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.