Effects of nutrient addition on leaf chemistry,morphology, and photosynthetic capacity of three bog shrubs |
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| Authors: | Jill L. Bubier Rose Smith Sari Juutinen Tim R. Moore Rakesh Minocha Stephanie Long Subhash Minocha |
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| Affiliation: | (1) Environmental Studies Program, Mount Holyoke College, 50 College Street, South Hadley, MA 01075, USA;(2) Department of Geography, Global Environmental & Climate Change Centre, McGill University, 805 Sherbrooke St. W, Montreal, QC, H3A 2K6, Canada;(3) US Department of Agriculture, Forest Service, Northern Research Station, 271 Mast Road, Durham, NH 03824, USA;(4) Department of Biological Sciences, University of New Hampshire, Durham, NH 03824, USA;(5) Present address: Ecosystems Center, 7 MBL St, Woods Hole, MA 02543, USA;(6) Present address: Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland |
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| Abstract: | Plants in nutrient-poor environments typically have low foliar nitrogen (N) concentrations, long-lived tissues with leaf traits designed to use nutrients efficiently, and low rates of photosynthesis. We postulated that increasing N availability due to atmospheric deposition would increase photosynthetic capacity, foliar N, and specific leaf area (SLA) of bog shrubs. We measured photosynthesis, foliar chemistry and leaf morphology in three ericaceous shrubs (Vaccinium myrtilloides, Ledum groenlandicum and Chamaedaphne calyculata) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada, with a background deposition of 0.8 g N m−2 a−1. While biomass and chlorophyll concentrations increased in the highest nutrient treatment for C. calyculata, we found no change in the rates of light-saturated photosynthesis (A max), carboxylation (V cmax), or SLA with nutrient (N with and without PK) addition, with the exception of a weak positive correlation between foliar N and A max for C. calyculata, and higher V cmax in L. groenlandicum with low nutrient addition. We found negative correlations between photosynthetic N use efficiency (PNUE) and foliar N, accompanied by a species-specific increase in one or more amino acids, which may be a sign of excess N availability and/or a mechanism to reduce ammonium (NH4) toxicity. We also observed a decrease in foliar soluble Ca and Mg concentrations, essential minerals for plant growth, but no change in polyamines, indicators of physiological stress under conditions of high N accumulation. These results suggest that plants adapted to low-nutrient environments do not shift their resource allocation to photosynthetic processes, even after reaching N sufficiency, but instead store the excess N in organic compounds for future use. In the long term, bog species may not be able to take advantage of elevated nutrients, resulting in them being replaced by species that are better adapted to a higher nutrient environment. |
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