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.
Highlights
After water, sand is the second most consumed resource worldwide: 400 billion tons a year
The introduction of the carob tree, a plant of socio-economic value, well- adapted to the soil and climatic conditions of the area is an essential prerequisite for the achievement of any soil restoration program, even more so as annual rainfall has become rare or irregular with long dry summer periods combined with anthropic pressure (Ait Chitt et al, 2007; Makhzoumi, 1997)
The soils are poor in organic matter with L. creticus and L. criticus + R. monosperma being the richest with rates of 0.12% and 0.14% respectively (Table 1)
Summary
Sand is the second most consumed resource worldwide: 400 billion tons a year. It represents a trading volume of 70 billion dollars a year, 56 million tons of which are consumed in Algeria, mainly used in the building and construction sector (Denis, 2013; Richer, 2018). Sand extraction in quarries leads to the loss of plant cover, and without human intervention in those damaged zones, vegetation is in the incapacity to regenerate itself. The damage caused by sand extraction facilitates water and wind erosion which manifests itself as an alteration of the soils’ physical, chemical and biological properties (Albaladejo et al, 1988; Tuo et al, 2018). The introduction of the carob tree, a plant of socio-economic value, well- adapted to the soil and climatic conditions of the area is an essential prerequisite for the achievement of any soil restoration program, even more so as annual rainfall has become rare or irregular with long dry summer periods combined with anthropic pressure (Ait Chitt et al, 2007; Makhzoumi, 1997)
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