© 2006 Heron Publishing—Victoria, Canada
Phosphorus and nitrogen limitations to photosynthesis in Rocky Mountain bristlecone pine (Pinus aristata) in Colorado
Richard L. Boyce (1, 2), Jennifer R. Larson (3, 4) and Robert L. Sandford, Jr. (3)
1. Department of Biological Sciences, Northern Kentucky University, Nunn Drive, Highland Heights, KY 41099, USA / 2. Corresponding author (boycer@nku.edu) / 3. Department of Biological Sciences, University of Denver, Denver, CO 80208, USA / 4. Department of Biochemistry and Molecular Biology, Louisiana State University, Health Sciences Center, 1501 Kings Highway,
Shreveport, LA 71130, USA / Received February 25, 2005; accepted March 21, 2006; published online August 1, 2006
Summary
We examined Pinus aristata Engelm. stands in four locations in Colorado: Almagre Mountain, Black Mountain, Goliath Peak and Quartzville. All stands
are located at 3200–3700 m and face south-southeast. We measured maximum mass-based assimilation rates (Amax) and nitrogen (N) and phosphorus (P) foliar concentrations on six foliar age classes, from which instantaneous photosynthetic
N- and P-use efficiencies (PNUE and PPUE, respectively) and P:N ratios were estimated. Leaf mass per area (LMA) was also determined
for each foliar age class from each site.
Foliar age, P and N concentrations, and the P:N ratio explained the most variation in Amax when data from all sites were combined.
Leaf mass per area did not vary with foliar age class. Both P and N limit Amax, although P appears to be more limiting. The
critical P:N ratio is approximately 0.12. Results for Black Mountain differed from the other sites, as Amax was not correlated with age and was negatively correlated with LMA and P. Current findings showed no evidence of N saturation
at the Front Range sites (Almagre Mountain and Goliath Peak); however, because P is a limiting nutrient, increased anthropogenic
N availability at sites in the Front Range may cause adverse effects on photosynthesis, and perhaps growth, in the future.
Keywords:
bristlecone pine, foliar nutrients, gas exchange, LMA, PCA, SLA, specific leaf area.
