Flexible wearables for in-vivo plant health monitoring: the effect of colored and uncolored substrates on plant photosynthesis and transpiration

The monitoring of plant health is considered an attractive strategy for the optimization of crop growth practices. Recently, changes in the surrounding environment are posing a great challenge to crop sustenance by weakening plant resilience with a consequent food productivity reduction. Therefore, novel strategies and innovative tools have been proposed to monitor plant growth and its microclimate with the aim of increasing agriculture and food production in a sustainable way. One of the most promising technologies consists of wearable sensors for the detection of changes in morphological, physiological, and biochemical traits of plants. Most of these wearable systems are composed of a flexible matrix made of ultra-stretchable silicone embedding sensing elements like fiber optic sensors and conductive textiles or conductive inks directly brushed on the plant surface. Although it is reasonable to assume that these materials may impact drastically on basic functions of plant cells such as the response to light and water transpiration, no investigations of the impact of the long-lasting cohabitation of these systems with plant organs have been carried out.This study aims at analyzing for the first time the influence of colored and uncolored encapsulation matrices on two main basic functions of plant physiology: photosynthesis and transpiration. In particular, the effect of five colored matrices (black, blue, red, green, and white pigments) and an uncolored matrix (i.e., a transparent one) were investigated in terms of measurements of photosynthetic and gas-exchange parameters compared to the ones of an uncovered leaf part (i.e., the control area) over a period of 15 days. Findings suggest that no considerable differences were found in terms of photosynthetic effects on the leaf areas covered by green, white, and transparent silicone pads compared to the control area. Conversely, a difference in terms of influence on stomatal conductance to water was found between transparent and colored matrices. Hence, the transparent pad with its lowest effects on the plant basic functions, showed promising features to be an ideal substrate for integrating fiber optic sensors for plant wearables development.