Growth and allocation by a keystone wetland plant, Panicum hemitomon, and implications for managing and rehabilitating coastal freshwater marshes, Louisiana, USA

Mayence, C. Ellery; Hester, Mark W.

doi:10.1007/s11273-009-9155-5

Cited by 8 publications

(8 citation statements)

References 35 publications

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“…The larger roots act as metal tie-rods in the ecological cement to give structural strength to the organic whole. We agree with Mayence and Hester (2010) who suggested that ''Quantifying the relationship between root length, diameter and tensile strength would benefit our understanding of the interaction between nutrient level and mat strength and is therefore warranted.'' and have work underway to investigate this aspect further.…”

Section: Discussionsupporting

confidence: 84%

The belowground intersection of nutrients and buoyancy in a freshwater marsh

Turner

Bodker

Schulz

2017

Wetlands Ecol Manage

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An oligotrophic coastal freshwater marsh converted to open water within months after receiving partially-treated sewage water in fall 2006. Rafts of the upper 60 cm of marsh soil were found throughout the area within two years, as parts of the 1100 year-old marsh were re-distributed in the open water. We examined the marsh soils from 2009 to 2012 to determine some of the cause-and-effect consequences of their decomposition to the formation of these floating mats. There was a lack of herbivory damage in April 2009 where the outer boundary of the soil profile was weakened at 50-60 cm depth, and eventually converted to open water. A 2012 storm event flooded the area by 1.5 m, resulting in new marsh mat 'popups' whose bottom underside was coincidental with the layer of maximum decline in soil strength in the sewage treated area. We conclude that the addition of partially-treated sewage weakened the soil structure during this high water event and others to allow for the vertical separation of the marsh as the buoyancy forces exceeded the marsh's anchor strength, thereby exposing the softer older peats to decomposition, and smothering marsh underneath the mat's new location. A chronic effect of eutrophication on these marshes was, therefore, revealed in a dramatic flooding event. A bottom up (nutrient addition), not top-down stress (herbivory) contributed to wetland loss in the area, and is a potentially significant chronic stressor for other eutrophied marshes with significant aboveground flooding.

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Section: Discussionsupporting

confidence: 84%

The belowground intersection of nutrients and buoyancy in a freshwater marsh

Turner

Bodker

Schulz

2017

Wetlands Ecol Manage

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“…Greenhouse experiments, for example, document how flooding is required for vigorous root and rhizome production in P. hemitomon (Mayence and Hester, 2010). The results from these same greenhouse experiments also suggest that the % N and % P in plant tissue increases with higher nutrient loading, which, however, also leads to insignificant or negative effects on root diameter, specific gravity or volume after 3 months (Mayence and Hester, 2010).…”

Section: Methodsmentioning

confidence: 94%

“…5. Nutrient enrichments of P. hemitomon mesocosms (Mayence and Hester, 2010) demonstrate that the % N and % P content in P. hemitomon tissue will rise with eutrophication. That outcome will result in a change in litter quality -the % N will be higher -and decomposition rates will rise as a result.…”

Section: Discussionmentioning

confidence: 99%

“…There is concern that the anchored P. hemitomon mat converts to a detached thick-and then thin-floating mat if sediment (Mayence and Hester, 2010) or nutrient loading increases (Swarzenski et al, 2008;Mayence and Hester, 2010). It is unlikely that increased inundation is the primary cause of these changes because aerenchyma development, root elongation and root volume increase are common responses in wetland plants (Reddy and Delaune, 2008), and for this plant specifically (Willis and Hester, 2004;Mayence and Hester, 2010). Greenhouse experiments, for example, document how flooding is required for vigorous root and rhizome production in P. hemitomon (Mayence and Hester, 2010).…”

Section: Methodsmentioning

confidence: 99%

“…It is unlikely that increased inundation is the primary cause of these changes because aerenchyma development, root elongation and root volume increase are common responses in wetland plants (Reddy and Delaune, 2008), and for this plant specifically (Willis and Hester, 2004;Mayence and Hester, 2010). Greenhouse experiments, for example, document how flooding is required for vigorous root and rhizome production in P. hemitomon (Mayence and Hester, 2010). The results from these same greenhouse experiments also suggest that the % N and % P in plant tissue increases with higher nutrient loading, which, however, also leads to insignificant or negative effects on root diameter, specific gravity or volume after 3 months (Mayence and Hester, 2010).…”

Section: Methodsmentioning

confidence: 99%

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Nutrient-enhanced decomposition of plant biomass in a freshwater wetland

et al. 2015

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a b s t r a c tWe studied soil decomposition in a Panicum hemitomon (Schultes)-dominated freshwater marsh located in southeastern Louisiana that was unambiguously changed by secondarily-treated municipal wastewater effluent. We used four approaches to evaluate how belowground biomass decomposition rates vary under different nutrient regimes in this marsh. The results of laboratory experiments demonstrated how nutrient enrichment enhanced the loss of soil or plant organic matter by 50%, and increased gas production. An experiment demonstrated that nitrogen, not phosphorus, limited decomposition. Cellulose decomposition at the field site was higher in the flowfield of the introduced secondarily treated sewage water, and the quality of the substrate (% N or % P) was directly related to the decomposition rates. We therefore rejected the null hypothesis that nutrient enrichment had no effect on the decomposition rates of these organic soils. In response to nutrient enrichment, plants respond through biomechanical or structural adaptations that alter the labile characteristics of plant tissue. These adaptations eventually change litter type and quality (where the marsh survives) as the % N content of plant tissue rises and is followed by even higher decomposition rates of the litter produced, creating a positive feedback loop. Marsh fragmentation will increase as a result. The assumptions and conditions underlying the use of unconstrained wastewater flow within natural wetlands, rather than controlled treatment within the confines of constructed wetlands, are revealed in the loss of previously sequestered carbon, habitat, public use, and other societal benefits.

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