Taylor Bruchet,* Joan Davenport, and Tarah Sullivan 
*Washington State University, 605 NE Ruby st Apt#15, Pullman, WA 99163 (taylor.bruchet@wsu.edu)

Chlorosis, or leaf yellowing, is a nutritional disorder induced by iron (Fe) deficiency that affects more than 50% of Concord vineyards in central Washington. When chlorosis is severe, it can reduce root biomass, shoot elongation, and yield. The exact cause of chlorosis is unknown, but several studies have shown that calcareous soils high in bicarbonate have a detrimental physiological effect on grapevines and that foliar Fe supplements typically resolve the issue within a sea-son. When grapevines are exposed to high levels of bicarbonates and low levels of Fe, they produce greater quantities of the enzyme phosphoenolpyruvate carboxylase (PEPC), which leads to higher concentrations of citric and malic acids in the root tips to aid in Fe uptake. Acidification of the rhizosphere then reduces Fe3+ into the bioavailable Fe2+ form necessary for plant and microbial growth. However, in the alkaline soils of the central Washington grapegrowing region, bioavailable Fe may be rapidly complexed into orthophosphates like strengite within the rooting zone. We hypothesize that as grapevine chlorosis severity increases, greater concentrations of organic acids accumulate within the roots, resulting in rhizosphere microbial production of phosphatase to acquire bioavailable Fe. To test this hypothesis, we measured organic acid quantities in Concord grapevine roots and soil phosphatase activity via spectrometric methods in two different vineyards. The goal of this research was to determine the role of phosphorus in inhibiting the uptake of iron in strategy 1 plants to help reduce the economically detrimental effects of chlorosis. 

Funding Support: Washington State University