LEAF SURFACE WETNESS AND GAS EXCHANGE IN THE POND LILY NUPHAR POLYSEPALUM (NYMPHAEACEAE)

As part of a continuing study of the effects of leaf surface wetness on gas exchange, the occurrence of leaf surface wetting by dewfall and associated effects on photosynthesis were evaluated for floating and aerial leaves of the pond lily Nuphar polysepalum Engelm. Because of nighttime radiation exchange with a cold sky, high humidity, and the presence of adaxial stomata, we predicted that pond lily leaves would be particularly susceptible to wetting events such as dewfall. A substantial reduction in net photosynthesis (up to 20%) occurred for leaves that were experimentally misted to simulate leaf wetting by dewfall. Aerial leaves remained below dewpoint temperatures for long periods on clear nights. However, floating leaves rarely approached dewpoint temperatures at night because minimum nighttime temperatures of leaves were up to 10 C warmer than air temperature. Thus, floating leaves of N. polysepalum did not experience dew formation primarily because of strong thermal coupling to a substrate (water) that was much warmer than air temperature at night. This coupling to a warmer substrate prevented a potentially strong inhibition of photosynthetic CO₂ exchange the following morning.     

Vertical patterns and duration of surface wetness in an old-growth tropical montane forest, Indonesia

In tropical montane forests, the wetness of leaf surfaces is an important parameter which may influence gas exchange, growth and vitality of leaves, and forest productivity. Thirty surface wetness sensors were operated during May–August 2004 in a vertical profile inside an old-growth lower montane rain forest of Central Sulawesi, Indonesia, with the objective to analyse spatial and temporal patterns of surface wetness and to relate wetness duration to the microclimate inside the stand. The canopy was wet during 25–30% of time in this study period. In a dry period, however, surface wetness lasted for only 5% of the time, whereas the canopy was wet during 45–55% of the time in a rainy period. In the lower shade canopy, surface wetness continuously existed for periods of up to 22 h and more, although rainfall occurred only during afternoon thunderstorms of limited duration. The long duration of surface wetness has implications for forest interception models, which assume a complete drying of the canopy between subsequent rainfall events. In periods with rainfall, leaf wetness typically occurred in the afternoon, evening and first half of the night because intercepted water persisted on the leaves until about midnight. In dry periods, in contrast, surface wetness was mainly caused by dewfall in the second half of the night, and it occurred mainly in the uppermost canopy where radiative heat losses resulted in a substantial under-cooling of the leaves. Ecophysiological and hydrological importance is suggested by the long duration of surface wetting in this stand with possible implications for gas exchange, leaf growth, leaf colonization by epiphylls and the forest water balance.     

ADAPTIVE RELATIONSHIP BETWEEN LEAF WATER REPELLENCY,STOMATAL DISTRIBUTION,AND GAS EXCHANGE

Although numerous studies have considered the functional significance of the terrestrial plant leaf surface, the importance of water repulsion for enhancing photosynthetic carbon uptake (CO₂) has not been recognized and appears to involve an array of structural adaptations. The large majority of species tested had leaf surfaces that repelled water to such an extent that varying degrees of water-bead formation occurred. On more wettable leaves, the formation of a water surface film (dewfall) severely curtailed photosynthetic CO, uptake in the field, most likely because CO₂ diffuses 10⁴ times slower in water than air. Water bead formation not only enabled maintenance of high photosynthetic rates but also increased water use efficiency several fold. In 3 of 5 species tested in the field, water bead formation after artificial wetting resulted in greater stomatal opening and increases in photosynthesis of up to 34%. The most nonwettable leaf surface on a given leaf also had all or the majority of the leaf's stomata in 50 of the 57 species tested, indicating a potentially strong adaptive relationship between leaf surface wettability, stomatal occurrence, and photosynthetic performance.     

A comparative study of three leaf wetness sensors

The laboratory and field performance of two electrical resistance (ER) sensors of leaf surface wetness were compared with that of a beta-ray gauge (BRG). The BRG provided the most accurate measurements of wetness duration, which were in agreement with visual observations. A Campbell and a cotton cloth ER sensor consistently underestimated the duration of leaf surface wetness compared to the value obtained with the BRG in a dew chamber. However, the response of the Campbell sensor improved considerably with increase in the severity of dewfall. A superior performance of one of the two ER sensors could not be decisively established on the basis of the field experiments of 1989 and 1990 on soybean and tobacco crops, respectively. For studies where accurate measurements of surface wetness are critical, it is suggested that a beta-ray gauge should be used.     

Do plant mites commonly prefer the underside of leaves?

The adaxial (upper) and abaxial (lower) surfaces of a plant leaf provide heterogeneous habitats for small arthropods with different environmental conditions, such as light, humidity, and surface morphology. As for plant mites, some agricultural pest species and their natural enemies have been observed to favor the abaxial leaf surface, which is considered an adaptation to avoid rain or solar ultraviolet radiation. However, whether such a preference for the leaf underside is a common behavioral trait in mites on wild vegetation remains unknown. The authors conducted a 2-year survey on the foliar mite assemblage found on Viburnum erosum var. punctatum, a deciduous shrub on which several mite taxa occur throughout the seasons, and 14 sympatric tree or shrub species in secondary broadleaf-forest sites in Kyoto, west–central Japan. We compared adaxial–abaxial surface distributions of mites among mite taxa, seasons, and morphology of host leaves (presence/absence of hairs and domatia). On V. erosum var. punctatum, seven of 11 distinguished mite taxa were significantly distributed in favor of abaxial leaf surfaces and the trend was seasonally stable, except for Eriophyoidea. Mite assemblages on 15 plant species were significantly biased towards the abaxial leaf surfaces, regardless of surface morphology. Our data suggest that many mite taxa commonly prefer to stay on abaxial leaf surfaces in wild vegetation. Oribatida displayed a relatively neutral distribution, and in Tenuipalpidae, the ratio of eggs collected from the adaxial versus the abaxial side was significantly higher than the ratio of the motile individuals, implying that some mite taxa exploit adaxial leaf surfaces as habitat.     

Comparisons of beta-ray and electronic leaf wetness sensors in a dew chamber

The performances of a beta-ray gauge system (sensor A) and an electronic sensor (sensor B) as leaf surface wetness detectors were compared in a dew chamber. Sensor A recorded longer surface wetness durations than sensor B under identical conditions of dew formation. The agreement between the sensors was close in recording the time of dew wetting when a white gauze cloth was used as an artificial leaf on sensor B. Leaf surface wetness duration due to the formation of dew can be measured more realistically by sensor A than sensor B. This is attributed to the utilization of a real leaf for sensor A and a physical model for sensor B as condensing surfaces.     

Leaf traits of natural populations of <Emphasis Type="Italic">Adiantum reniforme</Emphasis> var. <Emphasis Type="Italic">sinensis</Emphasis>, endemic to the Three Gorges region in China

Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (P _max) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CC_A), and carbon content (C_A), but lower leaf nitrogen content per unit dry mass (N_M) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CC_A, but their cost/benefic ratios of CCA/P _max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf P _max. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment.     

How Tough are Sclerophylls?

Fracture toughness was estimated for a 'least tough' path inthe leaves of woody species from three sclerophyllous plantcommunities. Most of the species from Mediterranean, tropicalheath forest and lowland tropical rain forest habitats had verytough leaves, with toughness generally 600-1300 J m^-2, whichis two to four times higher than soft-leaved tropical pioneertrees. The toughest leaf (2032 J m^-2), Parishia insignis, camefrom the canopy of the lowland rain forest. Leaves from theshaded understorey of the rain forest did not appear any lesstough than those from the canopy.Copyright 1993, 1999 AcademicPress Leaf fracture toughness, sclerophylly, Mediterranean vegetation, tropical forest     

Performance and fate of tree seedlings on and around nests of the leaf‐cutting ant Atta cephalotes: Ecological filters in a fragmented forest

Habitat fragmentation is currently the most pervasive anthropogenic disturbance in tropical forests and some species of leaf‐cutting ants of the genus Atta (dominant herbivores in the neotropics) have become hyper‐abundant in forest edges where their nests directly impact up to 6% of the forest area. Yet, their impacts on the regeneration dynamics of fragmented forests remain poorly investigated. Here we examine the potential of Atta cephalotes nests to function as ecological filters impacting tree recruitment. Growth, survival and biomass partitioning of experimentally planted seedlings (six tree species) were examined at eight spatially independent A. cephalotes colonies in a large Atlantic Forest fragment. Seedling performance and fate (leaf numbers and damage) were monitored up to 27 months across three habitats (nest centre, nest edge and forest understorey). Plants at illuminated nest centres showed twice the gross leaf gain as understorey individuals. Simultaneously, seedlings of all species lost many more leaves at nests than in the forest understorey, causing a negative net leaf gain. Net leaf gain in the shaded understorey ranged from zero (Licania and Thyrsodium species) to substantial growth for Copaifera and Virola, and intermediate levels little above zero for Protium and Pouteria. Also seedling survival differed across habitats and species, being typically low in the centre and at the edge of nests where seedlings were often completely defoliated by the ants. Lastly, seedling survival increased strongly with seed size at nest edges while there was no such correlation in the forest. Our results suggest that Atta nests operate as ecological filters by creating a specific disturbance regime that differs from other disturbances in tropical forests. Apparently, Atta nests favour large‐seeded tree species with resprouting abilities and the potential to profit from a moderate, nest‐mediated increase in light availability.     

Effects of Leaf Wetness Duration and Inoculum Level on Resistance of Wheat Genotypes to Pyrenophora tritici-repentis

Percent leaf necrosis and lesion length on wheat genotypes increased markedly with increasing duration of leaf wetness (up to 24h or 48 h) following inoculation with Pyrenophora tritici-repentis. A long wetting duration favoured less disease development on resistant (Fink's'), and moderately resistant (Bon/YR/3/F3570//KAL/BB) genotypes than on susceptible Glenlea. No significant difference in per cent necrosis was detected among the upper three leaf positions within a genotype. A long wetness duration had a varying effect on the resistance of wheat genotypes, depending upon the inoculum level. Increasing the inoculum level along with the leaf wetness period increased the per cent leaf necrosis on all three wheat genotypes tested. However, the ranking of the genotype for resistance did not alter even after prolonged duration of leaf wetness (up to 96 h) and/or high inoculum level (12000 conidia/ml water). Various post-inoculation wet-periods in combination with high conidia concentrations in inoculum should be used in identifying highly resistant germplasm in breeding populations at the seedling stage of the wheats.     

How do leaf wetting events affect gas exchange and leaf lifespan of plants from seasonally dry tropical vegetation?

• Foliar uptake of dew is likely an important mechanism of water acquisition for plants from tropical dry environments. However, there is still limited experimental evidence describing the anatomical pathways involved in this process and the effects of this water subsidy on the maintenance of gas exchange and leaf lifespan of species from seasonally dry tropical vegetation such as the Brazilian caatinga.
• We performed scanning electron, bright‐field and confocal microscopic analyses and used apoplastic tracers to examine the foliar water uptake (FWU) routes in four woody species with different foliar phenology and widely distributed in the caatinga. Leaves of plants subjected to water stress were exposed to dew simulation to evaluate the effects of the FWU on leaf water potentials, gas exchange and leaf lifespan.
• All species absorbed water through their leaf cuticles and/or peltate trichomes but FWU capacity differed among species. Leaf wetting by dew increased leaf lifespan duration up to 36 days compared to plants in the drought treatment. A positive effect on leaf gas exchange and new leaf production was only observed in the anisohydric and evergreen species.
• We showed that leaf wetting by dew is relevant for the physiology and leaf lifespan of plants from seasonally dry tropical vegetation, especially for evergreen species.

     

Plant–Microbe Interactions: Wetting of Ivy (Hedera helix L.) Leaf Surfaces in Relation to Colonization by Epiphytic Microorganisms

Abstract Leaf wettability, cuticular wax composition, and microbial colonization of upper and lower leaf surfaces of ivy (Hedera helix L.) was investigated for young and old leaves sampled in June and September. Contact angles of aqueous buffered solutions measured on young leaf surfaces ranged between 76° and 86° and were not dependent on the pH value of the applied droplets. Contact angles measured on old leaf surfaces were up to 32°, significantly lower than on young leaf surfaces. Furthermore, contact angles were significantly lower using aqueous solutions of pH 9.0 compared to pH 3.0, indicating the influence of ionizable functional groups on leaf surface wetting properties. Observed changes in leaf wetting properties did not correlate with different levels of alkanoic acids in cuticular waxes. However, microscopic examination of the leaf surfaces indicated the influence of epiphytic microorganisms on wetting properties of old leaves, since their surfaces were always colonized by epiphytic microorganisms (filamentous fungi, yeasts, and bacteria), whereas surfaces of young leaves were basically clean. In order to analyze the effect of epiphytic microorganisms on leaf surface wetting, surfaces of young and clean ivy leaves were artificially colonized with Pseudomonas fluorescens. This resulted in a significant increase and a pH dependence of leaf surface wetting in the same way as it was observed on old ivy leaf surfaces. From these results it can be deduced that the native wetting properties of leaf surfaces can be significantly masked by the presence of epiphytic microorganisms. The ecological implications of altered wetting properties for microorganisms using the leaf/atmosphere interface as habitat are discussed. Received: 20 March 1999; Accepted: 5 July 1999; Online Publication: 18 July 2000     

Effects of Leaf Wetness Duration and Inoculum Level on Resistance of Wheat Genotypes to Pyrenophora tritici-repentis

Percent leaf necrosis and lesion length on wheat genotypes increased markedly with increasing duration of leaf wetness (up to 24h or 48 h) following inoculation with Pyrenophora tritici-repentis. A long wetting duration favoured less disease development on resistant (Fink's'), and moderately resistant (Bon/YR/3/F3570/KAL/BB) genotypes than on susceptible Glenlea. No significant difference in percent necrosis was detected among the upper three leaf positions within a genotype. A long wetnessduration had a varying effect on the resistance of wheat genotypes, depending upon the inoculum level. Increasing the inoculum level along with the leaf wetness period increased the per cent leaf necrosis on all three wheat genotypes tested. However, the, ranking of the genotype for resistance did not alter even after prolonged duration of leaf wetness (up to 96 h) and/or high inoculum level (12000 conidia/ml water). Various post-inoculation wet-periods in combination with high conidia concentrations in inoculum should be used in identifying highly resistant germplasm in breeding populations at the seedling stage of the wheats.     

Vulnerability to xylem embolism as a major correlate of the environmental distribution of rain forest species on a tropical island

Increases in drought‐induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P₅₀) of 13 woody species endemic to New Caledonia and with different xylem conduit morphologies. We examined the relation between P₅₀, along with other leaf and xylem functional traits, and a range of habitat variables. Selected species had P₅₀ values ranging between ?4.03 and ?2.00 MPa with most species falling in a narrow range of resistance to embolism above ?2.7 MPa. Embolism vulnerability was significantly correlated with elevation, mean annual temperature and percentage of species occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P₅₀. Commonly used functional traits such as wood density and leaf traits were not related to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as a major driver of species environmental distribution. Drought‐induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species.     

Safeguarding the rare woodland species Gagea spathacea: Understanding habitat requirements is not sufficient

A large proportion of temperate forest plant diversity is found in the herb layer. However, for many of its species, little is known about their autecology, which makes it difficult to assess potential threats and efficiently safeguard the diversity of understorey herbaceous communities. This also applies to Gagea spathacea (Liliaceae), a globally rare spring geophyte, which mainly occurs in deciduous forests of northern Central Europe. We investigated the causal relationships between population characteristics of G. spathacea and abiotic site conditions across different forest communities in the center of its distributional range. Leaf length (a surrogate of the species' vegetative propagation) was positively related to soil moisture and soil nitrogen. Consequently, mean leaf length was highest in moist forest communities of the alliance Alno-Ulmion. Moreover, mean variability in leaf length was lowest in those forests, indicating a higher and more stable vegetative propagation via bulbils. We found no support for a significant relationship between leaf length and leaf density or between leaf length and flower formation. Population density varied strongly among forest sites, but was not related to soil moisture and hardly influenced by soil nitrogen. Our results suggest that soil water and nutrient supply play a vital role in determining the species' vegetative propagation, whereas the duration of habitat continuity is most likely an important determinant of population size and density. Conservation strategies therefore require a better understanding of the complex interrelationships between abiotic site conditions and the historical context-dependency of habitats.     

扎龙湿地不同生境芦苇功能性状变异及其对土壤因子的响应

物种的遗传特征和外在环境条件的差异共同决定了植物功能性状的表达,植物功能性状可以反映物种对环境条件的适应策略。采用大样本抽样调查与统计分析方法,比较研究扎龙湿地4种生境（盐碱生境、旱生生境、湿生生境和水生生境）芦苇分株和叶功能性状,分析不同生境芦苇功能性状的分异规律及其对土壤因子的响应。结果表明：（1）不同生境芦苇功能性状均表现出中等程度变异。其中分株和叶性状均以盐碱生境最低（P<0.05）,分株及除叶面积和比叶面积以外的叶性状均以水生生境最高;株高和株重在种群内的变异系数为15.96%-48.61%和38.65%-87.82%,种群间的变异系数为46.58%和66.39%;叶性状在种群内的变异系数为13.21%-72.37%,种群间的变异系数为26.46%-57.03%;（2）不同生境芦苇功能性状间存在协同变化特征。芦苇的株高、株重、叶长、叶宽、叶面积和叶重之间均呈极显著正相关关系（P<0.01）,比叶面积与其他性状的相关性因生境不同存在一定变化;（3）不同生境芦苇的原位土壤因子表现出异质性特征,芦苇功能性状的变异是含水量、pH、有机质和速效氮等土壤因子综合作用的结果。其中含水量、有机质和速效氮为正向驱动,而pH为负向驱动。因此,芦苇通过自我调节功能性状更好地适应不同的生存环境,局域尺度不同生境的土壤因子是引起芦苇功能性状产生分异的导因。     

Epigeal movement of the smoky shrewSorex fumeus following precipitation in ridgetop and streamside habitats

Epigeal movement of smoky shrewsSorex fumeus (Miller, 1895) following precipitation was examined in two habitats with different moisture conditions. Shrews and invertebrates were collected in pitfall traps over several consecutive nights each month from August to November 1996 and from March to August 1997. Capture rates of smoky shrews significantly increased following rainfall at dry ridgetop sites (p=0.001) but not at moist streamside sites (p=0.335). In mesic environments, favorable conditions on the forest floor not associated with precipitation may increase movements of shrews. Available invertebrate biomass did not increase significantly with rainfall in either habitat type (p=0.121 and 0.368). Increased surface activity by smoky shrews after rain events is probably related more to their ecophysiology than to increased prey availability.     

Photosynthetic symmetry of sun and shade leaves of different orientations

Summary The photosynthetic responses to light of leaves irradiated on the adaxial or abaxial surfaces, were measured for plants with contrasting leaf orientations. For vertical-leaf species of open habitats (Eryngium yuccifolium and Silphium terebinthinaceum), photosynthetic rates were identical when irradiated on either surface. However, for horizontal-leaf species of open habitats (Ambrosia trifida and Solidago canadensis), light-saturated rates of photosynthesis for adaxial irradiation were 19 to 37% higher than rates for abaxial irradiation. Leaves of understory plants (Asarum canadense and Hydrophyllum canadense) were functionally symmetrical although they had horizontal orientation. Photosynthetic rates were measured at saturating CO₂, thus differences in the response to incident irradiance presumably resulted from complex interactions of light and leaf optical properties rather than from stomatal effects. Differences in absorptance (400–700 nm) among leaf surfaces were evident for horizontal-leaf species but the primary determinant of functional symmetry was leaf anatomy. Functionally symmetrical leaves had upper and lower palisade layers of equal thickness (vertical leaves of open habitats) or were composed primarily of a single layer of photosynthetic cells (horizontal leaves of understory habitats). Photosynthetic symmetry of vertical-leaf species may be an adaptation to maximize daily integrated carbon gain and water-use efficiency, whereas asymmetry of horizontal-leaf species may be an adaptation to maximize daily integrated carbon gain and photosynthetic nutrient-use efficiency.     

Comparative ecophysiology of CAM and C3 bromeliads. IV. Plant water relations

Abstract An investigation was carried out into the water relations of CAM and C₃ bromeliads in their natural habitat during the dry season in Trinidad. Measurements were made of xylem tension with the pressure chamber and of cell-sap osmotic pressure and titratable acidity on crushed leaf samples. A steady-state CO₂ and H₂O-vapour porometer was also used so that changes in leaf water relations during individual day-night cycles could be directly related to gas-exchange patterns in situ. Xylem tension changed in parallel with transpiration rate and in general reached its maximum value in CAM bromeliads at night and in C₃ bromeliads during the day. In addition, large nocturnal increases in cell-sap osmotic pressure and titratable acidity (ΔH⁺) typically occurred in the CAM bromeliads. The C₃-CAM intermediate Guzmania monostachia showed slight nocturnal acidification, but had higher values of xylem tension during the day. Very high values of AH+ were observed in the CAM species when the tanks of the epiphytic bromeliads contained water: Aechmea nudicaulis showed a mean maximum ΔH⁺ of 474 mol m^?3, the highest value so far observed for CAM plants. On some nights dew formed on the leaf surfaces of the epiphytes, partially curtailing gas exchange and leading to a marked decrease in xylem tension in both C₃ and CAM species. Between-site comparisons were also made for a wide range of habitats from arid coastal scrub to montane rain forest. Compared with values characteristic of other life-forms, xylem tension and cell-sap osmotic pressure were low for all bromeliads, and did not differ significantly in co-occurring CAM and C₃ bromeliads. Mean maximum xylem tension (10 species in total) ranged from 0.29 M Pa at the montane sites to 0.67 MPa at the most arid site, and mean minimum osmotic pressure (17 species) from 0.51 to 0.97 MPa. At the arid sites the bromeliads were exclusively CAM species, two of which (Aechmea aquilega and Bromelia plumieri) grew terrestrially in the undergrowth of the coastal scrub. Xylem tension in these species was low enough to indicate that they must be functionally independent of the substratum during the dry season. In the wetter part of Trinidad, no between-site differences in leaf water relations were found along an altitudinal gradient in the Northern Mountain Range; seasonal differences in this area were also small. Overall, leaf water relations and gas exchange in the bromeliads were strongly affected both by short-term changes in water availability and by longer-term climatic differences in the various regions of the island.     

The role of CAM in high rainfall cloud forests: an in situ comparison of photosynthetic pathways in Bromeliaceae

Crassulacean acid metabolism (CAM), an advanced photosynthetic pathway conferring water conservation to plants in arid habitats, has enigmatically been reported in some species restricted to extremely wet tropical forests. Of these, epiphytic Bromeliaceae may possess absorbent foliar trichomes that hinder gas‐exchange when wetted, imposing further limitations on carbon dioxide (CO₂) uptake. The hypothesis that the metabolic plasticity inherent to CAM confers an ecological advantage over conventional C₃ plants, when constant rainfall and mist might inhibit gas‐exchange was investigated. Gas‐exchange, fluorometry and organic acid and mineral nutrient contents were compared for the bromeliads Aechmea dactylina (CAM) and Werauhia capitata (C₃) in situ at the Cerro Jefe cloud forest, Panama (annual rainfall > 4 m). Daily carbon gain and photosynthetic nutrient use efficiencies were consistently higher for A. dactylina, due to a greater CO₂ uptake period, recycling of CO₂ from respiration and a dynamic response of CO₂ uptake to wetting of leaf surfaces. During the dry season CAM also had water conserving and photoprotective roles. A paucity of CAM species at Cerro Jefe suggests a recent radiation of this photosynthetic pathway into the wet cloud forest, with CAM extending diversity in form and function for epiphytes.