The Relative Importance of Nitrogen vs. Moisture Stress May Drive Intraspecific Variations in the SLA-RGR Relationship: The Case of Picea mariana Seedlings

Philippe LeBel, Robert L. Bradley, Nelson Thiffault

Centre d’étude de la forêt, Département de biologie, Université de Sherbrooke, Sherbrooke, Canada.
Centre d’étude de la forêt, Département de biologie, Université de Sherbrooke, Sherbrooke, Canada;.

DOI: 10.4236/ajps.2013.46158                

Abstract

Plants acclimate to nitrogen (N) or moisture stress by respectively increasing photosynthetic N use efficiency (PNUE) or water use efficiency (WUE), in order to maximize their relative growth rate (RGR). These two phenotypic adaptations have opposite effects on specific leaf area (SLA). Thus, intraspecific variations in the SLA-RGR relationship should reflect the relative importance of N vs. moisture stress in plants. In this study, we measured needle gas exchanges and N concentrations in order to derive PNUE and WUE, as well as SLA and RGR of black spruce (Picea mariana) seedlings growing on a rapidly drained site in the presence or absence of Kalmia angustifolia. The eradication of Kalmia had resulted in a ~140% increase in seedling growth over a 6 year period. We found a negative SLA-RGR relationship where Kalmia had been eradicated, and a positive one where Kalmia had been maintained. Kalmia eradication resulted in higher WUE when measurements were made directly on the seedlings, and in lower PNUE when twigs were rehydrated prior to gas exchange measurements. Our data suggest that the bigger seedlings on Kalmia-eradicated plots increase RGR by decreasing SLA, as a means of coping with moisture stress. By contrast, increasing SLA on noneradicated plots may be a means of coping with nutrient stress exerted by Kalmia. The SLA-RGR relationship could potentially be used to identify the limiting resource for black spruce seedlings in different environments.

Keywords

Black Spruce (Picea mariana); Kalmia angustif`olia; Moisture and Nitrogen Stress; PNUE and WUE, SLA-RGR Relationship

Conflicts of Interest

The authors declare no conflicts of interest.

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