Effects Of Nitrogen And Water Addition On Functional Plant Traits And Community Structure In A Typical Temperate Steppe

With the rapid development of industrialization and the intensification of human activities,the concentration of greenhouse gases in atmosphere has increased dramatically,leading to global warming which is accompanied by changes in global and regional precipitation regime.In addition,the excessive use of industrial nitrogen(N)fertilizer and the burning of fossil fuels lead to the continuous input of large amounts of N into terrestrial ecosystems,which enhances soil N pool.N and water availability are important limiting factors for plant growth and development.Changes in N and water availability can affect plant growth and community structure by changing the supply of nutrients and water resources in the soil,and consequently terrestrial ecosystem function and service.Therefore,research on the effects of simulated N input and changing precipitation on plant growth and community structure can enhance mechanistic understanding of changes in terrestrial ecosystem functions and services under global change scenarios,thus providing theoretical support for sustainable management of terrestrial ecosystems.Functional plant traits refer to the physiological,morphological and phenological attributes that affect plant growth,reproduction and survival during the long-term evolutionary period.Functional plant traits reflect the response and adaptation of plants to environmental changes and directly determine their fitness in the community,which affects community composition and diversity.The composition and diversity of plant communities provide material basis of ecosystem function and service.In addition,functional plant traits can reflect the responses of terrestrial ecosystems processes and functions to environmental changes.Previous studies have shown that functional traits are the main determinants of ecosystem processes and functions(such as productivity,soil C pool and soil nutrient dynamics)in various terrestrial ecosystems.At present,studies on functional plant traits and community structure has become the main research theme in the field of global change ecology.The temperate steppe in northern China is an important part of the Eurasia grassland and it covers more than 40% of the total land area in China.It is one of the largest terrestrial ecosystem types in China.The temperate steppe in northern China has typical and representative vegetation type because of its special geographical location.In addition,in the late 20 th century,human disturbances such as overgrazing and cultivation led to grassland degradation and declination of ecosystem stability and productivity,which made grassland ecosystem structure and function sensitive to environmental changes in this region.Therefore,the typical temperate steppe of northern China provides an ideal experimental platform for studying effects of N input and changing precipitation on functional traits and plant community structure in terrestrial ecosystems.As a part of the comprehensive research project(Global Change Multi-Factor Experiment-Duolun,GCME-Duolun)launched in April 2005,a field manipulative experiment with N and precipitation was performed to examine the effects of N addition and increased precipitation on functional traits and plant community composition and diversity in a temperate steppe in Duolun County,Inner Mongolia,China.In this study,measurements of functional traits and plant community survey were conducted during the growing seasons from 2015 to 2017 in the temperate steppe.The results showed that:(1)Nitrogen addition significantly increased leaf N content by 11.3%,but did not change leaf carbon(C)content,leading to a reduced leaf C/N ratio by 6.2%,leading to increase leaf dry matter content(LDMC)and leaf area(LA)by 10.11% and 46.5% respectively,and specific leaf area(SLA)were not influenced by N addition.Increased precipitation had no significant effect on leaf traits.In the terms of root traits,N addition significantly enhanced root depth,root length and root diameter of the dominate forb,Artemisia frigida,by 51.6%,101.6% and 70.2%,respectively,and fine root diameter of Stipa krylovii(dominant grass)by 8.3% in this study.Increased precipitation stimulated basal root diameter of Artemisia frigida by 11.3%,whereas reduced its root depth and length by 6.8% and 14.4%,respectively.(2)Nitrogen addition significantly affected the correlation between leaf area and leaf carbon content,and significantly affected the correlation between specific leaf area and leaf carbon content,leaf nitrogen content,leaf C/N ratio,and LDMC,respectively;while water addition significantly affected the correlations between leaf area and leaf carbon content and leaf nitrogen content,respectively,and the correlations between specific leaf area and leaf nitrogen content and leaf C/N ratio,but had no significant impact on the correlations between other leaf attributes.(3)Nitrogen and water addition significantly affected plant community composition.N addition decreased plant community richness by 34.2%,while water addition increased plant community richness 39.6%,but had no effect on community diversity index.For non-grasses,N addition significantly reduced their richness by 37.1%,while water addition significantly increased their richness by 51.3%;for grasses,N addition had no effect on their richness,while water addition had a tendency to increase their richness.The results have demonstrated that changes in N and water availability can alter the resource competition strategy of plant species,which may affect plant community structure in the temperate steppe.Under N addition,plants allocate more energy to belowground part to facilitate root growth,resulting in enhanced capacity of competing soil water resource.Plants enhance the capacity of acquiring aboveground resource and reduce the investment to belowground part when soil water availability is improved.The findings facilitate to mechanistic understanding of global change impacts on the dynamics of terrestrial vegetation and provide theoretical support for the ecological restoration and ecosystem management in the temperate steep of northern China.