Relations between carbohydrate, water status and adventitious root formation in leafy pea cuttings rooted under various levels of atmospheric CO2 and relative humidity

Three levels of atmospheric CO2 and 2 levels of relative humidity (RH) during the rooting period were tested for their effect on several factors presumed to influence adventitious root formation in leafy pea (Pisum sativum L. cv. Alaska) cuttings. Compared to normal CO2 levels (350 μl l−1), neither 1800 nor 675 μl l−1 CO2 affected the rooting percentage or the number of roots per cutting. However, 1800 μl l−1 CO2 increased root and shoot dry weight, root length, carbohydrate levels in the base of the cuttings and water potential (Ψw) of cuttings compared to normal levels of CO2. Compared to 87% RH. 55% RH decreased all of the above parameters, including the number of roots per cutting. A polyvinyl chloride antitranspirant (which partially blocks stomata and slows photosynthesis) applied simultaneously with 87% RH increased Ψw and root length but lowered all of the other above parameters, compared to 87% RH without antitranspirant. Increasing current photosynthate (products of photosynthetic activity after excision), carbohydrate, or Ψw either alone or together was associated with increased root system size but not necessarily with increased rooting percentage or root number. The data are consistent with a hypothesis that the number of roots per cutting increased with increasing current photosynthate and carbohydrate until some other factor became limiting. Also, the effect of Ψw on rooting percentage and root number was mediated through its effect on current photosynthate and carbohydrate.