Báo cáo lâm nghiệp: "Effects of soil temperature on gas exchange and morphological structure of shoot and root in 1 yr old Scots pine (Pinus sylvestris L.) seedlings"

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Nội dung Text: Báo cáo lâm nghiệp: "Effects of soil temperature on gas exchange and morphological structure of shoot and root in 1 yr old Scots pine (Pinus sylvestris L.) seedlings"

Effects of soil temperature on gas exchange and mor- phological structure of shoot and root in 1 yr old Scots pine (Pinus sylvestris L.) seedlings P. Puttonen J. Lippu Unioninkatu 40 B, 00170 Helsinki, Finland Department of Silviculture, University of Helsinki, Introduction Materials and Methods One yr old Scots pine seedlings growing 30 d at Low soil temperature is one of the envi- 13°C, 18 h photoperiod, 250 pmol-m- ir- 1 -s- 2 ronmental factors affecting early growth radiance and 7 mbar vapor pressure deficit in a and survival of forest seedlings in boreal mixture of low humified Sphagnum peat and ecosystems. With regard to gas exchange perlite were exposed to 3 different soil tempera- and growth, soil temperature is often ture treatments (8°C, 12°C and a changing tem- perature from 5.5 to 13.0°C). Soil temperature underoptimal in spring and early summer was controlled by immersing sealed pots into a (S6derstr6m, 1974). water bath thermostated by a Lauda RS-102 thermostat. Net C0 assimilation (A), transpira- In cold soils, the viscosity of water 2 tion (E) and leaf conductance to water vapor increases and the permeability of roots to measured LI-6200 by portable pho- (g) were an water decreases (Lopushinsky and Kauf- Inc.), which tosynthesis system (LI-COR, mann, 1977) which leads to decreased includes an LI-6250 infrared gas analyzer, an gas exchange and growth. LI-6200 control console and a leaf chamber. The relative height growth rate (RHGR) was The aim of this study was to examine 1 /H x calculated using the equation: RNGR = certain structural and physiological attri- dH/dt An index of photosynthetic efficiency butes of acclimation in Scots pine (Pinus (PE) or photosynthetic utilization of internal C0 2 sylvestris L.) seedlings at different soil was derived by dividing the rate of net photo- synthesis by the internal C0 concentration 2 temperatures. (Sasek et al., 1985). The following structural factors were examined: 1) timing and amount of shoot growth; 2) amount of needle and root Results growth. The following physiological factors were examined: 1) net C0 assimilation rate 2 The patterns of A at 2 constant soil tem- (A); 2) transpiration (E); and 3) conduc- peratures (12.0 and 8.7°C) were quite tance to water vapor (g). similar but at 12°C the photosynthetic rate
quite simi- soil temperature higher (Fig. 1However, after 11 d, changing were was throughout the experiment but the for- differences lar were no longer significant. mer was usually 20-30% higher (Fig. 3). A in seedlings at a changing soil tem- Conductance at a constant 12°C in- perature acted unusually: photosynthesis creased slighthy during the first 11 d and declined as soil temperature increased. then declined. The shape of the curve is After 18 d, photosynthesis recovered up to similar to that for transpiration. the level of other treatments. Photosynthe- tic efficiency decreased to 50-60% of the initial values in all treatments. The largest decrease occurred in seedlings at a Conclusions changing soil temperature (Table I). The transpiration rate increased in seedlings at constant 12°C during the first Initiation and development of current yr 11 d and then declined sharply (Fig. 2). At needles affected the results of gas constant 8.7°C, the transpiration rate exchange measurements. The decline in remained at the same level for 11 d and A after 11 d in all treatments may be due then declined. The transpiration rate in to new needles (see Teskey et aL, 1984), seedlings at changing soil temperature which were included in the measure- increased slightly and then decreased ments. The photosynthetic capacity of the after 11 d. All seedlings recovered 18 d developing current yr needles is fairly low after the onset of the experiment. (Troeng and Linder, 1982). Enclosing them in a cuvette causes errors in A, E The patterns of g evolution at the and g. constant temperature of 8.7°C and at a
Soil temperature affected gas exchange tial soil temperature resulted in a shock in pine seedlings. In general A and E were from which the seedlings did not recover higher in warm than in cold soil. At a until in the end of the experiment. Conifer changing soil temperature, the situation is seedlings coming out of cold storage more complicated. The net assimilation require a period of almost 3 wk to accli- rate declined, although the temperature mate physiologically to low soil tempera- was increasing, and the relative growth tures (Grossnickle and Blake, 1985). Low rate and the amount of root tips were high soil temperature restricts new root growth (Table II). A possible reason is that low ini- which in turn slows recovery from water
W. & Kaufmann M.R. (1977) stress in plants, despite the adequate sup- Lopushinsky Effects of cold soil on water relations and spring of soil water (Nambiar et al., 1979). ply growth of Douglas fir seedlings. For. Sci. 30, 628-634 Nambiar E.K.S., Bowen G.D. & Sands R. References (1979) Root regeneration and plant water status of Pinus radiata D. Don seedlings transplanted Grossnickle S.C. & Blake T.J. (1985) Acclima- to different soil temperatures. J. Exp. Bot. 30, tion of cold-stored jack pine and white spruce 1119-1131 seedlings: effect of low soil temperature on Sasek T.W., Del-ucia E.E. & Strain B.R. (1985) water relation patterns. Can. J. For. Res. 15, Reversibility of photosynthetic inhibition in cot- 544-550
Teskey R!O., Grier C.C. & Hinckley T,M. (i984) ton after long-term exposure to elevated C!2 concentrations. FVantP!ys