Nitrogen fertilization differentiates carbon and nitrogen sequestrations in terrestrial ecosystem: A meta-analysis

Background/Question/Methods Nitrogen (N), a key element in biological systems, is one of the most important factors to carbon (C) and N processes in terrestrial ecosystem. N limitation theory indicates that N is a limited factor for plant. However, how the N fertilization influences terrestrial ecosystem C storage is still uncertain. In this study, we extracted data from 151 independently published papers that study the effects of long-term manipulative N fertilization on terrestrial ecosystem C and N sequestrations. The database contains C and N pools of plant and soil, microbial biomass C and N, soil available N, and C:N ratios of plant, soil and microbe.Results/Conclusions Overall, our results show that N fertilization has different effects on plant, soil and microbe. Compared to the control group, averaged C and N pool sizes of plant (including aboveground plant and belowground plant) significantly increase in N fertilization group, ranging from a 24% increase in aboveground C pool to a 67% increase in aboveground N pool. The C and N contents in litter pools are consistently higher in N fertilization group than control group. N fertilization does not change the soil C pool but significantly increases the soil N pool and soil available N, ranging from a 11% increase in soil N pool to a 110% increase in soil available N. The microbial biomass C and N decrease by 12% and 6% respectively. Averaged C:N ratios of plant, soil, litter and microbe all significantly decrease. Different ecosystems (Cropland, Forest, Grassland, Wetland, Tundra etc.) and soil properties of different soil depths (0-15cm, 15-30cm and 30-55cm) have variant responses to long-term N fertilization. Our results also show that the effect of N fertilization on soil C pool is not influenced by latitude variation, N fertilizer rate or experiment duration. To some degree, even the N fertilization does not change the soil C pool, the net C accumulation in plant caused by N fertilization could help to sequestrate C in terrestrial ecosystem and prevent the rising of atmospheric CO₂.