Effects Of Ecological Restoration Measures On Plant Communities In Degraded Grassland

Grassland has important ecosystem service value,however,90% of grassland in China has deteriorated in varying degrees due to climate change and human activity.At present,various restoration measures have been adopted to restore the structure and function of the degraded grasslands.And reseeding is one of the common restoration measures in grasslands.Previous studies mainly focused on the effects of reseeding one species or a few species on degraded grasslands,and less attention has been paid to the role of species diversity of reseeding species.In addition,reseeding and other restoration measures showed various impacts on grasslands in different areas,and there is a lack of unified understanding.Previous studies have focused on the recovery of grassland communities,since plant functional groups largely determine the process and function of ecosystem,we still know little about their restoration pattern.Firstly,based on the reseeding platform of Inner Mongolia Grassland Ecosystem Research Station,Chinese Academy of Sciences,this study explores the changes in characteristics of the existing plant community,plant growth of reseeding species,and their relationship along a gradient of reseeding species diversity(1,2,4,and 8 species).Secondly,we conducted meta-analyses to quantitatively study the effects of reseeding and different ecological restoration measures(passive restoration,active restoration)on the growth of plant populations,functional groups and communities of degraded grasslands,and to explore the key driving roles of climate,soil,and recovery duration.The main results are as follows:(1)Reseeding had no significant effect on the characteristics of plant community in degraded grassland in the short term,which was not altered by the number of reseeding species.Reseeding species showed specie-specific differences in the plant growth,which were further influenced by the characteristics of plant community in degraded grassland.The seedling emergence rate of Allium ramosum was the best(13.85%),while the one of Potentilla tanacetifolia was the lowest(1.23%).The survival rate of Melissilus ruthenicus was the best(3.55%),while the one of P.tanacetifolia was the lowest(0.54%).The increase in plant density of community in degraded grasslands inhibited the seedling emergence of Achnatherum sibiricum and M.ruthenicus,but promoted that of P.tanacetifolia.The increase in plant density of perennial bunchgrasses(i.e.,Stipa grandis,Cleistogenes squarrosa)inhibited the seedling emergence of the A.sibiricum and A.ramosum,while the increase in plant density of C.squarrosa promoted the seedling emergence of Agropyron cristatum.(2)Reseeding generally promoted the recovery process of degraded grasslands in China.Compared with the degraded grassland,the biomass of grasses was increased by 253.57%,and the biomasses of plant community and legumes were increased by 96.48% and 134.81%,however,plant diversity and forbs’ biomass remained unchanged.In addition,the biomasses of plant communities and grasses had been restored to the level of natural grasslands,but the forbs’ biomass was not fully recovered.The enhancement of reseeding on degraded grassland was not affected by grassland type and the functional identity of reseeding species.Legumes could be better recovered in warm areas,and the biomasses of grasses,legumes and plant communities were better recovered in humid area,and reseeding-induced improvement on forbs’ biomass increased with the restoration time.(3)Generally,all kinds of ecological restoration measures have significantly promoted the recovery of plant biomass in degraded grasslands in China.Compared to the degraded grassland,the biomass of grasses increased by 195.26%,and biomasses of the legumes,sedges and dominant species increased by 98.04%,101.23% and 116.28%.The forbs’ biomass was slightly increased(22.88%),and that of common species was not significantly changed.At the same time,the biomasses of grasses,sedges and common species had been restored to the level of natural grasslands,in contrast,those of dominant species and forbs had not yet been fully restored.Although there was no obvious difference in the effect of different restoration measures on the growth of plant population and group,passive restoration measures benefited forbs more,while active restoration measures were not conducive to the recovery of common species.In warm and humid areas,grassland plant species and functional group attained better restoration outcomes.The recovery degree of dominant species increases with restoration duration.and the recovery of forbs,legumes and dominant species were driven by changes in soil moisture and nutrients.In addition,changes in the biomass of grassland communities were mainly influenced by those of grasses and dominant species,while plant diversity was mainly determined by the changes in forbs and legumes.Overall,the plant growth of reseeding species was influenced by the species identity and surrounding conditions,and reseeding of perennial plant species showed little effect on the degraded grassland community in the short term.The reseeding can effectively promote the biomass recovery of degraded grassland communities,but the restoration effect of plant diversity was limited.The restoration outcomes varied among different plant species or groups in degraded grassland,which were further influenced by the type of restoration measures,climate,soil,and restoration duration.In addition,the recovery of plant communities was driven by plant species and function groups in degraded grassland.This study is of great significance for understanding the dynamics and mechanism of community succession during the ecological restoration of degraded grasslands in China.