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Background Globally plants are the primary sink of atmospheric CO2, but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important. Methodology We combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either 13CO2 to leaves or 13C-glucose to shoots via xylem uptake. The translocation of 13CO2 from the source to other plant parts could be traced by 13C-labeled isoprene and respiratory 13CO2 emission. Principal Finding In intact plants, assimilated 13CO2 was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h−1. 13C label was stored in the roots and partially reallocated to the plants' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76–78%) from recently fixed CO2, to a minor extent from xylem-transported sugars (7–11%) and from photosynthetic intermediates with slower turnover rates (8–11%). Conclusion We quantified the plants' C loss as respiratory CO2 and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux. [ABSTRACT FROM AUTHOR]

In plants, isoprene plays a dual role: (a) as thermo-protective agent proposed to prevent degradation of enzymes/membrane structures involved in photosynthesis, and (b) as reactive molecule reducing abiotic oxidative stress. The present work addresses the question whether suppression of isoprene emission interferes with genome wide transcription rates and metabolite fluxes in grey poplar ( Populus x canescens) throughout the growing season. Gene expression and metabolite profiles of isoprene emitting wild type plants and RNAi-mediated non-isoprene emitting poplars were compared by using poplar Affymetrix microarrays and non-targeted FT-ICR-MS (Fourier transform ion cyclotron resonance mass spectrometry). We observed a transcriptional down-regulation of genes encoding enzymes of phenylpropanoid regulatory and biosynthetic pathways, as well as distinct metabolic down-regulation of condensed tannins and anthocyanins, in non-isoprene emitting genotypes during July, when high temperature and light intensities possibly caused transient drought stress, as indicated by stomatal closure. Under these conditions leaves of non-isoprene emitting plants accumulated hydrogen peroxide (H2O2), a signaling molecule in stress response and negative regulator of anthocyanin biosynthesis. The absence of isoprene emission under high temperature and light stress resulted transiently in a new chemo(pheno)type with suppressed production of phenolic compounds. This may compromise inducible defenses and may render non-isoprene emitting poplars more susceptible to environmental stress. [ABSTRACT FROM AUTHOR]

In order to identify the effects of land-use/cover types, soil types and soil properties on the soil-atmosphere exchange of greenhouse gases (GHG) in semiarid grasslands as well as provide a reliable estimate of the midsummer GHG budget, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes of soil cores from 30 representative sites were determined in the upper Xilin River catchment in Inner Mongolia. The soil N2O emissions across all of the investigated sites ranged from 0.18 to 21.8 μg N m-2 h-1, with a mean of 3.4 μg N m-2 h-1 and a coefficient of variation (CV, which is given as a percentage ratio of one standard deviation to the mean) as large as 130%. CH4 fluxes ranged from -88.6 to 2,782.8 μg C m-2 h-1 (with a CV of 849%). Net CH4 emissions were only observed from cores taken from a marshland site, whereas all of the other 29 investigated sites showed net CH4 uptake (mean: -33.3 μg C m-2 h-1). CO2 emissions from all sites ranged from 3.6 to 109.3 mg C m-2 h-1, with a mean value of 37.4 mg C m-2 h-1 and a CV of 66%. Soil moisture primarily and positively regulated the spatial variability in N2O and CO2 emissions (R2 = 0.15–0.28, P < 0.05). The spatial variation of N2O emissions was also influenced by soil inorganic N contents ( P < 0.05). By simply up-scaling the site measurements by the various land-use/cover types to the entire catchment area (3,900 km2), the fluxes of N2O, CH4 and CO2 at the time of sampling (mid-summer 2007) were estimated at 29 t CO2-C-eq d-1, -26 t CO2-C-eq d-1 and 3,223 t C d-1, respectively. This suggests that, in terms of assessing the spatial variability of total GHG fluxes from the soils at a semiarid catchment/region, intensive studies may focus on CO2 exchange, which is dominating the global warming potential of midsummer soil-atmosphere GHG fluxes. In addition, average GHG fluxes in midsummer, weighted by the areal extent of these land-use/cover types in the region, were approximately -30.0 μg C m-2 h-1 for CH4, 2.4 μg N m-2 h-1 for N2O and 34.5 mg C m-2 h-1 for CO2. [ABSTRACT FROM AUTHOR]

In a lysimeter experiment with juvenile beech trees ( Fagus sylvatica L.) we studied the development of depth gradients of soil organic matter (SOM) composition and distribution after soil disturbance. The sampling scheme applied to the given soil layers (0–2 cm, 2–5 cm, 5–10 cm and 10–20 cm) was crucial to study the subtle reformation of SOM properties with depth in the artificially filled lysimeters. Due to the combination of physical SOM fractionation with the application of 15N-labelled beech litter and 13C-CPMAS NMR spectroscopy we were able to obtain a detailed view on vertical differentiation of SOM properties. Four years after soil disturbance a significant decrease of the mass of particulate OM (POM) with depth could be found. A clear depth distribution was also shown for carbon (C) and nitrogen (N) within the SOM fractions related to bulk soil. The mineral fractions <63 µm clearly dominated C storage (between 47 to 60% of bulk soil C) and N storage (between 68 to 86% of bulk soil N). A drastic increase in aliphatic C structures concomitant to decreasing O/N-alkyl C was detected with depth, increasing from free POM to occluded POM. Only a slight depth gradient was observed for 13C but a clear vertical incorporation of 15N from the applied labelled beech litter was demonstrated probably resulting from faunal and fungal incorporation. We clearly demonstrated a significant reformation of a SOM depth profile within a very short time of soil evolution. One important finding of this study is that especially in soils with reforming SOM depth gradients after land-use changes selective sampling of whole soil horizons can bias predictions of C and N dynamics as it overlooks a potential development of gradients of SOM properties on smaller scales. [ABSTRACT FROM AUTHOR]

• The aerobic formation of methane in plants has been reported previously, but has been questioned by a number of researchers. Recently, isotopic evidence demonstrated that ultraviolet irradiation and heating lead to photochemical or thermal aerobic methane formation mainly from plant pectin in the absence of microbial methane production. However, the origin of aerobic methane formation from plant material observed under low temperature and low-light/dark conditions is still unclear. • Here we show that Grey poplar ( Populus × canescens, syn. Populus tremula × Populus alba) plants derived from cell cultures under sterile conditions released 13C-labeled methane under low-light conditions after feeding the plants with 13CO2. • Molecular biological analysis proved the absence of any microbial contamination with known methanogenic microorganisms and ruled out the possibility that methane emission from our poplar shoot cultures under aerobic low-light/dark and ambient temperature conditions could be of microbial origin. • The CH4 release rates in our experiment were in the range of 0.16--0.7 ng g-1 DW h-1, adding evidence to the growing opinion that the quantitative role of aerobic methane emissions from plants in the global methane budget, at least from cold temperate or boreal regions, is only of minor importance. [ABSTRACT FROM AUTHOR]

• Soil respiration is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere. Here, we tested the hypothesis that photosynthesis affects the diurnal pattern of grassland soil-respired CO2 and its C isotope composition (δ13CSR). • A combined shading and pulse-labelling experiment was carried out in a mountain grassland. δ13CSR was monitored at a high time resolution with a tunable diode laser absorption spectrometer. • In unlabelled plots a diurnal pattern of δ13CSR was observed, which was not explained by soil temperature, moisture or flux rates and contained a component that was also independent of assimilate supply. In labelled plots δ13CSR reflected a rapid transfer and respiratory use of freshly plant-assimilated C and a diurnal shift in the predominant respiratory C source from recent (i.e. at least 1 d old) to fresh (i.e. photoassimilates produced on the same day). • We conclude that in grasslands the plant-derived substrates used for soil respiratory processes vary during the day, and that photosynthesis provides an important and immediate C source. These findings indicate a tight coupling in the plant–soil system and the importance of plant metabolism for soil CO2 fluxes. [ABSTRACT FROM AUTHOR]

The contribution of West African savanna ecosystems to global greenhouse gas budgets is highly uncertain. In this study we quantified soil-atmosphere CH[sub4] and CO[sub2] fluxes in the southwest of Burkina Faso from June to September 2005 and from April to September 2006 at four different agricultural fields planted with sorghum (ii = 2), cotton, and peanut and at a natural savanna site with termite (Cubiterrnesfungifaber) mounds. During the rainy season both CH[sub4] uptake and CH[sub4] emission were observed in the savanna, which was on average a Cl4 source of 2.79 and 2.28 kg CH[sub4]-C ha[sup-1] a1 in 2005 and 2006, respectively. The crop sites were an average CH[sub4] sink of -0.67 and -0.70 kg CH[sub4]-C ha[sup-1] a[sup-1] in the 2 years, without significant seasonal variation. Mean annual soil respiration ranged between 3.86 and 5.82 t CO[sub2]-C ha1 a[sup-1] in the savanna and between 2.50 and 4.51 t CO[sub2]-C ha1 a[sup-1] at the crop sites. CH[sub4] emission from termite mounds was 2 orders of magnitude higher than soil CH[sub4] emissions, whereas termite CO[sub2] emissions were of the same order of magnitude as soil CO[sub2] emissions. Termite CH[sub4] and CO[sub2] release in the savanna contributed 8.8% and 0.4% to the total soil CH[sub4] and CO[sub2] emissions, respectively. At the crop sites, where termite mounds had been almost completely removed because of land use change, termite fluxes were insignificant. Mound density-based upscaling of termite CH[sub4] fluxes resulted in a global termite CH[sub4] source of 0.9 Tg a[sup-1], which corresponds to 0.15% of the total global CH[sub4] budget of 582 Tg a[sup-1], hence significantly lower than those obtained previously by biomass-based calculations. This study emphasizes that land use change, which is of high relevance in this region, has particularly affected soil CH[sub4] fluxes in the past and might still do so in the future. [ABSTRACT FROM AUTHOR]

In a combined field and laboratory study in the southwest of Burkina Faso, we quantified soil-atmosphere N2O and NO exchange. N2O emissions were measured during two field campaigns throughout the growing seasons 2005 and 2006 at five different experimental sites, that is, a natural savanna site and four agricultural sites planted with sorghum ( n = 2), cotton and peanut. The agricultural fields were not irrigated and not fertilized. Although N2O exchange mostly fluctuated between −2 and 8 μg N2O–N m−2 h−1, peak N2O emissions of 10–35 μg N2O–N m−2 h−1 during the second half of June 2005, and up to 150 μg N2O–N m−2 h−1 at the onset of the rainy season 2006, were observed at the native savanna site, whereas the effect of the first rain event on N2O emissions at the crop sites was low or even not detectable. Additionally, a fertilizer experiment was conducted at a sorghum field that was divided into three plots receiving different amounts of N fertilizer (plot A: 140 kg N ha−1; plot B: 52.5 kg N ha−1; plot C: control). During the first 3 weeks after fertilization, only a minor increase in N2O emissions at the two fertilized plots was detected. After 24 days, however, N2O emission rates increased exponentially at plot A up to a mean of 80 μg N2O–N m−2 h−1, whereas daily mean values at plot B reached only 19 μg N2O–N m−2 h−1, whereas N2O flux rates at plot C remained unchanged. The calculated annual N2O emission of the nature reserve site amounted to 0.52 kg N2O–N ha−1 a−1 in 2005 and to 0.67 kg N2O–N ha−1 a−1 in 2006, whereas the calculated average annual N2O release of the crop sites was only 0.19 kg N2O–N ha−1 a−1 and 0.20 kg N2O–N ha−1 a−1 in 2005 and 2006, respectively. In a laboratory study, potential N2O and NO formation under different soil moisture regimes were determined. Single wetting of dry soil to medium soil water content with subsequent drying caused the highest increase in N2O and NO emissions with maximum fluxes occurring 1 day after wetting. The stimulating effect lasted for 3–4 days. A weaker stimulation of N2O and NO fluxes was detected during daily wetting of soil to medium water content, whereas no significant stimulating effect of single or daily wetting to high soil water content (>67% WHCmax) was observed. This study demonstrates that the impact of land-use change in West African savanna on N trace gas emissions is smaller—with the caveat that there could have been potentially higher N2O and NO emissions during the initial conversion—than the effect of timing and distribution of rainfall and of the likely increase in nitrogen fertilization in the future. [ABSTRACT FROM AUTHOR]

Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R. China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other. Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were in a range of 0.5–4.1 mg N kg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15% of the observed site differences in gross N turnover rates. N2O and NO x flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between plots. Mean values of N2O fluxes varied between 0.39 and 1.60 μg N2O-N m−2 h−1, equivalent to 0.03–0.14 kg N2O-N ha−1 y−1, and were considerably lower than previously reported for the same region. NO x flux rates ranged between 0.16 and 0.48 μg NO x -N m−2 h−1, equivalent to 0.01–0.04 kg NO x -N ha−1 y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only less than 20% of the flux variance. [ABSTRACT FROM AUTHOR]

Oaks emit large amounts of isoprene, a compound that plays an important role in tropospheric chemistry. Isopentenyl diphosphate isomerase (IDI, E.C. 5.3.3.2) catalyzes the isomerization of isopentenyl diphosphate (IDP) to dimethylallyl diphosphate (DMADP), and in isoprene-emitting plants, isoprene synthase (IS) converts the DMADP to isoprene. To study the role of IDI in isoprene biosynthesis of oak leaves, we compared IDI and IS activities in pedunculate oak (Quercus robur L.) and pubescent oak (Quercus pubescens Willd.) with the isoprene emission rates of these species. We developed a non-radioactive enzyme assay to detect IDI activity in crude leaf extracts of Q. robur. The substrate dependency of IDI activity showed biphasic kinetics with Michaelis constants (Km(IDP)) of 0.7 ± 0.2 μM for a high-affinity phase and 39.5 ± 6.9 μM for a low-affinity phase, potentially attributable to different IDI isoforms. Under standard assay conditions, the temperature optimum for IDI activity was about 42 °C, but IDI activity was detectable up to 60 °C. A sharp pH optimum appeared around pH 7, with 20 mM Mg2+ also required for IDI activity. Neither IDI activity nor IS activity showed diurnal variation in Q. robur leaves. The sum of IDI activities showed a significant linear correlation with IS activity in both Q. robur and Q. pubescens leaves, and both enzyme activities showed a linear relationship to isoprene emission factors in leaves of these oak species, indicating the possible involvement of IDI in isoprene biosynthesis by oak leaves. [ABSTRACT FROM PUBLISHER]

Soil water sustains terrestrial life, yet its fate is uncertain under a changing climate. We conducted a deuterium labeling experiment to determine whether elevated atmospheric carbon dioxide (CO2), warming, and drought impact soil water storage and transport in a temperate grassland. Elevated CO2 created a wetter rootzone compared with ambient conditions, whereas warming decreased soil moisture. Soil water remained well mixed in all global change treatments except for summer drought combined with warming and elevated CO2. These combined treatments caused the grassland to conserve water and restricted soil water flow to large, rapidly draining pores without mixing with small, slowly draining pores. Our results suggest that drought in a warmer, more CO2-rich climate can severely alter grassland ecohydrology by constraining postdrought soil water flow and grassland water use. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Winter wheat is one of the most important crops in the world. Microplastics, as an emerging pollutant, are widespread in agricultural soils due to various modern agricultural practices and can have adverse impacts on agricultural soils and plant growth. Herein, we investigated the effects of 10 types of microplastics on the properties of three agricultural soil types and the growth of winter wheat. This study contributes insights toward the conservation of agricultural soils and potential wheat yield responses to microplastic. Understanding the mechanisms that underpin the differences in responses to this pollutant class is of great importance for management recommendations. Summary: Microplastics (MPs) (size < 5 mm) are increasingly recognized as anthropogenic contaminants that severely affect terrestrial ecosystems. These particles are always detected as a mixture of various polymer types and shapes. However, we have limited knowledge of the effect of combined MPs on plant–soil systems.To address this, we selected 10 types of MP, applied to three soil types singly and in combination along an increasing gradient of 1, 2, 5, 8, and 10 MP types at a content of 0.4% (w/v). After 8 weeks of pre‐incubation, winter wheat (TOBAK) was grown in each pot for another 8 weeks. Shoot and root biomass, soil aggregation, and carbon and nitrogen content were measured.The effects of the same MP on both soil and plant properties were drastically different (in size and effect direction) in the different soil types. However, no clear patterns were observed along an increasing number of microplastic types, suggesting that knowing the number of microplastic types in a sample, at equity of overall concentration, does not help predict effects.In contrast, our findings reveal the complex effects of multiple MPs on the soil–plant system and highlight that soil properties need to be taken into consideration when studying MP effects on terrestrial systems. [ABSTRACT FROM AUTHOR]

Aims: Successive winter wheat (WW) rotations are associated with yield reduction, often attributed to the unfavorable soil microbes that persist in the soil through plant residues. How rotational positions of WW affect the allocation of freshly assimilated carbon (C), an energy source for soil microbes, above and belowground remains largely unknown. Methods: A 13CO2 pulse labeling rhizotron experiment was conducted in the greenhouse to study freshly fixed C allocation patterns. WW was grown in soil after oilseed rape (W1), after one season of WW (W2), and after three successive seasons of WW (W4). We used an automatic manifold system to measure excess 13C of soil respiration at six depths and five different dates. Excess 13C was also measured in dissolved organic C (DOC), microbial and plant biomass pools. Results: There was a strong yield decline in successive WW rotations accompanied by distinct changes in root growth. Higher excess 13C of soil respiration was measured in W1 compared to W4, especially in the topsoil during at later growth stages. Higher excess 13C of the DOC and the microbial biomass was also traced in W1 and W4 compared to W2. Less 13C was taken up by successive WW rotations. Conclusions: Our study demonstrates a mechanism through which the rotational position of WW affects the allocation of freshly assimilated C above and belowground. WW after oilseed rape sustains belowground allocation of freshly assimilated C for a longer time than successively grown WW and incorporates more of this C to its biomass. [ABSTRACT FROM AUTHOR]

Incorporation of soil amendments with high organic carbon content (HCA) can reduce losses of mineral nitrogen (N) from agricultural soils. The magnitude of N immobilization and remobilization is strongly controlled by the availability of carbon (C) and phosphorus (P). However, the exact mechanisms and interactions between C, N, and P availability are poorly understood. An eight-month incubation experiment was conducted on recultivated mine soil with low organic C, mineral N and P background concentrations to investigate the effects of HCA in combination with 13C-labelled glucose and mineral P fertilization on greenhouse gas emissions, soil nutrient status (dissolved organic C (DOC), nitrate (NO3–), extractable P), and microbial biomass growth. The experiment had a factorial design of one N level × two P levels × six C treatments (control, wheat straw, poplar sawdust, glucose, and combinations of wheat straw or sawdust with glucose). The HCA increased the cumulative CO2 and CH4 emissions but decreased N2O emission, except for wheat straw. Addition of 13C-labelled glucose decreased the cumulative CH4 emission by 59 and 85 % in the sawdust and sawdust + P treatment, respectively. Glucose application reduced the NO3– content in the HCA-amended soil by 26–64 %, while P fertilizer further decreased the NO3– content in the wheat straw and sawdust treatments by 20 and 24 %, respectively. Both HCA and glucose treatments promoted microbial biomass growth and reduced the soil mineral N content. The δ13C of microbial biomass (δ13CMB) showed an increasing trend during the whole experiment, although 13C-labelled glucose was added only once at the beginning of the experiment. Addition of HCA decreased δ13CMB, while P addition had the opposite effect. In conclusion, adding a readily available C source to HCA may increase the efficacy of retaining N in post-harvest soils, particularly of more recalcitrant types of HCA like sawdust. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a key substance in atmospheric chemistry, influencing the formation and destruction of tropospheric ozone and the atmosphere's oxidizing capacity. It also affects the physiological functions of organisms. NO is produced, consumed, and emitted by soils, the effects of soil NO concentrations on microbial C and N cycling and associated trace gas fluxes remain largely unclear. This study describes a new automated 12-chamber soil mesocosm system that dynamically changes incoming airflow composition. It was used to investigate how varying NO concentrations affect soil microbial C and N cycling and associated trace gas fluxes under different moisture conditions (30% and 50% WFPS). Based on detection limits for NO, NO2, N2O, and CH4 fluxes of < 0.5 µg N or C m−2 h−1 and for CO2 fluxes of < 1.2 mg C m−2 h−1, we found that soil CO2, CH4, NO, NO2, and N2O were significantly affected by different soil moisture levels. After 17 days cumulative fluxes at 50% WFPS increased by 40, 400, and 500% for CO2, N2O, and CH4, respectively, when compared to 30% WFPS. However, cumulative fluxes for NO, and NO2, decreased by 70, and 40%, respectively, at 50% WFPS when compared to 30% WFPS. Different NO concentrations tended to decrease soil C and N fluxes by about 10–20%. However, with the observed variability among individual soil mesocosms and minor fluxes change. In conclusion, the developed system effectively investigates how and to what extent soil NO concentrations affect soil processes and potential plant–microbe interactions in the rhizosphere. [ABSTRACT FROM AUTHOR]

A tef-Acacia decurrens-charcoal production rotation system, a unique indigenous climate-smart agricultural technology of northwest Ethiopia, is increasingly seen as a promising strategy for improving soil properties. This study investigated the effect of the tef-Acacia decurrens-charcoal production rotation system on soil properties. In total, 112 soil samples (7 treatments × 4 depths × 4 replicates) were collected and analyzed inside and outside randomly selected charcoal production spots in the tef-Acacia decurrens-charcoal production rotation system and from an adjacent tef monocropping system. The soil properties examined generally exhibited significant variation between the tef monocropping system and the tef-Acacia decurrens-charcoal production rotation system, and between soil depths, as well as with respect to charcoal production spots in the system. The system resulted in a significant increase in SOC, TN, available phosphorus, available sodium, available nitrate and ammonium in general, and in total contents of K, P and Mn in the 0–20 cm depth. Charcoal production in the system significantly increased the total content of P, Al, and Fe, as well as the available nitrate and sulfate in the charcoal production spot. The variation in soil proprieties between the land use types and with respect to charcoal production spots in the TACP system were possibly due to the effect of the Acacia decurrens trees, and fire and fine charcoal residues from charcoal production, indicating the capacity of the tef-Acacia decurrens-charcoal production rotation system to improve soil properties. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) and nitric oxide (NO) are atmospheric trace gases that contribute to climate change and affect stratospheric and ground-level ozone concentrations. Ammonia oxidizing bacteria (AOB) and archaea (AOA) are key players in the nitrogen cycle and major producers of N2O and NO globally. However, nothing is known about N2O and NO production by the recently discovered and widely distributed complete ammonia oxidizers (comammox). Here, we show that the comammox bacterium Nitrospira inopinata is sensitive to inhibition by an NO scavenger, cannot denitrify to N2O, and emits N2O at levels that are comparable to AOA but much lower than AOB. Furthermore, we demonstrate that N2O formed by N. inopinata formed under varying oxygen regimes originates from abiotic conversion of hydroxylamine. Our findings indicate that comammox microbes may produce less N2O during nitrification than AOB. Ammonia-oxidizing bacteria and archaea are major producers of the gases nitrous oxide and nitric oxide. Here, Kits et al. show that a complete ammonia-oxidizing (comammox) bacterium emits nitrous oxide at levels that are comparable to those produced by ammonia-oxidizing archaea. [ABSTRACT FROM AUTHOR]

Gas exchange in the soil is determined by the size and connectivity of air‐filled pores. Root mucilage reduces air‐filled pore connectivity and thus gas diffusivity. It is unclear to what extent mucilage affects soil pore connectivity and tortuosity. The aim of this study was to gain a better understanding of gas diffusion processes in the rhizosphere by explaining the geometric alterations of the soil pore space induced by mucilage. We quantified the effect of a root mucilage analogue collected from chia seeds without intrinsic respiratory activity on oxygen diffusion at different water contents during drying–rewetting cycles in a diffusion chamber experiment. Quantification of oxygen diffusion showed that mucilage decreased the gas diffusion coefficient in dry soil without affecting air‐filled porosity. Without mucilage, a hysteresis in gas diffusion coefficient during a drying–rewetting cycle was observed. The effect depended on particle size and diminished with increasing mucilage content. X‐ray computed tomography imaging indicated a hysteresis in the connectivity of the gas phase during a drying–rewetting cycle for samples without mucilage. This effect was attenuated with increasing mucilage content. Furthermore, electron microscopy showed that mucilage structures formed in drying soil increase with mucilage content, thereby progressively reducing the connectivity of the gas phase. In conclusion, the effect of mucilage on soil gas diffusion highly depends on soil texture and mucilage content. The diminishing hysteresis with the addition of mucilage suggests that plant roots secrete mucilage to balance oxygen availability and water content, even under fluctuating moisture conditions. [ABSTRACT FROM AUTHOR]

In light of climate change and increasing global temperatures, it is important to equally prioritize the study of inorganic carbon dynamics in calcareous soils within temperate ecosystems, as has been done for arid or semiarid environments. A significant area of vineyards in Germany is established on calcareous soils. However, the potential influence of inorganic carbon on CO2 emissions in these vineyards has not been sufficiently explored when evaluating the carbon footprint of management practices in relation to carbon storage. Therefore, we aimed to differentiate between organic and inorganic sources of CO2 emissions from six vineyard soils located in the southwest of Germany that had previously received organic soil amendments (OA). Inorganic carbon content varied between 8 and 55 g kg−1 across different sites, with variations observed in the inorganic‐to‐organic carbon ratio. Soil samples were incubated under standard laboratory conditions for 48 h, and the source of emitted CO2 was determined using a two‐end‐member mixing model. The contribution of inorganic carbon to CO2 emissions was influenced by the quantity of inorganic carbon, with an increase in contribution with increasing inorganic‐to‐organic carbon ratio. On average, abiotic sources accounted for 5% to 40% of the emitted CO2 at the different sites, with one site showing no significant contribution of inorganic carbon. CO2 production from inorganic carbon was higher in the subsoil compared with the topsoil, likely related to the higher content of inorganic carbon in the subsoil. Notably, there was no discernible influence of OA on carbonate dissolution. This study emphasizes the significance of considering abiotic sources of CO2 emissions in addition to soil respiration in calcareous soils and highlights the need for further investigation to apply these findings at the field scale. [ABSTRACT FROM AUTHOR]

Summary: Root water uptake is a key ecohydrological process for which a physically based understanding has been developed in the past decades. However, due to methodological constraints, knowledge gaps remain about the plastic response of whole plant root systems to a rapidly changing environment.We designed a laboratory system for nondestructive monitoring of stable isotopic composition in plant transpiration of a herbaceous species (Centaurea jacea) and of soil water across depths, taking advantage of newly developed in situ methods. Daily root water uptake profiles were obtained using a statistical Bayesian multisource mixing model.Fast shifts in the isotopic composition of both soil and transpiration water could be observed with the setup and translated into dynamic and pronounced shifts of the root water uptake profile, even in well watered conditions.The incorporation of plant physiological and soil physical information into statistical modelling improved the model output. A simple exercise of water balance closure underlined the nonunique relationship between root water uptake profile on the one hand, and water content and root distribution profiles on the other, illustrating the continuous adaption of the plant water uptake as a function of its root hydraulic architecture and soil water availability during the experiment. [ABSTRACT FROM AUTHOR]

Chemodenitrification can be a substantial abiotic source of nitrous oxide (N 2 O) in soil. The isotopic signature of N 2 O from this process could support source partitioning, but it is currently unknown in sufficient detail. In this study, we determined the isotopic composition of N 2 O, produced by the reaction of nitrite (NO 2 −) with lignin, four lignin derivatives, and three types of soils, online with a quantum cascade laser absorption spectrometer (QCLAS). We present the first dataset of continuous measurements of δ15Nbulk (δ15Nbulk ≡ (δ15Nα + δ15Nβ)/2), δ18O, and site preference (SP N2O , SP N2O ≡ δ15Nα − δ15Nβ) of N 2 O from chemodenitrification in both chemical assays and soils. Considerable amounts of N 2 O were produced by chemical reduction of NO 2 −, indicating that chemodenitrification could dominate N 2 O emission in NO 2 −-rich environments. The values of SP N2O varied by more than 20‰ in the reactions of sodium nitrite with organic substances. Contrary to the common assumption that SP N2O values are constant for a distinct N 2 O source process, our results reveal a considerable shift in SP N2O over time for most experiments. The large SP N2O variability might be explained by the multiple pathways with hyponitrous acid or nitramide as N 2 O precursors. These findings provide important new information to improve our understanding about the dependency of N 2 O isotopic signatures on N 2 O production processes. [ABSTRACT FROM AUTHOR]

Abiotic conversion of the reactive nitrification intermediate hydroxylamine (NH2OH) to nitrous oxide (N2O) is a possible mechanism of N2O formation during nitrification. Previous research has demonstrated that manganese dioxide (MnO2) and organic matter (OM) content of soil as well as soil pH are important control variables of N2O formation in the soil. But until now, their combined effect on abiotic N2O formation from NH2OH has not been quantified. Here, we present results from a full-factorial experiment with artificial soil mixtures at five different levels of pH, MnO2 and OM, respectively, and quantified the interactive effects of the three variables on the NH2OH-to-N2O conversion ratio (RNH2OH-to-N2O). Furthermore, the effect of OM quality on RNH2OH-to-N2O was determined by the addition of four different organic materials with different C/N ratios to the artificial soil mixtures. The experiments revealed a strong interactive effect of soil pH, MnO2 and OM on RNH2OH-to-N2O. In general, increasing MnO2 and decreasing pH increased RNH2OH-to-N2O, while increasing OM content was associated with a decrease in RNH2OH-to-N2O. Organic matter quality also affected RNH2OH-to-N2O. However, this effect was not a function of C/N ratio, but was rather related to differences in the dominating functional groups between the different organic materials. [ABSTRACT FROM AUTHOR]

Soil microbial nitrate (NO3−) immobilization plays a vital role in enhancing the nitrogen (N) retention in the subtropical montane agricultural landscapes. However, how and why the potential microbial NO3− immobilization and the relative contribution of fungi and bacteria vary across different land use types remain still unclear in the subtropical mosaic montane agricultural landscapes. Thus, in the present study, soil gross microbial NO3− immobilization rates as well as the respective contribution of fungi and bacteria were determined throughout the whole soil profiles for three land use types (woodland, orchard, and cropland) by using the 15N tracing and amino sugar–based stable isotope probing (Amino sugars-SIP) techniques. The soil gross microbial NO3− immobilization rates in woodland soils were significantly higher than those in cropland and orchard soils across different soil layers (p < 0.05), and those of topsoil were significantly higher than those for subsoils (e.g., 20–40 cm) across different land use types (p < 0.05). Soil microbial biomass C (MBC) and N (MBN), organic C (SOC), total N (TN), and dissolved organic C (DOC) contents and C/N ratios were closely associated to gross microbial NO3− immobilization rates. Fungi played a greater role than bacteria in immobilizing soil NO3− in woodland and orchard soils, but the opposite occurred in cropland soils that over 85% of the variations in fungal and bacterial NO3− immobilization rates could be explained by their respective phospholipid fatty acid–derived (PLFA-derived) biomass. The present study indicated that afforestation may be effective to enhance soil NO3− retention in alkaline soils, thereby likely decreasing the risk of NO3− losses in subtropical mosaic montane agricultural landscapes through enhancing the soil NO3− immobilization by both fungi and bacteria. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi provide a range of functions in natural and managed ecosystems. However, the trajectory of AM fungal diversity after land degradation is poorly known. We studied the succession of AM fungi along an agricultural recultivation chronosequence after open-cast mining near Cologne, Germany. We used high-throughput sequencing of the large-subunit ribosomal RNA genes to characterize the soil AM fungal communities of 10 agricultural fields spanning 52 years of recultivation. During three years, soils are recultivated with a legume, and then converted to agriculture to be later returned to local farmers implementing conventional agriculture. Our data reveal a quick and strong recovery of AM fungal richness after a few years of recultivation, but also a rapid decline following years of conventional agriculture. The community structure was strongly correlated to mineral nitrogen and phosphorus, richness peaking at high N:P ratio. This work represents the first molecular data documenting temporal patterns of AM fungal communities in agriculture; it shows the deleterious effect of conventional agricultural practices on AM fungal communities developing over time. Nonetheless, the highly dynamic nature of AM fungal communities suggests strategies for site-level management for which considering N:P stoichiometry is crucial. [ABSTRACT FROM AUTHOR]

Balancing the nitrogen (N) budgets of agricultural systems is essential for sustaining yields at lower environmental costs. However, it is still rare to find reports on the total N budgets of agricultural systems including all N fluxes in the literature. Here, we conducted a comprehensive study on the effects of different N fertilizers (control, synthetic fertilizer, 60% synthetic fertilizer N plus 40% pig manure N, pig manure N applied at the same rate of 280 kg N ha −1 yr −1 ) on N pools, cycling processes, fluxes and total N balances in a subtropical wheat-maize rotation system in China by monitoring in situ N fluxes combined with field 15 N-tracer and 15 N isotope-dilution techniques. The warm and wet maize season was associated with significantly larger N losses via gaseous and hydrological pathways than the cooler and drier wheat season. Nitrate leaching and NH 3 volatilization were the main N loss pathways, accounting for 78% and 93% of the annual hydrological and gaseous N losses, respectively. The field 15 N tracing experiment showed that the wheat system had a high N retention capacity (∼50% of 15 N application), although the N residence time was short. In the subsequent maize season, 90% of the residual 15 N-labeled fertilizer in the soil that had been applied to the wheat system was utilized by plants or lost to the environment. The combined application of synthetic and organic fertilizers (pig manure) or application of pig manure resulted in significantly higher soil N retention and lower NO 3 − leaching, while yields remained unaffected. However, the application of manure resulted in larger NH 3 volatilization losses compared with the application of synthetic fertilizer alone. Thus, our study suggests that a combination of synthetic and organic N fertilizers is suitable for sustaining agricultural productivity while reducing environmental N losses by fostering interactions between the soil C and N cycles. [ABSTRACT FROM AUTHOR]

In alpine zones, soil microbial biomass and activity are strongly dependent on the seasonal snow cover. Current models assume that microbial biomass reaches an annual peak in winter under the insulating snowpack with a subsequent sharp decline during snowmelt. In this study, we investigated the seasonal dynamics of the soil microbial biomass in the Central Alps, where usually early snowfall buffers winter soil temperatures. We conducted a large-scale survey in three mountains around Davos (Switzerland) along altitudinal gradients from approximately 1900 to 2800 m above sea level. Using a space-for-time approach during snowmelt, soil samples were taken (1) under, (2) at the edge of, and (3) one meter away from remaining snow patches. One additional sample per site was taken in summer to further evaluate the seasonal dynamics. In total, 184 soil samples from 46 different sites were analyzed. We measured microbial biomass C and N, enzymatic activity and dissolved C and N. We observed an increase of microbial biomass and dissolved C during and immediately after snowmelt, as well as an increase from spring to summer. We suggest that the absence of soil freezing in winter and the growing amounts of dissolved C supported a continued growth, without a sudden collapse of the microbial biomass. Our results underline the importance of the insulating effect of the seasonal snow cover for the microbial dynamics. Global warming is modifying the timing and abundance of the seasonal snow cover, and our results will help to refine models for the dynamics of soil microbes in alpine ecosystems. [ABSTRACT FROM AUTHOR]

Aims: We aimed at assessing the influence of above- and below-ground environmental conditions over the performance of Centaurea jacea L., a drought-resistant grassland forb species. Methods: Transpiration rate, CO2 assimilation rate, leaf water potential, instantaneous and intrinsic water use efficiency, temperature, relative humidity, vapor pressure deficit and soil water content in one plant and root length density in four plants, all grown in custom-made columns, were monitored daily for 87 days in the lab. The soil water isotopic composition in eleven depths was recorded daily in a non-destructive manner. The isotopic composition of plant transpiration was inferred from gas chamber measurements. Vertical isotopic gradients in the soil column were created by adding labeled water. Daily root water uptake (RWU) profiles were computed using the multi-source mixing model Stable Isotope Analysis in R (Parnell et al. PLoS ONE 5(3):1–5, 2010). Results: RWU occurred mainly in soil layer 0–15 cm, ranging from 79 to 44%, even when water was more easily available in deeper layers. In wet soil, the transpiration rate was driven mainly by vapor pressure deficit and light intensity. Once soil water content was less than 0.12 cm3 cm− 3, the computed canopy conductance declined, which restricted leaf gas exchange. Leaf water potential dropped steeply to around − 3 MPa after soil water content was below 0.10 cm3 cm− 3. Conclusion: Our comprehensive data set contributes to a better understanding of the effects of drought on a grassland species and the limits of its acclimation in dry conditions. [ABSTRACT FROM AUTHOR]

Fertilizer nitrogen (N) application has been shown to impact both methane (CH 4 ) and nitrous oxide (N 2 O) emissions from rice-based crop systems, yet the responses of CH 4 and N 2 O fluxes to N fertilizer applications in subtropical rice–rapeseed rotation systems are not well documented. A three-year field experiment was conducted to simultaneously measure the fluxes of CH 4 and N 2 O from a subtropical rice–rapeseed rotation system under three N fertilization treatments (control with no N fertilizer addition [CK], optimized N fertilizer management practice in accordance with the recommended N fertilizer application rate of 150 kg N ha −1 season −1 [OP], local farmers common N fertilizer management practice with 250 kg N ha −1 season −1 [CP]) in southwestern China. Results showed great intra- and inter-annual variations in CH 4 and N 2 O emissions along with the temporal variations of environmental conditions, emphasizing the necessity of multi-year measurements to achieve representative estimates. Nitrogen fertilization tended to increase N 2 O emissions and to inhibit CH 4 emissions. The direct N 2 O emission factors (EF d ) for the rice systems (mean: 0.99%) were higher than those for the rapeseed systems (mean: 0.71%). In addition, the rice-growing season dominated annual CH 4 emissions (>97%), which on average represented 87% of the annual total global warming potential (GWP) of CH 4 and N 2 O emissions across experimental treatments and years. Linking total GWP of CH 4 and N 2 O emissions with grain yields, the average annual yield-scaled GWP for the control (1467 kg CO 2 -eq Mg −1 grain) was significantly higher than for the OP (700 kg CO 2 -eq Mg −1 grain) and CP (682 kg CO 2 -eq Mg −1 grain) treatments ( P < 0.05). Given the comparable area- and yield-scaled GWP between the CP and OP treatments, the OP treatment reduced local farmers’ common N fertilizer application rate by 40% and tended to maintain crop grain yields, however it also reduced N surplus and off-site N losses in the subtropical rice–rapeseed rotation systems of southwestern China. [ABSTRACT FROM AUTHOR]

Soil water status, which refers to the wetness or dryness of soils, is crucial for the productivity of agroecosystems, as it determines nutrient cycling and uptake physically via transport, biologically via the moisture‐dependent activity of soil flora, fauna, and plants, and chemically via specific hydrolyses and redox reactions. Here, we focus on the dynamics of nitrogen (N), phosphorus (P), and sulfur (S) and review how soil water is coupled to the cycling of these elements and related stoichiometric controls across different scales within agroecosystems. These scales span processes at the molecular level, where nutrients and water are consumed, to processes in the soil pore system, within a soil profile and across the landscape. We highlight that with increasing mobility of the nutrients in water, water‐based nutrient flux may alleviate or even exacerbate imbalances in nutrient supply within soils, for example, by transport of mobile nutrients towards previously depleted microsites (alleviating imbalances), or by selective loss of mobile nutrients from microsites (increasing imbalances). These imbalances can be modulated by biological activity, especially by fungal hyphae and roots, which contribute to nutrient redistribution within soils, and which are themselves dependent on specific, optimal water availability. At larger scales, such small‐scale effects converge with nutrient inputs from atmospheric (wet deposition) or nonlocal sources and with nutrient losses from the soil system towards aquifers. Hence, water acts as a major control in nutrient cycling across scales in agroecosystems and may either exacerbate or remove spatial disparities in the availability of the individual nutrients (N, P, S) required for biological activity. [ABSTRACT FROM AUTHOR]

Rationale: Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (Ni) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze δ15N in NO3− and NH4+ and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. Methods: Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure δ15N in NO3− and NH4+. The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms Ni to either N2O (CM‐N2O) or N2 (CM‐N2), and (c) the denitrifier (DN) methods. Results: The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM‐N2O performing superior for both NO3− and NH4+, followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM‐N2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%15N of Ni of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to ± 8.4‰ for NO3− and ± 32.9‰ for NH4+; SDs within laboratories were found to be considerably lower (on average 3.1‰). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered. Conclusions: The inconsistency among all methods and laboratories raises concern about reported δ15N values particularly from environmental samples. [ABSTRACT FROM AUTHOR]

Global annual coal consumption may reach 8038 Mt. in 2025, resulting in continuous post-coal minesoils creation. In Brazil, the Candiota Mine represents the largest country's coal reserves and originates minesoils with high acidity, compaction, and depletion of organic carbon content and soil biological attributes, hindering the re-establishment of vegetation, mesofauna and microbial activity. This study aimed to assess mesofauna attributes and microbial activity in a minesoil restored for 14.6 years with perennial grasses in Candiota, and to explore their relationships with soil physical, chemical, and humus properties. Our previous research showed that Urochloa brizantha improved soil physical and chemical attributes more effectively than other grasses, suggesting stronger links between soil biology and these properties in this treatment. After 14.6 years of revegetation with Hemarthria altissima , Cynodon dactylon , Panicum maximum , Urochloa humidicola , and U. brizantha a series of minesoil biological, chemical and physical attributes (0.00–0.10 m layer) were assessed. Control site consisted of minesoil with spontaneous vegetation. U. brizantha treatment exhibited significantly lower bulk density (1.2 Mg m−3) and higher macroporosity (0.16 m3 m−3) and total porosity (0.48 m3 m−3) compared to C. dactylon (1.4 Mg m−3, 0.07 and 0.40 m3 m−3, respectively). Treatments did not differ regarding total carbon and carbon content in humic fractions, but mostly increased it compared to control. The total number of fauna individuals across treatments ranged from 596 (P. maximum) to 1146 (U. brizantha) at the litter-soil interface and from 1305 (H. altissima) to 2397 (U. brizantha) in the minesoil. In the control these numbers were lower (539 and 483, respectively). Mites and springtails predominated in all treatments at both litter-soil interface (34–50 % and 36–44 %, respectively) and minesoil (76–85 % and 9–17 %, respectively). Treatments did not differ regarding fauna diversity. Axis 1 and 2 of canonical correspondence analysis (CCA) explained 51 and 45 % of data set variability, respectively. Moreover, CCA revealed that interrelations of fauna and microbial biomass carbon with other soil attributes were unspecific for grass species, contradicting our hypothesis. Despite the outstanding performance of U. brizantha to ameliorate physical soil attributes, further research is required before one grass species is prioritized for restoration of minesoil ecological functions. [ABSTRACT FROM AUTHOR]

Plant-soil feedbacks drive productivity in winter wheat (WW; Triticum aestivum L.) rotations. Although this is a frequent observation, the underlying plant-soil-microbe interactions remain unclear. We aimed to investigate the effects of WW rotational positions on soil bacterial and archaeal communities, as well as nitrogen (N) cycling, as potential drivers of WW yield decline in successively-grown WW. WW following oilseed rape (W1; Brassica napus L.) was compared with WW in self-succession (W2) in a rhizotron study using agricultural soil with a sandy loam texture. Samples were collected at tillering and grain ripening. At tillering, we found a higher NO 3 − content in W1 soil, especially in the 60–100 cm subsoil layer, associated with the N-rich residues of the preceding oilseed rape crop, while this trend was reversed at grain ripening. Analysis of enzyme kinetics revealed an increase in leucine aminopeptidase activity in W1 and an increase in β-glucosidase activity in W2 at tillering, possibly related to the residue quality of the preceding crop. No differences in bacterial and archaeal alpha diversity were observed at both sampling times, but beta diversity showed a significant role of both rotational position and soil depth in shaping the microbial community. The gene copy numbers of amoA genes of ammonia-oxidizing bacteria (AOB), nifH and nirS were significantly higher in W2 compared to W1 at tillering, suggesting a strong effect of rotational position on N cycling of the following WW. The abundances of amoA (AOB) and nirS were also higher in W2 at grain ripening. Our results highlight the persistent soil legacy of the preceding crop on both nutrient cycling and bacterial and archaeal community composition, contributing to yield reduction in successively grown WW. Understanding plant-microbe interactions and keeping them at the center of productive WW rotations is, and will continue to be, critical to future agriculture. • Self-succession of winter wheat (WW) results in a pronounced yield decline. • The soil legacy of oilseed rape creates a long-lasting beneficial effect on the growth of the following WW. • Lower NO 3 − in the subsoil of successively grown WW at tillering creates a disadvantage for later growth. • WW rotations shape the bacterial and archaeal community in response to soil nitrogen dynamics. [ABSTRACT FROM AUTHOR]

Hydroxylamine (HA) is a crucial intermediate in the first step of nitrification, i.e., the oxidation of ammonium to nitrite. Due to its reactivity, HA may play a key role in soil N2O emission. To determine soil HA concentrations and to explore the correlation between soil HA concentrations and N2O emission rates, we developed a novel, extremely sensitive method based on fast extraction of HA from the soil at pH1.7, oxidation of HA to N2O with Fe3+ and analysis of the N2O with gas chromatography (GC). The new method was tested on soil samples from a temperate Norway spruce forest, comparing soil HA concentrations with N2O emission rates determined with microincubations of the soil samples in GC vials. Our results demonstrate that the new GC method is extremely sensitive, being able to detect soil HA contents as low as 0.3 μg N kg-1 dry soil. HA content in the forest soil samples ranged between 0.3 and 34.8 μg N kg-1 dry soil. Moreover, N2O emission rates were significantly correlated with soil HA content (r²=0.80), suggesting a key role of HA in N2O formation under aerobic conditions. [ABSTRACT FROM AUTHOR]

Efficient nitrous oxide (N2O) mitigation strategies require the identification of the main source and sink processes and their contribution to total soil N2O production. Several abiotic reactions of nitrification intermediates leading to N2O production are known, but their contribution to total N2O production in soils is uncertain. As the site preference (SP) of 15N in N2O is a promising tool to give more insight into N2O production processes, we investigated the SP of N2O produced by different abiotic reactions in a laboratory study. All reactions involved the nitrification intermediate hydroxylamine (NH2OH) in combination with nitrite (NO2-), Fe3+, Fe2+ and Cu2+, reactants commonly or potentially found in soils, at different concentrations and pH values. N2O production and its four main isotopic species (14N14N16O, 15N14N16O, 14N15N16O, and 14N14N18O) were quantified simultaneously and online at high temporal resolution using quantum cascade laser absorption spectroscopy. Thereby, our study presents the first continuous analysis of δ18O in N2O. The experiments revealed the possibility of purely abiotic reactions over a wide range of acidity (pH 3-8) by different mechanisms. All studied abiotic pathways produced N2O with a characteristic SP in the range of 34-35‰, unaffected by process conditions and remaining constant over the course of the experiments. These findings reflect the benefit of continuous N2O isotopic analysis by laser spectroscopy, contribute new information to the challenging source partitioning of N2O emissions from soils, and emphasize the potentially significant role of coupled biotic-abiotic reactions in soils. [ABSTRACT FROM AUTHOR]

Space-for-time substitution, also known as pseudo chronosequence (PCS), is often used as a method to assess temporal changes in ecosystems without having to wait for the time span that the study is supposed to cover. However, the suitability of PCS studies is often questioned because convergent development of spatially separated plots over time is rarely guaranteed even under optimal conditions. To assess whether the PCS approach is justified and suitable, we studied the nematode soil food web development of free-living nematodes and biological and chemical soil components related to C and N mobilization (CO 2 and NO 3 -) and immobilization (microbial and soil organic carbon), in a PCS focusing on the critical early reclamation period of four years after open-cast lignite mining, and compared it with a real chronosequence (RCS) of a reclamation site monitored over four years. We hypothesized that: (I) nematode-derived indices indicate the same course of nematode soil food web development in the PCS and RCS, tolerating a range of variability in weather conditions, soil components, and management; (II) the development of nematode soil food web indicators can provide information on the status of C and N retention and cycling in the reclaimed soil. Our results show that the PCS and RCS approaches reach similar conclusions, indicating a rapidly developing nematode soil food web during the first four years after reclamation. They also suggest that the nematode faunal profile may indicate the status of C and N retention and cycling in reclaimed soil. Overall, it can be concluded that the PCS approach successfully predicts the temporal development of the nematode soil food web in loess-dominated reclaimed mining soils, even when there is a range of variability in soil components and management conditions. • Pseudo and real chronosequence showed similar food web developments in reclaimed soil. • Chronosequence conclusions were not confounded by natural and management variation. • Nematode faunal profile may indicate C and N retention and cycling status in reclaimed soil. [ABSTRACT FROM AUTHOR]

In northwestern Ethiopia, a conventional teff (Eragrostis tef (Zucc.) Trotter) monoculture was converted into a rotational agroforestry system (teff-Acacia agroforestry), which consists of the sequence i) teff-Acacia decurrens intercropping (1st year), ii) grass-A. decurrens silvopasture (2nd year), iii) A. decurrens plantation (3rd–4th year), and iv) on-site charcoal production from A. decurrens (end of 4th year). This study is the first one to comprehensively show how the agroforestry system affects soil organic carbon (SOC) and soil nutrients. Soil samples were collected from the teff-Acacia agroforestry and conventional teff fields at two different sites (site I and II) and they were used to determine soil pH, black carbon, SOC, soil total nitrogen (STN), extractable phosphorus (P), potassium (K), magnesium (Mg), sodium (Na), and calcium (Ca) contents. At site I (0–10 cm soil depth), charcoal production spots in teff-Acacia agroforestry had higher soil pH (20%), black carbon (164%), SOC (48%), P (687%), and K (788%) contents compared to outside charcoal production spots. Soil organic carbon and STN contents in the 1st and 2nd teff-Acacia agroforestry rotations were significantly higher (SOC: 112–169%, STN: 100–131%) than teff fields. At site II, SOC stocks (0–100 cm) in the 1st agroforestry rotation were not significantly different from teff fields. However, they were 159% and 244% greater in the 2nd and 3rd agroforestry rotations, respectively, compared to teff fields. Conversion of teff fields to teff-Acacia agroforestry for a 12-year period increased SOC stocks by 21 Mg C ha–1 per year. Our results demonstrated that locally adopted agroforestry practices can increase SOC and nutrients in the long term, thereby contributing to enhanced soil fertility and improved climate change mitigation strategies via carbon sequestration. [ABSTRACT FROM AUTHOR]

Abstract: Deoxy-xylulose phosphate synthase (DXS) catalyzes the first step of the methylerythritol phosphate (MEP) pathway and it might regulate the metabolic flux in plastidic isoprenoid biosynthesis. We developed a sensitive assay suitable for plant extracts that is based on the decarboxylation of labeled pyruvate (1-13C)-PYR and detection of 13CO2 by isotope ratio mass spectrometry. We tested our method investigating the DXS activity in poplar leaves. Apparent DXS activity showed Michaelis constants of 111 and 158μM for glyceraldehyde phosphate and pyruvate, respectively; pH and temperature optima were found at pH 8.6 and 45°C. DXS activity was inhibited when the competitive inhibitor β-fluoropyruvate was added to the reaction mixture. DXS activity strongly depended on leaf development with higher activity in young leaves and correlated fairly well with leaf isoprene emission potential. In mature poplar leaves, isoprene emission is the main metabolic sink of plastidic isoprenoid intermediates. Consequently, we found lower DXS activity in non-isoprene-emitting lines of poplar than in emitting plants as indicator of a lower demand of metabolic flux within the MEP pathway. [Copyright &y& Elsevier]

Plant residues with larger carbon (C) to nitrogen (N) ratios can stimulate microbial growth and thereby protect soil nutrients from leaching. In poorly fertilized soil, excessive immobilization may limit nutrient availability and thus plant growth. Little is known about the impact of a shallow straw incorporation on soil microbial regulation of top-dressing fertilizer nutrients and spring crop establishment. We aimed to evaluate if wheat straw in combination with mineral fertilizer has more positive effects on plant performance than mineral fertilization alone and if this relates to changes of the extractable C:N:P ratio and microbial activity close to the roots. In order to conduct small-scale sampling with minimal disturbance during growth of spring barley (Hordeum vulgare L.), we developed rhizotrons with resealable ports. Rhizotrons were filled with loamy-sandy soil and fertilized with an equivalent of 150 kg N and 80 kg P ha−1. Half of the rhizotrons received the top dressing together with 4500 kg wheat straw-C ha−1. Throughout a 90-day greenhouse experiment, we analyzed soil C:N:P dynamics, and carbon dioxide (CO2) and nitrous oxide (N2O) emission, together with microbial biomass, selected bacterial genes (abundance), and transcripts (activity) in bulk and root-affected soil at multiple times. We focused on nitrifiers and denitrifiers and linked our data to barley growth. Interactions between straw and roots caused shifts towards larger C:P and C:N ratios in root-affected soil. These shifts were associated with increased 16S rRNA transcripts and denitrifier activities. Straw increased microbial biomass by 124% in the topsoil and at the same time increased root biomass by 125% and number of tillers by 80%. We concluded that microbial activation at the root-straw interface may positively feed back on soil nutrient regulation and plant performance. Further research has to evaluate if plant roots actively prime mining of previously immobilized nutrients in the straw detritusphere or if effects of pathogen suppression and growth promotion are dominating. [ABSTRACT FROM AUTHOR]

Fairy rings promoting circular greening belts in the vegetation can shape soil microbial communities by altering soil conditions. Knowledge about soil variables involved in this process is incomplete. We characterised the soil microbial communities of six fairy rings in a montane grassland using phospholipid fatty acid (PLFA) profiling, and studied if changes in soil properties corresponded to changes in soil microbial PLFA patterns. Exchangeable potassium (K) decreased inside the current rings, while soil moisture increased in the zones where the greening belts were two years before sampling (R2015). Fairy ring associated changes in PLFA composition were highly related to soil K. Gram‐negative bacteria were associated with the zones outside the ring with the highest K content, whereas Gram‐positive bacteria proportions increased inside the ring‐affected zones. An environmental stress indicator, the iso to anteiso ratio of PLFA 17:0, decreased in the R2015 zones, coinciding with the highest soil moisture contents. Our findings highlight the unreported importance of soil K in fairy ring dynamics affecting microbial communities. This common omission could lead to incorrect conclusions. Hence, the effects of fairy rings on soil should be further tested. Highlights: Exchangeable potassium (K) decreased inside the current fairy rings.Fairy ring associated changes in PLFA microbial composition were present related to soil K.Soil moisture increased in the zones where the rings were 2 years before sampling.An environmental stress indicator decreased in those areas. [ABSTRACT FROM AUTHOR]

Modular Observation Solutions of Earth Systems (MOSES) is a novel observation system that is specifically designed to unravel the impact of distinct, dynamic events on the long-term development of environmental systems. Hydrometeorological extremes such as the recent European droughts or the floods of 2013 caused severe and lasting environmental damage. Modeling studies suggest that abrupt permafrost thaw events accelerate Arctic greenhouse gas emissions. Short-lived ocean eddies seem to comprise a significant share of the marine carbon uptake or release. Although there is increasing evidence that such dynamic events bear the potential for major environmental impacts, our knowledge on the processes they trigger is still very limited. MOSES aims at capturing such events, from their formation to their end, with high spatial and temporal resolution. As such, the observation system extends and complements existing national and international observation networks, which are mostly designed for long-term monitoring. Several German Helmholtz Association centers have developed this research facility as a mobile and modular "system of systems" to record energy, water, greenhouse gas, and nutrient cycles on the land surface, in coastal regions, in the ocean, in polar regions, and in the atmosphere—but especially the interactions between the Earth compartments. During the implementation period (2017–21), the measuring systems were put into operation and test campaigns were performed to establish event-driven campaign routines. With MOSES's regular operation starting in 2022, the observation system will then be ready for cross-compartment and cross-discipline research on the environmental impacts of dynamic events. [ABSTRACT FROM AUTHOR]

Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004–2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO2 uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'. [ABSTRACT FROM AUTHOR]

Aims: Root system responses to the limitation of either nitrogen (N) or phosphorus (P) are well documented, but how the early root system responds to (co-) limitation of one (N or P) or both in a stoichiometric framework is not well-known. In addition, how intraspecific competition alters plant responses to N:P stoichiometry is understudied. Therefore, we aimed to investigate the effects of N:P stoichiometry and competition on root system responses and overall plant performance. Methods: Plants (Hordeum vulgare L.) were grown in rhizoboxes for 24 days in the presence or absence of competition (three vs. one plant per rhizobox), and fertilized with different combinations of N:P (low N + low P, low N + high P, high N + low P, and high N + high P). Results: Shoot biomass was highest when both N and P were provided in high amounts. In competition, shoot biomass decreased on average by 22%. Total root biomass (per plant) was not affected by N:P stoichiometry and competition but differences were observed in specific root length and root biomass allocation across soil depths. Specific root length depended on the identity of limiting nutrient (N or P) and competition. Plants had higher proportion of root biomass in deeper soil layers under N limitation, while a greater proportion of root biomass was found at the top soil layers under P limitation. Conclusions: With low N and P availability during early growth, higher investments in root system development can significantly trade off with aboveground productivity, and strong intraspecific competition can further strengthen such effects. [ABSTRACT FROM AUTHOR]

Successive winter wheat (WW) rotations are associated with a substantial yield decline, and the underlying mechanisms remain elusive. An outdoor experiment was set up using sandy loam soil. WW was grown in rhizotrons, in soil after oilseed rape (KW1), after one season of WW (KW2), and after three successive seasons of WW (KW4). We applied zymography and harvested the plants at the stem elongation stage to observe changes in the activity of β -glucosidase (BGU) and leucine aminopeptidase (LAP), as well as using glucose (GLU) imaging to observe glucose release patterns in the rhizosphere of WW. Several biochemical and microbial properties of the bulk soil and the rhizosphere of the rotational positions were measured. KW2 and KW4 exhibited reduced plant biomass compared to KW1. There was a higher root length density and root mean diameter as well as a lower specific root length for KW1 compared to KW2 and KW4. KW1 soil had a lower mineral N concentration and microbial biomass carbon (C) and nitrogen (N) than KW2 and KW4, which translated to a lower plant C:N ratio. A greater rhizosphere extent of BGU and LAP across the soil profile was also visible for KW1 compared to KW2 and KW4 using zymography. Lower dissolved organic C and hotspot areas of GLU in the rhizosphere of successive WW might explain shifts in the microbial community composition, possibly leading to a dysbiosis with the soil microbes in the rhizosphere. Soil depth and rotational position explained most of the variance in the soil microbial communities. The relative abundance of Acidobacteriota , Gemmatimonadota , Nitrospirota , and Chloroflexi significantly varied among the rotational positions. Our results highlight the effect of WW rotational positions on soil and plant properties, as well as microbial community dynamics, and provide evidence for the pathways driving biomass decline in successively grown WW. [Display omitted] • Significant biomass decline in successively grown winter wheat (WW). • Contrasting root plastic responses in response to successive WW rotational positions. • Lower DOC in the rhizosphere of successively grown WW was related to microbial N immobilization. • WW rotational position strongly affected activity of C and N- acquiring enzymes. • Microbial community composition is affected by WW rotational position. [ABSTRACT FROM AUTHOR]