G. Barness

Decomposition of root litter and related microbial population dynamics of a Negev Desert shrub, Zygophyllum dumosum

Decomposition of root litter was studied using roots of the perennial shrub Zygophyllum dumosum , located at three depths (10, 20 and 30 cm). There were three diameter classes (1–3; 4–8; 9–16 mm) used during two consecutive years in the Negev Highland Desert, Israel. No significant differences in decomposition rates in root mass losses between the two treatments and years were found. In both treatments there was an annual mass loss of 15·5%, calculated kinetics (k) of 0·18 year −1 , with a turnover time of approximately 17 years. Rates of mass losses of root litter in the Negev Desert were found to be different than those reported for two evergreen shrubs from the Chihuahuan Desert but were found to be comparable to the data reported on Scots pine roots from the SECON research site in Sweden. These results suggest that linkage exists between rainfall (events, amount) events, root diameter, lignin and nitrogen concentration, and biotic activity where water availability is one of the most important regulators of decomposition in the Negev Desert.

Preliminary study of the soil nematode community at Machu Picchu Station, King George Island, Antarctica

Abstract. We studied the distribution and abundance of nematodes in one of the most extreme terrestrial environments in the world, at Machu Picchu, King George Island, off the coast of Admiralty Bay, Antarctica. We can report that the nematode community structure under the two most common plant covers was composed of three to four species. These species were found to belong functionally to microbial and omnivore/predator feeding types. Abundances of each of the nematode species were found to be negatively correlated to soil water content, generally decreasing their abundance with increasing soil water content. The results of this study demonstrate the importance of moisture availability to the nematode community and its species composition in this Antarctic soil ecosystem.

Fungal Community-Plant Litter Decomposition Relationships Along a Climate Gradient

Abstract 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.

Soil Biota in the Arava Valley of Negev Desert, Israel

Abstract Soil microorganism biomass and respiration and the soil nematode community were observed in the hypersaline desert valley that is found between the Dead Sea and the Red Sea. The lowest point of the valley is approximately 400 m below sea level, and is the lowest point on earth. Soil samples ( n = 72) were collected from the 0–10 and 10–20 cm soil layers at different altitudes (from −400 to +100 m) in the open spaces between plants during one of the most extreme xeric periods. Both soil microbial respiration and microbial biomass were found to be negatively dependent on soil moisture (SM) and organic matter (OM), and positively dependent on pH values. The physical-chemical characteristics of this hypersaline area were extremely unfavorable for the soil nematode communities, and the nematodes were entirely absent in the open area below sea level. The bacterivores were found to be the most resistant nematodes in this hyperarid region, with the Wilsonema being the most widespread genus. We suggest that nitrogen availability may play a crucial role in the below-ground soil interaction in this region, with bacterivore nematodes as indicators of nitrogen availability.

Soil carbohydrates along a topoclimatic gradient in a Judean desert ecosystem

Soil carbohydrates, which include polysaccharides, are partly of microbial origin, contributing to soil structure and improving soil aggregates. This study examined the effect of climate along a topoclimatic gradient in the Judean desert. Soil was sampled at four locations representing different abiotic environments along the transect during the 1994 and 1995 study period. Significant differences in soil organic matter between the locations were obtained, decreasing towards the dry extreme desert sites. Carbohydrates, which probably are mainly composed of microbial extracellular polysaccharides, were found to increase during the dry season reaching maximum values by the end of autumn. The spatial and temporal changes in carbohydrate content are of great importance, representing biological activity that contributes to bonding between soil particles and helps promote nutrient accessibility to microorganisms. Copyright

Effects of topoclimatic gradient on soil dehydrogenase activity in a Judean desert ecosystem

In this study, dehydrogenase activity assays were used to monitor microbial activity in Israels Judean Desert, a rain shadow desert along a topoclimatic transect. Four locations at this gradient were studied: the pair Givat Yaarim, Maale Adumim and the pair Mishor Adumim, Kalia. These locations range from semidesert in the west 650 ni above sea level with a 620 mm average annual rainfall to the most eastern station (Kalia) 60 m below sea level with less than 100 mm average annual rainfall. Monthly soil samples were collected between January 1994 and July 1996. The soils, which differ mainly in slope location, were analyzed for dehydrogenase activity in the laboratory using the triphenylformazan extraction method. Although both enzyme activity and soil moisture content were found to be significantly different at each location, no significant correlation between them was obtained. However, drying of the soil during the long summer period resulted in a reduction in dehydrogenase activity, while increased so...

Dynamics of Soil Nitrogen along a Topoclimatic Gradient in the Judean Desert

Nitrogen is considered to be one of the major deficient nutrient elements in desert soils, where levels of nitrogen and its fractions undergo rapid tempospatial and chemical changes with the changes in season, according to water availability. A better understanding of this knowledge would be useful for describing the nitrogen state and changes in arid to semiarid systems. The present study investigated mineral nitrogen content in soils sampled from four sites in the Judean Desert along a topoclimatic gradient ranging from Mediterranean to arid conditions, over a period of two years. It was concluded that, along the Judean Desert topoclimatic gradient, temporal dynamics in total soluble nitrogen (TSN) (0.4-80.0 mg kg -1 dry soil), mainly consisting of NH 4 + -N (0.03-28.1 mg kg -1 dry soil) and NO 3 - -N (0-57.2 mg kg -1 dry soil), are closely related to the soil moisture pattern. However, the effect of soil moisture on long-term TSN spatial dynamics is not so pronounced, due to leaching and denitrification. Significantly higher NH 4 + -N than NO 3 - -N levels exist in soils during dry periods, whereas an opposite pattern was observed during the wet seasons. Ammonia may be volatilized, preventing ammonium from accumulating with a decrease in soil clay content. More NO 2 - -N accumulated in a drier site than in moister sites, probably due to aridity having a different impact on different nitrification processes.