Light from below matters: Quantifying the consequences of responses to far-red light reflected upwards for plant performance in heterogeneous canopies.

ABSTRACT

In vegetation stands, plants receive red to far-red ratio (RFR) signals of varying strength from all directions. However, plant responses to variations in RFR reflected from below have been largely ignored despite their potential consequences for plant performance. Using a heterogeneous rose canopy, which consists of bent shoots down in the canopy and vertically growing upright shoots, we quantified upward far-red reflection by bent shoots and its consequences for upright shoot architecture. With a three-dimensional plant model, we assessed consequences of responses to RFR from below for plant photosynthesis. Bent shoots reflected substantially more far-red than red light, causing reduced RFR in light reflected upwards. Leaf inclination angles increased in upright shoots which received low RFR reflected from below. The increased leaf angle led to an increase in simulated plant photosynthesis only when this low RFR was reflected off their own bent shoots and not when it reflected off neighbour bent shoots. We conclude that plant response to RFR from below is an under-explored phenomenon which may have contrasting consequences for plant performance depending on the type of vegetation or crop system. The responses are beneficial for performance only when RFR is reflected by lower foliage of the same plants.