Greater Stomatal Density Research Articles

In vitro culture of Campomanesia pubescens under different light qualities: a morphoanatomical and physiological characterization

Campomanesia pubescens (gabiroba) is a fruit tree that is native to the Cerrado and that has commercial potential and medicinal properties. It has recalcitrant seeds that do not tolerate desiccation and storage. Here, C. pubescens plants were grown in vitro under different light qualities. Light-emitting diodes (LEDs) were used at wavelengths for white (W) and blue in combination with red in the proportions BR (1:1), BR (1:3) and BR (3:1), at 100 ± 5 μmol m-2 s-1 over a 16-hour photoperiod. The leaf anatomy, chlorophyll a fluorescence, chloroplast pigments and malondialdehyde (MDA) content were evaluated. Studies on Cerrado plants grown in vitro focusing on light quality and its effects on plant development and growth are scarce. Records of anatomical and physiological C. pubescens characteristics when grown in vitro under different lighting qualities using LEDs are nonexistent. In this context, the aim of this study was to analyze the anatomical and physiological responses of C. pubescens seedlings from in vitro cultivation under different light qualities, to support future studies on the propagation and conservation of this species. This work is a pioneer for this species. When the plants were cultivated in combinations of blue/red LEDs 1:1 and 3:1, they yielded higher biomass, presenting higher epidermis and chlorenchyma values with greater stomatal density and functionality, better photosynthetic efficiency, higher Y(II) values, qP and higher total chlorophyll concentrations, and thus these lights did not cause oxidative damage compared to the white (control) LEDs. This study contributed to a better understanding of the anatomical and physiological changes in C. pubescens plants grown in vitro under different light qualities. C. pubescens plants exhibited varied anatomical and physiological characteristics depending on the spectrum of light used here. The combinations of BR (1:1) or BR (3:1) LEDs are promising for the propagation of the species, given their positive influence on most of the studied traits.

Effects of elevation on growth, photosynthetic and Ni-accumulation responses in Bornmuellera emarginata (Brassicaeae)

Bornmuellera emarginata is a Balkan Ni-hyperaccumulator indicated as a promising candidate for agromining practices. Here, two elevation-contrasting accessions (250 m, Low Elevation plants LE, and at 1600 m, High Elevation plants, HE) were compared in terms of growth, photosynthetic activity, and Ni accumulation in controlled conditions to assess possible differences exploitable in practical applications. After two months of pot cultivation on garden and serpentine soil, plant biomass, gas exchanges and Ni concentrations were evaluated. A hydroponic trial with increasing NiSO4 concentration was performed to evaluate Ni tolerance and accumulation.Plants grown on serpentine soil showed reduced biomass as compared to those from garden soil, without any difference between LE and HE. In both accessions, growth in serpentine soil resulted in photochemical/biochemical limitations and reduction in stomatal conductance, especially in LE. HE showed low stomatal conductance in all the conditions, despite a greater stomatal density. Shoot Ni accumulation was higher in HE (∼1600 µg Ni g−1 d.w. and 1200 µg Ni g−1 d.w. in HE and LE respectively), thus resulting in a significantly higher metal content per plant in respect to LE (∼120 and ∼85 µg plant−1 in HE and LE respectively). In hydroponics, HE possessed higher Ni tolerance and accumulation in respect to LE.In conclusion underlying the higher shoot metal amount of HE, Ni tolerance seemed to play a pivotal role, overtaking possible negative effects of reduced transpiration rates compared to LE. Our results point to the opportunity of exploring and exploiting the variation in accumulation level among B. emarginata accessions for the implementation of environmental restoration and metal cropping practices.

Combined application of biochar and partial root-zone drying irrigation improves water relations and water use efficiency of cotton plants under salt stress

Reduced irrigation in combination with biochar application can improve stomatal anatomy, water relations and intrinsic water use efficiency (WUEi), thus having a positive effect on the alleviation of salinity and drought stresses. A split-root pot experiment was executed to explore the effects of two biochar applications (WSP: wheat straw biochar; SWP: soft wood biochar) in combination with three irrigation strategies (FI: full irrigation; DI: deficit irrigation, PRD: partial root-zone drying irrigation) on stomatal anatomy, water relations and WUEi of cotton plants under normal soil (S0, EC=0.36 dS m-1) and saline soil (S1, EC=16.55 dS m-1). The results revealed that both salinity and drought stresses negatively affected plant water relations and reduced stomatal conductance, carbon isotope discrimination (Δ13C), stomatal size (SS) and hydraulic conductance (Kl) while increased leaf abscisic acid (ABA) concentration ([ABA]leaf). However, biochar amendment under salt stress significantly decreased [ABA]leaf while improved leaf water relations, increased Kl, stomatal density (SD), SS, Δ13C and maximum stomatal conductance (gsmax). Meanwhile, compared with FI and DI, PRD plants had greater SD, gsmax, and WUEi but lowered stomatal conductance (gs). Among all treatments, the combined application of WSP and PRD significantly increased SD and gsmax, improved leaf water relations, Kl and [ABA]leaf and WUEi. It is concluded that the altered stomatal features caused by the biochar and irrigation treatments are associated with changes in [ABA]leaf and Kl, and have a major role in affecting plant hydraulic integrity and water use efficiency of cotton exposed to salinity stress.

Functional traits underlie specialist-generalist strategies in whitebark pine and limber pine

Plant species life history strategies are described by functional variation spanning an acquisitive and conservative resource use continuum. Specialist species can exhibit traits promoting one end of the continuum, while generalist species can display traits promoting both acquisitive and conservative resource use. Whitebark pine (Pinus albicaulis, PIAL) and limber pine (Pinus flexilis, PIFL) are two high-elevation pines that have similar growth and morphology, yet contrasting elevational distributions with PIAL viewed as a specialist inhabiting a narrower elevation range, and PIFL as a generalist inhabiting a broader elevation range. We compared the physiological and morphological traits of greenhouse-grown 5-year-old PIAL and PIFL. Our results suggest that PIFL’s acquisitive and conservative resource use traits contribute to its generalist strategy and ability to inhabit a greater range of elevations than PIAL. PIFL had greater acquisitive resource use traits including: high-light tolerance (greater Qsat, greater fascicle density), increased biomass allocation to photosynthetic tissue (higher needle biomass, aboveground:belowground biomass, needle:branch + stem biomass), and higher C and water uptake (greater stomatal density and size, higher C assimilation rate), as well as greater conservative resource use traits including: greater physical stress resistance (shorter height, higher stem and branch diameters, greater branch and stem diameter:length), drought tolerance (higher SWC, leaf starch proportion), and drought avoidance (earlier budburst phenology, smaller hydroscape area) than PIAL. Our results suggest that PIFL may make more efficient use of high-light loads and maximize C and water uptake when moisture is abundant during spring snowmelt before the onset of dry summer conditions. Other conservative resource use traits describing cold tolerance, heat tolerance, and drought tolerance did not differ between species, suggesting that both species exhibit traits that promote similar conservative resource use enabling their overlapping persistence at higher elevations. Comparing the physiology of PIAL and PIFL within the same environment enables us to identify physiological mechanisms that underlie species establishment and survival, and how juvenile physiology contributes to their contrasting distributions and their generalist-specialist strategies.

Stem and leaf functional traits allow successional classification in six pioneer and non-pioneer tree species in Tropical Moist Broadleaved Forests

More than half of the tropical forests are secondary forests that are undergoing a highly dynamic interplay of forest succession of uncertain outcome. Vegetation models can help predict forest trajectory but require simplifying the high biodiversity of these forests into a few distinct classes of functional or successional groups. The classification of tree species by successional groups has traditionally relied on qualitative criteria such as life span, or on parameters that are difficult to measure on mature trees in the field, like photosynthetic activity, in particular in tropical forests. Hence, quantitative traits that can be easily measured in a number of species may provide more accurate classification thresholds. The present study identifies quantitative anatomical and biochemical traits of leaf and stem of six species that are useful for classification of successional groups in the Tropical Moist Broadleaved Forest (TMBF) of south-eastern Brazil. Consistent with assumed fast growth and high light requirements of pioneers the investigated pioneer species presented higher stem glucose content (600%), larger vessel elements (162%), greater stomatal density (72%) and higher chloroplastic pigments concentrations (90%) than non-pioneer species. By contrast, non-pioneers were characterized by larger mesophyll cells (70%) and higher cell wall polymers concentrations (65–100%) in leaf and stem. The biggest differences between pioneer and non-pioneer species were observed in leaf blade thickness, followed by vessel lumen diameter, and stem lignin. We provide research laboratories a variety of different tools that they can use as a guideline to accurately assess the successional class of tree species in the TMBF of south-eastern Brazil.

Subtle precipitation differences yield adaptive adjustments in the mesic Nothofagus dombeyi

Climate change is impacting on natural systems and forests worldwide have suffered from massive mortality due to extreme droughts. That is the case of mesic Nothofagus dombeyi forests of northern Patagonia, whereas no climate-driven mortality was recorded towards drier areas. The aim was to examine population differences in relation to a small precipitation gradient at morphological, physiological, and genetic scales. Adaptive differences between seedlings collected from dry and mesic sites of N. dombeyi on the eastern slopes of the Andes were studied combining common garden and water stress manipulative experiments with genomic analyses. We recorded mortality, plant architectural and leaf traits during cultivation in the greenhouse. A set of plants were subjected to water deficit experiments and water potential was measured. Genomic differences were analyzed by Single Nucleotide Polymorphisms (SNPs). Plants from the mesic site grew taller with more branches and number of larger leaves, and greater stomatal density under optimum conditions yet with slightly more negative midday water potentials due to induced desiccation. Adaptive SNPs yielded similar divergence than quantitative traits which were greater than that of neutral SNPs. Five adaptive loci had a significant association to whole plant and leaf traits. These results show that in spite of the small climatic differences between sites and continuous gene flow populations showed adaptive adjustments and differed significantly in growth, ecophysiology, and genetically. This information can be used in climate-oriented restoration efforts.

Acclimatization capacity of leaf traits of species co-occurring in restinga and seasonal semideciduous forest ecosystems

Restingas and seasonal semideciduous forests (SSF) are phytophysiognomies of the Atlantic Forest that have many co-occurring species. However, the microclimatic and edaphic conditions of these phytophysiognomies are quite different. Restingas are characterized by low water availability, high irradiance and temperatures, and sandy and nutrient poor soil, which contrasts with the soil conditions of forests. In this sense, these environmental divergences would have forced species to become acclimatized in order to co-occur in these two distinct environments. The present study aimed to determine the main functional leaf traits that enabled Maytenus obtusifolia, Manilkara subsericea and Inga laurina to co-occur in both restinga and SSF. Morphological, physiological, nutritional and biochemical traits of the leaves of these three species in the restinga and SSF were analyzed. The results showed that in the restinga the species possess thicker leaves with a greater thickening of mesophyll cells; the adaxial and abaxial epidermis and cuticle. In addition, restinga leaves had higher specific leaf mass and greater stomatal density, as well as less leaf area than species in the SSF. The restinga species invested in the biosynthesis of osmoregulatory and photoprotective molecules. Photosynthetic performance was similar between phytophysiognomies for M. obtusifolia and M. subsericea, but I. laurina had lower photosynthetic performance in the restinga. We conclude that the species invested in structural, physiological and biochemical adjustments in the restinga in response to conditions of low water availability and high irradiance.

LEAF MORPHOLOGY AND ANATOMY OF JACQUINIA ARMILLARIS JACQ. (PRIMULACEAE) FROM TWO COASTAL RESTINGA ENVIRONMENTS

Jacquinia armillaris occurs in post-beach and rocky outcrops environments, which led to hypothesize that they are morphological and anatomical plasticity in its leaves to inhabit these two coastal formations. Anatomical, histochemical and micromorphometric analyzes were performed to understand the leaf plasticity. The leaf lamina is dorsiventral and hypostomatic, with glandular trichomes. The epidermis is uniseriate, possesses anomocytic stomata and is covered by a thick cuticle and epicuticular wax. The post-beach formation plants had the higher stomatal index and greater stomatal density, however, there are higher leaf size and glandular trichomes density in the rocky outcrop plants. The glandular trichomes are similar in structure to salt glands and may serve to reduce the impact of the local salinity. At first, the two environments present typical coastal environmental conditions, however, specific local characteristics were sufficient to trigger anatomic and morphologic plasticity, particularly associated with the distribution of stomata and leaf size.

Ultraviolet-A Radiation Stimulates Growth of Indoor Cultivated Tomato (Solanum lycopersicum) Seedlings

Ultraviolet-A (UV-A) is the main component of UV radiation in nature. However, its role on plant growth, to a large extent, remains unknown. In this study, tomato (Solanum lycopersicum ‘Beijing Cherry Tomato’) seedlings were cultivated in an controlled environment in which UV-A radiation was provided by UV-A fluorescent lamps (λmax = 369 nm) with a fluence rate of 2.28 W·m−2. The photoperiod of UV-A radiation was 0, 4, 8, and 16 hours, which corresponds to control, UV-A4, UV-A8, and UV-A16 treatments, respectively. The photosynthetic photon flux density (PPFD) was 220 μmol·m−2·s−1, which was provided by light-emitting diodes (LEDs) with a blue/red light ratio of 1:9, the photoperiod of PPFD was 16 hours. We showed that supplementing 8 and 16 hours of UV-A to visible radiation (400–700 nm) stimulated plant biomass production by 29% and 33%, respectively, compared with that of control. This resulted mainly from larger leaves (i.e., 22% and 31% in 8 and 16 hours UV-A, respectively), which facilitated light capture. Supplemental UV-A also enhanced photosynthetic capacity, as indicated by greater net photosynthesis rates in response to CO2 under saturating PPFD. Furthermore, the greatest stomatal conductance (gS) value was observed in UV-A16, followed by UV-A8, which correlated with the greater stomatal density in the corresponding treatments. Moreover, supplemental UV-A did not induce any stress, as the maximum quantum efficiency of photosynthetic system II (PSII) (Fv/Fm) remained ≈0.82 in all treatments. Similarly, chlorophyll content and leaf mass area (LMA) were also unaffected by UV-A radiation. Taken together, we conclude that supplementing reasonable levels of UV-A to visible radiation stimulates growth of indoor cultivated tomato seedlings.

Physiological activity and biomass production in crop canopy under a tropical environment in soybean cultivars with temperate and tropical origins

In order to explore the plant factors facilitating better adaptation of soybean to high temperatures, genotypic variability till the beginning of seed filling (R5) were examined with reference to biomass production, relative transpiration activity and relevant plant factors under a tropical environment. Twenty-nine (in 2014 and 2015) and 20 (in 2016) soybean cultivars of temperate (Japan and USA) and tropical (Indonesia-old, Indonesia-modern, and Others) origin were grown in Serang, Banten (2014 and 2015; Experiment 1) and in Bogor, West Java (2016; Experiment 2), Indonesia. In Experiment 1, aboveground biomass at R5 (TDWR5) of the temperate cultivars was one-third to one-fourth of that of the tropical cultivars. This was associated with less than half the amount of the cumulative intercepted radiation to R5 (CIRR5) due to their shorter growth duration and lower value of the mean fraction of canopy light interception till R5 (mean FVE-R5). In addition, the radiation use efficiency (RUE) at R5 of the temperate cultivars was also as low as 0.54gMJ−1, as compared to 0.87gMJ−1 in the tropical cultivars. The value of canopy temperature minus air temperature (CTd), as an indicator of relative transpiration activity, of temperate cultivars was markedly larger than that of the tropical cultivars, indicating lower transpiration activity in temperate cultivars, which was associated with the low RUE. In Experiment 2, greater activity of transpiration in tropical cultivars was attributed to their higher stomatal conductance (gs) and greater stomatal density (Nstoma) of upper leaves than that in those from the temperate regions. These results indicate that low biomass production in temperate cultivars occurs not only due to the cumulative intercepted radiation in the canopy but also due to low RUE and that the low RUE in temperate cultivars is associated with low gas exchange activity, in which leaf morphological traits are involved. Within temperate cultivars, US cultivars tended to perform better than the Japanese cultivars with respect to gas exchange activity.

Mechanisms of resistance in Brassica carinata, B. napus and B. juncea to Pseudocercosporella capsellae

Studies were undertaken to compare susceptible and resistant host responses to Pseudocercosporella capsellae in cotyledons of Brassica carinata, B. juncea and B. napus in order to define the mechanisms of resistance in these three species. On both resistant and susceptible hosts, hyphal penetration was always through stomatal openings and without infection pegs or appressoria. On resistant B. carinata ATC94129P, up to 72% of spores disintegrated and, generally, germination (<22%) and germ tube lengths (<25 μm) were comparatively low. Resistant B. napus Hyola 42 had the lowest germination (8%) and susceptible B. carinata UWA#012 had the highest (51%). On resistant B. carinata ATC94129P, germ tube extension was impeded across 24–60 h post‐inoculation (hpi) and percentage stomatal penetration lower (4%) at 60 hpi compared with susceptible B. carinata UWA#012 (26%). Stomatal densities (stomata/14 757 μm2) on resistant B. juncea Dune (2·12) and B. napus Hyola 42 (1·62) were lower than for susceptible B. juncea Vardan (2·40) and B. napus Trilogy (2·03). Resistant B. carinata ATC94129P had greater stomatal density (1·89) than susceptible B. carinata UWA#012 (1·58). Overall, B. juncea had greater stomatal density (2·26) compared with B. napus (1·83) and B. carinata (1·74). In resistant B. carinata ATC94129P, P. capsellae induced 28% stomata to close, while in susceptible B. carinata UWA#012 no such closure was induced. Epicuticular wax crystalloids were present only on resistant B. carinata ATC94129P and probably also contribute towards resistance.

Effects of temperature on leaf hydraulic architecture of tobacco plants

Modifications in leaf anatomy of tobacco plants induced greater leaf water transport capacity, meeting greater transpirational demands and acclimating to warmer temperatures with a higher vapor pressure deficit. Temperature is one of the most important environmental factors affecting photosynthesis and growth of plants. However, it is not clear how it may alter leaf hydraulic architecture. We grew plants of tobacco (Nicotiana tabacum) 'k326' in separate glasshouse rooms set to different day/night temperature conditions: low (LT 24/18 °C), medium (MT 28/22 °C), or high (HT 32/26 °C). After 40 days of such treatment, their leaf anatomies, leaf hydraulics, photosynthetic rates, and instantaneous water-use efficiency (WUEi) were measured. Compared with those under LT, plants exposed to HT or MT conditions had significantly higher values for minor vein density (MVD), stomatal density (SD), leaf area, leaf hydraulic conductance (K leaf), and light-saturated photosynthetic rate (A sat), but lower values for leaf water potential (ψ l) and WUEi. However, those parameters did not differ significantly between HT and MT conditions. Correlation analyses demonstrated that SD and K leaf increased in parallel with MVD. Moreover, greater SD and K leaf were partially associated with accelerated stomatal conductance. And then stomatal conductance was positively correlated with A sat. Therefore, under well-watered, fertilized conditions, when relative humidity was optimal, changes in leaf anatomy seemed to facilitate the hydraulic acclimation to higher temperatures, meeting greater transpirational demands and contributing to the maintenance of great photosynthetic rates. Because transpiration rate increased more with temperature than photosynthetic rate, WUEi reduced under warmer temperatures. Our results indicate that the modifications of leaf hydraulic architecture are important anatomical and physiological strategies for tobacco plants acclimating to warmer temperatures under a higher vapor pressure deficit.

English

This study aimed to evaluate  the effect of spectral light quality on different anatomical features of banana tree plantlets grown under coloured shade nets. Banana plants of five genotypes (Maçã, Thap Maeo, Caipira, BRS Platina and Princesa), obtained from micropropagation, were grown under white, blue, red and black nets, with shade of 50%, in a completely randomized design. After 90 days of acclimatization under nets, the leaves were collected and analyzed anatomically following basic protocol of plant microtechnique. Cultivation under white net provided greater thickness of epidermis cells, hypodermis on the adaxial face and palisade parenchyma; and greater stomatal density on the adaxial face; both the red and white nets, however, increased stomatal density on the abaxial face. The use of white net, during the acclimatization phase, is recommended  for cultivation of banana plantlets obtained of micropropagation.   Key words: Musa sp., acclimatization, spectral quality, anatomical plasticity.

Effects of soil water deficits on three genotypes of potted Campanula medium plants during bud formation stage

Abstract: Potted ornamental plants are often exposed to drought stress during shipping and retailing, which decreases the value and postharvest quality. Thus, selection of genotypes which can better withstand soil water deficits is essential for sustainable production. Here, the response of three genotypes of potted Campanula medium (denoted as G100, G102 and G104) to progressive soil drying was investigated and their post-production performance was evaluated for four weeks. The potted plants were grown in a climate controlled greenhouse and were either well-watered (W) or drought-stressed (D) at floral bud formation stage. Soil water status was expressed as the fraction of transpirable soil water (FTSW). In the D pots, FTSW declined fastest in G100, followed by G102, and slowest in G104 after withholding irrigation. In the W plants, stomatal conductance ( g s ) was similar among the three genotypes, whereas transpiration rate ( T ) differed significantly among genotypes and was highest for G100, intermediate for G102, and lowest for G104. Estimated by a linear-plateau model, g s and T of G100 started to decrease at significantly higher FTSW thresholds than did G102 and G104. An earlier closure of stomata and decrease of T in G100 would allow the plant to conserve water in the soil; however, owing to its putative larger leaf area and greater stomatal density on the adaxial leaf surface, G100 quickly depleted soil water and resulted in severe drought stress to the plants as exemplified by the significantly lowered g s , leaf area, and relative water content (RWC). In contrast, a smaller leaf area and a lower stomatal density on the adaxial leaf surface of G104 enabled the plants to slowly deplete soil water and maintain high g s , T , leaf area, and RWC 8 days after withholding irrigation. Coincided with these, the floral bud abortion rate in the D plants was significantly higher for G100 as compared with G102 and G104. It is concluded that in potted ornamentals, a low transpiration rate, hereby a slow rate of soil water depletion, is crucial for maintaining postharvest quality under drought stress.

Anatomical and morphological characteristics of <I>Populus euphratica</I> in the lower reaches of Tarim River under extreme drought environment

Populus euphratica Oliv. is an old desert tree species that has been naturalized and invades zones along the watercourses in many arid and semiarid regions. The plant species developed some plasticity to adapt to the gradual environmental gradients. The aim of this study was to test the hypothesis that the changes in leaf morphology of P. euphratica reflect the adaptability of the plant to the unique environment of the lower reaches of Tarim River in China. The foliar architecture, blade epidermal and internal anatomies of P. euphratica were ana- lyzed at different sites along the Tarim River. Compared with the abaxial surface of the leaves, their adaxial surface has more hairs, a greater stomatal density and opening, higher mesophyll proportion, and increased blade thick- ness, palisade width, and epidermal thickness. The long trichome of the roots found at site 6 in the Yinsu section may be an adapted structure of the plants in arid areas. The mature leaves of P. euphratica have comparatively more epidermis and cuticles, well developed palisades and more chloroplasts at different sites compared to the young leaves. Foliar morphological and anatomical variability in P. euphratica may be considered an adaptive ad- vantage that enables leaves to develop and function in different habitats, marked by strong variations in solar ra- diation, air temperature, humidity and water table.

Variation in Anatomical Characteristics in Leaves of Pecan Seedstocks from Mexico and the United States

Leaf anatomical traits of Mexican and U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] seedstocks grown in a single location were studied to determine patterns of ecogeographic variation within the natural range. Stomatal density was uniform among open-pollinated seedlings of a common maternal parent with twofold differences in stomatal density separating some seedstocks. There was an inverse relationship between stomatal density and epidermal cell density. Stomatal density and stomatal index of Mexican seedstocks were related to longitude and annual precipitation of origin. Stomatal density increased along the longitudinal gradient toward the east coast of Mexico; seedstocks originating from areas on the east coast of Mexico had greater stomatal density than seedstocks originating from the drier areas on the west coast. Stomatal density and stomatal index did not follow a pattern along latitude or longitude in the U.S. seedstocks. Although isotopic carbon (13C) discrimination did not vary greatly in Mexican seedstocks, the reduction in stomatal density in pecan trees from areas with reduced annual precipitation suggest the presence of an anatomical feature to reduce water losses.

Light intensity influences variations in the structural and physiological traits in the leaves of Iris pumila L.

Ambient light significantly influences the structural and physiological characteristics of Iris pumila leaves. A random sample of Iris clones native to an exposed site at the Deliblato Sands, Serbia was partially covered with a neutral screen that transmitted 35% of daylight, so that each clone experienced reduced and full sunlight at the same time. The sun-exposed leaves were significantly thicker, had greater stomatal density, exhibited higher lipid peroxidation, increased activities of SOD, APX, CAT enzymes and higher contents of non-enzymatic antioxidants (anthocyanins and phenols) and water deficit relative to shade-leaves. The activities of GR, GPX, and GST enzymes was unaffected by the irradiance level.

Effects of drought and changes in vapour pressure deficit on water relations of Populus deltoides growing in ambient and elevated CO2

The means by which growth CO(2) concentration ([CO(2)]) affects anatomy and water relations responses to drought and vapour pressure deficit (VPD) were studied for yearly coppiced, 4-year-old Populus deltoides clones that were grown in either 400 mumol mol(-1) (ambient) or 800 mumol mol(-1) (elevated) CO(2) for 3 years. It was hypothesized that, during drought, trees growing in elevated [CO(2)] would have a lower volume flux density of water (J(V)), stomatal conductance (g(s)) and transpiration per leaf area (E), as well as a lower stomatal density and a greater stomatal response to drought and changes in VPD than would trees in ambient [CO(2)]. Trees in elevated [CO(2)] actually had higher J(V) values throughout the study, but did not differ from trees in ambient [CO(2)] with respect to g(s) or E under saturating light or E scaled from J(V) (E(scaled)), all of which indicates that the higher J(V) in elevated [CO(2)] resulted from those trees having greater leaf area and not from differences in g(s). Furthermore, although plants in elevated [CO(2)] had greater absolute leaf loss during the drought, the percentage of leaf area lost was similar to that of trees in ambient [CO(2)]. g(s) and E under saturating light were affected by changes in VPD after the first 9 days of the experiment, which coincided with a large decrease in water potential at a soil depth of 0.1 m. Trees in elevated [CO(2)] had a greater stomatal density and a lower wood density than trees in ambient [CO(2)], both traits that may make the trees more susceptible to xylem cavitation in severe drought. Drought and VPD effects for the P. deltoides clone were not ameliorated by long-term growth in elevated [CO(2)] compared with ambient [CO(2)], and plants in elevated [CO(2)] possessed anatomical traits that may result in greater stress associated with long-term drought.

Variation in needle-trace diameter in respect of needle morphology in five conifer species

Needle traces have been used for revealing historical changes in needle longevity of Pinus sylvestris L. and Picea abies (L.) H. Karst. In this paper we compared the needle-trace diameter of five conifer species [Abies sibirica Ledeb., Picea abies, Pinus sylvestris, Pseudotsuga menziesii (Mirb.) Franco and Taxus baccata L.] in respect of needle size. In case of P. sylvestris, we studied how needle-trace diameter varied among different growing sites and among different shoots within a site, and related that variation to needle morphology and structure. Pinus sylvestris had the greatest diameter of needle traces (mean±SD =233±30 μm) followed by T. baccata (141±19 μm) and P. menziesii (121±30 μm). The smallest needle-trace diameter was in A. sibirica (85±21 μm) and P. abies (80±18 μm). Among species, the needle-trace diameter was strongly correlated with needle length (r =0.93, P <0.05). Within P. sylvestris, the needle-trace diameter was significantly affected by location (P <0.001) and varied significantly among shoots within a location (P <0.001). The shoots of P. sylvestris which had greater average diameter of needle traces, tended to have longer (r =0.36, P <0.05), wider (r =0.55, P <0.05) and heavier (r =0.64, P <0.05) needles with greater stomatal density (r =0.55, P <0.05). Although our results do not allow the use of needle-trace diameter to predict properties of needle structure at the present stage, they nevertheless indicate general trends and point to a need for further studies.

Developmental Light Level Affects Growth, Morphology, and Leaf Physiology of Young Carambola Trees

Growth and leaf physiology responses of container-grown `Arkin' carambola (Averrhoa carambola L.) trees to long-term exposure of ≈25%, ≈50%, or 100% sunlight were studied in four experiments in Guam and Florida. Shading increased rachis length and leaflet area, and decreased leaflet thickness. Shaded trees also had a more horizontal branch orientation. Shading reduced dark respiration (Rd) and light compensation and saturation points but increased chlorophyll concentration and N-use efficiency. Light-saturated net CO2 assimilation (A) was not affected by developmental light level. Trees in full sun had smaller total leaf area, canopy diameter, and shoot: root ratio and exhibited leaflet movement to avoid direct solar radiation. Also, trees grown in 100% sunlight had a more vertical branch orientation and greater stomatal density than shaded trees. The ratio of variable to maximum fluorescence (Fv/Fm) declined during midday in 100% sunlight trees. This pattern was accompanied by a midday suppression of A in 100% sunlight-grown trees in Guam. `Arkin' carambola trees exposed to ≈25%, ≈50%, or 100% sunlight for up to 39 weeks exhibited physiological and morphological adaptations that resulted in similar growth. These results indicate that carambola efficiently adapts to different developmental light intensities.