Plant-litter-soil feedbacks in common grass species are slightly negative and only marginally modified by litter exposed to insect herbivory

Purpose Insect herbivory affects plant growth, nutrient and secondary metabolite concentrations and litter quality. Changes to litter quality due to insect herbivory can alter decomposition, with knock on effects for plant growth mediated through the plantlitter- soil feedback pathway. 

Methods Using a multi-phase glasshouse experiment, we tested how changes in shoot and root litter quality of fast- and slow-growing grass caused by insect herbivores affect the performance of response plants in the soil in which the litter decomposed. 

Results We found that insect herbivory resulted in marginal changes to litter quality and did not affect growth when plants were grown with fast- versus slow-growing litter. Overall, presence of litter resulted in reduced root and shoot growth and this effect was significantly more negative in shoots versus roots. However, this effect was minimal, with a loss of c. 1.4% and 3.1% dry weight biomass in roots versus shoots, respectively. Further, shoot litter exposed to insect herbivory interacted with response plant identity to affect root growth.

Conclusions Our results suggest that whether litter originates from plant tissues exposed to insect herbivory or not and its interaction with fast- versus slow-growing grasses is of little importance, but species-specific responses to herbivory-conditioned litter can occur. Taken collectively, the overall role of the plant-litter-soil feedbackpathway, as well as its interaction with insect herbivory, is unlikely to affect broader ecosystem processes in this system.

Methods
De Long JR, Heinen R, Hannula E, Jongen R, Steinauer K, Bezemer M (2022) Plant-litter-soil feedbacks 

in common grass species are slightly negative and only marginally modified by litter exposed 

to insect herbivory. Plant and Soil. https://doi.org/10.21203/rs.3.rs-1403298/v1.

Litter and response species: fast (Arrhenatherum elatius, Holcus lanatus, Lolium perenne) and slow 

(Agrostis capillaris, Deschampsia flexuosa, Festuca ovina)

Exposed to aboveground herbivores (M. brassicae), belowground herbivores (Agriotes spp.), both or 

none (control)

Litter was then used in the second litter feedback phase of the experiment

Data here are carbon, nitrogen, total polyphenols obtained from dried, ground root and shoot litter 

and micronutrients from dried, ground root litter

Response plant species measurements: grams dry weight biomass of roots and shoots

Quality control was performed to ensure all values were reasonable