Interspecific variation in the rapid induced resistance and compensatory regrowth to herbivore in three Ficus saplings

Background/Question/Methods

Both induced resistance and tolerance are induced processes of plants against herbivores. Plants have been predicted to be either resistant or tolerant and the defensive strategies often involve a tradeoff. Plants evolved which defensive strategies may depend on successional stage and resource availability, while how these two strategies functioning among tropical woody plants is still not well understood. The aim of our study was to understand the interspecific variation in rapid induced resistance (RIR) and compensatory regrowth of three Ficus species against herbivore by generalist insect larvae (Asota caricae Fabricius) and its association with soil nutrient. Saplings of three Ficus species representing pioneer and mid-successional species were treated by herbivore and artificial injury with two levels of soil nutrient. Totally 264 saplings from three Ficus species with two levels of soil nutrient were adapted for RIR and compensatory regrowth experiments. All the saplings were placed under moth proof rain shelter. RIR was measured with consumed area by insect larvae on different treated tips. The compensatory regrowth was calculated by traits including total biomass, shoot and root mass, relative growth rate and photosynthetic characteristics.

Results/Conclusions

Three Ficus species behaved differently in response to herbivore and artificial injury. For the pioneer species F. hispida, both RIR and compensatory regrowth were triggered at both high and low soil nutrient level regardless of herbivore or artificial injury. For the two mid-successional species, the response to herbivore associated tightly with soil nutrient. F. racemosa displayed RIR only under the infertile condition and no significant compensatory regrowth under both two levels of soil nutrient and the response was only significant to herbivore but not the artificial injury. F. auriculata showed both RIR and compensatory regrowth under the infertile condition while RIR was triggered only by herbivore. The compensatory regrowth of F. hispida and F. auriculata ascribed to the increase of shoot and root mass respectively which resulted from significant increase in light saturated photosynthetic rates (P_max ). This study demonstrated the complex induced response to herbivore for saplings of three woody Ficus species. The interspecific different responses of three Ficus species against herbivore and artificial injury also implicate a better understanding of tropical rainforest species responding to the heterogenetic abiotic and biotic environments.