Non-destructive testing for combined stresses using high-resolution thermal infrared remote sensing and ‘‘three-temperature model’’: A case study on mangrove plant Kandelia obovata

Abstract:

Mangrove forests are currently facing serious heavy metal pollution and eutrophication problems. Remote sensing of vegetation is a non-invasive methodology to monitor physiological characteristics of plants. The potential of high-resolution thermal infrared remote sensing and the three-temperature model (3T model) for monitoring the effects of combined stresses on mangrove plant Kandelia obovata was assessed. The experiment consists of four levels of CdCl₂ stress (0, 1, 5 and 10 mg·L^-1) in each of four NH₄Cl stress levels: 0, 10, 50 and 100 mg·L^-1, respectively. The non-destructive testing indices, including plant transpiration transfer coefficient (h_at) and estimated instant transpiration rate, were calculated from thermal images and the 3T model. The photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) were also tested to validate the results of non-destructive testing. The results showed that: (1) The plant transpiration transfer coefficients (h_at) were changed from 0.246 to 0.928 and the estimated instant transpiration rates ranged from 0.590 to 6.119 mmol H₂O m^-2s^-1 among different combined stresses. With increasing stress, there were significant decreases for estimated instant transpiration rate and increases for h_at (P < 0.05). (2) The photosynthetic characteristics, including Pn, Gs and Tr, were significantly decreased with the increasing combined stresses (P < 0.05). (3) The effects of Cd, N, and their interaction on non-destructive indices and photosynthetic parameters were significant (P < 0.05). (4) The h_at was significantly negatively correlated with photosynthetic parameters and the T-3T was significantly positively correlated with photosynthetic parameters (P < 0.05). Therefore, the transpiration transfer coefficient (h_at) andestimated instant transpiration rate  detecting by infrared thermography device could be indicators to reflect the stress conditions. Based on high-resolution thermal infrared remote sensing, we developed a new method for health diagnose of mangrove under combined stress.