Simplified estimates of soil nematode body mass using maximum diameter: Insights from large-scale grasslands across China

Abstract

Soil nematode biomass is of growing importance in elucidating soil food web structure, ecosystem functioning, and global biogeographical cycling. However, a significant challenge exists in quickly obtaining body mass data for a large number of nematode specimens without compromising measurement quality. Recently, a simplified method has been proposed, utilizing only the maximum diameter of nematodes to evaluate their fresh weight (W) as a substitute for Andrássy's formula. This approach is based on strong linear correlations between nematode body length (L) and maximum diameter (D). Despite its effectiveness, further testing is needed in extensive regions with numerous specimens. For this purpose, we conducted a study comprising 24,465 nematode specimens obtained from 222 soil samples in five types of grasslands across China. Our findings provided a robust support for the wide use of this simplified method. Furthermore, we proposed new weight formulas for total nematodes, morphological groups, and trophic groups, which were all well fitted to power models as W = aDb/(1.6 × 106), with various values of a for different aggregations and approximately constant b ≈ 3. Based on additional comparative analyses of the formulas used to assess the mean weight of functional groups, community-weighted mean body size, and community metabolic functional footprints, we firstly recommend using trophic group-specific formulas to minimize weight deviations from Andrássy's formula. Our new simplified power-law formulas enable reliable estimates of nematode body mass and are therefore promising for future applications. Moreover, our findings suggest that the classical Euclidean scaling theory significantly contributes to precisely estimating the body mass of small-sized soil fauna using only maximum diameter. In a global approach with a large number of individuals, for functional biogeography studies for instance, measuring the maximum diameter of animals to calculate their biomass is intriguing and compelling to motivate scientists to embrace functional approaches.