Influence of near-ultraviolet light enhancement and photosynthetic photon flux density during photoperiod extension on the morphology and lignin content of black spruce seedlings

When containerized black spruce seedlings (Picea mariana (Mill.) B.S.P.) are grown rapidly in greenhouse culture, they sometimes bend over, grow horizontally and become deformed. This phenomenon has been known to affect between 5% and 10% of a winter greenhouse crop. In this study, near-ultraviolet lamps were used to supplement the artificial light received from high-pressure sodium lamps and the effects on seedling morphology and lignin contents were examined. Neither height to diameter ratios nor lignin concentrations were significantly affected by UV radiation flux density. However, seedling biomass, height, root collar diameter, lignin content, and lignin to cellulose ratios of stems were significantly correlated with total photosynthetic photon flux density (PPFD) received during photoperiod extension. Height to diameter ratios were negatively correlated with PPFD during photoperiod enhancement because of a greater relative increase in diameter growth compared with height growth. Neither UV nor PAR flux density affected the percentage of black spruce seedlings having stem deformations greater than 30 ° from the vertical.

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Résumé Lorsque des semis d'épinette noire (Picea mariana (Mill.) B.S.P.) en conteneur sont forcés d'avoir une croissance rapide en serre, leur tige est parfois courbée ou déformée. Ce phénomène peut affecter entre 5% et 10% d'une culture serricole hivernale. Dans la présente étude, un enrichissement du rayonnement près de l'ultraviolet a été appliqué sur des semis en complément à l'éclairage artificiel procuré par des lampes au sodium à haute pression. La morphologie et le contenu en lignine des semis ont alors été examinés. Le rapport entre la hauteur et le diamètre des semis, et la concentration en lignine n'ont pas été significativement affectés par la densité du flux photonique ultraviolet. Cependant, la biomasse, la hauteur, le diamètre au collet, le contenu en lignine et le ratio lignine: cellulose des tiges des semis ont été significativement corrélés à la densité du flux photonique photosynthétique (PPFD) reçue pendant l'extension de la photopriode. Le rapport entre la hauteur et le diamètre a été négativement corrélé à la PPFD pendant l'augmentation de la photopériode à cause de la plus grande croissance en diamètre des semis comparativement à leur croissance en hauteur. La densité du flux photonique au niveau de l'ultraviolet comme au niveau de la radiation photosynthétiquement active n'a pas affecté le pourcentage de semis d'épinette noire ayant des déformations de leur tige plus grande que 30 ° comparativement à la verticale.

     

The effect of photosynthetic photon flux density on development of frost hardiness in top and roots of Larix leptolepis seedlings

Seedlings of Larix leptolepis were grown in a growth chamber under short day conditions (8 h day) at 4 different photosynthetic photon flux densities (PPFD's). After a period of 8 weeks frost hardiness of the shoot tips and roots, dry matter content, dry weight (dw), content of glucose and starch were determined. The frost hardiness in the shoot tips increased from ‐15°C at a PPFD of 55μmol m^‐2s^‐1 to about ‐35°C at 440 μmol m^‐2s^‐1. No effect of PPFD was found on frost hardiness of the roots. A high PPFD results in a high dry matter content. The effect on dry matter content was most pronounced for the shoot tips and less pronounced for the roots. The total dry weight increased for both root and top with increasing PPFD. The height of the plants increased when the PPFD increased up to 220 μmol m^‐2s^‐1.     

Interacting effects of irradiance and water stress on dry weight and biomass partitioning in Fagus sylvatica seedlings

Abstract

Actual climate models for central Europe predict prolonged summer droughts. Knowledge on how the interaction between light and water availability affects regeneration will hence be of major importance. In an experiment carried out under controlled conditions, newly emerged beech seedlings were grown in pots with sand during 54 days. Three treatments applying three different light levels (2, 9 and 43% relative light intensity) were combined with two soil water treatments (control and drought). At the end of the experiment, seedlings were separated into leaves, stem and root and the seedlings’ dry mass, leaf area and stem length was determined. Low irradiance (2%) had a strong negative effect on dry weights of seedling components, leaf area and specific leaf mass. Drought clearly affected biomass partitioning for seedlings at high irradiance levels (43%). An interaction between irradiance and drought on biomass partitioning in beech seedlings was observed at medium irradiance level (9%). Within a wide range of light levels in the forests, both light and drought may affect biomass partitioning in young seedlings.     

欧洲山毛榉干燥工艺初探

通过试验研究探索出在国产蒸汽加热干燥窑上干燥欧洲山毛榉的干燥工艺,该工艺具有处理后干燥周期短、开裂和变形小的特点,达到了国家干燥锯材一级标准.     

Influence of direction and distance from trees on wheat yield and photosynthetic photon flux density (Qp) in a Paulownia and wheat intercropping system

A Paulownia-winter wheat intercropping experiment with the object of quantifying photosynthetically active radiation (PAR) and its effect on wheat yield was conducted 60 km south of Zhengzhou (35°N 113°E), Henan Province, PR China, from September 1991 to July 1992 using a tree and crop interface approach. The middle row of three 240 m long rows of 11-year-old trees was studied for its effects on the yield of irrigated and fertilized winter wheat. Photosynthetic photon flux density (Q_p) was quantified using a split-plot design with four blocks. There were four distance (subplot) treatments (2.5 m, 5 m, 10 m and 20 m) and two direction (main plot) treatments laid out to the east and west of a north-south tree line. Results showed no difference in direction effects but Q_p did affect total grain weight (P = 0.0047) between 2.5 m and 20 m. A regression equation was fit using the mean for each distance treatment: Y = 391.7 + 4.57X with r² = 0.9310 indicating a yield increase of 4.57 g m⁻² (45.7 kg ha⁻¹) over a distance of 2.5 m to 20 m from the trees.     

Effects of CO2 enrichment at varying photon flux density on the growth of picea abies (L) karst. seedlings

Seedlings of Norway spruce (Picea abies (L.)) were grown at 335 and 1000 μl CO₂ 1^?1 for 118 days in growth rooms at different irradiance levels. Photon flux density ranging from 8.6 to 34.6 mol m^?2 day^?t (PAR) was given either as constant light or as alternating levels in intervals of two or six hours. CO₂ enrichment increased the plant dry weight from 36% to 105% by increasing photon flux density from 8.6 to 25.9 mol m^?2 day^?1. At constant light the dry weight apparently reached its maximum at a photon flux density of 25.9 mol m^?2 day^?t. At the lower radiation levels alternating in CO₂ enriched air gave slightly higher dry weights compared to constant light levels. At the highest radiations the effect on dry weight was the opposite. High CO₂ concentration and 300 μmol m^?2 s^?1 constant light (25.9 mol m^?2 day^?1) gave the best growth and quality of plants. Top, root, stem and foliage weight were proportionally affected. Shoot length was enhanced by CO₂ enrichment. Shoot weight per cm was substantially increased both by CO₂ enrichment and increasing photon flux density.     

Growth and survival of Fagus sylvatica seedlings in relation to light intensity and soil water content

Previous investigations have shown different growth and root/shoot ratio increases of beech seedlings (Fagus sylvatica) with increased light intensity. In the present investigation both light intensity and soil water content were regulated on four levels in a factorial experiment. At the highest level of soil water content the seedling growth increased linearly with light intensity while the root/shoot ratio decreased with light intensity. At low levels of soil water content both the growth and root/shoot ratio slightly increased with increased light. The soil water content was also affected by the light intensity indicating that the soil water content may have caused unobserved effects in responding to increased light in previous investigations. It is concluded that both light intensity and soil water content should be quantified or manipulated even if only the effect of one of the two growth factors are investigated.     

Impacts of drought on mineral macro- and microelements in provenances of beech (Fagus sylvatica L.) seedlings

Beech seedlings originating from 11 German provenances with different climatic conditions were grown in pots and cultivated in a greenhouse. The composition of macro- and microelements in roots, axes and leaves was measured after half of the seedlings were subjected to a simulated summer drought. The recently described sensitivity of these provenances to drought was compared with drought-mediated changes in the elemental and ionic composition in organs of the seedlings; in addition, partitioning between roots and shoots was evaluated. A number of element concentrations were decreased in roots due to drought (K 94% of control, Mg 94%, Mn 75% and Zn 85%). However, chloride concentration increased in all organs (115-125%) and was the only element affected in leaves. Some changes in ionome can be related to sensitivity of provenances, but it is difficult to decide whether these changes are a result of, or a reason for, drought tolerance or sensitivity. Observed increases in chloride concentration in all plant parts of drought-treated beech seedlings can be explained by its function in charge balance, in particular since the level of phosphate was reduced. As a result of chloride accumulation, the sum of added charges of anions (and cations) in water extracts of leaf and root material was similar between drought and control plants. Since only the partitioning of Ca and Al (both only in axis) as well as Mn was affected and other elements (together with previously observed effects on C, N, S and P) remained unaffected by drought in all provenances, it can be concluded that direct effects by means of mass flow inhibition in xylem and phloem are unlikely. Secondary effects, for example on the pH of transport sap and the apoplastic space, cannot be excluded from the present study. These effects may affect partitioning between the apoplast and symplast and therefore may be significant for drought sensitivity.     

The applicability of a color acetate film for estimating photosynthetic photon flux density in a forest understory

The suitability of a color acetate film for estimating photosynthetic photon flux density (PPFD) in a forest understory was examined. The fading ratio of the film (F), the total PPFD (PPFD_total) to which the film was exposed, and the average daily maximum temperature during exposure (T) were obtained from measurements at multiple sampling points throughout an entire year within a natural secondary forest (n = 42). The ranges of the recorded values were as follows: F 35%–99%, PPFD_total 1.4–28.3molm^–2, and T 6°–32°C. PPFD_total was regressed by F and T with a high r ² (=0.94; P < 0.0001): PPFD_total = (100 – F)/(1.085 + 0.051T). The absolute error (|estimated PPFD_total – measured PPFD_total|) averaged 1.3molm^–2 with a maximum of 5.7molm^–2, indicating a good fit. These results indicated broad applicability of the film, both spatially and temporally, for estimating forest understory PPFD.     

Morphological and physiological responses of beech (Fagus sylvatica) seedlings to grass-induced below ground competition

We examined morphological and physiological responses of beech (Fagus sylvatica L.) seedlings to grass-induced below ground competition in full-light conditions. Two-year-old beech seedlings were grown during two growing seasons in 160-l containers in bare soil or with a mixture of five grass species widely represented in semi-natural meadows of central France. At the end of the second growing season, beech seedlings in the presence of grass showed significant reductions in diameter and height growth, annual shoot elongation, and stem, root and leaf biomass, but an increase in root to shoot biomass ratio. Grasses greatly reduced soil water availability, which was positively correlated with daily seedling diameter increment. Beech seedlings seemed to respond to water deficit by anticipating stomatal closure. There was evidence of competition for nitrogen (N) by grasses, but its effect on seedling development could not be separated from that of competition for water. By labeling the plants with 15N, we showed that beech seedlings absorbed little N when grasses were present, whereas grasses took up more than 97% of the total N absorbed in the container. We conclude that, even if beech seedlings display morphological and physiological adaptation to below ground competition, their development in full-light conditions may be strongly restricted by competition from grass species.     

Effect of photon flux density on carbon assimilation and chlorophyll a fluorescence of cold-stored white spruce and lodgepole pine seedlings

White spruce (Picea glauca (Moench.) Voss) and lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) seedlings previously held in dark, frozen storage (-2 degrees C) for 2.5 or 6 months, and nursery-grown white spruce seedlings lifted in summer were exposed to photon flux densities (PFDs) similar to those that might be encountered at planting. Photosynthetic gas exchange and chlorophyll a (chl a) fluorescence were examined in cold-stored and summer-lifted seedlings before and after a 9 h-exposure to artificial illumination of high PFD (2000 micro mol m(-2) s(-1)) or low PFD (ca. 500 micro mol m(-2) s(-1)), and during exposure to 400 micro mol m(-2) s(-1) for 4-9 days. In the 2.5-month-stored and summer-lifted seedlings, the high-PFD treatment caused a small decrease in carbon fixation and a large decrease in the ratio of variable to maximum fluorescence (F(v)/F(m)) relative to the effect of the low-PFD treatment. In contrast, in the 6-month-stored seedlings the high-PFD treatment caused a significant decrease in rate of light-saturated carbon fixation but little decrease in F(v)/F(m) relative to the effect of the low-PFD treatment, indicating that the mechanisms for maintaining integrity of the photochemical apparatus had changed during the storage interval.     

Bud dormancy in beech (Fagus sylvatica L.). Effect of chilling and photoperiod on dormancy release of beech seedlings

Two-year-old Fagus sylvatica L. seedlings were subjected to natural winter chilling or were overwintered in a heated greenhouse. Plants were then grown in controlled environment chambers with photoperiods of 9 or 13 h. Renewal of bud growth was found to be mainly determined by winter chilling. There was a slight interaction between chilling and photoperiod. Sprouting of apical buds took two to three times as long in unchilled plants as in chilled plants. Shoot elongation was influenced by chilling and was also greater in the 13-h photoperiod than in the 9-h photoperiod, but this may have been due at least in part to the higher irradiance. Chilling resulted in rapid dormancy loss and changed the growth pattern from basitonal to acrotonal.     

Hydraulic architecture correlates with bud organogenesis and primary shoot growth in beech (Fagus sylvatica)

In beech (Fagus sylvatica L.), the number of leaf primordia preformed in the buds determines the length and the type (long versus short) of annual growth units, and thus, branch growth and architecture. We analyzed the correlation between the number of leaf primordia and the hydraulic conductance of the vascular system connected to the buds. Terminal buds of short growth units and axillary buds of long growth units on lower branches of mature trees were examined. Buds with less than four and more than five leaf primordia formed short and long growth units, respectively. Irrespective of the type of growth unit the bud was formed on, the occurrence of a large number of leaf primordia was associated with high xylem hydraulic conductance. Xylem conductance was correlated to the area of the outermost annual ring. These results suggest that organogenesis and primary growth in buds correlates with secondary growth of the growth units and thus with their hydraulic architecture. Possible causal relationships between the variables are discussed.     

整株称重法和光合法测定杨树幼苗蒸腾速率的研究

以8个杨树品种(系)幼苗为试验材料,利用整株称重法和光合法测定蒸腾速率,结果表明:两种方法测定的幼苗蒸腾速率变化趋势相同,不同品种(系)从小到大的依次顺序为8328杨8325杨8801杨白林3号杨白城2号白城小黑杨8804杨白城5号杨,其中,8328杨和8325杨蒸腾速率与蒸腾量均较低,说明其抗旱能力优于其他品种(系)。两种测定方法具有显著线性相关关系,相关系数均达到0.7以上。     

Nutrient contents and concentrations in relation to growth of Picea abies and Fagus sylvatica along a European transect

Mineral nutrition of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) was investigated along a transect extending from northern Sweden to central Italy. Nitrogen (N) concentrations of needles and leaves in stands growing on acid soils did not differ significantly between central Italy and southern Sweden (1.0 +/- 0.1 mmol N g(-1) for needles and 1.9 +/- 0.14 mmol N g(-1) for leaves). In both species, foliar N concentrations were highest in Germany (1.2 mmol N g(-1) for needles and 2.0 mmol N g(-1) for leaves) and decreased by 50% toward northern Sweden (0.5 mmol N g(-1)). Both species showed constant S/N and P/N ratios along the transect. Calcium, K and Mg concentrations generally reflected local soil conditions; however, Mg concentrations reached deficiency values in Germany. Leaf area per unit dry weight varied significantly along the transect with lowest values for Norway spruce recorded in northern Sweden and Italy (3.4 m(2) kg(-1)) and a maximum in central Europe (4.7 m(2) kg(-1)). A similar pattern was observed for beech. Despite the low variation in foliar N concentrations on the large geographic scale, local and regional variations in N concentrations equalled or exceeded the variation along the entire continental transect. Furthermore, nutrient contents (i.e., nutrient concentration x dry weight per needle or leaf) showed a greater variation than nutrient concentrations along the transect. Nitrogen contents of Norway spruce needles reached minimum values in northern Sweden (2.4 micro mol N needle(-1)) and maximum values in Denmark (5.0 micro mol N needle(-1)). The N content of beech leaves was highest in Denmark (242 micro mol N leaf(-1)). At the German site, foliar N content rather than N concentration reflected the seasonal dynamics of foliar growth and N storage of the two species. During foliage expansion, there was an initial rapid increase in N content and a decrease in N concentration. This pattern lasted for about 2 weeks after bud break and was followed by 6 weeks during which dry weight and N content of the foliage increased, resulting in a further decrease in N concentration. During summer, dry weight and N content of mature needles of Norway spruce increased further to reach a maximum in autumn, whereas N concentration remained constant. In spring, reallocation of N from 1- and 2-year-old needles was 1.5 and 1.0 micro mol N needle(-1), respectively. This remobilized N was a major source of N for the development of new needles, which had an N content of 1.5 micro mol N needle(-1) after bud break. The seasonal remobilization of N from old foliage decreased with increasing needle age. Needle N content and dry weight decreased progressively with age (1 micro mol N needle(-1) between age classes 2 and 5), whereas N concentrations remained constant. For Norway spruce, annual stemwood production was correlated with needle N content but not with foliar N concentration or with the total amount of N in the canopy. Interspecific and geographical differences in plant nutrition are discussed on the basis of competitive demands for C and N between growth of foliage and wood.     

Mechanisms of xylem recovery from winter embolism in Fagus sylvatica

Hydraulic conductivity in the terminal branches of mature beech trees (Fagus sylvatica L.) decreased progressively during winter and recovered in the spring. The objective of this study was to determine the mechanisms involved in recovery. Two periods of recovery were identified. The first recovery of hydraulic conductivity occurred early in the spring, before bud break, and was correlated with the occurrence of positive xylem pressure at the base of the tree trunk. Active refilling of the embolized vessels caused the recovery. The second recovery of hydraulic conductivity occurred after bud break and was correlated with the onset of cambial activity. Formation of new functional vessels, leading to an increase in xylem diameter, was largely responsible for the increase in xylem conductivity. The two mechanisms were complementary: active refilling of embolized vessels occurred mostly in the root and the trunk, whereas formation of new functional vessels occurred mainly in young terminal shoots.     

The effects of a regeneration felling on photosynthetic photon flux density and regeneration growth in a <Emphasis Type="Italic">Nothofagus pumilio</Emphasis> forest

Photosynthetic photon flux density (PPFD) during the growing season and regeneration growth (height and base stem diameter) were investigated in two natural stands in the Patagonian region of Chile, one without silvicultural management and another with a regenerative felling under a shelterwood system. PPFD was measured by means of fifteen sensors (quantum Li-190SA) installed in each stand and distributed within three canopy openness grades. Four regeneration plots (1 m²) were established around each sensor. In each of the plots, the height and base diameter of ten labelled plants within the upper regeneration layer were measured in the growing seasons 2001–2002 and 2002–2003. In the stand with regeneration felling total PPFD in the growing season was 2.5–2.9 times higher than in the stand without intervention. In both stands, total PPFD in the growing season increased by about 420 mmol/m² when the relative canopy, which was in the range between 30 and 70%, was reduced by 10%. An identical behaviour was observed for the height and base stem diameter increases reflecting a clear effect of intervention and canopy coverage on the magnitude of PPFD received by the regeneration and its development.