Rhizosphere Bacterial Community Response to Continuous Cropping of Tibetan Barley.

Youhua Yao,Likun An,Xiaohua Yao,Deqing Xie,Yixiong Bai,Kunlun Wu

doi:10.3389/fmicb.2020.551444

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.

Highlights

High altitude ecosystems are generally characterized by low temperature, variable rainfall, reduced atmospheric pressure, and soil nutritional stress
Yields consistently decreased during 6 years of Tibetan barley monoculture, from 19.42 ± 0.74 kg ha−1 to 12.40 ± 0.45 kg ha−1 (Supplementary Figure S1)
Environmental parameters of the rhizosphere soil were influenced by continuous cropping, rhizosphere soil pH exhibited no obvious changes throughout the study and was slightly alkaline (Table 1)

Summary

Introduction

High altitude ecosystems are generally characterized by low temperature, variable rainfall, reduced atmospheric pressure, and soil nutritional stress. Cold in high altitude region is the major factor that has confounded effects on both microbial biodiversity and soil physicochemical properties (Kumar et al, 2019). Plants and microbes are co-evolved and interact with each other in the Monocropping Effet on Tibetan Barley environment. High altitude regions are the research center in understanding the interactions between certain microbes and the plants cultivated in the cold environment (Rawat et al, 2020). Lower species richness and diversity were observed in soil with higher elevations (Bryant et al, 2008; Wang et al, 2015). 4,000 m above sea level), soil bacteria exhibited more apparent elevational zonation features and decreased diversity patterns with increasing elevation (Wang et al, 2015). The microbial community structure of rhizosphere soil in high altitude region is less understood (Praeg et al, 2019)

Methods

Results

Conclusion