Light availability and photosynthesis of Pseudotsuga menziesii seedlings grown in the open and in the forest understory

The light environment, photosynthetic dynamics and steady-state net photosynthetic rates of lateral branch shoots of Pseudotsuga menziesii var. glauca (Beissn.) Franco seedlings growing in the open and in the forest understory were investigated in situ. Mean incident photosynthetic photon flux density (PPFD) was 702.5 micro mol m(-2) s(-1) on open-grown branches and 52.0 micro mol m(-2) s(-1) on understory-grown branches. Mean daily durations of PPFD greater than 500, 200, and 50 micro mol m(-2) s(-1) were 8.5, 31.5, and 270.3 min, respectively, on understory-grown branches, and 559.1, 700.7, and 803.3 min, respectively, on open-grown branches. Sunflecks accounted for 32.4% of total daily photosynthetically active radiation incident on understory branches. Following 10 min at a PPFD of 50 micro mol m(-2) s(-1), the induction time required for net photosysnthesis to reach 50 and 90% of steady-state rates was shorter at a PPFD of 200 than at a PPFD of 500 micro mol m(-2) s(-1) and shorter in understory-grown branches than in open-grown branches. On a leaf area basis, dark respiration rates of understory-grown branches were lower and net photosynthetic rates were higher than those of open-grown branches exposed to low PPFD. However, at high PPFDs, understory-grown branches had lower photosynthetic rates than open-grown branches. When measurements were expressed on a leaf dry mass basis, there was no difference in dark respiration rates between understory branches and open-grown branches, but net photosynthetic rates of understory branches were equal to or higher than those of open-grown branches at all PPFDs.     

Changes in photosynthesis and leaf characteristics with tree height in five dipterocarp species in a tropical rain forest

Variations in leaf photosynthetic, morphological and biochemical properties with increasing plant height from seedlings to emergent trees were investigated in five dipterocarp species in a Malaysian tropical rain forest. Canopy openness increased significantly with tree height. Photosynthetic properties, such as photosynthetic capacity at light saturation, light compensation point, maximum rate of carboxylation and maximum rate of photosynthetic electron transport, all increased significantly with tree height. Leaf morphological and biochemical traits, such as leaf mass per area, palisade layer thickness, nitrogen concentration per unit area, chlorophyll concentration per unit dry mass and chlorophyll to nitrogen ratio, also changed significantly with tree height. Leaf properties had simple and significant relationships with tree height, with few intra- and interspecies differences. Our results therefore suggest that the photosynthetic capacity of dipterocarp trees depends on tree height, and that the trees adapt to the light environment by adjusting their leaf morphological and biochemical properties. These results should aid in developing models that can accurately estimate carbon dioxide flux and biomass production in tropical rain forests.     

Shoot growth responses to light microenvironment and correlative inhibition in tree seedlings under a forest canopy

To examine the mechanisms underlying crown development, I investigated the dependence of shoot behavior on light microenvironment in saplings of the evergreen broad-leaved tree species, Litsea acuminata (Bl.) Kurata, growing on a forest floor. The local light environment of individual shoots (shoot irradiance) and plants (plant irradiance, defined as the shoot irradiance of the most sunlit shoot of a plant) were analyzed as factors affecting shoot behavior. Daughter shoots that developed under partially sunlit conditions were longer and less leafy than daughter shoots developed under shaded conditions. Shoot production increased with increasing shoot irradiance. Terminal shoots receiving 5% or less of full sunlight produced 0.67 daughter shoots on average, whereas shoots receiving 10% or more of full sunlight produced 1.72 daughter shoots. In terminal shoots receiving 5% or less of full sunlight, the probability of producing no daughter shoots was about 63% when other shoots on the plant received 10% or more of full sunlight, but was < 35% where the rest of the plant was also shaded. Shoot death was observed only in shoots receiving 5% or less of full sunlight. The mortality of shaded shoots was higher in plants growing in high irradiance than in plants growing in low irradiance. The ecological significance of correlative inhibition (the enhanced mortality and reduced production of new shaded shoots in the presence of partially-sunlit shoots) is discussed.     

Seasonal changes in photosynthesis and growth of Zizyphus attopensis seedlings in three contrasting microhabitats in a tropical seasonal rain forest

We hypothesized that photosynthesis and growth of tropical vegetation at its most northern distribution in Asia (Xishuangbanna, SW China) is adversely affected by seasonal drought and chilling temperatures. To test this hypothesis, we measured photosynthetic and growth characteristics of Zizyphus attopensis Pierre seedlings grown in three contrasting forest microhabitats: the understory, a small gap and a large gap. Photosynthetic capacity (light-saturated photosynthetic rate (A(max)), maximum rate of carboxylation and electron transport rate) and partitioning of leaf nitrogen (N) into carboxylation and electron transport differed significantly among seasons and microhabitats. Specific leaf area (SLA) did not change seasonally, but differed significantly among microhabitats and showed a negative linear relationship with daily integrated photon flux (PPF(i)). In contrast, leaf N concentration per unit area (N(a)) changed seasonally but did not differ among microhabitats. Measurements of maximum PSII photochemical efficiency (F(v)/F(m)) indicated that chronic photoinhibition did not occur in seedlings in any of the microhabitats during the study. Photosynthetic capacity was greatest in the wet season and lowest in the cool season. During the cool and dry seasons, the reduction in A(max) was greater in seedlings grown in the large gap than in in the understory and the small gap. Close logarithmic relationships were detected between PPF(i), leaf N(a) and photosynthetic capacity. Stem mass ratio decreased, and root mass ratio increased, in the dry season. We conclude that seasonal acclimation in growth and photosynthesis of the seedlings was associated with changes in biochemical features (particularly N(a) and partitioning of total leaf N between the different photosynthetic pools) and biomass allocation, rather than with changes in leaf morphological features (such as SLA). Local irradiance is the main factor driving seasonal variations in growth and photosynthesis in the study area, where the presence of heavy fog during the cool and dry seasons limits irradiance, but supplies water to the soil surface layers.     

Functional traits and plasticity in response to light in seedlings of four Iberian forest tree species

We investigated the differential roles of physiological and morphological features on seedling survivorship along an experimental irradiance gradient in four dominant species of cool temperate-Mediterranean forests (Quercus robur L., Quercus pyrenaica Willd., Pinus sylvestris L. and Pinus pinaster Ait.). The lowest photochemical efficiency (F(v)/F(m) in dark-adapted leaves) was reached in deep shade (1% of full sunlight) in all species except Q. robur, which had the lowest photochemical efficiency in both deep shade and 100% of full sunlight. Species differed significantly in their survival in 1% of full sunlight but exhibited similar survivorship in 6, 20 and 100% of full sunlight. Shade-tolerant oaks had lower leaf area ratios, shoot to root ratios, foliage allocation ratios and higher rates of allocation to structural biomass (stem plus thick roots) than shade-intolerant pines. Overall phenotypic plasticity for each species, estimated as the difference between the minimum and the maximum mean values of the ecophysiological variables studied at the various irradiances divided by the maximum mean value of those variables, was inversely correlated with shade tolerance. Observed morphology, allocation and plasticity conformed to a conservative resource-use strategy, although observed differences in specific leaf area, which was higher in shade-tolerant species, supported a carbon gain maximization strategy. Lack of a congruent suite of traits underlying shade tolerance in the studied species provides evidence of adaptation to multiple selective forces. Although the study was based on only four species, the importance of ecophysiological variables as determinants of interspecific differences in survival in limiting light was demonstrated.     

Growth, water relations and solute accumulation in osmotically stressed seedlings of the tropical tree Colophospermum mopane

Root and hypocotyl elongation, water status and solute accumulation were studied in osmotically stressed seedlings of the tropical tree, Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard, which grows in hot arid areas of southern and central Africa. Seeds were imbibed for 24 h and then subjected to a polyethylene-glycol-generated osmotic stress of -0.03 (control), -0.2, -0.8, -1.6 or -2.0 MPa for 60 h. Seedlings subjected to moderate water stress (-0.2 MPa) had higher root growth rates (2.41 +/- 0.24 mm h(-1)), greater final root lengths (111 +/- 3.8 mm) and longer cells immediately behind the root elongation zone than control seedlings (1.70 +/- 0.15 mm h(-1) and 93 +/- 3.9 mm, respectively). Root lengths of seedlings in the -0.8 and -1.6 MPa treatments were similar to those of control seedlings, whereas the -2.0 MPa seedlings had significantly shorter roots. Both root and hypocotyl tissues exhibited considerable osmotic adjustment to the external water potential treatments. Seedlings in the -0.03, -0.2, and -0.8 MPa treatments had similar cell turgor pressures (0.69 +/- 0.10, 0.68 +/- 0.07 and 0.57 +/- 0.04 MPa, respectively), whereas the -2.0 MPa treatment lowered cell turgor pressure to 0.17 +/- 0.04 MPa. Root vacuolar osmotic pressures were generally similar to sap osmotic pressures, indicating that the increased root elongation observed in moderately water-stressed seedlings was not caused by increased turgor pressure difference. Neutral-fraction solute concentrations, including the osmoticum pinitol, increased approximately two-fold in root sap in response to a low external water potential. In hypocotyl sap of seedlings in the -2.0 MPa treatment, pinitol more than doubled, sucrose increased from about 2 to 75 mol m(-3) but glucose and fructose remained unchanged and, as a result, total sugars increased only slightly. The benefits of rapid early root elongation and osmoticum accumulation under conditions of water stress are discussed in relation to seedling establishment.     

Thigmomorphogenesis versus light in biomechanical growth strategies of saplings of two tropical rain forest tree species

? In the dense tropical rainforest understorey, saplings exhibit different growth strategies aiming at reaching light levels better fitting their ecology. Investing mainly in height growth, at the expense of their width, a lot are close to mechanical instability. Tachigali melinonii, a long living heliophilic tree species, is frequently observed to be extremely slender and supported by neighbours. Such observations suggest an active growth control through the perception of mechanical environment.

? Mechanical environment or light availability, which one is the most influent on growth and slenderness (H/D)? To test this question, we recorded growth of control and staked saplings of two species with contrasting habits and ecology: T. melinonii, and Dicorynia guianensis, along a natural light gradient.

? Dicorynia, the more stable, responded more clearly to the staking treatment, showing slenderness increase when light is available, whereas for Tachigali, only light availability governed growth.

? For Tachigali, growth allocation is mainly governed by light availability and ontogeny, whereas Dicorynia is probably similar to the average tree strategy, using the thigmomorphogenetic physiological process to control its stability.

     

Net photosynthesis and leaf conductance of loblolly pine seedlings in 2 and 21% oxygen as influenced by irradiance, temperature and provenance

Carbon dioxide assimilation and transpiration by secondary needles of two-year-old loblolly pines (Pinus taeda L.) were measured at 2 and 21% (ambient) oxygen. Measurements were made with a Georgia provenance at irradiances (photosynthetic photon flux density) of 150, 300, 700 and 1200 micromol m(-2) s(-1) and a constant temperature of 25 degrees C, and at temperatures of 15, 25 and 35 degrees C and a constant irradiance of 1200 micromol m(-2) s(-1). Measurements were made with provenances from North Carolina, Florida, Arkansas, and Georgia at 25 degrees C and an irradiance of 1200 micromol m(-2) s(-1). There was no significant interaction between the effects of irradiance and oxygen on either net photosynthesis or leaf conductance. Taking all irradiances together, photosynthesis was 16% less and leaf conductance 28% less in 2% oxygen than in 21% oxygen. There was a significant interaction between the effects of temperature and oxygen concentration on both net assimilation and leaf conductance. Net photosynthesis at 21% oxygen relative to that at 2% was significantly reduced at 25 and 35 degrees C, but not at 15 degrees C, whereas leaf conductance at 21% oxygen relative to that at 2% was significantly increased at 15 and 25 degrees C, but not at 35 degrees C. In the provenance study, net photosynthesis was 11% higher and leaf conductance 36% lower in 2% oxygen than in 21% oxygen. There was no significant interaction between the effects of provenance and oxygen on either net photosynthesis or leaf conductance.     

Growth, nutrition, photosynthesis and transpiration responses of longleaf pine seedlings to light, water and nitrogen

Early growth and physiology of longleaf pine (Pinus palustris Mill.) seedlings were studied in response to light, water and nitrogen under greenhouse conditions. The experiment was conducted with 1-year-old seedlings grown in 11.3 l pots. The experimental design was a split-plot factorial with two levels (low and high) of each of the factors, replicated in three blocks. The four factorial combinations of water and nitrogen were randomly applied to 15 pots (sub-plots) in each of the light treatment (main plot). Data were collected on survival, root collar diameter (RCD), and height on a monthly basis. Biomass (shoot, root and needle), leaf area index, specific needle area, and needle nutrient (N, P, K, Ca, and Mg) concentrations were determined following final harvest after 16 months. Physiological data (net photosynthesis and transpiration) were collected monthly from March to July during the second growing season.

Height and RCD were significantly influenced by nitrogen and water and by the interaction between them with no apparent effect of light. Seedlings grew 93% taller in the high nitrogen and well watered (HNWW) treatment compared to the low nitrogen and water stressed (LNWS) treatment. Similarly, a significant increase (78%) in RCD was observed for seedlings in the HNWW treatment over the LNWS treatment. Light, along with water and nitrogen, played an important role in seedling biomass growth, especially when water was not limiting. Biomass partitioning (as measured by root:shoot ratio) was affected only by nitrogen and water. Nutrient stress had a greater influence on carbon allocation (69% increase in root:shoot ratio) than water stress (19% increase). Net photosynthesis (P_net) was significantly higher for seedlings in the high resource than in the low resource treatments with significant light×water and nitrogen×water interactions. Transpiration rate was higher (75%) under the WW treatment compared to the WS treatment. Longleaf pine seedlings grown under the LNWW treatment had the lowest foliar nitrogen (0.71%) whereas seedlings in the HNWS treatment had the highest (1.46%). Increasing the availability of light (through larger canopy openings or controlling midstory density) and soil nitrogen (through fertilization) may not result in greater P_net and improved seedling growth unless soil water is not limiting.     

Electric resistance as a measure of tree water status during seasonal drought in a tropical dry forest in Costa Rica

Variation in electric resistance of stem tissues was used to measure differences and changes in water status among trees in a tropical dry forest in Costa Rica during the dry season. For more than 30 tree species, stem water content (SWC), measured as electric resistance between nails driven 20 mm deep into tree trunks, correlated well with wood density, saturation water content, dehydration, measured with the pressure chamber, and tree development during drought. At dry sites, SWC was lowest in hardwood trees (characterized by high wood density) and highest in stem-succulent lightwood trees (characterized by low wood density). Among hardwood trees, SWC varied with soil water availability. During the dry season, SWC declined before leaf shedding and increased during rehydration preceding bud break. The time course of seasonal changes in SWC apparently constitutes an indirect measure of variation in the relative water content of outer stem tissues, which determines development of dry-forest trees during the dry season.     

The pH change in rhizosphere ofPinus koraiensis seedlings as affected by different nitrogen sources and its effect on phosphorus availability

Root mat method described by Kuchenbuch and Jungk was used to study the rhizosphere processes. The experiment was carried out on two years oldPinus koraiensis seedlings. Soil samples collected from the upper 20-cm soil layer in Changbai Mountain were treated with three different forms of nitrogen fertilizers: NO₃ ⁻−N, NH₄ ⁺−N and NH₄NO₃. The results showed that the soil pH and available P near the roots were all lower than in the bulk soil in control treatment. NH₄ ⁺−N application greatly decreased the soil pH near the roots compared to the control treatment and promoted the absorption of phosphorus, which led to a more remarkable depletion region of available P. On the contrary, the rhizosphere soil pH was higher than in the bulk soil in treatments with NO₃ ⁻−N and retarded the P absorption, which led to a nearly equal available P contents to the bulk soil. In treatment with NH₄NO₃, the rhizosphere soil pH was only a little lower than that in the control treatment and its effects on P absorption is mediate between the treatments with NH₄ ⁺−N and NO₃ ⁻−N. Foundation item: This paper was supported by National Natural Science Foundation of China (Grant No. 30170167). Biography: Chen Yong-liang (1969-), male, Ph. Doctor, lecture of Northeast Forestry University, Harbin 150040, Post-doctor in Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P.R. China. E-mail: ylchin@sohu.com Responsible editor: Seng Funan     

Demographic variation and habitat specialization of tree species in a diverse tropical forest of Cameroon

Background： Many tree species in tropical forests have distributions tracking local ridge-slope-valley topography. Previous work in a 50-ha plot in Korup National Park, Cameroon, demonstrated that 272 species, or 63% of those tested, were significantly associated with topography. Methods： We used two censuses of 329,000 trees ≥1 cm dbh to examine demographic variation at this site that would account for those observed habitat preferences. We tested two predictions. First, within a given topographic habitat, species specializing on that habitat （＇residents＇） should outperform species that are specialists of other habitats （＇foreigners＇）. Second, across different topographic habitats, species should perform best in the habitat on which they specialize （＇home＇） compared to other habitats （＇away＇）. Species＇ performance was estimated using growth and mortality rates. Results： In hierarchical models with species identity as a random effect, we found no evidence of a demographic advantage to resident species. Indeed, growth rates were most often higher for foreign species. Similarly, comparisons of species on their home vs. away habitats revealed no sign of a performance advantage on the home habitat. Conclusions＂ We reject the hypothesis that species distributions along a ridge-valley catena at Korup are caused by species differences in trees _〉1 cm dbh. Since there must be a demographic cause for habitat specialization, we offer three alternatives. First, the demographic advantage specialists have at home occurs at the reproductive or seedling stage, in sizes smaller than we census in the forest plot. Second, species may have higher performance on their preferred habitat when density is low, but when population builds up, there are negative density-dependent feedbacks that reduce performance. Third, demographic filtering may be produced by extreme environmental conditions that we did not observe during the census interval.     

不同氮源作用下红松苗木根际pH的变化及其对根际磷的影响(英文)

用Kuchenbuch与Jungk所描述的根垫法,研究了两年生红松苗木根际变化过程。土壤样品长白山20mm土壤层,用不同形式的氮肥(NO3--N,NH4+-N和NH4NO3)进行处理,结果表明: 对照处理时近根pH值与有效P均低于土体;与对照相比,NH4+-N处理显著降低近根处pH值并促进了P吸收,产生更为明显的有效磷亏缺区;与NH4+-N处理相反,NO3--N处理使根际pH值相对于土体增加,延缓了P的吸收,近根处有效P含量与土体基本持平。NH4NO3处理时,根际pH值仅比对照略低,其对磷吸收的影响与对照处理相似。     

Patterns of root respiration rates and morphological traits in 13 tree species in a tropical forest

The root systems of forest trees are composed of different diameters and heterogeneous physiological traits. However, the pattern of root respiration rates from finer and coarser roots across various tropical species remains unknown. To clarify how respiration is related to the morphological traits of roots, we evaluated specific root respiration and its relationships to mean root diameter (D) of various diameter and root tissue density (RTD; root mass per unit root volume; gcm(-3)) and specific root length (SRL; root length per unit root mass; mg(-1)) of the fine roots among and within 14 trees of 13 species from a primary tropical rainforest in the Pasoh Forest Reserve in Peninsular Malaysia. Coarse root (2-269mm) respiration rates increased with decreasing D, resulting in significant relationships between root respiration and diameter across species. A model based on a radial gradient of respiration rates of coarse roots simulated the exponential decrease in respiration with diameter. The respiration rate of fine roots (<2mm) was much higher and more variable than those of larger diameter roots. For fine roots, the mean respiration rates for each species increased with decreasing D. The respiration rates of fine roots declined markedly with increasing RTD and increased with increasing SRL, which explained a significant portion of the variation in the respiration among the 14 trees from 13 species examined. Our results indicate that coarse root respiration in tree species follows a basic relationship with D across species and that most of the variation in fine root respiration among species is explained by D, RTD and SRL. We found that the relationship between root respiration and morphological traits provides a quantitative basis for separating fine roots from coarse roots and that the pattern holds across different species.     

Some diseases of forest tree seedlings in India caused by Sclerotium rolfsii and Rhizoctonia solani1

Leaf blight of Bombax ceiba and B. insigne caused by Sclerotium rolfsii and collar rot of B. ceiba and Ailanthus triphysa caused by Rhizoctonia solani are reported for the first time from India.     

Photosynthesis of a tropical canopy tree, Ceiba pentandra, in a lowland forest in Panama

Diel (24 h) courses of CO(2) and water-vapor exchange of Ceiba pentandra (L.) Gaertn. (Bombacaceae) were studied under natural tropical conditions in the semi-evergreen moist forest of Barro Colorado Island, Panama. Measurements were conducted from early February 1991 (dry season), shortly after new leaves emerged, until mid-October 1991 (wet season), when leaves were shed. Rates of net CO(2) uptake were significantly higher in the dry season than in the wet season, and showed a linear decrease with leaf age. Leaf nitrogen concentrations and contents also decreased with age. Our estimate of annual carbon gain (2640 g CO(2) m(-2) year(-1) or 21 g CO(2) g(DW) (-1) year(-1)) is considerably higher than estimates available for temperate forest trees.     

Quantitative estimates of tree species selectivity by moose (Alces alces) in a forest landscape

Abstract

An extensive literature is available on browsing preference for certain tree species. However, useful predictive tools for estimating the impact of deer on forests production and biodiversity can still be improved. A step in that direction is not only to rank preference among tree species but also to quantify the relative risk of being browsed. The foraging selectivity of moose was evaluated using three different statistical methods developed to study habitat utilization. The general pattern for the three methods was consistent. From the results, groups of forage species were clustered and a quantitative index of selectivity was calculated for the groups. The selectivity index showed that rowan (Sorbus aucuparia), willow (Salix ssp.) and aspen (Populus tremula) had a 14 times higher probability of being browsed than a group consisting of Scots pine (Pinus sylvestris) and downy birch (Betula pubescens), while juniper (Juniperus communis) and silver birch (Betula pendula) had a 3.5 times higher probability than Scots pine and downy birch. Since the most preferred species were the least abundant, one should be cautious about the generality of the index between areas, as it may indicate that preference depends on plant species composition. The method used can easily be applied in forest management. Information on quantitative selectivity indices may improve the possibility of managing moose in accordance with acceptable browsing damage.     

Pioneer tree responses to variation of soil attributes in a tropical semi-deciduous forest in Brazil

The occurrence of pioneer tree species inside tropical forests is usually associated with canopy openness due to disturbances. The distribution of these species under different environmental conditions, aside from light presence, can be influenced by other variables such as soil attributes, water availability, and non-arborous species presence. This work evaluates pioneer tree distribution in the Pindorama Biological Reserve, Brazil, with respect to altitude, soil attributes, and non-arborous species in 65,400-m² plots in two toposequences of semi-deciduous forest. We evaluated the physical and chemical soil attributes altitude, basal area, height, and number of individuals of tree species with diameter at breast height (DBH) ≥5 cm in a randomly chosen quadrant in each plot. Pioneer trees were characterized by the following higher occurrence species: Acacia polyphylla, Aloysia virgata, Casearia sylvestris, and Croton floribundus. Cluster analysis suggested five similar groups among sampling plots. For each group, the mean of altitude, physical and chemical soil attributes, and degree of non-arborous species infestation was calculated. Principal components analysis correlated variables with pioneer tree data. C. floribundus occurred at low altitudes at lower or higher fertility, C. sylvestris occurred in lower fertility plots, and A. polyphylla and A. virgata occurred in higher altitude plots.     

Relationships of climate change and tree ring of Betula ermanii tree line forest in Changbai Mountain

Based on the tree-ring growth characteristics of Erman＇s birch （Betula ermanii charm.） and the relationships between it and climatic ）＇actors at elevation of 1950m, the sensitivity of tree lines in Changbai Mountain to climatic factors was assessed. The results indicated tree line forest in Changbai Mountain had an obvious sensitivity to climate factors. However, difference from other study sits is that the main climatic control factor on tree-ring growth was not current growth season temperatures, as might be expected, but previous winter and current March temperature. Although the precipitation in the region was quite abundant, the tree-ring growth was still significantly correlated with the precipitation during previous winter and current spring. Additionally, climatic factors which influenced the Erman＇s birch growth were not the yearly variables, but seasonal and monthly variables. Therefore, the reported increase in yearly mean temperature and total yearly precipitation since 1980s was not responded by sustained increase in ring widths in recent decades.     

Drought responses of an exotic tree (Eriobotrya japonica) in a tropical cloud forest suggest the potential to become an invasive species

New Forests - Eriobotrya japonica is a non-native tree expanding in secondary forests and threatening the tropical montane cloud forest of central Veracruz, Mexico. Our objective was to investigate...