Progress 01/15/01 to 08/31/03
Outputs
Fen wetlands fed by ground water high in base cations are a conservation priority due to their high plant species richness and large numbers of uncommon plants. Low levels of available nutrients, particularly phosphorus (P), restrict these plant communities to species able to acquire P from alternative mineral and/or organic sources and to species otherwise adapted to low nutrient availability. In a field survey of seven fens, we measured plant species richness against commonly used measures of nutrient availability and assessments of P pool heterogeneity via Hedley fractionation. Species richness was positively correlated with more recalcitrant soil P pools and negatively correlated with more labile fractions. No correlations were observed with more commonly used indices of nutrient availability. We also added labile nitrogen (N) alone and in conjunction with organic, stable mineral, and labile forms of P to two calcareous fens to understand effects of nutrient
additions on soil pools and processes, relate changes in fen soils to changes in plant species richness and mycorrhizal status, and determine if species considered indicative of calcareous conditions and more ubiquitous plant species respond differently to non-labile forms of P. Of 21 measured soil variables, only the highly recalcitrant P pool, as measured by Hedley fractionation, in the N + calcium-bound P treatment at one site showed significant change after three years. Neither total plant species richness nor vascular species richness changed at either site. Although soils and the vegetation community as a whole did not respond rapidly to moderate nutrient inputs, individual species are capable of obtaining nutrients from non-labile sources. We are continuing to investigate the role of mycorrhizal fungi in this interaction.
Impacts
We have documented that native plant communities in calcareous fens are able to respond rapidly to labile and recalcitrant mineral and organic phosphorus additions. This is in contrast to our findings within the soil profile that suggest that the soil environment has a high degree of biogeochemical buffering. These results are important considerations in the use of monitoring; reliance on soil pools and processes may be ineffective in determining eutrophication status and potential effect on the plant community.
Publications
- Hartman, W.H., Bedford, B.L. and Chapin, C.T. 2003. Size-dependent reproductive allocation of biomass and phosphorus in Soildago patula in response to manipulation of phosphorus availability. Annual Meeting of the Society of Wetland Scientists, June 8-13, 2003. New Orleans, LA.
- Weishampel, P.A. and Bedford, B.L. 2003. Microtopography influences mycorrhizal symbioses in calcareous fens. Annual Meeting of the Society of Wetland Scientists, June 8-13, 2003. New Orleans, LA
- Weishampel, P.A., Wolfe, B.E. and Bedford, B.L. 2003. Factors influencing colonization of arbuscular mycorrhizal fungi in plants of groundwater-dominated wetlands. The 4th International Conference on Mycorrhizae, August 10-15, 2003, Montreal, Canada.
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Progress 01/01/02 to 12/31/02
Outputs
Phosphorus (P) may control plant community structure in some rich fens. Because these wetlands receive high inputs of ground water rich in dissolved cations, P tends to be sequestered in relatively insoluble geochemical pools. As P often limits productivity in these rich fens, many plant species may have developed mechanisms for obtaining mineral-bound P. Correlation between calcium-bound P and species richness indicated that the species richness of these high cation fens is controlled by the degree of geochemical buffering. Mechanistically, this geochemical buffering of P maintains resource heterogeneity, which, in turn, may regulate species diversity. As an experimental test of this hypothesis, we added P to two cation-rich fens in labile, mineral-bound, and organic forms. We measured response as nutrient changes in soil-nutrient pools and plant tissue, and compared changes in plant community composition. Results indicate that calcicoles within the plant community
respond to calcium-bound phosphorus additions by increasing the concentration of P in leaf tissue. Other species responded to different forms of P, suggesting mechanistic responses other than direct uptake of ortho-P can occur.
Impacts
We have elucidated some of the underlying mechanisms in the limit of exotic plant invasion and the maintenance of native plant communities. Heterogeneity in the types of soil nutrient pools, as opposed to absolute pool size, appears to control species richness within calcareous wetland communities.
Publications
- Chapin, C. and B. Bedford. 2002. Native plant communities and invasive species: the role of phosphorus dynamics. BIOGEOMON, 4th International Symposium on Ecosystem Behavior, Reading, UK.
- Chapin, C. and B. Wolfe. 2002. Response of soil alkaline phosphatase activity to phosphorus addition in two calcareous fens. Proceedings of the Annual Meeting of the Society of Wetland Scientists, Lake Placid, NY.
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Progress 01/01/01 to 12/31/01
Outputs
Nutrient availability is a major factor in determining species composition of plant communities. Phosphorus, rather than nitrogen, may control plant community structure in fens. This study tests the hypothesis that plant species diversity in rich fens is maintained by low levels of available phosphorus coupled with the presence of species that are mechanistically able to access mineral-bound and organic forms of phosphorus. I have manipulated soil pools in two rich fens through direct addition of labile, mineral-bound, and organic forms of P, measured nutrient changes in soil-nutrient pools and plant tissue, and compared changes in plant primary productivity and community composition of the different treatments. Results from this study indicate that different species are able to use different forms of phosphorus with various physiological effects. In particular the calcicole species are positively affected by the calcium bound P to the same degree as the most labile P
addition. Other data suggests that while P limitation may limit the influence of invasive species, native vegetation in these sites are able to acquire P through different mechanisms.
Impacts
The unique aspect of this research is that although fertilization with phosphorus fractions has previously occurred in a greenhouse setting, the addition of these forms to a natural wetland community has not been reported. The results from this research will increase our understanding of the effects of anthropogenic phosphorus in wetlands and the resulting effects on plant species diversity.
Publications
- Cornwell, W.K., Bedford, B.L., and Chapin, C.T. 2001. Occurrence of arbuscular mycorrhizal fungi in a phosphorus-poor wetland and mycorrhizal response to phosphorus fertilization. American Journal of Botany 88, 1824-1829.
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Progress 01/01/00 to 12/31/00
Outputs
Although the official start date of the project was 09/01/2000, we have yet to receive (as of 1/22/01) any actual funding. This delay is in part due to a transfer of PI status from the post-doc awardee Carmen Chapin to her mentor Barbara Bedford. Cornell regulations prohibit post-doctoral associated from holding a PI status. However, we have collected the first season's field data which consist of plant samples for N and P analysis, soil samples for phosphorus fractionation, and resin bags for soil nutrient availability. At this point in time, lab processes concerning the above samples are proceeding on schedule. Data analysis for those samples is in progress. We anticipate presenting the preliminary results at a conference on wetland biogeochemistry to be held this June at Duke University.
Impacts
This research will aid management and conservation agencies in anticipating responses of wetland plant communities to phosphorus loading from agricultural and other anthropogenic sources.
Publications
- No publications reported this period
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