Evaluating the role of biotic and abiotic factors in hardwood tree development in the Central Hardwood Region (CHR).

Abstract

Background: Hardwood tree growth and development are influenced by the interplay between soil microbiota and tree physiology. Though unclear mechanistically, microbial community composition is associated with tree growth. We investigated how soil chemistry and prokaryotic communities impacted Quercus rubra (red oak) and Juglans nigra (black walnut) growth across three plantations in Indiana and Michigan. Trees exhibiting above- (high-performing or healthy) or below-average (low-performing or poor) growth rates were compared. Correlations with soil properties and microbial composition (16 S rRNA sequencing) were assessed to identify factors associated with variations in mean dominant tree height and diameter at breast height (DBH).

Results: Tree growth differed by site, species, and performance class. High-performing trees showed 25-40% higher AGR and 10-20% higher RGR across study sites. Larger trees occurred in Southern and Western Indiana than in Michigan. J. nigra outperformed Q. rubra in Indiana, and the reverse occurred in Michigan. DH and DBH were strongly correlated (R² = 0.8046, P < 0.001), and soil pH differed by species. Organic C, N, and CEC differed among species, but not among sites or performance class. Prokaryotic composition varied by species and site and explained 10.7%, 9.4%, and 7.6% of the variance. Microbial community structure was linked to DBH in J. nigra (r = 0.14, P = 0.002) and Q. rubra (r = 0.078, P = 0.028), and height only in J. nigra (r = 0.20, P = 0.001). Differential abundance analysis identified 88 and 122 growth-associated ASVs in J. nigra and Q. rubra, respectively. Random Forest models explained that soil texture (sand and silt) and microbial taxa (Bacillus, Arthrobacter, GP1, GP3) are key elements for growth.

Conclusions: Hardwood growth is more strongly associated with soil texture and specific microbial taxa than with overall microbial diversity. These species-dependent relationships suggest that microbial indicators of growth performance differ among hardwood species. Overall, the results improve our understanding of plant, soil, and microbe interactions and support using microbial indicators to monitor and improve hardwood plantation performance. Identifying microbial indicators associated with superior growth could inform reforestation and silvicultural practices in temperate hardwood ecosystems.