Growth and soil carbon dynamics of short rotation coppice species (Willow and Poplar) under variable nutrient and water availability

Kemp, Leigh-Anne and Sayer, Emma (2023) Growth and soil carbon dynamics of short rotation coppice species (Willow and Poplar) under variable nutrient and water availability. PhD thesis, Lancaster University.

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Abstract

Short rotation coppice (SRC) bioenergy crops are an attractive option to reduce anthropogenic greenhouse gas (GHG) emissions from primary energy production and agriculture. Fast-growing, high-yield SRC crops sequester large amounts of carbon in biomass, require minimum input, and can be grown on marginal land. However, we do not know how the carbon dynamics of SRC crops will be affected by future climate changes. Given that crops grown on marginal land often require nutrient additions and are subject to large fluctuations in soil moisture, I assessed the potential for inoculation with arbuscular mycorrhizal fungi (AMF) and fertilization to mitigate or exacerbate the effects of extreme weather events (drought and flood) on the growth, biomass, and soil GHG emissions of two SRC crop species (willow and poplar). I hypothesised that fertilization and AMF inoculation would mitigate the effects of extreme weather events on crop growth and biomass, but that nutrient addition would increase soil GHG emissions after drought and during flooding. My mesocosm experiments demonstrated that biomass increased by 26% with AMF inoculation and by 56% with nitrogen (N) addition. However, AMF inoculation stabilised soil CO2 emissions during a drought-rewetting event, whereas N-addition resulted in higher soil CO2 emissions during rewetting and after the drought. Furthermore, N-addition boosted soil CO2 and methane (CH4) emissions during flooding. Importantly, soil CO2 or CH4 emissions during flooding were higher in N-fertilized trees with a history of drought, and drought resulted in lower leaf biomass at the start of the subsequent growing season. The body of work presented in this thesis provides strong evidence that fertilization of SRC crops could increase soil GHG emissions during extreme weather events, and highlights promising new avenues for investigation into AMF inoculation as a potential alternative to boost SRC crop yield and resilience to drought.