Potential for the use of biostimulants in urban tree management

Abstract

Biostimulants are substances that, although not classified as nutrients or pesticides, are soil improvers and promote plant growth when applied in small quantities. They are categorized into four groups: acids, microorganisms, bioactive compounds of plant origin, and others. Their application in urban trees aims to improve vitality and enhance resilience under stress conditions. Commonly used biostimulants include seaweed extracts, humic acids, non-structural carbohydrates, paclobutrazol, and beneficial microorganisms. These have shown effectiveness against drought, water, and salinity stress, and in strengthening the immune system of trees. Commercial biostimulants based on humic acids have improved survival rates, root and shoot vigor, and overall vitality, as evidenced by increased chlorophyll fluorescence. Additionally, the application of starch and glucose increases starch levels in tree trunks—an important factor, as starch depletion under severe stress is associated with tree mortality. Among biostimulants, mycorrhizal fungi are the most extensively studied in urban forestry, consistently demonstrating benefits in growth variables and stress adaptation, even at the molecular level. Finally, although most biostimulant-related knowledge comes from agricultural systems, their potential use in urban arboriculture is significant. This work presents a review of their application in field and semi-controlled environments, as well as the challenges associated with their use in urban tree management.