排序方式: 共有27条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
7.
Assessing the effect of elevated carbon dioxide on soil carbon: a comparison of four meta-analyses 总被引:1,自引:0,他引:1
BRUCE A. HUNGATE KEES-JAN van GROENIGEN † JOHAN SIX‡ JULIE D. JASTROW§ YIQI LUO¶ MARIE-ANNE de GRAAFF CHRIS van KESSEL ‡ CRAIG W. OSENBERG 《Global Change Biology》2009,15(8):2020-2034
Soil is the largest reservoir of organic carbon (C) in the terrestrial biosphere and soil C has a relatively long mean residence time. Rising atmospheric carbon dioxide (CO2) concentrations generally increase plant growth and C input to soil, suggesting that soil might help mitigate atmospheric CO2 rise and global warming. But to what extent mitigation will occur is unclear. The large size of the soil C pool not only makes it a potential buffer against rising atmospheric CO2, but also makes it difficult to measure changes amid the existing background. Meta‐analysis is one tool that can overcome the limited power of single studies. Four recent meta‐analyses addressed this issue but reached somewhat different conclusions about the effect of elevated CO2 on soil C accumulation, especially regarding the role of nitrogen (N) inputs. Here, we assess the extent of differences between these conclusions and propose a new analysis of the data. The four meta‐analyses included different studies, derived different effect size estimates from common studies, used different weighting functions and metrics of effect size, and used different approaches to address nonindependence of effect sizes. Although all factors influenced the mean effect size estimates and subsequent inferences, the approach to independence had the largest influence. We recommend that meta‐analysts critically assess and report choices about effect size metrics and weighting functions, and criteria for study selection and independence. Such decisions need to be justified carefully because they affect the basis for inference. Our new analysis, with a combined data set, confirms that the effect of elevated CO2 on net soil C accumulation increases with the addition of N fertilizers. Although the effect at low N inputs was not significant, statistical power to detect biogeochemically important effect sizes at low N is limited, even with meta‐analysis, suggesting the continued need for long‐term experiments. 相似文献
8.
Interactions between plant growth and soil nutrient cycling under elevated CO2 : a meta-analysis 总被引:2,自引:1,他引:1
MARIE-ANNE de GRAAFF † KEES-JAN van GROENIGEN † JOHAN SIX BRUCE HUNGATE‡ CHRIS van KESSEL 《Global Change Biology》2006,12(11):2077-2091
free air carbon dioxide enrichment (FACE) and open top chamber (OTC) studies are valuable tools for evaluating the impact of elevated atmospheric CO2 on nutrient cycling in terrestrial ecosystems. Using meta‐analytic techniques, we summarized the results of 117 studies on plant biomass production, soil organic matter dynamics and biological N2 fixation in FACE and OTC experiments. The objective of the analysis was to determine whether elevated CO2 alters nutrient cycling between plants and soil and if so, what the implications are for soil carbon (C) sequestration. Elevated CO2 stimulated gross N immobilization by 22%, whereas gross and net N mineralization rates remained unaffected. In addition, the soil C : N ratio and microbial N contents increased under elevated CO2 by 3.8% and 5.8%, respectively. Microbial C contents and soil respiration increased by 7.1% and 17.7%, respectively. Despite the stimulation of microbial activity, soil C input still caused soil C contents to increase by 1.2% yr?1. Namely, elevated CO2 stimulated overall above‐ and belowground plant biomass by 21.5% and 28.3%, respectively, thereby outweighing the increase in CO2 respiration. In addition, when comparing experiments under both low and high N availability, soil C contents (+2.2% yr?1) and above‐ and belowground plant growth (+20.1% and+33.7%) only increased under elevated CO2 in experiments receiving the high N treatments. Under low N availability, above‐ and belowground plant growth increased by only 8.8% and 14.6%, and soil C contents did not increase. Nitrogen fixation was stimulated by elevated CO2 only when additional nutrients were supplied. These results suggest that the main driver of soil C sequestration is soil C input through plant growth, which is strongly controlled by nutrient availability. In unfertilized ecosystems, microbial N immobilization enhances acclimation of plant growth to elevated CO2 in the long‐term. Therefore, increased soil C input and soil C sequestration under elevated CO2 can only be sustained in the long‐term when additional nutrients are supplied. 相似文献
9.
10.
ANNE-MARIE SIMONPOLI PREMAVATHY RAJAGOPALAN-LEVASSEUR MONIQUE BRUN-PASCAUD GUYLENE BERTRAND MARIE-ANNE POCIDALO PIERRE-MARIE GIRARD 《The Journal of eukaryotic microbiology》1996,43(5):400-403
ABSTRACT Nitrite production by rat alveolar macrophages was studied to determine the role of L-arginine oxidation in the interaction between these cells and Pneumocystis carinii. Alveolar macrophages from rats obtained from two different breeders were used: rats from Janvier breeder had latent P. carinii infection, while those from Charles River breeder were bred in a germ-free environment. Pneumocystis carinii increased in vitro nitrite generation by unstimulated alveolar macrophages from Janvier rats only, and this was blocked by NG-monomethyl-L-arginine. Incubation of cells from Janvier and Charles River rats with lipopolysaccharide and/or interferon-gamma increased nitrite production to a similar extent. Pneumocystis carinii partially decreased nitrite release by activated alveolar macrophages, and this was still inhibited by NG-monomethyl-L-arginine. In the presence of P. carinii, superoxide dismutase used as a superoxide anion scavenger had no effect on nitrite production by activated cells. These results show that prior exposure to P. carinii leads to nitric oxide production by rat alveolar macrophages. Although the magnitude of this production seems to be moderate, it is of biological significance since cells of P. curinii-naive rats do not generate nitrite whereas those of latently infected rats do. 相似文献