Xeric Environments (xeric + environment)

Distribution by Scientific Domains


Selected Abstracts


Temporal and shrub adaptation effect on soil microbial functional diversity in a desert system

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2009
V. Saul-Tcherkas
Summary The Negev Desert is characterized by spatial and temporal patterns of resource distribution, in which soil biota are considered to be among the most sensitive biological characteristics, easily influenced by changes related to soil and abiotic factors. Soil water availability and organic matter are among the most important factors, acting as triggers that determine the length of the period of activity. The main source of organic matter in this xeric environment is input from annual and perennial shrubs. In order to persist and propagate in this xeric environment, the plants have developed different ecophysiological adaptations (e.g. the excretion of salt (Reaumuria negevensis) and chemical compounds (Artemisia sieberi) via the leaves). We found that the values of soil moisture obtained for soil samples collected in the vicinity of R. negevensis were larger than for samples collected in the vicinity of Noaea mucronata and A. sieberi and in the open area. The maximum values of CO2 evolution, microbial biomass and Shannon index (H,) were obtained for the samples collected from the vicinity of N. mucronata. Therefore, we assume that the vicinity of N. mucronata afforded the best conditions for the soil bacterial community. In the Negev Desert, we also found that water availability and pulses of rain compared with frequent rainfall influenced CO2 evolution, microbial biomass, qCO2 and the Shannon index (H,). The differences in water amount and availability between the two rainy seasons caused larger values in most of the properties during the first four seasons (December 2005,November 2006) compared with the last four seasons (December 2006,November 2007) for most of the samples. [source]


Temporal patterns of geographic parthenogenesis in a freshwater snail

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2007
FRIDA BEN-AMI
Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata: Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 711,718. [source]


Patterns and consequences of differential vascular sectoriality in 18 temperate tree and shrub species

FUNCTIONAL ECOLOGY, Issue 2 2006
A. E. ZANNE
Summary 1Resource delivery within plants depends on supply pathways. Some species have relatively constrained (sectored) vascular connections, while others have relatively unconstrained (integrated) vascular connections. 2In this study, patterns of vascular hydraulic sectoriality, anatomy and ecological tolerance were examined for 18 Northern Hemisphere temperate woody species growing at Arnold Arboretum, Jamaica Plain, MA, USA. A hydraulic technique was used to measure axial and tangential conductivity on branch segments. From a ratio of these values, a sectoriality index was calculated. 3Species that were more hydraulically sectored had greater vessel size, variation in vessel area and tangential nearest-neighbour distance, as well as lower vessel density, than did integrated species. 4Ecologically, higher tolerance to drought and wind was correlated with being sectored, while higher tolerance to flood and shade was correlated with being integrated. 5These results suggest that sectored species should be especially prominent in xeric environments where sectoriality may reduce embolism spread by minimizing vessel-to-vessel contact and pitting, and integrated species should be especially prominent when resources are spatially patchy or heterogeneous. [source]


Moisture availability influences the effect of ultraviolet-B radiation on leaf litter decomposition

GLOBAL CHANGE BIOLOGY, Issue 1 2010
W. KOLBY SMITH
Abstract Altered surface ultraviolet-B (UV-B) radiation resulting from a combination of factors that include changes in stratospheric ozone concentrations, cloud cover, and aerosol conditions may affect litter decomposition and, thus, terrestrial nutrient cycling on a global scale. Although litter decomposition rates vary across biomes, patterns of decomposition suggest that UV-B radiation accelerates litter decay in xeric environments where precipitation is infrequent. However, under more frequent precipitation regimes where litter decay rates are characteristically high, the effect of UV-B radiation on litter decomposition has not been fully elucidated. To evaluate this association between moisture regime and UV-B exposure, a litter decomposition experiment was designed for aspen (Populus tremuloides) leaf litter, where conditions that influence both abiotic (photodegradation) and biotic (microbial) processes could be manipulated quantitatively. We found that experimentally increasing UV-B exposure (0, 7.4, and 11.2 kJ m,2 day,1, respectively) did not consistently increase litter decomposition rates across simulated precipitation frequencies of 4, 12, and 24 days. Instead, a UV-B exposure of 11.2 kJ m,2 day,1 resulted in a 13% decrease in decomposition rates under the 4-day precipitation frequency, but an increase of 80% under the 24-day frequency. Furthermore, the same UV-B dose increased litter decomposition rates under the 24-day precipitation frequency by 78% even in conditions where microbial activity was suppressed. Therefore, under more xeric conditions, greater exposure to UV-B radiation increased decomposition rates, presumably through photodegradation. In contrast, when decomposition was not moisture-limited, greater UV-B exposure slowed decomposition rates, most likely from the resulting inhibition of microbial activity. Ultimately, these experimental results highlight UV-B radiation as a potential driver of decomposition, as well as indicate that both the direction and magnitude of the UV-B effect is dependent on moisture availability, a factor that may change according to future patterns in global precipitation. [source]


Discontinuous gas exchange and water loss in the keratin beetle Omorgus radula: further evidence against the water conservation hypothesis?

PHYSIOLOGICAL ENTOMOLOGY, Issue 4 2000
Mareza Bosch
Summary Discontinuous gas exchange cycles are demonstrated in Omorgus radula (Erichson) (Coleoptera, Trogidae) for the first time, thus extending evidence for such cycles to another family of beetles. The closed, flutter and open phases of the cycle were clearly distinguishable in this species, and the duration of these phases was 221 ± 28, 1403 ± 148 and 755 ± 43 s (mean ± SE), respectively. No evidence for significant intraspecific mass scaling of VCO2 or any of the components of the cycle was found. Although the prolonged F-phase recorded here is unusual for many insects, it has previously been found in other scarabaeoid beetles, especially those from xeric environments. It has been suggested that such modulation of the discontinuous gas exchange cycle may result in a reduced VCO2 and, consequently, reduced water loss. In O. radula VCO2 (15.25 ± 1.49 ,l/h) was considerably lower than that predicted from its body mass (0.207 ± 0.006 g). However, the small relative contribution of respiratory transpiration (6.5%) to total water loss indicated that reduced VCO2 has little to do with water economy. Rather, it may be a consequence of generally low activity levels of these beetles. The low respiratory water loss, but distinct subterranean component in the adult life of O. radula, lend some credence to the hypothesis suggesting that regular use of subterranean habitats might have been responsible for the evolution of discontinuous gas exchange cycles. However, non-adaptive hypotheses can still not be discounted. [source]


Cyclitols and carbohydrates in leaves and roots of 13 Eucalyptus species suggest contrasting physiological responses to water deficit

PLANT CELL & ENVIRONMENT, Issue 11 2006
ANDREW MERCHANT
ABSTRACT In many tree species, physiological adaptations to drought include the accumulation of osmotically active substances and/or the presence of particular compatible solutes, among them cyclitols. Recently, the cyclitol quercitol was identified in species of Eucalyptus, a diverse genus whose speciation is probably driven by adaptation to water availability. We subjected seedlings of 13 Eucalyptus species from different ecosystems (,mesic' and ,xeric') and different sub-generic taxonomic groups to 10 weeks of water deficit (WD) treatment. Pre-dawn water potentials (,pdwn) and relative water content (RWC) were determined in shoots, and total osmolality, soluble low-molecular-weight carbohydrates and cyclitols were measured in leaves and roots. Responses to water deficit followed two distinct patterns: Eucalyptus species from ,mesic' environments adjusted concentrations of sucrose (through increased levels of sucrose and decreases in RWC) in response to water deficit, whereas ,xeric' species increased concentrations of quercitol (through reductions in RWC). In root tissues, only species from xeric environments contained high levels of quercitol and mannitol, increasing under WD conditions. We suggest that the former (mesic) strategy may be beneficial to respond to short-lasting drought conditions, because sucrose is easily metabolized, whereas the latter (xeric) strategy may relate to an effective acclimation to longer-lasting drought. These physiological response groups are also related to taxonomic groups within the genus. [source]