Abstract
Positive plant–soil feedback depends on beneficial interactions between roots and microbes for nutrient acquisition; growth promotion; and disease suppression. Recent pyrosequencing approaches have provided insight into the rhizosphere bacterial communities in various cropping systems. However; there is a scarcity of information about the influence of root exudates on the composition of root-associated bacterial communities in ratooning tea monocropping systems of different ages. In Southeastern China; tea cropping systems provide the unique natural experimental environment to compare the distribution of bacterial communities in different rhizo-compartments. High performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) was performed to identify and quantify the allelochemicals in root exudates. A high-throughput sequence was used to determine the structural dynamics of the root-associated bacterial communities. Although soil physiochemical properties showed no significant differences in nutrients; long-term tea cultivation resulted in the accumulation of catechin-containing compounds in the rhizosphere and a lowering of pH. Moreover; distinct distribution patterns of bacterial taxa were observed in all three rhizo-compartments of two-year and 30-year monoculture tea; mediated strongly by soil pH and catechin-containing compounds. These results will help to explore the reasons why soil quality and fertility are disturbed in continuous ratooning tea monocropping systems; and to clarify the associated problems.
Highlights
Plant–soil feedback is a two-step process in which the presence of a plant alters the structure and composition of the rhizosphere microorganism community, and that change in the microorganism community alters the growth rate and development of the plant [1,2,3,4,5,6]
Autotoxicity and soil sickness are the typical results of negative plant–soil interactions, mainly driven by agricultural landscape simplification, such as continuous monoculture which is the cropping of the same plant in the same field for many consecutive years [11,12,13,14]
When compared to a new tea field planted two years ago, the tea field which was continuously monocultured for 30 years showed poor growth, chlorosis, wilting, and ratooning problems (Figure S1a,b)
Summary
Plant–soil feedback is a two-step process in which the presence of a plant alters the structure and composition of the rhizosphere microorganism community, and that change in the microorganism community alters the growth rate and development of the plant [1,2,3,4,5,6]. A negative plant–soil feedback exists, caused by the accumulation of phytotoxic compounds in soil This feedback inhibits beneficial microbes but promotes parasites and pathogen outbreaks, and in turn results in autotoxicity or soil sickness, and the hindrance of plant growth and development, which reduces plant yield and quality [8,9,10]. Most studies addressing the problems related to continuous tea monocropping systems have investigated the numerical responses of microbial communities mediated by the soil physiochemical properties [35,36]. The influence of root exudates on the distribution of rhizosphere bacterial communities in a continuous monocultured tea garden has not been studied. We hypothesized that different lengths of time of ratooning tea monoculture fields share bacteria to varying degrees and potentially this would be mediated over time by the variations in soil physiochemical properties and root exudates
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