Lower Variation in Horizontal Root Density in Grassland Mixtures Compared to Monocultures

Many of the benefits of plant diversity can be directly related to the rooting system; i.e. higher root density can improve nutrient access and retention, erosion resistance and recovery after disturbance. The focus of research to date has been mainly on vertical patterns, however, root distribution and homogeneity in the horizontal plane are also important, particularly for erosion resistance. There is very little information on the horizontal spatial properties of root systems of grassland plant communities, and data allowing quantification of horizontal root variation is rare.

The objective was to assess the horizontal variation in root density of grassland monocultures compared to mixtures, both at species level and at community level. To this end, we reanalysed the data from two unique datasets containing root data in which the root biomass and species identity of multiple root cores per experimental unit were measured separately in both monocultures and mixtures. We hypothesized that if roots show more interspecific intermingling (which is expected as a strategy to avoid detrimental species-specific pathogens) as opposed to interspecific segregation (expected under the niche differentiation theory), this results in less variation in horizontal root density in mixtures compared to monocultures, both at the whole plant community and at the species level.

For the whole plant community, the observed horizontal variation in root density in mixtures tended to be lower than expected based on the variation in monocultures. At individual plant level, the CV in observed mixtures was generally lower than in monocultures, particularly for grasses. These results suggest a higher level of (interspecific) intermingling of plant roots in mixtures (which is in line with the pathogen theory), resulting in a more homogenous filling at the horizontal plane. This work can feed into research on the development of vegetation plans aimed at erosion control.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No 655771