Co-limitation is defined as the coincident limitation of biological activity by multiple resources. According to theories of resource optimization, co-limitation should be common as organisms adjust to changes in the availability of resources in the environment. We review the multi-faceted nature of the co-limitation concept and provide a synthesis of recent experimental studies of co-limitation in northern hardwood forests to illustrate the complexities of nitrogen (N) and phosphorus (P) co-limitation and possible responses to environmental stressors such as acid rain, N deposition, elevated CO2, land-use, and climate change. In a factorial nutrient addition experiment, cycling of one nutrient changed in response to addition of the other through synergistic interactions and feedbacks between N and P, including microbial recycling, soil enzyme activity, and foliar nutrient resorption; these responses were suggestive of some degree of N–P co-limitation in these forests. After 8 years of treatment, aboveground growth increased in response to either N or P added individually and even more in response to N + P addition, indicating N–P co-limitation. Surprisingly, fine root growth increased in response to nutrient addition, with significantly greater root growth in N + P plots in five successional stands and in N plots in three mature stands. In contrast, fine litterfall did not respond significantly to nutrient addition. Collectively, these results demonstrate the complexity of the interactions between macronutrients in regulating production processes in forest ecosystems.
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Elevated P availability slows N recycling in northern hardwood forests
Nutrient cycling in forest ecosystems can be sensitive to disturbances that change the availability of one nutrient relative to others, altering the synchrony in nutrient cycles that is expected to develop in undisturbed systems. We asked whether the relative availabilities of nitrogen (N) and phosphorus (P) differ with forest successional age after harvest, and tested effects of adding one nutrient on availability and recycling of the other, in a factorial nitrogen (N) × phosphorus (P) fertilization study in multiple early- and mid-successional and mature northern hardwood forest stands in central NH, USA. We did not find effects of forest age on resin-available N:P ratios, which varied widely among successional forest stands and were related to net N mineralization potentials in the forest floor of each stand. P addition suppressed resin-N availability by 31 % and lowered litterfall N recycling by 10 %, but we detected no effects on net N mineralization potentials. P addition also increased nitrification potentials in the organic horizon by up to 60 %, mostly in combination with added N. The effects of added N depended on P; lower resin-P in mature stands and lower litterfall P recycling in stands of all ages were detected only when P was added with N. We conclude that P limitation influences N recycling across forest age classes in these northern hardwoods, with some indication of stronger effects in successional stands. However, net N mineralization potentials better predicted the resin-N response to added P than did stand age. Our results suggest that alleviating P limitation promotes N limitation over time, especially in more rapidly growing successional forests, by increasing biotic demand for N, reducing its recycling in litterfall, and potentially by reducing net N mineralization.
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- Award ID(s):
- 1637685
- PAR ID:
- 10572688
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Forest Ecology and Management
- Volume:
- 570
- Issue:
- C
- ISSN:
- 0378-1127
- Page Range / eLocation ID:
- 122203
- Subject(s) / Keyword(s):
- N and P cycling N:P ratios Northern hardwoods Nutrient fertilization Nutrient limitation Plant-soil feedbacks
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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