tailieunhanh - Báo cáo lâm nghiệp: " Effects of long-term water stress on net photosynthesis, growth and water-use efficiency of conifers in the field"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Effects of long-term water stress on net photosynthesis, growth and water-use efficiency of conifers in the field. | 411s Ann. Sci. For. 1989 46 suppl. 401s-415s Forest Tree Physiology E. Dreyer ef al. eds. Elsevier INRA Effects of long-term water stress on net photosynthesis growth and water-use efficiency of conifers in the field K. Gross Institute of Silviculture University of Freiburg D-7800 Freiburg . Introduction Water stress strongly influences growth of trees and might also be involved in today s forest decline. There are considerable differences in susceptibility to environmental constraints in populations and between species. In the present study a defined water stress was applied to young trees of Norway spruce and Douglas fir under otherwise natural environmental conditions. Both species were analyzed for differences in water-use efficiency and biomass production. Materials and Methods Sixteen 10-15 yr old and m high trees 10 spruces Picea abies and 6 Douglas firs Pseudotsuga menziesii were transplanted into containers and divided into 3 groups. Four spruces originated from a single clone the Douglas firs were not genetically uniform. One group was provided with optimal amounts of water and the other 2 received less water. The predawn water potential i gd was used 3S a measure of water supply. This potential was held at a constant level in each group for a period of 2 yr by controlling the water supply Table I . An NPK-fertilizer was applied to all trees in the spring. Gas exchange was repeatedly measured In 3 fully climatized chambers Koch systems throughout the vegetation period on the same current year s shoots alternating between spruces and Douglas firs The results were based on needle dry weight at the end of the vegetation period. Water relation parameters of the youngest twigs were determined by means of the pressure-volume technique Tyree et al. 1978 Gross and Pham-Nguyen 1987a . Growth in height and width was measured at regular 2 wk intervals. After 2 yr of experimentation the majority of the trees were felled analyzed and dried. Dry matter of

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