title: How does P affect photosynthesis and metabolite profiles of Eucalyptus globulus?
abstract: Phosphorus (P) has multiple effects on plant metabolism, but there are many unresolved questions especially for evergreen trees. For example, we do not know the general effects of P on metabolism, or if P affects photosynthesis via the internal conductance to CO(2) transfer from sub-stomatal cavities to chloroplast or amounts of Rubisco. This study investigates how P deficiency affects seedlings of the evergreen tree Eucalyptus globulus grown for 2.5 months with four nutrient solutions differing in P concentration. To determine why photosynthesis was affected by P supply, Rubisco was quantified by capillary electrophoresis, internal conductance was quantified from gas exchange and carbon isotope discrimination, and biochemical parameters of photosynthesis were estimated from A/C(c) responses. Additional insights into the effect of P on metabolism were provided by gas chromatography-mass spectrometry (GC-MS) metabolite profiling. Larger concentrations of P in the nutrient solution led to significantly faster rates of photosynthesis. There was no evidence that stomatal or internal conductances contributed to the effect of P supply on photosynthesis. The increase in photosynthesis with P supply was correlated with V(cmax), and amounts of P, phosphate and fructose 6-phosphate (6-P). Phosphorous supply affected approximately one-third of the 90 aqueous metabolites quantified by GC-MS, but the effect size was generally smaller than reported for experiments on herbaceous species. Phosphorus deficiency decreased concentrations of phosphate, glucose 6-P and fructose 6-P more than it decreased photosynthesis, suggesting faster turnover of smaller pools of phosphate and phosphorylated intermediates. The effect of P supply on most amino acids was small, with the exception of arginine and glutamine, which increased dramatically under P deficiency. P deficiency had small or non-significant effects on carbohydrates and organic acids of the tricarboxylic acid (TCA) cycle. The small effect of P on carbohydrates, organic acids and (most) amino acids likely reflects a functional homeostasis among C metabolism (glycolysis, TCA and pentose P cycles), rates of photosynthesis and growth. The strong functional homeostasis in E. globulus may reflect a conservative, long-term growth and metabolic strategy of evergreen trees.
authors.affiliation: School of Biological Sciences, University of Sydney, Sydney, NSW 2006, Australia. charles.warren@sydney.edu.au
authors.forename: Charles R
authors.initials: CR
authors.lastname: Warren
mesh_terms: D018533:Biomass; D005052:Eucalyptus / Q000254:growth & development / Q000378:metabolism*; D055442:Metabolome; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000172:deficiency*; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism*
chemical_list: D010758:Phosphorus; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen