title: Balanced allocation of organic acids and biomass for phosphorus and nitrogen demand in the fynbos legume Podalyria calyptrata.
abstract: Podalyria calyptrata is from fynbos soils with low availability of phosphorus (P) and nitrogen (N). We investigated the physiological basis for tolerance of low P supply in nodulated P. calyptrata and examined responses to increased supply of combined-N as Ca(NO3)2 and P. It was hypothesized that increasing supply of combined-N would stimulate P-acquisition mechanisms and enhance plant growth with high P supply. Biomass, leaf [N] and [P], organic acid and phosphatase root exudates, and phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH) activity in nodules and roots were examined in two N×P experiments. Low P supply decreased leaf [P] and limited growth, decreasing the nodule:root ratio but increasing nodular PEPC and MDH activity for enhanced P-acquisition or P-utilization. At low P supply, a N-induced demand for P increased root exudation of citrate and PEPC and MDH activity in roots. Greater combined-N supply inhibited nodulation more at low P supply than at high P supply. With a P-induced demand for N the plants nodulated prolifically and increased combined-N supply did not enhance plant growth. The physiological basis for N2-fixing P. calyptrata tolerating growth at low P supply and responding to greater P supply is through balanced acquisition of P and N for plant demand.
authors.affiliation: Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
authors.forename: Pravin M
authors.initials: PM
authors.lastname: Maistry
authors.affiliation: Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
authors.forename: A Muthama
authors.initials: AM
authors.lastname: Muasya
authors.affiliation: Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Valentine
authors.affiliation: Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa. Electronic address: samson.chimphango@uct.ac.za.
authors.forename: Samson B M
authors.initials: SB
authors.lastname: Chimphango
mesh_terms: D018533:Biomass; D002264:Carboxylic Acids / Q000378:metabolism*; D005110:Extracellular Space / Q000201:enzymology; D007887:Fabaceae / Q000378:metabolism*; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010758:Phosphorus / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D053204:Root Nodules, Plant / Q000187:drug effects / Q000378:metabolism; D012987:Soil; D012996:Solutions
chemical_list: D002264:Carboxylic Acids; D009566:Nitrates; D012987:Soil; D012996:Solutions; D010758:Phosphorus; D010749:Phosphoprotein Phosphatases; D009584:Nitrogen
keywords: N(2)-fixation; N×P interaction; P-acquisition; P-limitation; Phosphoenolpyruvate carboxylase