Soil depth: an overriding factor for distribution of arbuscular mycorrhizal fungi

Journal of Soil Science and Plant Nutrition, 2013, 13(1), 23-33 . Soil depth: an overriding factor for distribution of arbuscular mycorrhizal fungi A. Shukla1*, D Vyas1, Anuradha Jha2 Laboratory of Microbial Technology and Plant Pathology, Department of Botany, Dr Hari Singh Gour Central University, Sagar 470 003, Madhya Pradesh, India; 2National Research Centre for Agroforestry, Opposite Pahuj Dam, Gwalior Road, Jhansi 284 003, Uttar Pradesh, India. *Corresponding author: 1 Abstract Present study deals with the distribution and diversity of arbuscular mycorrhizal fungi (AMF) in naturally growing Withania somnifera and Ocimum sanctum. Variations in soil pH and moisture content (%) at different soil depths (0-10, 10-20, 20-30 and 30-40 cm) and their possible influences on AMF spore populations were studied at two sites i.e. Jaitpur and Karaiya. A total of 27 AMF species (8 Acaulospora, 1 Cetraspora, 1 Claroideoglomus, 1 Entrophospora, 1 Funneliformis, 13 Glomus, 1 Simiglomus and 1 Septoglomus) were identified. Results revealed that W. somnifera harbors relatively more AMF species (21) than O. sanctum (14). Acaulospora scrobiculata, Sep. deserticola and Sim. hoi dominated the rhizosphere of W. somnifera, while A. scrobiculata, Sep. deserticola and G. fasciculatum were predominant in O. sanctum. Spore populations, soil pH and moisture content varied significantly across soil depths. Moreover, the ability of soil to support AMF population decreased significantly with increased soil depth. Results clearly indicated the involvement of factor other than soil pH and moisture content in AMF distribution. Thus, it may be stated that overriding factor was depth, and this can be justified by fewer roots and fewer mycorrhizae in deeper soil layers. Keywords: Arbuscular mycorrhiza, moisture content, shannon-weaver index, Ocimum sanctum, Withania somnifera. 1. Introduction Arbuscular mycorrhizal fungi (AMF) are below ground symbiotic associations between plant roots and fungi (Shukla et al., 2012a) which adds dimension to the plant-soil-microbe systems. AMF are able to develop associations with more than 80% of vascular or non-vascular terrestrial plants (Brundrett, 2002). These are recognized as an important component of soil ecosystem (Oehl et al., 2004 and 2005; Shukla et al., 2012b). AMF can improve plant growth under low fertility conditions, improve water balance of the plants and help plants to establish in new areas (Jha et al., 2011; Shukla et al., 2012c). Distribution of AMF is a result of contemporary ecological processes (Shukla et al., 2009). Several factors viz., soil pH, moisture content, soil disturbances and above-ground vegetations determine its distribution (Yang et al., 2010; Sturmer and Siqueira, 2011). According to Smith and Read (2008), AMF are ubiquitous in occurrence, 23 24 Shukla et al. but there are some conflicting reports regarding its association with medicinal plants. Previous studies suggested the absence of AMF in such plants (Kumar and Mahadevan, 1984) but later on the association of these fungi with medicinal plants were widely studied (Copetta et al., 2006; Soni and Vyas, 2007; Zubek and Blaszkowski, 2009; Mishra et al.,2011). Medicinal plants are the sources of several pharmaceutically important compounds which play a vital role in human health care. According to World Health Organization (WHO), more than 80% of the world’s population relies on the use of traditional medicines for their primary healthcare (Radhika and Rodrigues, 2010). Withania somnifera (L.) Dunal (Indian Ginseng) and Ocimum sanctum L. (Holy Basil) are two most important medicinal plants. Both the plant species are being utilized for the treatment of various ailments since time immemorial. They are wildly grown in warmer parts of India especially in Madhya Pradesh of Bundelkhand region (Khare, 2004; Soni and Vyas, 2007). Due to growing recognition of natural products, their non-toxicity and easy availability, the demand of these plants are being increased (Kapoor, 2005), and to fulfill this demand, locally collected plants are being exploited commercially for the preparation of medicines (Misra and Gupta, 2010). In India, most of the knowledge regarding association of AMF with medicinal plants comes from arid region, western and southern parts of India (Khade et al., 2002; Muthukumar et al., 2006; Panwar and Tarafdar, 2006; Kumar et al., 2010; Radhika and Rodrigues, 2010). The literature survey clearly indicates that there is much to be learnt from the soil about association of AMF with W. somnifera and O. sanctum. Furthermore, systematic work on mycorrhizal investigations regarding these plant species has not been conducted in Central India. Therefore, an extensive investigation was carried out to determine the distribution and diversity of AMF in these plants over the range of soil depth (up to 40 cm). For the present investigation, two sites i.e. Jaitpur and Karaiya of Sagar district were selected because the edaphic factors of these sites showed variable soil textures. Journal of Soil Science and Plant Nutrition, 2013,13(1), 23-33 2. Materials and methods 2.1. Site description Present study was carried out at Dr. Hari Singh Gour Central University, Sagar, India. The region (23°10’24°27’ N latitude and 78°4’-79°21’ E longitude) is situated between North of Tropic of Cancer on an average altitude of 580 m above mean sea level. Sagar lies in Agro-ecoregion 10; Central Highlands, Hot Sub-Humid Ecoregion with medium and deep black soils (I5C3) (Sehgal et al., 1990). The region has monsoonal climate where 90% of the annual rainfall takes place during the southwest monsoon period (June to September). The mean annual rainfall of the region is 1234 mm. January is the coldest while May and June are the hottest months. The maximum recorded temperature on a particular day often touches 47–48 °C during summer. In order to study the AMF diversity of W. somnifera and O. sanctum, five naturally growing plants of each species (almost similar age groups) were marked at Jaitpur and Karaiya, respectively. It is worth mention that no other plants were growing in the close proximity of selected plants. The main soil type at Jaitpur was vertisol (mixture of clay and loam), highly water retentive; its pH (1:2.5 H2O) varied from 6.25 to 7.16 and organic carbon varied from 0.45 to 0.70%. While, at Karaiya, soil was alfisol (gravelly in texture), pH varied from 6.38 to 7.24 and organic carbon varied from 0.38 to 0.65%. (Table 1). The test sites were open and the process of retention of rain water was very poor. At selected sites, rainfed conditions were prevailing. 2.2. Sampling, extraction and identification of AMF To isolate AMF spores, soil samples were collected at different depths viz., 0-10, 10-20, 20-30 and 30-40 cm in triplicates in the month of October 2010. Samples were taken as close as possible to the base of the plant (0 to 15 cm from stem) by removing the topsoil. From eac (...truncated)