| Summary: | Plant growth is constrained not only by the availability of soil nutrients, but also by the physical underground space where it grows. However, few studies have considered the effect of dimensional variations of soil space on the growth of a large set of plants and whether the effect differs among plant functional groups. We grew each of 19 common grassland plant species from three functional groups (grasses, legumes, and forbs) in three types of soil space [a cylindrical space of 15 cm in diameter and 15 in height (D15H15), a cylindrical space of 30 cm in diameter and 15 cm in height (D30H15), and a cylindrical space of 15 cm in diameter and 60 cm in height (D15H60)] with the same amount of essential nutrients. Irrespective of plant functional groups, plant species performed better in the soil with deeper vertical space (D15H60) than in the soil with shallower vertical space (D15H15 and D30H15) in terms of root biomass. Shoot mass and/or total mass in the different types of soil space varied with species. Within each functional group, species with larger body sizes tended to accumulate more shoot mass in soils with deeper vertical space (D15H60), while those with smaller body sizes did not respond differently. These results suggest that the dimensional variations of soil space, especially variations in the vertical dimensions, can be a key factor influencing the performance of plant species.
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