PubMed · 2026-05-29
Scientists discovered that the top and bottom surfaces of leaves host distinctly different communities of bacteria and fungi, and that these differences are driven by the contrasting environments each surface provides — not just random chance. This challenges the common practice of studying leaves as a single uniform unit.
Bacterial and fungal communities on the upper (adaxial) and lower (abaxial) leaf surfaces were consistently and compositionally distinct across all seven temperate tree species studied over six months.
The underside of leaves showed a higher proportion of negative (competitive) microbial interactions in co-occurrence networks compared to the upper surface, suggesting more intense ecological competition in that resource-rich zone.
Upper-surface microbes were enriched in nutrient-degradation pathways (consistent with a stressful, nutrient-poor habitat), while lower-surface microbes were enriched in biosynthesis and energy-generating functions (consistent with a resource-rich environment near stomata).