PARENT SESSION
Oral Session #63: Plant Ecology: Water Relations. Presiding: J. Cleverly.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.
Environmental and ontogenetic controls over transpiration of Pinus flexilis and P. ponderosa in northern Arizona.
Fischer, Dylan 1, Kolb, Tom1, DeWald, Laura1, 1
ABSTRACT- Comparisons of whole-tree water use between co-occurring species are important for understanding vegetation influences on site water balance. Sap-flux (gH2O/m2 sapwood/s) was measured in the stems of 6 Pinus flexilis and 8 Pinus ponderosa semi-continuously between June 6 and September 1, 2000. Measurement trees included the full range of tree sizes/ages on the site (0.5 cm to 66.7 cm DBH). Average daily whole-tree water use, canopy conductance (Gc; gH2O/m2 leaf/s/kPa), and leaf-specific transpiration rate (El; gH2O/m2 leaf/s) were higher for P. flexilis than for P. ponderosa, and whole-tree water use was positively related to diameter at the base of the live crown (DBLC) for both species. El was not related to DBLC for either species. For both species, El was parabolically related to vapor pressure deficit, and positively and linearly related to photosynthetically active radiation. For P. flexilis, Gc decreased and leaf area:sapwood area ratio (LA:SA) increased as DBLC increased. For P. ponderosa, there was no consistent trend in Gc and LA:SA with DBLC. However, Gc and LA:SA in P. ponderosa were related to a competition index which suggests that tree-to-tree competition influenced environmental variables that controlled water use in this species. Our results show species differences in environmental and ontogenetic controls on whole-tree transpiration that could differentially influence site water balance.
KEY WORDS: Transpiration, Sap-Flux, Conductance, Ontogeny