A MECHANISTIC STUDY ON THE EFFECTS OF SOIL-HEATING ON FLOWERING TIME AND FLOWER QUALITY OF 'HUNTING SONG' GLADIOLUS

Corms of gladiolus (Gladiolus grandiflorus ‘Hunting Song’) were planted on beds of two soil-heating treatments (150 W m^-2 thermal cable, maximum temperature 25oC; 100 W m-2 thermal cable, maximum temperature 20 ^oC) and unheated beds (control) during winter flower forcing in a glasshouse in Beijing, China. Dimensions, fresh weight and dry weight of root, corm, leaf and flower spike were measured every 10-20 days until anthesis. Leaf chlorophyll content and photosynthesis rate were measured monthly. Flower quality (spike length and flower number per spike), mineral (N, P, K, Ca, and Mg) concentrations in root, corm, leaf and flower spike were measured at anthesis, and the distribution rates of dry matter and minerals among different organs of the plant were calculated. Root and leaf growth and carbon assimilation were increased by soil heating during the early growth stages. Dry matter and minerals (N, P, K, Ca, and Mg) allocated to the flower spike were also increased. Spike development was accelerated and flowering time in heated treatments was 16 and 14 days earlier than in the control. However, the root senesced earlier and the leaf’s photosynthesis rate declined more severely during the rapid spike development period in heated beds than in control. Consequently, the spike length and flower number per spike at harvest was reduced by soil heating. It is recommended that soil heating is necessary for ‘Hunting Song’ gladiolus only if the soil temperature is lower than 16 ^oC.

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