Quantitative and Qualitative Aspects of Dissolved Organic Carbon Leached from Senescent Plants in an Oligotrophic Wetland

Abstract

We conducted a series of experiments whereby dissolved organic matter (DOM) was leached from various wetland and estuarine plants, namely sawgrass (Cladium jamaicense), spikerush (Eleocharis cellulosa), red mangrove (Rhizophora mangle), cattail (Typha domingensis), periphyton (dry and wet mat), and a seagrass (turtle grass; Thalassia testudinum). All are abundant in the Florida Coastal Everglades (FCE) except for cattail, but this species has a potential to proliferate in this environment. Senescent plant samples were immersed into ultrapure water with and without addition of 0.1% NaN 3 (w/ and w/o NaN 3 , respectively) for 36 days. We replaced the water every 3 days. The amount of dissolved organic carbon (DOC), sugars, and phenols in the leachates were analyzed. The contribution of plant leachates to the ultrafiltered high molecular weight fraction of DOM (>1 kDa; UDOM) in natural waters in the FCE was also investigated. UDOM in plant leachates was obtained by tangential flow ultrafiltration and its carbon and phenolic compound compositions were analyzed using solid state 13 C cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C CPMAS NMR) spectroscopy and thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH thermochemolysis), respectively. The maximum yield of DOC leached from plants over the 36-day incubations ranged from 13.0 to 55.2 g C kg À1 dry weight. This amount was lower in w/o NaN 3 treatments (more DOC was consumed by microbes than produced) except for periphyton. During the first 2 weeks of the 5 week incubation period, 60-85% of the total amount of DOC was leached, and exponential decay models fit the leaching rates except for periphyton w/o NaN 3 . Leached DOC (w/ NaN 3 ) contained different concentrations of sugars and phenols depending on the plant types (1.09-7.22 and 0.38-12.4 g C kg À1 dry weight, respectively), and those biomolecules comprised 8-34% and 4-28% of the total DOC, respectively. This result shows that polyphenols that readily leach from senescent plants can be an important source of chromophoric DOM (CDOM) in wetland environments. The O-alkyl C was found to be the major C form (55 ± 9%) of UDOM in plant leachates as determined by 13 C CPMAS NMR. The relative abundance of alkyl C and carbonyl C was consistently lower in plant-leached UDOM than that in natural water UDOM in the FCE, which suggests that these constituents increase in relative abundance during diagenetic processing. TMAH thermochemolysis analysis revealed that the phenolic composition was different among the UDOM leached from different plants, and was expected to serve as a source indicator of UDOM in natural water.Polyphenols are, however, very reactive and photosensitive in aquatic environments, and thus may loose their plant-specific molecular characteristics shortly. Our study suggests that variations in vegetative cover across a wetland landscape will affect the quantity and quality of DOM leached into the water, and such differences in DOM characteristics may affect other...

Spatial, geomorphological, and seasonal variability of CDOM in estuaries of the Florida Coastal Everglades

“…3; Table 1), suggesting that the CDOM in FB is not substantially derived from the freshwater marshes or the fringe mangroves in the Everglades, but instead probably produced in FB directly or indirectly by seagrass/phytoplankton community. This interpretation is in agreement with previous reports (Maie et al, 2005;Maie et al, 2006) and further supported by the d 13 C value of high molecular weight fraction of DOM collected from the FB, which is significantly heavier ($)14&) than that from the Everglades ($)27&) (Maie, personal communication). The longer k max values for all regions during the wet season compared to the dry season suggest a higher input of terrestrial DOM from the Everglades during wet season.…”

“…DOM with different C:N ratios reflect different DOM sources and/or diagenetic processing (e.g., DOM originating from higher plants has greater C:N values than DOM from microbes; Caraco & Cole, 2003;McKnight et al, 2003). A high C:N ratio during the wet season in the FCE estuaries may be due to a large contribution of DOM freshly leached from senescent plant biomass (Maie et al, 2006).…”

Phenolic content and growth of wetland macrophytes: Is the allocation to secondary compounds driven by nutrient availability?

“…The phenolic and lignin content of EC was less than half of TD from both the greenhouse experiment and the marshes. In a related study, Maie et al (2006) found that litter of TD leached about 4× more phenolics than litter of Eleocharis sp. Apparently, the lower concentration of these compounds in EC as compared to TD is a result of genetic differences between the species.…”

Molecular composition of plant parts and sediment organic matter in a Mediterranean seagrass (Posidonia oceanica) mat

“…As far as we know, THM-GC-MS has not been applied to P. oceanica materials yet. Kristensen et al (2009) analyzed an undefined seagrass, while Maie et al (2006) analyzed leachates from turtle grass (i.e.…”