Warming combined with more extreme precipitation regimes modifies the water sources used by trees.
The persistence of vegetation under climate change will depend on a plant's capacity to exploit water resources. We analyzed water source dynamics in piñon pine and juniper trees subjected to precipitation reduction, atmospheric warming, and to both simultaneously. Piñon and juniper exhibited different and opposite shifts in water uptake depth in response to experimental stress and background climate over 3 yr. During a dry summer, juniper responded to warming with a shift to shallow water sources, whereas piñon pine responded to precipitation reduction with a shift to deeper sources in autumn. In normal and wet summers, both species responded to precipitation reduction, but juniper increased deep water uptake and piñon increased shallow water uptake. Shifts in the utilization of water sources were associated with reduced stomatal conductance and photosynthesis, suggesting that belowground compensation in response to warming and water reduction did not alleviate stress impacts for gas exchange. We have demonstrated that predicted climate change could modify water sources of trees. Warming impairs juniper uptake of deep sources during extended dry periods. Precipitation reduction alters the uptake of shallow sources following extended droughts for piñon. Shifts in water sources may not compensate for climate change impacts on tree physiology.
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Charlotte
C
Grossiord
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Sanna
S
Sevanto
Center for Stable Isotope Biogeochemistry and the Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA.
Todd E
TE
Dawson
Department of Plant Biology, Ecology, and Evolution, Oklahoma State University, Stillwater, OK, 74078-3013, USA.
Henry D
HD
Adams
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Adam D
AD
Collins
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Lee T
LT
Dickman
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Brent D
BD
Newman
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Elizabeth A
EA
Stockton
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Nate G
NG
McDowell
D057231:Climate Change; D003903:Deuterium / Q000378:metabolism; D007553:Isotope Labeling; D008962:Models, Theoretical; D010103:Oxygen Isotopes / Q000378:metabolism; D011891:Rain; D012621:Seasons; D012987:Soil / Q000737:chemistry; D013045:Species Specificity; D014197:Trees / Q000502:physiology*; D014867:Water / Q000502:physiology*
D010103:Oxygen Isotopes; D012987:Soil; D014867:Water; D003903:Deuterium

Juniperus monosperma
; 
Pinus edulis
; climate change; gas exchange; water extraction depth; δ18O; δ2H