Water relations and leaf chemistry of Chrysothamnus nauseosus ssp. consimilis (Asteraceae) and Sarcobatus vermiculatus (Chenopodiaceae)

At Mono Lake, California, we investigated field water relations, leaf and xylem chemistry, and gas exchange for two shrub species that commonly co-occur on marginally saline soils, and have similar life histories and rooting patterns. Both species had highest root length densities close to the surface and have large tap roots that probably reach ground water at 3.4-5.0 m on the study site. The species differed greatly in leaf water relations and leaf chemistry. Sarcobatus vermiculatus had a seasonal minimum predawn xylem pressure potential (ψ_pd) of -2.7 MPa and a midday potential (ψ_md) of -4.1 MPa. These were significantly lower than for Chrysothamnus nauseosus, which had a minimum ψ_pd of -1.0 MPa and ψ_md of -2.2 MPa. Sarcobatus had leaf Na of up to 9.1 % and K up to 2.7 % of dry mass, and these were significantly higher than for Chrysothamnus which had seasonal maxima of 0.4% leaf Na and 2.4 % leaf K. The molar ratios of leaf K/Na, Ca/Na, and Mg/Na were substantially lower for Sarcobatus than for Chrysothamnus. Xylem ionic contents indicated that both species excluded some Na at the root, but that Chrysothamnus was excluding much more than Sarcobatus. The higher Na content of Sarcobatus leaves was associated with greater leaf succulence, lower calculated osmotic potential, and lower xylem pressure potentials. Despite large differences in water relations and leaf chemistry, these species maintained similar diurnal patterns and rates of photosynthesis and stomatal conductance to water vapor diffusion. Sarcobatus ψ_pd may not reflect soil moisture availability due to root osmotic and hydraulic properties.     

Effects of salinity on uptake and distribution of Na+, Cl- and K+ in two wheat cultivars

Plants of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance were grown in sand with nutrient solutions. 35-d-old plants were subjected to 5 levels of salinity created by adding NaCl, CaCl₂ and Na₂SO₄. Growth reduction caused by salinity was accompanied by increased Na⁺ and Cl^- concentrations, Na⁺/K⁺ ratio, and decreased concentration of K⁺. The salt tolerant cv. Kharchia 65 showed better ionic regulation. Salinity up to 15.7 dS m^-1 induced increased uptake of Na⁺ and Cl^- but higher levels of salinity were not accompanied by further increase in uptake of these ions. Observed increases in Na⁺ and Cl^- concentrations at higher salinities seemed to be the consequence of reduction in growth. Uptake of K⁺ was decreased; more in salt sensitive cultivar. This was also accompanied by differences in its distribution.     

Keratella distribution in North Patagonian lakes (Argentina)

The distribution of Keratella species from 15 different lakes in North Patagonia (Argentina) was analysed. The genus was not present at altitudes above 1000 m. K. tropica was restricted to Patagonian Plateau lakes with a comparatively high conductivity. A morphometric analysis of the widely distributed K. cochlearis was performed. Results showed three groups of K. cochlearis corresponding to Andean lakes, Patagonian Plateau lakes and a Patagonian Reservoir.     

Aquatic Oligochaeta in Italy, with special reference to Naididae

We present a list of Italian freshwater and marine Oligochaeta in the families Lumbriculidae, Haplotaxidae, Tubificidae, Naididae, Propappidae, Criodrilidae, and Lumbricidae, representing 57 genera and 130 species. Published data reflect the incomplete knowledge of the Italian oligochaete fauna, restricted to certain geographical areas. Subterranean aquatic and marine fauna are of particular interest as these have been studied the least. We provide a comprehensive review of the Naididae including, for the first time, southern Italy and the islands of Sicily and Sardinia. The distribution of species is discussed and taxonomic problems arising from the morphological variability of Italian material are examined.     

Changes in foliage distribution with relative irradiance and tree size: Differences between the saplings ofAcer platanoides andQuercus robur

Dependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings ofAcer platanoides andQuercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length of live crown per TH) greater in taller trees. However, the distribution was more uniform inA. platanoides than inQ. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased inQ. platanoides and decreased inQ. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with decreasing irradiance inA. platanoides, but it was independent of irradiance inQ. robur. Higher foliage maximum at lower irradiance in more shade-tolerantA. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability of this species in light-limited environments. Consequently, these differences in crown architecture and foliage distribution may partly explain the superior behavior ofA. platanoides in understory.     

Analysis of the multi-stem clump structure ofLitsea japonica Juss. growing in a coastal dwarf forest

The multi-stem clump structure of a coastal dwarf forest dominated byLitsea japonica Juss. was investigated in order to clarify the sprouting characteristics and self-maintenance of clumps by stem alternation. The size and age distribution of multi-stem clumps were analyzed using cumulative relative frequency curves.L. japonica had a large number of stems and an even height distribution or young age-biased distribution of stems within a clump. These results indicated the sequential flushing of sprouts at high frequency. Height distribution within a clump ofL. japonica was relatively even compared to other species. This clump structure suggested the stable self-maintenance of individuals in all ranges of size and age without disturbances. It originated specific sprouting characteristics as a response to the severe stress of salty wind.Ardisia sieboldii Miq. had few stems within a clump. Although the stem height distribution of large individuals tended to be even, most clumps had a large size-biased distribution of stem height which indicated simultaneous sprouting. From this structure, sprouts of this species were thought to be of less significance in the stable self-maintenance of individuals thanL. Japonica.     

High elevation coniferous vegetation of Guatemala

A phytosociological study of the juniper (locally called huito), pine (locally called sacch), pine-alder and fir forests of the Sierra de los Cuchumatanes and Cadena Volcánica in Guatemala was carried out. The Zürich-Montpellier approach was followed. In total 119 relevés were sampled and the data were organised in phytosociological tables to distinguish vegetation clusters. TWINSPAN was used to evaluate major differences among plant communities. Seven zonal plant communities were distinguished and described, namely: (1)Relbunium microphyllum-Agrostis tolucensis, (2)Werneria nubigena-Agrostis exserta, (3)Lachemilla vulcanica-Pinus hartwegii, (4)Holodiscus argenteus-Pinus hartwegii, (5)Hypnum cypressiforme-Juniperus standleyi, (6)Agave hurteri-Alnus firmifolia and (7)Sabazia pinetorum-Abies guatemalensis. This paper provides a thorough floristic characterisation of each community and outlines the major anthropogenic activities. To conclude, ecologic and floristic (dis)similarities between plant communities of the study area and those of Central Mexico, like the different altitudinal distribution of fir forests and the establishment of mid-successional communities such as theAgave hurteri-Alnus firmifolia were discussed.     

The vegetation of the Puna Belt at laguna de Pozuelos Biosphere Reserve in northwest Argentina

The presence of species and their cover values together with soil and topographic characteristics were recorded at 40 sites along an altitudinal gradient of the Puna Belt at Pozuelos, in the High Andes in northwest Argentina. Classification and ordination of plant assemblages showed that soil and topography were the best predictors of the variation in species distribution. The different plant assemblages which occur along the topographic gradient follow the geographic variation in rainfall in this Andean region. Perennial bushes and grasses colonize the plains and slopes with fine textured soils which retain their water content. In contrast, deciduous bushes and cactuses grow on steep, rocky, dry slopes. Open woods also occur on east-facing steep, rocky slopes which are sheltered from winds.     

The status and ecology of a Juniperus excelsa subsp. polycarpos woodland in the northern mountains of Oman

Juniperus excelsa subsp. polycarpos (K. Koch) Takhtajan is found in mountain areas from Turkey through to India and as an isolated population on Jebel Akhadar in the northern mountains of Oman. Juniperus is one of the dominant plant species in these mountains and a major landscape feature of several proposed National Nature and Scenic Reserves and of Hayl Juwari, a wooded valley at 2250 m altitude proposed as a Botanical Site of Special Interest. Above 2400 m altitude the Juniperus woodlands generally appear to be regenerating and in good condition, both on exposed slopes and in wadis and sheltered gullies, whereas below 2400 m most stands are in poor condition and exhibit few signs of regeneration. If the apparently poor condition of the lower altitude woodlands is due to any long term change in climatic conditions, both tree status and regeneration would be poorer in relatively more xeric habitats. To test this prediction we have carried out a detailed survey of the status and ecology of a 32 ha area of Hayl Juwari, and analysed differences in tree status and regeneration between wadis (relatively more nesic sites) and non-wadi areas (relatively more xeric). Approximately one third of the trees are dead, and an analysis of the height, condition, regeneration, female cone production, preferred germination sites and spatial distribution of trees indicates the importance of topography, hydrology and microclimate for growth. However, although there are relatively greater numbers of dead and poor-condition trees in the more xeric non-wadi habitat, there is no unequivocal evidence that the present distribution of small, sexually immature trees in both habitats could not form a pattern of larger, sexually mature trees similar to that seen today. We speculate, however, that the climate at this altitude may be marginal for the survival of a J. excelsa subsp. polycarpos woodland and that even small increases in climatic stress could imperil the woodland's present status.