Influence of initial root length on physiological responses of cherrybark oak and Shumard oak seedlings to field drought conditions

One-year-old bareroot seedlings of cherrybark oak (Quercus pagoda Raf.) and Shumard oak (Quercus shumardii Buckley) were studied to describe their sensitivity to changes in environmental moisture in relation to initial root characteristics at the time of planting. Shumard oak seedlings with greater initial lateral root lengths and shoot heights sustained higher leaf gas exchange rates during both non-drought and drought periods. On the contrary, cherrybark oak seedlings had high leaf water potential ((psi)) and water use efficiency (WUE) and maintained low stomatal conductance (gs). This strategy generally allows for adequate gas exchange while minimizing water loss during drought. Initial lateral root:shoot ratio (LRSR) was negatively related to leaf gas exchange and water status, suggesting that excessive water loss of large seedlings with large root volume may negatively affect their drought hardiness. The responses of these floodplain oak species to drought was likely mediated by the absolute development of root systems at the time of planting and the balance between functioning root absorbing surface and transpirational leaf area. Responses of both species to drought in the subsequent growing seasons must be studied to determine their unique responses to water stress.