Plasticity in the expression of direct and indirect defence traits of young plants of Mallotus japonicus in relation to soil nutritional conditions

Abstract

Although soil nutrients can influence the defence strategy of plants that have multiple defence traits, to date, there have been few studies to examine this. To evaluate the effect of soil nutrients on multiple plant defences, we cultivated Mallotus japonicus under three soil nutritional conditions in the field, and experimentally examined the expression of a physical defence trait (trichomes), chemical traits (pellucid dots), and biotic traits (extrafloral nectaries (EFNs) and pearl bodies) of the plants, and the number of ants visiting them. Under the low soil nutritional condition, plants strongly expressed the physical defence by trichomes and chemical defence by pellucid dots, meaning that the young plants adopted direct defences under the poor soil nutritional condition. Under the high soil nutritional condition, in contrast, the plants strongly expressed the indirect defence traits. They produced abundant EFNs and pearl bodies, and attracted many ants. These results suggest that young plants of M. japonicus use different defence modes in response to different soil nutritional conditions.

Different combinations of multiple defence traits in an extrafloral nectary‐bearing plant growing under various habitat conditions

“…and Macaranga triloba, the productivity of food bodies depends on the amount of available soil nutrients (Folgarait & Davidson 1995;Heil et al 2002). Yamawo & Hada (2010), Yamawo, Hada & Suzuki (2012) and Yamawo et al (2012a) reported that food bodies of M. japonicus increased under low light conditions or under high soil water/nutrient conditions. At treefall gaps, light availability is low and soil water contents are high.…”

“…Yamawo & Hada (2010) reported that the increase in EFN size and the decrease in food bodies occurred under high light conditions in young M. japonicus plants. Moreover, Yamawo, Hada & Suzuki (2012) and Yamawo et al (2012a) demonstrated that, in high soil nutrient and high moisture conditions, young M. japonicus increased EFNs and EF-nectar volume and decreased the densities of trichomes and pellucid dots. However, the effects of these resistance traits on herbivory and the plant tolerance to herbivory under different abiotic conditions have not been reported in the literature.…”

“…EFNbearing plant species, which are well known to entrust defence to ants (Koptur 1992), often show simultaneous expressions of various defensive traits (Steward & Keeler 1988;Agrawal & Spiller 2004;Rudgers, Strauss & Wendel 2004;Kobayashi et al 2008;Young et al 2010;Yamawo et al 2012a), as other plants do. For example, the empress tree (Paulownia tomentosa) and Japanese mallotus (Mallotus japonicus) use trichomes as suitable physical defences (Kobayashi et al 2008;Yamawo et al 2012a).…”

“…Plants can change the intensities of antiherbivore defences depending on abiotic factors such as light, soil water and soil nutrients (Wise & Abrahamson 2007, 2008Yamawo, Hada & Suzuki 2012;Yamawo et al 2012a). When each defence trait is plastic, plants might be well adapted to many environments (Bradshaw 1965;Pigliucci 2001).…”

Concentration and retention of chlorophyll around the extrafloral nectary of Mallotus japonicus

“…We used seedlings of M. japonicus , a pioneer plant that grows in gaps and disturbed areas in temperate and subtropical regions of eastern Asia. The plant bears EFNs on its leaf edges (Yamawo, Katayama, Suzuki, & Hada, ), which secrete nectar that contains primary sugars used in the production of leaves (Yamawo et al., ). Instead, of the physical and chemical defenses provided by trichomes and pellucid dots, which function on young leaves, the EFNs mostly function on middle‐aged leaves and attract ants, thereby reducing leaf damage by eliminating herbivores from the plant (Yamawo, Tagawa, Hada, & Suzuki, ; Yamawo, Suzuki, et al., ).…”