Phosphorus (P) deficiency in plants causes detrimental effects on their growth and development, as P is a key macronutrient used in various physiological, biochemical and cell signaling processes. Research has shown that P-deficient plants exhibit several symptoms such as changes in leaf coloration, root morphology, and plant growth. However, many of those studies ignore gas exchange parameters. In this research, we studied the connection between P-deficiency and carbon (C) gain and loss in southern highbush blueberry (SHB, Vaccinium corymbosum interspecific hybrids) young plants to estimate the C cost of P-deficiency. The experiment was conducted using a hydroponic system where three-month old plants of ‘Farthing’ and ‘Keecrisp’ varieties grew in individual 2-L reservoirs filled with continuously-aerated complete nutrient solution containing 15 mg/L P during a 35-day acclimation period. After the acclimation period, plants were separated into two groups and continued to grow for 56 more days (treatment period). One group ( P) was grown in the complete nutrient solution, while the second group (-P) was grown in a P-free nutrient solution (0 mg/L P). We designed and tested a whole-plant gas exchange system that utilizes two infrared gas analyzers (CIRAS-3 and CIRAS-4) to simultaneously measure root system respiration and whole-plant C assimilation. Additionally, we measured root C exudation, fresh and dry mass accumulation, and P concentration and content. We induced P-deficiency as -P plants of both varieties had mature and young leaf P concentration below 0.12% (reference deficiency level). P plants had higher P concentration after treatment period. -P ‘Farthing’ plants had 89% less daily C assimilation than P plants, while no differences were observed in ‘Keecrisp’. Daily root respiration and C exudation, considered as ways of C loss, were, 3.5 and 2.9 times higher in -P than in P plants of ‘Farthing’. Similarly, -P ‘Keecrisp’ plants had 3.8 and 2.5 times more daily root respiration and C exudation compared to those under P. Ultimately, P deficiency caused a 136% reduction in daily C gain of ‘Farthing’ plants, while there were no differences between treatments in ‘Keecrisp’ plants. Our findings suggest that responses to P deficiency in SHB are genotype-specific, and that C budget and distribution in the plant play an important role in the responses to P-deficiency.
