2018 ASHS Annual Conference

Hydroponic growing systems are an effective tool for studying plant nutritional physiology because nutrient concentrations can be easily controlled. Typically, these studies entail exposing the entire root system to the same nutrient solution. This design fails to account for soil heterogeneity. Moreover, it poses a challenge for plant nutritional physiology experiments where local and systemic responses need to be isolated. Previous studies suggest that southern highbush blueberry (SHB, Vaccinium corymbosum interspecific hybrids) and other Vaccinium spp. do not acidify their rhizosphere. However, these studies used single-reservoir hydroponic systems, which confound direct and nutrient uptake-dependent rhizosphere acidification. We designed a split-root hydroponic system to distinguish between nutrient-uptake dependent rhizosphere acidification (local response) and direct, H+-ATPase-mediated rhizosphere acidification (systemic response) in hydroponically-grown SHB. One-year old rooted cuttings of ‘Emerald’ SHB were transplanted to a hydroponic growth system where each half of the root system was in a different reservoir. One reservoir was supplied with a buffered, complete nutrient solution containing 2.5 mM NH4+. The other reservoir was supplied with a non-buffered nutrient solution containing either 2.5 mM NH4+ (treatment NH4+ /NH4+) or no nitrogen (treatment NH4+ /None). All nutrient solutions were continuously aerated. Fresh nutrient solutions were supplied every 7 days. Hydroponic solution pH was measured periodically. Root relative electrolyte leakage (REL), and tissue N content were measured destructively after 35 days of treatment. Plants in both treatments exhibited similar, adequate leaf N levels (P > 0.05) and similar root REL (P > 0.05), suggesting that the split root design and treatments did not cause N deficiency or root stress. Both NH4+ uptake-dependent rhizosphere acidification and direct rhizosphere acidification were observed. NH4+ uptake-dependent rhizosphere acidification occured at a higher rate than direct rhizosphere acidification. These findings suggest that SHB exhibits both systemic and localized rhizosphere acidification. Using a split-root hydroponic growth system helped distinguish between these two responses.