Lagging Response of Belowground Functional Traits to Environmental Cues in a Mature Amazonian Tropical Rainforest

Context/Purpose: The stress-dominance hypothesis (SDH) is a model of community assembly predicting that the relative importance of environmental filtering increases and competition decreases along a gradient of increasing environmental stress. Therefore, trait variation at the community level should increase as resources are more available. Although the SDH was designed to explain spatial changes in plant communities based on aboveground traits, it is possible that root communities show similar switches in strategies at temporal scales in response to pulses in resource availability. Methods: To test this hypothesis we sampled for two years the morphological changes in root systems in a mature tropical forest in Central Amazon. Thirty-six samples along a 500 m transect were taken each three months from February 2016 to February 2018, separating the uppermost organic layer (0-5 cm) from the mineral soil (5-15 cm). Besides root biomass, we scanned approximately 20% of the total root systems to calculate specific root length (SRL), average diameter (D), root tissue density (RTD), and branching index (BI). Spatially, we expected shifts from acquisitive to conservative syndromes as roots penetrate in the mineral soil. Temporarily, we hypothesized that traits associated with resource acquisition (SRL, SRTA, BI) will increase with soil moisture. Moreover, we expected that trait range will increase as resources become more available. Results: We found significant differences in biomass and morphological traits between the organic and mineral soils. We found no patterns between biomass increases in seasonality, but mean community traits change significantly with seasonal rain patterns. More interestingly, changes in mean and range values were more strongly associated with rain events three months before the collecting date, suggesting a lagging between rain events and belowground community responses. Conclusions: Belowground dynamics are structured spatially and temporarily in tropical forests, in synchrony with the availability of resources, as predicted by the SHD. Our results suggest that species tend to show similar traits during stressful times but diverge during acquisition periods. The results suggest a belowground dimension to niche segregation little explored in tropical biomes to date

Characterization of the n-TOF EAR-2 neutron beam

The experimental area 2 (EAR-2) at CERNs neutron time-of-flight facility (n-TOF), which is operational since 2014, is designed and built as a short-distance complement to the experimental area 1 (EAR-1). The Parallel Plate Avalanche Counter (PPAC) monitor experiment was performed to characterize the beam prole and the shape of the neutron 'ux at EAR-2. The prompt γ-flash which is used for calibrating the time-of-flight at EAR-1 is not seen by PPAC at EAR-2, shedding light on the physical origin of this γ-flash

The measurement programme at the neutron time-of-flight facility n-TOF at CERN

Neutron-induced reaction cross sections are important for a wide variety of research fields ranging from the study of nuclear level densities, nucleosynthesis to applications of nuclear technology like design, and criticality and safety assessment of existing and future nuclear reactors, radiation dosimetry, medical applications, nuclear waste transmutation, accelerator-driven systems and fuel cycle investigations. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. CERN's neutron time-of-flight facility n-TOF has produced a considerable amount of experimental data since it has become fully operational with the start of its scientific measurement programme in 2001. While for a long period a single measurement station (EAR1) located at 185 m from the neutron production target was available, the construction of a second beam line at 20 m (EAR2) in 2014 has substantially increased the measurement capabilities of the facility. An outline of the experimental nuclear data activities at n-TOF will be presented

Fine roots stimulate nutrient release during early stages of leaf litter decomposition in a Central Amazon rainforest

Purpose Large parts of the Amazon rainforest grow on weathered soils depleted in phosphorus and rock-derived cations. We tested the hypothesis that in this ecosystem, fine roots stimulate decomposition and nutrient release from leaf litter biochemically by releasing enzymes, and by exuding labile carbon stimulating microbial decomposers. Methods We monitored leaf litter decomposition in a Central Amazon tropical rainforest, where fine roots were either present or excluded, over 188 days and added labile carbon substrates (glucose and citric acid) in a fully factorial design. We tracked litter mass loss, remaining carbon, nitrogen, phosphorus and cation concentrations, extracellular enzyme activity and microbial carbon and nutrient concentrations. Results Fine root presence did not affect litter mass loss but significantly increased the loss of phosphorus and cations from leaf litter. In the presence of fine roots, acid phosphatase activity was 43.2% higher, while neither microbial stoichiometry, nor extracellular enzyme activities targeting carbon- and nitrogen-containing compounds changed. Glucose additions increased phosphorus loss from litter when fine roots were present, and enhanced phosphatase activity in root exclusions. Citric acid additions reduced litter mass loss, microbial biomass nitrogen and phosphorus, regardless of fine root presence or exclusion. Conclusions We conclude that plant roots release significant amounts of acid phosphatases into the litter layer and mobilize phosphorus without affecting litter mass loss. Our results further indicate that added labile carbon inputs (i.e. glucose) can stimulate acid phosphatase production by microbial decomposers, highlighting the potential importance of plant-microbial feedbacks in tropical forest ecosystems

Neutron spectroscopy of 26Mg states : Constraining the stellar neutron source 22Ne(α,n)25Mg

This work reports on accurate, high-resolution measurements of the 25Mg(n,γ)26Mg and 25Mg(n,tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved 25Mg(n,γ)26Mg parametrization. The relevant resonances for n+25Mg were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in 26Mg. With this information experimental upper limits of the reaction rates for 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg were established, potentially leading to a significantly higher (α,n)/(α,γ) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M⊙

Experimental setup and procedure for the measurement of the 7Be(n,α)α reaction at n-TOF

The newly built second experimental area EAR2 of the n-TOF spallation neutron source at CERN allows to perform (n, charged particles) experiments on short-lived highly radioactive targets. This paper describes a detection apparatus and the experimental procedure for the determination of the cross-section of the 7Be(n,α)α reaction, which represents one of the focal points toward the solution of the cosmological Lithium abundance problem, and whose only measurement, at thermal energy, dates back to 1963. The apparently unsurmountable experimental difficulties stemming from the huge 7Be γ-activity, along with the lack of a suitable neutron beam facility, had so far prevented further measurements. The detection system is subject to considerable radiation damage, but is capable of disentangling the rare reaction signals from the very high background. This newly developed setup could likely be useful also to study other challenging reactions requiring the detectors to be installed directly in the neutron beam

Radiative Neutron Capture Cross-Section Measurement of Ge Isotopes at n_TOF CERN Facility and Its Importance for Stellar Nucleosynthesis

This work was supported by the Austrian Science Fund FWF (J3503), the Adolf Messer Foundation (Germany), the UK Science and Facilities Council (ST/M006085/1), and the European Research Council ERC-2015-StG No. 677497. We also acknowledge the support of the National Science Centre, Poland, under the grant UMO-2016/22/M/ST2/00183, the MSMT of the Czech Republic and the Croatian Science Foundation under the project IP-2018-01-8570.This manuscript summarizes the results of radiative neutron capture cross-section measurements on two stable germanium isotopes, Ge-70 and Ge-73. Experiments were performed at the n_TOF facility at CERN via the time-of-flight technique, over a wide neutron energy range, for all stable germanium isotopes (70,72,73,74, and 76). Results for Ge-70 [Phys. Rev. C 100, 045804 (2019)] and Ge-73 [Phys. Lett. B 790, 458 (2019)] are already published. In the field of nuclear structure, such measurements allow to study excited levels close to the neutron binding energy and to obtain information on nuclear properties. In stellar nucleosynthesis research, neutron induced reactions on germanium are of importance for nucleosynthesis in the weak component of the slow neutron capture processes.Austrian Science Fund (FWF) J3503Adolf Messer Foundation (Germany)UK Science and Facilities Council ST/M006085/1European Research Council (ERC)European Commission 677497National Science Centre, Poland UMO-2016/22/M/ST2/00183Ministry of Education, Youth & Sports - Czech RepublicCroatian Science Foundation IP-2018-01-857