Root depth development in tropical perennial forage grasses is related to root angle, root diameter and leaf area

Aims Tropical perennial grasses that can rapidly establish deep roots have a greater potential to survive soil surface drying sooner after establishment. This research aimed to identify species that establish deep roots quickly and to investigate the mechanisms that drove rapid vertical root development. Methods Perennial grass speciesBrachiaria brizantha,Brachiaria decumbens,Brachiaria humidicola,Brachiariahybrid Mulato II,Brachiaria mosambicensis,Panicum maximum,Setaria sphacelataandCynodon dactylonwere grown in rhizotrons that facilitated measurement of the rate of root depth development, the rate of root length development, photosynthesis and morphological traits. Principal component analysis was employed to separate grass species according to functional traits of vertical root development and their growth strategies. Results P. maximumestablished roots more rapidly to 50 cm depth than the other species examined and accumulated biomass and leaf area faster. It was differentiated from other species by a greater percentage of fine root length (< 0.2 mm diameter), a higher photosynthetic rate and ratio of root length to leaf area according to the principal component analysis. The growing degree days required for root establishment to 50 cm depth was negatively correlated with the percentage of fine root length, and positively correlated with root angle. The exponential rate of root depth development per growing degree day increased with average root diameter inB. humidicolaandB.hybrid Mulato II, indicating a conservative growth strategy. Conclusion Rapid vertical root development with a narrow root angle, higher photosynthetic rate, higher ratio of root length to leaf area and higher percentage of fine roots were apparent mechanisms that enabledP. maximumto establish deep roots faster than other species.P. maximumappears to be better able to avoid water stress during surface drying by accessing profile moisture. Greater average root diameter and percentage of root length with higher diameters was related to increased exponential rate of root depth development and wide root angle.