In conventional tea plantations, a large amount of pruned material returns to the soil surface, putting a high quantity of polyphenols into the soil. The accumulation of active allelochemicals in the tea rhizosphere and subsequent shift in beneficial microbes may be the cause of acidification, soil sickness, and regeneration problem, which may be attributed to hindrance of plant growth, development, and low yield in long-term monoculture tea plantation. However, the role of pruning leaf litter in soil sickness under consecutive tea monoculture is unclear. Here, we investigated soil samples taken from conventional tea gardens of different ages (2, 15, and 30 years) and under the effect of regular pruning. Different approaches including liquid chromatography–mass spectrometry (LC-MS) analysis of the leaf litter, metagenomic study of root-associated bacterial communities, and in vitro interaction of polyphenols with selected bacteria were applied to understand the effect of leaf litter-derived polyphenols on the composition and structure of the tea rhizosphere microbial community. Our results indicated that each pruning practice returns a large amount of leaf litter to each tea garden. LC-MS results showed that leaf litter leads to the accumulation of various allelochemicals in the tea rhizosphere, including epigallocatechin gallate, epigallocatechin, epicatechin gallate, catechin, and epicatechin with increasing age of the tea plantation. Meanwhile, in the tea garden grown consecutively for 30 years (30-Y), the phenol oxidase and peroxidase activities increased significantly. Pyrosequencing identified Burkholderia and Pseudomonas as the dominant genera, while plant growth-promoting bacteria, especially Bacillus, Prevotella, and Sphingomonas, were significantly reduced in the long-term tea plantation. The qPCR results of 30-Y soil confirmed that the copy numbers of bacterial genes per gram of the rhizosphere soil were significantly reduced, while that of Pseudomonas increased significantly. In vitro study showed that the growth of catechin-degrading bacteria (e.g., Pseudomonas) increased and plant-promoting bacteria (e.g., Bacillus) decreased significantly with increasing concentration of these allelochemicals. Furthermore, in vitro interaction showed a 0.36-fold decrease in the pH of the broth after 72 h with the catechin degradation. In summary, the increase of Pseudomonas and Burkholderia in the 30-Y garden was found to be associated with the accumulation of catechin substrates. In response to the long-term monoculture of tea, the variable soil pH along with the litter distribution negatively affect the population of plant growth-promoting bacteria (e.g., Sphingomonas, Bacillus, and Prevotella). Current research suggests that the removal of pruned branches from tea gardens can prevent soil sickness and may lead to sustainable tea production.

The current study was undertaken to elucidate the mechanism of yield decline in ratoon sugarcane using soil metaproteomics combined with community level physiological profiles (CLPP) analysis. The available stalk number, stalk diameter, single stalk weight and theoretical yield of ratoon cane (RS) were found to be significantly lower than those of plant cane (NS). The activities of several carbon, nitrogen and phosphorus processing enzymes, including invertase, peroxidase, urease and phosphomonoesterase were found to be significantly lower in RS soil than in NS soil. BIOLOG analysis indicated a significant decline in average well-color development (AWCD), Shannon’s diversity and evenness indices in RS soil as compared to NS soil. To profile the rhizospheric metaproteome, 109 soil protein spots with high resolution and repeatability were successfully identified. These proteins were found to be involved in carbohydrate/energy, amino acid, protein, nucleotide, auxin and secondary metabolisms, membrane transport, signal transduction and resistance, etc. Comparative metaproteomics analysis revealed that 38 proteins were differentially expressed in the RS soil as compared to the control soil or NS soil. Among these, most of the plant proteins related to carbohydrate and amino acid metabolism and stress response were up-regulated in RS soil. Furthermore, several microbial proteins related to membrane transport and signal transduction were up-regulated in RS soil. These proteins were speculated to function in root colonization by microbes. Our experiments revealed that sugarcane ratooning practice induced significant changes in the soil enzyme activities, the catabolic diversity of microbial community, and the expression level of soil proteins. They influenced the biochemical processes in the rhizosphere ecosystem and mediated the interactions between plants and soil microbes.

Tea is an economic shrubby plant in tropical and subtropical regions of the world. To obtain high yield in tea cultivation, chemical fertilizer application rates have generally been used. However, a large quantity of chemical fertilizer application in a long-term continuously ratooned and monoculture tea orchard can inevitably lead to soil acidification and a decline in fertility. Therefore, the restoration of soil fertility and the sustainable development of tea planting by organic ways are critical for the tea industry. In this study, field trials were conducted in the tea orchard that was continuously ratooned and mono-cultured for 20 years. Nitrogen fertilizer (NF), Laredo soybeans green manure (LF), and goat manure (GM) treatments were applied to restore optimum acidity, soil fertility, microbial activity, and the community structure of a long-term continuously monoculture tea orchard. This paper investigated that the pH value was increased from 4.23 to 4.32 in GM and LF, respectively. Similarly, the content of exchangeable acidity (EA) was decreased by 1.21 and 1.46 cmol·kg⁻¹ in GM and LF, respectively. Available nutrient results indicated that the content of NH₄⁺-N was increased by 3.96, 4.38, NO₃⁻-N by 1.07, 2.16, AP by 3.46, 6.86, AK by 0.26, 0.3 mg kg⁻¹ in GM and LF treatments, respectively. Enzyme analysis revealed that the activity of urease and sucrase was promoted by 7.98 mg·g⁻¹·24 h⁻¹ and 6.77 mg·g⁻¹·24 h⁻¹, respectively, in LF treatment. Likewise, the activity of acid phosphatase and polyphenol oxidase was sharply increased by 2.3 mg·g⁻¹ h⁻¹ and 63.07 mg·g⁻¹ h⁻¹ in LF treatments. Additionally, the activity of urease, sucrase, acidic phosphatase, polyphenol oxidase, and peroxidase were also significantly increased by applying GM treatments. Meanwhile, LF and GM treatments significantly improved soil microbial biomass as well as low weight organic acid content in degraded tea rhizosphere. Furthermore, high throughput sequence results illustrated that the relative abundance of Rhizobiaceae and Bradyrhizobiaceae families increased in LF and GM treatments, respectively, which are mostly a kind of nitrogen fixer and plant growth promoting bacteria. Taken together, the physiological traits of the new sprouts and the biochemical components of new tea leaves were also significantly improved by GM and LF treatments. From this study, it is concluded that LF and GM are good agriculture management practices, which promote plant growth, yield, and nutrient availability by maintaining and improving pH, enhancing available nutrients status, improving the secretion of low molecular weight organic acids, and balancing the microbial community structure in the long-term mono-cultured tea orchard.

Continuous monoculture problems of medicinal plants are threatening the supply and quality safety of the source products in intensive traditional Chinese medicine agricultural practice. Therefore, it is of great ecological and economic significance to intensively explore the ecological restoration of conducive-disease soil. Radix pseudostellariae is a tuberous Chinese medicine that suffers from serious continuous cropping impediments under intensive cultivation. In this study, to evaluate the effects of different treatments on alleviating the continuous cropping obstacle of R. pseudostellariae and uncover the mechanism from the perspective of soil micro-ecological environment, four different soil intensification treatments including tuber reserved, fallow, flooding and rice rotation were set between two crops of R. pseudostellariae, and dynamically detected the changes of photosynthesis, stress-resistance physiology, and dry matter translocation.The results showed that, compared with fallow treatment, rice rotation treatment significantly slowed down the downtrend of soil pH, and the organic matter content in soil. The abundance of beneficial microorganisms and nitrogen cycling genes in the rhizosphere of R. pseudostellariae was increased while the pathogenic microorganisms decreased when rotated with rice in comparison with the fallow regime. This in turn led to significantly increased net photosynthetic rate and improved process of dry matter translocation of R. pseudostellariae under rice rotation treatment, indicating that the yield of R. pseudostellariae and the contents of polysaccharides and total saponins were significantly increased by 19.5%, 22.9%, and 5.8%, respectively. The improved grey T’s correlation degree analysis showed that soil pH, soil organic matter content, the abundance of specific microorganisms, the abundance of nitrogen cycling genes, the photosynthetic rate and antioxidant enzyme system in leaves of R. pseudostellariae were highly correlated with the yield of tuberous roots (Absolute correlation degree >0.6). In addition, the physiological parameters of R. pseudostellariae reflecting the growth status and the improvement of soil environment in middle and pre-phases of tuberous root greatly contributed to high-yielding formation of the medicinal plants when rotated with rice crop. Therefore, the seedling stage, early and middle tuberous root expansion stages of R. pseudostellariae were critical to alleviate the continuous cropping obstacles of R. pseudostellariae. This study also suggested that rice exudates and its residual bio-degradants entering soil ecosystem were conducive to accelerating the reconstruction of specific microflora, alleviating soil acidification, and improving nutrition sequestration after rice rotation treatment, thus resulting in the decreased environmental stress intensity, improved energy and nutrition metabolism, and optimized dry matter allocation in the growth and development prophase, consequently improved yield and quality of the medicinal plants. These results provided a theoretical basis for the ecological remediation of continuous cropping obstacles and the construction of the pivotal technology system in ecological sustainable cultivation practice.