Growth and posture control strategies in Fagus sylvatica and Acer pseudoplatanus saplings in response to canopy disturbance

Background and Aims

Forest tree saplings that grow in the understorey undergo frequent changes in their light environment to which they must adapt to ensure their survival and growth. Crown architecture, which plays a critical role in light capture and mechanical stability, is a major component of sapling adaptation to canopy disturbance. Shade-adapted saplings typically have plagiotropic stems and branches. After canopy opening, they need to develop more erect shoots in order to exploit the new light conditions. The objective of this study was to test whether changes in sapling stem inclination occur after canopy opening, and to analyse the morphological changes associated with stem reorientation.

Methods

A 4-year canopy-opening field experiment with naturally regenerated Fagus sylvatica and Acer pseudoplatanus saplings was conducted. The appearance of new stem axes, stem basal diameter and inclination along the stem were recorded every year after canopy opening.

Key Results

Both species showed considerable stem reorientation resulting primarily from uprighting (more erect) shoot movements in Fagus, and from uprighting movements, shoot elongation and formation of relay shoots in Acer. In both species, the magnitude of shoot uprighting movements was primarily related to initial stem inclination. Both the basal part and the apical part of the stem contributed to uprighting movements. Stem movements did not appear to be limited by stem size or by stem growth.

Conclusions

Stem uprighting movements in shade-adapted Fagus and Acer saplings following canopy disturbance were considerable and rapid, suggesting that stem reorientation processes play a significant role in the growth strategy of the species.     

Competition for nitrogen sources between European beech (Fagus sylvatica) and sycamore maple (Acer pseudoplatanus) seedlings

To investigate the short‐term consequences of direct competition between beech and sycamore maple on root N uptake and N composition, mycorrhizal seedlings of both tree species were incubated for 4 days (i.e. beech only, sycamore maple only or both together) in an artificial nutrient solution with low N availability. On the fourth day, N uptake experiments were conducted to study the effects of competition on inorganic and organic N uptake. For this purpose, multiple N sources were applied with a single label. Furthermore, fine roots were sampled and analysed for total amino acids, soluble protein, total nitrogen, nitrate and ammonium content. Our results clearly show that both tree species were able to use inorganic and organic N sources. Uptake of inorganic and organic N by beech roots was negatively affected in the presence of the competing tree species. In contrast, the presence of beech stimulated inorganic N uptake by sycamore maple roots. Both the negative effect of sycamore maple on N uptake of beech and the positive effect of beech on N uptake of sycamore maple led to an increase in root soluble protein in beech, despite an overall decrease in total N concentration. Thus, beech compensated for the negative effects of the tree competitor on N uptake by incorporating less N into structural N components, but otherwise exhibited the same strategy as the competitor, namely, enhancing soluble protein levels in roots when grown under competition. It is speculated that enhanced enzyme activities of so far unknown nature are required in beech as a defence response to inter‐specific competition.     

Importance of mineral nutrition for photosynthesis and growth of Quercus petraea, Fagus sylvatica and Acer pseudoplatanus planted under Norway spruce canopy

The aim of this study was to combine data on photosynthetic performance, growth and mineral nutrition of Quercus petraea, Fagus sylvatica and Acer pseudoplatanus growing six years under a Norway spruce canopy. Three years old saplings were planted on several adjoining plots from the forest edge up to 35 m inside the spruce forest on nutrient poor dystric cambisols. Growth parameters, photosynthetic capacity and leaf nutrition were repeatedly measured on 11 to 13 selected plants for each species every year from 1996 to 2001. The general performance of the plants growing along the light gradient from forest edge into the closed canopy decreased in the order F. sylvatica, Q. petraea and A. pseudoplatanus. The photosynthetic performance of Acer declined from the second year onwards as consequence of low nutrient supply. The plants had in most cases higher leaf nitrogen concentration in shade. This increase going along with declining light input was the best in Quercus and was found in Acer leaves only in the second year after the planting. The growth parameters of all investigated plants were not correlated to the light environment within the range of canopy gap fraction between 0.05 and 0.62. However, the total leaf area as well as nutrient amounts in the foliage were good predictors for total plant height and plant diameter at root collar of Fagus and Quercus, but failed in most cases for Acer. These results emphasise the important role of nutrient acquisition for young broadleaves introduced in Norway spruce stands and underline the different requirements for nutrient supply at the species level.     

Cellulase and cell differentiation in Acer pseudoplatanus

Summary Homogenates of differentiating xylem and phloem tissue have higher cellulase activities than cambial samples; the highest activity is always found in phloem. Callus tissue, in which no vascular differentiation occurs, contains only low cellulase activity. The results suggest that cellulase is involved in vascular differentiation. Different pH optima of cellulase activity were found: in cambium, xylem and phloem tissue, cellulase activity with an optimum at about pH 5.9 is predominantly membrane-bound; it is sedimentable at 100,000 g and releasable by Triton X-100. The same may be true of activity with an optimum at pH 5.3. Phloem tissue also contains a soluble, cytoplasmic cellulase of high activity at pH 7.1, and xylem tissue contains cytoplasmic cellulase with an optimum at pH 6.5. Low cellulase activity with a pH optimum similar to that of xylem homogenates was found in xylem sap. Cellulase activity in abscission zones increases greatly just before leaf abscission. Abscission zone cellulase has two pH optima, et 5.3 and 5.9; both activities are increased by Triton treatment of homogenates. The possible existence of several different cellulases forming part of a cellulase complex, and the rôle of the enzymes in hydrolysing wall material during cell differentiation are discussed.     

Factors controlling micropropagation of mature Fagus sylvatica

The influence of several endogenous factors on micropropagation of mature elite trees of beech (Fagus sylvatica L.) has been investigated. February was the most beneficial month for explantation of dormant buds, since infection with endogenous bacteria was still low and in vitro growth of the plant material was the highest. The genotypes tested gave different results concerning their growth on various tissue culture media. Out of 51 mature grafted genotypes only seven could be established in vitro. Grafting of branches of mature stock plants on juvenile rootstocks resulted in a high increase of multiplication rate compared with corresponding mature material, which could not be subcultured in vitro. Apical buds, larger than 20 mm, from 1-year-old shoots proved to be the most suitable explant source. Plant material could be subcultured for several years and rooted successfully.Abbreviations BA benzyladenine - BTM Broad-leaved Tree Medium - GD Gresshoff Doy Medium - IBA indole-3-butyric acid - MS Murashige Skoog Medium - PVP polyvinylpyrrolidone - SH Schenk Hildebrandt Medium - WPM Woody Plant Medium     

Regulation of Pi,uptake by Acer pseudoplatanus cells

In view of the importance of P_i in the control of cell metabolism, it was of interest to study the mechanism and regulation of P_i uptake by Acer pseudoplatanus cells grown as cell suspensions. At low external P_i concentrations up to 10 mm, sycamore cells incorporate phosphate against a concentration gradient, by a process which is energy dependent. Under these conditions the intracellular P_i concentration is maintained constant (2–3 mm). On the contrary at high external P_i concentrations, higher than that which counterpoises the cytoplasmic P_i concentration (approximately 10 mm), P_i enters the cell by slow diffusion and the intracellular P_i concentration increases continuously as the extracellular P_i concentration increases from 15 to 50 mm. When sycamore cells are transferred to a phosphate-deficient medium, growth slows down considerably and ceases after 4–5 days. During this time, intracellular P_i concentration falls from 3 to 0.1 mm and phosphate esters from 8 to 2 mm. Phosphate starvation stimulates the uptake indicating that phosphate uptake depends on the intracellular phosphate and/or cytoplasmic ester-P pool. P_i uptake by P_i-starved cells is strongly dependent on the pH of the medium.     

Localization of chitinolytic activities in Fagus sylvatica mycorrhizas

 Localization of chitinolytic activities in Fagus sylvatica (beech) mycorrhizas was examined using a range of fluorogenic 4-methylumbelliferyl [4-MU-(GlcNAc)_1–4] substrates in order to distinguish between exochitinase, endochitinase and β-N–acetylglucosaminidase activities. The validity of the technique was confirmed using onion epidermis cells. In the beech mycorrhiza, endochitinase activity was not detectable above background fluorescence. Exochitinase activity was detected in the fungal sheath and the Hartig net. β-N–Acetylglucosaminidase activity was also mainly associated with the fungal sheath and Hartig net. Individual fungal hyphae extending from these structures also showed substantial β-N–acetylglucosaminidase activity. The cortical cell walls of the host in the Hartig net region also fluoresced brightly. The localization of β-N–acetylglucosaminidase activity was confirmed using a chromogenic histochemical reagent, 5-bromo-4-chloro-3-indolyl-N–acetyl-β-d-glucosaminide (X-GlcNAc). Accepted: 5 December 1995     

Hydroxyproline-Rich Protein Material in Wood and Lignin of Fagus sylvatica

The nitrogen content, distribution, and amino acid composition of protein material were determined in wood and lignin of Fagus sylvatica. The data indicated that the nitrogen originated from hydroxyproline-rich cell wall glycoprotein, about half of which may be bound to the lignin polymer. The implications for lignocellulose biodegradation are discussed.     

Oxygen availability and ABA metabolism in Fagus sylvatica seeds

At harvest, beechnuts have a very deep dormancy whichlies both in the structures surrounding the embryo andwithin the embryo itself. Covering structures preventembryo germination by interfering with water uptakeand gaseous exchange. To understand the role of thecovering structures and oxygen availability on ABAcatabolism, (+)-[³H] ABA metabolism was studied in isolated embryos as well as in intact seeds. ABAdegradation resulted essentially in oxidative products(PA, DPA). These products were more abundant inisolated embryos than in intact seeds. Theyaccumulated mainly as alkali-nonhydrolyzableconjugates of DPA. A small amount of free andesterified forms were oftenobserved. In isolated embryos a decrease in oxidativeproducts was observed either by lowering the oxygenavailability or by feeding embryos with tetcyclasis(an inhibitor of monooxygenase). In the presence of the covering structures, these oxidative products werereduced in the same manner, indicating that coveringstructures were probably responsible for limiting theoxygen supply to the embryo and for the lowgermination percentage observed in the case of intactseeds.     

Subunit Structure of Legumin-like Globulins of Fagus sylvatica Seeds

The 11S (legumin-like) globulins, which are the major seed proteinsof Fagus sylvatica L., have been isolated and characterized.The subunit structure of the 280 kD oligomers was investigatedusing different two-dimensional electrophoretic methods. Sucha structure is within the accepted model for this type of protein.However, an acidic polypeptide with 20 kD was found not to becovalently linked to any other component of the oligomers.     

Development of protein bodies in cotyledons of Fagus sylvatica

Electron microscopic analysis of cotyledons of beech ( Fagus sylvatica ) at different stages of seed maturation indicates that protein bodies originate by gradual subdivision of the vacuoles in which reserve proteins are deposited. The majority of protein bodies show a proteinaceous matrix and a number of globoid inclusions of different sizes. In a small number of cells, druse-like inclusions were observed. Analysis by SDS-PAGE of proteins extracted from isolated protein bodies shows that the majority correspond to beech seed storage globulins.     

Effect of vanadate on the vacuolar ATPase of Acer pseudoplatanus

The ATPase of vacuoles isolated from Acer pseudoplatanus cells is strongly inhibited by vanadate, a specific inhibitor of plasma membrane ATPase. The degree of inhibition depends upon the ionic composition, ATP and magnesium concentrations of the reaction medium and the inhibition is reversed by EDTA which complexes vanadate. In absence of factor which may interfere with the effectiveness of inhibitor, vanadate inhibits the ATPase non-competitively.     

Mechanism of freeze-induced embolism in Fagus sylvatica L.

 The mechanism of freeze stress-induced embolism in Fagus sylvatica L. branches was analyzed under controlled conditions. Excised branches were exposed to successive freeze-thaw cycles in temperature controlled chambers. Thermocouples were placed on the bark to detect sap freezing exotherms. The degree of xylem embolism was estimated after each cycle by the loss of hydraulic conductivity. After one freeze-thaw cycle the degree of embolism was found to decrease with xylem specific hydraulic conductivity, small apical shoots being more susceptible to embolism. Exotherms revealed that distal shoots were freezing first and exuded sap as a result of water expansion. The lower water content in apical shoots upon freezing probably induced higher sap tensions which promoted air bubble expansion and vessel cavitation preferentially near the apices. When the decrease in water content was experimentally prevented, embolism developed to a lesser extent. The higher vulnerability of shoot apices may protect the rest of the branch from winter damage. Received: 29 May 1998 / Accepted: 15 August 1998     

Respiratory Response of Acer pseudoplatanus Cells to Pyruvate and 2,4-Dinitrophenol

The endogenous respiration rate of unstarved cultured cells of Acer pseudo-platanus L. is markedly stimulated by 2,4-dinitrophenol. Pyruvate is also stimulatory but to a lesser degree than dinitrophenol. Exogenously supplied sugars cause no short-term stimulation. Pyruvate does not enhance the elevated rate of O₂ uptake in the presence of dinitrophenol but does cause additional CO₂ evolution. The endogenous concentration of pyruvate is elevated in the presence of dinitrophenol. These observations suggest that the rate of O₂ uptake by the unstarved intact cells is limited by the rate of glycolysis and that rate of glycolysis is regulated by the intracellular concentration of adenine nucleotides or inorganic phosphate. Dinitrophenol stimulation of endogenous respiration is due in part to an indirect acceleration of glycolysis but also to a more direct facilitation of oxidation in the presence of excess mitochondrial substrate.     

Microscopic Features of Wind Damage to Leaves of Acer pseudoplatanus L

Damage done when wind causes leaves of Acer pseudoplatanus L.to rub against each other is characterized by dark and lightbrown lesions and by holes and deformations of the leaf. Lightand scanning electron microscope observations show that thisdamage is associated with collapse of adaxial and abaxial epidermalcells, collapse of the mesophyll and disruption of the abaxialepicuticular waxes. Some damage may occur even when no discolorationis evident. Topographical features suggest that the adaxialsurface of the leaf is more likely to be abraded than the abaxialsurface yet in practice it generally sustains less severe damage;the results of artificial abrasion indicate that the adaxialsurface is structurally more resistant. Some of the implicationsof such damage for the plant are discussed. Acer pseudoplatanus L., sycamore, wind damage     

Inhibition of the vacuolar ATPase of Acer pseudoplatanus cells by vanadate

Unlike most tonoplast ATPases, the vacuolar ATPase of Acer pseudoplatanus cells (Km = 0.4 mM) was strongly inhibited by vanadate (I50 = 10 microM). The inhibition was non-competitive. Chemicals usually added in the reaction mixture either increase (NH+4, K+) or decrease (Na+, EDTA) the ATPase inhibition. However, these results do not explain the insensitivity to vanadate of most tonoplast ATPases. We suggest that the tonoplast contains 2 classes of ATPases, one sensitive to vanadate, the other insensitive; each class should be more or less abundant (or active) according to the plant species studied or its physiological state of growth. It appears from this study that sensitivity or insensitivity of an ATPase to vanadate is not really a good criterion to distinguish between plasmalemma and tonoplast.     

Fluoride Inhibition of Respiration and Fermentation in Cultured Cells of Acer pseudoplatanus

Low concentrations of sodium fluoride severely inhibit anaerobic CO₂ evolution in Acer pseadoplatanus L. cells but have relatively little effect on aerobic respiration. The insensitivity of respiratory O₂ uptake to fluoride is due in part to the fact that fluoride reduces the intracellular pyruvate concentration to only a relatively minor extent under aerobic conditions, although it prevents the several fold increase in endogenous private which is normally brought about by anoxia. The respiratory insensitivity is also ascribable to the existence of a respiratory component which is unaffected by the decrease in endogenous private resulting from fluoride treatment. The extremely severe respiratory inhibition brought about by fluoride plus dinitrophenol is not appreciably relieved by exogenous private, indicating that this inhibition is the result of interference with the aerobic oxidation process per se and is not solely a consequence of glycolytic inhibition.