Real-time monitoring of water and ice content in plant stem based on latent heat changes

Abstract

With the development of water detection instruments, it is feasible to detect the stem liquid water content. However, real-time and non-destructive monitoring of liquid water and ice content of plant stems in winter remains challenging. Here, we developed a living wood freeze–thaw detection (LWFTD) sensor to detect the liquid water and ice content of plant stems in situ, in real time, and micro-destructively. First, based on the latent heat effect and using a retractable ring-type shrapnel probe, we monitored the freeze–thaw front of the stem water in real time and micro-destructively. Second, using calibration data and infrared detection data, the reliability of the LWFTD sensor and the feasibility of stem freeze–thaw detection based on the latent heat effect were proven. Finally, by simulating a freeze–thaw cycle and analyzing the changes in the stem liquid water content and stem temperature, an ice content model was constructed to calculate the ice content and freeze–thaw fronts. In field experiments, we recorded stem water content and freeze–thaw data of Pachira glabra, Populus tomentosa, and Lagerstroemia indica during an overwintering period. The results showed that the LWFTD sensor can effectively detect the changes in water-related physiological parameters during plant freeze–thawing in real time and that the ice content in the stem volume exhibits diurnal changes, with a single-peak, single-valley wave pattern. Our study provides a reference for evaluating the effects of freeze–thaw on plant metabolism and vitality. Furthermore, this study provides an advanced technical tool for in situ, real-time, and micro-destructive monitoring of the water and ice content in plant stems, which will help further our understanding of the water transport process and freeze–thaw-induced embolism of woody plants during winter.