6 research outputs found
Fire affects the taxonomic and functional composition of soil microbial communities, with cascading effects on grassland ecosystem functioning
Fire is a crucial event regulating the structure and functioning of many ecosystems.Yet few studies have focused on how fire affects taxonomic and functional diversiâties of soil microbial communities, along with changes in plant communities and soil carbon (C) and nitrogen (N) dynamics. Here, we analyze these effects in a grasslandecosystem 9 months after an experimental fire at the Jasper Ridge Global ChangeExperiment site in California, USA. Fire altered soil microbial communities con âsiderably, with community assembly process analysis showing that environmentalselection pressure was higher in burned sites. However, a small subset of highly connected taxa was able to withstand the disturbance. In addition, fire decreasedthe relative abundances of most functional genes associated with C degradationand N cycling, implicating a slowdown of microbial processes linked to soil C and N dynamics. In contrast, fire stimulated aboveâ and belowground plant growth, likely enhancing plantâmicrobe competition for soil inorganic N, which was reduced by a factor of about 2. To synthesize those findings, we performed structural equationmodeling, which showed that plants but not microbial communities were responsiâble for significantly higher soil respiration rates in burned sites. Together, our resultsdemonstrate that fire ârebootsâ the grassland ecosystem by differentially regulating plant and soil microbial communities, leading to significant changes in soil C and N dynamics
Long-term elevated CO2 shifts composition of soil microbial communities in a Californian annual grassland, reducing growth and N utilization potentials
International audienceThe continuously increasing concentration of atmospheric CO2 has considerably altered ecosystem functioning. However, few studies have examined the long-term (i.e. over a decade) effect of elevated CO2 on soil microbial communities. Using 16S rRNA gene amplicons and a GeoChip microarray, we investigated soil microbial communities from a Californian annual grassland after 14 years of experimentally elevated CO2 (275 ppm higher than ambient). Both taxonomic and functional gene compositions of the soil microbial community were modified by elevated CO2. There was decrease in relative abundance for taxa with higher ribosomal RNA operon (rrn) copy number under elevated CO2, which is a functional trait that responds positively to resource availability in culture. In contrast, taxa with lower rrn copy number were increased by elevated CO2. As a consequence, the abundance-weighted average rrn copy number of significantly changed OTUs declined from 2.27 at ambient CO2 to 2.01 at elevated CO2. The nitrogen (N) fixation gene nifH and the ammonium-oxidizing gene amoA significantly decreased under elevated CO2 by 12.6% and 6.1%, respectively. Concomitantly, nitrifying enzyme activity decreased by 48.3% under elevated CO2, albeit this change was not significant. There was also a substantial but insignificant decrease in available soil N, with both nitrate (NO3) (-27.4%) and ammonium (NH4+) (-15.4%) declining. Further, a large number of microbial genes related to carbon (C) degradation were also affected by elevated CO2, whereas those related to C fixation remained largely unchanged. The overall changes in microbial communities and soil N pools induced by long-term elevated CO2 suggest constrained microbial N decomposition, thereby slowing the potential maximum growth rate of the microbial community
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Long-term nitrogen deposition enhances microbial capacities in soil carbon stabilization but reduces network complexity.
BackgroundAnthropogenic activities have increased the inputs of atmospheric reactive nitrogen (N) into terrestrial ecosystems, affecting soil carbon stability and microbial communities. Previous studies have primarily examined the effects of nitrogen deposition on microbial taxonomy, enzymatic activities, and functional processes. Here, we examined various functional traits of soil microbial communities and how these traits are interrelated in a Mediterranean-type grassland administrated with 14 years of 7 g m-2 year-1 of N amendment, based on estimated atmospheric N deposition in areas within California, USA, by the end of the twenty-first century.ResultsSoil microbial communities were significantly altered by N deposition. Consistent with higher aboveground plant biomass and litter, fast-growing bacteria, assessed by abundance-weighted average rRNA operon copy number, were favored in N deposited soils. The relative abundances of genes associated with labile carbon (C) degradation (e.g., amyA and cda) were also increased. In contrast, the relative abundances of functional genes associated with the degradation of more recalcitrant C (e.g., mannanase and chitinase) were either unchanged or decreased. Compared with the ambient control, N deposition significantly reduced network complexity, such as average degree and connectedness. The network for N deposited samples contained only genes associated with C degradation, suggesting that C degradation genes became more intensely connected under N deposition.ConclusionsWe propose a conceptual model to summarize the mechanisms of how changes in above- and belowground ecosystems by long-term N deposition collectively lead to more soil C accumulation. Video Abstract
Patient Perspective on Acute Intermittent Porphyria with Frequent Attacks: A Disease with Intermittent and Chronic Manifestations
Discovery of Clinical Candidate 1â(4-(3-(4-(1<i>H</i>âBenzo[<i>d</i>]imidazole-2-carbonyl)phenoxy)pyrazin-2-yl)piperidin-1-yl)ethanone (AMG 579), A Potent, Selective, and Efficacious Inhibitor of Phosphodiesterase 10A (PDE10A)
We report the identification of a
PDE10A clinical candidate by
optimizing potency and in vivo efficacy of promising keto-benzimidazole
leads <b>1</b> and <b>2</b>. Significant increase in biochemical
potency was observed when the saturated rings on morpholine <b>1</b> and <i>N</i>-acetyl piperazine <b>2</b> were
changed by a single atom to tetrahydropyran <b>3</b> and <i>N</i>-acetyl piperidine <b>5</b>. A second single atom
modification from pyrazines <b>3</b> and <b>5</b> to pyridines <b>4</b> and <b>6</b> improved the inhibitory activity of <b>4</b> but not <b>6</b>. In the in vivo LCâMS/MS target
occupancy (TO) study at 10 mg/kg, <b>3</b>, <b>5</b>,
and <b>6</b> achieved 86â91% occupancy of PDE10A in the
brain. Furthermore, both CNS TO and efficacy in PCP-LMA behavioral
model were observed in a dose dependent manner. With superior in vivo
TO, in vivo efficacy and in vivo PK profiles in multiple preclinical
species, compound <b>5</b> (AMG 579) was advanced as our PDE10A
clinical candidate