Dry matter, phosphorus and nitrogen partitioning in three Eucalyptus species grown under a nutrient deficit

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Seedlings of Eucalyptus grandis Hill ex Maiden, E. gummefera (Sol. ex Gaertner) Hochr. and two provenances of E. pilularis Smith [Coffs Harbour (CH) and Myall Lakes (ML)] were grown for 21 weeks in sand culture under nutrient-limiting conditions. Over this period the seedlots originating in the more phosphorus-deficient sites, E. gummifera and E. pilularis (ML), produced a larger mass and extracted 2–5 times more phosphorus (but 60–70% less nitrogen) from the sand than did the representatives from fertile habitats, E. grandis and E. pilularis (CH). Large seed reserves of phosphorus were a contributing factor to the success of E. gummifera and in both species adapted to low phosphorus, the early establishment of a larger root system conferred an advantage.

E. grandis and E. pilularis (CH) had lower tissue phosphorus concentrations (approx. 160 μg g−1) and hence by definition would be considered more efficient utilizers of phosphorus. However, this ‘efficiency’ was the result of an internal partitioning strategy that permitted growth to proceed unchecked and phosphorus dilution to continue. Under the severe limitations to phosphorus supply of this experiment, the more effective strategy was that adopted by E. pilularis (ML) and E. gummifera. These species developed a storage or buffer strategy which would allow longer-term survival by ensuring critically low phosphorus concentrations were not reached. The difficulties of the less tolerant E. grandis and E. pilularis (CH) were compounded by a disproportionate amount of nitrogen uptake which created an ion imbalance in the tissues.

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