Accelerated organic matter decomposition in thermokarst lakes upon carbon and phosphorus inputs

Mineralization of dissolved organic matter (DOM) in thermokarst lakes plays a non-negligible role in the permafrost carbon (C) cycle, but remains poorly understood due to its complex interactions with external C and nutrient inputs (i.e., aquatic priming and nutrient effects). Based on large-scale lake sampling and laboratory incubations, in combination with ¹³C-stable-isotope labeling, optical spectroscopy, and high-throughput sequencing, we examined large-scale patterns and dominant drivers of priming and nutrient effects of DOM biodegradation across 30 thermokarst lakes along a 1100-km transect on the Tibetan Plateau. We observed that labile C and phosphorus (P) rather than nitrogen (N) inputs stimulated DOM biodegradation, with the priming and P effects being 172% and 451% over unamended control, respectively. We also detected significant interactive effects of labile C and nutrient supply on DOM biodegradation, with the combined labile C and nutrient additions inducing stronger microbial mineralization than C or nutrient treatment alone, illustrating that microbial activity in alpine thermokarst lakes is co-limited by both C and nutrients. We further found that the aquatic priming was mainly driven by DOM quality, with the priming intensity increasing with DOM recalcitrance, reflecting the limitation of external C as energy sources for microbial activity. Greater priming intensity was also associated with higher community-level ribosomal RNA gene operon (rrn) copy number and bacterial diversity as well as increased background soluble reactive P concentration. In contrast, the P effect decreased with DOM recalcitrance as well as with background soluble reactive P and ammonium concentrations, revealing the declining importance of P availability in mediating DOM biodegradation with enhanced C limitation but reduced nutrient limitation. Overall, the stimulation of external C and P inputs on DOM biodegradation in thermokarst lakes would amplify C-climate feedback in this alpine permafrost region.     

Fertilization effects on microbial community composition and aggregate formation in saline‐alkaline soil

Plant and Soil - Soil was sampled (0–20 cm) from a 5-year Yellow River Delta paddy field experiment: no fertilizers (Control), mineral fertilizers (NPK), and NPK plus organic...     

C and N allocation in soil under ryegrass and alfalfa estimated by 13C and 15N labelling

Background and Aims

Below-ground translocated carbon (C) released as rhizodeposits is an important driver for microbial mobilization of nitrogen (N) for plants. We investigated how a limited substrate supply due to reduced photoassimilation alters the allocation of recently assimilated C in plant and soil pools under legume and non-legume species.

Methods

A non-legume (Lolium perenne) and a legume (Medicago sativa) were labelled with ¹⁵N before the plants were clipped or shaded, and labelled twice with ¹³CO₂ thereafter. Ten days after clipping and shading, the ¹⁵N and ¹³C in shoots, roots, soil, dissolved organic nitrogen (DON) and carbon (DOC) and in microbial biomass, as well as the ¹³C in soil CO₂ were analyzed.

Results

After clipping, about 50 % more ¹³C was allocated to regrowing shoots, resulting in a lower translocation to roots compared to the unclipped control. Clipping also reduced the total soil CO₂ efflux under both species and the ¹³C recovery of soil CO₂ under L. perenne. The ¹⁵N recovery increased in the shoots of M. sativa after clipping, because storage compounds were remobilized from the roots and/or the N uptake from the soil increased. After shading, the assimilated ¹³C was preferentially retained in the shoots of both species. This caused a decreased ¹³C recovery in the roots of M. sativa. Similarly, the total soil CO₂ efflux under M. sativa decreased more than 50 % after shading. The ¹⁵N recovery in plant and soil pools showed that shading has no effect on the N uptake and N remobilization for L. perenne, but, the ¹⁵N recovery increased in the shoot of M. sativa.

Conclusions

The experiment showed that the dominating effect on C and N allocation after clipping is the need of C and N for shoot regrowth, whereas the dominating effect after shading is the reduced substrate supply for growth and respiration. Only slight differences could be observed between L. perenne and M. sativa in the C and N distribution after clipping or shading.     

Bicarbonate as tracer for assimilated C and homogeneity of 14C and 15N distribution in plants by alternative labeling approaches

Aims

Application of carbon (C) and nitrogen (N) isotopes is an essential tool to study C and N flows in plant-soil-microorganisms systems. When targeting single plants in a community the tracers need to be added via e.g., leaf-labeling or stem-feeding approaches. In this study we: (i) investigated if bicarbonate can be used to introduce ¹⁴C (or ¹³C) into white clover and ryegrass, and (ii) compared the patterns of ¹⁴C and ¹⁵N allocation in white clover and ryegrass to evaluate the homogeneity of tracer distribution after two alternative labeling approaches.

Methods

Perennial ryegrass and white clover were pulse labeled with ¹⁵N urea via leaf-labeling and ¹⁴C either via a ¹⁴CO₂ atm or with ¹⁴C bicarbonate through leaf-labeling. Plants were sampled 4 days after labeling and prepared for bulk isotope analysis and for ¹⁴C imaging to identify plant parts with high and low ¹⁴C activity. Subsequently, plant parts with high and low ¹⁴C activity were separated and analyzed for ¹⁵N enrichment.

Results

Bicarbonate applied by leaf-labeling efficiently introduced ¹⁴C into both white clover and ryegrass, although the ¹⁴C activity in particular for white clover was found predominantly in the labeled leaf. Using ¹⁴C imaging for identification of areas with high (hotspots) and low ¹⁴C activity showed that ¹⁴C was incorporated very heterogeneously both when using bicarbonate and CO₂ as expected when using pulse labeling. Subsequent analysis of ¹⁵N enrichment in plant parts with high and low ¹⁴C activity showed that ¹⁵N also had a heterogeneous distribution (up to two orders of magnitude).

Conclusion

Bicarbonate can efficiently be used to introduce ¹⁴C or ¹³C into plant via the leaf-labeling method. Both ¹⁴C and ¹⁵N showed heterogeneous distribution in the plant, although the distribution of ¹⁵N was more even than that of ¹⁴C.     

Anti-influenza active and low toxic N-phenyl-substituted β-amidoamidines structurally related to natural antibiotic amidinomycin

A set of racemic N-phenyl-substituted β-amidoamidines hydrochlorides 4, which are structurally related to natural antiviral agent amidinomycin (1), was synthesized in four steps starting from methacryloyl anilide (5). In the final step of the synthetic route, an uncommon monoacylation of β-aminoamidine 8 at the less reactive β-phenylamino-group took place. To rationalize this result, a mechanism which involves initial acylation at the more active amidine-function followed by intramolecular acyl-group transfer to β-phenylamino-group was suggested. All three β-amidoamidines 4d–f bearing long linear aliphatic chain (from n-C₈H₁₇ to n-C₁₂H₂₅) revealed significant in vitro activity against influenza A virus (H3N2) and modest cytotoxicity. The in vitro antiviral potency of 4d,e is 6–20 times greater than that of commercial rimantadine with lower EC₅₀ values and higher therapeutic index. The non-toxic in vivo compounds 4d–f showed a beneficial protective effect in influenza A (H3N2) infected mice.     

Maize rhizosphere priming: field estimates using <Superscript>13</Superscript>C natural abundance

Introduction

Root-mediated changes in soil organic matter (SOM) decomposition, termed rhizosphere priming effects (RPE), play crucial roles in the global carbon (C) cycle, but their mechanisms and field relevance remain ambiguous. We hypothesize that nitrogen (N) shortages may intensify SOM decomposition in the rhizosphere because of increase of fine roots and rhizodeposition.

Methods

RPE and their dependence on N-fertilization were studied using a C₃-to-C₄ vegetation change. N-fertilized and unfertilized soil cores, with and without maize, were incubated in the field for 50 days. Soil CO₂ efflux was measured, partitioned for SOM- and root-derived CO₂, and RPE was calculated. Plant biomass, microbial biomass C (MBC) and N (MBN), and enzyme activities (β-1,4-glucosidase; N-acetylglucosaminidase; L-leucine aminopeptidase) were analyzed.

Results

Roots enhanced SOM mineralization by 35 % and 126 % with and without N, respectively. This was accompanied by higher specific root-derived CO₂ in unfertilized soils. MBC, MBN and enzyme activities increased in planted soils, indicating microbial activation, causing positive RPE. N-fertilization had minor effects on MBC and MBN, but it reduced β-1,4-glucosidase and L-leucine aminopeptidase activities under maize through lower root-exudation. In contrast, N-acetylglucosaminidase activity increased with N-fertilization in planted and unplanted soils.

Conclusions

This study showed the field relevance of RPE and confirmed that, despite higher root biomass, N availability reduces RPE by lowering root and microbial activity.

     

Object selection by an oscillatory neural network

We describe a new solution to the problem of consecutive selection of objects in a visual scene by an oscillatory neural network with the global interaction realised through a central executive element (central oscillator). The frequency coding is used to represent greyscale images in the network. The functioning of the network is based on three main principles: (1) the synchronisation of oscillators via phase-locking, (2) adaptation of the natural frequency of the central oscillator, and (3) resonant increase of the amplitudes of the oscillators which work in-phase with the central oscillator. Examples of network simulations are presented to show the reliability of the results of consecutive selection of objects under conditions of constant and varying brightness of the objects.     

4-(2-pyridyl)piperazine-1-carboxamides: potent vanilloid receptor 1 antagonists

A series of 4-(2-pyridyl)piperazine-1-carboxamide analogues based on the lead compound 1 was synthesized and evaluated for VR1 antagonist activity in capsaicin-induced (CAP) and pH (5.5)-induced (pH) FLIPR assays in a rat VR1-expressing HEK293 cell line. Potent VR1 antagonists were identified through SAR studies. From these studies, 18 was found to be very potent in the in vitro assay [IC(50)=4.8 nM (pH) and 35 nM (CAP)] and orally available in rat (F%=15.1).