Changes of Root Endophytic Bacterial Community Along a Chronosequence of Intensively Managed Lei Bamboo (Phyllostachys praecox) Forests in Subtropical China

Root Endophytic Microorganisms Contribute to the Attribute of Full-Year Shooting in Woody Bamboo Cephalostachyum pingbianense

Cephalostachyum pingbianense (Hsueh & Y.M. Yang ex Yi et al.) D.Z. Li & H.Q. Yang is unique among bamboo species for its ability to produce bamboo shoots in all seasons under natural conditions. Apart from the physiological mechanism, information regarding the effects of endophytic microorganisms on this full-year shooting characteristic is limited. We hypothesize that root endophytic microorganisms will have a positive impact on the full-year bamboo shooting characteristic of C. pingbianense by increasing the availability or supply of nutrients. To identify the seasonal variations in the root endophytic bacterial and fungal communities of C. pingbianense, and to assess their correlation with bamboo shoot productivity, the roots of C. pingbianense were selected as research materials, and the 16S rRNA and ITS rDNA genes of root endophytic microorganisms were sequenced using the Illumina platform. Following this sequencing, raw sequencing reads were processed, and OTUs were annotated. Alpha and beta diversity, microbial composition, and functional predictions were analyzed, with correlations to bamboo shoot numbers assessed. The results showed that seasonal changes significantly affected the community diversity and structure of root endophytic microbes of C. pingbianense. Bacterial communities in root samples from all seasons contained more nitrogen-fixing microorganisms, with members of the Burkholderiales and Rhizobiales predominating. The relative abundances of ectomycorrhizal and arbuscular mycorrhizal fungi in the autumn sample were significantly higher than in other seasons. Correlation analysis revealed that the bamboo shoot productivity was significantly and positively correlated with bacterial functions of nitrogen fixation, arsenate detoxification, and ureolysis, as well as with symbiotrophic fungi, ectomycorrhizal fungi, and arbuscular mycorrhizal fungi. At the genus level, the bacterial genus Herbaspirillum and the fungal genera Russula, unclassified_f_Acaulosporaceae, and unclassified_f_Glomeraceae were found to have a significant positive correlation with bamboo shoot number. Our study provides an ecological perspective for understanding the highly productive attribute of C. pingbianense and offers new insights into the forest management of woody bamboos.

Comparative analysis of endophytic fungal communities in bamboo species Phyllostachys edulis, Bambusa rigida, and Pleioblastus amarus

Fungal endophytes in plant leaf mesophyll form mutually beneficial associations through carbon assimilation, synthesis of biologically active chemicals, and enhancement of aesthetic and nutritional value. Here, we compared community structure, diversity, and richness of endophytic fungi in the leaves of three bamboo species, including Phyllostachys edulis (MZ), Bambusa rigida (KZ), and Pleioblastus amarus (YT) via high-throughput Illumina sequencing. In total, 1070 operational taxonomic units (OTUs) were retrieved and classified into 7 phylum, 27 classes, 82 orders, 185 families, 310 genus, and 448 species. Dominant genera were Cladosporium, Trichomerium, Hannaella, Ascomycota, Sporobolomyces, Camptophora and Strelitziana. The highest fungal diversity was observed in Pleioblastus amarus, followed by Bambusa rigida, and Phyllostachys edulis. Comparatively, monopodial species Ph. edulis and sympodial B. rigida, mixed P. amarus revealed the highest richness of endophytic fungi. We retrieved a few biocontrol agents, Sarocladium and Paraconiothyrium, and unique Sporobolomyces, Camptophora, and Strelitziana genera. FUNGuild analysis revealed the surrounding environment (The annual average temperature is between 15 and 25 °C, and the relative humidity of the air is above 83% all year round) as a source of fungal accumulation in bamboo leaves and their pathogenic nature. Our results provide precise knowledge for better managing bamboo forests and pave the way for isolating secondary metabolites and potential bioactive compounds.

Evaluating the Rhizosphere and Endophytic Microbiomes of a Bamboo Plant in Response to the Long-Term Application of Heavy Organic Amendment

Root-associated bacteria play a major role in plant health and productivity. However, how organic amendment influences root-associated bacteria is uncertain in Lei bamboo (Phyllostachys praecox) plantations. Here, we compared the rhizosphere and endophytic microbiomes in two Lei bamboo plantations with (IMS) and without (TMS) the application of organic amendment for 16 years. The results showed IMS significantly increased (p < 0.05) the relative abundance of Proteobacteria and significantly decreased (p < 0.05) the relative abundance of Acidobacteria, Bacteroidetes, and Verrucomicrobiota. The root endophytic Proteobacteria and Acidobacteria were significantly higher in abundance (p < 0.05) in the IMS than in the TMS, while Actinobacteria and Firmicutes were significantly lower in abundance. Five taxa were assigned to Proteobacteria and Acidobacteria, which were identified as keystones in the rhizosphere soil microbiome, while two species taxonomically affiliated with Proteobacteria were identified as keystones in the root endophytic microbiota, indicating this phylum can be an indicator for a root-associated microbiome in response to IMS. The soil pH, soil total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), available potassium (AK), and TOC:TP ratio were significantly correlated (p < 0.05) with the bacterial community composition of both rhizosphere soils and root endophytes. TMS increased the microbial network complexity of root endophytes but decreased the microbial network complexity of rhizosphere soil. Our results suggest IMS shapes the rhizosphere and endophytic bacterial community compositions and their interactions differently, which should be paid attention to when designing management practices for the sustainable development of forest ecosystems.

Converting rice husk to biochar reduces bamboo soil N2O emissions under different forms and rates of nitrogen additions

The effects of biochar application combined with different forms and rates of inorganic nitrogen (N) addition on nitrous oxide (N2O) emissions from forest soils have not been well documented. A microcosm experiment was conducted to study the effects of rice husk and its biochar in combination with the addition of N fertilizers in different forms (ammonium [NH4+] and nitrate [NO3-]) and rates (equivalent to 150 and 300 kg N ha-1 yr-1) on N2O emissions from Lei bamboo (Phyllostachys praecox) soils. The application of rice husk significantly increased cumulative N2O emissions under the addition of both NO3--N and NH4+-N. Biochar significantly reduced cumulative N2O emissions by 15.2 and 5.8 μg N kg-1 when co-applied with the low and high rates of NO3--N, respectively, compared with the respective NO3--N addition rate without biochar. There was no significant difference in soil N2O emissions between the two NH4+-N addition rates, and cumulative N2O emission decreased with increasing soil NH4+-N concentration, mainly due to the toxic effect caused by the excessive NH4+-N on soil N2O production from the nitrification process. Cumulative N2O emissions recorded 18.74 and 14.04 μg N kg-1 under low and high rates of NO3--N addition, respectively, which were higher than those produced by NH4+-N addition. Our study demonstrated that the conversion of rice husk to biochar could reduce N2O emissions under the addition of different N forms and rates. Moreover, rice husk or its biochar in combination with NH4+-N fertilizer produced less N2O in Lei bamboo soil, compared with NO3--N fertilizer.