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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Nội dung Text: 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 field K. Gross Freiburg, F.R.G. Institute of Silviculture, D-7800 University of Freiburg, An NPK-fertilizer was applied to all trees in Introduction the spring. Gas exchange was repeatedly measured in 3 Water stress strongly influences growth of fully climatized chambers (Koch systems) throughout the vegetation period on the same trees and might also be involved in today’s current year’s shoots alternating between forest decline. There are considerable dif- spruces and Douglas firs. The results were ferences in susceptibility to environmental based on needle dry weight at the end of the constraints in populations and between vegetation period. species. In the present study, a defined Water relation parameters of the youngest water 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 in otherwise natural environmental condi- height and width was measured at regular, 2 wk tions. 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 final Materials 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 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 ( was used as a ) d p Vf measure of water supply. This potential was held 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 the Results fir was superior to spruce. Net photo- synthesis in trees with limited or very limit- water supply Trees receiving optimal ed water supply was reduced (Figs. 1, 2). photosynthesis showed the highest net The degree of reduction depended pri- PICEA
upon intensity of water stress but consideration. Thus, the reduction in net marily also modified by water vapor satura- photosynthesis was always greater on was tion deficit (WSD) and the level of the long and sunny summer days with high turgor loss point (Figs. 1, 2). In contrast to daily integrals of water vapor saturation experiments under steady state conditions deficit. On moist and overcast days or in the lab with fixed values of air humidity, short days in autumn, however, with low daily integrals of WSD seem to be more daily integrals of WSD, the reduction in useful under field conditions, since they net photosynthesis was less pronounced take seasonal changes in daylength into (Figs. 1, 2).
The turgor loss point ( sank from No symptoms typical of forest decline ) Vtl about -1.6 to -2.6 MPa in spruce and observed. were from -1.7 to -3.0 MPa in Douglas fir be- tween the end of June and November (Fig. 1Parallel to this, relative water content at loss of turgor (RWC was re- ) P Conclusions duced from 85 to 74%. Additional exper- iments have shown that net photosynthe- species differed in 2 essentials fea- Both sis was reduced to zero when the reflecting adaptations to their natural tures predawn water potential reached the tur- habitat: 1) under conditions of good water gor loss point, reflecting complete stoma- supply, Douglas fir had a higher water-use tal closure. Consequently, the reduction of efficiency than Norway spruce; 2) turgor net photosynthesis in trees with limited loss point values for mature Douglas fir and very limited water supply was more twigs were lower than those of spruce, pronounced in summer than in autumn a better water stress toler- thus indicating (Fig.1).. ) Both features probably are reasons ance. Water-use efficiency was greater for for the high productivity of Douglas fir in both species under conditions of limited central Europe. water supply, indicating different kinetics for C0 and water vapor diffusion or sto- 2 matal conductance (cf. Larcher, 1960). Under conditions of good water supply, Acknowledgments Douglas firs were more efficient than spruce trees (Figs. 3 and 4). Long-term water stress had no effect on This work was supported by Deutsche For- supply of essential nutrients to the trees. schungsgemeinsc:haft. !nn- -
photosynthesis and growth of young References net (Picea abies [L.] Karst) and Douglas spruces firs (Pseudotsuga menziesii [Mirb.] Franco) in Gross K. (1988) Net photosynthesis, biomass the field (in German). Forstwiss. Centralbl. 106, production and water-use efficiency of young 7-26 Norway spruces and Douglas firs, given dif- Larcher W. (1960) Transpiration and photosyn- ferent levels of water supply for several years in thesis of detached leaves and shoots of Quer the field (in German). Allg. Forst Jagdztg. 159, cus pubescens and Q. ilex during desiccation 230-239 under standard conditions. Bull. Res. Counc. Gross K. & Pham-Nguyen T. (1987a) Pressure- Isr. Sect D 8. 213-224 volume analyses on shoots of Picea abies and Tyree M.T., Cheung YN.S., MacGregor M.E. & leaves of Coflea liberica at various tem- Talbot A.J.B. (1978) The characteristics of sea- peratures. Physiol. Plant.70, 189-195 sonal and ontogenetic changes in the Gross K. & Pham-Nguyen T. (1987b) The tissue-water relations of Acer, Populus, Tsuga, influence of constant long-term water stress on and Picea. Can. J. Bot 56, 635-647