Plant intraspecific trait variation (ITV) is known to shape community assembly and ecosystem functioning. However, its influence on rhizosphere organisms, ranging from bacteria and fungi to nematodes, remains largely unexplored.

In a recent study published in Plant and Soil, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences (CAS) found that even subtle differences in root traits among trees of the same species can restructure the microscopic food web in the rhizosphere, the narrow zone of soil directly influenced by root secretions.

In this study, the researchers focused on how ITV affects soil biodiversity in tropical plantations within the framework of the Root Economic Space (RES), which classifies roots along two main strategies: collaborative (partnering with soil fungi) and conservative (slower, denser roots). They examined whether differences in these strategies among individual trees regulate the diversity and interaction networks of bacteria, fungi and nematodes.

The researchers selected 12 common tree species, half forming partnerships with arbuscular mycorrhizal (AM) fungi and half with ectomycorrhizal (ECM) fungi. They measured fine-root traits such as specific root length (SRL) and root tissue density, along with soil pH and nutrient levels. Then, using high-throughput DNA sequencing and nematode community analysis, they mapped the bacterial, fungal, and nematode communities living in the rhizosphere.

According to the researchers, the results showed that root ITV significantly altered interspecific trait variation within the RES framework.

For ECM trees that followed a "do-it-yourself" strategy characterized by high SRL and an "acquisitive" strategy characterized by high root nitrogen, fungal and nematode diversity increased markedly.

In contrast, for AM trees, higher soil pH was the main factor associated with greater bacterial diversity. The acquisitive strategy also enhanced nutrient cycling, which in turn strengthened cross-trophic interactions, leading to more complex co-occurrence networks.

Furthermore, the researchers found that high nutrient levels raised nematode diversity in ECM trees, while elevated pH similarly benefited bacterial diversity in AM trees. Interestingly, root exudates from ECM trees were more stable overall but varied more from individual to individual, making their microbial communities more responsive to ITV.

"Plant ITV is a critical driver of community assembly and function," said XIA Shangwen of XTBG. "This is one of the few studies that simultaneously examines bacteria, fungi, and nematodes within the same root system. Our results underscore the pivotal role of plant phenotypic diversity in shaping belowground communities and highlight its importance for soil biodiversity conservation and ecosystem management."