氮磷元素对碳元素的循环具有重要作用。氮磷元素是植物维持生理活动的重要元素，当氮磷元素含量不能满足植物体需要时，植物体光合作用过程会受到限制，从而生态系统的碳输入会减少，进而影响生态系统的碳存储量。为了准确评估未来全球变化过程对陆地碳存储量的影响，需要确定生态系统是否处于氮磷元素限制中。本研究结合生物化学循环模型CENTURY，改进其植被固碳过程中的氮磷元素限制作用，探究氮磷元素在碳循环过程中的作用，以及氮磷元素限制作用对土壤各个碳库间通量的影响，并由此分析氮磷元素对整个生态系统的碳循环的影响。本文基于大兴安岭呼中自然保护区森林生态系统，模拟当地森林生态系统的植被碳库和土壤碳库碳储量，模拟达到平衡状态时的植被碳库碳储量为4874.47 g/m2，在观测值2430.08--10001.7 g/m2的范围之内，土壤碳库的平衡值为8353.42 g/m2，与观测值8244.23 g/m2差别不大，由此可见CENTURY模型在研究区域有较好的适用性。依据IPCC AR5中两个极端的排放情景RCP2.6和RCP8.5，参考其预测的气象条件，预测未来气候变化情景下当地森林碳库储量的变化情况。在较高的排放情景下，植被碳库储量下降，土壤碳库的储量略微升高，生态系统总碳库明显下降。说明在升温条件下，生态系统的碳输入（植被叶片光合作用）和碳输出（植被、土壤以及微生物的呼吸作用）的差值为负值，碳汇减小，生态系统的碳存储能力下降。氮元素土壤中含量在RCP8.5时具有较高值，而磷元素在RCP8.5具有较低值。植被库中，氮元素在两种情景下都呈现出先下降再上升的趋势，但是RCP8.5绝对值含量仍大于RCP2.6，而磷元素跟氮元素具有相反的趋势，在RCP8.5时，模拟值较高。修改CENTURY模型中氮磷元素的限制作用，探究氮磷元素限制作用对土壤和植被各个碳库及碳通量的影响。修改氮磷元素限制作用后，植被碳库、土壤碳库、通量和生态系统碳储量都明显下降。植被碳库受限制作用影响较大，限制程度均在31%以上，即修改限制作用后，植被碳库约减少为原模拟值的2/3。土壤碳库中表层碳库受到的影响程度更大，碳储量约降低33%，而惰性碳库由于分解速率较慢，对影响的反馈较慢，且受影响程度相对较小。其原因主要是植被生物量的减少使土壤有机物的输入减少，导致土壤碳库储量的降低。微生物呼吸作用及分解作用产生的CO2通量也相应减少，主要因为土壤的分解速率同土壤有机物的氮碳磷碳比值直接相关，修改氮磷元素限制后，植被凋落物中氮磷元素与碳元素的比值变小，从而使土壤的分解速率降低。氮库在修改限制作用后，除了表层代谢库有较小的升高趋势外，其余库均呈现出增高趋势；与此相反，土壤磷库则表现出增加趋势，植被磷库表现出降低趋势，综合起来，生态系统整体表现出降低趋势，降低幅度较小，为6%。

Nitrogen and phosphorus play an important role in carbon cycles. Nitrogen and phosphorus are basic elements to maintain the plant physiological activities. Plant photosynthesis process will be limited when the two elements can not meet the demands of plants. In this way, the ecosystem carbon input will be reduced, and thereby affect the amount of carbon stored in ecosystems. In order to accurately assess the impact of climate change on global terrestrial carbon storage capacity, to determine whether the ecosystem is limited by nitrogen and phosphorus is very important. This study based on biogeochemical model CENTURY, improving the nitrogen and phosphorus limitation progress in vegetation carbon sequestration process, to explore the role of nitrogen and phosphorus in the soil carbon cycles. Furthermore, based on the impacts of nitrogen and phosphorus on soil carbon pools and carbon flux, we are trying to analyze the impact of nitrogen and phosphorus on the ecosystem carbon cycles. Our study is based on the forest ecosystem Huzhong Reserve in Northeast China. We simulated the vegetation carbon stocks and carbon storage in soil carbon pools in local area. When the model reaches balance, the vegetation carbon storage equilibrium state is 4874.47 g/m2, is in the range of observed value 2430.08--10001.7 g/m2. The soil equilibrium state is 8353.42 g/m2, also similar to the observed value 8244.23 g/m2. So we consider the model has well applicability in the study area. According to the two extreme emission scenarios RCP2.6 and RCP 8.5 in IPCC AR5, using its forecast weather conditions(temperature and precipitation), we want to forecast the forest carbon storage changes in the future under the different climate change scenarios. Under higher emission scenarios, vegetation carbon storage declines, soil carbon storage increased slightly and the total ecosystem carbon storage decreased significantly. That results indicates that at higher temperature, the deference between ecosystem carbon input (vegetation leaf photosynthesis) and carbon output (vegetation, soil and microbial respiration) is negative, the carbon sink declines and the capability of the ecosystem carbon storage is limited. In the soil pool, nitrogen content has a higher value in RCP8.5, and phosphorus has a lower value in the same scenario. In the vegetation pools, nitrogen content has the same trends that raising in the beginning and falling later. The nitrogen content in the RCP8.5 is greater than the RCP2.6. The phosphorus in vegetation pools has the opposite trend compare to the phosphorus in soil pools that the value in RCP8.5 is higher. We modify the limiting progress of nitrogen and phosphorus in the CENTURY model to explore the impact of nitrogen and phosphorus limitation on soil and vegetation carbon pools. After modifying the nitrogen and phosphorus limiting process, vegetation carbon storage, soil carbon storage, soil sink, and ecosystem carbon storage all have a significant decreasing. In the soil carbon pools , surface carbon pool has larger impacts than the soil pools, and the decreasing is about 33%. The passive carbon pool has a slow decomposition rate and the impacts if very litter. The reason of the decreasing is that the vegetation net primary production decreasing leads to the decreasing of soil organic materials inputs, and in this way the soil carbon storage decreased. The CO2 flux in microbial and soil respiration is also decreased; the most important reason is that the decomposition rate has a direct correlation on soil C/N and C/P ratio. The litter residues of the vegetation have a lower nitrogen and phosphorus content when the limitation progress is modified, so the soil decomposition rate is decreasing. When the limitation progressing modified, except the metabolic nitrogen storage has a slight increase, all of the other pools have significantly decreasing trend; contrast, the soil phosphorus storage has an increasing trend and the vegetation phosphorus storage has a decreasing trend. Combining the soil and vegetation pools, the ecosystem phosphorus has a slightly decrease trend with decreasing 6%.