Sponsor: INTECOL
Co-Chairs:
Dr. Jos T.A. Verhoeven
Landscape Ecology
Utrecht University
P.O. Box 80084
Utrecht, The Netherlands 3508 TB
Phone: 31-30-253-6700
Fax: 31-30-251-8366
E-mail: j.t.a.verhoeven@bio.uu.nl
and
Dr. D.F. Whigham
Smithsonian Environmental Research Center
P.O. Box 28
Edgewater, Maryland
USA 21037
E-mail: whigham@serc.si.edu
Overview of Symposium:
In wetland ecosystems, nutrient recycling as well as carbon storage are controlled by the decomposition of plant-derived detritus. The chemical quality of this detritus strongly influences the rate of decomposition. Initial nitrogen and phosphorus concentrations, and the organic chemistry (i.e., soluble as well as cell-wall-bound phenolics) are important in this respect. Chemical litter quality may change in wetland ecosystems in two ways. First, nitrogen and phosphorus concentrations can be influenced by anthropogenic nutrient enrichment. Second, the overall content of nutrient and secondary plant compounds in the detritus may change as a result of shifts in the species composition. Changes in decomposition process may have large impacts on the production of gases (carbon dioxide, methane and nitrous oxide) in the wetland ecosystem. In this symposium, field and mesocosm studies of the relation between decomposition and detritus quality in wetlands will be presented, with special emphasis on the effects of environmental change (climate, nutrient enrichment) on these interactions.
Mats Nilsson; Elisabet Bohlin; and Malin Klarqvist, Department of Forest Ecology, SLU, Umeå, Sweden - Temporal and spatial variability in Sphagnum decomposition and peat accumulation in boreal mires.
Abstract is unavailable.
Jane M. Chambers and Arthur J. McComb, Environmental Science, Murdoch University, Murdoch, Western Australia - The effect of nutrient enrichment on the dynamics of sedge communities, Western Australia.
The Swan Coastal Plain is a nutrient-poor, low-lying plain containing numerous freshwater wetlands. The sedges in these wetlands are nutrient efficient, retranslocating nutrients from senescing leaves into the plant and having a slow leaf turnover. Agricultural practices have markedly increased the nutrient status of these wetlands. In three seasonal wetlands, from undisturbed (water concentration: 0.05-0.36 mg P /l) to eutrophic (2.3-30 mg P /l), the dominant sedge Lepidosperma longitudinale responded to nutrient input with increased productivity, biomass, nutrient content, rate of leaf turnover and size of the litter component but with less efficient nutrient recycling. The rate of decomposition is low in this highly lignified sedge, which showed increases of 300% in N and P in the first year, presumably due to the establishment of microbial communities. In undisturbed wetlands, Lepidospermaconserves nutrients. Under eutrophic conditions, it actively removes nutrients from water and increases litter storage, reducing the availability of inorganic nitrogen and phosphorus in the wetland.
Scott D. Bridgham, Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, USA; Karen Updegraff, Department of Forest Resources, University of Minnesota, Duluth, Minnesota, USA; John Pastor, Natural Resources Research Institute, University of Minnesota, St. Paul, Minnesota, USA, Jason Keller, Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, USA; Peter Weishampel, Department of Natural Resources, Cornell University, Ithaca, New York, USA; and Calvin Harth and B. Dewey, Department of Forest Resources, University of Minnesota, St. Paul, Minnesota, USA - Ecosystem respiration response in peatlands to climate change.
We constructed a large mesocosm facility in northern Minnesota to examine the effects of climate change on peatlands. Twenty-seven intact peat monoliths (2.1 m2, 60-cm depth) were removed each from a bog and intermediate fen and subjected to three infrared-loading treatments and three water-table treatments. Net ecosystem respiration as CO2 responded only to soil temperature and did not differ between bog and fen plots, suggesting that respiratory flux of CO2 in northern peatlands will directly increase with increases in temperature with climate change. CH4 flux was strongly dependent on both water-table elevation and soil temperature and the strength of this relationship increased over years, suggesting a long lag period for methanogens to respond to environmental conditions. CH4 flux increased with net N retention and was negatively correlated with porewater ammonium concentrations, suggesting an inhibitory effect of N on methanogens. Plant productivity was poorly correlated with CH4 flux except in fen mesocosms with high water tables. Seasonal CH4 flux was on average 3 times higher in bog than in fen plots. We suggest that this difference can be explained by higher CH4 oxidation at similar water-table elevations and higher soil N availability in fens than in bogs. Changes in peat volume and net ecosystem production estimates for the mesocosms show that the fens are losing C whereas the bogs are gaining C under all treatments.
Jos T.A. Verhoeven and Robbert A. Scheffer, Landscape Ecology, Utrecht University, Utrecht, The Netherlands - Sphagnum versus Carex decomposition in fen ecosystems.
Curtis J. Richardson, Duke University Wetland Center, Durham, North Carolina, USA; and Robert G. Qualls, University of Nevada Reno, Reno, Nevada, USA - The influence of nutrients on plant decomposition, litter quality and production in the Everglades.
The P-limited Everglades peatlands of Florida were subjected to nutrient additions to determine the influence of water column N and P enrichment on litter decomposition rates and nutrient immobilization by litter. In order to isolate the short-term (~1 year) effects of P enrichment in the Everglades litter bags containing Typha domingensis and Cladium jamaicense litter were placed into 2 replicated sets of experimental dosing channels. Five different Phosphate concentrations were added continuously for several years. Loss of C increased linearly with increasing phosphate additions with a similar slope for both species but Cladium loss rates were less than Typha loss rates. Immobilization caused a nine-fold increase in litter P content in the highest treatments as compared to controls. Nitrogen, Ca, and K did not vary with water P concentrations.
A direct and significant effect of maintaining increased Phosphate concentrations in the water column is both an excelerated short-term decomposition rate and increased long-term peat accretion rate in the Everglades. The explanation for this is related to the long-term balance between plant production, litter accumulation and decomposition. This is explored in this system by analyzing standing crop, litter and peat accretion along a 30 year P nutrient gradient.
Candy Feller, and Dennis F. Whigham, Smithsonian Environmental Research Center, Edgewater, Maryland, USA; Karen L. McKee, National Wetlands Research Center, Lafayette, Louisiana, USA; and Catherine Lovelock and John P. O'Neill, Smithsonian Environmental Research Center, Edgewater, Maryland, USA - Decomposition and nutrient limitations in tropical mangroves
Our objectives were to compare nutrient cycling across an ecotonal gradient in nitrogen- vs. phosphorus-limited soils in disturbed (Florida) and undisturbed (Belize) mangrove forests. At each location, we conducted a fertilization (control, N, P) experiment across three zones (fringe, transition, dwarf), with tree heights of 5-6, 2-4, and 1.5m, respectively. The Florida site is a black-mangrove dominated forest in an abandoned mosquito impoundment with a sharp salinity gradient. The Belize site is a red-mangrove dominated forest on an offshore island with little variation in salinity. Plant growth at the Florida site was uniformly N limited. In Belize, plant responses indicated a more complex pattern: 1) fringe trees were N limited; 2) dwarf trees were P limited; 3) transition trees were co-limited by N and P. We used cotton burial strips to assess effects on nutrient availability on belowground decomposition. In Florida, decomposition rates increased in response to N enrichment in the fringe and to P fertilizer in the transition and fringe. Enrichment had little effect on decomposition in the dwarf zone. In Belize, belowground decomposition increased in response to P enrichment in all zones. This study shows: 1) essential nutrients are not uniformly distributed among or even within mangrove ecosystems; 2) not all ecological processes (e.g., growth, decomposition) respond similarly to, or are limited by, the same nutrient.
