INFLUENCE OF IRRADIANCE ON WATER RELATIONS AND CARBON FLUX DURING ROOTING OF SHOREA-LEPROSULA LEAFY STEM CUTTINGS

Single-node leafy stem cuttings of Shorea leprosula Miq. were subjecte d to a high, intermediate or low irradiance treatment for 16 weeks in an enclosed mist propagation system. Before rooting, maximum photosynt hesis of the cuttings occurred at an irradiance of 400 mu mol m(-2) s( -1). Although none of the irradiance treatments affected the number of roots produced per cutting, the numbers of cuttings that formed roots were 50 and 30% in the high irradiance (diurnal range of 0-658 mu mol m(-2) s(-1)) and low irradiance (diurnal range of 0-98 mu mol m(-2) s (-1)) treatments, respectively, compared with 62% in the intermediate irradiance treatment (diurnal range of 0-360 mu mol m(-2) s(-1)). Low rooting frequency of cuttings in the high irradiance treatment was ass ociated with water deficits (maximum leaf-to-air vapor pressure defici t (VPD) = 3.6 kPa), whereas cuttings in the low irradiance treatment h ad a low rooting frequency because they were below the light compensat ion point most of the time. In the intermediate irradiance treatment, cuttings withstood a daily maximum VPD of 1-2 kPa and recovered overni ght from the previous day's deficit, as indicated by higher relative w ater content (RWC) and stomatal conductance (g(s)) in the morning than in the previous afternoon and evening. Higher RWC and g(s) of cutting s in all treatments on Days 14 and 21 compared with Day 8 probably ind icated recovery from water deficit following severance and insertion o f the cuttings in rooting medium. There were negative relationships be tween stem volume of cuttings and both number of cuttings that rooted and number of roots per cutting.