Natural disturbances influence wetland carbon cycling, and fire is a key driver of terrestrial carbon stocks. However, the influence of fire on wetland carbon cycling remains poorly understood. Here, we investigated how prescribed fire and wildfire impact soil carbon storage in a forested floodplain of south-eastern Australia. We sampled four areas within Murray Valley National Park, the world’s largest river red gum (Eucalyptus camaldulensis) stand, and compared soil carbon (C), nitrogen (N) and C:N ratios between control (unburnt in the 50 years prior to sampling), prescribed burn and wildfire-impacted floodplain areas. Mean soil C and N concentrations were 4.7% ± 0.32% and 0.36% ± 0.02%, respectively, and mean C:N ratios were 14.23 ± 0.33. Carbon concentrations and C:N were highest in control areas of the floodplain, while N concentrations were highest at wildfire-impacted areas. However, flood frequency was a stronger driver of soil C than fire disturbance. Soils at more frequently flooded areas had higher C concentrations compared to less frequently flooded areas, suggesting that resilience to C loss through fire could be enhanced through hydrological restoration. We believe this warrants further research as a potential nature-based climate measure. Mean C density data indicate soil C stocks of 9.4 Tg across Barmah-Millewa Forest, highlighting the significant carbon storage value of this ecosystem.

Samples of the bones of 47 individuals from 46 Czech and Moravian ossuaries were dated by the 14C method and analyzed for the collagen isotopic composition of carbon (δ13C) and nitrogen (δ15N). Most of the data for the ages of the remains corresponded to the cooler and damper periods described over the past 1000 years. Of the studied samples, the greatest number of remains corresponded to the Spörer (1400–1570), Dalton (1790–1830) and Wolf minima (1280–1350). One sample studied falls within the Maunder minimum (1645–1715). It can be assumed that these minima are connected with a reduced production of food and fodder, that may have initiated famines, epidemics and armed conflicts. Individual climatic minima showed positive correlations between δ13C and δ15N values, indicating that the individuals studied consumed complementary plant or animal diets to different degrees. The elevated δ15N values in our studied samples compared to the skeletal compositions of the population of the La Tène period (380 – 150 BC) and Germanic inhabitants in the territory of Bohemia (5th–6th centuries AD) and Great Moravia (9th–early 10th centuries AD) might reflect the effect of greater consumption of animal proteins or the proteins of omnivorous animals and fish, which compensated for the lack of plant foodstuffs during the colder periods.

The isotopic composition of carbon and nitrogen of the bone collagen for the Spörer and Dalton minima differs from the Wolf minimum. The younger minima show higher δ15N values for a given δ13C value.

Freshwater ecosystems are responsible for a large proportion of global methane emissions to the atmosphere. The radiocarbon (14C) content of this aquatic methane is useful for determining the age and source of this important greenhouse gas. Several methods already exist for the collection of aquatic methane for radiocarbon analysis, but they tend to only sample over short periods of time, which can make them unsuitable for characterizing aquatic methane over longer timespans, and vulnerable to missing short-term events. Here, we describe a new time-integrated method for the collection of aquatic methane that provides samples suitable for radiocarbon analysis, that are representative for periods of up to at least 16 days. We report the results of a suite of tests undertaken to verify the reliability of the method, and the 14C age of aquatic methane from field trials undertaken at sites within Scotland, UK. We believe that this new method provides researchers with a simple approach that is easily deployable and can be used to collect representative time-integrated samples of methane for radiocarbon analysis from a wide range of aquatic environments.

Nitrogen availability has an important influence on agricultural weed growth, because many weeds in annual cropping systems are more competitive in high-nitrogen soils. A potential method to control nitrogen availability is through soil carbon amendments, which stimulate soil microbial growth and immobilize nitrogen. Additionally, carbon amendments may alter soil microbial community composition, increase soil biological functioning, and improve soil health. In a 2-yr field experiment in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], we implemented five amendment treatments to test their ability to alter weed and crop growth through soil nitrogen availability and soil biological functioning. The treatments included: an untreated control, an unamended weed-free control, rye hay adding 3,560 kg C ha−1 and 3,350 kg C ha−1 in 2020 and 2021, respectively, sawdust adding 5,030 kg C ha−1 and 4,350 kg C ha−1 in 2020 and 2021, respectively, and a rye hay and sawdust combined treatment adding 8,590 kg C ha−1 and 7,700 kg C ha−1 in 2020 and 2021, respectively. Each treatment was replicated five times in corn and six times in soybean. Each season, we explored correlations between crop and weed biomass and weed community composition and nitrogen immobilization measured through soil respiration and nitrogen availability. We also explored changes to the soil microbial community composition and soil health as a secondary result of the carbon amendment treatments. Nitrogen availability was lowest in plots treated with the highest C:N amendment. Increasing carbon improved soil health metrics, but the microbial community composition was most affected by the rye hay treatment. Amendments with high C:N reduced weed growth in both soybean and corn plots but only selected for specific weed communities in soybean, leading to improved soybean competitiveness against weeds. In corn, crop growth and weed community composition remained consistent across amendment treatments. Targeted nitrogen immobilization may improve leguminous crop competition in some weed communities as part of an integrated weed management program.

The sorption properties of carbon-composite materials based on montmorillonite and hydrotalcite matrices have been studied using nitrogen adsorption isotherms and inverse gas chromatography. Carbon composite materials derived from both types of inorganic precursors contain pore structure accessible for adsorbate molecules. Adsorption capacity per unit mass of these composite adsorbents is larger in the case of hydrotalcite than in montmorillonite-based materials. Exposing these materials to ambient conditions results in their hydration. Subsequent water removal by heating under vacuum increases nitrogen adsorption capacity, which is explained by the opening of the adsorption space. The water content of hydrated samples and its effect on adsorption capacity is greater for the case of hydrotalcite-based materials. No direct relationship between carbon content and adsorption properties of the materials studied is observed.

While simultaneous radiocarbon and δ13C measurements have been available for organic materials (by accelerator mass spectrometry, AMS, and isotope ratio mass spectrometry, IRMS, respectively), this has not been possible for carbonates until now. Using an existing interface for gas ion source AMS measurements, we developed a prototype for a universal gas interface that allows simultaneous measurement of both carbon isotope ratios from potentially any source of CO2. First results obtained from reference materials (IAEA-C6, OxaII, PhA, IAEA-C1, IAEA-C2, ETH-4) show that for both organic as well as carbonate samples, the precision of radiocarbon measurements in the coupled mode is comparable to routine standalone AMS measurements. For IRMS δ13C measurements, the performance for different materials shows more variation with precisions ranging from 0.07‰ to 0.47‰. However, both organic materials and carbonates can achieve precisions as good as 0.13‰. Once fully automated, the method shows potential for filling the gap of simultaneous carbon isotope measurements for non-organic materials.

Biochar is increasingly used in crop production as a fertilizer; however, its effects on nutrient cycling and stoichiometry in rice paddy soil–plant systems are unclear. We tested for effects of contrasting rates of biochar on soil and rice plant organ carbon (C), nitrogen (N), and phosphorus (P) concentrations and stoichiometry and soil physicochemical properties in early and late paddies. Overall, biochar reduced soil bulk density by an average of 7.4%, while application at 10, 20, and 40 t ha−1 increased soil C and N concentrations in early paddies by 31.6, 41.3, and 104.2%, respectively, and by 8.0, 5.0, and 21.8%, respectively; in late paddies, there were increases of 23.0, 94.1, and 117.0%, respectively, and 6.7, 15.4, and 18.0%, respectively (P < 0.05). Following biochar application at 10, 20, and 40 t ha−1, soil concentration of P decreased in early paddies by 10.9, 19.0, and 13.9%, respectively, and increased in late paddies by 4.3, 16.4, and 20.1%, respectively. Biochar increased ratios of soil C:N and C:P in early and late paddies (P < 0.05), and there was no effect on concentration and stoichiometry of soil available nutrients. Biochar reduced rice plant organ concentration of N and P in early rice and increased leaf N:P ratios. Despite the biochar application improved nutrient status in plant–soil system, we did not observe a significant increase in yield (P > 0.05). According to the N:P value of leaves between treatments, it was found that biochar alleviated the current situation of N limitation in paddy fields during the mature period and transformed the N limitation of early rice into a joint limitation of N and P. These results show that the addition of biochar to subtropical paddy soils leads to a short-term reduction in soil bulk density and increases in soil C and N concentrations and soil fertility. Thus, biochar applied at optimal rates is likely to improve the sustainability of subtropical paddy rice production.

N-enriched biochar can increase the accumulation of carbon (C), nitrogen (N), phosphorus (P), and biomass in rice plants. On the other hand, the biomass and C, N, and P contents of plant organs are important indicators to reflect plant C, N, and P storages. We established control, 4 t ha−1, and 8 t ha−1 N-enriched biochar treatment plots in a subtropical paddy field in China to investigate the effect of these treatments on C, N, and P storages, ecological stoichiometry in various rice plant organs, and their relationships with edaphic factors. The application of N-enriched biochar increased the biomass and storages of C, N, and P in rice roots, stems, leaves, and grains, mainly at 4 t ha−1. The application of N-enriched biochar decreased the C/N and C/P ratios of rice organs, but increased their N/P ratio. Changes in C/N were mainly due to the changes in storage, while N/P was positively correlated with N storage of stems, leaves, and grains and negatively correlated with P storage in roots. Pearson’s correlation analysis revealed that pH was negatively correlated, and soil N content was positively correlated with P storage in various organs of rice. In addition, soil P content and chlorophyll were positively correlated with N storage. In conclusion, we found that the application of N-enriched biochar improved plant N and P storage and stoichiometrical relations among rice organs.

The oceans store a substantial fraction of carbon as calcium carbonate (CaCO3) and organic carbon (Corg) and constitute a significant component of the global carbon cycle. The Corg and CaCO3 flux depends on productivity and is strongly modulated by the Asian monsoon in the tropics. Anthropogenic activities are likely to influence the monsoon and thus it is imperative to understand its implications on carbon burial in the oceans. We have reconstructed multi-decadal CaCO3 and Corg burial changes and associated processes during the last 4.9 ky, including the Meghalayan Age, from the Gulf of Mannar. The influence of monsoon on carbon burial is reconstructed from the absolute abundance of planktic foraminifera and relative abundance of Globigerina bulloides. Both Corg and CaCO3 increased throughout the Meghalayan Age, except between 3.0–3.5 ka and the last millennium. The increase in Corg burial during the Meghalayan Age was observed throughout the eastern Arabian Sea. The concomitant decrease in the Corg to nitrogen ratio suggests increased contribution of marine organic matter. Although the upwelling was intense until 1.5 ka, the lack of a definite increasing trend suggests that the persistent increase in Corg and CaCO3 during the early Meghalayan Age was mainly driven by higher productivity during the winter season coupled with better preservation in the sediments. Both the intervals (3.0–3.5 ka and the last millennium) of nearly constant carbon burial coincide with a steady sea-level. The low carbon burial during the last millennium is attributed to the weaker-upwelling-induced lower productivity.

The solubility limit of carbon in α-Al2O3 (alumina) equilibrated at 1,600°C under He in a graphite furnace was measured by wavelength-dispersive spectroscopy. Undoped alumina and alumina containing carbon at a concentration resulting in the precipitation of a second phase were prepared and equilibrated at 1,600°C. The undoped alumina was used to quantify the amount of carbon deposited on the surface of samples because of hydrocarbon contamination in the electron microscope, and this background level was removed from the signal measured from carbon-doped samples. The solubility limit of carbon in alumina was found to be 5,300 ± 390 at. ppm, and it is believed that carbon substitutes oxygen as an anion and is charge-compensated by oxygen vacancies. Doping alumina with carbon at concentrations below the solubility limit does not impede densification and reduces grain growth. Doping above the solubility limit hinders densification during sintering.

Litter production plays an important role in the functioning of the ecosystem, providing several ecosystem services, such as nutrients cycling and carbon storage. We studied litter production patterns and its relationship with forest structure over a chronosequence of secondary forests in southern Bahia, Brazil. In the study area, 15 pairs of mature and secondary forest were used, in a chronological sequence, being 10, 25 and 40-year-old secondary forests and mature forests. Plots were created for the collection of aboveground biomass data, and within these plots, litter collectors were installed and monitored for 1 year. The results showed that litter production was lower in 10-year-old secondary forests when compared with older forests. On the other hand, in the 10-year-old forests, annual litter production represents 47.8% of the stored biomass, while in mature forests annual litter production represents only 4%. We found that structural variables (basal area, number of stems and canopy opening) influence significantly litter production, as well as litter as percentage of forest biomass. The study emphasizes the importance of biomass production through litterfall in regenerating tropical forests, and its importance for carbon storage and for the maintenance of ecosystem services.

Developmental signals and environmental stresses regulate carbon distribution in the vegetative and reproductive organs of plants and affect seed yield. Cleistogenes songorica is a xerophytic grass with great potential application value in ecological restoration. However, how carbohydrate transport and distribution during grain filling affect the seed yield of C. songorica under water stress is not clear. The present study showed that the soluble sugar and starch contents of cleistogamous (CL) spikes and chasmogamous (CH) spikes were significantly higher at the milk stage, which was attributed to a significantly higher seed number and seed yield per spike under water stress conditions than under well-watered conditions (P < 0.01). RNA-seq data revealed a total of 54,525 differentially expressed genes (DEGs) under water stress conditions, but only 3744 DEGs were shared among all comparison groups. Weighted gene co-expression network analysis showed that the transport and distribution of carbohydrates were regulated by ABA-responsive genes (CsABA8OX1_1, CsABA8OX1_2, CsABA8OX2_1, CsABA8OX2_2, CsNCED3, CsNCED1_1, CsNCED1_2 and CsNCED4_1) and sugar transport and starch synthesis genes (CsSUS1, CsSUS2, CsSUS3, CsAGP1, CsAGP4, CsAGP5, CsSSS1 and CsSBE5) under water stress conditions. These genes jointly regulated carbohydrate remobilization in sources (stems, leaves and sheaths) to promote grain filling and improve seed yield. The present study helped to clarify the phenotypic, metabolic and transcriptional response mechanisms of vegetative organs, such as stems and leaves, and reproductive organs, such as CL spikes and CH spikes, to promote carbohydrate redistribution under water stress, and it provides theoretical guidance for improving seed yields.

The sustainability of an agricultural field is largely influenced by crop growth habit and management practices such as tillage. Both strongly interact to shape ecosystem properties such as the fluxes and stocks of carbon and nitrogen. Recently, researchers have worked to develop perennial grain crops in order to enhance key ecosystem processes, such as carbon cycling and nitrogen fixation, with the use of perennial crops rather than traditionally used annual crops. In this study, we aimed to understand how soil disturbance combined with vegetation type [annual monoculture crops vs. perennial monocultures (intermediate wheatgrass (IWG)) vs restored native vegetation (RNV)] influenced the soil carbon and nitrogen dynamics. We collected soil samples at two depths (0–15 cm and 15–30 cm) from each vegetation treatment and incubated the soils in the laboratory for 120 days to determine the efflux of carbon and also analyzed the mineralization of both carbon and nitrogen. The results demonstrated the soils from the IWG had the greatest carbon flux, as well as carbon and nitrogen storage (annual monoculture < RNV < IWG). The differences in carbon flux, carbon and nitrogen storage from the IWG to the annual monoculture were 27, 40, 20%, respectively, while the IWG to the RNV was 11, 20, 10%. Shallow soil samples exhibited greater differences in all C and N comparisons between treatments compared to deeper soil samples. Taken together, our findings indicate that crop vegetation type and soil depth strongly influence carbon and nitrogen dynamics.

We are observing a dramatic increase of CO2 in the atmosphere, unprecedented in the last several million years. Carbon isotopic ratios have been very useful in helping to untangle the respective roles of anthropogenic emissions and sources/sinks of CO2 in the oceans or terrestrial biosphere. However, this untangling has not been as simple as was often hoped. The isotope ratio signatures produced by emissions and removals that are present in atmospheric CO2 are always vigorously being erased by isotopic exchange with the oceans and terrestrial ecosystems, without there necessarily being any effect on total CO2. Especially in the last decades this pure isotopic exchange effect has led to gross errors that have clouded the public debate on climate change, obscuring mankind’s role. This paper traces my own struggle with the scientific and public sides of this issue, which I ran into from the start of my career in Groningen and throughout my years at NOAA. It is still relevant today.