Xerophytic Species Research Articles

Anatomical adaptations in the leaves of selected fynbos species

Fynbos plants experience very harsh conditions during the hot and dry summer months and their leaves are adapted to reduce the loss of water due to transpiration. The leaves of 46 selected fynbos species of 24 families were examined to determine which anatomical adaptations contribute to the reduced rate of transpiration and subsequent reduced water loss. Without exception, all species examined show leaf adaptations typical of xerophytic species. Four typical leaf types are recognized and proposed as models of leaf adaptation: 1. Myrsine type — dorsiventral or isobilateral leaves; more palisade parenchyma present than spongy parenchyma; tissues contain large amounts of phenolic substances. 2. Metalasia type — small dorsiventral leaves with involute margins and a single groove in the adaxial surface; mesophyll is usually inverted. 3. Retzia type — dorsiventral or isobilateral leaves with revolute margins and one or two grooves in the abaxial surface; spongy parenchyma is the main component of the mesophyll. 4. Spatalla type — small centric or near-centric leaves; little or no spongy parenchyma tissue.

Osmoregulatory effect in some metabolites in response to salinity in Atriplex halimus var. schweinfurthii (Chenopodiaceae) With 4 Figures and one Table

AbstractThe present work was conducted to elucidate the biochemical adaptation, and revealed that some of the parameters used serve as good indicators of salinity tolerance and drought resistant in Atriplex halimus L. var. schweinfurthii which distributed in the Mediterranean desert of Egypt. The growth of these plants was not affected by salinity. The metabolic role in osmoregulation is achieved through the accumulation of minerals and proline. Salt stress stimulates the accumulation of all these metabolic products. These accumulation decreased rapidly in plants transferred back to control medium.As suggested for other xerophytic species, it could be assumed that the high tolerance of A. halimus to salinity plays an important role in its ability to endure periods of drought. The role of mineral nutrients and proline accumulation in osmoregulation was discussed.

Leaf surface and anatomy of two xerophytic plants from southern Africa

Leaves of Rhus burchelli Sond. ex Engl. and Eriocephalus ericoides (L.f.) Druce, two xerophytic species from the arid regions of Namaqualand, southern Africa, were investigated. The leaves do not exhibit many xeromorphic features, but some are regarded as of ecological significance. These include the presence of a resinous covering on the leaves of R. burchelli and an oily layer on the leaf surface of E. ericoides. Other features assumed to be of ecological importance include a dense indumentum on young leaves of E. ericoides and large amounts of tanniniferous substances in the leaves of both species. Leaf structure is described and discussed in relation to its ecological significance.

<p><strong>On the occurrence of bryophytes and macrolichens in different lowland rain forest types at Mabura Hill, Guyana</strong></p>

A floristic and ecological study of bryophytes and macrolichens in different lowland rain forest types around Mabura Hill, Guyana, South America, yielded 170 species: 52 mosses, 82 liverworts and 36 macrolichens. Lejeuneaceae account for about 30% of the species and are the dominant cryptogamic family of the lowland rain forest. Special attention was paid to the flora of the forest canopy, by using mountaineering techniques. It appeared that 50% of the bryophyte species and 86% of the macrolichens occurred exclusively in the canopy. Dry evergreen ‘walaba’ forest on white sand is particularly rich in lichens whereas the more humid ‘mixed’ forest on loamy soil is characterized by a rather rich liverwort flora. More species are exclusive to the mixed forest than to dry evergreen forest due to the ‘canopy effect’, i.e. the occurrence of xerophytic species in the outer canopy of both dry and humid forests. Furthermore, canopy species have wider vertical distributions on trees in the dry evergreen forest than in the mixed forest, due to the more open canopy foliage of the dry evergreen forest.

A survey of angiosperm species to detect hypodermal Casparian bands. I. Roots with a uniseriate hypodermis and epidermis

Roots of 181 species from 53 families were surveyed to determine the frequency of Casparian bands in hypodermal layers. For six species, inconclusive data were obtained. The roots of the remaining 175 species were divided into three categories on the basis of this survey. In the first, a hypodermis is absent (12 species): no wall modifications were observed in the outer cortex and this region was permeable to the apoplastic dye Cellufluor. In the second, a hypodermis is present, but a hypodermal Casparian band is absent (seven species). In roots of six species, no wall modifications were detected in the hypodermis; the one remaining species had lignified phi thickenings which were permeable to Cellufluor. In the third, both a hypodermis and a hypodermal Casparian band are present (156 species). These Casparian bands consisted of suberin deposits throughout the width of the anticlinal walls of the hypodermis. The tangential walls of the hypodermis were also suberized, indicating that suberin lamellae were probably also present. Hypodermal Casparian bands were found in roots of hydrophytic, mesophytic and xerophytic species and in members of primitive as well as advanced families. The widespread occurrence of these bands (in 89% of the species surveyed) suggests that they were present in the type ancestral to the flowering plants and that this feature has been retained by many species in this group. The epidermal cell walls of the majority of species examined were suberized but were permeable to Cellufluor.

A survey of angiosperm species to detect hypodermal Casparian bands. II. Roots with a multiseriate hypodermis or epidermis

PERUMALLA, C. J., PETERSON, C. A. & ENSTONE, D. E., 1990. A survey of angiosperm species to detect hypodermal Casparian bands. I. Roots with a uniseriate hypodermis and epidermis. Roots of 181 species from 53 families were surveyed to determine the frequency of Casparian bands in hypodermal layers. For six species, inconclusive data were obtained. The roots of the remaining 175 species were divided into three categories on the basis of this survey. In the first, a hypodermis is absent (12 species): no wall modifications were observed in the outer cortex and this region was permeable to the apoplastic dye Cellufluor. In the second, a hypodermis is present, but a hypodermal Casparian band is absent (seven species). In roots of six species, no wall modifications were detected in the hypodermis; the one remaining species had lignified phi thickenings which were permeable to Cellufluor. In the third, both a hypodermis and a hypodermal Casparian band are present (156 species). These Casparian bands consisted of suberin deposits throughout the width of the anticlinal walls of the hypodermis. The tangential walls of the hypodermis were also suberized, indicating that suberin lamellae were probably also present. Hypodermal Casparian bands were found in roots of hydrophytic, mesophytic and xerophytic species and in members of primitive as well as advanced families. The widespread occurrence of these bands (in 89% of the species surveyed) suggests that they were present in the type ancestral to the flowering plants and that this feature has been retained by many species in this group. The epidermal cell walls of the majority of species examined were suberized but were permeable to Cellufluor.

A fast method to detect the occurrence of nonhomogeneous distribution of stomatal aperture in heterobaric plant leaves : Experiments with Arbutus unedo L. during the diurnal course.

Pressure infiltration of water into a leaf via the stomatal pores can be used to quickly determine whether all stomata are open, or as recently described for several mesophytic and xerophytic species, whether there is a non-homogeneous distribution of stomatal opening (stomatal patchiness) on the leaf surface. Information about this phenomenon is important since the commonly used algorithms for calculation of leaf conductance from water vapor exchange measurements imply homogeneously open stomata, which in the occurrence of stomatal patchiness will lead to erroneous results. Infiltration experiments in a growth chamber with leaves of the Mediterranean evergreen shrub Arbutus unedo, carried out under simulated Mediterranean summer day conditions, where the species typically exhibits a strong midday stomatal closure, revealed a temporary occurrence of stomatal patchiness during the phase of stomatal closure in the late morning and during the stomatal reopening in the afternoon. Leaves were, however, found to be fully (i.e. homogeneously) infiltratable in the morning and in the evening. At midday during maximum stomatal closure, leaves were almost non-infiltratable. During the day, the infiltrated amount of water was found to be linearly correlated with porometer measurements of leaf conductance of the same leaves, carried out with the attached leaves immediately before infiltration.

Rhizosheaths -a neglected phenomenon in Australian agriculture

Rhizosheaths are formed as a result of a proliferation of root hairs that enmesh sand grains to form cylinders on non-branching roots, usually of xerophytic plant species. Their occurrence in eastern Australia on the roots of the mesophytic grasses, Secale montanum and Triticum aestivum, is reported and their probable importance discussed. A technique for separating soil particles from the root hairs is described which should facilitate the study of these structures in other plants.

Xerophytic species evaluated for renewable energy resources

Previously, the USDA Northern Regional Research Center has examined 600 plant species in 88 families for their multipurpose, energy-producing potential. About three-fourths of these species have been from central and southern Illinois, but only about 2% have been from arid or semiarid regions of the United States. For this report, 100 species collected from Arizona were evaluated, bringing the total number of species evaluated at this Center to 700 in 96 families. Plant specimens were analyzed for yields of fractions referred to as “oil,” “polyphenol,” “hydrocarbon,” and protein and were examined for botanical characteristics. Oil and hydrocarbon fractions of selected species were partially characterized. Ten species gave high yields of oil and/or polyphenol. For example,Asclepias linaria yielded 8.7% oil (dry, ash-free sample basis) + 11.7% polyphenol (1.9% hydrocarbon).Rhus choriophylla yielded 7.0% oil + 20% polyphenol (0.4% hydrocarbon) andJuglans major yielded 7.0% oil + 9.4% polyphenol (0.2% hydrocarbon).Pittosporum tobira gave the highest yield of hydrocarbon (23%). Fourteen species contained at least 18% protein. In general, the percentages of species yielding substantial amounts of oil and/or polyphenol were considerably higher for the Arizona species than for those 600 species previously analyzed. Complete analytical data are presented for 38 species and are discussed in relationship to the 600 species previously reported.

Resinous plants as an economic alternative to bioenergy plantations

The resin-producing xerophytic species Grindelia camporum is an economical alternative for bioenergy plantations in arid lands. A hypothetical bioenergy farm consists of the land and agricultural facilities needed to grow, harvest and transport 272, 100 Mg of biomass to the central processing plant, where the plant material is extracted and the bagasse is converted into electricity. A farm of this type could produce plant extractives that are equivalent to crude oil, with a net positive energy balance. Economic analyses of a series of scenarios based on a plantation of this size indicate that bioenergy production in arid lands must be integrated with the generation of higher-priced chemical commodities, such as naval stores rosin.

Photosynthetic pathways in the Bromeliaceae of Trinidad: relations between life-forms, habitat preference and the occurrence of CAM.

An investigation was carried out into the photosynthetic pathways of the complete bromeliad flora of Trinidad (West Indies). Carbon-isotope ratios (δ13C values) were used to distinguish obligate C3 and crassulacean acid metabolism (CAM) species. Measurements were also carried out on some species in the field to test for day-night changes in leaf titratable acidity.A wide range of δ13C values was found. The obligate CAM species had values of -10 to -20‰ and the obligate C3 species of -23 to -35‰ CAM was found (a) in the majority of Tillandsia spp. (Tillandsioideae) and (b) in all species of Bromelioideae. The other genera of the Tillandsioideae appeared to be at least predominantly C3. One species, Guzmania monostachia var. monostachia, was identified as a C3-CAM intermediate, and others may well exist in the Trinidad flora. The influence of factors such as source CO2, photosynthetic photon flux density and ambient humidity in determining the δ13C values is discussed.The taxonomic distribution of C3 and CAM species within the Bromeliaceae is analyzed in terms of the life-forms and ecological types recognized by Pittendrigh (1948). The most xerophytic species (the light-demanding "atmospherics") all show CAM and are restricted to the drier parts of the island. Most of the species with waterstoring "tanks" have a wide geographic distribution: these include light-demanding C3 plants and less light-demanding CAM plants. The shade-tolerant bromeliads, which show a requirement for high ambient humidity, are all C3 plants. We discuss the phylogenetic origins of CAM and the epiphytic habit in the Bromeliaceae.

Genetic control of gynoecy in the buffalo gourd

The buffalo gourd, Cucurbits foetidissima HBK., is currently under Investigation as a possible domesticate. This xerophytic species is sexually dimorphic, developing both monoecious and gynoecious sex types. Male floral buds on gynoecious plants are antherless and abort in early phases of development. High yield potential associated with gynoecy and the breeding implications of sexual dimorphism indicate the future importance of this trait. Progeny from gynoecious X monoecious crosses, monoecious X monoecious crosses, and monoecious self-pollinations were studied to elucidate the mechanism of genetic control of sex expression. A high percentage of plants remained vegetative during their first growth season making statistical treatment of the data difficult. However, observations on the data support a control scheme involving at least one major locus as follows: monoecy results from the homozygous recessive state (m m), whereas gynoecious plants are obligately heterozygous (M m).

Effects of Sulfur Dioxide Fumigation on Photosynthesis, Respiration, and Chlorophyll Content of Selected Lichens

Four lichens-Parmelia bolliana Mull. Arg., Physcia stellaris (L.) Nyl., Xanthoria fallax (Hepp) Am., and Physconia grisea (Lam.) Poelt--listed in order of decreasing mesophytism, were fumigated for 4 hr at 0.01, 0.1, 1.0, and 2.5 ppm sulfur dioxide to determine the effects on photosynthesis, respiration, and chlorophyll content. The lichens had been collected from Populus deltoides Marsh or Tilia americana L. in northeastern South Dakota near a lignite-fired power generator. Photosynthesis decreased after fumigation at 1.0 and 2.5 ppm, but significant decreases occurred only after fumigation at 2.5 ppm. Expressed on the basis of per unit weight chlorophyll content, photosynthesis of Physconia grisea was most sensitive followed by that of Xanthoria fallax, Physcia stellaris and Parmelia bolliana. Expressed on the basis of per unit dry weight of lichen sample, photosynthesis of Physconia grisea was most sensitive followed by Xanthoria fal- lax, Physcia stellaris, and Parmelia bolliana. In both cases, the more xerophytic species were more sensitive. Chlorophyll content in these species was not mea- surably altered by fumigation. Comparison of chlorophyll a and b absorption spec- tra peaks for fumigated and control samples indicated that no phaeophytinisation occurred. Insignificant and inconsistent differences in chlorophyll a/b ratios were observed. Respiration of Physcia stellaris and Parmelia bolliana decreased signif- icantly following fumigation with 2.5 ppm S02; both species were more sensitive than Xanthoria fallax. Physconia grisea was not tested for respiratory responses. The effects of S02 fumigation on measured metabolic rates differed with the species. Photosynthetic rates of the xerophytic Xanthoria fallax and Physconia grisea were more sensitive than the more mesophytic Parmelia bolliana and Phy- scia stellaris. In contrast, respiratory sensitivities to S02fumigation were greater for P. bolliana and P. stellaris. It is well known that lichens are sensitive to air pollution, particularly to sulfur dioxide. Field studies from a variety of locations have reported evidence of the phytotoxicity of sulfur dioxide. Hawksworth's (1971) review of the literature is comprehensive; studies done since 1971 have left his basic conclusions unchanged. Experimental studies to examine the basis of lichen sensitivity have produced inter- esting results, which in some cases are not altogether consistent with field observations. Summaries of experimental studies have been presented by Gilbert (1973) and Nieboer et al. (1976). Experimentally, lichens have been exposed to both low and high concentrations of sulfur dioxide. In studying the effects of exposure on photosynthesis, Pearson & Skye (1965) used concentrations ranging from 102 ppm to 105 ppm. Puckett et al. (1973) used

Air pollutant uptake by xerophytic vegetation: Fluoride

Drought resistance has been found to correlate in some species with resistance to air pollutants. In xerophytic species, drought resistance is often associated with anatomical and physiological leaf characteristics, which control plant water loss. The characteristic path of pollutant uptake in these species could be different from that reported as widespread among mesophytic plants. Measurements of fluoride content in intact and washed plant leaves, leaf water potentials, and exposure to pollutant carrying winds were performed in the vicinity of an aluminum smelter. Electronic fluorine specific microprobe measurements were made to localize fluoride in leaf tissues. The results indicate that fluoride uptake by these species consists in a deposition-adsorption upon the external leaf surface, followed by a slow diffusion to inner tissues which is regulated by the water potential at the epidermis and cuticle. The absence of fluorine accumulation in substomatic tissues suggests that the uptake of gaseous fractions of fumes through stomata would be relatively unimportant when quantitatively compared to the above mechanism.

An equable glaciopluvial in the West: Pleniglacial evidence of increased precipitation on a gradient from the Great Basin to the Sonoran and Chihuahuan Deserts

Dated macrofossil evidence documents the widespread occurrence of woodland in what are now desert lowlands of southwestern North America from the last pleniglacial (ca. 20,000 yr B.P.) to late glacial/Holocene transition (12,000–8000 yr B.P.). The composition of the Pleistocene woodlands indicates that they had already differentiated geographically in modern form, though immensely more extensive than today. The pinyon-juniper woodland ( Pinus monophylla, Juniperus osteosperma) of the Mohave Desert province had not yet penetrated the central Great Basin, but extended from southern Nevada south through the vast lowlands of the Mohave and westernmost Sonoran Deserts to southeastern California and Baja California. The strongly xerophytic Mohavean woodland was characterized by a very well-marked altitudinal and latitudinal zonation with juniper-Joshua tree ( Yucca brevifolia) sorting out below pinyon-juniper woodland, and with live oaks restricted to the upper level along the lower Colorado River drainage. Southeastward, the Sonoran Desert province was similarly zoned, but with the more slender-leaved Pinus edulis var. fallax as pinyon and with more live oaks in the upper zone. However, the pleniglacial woodland of the Chihuahuan Desert province was almost unzoned, inasmuch as the less xerophytic species of pinyon and live oaks prevailed over the entire span of available elevation; the pinyon was the very slender-leaved P. cembroides var. remota. The overall paleozonation indicates a strong northwest-to-southeast gradient of increasing summer rain with decreasing distance from the monsoonal source area over the Gulf of Mexico, as at present, but augmented pluvially along the same gradient. A key piece of evidence is the counterintuitive latitudinal-zonational anomaly between about 30 and 40° N in southwestern North America; the lower limits of modern vegetational zones are depressed with decreasing latitude (e.g., ca. 500 m lower at 34° than at 36° N). The axis of the gradient actually extends from northwest to southeast, paralleling the monsoonal gradient of increasing summer rain, which no doubt causes the apparent anomaly. During the Wisconsinan glacial, the latitudinal anomaly was greatly steepened, a fact requiring a pluvial increase in precipitation over the Southwest. The monsoonalpluvial pattern is supported by the Neotoma record of a northwest-to-southeast gradient of increasing diversity of evergreen oaks requiring summer rain, and by a parallel segregation of pinyon species. Equability of seasons during the last glacial is also suggested by the Neotoma macrofossil data.

Ferns of Rajasthan-behaviour of chlorophyll and carotenoids in drought resistance

The relationship of chlorophylls and carotenoids with drought resistance has been studied in some of the ferns found in Rajasthan, without heating as well as after heating the fronds at 60°C. The xerophytic species showed lesser degradation of chlorophyll and exhibited higher carotenoid contents.

A NUMERICAL–TAXONOMIC STUDY OF THE GENUS BULNESIA (ZYGOPHYLLACEAE): CLUSTER ANALYSIS, ORDINATION AND SIMULATION OF EVOLUTIONARY TREES

Cluster analysis by four methods, ordination by principal component analysis (PCA) and simulation of evolutionary trees (Wagner Trees) were performed on morphological data from 43 characters of eight species of the South American genus Bulnesia (Zygophyllaceae). The results of cluster analysis and principal component analysis in general agree and show that there are three pairs of taxa that appear, or obviously are, closely related. These are the pairs B. arborea–B. carrapo, B. foliosa–B. schickendantzii and B. retama–B. chilensis. These methods also indicate that the southern species B. bonariensis occupies an intermediate position between the pair of northern tropical species (B. arborea, B. carrapo) and the remaining southern species. From the beginning it was assumed that these three multifoliolate species with large flowers may be rather primitive. The Prim network indicates that these three species are closely related among themselves. Also in two of the three Wagner Trees they are placed in a group. In all cases B. sarmientoi is shown as the more remote and isolated of all species. It is regarded as a unique, specialized arboreal species showing extreme reduction in number of leaflets and carpels, leaf and flower size, etc. All graphic representations (Fig. 1–3) show the phenetic similarity or the close phylogenetic relationships of the pairs B. foliosa–B. schickendantzii and B. retama–B. chilensis to each other. These four species would represent a rather advanced group. The most xerophytic species B. retama and B. chilensis are regarded as the most advanced taxa and the most specialized histophysiologically. These occupy extreme and distant positions in PCA diagrams and Prim network, and top positions in the Wagner Trees.

A Numerical-Taxonomic Study of the Genus Bulnesia (Zygophyllaceae): Cluster Analysis, Ordination and Simulation of Evolutionary Trees

Cluster analysis by four methods, ordination by principal component analysis (PCA) and simulation of evolutionary trees (Wagner Trees) were performed on morphological data from 43 characters of eight species of the South American genus Bulnesia (Zygophyllaceae). The results of cluster analysis and principal component analysis in general agree and show that there are three pairs of taxa that appear, or obviously are, closely related. These are the pairs B. arborea–B. carrapo, B. foliosa–B. schickendantzii and B. retama–B. chilensis. These methods also indicate that the southern species B. bonariensis occupies an intermediate position between the pair of northern tropical species (B. arborea, B. carrapo) and the remaining southern species. From the beginning it was assumed that these three multifoliolate species with large flowers may be rather primitive. The Prim network indicates that these three species are closely related among themselves. Also in two of the three Wagner Trees they are placed in a group. In all cases B. sarmientoi is shown as the more remote and isolated of all species. It is regarded as a unique, specialized arboreal species showing extreme reduction in number of leaflets and carpels, leaf and flower size, etc. All graphic representations (Fig. 1–3) show the phenetic similarity or the close phylogenetic relationships of the pairs B. foliosa–B. schickendantzii and B. retama–B. chilensis to each other. These four species would represent a rather advanced group. The most xerophytic species B. retama and B. chilensis are regarded as the most advanced taxa and the most specialized histophysiologically. These occupy extreme and distant positions in PCA diagrams and Prim network, and top positions in the Wagner Trees.

Artificial Hybridization in Hedeoma (Labiatae)

Thirteen species of Hedeoma, representing three subgenera, and one species of Poliomintha were artificially crossed to attempt 52 hybrid combinations. Crossability was generally high, and 83% of the attempted hybridizations between species pairs were successful. Intrasubgeneric hybrids within the subgenus Sature- joides were the most easily obtained, whereas intersubgeneric and intergeneric hy- bridization attempts accounted for most of the crossing failures. Only nine F1 hybrids set viable seed, and almost all of these were intrasubgeneric crosses within subg. Saturejoides. Hybrid sterility is seemingly an important reproductive barrier in Hede- oma; translocations and inversions were among the observed meiotic irregularities. One nearly sterile hybrid was selfed to produce a relatively fertile F2 generation. Intercorrelation analysis of the F2 revealed significant correlations only among re- lated morphological characters and no significant correlations were found between morphology and pollen stainability. It is concluded that, at least in this instance, the barrier of hybrid sterility can be easily overcome and hybridization may be a source of naturally occurring interpopulational variation. Hedeoma in its most recent treatment (Irving, in press) consists of 38 species and five varieties. The genus is most abundantly represented in the American southwest and northern Mexico; five species are also rec- ognized for South America. Hedeoma comprises four subgenera, three of which were part of the present study. The subgenus Poliominthoides consists of shrubby desert species whose relationship to the more her- baceous members of Hedeoma and to the genus Poliomintha has long been questioned (Gray, 1878; Briquet, 1897; Epling & Stewart, 1939; Irving, in press). The subgenus Ciliatum is made up of caespitose perennials with relatively localized distributions. These form a morphologically dis- continuous unit in Hedeoma which may be best treated as a separate genus, as was done by Epling (1940). The subgenus Saturejoides houses the majority of the species of Hedeoma. Typically, members of this group are inbreeding, herbaceous perennials which are widespread in arid re- gions. Within subg. Saturejoides four xerophytic species groups have been discerned, each linked morphologically to a more restricted, outbreed- ing, montane species. It has been suggested by Irving (1976; in press) that the outbreeding species are ancestral for their respective complexes and evolved from a common stock subsequent to geographic separation. The inbreeding xerophytes, in turn, are believed to have evolved con- comitant with the formation of reproductive barriers, isolating them from their outbreeding ancestors.

Energy exchange phenomena, physiological rates and leaf size variation.

Leaf temperatures have often been observed to crossover air temperatures in such a way that they vary less than air temperature. The significance of this bevavior to optimal leaf size is examined both from the aspect of energy balance and leaf photosynthesis and transpiration. Larger leaves are shown to be buffered more from air temperatures than smaller leaves, but this benefit is more than offset by reductions in photosynthesis. Under certain conditions, however, leaf temperature and photosynthesis is leaf size independent. The location of this size independent behavior along an air temperature gradient is related to changes in leaf resistance and suggests a mechanism by which high levels of leaf size variation are maintained in plants and leads to the prediction that leaf size variation is greater in mesophytic species than in xerophytic species.