Effects Of Climate Warming And Nitrogen Deposition On Plant Phenology In A Temperate Grassland

Climate warming and nitrogen deposition have become a recognized environmental problem and have a profound impact on plant growth and development.Plant phenology is the most direct response to climate change,but there are still significant differences in the current research results across different latitudes,regions and species.Therefore,this study used field control experiments and meta-analysis to investigate the effects of climate warming and nitrogen deposition on grassland plant phenology.On the one hand,based on the long-term warming and nitrogen deposition simulation experiments in the desert steppe from 2021 to 2022,the reproductive phenology of 7 major plants was observed.On the other hand,the effects of climate warming on plant phenology in grasslands of northern China were studied through literature collection and meta-analysis.The main findings are the following:(1)The flowering and fruiting time of the different species were significantly different between among years.In 2021,warming significantly advanced the flowering time and fruiting time of Stipa breviflora by 5.5 days and 5.0 days,respectively.Nitrogen addition significantly delayed the flowering time of Cleistogenes songorica by 9.0 days,and significantly advanced the flowering time and fruiting time of Bassia prostrata by6.1 days and 5.2 days,respectively.Warming + nitrogen addition significantly delayed the flowering time of Cleistogenes songorica by 8.9 days.In 2022,warming significantly advanced the flowering time of Convolvulus ammannii and Bassia prostrata by 1.3 days and 1.7 days,respectively,and significantly delayed the flowering time of Artemisia frigida by 1.9 days.Warming + nitrogen addition significantly delayed the flowering time of Artemisia frigida by 1.8 days,and significantly advanced the fruiting time of Cleistogenes songorica by 3.0 days.(2)The reproductive growth periods of different species were significantly different among years.The reproductive growth periods of 7 species were longer in 2021 than in2022 in the Inner Mongolian desert steppe.In 2021,warming significantly prolonged the reproductive growth of Cleistogenes songorica by 5.5 days,and warming + nitrogen addition significantly prolonged the reproductive growth of Convolvulus ammannii by10.8 days.In 2022,nitrogen addition significantly prolonged the reproductive growth by3.6 days.(3)There was a significant correlation between growing season precipitation and phenology of major plants in Inner Mongolia desert steppe.Specifically,the reproductive growth of the 7 plants was significantly positively correlated with precipitation.Precipitation was significantly positively correlated with the flowering and fruiting time of Stipa breviflora,Convolvulus ammannii,and Allium mongolicum,and significantly negatively correlated with the flowering and fruiting time of Cleistogenes songorica,Bassia prostrata,Artemisia frigida,and Allium mongolicum.There was no significant relationship between soil temperature and flowering time,fruiting time and reproductive growth of 7 plants,while soil moisture was significantly negatively correlated with fruiting time of Bassia prostrata and Allium tenuissimum,and significantly positively correlated with reproductive growth of Artemisia frigida and Bassia prostrata.(4)Climate warming advanced the leaf expansion time of grassland plants and delayed the leaf yellowing time,thus prolonging the vegetative phenology across grasslands in northern China.Furthermore,it advanced the flowering time and fruiting time and prolonged the reproductive phenology of plants.Specifically,climate warming significantly advanced the leaf expansion time by 5.2 days,flowering time by 1.6 days and fruit ripening time by 1.5 days.In terms of phenological changes of different functional groups,climate warming advanced the vegetative phenology of grasses,shrubs and semi-shrubs,delayed the germination time and leaf yellowing time of legumes,sedges and forbs,but advanced their leaf expansion time;meanwhile,climate warming advanced the reproductive phenology of grasses,legumes,forbs,shrubs and semi-shrubs,and delayed the reproductive phenology of sedges.This study shows that climate warming has advanced the phenological period of plants and prolonged the growing season of plants.The response of plant phenology to climate warming in the desert steppe of Inner Mongolia was consistent with that of temperate steppe plants in northern China.It is of great significance for the research of plant growth and ecosystem diversity.In the future,more research should focus on the effects of climate change,spatial difference,and aboveground and belowground biomass of plants on plant phenology to provide more scientific basis for the study of grassland ecosystem and grassland carbon sink under climate change.