Evergreen Tree Species Research Articles

N concentration of old leaves and twigs is more sensitive to stand density than that of young ones in Chinese fir plantations: a case study in subtropical China

Young leaves are conventionally used in the analysis to study the nutrient status of evergreen plants and their responses to environmental changes, but the role of old leaves remains poorly understood. We selected two stand types in 31-year-old Chinese fir (Cunninghamia lanceolata) plantations with similar soil conditions but different stand densities, to test the hypothesis that nitrogen (N) concentration of old leaves and twigs is more sensitive to stand density than that of young ones. Leaves and twigs were sampled and sorted into young (one-year-old) and old (two- and three-year-old) groups. Significant differences in N concentration and carbon: nitrogen ratio between the low-density stand and high-density stand were only found in the old leaves and twigs but not in the young ones. Although the N resorption efficiency did not vary significantly with stand density, the annual N resorption rates were increased in old leaves and relatively young twigs at high stand density. These results show the potential use of old tissues in the nutrient analysis in Chinese fir plantations. Testing the generality of these results could improve the use of foliar analysis as an indicator of nutrient status and environmental changes in evergreen tree species.

Adaptation and acclimation both influence photosynthetic and respiratory temperature responses in Corymbia calophylla.

Short-term acclimation and long-term adaptation represent two ways in which forest trees can respond to changes in temperature. Yet, the relative contribution of thermal acclimation and adaptation to tree physiological responses to temperature remains poorly understood. Here, we grew two cool-origin and two warm-origin populations of a widespread broad-leaved evergreen tree species (Corymbia calophylla (Lindl.) K.D.Hill & L.A.S.Johnson) from a Mediterranean climate in southwestern Australia under two growth temperatures representative of the cool- and warm-edge of the species distribution. The populations selected from each thermal environment represented both high and low precipitation sites. We measured the short-term temperature response of leaf photosynthesis (A) and dark respiration (R), and attributed observed variation to acclimation, adaptation or the combination of both. We observed limited variation in the temperature optimum (Topt) of A between temperature treatments or among populations, suggesting little plasticity or genetic differentiation in the Topt of A. Yet, other aspects of the temperature response of A and R were dependent upon population and growth temperature. Under cooler growth temperatures, the population from the coolest, wettest environment had the lowest A (at 25 °C) among all four populations, but exhibited the highest A (at 25 °C) under warmer growth temperatures. Populations varied in R (at 20 °C) and the temperature sensitivity of R (i.e., Q10 or activation energy) under cool, but not warm growth temperatures. However, populations showed similar yet lower R (at 20 °C) and no differences in the temperature sensitivity of R under warmer growth temperatures. We conclude that C. calophylla populations from contrasting climates vary in physiological acclimation to temperature, which might influence how this ecologically important tree species and the forests of southwestern Australia respond to climate change.

Geographical and climatic gradients of evergreen versus deciduous broad-leaved tree species in subtropical China: Implications for the definition of the mixed forest.

Understanding climatic influences on the proportion of evergreen versus deciduous broad‐leaved tree species in forests is of crucial importance when predicting the impact of climate change on broad‐leaved forests. Here, we quantified the geographical distribution of evergreen versus deciduous broad‐leaved tree species in subtropical China. The Relative Importance Value index (RIV) was used to examine regional patterns in tree species dominance and was related to three key climatic variables: mean annual temperature (MAT), minimum temperature of the coldest month (MinT), and mean annual precipitation (MAP). We found the RIV of evergreen species to decrease with latitude at a lapse rate of 10% per degree between 23.5 and 25°N, 1% per degree at 25–29.1°N, and 15% per degree at 29.1–34°N. The RIV of evergreen species increased with: MinT at a lapse rate of 10% per °C between −4.5 and 2.5°C and 2% per °C at 2.5–10.5°C; MAP at a lapse rate of 10% per 100 mm between 900 and 1,600 mm and 4% per 100 mm between 1,600 and 2,250 mm. All selected climatic variables cumulatively explained 71% of the geographical variation in dominance of evergreen and deciduous broad‐leaved tree species and the climatic variables, ranked in order of decreasing effects were as follows: MinT > MAP > MAT. We further proposed that the latitudinal limit of evergreen and deciduous broad‐leaved mixed forests was 29.1–32°N, corresponding with MAT of 11–18.1°C, MinT of −2.5 to 2.51°C, and MAP of 1,000–1,630 mm. This study is the first quantitative assessment of climatic correlates with the evergreenness and deciduousness of broad‐leaved forests in subtropical China and underscores that extreme cold temperature is the most important climatic determinant of evergreen and deciduous broad‐leaved tree species’ distributions, a finding that confirms earlier qualitative studies. Our findings also offer new insight into the definition and distribution of the mixed forest and an accurate assessment of vulnerability of mixed forests to future climate change.

Tree mortality across biomes is promoted by drought intensity, lower wood density and higher specific leaf area.

Drought events are increasing globally, and reports of consequent forest mortality are widespread. However, due to a lack of a quantitative global synthesis, it is still not clear whether drought-induced mortality rates differ among global biomes and whether functional traits influence the risk of drought-induced mortality. To address these uncertainties, we performed a global meta-analysis of 58 studies of drought-induced forest mortality. Mortality rates were modelled as a function of drought, temperature, biomes, phylogenetic and functional groups and functional traits. We identified a consistent global-scale response, where mortality increased with drought severity [log mortality (trees trees-1 year-1 ) increased 0.46 (95% CI=0.2-0.7) with one SPEI unit drought intensity]. We found no significant differences in the magnitude of the response depending on forest biomes or between angiosperms and gymnosperms or evergreen and deciduous tree species. Functional traits explained some of the variation in drought responses between species (i.e. increased from 30 to 37% when wood density and specific leaf area were included). Tree species with denser wood and lower specific leaf area showed lower mortality responses. Our results illustrate the value of functional traits for understanding patterns of drought-induced tree mortality and suggest that mortality could become increasingly widespread in the future.

Species-specific effects of genetic diversity and species diversity of experimental communities on early tree performance

Aims Changing biodiversity can affect ecosystem functioning. However, the role of genetic diversity within species, relative to the one of species diversity, has hardly been addressed. Methods To address the effects of both genetic diversity and species diversity during the important stage of early tree life, we used eight seed families (SF) taken from each of 12 evergreen and deciduous tree species of subtropical forest to perform a factorial experiment. We established 264 communities of 16 trees each. Each community had a species diversity of either one or four species and a genetic diversity of either one, two or four SF per species. We measured plant survival, growth rate, final biomass and herbivory 20 months after sowing. Important Findings Species differed from each other in biomass, growth rate, herbivory and survival (P < 0.001). Deciduous species tended to have much higher biomass (P < 0.1) and experienced higher herbivory (P < 0.05) than evergreen species. Species diversity affected the performance of different species differently (species diversity by species interaction, P <0.001 for all variables but survival). Biomass differed between SF and increasing genetic diversity from one to two, and from two to four, SF per species increased biomass for some species and decreased it for others (P < 0.001). Our study showed pronounced species–specific responses of early tree performance to species diversity and less pronounced responses to genetic diversity. These species–specific responses suggest feedbacks of species diversity and genetic diversity on future species composition.

Divergent Hydraulic Safety Strategies in Three Co-occurring Anacardiaceae Tree Species in a Chinese Savanna.

Vulnerability segmentation, the condition under which plant leaves are more vulnerable to drought-induced cavitation than stems, may act as a “safety valve” to protect stems from hydraulic failure. Evergreen, winter-deciduous, and drought-deciduous tree species co-occur in tropical savannas, but there have been no direct studies on the role of vulnerability segmentation and stomatal regulation in maintaining hydraulic safety in trees with these three leaf phenologies. To this end, we selected three Anacardiaceae tree species co-occurring in a Chinese savanna, evergreen Pistacia weinmanniifolia, drought-deciduous Terminthia paniculata, and winter-deciduous Lannea coromandelica, to study inter-species differentiation in leaf and stem hydraulic safety. We found that the two deciduous species had significantly higher sapwood-specific hydraulic conductivity and leaf-specific hydraulic conductance than the evergreen species. Moreover, two deciduous species were more vulnerable to stem cavitation than the evergreen species, although both drought-deciduous species and evergreen species had drought-resistance leaves. The evergreen species maintained a wide hydraulic safety margin (HSM) in stems and leaves; which was achieved by embolism resistance of both stems and leaves and isohydric stomatal control. Both deciduous species had limited HSMs in stems and leaves, being isohydric in the winter-deciduous species and anisohydric in drought-deciduous species. The difference in water potential at 50% loss of hydraulic conductivity between the leaves and the terminal stems (P50leaf−stem) was positive in P. weinmanniifolia and L. coromandelica, whereas, T. paniculata exhibited a lack of vulnerability segmentation. In addition, differences in hydraulic architecture were found to be closely related to other structural traits, i.e., leaf mass per area, wood density, and sapwood anatomy. Overall, the winter-deciduous species exhibits a drought-avoidance strategy that maintains the hydraulic safety of the more carbon-costly stems by sacrificing cheaper and more vulnerable leaves, while the evergreen species exhibits a hydraulic strategy of drought tolerance with strong stomatal regulation. In contrast, the drought-deciduous species lacks vulnerability segmentation and sheds leaves at the expense of top shoots during peak drought. This study demonstrates that even sympatric tree species that differ in leaf phenology can exhibit divergent adaptive hydraulic safety strategies.

Shade tolerance and herbivory are associated with RGR of tree species via different functional traits.

Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade-off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth-related functional traits. Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth-related functional traits and (i) species' shade-tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth-related functional traits. We found that RGR was associated negatively with shade-tolerance and positively with herbivory rate. However, herbivory rate and shade-tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (Amax ) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade-tolerance was strongly related to Amax and to a lesser extent to leaf mass ratio (LMR) and dark respiration (Rd ), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content. The effects of low light on RGR would be mediated by Amax , while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource-uptake functional traits.

Leaf Demography of Some Evergreen and Deciduous Tree and Shrub Species of Kumaun Himalaya, India

Leaf demography was studied in 9 trees (6 Evergreen (ES), 1 Semideciduous (SD) and 2 Deciduous (DS)) and 10 shrubs (7 Evergreen (ES) and 3 Deciduous (DS)) occurring between 350 to 2500 m elevation in the Kumaun Himalaya, India. Although each species had its own pattern about seasonality of leaf recruitment, it was possible to group the species based on leaf expansion behavior. The result shows the leaf expansion rate was greater for deciduous species compared to Evergreen species. The percent leaf area after four weeks of expansion was also greater for deciduous species.

Habitat heterogeneity explains mosaics of evergreen and deciduous trees at local‐scales in a subtropical evergreen broad‐leaved forest

AbstractQuestionsMosaics of evergreen and deciduous trees that are characteristic of evergreen broad‐leaved forests (EBLF) are thought to arise from habitat heterogeneity, but empirical evidence for this is limited. We test this assertion asking: (1) whether environmental heterogeneity explains the distribution of deciduous and evergreen trees; (2) which are the most important environmental variables; and (3) does their importance change with scale?LocationTiantong National Forest Park, Ningbo, Zhejiang, China.MethodsWe used data from a 20‐ha individual‐mapped EBLF in spatial point‐pattern analyses testing the scale of aggregation within, and segregation between, the two life forms. We used a heterogeneous Poisson process model to remove the effects of environmental heterogeneity, predicting segregation would disappear if the mosaic was due to habitat heterogeneity alone. Finally, we tested the relative importance of theoretically important environmental variables using multivariate regression trees at three spatial scales (10, 20 and 50 m grid cells).ResultsWe found evergreen and deciduous trees were aggregated at scales below 125 m and 60 m, respectively, and mutually exclusive at scales &lt;120 m. Evidence of any spatial segregation between the life forms was removed at all scales after controlling for environmental heterogeneity. Only soil phosphorus concentrations contributed to spatial patterns at all scales, with values &gt;0.27–0.30 g·kg−1 favouring deciduous species.ConclusionsOur study is consistent with habitat heterogeneity creating the observed mosaics of evergreen and deciduous tree species, but micro‐habitat heterogeneity contributed even at scales &lt;20 m. Soil phosphorus availability appears to be the major environmental variable maintaining these mosaic patterns at hillslope scales in EBLF.

Latitudinal Patterns and Climatic Drivers of Leaf Litter Multiple Nutrients in Chinese Broad-Leaved Tree Species: Does Leaf Habit Matter?

Leaf litter nutrients play a key role in nutrient cycling in forest ecosystems, yet our current knowledge of the ways in which climate controls leaf litter nutrients remains uncertain, especially for broad-leaved tree species in China. We performed a meta-analysis of geographic patterns of leaf litter nutrients of Chinese broad-leaved tree species in relation to climatic variables and leaf habit (as a discrete classification of tree species). We found that mean leaf litter carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were 458.36, 10.11, 0.72, 6.37, 14.22 and 2.59 mg−1 g, respectively. Leaf litter nutrients did not diverge between leaf habits where they coexisted. These leaf litter nutrients displayed significant latitudinal trends, partly driven by climatic factors and a shift in leaf habit. Mean annual precipitation explained the largest amount of total variation in leaf litter C, N, P and K, and mean annual temperature was the most important predictor for leaf litter Mg, whereas leaf habit was the largest contributor to total variation in leaf litter Ca. We further found that the relationships between climate and leaf litter nutrients were distinguishable for evergreen and deciduous broad-leaved tree species. Collectively, our study differed from previous studies that evaluated leaf litter nutrients and only focused on N and P, and substantiated that leaf litter nutrients in forest ecosystems were affected by climate and leaf habit, but the strengths of the influences of these factors were strongly contingent on leaf litter nutrient identity. Therefore, alteration of climate would directly and indirectly (via a shift in species composition) affect latitudinal patterns of leaf litter nutrients and thus the associated nutrient flux and ecosystem functioning. Our study also underlined the need to include multiple nutrients to explore the influence of climate on leaf litter nutrient stoichiometry.

Photosynthetic CO2 uptake and carbon sequestration potential of deciduous and evergreen tree species in an urban environment

Urban tree planting programmes are increasingly promoted as a way to reduce atmospheric carbon dioxide (CO2) mixing ratios. However, few studies have investigated the photosynthetic CO2 uptake potential of different urban tree species across seasons. In particular little is known about photosynthetic CO2 uptake in cities with a subtropical, oceanic climate where evergreen species are dominant. We addressed this shortcoming by measuring net photosynthetic rates of ten native and exotic tree species during different seasons and times of the day in Auckland, New Zealand. We also assessed the potential of leaf nitrogen (N) concentration as a proxy for net photosynthetic capacities of urban trees, which is of particular importance to upscale leaf-level photosynthetic CO2 uptake to local and regional scales. In addition, we compared measured net photosynthetic capacities (light-saturated net photosynthetic rates) with carbon (C) sequestration rates estimated using tree growth measurements and allometric equations. Mean net photosynthetic capacities ranged between 2.37 and 10.48 μmol m−2 s−1 across all seasons and were closely related to tree C sequestration rates, suggesting that increased photosynthesis enhances growth rates and therefore tree C sequestration rates. Given that winter net photosynthetic capacities remained high in evergreen species (3.38–13.96 μmol m−2 s−1), with almost 50% higher mean net photosynthetic capacity compared to summer across all species, we suggest that tree planting programmes for CO2 mitigation should favour long living evergreen tree species with high basal area increments (BAI). Leaf N explained 43% and 57% of the variability of photosynthetic capacities across species in summer and winter, respectively. These results indicate that leaf N may be used as a proxy for net photosynthetic capacities of commonly planted urban trees in Auckland. However, further research is required to provide robust models that may be used to estimate photosynthetic CO2 uptake at a local and urban scale.

Contrasting water sources of evergreen and deciduous tree species in rocky mountain area of Beijing, China

Trees growing in the Beijing mountain area are often located on rocky outcrops. As water sources for these trees are poorly understood, we investigated seasonal water sources of four typical tree species (Platycladus orientalis, Pinus tabuliformis, Robinia pseudoacacia and Quercus variabilis) using stable hydrogen and oxygen isotope methods in this area. Results indicate that P. orientalis predominantly utilized water from natural springs (57.8%) during the dry season and uptake water from shallow layer (0–20cm, 78.4%) during the wet season. P. tabuliformis predominantly utilized shallow (46.8% and 37.7%, respectively) and deep (60–100cm, 24.9% and 27.6%, respectively) soil water in the dry and wet seasons. R. pseudoacacia mainly absorbed shallow soil layers water (54.3%) during the dry season and switched its water source to all of the soil layers (19.2–30.9%) during the wet season. Q. variabilis predominantly extracted water from the shallow (29.8%) and middle (20–60cm, 38.6%) soil layers during the dry season; and it primarily relied on middle layer soil water (25.9%) and natural springs (40.5%) in the wet season. These four tree species showed a strong adaptation to drought periods and our findings provide valuable information which can be used when selecting tree species and planning long-term ecological management of afforestation around the Beijing mountain area.

Recent climate hiatus revealed dual control by temperature and drought on the stem growth of Mediterranean Quercus ilex.

A better understanding of stem growth phenology and its climate drivers would improve projections of the impact of climate change on forest productivity. Under a Mediterranean climate, tree growth is primarily limited by soil water availability during summer, but cold temperatures in winter also prevent tree growth in evergreen forests. In the widespread Mediterranean evergreen tree species Quercus ilex, the duration of stem growth has been shown to predict annual stem increment, and to be limited by winter temperatures on the one hand, and by the summer drought onset on the other hand. We tested how these climatic controls of Q.ilex growth varied with recent climate change by correlating a 40-year tree ring record and a 30-year annual diameter inventory against winter temperature, spring precipitation, and simulated growth duration. Our results showed that growth duration was the best predictor of annual tree growth. We predicted that recent climate changes have resulted in earlier growth onset (-10days) due to winter warming and earlier growth cessation (-26days) due to earlier drought onset. These climatic trends partly offset one another, as we observed no significant trend of change in tree growth between 1968 and 2008. A moving-window correlation analysis revealed that in the past, Q.ilex growth was only correlated with water availability, but that since the 2000s, growth suddenly became correlated with winter temperature in addition to spring drought. This change in the climate-growth correlations matches the start of the recent atmospheric warming pause also known as the 'climate hiatus'. The duration of growth of Q.ilex is thus shortened because winter warming has stopped compensating for increasing drought in the last decade. Decoupled trends in precipitation and temperature, a neglected aspect of climate change, might reduce forest productivity through phenological constraints and have more consequences than climate warming alone.

Depletion of atmospheric gaseous elemental mercury by plant uptake at Mt. Changbai, Northeast China

Abstract. There exists observational evidence that gaseous elemental mercury (GEM) can be readily removed from the atmosphere via chemical oxidation followed by deposition in the polar and sub-polar regions, free troposphere, lower stratosphere, and marine boundary layer under specific environmental conditions. Here we report GEM depletions in a temperate mixed forest at Mt. Changbai, Northeast China. The strong depletions occurred predominantly at night during the leaf-growing season and in the absence of gaseous oxidized mercury (GOM) enrichment (GOM &lt; 3 pg m−3). Vertical gradients of decreasing GEM concentrations from layers above to under forest canopy suggest in situ loss of GEM to forest canopy at Mt. Changbai. Foliar GEM flux measurements showed that the foliage of two predominant tree species is a net sink of GEM at night, with a mean flux of −1.8 ± 0.3 ng m2 h−1 over Fraxinus mandshurica (deciduous tree species) and −0.1 ± 0.2 ng m2 h−1 over Pinus Koraiensis (evergreen tree species). Daily integrated GEM δ202Hg, Δ199Hg, and Δ200Hg at Mt. Changbai during 8–18 July 2013 ranged from −0.34 to 0.91 ‰, from −0.11 to −0.04 ‰ and from −0.06 to 0.01 ‰, respectively. A large positive shift in GEM δ202Hg occurred during the strong GEM depletion events, whereas Δ199Hg and Δ200Hg remained essentially unchanged. The observational findings and box model results show that uptake of GEM by forest canopy plays a predominant role in the GEM depletion at Mt. Changbai forest. Such depletion events of GEM are likely to be a widespread phenomenon, suggesting that the forest ecosystem represents one of the largest sinks ( ∼ 1930 Mg) of atmospheric Hg on a global scale.

Cold resistance of four evergreen broad-leaved tree species

The leaves of four evergreen plants, i.e., Fatsia japonica, Nerium indicum, Mahonia bealei and Acer cinnamomifolium were used as the experimental materials. By measuring the changes of in vitro leaf in soluble sugar, soluble protein, free proline, POD activity, chlorophyll content and relative electrolytic conductivity under aritificial simulated low temperature, combining the measurements of SPAD, leaf surface features and anatomical changes in organizational structure in the process of natural wintering, the cold resistance of four evergreen tree species was evaluated comprehensively. The results showed that in the process of artificial low temperature stress, the chlorophyll content of the leaves of four evergreen species decreased, the content of soluble protein pea-ked at -20 ℃, and the soluble sugar, free proline, POD activity and relative electrolytic conductivity showed an overall upward trend. The semilethal temperatures of four species were -8.0, -13.4, -19.4 and -14.8 ℃, respectively. During the winter, the leaf SPAD of the four species changed markedly, reflecting that the change of relative chlorophyll content was related to the change of temperature. Meanwhile, the leaf thickness, cutin layer thickness, stockade tissue thickness and tightness of four species increased and the plasmolysis occurred thereafter. Also the content of starch grains and calcium oxalate cluster crystal increased. The typical stomatal pits and the intensive non-glandular trichome within the pits of N. indicum and the sclerenchyma of M. Bealei could improve the cold resistance of plants to some extent. In addition, the phenomena like the breakage of wax layer in leaf surface, the fracture of epidermal hair and the deformation of palisade tissue indicated that plants were damaged to a certain extent by low temperature.

Responses of plant water use to a severe summer drought for two subtropical tree species in the central southern China

Abstract Study region Western suburb of Changsha, Hunan Province, the central southern China. Study focus Plant transpiration plays a significant role in the terrestrial water cycle and is closely associated with ecosystem primary production. Summer drought in the study area poses a stress on plant water use and associated carbon assimilation in growing season. In this study, water use response of two evergreen tree species to variation in environmental conditions was examined during a severe summer drought. New hydrological insights The results show that a decrease in water use during the drought for both two species is closely associated with an increase in vapor pressure deficit and a decrease in stem water potential. The two species appear to be anisohydric, but to a different degree in response to the drought. The hydrodynamic water potential gradient (Δψ) maintains relatively constant with an average value of 0.59 MPa for C. camphora, and 1.59 MPa for O. fragrans. O. fragrans is less sensitive to drought than C. camphora, while C. camphora shows an effective survival mechanism via leaf shedding and dieback of shoots.

Crecimiento diamétrico de arboles caducifolios y perennifolios del bosque mesófilo de montaña en los alrededores de Xalapa

El crecimiento diamétrico anual de los árboles es una variable esencial para eligir las especies que deben usarse para reforestación, en plantaciones, en proyectos de restauración ecológica, y aún para plantarse en jardines y calles. El objetivo del presente trabajo fue determinar las tasas de crecimiento en diámetro de algunas especies arbóreas caducifolias y perennifolias, dominantes en el bosque mesófilo de montaña de los alrededores de Xalapa, Veracruz. El crecimiento diamétrico anual de 29 especies arbóreas se midió durante cinco años en el bosque del Jardín Botánico Clavijero (112 individuos) y en el Parque Ecológico Clavijero (80 individuos), y durante un año en un bosque al norte de Banderilla (36 individuos). La tasa de crecimiento diamétrico de los árboles del bosque manejado en el Jardín Botánico (0.83 cm/año) fue significativamente mayor que la de los otros dos bosques naturales (0.29 cm/año), lo cual puede indicar el potencial de crecimiento de muchas especies. Además, la tasa de crecimiento diamétrico para el bosque natural es rápida en comparación con la estimada para otros bosques de montaña. Las especies con tasa de crecimiento más alta fueron Platanus mexicana, Quercus acutifolia, Cornus disciflora y Liquidambar styraciflua var. mexicana en el Jardín Botánico, y L. styraciflua var. mexicana, Q. xalapensis, Clethra mexicana y Q. acutifolia en el bosque natural. La tasa de crecimiento diamétrico para las especies caducifolias fue 0.94 cm/año en el Jardín Botánico y de 0.36 cm/año en el bosque natural, y para las especies perennifolias fue 0.60 y 0.15 cm/año, respectivamente.

Responses of photosynthetic parameters to differences in winter temperatures throughout a temperature gradient in two evergreen tree species

The temperature dependence of photosynthetic parameters has been a focus of interest during recent years owing to its profound implications in the new climate scenario. Many studies have addressed the short-term responses of photosynthetic parameters to temperature change. Less attention has been given to the intraspecific variability in the biochemical parameters of photosynthesis in response to differences in growth temperature. This study explores the effects of winter harshness on the leaf traits of two evergreen tree species (Quercus ilex and Q. suber). Leaf mass per unit area (LMA) and the concentrations of fiber, nitrogen (N), soluble protein, chlorophyll and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) were determined in both species throughout a temperature gradient. Several photosynthetic parameters [maximum carboxylation rate (V cmax), maximum light-driven electron flux (J max), day respiration rate (R d) and relative stomatal limitation to photosynthesis] were assessed by measuring leaf response curves of net CO2 assimilation versus intercellular CO2 partial pressure. LMA and structural carbohydrate concentrations increased with the decrease in winter temperatures, whereas N concentrations did not show definite patterns. Chlorophyll, soluble proteins, Rubisco, V cmax and J max declined with the decrease in winter temperatures, whereas R d at a set common temperature (25 °C) was higher at colder sites. Our results suggest that an increase in LMA and in the concentration of structural carbohydrates in cold environments is associated with a reduced N allocation to the photosynthetic machinery, which leads to reduced photosynthetic capacity.

Digital image analysis of different crown shape of Platycladus orientalis

Platycladus orientalis (L.) Franco is a beautifully crown-shaped evergreen tree species used for ornamental cultivation. These trees are also important afforestation plants at hill sites containing calcareous parent rocks and exhibit high tolerance to drought and barren sites. However, Platycladus orientalis trees with abnormal crowns, such as fusiform and torch-form, have been identified at sites with extreme drought and barren hills in Shandong, China, although the abnormal crowns does not reduce the ornamental value of these trees. In the present study, we used the RGB imaging and geographical statistical analyses through the construction of meteorological indices. The results indicate that variations of abnormal Platycladus orientalis crowns are associated with both the internal metabolism of these trees and the external environment. Crown shapes are strongly affected by the local dry, hot and windy meteorological environment, particularly individuals planted at poor hill site conditions. In response to extreme events of drought, high temperature and strong winds, the twigs and scale leaves of Platycladus orientalis typically wilt from the lower part to the upper part of the crown. The fusiform and torch-form crowns are formed through the wilting of partial twigs and scale leaves to avoid the entire wilt of the trees, thereby saving the life of the tree at the expense of partial twigs and scale leaves.

Nutrient-Induced Modifications of Wood Anatomical Traits of Alchornea lojaensis (Euphorbiaceae)

Regarding woody plant responses on higher atmospheric inputs of the macronutrients nitrogen (N) and phosphorous (P) on tropical forests in the future, an adaptive modification of wood anatomical traits on the cellular level of woody plants is expected. As part of an interdisciplinary nutrient manipulation experiment (NUMEX) carried out in Southern Ecuador, we present here the first descriptive and quantitative wood anatomical analysis of the tropical evergreen tree species Alchornea lojaensis (Euphorbiaceae). We sampled branch wood of nine individual trees belonging to treatments with N fertilization, N+P fertilization, and a control group, respectively. Quantitative evaluations of eleven different vessel parameters were conducted. The results showed that this endemic tree species will be able to adapt well to the future effects of climate change and higher nutrient deposition. This was firstly implied by an increase in vessel diameter and consequently a higher theo. area-specific hydraulic conductivity with higher nutrient availability. Secondly, the percentage of small vessels (0-20µm diameter) strongly increased with fertilization. Thirdly, the vessel arrangement (solitary vessels vs. multiple vessel groupings) changed towards a lower percentage of solitary vessel fraction (VS), and concurrently towards a higher total vessel grouping index (VG) and a higher mean group size of non-solitary vessels (VM) after N and N+P addition. We conclude that higher nutrient availability of N and N+P triggered higher foliage amount and water demand, leading to higher cavitation risk in larger vessels. This is counteracted by a stronger grouping of vessels with smaller risk of cavitation to ensure water supply during drier periods that are expected to occur in higher frequency in the near future.