| Sulfur?S?element,as one of the biogenic elements for plant growth,participates in physiological metabolism and plays an important role in driving the biogeochemical cycling.S deposition has doubled over the past two decades in the eastern of Inner Mongolia.S deposition–induced soil acidification is one of the major threats to grassland ecosystem structure and functioning in part because of soil base cation leaching,microelement activation and nutrient imbalance.There is lack a comprehensive understanding of how S deposition affects plant nutrient characteristics and trait variability,biodiversity and productivity related to soil acidification.A long-term S addition experiment,which included eight rates(0.00,1,2,5,10,15,20,50 gSm-2yr-1),was carried out in a semi-arid meadow grassland.Based on yearly?2017-2019?continuous sampling and measurement on botanical composition,plant nutrients,functional traits and related soil characteristics,biodiversity and productivity response to S addition were analyzed in community analyses.The key findings are summarized as following:?1?Leaf N,P,S concentrations were convergent across the growing seasons?June,July,August and October?of 2018 at species-level.The four elements were low early in the season,and high in mid-growing season,and then significantly decreased later in the season after plant senescence.There were no consistent changes in leaf Ca,Mg,K and microelements of different species,whereas most elements accumulated in senesced leaves.Compared to grasses,the response in leaf element concentrations of forbs were more sensitive to S addition treatment.An antagonism effect exists between leaf Fe and Mn uptake in forbs,and leaf B and Mo decreased by S addition.The relative contributions of intraspecific variation and species turnover on community nutrients varied with different elements.Leaf S and Mn concentrations showed significant intraspecific variation,indicating that community composition and dominant species had strong resistance to environmental changes.Leaf N and P concentrations showed significant interspecific variation,indicating that species turnover would aggravate the imbalance of N and P in grassland plants under soil acidification induced by S addition.?2?Leaf nutrient resorption patterns among species depended on different precipitation in 2018 and 2019.S addition significantly decreased nitrogen,phosphorus and sulfur nutrient resorption efficiency of Leymus chinensis.The Carex duriuscula,demonstrated remarkably reduced sulfur nutrient resorption efficiency by S addition,responding with different nitrogen and phosphorus nutrient resorption patterns under dry and wet years.Nutrient resorption efficiency was regulated by soil p H and available sulfur.Leaf N and P concentrations in senesced leaves were tightly correlated in wet year but different in dry year.?3?Soil acidification had significant effects on dominant species traits.S addition significantly decreased specific leaf area?SLA?and increased leaf dry matter content?LDMC?of L.chinensis to reduce the loss of water and nutrients.To the contrary,root traits of C.duriuscula exhibited high plasticity,and invest more in root N,root P,root S,specific root length via the fast acquisition of nutrient for growth in response to S addition.The contrary results indicated that,different species have evolved diverse adaptive strategies in response to soil acidification in semi-arid regions.Community traits were relatively constant,and were mainly regulated by dominant species traits,soil p H and soil nutrient availability under S addition.?4?S addition significantly decreased species diversity.The results supported the predictions of randomly loss hypothesis and forb-grass hypothesis,regarding the mechanisms of acidification-induced the decrease of forbs and rare: common species richness ratio.Three species were excluded from plots per square meter which received high S input(50 gSm-2yr-1)with a loss rate up to 42%.It indicated that the response of species richness on calcareous soil to soil p H was higher than the critical threshold in acidic soil.Functional richness and dispersion were enhanced by S addition,while functional divergence was reduced.Soil N and S availability,community leaf Mn concentration,soil acidification and functional diversity?functional dispersion decreased?accounted for the reduction in species diversity.?5?With respect to species composition,S addition facilitated the growth of L.chinensis?perennial rhizome grass?with high acid tolerance and C.duriuscula?Sedge?with nutrient acquisitive strategy.The aboveground biomass of the two species showed neutral and positive responses to S addition,whereas the relative biomass of perennial bunchgrasses and forbs with low acid tolerance decreased.The aboveground net primary productivity?ANPP?and species asynchrony increased slightly when less than 5 gSm-2yr-1 was treated,and decreased significantly when more than 5 gSm-2yr-1 was treated.The temporal stability of ANPP was not changed.ANPP was not related to species richness,but the structural equation model revealed that increasing soil available nutrients?available sulfur?and decreasing soil p H could indirectly affect community structure by species evenness,dominance and rarity.Above all,the results showed that S addition had substantial effects on plant leaf nutritional characteristics,nutrient resorption,functional traits and community diversity and so on.Dominant species contributed more to ANPP and rare species is more sensitive to S addition compared to common species.This study would make a theoretical basis and data support for the nutrient cycling process of the semi-arid grassland ecosystem,the protection of grassland biodiversity and productivity under the scenarios of atmospheric S deposition and soil acidification. |
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