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Nutrient Stoichiometry of Sea Grasses
[edit]The primary nutrients determining sea grass growth are carbon, nitrogen, phosphorous, and light for photosynthesis. N and P can be acquired from sediment pore water or from the water column, and sea grasses can uptake both N in both ammonium (NH4+) and nitrate (NO3-) form.[1]
A number of studies from around the world have found that there is a wide range in the concentrations of C, N, and P in seagrasses depending on their species and environmental factors. For instance, plants collected from high-nutrient environments had lower C:N and C:P ratios than plants collected from low-nutrient environments. Sea grass stoichiometry does not follow the Redfield ratio commonly used as an indicator of nutrient availability for phytoplankton growth. In fact, a number of studies from around the world have found that the proportion of C:N:P in sea grasses can vary significantly depending on their species, nutrient availability, or other environmental factors. Depending on environmental conditions, sea grasses can be either P-limited or N-limited. [2]
For example, sea grasses from meadows fertilized with bird excrement have shown a higher proportion of phosphate than unfertilized meadows. Alternately, sea grasses in environments with higher loading rates and organic matter diagenesis supply more P, leading to N-limitation. P availability in T. testudinum is the limiting nutrient. (Fourqurean et al., 1992) The nutrient distribution in T. testudinum ranges from 29.4-43.3% C, 0.88-3.96% N, and 0.048-0.243% P. This equates to a mean ratio of 24.6 C:N, 937.4 C:P, and 40.2 N:P.[3]
An early study of sea grass stoichiometry suggested that the “Redfield” balanced ratio between N and P for sea grasses is approximately 30:1.[4] However, N and P concentrations are strictly not correlated, suggesting that sea grasses can adapt their nutrient uptake based on what is available in the environment. This information can also be used to characterize the nutrient availability of a bay or other water body (which is difficult to measure directly) by sampling the sea grasses living there.[3]
Light availability is another factor that can affect the nutrient stoichiometry of sea grasses. Nutrient limitation can only occur when photosynthetic energy causes grasses to grow faster than the influx of new nutrients. For example, low light environments tend to have a lower C:N ratio.[3] Alternately, high-N environments can have an indirect negative effect to sea grass growth by promoting growth of algae that reduce the total amount of available light.[1] (Touchette and Burkholder 2000)
Nutrient variability in sea grasses can have potential implications for wastewater management in coastal environments. High amounts of anthropogenic nitrogen discharge could cause eutrophication in previously N-limited environments, leading to hypoxic conditions in the sea grass meadow and affecting the carrying capacity of that ecosystem. (Fourqurean and Zieman, 2002??)
Conceptual Model of Sea Grass Nutrient Stoichiometry
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Engineered Approaches to Blue Carbon
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- ^ a b * Touchette, Brant W, and JoAnn M Burkholder. 2000. “Review of Nitrogen and Phosphorus Metabolism in Seagrasses.” ''Journal of Experimental Marine Biology and Ecology'' 250 (1–2): 133–67. doi:10.1016/S0022-0981(00)00195-7.
- ^ * Fourqurean, James W., Joseph C. Zieman, and George V. N. Powell. 1992. “Phosphorus Limitation of Primary Production in Florida Bay: Evidence from C:N:P Ratios of the Dominant Seagrass Thalassia Testudinum.” ''Limnology and Oceanography'' 37 (1): 162–71. doi:10.4319/lo.1992.37.1.0162.
- ^ a b c Fourqurean, James W., and Joseph C. Zieman. 2002. “Nutrient Content of the Seagrass Thalassia Testudinum Reveals Regional Patterns of Relative Availability of Nitrogen and Phosphorus in the Florida Keys USA.” Biogeochemistry 61 (3): 229–45. doi:10.1023/A:1020293503405.
- ^ Atkinson, M. J., and S. V. Smith. 1983. “C:N:P Ratios of Benthic Marine plants1.” Limnology and Oceanography 28 (3): 568–74. doi:10.4319/lo.1983.28.3.0568.