The current debate in the scientific community (and by default the political community) regarding the restoration of coastal Louisiana includes a discussion on the impact of nutrients on the production of belowground biomass. Some research indicates that belowground biomass may decrease with nutrient enrichment. This may subject the receiving wetlands of freshwater diversions and wastewater effluent to increased erosion and wind throw, which could hinder storm buffering benefits. The objective was to utilize an ongoing mesocosm experiment to investigate the effects of nutrient loading from river diversions and treated wastewater on the (a) above- and belowground biomass production of wetland plants, (b) depth of root foraging activity, (c) overall effect on root to shoot ratio (R:S) and (d) soil elevation. The water quality experiment was set up as a completely randomized 2*2*3*4 factorial design. Four types of water quality (fresh water, fresh water with nutrients (90 g N m-2 yr -1), 3 ppt and 6 ppt) were crossed with three types of wetland hydrology (mesic, permanently flooded and constant throughput), sediment addition (yes, no) and a simulated hurricane (yes, no). After 5 years of growth, root to shoot ratio decreased (F=16.92,p<0.001), even though belowground biomass doubled (F=24.79,p<0.001) with nutrient additions. Moreover, absolute amount of belowground biomass increased in deeper soil sections (>30 cm) over the other water quality treatments (F=16.44,p<0.001). Soil elevation was positively related to the amount of belowground biomass(R2=.34,p<0.001). Further, only nutrient treated mesocosm vessels produced enough root material to more than offset soil subsidence of 5 mm/year (F=32.48,p<0.001). A second baldcypress (Taxodium distichum) and water tupelo ( Nyssa aquatica</italic>) nitrogen dosing experiment was set up as a completely randomized 2*6 factorial design. The two tree species were crossed with six loading rates of fertilizer (0, 10, 50, 100, 200, and 400 g N m-2 yr-1). After two growing seasons, nitrogen loading had the strongest effect on aboveground biomass (F=18.77,p< 0.001), but also significantly affected root to shoot ratio (F=2.41,p=0.004) and belowground biomass (F=2.30,p=0.049). Tree species differed in root to shoot allocation (F=7.66,p=0.006) and aboveground biomass (F=10.43,p=0.002), but not belowground biomass. Finally, wood density increased for both species from 0-100 g N m-2 yr-1(F=3.38,p=0.007), then decreased for baldcypress, but not for water tupelo. The results of these experiments should be used to promote beneficial use of river diversions and treated wastewater to restore the wetlands of coastal Louisiana.
|Advisor:||Shaffer, Gary P.|
|Commitee:||Bossart, Janice, Stiller, Volker|
|School:||Southeastern Louisiana University|
|School Location:||United States -- Louisiana|
|Source:||MAI 50/03M, Masters Abstracts International|
|Subjects:||Biostatistics, Plant biology|
|Keywords:||Aboveground biomass, Belowground biomass, Root to shoot|
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