Leaf inorganic phosphorus as a potential indicator of phosphorus status, photosynthesis and growth of Eucalyptus grandis seedlings

Dane S. Thomas, Kelvin D. Montagu, Jann P. Conroy

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    63 Citations (Scopus)

    Abstract

    In eucalypts the reduction in CO2 assimilation and total leaf area at low phosphorus (P) supply is not associated with lower leaf total P concentrations. We tested the hypothesis that the leaf concentration of inorganic phosphorus ([Pi]) may be a better indicator of P nutrition status in Eucalyptus grandis W. Hill ex Maiden by growing seedlings in P deficient soil supplemented with P supplies ranging from 3 to1000 mg kg?1. Height, biomass accumulation, gas exchange, chlorophyll fluorescence and concentrations of total P ([Pt]), organic P ([Po]) and [Pi] of the last fully expanded leaves were measured when harvested at 19 weeks. All parameters of growth increased with larger applications of soil P with most becoming saturated at additions of 500 mg P kg?1 soil. Soil P supply had larger effects on biomass and canopy leaf area, by both increased in leaf initiation and expansion, than on CO2 assimilation (A). Leaf [Pt] and [Po] concentrations were largely invariant to soil P supply and were not correlated with any of the measured growth and photosynthetic parameters. By contrast, leaf [Pi] increased from 171 to 398 mg kg?1 with increasing soil P supply. Furthermore, number of leaves, total leaf area and seedling biomass increased exponentially with leaf [Pi], while individual leaf area and A increased linearly with leaf [Pi], and quantum yield of photosystem II similarly increased, and non-photochemical quenching decreased, with increasing leaf [Pi]. The response of A to internal CO2 concentration (Ci) indicated that at lower P supplies A became increasingly restricted by limitations associated with Rubisco and RuBP regeneration. Stomatal limitation may in part be masking the full effect of P supply on A as Ci declined with either increasing soil P or leaf [Pi] supply. We conclude that leaf [Pi] was a potentially better indicator than [Pt] or [Po] for correlating the effects of soil P supply on growth and photosynthesis of E. grandis. Furthermore, as A achieved at saturating Ca increased with increasing P supply leaf [Pi], these findings suggest that a greatly increased rate of canopy assimilation could be achieved at higher P supply in response to the expected increase in global CO2 levels.
    Original languageEnglish
    JournalForest Ecology and Management
    Publication statusPublished - 2006

    Keywords

    • eucalyptus
    • homeostasis
    • phosphorus
    • photosynthesis
    • plant canopies
    • soil management

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