【森林碳的长期变化】Kathleen E. Savage et al. Long-term changes in forest carbon under temperature and nitrogen amendments in a temperate northern hardwood forest. Global Change Biology
Abstract
Currently forests in the northeastern United States are net sinks of atmospheric carbon. Under future climate change scenarios the combined effects of climate change and nitrogen deposition on soil decomposition aboveground processes and the forest carbon balance remain unclear. We applied carbon stock flux and isotope data from field studies at the Harvard forest Massachusetts to the ForCent model which integrates above- and belowground processes. The model was able to represent decadal-scale measurements in soil C stocks mean residence times fluxes and responses to a warming and N addition experiment. The calibrated model then simulated the longer term impacts of warming and N deposition on the distribution of forest carbon stocks. For simulation to 2030 soil warming resulted in a loss of soil organic matter (SOM) decreased allocation to belowground biomass and gain of aboveground carbon primarily in large wood with an overall small gain in total system carbon. Simulated nitrogen addition resulted in a small increase in belowground carbon pools but a large increase in aboveground large wood pools resulting in a substantial increase in total system carbon. Combined warming and nitrogen addition simulations showed a net gain in total system carbon predominately in the aboveground carbon pools but offset somewhat by losses in SOM. Hence the impact of continuation of anthropogenic N deposition on the hardwood forests of the northeastern United States may exceed the impact of warming in terms of total ecosystem carbon stocks. However it should be cautioned that these simulations do not include some climate-related processes different responses from changing tree species composition. Despite uncertainties this effort is among the first to use decadal-scale observations of soil carbon dynamics and results of multifactor manipulations to calibrate a model that can project integrated aboveground and belowground responses to nitrogen and climate changes for subsequent decades.
【冠层蒸散率对开放系统CO2】Hiroyuki Shimono et al. Lower responsiveness of canopy evapotranspiration rate than of leaf stomatal conductance to open-airCO2elevation in rice. Global Change Biology
Abstract
An elevated atmospheric CO2 concentration ([CO2]) can reduce stomatal conductance of leaves for most plant species including rice (Oryza sativa L.). However few studies have quantified seasonal changes in the effects of elevated [CO2] on canopy evapotranspiration which integrates the response of stomatal conductance of individual leaves with other resp