Báo cáo lâm nghiệp: "Allocation of dry matter in Eucalyptus in response to nitrogen supply grandis seedling"

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Allocation of dry matter in Eucalyptus grandis seedlings in response to nitrogen supply P.G. Jarvis 2 R.N. Cromer 1 CSIRO Division of Forestry and Forest Products, Box 4008, Queen Victoria Terrace, A.C.2600, P ro and Australia, and Department 2 of Forestry and Natural Resources, University of Edinburgh, The Kings Buildings, Mayfield Road, Edinburgh EH9 3JU, U.K Material and Methods Introduction Seedlings of Eucalyptus grandis were grown in It is well established that a high level of a naturally lit glass house with day/night tem- nutrient supply increases shoot growth peratures of 27i21°C, for 8 and 16 h, respec- relative to root growth in trees and a shift tively. Seedlings were grown in 5 aeroponic in carbon allocg±ian to roots was observed ’growth units’ designed to permit seedlings to grow at constant relative growth rates (Rg) and in seedlings of Eucalyptus delegatensis stable internal nutrient concentrations (Ingestad with increasing nutrient stress (Cromer et and Lund, 1986). Nutrient solutions, made up a/., 1984). This shift can have a major so that nitrogen was the element most limiting effect on stemwood production but similar growth, were added to circulating solutions at relative addition rates between 0.04 and 0.12 2 studies have not been reported for E d- This technique enabled stable seedling . 1 grandis. nitrogen concentrations [N] and R to be main- 9 Despite reports of (often dramatic) tained during experimental periods of 40-60 d in 4 growth units. Seedlings from each growth increases ingrowth of E. grandis following unit were harvested on 4 occasions at intervals application of nutrients, we have little of 7-14 d depending upon growth rate. of mecha- understanding physiological responsible for such responses. It is nisms recognised that leaf area is a major deter- minant of plant productivity but the impor- Results tance of leaf development in comparison with dry matter partitioning and rate of assimilation is not well understood 2 C0 Rg and [N] were relatively stable over time (see Cannel, 1985). In this paper, for each treatment (data not shown). Allo- we ex- amine the way in which rate of nitrogen cation of dry matter to stems and roots supply to E. grandis seedlings affects allo- was examined in relation to leaf mass and cation of dry matter. data from each harvest and treatment
This resulted in a strong linear correla- combination were pooled and tested using tion (r2= 0.988) between Ln f and Ln an allometric relationship (Ledig, 1983): IN! but with a major influence of [N] on Ln W!=a+/3!Ln W (1) allocation as shown in Fig. 2. The regres- sion slope was not significantly different where W is stem mass, W is leaf mass, S from unity and the ratio of W! to W was a is a constant and 0 is the slope. A 1.0 when [N] approximated 16 6 mg.g-I . At strong linear correlation (r 0.992) was 2 = values of [N] above this, root to leaf ratio found between Ln W and Ln W as shown S was less than 1.0. in Fig. 1. Leaf growth was initially a stronger sink for carbon than stem growth and allocation of dry matter was less to stems than leaves. However, the slope of Discussion the regression exceeded unity and this dif- ference between stem and leaf mass dim- inished with ontogeny. Many investigators have sought to de- scribe effects of environmental variables A satisfactory relationship between root or silvicultural treatments on growth and (W and W was not obtained using ) r mass allocation of dry matter by analysis of eqn 1 and an additional term was inserted shoot/root ratio (mass of top/mass of root) to account for the effect of nutrient treat- but use of this ratio has frequently led to ments: incorrect interpretations because of failure Ln r W + y[N] Ln ’ {3 W, (2) a to recognise that it changed with ontogeny + =
ontogeny. [N] had a strong influence on (Ledig et al., 1970). Comparison of shoot/root ratio of plants of different sizes the ratio of 1!1/! to W which was stable across a wide range of plant sizes. is therefore open to serious criticism. Slopes of allometric relationships be- Comparison of regression coefficients of lNs and W would be expected to the allometric formula has been suggested tween exceed one in forest trees and absolute as the most useful test of allocation be- tween root and shoot, where different values of these slopes may provide an treatment effects will appear as different indicator of comparative efficiency for wood production. In the present experi- regression slopes, 0 in eqn 1 (Ledig et al., ment, this slope was 1.26 for E. grandis, 1970). However, examination of allometric but of greater interest is the fact that relationships between foliage and root mass in E. grandis demonstrated that nutrient treatment had no effect on slope nitrogen nutrition influenced partitioning or intercept of this allometric relationship. such that an additional term was required Some reports dealing with relationships to form eqn 2. This term incorporating [N] between shoot and root indicate that allo- had the effect of altering regression inter- cation to stern is influenced by nutrition cept, but had no influence on slope {3 (Fig. (e.g., Ingestad and Lund, 1979). However, 2.). Under conditions of stable relative our data suggest that above versus below nutrient addition rate and thus stable Rg, a ground allocation depends upon [N] but a slope between foliage and root conservative relationship exists between constant aboveground components (stem and foli- mass is to be expected or differences in mass of these organs would increase with age).
concepts presented and constructive criticism Conclusions of the manuscript. An allometric relationship derived between W and W in E. grandis was dependent S References upon organ mass, with greater allocation to stem occurring with ontogeny (slope = 1.26). This relationship was not influenced Cannell M.G.R. (1985) Dry matter partitioning in by seedling [N]. On the other hand, allo- tree crops. In: Attributes of Trees as Crop Plants. (Cannel M.G.R. & Jackson J.E., eds.), metric relations between W and W were r Inst. Terrestrial Ecol. Huntingdon, U.K. pp. 160- dependent upon seedling [N], which 193 influenced regression intercept but not Cromer R.N., Wheeler A.M. & Barr N.J. (1984) slope, which was equal to unity. Environ- Mineral nutrition and growth of eucalyptus mental influences on allocation of dry mat- seedlings. New Zealand J. For. Sci 14, 229-239 ter, among leaf, stem and root compo- T. & Lund A.B. (1979) Nitrogen stress Ingestad nents in complex woody perennials, are seedlings. I. Growth technique and in birch profound that and nutrient effects are so growth. Physioi. Plant. 45, 137-148 will seriously omission of this variable Ingestad T. & Lund A.B. (1986) Theory and techniques for steady state mineral nutrition compromise results. and growth of plants. Scand. J. For. Res. 1, 439-453 Ledig F.T. (1983) The influence of genotype and environment on dry matter distribution in plants. Acknowledgments In: Plant Research and Agroforestry. (Huxley P.A., ed.), Intl. Council for Res. in Agroforestry, Nairobi, pp. 427-454 The authors wish to thank David Bellingham, Ledig F.T., Bormann F.H. & Wenger K.F. (1970) Wanda Pienkowska and Leroy Stewart for The distribution of dry matter growth between excellent assistance with various aspects of this shoot and roots in loblolly pine. Bot. Gaz. 131, experiment. We are indebted to Paul Kriede- 349-359 mann and Ross McMurtrie for discussion of