Rhizosphere Bacterial Networks, but Not Diversity, Are Impacted by Pea-Wheat Intercropping

Abstract

Plant-plant associations, notably cereal-legume intercropping, have been proposed in agroecology to better value resources and thus reduce the use of chemical inputs in agriculture. Wheat-pea intercropping allows to decreasing the use of nitrogen fertilization through ecological processes such as niche complementarity and facilitation. Rhizosphere microbial communities may account for these processes, since they play a major role in biogeochemical cycles and impact plant nutrition. Still, knowledge on the effect of intecropping on the rhizosphere microbiota remains scarce. Especially, it is an open question whether rhizosphere microbial communities in cereal-legume intercropping are the sum or not of the microbiota of each plant species cultivated in sole cropping. In the present study, we assessed the impact of wheat and pea in IC on the diversity and structure of their respective rhizosphere microbiota. For this purpose, several cultivars of wheat and pea were cultivated in sole and intercropping. Roots of wheat and pea were collected separately in intercropping for microbiota analyses to allow deciphering the effect of IC on the bacterial community of each plant species/cultivar tested. Our data confirmed the well-known specificity of the rhizosphere effect and further stress the differentiation of bacterial communities between pea genotypes (Hr and hr). As regards the intercropping effect, diversity and structure of the rhizosphere microbiota were comparable to sole cropping. However, a specific co-occurrence pattern in each crop rhizosphere due to intercropping was revealed through network analysis. Bacterial co-occurrence network of wheat rhizosphere in IC was dominated by OTUs belonging to Alphaproteobacteria, Bacteroidetes and Gammaproteobacteria. We also evidenced a common network found in both rhizosphere under IC, indicating the interaction between the plant species; this common network was dominated by Acidobacteria, Alphaproteobacteria, and Bacteroidetes, with three OTUs belonging to Acidobacteria, Betaproteobacteria and Chloroflexi that were identified as keystone taxa. These findings indicate more complex rhizosphere bacterial networks in intercropping. Possible implications of these conclusions are discussed in relation with the functioning of rhizosphere microbiota in intercropping accounting for its beneficial effects.

Intercropping Systems Modify Desert Plant-Associated Microbial Communities and Weaken Host Effects in a Hyper-Arid Desert

“…The α-diversity of bacterial communities in the intercropping system did not differ markedly from that in the monoculture (Figure 3A), which is similar to the findings of previous studies on wheat-faba bean and wheat-pea monoculture/intercropping systems (Tang et al, 2016;Pivato et al, 2021), suggesting a conservative response of bacterial richness to planting patterns, that is, bacterial richness is independent of their neighboring plants. This is consistent with the view of Tkacz et al (2020), who found that microbial communities are more affected by roots than by soil or plant species.…”

“…For example, members of Firmicutes are salt-tolerant and nitrogen-fixing, which can promote plant growth (Mukhtar et al, 2017(Mukhtar et al, , 2021Solanki et al, 2020). In the rhizosphere, there was a higher abundance of psASVs from Firmicutes in intercropping systems than monoculture, but similar results were not observed in bulk soil (Supplementary Figure 4), indicating rhizosphere microbes may account for the added value of intercropping systems by recruiting more beneficial microbial communities into the rhizosphere (Pivato et al, 2021). The association between changes in Firmicutes to the monoculture/intercropping system was found in earlier studies (Zhang M. M. et al, 2018;Gong et al, 2019;Solanki et al, 2020).…”

“…However, the similarity of bacterial α-diversity between intercropping and monoculture systems may also be attributed to the characterization methods of microbial communities. These methods only provide information on the taxonomic composition and diversity; they do not provide information on the interactions between microbiomes or their functions ( Pivato et al, 2021 ). Thus, we compared the microbial co-occurrence patterns of bulk soil and rhizosphere communities in intercropping and monoculture systems ( Figure 4 and Supplementary Figure 6 ).…”

Importance of the Rhizosphere Microbiota in Iron Biofortification of Plants

“…Interestingly, the rhizosphere microbiota of these associated plant species differed from the rhizosphere microbiota of these same plants cultivated separately ( Sun et al, 2009 ; Zhang et al, 2012 ; Wahbi et al, 2016a ; Taschen et al, 2017 ). A more complex rhizosphere bacterial network was recently shown in pea-wheat intecropping ( Pivato et al, 2021 ). Thus, we can hypothesize that the rhizosphere microbiota accounts for the increased iron uptake by intercropped plants.…”

“…The mycorrhizosphere of associated plants, formed by AMF-colonized roots and hyphae, increases microbiota functionalities ( Wahbi et al, 2016b ). Intercropping impacts the abundance, diversity, activity and co-occurrence network of rhizosphere microbial communities ( Li et al, 2016 , 2018 ; Wahbi et al, 2016a ; Duchene et al, 2017 ; Taschen et al, 2017 ; Gao et al, 2019 ; Zaeem et al, 2019 ; Liu et al, 2021 ; Pivato et al, 2021 ). This is in agreement with the well-known positive relationship between plant and microbial diversity ( Spehn et al, 2000 ; Carney and Matson, 2005 ; Qiao et al, 2012 ; Ahmad et al, 2013 ).…”