Turnover of Detrital Organic Carbon in a Nutrient‐Impacted Everglades Marsh

Abstract

Phosphorus loading to the Everglades from nearby agricultural areas has become a major concern, and is considered to be a significant factor in the encroachment of cattail (Typha domingensis Pers.) and other rapidly growing vegetation into endemic sawgrass (Cladium jamaicense Crantz) marsh. The objectives of this research were to evaluate the variability in turnover of organic C in plant and soil detrital pools along a P enrichment gradient in an Everglades marsh and to identify substrate characteristics and environmental factors controlling C turnover. Potential rates of C mineralization in plant litter and peat were determined by measuring aerobic and anaerobic microbial respiration under controlled conditions in laboratory incubations. Potential C mineralization decreased with depth and, consequently, substrate age, in the plant‐soil profile. Within individual detrital pools [standing dead plant material, soil litter layer, surface peat (0–10 cm depth) and subsurface peat (10–30 cm depth)], potential C mineralization decreased down gradient from the source of nutrient loading to WCA‐2A. Overall, 91% of the variability in aerobic C mineralization in peat and plant litter was accounted for by substrate P concentration and lignocellulose composition. Anaerobic C mineralization rates were consistently about one‐third of aerobic rates. Results indicated that organic C turnover in detrital pools in WCA‐2A is significantly affected by accelerated P loading, but is also controlled by O2 availability and substrate C quality.

Plant carbohydrate limitation on nitrate reduction in wetland microcosms

“…Although direct carbon quality measures (e.g., C : N, lignin) are often used to explain rates of litter decomposition [11], they do not explain the differences in the denitrification rate constants here as well as the acid soluble carbohydrate fraction of the litter. The characteristically low litter C : N of the two floating aquatics (marsh pennywort and duckweed) did not correspond to consistently higher rate constants, only the bulrush litter exhibited significantly lower denitrification rate constants at high lignin and C : N ratios.…”

“…It is possible that this may have affected the carbon supplied for subsequent experimental conditions, since these materials appear to be very rapidly assimilated by attached bacteria in wetlands [5]. Other authors have shown senescent wetland plants and litter become rapidly depleted of their soluble carbohydrates and higher molecular weight compounds such as lignins with low hydrolysis rates [19] are selectively concentrated in the remaining litter [11]. For this reason, carbon supplied by the developing peat and litter arriving from the prior year's plant productivity may contribute less to denitrification activity than the rapidly hydrolyzed carbohydrates in fresh and senescent litter.…”

“…Although common wetland plants differ only slightly in carbon content, the differences in lignin and cellulose content strongly influence the degradation rates of wetland litter [11]. This suggests denitrification activity in wetlands is affected by the carbon quality (e.g., C : N, lignin, carbohydrates) of the different plants that make up the litter.…”

Impacts of alien invasive plants on soil nutrients are correlated with initial site conditions in NW Europe

“…This may result in "nutrient leakage". Organic matter turnover rates and nutrient leaching losses are often increased in eutrophic sites (Wedin and Tilman 1996;Debusk and Reddy 1998). In NW Europe, eutrophic sites are most often invaded by F. japonica, S. gigantea, I. glandulifera and H. mantegazzianum.…”

Daily soil surface CO2 flux during non-flooded periods in flood-irrigated rice rotations

“…Generally, an abundant oxygen supply promotes rapid soil organic matter decomposition, whereas a deficiency in oxygen results in a substantially lower decomposition rate (DeBusk et al 2001;Shaffer and Ma 2001), with the carbon mineralization rates in aerobic conditions being as much as three times faster than under anaerobic conditions (DeBusk and Reddy 1998). Thus, the presence of saturated soil conditions that occur in rice-based cropping systems can affect the release rates and patterns of carbon gas emissions from the soil.…”