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The long-term stability of soil organic carbon (SOC) is controlled by stabilization mechanisms, among which physical stabilization through microaggregate (

Rice cultivation requires high amounts of phosphorus (P). However, significant amounts of P fertilizer additions may be retained by Fe oxides and are thus unavailable for plants. At the same time, rice cultivation has a high demand for Si, reducing Si availability after short duration of rice cultivation. By studying a paddy chronosequence with rice cultivation up to 2000 years, we show that silicic acid (Si) limitation, observed as early as a few decades of rice cultivation, is limiting P availability along the paddy soils chronosequence. Using Near edge X-ray absorption Fine Structure spectroscopy (NEXAFS) in a scanning transmission (soft) X-ray microscope (STXM) we show respective release of available P was linked to a Si-induced change in speciation of Fe-phases in soil particles and competition of Si with P for binding sites. Hence, low Si availability is limiting P availability in paddy soils. We propose that proper management of Si availability is a promising tool to reduce the requirements of paddy soils for P fertilization, making rice production more sustainable in future.

Biological nitrification inhibition (BNI) has been considered a plant strategy to increase N use efficiency by reducing N losses via N2O emissions or nitrate leaching. However, recent studies have revealed no difference in gross nitrate production among Urochloa humidicola genotypes with previously described high- and low-BNI capacity and pointed towards a crucial role for microbial N immobilization. In the current greenhouse study, we compared the 15 N acquisition by two U. humidicola genotypes (with high- and low-BNI capacity) and their soil-associated microorganisms at four points in time after fertilization (50 kg N ha−1). Soil microorganisms slightly out-competed both genotypes during the first 24 h after fertilization, and microorganisms associated with high-BNI genotype immobilized more N than microbes associated with low-BNI plants. Nevertheless, by the end of the experiment, low-BNI plant genotype had acquired more 15 N, despite higher to N2O emissions. Furthermore, higher 15 N root-to-shoot transfer was observed in low-BNI plants, potentially indicating higher contribution of nitrate to plant N uptake. In conclusion, our results confirm higher importance of microbial N immobilization in high-BNI genotypes, at least in the short-term. However, this did not result in higher N uptake by the high BNI genotype during the first 3 weeks after fertilization as could be expected. Long-term field studies are required to better understand the implications of direct (BNI sensu stricto) and indirect mechanisms (including differences in rhizosphere microbial biomass, activity and composition between high- and low-BNI genotypes), processes on plant N use efficiency, N storage in soil, and N losses to the environment.

Microaggregates (250 µm) that resisted 60 J mL−1 ultrasonic dispersion. Afterwards, we assessed the C, N, Fe, and Si stable isotope composition in each size fraction. After four weeks we found a rapid build-up of stable macroaggregates comprising almost 50 % of soil mass in the treatment with plants and respective soil rooting, but only 5 % when plants were absent. The formation of these stable macroaggregates proceeded with time. Soil organic carbon (SOC) contents were elevated by 15 % in the large macroaggregates induced by plant growth. However, the recovery of EPS-derived 13C was below 20 % after 4 weeks, indicating rapid turnover in treatments both with and without plants. The remaining EPS-derived C was mainly found in macroaggregates when plants were present and in the occluded small microaggregates (

Stable carbon and oxygen isotope compositions in soil carbonates and in soil organic matter provide insights into (paleo) climatic conditions, especially in arid and semiarid regions where carbonate is abundant in soils. We here investigate δ13C and δ18O isotope composition of bulk carbonate, pedogenic carbonate nodules and organic carbon from modern soils developed along a precipitation gradient (Entisol, Inceptisol, Mollisol and Alfisol) and paleosols formed within loess units in northern Iran. δ13C values of organic carbon in the modern soils ranged from −19.5‰ in the arid and semiarid regions to −24‰ in the more humid regions with forest vegetation. δ13C values of bulk carbonate in the modern soils ranged from −12.1‰ at the wettest sites to −0.8‰ at the drier sites and thus, a 550 mm increase in precipitation leads to a ~11‰ decrease in δ13C values of bulk carbonate. In the modern soils, δ13C values of pedogenic carbonate nodules in the semiarid areas show higher values by ~3–4‰ more than the regions with forest vegetation. Unlike δ13C values of pedogenic carbonate nodules the δ18O values of pedogenic carbonate nodules of modern soils in this study did not display pronounced changes across the sections. The change in δ13C of carbonates and organic carbon is consistent with the present above-ground vegetation, consisting of a mosaic of habitats with differences in the proportion of C3 and C4 vegetation tending to larger C4 contribution with increasing aridity. The δ13C values of carbonates coupled with climate data of the region confirm seasonal bias in the formation of carbonate nodules in the modern soils seen in studies elsewhere. The δ13C values of pedogenic carbonate nodules in the paleosols range from −10‰ in humid areas to −7.2‰ in semiarid areas. The trends in δ13C composition in modern soils are also visible in the δ13C composition in the paleosols, suggesting that in the foothills of the Alborz and Iranian loess plateau, a precipitation gradient existed also in the last interglacial.

Whereas many researchers still approach Terra Preta (TP) as a soil category, new evidence suggests that TP refers to a directional grading of soil property changes (i.e., color, pH, nutrients, etc.) within human-made soils, originating from human activities in pre-Columbian times. Currently, most TP research focuses on the Brazilian part of the Amazon basin, but only little information is available on TP soils in the Colombian Amazon. Here, we sampled four TP and surrounding soils in the Colombian Amazon region at different soil depths and analyzed them for (i) general soil properties such as color, pH and texture, (ii) soil organic carbon and black carbon (BC) contents, the latter using benzene polycarboxylic acids as molecular marker, (iii) phosphorus availability based on sequential fractionation, and (iv) microbial residue contents using amino sugars. Our data from Colombia’s middle Caquetá River and Leticia confirmed that SOC, BC, and total P were present in significantly higher concentrations in the TP areas than the surrounding soils, while pH values and microbial residue contents were unchanged. The enrichment of P forms comprised both easily extractable and stable P pools, which both dominated to a different degree, both in TP and adjacent soils. The different degree of SOC, BC and P enrichment suggests different amounts of waste disposal by the ancient populations at different TP sites, now warranting further research for reconstructing ancient population sizes from TP chemical analyses.

Fire condensates from vegetation and household burnings occur ubiquitously in the environment. Until now, however, it was difficult to estimate their origin and any relation to pyrogenic carbon deposited as charcoal. Our aim here was: (i) to differentiate the chemical composition of fire condensates from charcoal particles, and (ii) to relate this to fuel origins from grass, softwood or hardwood. We analysed δ13C and δ15N isotope composition, lignin-derived phenols, benzene polycarboxylic acids (BPCA) and polycyclic aromatic hydrocarbons (PAH), in lab-produced charcoals and condensates at combustion temperatures of 300, 350, 400, 450, 500 and 600 °C. We found that the BPCA and PAH composition of condensates differed significantly from that of charcoals. Condensates exhibited larger portions of benzene penta- to hexacarboxylic acids (B5CA to B6CA), phenanthrene (p

The stable 13C/12C isotope composition usually varies among different organic materials due to isotope fractionation during biochemical synthesis and degradation processes. Here we introduce a novel laser-ablation stable isotope-mass-spectrometry methodology (LA-IRMS) that allows highly resolved spatial analysis of carbon isotope signatures in solid samples down to a spatial resolution of 10 µm. The presented instrumental setup includes in-house-designed exchangeable ablation cells (3.8 and 0.4 mL, respectively) and an improved sample gas transfer, which allow accurate δ13C measurements of an acryl plate standard down to 0.6 and 0.4 ng of ablated carbon, respectively (standard deviation 0.25‰). Initial testing on plant and soil samples confirmed that microheterogeneity of their natural 13C/12C abundance can now be mapped at a spatial resolution down to 10 µm. The respective δ13C values in soils with C3/C4 crop sequence history varied by up to 14‰ across a distance of less than 100 µm in soil aggregates, while being partly sorted along rhizosphere gradients of < 300 µm from Miscanthus plant roots into the surrounding soil. These very first demonstrations point to the appearance of very small metabolic hotspots originating from different natural isotope discrimination processes, now traceable via LA-IRMS.

Crop rotations with maize and flooded rice lead to temporally aerobic soil conditions. This promotes the development of desiccation cracks in the soil, which can act as preferential flow pathways for water and solutes. We hypothesized that these cracks are enriched with organic carbon (C), plant nutrients and microbial residues (amino sugars) and that they can thus also serve as hot spots of fertilizer and C cycling. To test this hypothesis, we applied 13C-labelled rice straw and 15N-labelled urea to rice fields of the International Rice Research Institute (Los Banos, Philippines). We then traced the fate of the 13C-labelled rice straw and the 15N-labelled urea in crack and bulk soil and in microbial residues in two approaches, i) in the short term, i.e., 24 h after application of straw and fertilizer jointly with a dye tracer (Brilliant Blue) prior to maize seeding in the paddy - maize cropping system, as well as ii) in the long-term, i.e., during one year and for three different crop rotations (continuous paddy rice, paddy rice – maize, and paddy rice – maize with straw mulching and cover cropping). The short-term analyses of the dye tracer depth profiles showed that flow path areas decreased with increasing depth. A typical impermeable plough pan was not identified. Instead, we observed rapid infiltration of irrigation water down to 60 cm soil depth. The dyed flow paths were enriched in organic C (+12%) and plant nutrients (N: +21%, Ca2+: +59%, K+: +39%, Mg2+: +39%) relative to the bulk soil. The labelled straw and fertilizer quickly reached 60 cm depth with the dye tracer. We could not identify elevated microbial biomass along the flow paths, however, we did find larger microbial activities along the cracks in the long-term experiment than in the surrounding bulk soil. The increased activity fostered microbial uptake of fertilizer 15N along the cracks, which was detected mainly for fungal residues and only in the trials receiving straw (crack soil: 0.6 ± 0.1 mg glucosamine-15N kg soil−1, bulk soil: 0.2 ± 0.1 mg glucosamine-15N kg soil−1). We conclude that analysis of homogenized bulk soil samples can underestimate C and nutrient availability, as well as their microbial processing in paddy rice soils, when crack systems are not considered.

Fires have accompanied terrestrial life from the beginning, yet with incomplete knowledge about feedback to paleoclimate and vegetation. Here, we have assessed how climate triggered the activity of vegetation fires in a 600,000 years continental record. We recorded benzene polycarboxylic acids as markers for burned organic carbon residues (BC) in sediments of Lake Van (Turkey), one of the oldest lacustrine archives currently available on Earth. Though fire and BC peaks were assumed to occur during dry climates, BC concentration and related fire temperatures were largest during periods of warm/humid climatic conditions. During humid periods, we recorded up to 45 mg BC per cm 3 sediment (precipitation ∼ 800 mm/a), while BC amounts during dry climates were smaller by a factor of 10 ( 3 sediment, precipitation

Apple replant disease (ARD) occurs when apple or a closely related species are replanted at the same site leading to severe growth reduction and losses in fruit yield and quality. This complex disease phenomenon is a worldwide problem for tree nurseries and apple orchards. Its causes are not fully understood up to now and economically feasible and sustainable countermeasures do not exist. Research studies to unravel the etiology of ARD are in urgent need of sites differing in soil characteristics with a defined, comparable cropping history including appropriate control (healthy) plots. Thus, the first aim of this study was to induce ARD at three different sites with topsoils covering textures from sand, loamy sand to silt loam (Podzols to Luvisols). Grass plots served as controls. After eight years of repeatedly replanting the apple rootstock ‘Bittenfelder’, growth suppression was observed at the ARD plots on all three sites. Because until now no systematic correlation to soil parameters was approached, the second aim was to study the replant severity in the three different soils. Soil properties were investigated at different spatial scales. Significant differences occurred between sites in soil texture, pH, and C and N contents. Within plots, non-invasive soil sensing (EMI, gamma-spectrometry) helped to ensure homogeneous conditions and to exclude unexplained ARD effects due to small-scale soil heterogeneity. Soil from each site was submitted to a bio-test in which growth of in vitro propagated M26 plantlets in untreated and disinfected soil was compared to determine the ARD severity. Soil disinfection by gamma irradiation resulted in a significant increase in M26 shoot biomass, most pronounced in soil from ARD plots. Thus, on all soils, ARD was successfully induced with a negative correlation between ARD intensity and soil clay content, and a positive correlation with C/N ratio.

We present a multi-proxy approach to reconstruct Middle Bronze Age (MBA, 1600-1250 BCE) land use practices in the north-western Alpine foreland (SW Germany, Hegau). We combined biogeochemical proxies from multi-layered colluvial deposits and archaeobotanical and archaeozoological data within and in the surrounding of the archaeologically well-documented settlement site of Anselfingen. Offsite pollen data from two peat bogs were used to place the onsite and near-site vegetation and land use data to a regional context.Phases of colluvial deposition were reconstructed by optically stimulated luminescence (OSL) and radiocarbon (AMS 14C) dating. The first phase of major colluviation could be correlated with MBA land use followed by phases of colluvial deposition during the Iron Age, the Medieval period, and modern times. Charcoal spectra from colluvial deposits and archaeological structures indicate MBA forest management favoring Quercus in the surrounding area north of the settlement. The analysis of faecal biomarker (5ß-stanols up to 40 %) and excavated pig bones (up to 14 %) suggest the presence of a forest pasture mainly used for pig farming. In the surrounding area south of the settlement, an arable field with a buried MBA plough horizon (2Apb) could be verified by soil micromorphological features such as very dusty clay coatings and a banded microstructure and by high concentrations of grass phytoliths from leaves and stems. Agricultural practices (e.g. ploughing) focused on five staple cereal crops (Hordeum distichon/vulgare, Triticum dicoccum, Triticum monococcum, Triticum spelta, Triticum aestivum/turgidum) as indicated by the onsite archaeobotanical records. Stilted pantries, reconstructed from MBA post-holes, were interpreted as storage facilities, while excavated heat stones are likely to indicate post-harvest processing of cereal crops and other agrarian products. Higher levels of urease activity compared to microbial biomass carbon (up to 2.1 µg N µg Cmic-1), and input of herbivorous animal faeces indicate livestock husbandry on fallow land or manuring practices. The suites of polycyclic aromatic hydrocarbons (PAHs) and their spatial distribution indicate the use of fire for various purposes, e.g. for landscape opening and maintenance, for domestic burning and for technical applications. The offsite pollen data support the onsite and near-site vegetation change. During the MBA, fire played a major role in shaping the landscape (peak of micro-charcoal during the MBA in the offsite pollen records) and anthropogenic activities promoted oak dominated forest vegetation at the expense of natural beech forests. This approves a broad regional human influence in the north-western Alpine foreland during the MBA.Our data allow in-depth insights into the MBA subsistence economy on a local and regional scale, which was not limited to settlements at lakeshore sites. The MBA in the north-western Alpine foreland was a period of establishing settlements with sophisticated land management and land use practices also at low and mid altitude inland sites. We could further show that colluvial deposits are promising archives for the reconstruction of past land use practices.

This paper aims to reconstruct Middle Bronze Age (MBA; 1600–1250 BCE) land use practices in the northwestern Alpine foreland (SW Germany, Hegau). We used a multi-proxy approach including the analysis of biogeochemical proxies from colluvial deposits and buried topsoils in the surroundings of the well-documented settlement site of Anselfingen and off-site pollen data from two peat bogs. This approach allowed for in-depth insights into the MBA subsistence economy and shows that the MBA in the northwestern Alpine foreland was a period of establishing settlements with sophisticated land management and land use practices. The reconstruction of phases of colluvial deposition was based on ages from optically stimulated luminescence (OSL) and radiocarbon (AMS14C) dating from multi-layered colluvial deposits and supports the local archaeological record with the first phase of major colluvial deposition occurring during the MBA followed by phases of colluvial deposition during the Iron Age, the Medieval period and modern times. The on-site deposition of charred archaeobotanical remains and animal bones from archaeological features, as well as polycyclic aromatic hydrocarbons (PAHs), charcoal spectra, phytoliths, soil microstructure, urease enzymatic activity, microbial biomass carbon (Cmic) and heavy metal contents from colluvial deposits, were used as proxies for on-site and near-site land use practices. The charcoal spectra indicate MBA forest management which favored the dominance of Quercus in the woodland vegetation in the surrounding area north of the settlement site. Increased levels of 5β stanols (up to 40 %) and the occurrence of pig bones (up to 14 %) support the presence of a forest pasture mainly used for pig farming. In the surrounding area south of the settlement, an arable field with a buried MBA plow horizon (2Apb) could be verified by soil micromorphological investigations and high concentrations of grass phytoliths from leaves and stems. Agricultural practices (e.g., plowing) focussed on five staple crops (Hordeum distichon/vulgare, Triticum dicoccum, Triticum monococcum, Triticum spelta, Triticum aestivum/turgidum), while the presence of stilted pantries as storage facilities and of heat stones indicate post-harvest processing of cereal crops and other agrarian products within the settlement. In the area surrounding the settlement, increased levels of urease activity, compared to microbial biomass carbon (up to 2.1 µg N µg Cmic-1), and input of herbivorous and omnivorous animal faeces indicate livestock husbandry on fallow land. The PAH suites and their spatial distribution support the use of fire for various purposes, e.g., for opening and maintaining the landscape, for domestic burning and for technical applications. The off-site palynological data support the observed change in on-site and near-site vegetation as well as the occurrence of related land use practices. During the Early and Middle Bronze Age, fire played a major role in shaping the landscape (peak of micro-charcoal during the MBA), and anthropogenic activities promoted Quercus-dominated forest ecosystems at the expense of natural beech forests. This indicates a broader regional human influence in the northwestern Alpine foreland at low- and mid-altitude inland sites during the Middle Bronze Age.

Bioturbation involves the incorporation of residues from the surface soil into the subsoil; however, common small soil ‘bioengineers’, such as earthworms or termites, are unlikely to transport human artifacts to deeper soil horizons. However, such artifacts occur in the deeper soil horizons within Amazonian Anthrosols (Terra Preta). Here we test the assumption that such tasks could be carried out by fly larvae, which could thus play a crucial role in waste decomposition and associated soil mixing under tropical conditions. We performed two greenhouse experiments with sandy substrate covered with layers of organic waste, ceramic fragments, and black soldier fly larvae (BSFL) (Hermetia illucens (L.) (Dipt.: Stratiomyidae)). We used in-situ images to assess the rate of bioturbation by BSFL, and then designed our main study to observe waste dissipation (reduction of organic carbon and phosphorus contents from waste model trials with and without charcoal) as related to larval-induced changes in soil properties. We found that the bioturbation of macroinvertebrates like BSFL was able to bury even large (> 5 cm) ceramic fragments within hours, which coincided with high soil growth rates (0.5 cm h-1). The sandy soil was subsequently heavily enriched with organic matter and phosphorus originating from organic waste. We conclude that BSFL, and possibly other fly species, are important, previously overlooked soil ‘bioengineers’, which may even contribute to the burial of artifacts in Anthrosols and other terrestrial waste dumps.

Loess-paleosol sequences are terrestrial archives of past climate change. They may host traces of ancient microbial life, but little information is available on the recovery of microbial biomarkers from such deposits. We hypothesized that microbial communities in soil horizons up to an age of 127 kyr carry information related to past environments. We extracted DNA from a loess-paleosol sequence near Toshan, Northern Iran, with 26 m thick deposits showing different degrees of soil development, performed quantitative PCR and 16S rRNA gene amplicon sequencing. Periods of soil formation archived within the loess sediment led to higher diversity and bacterial abundance in the paleosol horizons. Community composition fluctuated over the loess-paleosol sequence and was mainly correlated with age and depth, (ADONIS R 2

Colloids and their subset nanoparticles are key soil constituents for nutrient and Organic Carbon (OC) storage and transport, yet little is known about their specific role in overall transfer of elements under hyper-arid conditions. We analyzed the Water Dispersible Colloids (WDCs) of two adjacent soil profiles, located either on the active (named: Fan) or passive (named: Crust) sections of an alluvial fan. Colloidal particles (

Steroids are used as biomarkers for tracing faecal material in the environment, but their dissipation behaviour in the course of composting has remained unclear. To assess their stability, we tracked the fate of Δ5-sterols, 5α-stanols, 5β-stanols, epi-5β-stanols, stanones and bile acids after 0, 7, 14, 28, 56, 112 and 168 days and after 0 and 168 days of composting cattle and horse farmyard manure, respectively. After composting, extractable steroid content decreased by 93.8–99.9% for cattle manure and by 54.0–100% for horse manure relative to the initial amount. The loss was with 98.8–99.9%, particularly pronounced for bile acids in the cattle manure compost. Our findings challenge the assumption that bile acids are generally more resistant towards degradation than other steroids. Contrary to the bile acids, the Δ5-sterol content did not decrease constantly, but showed a temporary increase, pointing to a delayed release from straw (β-sitosterol, stigmasterol and cholesterol) or to temporary production by fungi (cholesterol). Similarly, there was no continued loss of cholesterol transformation products (5α-cholestanol, cholestanone and epicoprostanol); they either increased temporarily or showed delayed degradation. These changes in steroid patterns complicate the identification of compost as faecal matter by way of commonly used steroid ratios and stress the importance of additional bile acid analysis in geo-archaeological research. Nevertheless, slower dissipation and smaller relative loss of epi-5β-stanols vs. 5β-stanols increased the value of r = epi-5β-stigmastanol/5β-stigmastanol + epicoprostanol/coprostanol during composting and allowed differentiation between fresh farmyard manure, and immature and mature compost.

Due to their extreme aridity, high rate of UV irradiation and low soil carbon (C) content, the soils of the Atacama Desert represent one of the world's most hostile environments for microbial life and its survival. Although infrequent, climatic conditions may, however, prevail which temporarily remove these stresses and allow life to briefly flourish. In this study we investigated the response of soil microbial communities to water and C availability across an aridity gradient (semi-arid, arid, hyper-arid) within the Atacama Desert. We simulated the impact of hyper-dry spells, humid fogs and precipitation events on the activation of the microbial community and the subsequent mineralization of low (glucose) and high (plant residues) molecular weight C substrates. Our results showed that mineralization rate followed the trend: semi-arid > arid > hyper-arid. Some glucose mineralization was apparent under hyper-arid conditions (water activity, aw = 0.05), although this was 10-fold slower than under humid conditions and ca. 200-fold slower than under wet conditions. A lag phase in CO2 production after glucose-C addition in the hyper-arid soils suggested that mineralization was limited by the low microbial biomass in these soils. No lag phase was apparent in the corresponding semi-arid or arid soils. In contrast, the breakdown of the plant residues was initially much slower than for glucose and involved a much longer lag phase in all soils, suggesting that mineralization was limited by low exoenzyme activity, particularly in the humid and hyper-dry soils. Our results also showed that microbial C use efficiency followed the trend: hyper-arid > arid > semi-arid. In conclusion, we have shown that even under hyper-arid conditions, very low levels of microbial activity and C turnover do occur. Further, the microbial communities are capable of rapidly responding to available C once water becomes more abundant, however, this response is both biomass and metabolically limited in hyper-arid soils.

In southern Eurasia recurrent phases of aridization, dust source extension and enhanced Aeolian sedimentation alternated with moister intervals, promoting reduced deflation areas and dust accumulation in the context of late Pleistocene climate changes. Weathering and soil forming intensity in this greater region are, hence, mainly governed by fluctuations in the balance between dust supply and moisture availability. Among the hitherto known sections, the Toshan loess-soil sequence (LPS) represents a key site due to the quality of the record and the multitude of available data giving detailed insights into the timing and magnitude of dust accumulation and soil formation of the region. To elucidate these dynamics for much of the past 130.000 years bulk mineralogical and geochemical data are presented supplemented by a high resolution magnetic susceptibility record and by the results of a detailed micromorphological study of loess at Toshan. The last interglacial Luvisol/Phaeozem-like (∼MIS 5e) and the early glacial interstadial steppic palaeosols (∼MIS 5 c and a) are characterized by gradually increasing grain-size and decreasing degrees in decomposition of micaceous and mafic minerals. Pronounced feldspar weathering is detected in the last interglacial and modern soils only, which formed under reduced or absent dust deposition on penultimate and last glacial loess, respectively (postsedimentary). The overall pedosedimentary conditions correspond to large scale trends of increasing drought, dust accumulation and wind strength in southern Eurasia in relation to decreasing moisture availability towards the early Pleniglacial (∼MIS 4), causing soil formation under ongoing dust deposition (synsedimentary). Similar intervals of synsedimentary soil formation are recorded during the interglacial/interstadial-stadial transitions of the early glacial and during pleniglacial (∼MIS 4 to 2) interstadials. The latter are marked by gradual increases in magnetic susceptibility, colour and decreasing texture. Conversely, silicate weathering could not be detected, suggesting that grain-size fluctuations are a primary feature. Thus, windy and arid pleniglacial conditions in southern Eurasia were interrupted by intermittent phases of synsedimentary soil formation, in response to short-lived and relatively moist interstadials. Although the interrelation of these incipient soils, throughout southern Eurasia is afflicted with considerable restrictions, the oscillatory pattern of the Toshan LPS bears great similarity with millennial-scale oscillations recorded in limnic archives of western Asia.

Farmers in South Asia increasingly switch from continuous paddy-rice cropping to rotations including non-flooded crops, such as growing maize in the dry season. We hypothesized that the introduction of maize into a permanent paddy-rice cropping system boosts drainage and leaching losses of nitrogen (N) and dissolved organic carbon (DOC) in the initial years of maize establishment, due to the disturbance of the equilibrated soil conditions established under continuous paddy cropping. We tested this hypothesis in a 3.5-year field experiment using monolith lysimeters cropped with either (i) single paddy rice in the wet season and maize in the dry season (maize-paddy rice, M-MIX), or (ii) double paddy rice (R-WET) as control. Expandable and compressible pads minimized the formation of a gap at the interface between soil monolith and lysimeter casing during shrinking and swelling of the clay soil. In the first year of introducing maize, drainage (606 l m −2 yr −1 ) and leaching of total nitrogen (TN, 6.8 g N m −2 yr −1 ) and DOC (2.7 g m −2 yr −1 ) were significantly larger in M-MIX than in R-WET (water: 149 l m −2 yr −1 , TN: 0.1 g m −2 yr −1 , DOC: 0.7 g m −2 yr −1 ). However, the additional losses of water, nitrogen, and DOC caused by the introduction of maize disappeared in the following years. In the last two dry seasons of our study, drainage and leaching losses of TN, and DOC were even significantly smaller in M-MIX than in R-WET. In the dry seasons of the 2nd to 4th year after introducing maize (2013–2015), M-MIX saved on average 388 l m −2 of percolation water losses compared to R-WET and leaching losses of TN and DOC under maize were reduced on average by 0.6 g m −2 and 1.6 g m −2 , respectively. We conclude that leaching losses of water and nutrients are only transiently boosted during the first year after introducing maize in perennial rice cropping systems, so that maize cropping in the dry season could save water and reduce nutrient leaching in comparison to continuous paddy-rice cropping in the long run. Long-term field trials are necessary to validate the lysimeter results.

Soil aggregates may stabilize carbon at mineral surfaces and in the interior, but resolving such micro-scale carbon (C) turnover at a scale of soil aggregates

Long-term paddy management promotes nitrogen (N) sequestration, but it is unknown to what extent the properties of the parent soil modify the management-induced N sequestration in peptide-bound amino acids (AA-N). We hypothesized that paddy management effects on the storage of AA-N relate to the mineral assembly. Hence, we determined contents and chirality of peptide-bound amino acids in paddy soils developed on contrasting parent material (Vertisols, Andosols, Alisols in Indonesia, Alisols in China, and Gleysol/Fluvisol in Italy). Adjacent non-paddy soils served as references. Selected samples were pre-extracted with dithionite–citrate–bicarbonate (DCB) to better understand the role of reactive oxide phases in AA-N storage, origin, and composition. The results showed that topsoil N and AA-N stocks were significantly larger in paddy-managed Andosols and Chinese Alisols than in their non-paddy counterparts. In other soils, however, paddy management did not cause higher proportions of N and AA-N, possibly because N fixing intercrops masked the paddy management effects on N sequestration processes. Among the different soils developed on contrasting parent material, AA-N stocks were largest in Andosols, followed by Alisols and Fluvisols, and lowest in Vertisols. The N storage in amino acid forms went along with elevated d-contents of bacteria-derived alanine and glutamic acid, as well as with increasing stocks of DCB-extractable Fe, Mn, and Al. Other d-amino acids, likely formed by racemization processes, did not vary systematically between paddy and non-paddy managed soils. Our data suggest that the presence of oxides increase the N sequestration in peptide-bound amino acids after microbial N transformations.

Loess areas in Central Europe have been settled since ancient times and are therefore predestined to archive information about both the paleoenvironment with and without human activities. In gentle rolling loess-landscapes distinct short and shallow valleys, so-called dells, are prominent landscape elements that act as sediment traps. The loess-paleosol-colluvium (LPC) sequence of Gambach (Wetterau, Germany) can be regarded as an exceptional sequence for Lateglacial-Holocene pedogenesis and human impact in dry loess landscapes with The LPC sequence of Gambach reflects climate-controlled pedogenesis from ca. 15 ka to 4.7 ka with the formation of a Cambisol having some properties related to Chernozem soil forming processes during the Lateglacial. A Chernozem is developed in the deposits of the Laacher See Tephra, which still show the influence of periglacial climate in their lowermost part. The upper part of these deposits was relocated by colluvial processes at around 6.7 ka. Chernozem soil forming processes were still ongoing until 4.7 ka when these shifted to Luvisol formation, which is still active today. Since 4.7 ka, extended land use - with indications of agricultural fire use since at least 2.3 ka - led to the formation of colluvial deposits combined with a topographic leveling of upland positions on a landscape-scale. The results of the formative element of humans on loess landscapes from the Wetterau can also be taken as representative for around 9400 km2 of dry loess landscapes in Central Europe.

Paddy soil management is generally thought to promote the accumulation of soil organic matter (SOM) and specifically lignin. Lignin is considered particularly susceptible to accumulation under these circumstances because of the recalcitrance of its aromatic structure to biodegradation under anaerobic conditions (i.e., during inundation of paddy fields). The present study investigates the effect of paddy soil management on SOM composition in comparison to nearby agricultural soils that are not used for rice production (non-paddy soils). Soil types typically used for rice cultivation were selected, including Alisol, Andosol and Vertisol sites in Indonesia (humid tropical climate of Java) and an Alisol site in China (humid subtropical climate, Jiangxi province). These soil types represent a range of soil properties to be expected in Asian paddy fields. All upper-most A horizons were analysed for their SOM composition by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and for lignin-derived phenols by the CuO oxidation method. The SOM composition was similar for all of the above named parent soil types (non-paddy soils) and was also not affected by paddy soil management. A substantial proportion (up to 23%) of the total aryl-carbon in some paddy and non-paddy soils was found to originate from condensed aromatic-carbon (e.g., charcoal). This may be attributed to the burning of crop residues. On average, the proportion of lignin was low and made up 20% of the total SOM, and showed no differences between straw, particulate organic matter (POM), and the bulk soil material. The results from CuO oxidation are consistent with the data obtained from solid-state 13C NMR spectroscopy. The extraction of lignin-derived phenols revealed low VSC (vanillyl, syringyl, cinnamyl) values for all investigated soils in a range (4 to 12 g kg−1 OC) that was typical for agricultural soils. In comparison to adjacent non-paddy soils, the data do not provide evidence for a substantial accumulation of phenolic lignin-derived structures in the paddy soils, even for those characterized by higher organic carbon (OC) contents (e.g., Andosol- and Alisol (China)-derived paddy soils). We conclude that the properties of the parent soil types are more important for the lignin content of the soils than the effect of paddy management itself.

Nitrite (NO2 −) as an important intermediate of the biological nitrogen cycle is particularly reactive in acidic soils and acts as a source of N2O and NOx (NO and NO2). However, abiotic and biotic pathways of NO2 −-driven N2O and NOx production in forest soil and the role of soil organic matter (SOM) in these processes are still unclear. In this study, NO2 − was applied to both unsterile and sterilized soil samples as well as to different SOM fractions from a Norway spruce forest. Biotic and abiotic N2O emission was measured with an infrared absorption analyzer and gas chromatography, while NOx emission was quantified with a chemiluminescence analyzer. Isotopic signatures of N2O (δ15Nbulk, δ18O, and 15N-N2O site preference) were analyzed with an isotope ratio mass spectrometer. After NO2 − addition, a large amount of NOx was emitted immediately, while N2O emission occurred 15–60 min later and was much lower compared to NOx. Sterilization of soil decreased N2O emission significantly, but not NOx emission. The 15N site preference of N2O ranged from 7.98 to 11.58‰ for abiotic and 4.69–7.42‰ for biotic sources. The fulvic acid fraction contributed the most to abiotic N2O emission, while the fastest NO and N2O emission occurred after NO2 −application to the humin fraction, followed by the humic acid fraction. These results are important for the future understanding of NOx and N2O sources, as well as the use of isotopic signatures for source-partitioning N2O emission from soil.

The Northern Iranian loess profiles host important information on Quaternary climate and palaeoenvironmental changes in the region. They build an important link between the Eurasian loess belt and European and Central Asian archives. Due to a climatic gradient with decreasing precipitation from the west to the east and from the south to the north, loess-palaeosol sequences formed synchronously under different climatic conditions can be studied over short distance in the Iranian Caspian Lowland. The Agh Band profile is located in the so called Iranian “Loess Plateau”, a semi-arid region with 200–350 mm annual precipitation. The loess deposits at Agh Band reach a thickness of >60 m. An about 50 m thick step-profile was prepared and the litho/pedostratigraphy was investigated. Samples for laser-diffractometry grain-size measurements were taken every 2 cm. The magnetic susceptibility was measured in 4 cm intervals and the CaCO3-content in 8 cm intervals. To establish a chronological framework a pIRIR290 luminescence dating approach was applied to the 4–11 μm polymineral fraction. The results show that the Agh Band profile yields a climate archive reaching from MIS 7 to MIS 2. Several chronological hiatuses of some 10 ka show that periods of intense loess accumulation were interrupted by phases of only minor loess sedimentation and/or erosion. The Agh Band profile is subdivided by several shifts in grain-size distribution. The coarsening- and fining up trends correlate with increasing and decreasing wind-velocity, respectively. In the central part of the Agh Band loess sequence a weakly developed palaeosol is preserved which was developed at around 80 ka. Furthermore, the loess deposits formed from about 100 ka to 60 ka ago show banded structures. A pedocomplex including two well-developed palaeosols consisting of Bw(y) horizons and a CB-horizon as well as intercalated loess can be found in the lower part of the sequence also evidenced by the increased values of magnetic susceptibility. The corresponding luminescence age estimates indicate that the palaeosols represent a period of increased humidity and landscape stability during late MIS 7 and MIS 6. Hence, in the Agh Band loess, various changes in the palaeo-sedimentary system, triggered by changes in climate can be observed. This yields important information on the sensitive response of sedimentary systems and landscapes within semi-arid regions to shifts in moisture and possibly temperature.

In Northern Iran mean annual precipitation and vegetation vary significantly over short distance from a semi-desert to a forest biome. These ecosystems likely responded differently on past climate changes. We here aim at i) testing the applicability of biomarkers (leave-derived n-alkanes, their stable carbon isotope composition, and C and N stable isotopes of soil organic matter) in loess-derived soils to identify and differentiate past ecosystems, and ii) elucidating the variability of these biomarkers in palaeosols. We sampled modern topsoils and palaeosol horizons within an ecological gradient covering a range in mean annual precipitation from 200 to 750 mm from the Kopet Dag semi-desert to the Hyrcanian forest on the footslopes of the Alborz Mountains. C org , N, δ 13 C org , δ 15 N, and n-alkanes (and their compound-specific δ 13 C) were analyzed to characterize organic matter composition and sources. In modern soils a systematic increase in C org and N was observed with precipitation. The δ 15 N decreased from about 6 to 4‰ pointing to systematically more degraded organic matter in semi-desert soils. The leave-wax specific ratio of (nC 31 + nC 33 )/(nC 27 + nC 29 )-n-alkanes was >1 for semi-desert soils and 13 C org showed no systematic trend in this gradient. In loess and palaeosol profiles, contents of C org , N and n-alkanes dropped about a factor 10 compared to modern soils. The n-alkane ratio and δ 15 N ratios remained on comparable levels as did the compound-specific δ 13 C in n-alkanes. However, bulk δ 13 C org was altered from about −27 in modern soil to −23‰ in loess-palaeosols. Systematically higher C org and N values were observed in palaeo-topsoils compared to loess and subsoil. Stable C isotopes varied rather unsystematically within loess-palaeosol sequences, while δ 15 N revealed trends within palaeosols, however, in contrasting directions with palaesol depth. The (temporal) average n-alkane ratio for all palaeosol horizons of one site systematically followed the modern precipitation gradient indicating that in all periods of soil formation a climatic gradient developed.

Loess-palaeosol sequences are highly resolved archives for palaeoenvironmental reconstruction and build an important link to correlate European and Central Asian loess sequences. For the loess palaeosol sequence at Toshan, Northern Iran, a luminescence-based chronological framework was established. The timing of dust accumulation and soil formation was investigated and thereby information on changes in palaeoenvironmental conditions in the region obtained. For luminescence dating, the 4e11 mm grain size fraction was used and the pIRIR290 approach was applied to polyminerals. Tests concerning bleachability, dose recovery and anomalous fading were conducted. The results show that residual doses have only minor influence on the determination of the equivalent dose. The Eemian (MIS 5e) soil seems to be preserved but a chronological classification based on luminescence ages for this soil remains difficult. The pIRIR290 age estimates from the lower part of the profile range from 104 ± 9t o 127± 8 ka. Lumi- nescence ages from the central profile-part point to an increase in dust accumulation starting around the MIS 4/MIS 3 transition. Furthermore, a chronological framework for interstadial soils was developed indicating e.g. soil formation at around 40 ka during MIS 3 and 26 ka during MIS 2. The top part of the profile was dated to about 22 ka. The age estimates show that the Toshan loess profile is a highly resolved loess record providing a valuable climate archive for the last glacialeinterglacial cycle reflecting several climatic shifts represented by dust accumulation or enhanced degrees of soil formation (stadials and interstadials).

The stable

The physical arrangement of compounds in soil microaggregates is controlling many ecosystem functions such as soil stability and C sequestration. However, little is known about the spatial arrangement of organic and inorganic compounds in soil microaggregates, due to the lack of in-situ analyses of undisturbed material. We hypothesized that microaggregates are spatially organized due to interactions between organic matter and mineral phases. To test this, we separated the water stable, occluded, large and small microaggregate fractions (250–53 and 53–20 µm, 60 J ml−1 dispersion energy) from Ap horizons of a toposequence of sandy to loamy Luvisols (Germany) with increasing clay contents (19 to 35% clay), and subjected in total 60 individual aggregates to elemental mapping by electron probe micro analysis (EPMA), which recorded C, N, P, Al, Fe, Ca, K, Cl, and Si contents at 1 × 1 µm resolution. Stoichiometric element ratios characteristic for organic and inorganic matter were used to define discrete components of the aggregates and analyze their spatial arrangement. We found a pronounced heterogeneity in content and arrangement of discrete aggregate components, which was not reproducible for different specimens from the same soil microaggregate fraction, and thus largely independent of clay content in soil. However, nearest neighbor analyses revealed close spatial correlations between plant detritus (C:N app. 100:10) and microbial organic matter (C:N app. 10:1) indicating a spatial relationship between source and consumer. There was no systematic relationship between soil minerals and organic matter, suggesting that well-established macroscale correlations between contents of pedogenic oxides and clay minerals with soil organic matter storage do not apply to soil microaggregates.

Colluvial deposits are considered as sedimentary archives for the reconstruction of the sedimentation and climate history, past pedogenesis and phases of land use. However, the human contribution to the formation of colluvial deposits is mainly based on assumptions derived from the local chronostratigraphy and archaeology. For this reason, there is often a substantial gap in the identification of specific land use practices that promoted prehistoric soil erosion and sedimentation processes. We use an archaeopedological multi-proxy approach on a multi-layered colluvial deposit (six colluvial horizons) at the prehistoric site of Furstenberg (Southwest Germany) to gain detailed insights into the sedimentation history, past pedogenesis and land use practices since the Neolithic. Soil and geochemical analyses such as X-ray fluorescence (XRF), X-ray diffraction (XRD), pedogenic oxides, pH-value and calcium carbonate content support the chronostratigraphy based on ages from optically stimulated luminescence (OSL) and AMS 14C dating. Further, biogeochemical analyses of phytoliths, charcoal spectra, black carbon (BC), soil organic matter (SOM) composition by using pyrolysis-field ionization mass spectroscopy (Py-FIMS), urease activity, steroid biomarker and heavy metals (HM) are used as land use proxies. The OSL and 14C ages and the local archaeological record indicate six phases of colluvial deposition that occurred through five phases of land use comprising the Early to Younger Neolithic, the Urnfield to Hallstatt period, the Iron to Roman Age, the High Middle Ages, and the pre-modern period. The soil and geochemical proxies correlate with a phase of geomorphodynamic stability between the Early to Younger Neolithic and the Urnfield to Hallstatt period. The high abundance of grass morphotypes since the Neolithic and the increase of Juniperus since the Urnfield to Hallstatt period indicate a persistent anthropogenic impact on the vegetation. Considerable amounts of burned OM (up to 676 g BC kg−1 SOC, also identified as thermally stabilized SOM compounds by Py-FIMS) in colluvial horizons provide information that fire clearing (e.g. slash-and-burn) was especially used to open and maintain the landscape until the Roman Age. The absence of phytolith species originating from cereals, the occurrence of Juniperus and the evidence from the analysis of urease activity and faecal biomarkers indicate that the slopes of the Furstenberg were mainly used for livestock farming and wood procurement. Thus, the application of specific soil-biogeochemical proxies to colluvial deposits provide new information on the nature of past land use practices that caused the formation of colluvial deposits at that time. In general, archaeopedological multi-proxy analyses of colluvial deposits, integrating the local archaeological record, contributes to a refined understanding of how humans have shaped the landscape since the Neolithic.

Lake sediments can provide useful archives to reconstruct past vegetation changes or fire history. To comprehend how vegetation and fire history have correlated during the last 130,000 years, we used two lake sediment records with known patterns of pollen and botanical macro remains and supplemented this data by analyses of lignin-derived phenols as markers for local vegetation inputs and by benzene polycarboxylic acids (BPCAs) as markers for total fire residue inputs (black carbon, BC). The two sediment archives originated from two maar lakes in the Eifel, which is part of the low mountain ranges in central Germany. A lignin-derived phenol index showed woody angiosperms and gymnosperms as fire fuel in the periods with the highest BC amounts. We recorded 3 g BC per kg sediment for phases covered by forest, while BC contents during colder and drier climates were much smaller (≤0.2 g BC per kg sediment), confirming the hypothesis that fires mostly occurred during humid periods in which forest were established. Both records pointed to forested phases with strong fire activity from 48,000–60,000 years before the year 2000 (b2k). Furthermore, the record reaching back to 130,000 years showed a strong fire activity at about 28,000–30,000 yr b2k, and was free of vegetation macro remains and fire markers from 60,000–118,000 yr b2k. All paleobotanical and chemical biomarker results documented the next oldest forested and fire interval, from 118,000 to 130,000 yr b2k, which includes the Eemian of the last interglacial. Thus, nearly all forested phases were accompanied by fire peaks. Overall, biomarker analyses confirmed that analyses of pollen and botanical macro remains. Fire events were highest during warm and humid forested phases.

Although the Atacama is the oldest and most continuous dry desert on Earth, organic matter (OM) is ubiquitous in its surface sediments. Today, vegetation growth is restricted to the Coastal Cordillera and the Andean foothills, which are predominantly supplied by fog or rainfall. The sources of OM in topsoils of hyperarid regions and deep sediments remain an open question; therefore, we hypothesized that desert plants exhibit specific n-alkane compositions that can be traced in adjacent topsoils and assessed possible OM sources and formation processes in hyperarid regions and soil depths of desert. We determined the n-alkane signatures of plants (n = 28), of soil OM in their vicinity, of hyperarid surface sediments (n = 82), and of four depth profiles (up to 200 cm). We found that n-alkane distributions in fog-fed plants were dominated in order by nC31, nC29, nC33, and nC27 alkanes, while rain-fed plants were dominated by nC29 and nC31 alkanes. When the ratio of nC27+nC33/nC29+nC31 was applied as a “fog-to-rain n-alkane ratio”, the data in surface soils and sediments below 1200 m a.s.l. (in the west of the desert) indicated fog-influenced formation of organics, while all soils and sediments formed higher than 1200 m a.s.l. (in the center and east of the desert) archived n-alkanes from plants fed by rain. Surprisingly, 75–98% of the desert’s OM was found in deep sediments, even under recent vegetation cover. Hence, our findings indicate that currently vegetation-free hyperarid regions of the Atacama Desert once varied in size depending on climate change.

Despite increasing need for cargo shipping, little knowledge exists on emissions from inland navigation. Here we characterized and compared patterns of metals, and parent-, thio- and alkylated PAHs in gaseous and particulate emissions from inland navigation vessels (INVs) with those of road traffic, domestic heating (solid fuels) and ocean going vessels (OGVs) using data from this study and the literature. Diagnostic tools for tracing the environmental impact of inland navigation are proposed. INV and diesel fueled road traffic emissions were differentiated from OGVs and coal combustion via V/Ni values. The PAH inventory of particulate INV emissions also differed significantly from other emitters via a higher proportion of three ring PAHs. The ratio of phenanthrene to dibenzothiophene distinguished diesel fueled road traffic, lignite combustion, OGVs and INVs from gasoline fueled road traffic and wood combustion. The 1,7/(1,7 + 2,6) and 1,7/(1,7 + x4) dimethylphenanthrene ratios (x4 = sum of 1,3-, 2,10-, 3,9- and 3,10-dimethylphenanthrene) separated INV, road traffic (diesel), domestic heating and OGV emissions and are recommended for future application in environmental quality studies.

Rice straw burning in agroecosystems delivers BC (black carbon) to soil/sediment but its contribution relative to other BC sources is unspecified. We have differentiated for the first time combustion residues (CRs) derived from autochthonous and pyrogenic agricultural vs. allochthonous and biogenic riverine input by way of complementary analysis of BC and PAH (polycyclic aromatic hydrocarbon) abundance and composition. Both CR markers in four upland and six periodically flooded paddy soils having different cultivation times were analyzed. BC was the quantitatively dominant CR fraction at 16-512 mg/g SOC (soil organic carbon), whereas PAHs yielded trace amounts of eleven EPA-PAHs at 1.5-47.0 mu/g SOC. CR concentrations in paddy soils exceeded those in upland topsoil. The lowest BC and PAH concentration occurred in subsoil = 700 yr old. Exceptional BC enrichment and composition of benzene polycarboxylic acid (BPCA) products revealed dark buried horizons (700 and 1000 yr sites) as former topsoil. Relative distributions of 5-ring PAHs differentiated CRs from biogenic residues in substrate, topsoil and subsoil. Perylene was enriched in tidal wetland substrate, indicating allochthonous input from soil/sediment erosion in the Yangtze River catchment. An identical pattern was observed in subsoil. Present and former topsoil yielded a distinctive distribution of rice ash PAHs. Although PAHs occurred in traces, their wider compositional variation improved source discrimination power exceeding that of BPCAs. The former are recommended for source identification and the latter for quantifying CR input to soil/sediment. Parallel application of both methodological approaches is advocated for investigating combustion processes in ecosystems. (C) 2016 Elsevier Ltd. All rights reserved.

The knowledge of palaeoclimate in Iran is still limited. However, insight into the timing and the dynamics of Quaternary climate change in Iran might offer valuable information to improve the global palaeoclimate record. The loess-soil sequence of Toshan provides the first high-resolution record of late Pleistocene climate dynamics in Iran and complements the hitherto known sections at Neka, Now Deh and Agh Band to establish a pedostratigraphic record of the north-eastern Caspian Lowland. Our spectroscopic and grain-size analysis are combined to propose (i) a pedostratigraphical scheme for the sequence at Toshan, (ii) describe and estimate the degree of soil development of selected stratigraphical units, (iii) infer palaeoclimatic information, and provide (iv) a correlation with previous loess-palaeosol records of N-Iran as based on pedostratigraphic assumptions. The section at Toshan hosts a strongly developed reddish-brown argillic palaeosol (Bt) as well as eight moderately to weakly developed brownish palaeosol horizons lacking clay illuviation features (Bw/Bwk). These remnants of fossil soils are separated by finely textured loess and horizons that host characteristics of both loess and mineral subsoils (CB/CBk), giving evidence for syngenetic soil formation. The stratigraphical succession of palaeosols, loess and syngenetically altered sediments, covering the last ca. 130 ka, gives evidence for recurrent climate changes as well as fluctuations between dominance of soil formation or dust accumulation in relation to changes in moisture regime. The formation of Bt and Bw/Bwk-horizons is related to relatively humid and warm conditions likely corresponding with interglacial and interstadial climate.

For the assessment of black carbon (BC), its oxidation to benzene polycarboxylic acids (BPCAs) is an established method. However, doubts about biological precursors remain and not all published data were obtained at low carbon concentration. We hypothesised that a considerable proportion of BC may be produced during sample treatment in the presence of a high amount of organic carbon (OC). We therefore tested whether and to which degree (i) BC-free material from stems of Zea mays L. (maize straw) and leaves of Capsicum annuum L. (bell pepper), as well as (ii) cyclic and non-cyclic carbon forms (chlorophyllin, ellagic acid and β-carotene) afford BPCAs when method protocols are overloaded with a sample above the recommended amount of 5 mg OC. The results showed that small amounts (

Interchanging submergence and drainage in paddy soils induce alternating redox conditions. It is known that this causes changes in organic carbon stocks, in amounts and crystallinity of Fe oxides as well as transformation of clay minerals and subsequent changes in cation exchange capacity (CEC). However, the influence of the initial soil type on the extent of these changes is not yet well understood. Therefore, we studied paddy soils that derived from three different soil types (Vertisols, Andosols, Alisols) on volcanic parent material in Java (Indonesia). To account for the variability in parent materials, we additionally sampled sandstone-derived Alisols in China. Adjacent non-paddy soils were sampled as references. Samples were analyzed for texture, bulk density, clay mineral composition, total element content, pH, CEC, phosphorus retention, organic carbon (OC), and acid oxalate- (Feox) and dithionite–citrate–bicarbonate-extractable Fe (FeDCB). Only the Alisol-derived paddy soil in China showed textural changes, compared to the non-paddy soil. Evidence for paddy management induced ferrolysis was not found. The smaller topsoil clay content in the paddy soil is most probable caused by clay migration. Only minor differences in clay minerals were found; topsoils of Andosol-derived paddy soils, however, tend to be less desilicated, indicating phytolith accumulation. Except for Vertisols, paddy management caused significant depletion in Fe oxides in the topsoils (puddled layer and plow pan) due to redox processes. The extent to which the reduced Fe was leached or re-oxidized as short range-ordered Fe oxides depended on the soil texture. Andosols and sandy Alisols facilitated leaching, clayey Alisols re-oxidation. In either case, the stocks of crystalline Fe oxides diminished, causing increased proportions of short range-ordered Fe oxides. Retention of phosphorus was directly related to changes in the absolute amounts of short range-ordered Fe oxides. An accumulation of Fe oxides in paddy subsoils was not found. Lateral transport with drainage water might be a reason. In highly permeable soils with large vertical water fluxes (e.g., Andosols under paddy management), colloidal transport might also play a role. Despite losses in potential OC storage capacity (i.e., Fe oxides, clay minerals, allophane), paddy soils derived from Andosols and sandy Alisols in China had larger OC concentrations in the puddled topsoil, whereby the other soils showed no increase in OC under paddy management. Therefore, paddy management does not necessarily enhance carbon sequestration. Rather, differences in organic matter input between non-paddy and paddy soils seem to determine whether OC is accumulated under paddy management or not. Effects of paddy management on CEC were little and mainly due to OC accumulation and Fe oxide coating removal from clay minerals. Overall, paddy management-induced changes were partly influenced by the original soil and the parent material. In turn, the main characteristics of the initial soil type were preserved and not overridden by paddy management.

Crop rotations encompassing flooded rice and an upland crop are commonly found in large parts of South and East Asia. However, also rice farmers in Southeast Asia increasingly switch from double-cropping paddy rice to one non-flooded crop–such as maize–in the dry season. We hypothesized that introducing maize (maize–paddy rice, M-MIX) into a double paddy rice (R-WET) cropping system will increase carbon (C) release from rice roots into the rhizosphere and the dissolved soil C pool. To test this hypothesis we assessed the kinetics of C release by the rice plants in a hydroponic greenhouse experiment, and used these data for interpreting their C release in field experiments using 13C pulse labeling of rice plants. In the greenhouse we observed that rice roots released 13C labeled dissolved organic carbon (DOC) for 21 days with a mean residence time (MRT) of 19 days after exposure to a 13CO2 pulse. The MRT of labeled dissolved inorganic carbon (DIC) released from rice roots was only 2 days. In the field 13CO2 pulse labeling increased the 13C excess of rhizosphere soil up to 0.7 ± 0.2 mg 13C kg−1 in R-WET and 0.9 ± 0.3 mg kg−1 in M-MIX. The 13C signature of bulk soil remained unaffected. DOC concentrations in R-WET were significantly higher than in M-MIX during the mature grain stage of the rice plants. Nevertheless, the 13C excess in DOC transiently increased by only 0.5 μg L−1 after labeling in 13 cm depth in one of three lysimeters previously cropped with maize (M-MIX), while no labeled DOC was detected in 13 cm depth of the R-WET lysimeters and in 60 cm depth of both treatments. In contrast, the 13C excess of DIC increased by 42.4–93.1 μg L−1 a few days after labeling with a MRT of 53–66 days in both treatments. Considering the results of the greenhouse experiment, this suggests a rapid mineralization of labeled rhizodeposits in the field and an effective transient storage of CO2 produced by respiration in soil water.