Large animals including waterbirds are traditionally considered passengers in wetland ecosystems and used as indicator, flagship or umbrella species in wetland conservation, but whether they are drivers of wetland ecosystem patterns and dynamics is poorly understood. Combining a field experiment in a tidal flat in the Yangtze estuary and a global meta-analysis, we tested the hypothesis that waterbirds exert top-down control on wetland macrofauna. Waterbird exclusion more than doubled the abundance of grazing crabs in our field experiment but did not affect other macrofauna. Conversely, excluding grazing crabs to simulate above-current levels of waterbird predation increased macrofauna abundance and biomass and decreased their diversity, ostensibly by allowing the establishment of habitat-engineering plants otherwise eliminated by crab grazing. Meta-analysis of 135 tests revealed that waterbirds had negative, positive, or neutral effects on macrofauna, with an overall significantly negative effect. This finding was evident across different seasons, wetland types and macrofauna classes and was largely based on tests from coastal rather than inland wetlands in Europe and Americas and none in Asia and Australasia. Our results suggest that the roles of waterbirds in wetlands are more diverse and profound than currently recognized and that their driver roles in shaping wetland ecosystems warrant incorporation into conservation decisions.

Aboveground litter inputs from plants are among the most important pathways for carbon and nutrient fluxes to the soil. Previous studies on the effects of aboveground litter from invasive plants on ecosystem processes have primarily focused on biogeochemical cycling processes such as C and N mineralization, whereas the effects of aboveground litter from invasive plants on nitrogen removal processes are not well understood. In this study, the effects of the aboveground litter of native Phragmites australis and exotic Spartina alterniflora on soil nitrification and denitrification were compared. Results showed that the removal of the aboveground litter of both species had no effect on nitrification or denitrification in the early growth phase. However, after aboveground litter removal in the late growth phase, nitrification and denitrification in the P. australis stands decreased by 41.18% and 25.11%, respectively, whereas no such changes were observed in the S. alterniflora stands. These results indicate that the impacts of aboveground litter on nitrification and denitrification are species-specific. The aboveground litter from indigenous P. australis affected the SOC content and then indirectly affected nitrification or denitrification, and these effects were clearer in the late growth phase. Although other studies have reported that the invasive S. alterniflora have strong impacts on nitrogen removal processes, our study showed that the aboveground litter from S. alterniflora did not alter nitrification or denitrification, which indicates that other pathways may play important roles in nitrogen removal processes than its aboveground litter does.

Root traits are fundamental characteristics of belowground ecosystems that regulate plant growth and drive ecosystem functioning. Nevertheless, the way root traits respond to environmental factors and consequently influence productivity remains unexplored on large geographic scales. We examined the root traits of exotic Spartina alterniflora and native Phragmites australis across China’s coastal salt marshes. Using structural equation models (SEMs), we quantified the direct and indirect effects of mean annual temperature, soil nutrients (e.g., soil dissolved inorganic nitrogen and phosphorus), and root traits on aboveground net primary productivity. Our results showed that root traits of S. alterniflora were more sensitive to changing soil nutrient availability than those of P. australis. The SEMs indicated that soil nutrient availability increased S. alterniflora productivity by increasing root nitrogen concentration and root length density. In P. australis, temperature could increase productivity by both increasing root length density and soil nutrient-mediated root nitrogen concentration. The studied root architectural trait (root length density) and nutrient trait (root nitrogen concentration) were effective in predicting productivity, whereas none of the root morphological traits (i.e., specific root length, root tissue density, and root diameter) significantly affected productivity. We provide the first empirical evidence that root trait-based responses modulate the effects of climate and soil nutrients on geographic variation in vegetation productivity, but these effects are species specific.

Background: Conserving migratory birds is challenging due to their reliance on multiple distant sites at different stages of their annual life cycle. The concept of "flyway", which refers to all areas covered by the breeding, nonbreed-ing, and migrating of birds, provides a framework for international cooperation for conservation. In the same flyway, however, the migratory activities of the same species can differ substantially between seasons and populations. Clarifying the seasonal and population differences in migration is helpful for understanding migration ecology and for identifying conservation gaps.Methods: Using satellite-tracking we tracked the migration of Whimbrels（Numenius phaeopus variegatus） from non-breeding sites at Moreton Bay（MB） and Roebuck Bay（RB） in Australia in the East Asian–Australasian Flyway. Mantel tests were used to analyze the strength of migration connectivity between the nonbreeding and breeding sites of MB and RB populations. Welch’s t test was used to compare the migration activities between the two populations and between northward and southward migration.Results: During northward migration, migration distance and duration were longer for the MB population than for the RB population. The distance and duration of the first leg flight during northward migration were longer for the MB population than for the RB population, suggesting that MB individuals deposited more fuel before departing from nonbreeding sites to support their longer nonstop flight. The RB population exhibited weaker migration connectivity（breeding sites dispersing over a range of 60 longitudes） than the MB population（breeding sites concentrating in a range of 5 longitudes in Far Eastern Russia）. Compared with MB population, RB population was more dependent on the stopover sites in the Yellow Sea and the coastal regions in China, where tidal habitat has suffered dramatic loss. However, RB population increased while MB population decreased over the past decades, suggesting that loss of tidal habitat at stopover sites had less impact on the Whimbrel populations, which can use diverse habitat types. Different trends between the populations might be due to the different degrees of hunting pressure in their breeding grounds.Conclusions: This study highlights that conservation measures can be improved by understanding the full annual life cycle of movements of multiple populations of Whimbrels and probably other migratory birds.

Litter types and soil properties can affect litter decomposition rate and litter carbon (C) transformation, consequently regulating soil C cycling. Yet, litter C transformations of leaves and roots of invasive plants are poorly understood, which limits our understanding of the role of plant residues in soil C sequestration during plant invasion. In a laboratory incubation experiment lasting for 153 days, we used two types of soil which were collected from invasive S. alterniflora and native Phragmites australis marshlands, and traced the transformation of 13C from leaf and root litter of invasive Spartina alterniflora into CO2, soil-dissolved organic C (DOC), microbial biomass C (MBC), and soil organic C (SOC). The leaf litter of S. alterniflora decomposed faster than root litter, resulting in higher soil respiration and higher transformation of litter-derived 13C into CO2, MBC, and DOC. Although the root litter of S. alterniflora decomposed slowly, SOC comprised up to 24% of litter-derived 13C. Furthermore, the litter C transformations of S. alterniflora showed a positive home-field advantage effect. Soil respiration, MBC, fractions of litter-derived 13C in Gram-negative bacteria, 13C recovered in CO2, DOC, and SOC were higher in the soil colonized by S. alterniflora than in the soil colonized by P. australis, with the home-field advantage effect being more pronounced in root than leaf litter treatments. Therefore, litter type and soil source had differential impacts on litter C transformation patterns of S. alterniflora and the root litter of invasive S. alterniflora played an important role in SOC formation and C sequestration in soils from its invaded ecosystems.

Biochar application and rising carbon dioxide (CO2) concentrations are likely to influence both aboveground and belowground plant processes. However, little is known about the influence of biochar and CO2 enrichment on root exudation, as well as their interactive effects. The aim of this study was to reveal whether rice paddy root exudates responded to biochar and CO2 enrichment and whether this effect varied at different plant growth stages. Rice was grown in growth chambers with different biochar addition rates (1%, 2%, 3%, 4%, and 5% by weight) under both ambient (aCO(2) , 400 ppm) and elevated (eCO(2) , 700 ppm) CO2 levels. Root exudation variables were measured at the tillering and stem elongation stages. Electrical conductivity (EC), amino acid (AA), indole acetic acid (IAA), and abscisic acid (ABA) levels were significantly increased but cytokinin (CYT) concentrations decreased in response to biochar addition rates. In addition, eCO(2) increased root and shoot biomass but decreased the root-to-shoot ratio. eCO(2) significantly decreased EC, potassium (K+), ABA, and CYT concentrations, while the opposite pattern was found for AA and IAA. Significant interactive effects between biochar addition and eCO(2) were only found on CYT and AA concentrations, while no significant interactive effects of plant growth stage, biochar addition, and eCO(2) were found on root exudation. These results indicate that the additive effects of biochar and eCO(2) should be integrated into assessments of carbon storage ability in the future. Understanding the different responses of these variables within the rhizosphere is crucial for predicting changes in the carbon balance in response to biochar application and climate change.

Biochar can store carbon in soils for decades to centuries, and is considered to have some potential to contribute to mitigating climate change. However, both biochar and elevated atmospheric CO2 (eCO(2)) can influence the rhizosphere priming effect (RPE) on pre-existing soil organic carbon (SOC) decomposition, leading to uncertainty in comprehensively evaluating the soil carbon sequestration potential of biochar under future climate change. In the present study, we investigated the RPE on pre-existing SOC decomposition of paddy rice in a soil-plantbiochar system under eCO(2) (700 ppm). Plant-derived sources of carbon were separated from soil-derived sources using a continuous C-13-labelling method. We found that the RPEs decreased significantly with increasing biochar addition rates (1%, 2%, 3%, 4%, and 5% by weight) with mean reductions of 12% and 40% on day 31 and 54 after sowing, respectively, suggesting that biochar can enhance the stability of pre-existing SOC by decreasing the RPE. Although compared to ambient CO2 (aCO(2), 400 ppm), eCO(2) significantly decreased RPEs by 33% and 37% on day 31 and 54 after sowing, respectively, the decline in the RPE in response to biochar was weaker under eCO(2). Decreases in soil enzyme activities and microbial biomass carbon could explain the decline in the RPE in response to biochar addition. Our findings highlight that biochar can inhibit the decomposition of pre-existing SOC by reducing the RPE, while this effect will be weakened in the face of atmospheric CO2 increase in the future.