Ornithophily for the nonspecialist: Differential pollination efficiency of the Macaronesian island paleoendemic Navaea phoenicea (Malvaceae) by generalist passerines.

PREMISE OF THE STUDY: A bird pollination syndrome exists in the Canary Islands archipelago across independent plant lineages despite the absence of specialist birds. The pollination efficiency of current floral visitors remains unknown for many plant species despite this being a fundamental factor in testing hypotheses about the origin of the syndrome. Here, we studied the components of pollination efficiency in the paleoendemic Navaea phoenicea, a species exhibiting conspicuous anatomical modifications associated with bird pollination. METHODS: We measured the components of the pollination efficiency (PE) of species foraging on flowers. The measured quantitative components were visitation frequency patterns to plants and individual flowers. The qualitative components were the contributions to the fitness of male and female functions (pollen removal and deposition and fruit set). KEY RESULTS: Pollination by warbler species was highly efficient, but visit frequency was low; conversely, Canarian chiffchaffs had high visit frequency and low efficiency. Overall PE was almost 0 for blue tits due to disruptive behavior. We also found insects acting as nectar robbers. CONCLUSIONS: Pollination efficiency of three of the four bird species visiting flowers of Navaea phoenicea may be high enough to maintain selective pressure on floral traits of a relict pollination syndrome. The behavior of these birds plays a crucial role in their pollination efficiency. Perching, by generalist passerines when visiting N. phoenicea flowers, is the most efficient habit. The frequency and PE of insect visits calls into question their role as legitimate visitors.

Comparative performance of three experimental hut designs for measuring malaria vector responses to insecticides in Tanzania.

BACKGROUND: Experimental huts are simplified, standardized representations of human habitations that provide model systems to evaluate insecticides used in indoor residual spray (IRS) and long-lasting insecticidal nets (LLINs) to kill disease vectors. Hut volume, construction materials and size of entry points impact mosquito entry and exposure to insecticides. The performance of three standard experimental hut designs was compared to evaluate insecticide used in LLINs. METHODS: Field studies were conducted at the World Health Organization Pesticide Evaluation Scheme (WHOPES) testing site in Muheza, Tanzania. Three East African huts, three West African huts, and three Ifakara huts were compared using Olyset(®) and Permanet 2.0(®) versus untreated nets as a control. Outcomes measured were mortality, induced exophily (exit rate), blood feeding inhibition and deterrence (entry rate). Data were analysed using linear mixed effect regression and Bland-Altman comparison of paired differences. RESULTS: A total of 613 mosquitoes were collected in 36 nights, of which 13.5% were Anopheles gambiae sensu lato, 21% Anopheles funestus sensu stricto, 38% Mansonia species and 28% Culex species. Ifakara huts caught three times more mosquitoes than the East African and West African huts, while the West African huts caught significantly fewer mosquitoes than the other hut types. Mosquito densities were low, very little mosquito exit was measured in any of the huts with no measurable exophily caused by the use of either Olyset or Permanet. When the huts were directly compared, the West African huts measured greater exophily than other huts. As unholed nets were used in the experiments and few mosquitoes were captured, it was not possible to measure difference in feeding success either between treatments or hut types. In each of the hut types there was increased mortality when Permanet or Olyset were present inside the huts compared to the control, however this did not vary between the hut types. CONCLUSIONS: Both East African and Ifakara huts performed in a similar way although Ifakara huts allowed more mosquitoes to enter, increasing data power. The work convincingly demonstrates that the East African huts and Ifakara huts collect substantially more mosquitoes than the West African huts.

Strength through unity: spatial affinity between morphs improves fitness in incompatible heterostylous Melochia (Malvaceae) species.

In heterostylous plants, both stylar polymorphism and incompatibility system favor legitimate pollination among individuals. Weak or partial expression of incompatibility may ensure progeny when mates or pollinators are scarce in unstable habitats, but under these conditions plants with heteromorphic incompatibility would be in disadvantage. In this work we determine how the spatial distribution of morphs and the effect of proximity to the nearest potential mates affect plants' reproductive output in four Melochia species. The general prediction of decreasing reproductive success with an increasing isolation of floral morphs in plants with heteromorphic incompatibility was corroborated only in one species (i.e. M. tomentosa). Meanwhile, the other species exhibit a spatial affinity between morphs (i.e. the number of individuals with the nearest neighbor of the opposite morph exceeds expectations upon a random distribution). For M. savannarum and M. villosa we could not detect any effect of proximity to potential mates on the seed-ovule ratio. This may be due to: (1) existence of pollinators with long flying distances, like butterflies, in the populations and/or, (2) the possible occurrence of resource limitation. Spatial affinity between morphs in populations of heterostylous plants with heteromorphic incompatibility system increases reproductive success and may facilitate colonization of ephemeral habitats.

Physiological responses of Kosteletzkya virginica to coastal wetland soil.

Effects of salinity on growth and physiological indices of Kosteletzkya virginica seedlings were studied. Plant height, fresh weight (FW), dry weight (DW), and net photosynthetic rate (Pn) increased at 100 mM NaCl and slightly declined at 200 mM, but higher salinity induced a significant reduction. Chlorophyll content, stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration rate (E) were not affected under moderate salinities, while markedly decreased at severe salinities except for the increased Ci at 400 mM NaCl. Furthermore, no significant differences of Fv/Fm and ΦPSII were found at lower than 200 mM NaCl, whereas higher salinity caused the declines of Fv/Fm, ΦPSII, and qP similar to Pn, accompanied with higher NPQ. Besides, salt stress reduced the leaf RWC, but caused the accumulation of proline to alleviate osmotic pressure. The increased activities of antioxidant enzymes maintained the normal levels of MDA and relative membrane permeability. To sum up, Kosteletzkya virginica seedlings have good salt tolerance and this may be partly attributed to its osmotic regulation and antioxidant capacity which help to maintain water balance and normal ROS level to ensure the efficient photosynthesis. These results provided important implications for Kosteletzkya virginica acting as a promising multiuse species for reclaiming coastal soil.

Antioxidant enzyme activities and hormonal status in response to Cd stress in the wetland halophyte Kosteletzkya virginica under saline conditions.

Salt marshes constitute major sinks for heavy metal accumulation but the precise impact of salinity on heavy metal toxicity for halophyte plant species remains largely unknown. Young seedlings of Kosteletzkya virginica were exposed during 3 weeks in nutrient solution to Cd 5 µM in the presence or absence of 50 mM NaCl. Cadmium (Cd) reduced growth and shoot water content and had major detrimental effect on maximum quantum efficiency (F(v) /F(m) ), effective quantum yield of photosystem II (Y(II)) and electron transport rates (ETRs). Cd induced an oxidative stress in relation to an increase in O(2) (•-) and H(2) O(2) concentration and lead to a decrease in endogenous glutathione (GSH) and α-tocopherol in the leaves. Cd not only increased leaf zeatin and zeatin riboside concentration but also increased the senescing compounds 1-aminocyclopropane-1-carboxylic acid (ACC) and abscisic acid (ABA). Salinity reduced Cd accumulation already after 1 week of stress but was unable to restore shoot growth and thus did not induce any dilution effect. Salinity delayed the Cd-induced leaf senescence: NaCl reduced the deleterious impact of Cd on photosynthesis apparatus through an improvement of F(v) /F(m) , Y(II) and ETR. Salt reduced oxidative stress in Cd-treated plants through an increase in GSH, α-tocopherol and ascorbic acid synthesis and an increase in glutathione reductase (EC 1.6.4.2) activity. Additional salt reduced ACC and ABA accumulation in Cd+NaCl-treated leaves comparing to Cd alone. It is concluded that salinity affords efficient protection against Cd to the halophyte species K. virginica, in relation to an improved management of oxidative stress and hormonal status.

Biochar mitigates negative effects of salt additions on two herbaceous plant species.

Addition of pyrolyzed biomass ("biochar") to soils has commonly been shown to increase crop yields and alleviate plant stresses associated with drought and exposure to toxic materials. Here we investigate the ability of biochar (at two dosages: 5 and 50 t ha(-1)) to mitigate salt-induced stress, simulating road salt additions in a factorial glasshouse experiment involving the broadleaved herbaceous plants Abutilon theophrasti and Prunella vulgaris. Salt additions of 30 g m(-2) NaCl to unamended soils resulted in high mortality rates for both species. Biochar (Fagus grandifolia sawdust pyrolyzed at 378 °C), when applied at 50 t ha(-1) as a top dressing, completely alleviated salt-induced mortality in A. theophrasti and prolonged survival of P. vulgaris. Surviving A. theophrasti plants that received both 50 t ha(-1) biochar and salt addition treatments showed growth rates and physiological performance similar to plants without salt addition. Biochar treatments alone also substantially increased biomass of P. vulgaris, with a ∼50% increase relative to untreated controls at both biochar dosages. Biochar did not significantly affect photosynthetic carbon gain (Amax), water use efficiency, or chlorophyll fluorescence (Fv/Fm) in either species. Our results indicate that biochar can ameliorate salt stress effects on plants through salt sorption, suggesting novel applications of biochar to mitigate effects of salinization in agricultural, urban, and contaminated soils.

Evidence for leaf fold to remedy the deficiency of physiological photoprotection for photosystem II.

An interesting phenomenon is that some light-demanding plants fold their leaves when exposed to high light. Since high light could induce selective photodamage to photosystem II (PSII), we suggest that the leaves fold themselves to diminish the absorption of light energy and remedy the deficiency of physiological photoprotection for PSII. To test this hypothesis, we determined light responses of non-photochemical quenching (NPQ) and cyclic electron flow (CEF) and the effect of high light on PSII activity in Microcos paniculata (non-foldable species) and Bauhinia tenuiflora (foldable species). Under high light B. tenuiflora showed much lower NPQ and CEF than M. paniculata. Meanwhile, the excess light energy that cannot be harmlessly dissipated in B. tenuiflora was more compared with that in M. paniculata. After exposure to a high light of 1,900 µmol photons m(-2) s(-1) for 2 h, the maximum quantum yield of PSII, as estimated by variable to maximal fluorescence (F (v) /F (m)) decreased from 0.7 to 0.52 in the foldable species B. tenuiflora but was stable at 0.7 in the nonfoldable species M. paniculata. These results indicate that the foldable species B. tenuiflora has more sensitivity of PSII to high light stress than the nonfoldable species M. paniculata, partly as a result of less CEF and NPQ in B. tenuiflora. Our results suggest that sun leaves fold themselves under high light to remedy the deficiency of physiological photoprotection for PSII.

Paleocene Malvaceae from northern South America and their biogeographical implications.

PREMISE OF THE STUDY: The clade Bombacoideae + Malvoideae ('Malvatheca group' sensu Baum et al.) in Malvaceae comprises a mostly tropical lineage with derived taxa that now thrive in higher latitudes. The sparse fossil record, especially for Malvoideae, obscures interpretations of past distributions. We describe fossil leaves of Malvoideae from the middle-late Paleocene Cerrejón Formation in Colombia, which contains evidence for the earliest known neotropical rainforest. METHODS: Fifty-six leaf compressions belonging to Malvaceae were collected from the Cerrejón Formation in northern Colombia. Leaf architectural characters were scored and optimized for 81 genera of Malvaceae. Synapomorphic characters and unique character combinations support natural affinities for the fossil leaves. Fossil pollen from the same formation was also assessed. KEY RESULTS: Despite convergence of overall leaf architecture among many Malvaceae, Malvaciphyllum macondicus sp. nov. can be assigned to the clade Eumalvoideae because of distal and proximal bifurcations of the costal secondary and agrophic veins, a synapomorphy for this clade. CONCLUSIONS: The leaf compressions, the oldest fossils for Eumalvoideae, indicate a minimum divergence time of 58-60 Ma, older than existing estimates from molecular analyses of living species. The abundance of eumalvoid leaves and of bombacoid pollen in the midlate Paleocene of Colombia suggests that the Malvatheca group (Malvoideae + Bombacoideae) was already a common element in neotropical forests and does not support an Australasian origin for Eumalvoideae.

Disperser limitation and recruitment of an endemic African tree in a fragmented landscape.

Forest fragmentation may have positive or negative effects on tropical tree populations. Our earlier study of an endemic African tree, Leptonychia usambarensis (Sterculiaceae), in the East Usambara Mountains of Tanzania, found poorer recruitment of seedlings and juveniles in small fragments compared to continuous forest, and concomitant reduction of seed-dispersal agents and seed dispersal. However, the possibility that other biotic or abiotic consequences of the fragmentation process contribute to diminished recruitment in fragments was left open. Here we test whether excessive seed predation, diminished fecundity, low seed quality, or adverse abiotic effects acted independently or in concert with reduced seed dispersal to limit seedling and juvenile recruitment in fragments. Extended observations of disperser activity, a seed placement experiment, seed predator censuses, and reciprocal seedling transplants from forest and fragment sources failed to support the alternative hypotheses for poorer seedling and juvenile recruitment in fragments, leaving reduced seed dispersal as the most plausible mechanism. Poorer recruitment of this species in forest fragments, where high edge-to-area ratios admit more light than in continuous forest, is particularly striking because the tree is an early successional species that might be expected to thrive in disturbed microhabitats.

Pollen grain morphology is not exclusively responsible for pollen collectability in bumble bees.

Bee-pollinated plants face a dilemma in that bees both passively transport pollen grains among conspecific flowers and actively collect pollen to feed their larvae. Therefore, mechanisms that reduce pollen collection by bees have evolved in melittophilous plants. Malvaceae pollen is uncollectable for corbiculate bees which has previously been ascribed to pollen size, spines, and pollenkitt. We analysed the influence of pollen grain properties (diameter, spine length, spine density) on the collectability of echinate (spiny) pollen by bumble bees (Bombus terrestris). Workers individually foraging on one of eight plant species from six families performed significantly less pollen foraging on plants which have large, echinate pollen grains. Nevertheless, neither pollen grain size, spine length, nor spine density prove to be an absolute disqualifier for collectability. While pollen foragers did not shift to nectar collection but seized visiting flowers with uncollectable pollen, nectar foragers performed regular foraging bouts on these plants. Pollen that is uncollectable for corbiculate bees limits pollen depletion by generalist bumble bees and probably also honey bees while maintaining them as pollinators, which is an effective solution to the pollen dilemma. As previous assumptions about the impact of pollen morphology on its collectability are disproved, potentially determining factors are discussed.

Dose-dependence of growth and ecophysiological responses of plants to biochar.

Charcoal is a ubiquitous legacy of wildfire in terrestrial systems that often contributes to rapid revegetation following disturbance; the use of charcoal soil amendments, or "biochars", to promote plant growth has received recent research attention and increasing applied use. Despite its widespread use, well-resolved quantitative estimates of dose-response relationships for biochar effects on plant growth are nonexistent, and studies of biochar dosage effects on plant ecophysiology are minimal. We investigated the effects of biochar dosage on plant growth and ecophysiology in a glasshouse experiment involving two common early-successional plants, Abutilon theophrasti and Trifolium repens. Plants were grown in disturbed temperate soils with increasing dosages of wood biochars: 0, 2, 4, 6, 8, 10, 20, 30, 40, 50 t/ha. We measured leaf-level gas-exchange traits (Amax, gs, WUE), chlorophyll concentration, and leaf area growth throughout the experiment. At the end of the experiment, we measured biomass, foliar nutrition, and soil properties (pH, EC, C and N). Responses of biomass and physiological traits were highly dose-dependent, followed primarily unimodal forms, and differed in some traits between species. Increases in the uptake of K, P, and Mg, were responsible for accelerated growth. Biochars also generally increased the concentration of micronutrients, especially B. As a result, nutrient stoichiometry shifted substantially: in A. theophrasti, biochars increased C:N, P:N, and K:N ratios, suggesting nitrogen dilution or induced deficiency at higher dosages. This work supports the general hypothesis that ecophysiological responses to biochar are dose-dependent and driven mainly by changes in nutrient availability. Additional work is necessary to understand the broader ecological impacts of heterogeneity in soil pyrogenic C levels to succession and ecosystem function.

Unexpected drought resistance strategies in seedlings of four Brachychiton species.

Functional traits associated with drought resistance can be useful for predicting tree responses to a drying climate. Yet drought resistance is likely achieved through a complex combination of constitutive traits (traits expressed even in benign environments) and plastic traits (traits expressed only in response to drought). Because few studies measure multiple traits for multiple species under both well-watered and drought conditions, we often struggle to identify suites of constitutive and plastic traits indicative of drought resistance strategies. Using a greenhouse experiment, we examined nine drought resistance traits (six morphological/allocation traits plus assimilation, stomatal conductance and water-use efficiency) in well-watered and water-stressed seedlings of four Brachychiton (Malvaceae Juss.) species with ranges spanning a strong aridity gradient in east-central Australia. In benign conditions, constitutive biomass allocation was consistent with expectations, with xeric species investing more heavily in roots and stem tissue and less in leaf tissue than mesic species (P = 0.004). Under drought conditions, xeric species decreased relative biomass allocation below-ground while mesic species increased relative below-ground allocation (treatment × species interaction P = 0.0015). Relative water content of the stems was slightly higher in xeric species (P = 0.055), and remained stable during drought while decreasing in mesic species (treatment × species P = 0.001). Specific leaf area (SLA) and leaf dry matter content (LDMC) did not fit with expectations under either benign or water-limited conditions. Moreover, stomatal conductance and carbon assimilation were unexpectedly highest and intrinsic water-use efficiency (WUEi) lowest in the xeric species in benign conditions. Only under drought did the xeric species manifest higher WUEi than the mesic species (treatment × species P < 0.0001). We found that even closely related species exhibited diverse combinations of drought resistance traits. Notably, traits commonly used as proxies for drought tolerance (e.g., SLA, LDMC, well-watered WUEi) performed more poorly than constitutive allocation traits. This study highlights the need to consider multiple traits and phenotypic plasticity when assessing species' drought resistance for forest management in the face of climate change.

Effects of atmospheric pressure plasma jet operating with DBD on Lavatera thuringiaca L. seeds' germination.

The paper presents the results of an experiment on the effect of pre-sowing stimulation of seeds with atmospheric pressure plasma jet operating with dielectric barrier discharge (DBD plasma jet) on the process of germination of Thuringian Mallow (Lavatera thuringiaca L.). Five groups of seeds characterized by a different exposure times (1, 2, 5, 10 and 15 minutes) as well as untreated seeds-control were used. Pre-sowing plasma stimulation of seeds improved germination parameters such as: germination capacity and germination energy for all tested groups relative to control. The highest germination parameters were obtained for seeds stimulated with plasma for the exposure times of 2 and 5 min. The analysis of the contact surface angle indicated the decrease of its' mean values upon seed stimulation while no statistical effects were observed. Analysis of the SEM scans revealed the increase in seed pattern intensity which could be attributed to removing of the surface parts of cuticle possibly covered with wax upon short time-2 and 5 min plasma treatment. Such a phenomenon can act similarly to mechanical scarification of seeds. Longer exposure of seeds to plasma resulted in affecting the deeper zone of cuticle and damage or fracture of some parts of the cuticle. Lower germination parameters of seeds upon longer exposure times to plasma may indicate mechanical damage of the seeds.

Positive indirect interactions between neighboring plant species via a lizard pollinator.

In natural communities, species are embedded in networks of direct and indirect interactions. Most studies on indirect interactions have focused on how they affect predator-prey or competitive relationships. However, it is equally likely that indirect interactions play an important structuring role in mutualistic relationships in a natural community. We demonstrate experimentally that on a small spatial scale, dense thickets of endemic Pandanus plants have a strong positive trait-mediated indirect effect on the reproduction of the declining endemic Mauritian plant Trochetia blackburniana. This effect is mediated by the endemic gecko Phelsuma cepediana moving between Pandanus thickets, a preferred microhabitat, and nearby T. blackburniana plants, where it feeds on nectar and pollinates the plants. Our findings emphasize the importance of considering plant-animal interactions such as pollination at relatively small spatial scales in both basic ecological studies and applied conservation management.

Seasonal patterns of leaf gas exchange and water relations in dry rain forest trees of contrasting leaf phenology.

Diurnal and seasonal patterns of leaf gas exchange and water relations were examined in tree species of contrasting leaf phenology growing in a seasonally dry tropical rain forest in north-eastern Australia. Two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., and two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret. were studied. The deciduous species had higher specific leaf areas and maximum photosynthetic rates per leaf dry mass in the wet season than the evergreens. During the transition from wet season to dry season, total canopy area was reduced by 70-90% in the deciduous species and stomatal conductance (g(s)) and assimilation rate (A) were markedly lower in the remaining leaves. Deciduous species maintained daytime leaf water potentials (Psi(L)) at close to or above wet season values by a combination of stomatal regulation and reduction in leaf area. Thus, the timing of leaf drop in deciduous species was not associated with large negative values of daytime Psi(L) (greater than -1.6 MPa) or predawn Psi(L) (greater than -1.0 MPa). The deciduous species appeared sensitive to small perturbations in soil and leaf water status that signalled the onset of drought. The evergreen species were less sensitive to the onset of drought and g(s) values were not significantly lower during the transitional period. In the dry season, the evergreen species maintained their canopies despite increasing water-stress; however, unlike Eucalyptus species from northern Australian savannas, A and g(s) were significantly lower than wet season values.

Mosquito development and biological control in a macrophyte-based wastewater treatment plant.

A one-year study of the proliferation of mosquito in a Pistia stratiotes-based waste stabilization ponds in Cameroon revealed that Mansonia and Culex were the main breeding genera with about 55% and 42% of the total imagoes respectively. Though the ponds represent a favorable breeding ground for mosquitoes, only 0.02% of captured imagoes was Anopheles gambiae, suggesting that this wastewater treatment plant does not significantly contribute to the development of the malaria vector in the area. Gambusia sp. introduced to control mosquito population in the ponds acclimatized relatively well in most of the ponds (B3-B7) and their feeding rate without any diet ranged from 15.0 to 50.2 larvae/day for a single fish.

Beneficial Effects of Ants and Spiders on the Reproductive Value of Eriotheca gracilipes (Malvaceae) in a Tropical Savanna.

Predators affect plant fitness when they forage on them and reduce the action of herbivores. Our study evaluates the complementary effects of spiders and ants that visit the extrafloral nectaries of Eriotheca gracilipes (Malvaceae) on the production of fruits and viable seeds of these savanna trees. Four experimental groups were established: control group - with free access of spiders and ants; exclusion group - spiders and ants excluded; ant group - absence of spiders; and spider group - absence of ants. The presence of ants reduced the spider richness; however, the presence of spiders did not affect the ant richness. A significantly higher number of fruits per buds were found in the presence of spiders alone or spiders and ants together (control group) compared with the absence of both predators (exclusion group). The number of seeds per fruits and seed viability were higher in the control group. This is the first study showing that spiders and ants may exert a positive and complementary effect on the reproductive value of an extrafloral nectaried plant. Mostly the impact of ants and/or spiders on herbivores is considered, whereas our study reinforces the importance of evaluating the effect of multiple predators simultaneously, exploring how the interactions among predators with distinct skills may affect the herbivores and the plants on which they forage.

Global Gene Expression of Kosteletzkya virginica Seedlings Responding to Salt Stress.

Soil salinization is becoming a serious threat to crop yield all over the world. Nowadays, acquainting the specific molecular mechanisms underlying various abiotic stresses especially to salt stress should be of great importance. While the development of the high-throughout sequencing technology promoted the progress powerfully. The intricate perception, transduction and regulation mechanisms underlying salt stress are being illustrated more and more clearly. As a perennial halophytic plant, Kosteletzkya virginica is able to help us to understand the mechanisms more directly and effectively. We carried out the whole transcriptome analysis on young seedlings with or without salt treatment through high-throughout sequencing technology. The results revealed that the numbers of different expressed transcripts between control and different treatments are 4145 and 9134, respectively. The ORF prediction suggested that there were 94308 ORF out of the 103489 (91.10%) total transcripts. We also carried out further differential expression analysis through gene ontology (GO) classification, cluster of orthologous groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. In a word, our transcriptome study on Kosteletzkya virginica would provide direct and effective references for researches on molecular mechanisms of salt-tolerance, extending our view of salt tolerance in plant further. Above all, the related report in this paper is the first about Kosteletzkya virginica.

Leaf gas exchange and carbohydrates in tropical trees differing in successional status in two light environments in central Amazonia.

Monoculture and mixed stands of mahogany (Swietenia macrophylla King) and tonka bean (Dipteryx odorata Willd.) trees were established on degraded land in central Amazonia to compare leaf gas exchange parameters between plants grown in sunlight in an open field and in shade beneath a balsa wood (Ochroma pyramidale Cav.) canopy. Shading increased specific leaf area by about 50% in both species. Shading reduced height and diameter growth of S. macrophylla, whereas it increased these parameters for D. odorata. Light-saturated photosynthesis (Amax), stomatal conductance (gs) and transpiration (E) were higher in S. macrophylla than in D. odorata. In S. macrophylla, Amax was higher in sun leaves (12.9 +/- 0.9 micromol m-2 s-1) than in shade leaves (10.2 +/- 1.0 micromol m-2 s-1), whereas light environment had no significant effect on Amax of D. odorata. In both species, CO2-saturated photosynthesis (Apot) was higher in sun leaves (22 +/- 1.4 micromol m-2 s-1) than in shade leaves (17-20 +/- 0.8 micromol m-2 s-1). Stomatal conductance and E increased in sun leaves of S. macrophylla by 45 and 38%, respectively, whereas light environment did not affect gs and E of D. odorata. Photorespiration rates (Pr) varied from 28 to 36% of net photosynthesis (A) at ambient atmospheric CO2 concentration (Ca) but declined to around 7% of A at higher Ca. Leaf dark respiration (Rd) and the CO2 compensation point (Gamma) were lower in shade-grown plants than in open-grown plants. Compared with shade-grown plants, total nonstructural carbohydrate (TNC) concentrations increased by 56% in S. macrophylla and by 30% in D. odorata in the open field. Leaf nitrogen (NL) concentrations were higher in open-grown plants than in shade-grown plants of both species, and TNC and NL concentrations were negatively correlated (r = -0.77). High TNC accumulation in S. macrophylla in the open field suggests that photosynthesis is unlikely to be growth-limiting at this site. We conclude that photosynthetic parameters of D. odorata are less affected by light environment than those of S. macrophylla, indicating that D. odorata has lower physiological plasticity to light than S. macrophylla.