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Background: Litter-derived dissolved organic matter (DOM) plays an important role in biogeochemical cycling for wetlands. However, there are few studies to clarify how plant community alteration affects litter-derived DOM degradation. Moreover, little is known about the specific influence of temperature on the degradation, even though it is particularly important when the warming climate is taken into account. Therefore, it is urgently needed to determine interspecific differences in the DOM degradation rates and the responses to temperature increase. Methods: Based on a 42-day incubation experiment regarding nine species from a temperate wetland, we determined litter-derived DOM degradation at 10oC, 20oC and 30oC, and compared their temperature sensitivity coefficient Q10. Results: These species exhibited interspecific variations in degradation at all temperatures, which related closely to initial chemical characteristics, including stoichiometry, aromaticity and molecular weight. Increased temperature generally promoted DOM degradation, especially at 10–20oC range, with Q10 ranging from 1.42 to 3.82 and the mean up to 2.57. Specifically, the temperature sensitivity usually correlated negatively with aromaticity, but positively with carbon:nutrient ratios. The aromaticity, by contrast with other chemical characteristics, explained more interspecific variations in DOM degradation and the temperature sensitivity. Conclusion: Degradation rates of litter-derived DOM and the responses to temperature increase vary greatly among species, where the aromaticity could be considered as a decisive indicator for such interspecific differences. This study highlights considerable promotion of climate warming on litter-derived DOM degradation, and sheds new light on influences of plant community on biogeochemical processes in wetlands. [ABSTRACT FROM AUTHOR]

Background: In boreal peatlands, climate warming and associated soil drying facilitate the growth of vascular plants at the cost of moss species, resulting in an alteration of species dominance in plant communities. However, how altered dominant species and evenness affect litter mixture decomposition is still unclear in these ecosystems. Methods: We collected fresh litter from Larix gmelinii (tree), Betula fruticosa (shrub), Eriophorum vaginatum (sedge), and Sphagnum magellanicum (moss), and determined mass loss and nitrogen (N) release of four-species mixtures with varying dominant species and evenness at 10 and 20 oC during 360-day decomposition. Results: Irrespective of the incubation temperature, B. fruticosa-dominated litter mixtures had greatest mass loss and N release throughout decomposition, while S. magellanicum-dominated litter mixtures had lowest values. Moreover, mass loss and N release of B. fruticosa-dominated litter mixtures decreased with elevating evenness after 360 days of decomposition, but the opposite trends were observed for litter mixtures dominated by the other three species. Increasing incubation temperature facilitated decomposition of all litter mixtures, with the lowest magnitude for S. magellanicum-dominated mixtures. Non-additive effects, especially positive effects, on mass loss and N release were common, which played a key role in enhancing the influences of dominant species and evenness on litter mixture decomposition. Moreover, the incidence of positive non-additive effects on mass loss decreased at 20 oC as litter decomposition proceeded. Conclusions: Warming-induced increased dominance of vascular plants, especially shrubs, will amplify the warming effect on litter decomposition and N availability in boreal peatlands, thus generating positive feedback to climate warming. [ABSTRACT FROM AUTHOR]

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]