Effect of Pyroligneous Acid Application on Tomato Growth and Alleviation of Aluminum Stress

Abstract

Aluminum (Al) toxicity is a major constraint to global crop production in acidic soils. Pyroligneous acid (PA), a reddish-brown smoky liquid produced during the pyrolysis of biomass, can enhance crop growth and tolerance to diverse environmental stresses. However, its use in enhancing crop productivity and resilience to Al stress is unknown. This thesis investigated the biostimulatory effect of PA on productivity and its regulatory mechanism in promoting Al tolerance in tomato (Solanum lycopersicum ‘Scotia’). Soil application of 0.25% PA increased plant morpho-physiological parameters while 0.5% PA increased fruit yield. However, soil application of 2% PA reduced plant growth and yield, but considerably increased fruit phytochemical contents. Foliar application of 0.25% and 0.5% PA combined with full NPK (0.63, 0.28, 1.03 g/L) rate increased chlorophyll fluorescence indices, while 2% PA increased leaf chlorophyll content. The 2% PA combined with full NPK rate increased fruit yield, number of marketable fruits and fruit phytochemicals. Seed priming with 2% PA for 24 h enhanced seed germination and seedling growth parameters under Al stress. Treatments of four-week-old tomato seedlings with 0.25% and 0.5% PA enhanced root growth, leaf gas exchange parameters and chlorophyll content under Al stress, while 1% PA exacerbated Al phytotoxicity on plant morphology. Seed priming and seedling treatment with PA reduced hydrogen peroxide and malonaldehyde contents, and increased osmolyte content. Seedlings of PA-primed seeds exhibited enhanced antioxidant activity and relatively high expression of auxin response factor and antioxidant genes. Seedling treatment with PA under Al stress increased antioxidant enzymes and reactive oxygen species-scavenging activities, restricted Al uptake and facilitated the availability and translocation of boron, manganese, sodium and phosphorus in tomato plants. Analysis of central carbon metabolism (CCM) revealed increased glycolysis, tricarboxylic acid cycle and electron transport chain metabolites in PA-treated plants. However, the Calvin-Benson cycle and pentose phosphate pathway metabolites were reduced. The CCM pathway metabolites exhibited a strong coordinated association in PA-treated plants. The findings of this thesis indicate that PA application in mainstream agriculture represents an eco-friendly strategy that can be used to: (1) increase crop productivity and nutritional qualities; (2) improve early crop establishment, detoxify Al and enhance Al tolerance in agricultural production systems.