PHYSIOLOGICAL AND GROWTH-RESPONSES OF 3 SIZES OF CONTAINERIZED PICEA-MARIANA SEEDLINGS OUTPLANTED WITH AND WITHOUT VEGETATION CONTROL

Three different stock sizes of containerized black spruce (Picea maria na [Mill.] B.S.P.) seedlings were planted in an abandoned agricultural field. The small planting stock was of a conventional type produced i n 110 cm(3) containers. The experimental medium and large stock types were produced in 340 and 700 cm(3) containers, respectively. Gas excha nge, xylem water potential and dry masses were measured six times duri ng each of the first two growing seasons in held plots with and withou t vegetation control. During the first growing season, the effect of p lanting shock masked most physiological and growth differences among s eedling types. During the second growing season, in plots with vegetat ion control, small and medium seedlings had similar values of physiolo gical variables and of growth as measured by relative growth rates (RG R), but the large seedlings showed lower values of both net photosynth esis and of RGR, a difference attributed to low initial quality of the root system in the larger seedlings. In plots without vegetation cont rol, the trend was identical, but differences were not significant; th e greater height of the larger seedlings, and the resulting greater ac cess to light, compensated for their lower initial quality. The simila rity in response between the medium and the small seedlings shows that a fourfold increase in shoot size (1.68-6.82 g) in the initial size a nd a doubling of the shoot : root ratio (2.17-4.54) of the planting st ock did not result in increased planting shock or reduced growth in th ese containerized conifer stock types. The results also show the impor tance of the interaction between stock height and the vertical light p rofile created by the competing vegetation in the final assessment of stock performance. (C) 1998 Elsevier Science B.V.