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<p><strong>Abstract.</strong> Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and net primary productivity are not well understood. A field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and productivity in a temperate meadow ecosystem in northeast China. Experimental warming significantly increased species richness, evenness and diversity, by contrast, N addition highly reduced species richness, evenness and diversity. Warming reduced the importance value of gramineous species but increased in forbs, N addition had the opposite effect. Warming had a significant positive effect on belowground productivity, but had a negative effect on aboveground biomass. The influences of warming on aboveground productivity were dependent on precipitation. Experimental warming had little effect on aboveground productivity in the years with higher precipitation, but significantly suppressed the growth of aboveground in dry years. Our results suggest that warming had indirect effects on plant productivity via altering water availability. Nitrogen addition significantly increased above- and belowground productivity, suggesting that N is one of the most important limiting factors which determine plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground productivity were also detected. Our observations revealed that climate changes (warming and N deposition) plays significant roles in regulating plant community composition and productivity in temperate meadow steppe.</p>

Nocturnal warming has various effects on plant biomass production. To understand how biomass production of the dominant grassland species Leymus chinensis responds to summer nocturnal warming in the eastern temperate Eurasian steppes, we simulated summer nocturnal warming (+4°C) using a phytotron system for 100 days operated based on the variation of diurnal temperatures over the past 12 years in the Songnen Grasslands. Our results show summer nocturnal warming significantly increased above-ground biomass production of parent and daughter shoots as well as increased below-ground root and rhizome biomass production; rhizome biomass increased faster than root biomass leading to an increase in the rhizome biomass to root biomass ratio. Nocturnal warming slightly increased the number of daughter shoots per plant, and significantly increased the number of buds in the below-ground bud bank and the number and length of rhizomes per plant. Also, the dark respiratory and net photosynthetic rates, J max , the rate of triosephosphate utilization and chlorophyll fluorescence parameters (Φ PSII and qP) were significantly higher under nocturnal warming conditions. These findings show that nocturnal warming in this ecosystem improves individual biomass accumulation due to photosynthetic compensation, and may enhance the population density and productivity of L. chinensis by increasing bud number in the below-ground bud bank during the early stage of ecological succession for grasslands dominated by L. chinensis.