Print PageDue to land-use change and fossil fuel combustion, the atmospheric CO2 concentration has gradually increased by more than 100 pmm in the past 150 years and is expected to reach 700 ppm in 2085. As a consequence of rising CO2 and other greenhouse gases, the Earth’s surface temperature has increased by 0.74 oC in the 20th century. In the US Great Plains, air temperature is predicted to increase by 2 to 4oC with a doubling of current CO2 concentration. Precipitation is expected to increase by 16-22% per decade, mainly in heavy rainfall events.
To develop predictive understanding of ecosystem responses to multifactor global change, we have conducted three experiments in the southern Great Plains with treatments of temperature, precipitation, and biomass harvest. Meanwhile, we have conducted modeling analysis that has incorporated experimental results to improve model prediction of ecosystem responses to global change.
Results/Conclusions
Experimental warming caused significant increases in green biomass in spring and autumn and total biomass in summer. Elevated temperature increased net N mineralization in the first year but decreased it in the second year, likely due to stimulated plant growth and belowground C allocation that consequently enhanced microbial N immobilization. Warming-induced changes in soil respiration were proportional to those of total aboveground biomass. Warming advanced phenology of early-flowering species and delayed phenology of late-flowering species, leading to an extension of the growing season. Since leaf photosynthesis was not affected by warming, the extended growing season is likely the major mechanism of increased plant production. The latter is counterbalanced by moderate increases in soil respiration, leading to little change in soil C content. The increased production was accompanied by substantial increases in nitrogen use efficiency and slight increases in plant nitrogen uptake. Warming also considerably increased C4 plant biomass and caused slight decreases in growth of some C3 species. Increased C4 biomass, combined with decreased nitrogen concentration in litter, resulted in decreases in quality of bulk litter at the ecosystem scale, likely leading to decreased nitrogen availability over time.
We conducted modeling studies on ecosystem responses to climate change. We also used a data assimilation approach to estimate model parameters from experimental results and develop an ecological forecasting system to predict future changes in ecosystem dynamics under various global change scenarios.
