The aboveground biomass dynamics and net primary productivity were investigated to assess the productive potential of Diptero- carpus forest in Manipur, Northeast India. Two forest stands （stand Ⅰ and Ⅱ） were earm...The aboveground biomass dynamics and net primary productivity were investigated to assess the productive potential of Diptero- carpus forest in Manipur, Northeast India. Two forest stands （stand Ⅰ and Ⅱ） were earmarked randomly in the study site for the evaluation of biomass in the different girth classes of tree species by harvest method. The total biomass was 22.50 t.ha^-1 and 18.27 t.ha^-1 in forest stand I and II respectively. Annual aboveground net primary production varied from 8.86 to 10.43 t.ha^-1 respectively in two forest stands （stand Ⅰ and Ⅱ）. In the present study, the values of production efficiency and the biomass accumulation ratio indicate that the forest is at succession stage with high productive potential.展开更多
The maximum rate of carboxylation （Vcax） is a key photosynthetic parameter for gross primary produc- tion （GPP） estimation in terrestrial biosphere models. A set of observation-based Vcax values, which take the ni...The maximum rate of carboxylation （Vcax） is a key photosynthetic parameter for gross primary produc- tion （GPP） estimation in terrestrial biosphere models. A set of observation-based Vcax values, which take the ni- trogen limitation on photosynthetic rates into consideration, are used in version 4.5 of the Community Land Model （CLM4.5）. However, CLM4.5 with carbon-nitrogen （CN） biogeochemistry （CLM4.5-CN） still uses an inde- pendent decay coefficient for nitrogen after the photosyn- thesis calculation. This means that the nitrogen limitation on the carbon cycle is accounted for twice when CN bio- geochemistry is active. Therefore, to avoid this double nitrogen down-regulation in CLM4.5-CN, the original Vcmax scheme is revised with a new one that only accounts for the transition between Vcmax and its potential value （without nitrogen limitation）. Compared to flux tower- based observations, the new Vcmax scheme reduces the root-mean-square error （RMSE） in GPP for China's Mainland by 13.7 g C m-2 yr-1, with a larger decrease over humid areas （39.2 g C m 2 yr-1）. Moreover, net primary production and leaf area index are also improved, with reductions in RMSE by 0.8% and 11.5%, respectively.展开更多
Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,tra...Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition,which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition.Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass.By independently manipulating the frequencies(2 times vs.12 times N addition yr^(–1))and the rates(0–50 g N m^(−2) yr^(−1))of N addition,our study aimed to examine the response of soil microbial biomass C(MBC)to different N addition frequencies with increasing N addition rates.Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies,while the soil MBC decreased more at low frequency of N addition,suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass.The greater soil microbial biomass loss with low N frequency resulted from the intensifed soil acidifcation,higher soil inorganic N,stronger soil C and N imbalance,less net primary production allocated to belowground and lower fungi to bacteria ratio.To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies,it is necessary to employ both the dosage and the frequency of N addition.展开更多
文摘The aboveground biomass dynamics and net primary productivity were investigated to assess the productive potential of Diptero- carpus forest in Manipur, Northeast India. Two forest stands （stand Ⅰ and Ⅱ） were earmarked randomly in the study site for the evaluation of biomass in the different girth classes of tree species by harvest method. The total biomass was 22.50 t.ha^-1 and 18.27 t.ha^-1 in forest stand I and II respectively. Annual aboveground net primary production varied from 8.86 to 10.43 t.ha^-1 respectively in two forest stands （stand Ⅰ and Ⅱ）. In the present study, the values of production efficiency and the biomass accumulation ratio indicate that the forest is at succession stage with high productive potential.
基金supported by the National Natural Science Foundation of China(Grant Nos.91125016 and 41305066)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA05110102)
文摘The maximum rate of carboxylation （Vcax） is a key photosynthetic parameter for gross primary produc- tion （GPP） estimation in terrestrial biosphere models. A set of observation-based Vcax values, which take the ni- trogen limitation on photosynthetic rates into consideration, are used in version 4.5 of the Community Land Model （CLM4.5）. However, CLM4.5 with carbon-nitrogen （CN） biogeochemistry （CLM4.5-CN） still uses an inde- pendent decay coefficient for nitrogen after the photosyn- thesis calculation. This means that the nitrogen limitation on the carbon cycle is accounted for twice when CN bio- geochemistry is active. Therefore, to avoid this double nitrogen down-regulation in CLM4.5-CN, the original Vcmax scheme is revised with a new one that only accounts for the transition between Vcmax and its potential value （without nitrogen limitation）. Compared to flux tower- based observations, the new Vcmax scheme reduces the root-mean-square error （RMSE） in GPP for China's Mainland by 13.7 g C m-2 yr-1, with a larger decrease over humid areas （39.2 g C m 2 yr-1）. Moreover, net primary production and leaf area index are also improved, with reductions in RMSE by 0.8% and 11.5%, respectively.
基金supported by the National Natural Science Foundation of China(42130515 and31770506)the Open Foundation of the State Key Laboratory of Urban and Regional Ecology of Chinathe Open Foundation of the State Key Laboratory of Grassland Agro-ecosystems of China。
文摘Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition,which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition.Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass.By independently manipulating the frequencies(2 times vs.12 times N addition yr^(–1))and the rates(0–50 g N m^(−2) yr^(−1))of N addition,our study aimed to examine the response of soil microbial biomass C(MBC)to different N addition frequencies with increasing N addition rates.Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies,while the soil MBC decreased more at low frequency of N addition,suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass.The greater soil microbial biomass loss with low N frequency resulted from the intensifed soil acidifcation,higher soil inorganic N,stronger soil C and N imbalance,less net primary production allocated to belowground and lower fungi to bacteria ratio.To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies,it is necessary to employ both the dosage and the frequency of N addition.
