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PhD offer | Microbial community functional and structural responses along a gradient of soil use intensification in climatic change context

par Webmaster - 17 février 2016 ( dernière mise à jour : 8 mars 2016 )

To apply, contact jean-christophe.clement@ujf-grenoble.fr before March 20th 2016

One of the major issues related to global change is the multiplicity of sources of disturbances and of their potential interactions on ecosystem functioning. The objective is to assess how the resistance and resilience of soil communities to extreme climatic events is modulated by agricultural practices. This project is based on the rationale that resource availability could influence the resistance and the resilience of soil communities to disturbances (Schimel et al. 2007, Wallenstein and Hall 2011). For example, a recent study reported evidence that plant belowground inputs can promote the recovery of soil communities after drought (de Vries et al. 2012). Within this context it is likely that agricultural practices can drive the ability of soil communities to withstand disturbances through modifications in soil carbon and nutrient availability. Indeed, soil carbon and nutrient availability can be impacted by agricultural practices either directly through fertilization or indirectly through changes in plant functional traits and associated changes in litter quality and root exudates. Moreover, indirect effects on soil functioning can arise through modifications in soil physical properties such as water retention potential that can be influenced by soil carbon content (Rawls et al. 2003).

In this context, soil organic matter (quality and quantity) related to coupled effect of climatic conditions and land-uses should affect microbial activities and community composition, plant functional traits, plant growing performance, and nutrient leaching and retention.

The following hypotheses will be tested :
a - Increased resource availability associated with fertilization or exploitative plant community should favor soil community resilience
b - Selection of organisms adapted to disturbance regime promote increased community resistance to additional disturbance

The experimental design will involve field and laboratory experiments. Field approach will be conducted on agricultural soils under different management conditions. Laboratory experiments will involve soil mesoscoms corresponding to different management and climatic history. These soils will be submitted to various climatic regimes under controlled conditions.
The functional potential of soil microbial communities will be estimated through measurements of activities involved in the decomposition of organic matter and the recycling of nutrients. Measurements of aerobic respiration, nitrogen mineralization, nitrification and denitrification potential will be conducted. Potential activities of extracellular enzymes involved in C, N and P processing will be also measured.
The structure of microbial communities will be assessed through molecular techniques (metabarcoding, quantification of functional genes involved in the C and N cycle).
The combined characterization of the structure and functions of microbial communities will allow us to explore the links biodiversity-functioning relationship and weight the relative influence of abiotic and biotic parameters on the functioning of soil ecosystems.

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