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Phosphorus requirement for biomass accumulation is higher compared to photosynthetic biochemistry for three ornamental shrubs

Shital Poudyal, James S. Owen, Thomas D. Sharkey, R.T. Fernandez, Bert Cregg
Scientia horticulturae 2021 v.275 pp. 109719
Cornus amomum subsp. obliqua, Hydrangea quercifolia, Physocarpus opulifolius, biomass production, carbon dioxide, carboxylation, dry matter partitioning, enzyme activity, leaf area, nutrient content, nutrient requirements, nutrient solutions, ornamental woody plants, phosphorus, phosphorus fertilizers, photosynthesis, ribulose-bisphosphate carboxylase, root growth, shrubs, soilless media, trioses
Ornamental nursery producers grow a variety of plant taxa in soil-less substrates and rely on frequent water and nutrient applications to maximize plant growth and quality. This study was performed to understand the morpho-physiological basis of plant response to phosphorus (P) additions and to identify the optimum P concentration required for three common woody ornamental taxa: Hydrangea quercifolia ‘Queen of Hearts’, Cornus obliqua ‘Powell Gardens’ and Physocarpus opulifolius ‘Seward’. In a greenhouse experiment, all plants were watered with a complete nutrient solution that varied in P concentration (0, 0.7, 1.3, 2.5, 3.7, 6.5 mg L⁻¹). Optimum P concentration for photosynthetic biochemistry was dependent on taxa and ranged between 2.5 and 3.7 mg L⁻¹. For total dry biomass, the optimum P concentration was approximately 4.0 mg L⁻¹ for all three taxa. Phosphorus concentration below 2.5 mg L⁻¹ reduced leaf size and resulted in greater partitioning of biomass and P to root growth. Analysis of responses of photosynthesis to intercellular carbon dioxide concentration (A/Ci curves) indicated a continuous increase in photosynthetic parameters to increasing P concentration. Rate of rubisco for carboxylation (Vcₘₐₓ), RuBP regeneration rate (J), and the rate of triose phosphate use (TPU) limited photosynthesis in P-deficient plants for all three taxa. Light-harvesting efficiency (Fv’/Fm’) for all three taxa was less sensitive to P addition than photosynthetic biochemistry or plant growth. The optimal P concentrations identified in this study are lower than common recommendations and less than the amounts provided by typical commercial fertilizers. Thus, for these three taxa, application of P above 4 mg L⁻¹ in combination with excess irrigation resulting in leachate could have negative environmental consequences without improving crop growth or physiology.