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

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Báo cáo lâm nghiệp: " Effects of long-term water stress on net photosynthesis, growth and water-use efficiency of conifers in the field"Effects of long-term water stress on net photosynthesis,growth and water-use efficiency of conifers in the fieldK. Gross Freiburg, F.R.G.Institute of Silviculture, D-7800 University of Freiburg, An NPK-fertilizer was applied to all trees inIntroduction the spring. Gas exchange was repeatedly measured in 3Water stress strongly influences growth of fully climatized chambers (Koch systems) throughout the vegetation period on the sametrees and might also be involved in today’s current year’s shoots alternating betweenforest decline. There are considerable dif- spruces and Douglas firs. The results wereferences in susceptibility to environmental based on needle dry weight at the end of theconstraints in populations and between vegetation period.species. In the present study, a defined Water relation parameters of the youngestwater stress was applied to young trees of were determined by means of the pres- twigs sure-volume technique (Tyree et al., 1978;Norway spruce and Douglas fir under Gross and Pham-Nguyen, 1987a). Growth inotherwise natural environmental condi- height and width was measured at regular, 2 wktions. Both species were analyzed for dif- intervals.ferences in water-use efficiency and bio- After 2 yr of experimentation, the majority of production.mass the trees were felled, analyzed and dried. Dry matter of the needles, twigs, branches, trunk and large (> 10 mm) and fine (< 10 mm) roots were determined, with reference to their year of generation. Increase in biomass over the finalMaterials and Methods vegetative period and water-use efficiency were calculated (Gross and Pham-Nguyen 1987b; Gross 1988).Sixteen 10-15 yr old and 1.5-2.5 high trees m(10 spruces (Picea abies) and 6 Douglas firs(Pseudotsuga menziesii) were transplanted intocontainers and divided into 3 groups. Fourspruces originated from a single clone; theDouglas firs were not genetically uniform. Onegroup was provided with optimal amounts ofwater and the other 2 received less water. Thepredawn water potential ( was used as a ) d p Vfmeasure of water supply. This potential washeld at a constant level in each group for a pe-riod of 2 yr by controlling the water supply(Table I). and thus also ’ fastest growth. Douglas theResults fir was superior to spruce. Net photo- synthesis in trees with limited or very limit- water supplyTrees receiving optimal ed water supply was reduced (Figs. 1, 2). photosynthesisshowed the highest net The degree of reduction depended pri- PICEA upon intensity of water stress but consideration. Thus, the reduction in netmarily also modified by water vapor satura- photosynthesis was always greater onwastion deficit (WSD) and the level of the long and sunny summer days with highturgor loss point (Figs. 1, 2). In contrast to daily integrals of water vapor saturationexperiments under steady state conditions deficit. On moist and overcast days orin the lab with fixed values of air humidity, short days in autumn, however, with lowdaily integrals of WSD seem to be more daily integrals of WSD, the reduction inuseful under field conditions, since they net photosynthesis was less pronouncedtake seasonal changes in daylength into (Figs. 1, 2). The turgor loss point ( sank from No symptoms typical of forest decline ) Vtlabout -1.6 to -2.6 MPa in spruce and observed. werefrom -1.7 to -3.0 MPa in Douglas fir be-tween the end of June and November(Fig. 1Parallel to this, relative watercontent at loss of turgor (RWC was re- ) P Conclusionsduced from 85 to 74%. Additional exper-iments have shown that net photosynthe- species differed in 2 essen ...