In microbiology, the phyllosphere is the total above-ground surface of a plant when viewed as a habitat for microorganisms. The phyllosphere can be further subdivided into the caulosphere (stems), phylloplane (leaves), anthosphere (flowers), and carposphere (fruits). The below-ground microbial habitats (i.e. the thin-volume of soil surrounding root or subterranean stem surfaces) are referred to as the rhizosphere and laimosphere.
Most plants host diverse communities of microorganisms including bacteria, fungi, archaea, and protists . Some are beneficial to the plant, others function as plant pathogens and may damage the host plant or even kill it.
The leaf surface, or phyllosphere, harbours a microbiome comprising diverse communities of bacteria, archaea, fungi, algae and viruses. Microbial colonizers are subjected to diurnal and seasonal fluctuations of heat, moisture, and radiation. In addition, these environmental elements affect plant physiology (such as photosynthesis, respiration, water uptake etc.) and indirectly influence microbiome composition. Rain and wind also cause temporal variation to the phyllosphere microbiome.
The phyllosphere includes the total aerial (above-ground) surface of a plant, and as such includes the surface of the stem, flowers and fruit, but most particularly the leaf surfaces. Compared with the rhizosphere and the endosphere the phyllosphere is nutrient poor and its environment more dynamic.
Interactions between plants and their associated microorganisms in many of these microbiomes can play pivotal roles in host plant health, function, and evolution. Interactions between the host plant and phyllosphere bacteria have the potential to drive various aspects of host plant physiology. However, as of 2020 knowledge of these bacterial associations in the phyllosphere remains relatively modest, and there is a need to advance fundamental knowledge of phyllosphere microbiome dynamics.