Effect of applying a calcined kaolin-based particle film on the photosynthetic capacity and growth of young eucalyptus plants

In scenarios of climatic change when increased global temperatures can be expected, it is essential to search for technologies that favor sapling survival and growth after planting and increase yield in the field. Kaolin-based particle films (KBPF) have been applied as barriers against the deleterious effects of high levels of solar radiation. The objective of the present study was to assess the effects of applying purified calcined kaolin-based particle film to young eucalyptus plants. Five treatments were carried out: 0% (just water), 3%, 5%, 7%, and 10% calcined kaolin applied to the adaxial part of the leaves. A complete randomized block design was used with five treatments and ten replicates. The plants were assessed for height, diameter at ground level, gas exchanges (net photosynthetic CO2 assimilation, stomatal conductance and transpiration), instantaneous (WUE) and intrinsic water use efficiency (IWUE), chlorophyll a fluorescence (maximum quantum yield of photosystem II (PSII) (Fv/Fm), concentration of active reaction centers in relation to the quantity of photons absorbed (RC/ABS) and the maximum ratio of quantum yields of photochemical and concurrent non-photochemical processes in PSII (Fv/F0), SPAD reading and leaf ontogeny. The 3% KBPF concentration showed the best responses in biometric assessments 80 days after planting (DAP) and were corroborated by the responses of the leaf, stem and shoot dry matter production as a whole. The leaf ontogeny assessments showed positive responses following KBPF application when considering leaf development, with 7% KBPF concentration resulting in the highest mean values. The mean specific leaf mass had negative response to high KBPF concentrations. At 60 DAP, the gas exchange variables during both assessment periods declined with an increase in KBPF concentration. Significant differences as a result of KBPF applications were found only at the start of the assessments (34 DAP) for both WUE and for IWUE. Leaf ‘greenness’ (SPAD reading) at 47 days showed a quadratic relationship in both periods. The variables of chlorophyll fluorescence showed a linear response at 34 DAP and a quadratic response 60 DAP. KBPF application increased height and diameter growth in plants treated with 3% KBPF but this response was not associated with photochemical efficiency and photosynthetic carbon assimilation values on a single-leaf basis. The best performance among the variables was provided by 3% KBPF application.