ANALYSIS OF ROOT RESPIRATION OF SOLANUM-TUBEROSUM AS RELATED TO GROWTH, ION UPTAKE AND MAINTENANCE OF BIOMASS

The specific respiratory costs for growth (1/Y; mmol O-2 g(-1) DW), io n uptake (1/U; mol O-2 mol(-1) NO3-) and maintenance (m; nmol O-2 s(-1 ) g(-1) DW) of roots of potato (Solanum tuberosum L.) were determined in two experiments, and compared to process-based calculations and lit erature data. Both experiments yielded similar estimates for 1/Y (9.8- 9.9), 1/U (0.39-0.67), and m (10.2-14.8). The range of 1/Y agreed with the literature data (6.2-10.9), but was high compared to the theoreti cal expectations (4.3-5.5). Our estimates of 1/U appeared affected by perturbation. It was deduced that overall costs for maintaining solute gradients correlates to 1/U (instead of m), and accounts for up to 33 % of the overall costs of nitrate influx. The absence of these costs f or maintaining solute gradients in present estimates of 1/U explains t he good agreement with our calculation (0.43), and why these estimates are lower than most literature values (0.83-1.16). Costs of protein t urnover (3.7-16 nmol O-2 s(-1) g(-1) DW) can fully account the experim ental value of m, although m was relatively high compared to most lite rature data (4.0-7.0).