Effects of on- and off-year management practices on the soil organic C fractions and microbial community in a Moso bamboo (Phyllostachys edulis) forest in subtropical China.

On- and off-year management practices are usually adopted in Moso bamboo (Phyllostachys edulis) forests to achieve higher productivity. However, little is known about the effects of these management practices on soil C sequestration and microbial community structure. In the present study, soil nutrient content, organic C fractions, and bacterial and fungal communities were comparatively investigated in on- and off-year bamboo stands. The results showed that soil organic C (SOC), alkali-hydrolyzable N (AN), and available P (AP) in the on-year were significantly lower (p ≤ 0.05) than those in the off-year. Among the different soil organic C fractions, easily oxidizable organic C (EOC), microbial biomass C (MBC), Ca-bound SOC (Ca-SOC), and Fe/Al-bound SOC (Fe/Al-SOC) also had significantly higher contents in the off-year than in the on-year, with MBC and EOC decreasing by 56.3% and 24.5%, respectively, indicating that both active and passive soil organic C pools increased in the off-year. However, the alpha diversities of both soil bacteria and fungi were significantly lower in the off-year soils than in the on-year soils. The bacterial taxa Actinobacteria, Planctomycetes, WPS-2, Acidothermus, Candidatus_Solibacter, Burkholderia-Caballeronia-Paraburkholderia, and Candidatus_Xiphinematobacter were increased in off-year soils relative to on-year soils. Meanwhile, fungal taxa Ascomycota, Mortierella, Hypocrea, Cryptococcus, Clitopilus, and Ceratocystis were significantly increased in on-year soils. Soil pH, SOC, AP, MBC, EOC, and Ca-SOC were significantly correlated with bacterial and fungal communities, with soil pH being the most important driving factor for the shift in bacterial and fungal communities. Our findings showed that the studied bamboo forest possessed an inherent restorative ability in the off-year, which can reverse the soil nutrient and C depletion in the on-years and ensure soil fertility in the long term.

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.

Changes in Soil Organic Carbon Fractions and Fungal Communities, Subsequent to Different Management Practices in Moso Bamboo Plantations.

Moso bamboo (Phyllostachys pubescens) has an extremely fast growth rate and major carbon sequestration potential. However, little information is available on the dynamics of soil C accumulation and fungi communities related to different management practices. Here, we investigated changes in the soil organic carbon (SOC) fractions and fungal communities of a Moso bamboo plantation under three different management practices (M0: undisturbed; M1: extensively managed; and M2: intensively managed). Compared with M0, SOC levels were reduced by 41.2% and 71.5% in M1 and M2, respectively; furthermore, four SOC fractions (C1: very labile; C2: labile; C3: less labile; and C4: nonlabile) and the carbon management index (CMI) were also significantly reduced by plantation management. These practices further altered fungal communities, for example, by increasing Basidiomycota and Mortierellomycota, and by decreasing Ascomycota and Rozellomycota. Pyrenochaeta, Mortierella, Saitozyma, and Cladophialophora were identified as keystone taxa. Soil fungal communities were significantly related to the pH, NH4-N, AP, C3, and the C4 fractions of SOC. Random forest modeling identified soil C3 and Mortierella as the most important predictors of the CMI. Our results suggest that reducing human interference would be beneficial for fungal community improvement and C sequestration in Moso bamboo plantations.

Corrigendum: Effects of on- and off-year management practices on the soil organic C fractions and microbial community in a Moso bamboo (Phyllostachys edulis) forest in subtropical China.

[This corrects the article DOI: 10.3389/fpls.2022.1020344.].

Metagenomic insights into the characteristics of soil microbial communities in the decomposing biomass of Moso bamboo forests under different management practices.

Introduction: Considering the rapid growth and high biomass productivity, Moso bamboo (Phyllostachys edulis) has high carbon (C) sequestration potential, and different management practices can strongly modify its C pools. Soil microorganisms play an important role in C turnover through dead plant and microbial biomass degradation. To date, little is known about how different management practices affect microbial carbohydrate-active enzymes (CAZymes) and their responses to dead biomass degradation. Methods: Based on metagenomics analysis, this study analyzed CAZymes in three comparable stands from each Moso bamboo plantation: undisturbed (M0), extensively managed (M1), and intensively managed (M2). Results: The results showed that the number of CAZymes encoding plant-derived component degradation was higher than that encoding microbe-derived component degradation. Compared with the M0, the CAZyme families encoding plant-derived cellulose were significantly (p < 0.05) high in M2 and significantly (p < 0.05) low in M1. For microbe-derived components, the abundance of CAZymes involved in the bacterial-derived peptidoglycan was higher than that in fungal-derived components (chitin and glucans). Furthermore, M2 significantly increased the fungal-derived chitin and bacterial-derived peptidoglycan compared to M0, whereas M1 significantly decreased the fungal-derived glucans and significantly increased the bacterial-derived peptidoglycan. Four bacterial phyla (Acidobacteria, Actinobacteria, Proteobacteria, and Chloroflexi) mainly contributed to the degradation of C sources from the plant and microbial biomass. Redundancy analysis (RDA) and mantel test suggested the abundance of CAZyme encoding genes for plant and microbial biomass degradation are significantly correlated with soil pH, total P, and available K. Least Squares Path Modeling (PLS-PM) showed that management practices indirectly affect the CAZyme encoding genes associated with plant and microbial biomass degradation by regulating the soil pH and nutrients (total N and P), respectively. Discussion: Our study established that M2 and M1 impact dead biomass decomposition and C turnover, contributing to decreased C accumulation and establishing that the bacterial community plays the main role in C turnover in bamboo plantations.

Understanding variations in soil properties and microbial communities in bamboo plantation soils along a chromium pollution gradient.

With high biomass productivity and resistance to heavy metals (HM) stress, bamboo has strong potential for HM phytoremediation. However, few studies have been conducted under field conditions to explore changes in soil physicochemical and microbial properties of bamboo forests with HM-contaminated soils. This study established bamboo (Phyllostachys praecox) plantations in five Cr-contaminated sites with different pollution levels (low, L; low-moderate, LM; moderate, M; moderate-high, MH; and high, H). We determined soil chemical properties, total and available Cr content, as well as bacterial and fungal community structures from 0 to 20 cm depth along the pollution gradient, and evaluated their interactions. The results revealed a corresponding decrease in soil pH, alkali-hydrolysable N (AN), along with urease and sucrase activities, as Cr pollution increased. In contrast, total organic carbon (TOC) increased with increasing Cr pollution. Soil available P (AP) and acid phosphatase activity did not differ significantly. Different pollution level resulted in distinct bacterial and fungal communities, with Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota, and Basidiomycota being the dominant phyla across the five bamboo soils. Both total Cr (TCr) and HCl-extractable Cr (ACr) negatively correlated with alpha indices (Chao1 and Shannon) for bacteria but not for fungi, indicating that the latter is more resistant to Cr pollution. Decrease in soil pH and increase in TCr and ACr from L to H were closely related to the shift of bacterial and fungal communities. These changes reduced soil N and C cycles. Our findings suggest that improving soil acidic conditions and N availability enhances carbon and nitrogen cycles via altering soil microbial structure and activities. This, in turn, can increase phytoremediation efficiency in the bamboo ecosystem.

Soil carbon and associated bacterial community shifts driven by fine root traits along a chronosequence of Moso bamboo (Phyllostachys edulis) plantations in subtropical China.

Moso bamboo (Phyllostachys edulis) is widely considered to be effective in capturing and sequestering atmospheric C, but the long-term effects of extensive management strategies on soil organic carbon (SOC), bacterial communities, fine root (FR, ø ≤ 2 mm) traits, and their inherent connection remain unclear. In this study, we simultaneously measured the SOC content of the bulk and rhizosphere soil fractions, the aggregate stability, the chemical composition of SOC (solid-state 13C nuclear magnetic resonance [NMR]), the bacterial community structure in the rhizosphere, and the FR morphological traits including biomass, specific root length (SRL), and root length density (RLD) along a chronosequence (stand age of 19, 37, and 64 years) of extensively managed Moso bamboo plantations and in an adjacent secondary forest as a control. The organic C content in both the rhizosphere and bulk soil increased rapidly with plantation age in the 0-20- and 20-40-cm soil layers, accompanied by an increase in the aggregate stability. FR traits including biomass, SRL, and RLD also increased continuously in response to soil C:N:P stoichiometry. All of these traits were significantly correlated with SOC, occluded particulate organic C (oPOC), and mineral-associated organic C (MOC), suggesting that FR traits could drive the soil C sequestration with the plantation age. Further analysis indicated that the microbial biomass C (MBC) content, MBC/total organic carbon (TOC) ratio, and bacterial abundance decreased with the plantation age, and the shift from soil oligotrophy to copiotrophy bacteria were mainly driven by changes in FR traits and SOC properties. Such a reassembly of bacterial communities combined with an increase in root biomass is favorable for the accumulation of stable C functional groups (alkyl C or aromatic C). Our findings indicate that extensive management regimes of Moso bamboo plantations could promote long-term soil C sequestration especially in the rhizosphere by promoting the formation of soil aggregates and organic-mineral complexes and by shifting bacterial community composition, and that these changes can be inferred through changes in the FR traits.

Deciphering the rhizosphere microbiome of a bamboo plant in response to different chromium contamination levels.

Bamboo has been considered a potential plant species for phytoremediation due to its high biomass and heavy metal (HM) resistance. However, little is known about the interactions between bamboo and soil microbial activities in HM-contaminated soils. Here, we investigated the characteristics of microbial communities in the rhizosphere soil of Lei bamboo (Phyllostachys praecox) along a chromium (Cr) gradient. We found that the soil Cr content was positively correlated with the total organic carbon (TOC) and HCl-extractable Cr but negatively correlated with the pH and bacterial and fungal Shannon indices. Proteobacteria and Ascomycota predominated in the bamboo rhizosphere under Cr pollution. A co-occurrence network showed that two of the most Cr-sensitive bacterial genera and keystone taxa were from the Acidobacteria, indicating that this phylum can be as an indicator for the studied Cr-polluted soils. Redundancy analysis revealed that both the soil bacterial and fungal community compositions were significantly correlated (p < 0.05) with Cr, pH, TOC, alkali-hydrolysable N (AN), and available phosphorus (AP). The increase in TOC as the Cr content increased can be ascribed to an adverse Cr effect on the soil microflora, probably because the microbial biomass was less effective in mineralizing soil C under Cr-polluted conditions.

Bamboo - An untapped plant resource for the phytoremediation of heavy metal contaminated soils.

Phytoremediation is a green technology used for the remediation of heavy metal soils. However, up to now, very few plants are known to be both hyperaccumulators and fast-growers. In contrast, some non-hyperaccumulators, which possess lower extraction capacities than hyperaccumulators, are fast-growing species with much higher total biomass yields and are potential alternative phytoremediators. Bamboo is a taxonomic group comprised of 1439 species that are mostly distributed in the tropics and subtropics. Although limited studies on bamboo for phytoremediation, recent studies have shown that some bamboo species have high ability to adapt to metalliferous environments and a high capacity to absorb heavy metals. Bamboo tissues in the rhizome and culm can accumulate a large amount of heavy metals that mainly accumulate in the cell wall, vacuole, and cytoplasm. Certain bamboo species such as moso bamboo, Phyllostachys praecox, have been shown to have a high endurance in metal contaminated soils, enabling a considerable uptake and accumulation of heavy metals. However, excessive concentrations of heavy metals may cause oxidative stress and damage bamboo plants. Therefore, several management strategies have been developed to improve the phytoremediation ability of bamboo species, including the selection of tolerant bamboo species, intercropping with hyperaccumulators, fertilization applications, and employment of chelate in soil. This review demonstrates that bamboo species, which have high biomass productivity, short rotation, and high economic value, can be used for phytoremediation. However, the mechanisms of heavy metal uptake, transport, sequestration, and detoxification of different bamboo species require urgent investigation.

[Effects of management measures on organic carbon, nitrogen and chemical structure of different soil fractions in Phyllostachys edulis plantations.] / 经营措施对毛竹林土壤不同组分有机碳、氮及化学结构的影响.

To examine the effects of management measures on carbon and nitrogen contents, as well as their distribution and structural characteristics of different soil fractions in Moso bamboo plantations, we compared three types of the bamboo forests (undisturbed, extensively managed, and intensively managed) and the control secondary broadleaved evergreen forest using the methods of physical fractionation, chemical and biological analysis and Fourier-transform infrared spectroscopy (FTIR). The results showed that soil total organic carbon (TOC) and total nitrogen (TN) content, as well as free particulate organic carbon and nitrogen, soluble organic carbon and nitrogen (DOC, DON), and mineral-associated organic carbon and nitrogen in the undisturbed and extensively managed Moso bamboo plantations were significantly increased compared with that in the control. The distribution ratio of free particulate organic carbon and nitrogen in the undisturbed Moso bamboo plantation significantly increased, with mineral-associated organic carbon being the largest reservoir of soil organic carbon (67.6%). Intensive management resulted in the decrease of soil organic carbon, total nitrogen storage, and the contents of each component, but significantly increased DOC/TOC, the ratio of microbial biomass nitrogen to TN as well as the ratio of microbial biomass carbon to TOC (microbial quotient). Management measures significantly affected the chemical structure of SOC. Compared with the control, the relative intensities of phenolic and alcoholic-OH, aliphatic methyl and methylene, aromatic C=C, and carbonyl C=O absorption were higher in the SOC of undisturbed and extensively managed Moso bamboo plantations, and soil hydrophobicity was significantly increased. Results from correlation analysis showed that soil hydrophobicity and the content of aliphatic and aromatic groups were negatively correlated with microbial quotient and positively correlated with TOC and TN content. In conclusion, the increased inputs of organic matter residues (such as litter and roots) could contribute to the relative accumulation of chemical resistance compounds with reduced human disturbance, which significantly enhanced chemical stability of soil organic carbon. Soil clay minerals played a key role in protecting soil organic carbon through the formation of mineral-organic compounds, which facilitate the stability of soil carbon storage and the long-term preservation of soil carbon.

Responses of soil nutrients and microbial communities to intercropping medicinal plants in moso bamboo plantations in subtropical China.

Bamboo forests are one of the most important forest resources in subtropical China. A pure, single-layer bamboo forest is considered an optimal habitat for intercropping medicinal herbs. Soil microorganisms have an important role in various ecological processes and respond quickly to environmental changes. However, changes in soil nutrients and microbial communities associated with agroforestry cultivation methods remain poorly documented. In the present study, a pure moso bamboo (Phyllostachys edulis) forest (Con) and three adjacent moso bamboo-based agroforestry (BAF) systems (moso bamboo-Paris polyphylla (BP), moso bamboo-Tetrastigma hemsleyanum (BT) and moso bamboo-Bletilla striata (BB)) were selected; and their soil chemical properties and bacterial communities were studied and compared to evaluate the effects of agroforestry on soil bacterial communities and the relationship between soil properties and bacterial communities in BAF systems. Results showed that compared with soils under the Con, soils under the BAF systems had more (p < 0.05) soil organic carbon (SOC) and available nitrogen (AN) but lower (p < 0.05) pH and available potassium (AK). In addition, compared with the Con system, the BB and BT systems had significantly greater (p < 0.05) available phosphorus (AP). Compared with that in the Con system, the Shannon index in the BAF systems was significantly greater (p < 0.05), but the Chao1 index not different. On the basis of relative abundance values, compared with the Con soils, the BAF soils had a significantly greater abundance of (p < 0.05) Bacteroidetes and Planctomyces but a significantly lower abundance of (p < 0.05) Verrucomicrobia, Gemmatimonadetes and Candidatus Xiphinematobacter. Moreover, compared with the Con system, the BB and BT systems had a greater (p < 0.05) abundance of Actinobacteria, Rhodoplanes, Candidatus Solibacter and Candidatus Koribacter. Redundancy analysis (RDA) revealed that soil pH, SOC and AP were significantly correlated with bacterial community composition. Results of this study suggest that intercropping medicinal herbs can result in soil acidification and potassium (K) depletion; thus, countermeasures such as applications of K fertilizer and alkaline soil amendments are necessary for BAF systems.

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

Endophytic bacteria widely exist inside plant tissues and have an important role in plant growth and development and the alleviation of environmental stress. However, little is known about the response of root-associated bacterial endophytes of Lei bamboo (Phyllostachys praecox) to intensive management, which is a common management practice for high bamboo shoot production in subtropical China. In this study, we comparatively investigated the root endophytic bacterial community structures in a chronosequence of intensively managed (5a, 10a, 15a, and 20a) and extensively managed plantations (as control, Con). The results showed that endophytic Proteobacteria was the dominant bacterial phylum in the bamboo roots. Intensive management significantly increased (p < 0.05) the bacterial observed species and Chao1 (except 5a) indices associated with bamboo roots. The relative abundances of Firmicutes, Bacteroidetes, and Actinobacteria (except 15a) in the intensively managed bamboo roots significantly increased (p < 0.05) compared with those in Con, while the relative abundance of Proteobacteria significantly decreased in intensively managed bamboo roots (p < 0.05). The phyla Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes were the biomarkers in Con, 5a, 15a, and 20a, respectively. Redundancy analysis (RDA) showed that soil alkali-hydrolysable N (AN), available phosphorus (AP), available K (AK), and total organic carbon (TOC) were significantly correlated (p < 0.05) with the bacterial community compositions. Our results suggest that the root endophytic microbiome of Lei bamboo was markedly influenced by intensive management practices, and the available nutrient status could be the main driving factor for such shifts. Although heavy fertilization in the intensive management system increased the diversity indices, the rapid changes in root endophyte communities and their relevant functions might indicate a high risk for sustainable management.

Comparison of heavy metal phytoremediation in monoculture and intercropping systems of Phyllostachys praecox and Sedum plumbizincicola in polluted soil.

A bamboo species (Phyllostachys praecox) and a Cd/Zn hyperaccumulator (Sedum plumbizincicola) were tested under different planting systems to compare their heavy metal phytoremediation ability. P. praecox (MP), S. plumbizincicola (MS) and P. praecox × S. plumbizincicola (IPS) plantations were established in Cu, Zn, and Cd-contaminated soil. Soil properties and heavy metal contents in plants were determined and compared after four years of plantation establishment. The rankings of available and total metal contents in soil layers were MP > MS > IPS (0-20 cm) and MP > IPS > MS (20-40 cm, except for Cu), respectively. The Cu and Zn contents in mature bamboo tissues were significantly lower, but the Cd contents in bamboo tissues (except for leaves) higher, in the IPS than in the MP. The bioconcentration and the translocation factors in most of bamboo tissues showed an increasing trend from the MP to the IPS. Heavy metal distribution in plants is greatly affected by the planting patterns. The tested intercropping system of two plant species showed higher biomass productivity, implying more heavy metals can be removed from the soil through the harvesting of plants. Therefore, the IPS leads to significant improvement of soil phytoremediation.

Phytoremediation potential of moso bamboo (Phyllostachys pubescens) intercropped with Sedum plumbizincicola in metal-contaminated soil.

This study was conducted to investigate the capability of moso bamboo grown alone and in combination with Sedum plumbizincicola to remediate heavy metals. Monoculture of moso bamboo (MM), intercropping of moso bamboo × S. plumbizincicola (IMS), and control (uncultivated, CK) were established in Cu-, Zn-, and Cd-contaminated soil. Soil properties and heavy metal removal capacity were assessed. Results showed that the available and total heavy metal contents in soil (0-20 and 20-40 cm soil layers) were ranked IMS < MM < CK. Available Cu, Zn, and Cd contents were 65.0, 28.7, and 48.4% lower in the IMS and 52.8, 24.8, and 45.5% lower in the MM than those in the CK, respectively. In plants, Cu contents in bamboo rhizomes, branches, and leaves and those of Zn and Cd in all bamboo tissues were significantly higher in the IMS than in the MM. The bioconcentration and translocation factors of bamboo tissues showed an obviously increasing tendency from MM to IMS. Moso bamboo possessed the properties of endurance to heavy metals and high biomass production. Phytoremediation by moso bamboo in association with S. plumbizincicola is an economical strategy to promote heavy metal removal from metal-contaminated soil.