Plant-Microbe interactions in a changing climate

Peatlands are important ecosystems in the global C cycle as they lock away about one-third of the global terrestrial carbon (Yu 2012). There is, however, growing concern that peatland carbon dynamics will be affected by global climate change. These effects can be direct, but also indirect through changes in plant species richness or plant community composition and associated functional responses. As an example of a direct effect, repeated extreme events (extreme temperature and/or prolonged drought) strongly decreased productivity and enhanced the release of carbon (Kuiper et al. 2014; Bragazza et al. 2016), resulting in a positive climate feedback. Whilst the effects of climate warming on microbial respiration are well understood, recent research has shown that mixotrophic microorganisms (i.e. micro-organisms that can switch between heterotrophy and autotrophy (depending on the presence of carbon resource) play an important role in the uptake of carbon in peatlands, and that their loss, which could be associated with enhanced warming, is linked to a significant loss in net ecosystem carbon uptake (Jassey et al. 2015).

In addition to increases in temperature, other recent changes in environmental conditions, such as enhanced nitrogen deposition, are known to impact plant species richness negatively (Duprè et al. 2009). Such a decrease in species richness has often been linked to eroded ecosystem function (Isbell et al. 2011). Nonetheless, a large scale survey across UK systems highlighted that whilst environmental change negatively impacted species richness in a range of ecosystems, peatlands seemed to be least affected (Field et al. 2014). Recent observations from a cross-European peatland survey have shown the effects of environmental change on peatland species richness are indeed marginal (Robroek et al. 2017). Moreover, environmental change seems to result in a reshuffling of the plant community composition, but species that are lost seem to be replaced by functionally ‘alike’ species. These results would suggest a self-regulating mechanism by which the effects of environmental change on ecosystem functioning is moderated through the specific replacement of species which maintains functionality at the ecosystem level. Indeed, the effects of warming on peatland carbon fluxes have been shown to be moderated by alterations in the composition of the main plant groups (Ward et al. 2013). Over much longer time-scales, peatland vegetation has been shown to recover from extreme disturbance (Swindles et al. 2016). Despite a potential self-regulating mechanism in peatland plant communities there is growing evidence that shifts in species composition cascade to the function of ecosystems (Bardgett & Van der Putten 2014), most likely through specific relationships between plant and microbial communities (Robroek et al. 2015). Yet, the consequences of microbial shifts on ecosystem functioning remain relatively unexplored (Classen et al. 2015). To advance our understanding of the consequences of climate change on ecosystem functioning we need to better understand the relationships between above and below ground components of ecosystems.

Project aims
The aim of this studentship is to identify specific plant-microbe interactions and to study if apparent plant-microbe relationships are affected by climate and environmental change. To achieve these aims, we will first (challenge 1) make use of eight-year plant removal experiment which will allow us to test the proof-of-principle that plant communities select for a specific microbiome. We will next (challenge 2) test the robustness of apparent plant-microbial links along environmental gradients (e.g. temperature, annual precipitation, nitrogen deposition). Palaeoecological approaches can be of great use to further understand the role of climate and environmental change on plant-microbe interaction, and subsequent processes such as carbon sequestration, including the resistance of these plant-microbe interactions to climatic change. Hence, we will (challenge 3) use the palaeorecord (500 years b.p) to identify relations on plant and microbial compositions and link shifts therein to historical climate records.