The effects of soil nitrogen availability on the allocation of nitrogen to leaf processes for an invasive grass, Phalaris arundinacea, and native Carex species Chelsea M. Griffin, Elizabeth F. Waring, and A. Scott Holaday Texas Tech University, Department of Biological Sciences, Lubbock, TX, USA Introduction Wetlands that receive a high nitrogen load are vulnerable to invasion by non-native species whose nitrogen-use strategies are favored by such conditions. The invasive grass, Phalaris arundinacea, thrives in nitrogen-rich sites that once supported Carex species adapted to lower nitrogen conditions. Our findings will improve the understanding of physiological bases for the success or vulnerability of each species under variable nitrogen supply. Hypotheses At high nitrogen levels, P. arundinacea will allocate nitrogen to photosynthetic enzymes and less to storage, in contrast to Carex species. At low nitrogen levels, Carex species will maintain photosynthesis by allocating nitrogen storage to photosynthesis. Carex. lacustris is more similar to P. arundinacea at high nitrogen supply and more similar to C. stricta at low nitrogen supply. Vacuolar nitrate is allocated for photosynthesis during nitrogen deprivation in all species. Conclusions For all species, the age of leaf did not affect nitrogen allocation. Decreasing available nitrogen : Reduced photosynthetic parameters and soluble protein by more than 50% for P. arundinacea Reduced photosynthetic parameters and soluble protein by 40% or less for C. stricta Reduced by 28% or less in young C. stricta leaves The responses for C. lacustris were closer to that for P. arundinacea Stored leaf nitrate is not allocated toward photosynthesis under low nitrogen levels by any of these species. Methods TTU Biology greenhouse 3 species (N=5): Phalaris arundinacea Carex stricta Carex lacustris Grown for 7 weeks with 15mM N nutrient solution Followed by 7 weeks under 0.15mM N nutrient solution Analyses: Photosynthetic parameters Collected with Li-6400XT Analyzed in R using plantecophys package (Duurama 2013) Soluble protein content using Bradford method (1975) Total leaf nitrogen analyzed using elemental analyzer Nitrate reductase activity using method from Munzarova et al. (2006) Nitrate content analyzed using Catalado method (1975) Data analyzed using Mixed-effects ANCOVA in R (nlme package, Pinheiro et al. 2013) Acknowledgements Dallas Ann Drazen for lab assistance, Dr. Ray Lee for analysis of leaf nitrogen samples, TTUAB for grant support Literature Cited Bradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry 72: Catalado DA, Harron M, Schrader LE, Youngs VL (1975) Rapid colormetric determination of nitrate in plant tissue by nitrification of salicyclic acid. Communications in Soil Science and Plant Analysis 6: Duursma R (2013). plantecophys: Modelling and analysis of leaf gas exchange data. R package version 0.2. Munzarova E, Lorenzen B, Brix H, Vojtiskova L, Votrubova O (2006). Effect of NH 4+/NO 3− availability on nitrate reductase activity and nitrogen accumulation in wetland helophytes Phragmites australis and Glyceria maxima. Environmental and Experimental Botany 55: Pinheiro J, Bates D, DebRoy S, Sarkar D, and the R Development Core Team (2013). nlme: Linear and Nonlinear Mixed Effects Models. R package version Figure 6: Mean nitrate reductase activity (NR) ± standard error. NR activity differed significantly between species (p=0.0362). However, leaf age and treatment did not affect NR activity. Figure 7: Mean leaf level nitrate content per gram of leaf tissue ± standard error. Nitrate content differed significantly between species (p<0.0087),and the interaction of species X treatment (p=0.0185). Nitrate content was not affected by leaf age nor was stored nitrate used in low nitrogen conditions. Figures 1 and 2: Mean photosynthetic parameters (V cmax and J max ) ± standard error. V cmax and J max differed signficantly between species (p<0.0001) and treatments (p<0.0001). There was a significant interaction of species X treatment for V cmax (p=0.001) and J max (p=0.0223) as well as species X leaf age V cmax (p=0.0158) and J max (p=0.005). Figure 3: Mean total leaf N ± standard error. Leaf N was significantly different between species (p<0.0001), treatment (p<0.0001), and the interaction of species X treatment (p<0.0001). Total leaf N was not affected by leaf age. Figure 4: Mean photosynthetic nitrogen-use efficiency (PNUE) ± standard error. PNUE differed significantly between species (p=0.0009), treatment (p=0.0100), and the interaction of species X treatment (p<0.0001). Leaf age did not affect PNUE. Figure 5: Mean leaf level soluble protein per gram of leaf tissue ± standard error. Protein content differed significantly between species (p<0.0001), treatment (p<0.0001), and the interaction of species X treatment (p=0.0008). Protein content was not affected by leaf age.