Integrated biostimulant applications improve growth, physiological performance and soil properties of pistachio ( Pistacia vera L.)

ABSTRACT

The pistachio tree ( Pistacia vera L.) is a globally valuable nut tree due to its economic and nutritional properties. Sustainable management strategies, including microbial biostimulants such as biochar (Bc), Trichoderma and arbuscular mycorrhizal fungi (AMF), have been proposed to enhance tree performance under variable environmental conditions. This study investigated the combined effects of Trichoderma harzianum Rifai KRL-AG2, two different Bc rates (1% and 3%) and the commercial AMF Endo Roots Soluble on the growth, physiological performance, leaf nutrient content and soil microbial activity of 3-year-old pistachio trees in Adıyaman, Türkiye. Two sampling periods were considered to capture the early (May) and late (September) growth stages. Morphological assessments included shoot length, stem diameter and branch number, while physiological assessments covered photosynthetic efficiency index (PEI), chlorophyll content and leaf colour. Soil pH, electrical conductivity and AMF spore density were also evaluated. At the beginning of the season, Trichoderma and 1% Bc significantly increased shoot length, stem thickening and branch formation compared to the control group, while AMF synergistically improved physiological performance towards the end of the season. Combined applications increased shoot length (39%) and branch count; in the most effective treatment, the branch count nearly doubled. The PEI increased by 60% in the early stages, and the leaf nutrient content (46.6%) and the colonisation of AMF in the soil were positively affected; thus demonstrating the synergistic effect of these biostimulants. The use of Trichoderma , AMF, and Bc can support sustainable pistachio production by improving growth, physiological performance, and nutrient status.