Effects of Soil Factors on Manifestation of Allelopathy in Cytisus scoparius

Abstract

Samples of two types of soil, Andosol and ‘Masa’ soil, packed in pots were placed under the canopy of broom (Cytisus scoparius (L.) Link) for 1 year, so that the leachates from the foliage of C. scoparius could accumulate in the soils. There-after samples of surface soil at a depth of 0-3cm and 3-6cm were collected and the allelopathic activity was examined. Samples of each soil were packed in a cellulose tube (cutoff 8, 000MW, diameter 3.2cm) set at one corner of a plant box (W6×D6×H10cm) filled with 0.5% of agar. Lettuce (Great lakes 366) was seeded at a spacing of 1cm on the agar surface. The length of the lettuce radicle was measured 5 days after seeding. The elongation of the radicle was inhibited by the ‘Masa’ soil into which the leachates of C. scoparius accumulated at a depth of 0-3cm, but not at a depth of 3-6cm (Fig. 1, Table 1). Andosol at a depth of either 0-3cm or 3-6cm did not cause any inhibitory effect.
F-1 (mainly acidic), F-2 (mainly basic) and F-3 (mainly amphoteric) fractions of dry foliage water extract were found to contain allelochemicals (Table 2). However, when the foliage was incorporated into soil, only the F-1 fraction from the ‘Masa’ soil showed on inhibitory activity after 3 days of incubation at 25°C (Table 3).
In the ‘Masa’ soil, the growth of cucumber was inhibited by the addition of L-3, 4-dihydroxy-phenylalanine (DOPA) which had been identified as one of the allelochemicals of C. scoparius. The inhibition was particulary strong under nutrient stress (Table 5. test 1).
In the Andosol, the effect of DOPA application on cucumber growth was not significant. Addition of leachates and incorporation of dry foliage did not affect the plants. The absence of allelopathic activity in the Andosol was attributed to the adsorption of the allelochemicals onto the soil.
It was concluded that the characteristics of soil and physiological conditions of the recipient plant were the major factors involved in the manifestation of allelopathic phenomena.