Do Phytotoxic Compounds in Soils after Scale-infested Cycas micronesica Litter Deposits Explain Reduced Plant Growth?

Abstract

We used activated charcoal methods to test for the presence of phytotoxic substances in soils that had received inputs of decomposing Cycas micronesica K.D. Hill leaves and stems that were heavily infested with the armored scale Aulacaspis yasumatsui Takagi. Velocity of Momordica charantia Descourt. and Carica papaya L. seedling emergence was increased by the addition of charcoal to these soils. Furthermore, M. charantia and C. papaya seedling height and dry weight were among the response variables that were increased by the addition of charcoal. Legacy effects of scale-infested C. micronesica plant litter deposited in these soils resulted in phytotoxic compounds that inhibited seedling emergence and plant growth. Scale-infested Cycas leaves should not be used as mulch or in compost until phytotoxic causal mechanisms are more fully understood.