Effects Of Nutrient Additions On Plant Functional Traits In Temperate Grassland Of Inner Mongolia

Nitrogen (N) and Phosphorus (P) are two key elements for plant growth and net productivity of terrestrial ecosystems. Plant functional traits represent the ecological strategies that response to environmental conditions, and the basis for maintaining ecosystem functions. Studying the changes of plant functional traits when N and P are added to an ecosystem provides a machanistic basis for understanding the plant behavior.Here we select three herbaceous plants from typical steppe (located in Xilingol) and five species from meadow steppe (located in Hailar) of Inner Mongolia, and measured plant height and leaf traits. Our objects were to determine (1) how N and P additions impact plant traits, and whether these responses vary among species, and (2) whether limiting nutrients and drought interactively affect plant traits.(1) After two year of observations, experiment yielded similar effects on plant traits between ecosystems. On average, we found few effects of P and N alone on plant height, and N and P additions combined resulted in stronger effects than either alone. Surprisingly, the morphological traits (including leaf thickness, leaf dry matter content, and specific leaf area) of plants have little responses to N and P additions. Leaf N concentration or P concentration of plants significantly increased after N or P addition alone.(2) Effects of fertilization on plant height varied among species. Only dominant species (Leymus chinensis) in both ecosystems showed stronger response to N alone, and N and P combined addition, but few responses to P alone.(3) Nutrient addition had little effects on plant morphological characteristics for most species. Three morphologic traits showed large changes between years, which may indicate more stronger regulations by year drought than limiting nutrient elements.(4) Plant leaf chemical properties are the most sensitive to N and/or P addition. Nitrogen addition promoted leaf N concentration of most species, but the effects varied between years. In contrast, P enrichment alone resulted large and concurrent increases in leaf P concentration over time. The interaction effect of N and P combined addition showed that P fertilization tended to promotes N reserved by plants, but N addition commonly reduced the P concentration of plants.Our study indicates that N and P additions alone or interacted to drive changes in plant functional traits, particularly large changes in plant height and leaf N and P concentration, which have potential effects on ecosystem functions. The responses of plant traits varied among different species. Thus, the different alterations with nutrient availability have unpredictable consequence in ecosystem function over time, particularly within the context of climate change.