ABSTRACT: The impact of land-use/land-cover and climate changes on ecosystem productivity and carbon cycle is one of the most important
issues in global change studies. In the past 20 years, the climate and land-use in China have changed significantly and have
had important ecological consequences, especially in ecologically sensitive regions, e.g. the cropping-grazing transition
zone (CGTZ). Here we present a study that used a process-based ecosystem model and data of land-use changes based on remote
sensing and of climate change at high spatial and temporal resolution to estimate the impacts of land-use and climate changes
on net primary productivity (NPP), vegetation carbon storage, soil heterotrophic respiration (HR), carbon storage and net
ecosystem productivity (NEP) in the CGTZ of China. The results show that the warming and decreases in precipitation in CGTZ
reduced NPP by 3.4%, increased HR by 4.3%, and reduced annual mean total NEP by 33.7Tg from the 1980s to the 1990s. Although
carbon storage in vegetation and soil was increasing because the mean NPP for the period was higher than HR, the decreasing
NEP indicate that climate change reduced the carbon uptake rate. However, land-use changes in this zone caused increases in
NPP by 3.8%, vegetation carbon storage by 2.4%, and annual total NEP by 0.59Tg. The land-use changes enhanced ecosystem carbon
uptake, but not enough to offset the negative effect of the climate change. The climate change had greater impacts than the
land-use change for the whole CGTZ zone, but had smaller impacts than the land-use change in the regions where it occurred.
Science in China Series D Earth Sciences 04/2012; 48(9):1479-1491. · 1.59 Impact Factor
ABSTRACT: Using data from eddy covariance measurements in a subtropical coniferous forest, a test and evaluation have been made for
the model of Carbon Exchange in the Vegetation-Soil-Atmosphere (CEVSA) that simulates energy transfers and water, carbon and
nitrogen cycles based on ecophysiological processes. In the present study, improvement was made in the model in calculating
LAI, carbon allocation among plant organs, litter fall, decomposition and evapotranspiration. The simulated seasonal variations
in carbon and water vapor flux were consistent with the measurements. The model explained 90% and 86% of the measured variations
in evapotranspiration and soil water content. However, the modeled evapotranspiration and soil water content were lower than
the measured systematically, because the model assumed that water was lost as runoff if it was beyond the soil saturation
water content, but the soil at the flux site with abundant rainfall is often above water saturated. The improved model reproduced
79% and 88% of the measured variations in gross primary production (GPP) and ecosystem respiration (R
e), but only 31% of the variations in measured net ecosystem exchange (NEP) despite the fact that the modeled annual NEP was close to the observation. The modeled NEP was generally lower in winter and higher in summer than the observations. The simulated responses of photosynthesis and respiration
to water vapor deficit at high temperatures were different from measurements. The results suggested that the improved model
underestimated ecosystem photosynthesis and respiration in extremely condition. The present study shows that CEVSA can simulate
the seasonal pattern and magnitude of CO2 and water vapor fluxes, but further improvement in simulating photosynthesis and respiration at extreme temperatures and
water deficit is required.
Keywordsecosystem CO2 and water flux-CEVSA-eddy covariance-subtropical coniferous forest
Science in China Series D Earth Sciences 04/2012; 49:241-251. · 1.59 Impact Factor
ABSTRACT: Arable land soils generally have lower organic carbon (C) levels than soils under native vegetation; increasing the C stocks through improved management is suggested as an effective means to sequester CO2 from the atmosphere. China's arable lands, accounting for 13% of the world's total, play an important role in soil C sequestration, but their potential to enhance C sequestration has not yet been quantitatively assessed. The C sequestration by agricultural soils is affected by many environmental factors (such as climate and soil conditions), biological processes (crop C fixation, decomposition and transformation), and crop and soil management (e.g. tillage and manure application). Estimation of the C sequestration potential requires the quantification of the combined effects of these factors and processes. In this study, we used a coupled remote sensing- and process-based ecosystem model to estimate the potential for C sequestration in agricultural soils of China and evaluated the sustainability of soil C uptake under different soil management options. The results show that practicing no-tillage on 50% of the arable lands and returning 50% of the crop residue to soils would lead to an annual soil C sequestration of 32.5 Tg C, which accounts for about 4% of China's current annual C emission. Soil C sequestration with improved soil management is highly time-dependent; the effect lasted for only 20–80 years. Generally, practicing no-tillage causes higher rate and longer sustainability of soil C sequestration than only increasing crop residue into soils. The potential for soil C sequestration varied greatly among different regions due to the differences in climate, soil conditions and crop productivity.
Agriculture, Ecosystems & Environment.
ABSTRACT: China's cultivated land has been undergoing dramatic changes along with its rapidly growing economy and population. The impacts of land use transformation on food production at the national scale, however, have been poorly understood due to the lack of detailed spatially explicit agricultural productivity information on cropland change and crop productivity. This study evaluates the effect of the cropland transformation on agricultural productivity by combining the land use data of China for the period of 1990–2000 from TM images and a satellite-based NPP (net primary production) model driven with NOAA/AVHRR data. The cropland area of China has a net increase of 2.79 Mha in the study period, which causes a slightly increased agricultural productivity (6.96 Mt C) at the national level. Although the newly cultivated lands compensated for the loss from urban expansion, but the contribution to production is insignificant because of the low productivity. The decrease in crop production resulting from urban expansion is about twice of that from abandonment of arable lands to forests and grasslands. The productivity of arable lands occupied by urban expansion was 80% higher than that of the newly cultivated lands in the regions with unfavorable natural conditions. Significance of cropland transformation impacts is spatially diverse with the differences in land use change intensity and land productivity across China. The increase in arable land area and yet decline in land quality may reduce the production potential and sustainability of China's agro-ecosystems.
Global and Planetary Change.