Swift Acid Rain Sensing by Synergistic Rhizospheric Bioelectrochemical Responses

Acid rain poses significant threats to crops and causes a decline in food production, but current monitoring and response to acid rain damage is either slow or expensive. The direct damage observation on plants can take several hours to days when the damage is irreversible. This study presents a real time bioelectrochemical monitoring approach that can detect acid rain damage within minutes. The rhizospheric bioelectrochemical sensor (RBS) takes advantage of the fast chain responses from leaves to roots, and then to the microbial electrochemical reactions in the rhizosphere. Immediate and repeatable current fluctuations were observed within 2 min after acid rain, and such changes were found to correspond well to the changes in rhizospheric organic concentration and electrochemical responses. Such correlation not only can be observed during acid rain events that can be remedied via rinsing, but it was also validated when such damage is irreversible, resulted in zero current, photosynthetic efficiency, and electrochemical signals. The alanine, aspartate, and glutamate metabolism and galactose metabolism in leaves and roots were inhibited by the acid rain, which resulted in the decrease of rhizodeposits such as fumaric acid, d-galactose, and d-glucose. These changes resulted in reduced electroactivity of anodic microorganisms, which was confirmed by a reduced redox current, a narrower spectrum in differential pulse voltammetry, and the loss of peak in the Bode plot. These findings indicate that the RBS process can be a simple, swift, and low-cost monitoring tool for acid rain that allows swift remediation measures, and its potential may be broadened to other environmental monitoring applications.