Understanding and exploiting a nitrogen-fixing endophyte for enhancing sustainability and productivity of vertical farming

The UK imports 40% of its fruit and vegetables with these supply chains subject to disruption through weather in production areas and geopolitical issues, with shortages of produce becoming more common in the UK. Increasing UK production in a sustainable manner is critical to provide resilience to UK fruit and vegetable supply. Vertical farming is a rapidly-growing sector offering reliable year-round production for increased productivity, production on non-agricultural land with minimal chemical inputs (fertilizer/pesticides), no run-off pollution and highly-efficient water use. The controlled conditions of vertical farming maximise growth (minimising time-to-harvest) and prevent waste (from unfavourable climate). However, a key challenge to UK production of PACE horticulture edibles is the high energy cost and associated GHG emissions. Significant increases in the yield of these crops and/or reduction in days-to-harvest, without increasing the environmental burden of production, is the only solution to ensure a stable and sustainable supply. Our project is aimed at increasing resource use efficiency - enhancing productivity whilst reducing costs and GHG emissions per kg of produce.

Availability of nitrogen is a limiting factor for crop yield, but fertilizer use contributes significantly to GHG emissions, even in controlled environment agriculture. Here, we investigate an endophytic bacterium that is able to fix nitrogen from the air and exploit this endophyte to enhance resource use efficiency of vertical farming. Gluconacetobacter diazotrophicus was first identified from sugarcane and able to colonise many different crops. It stimulates plant growth via two main mechanisms; nitrogen fixation that provides ammonia to plant cells; and secretion of phytohormones and small molecules that induce changes in root system architecture, resulting in enhanced nutrient use efficiency. It is clear that in sugarcane G. diazotrophicus can provide a significant proportion of the nitrogen required by the plant and G. diazotrophicus treatment can increase potato yield by up to 30% in the field. However, we know that different varieties of crops vary in G. diazotrophicus colonisation and growth response, and the impact of G. diazotrophicus colonization has not been tested in vertical farming systems.

Lettuce is the most valuable leafy vegetable grown in the UK and an increasing proportion of production is via controlled environment agriculture. In this project we will use quantitative genetics and transcriptome profiling of a lettuce diversity set to identify genetic loci and candidate mechanisms determining lettuce colonisation and/or response to G. diazotrophicus. We will investigate the impact of G. diazotrophicus on yield/days to harvest, the contribution of endophyte nitrogen-fixation to lettuce nitrogen content and the relative importance of nitrogen fixation versus root system changes. We will quantify the effects of G. diazotrophicus colonization on lettuce when grown in a commercial-scale vertical farming system and determine the impacts of G. diazotrophicus on GHG emissions and economics of lettuce production in a vertical farm.

Our proposal addresses three of the PACE challenge areas (Genetic improvement of crops for increased yield, Reducing environmental impacts and progressing towards sustainability targets, and Sustainably increasing yield, quality and productivity by designing better systems). Project outcomes will sustainably enhance lettuce production in vertical farming systems with environmental and economic benefits across the lettuce CEA supply chain. Outcomes will drive breeding and/or selecting lettuce varieties for enhanced resource use efficiency via G. diazotrophicus colonisation; optimised growing recipes and technology for Vertical Future clients; and new markets for Azotic products.