(UNESCO / Japan Young Researchers' fellowships programme)

Characterisation of soil bacterial community in Avdat: arid ecosystem

Summary of research carried out: 
Characterisation of soil bacterial community in Avdat: arid ecosystem

Two papers have been written during the fellowship programme. The first, entitled “Are microbial communities in the phyllosphere and laimosphere habitats of a desert ecosystem shaped by the ecophysiological adaptation of plants?”, has already been submitted to the journal Soil Biology and Biochemistry and the second, “Next-generation sequencing of microbial communities in laimospheres and phyllospheres affected by plant ecophysiological adaptations”, is currently being completed.

Rainfall alteration as part of global climate change will be one of the most influential triggers for ecophysiological adaptations in the water-use strategies of plants in desert ecosystems. This will lead to significant interspecific differences in plant adaptations and the composition of desert communities. Such ecophysiological adaptations of plants lead to the creation of unique micro-environments upon the canopy – the leaf surface  – and below, forming among the largest, superior, habitats and playing an important role in determining the composition and abundance of terrestrial biota in desert ecosystems. Desert ecosystems are characterized by scarce rainfall that is unpredictable in time and place, high soil salinity and high temperatures. These were found to be among the main limiting factors in desert environments and to play an important role in shaping the ecophysiological adaptation of desert organisms. The diversity of possible resources supplied by three typical desert halophyte shrubs with differing ecophysiological adaptations – Atriplex halimus, Artemisa herba-alba and Hammada scoparia – was the trigger for the present study on microbial communities in above-canopy (phyllosphere) and below-canopy (laimosphere) habitats. The aim was to determine the effects of plant ecophysiological adaptations on phyllosphere and laimosphere-inhabiting, leaf-surface microbial communities. Soil and leaf samples were collected from the two habitats of each of the three shrubs at the end of the dry season and an “interplant open area” was used as a control. We hypothesized that the physiological parameters of phyllosphere-inhabiting microbial communities, such as carbon dioxide evolution, biomass, microbial metabolic quotient, substrate utilization and so on would be partly determined by the laimosphere community and by the shrub’s perennial ecophysiological adaptations.

Specifically, we addressed four questions: first whether there were any intraspecific differences between the phyllosphere and laimosphere in a desert ecosystem; secondly whether distinct plant species “hosted” different phyllosphere communities; thirdly whether the phyllosphere community structure could be predicted based on plant-species ecophysiological adaptation; and fourthly whether the phyllosphere microbial community controlled the laimosphere microbial community.

Based on the obtained data, the answer to the first question is that there are obvious intraspecific differences between the phyllosphere and laimosphere communities. While some variation was detected in individual plants within a single plant species, interspecific variability exceeded intraspecific variability. Thus, ecophysiological adaptations of plants plays a key role in the microbial community structure. This also answers the second and third questions: the phyllosphere community structure could be predicted according to the species of plant. To answer the fourth question, we can confirm that there is some level of control: the phyllosphere microbial community does routinely control the laimosphere community.

Based on our data, we assume that plant ecophysological adaptation plays an important role in structuring phyllosphere and laimosphere microbial communities and that there is a pronounced variability in the communities in different plant species. We also assume that phyllospheric diversity does have control over laimospheric diversity but not absolute, 100 per cent, control. While the shrub effect was observed to have a major impact on the microbial community, a more detailed study will be necessary to evaluate the impact on the microbial species’ composition, as well as on the temporal and spatial vertical components. Such studies will help to resolve the controversy regarding the relationship between shrub ecophysiological adaptation and the microfloral community.