Correlation between stand photosynthesis and composition at micro-scale in loess grassland

Introduction Compositional and functional patterns and trends in micro-scale, that of the organization of grassland communities, are more difficult to explain than phenomena of the population or macro ecological level (Lawton 1999). To observe rules and forces, mechanisms that govern them, selection of appropriate scales is necessary (Bartha 2000, Elmore 1980). Small-scale spatial heterogeneity of CO2 gas exchange in grasslands partly depends on plant community compositional traits. Species richness, species composition, horizontal and vertical structure and green leaf area index (LAI) of grasslands are diverse in space, and affect net ecosystem CO2 exchange through its components (gross photosynthesis, soil respiration etc.). Study of the rapport of diversity and productivity has long history. LAI and NDVI, considered here with reference to compositional richness (Csillag et al. 2001, Kertesz et al. 2001) are usually related to photosynthetic performance. Papers published on the relationships of the CO2 exchange and diversity (Craine et al. 2001, Spehn et al. 2000, Stocker et al. 1999) report that diverse ecosystems perform better both aboveand below-ground, than monocultures, other articles on the topic of photosynthesis and species dominance or cover (LeCain et al. 2002, McAllister et al. 1998) emphasize that dominant species with high cover are more effective in their gas exchange, than rare species, but these studies mainly refer to leaf level photosynthesis and CO2 enrichment experiences. We investigated the effect of species richness and surface cover on photosynthesis at the same spatial scale: stand-level gross photosynthesis and composition of the measured stand patches have been compared to: (i) find the relationships between photosynthesis and vegetation cover, (ii) reveal the rapport between species number and photosynthesis and the importance of the dominant species.