Initial growth and physiology of guanandi (Calophyllum brasiliense Cambess) seedlings treated with humic acids and aqueous vermicompost extract

ABSTRACT The guanandi is a tropical tree from the American continent suitable to compose agroforestry systems and forest-farming-livestock integration whose growth and development stages can be enhanced with the use of biostimulants. In this work, humic acids (HA) and aqueous extracts produced from vermicomposting cattle manure (AEVC), biostimulants commonly employed in short-cycle crops, were characterized and evaluated for initial growth and gas exchange in guanandi seedlings. The HA showed higher levels of C and N and lower H and O compared to AEVC, in addition to three times higher total acidity, higher aromaticity index, and clearer signals regarding symmetric stretching in carboxyl groups and C-O stretching of polysaccharides. Greater stimulation of guanandi growth, via the concentration-response test, was observed for concentrations of 22.24 mg L−1 for HA and 25.55 mg L−1 for AEVC. Increases in net CO2 assimilation, stomatal conductance and transpiration were detected only in seedlings receiving HA. Main root diameter, leaf area and aboveground wet mass increased for both treatments with HA (19.9, 11.0, and 22.8%) and AEVC (16.9, 11.2, and 18.6%). The set of responses associated with the use of HA and AEVC allow categorizing these materials as biostimulants capable of enhancing the initial growth of guanandi seedlings.