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Arid Lands (arid + land)
Selected AbstractsInfluence of temperature and salinity on the germination of Lotus creticus (L.) from the arid land of TunisiaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010Mokhtar Rejili Abstract Effects of salinity, temperature and their interactions on the rate and final percentage of germination were evaluated for two populations (Msarref, Oued dkouk) of the invasive glycophyte Lotus creticus Linné, grown under arid environmental conditions of the Tunisia. Seeds that were not treated with NaCl germinated well in a wide range of temperatures. For both populations, maximum germination occurred in distilled water at 25°C and lowest germination for all salinities was at 35°C. Germination was substantially delayed and significantly reduced with an increase in NaCl to levels above 300 mm. Compared to the Oued dkouk population, final germination and germination rate of the Msarref population was completely inhibited at 300 mm NaCl. The interactive effect of temperature and NaCl concentration on final germination and germination rate was significant (P < 0.01), indicating that the germination response to salinity depended on temperature. The inhibition of Oued dkouk population seed germination at high salt concentration was mostly due to osmotic effects while ionic effects were noted at Msarref population. The germination behaviour of the Oued dkouk population would therefore imply adaptive mechanisms to saline environments, while in the Msarref population such mechanisms seem to be absent. Since seed germination is more sensitive to salinity stress than the growth of established plants, the greater tolerance to salinity of Oued dkouk population would be an adaptive feature of this population to saline environment. Résumé L'effet de l'interaction de la salinité et de la température sur la germination de deux populations (Msarref et Oued Dkouk) du lotier de crête (Lotus creticus L.), glycophyte poussant dans des conditions environnementales arides en Tunisie, est étudié. Chez les deux populations, le taux de germination le plus élevé est obtenu à 25°C et le plus faible à 35°C. A 300 mm de NaCl, la germination de la population d'Oued Dkouk est ralentie alors que celle de Msarref est complètement inhibée. L'effet de l'interaction de deux stress est hautement significatif (P < 0,01). Il semble, ainsi, que l'effet de chacun de deux stress est intensifié par l'autre. Cependant, les deux populations montrent un comportement halophytique différent. L'inhibition de la germination, par la salinité, chez Oued Dkouk est due à un effet osmotique alors que chez Mserref, il est ionique. Il en résulte que la population de oued Dkouk présente une capacité adaptative à l'aridité plus importante que celle observée chez la population Msarref. [source] Export of nitrogenous compounds due to incomplete cycling within biological soil crusts of arid landsENVIRONMENTAL MICROBIOLOGY, Issue 3 2007Shannon L. Johnson Summary Second only to water among limiting factors, nitrogen controls the fertility of most arid regions. Where dry and wet depositions are weak, as in the western US deserts, N inputs rely heavily on biological N2 fixation. Topsoil cyanobacterial communities known as biological soil crusts (BSCs) are major N2 fixation hot spots in arid lands, but the fate of their fixed N remains controversial. Using a combination of microscale and mesoscale process rate determinations, we found that, in spite of theoretically optimal conditions, denitrification rates in BSCs were paradoxically immaterial for nitrogen cycling. Denitrifier populations within BSCs were extremely low. Because of this absence of denitrification, and because of the limitation of respiration and ammonia oxidation by diffusive O2 supply, we could demonstrate that BSCs function as net exporters of ammonium, nitrate and organic N to the soils they cover, in approximately stoichiometrically equal proportions. Overall export rates during periods of biological activity are in the range of tens to hundreds of ,mol-N m,2 h,1, commensurate with those of N2 fixation. These results explain the long-term dependence of BSCs on N2 fixation, confirm their role in landscape fertility, and provide a robust argument for conservation of these endangered communities. [source] The uptake of applied ecologyJOURNAL OF APPLIED ECOLOGY, Issue 1 2002S. J. Ormerod Summary 1We asked 229 authors who have published recently in the Journal of Applied Ecology (1999,2001) whether their papers made management or policy recommendations and whether they had evidence of consequent uptake. 2A total of 108 respondents working in the UK (34%), Europe (30%), the Americas (12%), Australasia (11%), Asia (7%) and Africa (6%) reported on 110 papers. They represented agro-ecosystems (35%), temperate forests or woodlands (16%), savanna, grass or arid lands (11%), rivers or wetlands (10%), estuaries or marine systems (7%) and tropical forests (5%). The major organisms were invertebrates (27%), birds (24%), mammals (21%) and higher plants (21%). Topics apparently under-represented in recent coverage include ecosystem science, urban areas, soils, mountain systems, fish, amphibians and lower organisms such as algae. 3Almost all papers (99%) carried recommendations and for 57% there was evidence of uptake in the broad categories of ,environmental management or models', ,information, training and education' and ,monitoring and assessment'. Most uptake involved large geographical scales through habitat or species management plans (32% of cases), effects on reserve design or designation (6%), and effects on agri-environmental policy (5%). The development of further research (11%), the communication of methods to other ecologists (9%), the dissemination of recommendations to practitioners or agencies (7%), and uptake in training or education (5%) were important uses of information. 4Prestige from publication in the Journal of Applied Ecology aided several authors in convincing end-users of research value. User involvement in research as participants or funders was widespread (> 42% of papers), a fact which almost certainly promotes uptake along with the parallel dissemination of management messages. We view applied issues as an important interface between end-users and ecologists of value to ,both' communities but suggest that improved communication will further benefit the sponsorship and application of ecological science. 5The major reason offered for lack of uptake was that it was still too soon after publication (21% of respondents). Costs, difficulty of implementation, the scale of the problem, and ,challenges to existing thinking' each figured in more than one response. 6For some respondents, papers were led by curiosity rather than the need for direct application. Several authors published in the Journal to share ideas internationally, or said that recommendations were general, conceptual or long-term rather than specific. The editors of the Journal of Applied Ecology recognize the seminal importance of contributions that affect policy incrementally and conceptually as much as those with specific application. 7These data provide evidence that ecological science is aiding environmental management and policy across a wide range of regions, ecosystems and types of organisms; rather than merely detecting problems, applied ecology is offering solutions both directly and more diffusely through conceptual advance. We invite the user community to offer their own perspectives about the value of research-led publications such as this Journal, about how links between researchers and users might be strengthened, and about how the uptake of applied ecology might be further advanced. [source] Desert shrubs have negative or neutral effects on annuals at two levels of water availability in arid lands of South AustraliaJOURNAL OF ECOLOGY, Issue 6 2008James T. Weedon Abstract 1Perennial plants have been shown to facilitate understorey annual plant species in arid lands through the modification of spatial patterns of resources and conditions. This effect can result from a balance between simultaneously positive and negative interactions, both direct and indirect. This balance may shift with temporal variability in water availability. 2We conducted a field experiment in a chenopod shrubland in South Australia to separate the effects of shade, below-ground competition, and soil modification by shrubs on the performance of annual plants, and to determine if the strength and direction of the interaction shifted with changes in water availability. 3Annual plant diversity and seedling density was highest in plots established in open sites away from the dominant shrubs (Maireana sedifolia). Experimental removal of M. sedifolia increased seedling density compared to plots under undisturbed shrubs and plots where the removed shrub was replaced with artificial shade. Shading of open plots also reduced seedling density. Annual plant biomass was highest in areas where shrubs had been removed and was reduced by artificial shading. Biomass was higher in open plots than under intact shrubs. Experimental water addition did not alter plant density, but increased biomass across all treatments, particularly in artificially shaded bush plots. 4Synthesis. Our results show that the overall effect of shrubs on the annual plant community in the system is negative under the range of water availabilities experienced during the experiment. This negative net-effect results from a combination of simultaneous facilitation via soil modification, and above- and below-ground competition. Assessment in different systems of different combinations of mechanisms that have simultaneously positive and negative effects will allow us to refine hypotheses seeking to explain the relative importance of facilitation across spatial and temporal gradients. [source] Litter effects on plant regeneration in arid lands: a complex balance between seed retention, seed longevity and soil,seed contactJOURNAL OF ECOLOGY, Issue 4 2005JOSÉ L. ROTUNDO Summary 1The recovery of rare, threatened plant populations can sometimes be achieved through modification of the disturbance regime. Accumulation of litter is likely to follow a reduction in grazing pressure and we therefore examine its effects on seedling recruitment of a threatened species in a temperate arid rangeland. 2We studied the effects of litter on seed longevity in the field and performed glasshouse and field experiments with natural and plastic litter to assess their physical and biological/chemical nature. Seeds were sown on the soil surface, buried or within the litter layer. Published data on spatial distribution of seeds were used to calculate the net effect of litter on seedling recruitment. 3Litter increased seed longevity. In the glasshouse, litter increased seedling emergence and growth for surface, but not for buried, seeds. Seeds within the litter layer (no seed-soil contact) showed reduced seedling emergence and growth. In the field, litter did not have a direct effect but emergence was promoted by burial. 4Integrating the effects of microsite quality and seed density showed that litter microsites recruited c. 50% of Bromus pictus seedlings, double that expected from its cover (25%). The positive effect of litter on seed density and on seed longevity outweighed the negative effect of litter acting as a mechanical barrier to burial. 5Inconsistent effects of litter on plant recruitment in arid environments may be due to responses being dependent on seed size and shape, and thus may represent indirect effects acting via the probability of burial. Alternatively, studies may report effects only on seed retention or emergence and growth rather than net effects on establishment. [source] Compositional nutrient diagnosis and main nutrient interactions in yellow pepper grown on desert calcareous soilsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2004José Luis García-Hernández Abstract Mineral-nutrient stress is one of the main factors limiting crop production, especially in arid lands. The mineral requirement of a crop is difficult to determine, and the interpretation of foliar chemistry composition is not easy. This study was conducted to compute the minimum yield target for fresh fruit of yellow pepper (Capsicum annuum L.) and the corresponding Compositional Nutrient Diagnosis (CND) as well as to identify significant nutrient interactions of this crop in desert calcareous soils. Preliminary CND norms were developed using a cumulative variance-ratio function and the chi-square distribution function. From a small database, we computed means and standard deviations of row-centered log ratios, VX, of five nutrients (N, P, K, Ca, and Mg) and a filling value, R, which comprises all nutrients not chemically analyzed and quantified them in 54 foliar samples of the popular yellow pepper cv. ,Santa Fé'. This cultivar is widely grown in northwest Mexico under arid conditions. These norms are associated to fresh fruit yields higher than 15.04 t ha,1. Principal-component analyses, performed using estimated CND nutrient indexes, allowed us to identify four interactions: negative P-Ca, P-Mg, and N-K, and positive Ca-Mg. Pepper plants growing on calcareous soils tend to take up more Ca and Mg than considered as optimum in other soil conditions. [source] Why do some species in arid lands increase under grazing?AUSTRAL ECOLOGY, Issue 5 2009Mechanisms that favour increased abundance of Maireana pyramidata in overgrazed chenopod shrublands of South Australia Abstract While the abundance of some plant species decreases under high grazing intensity, others become more abundant. Release from competition by decreaser species contributes to this pattern in mesic systems, but this may not be the case in xeric systems where competition may be less intense. Here we examine three mechanisms that may be involved: (i) increased recruitment and growth because of soil changes produced by grazing, for example, increased soil nutrient availability through dung accumulation; (ii) increased recruitment favoured by the breaking up of the lichen crust; and (iii) reduced competition because of the decline of decreaser species. We used field and glasshouse experiments to determine the possible contribution of these mechanisms to the increase of the chenopod Maireana pyramidata around a watering point in a chenopod shrubland of South Australia. There was no evidence of nutrient accumulation close to the watering point, and while seedlings of M. pyramidata responded to nutrient addition, their growth was the same in soil collected from areas with different grazing intensity. While a broken lichen crust increased the emergence of both M. pyramidata and the decreaser Atriplex vesicaria, the effect was larger for the former. We found no competition between seedlings of the two species or between juveniles of A. vesicaria and seedlings of M. pyramidata in glasshouse experiments. Adult plants of both A. vesicaria and M. pyramidata produced similar growth reduction in seedlings of M. pyramidata. Furthermore, a field removal experiment failed to detect any competitive effect of A. vesicaria on M. pyramidata. Our data indicate that the disintegration of the soil crust by grazer activities can be a major factor controlling floristic changes in overgrazed rangelands. These results imply that factors that control establishment may be more important than competition in shaping shrub population dynamics in these systems. Ground surface itself can affect establishment opportunities, and this should be taken into account in management and restoration efforts in arid lands. [source] Climate Change and Pastoral Economy in Kenya: A Blinking FutureACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009Julius M. HUHO Abstract: The present paper examines the changing climatic scenarios and associated effects on livestock farming (pastoralism) in the arid and semi arid lands (ASAL) of Kenya, which cover over 80% of the country. The study was carried out in the semi arid Mukogodo Division of Laikipia District in Kenya. This division received a mean annual rainfall of approximately 507.8 mm and the main source of livelihood was pastoralism. Questionnaire, structured interview, observation and literature review were the main methods of data collection. Rainfall was used in delineating changes in climate. Standardized precipitation index (SPI) and Markov process were used in analyzing drought severity and persistence, respectively. Approximately 38% of all droughts between 1975 and 2005 were prolonged and extremely severe, with cumulative severity indices ranging between ,2.54 and ,6.49. The probability that normal climatic conditions persisted for two or more consecutive years in Mukogodo Division remained constant at approximately 52%. However, the probability of wet years persisting for two or more years showed a declining trend, while persistence of dry years increased with duration. A drying climatic trend was established. This drying trend in the area led to increased land degradation and encroachment of invasive nonpalatable bushes. The net effect on pastoralism was large-scale livestock loss through starvation, disease and cattle rustling. Proper drought monitoring and accurate forecasts, community participation in all government interventions, infrastructural development in the ASAL and allocation of adequate resources for livestock development are some of the measures necessary for mitigating the dwindling pastoral economy in Kenya and other parts of the world. [source] | |||||||||||||