Rhizobacteria inoculation benefits nutrient availability for phytostabilization in copper contaminated soil:Drivers from bacterial community structures in rhizosphere

Plant growth-promoting rhizobacteria (PGPR) and rhizobia are potentially advantageous in improving plant growth in heavy metal contaminated soils. However, only limited information is available in literature on the manner through which the co-inoculation of PGPR and rhizobia can potentially supply nutrients to benefit plant growth in heavy metal contaminated soil. Accordingly, this study investigated the effects of Paenibacillus mucilaginosus (PGPR) and Sinorhizobium meliloti (rhizobia) co-inoculation on soil nutrients, enzyme activities, and microbial biomass in copper (Cu) contaminated soil planted with alfalfa (Medicago sativa). Moreover, we assessed soil bacterial community structure using high-throughput Illumina sequencing of 16S rRNA genes. Results showed that PGPR and/or rhizobia inoculation improved alfalfa growth. In particular, we found that this co-inoculation approach decreased Cu accumulation (48.6%) in shoots compared to the control (uninoculated). Both partial least squares path modeling (PLS-PM) and the relative importance of regressors in the linear models identified that enzyme activities, microbial biomass, and microbial community structure in Cu contaminated soil were major controlling variables of soil nutrient availability. The co-inoculation treatment significantly increased soil carbon (C) and nitrogen (N) concentrations by increasing urease (55.6%), saccharase (29.5%), and β-glucosidase (31.4%) activities compared to the control. Furthermore, the rhizosphere microbial community structure in the co-inoculation treatment was mainly regulated by soil N concentrations (i.e., both total N and available N) while altering alpha diversity (α-diversity). The relative abundances of Firmicutes (including biomarkers of the Bacillus genus) and Acidobacteria were enriched in the co-inoculated treatment, which can potentially improve soil nutrient availability and subsequently benefit plant growth. These findings indicated that the co-inoculation of PGPR and rhizobia plays an important role in promoting plant growth in Cu contaminated soil. This is because this approach can increase soil nutrient availability by enhancing soil enzyme activities and regulating rhizosphere microbial community structure

Reduction of Cu and nitrate leaching risk associated with EDDS-enhanced phytoextraction process by exogenous inoculation of plant growth promoting rhizobacteria

Biodegradable chelant (S,S)-N,N '-ethylenediaminedisuccinic acid (EDDS) has the more advantages of enhanced metal mobility, rapid degradation, environmental friendliness, and ammonium release. However, the risk of metal and/or nitrate residues and leaching within EDDS biodegradation remains as the bottleneck for the widespread application of EDDS-induced phytoremediation. This study aims to explore if the inoculation of plant growth-promoting rhizobacteria (PGPRs) can eliminate the risk associated with the short-term application of EDDS by investigating Cu phytoextraction and soil nitrate content. Results showed that EDDS application significantly increased the copper (Cu) concentration in shoots, soil total Cu, NH4+-N and NO3--N content, but decreased plant biomass. The inoculation of PGPRs in the soil showed a strong ability to increase plant biomass, Cu phytoextraction and soil NH4+-N content, and decrease soil Cu and NO3--N content. Moreover, bacterial dominant taxa were found to be the largest contributors to soil NH4+-N and NO3--N variation, and the abundance of denitrifying bacteria (Bacteroidetes and Stenotrophomonas) decreased in the treatment with PGPRs. The risk of residual Cu and nitrate leaching was reduced by the inoculation of PGPRs without significantly changing the stability of the bacterial community. These new findings indicate that the exogenous application of beneficial rhizobacteria can provide an effective strategy to reduce the risk in metal-contaminated soils of chelant-assisted phytoextraction.</p

New perspectives on microbiome and nutrient sequestration in soil aggregates during long-term grazing exclusion

15 páginas.- 5 figuras.- referencias.-Grazing exclusion alters grassland soil aggregation, microbiome composition, and biogeochemical processes. However, the long-term effects of grazing exclusion on the microbial communities and nutrient dynamics within soil aggregates remain unclear. We conducted a 36-year exclusion experiment to investigate how grazing exclusion affects the soil microbial community and the associated soil functions within soil aggregates in a semiarid grassland. Long-term (36 years) grazing exclusion induced a shift in microbial communities, especially in the 2 mm aggregates, and reduced carbon (C) sequestration potential thus revealing a negative impact of long-term GE. In contrast, 11–26 years of grazing exclusion greatly increased C sequestration and promoted nutrient cycling in soil aggregates and associated microbial functional genes. Moreover, the environmental characteristics of microhabitats (e.g., soil pH) altered the soil microbiome and strongly contributed to C sequestration. Our findings reveal new evidence from soil microbiology for optimizing grazing exclusion duration to maintain multiple belowground ecosystem functions, providing promising suggestions for climate-smart and resource-efficient grasslands.This work was financially supported by the National Natural Science Foundation of China (32061123007, 41977031), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40020202), and the Natural Science Foundation of Hubei Province, China (2020CFA013). Manuel Delgado-Baquerizo acknowledges support from the Spanish Ministry of Science and Innovation for the I+D+i project PID2020-115813RA-I00 and TED2021-130908B-C41 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe

Disconnection between plant–microbial nutrient limitation across forest biomes

11 páginas.- 7 figuras.- 1 tabla.- 41 referencias.- Additional supporting information can be found online in the Supporting Information section at the end of this article..- Read the free Plain Language Summary for this article on the Journal blog.Nitrogen (N) and phosphorus (P) are essential elements limiting plant–microbial growth in forest ecosystems. However, whether the pattern of plant–microbe nutrient limitation is consistent across forest biomes and the associated potential mechanisms remain largely unclear, limiting us to better understand the biogeochemical processes under future climate change. Here, we investigated patterns of plant–microbial N/P limitation in forests across a wide environmental gradient and biomes in China to explore the divergence of plant–microbial N/P limitation and the driving mechanisms. We revealed that 42.6% of the N/P limitation between plant–microbial communities was disconnected. Patterns in plant–microbial N/P limitations were consistent only for 17.7% of N and 39.7% of P. Geospatially, the inconsistency was more evident at mid-latitudes, where plants were mainly N limited and microbes were mainly P limited. Furthermore, our findings were consistent with the ecological stoichiometry of plants and microbes themselves and their requirements. Whereas plant N and P limitation was more strongly responsive to meteorological conditions and atmospheric deposition, that of microbes was more strongly responsive to soil chemistry, which exacerbated the plant–microbe N and P limitation divergence. Our work identified an important disconnection between plant and microbial N/P limitation, which should be incorporated into future Earth System Model to better predict forest biomes–climate change feedback. Read the free Plain Language Summary for this article on the Journal blog. © 2023 The Authors. Functional Ecology © 2023 British Ecological SocietyNational Natural Science Foundation of China, Grant/Award Number: 42207107; Catalan Government Grant, Grant/Award Number: SGR2017-1005; Fundación Ramón Areces grant, Grant/Award Number: CIVP20A6621; National Key Research and Development Program of China, Grant/Award Number: 2021YFD1901205; Open Fund of Key Laboratory of Agro-Ecological Processes in Subtropical Region, Chinese Academy of Sciences, Grant/Award Number: ISA2021101; Spanish Government, Grant/Award Number: PID2019-110521GB-I00 and PID2020-115770RB-I00; Strategic Priority Research Program of Chinese Academy of Sciences, Grant/Award Number: XDB40020202Peer reviewe

A Rice Plastidial Nucleotide Sugar Epimerase Is Involved in Galactolipid Biosynthesis and Improves Photosynthetic Efficiency

Photosynthesis is the final determinator for crop yield. To gain insight into genes controlling photosynthetic capacity, we selected from our large T-DNA mutant population a rice stunted growth mutant with decreased carbon assimilate and yield production named photoassimilate defective1 (phd1). Molecular and biochemical analyses revealed that PHD1 encodes a novel chloroplast-localized UDP-glucose epimerase (UGE), which is conserved in the plant kingdom. The chloroplast localization of PHD1 was confirmed by immunoblots, immunocytochemistry, and UGE activity in isolated chloroplasts, which was approximately 50% lower in the phd1-1 mutant than in the wild type. In addition, the amounts of UDP-glucose and UDP-galactose substrates in chloroplasts were significantly higher and lower, respectively, indicating that PHD1 was responsible for a major part of UGE activity in plastids. The relative amount of monogalactosyldiacylglycerol (MGDG), a major chloroplast membrane galactolipid, was decreased in the mutant, while the digalactosyldiacylglycerol (DGDG) amount was not significantly altered, suggesting that PHD1 participates mainly in UDP-galactose supply for MGDG biosynthesis in chloroplasts. The phd1 mutant showed decreased chlorophyll content, photosynthetic activity, and altered chloroplast ultrastructure, suggesting that a correct amount of galactoglycerolipids and the ratio of glycolipids versus phospholipids are necessary for proper chloroplast function. Downregulated expression of starch biosynthesis genes and upregulated expression of sucrose cleavage genes might be a result of reduced photosynthetic activity and account for the decreased starch and sucrose levels seen in phd1 leaves. PHD1 overexpression increased photosynthetic efficiency, biomass, and grain production, suggesting that PHD1 plays an important role in supplying sufficient galactolipids to thylakoid membranes for proper chloroplast biogenesis and photosynthetic activity. These findings will be useful for improving crop yields and for bioenergy crop engineering

Paper or interactive? a study of prototyping techniques for ubiquitous computing environments

We studied the effects of varying the fidelity and automation levels of a Ubicomp application prototype. Our results show that the interactive prototype captured the same usability issues that the paper prototype studies did and more. We found that paper prototyping is insufficient for supporting unique Ubicomp requirements, such as scalability, but a prototype with higher fidelity and automation levels can enhance the quality of interaction data available for evaluation

A novel hybrid bat algorithm for solving continuous optimization problems

The Bat Algorithm (BA), which is a global optimization method, performs poorly on complex continuous optimization problems due to BA’s disadvantages such as the premature convergence problem. In this paper, we propose a novel Hybrid Bat Algorithm (HBA) to improve the performance of BA. Three modification methods are incorporated into the standard BA to enhance the local search capability and the ability to escape from local optimum traps. The effectiveness and contribution of these three modification methods are analyzed by using classical benchmark functions. Moreover, the performance of HBA is evaluated on the numerical functions from the CEC 2014 test suite and compared with those of well-known optimization algorithms. The statistical test results indicate that HBA is a significant improvement