Wide Range Of Light Environments Research Articles

Campomanesia xanthocarpa (Myrtaceae: Myrtoideae) seedlings reveal morpho-physiological plasticity under shade conditions.

Plants exposed to different light intensities generate physiological, morphological, and anatomical changes conducting to plasticity. Thus, this characteristic establishes the ability of plants to present phenotypic adjustments by the same genotype under different environmental conditions. The objective of this study was to verify the morphophysiological alterations in Campomanesia xanthocarpa (Mart.) O. Berg (guabiroba) seedlings cultivated in different shading levels. The seedlings were grown for 21 months under full sun or 30%, 50%, and 80% under shading. Growth, photosynthetic pigments, gas exchange rate, chlorophyll fluorescence, and leaf anatomy were evaluated. In all the treatments subjected to shading, plasticity mechanisms involved structural and physiological changes such as an increase in leaf area and chlorophyll content (total and Chl a), reduction in leaf thickness, and increased gas exchange and quantum yield of photosystem II. The guabiroba seedlings can be cultivated in full sun or different shading environments; even under high shading intensity (80%), the plants showed vigor similar to those produced in a sunny environment. These results confirmed our hypothesis about guabiroba acclimation capacity to shading, noteworthy information for nurseries, orchards, agroforestry systems, or forest restoration in a wide range of light environments.

Visual system plasticity is differently mediated by cone opsin expression and chromophore composition in closely related cichlid species

Phenotypic plasticity allows organisms to rapidly adjust to environmental changes. Cichlid fish inhabit a wide range of light environments and show a large diversity in visual system properties, which makes them a good model system to address the role of phenotypic plasticity in visual adaptation. Cichlid retinal cone pigments consist of opsin proteins bound to Vitamin A1 or A2-derived chromophores. Plasticity in expression has been shown for cichlid opsin genes, but less is known about the contribution of cyp27c1, the enzyme that converts Vitamin A1 into A2,. Here, we studied both opsin and cyp27c1 expression patterns for three closely related cichlid species from different visual habitats in Lake Victoria, across different light treatments. We found differences in cyp27c1 as well as in opsin expression patterns between the three species. Experimental light treatments affected the developmental trajectory of cyp27c1 expression in one species and opsin expression in all three species. Within each species, we found large individual variation in cyp27c1 expression levels and no consistent association with opsin expression levels. These results indicate that visual system plasticity of even closely related species can be differentially mediated by opsin and cyp27c1 expression, possibly associated with species differences in visual niche.

Efficient light‐harvesting of mesophotic corals is facilitated by coral optical traits

Abstract Sustained light‐dependent coral reef communities can be found at a wide range of light environments, extending from the sea level to as deep as 150 m (i.e. esophotic). How mesophotic corals thrive despite extremely limited light conditions still requires further investigation. Here, we undertook a comprehensive ecophysiological and bio‐optical study on four depth‐generalist coral species aiming to delineate the functional role that optical trait properties have in light‐harvesting, at contrasting light regimes. We show that the optical traits of coral skeletons are adjusted to their ambient light conditions and complement the microalgal demands for sufficient light, thus exhibiting a spatially efficient photosymbiotic system. In contrast to shallow corals, mesophotic corals absorbed up to three fold more light, resulting in excellent photosynthetic response under light conditions of only ~3% of the incident surface irradiance. The enhanced light‐harvesting capacity of mesophotic corals was achieved by redistributing light in the coral skeleton through optical scattering, thereby facilitating light transport and absorption by densely pigmented host tissue. Our findings provide fundamental insight into the light‐harvesting mechanisms underlying the productivity of mesophotic coral reef ecosystems, yet also raise concerns regarding their ability to withstand prolonged environmental disturbances. A free Plain Language Summary can be found within the Supporting Information of this article.

Photosynthetic performance and growth responses of Liriope muscari (Decne.) L.H. Bailey (Asparagaceae) to different levels of irradiance in three seasons

Plants in natural environments are often exposed to different irradiance in different seasons, and leaf-level acclimation to light may be affected by those changes. To investigate this, photosynthetic characteristics of lilyturf (Liriope muscari), a shade-tolerant evergreen groundcover of forest origin native to East Asia, were compared in summer, autumn and winter in plants growing in two light environments: an open field with high irradiance (HI) and under a winter-deciduous forest canopy (LI). Light saturation point, light compensation point, photon-saturated photosynthetic rate and in situ net photosynthetic rate (PN) were highest in HI, as was whole-plant biomass. Photon-saturated rates of net photosynthesis were higher in autumn and winter than in summer. Substantial declines in PN, stomatal conductance (gs) and intercellular CO2 were observed in HI plants during midday in summer, but not in LI or in autumn and winter. Chlorophyll fluorescence indicated that HI plants were photoinhibited during midday in both summer and winter and consequently performed best in autumn. In contrast, LI plants were light-limited in summer and performed better when the canopy was leafless, especially in winter. Winter and autumn photosynthesis may make critical contributions to the carbon economy of lilyturf integrated over the year, facilitating its growth and survival in a wide range of light environments.

Structural features of the diatom photosystem II-light-harvesting antenna complex.

In photosynthesis, light energy is captured by pigments bound to light-harvesting antenna proteins (LHC) that then transfer the energy to the photosystem (PS) cores to initiate photochemical reactions. The LHC proteins surround the PS cores to form PS-LHC supercomplexes. In order to adapt to a wide range of light environments, photosynthetic organisms have developed a large variety of pigments and antenna proteins to utilize the light energy efficiently under different environments. Diatoms are a group of important eukaryotic algae and possess fucoxanthin (Fx) chlorophyll a/c proteins (FCP) as antenna which have exceptional capabilities of harvesting blue-green light under water and dissipate excess energy under strong light conditions. We have solved the structure of a PSII-FCPII supercomplex from a centric diatom Chaetocerosgracilis by cryo-electron microscopy, and also the structure of an isolated FCP dimer from a pennate diatom Phaeodactylumtricornutum by X-ray crystallography at a high resolution. These results revealed the oligomerization states of FCPs distinctly different from those of LHCII found in the green lineage organisms, the detailed binding patterns of Chl c and Fxs, a huge pigment network, and extensive protein-protein, pigment-protein, and pigment-pigment interactions within the PSII-FCPII supercomplex. These results therefore provide a solid structural basis for examining the detailed mechanisms of the highly efficient energy transfer and quenching processes in diatoms.

Modular, hollow culms of rain-forest bamboos explain their persistence across a wide range of light environments

Abstract:Tropical bamboos persist in a wide range of light conditions and quickly respond to changes in light availability. However, the mechanisms underpinning this ability remain unknown. In order to test the hypothesis that the modular and hollow culm architecture of bamboos explains their performance in a wide range of light environments, we determined the allometric relationships of two dominant bamboo species of the upper hill dipterocarp forests of Malaysia, Gigantochloa ligulata (n = 29) and Schizostachyum grande (n = 25), via destructive sampling. We also monitored biomass turnover of bamboos and woody trees in 24 permanent plots (1.92 ha in total) over a one-year period. Compared with woody trees, bamboo culms attained 1.5 times the height and their clumps supported four times as much total leaf area at the same above-ground biomass. In addition, at a given height, bamboo clumps had six times larger crown projection area than trees while having a similar amount of total leaf area per unit of crown projection area. Finally, bamboos’ biomass turnover rate was three times higher than trees, and G. ligulata increased its specific rate of biomass increase after canopy disturbance, while trees decreased. We conclude that the unique architecture of bamboos allows them to persist under closed forest canopy light conditions and to respond to gap formation via high biomass turnover rate.

Photosynthetic Performance of Invasive Vincetoxicum Species (Apocynaceae)

Knowledge of photosynthetic capacity is crucial for fully understanding a species’ invasive potential and for the development of appropriate control strategies. Although growth and reproductive data are available for the invasive swallowwort vines Vincetoxicum nigrum and V. rossicum, photosynthetic data are wanting. These herbaceous, perennial congeners were introduced from separate European ranges during the late 19th century and became invasive during the following century in the northeastern United States and southeastern Canada. Vincetoxicum nigrum has been observed growing mainly in high light environments, whereas V. rossicum occurs across a wide range of light environments, suggesting niche divergence and that different management strategies might be needed for the two species. In this work, we investigated whether the differing habitat associations of these species is reflected in their photosynthetic capacities and leaf morphology. Photosynthetic parameters and specific leaf mass were determined across a range of light environments represented by four field habitats (common garden, forest edge, old field, and forest understory) and two greenhouse environments (high and low light). In the high-light common garden habitat, V. nigrum achieved 37% higher maximum photosynthetic rates than V. rossicum, but photosynthetic performance of the two species was the same in the forest edge habitat. Additionally, species’ performance was virtually identical in high light, low light, and transitions between high and low light regimes in the greenhouse. Specific leaf mass of V. nigrum was 17% higher in the common garden and 19% higher in the greenhouse compared with V. rossicum. Both invasive Vincetoxicum spp. appear capable of growing within a broad range of light environments and their management should be similar regardless of light environment. Other explanations are required to explain the scarcity of V. nigrum in low light natural areas.

The success of the cyanobacterium Cylindrospermopsis raciborskii in freshwaters is enhanced by the combined effects of light intensity and temperature

<p>Toxic cyanobacterial blooms in freshwaters are thought to be a consequence of the combined effects of anthropogenic eutrophication and climate change. It is expected that climate change will affect water mixing regimes that alter the water transparency and ultimately the light environment for phytoplankton. Blooms of the potentially toxic cyanobacterium <em>Cylindrospermopsis raciborskii</em> are expanding from tropical towards temperate regions. Several hypotheses have been proposed to explain this expansion, including an increase in water temperature due to climate change and the high phenotypic plasticity of the species that allows it to exploit different light environments. We performed an analysis based on eight lakes in tropical, subtropical and temperate regions to examine the distribution and abundance of <em>C. raciborskii</em> in relation to water temperature and transparency. We then conducted a series of short-term factorial experiments that combined three temperatures and two light intensity levels using <em>C. raciborskii</em> cultures alone and in interaction with another cyanobacterium to identify its growth capacity. Our results from the field, in contrast to predictions, showed no differences in dominance (>40% to the total biovolume) of <em>C. raciborskii</em> between climate regions. <em>C. raciborskii</em> was able to dominate the phytoplankton in a wide range of light environments (euphotic zone = 1.5 to 5 m, euphotic zone/mixing zone ratio <0.5 to >1.5). Moreover, <em>C. raciborskii </em>was capable of dominating the phytoplankton at low temperatures (<15°C). Our experimental results showed that <em>C. raciborskii</em> growing in interaction was enhanced by the increase of the temperature and light intensity. <em>C. raciborskii </em>growth in high light intensities and at a wide range of temperatures, suggests that any advantage that this species may derive from climate change that favors its dominance in the phytoplankton is likely due to changes in the light environment rather than changes in temperature. Predictive models that consider only temperature as a drive factor can therefore fail in predicting the expansion of this potentially toxic cyanobacterium.<em></em></p>

Trade‐offs in juvenile growth potential vs. shade tolerance among subtropical rain forest trees on soils of contrasting fertility

Summary Plant adaptation to gradients of light availability involves a well‐studied functional trade‐off, as does adaptation to gradients of nutrient availability. However, little is known about how these two major trade‐offs interact, and thus, it remains unclear whether and how the nature of the growth–shade tolerance trade‐off differs on soils of contrasting fertility. We asked whether juvenile growth–shade tolerance trade‐offs differed in slope and elevation between tree assemblages on nutrient‐rich basalt and nutrient‐poor rhyolite soils in an Australian subtropical rain forest. We measured the growth of, and the range of light environments occupied by, juveniles (40–120 cm tall) of eight basalt specialists, six rhyolite specialists, and one generalist that was common on both substrates. In situ minimum light requirements were estimated from the 5th percentile of the distribution of naturally regenerated juveniles in relation to daily light transmittance. Stem growth was measured for 12–16 months across a wide range of light environments to estimate the light compensation point of growth of each species. Light compensation points of growth showed nearly a 1 : 1 correspondence with in situ minimum light requirements of species, indicating that whole‐plant carbon balance is a key driver of ecological success in low light. Minimum light requirements were negatively correlated with relative growth rate in low light, but correlated positively with growth in high light. Soil type had no effect on either the slope or the elevation of this trade‐off, all species aligning around a common growth–shade tolerance trade‐off, but our results do show a wider range of growth rates and shade tolerance on the nutrient‐rich basalt soil than on the nutrient‐poor rhyolite. Our results suggest that adaptation to light availability involves fundamentally similar trade‐offs on these two substrates of differing fertility. However, a wider range of growth rates and shade tolerance on the nutrient‐rich basalt soil than on the nutrient‐poor rhyolite may help to explain the higher species richness and greater structural complexity of forest stands on the former substrate.

Separating effects of crown structure and competition for light on trunk growth of Sequoia sempervirens

Tree-level productivity is largely determined by crown size and aboveground vigor, but light availability ultimately controls growth. Competition indices are typically used in modeling instead of actual measurements of light. Our goals were to determine which measure of light best predicts trunk growth increments of Sequoia sempervirens, to quantify the amount of growth variation explained by light after accounting for effects of tree structure, and to compare model fitness of various competition indices. Twenty-four trees spanning a wide range of light environments were randomly selected from stands of different ages, including trees 23–72m tall and 20–560years old. Tree structure and trunk growth increments were quantified via direct measurements of all branches and coring main trunks at multiple heights. Light availability was quantified via hemispherical photography throughout tree crowns. Competition indices were computed by measuring the size and distribution of neighboring trees. The largest tree had 69m3 of wood and bark, 3208m2 of leaf area, and produced 1.04m3yr−1 of wood in the main trunk, whereas the smallest tree had less than 1m3 of wood and bark, 134m2 of leaf area, and produced 0.04m3yr−1 of wood in the main trunk. After accounting for tree structure, light availability explained an additional 10% of variation in trunk wood volume increment. Light availability alone explained 49% of the variation in wood volume increment, while tree size alone explained 41%. The growth model with average mid-crown openness as the measure of light availability was 19 times more likely than the model without a term for light. A distance-dependent competition index computing neighboring tree crown volume (DDCV) was >1200 times more likely than any other competition index in the best growth model. Together with tree size and aboveground vigor, DDCV explained 91% of variation in trunk wood volume increment.

A conifer–angiosperm divergence in the growth vs. shade tolerance trade‐off underlies the dynamics of a New Zealand warm‐temperate rain forest

Summary A central tenet of forest ecology is that succession and regeneration dynamics are driven by an interspecific trade‐off between juvenile growth rates in high light and shade tolerance. There is evidence, however, that a single trade‐off axis may fail to explain the dynamics of mixed conifer–angiosperm rain forests in the Southern Hemisphere, especially in New Zealand. We tested for growth vs. shade tolerance trade‐offs by measuring juvenile growth of five podocarps and five broadleaved canopy angiosperms across a wide range of light environments in a New Zealand warm‐temperate rain forest. The light compensation point of growth was used as a measure of species light requirements, which we then compared with height growth in 10% light, approximating the environments encountered beneath small treefall gaps. Despite considerable overlap between the ranges of both growth rates and compensation points found in the two lineages, major axis tests showed that the growth vs. shade tolerance trade‐off differed significantly between podocarp and angiosperm species. At a common compensation point, angiosperms were faster growing than podocarps in 10% light. However, juveniles of these angiosperm species were notably scarce in the more open environments associated with forest margins. Synthesis. A conifer–angiosperm divergence in the growth vs. shade tolerance trade‐off may explain long‐standing problems of the dynamics of these forests. Although juveniles of most lowland podocarps can tolerate considerable shade, the more vigorous response of broadleaved angiosperms to small canopy openings enables them to out‐compete podocarps in old‐growth stands. The greater abundance of podocarp juveniles on forest margins cannot be attributed to them out‐competing angiosperm species where light is abundant and is likely to reflect superior resistance to frost and/or drought. The drivers of the dynamics of New Zealand's podocarp–broadleaved forests therefore differ appreciably from those ascribed to tropical and north‐temperate forests.

Species-independent down-regulation of leaf photosynthesis and respiration in response to shading: evidence from six temperate tree species.

The ability to down-regulate leaf maximum net photosynthetic capacity (Amax) and dark respiration rate (Rdark) in response to shading is thought to be an important adaptation of trees to the wide range of light environments that they are exposed to across space and time. A simple, general rule that accurately described this down-regulation would improve carbon cycle models and enhance our understanding of how forest successional diversity is maintained. In this paper, we investigated the light response of Amax and Rdark for saplings of six temperate forest tree species in New Jersey, USA, and formulated a simple model of down-regulation that could be incorporated into carbon cycle models. We found that full-sun values of Amax and Rdark differed significantly among species, but the rate of down-regulation (proportional decrease in Amax or Rdark relative to the full-sun value) in response to shade was not significantly species- or taxon-specific. Shade leaves of sun-grown plants appear to follow the same pattern of down-regulation in response to shade as leaves of shade-grown plants. Given the light level above a leaf and one species-specific number (either the full-sun Amax or full-sun Rdark), we provide a formula that can accurately predict the leaf's Amax and Rdark. We further show that most of the down regulation of per unit area Rdark and Amax is caused by reductions in leaf mass per unit area (LMA): as light decreases, leaves get thinner, while per unit mass Amax and Rdark remain approximately constant.

Photosynthetic acclimation within individual Typha latifolia leaf segments

Growing Typha latifolia leaf segments traverse a wide range of light environments as they are pushed upward from basal meristems through sediment, water, and dense litter and leaf layers. We used light transfer experiments in a greenhouse to investigate the photosynthetic acclimation of individual Typha leaf segments. Fully expanded leaf segments exhibited strong and symmetrical acclimation to increases or decreases in light. The photosynthetic light response curves of shade grown segments that were transferred to high light acclimated within 10–15 days to match those of segments that grew and remained in high light. Acclimation was highly localized; the light response curves of shade grown segments that remained shaded did not change, even as adjacent segments acclimated to high light. Leaf segments exposed to various treatments did not differ significantly in leaf mass per area; Typha leaves are apparently morphologically preformed to function in high light and allow high photosynthetic capacity, regardless of the growth environment. Likewise, nitrogen content did not differ significantly between treatments, and photosynthetic acclimation may involve a reallocation or activation of nitrogen within a leaf segment, rather than a net nitrogen translocation into or out of a segment. We interpret these patterns as an adaptive strategy that maximizes carbon gain by monocot leaves growing in a vertically heterogeneous light environment

The whole‐plant compensation point as a measure of juvenile tree light requirements

Summary Although ‘shade tolerance’ has featured prominently in the vocabulary of foresters and ecologists for a century, we have yet to agree on a standardized method for quantifying this elusive property. The ‘whole‐plant compensation point’, interpolated from stem growth measurements across a wide range of light environments, has been proposed as a simple, robust measure of species shade tolerance. Others have argued that shade tolerance is primarily a function of differential ability to survive periods of slow growth (‘suppression’), implying that measurements of survival are vital. We measured growth of juveniles (500–1000 mm tall) of five evergreen trees over 12 months in a cool‐temperate rain forest in New Zealand, to determine whether whole‐plant compensation points predicted species differences in occupancy of understorey light environments, which were quantified using hemispherical photography. The five species encompassed 3·5‐fold variation in whole‐plant compensation points. Compensation points of most species fell within the first quartile of the distribution of light environments occupied by juveniles; they were also correlated with low‐light mortality rates of juveniles, estimated from permanent plot data archived in the National Vegetation Survey Databank. Compensation points were also significantly positively correlated with height growth rates in high light, confirming the presence of the growth vs. shade tolerance trade‐off detected in many other forest tree assemblages. Results show that, in temperate evergreen forests, the whole‐plant compensation point distinguishes reliably between species of differing shade tolerance. Excepting situations involving parameterization of demographic models, shade tolerance can therefore be assessed without survival measurements. However, estimating whole‐plant compensation points may prove more difficult in deciduous forests, where seasonal variation in understorey light transmission poses additional challenges.

Growth and photosynthetic responses of Fraxinus mandshurica seedlings to various light environments

To determine light requirement and adaptability of Fraxinus mandshurica seedlings, the seasonal variations of photosynthetic variables were measured in 3-year-old seedlings grown under four light levels (100%, 60%, 30%, and 15% of full sunlight) with a LI-6400 portable photosynthesis system. The leaf chlorophyll content, special leaf weight, annual height and basal diameter increment of seedlings were also observed. The maximum and minimum values of net photosynthetic rate, maximum rate of carboxylation, and maximum rate of electron transport of F. mandshurica seedlings were detected with 60% and 15% of full sunlight treatments, respectively. With the decrease of light level, both light saturation point and special leaf weight significantly declined (p < 0.05), but leaf chlorophyll content significantly increased (p <0.05). Annual height and basal diameter increments of seedlings grown under 60% of full sunlight treatment were significantly greater than those of seedlings under other treatments (p < 0.05). It was concluded that F. mandshurica seedlings can adapt to a wide range of light environments from 15% to 100% of full sunlight by adjusting light saturation point, leaf chlorophyll content and special leaf weight. According to the maximum of relative growth, 60% of full sunlight treatment is the optimum light level for the growth of 3-year-old F. mandshurica seedlings.

Growth and physiological response of six Australian rainforest tree species to a light gradient

An understanding of growth and photosynthetic potential of subtropical rainforest species to variations in light environment can be useful for determining the sequence of species introductions in rainforest restoration projects and mixed species plantations. We examined the growth and physiology of six Australian subtropical rainforest tree species in a greenhouse consisting of three artificial light environments (10%, 30%, and 60% full sunlight). Morphological responses followed the typical sun-shade dichotomy, with early and late secondary species ( Elaeocarpus grandis, Flindersia brayleyana, Flindersia schottiana, and Gmelina leichhardtii) displaying higher relative growth rate (RGR) compared to mature stage species ( Cryptocarya erythroxylon and Heritiera trifoliolatum). Growth and photosynthetic performance of most species reached a maximum in 30–60% full sunlight. Physiological responses provided limited evidence of a distinct dichotomy between early and late successional species. E. grandis and F. brayleyana, provided a clear representation of early successional species, with marked increase in A max in high light and an ability to down regulate photosynthetic machinery in low light conditions. The remaining species ( F. schottiana, G. leichhardtii, and H. trifoliolatum) were better represented as falling along a shade-tolerant continuum, with limited ability to adjust physiologically to an increase or decrease in light, maintaining similar A max across all light environments. Results show that most species belong to a shade-tolerant constituency, with an ability to grow and persist across a wide range of light environments. The species offer a wide range of potential planting scenarios and silvicultural options, with ample potential to achieve rapid canopy closure and rainforest restoration goals.

Intraspecific variation in leaf morphology and photosynthetic traits in Boninia grisea Planchon (Rutaceae) endemic to the Bonin Islands, Japan

Abstract Boninia grisea is a woody species comprising two varieties that have adapted to habitats with different wind conditions. Boninia grisea var. grisea is a tree occurring in forests on mountain slopes, whereas B. grisea var. crassifolia is a shrub occurring at sites exposed to strong wind at forest edges and on mountain plateaus. The former has somewhat larger and thinner leaves than the latter. Despite the differences in habitat wind conditions and leaf morphology, plants of both taxa are found in a wide range of light environments from sunny to shady. We measured leaf morphological and photosynthetic traits for B. grisea plants of both taxa growing in the field and attempted to clarify the differences between them in terms of leaf morphological and photosynthetic acclimation to sun and shade. Boninia grisea var. crassifolia had a thicker leaf upper epidermis and a thicker spongy mesophyll layer with thicker cell walls than B. grisea var. grisea, suggesting that the former had mechanically tough leaves. Under sunny conditions, the stomatal conductance and area‐based photosynthetic capacities of the two B. grisea taxa were comparable. Under shady conditions, B. grisea var. crassifolia had thicker leaves with a higher photosynthetic light saturation, area‐based nitrogen content and stomatal conductance than B. grisea var. grisea, suggesting that the former was less acclimated to deep shade than the latter.

Comparison of film and digital hemispherical photography across a wide range of canopy densities

Hemispherical photography is a widely used method for assessing the light environment beneath forest canopies. As technology advances, digital photography is expected to increasingly replace conventional film photography for such work. However, in the absence of satisfactory comparisons between the two methods, caution is needed in the use of a digital camera for hemispherical photography. In this study, paired digital and film hemispherical photographs were taken in conifer plantations in southern and central Scotland, with a wide range of light environments. The analysis package Hemiview was used to calculate canopy openness, diffuse and direct transmittance, and leaf area index (LAI). There was strong positive correlation between the results from the two systems, with no systematic differences over a range of transmittance from 10 to 70%. Beneath very dense canopies (below 10% transmittance) the film camera is known to produce inaccurate values of transmittance, so the utility of the digital camera in these environments could not be ascertained. We concluded that using the cameras and analysis package described, film and digital hemispherical photography produce comparable results.

Microenvironmental Heterogeneity and Space Utilization by Desert Vines within their Host Trees

The three-dimensional biomass distribution and the microenvironments experienced by several desert vine species growing within the canopy of host trees were studied at the Centro Ecológico de Sonora in México. The light environment within the crown of the host tree Cercidium microphyllum showed a horizontal and vertical gradient from the base of the trunk to the edges of the canopy. Within this gradient total daily photosynthetically active radiation (PAR) varied from 47.8 mol m−2outside the crown to 4.6 mol m−2at the centre of the crown and close to the ground. Maximum air temperature was 3 °C lower beneath the crown than outside. Within the canopy, most vines experienced less than 50% of the daily available PAR outside the canopy. For most of the day, leaves of vines received 15% or less of the maximum available PAR. Our study shows that vines do not grow towards full sunlight but rather they exploit different habitat possibilities within their host tree crown. Leaves along the stems of vines experienced a wide range of light environments, showing coefficients of variation (CV) in total daily PAR from 36.4 to 94.6%. Daily courses of PAR also showed that leaves within the canopy experienced short-term temporal variation in the light environment. Differences in CV of daily PAR values and preferences in heterogeneous light microenvironments among species suggested that different vine species might be spatially separated in the canopy. We suggest that in desert habitats, conditions within the crown of host trees result in an important microhabitat that vines can exploit, allowing them to avoid the high light, temperature and water deficits found in the surrounding environment.

Seedling Distribution and Potential Persistence of the Exotic Shrub Lonicera maackii in Fragmented Forests

-Successful invasion of eastern deciduous forests by the exotic shrub Lonicera maackii (Rupr.) Maxim. is well-documented, but little is known about seed germination or seedling establishment in this species. Our research suggested that most seeds are dispersed in a nondormant condition. After 88 days, mean cumulative germination percentages of untreated seeds ranged from 54-81% in light and from 31-55% in dark. Seedling density and light availability declined in parallel along transects extending from forest edges to forest interiors. Mean seedling densities ranged from 5-328 seedlings/mi2. Gap formation in forest interiors was not as conducive to seedling establishment as was the presence of edges. Still, this invasive shrub can establish seedlings throughout a wide range of light environments in