Changes in soil microbial communities after exposure to neonicotinoids: A systematic review

Abstract

Neonicotinoids are a group of nicotine‐related chemicals widely used as insecticides in agriculture. Several studies have shown measurable quantities of neonicotinoids in the environment but little is known regarding their impact on soil microbial populations. The purpose of this systematic review was to clarify the effects of neonicotinoids on soil microbiology and to highlight any knowledge gaps. A formal systematic review was performed following PRISMA (Preferred Reporting Items for Systematic Review and Meta‐Analyses) guidelines using keywords in PubMed, SCOPUS and Web of Science. This resulted in 29 peer‐reviewed articles, whose findings diverged widely because of variable methodologies. Field‐based studies were few (28%). Imidacloprid was the most widely used (66%) and soil microbial communities were most sensitive to it. Spray formulations were used in 83% of the studies and seed treatments in the rest. Diversity indices were the most frequently reported soil microbial parameter (62%). About 45% of the studies found that neonicotinoids had adverse impacts on soil microbial community structure, composition, diversity, functioning, enzymatic activity and nitrogen transformation. Interactions with soil physicochemical properties were poorly addressed in all studies. The need for more research, particularly field‐based research on the effects of neonicotinoids on soil microorganisms was highlighted by this review.

Nontarget impacts of neonicotinoids on nectar‐inhabiting microbes

“…With a few exceptions, NNs negatively impacted bacterial growth metrics, but bacterial species differed in terms of the NN concentration at which effects on their growth were observed, if at all. This is consistent with other studies on NNs and soil‐inhabiting microbes, which often find microbial taxa vary widely in their responses to NN exposure (Akter et al, 2023; Cycoń et al, 2013). Four of our five assayed bacterial species belong to various sub‐groups of Pseudomonadota Garrity et al 2021 (synonym Proteobacteria), which are common in nectar (Álvarez‐Pérez et al, 2012; Fridman et al, 2011), though we did not select bacterial taxa based on taxonomy.…”

“…We echo calls by Akter et al (2023) that further understanding of the physiochemical properties of microbial habitats and their effects on growth is neededspecifically how these properties are influenced by NNs, and how this mediates microbial responses.…”

“…Environmental context, in addition to genetic or physiological variation within taxa, is likely critically important when discussing bacterial responses to NNs, making it difficult to draw conclusions about general trends (Akter et al, 2023). The same considerations also apply to fungi, in that certain studies find fungal abundance is not affected by imidacloprid in soils (Cycoń et al, 2013; Zhang et al, 2015) while others find it decreases (Cai et al, 2016).…”

“…This is expected given that NNs are normally sprayed on plants or applied to the soil. Succinctly summarising this body of work is challenging due to diverging methodologies and contexts (Akter et al, 2023). Some studies have documented a range of adverse impacts from NN exposure on soil microbes (e.g., Cai et al, 2016; Streletskii et al, 2022; Yu et al, 2020).…”

“…Imidacloprid, the most commonly used NN, is known to alter the structure of bacteria and fungi communities in soils and phyllospheres (Moulas et al, 2013; Parizadeh et al, 2021) by either inhibiting (Ahmed & Ahmad, 2006) or enhancing (Moulas et al, 2013; Zhang et al, 2015) growth of different taxa or altering their metabolic activity (Wang et al, 2014). A recent review (Akter et al, 2023) on soil microbes and NNs underscored the need for more studies taking place in field settings, outside the laboratory, and studies examining commercial NN formulations.…”