HR: 1340h
AN: B23A-0921    [Abstracts]
TI: Stable Carbon Isotopes As Indicators of Plant Water Use Efficiency
AU: * Powers, E M
EM: epowers@vandals.uidaho
AF: University of Idaho, College of Natural Resources Room 203, Moscow, ID 83844, United States
AU: Marshall, J D
EM: jdm@uidaho.edu
AF: University of Idaho, College of Natural Resources Room 203, Moscow, ID 83844, United States
AU: Ubierna Lopez, N
EM: nerea.ubiernalopez@vandals.uidaho.edu
AF: University of Idaho, College of Natural Resources Room 203, Moscow, ID 83844, United States
AB: Stable carbon isotopes have been utilized to better understand how environmental variables influence the efficiency of photosynthesis, specifically what factors limit the uptake and absorption of CO₂ during photosynthesis. An understanding of the controls over both gas exchange and stomatal conductance can provide an explanation for the possible environmental influences on plant WUE. The δ¹³C of extractive-free wood was used as an index of plant water use efficiency at Mica Creek Experimental Watershed, Shoshone County, ID. The δ¹³C values of tree rings were used to determine the effects of clear cut and partial cut harvesting practices, the effect of elevation, and species differences in intrinsic water use efficiency (WUE) among coniferous species including: Thuja plicata, Larix occidentalis, Picea engelmannii, Pseudotsuga menziesii, Abies lasiocarpa, and Abies grandis. We found significant effects of harvest treatments (p=0.0197), elevation (p= 0.0268), and species (p<0.001) on tree δ¹³C. The significantly more enriched isotopic signatures observed in Thuja plicata (δ¹³C = -23.37 ±0.17‰), indicate that it is a more water use efficient species compared to Larix occidentalis (δ¹³C = -25.66 ±0.43‰), and Abies grandis (δ¹³C = -25.83 ±0.15‰). There was also an overall trend of δ¹³C enrichment with elevation. The isotopic composition of tree rings has been estimated to increase by 0.003 ‰ per meter of elevation gain, which may be related to a decrease in soil moisture with elevation. Finally, the mean δ¹³C values observed on partial cut (δ¹³C = -24.73 ±0.10‰) and clear cut treatments (δ¹³C = -24.45 ±0.29‰) were significantly more enriched than the mean value for the control treatment (δ¹³C = -25.25 ±0.19‰). The more enriched isotopic signatures observed on the harvested treatments indicate that the trees are more water use efficient, which may be a result of increased photosynthetic capacity with an increase in the availability of water, foliar nitrogen, and light to individual trees on the harvested treatments. The reduction of stand density through harvesting may reduce the transpirational water losses on a stand level, thus increasing the water availability for individual trees.
DE: 0400 BIOGEOSCIENCES
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting