Impact of defoliation on below-ground carbon dynamics and arbuscular mycorrhizal fungi in grassland

Abstract

70% of all agricultural land is dedicated to grazing, therefore it is significant that grazed grasslands are appropriately managed to minimise environmental consequences. This may be achieved by identifying a suitable grazing frequency to promote arbuscular mycorrhizal (AM) fungi inoculation of grassland plant, therefore enhancing AM fungal benefits to the environment. However, there is no consensus in current research on the effects of different grazing frequencies on AM fungal inoculation. This greenhouse study aimed to identify a suitable grazing frequency to promote AM fungal inoculation by using defoliation to stimulate three grazing frequencies: none, every 3 weeks and weekly. The study explored three questions: 1. How does the defoliation frequency and AM fungal inoculation influence the allocation and flux of carbon between the ecosystem, shoots, roots and hyphosphere? 2. How does the defoliation frequency influence AM fungal colonisation? 3. How does the defoliation frequency influence phosphorus supply from AM fungi to host plant? Fluxes and capture of carbon and recently fixed photosynthate were measured using 13C. The influence of defoliation frequency on AM fungal colonisation and phosphorus supply was insignificant in this study. 13C allocation was higher to shoots than roots in H. lanatus, being highest in the absence of defoliation and AM colonisation. Defoliation frequency had a significant effect on rates of ecosystem respiration and photosynthesis, with no significant effect on hyphosphere respiration. This study utilised 13C to provide insight into the terrestrial carbon cycle, with findings suggesting that defoliation, as part of grazing, has important effects on ecosystem functioning in grassland.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Marina Semchenko (Supervisor)