Eucalypts and low phosphorus availability: between responsiveness and efficiency

Background and aims Twenty-four species of eucalypts were studied regarding their ability to grow under low P and their responsiveness to P inputs. Methods Growth and photosynthesis-related parameters were evaluated. Results Growth of all species was influenced by low P availability. No significant correlation was found between leaf P concentration and biomass, indicating that P concentrations in leaves cannot be solely considered an indication of the responsiveness to P in eucalypts. Species responsive to P-input (high agronomic P efficiency values, APE) were those with low P use efficiency - PUE (here assessed as relative efficiency of P-use, REP) and low P uptake efficiency (PUpE). But, non-responsive species were related to higher P-efficiency under low soil P-availability. Eucalyptus tereticornis , E. cladocalyx , E. globulus and E. camaldulensis were efficient under low-P availability. Whereas, E. crebra and E acmenoides were the most responsive species, with high APE, suggesting that for these species P-inputs are needed to guarantee plant growth. The root:shoot ratio remained constant at different P availabilities, suggesting that biomass allocation towards the root in response to P and greater investment in roots were not correlated with greater PUE. Under limited P, E. robusta and E. botryoides exhibited low foliar P contents and higher root:shoot ratios than those of other species with higher P contents, indicating that greater root investment does not necessarily result in greater PUE. Conclusion The results suggest that the divergence among species is probably related to different mechanisms, which may improve P-use efficiency.