Growing perennial rhizomatous grasses on contaminated land: a strategy for combining phyto-management with sustainable biomass production?

To investigate this strategy, 15 field scale trials were implemented in five countries [1].  These have evaluated the performance of Phalaris, Miscanthus, 2 x Saccharum and 2 x Pennisetum species for combined energy crop production, phyto-remediation and or phyto-management of contaminated land in Brazil and Europe.  Reed canarygrass (Phalaris arundinacea) is a native perennial rhizomatous C3 species suitable for non-agricultural or marginal lands and climatic zones such as Scotland (where C4 Miscanthus x giganteous cannot be grown effectively).  Our phytoremediation trials using Phalaris in Italy and Ukraine are the first we are aware of. Given the wide variety of non-agricultural marginal lands [2], species selection must combine significant biomass production on marginal land with acceptable levels of biomass contamination for subsequent use or energy conversion.  Whereas specialist hyperaccumulator plants may achieve higher absolute concentrations of contaminants and exhibit greater bioconcentration and translocation factors, their inherently lower biomass productivity means that both biomass, energy yield and total mass of contaminants removed per unit area will be relatively small.  In contrast, high yielding, low contaminant uptake characteristics, such as for conventional energy crop species, would result in greater energy production, economic viability and greater potential for biomass utilisation. In the UK the CERESiS project has utilised long-term field trials originally established during the BioReGen (Biomass, Remediation, re-Generation: Reusing Brownfield Sites for renewable energy crops) EU Life demonstration Project (LIFE05 ENV/UK/000128) in 2007.  These allowed direct comparison of the actual contaminant removal rates of three crop species:  Although the biomass of Miscanthus and short-rotation coppice Salix contained higher concentrations of certain elements, Phalaris far out-performed these in terms of biomass, ease and economy of production [3].  Surprisingly, despite lower contaminant concentrations in Phalaris, such was the increased biomass yield that the total mass removed was still greater than for Miscanthus or Salix.  Likewise Pennisetum (Napier and Capiaçu grasses) shows similar promise in Brazil as the most productive, resulting in the highest offtake of Cr from soils contaminated with this element.  This suggests that low-uptake phyto-excluding plants which can tolerate contaminated soils and grow productively might still represent the best and most economically viable option for clean-up of contaminated sites. Meanwhile this nature-based solution can simultaneously deliver a variety of wider societal and environmental benefits, such as greening-up derelict land or the enhanced storage of carbon in soil [4]. This paper will investigate this strategy by comparing biomass yield, biomass contamination and the calculated offtake of contaminants for a wide range of generic contaminants across all of the CERESiS trial sites.  This will be used to evaluate the potential trade-offs between biomass suitability for use and phyto-management of contaminated land.    [1] This study is part of the CERESiS (ContaminatEd land Remediation through Energy crops for Soil improvement to liquid biofuels Strategies) Project which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 101006717, www.ceresis.eu  [2] Mellor et al 2020, RaSER 135, 110220  [3] Lord, 2015, BioBE 78, 110-125  [4] Lord & Sakrabani, 2019, STotEn 686, 1057-68