Pecans [Carya illinoinensis (Wangenh.) K. Koch] are an economically significant nut crop, with native pecans naturally distributed across 14 U.S. states, primarily concentrated in Oklahoma, Texas, and Mexico. Oklahoma leads in native pecan production, contributing approximately 79% (13.8 million pounds) of the total U.S. native pecan production (USDA, 2023). Economically, native pecans are valuable due to their desirable kernel traits suitable for commercial processing and their unique oil profile, rich in polyunsaturated fatty acids, enhancing market demand in the food industry. Microbial communities in the rhizosphere, comprising diverse fungi and bacteria, are crucial for nutrient cycling, soil fertility, and plant health. Despite their recognized importance, microbial dynamics associated with native pecan groves remain poorly understood. This study aimed to evaluate microbial diversity associated with native pecan trees and how it varies with fertilization treatments and grove management. Two native pecan groves: A -Tod's (35°55′42″ N, 96°13′24″ W) (with short grass and cattle grazing) and B- Shelly’s (35°57′32″ N, 96°7′38″ W) (only growing hays without cattle) in Sapulpa, Oklahoma were used in this experiment. Two fertilizer treatments: control (no NPK: nitrogen, phosphorus, and potassium) and full NPK (recommended amount based on soil tests), were applied in March 2023. For each sampling event, five trees per NPK treatment were randomly selected from each grove. Root and rhizosphere soil samples were collected from each tree across three sampling times: February (before fertilizer application), May, and September (after fertilizer application). Microbial DNA was extracted and sequenced using fungal ITS and bacterial 16S rRNA primers using Illumina sequencing. Bioinformatics analysis (using Mothur v. 1.48 and R version 4.4.1) was performed to identify community structure and functional groups. The results revealed that fungal and bacterial community between rhizosphere soil and roots was significantly different in both groves. Fungal communities exhibit greater variation across fertilizer treatments, habitats (roots vs. rhizosphere soil), and groves (Tod's vs. Shelly's) than bacterial communities. In roots, Russula and Tuber genus were the most dominant in Tod’s grove, while Russula and Inocybe genus were the most dominant fungi genera in Shelly’s grove. The core bacterial communities in both groves were primarily dominated by families Xanthobacteraceae and Micromonosporaceae in roots and Chthoniobacteraceae, Xanthobacteraceae, and Planctomycetes in rhizosphere soil. These findings suggest that fertilizer treatments and grove management distinctly shape microbial communities, providing insights to optimize soil health and productivity in native pecan groves.
