The USCCC network of eddy covariance study sites in China has measured the carbon and water exchanges in 16 ecosystems since 2005-2006. These include forests (poplar plantations in temperate and subtropical climate, in Hebei, Hunan and Anhui province), native and grazed grasslands (Inner Mongolia), desert shrublands (Inner Mongolia) and coastal wetlands (Liaoning and Shanghai province). In current overview, we will present key findings from three case studies: (i) carbon and water exchange over a Phragmites wetland in NE China, (ii) the tidal influences on the carbon exchange of Phragmites and Spartina wetlands in SE China, and (iii) the influence of anthropogenic land conversion on the carbon and water balance of semiarid grasslands and deserts in Inner Mongolia.

Results/Conclusions

The Phragmites wetland in Liaoning province in NE China appears to be a weak C sink (NEP=65±14 g C m^-2 yr^-1, ANPP=413 g C m^-2 yr^-1), which is sustained by removal of aboveground biomass in reed harvests. In contrast, work in estuarine wetlands (aboveground biomass ranging from 400 to 1170 g C m^-2) in Shanghai province indicates that the C balance cannot be closed without consideration of lateral transport by tides. The three site pairs of actively managed and unmanaged ecosystems along a two-fold (200-400 mm yr^-1) precipitation gradient in Inner Mongolia show that while management alters ecosystem C balance, the differences triggered by interannual climate variability are similar to or greater in magnitude than the management effects. Differences in evapotranspiration are almost entirely driven by climate and evaporative demand, with vegetation type having very little influence. Overall, the studies by USCCC participant institutions address carbon and water cycling in several underrepresented ecosystems, lending new insights into the mechanisms governing their biogeochemical cycles.