Influences of air humidity during the cultivation of plants on wax chemical composition, morphology and leaf surface wettability

Changes of cuticular wax morphology, chemistry, and wettability of Brassica oleracea (Brassicaceae), Eucalyptus gunnii (Myrtaceae) and Tropaeolum majus (Tropaeolaceae), with different types of surface waxes, cultivated at three levels of relative air humidities (RH) (a: 20–30%, b: 40–75% and c: 98% RH) have been investigated. Wax chemistry was investigated by gas chromatography (GC) and mass spectroscopy (MS), micro morphology by scanning electron microscopy (SEM) and surface wettability by measuring the contact angle. Grown at 98% RH, all species showed decreased total wax mass and wax crystal density but significantly increased leaf surface wettability. In contrast cultivation at 20–30% RH led to increased total amounts of wax and reduced surface wettability. SEM investigations and GC/MS analysis revealed that wax crystal morphology and qualitative wax composition of Brassica were altered after cultivation at 98% RH, whereas chemical composition and morphology of wax crystals in Tropaeolum and Eucalyptus remained unchanged.