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Title: The nature of photosynthetic phosphorus limitations for tropical tree species
Author: Bloomfield , Keith John
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2012
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Tropical soils are often characterised by low phosphorus availability prompting the view that the productivity of many tropical forests may be phosphorus (P) rather than nitrogen (N) limited. Nevertheless, to date, no study has assessed the mechanisms by which P-deficiency might be limiting rates of photosynthesis in tropical trees. A controlled glasshouse experiment investigated the effect of P deficiency on rates of photosynthesis (A) and related leaf traits for seven Australian tropical tree species drawn from different plant functional types (pFTs) thought to differ in their photosynthesis/nutrient relationships. Measurements of gas exchange and leaf structure were combined with laboratory assays ofleaf nutrients; subsequent field campaigns were conducted in tropical Queensland (also comparing forest with savanna), Peru and French Guiana. The greenhouse results showed that the A- [N] relationship is affected by P supply, but PFT effects were not as predicted and in Queensland savanna species were found to have higher photosynthetic N use efficiency compared with forest trees - despite lower leaf [P]. In South America, an expected cross-basin gradient in P availability was' confirmed with higher [P] for the Peruvian trees, but Ama.'{ did not differ between the two Peruvian plots despite a 48% increase in mean [P]. The combined field dataset, including more than 80 species, allowed novel cross-continental comparisons of major leaf fractions of P and N - these were found to differ at each hierarchical level: country, site and species. Attempts to define a unifying photosynthetic model for tropical trees confirmed a dominant role for N, but with a critical role for P also invoked. Model performance was, however, improved by allowing for specific geographic and phylogenetic effects. A current lack of understanding as to the basis of these unexplained phytogeograhic effects on photosynthesis/nutrient relationships constitutes a major obstacle in the development of universally-applicable large-scale photosynthesis models.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available