SOIL FERTILITY AND SPECIES IDENTITY CONTROL COMMUNITY PRODUCTIVITY IN AN EXPERIMENTAL PLANT COMMUNITY IN AN AREA OF SUBALPINE MEADOW Soil nitrogen dynamics and productivity of snowpack Sanguisorba sitchensis community in alpine tundra of Changbai Mountain, China Effect of sampling scale on the relationship between species diversity and productivity in subalpine meadows Effects of fertilization and clipping on species diversity, productivity and their relationship in subalpine meadow Study on the Relationship between Species Variation and Productivity of Different Degraded Plant Communities on Leymus chinensis