Architectural characteristics of roots in typical coastal psammophytes of South China

Aims Roots are an important part of plants; they not only facilitate the utilization of soil water and nutrients, but also successively anchor the plants against wind and water wave erosion. This study was conducted to determine the adaptive strategy of root architectural characteristics in different plant life forms, in order to assist the selection of most suitable plant species for the coastal dune restoration.
Methods After a detailed field investigation of sand dunes in South China, four species were sampled on a damaged coastal sand dune, including Casuarina equisetifolia, Ipomoea pes-caprae, Spinifex littoreus and Cynodon dactylon, and roots were excavated for analyzing their architectural characteristics such as root bifurcation ratio, root link length, root topological index and root-shoot ratio.
Important findings There were great differences as well as similarities in the root architectural characteristics among the four plant species. The total root bifurcation ratios in Spinifex littoreus and Cynodon dactylon were apparently higher than in other two species, and was lowest in Ipomoea pes-caprae, indicating that herbaceous plants are more competitive for soil resources by having a higher root bifurcation ratio. With except of Casuarina equisetifolia, all other three species were easily sand buried due to their flatten and extended shoots, which might further improve the transportation efficiency of soil resources. The average root link lengths of the four species were smaller in coastal sandy dunes than which in inland areas; Casuarina equisetifolia had the greatest average root link length of 19.25 cm among the four species studied, and greater proportion of transportation roots than other three species. This demonstrated that an increase in average root link length and proportion of transportation roots would favor the reduction of root competition for soil resources and high efficiency of resources transportation. Ipomoea pes-caprae had a smaller proportion of the assimilation roots, but the adventitious roots on the shoot compensated for the low assimilation efficiency of resources. All the four species showed a dichotomous structure, of which the herbaceous species had more similar root architectures, indicating that herbaceous species are less affected by limitation of environmental resources and better to colonize the coastal dunes if being used in restoration. Compared with species in inland areas, there are greater differences for the species in coastal sandy areas in the acquisition of soil resources and spatial expansion, indicating different adaptive strategies among the four species. Herbaceous species should be used as preferred plants for the restoration of coastal dunes, especially those with adventitious roots, but not the trees.