The effect of leaf shape on the leaf microbiome

Background/Question/Methods

Plants host many different communities of microbes, one of the most prominent being the leaf microbiome, known as the phyllosphere. Host genotype has been shown to affect the leaf microbiome in some species, but how widespread this phenomenon is and the underlying processes producing genotype-specific phyllospheres is still unclear. The shape of a leaf can create different microclimates which could affect the assembly of a microbiome, and so leaf shape is a possible, but unstudied, contributor to genotype-specific phyllospheres. In Ipomoea hederacea, ivyleaf morning glory, leaf shape is heart-shaped, lobe-shaped or intermediate between the two, and leaf shape is determined by a single Mendelian locus. I will determine if leaf microclimate differs between genotypes and test my a priori hypothesis that leaf shape alters the phyllosphere. I will also identify other drivers of the leaf microbiome, and heritable microbes, in the otherwise uncharacterized I. hederacea. I grew 240 individuals of 80 inbred lines of I. hederacea (3 replicates per line) in a 1:2:1 leaf shape genotype ratio in a common garden experiment at the Koffler Scientific Reserve, in Ontario, Canada. I collected leaves during the summer of 2021, then photographed, and characterized them using 16S rRNA amplicon sequencing.

Results/Conclusions

Data is preliminary so far. I have found evidence that each leaf shape has a different microclimate; in my common garden, shape significantly affected temperature and conductance, with lobe genotypes having lower stomatal conductance for a given temperature, potentially affecting the phyllosphere and selection on plant genotype. Sampled leaves had consistent surface area, but circularity differed significantly among genotypes. Despite microclimate differences, leaf shape was not a major contributor to overall microbiome structure differences, although I will soon be identifying if any specific microbes or taxa differ between genotypes and line (i.e., are heritable). I found instead that flowering day of the year affects the similarity of microbiomes, with early-flowering plants having more similar microbiomes. Later-flowering plants and non-flowered plants at the time of collection had more variability in microbiome composition and were more dissimilar from one another. This suggests leaf shape microclimate effects may be weaker than other possible drivers of the leaf microbiome, for example, host age and life stage. Understanding host factors influencing microbial community assembly is one of the main goals of microbial ecology, as microbiomes influence plant performance and fitness, and can mediate selection on plants.