Báo cáo lâm nghiệp: "How the absolute growth rate of poplar adapts to the light-NO -dosage 3 G.A. Pieter"

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How the absolute growth rate of poplar adapts to the light-NO -dosage 3 - G.A. Pieters Department of Plant Physiological Research. Agricultural University Gen. Foulkesweg !2. 6703 8W Wageningen, The Netherlands Introduction bundles in the vascular cylinder increase in a systematic way; at the same time, phyllotactic order increases. According to Larson’s analyses, new procambial traces The growth of leaves and internodes on a develop long before the primordia they will branch of poplar, grown under constant serve are visible at the apex. conditions, proceeds according to growth patterns, which: 1) can be defined as Combining Larson’s data with ours, we organ-specific relations between the rela- established a striking correspondence be- tive growth rate (RGR) and the age of the tween the development of the vascular organ; and 2) are independent of irradi- system of poplar, the growth of the organs ance. Consequently, the absolute growth and the development of absolute growth rate of such a branch cannot adapt to irra- rate of the plant. Adaptation proceeds via diance via these growth patterns. A poplar enlargement of the primary vascular sys- plant adapts its absolute growth rate to (Pieters and van den Noort, 1988). A tem high irradiance by a gradually faster pro- larger vascular system is reflected in a lar- duction of proportionally larger primordia ger apical volume and produces propor- at its apex. At the same time, the apical tionally more and larger leaf primordia, volume and the phyllotactic order are which grow out to a proportionally larger increasing. It could be shown that the api- final size. Whenever an equilibrium is cal volume is proportional to the rate of reached between assimilate production leaf area production (Pieters and van den and use in the plant, the primary vascular Noort, 1988). Under optimal conditions, system stops expansion and the branch the stem elongation rate increases propor- grows linearly with time. Because the tionally to the leaf production rate and, on vascular system develops before the the average, this results in internodes with primordia, we suggest that the growth of a constant mature length. plant is a reflection of the development ct the vascular system. Larson (1975) analyzed the develop- ment of the vascular system of poplar. The Preliminary experiments with sunflower number and the length of the vascular and poplar (Pieters and van den Noort,
to the scheme presented 35:45:20), according 1985) suggested that the absolute growth in Table. I rate of a branch adapts in a way similar to Six and four plants were used, respectively, that of nitrate dosage. As the availability of for the 2 highest and the lowest nitrate dosage. (reduced) nitrate in the plant becomes Three times per week, length and thickness, limiting, the expansion of the vascular sys- respectively diameters of leaves and internodes tem stops and the branch grows linearly were measured. The other measurements were made on harvested plants. The plants were with time. harvested 3 times, and those grown at The aim of this article is to report the 0.0 mmol N0 twice. 3 effects of photon fluence rate (PFR) and Chlorophyll was determined according to nitrate dosage on growth and some chem- Bruinsma (1963), the chemical analyses using ical properties of a poplar branch during the methods described by the Department of Soil Science and Plant Nutrition, AU, Wagenin- the adaptation to a nitrate dosage that is: gen. 1) linear with time, and 2) in proportion to irradiance (cf. Ingestad, 1987). Results Materials and Methods Relative growth rate (RGR) at half mature length of an organ (RGR was nearly ) SO Fresh cuttings of Populus euramericana (Dode) Guinier cv Robusta, on which one branch was independent of the absolute N0 dosage 3 allowed to grow, were cultivated in growth or PFR (Table II, N°3’-codes 1 and 2). At a rooms at 22 60% RH and a day length C, * nitrate dosageof 0.0 mmol ’d- 1 planr ’ of 16 h on a nitrate-free culture solution. 3) (N0 the nitrate reserve in the cut- code 3 Nitrate was added daily as a solution of KN0 Ca(N0 and Mg(N0 (molar ratio: ,) 33 2 2 ) 3 ting was rapidly used up and redistribution T_L..I- II M-.I_.:..- --_...a.L....-...-- &dquo;&dquo;_1.1.mo1&dquo;ro 1.!Mh lO/20__1 nf 1.o.&dquo;3B1.o! &dquo;:lInn -...
of nitrate could not sustain a high RGR between PFR and nitrate-dosage (PIN- 50 in growing leaves. quotient). Also the root-shoot ratio de- Dry matter- (Fig. 1) and N- (Fig. 2) distri- pended on the PIN-quotient and not on bution depended mainly upon the ratio the absolute PFR or nitrate dosage (see .....-, --, - - - - ....
plants continued to grow, while at low irra- Fig. 1At high irradiance, the nitrate diance and limiting N-dosage the N-distri- concentration (Fig. 2) showed a prolonged bution was frozen by induced dormancy adaptation in respect to that of the plants, grown at low irradiance, because the (no growing leaves at the last harvest). At
nitrate dosage of As expected, chlorophyll content de- the mmol! 0.0 at 7.5 W- 2 - M , 1 plant-1’day- plants grown clined with rising deficiency. At high irradi- ance, thicker leaves were formed: the dormant at the first harvest and were those grown at 30 W-m- were dormant , 2 measured leaf thickness was 220 pm in at the second harvest. The nitrate defi- sun leaves and 120 pm in shade leaves. The higher chlorophyll contents in leaves ciency was evenly distributed over mature of the 30 W!m-2 plants in respect to and growing leaves. 7.5 W- plants (Fig. 4) was likely 2 - M Nitrate-reductase activity (NR-act, Fig. caused by this difference in thickness. 3) and leaf chlorophyll content (Fig. 4) depended also mainly upon the P/N-quo- tient. As expected, NR-act declined with the (relative) availability of nitrate and with Discussion (mean) age of the (increasing) group of older mature leaves. The NR-act of grow- ing leaves was generally lower than that of The growth patterns of leaves and inter- young mature leaves; this difference be- nodes are not influenced by the absolute came smaller with rising deficiency. NR- nitrate dosage and irradiance, as judged act in the roots was found to be insignifi- by the development of individual leaves and internodes in the linear phase of cant.
relative growth and by ine constancy of + 2 Mg and reacts with immediate deficien- rate at half mature length (RGR ). 50 growth cy symptoms (Dorenstouter ef aL, 1985). presented in this paper, there- The data Linear dosage of nitrate in proportion to fore, suggest that a plant adapts its abso- PFR revealed that for optimal growth with lute growth rate to a linear nitrate dosage, minimal deficiency symptoms, an optimal as to PFR, through adaptation of the size ratio exists between PFR and the dosage of the apex, casu quo of the vascular sys- of N0 and, presumably p Although o3-. 3 tem. The increase in size of the apex of we have not yet analyzed this ratio quanti- plants, growing in optimal root environ- tatively, we propose that the constancy of ment, proceeds linearly with time with a this ratio points to a morphogenetic signifi- rate proportional to irradiance (data not cance of protein synthesis for the enlarge- shown). As explained in the Introduction, a ment of the vascular system. larger apex produces proportionally faster and larger primordia, which grow to matu- rity according to a pattern independent of PFR and nitrate dosage. Acknowledgments Presumably, plant growth reacts similar- on a deficiency of p (members of o3- ly the Department of Plant Nutrition, AU, per- The members of the Department of Soil Sci- sonal communication). The plant is not ence and Plant Nutrition, AU, Wageningen, are able to adapt to a deficiency of, e.g., K or + duly acknowledged for their help and advice.
forest trees and stands. Geoderma 40, 237- References 252 Larson P.R. (1975) Development and organiza- Bruinsma J. (1963) The quantitative analysis of tion of the primary vascular system in Populus chlorophylls a and b in plant extracts. Photo- dettoides according to phyllotaxy. Am. J. Bot chem. Phytobiol. 2, 241-249 62, 1084-1099 Dorenstouter H., Pieters G.A. & Findenegg Pieters G.A. & van den Noort M.E. (1985) Leaf G.R. (1985) Distribution of magnesium between coefficient of some Populus euramericana area chlorophyll and other photosynthetic functions strains. Photosynthetica 19, 189-193 in magnesium deficient ’sun-’ and ’shade-’ Pieters G.A. & van den Noort M.E. (1988) Effect leaves of poplar. J. Plant Nutr. 8, 1089-1101 of irradiance and plant age on the dimensions Ingestad T. (1987) New concepts on soil fertility of the growing shoot of poplar. Physiol. Plant. and plant nutrition as illustrated by research on 74,467-472