Rhizosphere Bacterial Community Response to Continuous Cropping of Tibetan Barley

Abstract

Long-term continuous cropping influences the nutrient of soil and microbiome of the rhizosphere, resulting in the yield decrease of crops. Tibetan barley is a dominant cereal crop cultivated at high altitudes in Tibet. Its growth and yield are negatively affected by continuous cropping; however, the response of the rhizosphere microbial community to continuous cropping remains poorly understood. To address this question, we investigated the bacterial community structure and conducted predictive functional profiling on rhizosphere soil from Tibetan barley monocropped for 2–6 years. The results revealed that long-term continuous cropping markedly decreased total nitrogen and available nitrogen in rhizosphere soil. Illumina high-throughput sequencing of 16S rRNA genes indicated that the bacterial community was altered by continuous cropping; operational taxonomic units (OTUs), Shannon index, and Faith Phylogenetic Diversity decreased with increasing monocropping duration. Relative abundances of family Pseudomonadaceae, Cytophagaceae, and Nocardioidaceae were significantly increased, while those of Chitinophagaceae and Sphingomonadaceae were significantly decreased (all p < 0.05). Besides, continuous cropping significantly increased the abundance of bacteria associated with chemoheterotrophy, aromatic compound degradation, and nitrate reduction (p < 0.05). Generalized boosted regression model analysis indicated that total nitrogen was the most important contributor to the bacterial community diversity, indicating their roles in shaping the rhizosphere bacterial community during continuous cropping. Overall, continuous cropping had a significant impact on the structure of bacterial communities in rhizosphere soil of Tibetan barley, and these results will improve our understanding of soil bacterial community regulation and soil health maintenance in Tibetan barley farm systems.

Soil metabolomics and bacterial functional traits revealed the responses of rhizosphere soil bacterial community to long-term continuous cropping of Tibetan barley

“… Zhao et al (2020) showed that bacterial richness (ACE) significantly decreased after 5–10 years of continuous cropping and recovered after 30 years, while bacterial diversity (Shannon) significantly increased after continuous cropping (5, 10, and 30 years). In the present study, bacterial diversity (Shannon) did not differ during short continuous cropping years, but bacterial richness (Chao1 and ACE) and PD significantly declined after short-term continuous cropping of Tibetan barley, which is consistent with the findings of Yao et al (2020) , but surprisingly recovered after long-term continuous cropping ( Table 1 ). This phenomenon may be due to the fact that all environmental filters require specific adaptation strategies for survival; stronger selection acting on bacteria often leads to a new cohort of microbiota that adapt to the environment ( Fierer, Bradford & Jackson, 2007 ; Meola, Lazzaro & Zeyer, 2014 ).…”

“…A relevant study pointed out that the continuous cropping of Tibetan barley significantly increased the bacteria associated with chemo-heterotrophy, aromatic compound degradation, and nitrate reduction ( Yao et al, 2020 ). This study showed that the dominant shared genera, Sphingomonas , exerted significant negative effects on nitrification gene abundances ( amoA and nxrA ), leading to the imbalance of nitrification and denitrification.…”

“…The study site consisted of independent plots over many years of the successive monoculture of Tibetan barley. Tibetan barley seeds were cultivated in April each year after the annual application of blended fertilizer and harvested in August following previously described methods ( Yao et al, 2020 ). Briefly, in July 2020, we selected three 5 m × 5 m quadrats including 2, 5, and 10 years of successive monocropping of Tibetan barley, which we named CCY02, CCY05, and CCY10, respectively.…”

“…For example, successive monoculture practices were found to decrease bacterial community diversity ( Sun et al, 2018 ), increase harmful populations, and inhibit beneficial ones ( Gao et al, 2019 ). In our previous study, we found that the continuous cropping of Tibetan barley resulted in a significant decline in crop yields and bacterial community diversity, as well as increased the relative abundances of bacteria associated with chemo-heterotrophy, aromatic compound degradation, and nitrate reduction, per a FaProTax prediction ( Yao et al, 2020 ). However, research on how continuous cropping practices affect soil microbial functional traits is lacking.…”

Response of Plant Rhizosphere Microenvironment to Water Management in Soil- and Substrate-Based Controlled Environment Agriculture (CEA) Systems: A Review

“…As growing cycles of replanting can be very short (e.g., less than 4 weeks for some leafy greens) in CEA systems, replant disease and negative legacy effects during certain planting generations can be significant due to nutrient consumption, rhizosphere bacterial community reshaping, and unfavorable rhizodeposition ( Yuan et al, 2018 ; Sun et al, 2019 ; Yao et al, 2020 ). There were clear legacy effects from moisture regimes prior to planting on soil, specifically in terms of physicochemical properties, plant growth and nutrition, and the formation of microbial responsiveness ( Cavagnaro, 2016 ).…”