Minimum sampling density determines soil bacterial diversity through ecosystem multifunctionality in a typical steppe

Abstract

Ensuring an appropriate sampling density will accurately reflect the ecosystem condition. However, the knowledge gap of the minimum sampling density limits our deeper comprehension of the significance of ecosystem multifunctionality in maintaining soil bacterial diversity. We established a long-term grazing trial in a typical steppe since 2001 and have now formed a stable heterogeneous environment. Based on this, we conducted a full-factorial sampling density experiment in 2024. By analyzing 4016 sample combinations, we quantified the characteristics of bacterial communities (structure, function, and diversity), biotic factors (plant diversity, aboveground biomass, as well as the total carbon, nitrogen, and phosphorus contents in plants), and abiotic factors (organic carbon, total nitrogen, total phosphorus, nitrate, ammonium, and available phosphorus contents in soil). Using inflection points of exponential decay curves of the coefficient of variation of sampling density, we determined the minimum sampling density for each indicator. Our findings reveal that asynchronous responses result in differences in minimum sampling densities among different indicators. Although the minimum sampling density for bacterial richness was 0.76 m² ha⁻¹, multi-dimensional trade-offs suggest that a range of 1.0–1.3 m² ha⁻¹ is suitable for the typical steppe. Path analysis shows that sampling density primarily regulates bacterial diversity through the direct positive effect of bacterial community composition and the indirect negative effects of biotic factors. It is crucial to establish a causal relationship between determining the minimum sampling density, constraining maximum multifunctionality, and assessing stable species diversity. This will prevent biodiversity misestimation and reverse biodiversity loss.