Nitrogen use efficiency of C3 and C4 wetland Cyperus species in a long-term greenhouse experiment.
Faulkner, Alison*,1, Holland, Marjorie1, Moore, Matthew 2, Cooper, Charles2, 1 University of Mississippi Department of Biology, University, MS, USA2 USDA-ARS National Sedimentation Laboratory, Oxford, MS, USA
ABSTRACT- The C4 pathway in Cyperus species is evidently an adaptation to temperate wetlands and sandy, infertile environments. Cyperus species using the C4 pathway have a high photosynthetic nitrogen use efficiency (NUE), which appears to confer a high degree of success in wetlands with low nitrogen concentrations. This translates to a possible competitive advantage over their C3 Cyperus counterparts where the latter conditions exist. This six-month greenhouse experiment was designed to quantify nitrogen use efficiency in two Cyperus species with differing photosynthetic pathways: Cyperus haspan, a C3 sedge, and Cyperus erythrorhizos, a C4 sedge. Both species co-occur in wetlands and ditches at the University of Mississippi Field Station in Lafayette Co., MS. Each species was subjected to nitrogen dosing at 2.5 ppm and 4.0 ppm, representing typical lower and higher nitrogen concentrations in agricultural runoff in Lafayette Co. Mean NO3-N analyzed from soil and interstitial water samples thus far are at undetectable levels (0.0-0.4 ppm) in all treatments, while mean NH3-N ranges from 0.20-0.57 ppm in soil samples and 0.75-9.0 ppm in interstitial water samples. Results suggest that nitrates are being reduced into ammonium form, which is expected in an anoxic environment. A combination of C3 and C4 sedges planted in treatment wetlands and agricultural ditches has the potential to partially treat fluctuating levels of nonpoint source pollution better than using either of the two types singly, since C3 sedges function to remove nitrogen at higher concentrations while C4 sedges tend to remove nitrogen more efficiently at lower concentrations.
Key words: nitrogen use efficiency, Cyperus species, wetlands
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