Interspecific Variation in Oilseed Brassica Growth, Development and Physiological Responses to Early Season N Deficiency.

Nitrogen availability is a major limiting factor controlling plant growth and developmental physiology in both natural ecosystems and modern production agriculture. Brassicas have a low NUE and remobilization during the vegetative phase and species may differ in their response to N deficiency.  A greenhouse study was conducted at NFREC, Quincy, Florida during 2014/2015 to determine the effects of N deficiency on B. carinata var. A110 and B. napus var. 1918 growth, development and physiology. Four N treatments (0, 33, 66 and 100% of N in full strength Hoagland Solution) were imposed 30 days after planting. Plant height, leaf area, number of nodes, primary branches and total biomass, leaf, stem and root dry weights in both species decreased linearly with N reduction.  Partitioning biomass to various plant components differed between the species and was modified by N availability. B. carinata apportioned >53% of total biomass in the stem component across all N rates while in B. napus stems comprised 17–34% of total biomass. In both species, root dry matter generally decreased with increasing N availability.  At 55 DAT, photosynthesis and leaf area for both species increased linearly with N rate.  B. carinata stomatal conductance and transpiration were higher at 0, 33 and 66% N than B. napus and declined to similar levels at 100% N in both species. Leaf photosynthetic responses to PAR exhibited similar exponential increases in net photosynthesis for both species across all N levels. Total chlorophyll, Chla and Chlb concentrations in B. napus showed a steeper increase with N level than B. carinata. These results suggest that early season N deficiency alters B. carinata and B. napus growth, development and physiology, although resource partitioning differed between the species which may have implications for N use efficiency and recovery.