Understanding and managing soil biodiversity: a major challenge in agroecology

Abstract

International audienceSoils are living environments in which particularly abundant and diverse microbiome and fauna are evolving. The resulting biological functioning has a direct impact not only on soil fertility but also on a series of ecosystems services. Thus, microbial communities are involved in geochemical cycles in which microbial enzymes catalyse the different steps. Modulation of the corresponding activities is essential as these affect plant growth and environmental quality. In general, biodiversity affects both the productivity and stability of agroecosystems. It is therefore of paramount importance to take soil biodiversity and biological functioning into account when designing cropping systems and evaluating their impacts. The progress achieved in soil microbiology in recent years now makes it possible to propose analyses of soil biology, as has been feasible for many years for soil physicochemistry. These analyses obviously require the use of standardized procedures for soil sampling, measuring the abundance and diversity of the microbial communities, as well as the identification of bioindicators. Similarly, referential systems need to be established to interpret these analyses and diagnose the biological status of soils, and, more especially, to determine whether the obtained values are within the range of variations normal for a given soil type and land use. Great progress to standardize such procedures and establish referential systems has been achieved during large-scale research programmes carried out to characterize biodiversity on national and European scales. These diagnostic elements need to be accompanied by recommendations. The aim of ongoing research is thus to propose aids for decision-making, based on the results of biological analyses, so attempts can be made to monitor and manage biodiversity to satisfy soil fertility requirements and ensure the ecosystem services expected of soils

A new analytical framework of farming system and agriculture model diversities. A review

“…trichogram in maize) and other service-providing organisms (e.g. azotobacters, probiotics, arbuscular mycorrhizal fungi), soil biostimulants and bioinoculants, farmers seek to develop ecological processes underpinning ecosystem services which naturally arise in diversified ecosystems (Lemanceau et al 2015;Philippot et al 2013). They can also use biopesticides to avoid eco-toxicity of chemical pesticides.…”

“…While their effects are well known, and their efficacy has been demonstrated by research on some iconic living inputs (e.g. inoculation of Rhizobia in leguminous cropping systems; Lemanceau et al 2015), the actual effects of many biological inputs such as biostimulants have not been soundly demonstrated at the field level (Reeve et al 2016). Moreover, they generally have low resilience, leading farmers to apply Fig.…”

Potential of biofertilisers to improve performance of local genotype tomatoes

“…The extra radicular hyphae increase the exploitation area of associated plants, which results in an efficient usage of the soil resources, together with the promoted growth and development (Brundrett and Ashwath, 2013;Conversa et al, 2012;Garg and Chandel, 2010;Jayne and Quigley, 2014;Koltai and Kapulnik, 2010;Lambers et al, 2009). Inoculating the soil had beneficial results in the productive ecosystems, especially when the indigenous mycorrhizal flora is not infectious or efficient enough (Hoeksema et al, 2010;Lemanceau et al, 2015;Rillig et al, 2014). The success of mycorrhizal inoculum depends on the capacity to compete for resources of alien species and the association speed with the rhizospheres plants to which these are introduced to (Garg and Pandey, 2015;Gianinazzi et al, 2010;Vicente-Sánchez et al, 2014;Watts-Williams and Cavagnaro, 2014;Wezel et al, 2014).…”

Causes and consequences of soil bacterial rarity

“…It has been suggested that the high number of species in microbial communities compared to communities of macroorganisms would lead to an even higher functional redundancy, so that a reduction of microbial species would not matter for ecosystem functioning (Franklin andMills 2006, Wertz et al 2006). However, just as for macroorganisms, this redundancy is essential for ecosystem stability as species with differing sensitivities to environmental conditions can support ecosystem functions upon environmental changes (Lemanceau et al 2015). In support of this concept, studies repeatedly found a high number of taxa that fluctuate in abundance in space and time, the so called conditionally rare taxa (Shade et al 2014).…”

“…As a consequence, it has been suggested to improve the indigenous community in order to enhance its plant-beneficial properties . As a first step towards this goal, Lemanceau et al (2015) proposed to identify both plant genotype and compatible bacterial strains in the soil that together show the best performance. Second, practices could be tested to promote these strains within the community.…”