EARLY DETECTION OF NITROGEN STRESS IN COTTON PLANTS WITH A VOLATILE ORGANIC COMPOUND SENSOR

This work presents a leaf-mounted flexible sensor developed to detect methanol volatile organic compounds (VOCs) released from cotton leaves under nitrogen (N) stress. Plants emit methanol in response to numerous stresses, including N deficiency. These plant VOCs play crucial functions as signaling molecules in the defense mechanisms and stress responses of plants. Gas chromatography-mass spectrometry is commonly employed for the accurate detection of VOCs; however, this technique does not facilitate real-time monitoring, necessitates intricate sample preparation procedures, and incurs high costs. Our low-cost, flexible sensor comprises a 4mm x 19mm methanol sensor. The methanol sensor is fabricated from a mixture of metal oxide and nanoparticles composite. The sensor is incorporated inside a three-dimensional printed enclosure measuring 33.8mm x 35mm x 8.5mm for the in-situ collection and measurement of VOCs emitted by cotton leaves. The cotton plants were cultivated in six pots under two nitrogen conditions: absence of nitrogen and elevated nitrogen (250 ppm nitrate per kilogram of soil), with three plants allocated to each treatment. When plants are under stress, the stomatal closes to reduce water loss through transpiration. Again, nutrient stress, especially nitrogen deficiency, reduces chlorophyll production hence stomatal conductance, chlorophyll index, soil nitrate was correlated with methanol concentration. Our findings reveal elevated levels of methanol from plants without nitrogen treatment compared to those treated with 250 ppm nitrate. The p-values from statistical analysis further validates the results which showed a significant difference in methanol concentration among the two treatment groups. These results corroborate the existing literature, which indicates that nitrogen-stressed plants emit higher concentrations of VOCs than non-stressed plants. Moreover, methanol was found to be a potential VOC marker for early detection of N stress.