium, 15 ~ 20 cm; and large, 20 ~ 30 cm) in the Sanjiang Plain of Northeast China. Results: Regardless of shrub species, SOC stock initially decreased after shrub expansion, but gradually recovered to the initial level of herbaceous wetlands. Moreover, SOC stock correlated positively with fine root biomass, but showed no significant relationship with floor litter mass. The responses of SOC fractions to shrub expansion mainly occurred in the surface soils (0–15 cm), despite a slight change in recalcitrant C pool in 15–50 cm layer. In the surface soils, labile C pool decreased substantially, whereas recalcitrant C pool and recalcitrant index of SOC elevated with increasing shrub sizes. Conclusions: Shrub encroachment can recover SOC pool and enhance SOC recalcitrance in temperate herbaceous wetlands, and altered fine root biomass would account for shrub encroachment-induced SOC dynamics. [ABSTRACT FROM AUTHOR]

Background and aims: Graminoid-dominated wetlands have been subjected to widespread shrub encroachment, yet the effect of this shift in species composition on litter decomposition remains unclear, especially in the standing-dead stage. Methods: We collected labile (Deyeuxia angustifolia) and recalcitrant (Carex schmidtii) graminoid leaf litter from a freshwater wetland in northeast China, and used the litterbag method to characterize litter ash-free dry mass (AFDM) loss and nitrogen (N) release in the air and on the soil surface in open wetlands and two shrub islands (Salix floderusii producing phenol-poor litter and Betula fruticosa producing phenol-rich litter) over 360 days of decomposition. Results: Litter decomposition in the air and on the soil surface responded differentially to shrub expansion. In the air, AFDM loss and N release for both labile and recalcitrant litter were often lower in shrub islands than in open wetlands. On the soil surface, labile litter decomposition was decelerated in the presence of shrubs with phenol-rich litter, but accelerated in the presence of shrubs with phenol-poor litter. Despite the absence of significant differences in N release, recalcitrant litter AFDM loss was lower in shrub islands than in open wetlands after 360 days of decomposition on the soil surface. Conclusions: Shrub encroachment retards litter decomposition in the air, but the effects on litter decomposition on the soil surface vary with shrub type and litter degradability in graminoid-dominated wetlands. Moreover, these findings emphasize that standing litter decomposition should be considered to enhance our understanding of shrub encroachment effects on litter decomposition in these wetlands. [ABSTRACT FROM AUTHOR]