Microbiome diversity, composition and assembly in a California citrus orchard

Abstract

The citrus root and rhizosphere microbiomes have been relatively well described in the literature, especially in the context of Huanglonbing disease. Yet questions addressing the assembly of root microbial endophytes have remained unanswered. In the above ground tree tissues, leaves and stems have been the research focus point, while flush and flower microbiomes, two important tissues in the vegetative and reproductive cycles of the tree, are not well described. In this study, the fungal and bacterial taxa in five biocompartments (bulk soil, rhizosphere, root endosphere, flower and flush) of citrus trees grown in a single California orchard were profiled using an amplicon-based metagenomic Illumina sequencing approach. Trees with no observable signs of abiotic or biotic stresses were sampled for two consecutive years during the floral development phase. The rhizosphere was the most biodiverse compartment compared to bulk soil, root endosphere, flower and flush microbiomes. In addition, the belowground bacteriome was more diverse than the mycobiome. Microbial richness decreased significantly from the root exosphere to the endosphere and was overall low in the above ground tissues. Root endophytic microbial community composition shared strong similarities to the rhizosphere but also contained few taxa from above ground tissues. Our data indicated compartmentalization of the microbiome with distinct profiles between above and below ground microbial communities. However, several taxa were present across all compartments suggesting the existence of a core citrus microbiota. These findings highlight key microbial taxa that could be engineered as biopesticides and biofertilizers for citriculture.

Potential functions of the shared bacterial taxa in the citrus leaf midribs determine the symptoms of Huanglongbing

“…(2022) . Similarly, Pseudomonas , Sphingomonas , and Streptomyces were identified as shared taxa in the rhizosphere, root endosphere, flower and flush of citrus in California by Xi et al. (2023) .…”

Endomicrobiome of in vitro and natural plants deciphering the endophytes-associated secondary metabolite biosynthesis in Picrorhiza kurrooa , a Himalayan medicinal herb

“…The phyllosphere diversity of Bourardia ternifolia, a medicinal plant, is less than root and rhizosphere ( 61 ). Microbiome diversity analysis of California citrus orchard also revealed that the overall diversity in above-ground tissues was less than root exosphere and endosphere ( 62 ). The predominant phyla found in the different parts of P. kurrooa are also known to colonize as endophytic bacterial communities in other plants, including Arabidopsis, Maize, Tamarix, B. ternifolia, Seagrass, and Cinnamon ( 63 – 68 ).…”

Soil Microbial Communities in Lemon Orchards Affected by Citrus Mal Secco Disease

“…Like other crops, soil microbial communities participate in root microbial assembly in citrus, as specific microbes are selected from the soil and recruited into the rhizosphere, with root exudates acting as signal molecules and nutrition sources. Citrus recruits rhizosphere microbial communities from the extensive soil biodiversity, and the microbiome is considered to play a significant role in maintaining citrus health [24][25][26][27][28][29]. An increasing number of studies, primarily utilizing amplicon-based metagenomics and also whole-genome shotgun metagenomics, have delved into the microbial communities associated with citrus [25,26,30,31].…”