Search

Soil nitrous oxide (N2O) and dinitrogen (N2) emissions from denitrification are crucial to the nitrogen (N) cycle. However, the temperature sensitivities (Q10) of gaseous N losses in forest soils are poorly understood, with implications for prediction of N cycle responses to warming. Here, we quantify temperature sensitivities of denitrification-derived potential N2O and N2production. Using soils from 18 forest sites in China along a 4,000 km north–south transect we find that N2O and N2production rates increased with temperature, with large variations across soils. In contrast, the Q10values for N2O (2.1 ± 0.5) and N2(2.6 ± 0.6) were similar across soils. N2was more sensitive to temperature than N2O, suggesting that warming could promote complete denitrification. Moreover, the Q10for denitrification (2.3 ± 0.5) was comparable to Q10for aquatic sediments. This finding of universal temperature sensitivity of gaseous N losses from denitrification will facilitate modelling N losses in response to warming globally.

Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (Δ17O) of nitrate (NO3–) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha–1yr–1(average 94 ± 10 kg N ha–1yr–1) over the 4 years in this forest. This result and high stream NO3–loss (4.2–8.9 kg N ha–1yr–1) suggest that the forested catchment may have been N-saturated. At the catchment scale, the total N output of 10.7 kg N ha–1yr–1, via leaching and gaseous losses, accounts for 56% of the N input from bulk precipitation (19.2 kg N ha–1yr–1). This result indicates that the forested catchment is still retaining a large fraction of N from atmospheric deposition. Our study suggests that estimating in situ catchment-scale GNR over several years when combined with other conventional flux estimates can facilitate the understanding of N biogeochemical cycling and changes in the ecosystem N status.

Human activities have released a large amount of nitric oxides (NOx) into the atmosphere, leading to elevated regional atmospheric NOx concentration and nitrogen (N) deposition. Several studies have observed a downward NOx or NOy (NOx and its oxidation products) flux to the forest canopy, but attributed it to the photochemical reactions and conversion from gaseous N to particulate N. Here, we focus on the possibility of NOx sink by forest canopy based on an observed downward NOx flux of 0.28 kg N ha−1yr−1in a temperate forest of northeastern China, using hourly monitoring of NOx fluxes. In combination with results from previous studies, we find that the downward NOx or NOy fluxes ranged from 0.2 to 1.4 kg N ha−1yr−1in temperate forests and from 5.3 to 8.5 kg N ha−1yr−1in subtropical forests and they were positively related to atmospheric NOx concentration, mean annual air temperature and annual precipitation across eight forest sites from around the world. If assuming 50% of downward NOx or NOy was directly taken up by the canopy, we estimate a NOx or NOy sink of 0.2 and 1.1 Tg N yr−1by global respective temperate and subtropical forests, representing an effective scavenger of atmospheric NOx and a considerable N source to forests. We suggest that interception of NOx or NOy by forest canopy should be considered in global NOx budgets and their contribution to the global forest N pool in global Earth System's models. Canopy interception of reactive N has gained wide attention in recent several years, however, its quantification is still unclear. In the present work, we demonstrate the NOx downward movement in a typical temperate forest in northeastern China was partially driven by canopy biological uptake, and then combined results of our in situ observation of canopy NOx flux with other existing 10 monitoring sites worldwide. We estimated an N input of 0.2 and 1.1 Tg N yr−1in global respective temperate and subtropical forests via downward NOx movement, representing an effective scavenger of atmospheric NOx and a considerable N source to forests. The potential importance of canopy NOx uptake by forests for atmospheric NOx concentration and forest N pools is unclearCombining present and previous study results, we estimated a canopy N input of 0.2–1.1 Tg yr−1in global temperate and subtropical forestsWe suggest that interception of NOx by forest canopy should be considered in global NOx budgets and forest N pools The potential importance of canopy NOx uptake by forests for atmospheric NOx concentration and forest N pools is unclear Combining present and previous study results, we estimated a canopy N input of 0.2–1.1 Tg yr−1in global temperate and subtropical forests We suggest that interception of NOx by forest canopy should be considered in global NOx budgets and forest N pools

The network diameter is an important characteristic parameter of a complex network. Calculation for a large-scale complex network's diameter has been an important subject in the study of complex networks. If the network diameter is calculated directly, the problem mainly exists in efficiency for searching and counting the shortest paths. If the network diameter is calculated indirectly by studying the statistical function about the relationship between the network diameter and parameters affecting the diameter, the problems not only exist in the efficiency of statistic, but also exist in the function which may be not applicable to all kinds of networks. An algorithm for the complex network diameter based on the k order distance matrix is proposed with a matrix multiplication approach, and a mathematical proof for the algorithm correctness is given as well. Furthermore, some relevant propositions and deductions for reducing the complexity of this algorithm are put forward. With a good theoretical basis and a simple calculation process, this algorithm can be used to calculate the diameter of a large-scale complex network with small-world effect more accurately and efficiently. Two cases about the advanced research projects agency (ARPA) network model and the Chinese airline network model are adopted to verify the effect of this algorithm. [ABSTRACT FROM AUTHOR]

Background: Forest succession is an important ecological process and has been studied for more than a century. However, changes in nitrogen (N) availability during succession remain unclear as they may lead to either N saturation or N limitation. Here, we propose a conceptual model to illustrate changes in N availability during four stages of secondary succession using the natural abundance of 15N in plant leaves (foliar δ15N). We predicted that N availability would decline in the early stages of succession and then increase in late stages, coinciding with the changes in foliar δ15N, with the inflection point varying in different climate zones. Data on foliar δ15N from 16 succession sequences were synthesized to explore changes in N availability during forest succession. Results: The compiled data were consistent with the proposed conceptual model. Foliar δ15N in boreal and temperate forests decreased significantly in the first two stages of succession (estimated to last at least 66 years in temperate forests), at a rate of 0.18‰ and 0.38‰ per decade, respectively, and decreased slightly in tropical forests in the first 23 years. Foliar δ15N is projected to increase in later stages in all forests, which is supported by observations in both temperate and tropical forests. The inflection points of N availability when N limitation peaked during succession were different in different climate zones, implying different ecosystem N turnovers. Conclusions: Our study reconciles the controversies regarding changes in N availability during forest secondary succession. Our findings are also useful for predicting the recovery of N and carbon accumulation during succession. Nonetheless, studies on forest secondary succession using foliar δ15N have thus far been limited, and more research should be conducted to further verify the conceptual model proposed here.

The overproduction of cortisol is associated with many severe and life-threatening diseases, such as Cushing’s syndrome (CS) and chronic wound healing. 11β-Hydroxylase (CYP11B1) is considered as an attractive target for treating these diseases, since it is a key enzyme responsible for the last step in cortisol biosynthesis. Nowadays, medical therapy has become increasingly important for CS patients, especially for those who are in need of surgery or suffer from surgery failure and those in early phases of radiation therapy. In clinic, steroidogenesis blockers including CYP11B1 inhibitors are utilized most frequently. Nevertheless, drugs that inhibit CYP11B1 are inevitable with side effects due to lack of selectivity over other steroidogenesis enzymes. Recent advances in the development of novel CYP11B1 inhibitors might overcome these limitations. In addition, the beneficial effects of down-regulation of cortisol levels to wound closure have been recently disclosed and have stimulated topical application of CYP11B1 inhibitors as a novel therapeutic strategy for curing chronic wounds. Herein, we provide a review of the current CYP11B1 inhibitors in clinic combating CS and the latest development of novel CYP11B1 inhibitors for treating CS and chronic wounds.

ABSTRACTCBR703 was reported to inhibit bacterial RNA polymerase (RNAP) and biofilm formation, considering it to be a good candidate for further optimization. While synthesized derivatives of CBR703 did not result in more-active RNAP inhibitors, we observed promising antibacterial activities. These again correlated with a significant cytotoxicity toward mammalian cells. Furthermore, we suspect the promising effects on biofilm formation to be artifacts. Consequently, this class of compounds can be considered unattractive as antibacterial agents.

When a huge river in an industrialized country drains into a partly enclosed bay, the challenge of improving the water quality in the bay is a big one. In order to reduce the nutrient loading of Chesapeake Bay, USA, by 40 per cent, farmers and local communities in the upper reaches of the catchment are involved in implementing a 'multi-barrier approach'. Education and community involvement play a major part in meeting this challenge

The effects of live and dead roots on soil fungi were investigated experimentally in a spodosolic soil of the New Jersey Pinelands. Field mesocosm plots were constructed to have a layer of either C- and N-rich organic soil or a vermiculite substitute overlying a layer of sandy mineral soil with a very low organic content. The plots were also supplied with live pitch pine and blueberry roots or dead pitch pine roots in varying quantities based on anturally occurring densities (half, same, and double the ambient quantities). All plots were sampled 1 year after construction (June 1991), and three more times in two subsequent years (November 1991, June 1992, June 1993). In the presence of live roots, fluorescein diacetate-determined (FDA-active) fungal hyphae, total fungal hyphae, and soil moisture decreased significantly in the organic material, while no change was associated with the dead roots. The FDA-active fungal length in the live-root plots ranged from 40 to 165 mg-1 soil, and from 55 to 335 mg-1 soil in the dead-root plots. While the total fungal length in live-root plots remained constant over time (~3000 mg-1 soil), the total fungal length in the dead-root plots increased from an initial value of 3000 to >4000 mg-1 soil at the conclusion of the study. Fungal lengths in mineral soil were higher under organic material than under the vermiculite substitute. Soil moisture was higher in the presence of live roots in mineral soils, but this did not increase the fungal abundance. Inputs of dead roots did not alter the fungal abundance. Overall, we demonstrated that live and dead roots had different effects on fungal abundance in soils with contrasting qualities, and in a spodosolic forest soil, roots could have ecosystem effects very different from those in agricultural soils.

Measuring the nitrogen isotope compositions (δ15N) of nitric oxide (NO) from different sources helps to quantify the relative contributions of atmospheric NOx. Soil is one of the most important sources of atmospheric NOx, but only limited measurements on the δ15N of soil‐emitted NO exist, hampering our ability to partition sources to air pollution. Here we conducted soil incubations to measure the δ15N‐NO under defined aerobic or anaerobic conditions, favoring either nitrification or denitrification. Soils were collected from seven sites spanning three ecosystems in northern China (two agricultural, two forest, and three grassland sites). We found that the δ15N‐NO and their associated N isotope fractionations were significantly different between anaerobic and aerobic conditions in seven soils. Under aerobic condition, the δ15N‐NO ranged from −62‰ to −50‰ (averaged −56 ± 4‰), being significantly more negative (by 23‰) than those under anaerobic condition (−45‰ to −23‰, averaged −33 ± 7‰). The apparent N isotope fractionation for NO production under aerobic condition (15εaerobic= 61 ± 3‰) was significantly higher (by 26‰) than under anaerobic condition (15εanaerobic= 35 ± 6‰), with a small variability among ecosystem types. Our study demonstrates that the δ15N‐NO from different soils are very different from fuel combustions (mainly from 0‰ to +20‰), supporting that measuring 15N is a useful tool to partition the contributions of soil NO to atmospheric NOx. Our results also imply δ15N‐NO produced by nitrification and denitrification distinctly different, as these two processes are dominant processes producing NO under aerobic and anaerobic conditions, respectively. Nitric oxide (NO) affects the atmosphere chemistry and NO itself a key component of air pollution and a precursor to other air pollutants like particulate matter and ozone. To reduce the air pollution, it is crucial to identify the atmospheric NO sources. Measuring 15N natural abundance has been considered as a promising tool to identify different sources, but the measurement on δ15N for soil‐emitted NO is limited, adding to the large uncertainties on NO partitioning. Here we measured the δ15N‐NO emitted from three ecosystem types across seven sites (two agriculture, two forest, and three grassland sites) under defined anaerobic or aerobic conditions. We found that soil‐emitted NO was 15N‐depleted (−62‰ to −23‰) related to the source from fossil fuel combustion (0–20‰), suggesting that δ15N can be used to separate these two sources. We also found that the δ15N‐NO under aerobic condition (nitrification prevailing, −62‰ to −50‰) was much lower than under anaerobic condition (denitrification prevailing, −45‰ to −23‰), which provide a useful tool to better understand the relative contributions of different sources of NO. In sum, soil‐emitted NO has their own different isotope fingerprint, depending on the soil oxygen conditions, and can be used to partition sources. The δ15N‐NO from soil (−62‰ to −23‰) is different from fuel combustion (0‰ to 20‰), allowing effective source partitionThe δ15N‐NO produced under aerobic condition (favor nitrification) was more negative than under anaerobic condition (favor denitrification)The 15εfor NO production under aerobic condition (61 ± 3‰) was significantly higher than under anaerobic condition (35 ± 6‰)