Effects Of Seasonal Warming On Plant Phenology And Nutrient Resorption In An Alpine Meadow

Plant phenology refers to the growth and development rhythms of plants that have adapted to cyclical changes in environmental conditions over time,and is also considered to be the most sensitive bioindicator of climate warming.The timing of plant leaf out and leaf colour determines length of the growing season of plants andregulates the effective photosynthetic time of plants,with subsequently impact on plant carbon uptake in terrestrial ecosystems.Nutrient resorption,a biological process by which plants transfer and redistribute nutrients from senescing tissues,plays an important role in the nutrient conservation of plants and ecosystem nutrient cycling.It has well documented that nutrient resorption is influenced by plant leaf senescence phenology.Therefore,it is important to explore the responses of plant phenology and nutrient resorption to climate warming and their associated relationships.The Qinghai-Tibet Plateau is one of the largest plateaus in the world with the highest average altitude,and is known as the "third pole of the earth".During the past50 years(1960-2010),the Tibetan Plateau has experienced a warming of 0.4°C per decade,which is much larger than the global average.In addition,the warming magnitude of the Tibetan Plateau is not uniform across seasons,with higher warming in autumn and winter than in spring and summer.However,little is known about seasonal warming effect on plant phenology and nutrient resorption in alpine grasslands on the Qinghai-Tibet Plateau,which greatly limits the prediction of future vegetation growth dynamics.Therefore,based on the "seasonal warming" field control experiment in an alpine meadow on the Qinghai Tibetan Plateau,this work assessing the response of leaf out,leaf colour and nutrient resorption of 11 common species to explore the seasonal warming impact on plant phenology,nutrient resorption and their associated relationships.The main results are as follows:(1)Spring warming had a greater impact on the leaf out time of common species than summer,autumn,and winter warming.In 2021 and 2022,spring warming advanced 70% and 54% of observed species,with an average of 7.0 and 3.4 days,respectively.In contrast,spring warming and winter warming had a limited impact on the phenology of common species during leaf colour,while summer warming and autumn warming had an opposite impact on the end time of leaf colour.Summer warming advanced the leaf colour time of 80% of common species in 2021,but autumn warming delayed the leaf colour timing of 64% and 45% of species in 2021 and 2022,respectively.In addition,there were interspecific differences in the response of plant phenology to seasonal warming.Under spring warming,leguminous species showed a greater degree of advance in leaf out(with an average advance of 9.8 days)compared to other species(with an average advance of 3.5 days),while the end time of leaf colour and leaf out of Oxytropis kansuensis had no response to seasonal warming.(2)Nitrogen resorption efficiency of all target species did not respond significantly(P > 0.05)to seasonal warming.Similarly,phosphorus resorption efficiency had no significant response to seasonal warming(P > 0.05),except for Kobresia humilis under autumn warming and Potentilla saundersiana under spring warming.In addition,plant nutrient resorption efficiency was non-linearly correlated with autumn phenology.The results showed that the later the plant leaf turn yellow,the higher the phosphorus resorption efficiency were.In addition,plant phosphorus nutrient resorption efficiency was non-linearly correlated with the occurrence of the next year spring leaf out: the higher the phosphorus nutrient resorption efficiency,the earlier the occurrence of the following spring leaf out phenology.In summary,these findings demonstrated the substantial impact of seasonal warming on plant phenology in alpine grasslands.In addition,the results further revealed that the elevated temperature in spring had a greater impact on plant phenology than warming in other seasons.Moreover,this results also demonstrated the significant relationships between plant nitrogen cycling and phenological changes under seasonal warming.These findings will deepen our understanding of the growth dynamics of alpine vegetation in face of future climate change scenarios.