RESUMEN

Long-term greenhouse cultivation has an adverse effect on ecosystem functions such as soil carbon (C) and nitrogen (N) pools and greenhouse gas (GHG) emissions, but the underlying microbial mechanisms still remain unclear. Here, different sites under long-term greenhouse cultivation in a subtropical agricultural ecosystem were selected to measure soil C and N contents, extractable organic C (EOC) and N (EON) contents, and potential GHG emissions. Metagenomic analysis and 16S rRNA high-throughput sequencing were used to measure microbial communities. The results showed that long-term greenhouse cultivation increased soil salinity, and significantly increased soil total C and N contents, EOC and EON contents, and N2O emission potentials, although it significantly decreased CO2 emission and CH4 oxidation potential compared with the ambient control. Changes in soil CH4 oxidation and N2O emission potential exhibited similar patterns in the corresponding key functional genes based on according to our metagenomic analysis. In addition, long-term greenhouse cultivation did not change microbial diversity, although it clearly affected soil microbial community composition. Soil microbial communities were further classified into rare and abundant microbial taxa. Rare rather than abundant microbial taxa could adequately explain the changes in ecosystem functions, except for CH4 oxidation potential across the treatments. To our knowledge, this is the first study to quantify the importance of microbial subcommunities to ecosystem functions on the basis of microbial co-occurrence network analysis under greenhouse cultivation in agricultural ecosystems. Overall, our results indicated that rare rather than abundant microbial taxa could act as indicators of variations in ecosystem functions under long-term greenhouse cultivation in subtropical agricultural soils, which might be useful for better management practices and improving crop yields in agricultural ecosystems.

Asunto(s)

Gases de Efecto Invernadero , Suelo , Agricultura , Dióxido de Carbono , Ecosistema , Efecto Invernadero , Metano , Óxido Nitroso , ARN Ribosómico 16S

RESUMEN

Excessive cadmium (Cd) accumulation in soil can adversely affect plants, animals, microbes, and humans; therefore, novel and uncharacterized Cd-resistant plant-growth-promoting rhizobacteria (PGPR) are required to address this issue. In the paper, 13 bacteria were screened, their partial 16S rRNA sequences determined, and the isolates, respectively, clustered into Curtobacterium (7), Chryseobacterium (4), Cupriavidus (1), and Sphingomonas (1). Evaluation of PGP traits, including indole-3-acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, siderophore secretion, and cyanhydric acid production, identified Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 as promising candidates for PGPR based on high IAA or ACC deaminase production. Additionally, root-elongation assays indicated that inoculating GX_5, _15, or _31 increased Brassica napus root length both in the presence and absence of Cd by 19.75-29.96% and 19.15-31.69%, respectively. Pot experiments indicated that inoculating B. napus with GX_5, _15, and _31 significantly increased the dry weight of above-ground tissues and root biomass by 40.97-85.55% and 18.99-103.13%, respectively. Moreover, these isolates significantly increased Cd uptake in the aerial parts and root tissue of B. napus by 7.38-11.98% and 48.09-79.73%, respectively. These results identified GX_5, _15, or _31 as excellent promoters of metal remediation by using microorganism-associated phytoremediation.

Asunto(s)

Bacterias/metabolismo , Brassica napus/microbiología , Brassica napus/fisiología , Cadmio/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Contaminantes del Suelo/metabolismo , Bacterias/clasificación , Bacterias/genética , Bacterias/aislamiento & purificación , Biodegradación Ambiental , Biomasa , Brassica napus/crecimiento & desarrollo , Brassica napus/metabolismo , Liasas de Carbono-Carbono/metabolismo , ADN Bacteriano/genética , Ácidos Indolacéticos/metabolismo , Filogenia , Reguladores del Crecimiento de las Plantas/clasificación , Reguladores del Crecimiento de las Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Raíces de Plantas/microbiología , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADN , Sideróforos/metabolismo , Suelo/química , Microbiología del Suelo

RESUMEN

A series of N-doped carbon materials (NCs) were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile one-step pyrolysis method. The characterization of microstructural features shows that the NCs samples are composed of few-layered graphene-like nanoflakes with controlled in situ N doping, which is attributed to the confined pyrolysis of citric acid within the interlayers of the dicyandiamide-derived g-C3N4 with high nitrogen contents. Evidently, the pore volumes of the NCs increased with the increasing content of dicyandiamide in the precursor. Among these samples, the NCs nanoflakes prepared with the citric acid/dicyandiamide mass ratio of 1:6, NC-6, show the highest N content of ~6.2 at%, in which pyridinic and graphitic N groups are predominant. Compared to the commercial Pt/C catalyst, the as-prepared NC-6 exhibits a small negative shift of ~66 mV at the half-wave potential, demonstrating excellent electrocatalytic activity in the oxygen reduction reaction. Moreover, NC-6 also shows better long-term stability and resistance to methanol crossover compared to Pt/C. The efficient and stable performance are attributed to the graphene-like microstructure and high content of pyridinic and graphitic doped nitrogen in the sample, which creates more active sites as well as facilitating charge transfer due to the close four-electron reaction pathway. The superior electrocatalytic activity coupled with the facile synthetic method presents a new pathway to cost-effective electrocatalysts for practical fuel cells or metal-air batteries.