Physiological and growth responses of three sizes of containerized Picea mariana seedlings outplanted with and without vegetation control.

摘要

Three different stock sizes of containerized black spruce (Picea mariana) seedlings were planted in an abandoned agricultural field in Quebec, Canada, in May 1993. The small planting stock was of a conventional type produced in 110 cm3 containers. The experimental medium and large stock types were produced in 340 and 700 cm3 containers, respectively. Gas exchange, xylem water potential and dry masses were measured 6 times during each of the first 2 growing seasons in field plots with and without vegetation control (using the herbicide glyphosate). During the first growing season, the effect of planting shock masked most physiological and growth differences among seedling types. During the second growing season, in plots with vegetation control, small and medium seedlings had similar values of physiological variables and of growth as measured by relative growth rates (RGR), but the large seedlings showed lower values of both net photosynthesis and of RGR, a difference attributed to low initial quality of the root system in the larger seedlings. In plots without vegetation control, the trend was identical, but differences were not significant; the greater height of the larger seedlings, and the resulting greater access to light, compensated for their lower initial quality. The similarity in response between the medium and the small seedlings shows that a 4-fold increase in shoot size (1.68-6.82 g) in the initial size and a doubling of the shoot:root ratio (2.17-4.54) of the planting stock did notresult in increased planting shock or reduced growth. The results also show the importance of the interaction between stock height and the vertical light profile created by the competing vegetation in the final assessment of stock performance.