PS 20-3 - How does canopy leaf reduction of plants alter wood endophyte communities?

Abstract: Photosynthesis provides usable carbon for plant physiology and accumulation of biomass, which is ultimately a starting point for many plant-associated or herbivorous organisms. Thus, manipulation of these carbon source will affect other organisms like for example microbes (beneficial and pathogenic) as well. A major question in this regard is how plant-associated microbial communities will react when photosynthesis i.e. carbon fixation of plants is manipulated. Beside ecological questions, this has also strong implications for agricultural systems. For example, winegrowers rely on the microbial “universe”, which gives wine the typical “terroir”, and this normally shall not change drastically by canopy i.e. photosynthesis manipulations in the field.

In this study we reduced the leaf area of Vitis vinifera L. (cv. Riesling) for 10 consecutive years by - 50%, analyzed the microbial communities in root, trunk, cordon and shoot by a metabarcoding approach and analyzed plant physiological and wood chemical parameters as well. We followed the hypothesis that 10 years of this manipulation changed the plant physiology and thereof the endophytic microbial communities in the wood compartments.

The leaf management affected significantly net assimilation rate (-18.21 %, averaged over the season) and transpiration rate (-19.16%), potassium content in cordon (up to -8.6%), d¹³C in the shoots (-0.89%) and glucose content in trunk (+15%), cordon (+10.7%) and shoot (+12.7%). However, the effects for the microbial richness and community composition were subtle, with slight differences only in wood samples from the roots. There, the fungal richness was twice as high under leaf reduction (154±24) compared to control samples (73±41).

Strongest microbial community differences were mainly found among the different plant compartments (root vs. trunk vs. cordon). A goodness-of-fit statistic revealed that wood parameters like glucose and fructose content, water-soluble lignin fragments, content of extractives (e.g. resins), microbial species richness and zinc significantly contributed to structuring of the fungal and bacterial community.

From an applied perspective, since we analyzed grapevine in this study, the canopy manipulation seems not to have drastically effects on the plant-microbe ’system’ in the wood. This is crucial to know for winegrowers that manipulate the plant canopy for example for reduction of sugar content in the berries, i.e. to reduce ultimately the alcohol content in the wine, or to delay in ripening due to climatic changes.