PARENT SESSION
Oral Session #62: Forest Carbon Dynamics.
Presiding: R. Norby
Wednesday, August 7. 1:00 PM to 4:45 PM. Greenlee Meeting Room, TCC.

Sources of variation in ecophysiological parameters in Douglas-fir and grand fir.

Nippert, Jesse^*,1, Marshall, John¹, ¹ University of Idaho, Moscow, ID, 83844-1133

ABSTRACT- Forest process models predict ecosystem-level responses from physiological parameters. However, sources and magnitude of the variation in these parameters are incompletely known. In this study, we sampled Abies grandis and Pseudotsuga menziesii var. glauca trees from eight fertilized sites distributed across the interior northwest of North America. At each site, we measured several variables identified as influential by sensitivity analyses of process models. Quantum yield () varied by canopy position in both species (p<0.0001). Average values (mol CO₂/ absorbed photon) (SE) were 0.048±0.006 for sun foliage and 0.067±0.007 for shade foliage in A. grandis. Average values for P. menziesii were 0.032±0.003 for sun foliage and 0.047±0.004 for shade foliage. SLA and %N also differed between sun and shade foliage, as well as date of sampling (p<0.0001). SLA was positively correlated with %N (p=0.007). Maximum photosynthetic rate (A_max) was also related to %N, with slopes that differed among sampling dates (p=0.002). Our results show that , SLA, and %N are strongly influenced by treatment and site variables. Accounting for variation in these key ecophysiological parameters may improve productivity estimates from forest process models.

KEY WORDS: forest process models, quantum yield, specific leaf area, percent foliar nitrogen