Speaker
Description
Introduction
Intensive agriculture has been promoted since the green revolution in the 1960s to boost crop yields and satisfy increasing food demand (Mann, 1999). Such intensification led to modifications in agricultural practices with higher fertilization, increased pest control and intense varietal selection among others. Additionally, the increase in the overall agricultural land cover led to marked changes in land use at the expense of natural and semi-natural habitats (Tscharntke et al., 2005). Because of these changes occurring at local and landscape scales, agricultural intensification strongly shaped ecosystem properties (Matson et al., 1997) and resulted in an important loss of biodiversity in many taxonomic groups (e.g. Hole et al., 2005; Gonthier et al., 2014). Despite the key role of symbiotic microorganisms in plant nutrition and protection, the impact of agricultural intensification on these microorganisms is not fully understood. Organic farming, which has been proposed as an alternative farming system, aimed at promoting more efficient soil natural ecosystem services (e.g. organic matter cycling, storage, redistribution of mineral nutrient…), should be favorable for microorganisms. It may promote a higher microbial diversity thanks to lower anthropic disturbance and higher plant diversity. It is also expected to strongly affect species composition and result in changes in plant growth and health.
Materials, Methods
We sampled plants in pairs of winter wheat fields (one organic and one conventional) along a distance gradient to the edges (hedgerow versus grassy), in 20 landscape windows selected along an uncorrelated gradient of organic farming and hedgerow density. Firstly, we analyzed the relative effect of organic farming and field edge types on endophytic microbial assemblages associated with wheat plants. Secondly, we tested the effect of the farming practices characterizing farming systems on endophytic microbial assemblages associated with wheat plants, and related these changes with wheat performance in the field. To achieve these goals, we collected environmental data through farmer interviews, soil analyses, and plant inventories. We also analyzed root microbiota through next-generation sequencing at vegetative and flowering stages.
Results
We demonstrated that organic farming shaped microbial composition and increased fungal and bacterial richness in most phyla. In contrast to bacteria, fungal communities were heterogeneously distributed within fields, having a higher diversity for some phyla close to field edges. Fungi responded more strongly to the field scale while bacteria were more affected by landscape scale. Effect of organic farming at the field level was mostly due to soil characteristics and field management, and a little to plant diversity in the field. Microbial responses were more pronounced at the late developmental stage, likely as a result of accumulative effect of management actions during plant development. Seed production and resistance to pathogens were related to specific phyla that are important for seed production and/or wheat resistance to septoriose.
Discussion and conclusion
The present study provided a better understanding of the effect of organic farming and of its scale of influence on plant-associated microbiota. We showed the positivet effect of organic agriculture at both field and landscape scales on wheat endophytic richness providing evidence that agricultural management needs to be considered at several spatial scales. More especially, we demonstrated that increasing the percentage of organic agriculture at the landscape scale can maintain higher bacterial richness even in conventional fields. We stressed also the importance of soil characteristics and management in shaping microbiota composition and diversity. Plant seed production and resistance to pathogens were related with particular microbes, such as Alphaproteobacteria and Glomeromycota. This work advances our understanding of how farming system, and particular agricultural practices affect plant microbiota, and plant performance through microorganism-mediated changes. It supports the use of microorganisms as pillars of sustainable crop production.
References
Gonthier DJ et al., 2014. Biodiversity conservation in agriculture requires a multi-scale approach. Proc R Soc B., 281:1358
Hole DG et al., 2005. Does organic farming benefit biodiversity? Biological Conservation, 122:113-130.
Mann C., 1999. Crop scientists seek a new revolution. Science, 310-314.
Matson, PA et al. 1997. Agricultural intensification and ecosystem properties. Science, 277:504-509.
McLaughlin A, Mineau P, 1995. The impact of agricultural practices on biodiversity. Agri Ecosyst Environ., 55:201-212.
Tscharntke T, Klein AM, Kruess A, et al. 2005. Landscape perspectives on agricultural intensification and biodiversity – ecosystem service management. Ecology letters, 8:857-874.
| Keywords | Agricultural intensification; plant-microorganisms association; plant microbiota; farming practices |
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