Understanding the functioning of managed grassland ecosystems: evidence of strong liming effects on multiple soil biogeochemical properties

Abstract

Human-managed grasslands deliver a wide range of ecosystem services including food production and the regulation of nitrogen (N) and carbon (C) cycles between aboveground and belowground compartments. Common management practices, however, such as animal grazing, agricultural liming and nutrient fertilization can greatly influence the functioning of grassland ecosystems and reduce their long-term sustainability. This PhD study has specifically addressed how grazing, liming and nutrient additions might affect soil biogeochemistry and aboveground-belowground interactions in a grassland experiment established in 1991 at Silwood Park, Berkshire, UK.

Key findings from this study show how repeated liming applications have significantly (1) increased archaeal and bacterial (B) abundance while reducing fungal (F) abundance, (2) increased the C pool of soil smaller soil aggregate fractions (e.g. micro and silt clay aggregates), and (3) enhanced plant nitrogen use efficiency (NUE). Chronic nutrient fertilization has also significantly increased the abundance of ammonia oxidizing bacteria and decreased plant NUE.

A novel result of this study is no change in Fungal and Bacterial gene copies in response to multiple nutrient additions. This suggests that fungal taxa are benefitting from labile resources and not all functional bacterial groups are benefitting from an increase in labile resources returned to the soil. These findings are state of the art and in line with papers that are questioning the classic model of the soil food web where bacteria predominantly metabolise labile detritus and fungi predominantly metabolise recalcitrant detritus. These resources were thought to form part of two distinct basal energy channels, however, the findings in this study support an emerging conceptual framework that understands the food web to have one continuous C pool that can at different times benefit both bacteria and fungi.

Date of Award	Mar 2017
Original language	English
Supervisor	Dario Fornara (Supervisor), Paul McKenzie (Supervisor) & Geoffrey Mc Mullan (Supervisor)