Uasr18.3.-17972 295.299

Arid Land Research and Management 18: 295–299, 2004Copyright # Taylor & FrancisISSN: 1532-4982 print/1532-4990 onlineDOI: 10.1080/15324980490451483 Research Note: Spatial Variation of AM Fungal Spore Numbers under Canopies of Acacia raddiana Faculty of Life SciencesNorthwest Science and TechnologyUniversity of Agriculture and ForestryShaanxi, P.R. China and Faculty of Life SciencesBar-Ilan University, Ramat-Gan, Israel Faculty of Life SciencesBar-Ilan UniversityRamat-Gan, Israel The spatial variation of arbuscular mycorrhizal fungal spores under the canopy ofAcacia raddiana was studied in a desert system. Soils samples from the base of thestem, its canopy radius, and outside its canopy at four stations in the Negev desertwere collected from a 0 to 50 cm depth at sections of 10 cm each. The mean sporedensity was found to fluctuate between 265 100 gÀ1 to 105 100 gÀ1 in fluvisols andcalcaric fluvisols, respectively. Our results suggest that spore density and sporedistribution were found to be directly correlated with soil type, elucidating theimportance of soil physical composition on AM fungi distribution in desert soilecosystems.
arid ecosystem, Negev Desert, desert soils, fungal distribution Arbuscular mycorrhizal fungal (AMF) associations are ubiquitous in desertecosystems and may play an important role in plant establishment and growth bybridging between plant and soil (Allen, 1983; Dhillion & Zak, 1993; Skujin¸sˇ & Allen,1986). The abundance of arbuscular mycorrhizal fungi and their spores are depen-dent on type and physical characteristics of soil (Bethlenfalvay et al., 1988;Ortega-Larrocea et al., 2001).
Bever et al. (1996) and Sanders & Fitter (1992) have postulated that the host plant may play a significant role in every phase of the life history of AM fungi (sporegermination, hyphal development and colonization, and sporulation) by regulatingcarbon allocation to roots, producing secondary metabolites, or changing soilenvironmental conditions. Therefore, investigating the spatial distribution andrichness of AM fungal spores related to host plants in the Negev Desert might be Received 11 October 2003; accepted 20 January 2004.
Address correspondence to Prof. Y. Steinberger, Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel. E-mail: steinby@mail.biu.ac.il helpful for understanding the ecological role of AM fungi in desert ecosystems andthe relationship between AM fungal distribution and the growth of desert plants (Heet al., 2002a, 2002b).
We hypothesized that sampling location soil type and depth will strongly reflect the abundance and distribution of AM fungal spores in a desert ecosystem. The aimof this study was to determine the influence of soil type on the abundance anddistribution of AM fungal spores in the A. raddiana rhizosphere in a desert soilecosystem.
Soil samples were collected at four sites along a soil type gradient running from the northern Negev Desert 25 km east of Dimona (30058oN; 35020oE), with lithosoltype soil, mean annual temperature of 20oC and mean annual rainfall of 150 mm,south toward the Dead Sea, in the Arava Valley-Ein Ofarin (30045oN; 35018oE), withcalcaric fluvisol type soil, mean yearly temperature ranging between 22 and 24oC andmean rainfall of 42 mm, southwest toward the Faran Desert (30012oN; 34055oE), withfluvisol type soil, mean annual temperature range between 20 and 22oC, meanannual rainfall of approximately 50 mm, and to the north near Sede Boker, RamatBoker (30048oN; 34045oE), with yermosol type soil, mean annual temperature of18oC and mean annual rainfall of 97 mm (Dan et al., 1972, 1977). All four sitesrepresent arid conditions with a common feature of low and unpredictable rainfall,desert climate, mild, rainy winters and hot, dry summers.
Acacia raddiana Savi is a typical summer-active shrub that grows in many wadis.
It originates from the savannahs of Africa and penetrated the Negev from the farsouth (Evenari et al., 1982). Recent studies had shown an increase in VAM colo-nization in the root area of Acacia, reflecting vigorous growth of these trees (Ishii,2000).
Soil samples at the base of the A. raddiana stem, the canopy radius (2 m), and outsidethe canopy (2 m from canopy edge) as control (interplant) were collected at the foursites in the summer of 2000. The soil samples were collected in three replicates from adepth of 50 cm at each location and were divided into sections corresponding to0–10, 10–20, 20–30, 30–40 and 40–50 cm depths. They were placed in individualplastic bags and transported to the laboratory in an insulated container and sieved(2 mm mesh size) before processing.
Twenty-five grams of soil from each replicate were used for spore extraction.
The total AM fungal spore number was determined by wet sieving (45–500 mm),sucrose density centrifugation (Ianson & Allen, 1986) and counting under astereoscopic microscope at Â40.
All data were subjected to statistical analysis of variance using the SAS model (ANOVA, Duncan’s multiple range test and correlation coefficient) and were used toevaluate differences between separate means.
The mean spore density was found to be significantly higher (P < 0.05) at the Faransite (265 100 gÀ1 soil) than at Ramat Boker (127 100 gÀ1 soil), Dimona (162 100 gÀ1soil), and Ein Ofarin (105 100 gÀ1 soil). Similar differences were obtained betweenRamat Boker, Dimona, and Ein Ofarin. However, no significant differences(P > 0.05) were found between Ramat Boker and Ein Ofarin. Sampling locationrelative to plant stem had a significant effect on the mean spore density. These valueswere found to be significantly higher (P < 0.05) only at the base of the stem ratherthan in the canopy radius. At the 0–10 cm soil layer, the mean spore density wasfound to range between 96 100 gÀ1 soil and 268 100 gÀ1 soil, increased slightly with FIGURE 1 Mean spore density 100 gÀ1 soil samples taken at (A) canopy base, (B)canopy radius, and (C) control, at four sites: (I) Dimona; (II) Ramat Boker; (III) EinOfarin; and (IV) Faran, under A. raddiana ( depth and reached a maximum value of 285 100 gÀ1soil (Faran site), 110 100 gÀ1 soil(Ein Ofarin) at the 20–30 cm depth and 140 100 gÀ1 soil (Ramat Boker) and 168100 gÀ1 soil (Dimona) at the 30–40 cm depth, then declined gradually with depth.
A similar depth variation pattern was found in the different sampling locationsrelative to the plant stem, however, no significant differences were found betweensampling depths ( Figure 1).
Our results demonstrate that the mean spore density related to the canopy ofA. raddiana in a Negev Desert ecosystem was 165 100 gÀ1 soil, and the distribution ofspore density in the soil was extremely variable. Sampling location had a significanteffect on spore density. The mean spore density at the Faran site (265 100 gÀ1 soil) was significantly higher than in Ramat Boker (127 100 gÀ1 soil) and Ein Ofarin(105 100 gÀ1 soil). The highest spore densities under the canopy of A. raddiana in thefour sampling stations were found at different soil depths.
This result may be closely related to soil type and not to environmental condi- tions, which were found to be similar in soil moisture and organic matter content(Pen-Mouratov et al., 2003). At the Faran site, soil conditions were favorable forplant inhabitance and fungal reproduction, and vice versa in the other three stationswhere they were less auspicious (soil layers contain very little soil and numeroussmall stones).
The microenvironment of a relatively small gap surrounded by the tested shrub may not be greatly affected, and the roots from the bordering shrub may invade thegap. Thus, there may be no significant difference between small gaps and under thecanopy.
Our results suggest that spore density and spore distribution were found to be directly correlated with the soil type, elucidating the importance of soil physicalcomposition on AM fungal distribution in desert soil ecosystems.
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