Effect of the Rhizospheric Micro-organisms of Some Fabaceaes and Peat Substratum on the Growth of Carob Tree (Ceratonia siliqua L.)

Abstract

Intensive exploitation of sand quarry sites inevitably results in near total destruction of plant cover and soil degradation. The damage done is so important that without human intervention, soil scarification and vegetable return to growth may take several decades. In order to conduct a site rehabilitation programme successfully reforestation through the plantation of a native species such as the carob tree (Ceratonia siliqua) should be the appropriate choice. Because of their facilitation effect, the spontaneous leguminous plants present in the site, specifically Lotus creticus, Retama monosperma and L. creticus associated with R.monosperma can be used as nurse plants. Our assumption is that they possess a rhizosphere rich in microorganisms, which may positively impact the growth of carob. To this end, a study is conducted in order to: a) estimate the diversity of arbuscular mycorrhiza fungi (AMF) living underneath the spontaneous leguminous plants of the site; b) determine their combined effect with other microsymbionts (i.e., total bacteria and actinobacteria) on the growth of the carob tree; c) draw a comparison with carob grown in bare soil and in sterile soil mixed with peat regarding its growth parameters and mineral nutrition. The trees were grown in plastic pots under greenhouse conditions and, after 12 months, the results have shown that, against all odds, the soils of R. monosperma and L. criticus associated with R. monosperma do not significantly influence the growth of the tree whereas the impact of the soil of L. creticus is outright negative. On the other hand, peat improves the root and aerial growth of the tree, which shows in leaves number, branch number and capacity of nutrition in nitrogen. Because a little richer in actinobacteria, bare soil increases the length of the aerial parts and improves the tree’s phosphorus uptake.