Lack of acclimation of leaf area:sapwood area ratios in piñon pine and juniper in response to precipitation reduction and warming.

The leaf area to sapwood area ratios of trees (A(l):A(S)) can shift to maintain homeostatic gas exchange per unit leaf area in response to climate variability. We tested the hypothesis that trees alter their Al: AS ratios in response to long-term warming and reduced precipitation in order to maintain leaf-specific gas exchange rates under more stressful conditions. Whole-tree A(l):A(S) was measured on mature pinon pine (Pinus edulis Engelm.) and one-seed juniper (Juniperus monosperma (Engelm.) Sarg.) trees after 5 years (2012-16) of chronic exposure to increased temperature (+4.8 degrees C), precipitation reduction (-45%), or both simultaneously. No difference was found in A(l):A(s) among treatments for either species. Associated with this lack of shift in A(l):A(s) were large changes in predawn leaf water potential and stomatal conductance, consistent with theoretical expectations of interactions between leaf and whole-tree hydraulic supply. Our results suggest that a lack of whole-tree acclimation in A(l):A(s) results in the reductions in plant gas exchange and water status associated with long-term warming and reduced precipitation in semi-arid woodlands.