Species in the Populus taxa have shown potential as short rotation woody crops for biofuel harvest in the Southeast. They have exhibited high yields, possess an ability to thrive across a versatile range of sites and growing conditions and are already part of a well-established industry with existing infrastructure for harvest and transport. In order to reduce post-harvest transportation costs, establishment of Populusplantations may need to be close in proximity to mills or refineries and potentially on poor quality sites. However, knowledge is lacking on which Populustaxa perform best on poor quality sites, which are unsuitable for agriculture throughout the southeastern United States (US). Thus, the objective of this study was to elucidate high performing Populusvarietals utilizing ecophysiological data and growth at a selected site in the Southeast. This was accomplished through the measurement of height, leaf mass per area and gas exchange across three replicate blocks of five Populustaxa including P. deltoides (EC; 25 varietals),P. deltoides xP. maximowiczii(DM; 46 varietals), P. deltoides xP. nigra (DN; 11 varietals),P. trichocarpa ×P. deltoides (TD; 17 varietals)andP. trichocarpa ×P. maximowiczii (TM; 1 varietal).
Results/Conclusions
In terms of leaf gas exchange, we found that DM varietals had lower rates of photosynthesis and transpiration than all other taxa which did not differ significantly from each other. However, DM varietals, on average, grew 4.2 m tall, 0.37 to 1.2 m taller in the first year than other Populustaxa which did not differ significantly. We found that, across all varietals, year one height growth was significantly, negatively correlated with transpiration (p <0.0001) and positively correlated with water use efficiency (p <0.0001). Stomatal conductance was negatively correlated with height in EC andDM taxa (p = 0.043 and p = 0.0018 respectively) but not in other taxa. Neither net photosynthetic rates nor leaf mass per area were significantly correlated with height across Populus varietals (p= 0.454 and p=.0652 respectively). Our findings suggest that water availability and transport are stronger predictors of height growth than photosynthetic parameters for Populusvarietals and are limiting factors for height growth at this southeastern US upland site. Initial findings of year one height growth also suggest that DM varietals may be most suitable as a high yield, short rotation biofuel crop on upland sites in the Southeast although further research is needed.