Responses Of Alpine Meadow To Experimental Warming In The Tibetan Plateau Based On Root Functional Traits

As the third pole of the earth,the Qinghai-Tibet Plateau covers about one quarter of the land area in China,with an average altitude of more than 4,000 m.It is the highest,most complex and largest frozen plateau region in the world.The presentation of permafrost with high elevation makes the alpine ecosystem extremely fragile and especially sensitive to climate change.Over the past 50 years,the rate and magnitude of temperature increase in the permafrost regions of the Qinghai-Tibet Plateau have been significantly higher than the northern hemisphere and the global average.Climate warming has accelerated the melting of frozen soil,changed the process of soil freezing and thawing,and exerted a profound impact on the alpine ecosystem.To study the response of alpine ecosystem to climate warming in permafrost regions is helpful to understand the response characteristics and evolution trend of alpine ecosystem to global climate change,and to provide scientific and theoretical basis for the sustainable management and development of alpine grassland ecosystem.In the Fenghuoshan area where permafrost is widely developed on the QinghaiTibet Plateau,Kobresia pygmaea meadows and Kobresia tibetica swamp meadows are selected as the research objects,and OTCs are used to simulate warming.Clarify the response process of abiotic factors such as air temperature,soil water content,soil nutrients,soil freezing and thawing,and biological factors such as vegetation phenology,productivity of root,and root functional traits to simulated warming.Focus on clarifying the response process of two alpine meadows root functional traits to simulated warming,and reveal the underlying mechanism of net primary productivity of alpine meadow roots in permafrost regions in response to warming.The main results and conclusions are as follows:(1)The impact of simulated warming on the environmental factors of the two meadows differs between the growing season and the non-growing season,which is mainly reflected in the vegetation turning green period.The soil surface nutrients of the Kobresia pygmaea meadow increase,and the soils of the two meadows tend to warm and humid.In the growing season,the soils of the two meadows tended to warm and dry.OTCs increase the air temperature of the two meadows.The average annual temperature increase of Kobresia pygmaea is 1.69℃,and the temperature of the swampy Kobresia tibetica meadow increases by 2.51℃;the soil moisture in the growth season of the two meadows(May-September)decreases,but Soil moisture in the nongrowing season(from January to April and October to December)increased.At the same time,OTCs advanced the start date of soil ablation in the two meadows,delayed the start date of freezing,and prolonged the complete melting period.The content of available nitrogen and available phosphorus in the soil surface(0-10 cm)of Kobresia pygmaea meadow was in the greening period(5 May 5-May 26)increase.(2)OTCs promote the growth of roots in alpine meadows,and there are seasonal differences in the response of root biomass to warming.OTCs increase the root biomass of Kobresia pygmaea meadow during the vigorous and yellow periods,and increase the root biomass of the Kobresia tibetan meadow during the yellowish period.In the vigorous period,the increase in root biomass of Kobresia pygmaea meadow is related to the warming and drying of shallow soil during the growing season.In order to obtain soil water and nutrient resources,plants distribute more biomass downwards to stabilize plant growth.(3)The response of root morphology to warming differs in meadow types.For Kobresia pygmaea meadows,warming promotes the root system’s acquisition of soil resources during the turning green period,and increases the root stress resistance during the vigorous and yellow periods;for Kobresia tibetan In swamp meadows,warming has always promoted the rapid absorption and utilization of soil moisture and nutrients by plants,and has developed towards a rapid resource acquisition strategy.Specifically,OTCs significantly increased the total root length of Kobresia pygmaea meadow during the greening period.In the vigorous period,the temperature increase significantly increased the specific root length and specific root area of the Kobresia tibetan swamp meadow;increased the total root length of the Kobresia pygmaea meadow.During the yellowing period,increasing temperature increased the specific root length,specific root area and root diameter of the Kobresia tibetans swamp meadow;the specific root length and specific root area of the Kobresia pygmaea meadow decreased,while the root tissue density and root diameter increased.(4)There are seasonal differences in root carbon,nitrogen,phosphorus content and stoichiometric ratio in response to warming.During the turning green period,OTCs increase the carbon,nitrogen,and phosphorus nutrient elements in the roots of the two meadows,reduce the carbon,nitrogen,phosphorus content and the carbon to phosphorus ratio of the Kobresia pygmaea meadow roots in the vigorous period,and increase the root carbon content and the level of carbon:nitrogen ratio in the yellowing period.(5)During the greening period,OTCs promote the conversion of alpine meadow root starch into soluble sugar to increase plant metabolism and promote growth.During the yellowing period,OTCs increased the soluble sugar content,root starch content and total amount of non-structural carbohydrates in the root system of Kobresia pygmaea meadow,and increased the carbon storage of the root system of Kobresia pygmaea meadow in winter.(6)The effects of warming on the root productivity of alpine meadows are closely related to root characteristics and environmental factors;at the same time,the effects of warming on the phenology of two meadow communities are also closely related to the effects of temperature and soil freezing and thawing.Specifically,the greening period of the two meadows advances with the increase in annual average temperature and the start date of soil melting;the yellowing period is delayed with the delay of the soil freezing day and melting time;the length of the growing season varies with the annual average temperature.Increase,the delay of the soil freezing day and the increase of the soil thawing period will extend.For Kobresia pygmaea meadows,the root biomass at the turning-green stage was significantly positively correlated with the total root length,root tissue density,and root non-structural carbon storage content,and significantly negatively correlated with specific root length,root diameter,and root N content;The root biomass in the vigorous period was mainly negatively correlated with the water in the growing season;the root biomass in the yellowing period was significantly positively correlated with the root tissue density.For the Kobresia tibetan swamp meadow,the root biomass at the turning green stage was significantly positively correlated with the total root length,and significantly negatively correlated with the specific root length.