Climate Change, Allometry and the Hydraulics of Arid Trees
Investigators (most current known information)
The rise in atmospheric CO2 is expected to force a rise in temperature and atmospheric vapor pressure deficit (VPD) by the end of the 21st century. For trees, the most relevant allometric component controlling water transport is the ratio of biomass allocated to leaves versus sapwood (AL/AS). Within Pinus, trees decrease AL/AS in response to rising VPD. Thus, rises in air temperature and VPD may profoundly alter the water relations of trees and forests. With funding from the International Arid Lands Consortium, we used stands of ponderosa pine growing along a climate gradient (desert v. montane) in the western United States as a model system to determine the effects these climate-related shifts in biomass allocation on the water relations of mature trees.
We found that desert trees, because of larger diameter tracheids in the sapwood, had 37% higher rates of water transport per unit sapwood area than montane trees. The combination of low AL/AS and higher sapwood conducting efficiency led to two-fold higher hydraulic conductivity (KL), and thus higher transpiration in desert trees. Desert and montane trees had similar vulnerability to xylem embolism and soil-to-leaf water potential gradients during the growing season. Despite higher allocation to sapwood, desert and montane trees did not differ in their reliance on stored water reserves. Paradoxically, any gain in sapwood water storage capacity through high allocation to sapwood in desert trees was offset by a loss in foliage storage capacity. The primary advantage of high allocation to sapwood in a warm and dry environment is to increase KL in order to prevent xylem embolism induction. A growth chamber study revealed that there were no interactions between elevated CO2 and temperature on water transport. Similar to their adult counterparts in the field, ponderosa pine seedlings reduced AL/AS and had higher KL in response to elevated temperatures and VPD. These results suggest that rising temperatures and VPD may exert stronger influence on tree water relations than elevated CO2 in a future climate. A common garden study showed that although desert and montane populations differed genetically, none of this variation was associated with ecotypic divergence. Thus, differences in the water relations of desert and montane trees may be related to phenotypic plasticity.
Articles in Journals
DeLucia, E.H., H. Maherali and E.V. Carey. 1999. "Climate-driven changes in biomass allocation compromise the ability of pines to store atmospheric carbon." Bulletin of the Ecological Society of America.
DeLucia, E.H., H. Maherali and E.V. Carey. 1999. "Climate-driven changes in biomass allocation compromise the ability of pines to store atmospheric carbon." Global Change Biology.
Maherali, H.. and E.H. DeLucia. 1999. "Biomass allocation and branch architecture influence the hydraulic conductance of Pinus ponderosa." Functional Ecology.
Maherali, H. and E.H. DeLucia. 1999. "Divergence in the biomass allocation and water relations of ponderosa pine growing along a climate gradient:ecotypic variation or phenotypic plasticity?" Functional Ecology.
Maherali, H. and E.H. DeLucia. 1999. "Evidence that climate-related shifts in the biomass allocation & physiology of ponderosa pine are phenotypic." Functional Ecology.
Maherali, H. and E.H. DeLucia. 1999. "Hydraulic conductance, transpiration and stored water-use by ponderosa pine trees growing in an arid climate: Implications for tree responses to climate change." Oecologia.
Maherali, H. and E.H. DeLucia. 1999. "Interactive effects of elevated CO2 and temperature on the water transport of ponderosa pine." American Journal of Botany.
Maherali, H. and E.H. DeLucia. 1999. "Transpiration and stored water-use by ponderosa pine trees growing in contrasting climates: Implications for global climate change." Ecology.
Maherali, H. and E.H. DeLucia. 1999. "Xylem hydraulic conductance and vulnerability to drought-induced embolism of ponderosa pine in contrasting climates." Tree Physiology.
Maherali, H. and E.H. DeLucia. 1998. "Climate alters the aboveground hydraulic function of ponderosa pine." Abstract. Bulletin of the Ecological Society of America 79(4):90.
Maherali, Hafiz and Evan H. DeLucia. 1997. "Hydraulic consequences of climate induced variation in the branch architecture of Pinus ponderosa." Abstract. Bulletin of the Ecological Society of America 78(4):240.
Maherali, H. and E.H. DeLucia. 1997. "The effects of elevated CO2 and temperature on the hydraulic properties of ponderosa pine seedlings." Abstract "Critical assessment of the response of forest ecosystems to elevated atmospheric carbon dioxide." In Third International IGBP-GCTE workshop, October.