Abstract
Soil depth, slope position and different plantations can influence
bacterial community composition in Camellia oleifera forests.
However, prior studies have focused on the impacts of different depths,
slope positions, and forest types on bacterial diversity independently,
without comparing their combined impacts. This study aimed to assess
variation in soil bacterial community structures according to soil depth
and slope position and different forest types in the same plot. The
composition of soil bacterial communities was evaluated using
high-throughput sequencing of the 16S rRNA gene. Results indicate that
the soil organic carbon, humus, and total organic content increased, and
the bacterial composition and structure were significantly altered in
response to the G. jasminoides + C. oleifera low-yielding forest
in comparison to the other three forest types. The highest soil bacteria
numbers, Alpha and beta diversity, which improved the soil
microecological environment, were associated with the G.
jasminoides + C. oleifera forests and not the depth or slope position
treatments. The slope position did not have a significant influence on
the soil physicochemical and bacterial properties. Structural equation
modeling suggested that G. jasminoides + C. oleiferasignificantly affected the soil bacterial community diversity by
mediating the soil pH and NH4–N. The effects of forest
type on soil bacterial diversity were more important than soil depth and
slope position. This specific intercropping system was found to be an
effective strategy to improve soil health.
Keywords : Camellia
oleifera , bacterial communities, soil physicochemical properties,
forest type, depth, slope position
1 | INTRODUCTION
Camellia oleifera is an evergreen tree belonging to the Theaceae
family, which originates in China, and is a well-known woody oil tree
species used to produce Camellia seed oil (Zhang et al., 2020b). Hunan
Province is a key region for C. oleifera production in China. The
centralization and continuous distribution patterns of the large-scaleC. oleifera forests in this region have laid the foundation for
their future industrialization (Han, 2020).
Soil is one of the most important environmental factors that impact
plant physiology and affects the size and stability of C.
oleifera yields. Soil nutrient content and microbial communities are
crucial components of every ecosystem and are important drivers of
global biogeochemistry. Soil bacterial community composition can be used
to determine the type of land use and differentiate sites grouped
according to key physicochemical properties (Hermans et al., 2020).
As the main source of plant nutrients, the soil nutritional status is a
key factor that directly influences plant growth and development (Xiao
and He, 2019). Soil microorganisms are used as an index for soil
fertility and play a prominent role in soil productivity and fertility,
organic matter decomposition, nutrient cycling, and soil aggregate
formation (Six et al., 2004; Zhalnina et al., 2015; Müller et al., 2016;
Nacke et al., 2016; Ding et al., 2017). Plant diversity, nutrient
concentration, soil moisture, and soil type are also correlated with
variation in bacterial communities (Hermans et al., 2017).
Land use can have long-term effects on the soil microbiota structure and
diversity (Goss-Souza et al., 2017). Soil microbial characteristics are
controlled by changes in moisture and temperature and driven by seasonal
fluctuations and are closely associated with soil chemical
characteristics (Jiao et al., 2018), forest habitat, and other ecosystem
processes such as growth and development. Moderate growth of soil
microorganisms may promote transformation and storage of soil nutrients
and cause hormone disruption in the rhizosphere, as well as affecting
soil physicochemical properties. Metabolites produced by soil
microorganisms can be used as a source of nutrients for plant growth,
thereby affecting plant growth and development, succession, and
community diversity (Dunn et al., 2006; Van der Heijden et al., 2006).
The differences in the soil physico-structural characteristics under
different vegetation management measures in different forest types are
likely to affect soil bacterial diversity, community structures, and the
evolution of soil physico-structural properties and their ecological
function. Hermans et al. (2017) showed that key bacterial taxonomic
groups can reflect the impacts of specific anthropogenic activities and
provide strong evidence that microorganisms could be used as indicators
for soil condition.
The main areas for growing C. oleifera in the southern region of
China have predominantly acidic red and yellow soils. Red soil has poor
breathability, low organic matter content, and is relatively
nutrient-poor, which negatively affects plant growth. Compound, C.
oleifera special, and bioorganic fertilizers promote improved soil
nitrogen content, bacterial community abundance, biological activity,
and plant yield. The use of biological agents instead of chemical
fertilizers reduces environmental pollution and increases the yield ofC. oleifera (Wu et al., 2019).
In the red soil hilly region of southern China, C. oleifera helps
enhance and maintain soil fertility and the ecological quality of the
tree species planted (Tu et al., 2019). However, considering the long
growth cycle and low level of gains during the early growth stages of
economic forests, identifying a novel scientific approach for forestry
production is vital. Agroforestry management is an emerging land use and
management method that could address this problem that has attracted
considerable global attention. Intercropping C. oleifera with
peanuts has been found to improve soil porosity and conductivity, as
well as rhizosphere bacterial and fungal populations when compared withC. oleifera monocultures (Kroon et al., 2019; Lu et al., 2019;
Liu et al., 2020). Previous studies on plant–soil interactions have
highlighted many advantages associated with intercropping, such as
improved yield, accretion, decomposition of organic matter, and enhanced
iron and phosphorus availability. In mixed forest stands, bacterial
community diversity increased, inhibiting soil erosion, improving the
microclimate under the forest floor, increasing crop yields, and
contributing to the sustainable development of agriculture and forestry
(Dollinger and Jose, 2018; Mosquera-Losada et al., 2018). Intercropping
also improves forest productivity, provides important non-economic
benefits including social and environmental benefits. It can also
increase farm yields and agricultural income, improving the livelihood
of farmers (Li et al., 2019; Quandt et al., 2019).
Studies on soil bacterial communities inC. oleifera forests have
suggested that different climates, plantations, and morphological site
variation, such as soil depth can influence the bacterial community
composition of C. oleifera forests
(Tobias-Hünefeldt et al., 2019).
However, the structural composition of the bacterial microbiome in theC. oleifera intercropping system still requires further
exploration. Previous studies have focused on the impacts of different
depths, slope positions, and forest types on bacterial diversity
independently, without comparing their combined impacts (Lee et al.,
2015; Jiang et al., 2021).
Studying different tea-oil forests will help to deepen our understanding
of soil fertility and development in different forest types. It will
also help to explain the role of microorganisms in the growth and
development of tea-oil forest vegetation. It will also provide a
baseline for developing effective afforestation and forestry techniques
to improve the structure of existing tea-oil forests, promoting their
sustainable development.
In this study, we analyzed the effects of different soil depths, slope
positions, and different C. oleifera forest types in the same
plot in Tangjiapu, Dingcheng District, China, to examine the variation
in the soil bacterial structures. We also analyzed the correlation
between soil physicochemical properties and soil microorganisms to
determine whether depth, slope and forest type influenced the soil
bacteria for C. oleifera in the same plot. The study provides
reference data for informing effective and sustainable management ofC. oleifera in low-yielding forest plantations.