Physiological and morphological traits of lowbush blueberry (Vaccinium angustifolium Ait.) plants in relation to post-transplant conditions and water availability

Abstract

Experiments were conducted with the lowbush blueberry (Vaccinium angustifolium Ait.) to investigate 1) changes in leaf water potential (ψ1) of transplanted seedlings, and rhizome development under various surface mulches, and 2) the water relations of mature plants subjected to irrigation or water withholding. Pre-dawn ψ1 for seedlings in bare-ground, sand and bark mulch treatments was > −0.2 MPa for most of the season following transplant. Dusk ψ1 was lower than predawn ψ1 for the first 2 wk after transplant under mulch and for the first 3 wk in bare ground, but these differences were not sustained. Rhizome numbers were 40% and 120% greater under bark and sand mulch, respectively, when compared with bare ground after three growing seasons. Mature (15-yr old) plants of cultivars Fundy and Brunswick were grown for one season under either rain-sheltered, rainfed or irrigated conditions. Pre-dawn ψl showed little or no difference between treatments until early August when, with volumetric soil water content below 8%, ψ1 of sheltered plants was reduced to about −0.3 MPa as compared with −0.1 MPa in rainfed and irrigated plants. Similarly, midday ψl and stomatal conductance (gl) were lower in sheltered, than in irrigated plants during August. Irrigated plants produced more large (>12-mm diameter), and fewer small (<10 mm) fruit than those under shelter where size distribution was about equal (Fundy), or showed a predominance of medium and smaller fruit (Brunswick). Fundy and Brunswick differed in the degree to which reduced soil water affected ψ1, g1 and fruit size distribution. Both Fundy and Brunswick possessed deep penetrating root networks with 35 and 60% of roots, respectively, terminating below 40 cm. This suggests that mature plants can resist drought by accessing water resources well below the soil surface. Key words: Mulch, water potential, stomatal conductance, wild blueberry, root architecture