Upward transport in a canopy assisted by raindrop impacts on plant leaves

The interception of raindrops by plant leaves induces a redistribution of water, nutrients, and micro-organisms, from the surface of these leaves to their surroundings. It consequently shapes the plant ecosystem. For example, in wheat fields (as in most major crops), splashing raindrops are the main mechanism of spore dispersal for fungal diseases at the epidemic stage, with severe consequences on crop yield. Surprisingly, the observed dispersal is not only downward (wash off / dripping) or outward (splash), but also upward, which may considerably speed up the fungus propagation. Other nutrients and microorganisms might also benefit from such upward transport external to the plant.

In this work, we unravel an efficient and universal mechanism of upward transport: after a raindrop splashed on a plant leaf, the residual water on the leaf can be shot upward as the leaf springs back. We illustrate this phenomenon with several plant leaves. Then we present results obtained from systematic experiments with artificial leaves, thanks to which both the mechanics of rain-induced leaf motion and the fluid dynamics of leaf-induced droplet ejections are elucidated. We identify the range of mechanical properties of the leaf that makes upward shooting fully effective. Finally, we show that the efficiency of this upward transport increases more than proportionally with rain intensity. Its occurrence and role in shaping ecosystems will be largely amplified in the case of an increased frequency of extreme rain events.