Urbanization has changed the human living environment and played a “filter” role to microbial diversity. Often, alien plant species are introduced in urban areas to increase the beauty of urban landscapes, leading to ecosystem convergence. This convergence phenomenon leads to biodiversity decline, and homogenization of habitats lead to homogenization of urban soil microorganisms[1]. A reduction in contact with natural biodiversity weakens the microbiome and immune system of the human body, thereby affecting human health. Thus, rapid urbanization negatively impacts microbial biodiversity and consequently, human health[2–5]. Exposure to diverse urban greenspace habitats (UGSHs) can reduce blood pressure, relieve pain, and reduce mortality[6–8]. Although the mechanisms associated with these positive effects remain unclear, the effects may be due to the interaction of plants and soil microbial communities with humans and the soil microbiome can transfer to the residents, altering human microbiome composition, influencing immune function and health outcomes[9–11]. Therefore, it is necessary to improve our understanding of soil microbial diversity among different UGSHs.
UGSHs allow pollution degradation and remediation for human survival[12, 13], water resource management, carbon maintenance, nutrient cycling, and a series of basic ecosystem services[14–16], such as promoting biochemical cycles and soil processes[17, 18]; therefore, they are key in modern urban ecosystems[19]. “The microbiome rewilding hypothesis” proposes that microbial diversity in urban green spaces can effectively improve urban population health by providing a “natural” microbiome to urban residents[20, 21]. However, owing to environmental characteristics, artificial management, and maintenance types, different UGSHs differ considerably in structure and function. Urban and parked-road green belts are common UGSHs types. Road green belts promote isolation, safety, and ecological protection; these soils become relatively isolated habitats surrounded by concrete fences and are subject to multiple disturbances (for example, automobile exhaust emissions, dust fall, road management, and maintenance), which can influence soil enzyme activity and organic carbon content, affecting soil microbial diversity[22, 23]. Urban parks provide important ecological services such as air purification, climate regulation, environment beautification, and physical and mental health promotion of residents[24, 25]. Parks are often affected by human activities, and the soil surface is trampled and compacted, which affects soil pore connectivity, permeability, air permeability, temperature, rooting space, nutrient flow, and biological activity[26]. Human disturbance is the main factor affecting soil microbial diversity[27, 28]. Soil microbiomes in UGSHs play an important role in the sustainable and stable development of urban ecological environments by alleviating psychological pressure and physical health[25]. Strengthening the monitoring, evaluation, and research of soil microorganisms in UGSHs is of great scientific and practical significance.
Ectomycorrhizal fungi (EMF) play an important role in maintaining biodiversity and plant community succession[29]. Pinaceae, Fagaceae, Salicaceae, and other major tree species are EMF host plants that are widely distributed in most forest ecosystems[30]. EMF help host plants absorb nutrients (nitrogen, phosphorus, potassium, and other elements) and alleviate heavy metal pollution stress and antagonize diseases[31, 32]. Some EMF can form fruiting bodies during the completion of their life cycle and are often used as indicators of changes in UGSHs[33]. EMF allows for rapid establishment or promotion of early tree species colonization in disturbed areas[34]. Considering that many ectomycorrhizal host trees such as Pine, Poplar, and Salix are distributed in cities, UGSHs are characteristic of habitat isolation and long-term artificial perturbations (for example, exposed pollutants, artificial disturbance, and management activities) and obstruct the interspecies interactions of fungi, resulting in lower EMF diversity in UGSHs[35, 36]. Therefore, a deeper understanding of EMF diversity in UGSHs will allow for improved scientific management.
A large majority of studies on EMF diversity has focused on natural ecosystem habitats such as different forest types and grasslands[37, 38], reporting changes in soil microbial communities[39], but not on EMF diversity, in UGSHs. Therefore, in this study, we aimed to measure EMF diversity in three EMF host plants, namely, Cedrus deodara, Pinus massoniana, and Salix babylonica, in UGSHs. We hypothesized that under different UGSHs 1) EMF diversity differs among different tree species and 2) EMF diversity in the same tree species is different. In this study, we aim to provide a scientific reference for optimizing the design and scientific management of UGSHs.