Effects of transplanting and irrigation regime on growth and gas exchange of select tree species in a semi-arid climate
This research investigated effects of transplanting and irrigation on growth and gas exchange of select landscape free species. Experiment one investigated effects of irrigation regime on growth and gas exchange of four, field-grown (FG) landscape tree species. Trees were subjected to three irrigation treatments: low, medium, and high (33, 66, and 100%, respectively, of reference evapofranspiration [ETo]). Tree species studied were autumn blaze maple [Acer xfreemanii E. Murray 'Jeffersred' (Autumn Blaze®)], Shantimg maple (Acer truncatum Bunge), Mexican redbud [Cercis canadensis L. var. mexicana (J. N. Rose) M. Hopkins], and Texas redbud [Cercis canadensis L. var. texensis (S. Watson) M. Hopkins]. Trees irrigated at 33% of ETo were under greater water deficit stress, as indicated by more negative pre-dawn leaf water potential (I/'L), and tended to have lower mid-day stomatal conductance (gs) and growth when compared to trees with higher irrigation rates. Sensitivity of stomata to increasing leaf-to-air vapor pressure difference (LVPD) varied with species. However, all trees exhibited decreasing gs as LVPD increased. Results from this research indicate irrigating these FG landscape free species at 66% of ETo produces similar gas exchange and growth rates when compared to trees irrigated at 100% of ETo. A second study investigated effects of transplanting and mulch on growth and gas exchange of large-caliper, FG red oak (Quercus shumardii Buckli.) trees. Four treatment combinations included: mulch, non-transplanted; mulch, transplanted; no mulch, nontransplanted; and no mulch, transplanted. Throughout much of the experiment. transplanted trees showed greater water deficit stress (more negative I/'L) than nontransplanted frees. Mulch lowered water deficit stress by 40% for transplanted trees, but did not influence gas exchange. Transplanting resulted in a 59% decrease in mid-day gs compared to non-transplanted trees. The combination of water deficit stress and stomatal response to high evaporative demand reduced gas exchange and prevented recovery to control gas exchange levels. Trunk area increase, shoot elongation, and leaf area were also reduced in transplanted frees. In addition, non-transplanted trees with mulch tended to have less growth when compared to non-transplanted frees without mulch.