Pan Yude, Melillo Jerry M, McGuire A David, Kicklighter David W, Pitelka Louis F, Hibbard Kathy, Pierce Lars L, Running Steven W, Ojima Dennis S, Parton William J, Schimel David S
The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA Fax: +1-508-4571548; e-mail:
U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, AK 99775, USA, , , , , , US.
Oecologia. 1998 Apr;114(3):389-404. doi: 10.1007/s004420050462.
Although there is a great deal of information concerning responses to increases in atmospheric CO at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO. In this study, we analyze the responses of net primary production (NPP) to doubled CO from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO.
尽管在组织和植物层面有大量关于大气二氧化碳浓度升高响应的信息，但在综合碳、水和养分循环的背景下，研究生态系统层面响应的研究要少得多。由于我们对生态系统对二氧化碳浓度升高的响应的理解并不完整，建模是一种可用于研究植物与土壤相互作用在陆地生态系统对二氧化碳浓度升高响应中所起作用的工具。在本研究中，我们分析了植被/生态系统建模与分析项目（VEMAP）中的三个生物地球化学模型：生物地球化学循环模型（BIOME - BGC）、世纪模型（Century）和陆地生态系统模型（TEM）中，净初级生产力（NPP）对二氧化碳浓度从355 ppmv翻倍至710 ppmv的响应。对于美国本土，大气二氧化碳浓度翻倍导致世纪模型中的NPP增加5%，TEM模型中增加8%，BIOME - BGC模型中增加11%。对NPP对二氧化碳浓度翻倍的响应与生物群落或网格单元的年平均温度和年降水量之间进行的多元回归分析表明，对于所有三个模型，降水量与NPP对二氧化碳浓度翻倍的响应之间均存在负相关关系。相比之下，对于三个模型，温度与NPP对二氧化碳浓度翻倍的响应之间存在不同的关系：在BIOME - BGC模型的响应中存在负相关关系，在世纪模型的响应中无相关关系，在TEM模型中存在正相关关系。在BIOME - BGC模型中，NPP对二氧化碳浓度翻倍的响应受与叶片对水汽传导率降低相关的蒸腾作用变化的控制。这种变化影响土壤水分，进而影响叶面积发育，最终影响NPP。在世纪模型中，NPP对二氧化碳浓度翻倍的响应受与蒸散量减少导致土壤湿度增加相关的分解速率变化的控制。这种变化影响植物可利用的氮素，从而影响NPP。在TEM模型中，NPP对二氧化碳浓度翻倍的响应受羧化作用增强的控制，而羧化作用又受冠层传导率以及氮素限制导致光合作用下调程度的影响。这些不同机制的实施对NPP响应的空间格局产生影响，并且在一定程度上代表了对NPP响应控制的概念性不确定性。减少这些不确定性的进展需要聚焦于生态系统层面的研究，以了解碳循环、氮循环和水循环之间的相互作用如何影响NPP对大气二氧化碳浓度升高的响应。
