Seasonal patterns of cellulase concentration in desert soil

The concentration of cellulose in plant material greatly affects the decomposition rate of plant-derived litter and hence carbon availability. The disappearance of pure cellulose in soil was studied as a measure of plant decomposition and carbon turnover. Our objective was to understand the effect of various cellulose concentrations and plant material added to soil and collected during different seasons, on cellulase concentrations under laboratory conditions (e.g. constant soil moisture and incubation temperature). The percentage of recovery of the enzyme in the control soil and in samples amended with known amounts of cellulose powder was estimated. Several methods for estimating soil cellulase concentrations/activity are available, most based on the determination of released reducing sugars. The method used in this study is based on the cleavage of a cellulose-azure substrate by cellulase to spectrophotometrically detectable fragments. Our results showed a significant correlation (p<0.05) between cellulose concentration and cellulase levels in soil, which varied along the study period. When pure cellulose was added to the soil, cellulase was detected after 7 days of incubation, whereas when plant material was added to the soil, cellulase was detected after 14 days. The recovery of cellulase from soil was also found to be seasonally dependent. The method of cellulase determination used in this study was simple, safe and rapid. From the results presented in this study, it can be assumed that there are seasonally dependent factors that affect the existence and concentration of cellulase in soils of the arid Negev Desert, in addition to organic matter, water and temperature.     

Changes in sugars,acids, and volatiles during ripening of koubo [Cereus peruvianus (L.) Miller] fruits

The columnar cactus Cereus peruvianus (L.) Miller, Cactaceae (koubo), is grown commercially in Israel. The unripe fruits are green, and the color changes to violet and then to red when the fruit is fully ripe. The content of soluble sugars was found to increase 5-fold during ripening. Glucose and fructose were the main sugars accumulated in the fruit pulp, and each increased from 0.5 to 5.5 g/100 g fresh weight during ripening. The polysaccharides content decreased during ripening from 1.4 to 0.4 g/100 g fresh weight. The titratable acidity decreased and the pH increased during ripening. The major organic acid found in the fruit was malic acid, which decreased from 0.75 g/100 g fresh weight at the mature green stage to 0.355 g/100 g fresh weight in ripe fruits. Citric, succinic, and oxalic acids were found in concentrations lower than 0.07 g/100 g fresh weight. Prominent accumulation of aroma volatiles occurred toward the end of the ripening process. The main volatile found in the ripe fruit was linalool, reaching concentrations of 1.5-3.5 microg/g fresh weight.     

真菌群落沿气候梯度与植物凋落物分解之间的关系研究

The decomposition of plant litter is a major process of equivalent status to primary production in ecosystem functioning. The spatiotemporal changes in the composition and dynamics of litter fungal community along a climate gradient ranging from arid desert to humid-Mediterranean regions in Israel was examined using wheat straw litter bags placed at four selected sites along the climate gradient, arid, semi-arid, Mediterranean, and humid-Mediterranean sites. Litter samples were collected over a two-year decomposition period to evaluate litter weight loss, moisture, C：N ratio, fungal composition, and isolate density. The litter decomposition rate was found to be the highest during the first year of the study at the Mediterranean and arid sites. Although the Shannon-Wiener index values of the fungal communities in the litter samples were the highest at the humid-Mediterranean site, the number of fungal species was not significantly different between the four study sites. Different fungal groups were found to be related to different study sites： Basidiomycota, Mucoromycotina, and teleomorphic Ascomycota were associated with the humid-Mediterranean site, while Coelomycetes were mostly affected by the arid site. Our results indicate that climate factors play an important role in determining the structure of saprotrophic fungal communities in the decomposing litter and in mediating plant litter decomposition processes.     

Spatial heterogeneity of a microbial community in a sandy soil ecosystem

A fieldwork was carried out in Caesarea sand dunes, Israel, to determine the influence of fine-scale landscape-patch abiotic-factor heterogeneity on microbial activity in a Mediterranean region. Soil organisms in terrestrial systems are unevenly distributed in time and space, and are often aggregated. Spatio-temporal patchiness in the soil environment is thought to be crucial for the maintenance of soil biodiversity, providing diverse microhabitats that are tightly interwoven with resource partitioning. Determination of a ‘scale unit’ to help understand ecological processes has become one of the important and most debatable problems in recent years. To better understand the distribution of soil microbial communities at multiple spatial scales, a survey was conducted to examine the spatial organization of the community structure in two sandy soil ecosystems. One-hundred forty-four soil samples were collected from two patches 4000 m apart from each other. Basal respiration (CO₂ evolution without the addition of any external substrate), microbial biomass, functional diversity, and community-level physiological profile (CLPP) in soil were measured with a MicroResp? system. Soil abiotic analysis was performed by soil standard analytical methods. The results demonstrated that bacterial distributions can be highly structured, even within a habitat that appears to be relatively homogeneous at the plot and field scale. Different subsets of the microbial community were distributed differently across the plot. This is due to spatial heterogeneity associated with soil physical, chemical, and biological properties. Although spatial variability in the distribution of soil microorganisms is generally regarded as random, this variability often has a predictable spatial structure. This study provided evidence that a spatially explicit approach to soil ecology can enable the identification of factors that drive the spatial heterogeneity of populations and activities of soil organisms, at scales ranging from meters to hundreds of meters. Furthermore, there is increasing evidence that spatial soil ecology can yield new insights into the factors that maintain and regulate soil biodiversity, as well as on how the spatial distribution of soil organisms influences plant growth and plant community structure.     

A multipronged approach for the detection of leptospirosis in captive sloth bears (Melursus ursinus) in Agra and Bannerghatta sloth bear rescue centers in India

Leptospirosis is an exacerbating factor responsible for the drastic decline of sloth bear population in India. In this study, a multipronged approach based on antigen detection using Polymerase Chain Reaction (PCR) employing G1/G2 and LigBF/LigBR primers, antibody detection using Microscopic Agglutination Test (MAT) and recombinant LigBCon1-5 antigen based Latex Agglutination Test (rLigBCon1-5 LAT), serum biochemistry using hepatic (serum glutamate oxalo acetic transaminase (SGOT) and serum glutamate pyruvic transaminase (SGPT) and renal biomarkers (blood urea nitrogen (BUN) and Creatinine) and gross/histopathological evidence in liver and kidneys were employed to investigate leptospirosis in captive sloth bears. A total of 133 serum samples collected from Agra (n=113) and Bannerghatta (n=20) sloth bear rescue centers were screened using MAT and rLigBCon1-5 LAT. A total of 87 and 78 sera tested positive by MAT and LAT respectively. Pyrogenes was the leading serovar obtained using MAT followed by Icterohaemorrhagiae, Javanica, Grippotyphosa, Canicola and Tarassovi. The relative sensitivity, specificity and accuracy of rLigBCon1-5 LAT in comparison to MAT were 89.66%, 100% and 93.23% respectively. PCR performed on hepatic and renal tissues showed amplicon of 285 and 219 base pairs for G1/G2 and LigBF/LigBR primers respectively. Gross evidence (icteric liver, severely engorged hepatic sinusoids, congested kidneys with necrotic white spots on sub capsular surface), histopathology (severe hepatic degeneration and tubulointerstitial nephritis) and elevated hepatic/renal biomarkers were suggestive of leptospirosis. This study suggests that rLigBCon1-5 LAT can be employed as a pen-side test for detecting leptospirosis in sloth bears.     

沙漠系统中豆类作物根际附近区域土壤微生物群落研究

The aim of the current study was to gain a better understanding of the changes in soil microbial biomass and basal respiration dynamics in the vicinity of the bean caper （Zygophyllura duraosura） perennial desert shrub and the inter-shrub sites. Microbial biomasses as well as basal respiration were found to be significantly greater in the soil samples taken beneath the Z. duraosura shrubs than from the inter-shrub sampling sites, with no differences between the two sampling layers （0-10 and 10-20 cm） throughout the study period. However, seasonal changes were observed due to autumn dew formation, which significantly affected microbial biomass and basal respiration in the upper-layer inter-shrub locations. The calculated metabolic coefficient （qCO2） revealed significant differences between the two sampling sites as well as between the two soil layers, elucidating the abiotic effect between the sites throughout the study period. The substrate availability index was found to significantly demonstrate the differences between the two sites, elucidating the significant contribution of Z. duraosura in food source availability and in moderating harsh abiotic components. The importance of basal microbial parameters and the derived indices as tools demonstrated the importance and need for basic knowledge in understanding plant-soil interactions determined by an unpredictable and harsh desert environment.     

Origin and history of old cucurbit cultivars in Israel and the sources of several internationally important market types

Over the past century, Israel was a focal point for the improvement of local cucurbit landraces and introduction of cucurbit germplasm. Some improved open-pollinated cucurbit cultivars developed in Israel became established as market types of considerable economic importance far beyond its borders. The origin and history of these cultivars is not widely known and therefore the purpose of the present work was to collect and compare the records relevant to the development of these cultivars, and to describe them more fully. The four economically most important cultivars originated through mass-selection by amateur breeders and were named after their respective farming communities. The ‘Bet Alfa’ cucumber (Cucumis sativus) was selected from a local landrace and introduced in 1936. The ‘Malali’ watermelon (Citrullus lanatus) originated as a rogue in a local landrace and was commercialized around 1940. The ‘Ananas Yoqne‘am’ melon (Cucumis melo) was selected from a local landrace and commercialized around 1950. The ‘Ha‘Ogen’ melon was selected from a cultivar introduced from Hungary and commercialized in the 1950s. The outstanding fruit quality of these four cultivars resulted in their widespread planting in Israel and neighboring countries. Moreover, the quality of the cucumber and melon cultivars inspired successive improvements, notably introgression of disease resistance and development of hybrids, by Israeli breeder-geneticists. The ever-increasing demand for their high-quality fruits established as international market types the Bet Alfa cucumber, the Ananas Yoqne‘am melon, and the Ha‘Ogen melon and its derivative, the Galia melon, and each is intensively bred today by local and multinational seed companies.     

Nematode Population Dynamics under the Canopy of Desert Halophytes

The effects of soil conditions on nematode populations were investigated in a field study at the Avdat Research Farm, Israel. Soil samples from the upper soil layer (0-10 cm) were collected monthly during November 1997 and October 1998, under the canopy of three halophyte shrubs: Zygophyllum dumousum, Hammadetum scopariae and Reaumuria negevensis. Ecological indices such as fungivore to bac terivore ratio (F/B), ratio of fungivores and bacterivores to plant parasites (WI), trophic diversity (TD) and Shannon index (H') were used to assess and compare the response of nematode populations to the soil conditions. The mean numbers of total nematodes during January 1998 April 1998 were less under Z. dumosum than under H. scoparia, and those of total nematodes during April 1998 October 1998 were higher under R. negevensis than under the control soil. Bacterivores under the three shrubs were the most abundant trophic group. Significant differences were found between months and between treatments for total nematodes, bacterivores and plant parasites. The content of K + exhibited a positive correlation with total nematodes, bacterivores, plant parasites and omnivores-predators, and that of Ca 2+ presented a negative correlation with bacterivores. F/B, WI, TD, and H' were effetive in distinguishing differences in nematode populations during the study period.     

Soil microbial metabolic profiles in two geomorphological units in a semistable sand-dune ecosystem

The playas and microbiotic crust-covered interdunes are two geomorphological units in the Hallamish sand-dune field, Israel. As a depositional unit, a lack of vegetation and microbiotic crusts, as well as high contents of fine particles and salinity, may lead to low microbial activity and functional diversity at the playa. The present study was initiated in order to illuminate the spatiotemporal changes in the activity, biomass and metabolic profiles of soil microbial communities at the two habitats. Soil samples were collected from the 0–50-cm depth at the playa and interdune during the wet and dry seasons of 2010. Soil moisture and organic-carbon contents recorded at the playa were 2- to above 10-fold higher than at the crust-covered interdune throughout the study period. Nevertheless, opposite trends were recorded for fungal and bacterial CFUs, as well as microbial basal respiration and biomass, in most soil depths at the playa compared to the crust-covered interdune. The total substrate utilization rates of soil microbial communities fluctuated between 4.9 and 6.4 and between 3.9 and 14.9 μg CO₂–C g^?1 dry soil h^?1 at the playa and interdune during the wet season, while 3-fold higher values were recorded at the two habitats during the dry season. The total substrate utilization rates, carbohydrates and carboxylic-acid utilization rates, and functional diversity of soil microbial communities at the playa, were lower than at the crust-covered interdune at most soil depths, while higher utilization rates of aromatic acid were recorded in at least three soil layers at the playa.