REGULAR ARTICLE Multivariate control of root biomass in a semi-arid grassland on the Loess Plateau, China Huoxing Zhu & Bojie Fu & Nan Lv & Shuai Wang & Jian Hou Received: 11 August 2013 /Accepted: 17 February 2014 # Springer International Publishing Switzerland 2014 Abstract Aim Root biomass has long been under-represented in biodiversity–ecosystem functioning studies, despite its dominance in biomass in many arid and semi-arid eco- systems. We aimed to explore the multivariate control over root biomass by plant diversity, together with other biotic and abiotic factors and to evaluate the relative importance of these factors. Methods Above- and below-ground traits of 13 com- munities and soil properties were measured in semi-arid grasslands on the Loess Plateau, China. Structural equa- tion modeling (SEM) was used to evaluate the relative importance of the community and soil characteristics, emphasizing the direct and indirect effects of plant diversity on root biomass. Results Significant indirect effects of plant species rich- ness on root biomass were found, although no direct correlation was detected between them. In the indirect pathways, plant species richness showed a positive ef- fect on soil total nitrogen, but a significant negative influence on soil total carbon. Soil total nitrogen and plant diversity had the largest and smallest total effect respectively on root biomass in the model. Conclusions Plant species richness was not the stron- gest determinant of root biomass but had a significant indirect effect, mediated through soil total carbon and nitrogen. This study suggests that greater plant species richness, through a positive influence on soil total nitro- gen, may indirectly promote root carbon stock. Keywords Plant diversity . Root biomass . Structural equation modeling . Soil carbon sequestration . Soil total nitrogen retention Introduction Root biomass is an important component of ecosystem carbon stock (De Deyn et al. 2008) and a useful predic- tor for several processes such as soil erosion in many terrestrial ecosystems (Gyssels et al. 2005). Many fac- tors including biotic characteristics, such as plant spe- cies composition and diversity, and abiotic conditions, such as nutrient availability, influence the root biomass production (Hooper et al. 2005; Spehn et al. 2005). Understanding the underlying mechanisms for these controls over root biomass is of major interest to predict the capacity of ecosystem carbon sequestration under future global change scenarios (De Deyn et al. 2008), as well as to provide valuable information for more effec- tive erosion controlling practices (Gyssels et al. 2005; Reubens et al. 2007). Plant diversity plays a key role in determining ecosystem processes such as primary production, nu- trient cycling and has received much attention in biodiversity ecosystem functioning (BEF) studies (Naeem et al. 1994; Hooper and Vitousek 1997; Plant Soil DOI 10.1007/s11104-014-2067-z Responsible Editor: Kees Jan van Groenigen. H. Zhu : B. Fu (*) : N. Lv : S. Wang : J. Hou State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P. O. Box 2871, Beijing 100085, People’ s Republic of China e-mail: bfu@rcees.ac.cn