Root morphology and its contribution to a large root system for phosphorus uptake by <Emphasis Type="Italic">Rytidosperma</Emphasis> species (wallaby grass)

Aims

Rytidosperma species are native Australian grasses which have different growth rates and phosphorus (P) requirements. This study examined the role of root morphology traits in response to P supply.

Methods

Nine Rytidosperma species ranging from slow- to fast-growth were examined along with Lolium perenne and Bromus hordeaceus. Plants were grown in a glasshouse for 47 days in soil supplied with six levels of P between 0 and 60 mg P per pot. Root mass, length and diameter, root hair length and density, and extent of mycorrhizal colonisation were measured.

Results

Across all species there was a positive correlation (P < 0.001) between P uptake and root mass, length and root hair cylinder volume (RHCV; estimated using root diameter, root hair length and root length) at all levels of P supply. An exception was the RHCV of B. hordeaceus, where expected P uptake was not achieved due to a markedly reduced root length at low-P supply. For the Rytidosperma species, morphological plasticity for specific root length, root mass fraction and root hair length ranged from 1.5-fold to 2.7-fold between high- and low-P supply. However, across all species and P levels no single root morphological trait was identified for universally increasing the size of the root system and P uptake.

Conclusions

Fast-growing species took up more P as a result of an overall larger root mass, greater root length and larger RHCV.