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Abstract We use the Multiple Element Limitation (MEL) model to examine responses of 12 ecosystems to elevated carbon dioxide (CO2), warming, and 20% decreases or increases in precipitation. Ecosystems respond synergistically to elevated CO2, warming, and decreased precipitation combined because higher water‐use efficiency with elevated CO2and higher fertility with warming compensate for responses to drought. Response to elevated CO2, warming, and increased precipitation combined is additive. We analyze changes in ecosystem carbon (C) based on four nitrogen (N) and four phosphorus (P) attribution factors: (1) changes in total ecosystem N and P, (2) changes in N and P distribution between vegetation and soil, (3) changes in vegetation C:N and C:P ratios, and (4) changes in soil C:N and C:P ratios. In the combined CO2and climate change simulations, all ecosystems gain C. The contributions of these four attribution factors to changes in ecosystem C storage varies among ecosystems because of differences in the initial distributions of N and P between vegetation and soil and the openness of the ecosystem N and P cycles. The net transfer of N and P from soil to vegetation dominates the C response of forests. For tundra and grasslands, the C gain is also associated with increased soil C:N and C:P. In ecosystems with symbiotic N fixation, C gains resulted from N accumulation. Because of differences in N versus P cycle openness and the distribution of organic matter between vegetation and soil, changes in the N and P attribution factors do not always parallel one another. Differences among ecosystems in C‐nutrient interactions and the amount of woody biomass interact to shape ecosystem C sequestration under simulated global change. We suggest that future studies quantify the openness of the N and P cycles and changes in the distribution of C, N, and P among ecosystem components, which currently limit understanding of nutrient effects on C sequestration and responses to elevated CO2and climate change.
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Ecosystem Recovery from Disturbance is Constrained by N Cycle Openness, Vegetation-Soil N Distribution, Form of N Losses, and the Balance Between Vegetation and Soil-Microbial Processes
We present a framework for assessing biogeochemical recovery of terrestrial ecosystems from disturbance. We identify three recovery phases. In Phase 1, nitrogen is redistributed from soil organic matter to vegetation, but the ecosystem continues to lose nitrogen because the recovering vegetation cannot take up nitrogen as fast as it is released from soil. In Phase 2, the ecosystem begins re-accumulating nitrogen and converges on a quasi-steady state in which vegetation and soil-microbial processes are in balance. In Phase 3, vegetation and soil-microbial processes remain in balance and the ecosystem slowly re-accumulates the remaining nitrogen. Phase 3 follows a balanced-accumulation trajectory along a continuum of quasi-steady states that approaches the true steady state asymptotically. We examine the effects of three ecosystem properties on recovery: openness of the nitrogen cycle, nitrogen distribution in and turnover between vegetation and soils, and the proportion of nitrogen losses that are in a refractory form. Openness exacerbates Phase 1 nitrogen losses but speeds recovery in Phases 2 and 3. A high fraction of ecosystem nitrogen in vegetation, resulting from nitrogen turnover that is slow in vegetation but fast in soil, exacerbates Phase 1 nitrogen losses but speeds recovery in Phases 2 and 3. A high proportion of nitrogen loss in refractory form mitigates Phase 1 nitrogen losses and speeds recovery in Phases 2 and 3. Application of our conceptual framework requires empirical recognition of the continuum of quasi-steady states constituting the balanced-accumulation trajectory and a distinction between the balanced-accumulation trajectory and the true steady state.
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- PAR ID:
- 10188752
- Date Published:
- Journal Name:
- Ecosystems
- ISSN:
- 1432-9840
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10021-020-00542-3
