Stem-succulent Research Articles

Modification of Vegetative Phenology in a Tropical Semi-deciduous Forest by Abnormal Drought and Rain1

The control of vegetative phenology in tropical trees is not well understood. In dry forest trees, leaf abscission may be enhanced by advanced leaf age, increasing water stress, or declining photoperiod. Normally, it is impossible to dissect the effects of each of these variables because most leaves are shed during the early dry season when day length is near its minimum and leaves are relatively old. The 1997 El-Niño Southern Oscillation caused a ten-week long, severe abnormal drought from June to August in the semi-deciduous forests of Guanacaste, Costa Rica. We monitored the effect of this drought on phenology and water status of trees with young leaves and compared modifications of phenology in trees of different functional types with the pattern observed during the regular dry season. Although deciduous trees at dry sites were severely water stressed (ΨSTEM < −7MPa) and their mesic leaves remained wilted for more than two months, these and all other trees retained all leaves during the abnormal drought. Many trees exchanged leaves three to four months earlier than normal during the wet period after the abnormal drought and shed leaves again during the regular dry season. Irrigation and an exceptional 70 mm rainfall during the mid-dry season 1998/1999 caused bud break and flushing in all leafless trees except dormant stem succulents. The complex interactions between leaf age and water stress, the principal determinants of leaf abscission, were found to vary widely among trees of different functional types.

Water use trade‐offs and optimal adaptations to pulse‐driven arid ecosystems

Summary We introduce a hydraulic soil‐plant model with water uptake from two soil layers; one a pulse‐dominated shallow soil layer, the other a deeper soil layer with continuous, but generally less than saturated soil moisture. Water uptake is linked to photosynthetic carbon assimilation through a photosynthesis model for C3 plants. A genetic algorithm is used to identify character suites that maximize photosynthetic carbon gain for plants that experience a particular soil moisture pattern. The character suites include allocation fraction to stem, leaves and shallow root, stem capacitance and stem water storage capacity, maximal leaf conductance and sensitivity of leaf conductance to plant water potential, and a critical soil water potential at which shallow roots cease to transfer water. We find that if pulse water is a more important water source than deeper soil water in the environment, optimal phenotypes lean towards adaptations that maximize pulse water use (small root : shoot ratio, predominantly shallow root system, high leaf conductance with high stomatal sensitivity to plant water status). If deeper soil water is more important, phenotypes lean towards adaptations that maximize deeper soil water use (large root : shoot ratio, predominantly deep root system, lower leaf conductance with low stomatal sensitivity). Stem succulence is adaptive only when deeper soil water is unavailable. From among the continuum of derived phenotypes, four phenotypes are selected that resemble the character suites of winter annuals, drought‐deciduous perennials, evergreen perennials and stem succulents. Under common conditions, these phenotypes reproduce many of the responses to drought and water pulse observed in their respective life‐form counterparts. The comparison also highlights the differences in plant life‐form sensitivity to summer and winter drought conditions. Based on these results, we discuss the possible role of annual precipitation patterns in shaping plant adaptations and determining the plant composition of arid and semi‐arid environments.

Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees.

Tropical stem-succulent trees store large quantities of water in their trunks yet remain leafless during the early and mid dry season. In contrast to most other tropical trees, bud break of vegetative buds is not induced in fully hydrated stem succulents between the winter solstice and the spring equinox by leaf abscission, abnormal rain showers or irrigation. Vegetative buds of leafless trees are therefore in a state of endo-dormancy similar to that of temperate perennial plants during early winter. Highly synchronous bud break regularly occurs soon after the spring equinox, often weeks before the first rainfalls of the wet season. These observations suggested that endo-dormancy and bud break might be induced by declining and increasing photoperiods after the autumn and spring equinoxes, respectively. In phenological field observations, we confirmed highly synchronous bud break after the spring equinox in many trees of five stem-succulent species in the northern and southern hemispheres. Shoot growth of potted saplings of Plumeria rubra L. was arrested by a decline in day length below 12 h after the autumn equinox, but continued in saplings maintained in a 13-h photoperiod. Conversely, exposure to a 13-h photoperiod induced bud break of dormant apical buds in saplings and cuttings in January, whereas plants maintained in the natural day length of < 11.7 h remained dormant. Photoperiodic control of endo-dormancy of vegetative buds in stem succulents is thus supported by field observations and experimental variation of the photoperiod. At low latitudes, where annual variation of day length is less than 1 h, bud dormancy is induced and broken by variations in photoperiod of less than 30 min.

Burmannia larseniana (Burmanniaceae): a new species from Thailand

Zhang, D. X. & Saunders, R. M. K. 1999. Burmannia larsenianu (Burmanniaceae): a new species from Thailand. - Nord. J. Bot. 19: 241-244. Copenhagen. ISSN 0107055X. A new semi-mycotrophic species, Burmannia larseniana, is described from northern Thailand. The species is related to B. pusilla, a species widely distributed in Cambodia, Vietnam, Burma, India and Sri Lanka, but can be easily distinguished from the latter by its succulent stem, single-veined leaf, and the outer perianth lobes with double margins that encircle the inner perianth lobes. The ecological preferences of the species are also discussed.

A surprising discovery in the stem-succulent Cynanchum complex in Madagascar

Summary: A new short-stemmed, non-twining species of Karimbolea Descoings, K. mariensis Meve & Liede, is described from Cap Ste. Marie, the southernmost tip of Madagascar.

Wood and Bark Anatomy of Caricaceae; Correlations with Systematics and Habit

Wood and bark anatomy are described for four species of three genera of Caricaceae; both root and stem material were available for Jacaratia hassleriana. Wood of all species lacks libriform fibers in secondary xylem, and has axial parenchyma instead. Cylicomorpha parviflora has paratracheal parenchyma cells with thin lignified walls; otherwise, all cell walls of secondary xylem in Caricaceae except those of vessels have only primary walls. Vessels have alternate laterally elongate (pseudoscalariform) pits on vessel-vessel interfaces, but wide, minimally bordered scalariform pits on vessel-parenchyma contacts. Laticifers occur commonly in tangential plates in fascicular secondary xylem, and rarely in xylem rays. Proliferation of axial parenchyma by zones of tangential divisions is newly reported for the family. Bark is diverse in the species, although some features (e.g., druses) are common to all. Wood of Caricaceae is compared to that of two species of Moringaceae, recently designated the sister family of Caricaceae. Although the wood and bark of Moringa oleifera, a treelike species, differ from those of Caricaceae, wood and bark of the stem succulent M. hildebrandtii, the habit of which resembles those in Caricaceae, simulate wood and bark of Caricaceae closely. Counterparts to laticifers in Moringaceae are uncertain, however. Phloem fibers of Caricaceae form an expansible peripheral cylinder of mechanical tissue that correlates with the stem succulence of most species of Caricaceae.

Photosynthetic pathways inChenopodiaceae from Africa, Asia and Europe with their ecological, phytogeographical and taxonomical importance

Photosynthetic pathways are reported for 305 species ofChenopodiaceae from Africa, Asia and Europe. Ecological characteristics, phytogeography and life forms of all species are given, and their correlation with relevant CO2-fixation types are discussed. 205 species (67.2%) exhibit the C4-pathway and 100 species (32.8%) the C3-pathway of CO2-fixation. Most of the C4 species are of Irano-Turanian origin. The diversity of C4 species of the Irano-Turanian phytochoria, with very harsh winters, are interpreted by the active period of Chenopods in summer. There is a close relationship between some special morphotypes and respective photosynthetic type. Halophytes and xerophytes with articulated stems and stem succulents ofAnabasis-type are exclusively C4. Leaf succulent halophytes and xerohalophytes are predominantly C4. Hygrohalophytes with leaf or stem succulence are often C3. Probably many C4Salsoleae have been evolved in the Afroasiatic arid zone after the climatic changes of the Miocene. Among them there is a high proportion of annuals that have a younger origin. There is some evidence that the present Chenopods of the subfamily “Salsoloideae” may have their ancient stock in NW Africa. We found close taxonomic relationships between photosynthetic pathways and infrageneric classification in genera with both types of C3 and C4, likeAtriplex andSuaeda.

Leaf-like Structure in the Photosynthetic, Succulent Stems of Cacti

This research examined the hypothesis that as cacti evolve to the leafless condition, the stem epidermis and cortex become more leaflike and more compatible with a photosynthetic role. All cacti in the relict genus Pereskia have non-succulent stems and broad, thin leaves. All members of the derived subfamily Cactoideae are 'leafless', having and expanded cortex that is the plant's only photosynthetic tissue (...)

Pelargonium torulosum (Geraniaceae): A new species from the south-western Cape Province, southern Africa

Pelargonium torulosum E.M. Marais, is described as a new species. It resembles P. histrix Harv. and P. stipulaceum (L.f.) Willd. on account of its floral structure, succulent stem and closely spaced leaves. The pollen morphology of the three species as well as the stem and leaf anatomy are compared. An illustration and a distribution map are provided, as well as illustrations of anatomy and pollen.

Comparative Gas Exchange of Leaves and Bark in Three Stem Succulents of Baja California

Comparative Gas Exchange of Leaves and Bark in Three Stem Succulents of Baja California

COMPARATIVE GAS EXCHANGE OF LEAVES AND BARK IN THREE STEM SUCCULENTS OF BAJA CALIFORNIA

Arborescent stem succulents in tropical and subtropical deserts depend on scarce and uncertain rainfall. Gas exchange and the diurnal acidity fluctuation of bark and ephemeral leaves were measured under both dry and moist soil conditions in Fouquieria columnaris (cirio or boojum tree) and Pachycormus discolor (torote bianco or elephant tree) and in stems of the columnar cactus Pachycereus pringlei (cardon) in the Central Desert of Baja California, Mexico. Results demonstrated that ephemeral leaves were the only site of exogenous CO2 assimilation in F. columnaris and P. discolor; there was no measurable gas exchange across the green photosynthetic bark. The pattern of gas exchange in F. columnaris and P. discolor was consistent with that of C3 plants. P. pringlei was shown to be a typical Crassulacean acid metabolism plant on the basis of acid fluctuations and gas exchange. Chlorophyll fluorescence studies of the green bark of F. columnaris and P. discolor indicated that this tissue is photosynthetically functional, and that CO2 assimilation can rise above the compensation point under high CO2 concentrations, such as may occur within the plant. The green photosynthetic bark of these species may be an adaptation for surviving prolonged drought and may function to recycle endogenous respiratory CO2, thus maintaining the plant's energy reserves and permitting rapid production of leaves in response to infrequent rains.

Diel patterns of CO2 exchange for epiphytic cacti differing in succulence

Net CO: uptake over 24‐h periods was examined for 6 species of epiphytic cacti. which as a group number about 120 species that vary considerably in stem succulence. Nocturnal CO, uptake as a percentage of the total daily CO, uptake increased from 0% for Rhipsalis houlletiana to 14% for Epipliyl/urn pittieri to 21% for E. oxypetnluin to 51% for R. rhornbea to 87% for Schlumbergera truncata to 98% for Cryplocercus anthonyamis. For R. houlletiana and S. truncata, maximum net CO, uptake occurred at a photosynthetically active radiation of only 200 μmol m−2 s−1, as is typical for shade plants. Short‐term drought of R. rhombea caused a shift favoring nocturnal CO, uptake. For the 6 species examined, increased reliance on nocturnal CO, uptake characteristic of Crassulacean acid metabolism (CAM) was closely correlated with increases in stem thickness, fresh weight per unit area, water mass per unit area, and to a somewhat lesser extent with another measure of succulence, water mass per unit mass of chlorophyll.

Water relations of stem succulent trees in north-central Baja California.

Water relations of several stem succulent trees were measured in north-central Baja California in comparisons to other growth forms in the same habitat. Our research concentrated on three stem succulent species (Idria collumnaris, Pachycormus discolor and Bursera microphylla) each with a different succulent stem morphology. The stem succulent trees had 1 to 4 kg H2O/m3 of trunk while the other trees and shrubs in the same habitat had 0.6 to 0.8 kg H2O/m3. The diurnal and seasonal variation in leaf water potential was small for the stem succulent species in comparison to deciduous and evergreen species as a consequence of the stem-water, buffering capacity. In addition, the leaf conductance of the stem succulent species was low (60 mmol m-2 s-1) and yet, the leaf conductance decreased through the day similar to adjacent evergreen and deciduous species. The leaves of the stem succulent trees lost turgor at low saturated water deficits (0.06 to 0.14), had comparatively high osmotic potentials, and high values of elastic modulus in comparison to adjacent evergreen and deciduous species. The stem acts as an important buffering mechanism allowing for the maintenance of leaf turgor in these stem succulent trees. The low transpiration rates of the stem succulent trees may be a mechanism to minimize leaf saturated water deficit and extend leaf longevity.

A preliminary investigation of the phenology of subtropical thicket and karroid shrubland in the lower Sundays River Valley, SE Cape

I studied the phenology of a range of growth forms in four vegetation types along an aridity gradient in the lower Sundays River Valley to test two phenology models for semi-arid ecosystems. As aridity increased along the gradient, phenological activity became concentrated within a shorter period. For the most arid site, in the Central Lower Karoo, the data favour Noy-Meir’s (1973) view of a ‘pulse-activity’ phenological response to unpredictable rainfall. In the subtropical thicket communities, geophytes, lianes and leaf and stem succulents — all growth forms which contain water storage abilities — generally grew independently of seasonal rainfall. Communities with a greater number of species with adaptations for water storage generally showed a higher incidence of species which grew outside of the main rainfall period.

Water storage and osmotic pressure influences on the water relations of a dicotyledonous desert succulent

Abstract Water storage and nocturnal increases in osmotic pressure affect the water relations of the desert succulent Ferocactus acanthodes, which was studied using an electrical circuit analog based on the anatomy and morphology of a representative individual. Transpiration rates and osmotic pressures over a 24‐h period were used as input variables. The model predicted water potential, turgor pressure and water flow for various tissues. Plant capacitances, storage resistances and nocturnal increases in osmotic pressure were varied to determine their role in the water relations of this dicotyledonous succulent. Water coming from storage tissues contributed about one‐third of the water transpired at night: the majority of this water came from the nonphotosynthetic, water storage parenchyma of the stem. Time lags of 4 h were predicted between maximum transpiration and maximum water uptake from the soil. Varying the capacitance of the plant caused proportional changes in osmotically driven water movement but changes in storage resistance had only minor effects. Turgor pressure in the chlorenchyma depended on osmotic pressure, but was fairly insensitive to doubling or halving of the capacitance or storage resistance of the plant. Water uptake from the soil was only slightly affected by osmotic pressure changes in the chlorenchyma. For this stem succulent, the movement of water from the chlorenchyma to the xylem and the internal redistribution of water among stem tissues were dominated by nocturnal changes in chlorenchyma osmotic pressure, not by transpiration.

Anatomy of Succulence and CAM in 15 Species of Senecio

The ability of some species of the genus Senecio to perform Crassulacean acid metabolism (CAM) in plants growing both under controlled conditions and outdoors and the anatomy of their photosynthesizing organs, leaves, and/or stems were investigated. The studied species differed in leaf morphology and in degrees of leaf and stem succulence. Malate accumulation differed with environmental conditions. The carbon isotope ratio δ13C indicated that, in most of the species, the C3 carboxylation pathway was operating, although malate fluctuations indicated that CAM cycling occurred. In some species, carbon isotope ratios ranged between C3 and C4 values, indicating switching of photosynthetic pathways. Only two leafless species that were apparently obligate CAM species had a δ13C typical of plants assimilating CO2 through the phosphoenolpyruvate carboxylase pathway.

Partitioning of Foraging Space and Nest Sites in a Desert Shrubland Bird Community

Partitioning of foraging space and nesting substrates by birds was examined in a desert community in southern Arizona. The study site was dominated by low shrubs, with scattered thorn trees and stem succulents. Chi-square analysis demonstrated the importance of plant height, growth form, and patch location within the habitat in selection by birds of foraging and nesting substrates and, ultimately, in determination of bird community composition. Phainopeplas, ash-throated flycatchers, verdins, black-tailed gnatcatchers and gila woodpeckers favored thorn trees for feeding substrates, which they subdivided according to height, plant part and habitat patch. Most of these birds, as well as the common ground feeding species (cactus wrens, curve-billed thrashers, black-throated sparrows and Gambel's quail), also used thorn trees and succulents for nesting sites. The presence of thorn trees and stem succulents apparently enhances avian diversity in complex desert shrublands by providing protected nest sites and a structural framework that facilitates subdivision of foraging space. INTRODUCTION Most ecologists agree that vegetation exerts a major influence on the assemblage of breeding birds that occurs within a habitat. In addition to providing the architectural framework within which birds exist, vegetation affects the supply of both plant and animal foods, nest sites and song perches. MacArthur and MacArthur (1961) inspired a wealth of research into bird community structure when they found a predictive linear relationship between vegetation complexity and bird species diversity in forested habitats of the eastern U.S. Scholars subsequently studied bird communities in various temperate and tropical habitats in efforts to substantiate and refine MacArthur's predictive model (e.g, MacArthur et al., 1962; MacArthur et al., 1966; Recher, 1969; Karr, 1971). The arid portions of the southwestern U.S. are well-represented in this body of literature, with studies done by Tomoff (1974) and others (Austin, 1970; Carothers et al., 1974; Stamp, 1978). In keeping with the ecological attitudes of their day, most scholars studying desert bird communities during the 1970s were concerned with communities as units, which they often summarized with diversity indices. Little attention was paid to variation within communities, such as the use of different vegetation components by individual bird species. Indeed, Tomoff (1974) was one of the few students of arid lands of this era who sought underlying functional links between vegetation structure and birds by examining feeding and nesting habits of the community overall. More recently ecologists have probed beneath the superficial community generalizations that were an outgrowth of MacArthur's time to analyze both species interactions and spatial and temporal variation in community composition. Examples include recent studies of desert bird communities by Rosenberg et al. (1982) and Meents et al. (1983). Both studies are in-depth examinations of habitat characteristics and patterns of species occurrence, but, unlike Tomoffs work, do not attempt analysis of nesting patterns. The intent of this study is to examine patterns of vegetation use for feeding and nesting by common species breeding in a desert shrub habitat in southern Arizona. This analysis addresses two questions: (1) What plant cover characteristics separate the common bird species? (2) To what extent does partitioning of nest sites augment subdivision of foraging substrates in the determination of avian community composition in desert habitats?

A COMPARISON OF TWO NEW METHODS OF PREPARING CACTI AND OTHER STEM SUCCULENTS FOR STANDARD HERBARIUM MOUNTING

SummaryThe attributes of an ethanol bath method of preparing cacti and other stem succulents for mounting on standard herbarium sheets are compared to a microwave method.

Plant types and seasonality of wild-plant foods, Tanzania to Southwestern Africa: Resources for models of the natural environment

Pursuant to understanding the ecological adaptations of the African hominids, we have analysed some of the characteristics of 419 wild plant species exploited for food by humans in a broad portion of the African summer-rain climatic region running from Tanzania to southwestern Africa. With regard to general growth form: trees, arborescents (other woody forms that can mature as trees), and forbs provide the majority of edible species. Although the grasses are diverse and abundant, most appear not to provide food items for humans. Woody rosette forms (e.g. palms and cycads) and truc shrubs (as opposed to arborescents) are both species-poor. The woody vines and lianas appear to provide even fewer edible species. Stem succulents, parasites, and ferns provide almost no edible species. When scasonality and growth form are both taken into consideration, deciduous trees, perennial forbs, and mushrooms are the most species rich “edible” plant types. Deciduous trees primarily provide edible fruit/seed/pods, particularly during the rainy season, leaves in the rainy season and some underground parts on a more or less year-round basis. Perennial forbs provide flowers, fruit/seed/pods, or leaves in the rainy season, but most (78%) of the edible species also provide underground parts on a more or less year-round basis. The general pattern of species providing edible above-ground parts in the rainy season is reinforced by the mushrooms, evergreen/semi-evergreen trees, and arborescents, as well as the speciespoor plant types. The overall potential dictary pattern is that of a pronounced seasonal change in the quality of plant foods, from a variety of types of food items provided by several different types of plants during the rainy season to mainly fruit/seed/pods and/or underground parts in the dry season. This implies a predictable qualitative as well as quantitative scasonal shift in the wild-plant-food diet of prehistoric humans wherever the tropical summerrain climate imposed itself or remained in effect.

Stylites, a vascular land plant without stomata absorbs CO2 via its roots

Photosynthetic organs of most higher plants normally have access to atmospheric CO2 through stomatal pores which also serve as variable valves to control the loss of H2O vapour which accompanies CO2 uptake1. The acquisition of stomata is commonly thought to have been a crucial development permitting ‘conquest’ of land and direct access of plants to atmospheric CO2. Only in desert stem succulents during drought do stomata remain so tightly closed in the light that the photosynthetic tissues are dependent on internal CO2 generated through the photosynthetic pathway known as crassulacean acid metabolism2. Functional stomata are absent in submerged aquatic plants and in non-vascular land plants (for example, mosses) which are normally covered by a water film. Although it is now clearly established that some aquatic plants assimilate large amounts of CO2 from the sediment via roots3–5, terrestrial plants are thought to assimilate only insignificant amounts of CO2 via this path6. Here we report on a terrestrial plant, Stylites andicola, which lacks stomata and is unable to exchange gas with the aerial atmosphere. Rather, it derives nearly all of its photosynthetic carbon through its roots. In addition, this species possesses characteristics of crassulacean acid metabolism.