1 Introduction
Worldwide, half of primary and secondary forests, which are crucial for
maintaining biodiversity and ecosystem functions, are being converted
into monoculture plantations for the cultivation of timber, fuel
materials and other commodities. The annual expanding rates of
monoculture plantations have increased to 2% over the past 25 years
(FAO, 2015). Most conversion from natural forests to plantations has
occurred in subtropical regions(Lan et al., 2021) . Such conversion
results in alterations of ecosystem services and functions along with
changes in plant diversity and soil nutrients loss (Krashevska, Klarner,
Widyastuti, Maraun, & Scheu, 2015; Yang, Zhu, Xu, & Zheng, 2018). Soil
quality is defined as the capacity to sustain biological productivity,
maintain environmental quality, and promote plant and animal health
(Doran & Parkin, 1996). Various methods such as visual qualitative and
quantitative approaches have been used to assess soil quality (Bünemann
et al., 2018; Yakov et al., 2020). Quantitative evaluation incorporates
chemical, physical and biological indicators into the calculation of
soil quality index (SQI). Forest conversion may lead to reduced
vegetation coverage and forest productivity, soil quality deterioration
and erosion (Guillaume, Damris, & Kuzyakov, 2015), all of which will
have a negative impact on soil quality and health (Zarafshar et al.,
2020). Intensive management and short rotations are employed during
conversion, including site reclamation, clear-cutting, residue mulching,
herbicide weeding and fertilization. These practices can modify soil
quality, but the consequences for microorganisms and nutrient cycling
are not clear (Armenise, Redmile-Gordon, Stellacci, Ciccarese, &
Rubino, 2013). Thus, comprehensive and quantitative studies are needed
to better understand the impacts of forest conversion on soil quality
and functions in subtropical areas.
In forest ecosystems, fungi play fundamental ecological roles as
decomposers, symbionts, and tree pathogens (Uroz, Buée, Deveau,
Mieszkin, & Martin, 2016). They regulate organic matter decomposition
and nutrient cycling, and stimulate plant growth (Nakayama, Imamura,
Taniguchi, & Tateno, 2019). The establishment of fungal community is
determined by both abiotic (i.e. climate, spatial heterogeneity and
edaphic conditions) (Steidinger et al., 2019; van der Linde et al.,
2018) and biotic (i.e. host species) factors (Duhamel et al., 2019). The
conversion from natural forest to plantations is accompanied by changes
in the identity and diversity of host tree species and soil properties,
thereby affecting the fungal community and tropical-guild composition
(Mcguire et al., 2015). Compared with extensive studies on bacterial
communities (Kerfahi, Tripathi, Dong, Go, & Adams, 2016; Liu et al.,
2020), only a few studies have evaluated the response of soil fungi to
forest conversion. In addition, microbial activity is a valuable
indicator of soil quality (Bünemann et al., 2018). For instance,
microorganisms can maintain soil P bioavailability (Wu et al., 2019) and
alleviate N limitations (Johnson, Rowland, Corkidi, & Allen, 2008).
Hence, it is necessary to evaluate the impacts of forest conversion on
the fungal community, which play a vital role in shaping ecosystem
functions (e.g., soil nutrient cycling, carbon sequestration).
The aim of our study was to quantify the changes in soil quality and the
fungal community following forest conversion. Physico-chemical and
biological properties as well as the microbial community composition
were measured under a natural forest and four monoculture plantations
common for subtropical climate. The objectives were as follows: (1) To
investigate the impacts of forest conversion on soil quality and assess
the main influencing factors; (2) To evaluate the differences in
diversity, composition, and key taxa of fungal community after
conversion; (3) To clarify the relationship between soil quality and the
fungal community, and explore main driving factors of community changes
after conversion.