Comparing Drought Responses of Red Oak (Quercus rubra) and Red Maple (Acer rubrum) in Field-grown Nursery Production

.The plant nursery industry in Oregon faces increasing challenges from climate change, particularly concerning the cultivation of shade trees grown in nursery production. Shade trees are multimillion-dollar agricultural commodity in Oregon, the number one producer of shade trees in the United States. Oak, maple, and sycamore are common examples of shade trees. Our hypothesis posited that despite being commonly cultivated together in shadetree production blocks under similar management protocols, these trees employ distinct hydraulic strategies during growth. The aim of this research was to investigate the physiological response of Sunset Red Maple (Acer rubrum 'Franksred') and Red Oak (Quercus rubra) to variations in soil moisture and vapor pressure deficit (VPD). The research was carried out at the experimental field-grown nursery located at the North Willamette Research and Extension Center in Aurora, OR, USA. Stomatal conductance (g(s)) and stem water potential (Psi (s)) were measured to assess plant responses to soil moisture and VPD. When soil moisture was abundant, average Red Oak gs was 0.26 t 0.13 mmol m(-2) s(-1), twice as great as Red Maple, at 0.12 t 0.09 mmol m(-2) s(-1). Red Oak gs was 2.67 times greater than Red Maple gs under soil moisture deficit. Similarly, at any given soil moisture content Red Oak s was significantly less negative (-6.22 t 2.70 bars, n = 384) compared with Red Maple (-12.15 t 4.45 bars, n = 384). In general, our results revealed distinct responses between the two species, with Red Maple exhibiting greater sensitivity to soil moisture and VPD compared with Red Oak. Furthermore, we observed an important correlation between VPD and maple gs, with gs, decreasing in response to increasing VPD whether soil moisture was abundant (R-2 = 0.64) or lacking (R-2 = 0.69), highlighting the importance of considering atmospheric moisture dynamics in plant water management strategies. These findings underscore the complexity of plant responses to drought and emphasize the necessity of informed water management practices for sustainable nursery production. This research contributes to our understanding of plant hydraulic physiology and provides valuable insights for sustainable nursery management practices, particularly in the face of climate change-induced droughts.