We use an end-to-end model of planet formation, thermodynamic evolution, and atmospheric escape to investigate how the statistical imprints of evaporation depend on the bulk composition of planetary ...cores (rocky versus icy). We find that the population-wide imprints like the location of the "evaporation valley" in the distance-radius plane and the corresponding bimodal radius distribution clearly differ depending on the bulk composition of the cores. Comparison with the observed position of the valley suggests that close-in low-mass Kepler planets have a predominantly Earth-like rocky composition. Combined with the excess of period ratios outside of MMR, this suggests that low-mass Kepler planets formed inside of the water iceline but were still undergoing orbital migration. The core radius becomes visible for planets losing all primordial H/He. For planets in this "triangle of evaporation" in the distance-radius plane, the degeneracy in composition is reduced. In the observed planetary mass-mean density diagram, we identify a trend to more volatile-rich compositions with an increasing radius (R/R⊕ 1.6 rocky; 1.6-3.0 ices, and/or H/He; 3: H/He). The mass-density diagram contains important information about formation and evolution. Its characteristic broken V-shape reveals the transitions from solid planets to low-mass core-dominated planets with H/He and finally to gas-dominated giants. Evaporation causes the density and orbital distance to be anticorrelated for low-mass planets in contrast to giants, where closer-in planets are less dense, likely due to inflation. The temporal evolution of the statistical properties reported here will be of interest for the PLATO 2.0 mission, which will observe the temporal dimension.
Previous studies have revealed inconsistent correlations between fungal diversity and plant diversity from local to global scales, and there is a lack of information about the diversity–diversity and ...productivity–diversity relationships for fungi in alpine regions.
Here we investigated the internal relationships between soil fungal diversity, plant diversity and productivity across 60 grassland sites on the Tibetan Plateau, using Illumina sequencing of the internal transcribed spacer 2 (ITS2) region for fungal identification.
Fungal alpha and beta diversities were best explained by plant alpha and beta diversities, respectively, when accounting for environmental drivers and geographic distance. The best ordinary least squares (OLS) multiple regression models, partial least squares regression (PLSR) and variation partitioning analysis (VPA) indicated that plant richness was positively correlated with fungal richness. However, no correlation between plant richness and fungal richness was evident for fungal functional guilds when analyzed individually.
Plant productivity showed a weaker relationship to fungal diversity which was inter-correlated with other factors such as plant diversity, and was thus excluded as a main driver. Our study points to a predominant effect of plant diversity, along with other factors such as carbon: nitrogen (C: N) ratio, soil phosphorus and dissolved organic carbon, on soil fungal richness.
The judicious incorporation of a fluoroalkyl moiety often brings about beneficial effects on the properties of bioactive molecules. Consequently, efficient methods for selective fluoroalkylation are ...much sought after in drug discovery. Despite significant achievements in trifluoromethylation, selective mono- and difluoroalkylation is still undeveloped. Catalytic functionalization of fluorinated silyl enol ethers (FSEEs) emerges as a fruitful approach for the diversity-oriented synthesis of value-added α-mono or difluoroalkylated ketones. In this feature article, we detail our efforts in developing catalytic selective mono- and difluoroalkylation reactions using FSEEs. Specifically, we highlight our findings such as activating FSEEs by amines for catalytic enantioselective synthesis, taking advantage of the often observed high activity of FSEEs over the non-fluorinated analogues for reaction development, and the influence of C-F H-X interactions on reactivity and selectivity.
This feature article highlights our recent achievements in catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers (FSEEs).
Subsoils contain >50% of soil organic carbon (SOC) globally yet remain under‐investigated in terms of their response to climate changes. Recent evidence suggests that warmer, drier conditions in ...alpine grasslands induce divergent responses in SOC decomposition and carbon accrual in top‐ versus subsoils. However, longer term effects on microbial activity (i.e., catabolic respiration vs. anabolic growth) and belowground carbon cycling are not well understood. Here we utilized a field manipulation experiment on the Qinghai‐Tibetan Plateau and conducted a 110‐day soil incubation with and without 13C‐labeled grass litter to assess microbes' role as both SOC “decomposers” and “contributors” in the top‐ (0–10 cm) versus subsoils (30−40 cm) after 5 years of warming and drought treatments. Microbial mineralization of both SOC and added litter was examined in tandem with potential extracellular enzyme activities, while microbial biomass synthesis and necromass accumulation were analyzed using phospholipid fatty acids and amino sugars coupled with 13C analysis, respectively. We found that warming and, to a lesser extent, drought decreased the ratio of inorganic nitrogen (N) to water‐extractable organic carbon in the subsoil, intensifying N limitation at depth. Both SOC and litter mineralization were reduced in the subsoil, which may also be related to N limitation, as evidenced by lower hydrolase activity (especially leucine aminopeptidase) and reduced microbial efficiency (lower biomass synthesis and necromass accumulation relative to respiration). However, none of these effects were observed in the topsoil, suggesting that soil microbes became inactive and inefficient in subsoil but not topsoil environments. Given increasing belowground productivity in this alpine grassland under warming, both elevated root deposits and diminished microbial activity may contribute to new carbon accrual in the subsoil. However, the sustainability of plant growth and persistence of subsoil SOC pools deserve further investigation in the long term, given the aggravated N limitation at depth.
Warming and drought is found to reduce microbial mineralization potentials of soil organic carbon and grass litter in the subsoil of an alpine grassland on the Qinghai‐Tibetan Plateau. This phenomenon appears be related to an intensified N (and moisture) limitation, evidenced by lower hydrolase (especially leucine aminopeptidase) activity and reduced microbial efficiency for both biomass synthesis and necromass accumulation (relative to respiration). However, none of these effects are observed in the topsoil, suggesting that soil microbes become inactive and inefficient under warming and drought in the alpine grassland subsoil but not topsoil.
In contrast to the widespread use of α‐amino acid‐equivalent enolates for the preparation of non‐natural amino acids, the utilization of β‐amino‐acid counterparts has been limited. This deficit has ...resulted in a short supply of β2, 2‐amino acids bearing two substituents at the α‐carbon, especially for peptide synthesis. Herein, racemic 4‐substituted isoxazolidin‐5‐ones were used as precursors of β2‐amino acid enolates in the direct catalytic diastereo‐ and enantioselective C−C bond‐forming reactions, constructing two adjacent stereocenters in a highly stereoselective fashion. The obtained adducts were smoothly coupled with α‐amino acid‐derived α‐ketoacids to afford α/β2, 2‐hybrid dipeptides suitable for 9‐fluorenylmethoxycarbonyl (Fmoc)‐based solid‐phase peptide synthesis. Moreover, the Mannich adducts obtained from isatin‐derived imines were converted to spirocyclic β‐lactams, which have recently received increased attention due to their unique biological activities and conformational preferences.
Direct bonding: Direct catalytic diastereo‐ and enantioselective C−C bond‐forming reactions by using β‐amino acid enolates are presented. The obtained products are easily converted to α/β‐hybrid dipeptides suitable for 9‐fluorenylmethoxycarbonyl‐based solid‐phase peptide synthesis. Furthermore, the synthesis of a spirocyclic β‐lactam embedded in a peptide backbone is demonstrated.
Anthropogenic climate change has emerged as a critical environmental problem, prompting frequent investigations into its consequences for various ecological systems. Few studies, however, have ...explored the effect of climate change on ecological stability and the underlying mechanisms. We conduct a field experiment to assess the influence of warming and altered precipitation on the temporal stability of plant community biomass in an alpine grassland located on the Tibetan Plateau. We find that whereas precipitation alteration does not influence biomass temporal stability, warming lowers stability through reducing the degree of species asynchrony. Importantly, biomass temporal stability is not influenced by plant species diversity, but is largely determined by the temporal stability of dominant species and asynchronous population dynamics among the coexisting species. Our findings suggest that ongoing and future climate change may alter stability properties of ecological communities, potentially hindering their ability to provide ecosystem services for humanity.
The tremendous reservoir of soil organic carbon (SOC) in wetlands is being threatened by water-table decline (WTD) globally. However, the SOC response to WTD remains highly uncertain. Here we examine ...the under-investigated role of iron (Fe) in mediating soil enzyme activity and lignin stabilization in a mesocosm WTD experiment in an alpine wetland. In contrast to the classic 'enzyme latch' theory, phenol oxidative activity is mainly controlled by ferrous iron Fe(II) and declines with WTD, leading to an accumulation of dissolvable aromatics and a reduced activity of hydrolytic enzyme. Furthermore, using dithionite to remove Fe oxides, we observe a significant increase of Fe-protected lignin phenols in the air-exposed soils. Fe oxidation hence acts as an 'iron gate' against the 'enzyme latch' in regulating wetland SOC dynamics under oxygen exposure. This newly recognized mechanism may be key to predicting wetland soil carbon storage with intensified WTD in a changing climate.
Satellite data indicate significant advancement in alpine spring phenology over decades of climate warming, but corresponding field evidence is scarce. It is also unknown whether this advancement ...results from an earlier shift of phenological events, or enhancement of plant growth under unchanged phenological pattern. By analyzing a 35‐year dataset of seasonal biomass dynamics of a Tibetan alpine grassland, we show that climate change promoted both earlier phenology and faster growth, without changing annual biomass production. Biomass production increased in spring due to a warming‐induced earlier onset of plant growth, but decreased in autumn due mainly to increased water stress. Plants grew faster but the fast‐growing period shortened during the mid‐growing season. These findings provide the first in situ evidence of long‐term changes in growth patterns in alpine grassland plant communities, and suggest that earlier phenology and faster growth will jointly contribute to plant growth in a warming climate.
Climate change reshapes plant growth patterns by shifting phenology earlier, enhancing growth rate, and shortening growth period in a Tibetan alpine grassland over 35 years. The changes in growth patterns alters seasonal, but not annual, biomass production.
Aim
Most existing studies that examined the biotic mechanisms of ecosystem stability have focused on aboveground biodiversity. Whether and how belowground biodiversity affects the stability of ...natural ecosystems is largely unknown. In the present study, we investigated the relationships between above‐ and belowground biodiversity and the temporal stability of grassland biomass production across a large gradient of soil and climatic conditions.
Location
Tibetan Plateau.
Time period
2001–2016.
Major taxa studied
Alpine grass and soil bacteria, arbuscular mycorrhiza (AM) fungi and fauna.
Methods
We coupled a field biodiversity survey conducted in 54 alpine grassland ecosystems across the Tibetan Plateau with a satellite‐sensed proxy (enhanced vegetation index, EVI) of ecosystem productivity during 2001–2016. The temporal stability of primary productivity was calculated as the ratio of the mean annual peak EVI to the standard deviation of the annual peak EVI over this period. Plant diversity was determined using a classic vegetation survey approach, soil bacterial and AM fungal diversity were measured using a high‐throughput sequencing approach, and soil fauna was counted and identified at the order level after being extracted using a modified Berlese–Tullgren method.
Results
Our results demonstrated that both above‐ and belowground biodiversity were positively associated with ecosystem stability. Belowground biodiversity not only affected ecosystem stability directly, but also influenced it indirectly through plant diversity and soil fertility. Furthermore, soil pH, climate and its variability strongly influenced soil biodiversity, which in turn influenced ecosystem stability.
Main conclusions
Our study demonstrates the indispensable role of belowground biodiversity in regulating ecosystem stability, emphasizing the necessity of conserving this ‘hidden’ biodiversity in fragile alpine ecosystems facing ongoing environmental change.
Abstract
A more common and noninvasive predicting biomarker for programmed cell death 1 (PD-1) antibody remains to be explored. We assessed 46 patients with advanced gastric cancer who received PD-1 ...antibody immunotherapy and 425-genes next-generation sequencing (NGS) testing. Patients who had a > 25% decline in maximal somatic variant allelic frequency (maxVAF) had a longer progression free survival (PFS) and higher response rate than those who did not (7.3 months vs 3.6 months,
p
= 0.0011; 53.3% vs 13.3%,
p
= 0.06). The median PFS of patients with undetectable and detectable post-treatment circulating tumor DNA (ctDNA) was 7.4 months vs. 4.9 months (
p
= 0.025). Mutation status of TGFBR2, RHOA, and PREX2 in baseline ctDNA influenced the PFS of immunotherapy (
p
< 0.05). Patients with alterations in CEBPA, FGFR4, MET or KMT2B (
p
= 0.09) gene had greater likelihood of immune-related adverse events (irAEs). ctDNA can serve as a potential biomarker of the response to immunotherapy in advanced gastric cancers, and its potential role in predicting irAEs worth further exploration.
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