Energy use efficiency of root growth - a theoretical bioenergetics framework.

Metabolic efficiency of root growth is a crucial physiological parameter, contributing to the amount of photosynthate that plants need to invest into soil exploration. Common measurements of metabolic efficiency usually rely on CO2 respiration measurements with the underlying assumption that all metabolic processes are taking place under aerobic conditions. In this conceptual paper, we introduce energy use efficiency based on the quantification of heat dissipation and energy fluxes as an alternative metric to quantify the metabolic efficiency of root growth. In a theoretical framework, we adopted recently published heat dissipation data from wheat seedlings and show that energy use efficiency decreases in response to (i) soil hypoxia and (ii) increased soil penetration resistance. In contrast to traditional CO2 respiration measurements, heat dissipation measurements account for both aerobic as well as anaerobic respiration in growing roots. Hence, we advocate that the quantification of heat dissipation provides a more complete picture of the metabolic efficiency of root growth than CO2 respiration measurements alone. We therefore propose that energy use efficiency should be included in future studies assessing the metabolic efficiency of root growth.