Compensating effects to growth of changes in dry matter allocation in response to variation in photosynthetic characteristics induced by photoperiod, light and nitrogen

High N-nutrition, high light and long photoperiod increased photosynthetic capacity (A_max) per leaf area of Raphanus sativa × raphanistrum. The effect of A_max on growth was enhanced by an increased fraction of dry matter partitioned into the shoot, resulting in a larger canopy. Low N-nutrition, low light and a short photoperiod reversed these responses. At intermediate combinations, such as low light and long photoperiod or high light and short photoperiod, A_max and the actual net photosynthesis per leaf area (A) neither correlated with the carbon uptake rate of the canopy as a whole nor with whole plant growth. A compensatory effect to growth of changes in dry matter partitioning in response to variation in photosynthetic characteristics induced by light and N-nutrition is discussed in terms of 2 competitive feedbacks. For growth a long photoperiod compensated for low light or low N-nutrition. Extrapolations from rates to gains are only valid under defined environmental conditions, especially when different photoperiods and effects on leaf ontogeny are involved. -Authors