Water relations and drought response of Pinus strobiformis

Abstract

Southwestern white pine (Pinus strobiformis Engelm.) faces dual threats of climate change shifting its environmental niche and mortality due to a nonnative, invasive fungal pathogen. To inform efforts to sustain this species, we established experimental field trials in three common gardens along an elevational gradient with drought treatments to assess trait responses in southwestern white pine. We measured predawn and midday water potential on 44 maternal families from 10 populations at each garden. We used regression between predawn and midday water potentials to estimate hydroscape area, an index of stomatal regulation of transpiration. We measured leaf carbon isotope ratio and estimated carbon isotope discrimination and leaf mass per area to understand the effects of gardens and treatments on stomatal aperture and leaf structure. Water stress caused by experimental drought and temperature decreased leaf carbon isotope discrimination and leaf mass per area, indicating formation of thin leaves with low stomatal conductance in response to heat and drought. The hydroscape area of southwestern white pine suggests tight control of transpiration via stomatal closure, similar to other isohydric pines. Families with greater stomatal closure (inferred from carbon isotope ratio) at the warm, dry garden had higher survival than other families, suggesting an important role of isohydry in acclimation of southwestern white pine to expected habitat drying and warming.

Morphological Differences in Pinus strobiformis Across Latitudinal and Elevational Gradients

“…The ability of P. strobiformis to colonize its expected future range (Shirk et al, 2018) will be influenced by numerous factors, including colonization at the leading edge of the range shift, seed dispersal dynamics, resistance to white pine blister rust, competition with other species, introgression and hybridization (Menon et al, 2020), and genetic adaptation to local climate (Goodrich et al, 2016;Bucholz et al, 2020). Through our results, we have a better understanding of the environmental controls on cone and seed morphology, and we can more adequately evaluate seed provenances and transfer zones and provide better information for assisted migration strategies.…”

“…We recommend a proactive approach, in which reforestation programs incorporate both local and regional seed sources and allow for assisted gene flow (Aitken and Bemmels, 2016). For example, a manager of P. strobiformis might include seed sources from the provenance that is most similar to the projected future climate of the planting location (given climate predictions for the species; Shirk et al, 2018) alongside local sources on sites of least aridity (Bucholz et al, 2020). Such a strategy promotes the local genetic structure while providing for adaptation to changing climates and allowing managers flexibility in determining seed sources most suitable given other management considerations (e.g., white pine blister rust).…”

Climate Refugia for Pinus Spp. In Topographic and Bioclimatic Environments of the Madrean Sky Islands of México and the United States 

“…In contrast, species that exhibit tolerance to a wider range of conditions may be able to take advantage of variability along a climate continuum, dependent on species interactions and other factors. Species-speci c trait responses, such as tight control of transpiration via stomatal closure exhibited by P. strobiformis, will play a role in acclimation to drier and warmer climate (Bucholz et al 2020).…”

Quantitative Disease Resistance to White Pine Blister Rust at Southwestern White Pine’s (Pinus strobiformis) Northern Range

“…(Southwestern white pine) is a large, long-lived conifer native to the southwestern United States and Mexico (Looney and Waring, 2012). The species thrives in mixed-conifer stands at mid to high elevations (Looney and Waring, 2012;Shirk et al, 2018) where it is moderately shadetolerant (Goodrich and Waring, 2017) and drought-tolerant (Bucholz et al, 2020), often occurring in sky islands. Within the northern extent of its range, P. strobiformis is part of a moving hybrid zone with Pinus flexilis (Menon et al, 2020) with some evidence of increased fitness due to introgressed alleles from P. flexilis (Menon et al, 2021).…”