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

Authors: POUDYAL, SHITAL - Michigan State University; Owen Jr, James - Jim; SHARKEY, T - Michigan State University; FERNANDEZ, R - Michigan State University; CREGG, B - Michigan State University

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2020
Publication Date: 9/13/2020
Publication URL: https://handle.nal.usda.gov/10113/7135260
Citation: Poudyal, S., Owen Jr, J.S., Sharkey, T.D., Fernandez, R.T., Cregg, B. 2020. Phosphorus requirement for biomass accumulation is higher compared to photosynthetic biochemistry for three ornamental shrubs. Scientia Horticulturae. 275. Article 109719. https://doi.org/10.1016/j.scienta.2020.109719.
DOI: https://doi.org/10.1016/j.scienta.2020.109719

Interpretive Summary: Horticulture is a large and economically significant industry, both in the U.S. and around the world. In the U.S., the sale of horticultural crops was worth $13.8 billion in 2014. Phosphorus leaching is higher in soil-less media (pine bark, sphagnum peat, vermiculite or sand) in comparison to regular soil due to inherent phosphorous load from the bark itself along with poor retention due to low anion exchange capacity and preferential flow through the porous substrate when irrigated. Thus, 30-60% of applied P is commonly leached when using bark based substrate (Newman, 2014). This leachate and resultant irrigation return flow can pollute surface and groundwater systems. Our specific objectives were to (1) determine the effect of P on photosynthesis and morphological responses in three different ornamental plant taxa, (2) identify the type of photosynthetic limitation that may result from P deficiency, and (3) categorize P partitioning to plant growth and P runoff. We observed phosphorus availability affects biomass allocation to roots or shoots. Phosphorus limitation reduces photosynthesis primarily by a reduction in the rate of rubisco carboxylation. Biomass productivity was better correlated with photosynthesis biochemistry than quantum efficiency. A 25% reduction in phosphorus application can reduce phosphorus runoff by 50% to 90%. Overall, growth were optimized at approximately 7 mg·L-1 of P for all three taxa, which is much lower than those in water-soluble fertilizers or P release rate of controlled-release fertilizers that are commonly available and used in the nursery industry. Therefore, nursery growers may be able to reduce P fertilization without reducing crop growth.

Technical Abstract: Ornamental nursery producers grow a variety of plant species and rely heavily on water and nutrient applications to maximize plant growth and quality. We conducted the current study to understand the morpho-physiological basis of plant response to phosphorus (P) concentration and identify optimum phosphorus concentration required for three common woody ornamental taxa; Hydrangea quercifolia Bartr. ‘Queen of Hearts’, Cornus obliqua Raf. ‘Powell Gardens’ and Physocarpus opulifolius Maxim. ‘Seward’. In a greenhouse experiment, all plants were watered with a complete nutrient solution that varied only in P concentration (0, 1, 2, 4, 6, 8 mg·L-1). For total dry biomass growth, the optimum P concentration was close to 7 mg·L-1 for all three taxa. However, P. opulifolius required less phosphorus for maximum growth index (plant height + plant width in two directions) compared to H. quercifolia and C. obliqua. Phosphorus concentration below 4 mg·L-1 reduced leaf size and resulted in greater partitioning of biomass and phosphorus to root growth. Analysis of responses of photosynthesis to intercellular carbon dioxide (A/Ci curves) indicated a continuous increase in photosynthetic parameters to increasing phosphorus concentrations. Rate of rubisco for carboxylation (Vcmax), RuBP regeneration rate (J) and rate of triose phosphate use (TPU) limited photosynthesis in phosphorus-deficient plants for all three taxa. However, P requirement for photosynthesis biochemistry was less compared to growth. Light-harvesting potential (Fv’/Fm’) for all three taxa was least sensitive to P requirement. Optimum P concentrations for growth and photosynthetic biochemistry ranged between 4 and 7 mg·L-1, depending on taxa. These P concentrations are lower than common recommendations and less than the amounts provided by typical commercial fertilizers. Application of phosphorus above 7 mg·L-1 is above that needed for growth and physiological function and could contribute to phosphorus runoff from nurseries.