Hydroperiod Influence on Breakdown of Leaf Litter in Cypress-gum Wetlands

Abstract Many cypress-gum wetlands in the southeast United States are isolated from rivers and streams and are seasonally inundated by rainfall. Organic matter processing in these wetlands is caused primarily by biotic components (i.e., microbes and invertebrates), which are influenced by timing and duration of seasonal inundation, and low dissolved oxygen levels. Using litter bags, we examined breakdown of cypress (Taxodium spp.) and gum (Nyssa sylvatica var. biflora) leaves in three wetlands with different hydroperiods: (1) flooded exposed (FE; 5 mo flooded/6 mo litter exposed), (2) multiple flooded exposed (MFE; 6 mo flooded/exposed/flooded/exposed) and (3) permanently flooded (PF; 11 mo flooded). Breakdown was fastest in the MFE wetland suggesting cycles of wetting and drying accelerated decomposition by promoting microbial activity through aeration. Even though ergosterol content, an indicator of fungal biomass on the litter, was similar among wetlands, we hypothesized that within the MFE wetland microbial activity was promoted by exposed conditions, but during subsequent flooding microbial biomass was kept at a low level by invertebrate consumers. Macroinvertebrate density and biomass were comparable between litter types, but were highest in the PF wetland, followed by MFE, then FE wetlands. Chironomids, oligochaetes, Caecidotea and Crangonyx were the dominant taxa indicating litter inputs are vital in maintaining the aquatic foodweb in this system. Cypress litter (k = −1.61 y−1) had faster breakdown rates than gum litter (k = −1.02 y−1), most likely because of plant morphology and greater surface area available to microbial decomposers. Ergosterol (mg g−1 AFDM leaf material) levels were higher on cypress (34.5) than gum (22.5) litter. In both litter types initial C:N and N:P ratios were >20, and C:P ratios were >500, indicating a possible P or N/P co-limitation in cypress-gum wetlands. Elemental gains or losses in litter were influenced predominantly by litter type and to a lesser extent by hydrologic regime. Gum leaves accumulated P, N, Ca and K and lost Mg, whereas cypress leaves had initial declines of these elements, followed by some accumulations in P and K. Temporal patterns of P showed that the drier sites (FE and MFE) immobilized more P than the wetter site (PF), suggesting that exposed conditions promoted microbial activity. In addition, N and P accumulations on gum leaves were highest in the summer at the time when wetlands would normally dry, indicating a seasonal period when moisture and temperature conditions are optimal for microbial growth. Net flux rates to the 1+ y-old component of litter indicated that the FE wetland is accumulating more organic matter (172 g m−2 y−1) than the other wetlands (65 and 72 g m−2 y−1), which we attributed to higher cypress litter production. We concluded that hydrologic regime influences breakdown rates and element accumulations, but that net productivity is more important in determining litter accumulation rates.

[1]  J. Battle,et al.  Water Quality and Macroinvertebrate Assemblages in Three Types of Seasonally Inundated Limesink Wetlands in Southwest Georgia , 2001 .

[2]  T. D. Brock.  Principles of microbial ecology , 1967 .

[3]  S. R. Reice,et al.  Comparative leaf litter decomposition in temporary and permanent streams in semi-arid regions of Israel , 1982 .

[4]  J. Olson,et al.  Energy Storage and the Balance of Producers and Decomposers in Ecological Systems , 1963 .

[5]  É. Chauvet,et al.  Regulation of Leaf Breakdown by Fungi in Streams: Influences of Water Chemistry , 1995 .

[6]  S. Y. Newell,et al.  Fundamental Procedures for Determining Ergosterol Content of Decaying Plant Material by Liquid Chromatography , 1988, Applied and environmental microbiology.

[7]  F. Day,et al.  Decay Rates and Nutrient Dynamics in Confined and Unconfined Leaf Litter in the Great Dismal Swamp , 1983 .

[8]  D. J. Shure,et al.  Litter decomposition processes in a floodplain forest. , 1986 .

[9]  J. Anderson,et al.  Decomposition in Terrestrial Ecosystems , 1979 .

[10]  T. Cuffney,et al.  Leaf litter processing in Coastal Plain streams and foodplains of southeastern Georgia, U.S.A. , 1987 .

[11]  A. A. Levinson.  Book Review: Analytical methods for atomic absorption spectrophotometry. The Perkin-Elmer Corporation, Norwalk, Connecticut, 06852, U.S.A., 1968. $25.00 (looseleaf). Order as part number 303-0152 , 1969 .

[12]  R. Král,et al.  The ecology, status, and conservation of two non-alluvial wetland communities in the South Atlantic and eastern Gulf Coastal plain, USA , 1994 .

[13]  N. D. Cost,et al.  Estimating the forested-wetland resource in the southeastern United States with forest survey data , 1990 .

[14]  K. Cummins,et al.  An Introduction to the Aquatic Insects of North America , 1981 .

[15]  Jackson R. Webster,et al.  VASCULAR PLANT BREAKDOWN IN FRESHWATER ECOSYSTEMS , 1986 .

[16]  W. Mitsch,et al.  EFFECTS OF SEWAGE EFFLUENT APPLICATION ON LITTER FALL AND LITTER DECOMPOSITION IN CYPRESS SWAMPS , 1980 .

[17]  K. Vogt,et al.  Production, Turnover, and Nutrient Dynamics of Above- and Belowground Detritus of World Forests , 1986 .

[18]  M. Gessner,et al.  Ergosterol-to-Biomass Conversion Factors for Aquatic Hyphomycetes , 1993, Applied and environmental microbiology.

[19]  L. Kirkman,et al.  Biodiversity in Southeastern, Seasonally Ponded, Isolated Wetlands: Management and Policy Perspectives for Research and Conservation , 1999, Journal of the North American Benthological Society.

[20]  F. Day,et al.  Litter nutrient content and production in the Great Dismal Swamp [Virginia, tree communities]. , 1982 .

[21]  Frank P. Day,et al.  Litter Decomposition Rates in the Seasonally Flooded Great Dismal Swamp , 1982 .

[22]  T. J. Breen,et al.  Biostatistical Analysis (2nd ed.). , 1986 .

[23]  W. Moore.  Limnological Studies of Temporary Ponds in Southeastern Louisiana , 1970 .

[24]  E. L. Hendricks,et al.  Water-level fluctuations in limestone sinks in southwestern Georgia , 1952 .

[25]  M. Brinson.  DECOMPOSITION AND NUTRIENT EXCHANGE OF LITTER IN AN ALLUVIAL SWAMP FOREST , 1977 .

[26]  Peter Hietz,et al.  Decomposition and nutrient dynamics of reed (Phragmites australis (Cav.) Trin. ex Steud.) litter in Lake Neusiedl, Austria , 1992 .

[27]  P. Horwitz,et al.  Seasonal water regimes and leaf litter processing in a wetland on the Swan Coastal Plain, Western Australia , 1993 .

[28]  W. H. Patrick,et al.  Effect of alternate aerobic and anaerobic conditions on redox potential, organic matter decomposition and nitrogen loss in a flooded soil , 1975 .

[29]  M. Gessner,et al.  Comparison of ATP and Ergosterol as Indicators of Fungal Biomass Associated with Decomposing Leaves in Streams , 1993, Applied and environmental microbiology.

[30]  B. G. Lockaby,et al.  Hydroperiod Influences on Nutrient Dynamics in Decomposing Litter of a Floodplain Forest , 1996 .

[31]  Mark M. Brinson,et al.  The Role of Reference Wetlands in Functional Assessment and Mitigation , 1996 .

[32]  G. D. Wylie.  Decomposition and nutrient dynamics of litter of Quercus palustris and Nelumbo lutea in a wetland complex of southeast Missouri , 1987 .