Biostimulants as forest protection agents: Do these products have an effect against abiotic stress on a forest native species? Aspects to elucidate their action mechanisms

Projections of climatic change pose a challenging scenario for the management and adaptation of ecosystems. It is expected that forests around the world will be exposed to severe stress conditions such as imposed for drought, heat, and weather extremes. Forest native species of great economic-ecological importance will be affected. For example, in Argentina, Prosopis alba, a native species, is essential for restoring and reforestation of degraded areas. Hence, there is an imperious demand to find sustainable strategies to promote its tolerance to environmental changes. This work aims to evaluate the potential of phytoextracts from native plant species as biostimulants that increase the abiotic stress tolerance of P. alba, contributing to the biological resilience of native forests. We tested biochemical, physiological, and morphological characteristics (BPMc) on P. alba seedlings sprayed with phytoextracts of four different species. Measurements were made in the nursery as well as in the field. Our results showed that foliar application of Ilex paraguariensis and Larrea divaricata reduced an oxidative stress biomarker in P. alba 21 days after the acclimation phase began. Both extracts had high antioxidant activity. Notably, L. divaricata at 3 % w/v (LDa3%) exhibited significant potential as a biostimulant in the nursery and field. This phytoextract enhanced the BPMc of P. alba. Foliar applications of that biostimulant positively affected plant growth, increasing diameter, height, shoot biomass and root biomass. Indeed, seedlings sprayed with LDa3% demonstrated the best performance after transplanting from the nursery to the field. According to our results, foliar applications of LDa3% could stimulate the activity of cell antioxidants under abiotic stress conditions. Our results suggest that phytoextracts may be used as innovative products that improve the abiotic stress tolerance of P.alba, but the applied doses must be considered and evaluated. In the appropriate doses, we could observe that these products stimulate growth and activate plant defences against abiotic stress conditions on this forest species. Even though most of the research on biostimulants focuses on agricultural production, according to our results, these products have the potential to become a part of sustainable forestry during nursery production.