However, there is still a paucity of knowledge concerning the potential ecological impact resulting from propagule inoculation, as such methods could increase the competition between inoculated fungi and previously established indigenous AMF communities. Moreover, inoculation can be used to offset tillage effects on the number of indigenous spores. Inoculation with AMF spores has recently been shown to increase plant growth and the expression of nitrate and phosphate transporter genes in wheat roots. In addition, among AMF species, there are different levels of tolerance to the disruption of hyphae resulting from tillage. Spore density determines the capability of AMF to resist ecological and physical disturbances, such as periods during which suitable host plants are not present or following intensive tillage, as they both limit the ability of AMF to colonize the subsequent cultivated crops. The density of spores has been defined as an early and useful indicator of AMF colonization potential. Spore density of AMF together with the level of hyphal growth and branching are critical for successful root colonization. Although it has been shown that tillage (through aggregate disruption ) and N fertilization can reduce the colonization of crops by arbuscular mycorrhizal fungi, our knowledge of the factors that determine the successful establishment of an AMF symbiosis remains limited. However, AMF are particularly sensitive to physical, chemical, and biological disturbances caused by human activities that limit their establishment in agrosystems. It is commonly accepted that AMF develop obligate symbioses with at least 65% of vascular plants, including a large number of cereals grain crops and legumes, thus increasing their ability to acquire nutrients. The roots of the majority of land plant species are colonized by these fungi, extending the prospecting capacity of plants into the surrounding soil through mycorrhizosphere (a network formed by root-like extensions of the fungi known as hyphae), where the fungal spores are also formed. Symbiosis between arbuscular mycorrhizal fungi (AMF) and plants arose on earth more than 400 million years ago. It can be concluded that no-till, by preventing soil from structural and chemical disturbances, is a farming system that preserves the entire fungal life cycle and as such the production of viable spores of AMF, even under intensive N fertilization. Furthermore, the high nitrate content of ploughed soils appears to be detrimental both for the dehydrogenase enzyme activity and the production of AMF spores. Therefore, soil dehydrogenase activity and soil penetration resistance can be considered as good indicators of soil quality in agrosystems. We also observed that there were positive correlations between spore density, soil dehydrogenase enzyme activity, and soil penetration resistance and negative correlations with soil phosphorus and mineral N contents. Under no-till (NT) conditions, the density of AMF spore was at least two-fold higher, even under intensive N fertilization conditions. A field experiment conducted over six years revealed that AMF spore density was significantly lower under conventional tillage (CT) combined with intensive synthetic N fertilization. Therefore, we have studied the impact of different soil management techniques, including conventional moldboard ploughing and no-till under an optimal nitrogen (N) fertilization regime and in the absence of N fertilization, on AMF spore density and soil chemical, physical, and biological indicators in the top 20 cm of the soil horizon. However, agricultural practices can have deleterious effects on plant–fungi symbiosis establishment in soils, thus inhibiting its potential benefits on plant growth and development. Arbuscular mycorrhizal fungi (AMF) play major roles in nutrient acquisition by crops and are key actors of agroecosystems productivity.
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