Respiration wetlands

In addition to alkalinity inputs from rivers, estuaries can also receive inputs from bordering wetlands. For example, Cai et al. (1999) have shown that respiration rates in rivers/estuaries of Georgia (USA) cannot account for O2 consumption and CO2 degassing. It has since been shown that the missing DIC source is from marshes in the Satilla estuary (USA) (Cai et al., 2000). Other studies have also shown that intertidal marshes are important sources of DIC in estuaries (Raymond et al., 1997, 2000 Neubauer and Anderson, 2003). It has been further suggested that CO2 fixation of marsh grasses and the subsequent export of DIC and organic C to the coastal ocean can be described as... 

The outcome of competition between microorganisms for electron donors can be predicted from thermodynamic theory (Section 8.08.1.2 Table 1 Zehnder and Stumm, 1988), and these predictions are generally consistent with empirical data. Temporal succession of the microbial metabolic pathways that dominate respiration occurs upon the flooding of an oxidized soil or sediment (Figure 1). Not surprisingly, most examples of temporal succession in anaerobic respiration processes have come from wetland soils, which are subject to cycles of flooding and exposure (Turner and Patrick, 1968 Ponnamperuma, 1972 Achtnich et al., 1995a Yao et al., 1999). However, the same pattern is observed in sediments and even upland soils (Peters and Conrad, 1996). 

Drake B. G., Muche M. S., Peresta G., Gonzalez-Meier M. A., and Matamala R. (1996) Acclimation of photosynthesis, respiration and ecosystem carbon flux of a wetland on Chesapeake Bay, Maryland to elevated atmospheric CO2 concentration. Plant Soil 187, 111-118. 

Some plants can induce a release of O2 at the surface of roots and thus an increase in pO2 in the rhizosphere. This process is known to occur in an adaptation of plants to submerged soil conditions, as in wetland plants, and is well documented for lowland rice Oryza sativa). To cope with anoxic or hypoxic conditions occurring in the soil or sediments, such plants have evolved a specialized structure, the aerenchytna, which conducts O2 to root tissues from the atmosphere and the shoots. The portion of O2 that is not consumed in the roots for respiration leaks through the root apoplasm (cell walls) and ultimately into the rhizosphere. Two pieces of evidence support this phenomenon. First, an increase in redox potential... 

Diffusion of gases through water is 10,000 times slower than in air where oxidized forms act as electron acceptors. Wetland plants pump oxygen to the roots to assist in respiration. 

Plants have adapted to the harsh anaerobic conditions of wetland soils. Development of aerenchyma tissnes permit oxygen pumping to the roots, to support root respiration and aerobic bacteria in the root zone. 

The substrate-indnced respiration (SIR) method was developed as a rapid means of estimating microbial activities in soils (Beare et al., 1990 Neely et al., 1991). The use of selective inhibitors such as streptomycin for bacteria and cycloheximide for fungi, in conjunction with substrate additions, has been used to quantify bacterial and fungal contributions to the total metabolism of microbial decomposers. The SIR procedure involves addition of a labile carbon source (e.g., glucose or acetate) to provide a carbon nonlimiting condition. The short-term increase in carbon dioxide production is proportional to the active microbial biomass and activity. The concept of addition of labile carbon to determine the kinetics of substrate utilization by microorganisms has been extensively studied in various ecosystems including wetlands and aquatic systems. 

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