The rooting ability of Triplochiton scleroxylon cuttings: the interactions between stockplant irradiance, light quality and nutrients

Abstract

Stockplants of Triplochiton scleroxylon were grown in controlled-environment cabinets at the Institute of Terrestrial Ecology, Edinburgh, to test the effects of stockplant illumination on the rooting ability of leafy stem cuttings. The environmental variables were: (1) irradiance (PAR = 106 202 and 246 μmol m −2s −1) with a uniform light quality (red: far red ratio=1.75); (2) light quality ( R: FR = 1.6 and 6.3) with a uniform irradiance (PAR=294 μmol m −2s −1); and (3) irradiance (PAR=250 and 650 μmol m −2s −1) and nutrients (with and without 0.2% solution of 1:1:1, N:P:K) at a uniform light quality (R:FR=6.3). In all experiments, measurements were made of shoot length and leaf size and in the third experiment, the net photosynthetic rates of each leaf were determined prior to taking cuttings. Leaf area and leaf and stem dry weights were measured, as were their starch and reflux-soluble carbohydrate contents. The results showed that decreasing R:FR and irradiance independently increased both shoot growth and rooting ability. Strong positive relationships between photosynthesis and rooting were found when stockplants were grown at low irradiance (250 μmol m −2s −1) with and without fertilizers. A similar relationship was found, at high irradiance (650 μmol m −2s −1) only when nutrients were added. A strong negative relationship between the same parameters occurred without fertilizers at high irradiance. In addition, a weak negative relationship was found between rates of photosynthesis and the starch content of cuttings. It is concluded that end-product inhibition prevented the rooting of cuttings from stockplants grown without fertilizers at high irradiance with an R:FR ratio of 6.3.