The Effects of High Temperature Stress and its Mitigation Through the Application of Biostimulants in Controlled Environment Agriculture and Indoor Farming

Food security and supply networks are becoming an ever-increasing concern requiring innovative practices to deal with the contributing factors. Controlled Environment Agriculture (CEA) offers an alternative to conventional cropping systems for increasing the yields of certain produce types. Crop yields (tons/hectare/year) in CEA are reported to range between 10 and 100 times higher than open-field agriculture, and the water use in CEA is typically about 4.5–16% of that from conventional farms per unit mass of produce. However, these systems can be energy intensive due to temperature regulation requirements, compromising their environmental and economic viability. Energy is the second largest overhead cost in CEA with carbon footprints being reported as 5.6–16.7 times and 2.3–3.3 times greater than that of open-field agriculture for indoor vertical farms and greenhouses, respectively. This can be offset, in part, by reducing the reliance on cooling systems. However, high temperature stress negatively impacts crops at morphological, cellular, metabolic, and molecular levels, reducing produce quality and quantity. Biostimulants are additives which can benefit plant growth through ameliorating stress. This review considers recent research on the effects of heat stress on a variety of crops commonly grown in CEA and the categories of biostimulants that have known thermoprotective qualities. Seaweed extracts, chitin/chitosan, protein hydrolysates and amino acids, inorganic compounds, beneficial microorganisms, and humic substances are explored, alongside the known benefits, limitations, and knowledge gaps.