wAbstract
@Nitrogen (N) availability influences carbon (C) storage in forest
soils through effects on plant growth, litter production, and
soil C decomposition and stabilization. Soil C/N and net N-mineralization
are commonly reported empirical measures of soil N availability,
and changes in these variables due to N inputs may feed back to
soil C storage through a variety of biotic and abiotic pathways.
We conducted a meta-analysis of the response of soil C storage,
C/N, and net N-mineralization (Nmin) to N
inputs in north temperate forests. The modes of N addition we
considered were the establishment of N-fixing vegetation (Nfix), N-fertilization (Nfert),
and simulated chronic N deposition (Ndep).
Overall, N inputs increased soil C (+7.7) and Nmin
(+62), while decreasing C/N (-4.9). Soil C concentrations and
C storage (pool sizes) responded similarly to N inputs, although
increased soil C storage occurred only in the mineral soil (+12.2).
C/N shifts were restricted to the forest floor (-7.8), whereas
forest floor and mineral soil Nmin responses
to N inputs were very similar (+61 and +64, respectively). Significant
between-study variation in the effects of N inputs on soil parameters
was related to the mode of N addition, biogeographic factors,
and time. Temporal relationships between N inputs and soil response
parameters suggested that increases in forest floor and mineral
soil Nmin were large but transient, and were
followed by decadal-scale changes in forest floor C/N and mineral
soil C storage. Temporal patterns present in the dataset could
have been due to changes in soil organic matter decomposition
and stabilization, or increased plant productivity and litter
inputs. In either case, the results of this study quantitatively
demonstrate that managing forest N supply affects N availability
and soil C storage, and highlight the importance of long-term
measurements for accurately assessing the effects of N inputs
on forest soils.
Keywords: North temperate forest; Nitrogen inputs; Soil carbon;
Soil nitrogen; Meta-analysisx
1. Introduction
2. Materials and methods
@2.1. Literature searches and data extraction
@2.2. Meta-analysis
@2.3. Dataset information
3. Results and discussion
@3.1. Overview: effects of N inputs on soil parameters
@3.2. Forest floor vs. mineral soil responses to N inputs
@3.3. Mode of N addition
@3.4. Biogeographic groups
@3.5. Temporal patterns
@3.6. Other sources of variation
4. Conclusions
Acknowledgements
Appendix A. Study information for the references included in the
meta-analysis
References