Loblolly pine (Pinus taeda L.) seedlings and plantlets, produced from drought resistant genetic families were planted in east Texas and their relative water relations compared through the first two, sixth and seventh growing seasons. Stock type (seedling or plantlet) had a larger influence on water relations than did family source in the early years. Seedlings exhibited more of those characteristics generally considered to benefit survival under harsh environments. The principal difference between stock types was the degree of progressive decrease in predawn water potential (Ψpre) through the growing season. On average and across families, Psi;pre decreased through the first growing season by 32 and 17% for plantlets and seedlings, respectively. Complete stomatal closure was never observed for any genetic source or stock type even when water potential was below -2.0 MPa. However, seedlings exhibited more stomatal regulation by lowering their stomatal conductance when water deficit was encountered, and increasing it during periods of favorable soil moisture availability. Predawn water potential was never below -0.9 MPa for any tree in either of the two first growing seasons. Although significant differences between seedling and plantlet performance were observed, their magnitude was small and diminished in the later years (sixth and seventh growing seasons). We conclude that plantlets need further development to be considered as a viable regeneration source for loblolly pine plantations on sites where summer drought is common.
All Science Journal Classification (ASJC) codes
- Nature and Landscape Conservation
- Management, Monitoring, Policy and Law