TITLE:
The Relative Importance of Nitrogen vs. Moisture Stress May Drive Intraspecific Variations in the SLA-RGR Relationship: The Case of Picea mariana Seedlings
AUTHORS:
Philippe LeBel, Robert L. Bradley, Nelson Thiffault
KEYWORDS:
Black Spruce (Picea mariana); Kalmia angustif`olia; Moisture and Nitrogen Stress; PNUE and WUE, SLA-RGR Relationship
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.4 No.6,
June
25,
2013
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.