Response of gas exchange to leaf piercing explained by piecewise linear regression for two developmental forms of rape plant (Brassica napus L. ssp. oleifera Metzg)

Oilseed rape (Brassica napus L. ssp. oleifera Metzg) was the subject of the study in two forms: winter cv. ‘Muller’ (at the rosette stage – the first internode BBCH 30 – 31) and spring cv. ‘Feliks’ (at the yellow bud stage BBCH 59). The main gas-exchange parameters, net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and intercellular CO2 concentration (Ci) were measured on leaves prior to the piercing and immediately after the short-term piercing. The effect of mechanical wounding revealed different progress of the gas exchange process for the two forms. Piecewise linear regression with the breakpoint estimation showed that the plants at the same age but at a different vegetal stage, manage mechanical leaf-piercing differently. The differences concerned the stomatal conductance and transpiration changes since for rosette leaves the process consisted of five intervals with a uniform direction, while for stem leaves - of five intervals with a fluctuating direction. These parameters got stabilized within a similar time (220 mins) for both forms. The process of net photosynthetic rate was altered by the plant stages. ‘Muller’ plants at the rosette stage demonstrated dependence of PN on time in log-linear progression: y (PN) = 8.01+ 2.73 log10 (x t2); 7 < t2 < 220; R2 = 0.96. For stem leaves of ‘Feliks’ plants the process of transpiration, in terms of directions, was convergent with the process of photosynthesis. Those two processes were synchronized from 1st to 114th min of the test (r = 0.85; p < 0.001) in plants at the rosette stage and from 26th to 148th min in stem leaves (r = 0.95; p < 0.001).