Microbial and Non-Microbial Biostimulants as Innovative Tools to Increase Macro and Trace Element Mineral Composition of Tomato and Spinach

The use of biostimulants has gained popularity in recent years as a sustainable approach to increase the yield and quality of horticultural crops. However, information is missing concerning their ability to enhance the concentration of some beneficial elements (macro- and microelements) in the edible tissues of plants, which, in turn, are useful for human health. For this reason, we investigated the effects of different microbial and non-microbial biostimulants on the content of essential macro- and micro-nutrients (P, K, Ca, Mg, Cu, Fe, Mn, Zn, Se) in San Marzano and Datterino tomatoes (Solanum lycopersicum L.) and spinach (Spinacia oleracea L.) by atomic adsorption spectrometry, also estimating the Daily Intake (EDI) and the Nutrient Contribution (NC) of fresh produce. All the biostimulants were able to increase the content of macro- and micro-nutrients in the studied horticultural products. Specifically, compared with control, application of Trichoderma harzianum T22 on the Pixel tomato increased Fe, Zn, Cu, Mn and Se contents by 49.66, 38.68, 129.79, 64.03 and 72.72%. In the San Marzano tomato, higher values of Fe (55.16 µg 100 g−1 fw), Mn (30.63 µg 100 g−1 fw), Zn (20.89 µg 100 g−1 fw), Cu (1.91 µg 100 g−1 fw) and Se (0.266 µg 100 g−1 fw) were obtained after application of a tropical plant extract (TPE) biostimulant. Similarly, compared with control, application of a vegetal-derived protein hydrolysate (VPDH) on spinach increased EDI-Fe, EDI-Zn, EDI-Mn, EDI-Cu and EDI-Se by 98.98, 127.09, 125.93, 68.52 and 230.76%, respectively. Therefore, biostimulants, regardless of their origin and nature, could be an ecological tool for biofortification programs for both fruit and leafy vegetables.