Teratosphaeria leaf disease (TLD) causes considerable disease in young plantation species, a challenge exacerbated by climate change impacts (Wardlaw, 2021). To ensure sustainable production, understanding the interaction between eucalyptus and its associated microbes is crucial for enhancing plantation resilience against this disease and improving overall tree productivity. There is a growing interest in leveraging plant-associated microbiomes to bolster plant resistance to pests and diseases. However, within the forest industry, while there exists a wealth of knowledge on microbiome communities, critical aspects of how trees benefit from these interactions, such as increased productivity, survival rates, and defence mechanisms, remain significant gaps in our understanding.
To investigate these interactions, field studies were conducted to examine the relationship between TLD severity and soil microbial communities in Eucalyptus nitens plantations. Trees aged 1 to 5 years post-establishment were selected for disease assessments, and soil and root samples were collected from selected trees. Fungal and bacterial communities were characterized using high-throughput amplicon sequencing of ITS and 16S rDNA markers. In addition, glasshouse experiments were performed to evaluate whether the microbial communities from soils from sites with varying levels of TLD severity influence tree physiological responses—including net photosynthetic rate (NPR) and stomatal conductance (SC)—and productivity, measured as dry shoot weight (DSW). The glasshouse experiment used eight seedlots with varying degrees of plant resistance status to TLD, grown in potting mix amended with soils collected from sites with low and moderate TLD severity.
Analysis of fungal diversity revealed distinct site-specific clusters in both the root and rhizosphere fractions, indicating that fungal communities differed significantly across sites. However, fungal diversity did not vary with TLD severity. Similarly, bacterial diversity in the rhizosphere differed significantly across sites but showed no clear variation with TLD severity. In contrast, root-associated bacterial communities exhibited significant variation, particularly between trees in soils with very low/low TLD severity and those in moderate-severity sites.
Plant physiological responses were evaluated using mixed-effects models, which revealed that plant resistance status (i.e., inherent susceptibility or resistance to TLD) had no significant effect on net photosynthetic rate (NPR) or dry shoot weight (DSW). However, resistance status significantly influenced stomatal conductance (SC). Notably, the growth medium (soil origin) exerted a strong effect on all measured physiological parameters.
These findings suggest a relationship between the health status of Eucalyptus nitens and below-ground microbial communities. Furthermore, soils from diseased and healthy plantations differentially affect plant physiological responses and productivity, highlighting the importance of below-ground activities in plantation performance.