Ecophysiological Responses of Canarium madagascariense, an Endangered Tropical Tree Species to Water Stress and the Use of Potassium Silicate as a Mitigation Strategy

Canarium madagascariense is an endangered tree species that plays a key role in forest, ecology, and for humans. Understanding how it would cope with water stress remains important for reforestation and biodiversity conservation opportunities and is not well covered in the literature. This study aims to assess how C. madagascariense seedlings respond to stress and to the addition of a compound that promotes drought resistance: potassium silicate. To this end, a trial was conducted under semi-controlled conditions in which 120 one-year-old seedlings were subjected to different levels of irrigation: 100%, 50% and 25% of field capacity, to which 50 ml of a 10 mM solution of K2SiO3 was added to the soil. Morphometric parameters such as height, diameter and stomatal conductance were monitored throughout the experiment, while phytochemical analyses of sugars, phenolic compounds and antioxidant activity were carried out at the end. The results showed that with increasing stress, growth in diameter and height decreased by 40-80% and 42-62%, respectively, as stomatal conductance dropped below 0.10 mol m(-2) s(-1). The use of the potassium silicate alone had no effect on the growth and stomatal conductance. Leaf fructose content did not differ significantly between treatments. However, glucose content almost doubled as stress levels increased. The total content of phenolic compounds was significantly different between potassium silicate-treated and untreated plants. Three phenolic compounds namely, caffeic acid, epicatechin, and quercetin contents were found to decrease significantly in stressed plants compared with control plants. Our findings demonstrated the potential of these molecules as markers of water stress in C. madagascariense. Moreover, the effect of adding K2SiO3 to the soil was redirected towards a more biochemical dimension rather than towards growth.