Microbial co-operation in the rhizosphere

Abstract

Soil microbial populations are immersed in a framework of interactions known to affect plant fitness and soil quality. They are involved in fundamental activities that ensure the stability and productivity of both agricultural systems and natural ecosystems. Strategic and applied research has demonstrated that certain co-operative microbial activities can be exploited, as a low-input biotechnology, to help sustainable, environmentally-friendly, agro-technological practices. Much research is addressed at improving understanding of the diversity, dynamics, and significance of rhizosphere microbial populations and their co-operative activities. An analysis of the co-operative microbial activities known to affect plant development is the general aim of this review. In particular, this article summarizes and discusses significant aspects of this general topic, including (i) the analysis of the key activities carried out by the diverse trophic and functional groups of micro-organisms involved in co-operative rhizosphere interactions; (ii) a critical discussion of the direct microbe-microbe interactions which results in processes benefiting sustainable agro-ecosystem development; and (iii) beneficial microbial interactions involving arbuscular mycorrhiza, the omnipresent fungus-plant beneficial symbiosis. The trends of this thematic area will be outlined, from molecular biology and ecophysiological issues to the biotechnological developments for integrated management, to indicate where research is needed in the future.

Rhizosphere bacteria containing 1-aminocyclopropane-1- carboxylate deaminase increase growth and photosynthesis of pea plants under salt stress by limiting Na+ accumulation

“…Decreased photosynthesis in response to salt stress might be expected to decrease carbohydrate flow to the root system and root exudation, thereby limiting the establishment of symbiotic plant/microbe interactions in the rhizosphere. Although it is well known that high salinity can decrease nodulation of legumes by rhizobia (Steinborn and Roughley 1974;Steil et al 2003;Barea et al 2005), effects of salinity on associative PGPR inhabiting the rhizosphere may be variable. Although high salinity increased root colonisation of lettuce with PGPR Pseudomonas mendocina (Steil et al 2003), pea root colonisation of V. paradoxus 5C-2 was independent of salinity level (Table 1), similar to experiments where soil drying had no effect on, or even increased, colonisation of V. paradoxus 5C-2 (Belimov et al 2009).…”

Increase of multi-metal tolerance of three leguminous plants by arbuscular mycorrhizal fungi colonization

“…Andrade et al (2004) also reported that inoculation by Glomus macrocarpum increased root nodule numbers of soybean plants, which then attributed to better P nutrition in mycorrhizal plants. P is a key element in forming root nodules, and therefore the AMF colonization is beneWcial to the development of root nodules (Barea et al 2005). It was also reported by Chen et al (1999) that AMF could increase N accumulation in mycorrhizal plants because of higher nitrogenaseWxation activity in mycorrhizal plants and consequently increased eYciency of N 2 -Wxation.…”

Metaproteogenomic analysis of microbial communities in the phyllosphere and rhizosphere of rice

“…Moreover, despite the detection of Nif proteins, care has to be taken whether nitrogen fixation is an active process in plant-associated bacteria as they may not necessarily produce an active enzyme. These rice-associated bacteria may nevertheless exert a positive effect on plant growth, according to the hypothesis that phytohormone production rather than the nitrogen-fixing activity is responsible for the frequently described growth-stimulating effect of diazotrophic bacteria (Barea et al, 2005).…”