Organic Soil Horizons Research Articles

Restoration objectives create surface carbon cycle trade‐offs in coastal habitats

Coastal habitats are important and imperiled. To mitigate climate change impacts, carbon (C) sequestration has joined established restoration objectives, including habitat diversity, public access, and native vegetation. Changing topography, maintaining trails, and removing invasive plants may influence coastal C production and retention in different ways depending on how each activity influences the stabilization of organic matter in surface sediments. We quantified variation in litter and surface soil dynamics within and between coastal parks that varied in age from prerestoration to nearly 20 years old in Manatee County, Florida. Older parks had deeper soil organic horizons with higher levels of soil moisture and respiration, indicating that restoration sequesters soil C despite increases in microbial efficiency. However, variation within parks indicated that detrital C dynamics change depending on local management objectives. Relative to unmanaged locations, restored wetlands, including mangroves, salt marshes, and freshwater ponds, had soil organic horizons nearly 20 cm deeper, with high litter stabilization rates despite less litter mass and shorter projected soil sample C mineralization. In contrast, public access features like trails and kayak launches were associated with increased surface CO2 efflux and marginally reduced soil organic horizon depth. Removing invasives had little impact on detrital carbon pools and fluxes. Incorporating detrital C dynamics improved a multivariate model for variation in C pool sizes across sites. Overall, our results suggest that management objectives influence the C production and retention capacity of restored coastal habitats with restored uplands and public access points storing less C than relatively inaccessible wetlands.

New plant ecological scales of soil reaction for Leningrad region and St. Petersburg based on Ramensky’s method

The main biogeochemical processes are influenced by soil pH. For assessing pH by the method of vegetation indication a new database of the ecological scales of plant species describing the correlation between classes of species coverage and pH. Field data was collected at 800 sample plots. At sample plots the coverages of plant species and pH of organic upper soil horizons extracted by KCl solution were determined. Synoptic tables with average coverage for each species were compiled for forest types. The range of pH (2.5–5.5) was divided into 7 classes differ by 0.5 unit of pH each. For each species coverage class, the first and third quartile of pH were established. Ecological scales included these two values as minimum and maximum values (amplitude) of the pH for a given coverage class. Determining of soil pH using the ecological scales was a solution of the system of inequalities that are the set of amplitudes of the pH values corresponding to the coverages of species of the certain plant community. Comparing measured and indicated pH values using data for 45 sample plots that were not used for compilation of scales showed excellent match of measured and indicated values.

Formation of organic soil horizons during the initial pedogenesis in the taiga zone of the European Russian Northeast

Investigations were carried out in the European Russian Northeast (Komi Republic), -in the middle taiga subzone, in the (construction sand) quarry area. Formation of the soil profile within two decades after forest reclamation practices (Pinus sylvestris planting) was considered. Specifics of litter and humus horizons formation, processes of humus formation and accumulation on substrates of different granulometric composition were determined. It is shown that the rate of these processes is determined by the species composition and structure of the plant community. By the end of the second decade, up to 2.7 t·ha-1 of organic carbon accumulates in the humus-accumulative layer (0-20 cm) of sandy and sandy-loam soils, 6.3 t·ha-1 - in clay-loam soils, and 0.1 and 0.4 t·ha-1of nitrogen, respectively, accumulates there as well. The accumulation rate of Corg in the soil of the sandy and sandy-loam quarry reached 0.16, in the clay-loam quarry - 0.37 t·ha-1·year-1. The organic horizons of the forming soils demonstrate a decrease of the mass fraction of calcium, potassium, phosphorus and an increase in iron and aluminum down the profile.

Soil depth-dependent C/N stoichiometry and fungal and bacterial communities along a temperate forest succession gradient

The vertical stratification of nutrient availability and related microbial adaptations in different soil horizons vary along forest succession gradients. However, the driving forces behind such age-related nutrient statuses and microbial dynamics and their depth-dependent distinctions remain unclear. To bridge these knowledge gaps, the current study investigated the carbon (C) and nitrogen (N) contents, C- and N-acquiring extracellular enzyme activities and fungal and bacterial communities in the organic layer (O), surface mineral soil (A) and mineral subsoil (B) in three temperate forest stands (35 years (y), 82 y and 200 y) in the Changbai Mountain region of northeastern China. The O-horizon presented age-related increasing C/N ratios as well as decreases in N%, enzyme (e.g., β-N-acetyl-glucosaminidase) activities and fungal and bacterial richness and diversity. In addition, the dominant early-stage (i.e., 35 y) O-horizon fungal and bacterial species presented positive relationships with the N content and copiotrophic characteristics, such as a powerful ability to mobilize available nutrients. However, the dominant late-stage (i.e., 200 y) O-horizon microbial species were negatively related to the N content but positively associated with the C content and/or C/N ratio and were characterized by an oligotrophic capacity for adapting to N deficiency and recalcitrant substrate decomposition. In the A- and B-horizons, however, the substrate availability (e.g., C and N contents) and nutrient cycling activities (e.g., enzyme activities and fungal and bacterial diversities) exhibited either a decreasing tendency from the early to the middle stage (i.e., 82 y) or an increasing tendency from the middle to the late stage. Such different or even opposing nutrient statuses and microbial adaptations between the decomposed organic matter and soil horizons suggest that the belowground biochemical characteristics are strongly determined by litter quality succession and microbial feedbacks to the depth-dependent allocation of available nutrients.

Soil amendments from recycled waste differently affect CO₂ soil emissions in restored mining soils under semiarid conditions

Drylands affected by serious disturbances such as mining activities lose their vegetation cover and organic soil horizons, becoming CO2 emissions sources. Applications of organic amendments could be a good restoration solution that favours vegetation establishment and soil carbon sequestration; however, they are also associated with CO₂ emissions. Experimental plots with different organic amendments (sewage sludge, garden and greenhouse vegetable composts, and mixtures of both) and unamended soils were installed in a quarry in southeast Spain. The aim of this study was: i) to evaluate the magnitude and changes of in situ CO₂ emission from each experimental plot during a year and a half, and ii) to assess the effects of several physical–chemical (total organic carbon, total nitrogen, water retention, pH and electrical conductivity) and environmental parameters (moisture and temperature) in CO2 emissions. The results showed an initial CO2 emission (priming effect), produced from all restored plots just after the application of the organic amendment, which was significantly higher (P < 0.05) in soils with sewage sludge and their mixtures in comparison to vegetable compost. Garden compost had low emission rates, similar to soils without amendment and showed lower CO2 emission rates than the rest of the restoration treatments. Nevertheless, CO2 emissions decreased in each field campaign over time, showing that all restored soils had lower emissions than natural soils at the end of the sampled period. The different composition of organic amendments had a different effect on soil CO2 emissions. DistLM analysis showed that soil properties such as total organic carbon, total nitrogen, pH and soil moisture, associated with rainfall periods, strongly influenced CO₂ emissions, whereas temperature did not affect the CO2 flow. In conclusion, the compost from plant remains could serve better as treatment to restore degraded soils in drylands than sewage sludge because of its lower CO2 emissions and concomitant effect on climate warming and carbon balance.

The Impact of Overstory Species and Soil Properties on the Growth of Planted Silver Fir Abies alba in the Karkonosze Mountains, Poland

Silver fir Abies alba was once an abundant tree species in the Karkonosze Mts. in Poland but its population has decreased. The aim of our study was to assess 1) the impact of canopy trees on the growth dynamics of silver fir saplings and 2) the relationship between the growth rate of silver fir saplings and the soil properties, with special regard to the soil enzyme activity. The study was conducted in the Karkonoski National Park on five experimental plots. Silver fir seedlings were planted in Scots pine, European larch, Norway spruce, silver birch and European beech stands in 1999. In 2016, we measured the diameter at breast height (DBH) and height of the canopy trees and the height, DBH, height increments, needle width and length of 100 silver fir saplings. The dehydrogenase, urease, phosphatase and asparaginase activity was analysed in organic and humus soil horizons. The height, diameter and needle dimensions of young silver fir trees were significantly different under different canopies. The urease and asparaginase activity was the highest under the larch and spruce canopy in both soil horizons. Phosphatase activity was also the highest under larch canopy but only in organic soil horizon. Young silver fir (thicket) has grown under the canopy of all tested tree species but found best growth conditions under larch and pine canopies. The relative growth of silver fir is therefore a function of both stand canopy and soil properties.

Soil Microbiome Composition along the Natural Norway Spruce Forest Life Cycle

Stand-replacing disturbances are a key element of the Norway spruce (Picea abies) forest life cycle. While the effect of a natural disturbance regime on forest physiognomy, spatial structure and pedocomplexity was well described in the literature, its impact on the microbiome, a crucial soil component that mediates nutrient cycling and stand productivity, remains largely unknown. For this purpose, we conducted research on a chronosequence of sites representing the post-disturbance development of a primeval Norway spruce forest in the Calimani Mts., Romania. The sites were selected along a gradient of duration from 16 to 160 years that ranges from ecosystem regeneration phases of recently disturbed open gaps to old-growth forest stands. Based on DNA amplicon sequencing, we followed bacterial and fungal community composition separately in organic, upper mineral and spodic horizons of present Podzol soils. We observed that the canopy opening and subsequent expansion of the grass-dominated understorey increased soil N availability and soil pH, which was reflected in enlarged bacterial abundance and diversity, namely due to the contribution of copiotrophic bacteria that prefer nutrient-richer conditions. The fungal community composition was affected by the disturbance as well but, contrary to our expectations, with no obvious effect on the relative abundance of ectomycorrhizal fungi. Once the mature stand was re-established, the N availability was reduced, the pH gradually decreased and the original old-growth forest microbial community dominated by acidotolerant oligotrophs recovered. The effect of the disturbance and forest regeneration was most evident in organic horizons, while the manifestation of these events was weaker and delayed in deeper soil horizons.

Not all long-distance-exploration types of ectomycorrhizae are the same: differential accumulation of nitrogen and carbon in Scleroderma and Xerocomus in response to variations in soil fertility

Long-distance-exploration type (LDET) ectomycorrhizae have been reported to be best adapted to infertile soils, but variation within LDET ectomycorrhizae have not been thoroughly examined. Concentrations of nitrogen (N) and carbon (C) in LDET ectomycorrhizae were examined in Xerocomus-Pinus sylvestris and Scleroderma-Quercus petraea ectomycorrhizae. The study determined how concentrations of these elements vary in ectomycorrhizae in fertile (organic, uppermost mineral) and infertile (brunic) soil layers. The organic horizon in both Scots pine and sessile oak forest soils had the highest mineral status and exchange cations. In contrast, low mineral concentrations, high base saturation, and pH were characteristic of the brunic horizon in both forest stands. Xerocomus ectomycorrhizae had a higher concentration of N in the fertile (organic and uppermost mineral) soil horizons (3.4%) than in the infertile (brunic) soil horizon (2.2%). N concentration in Scleroderma ectomycorrhizae varied from 2.8%-3.0 % and did not differ between the studied soil horizons. The mean concentration of carbon in Xerocomus ectomycorrhizae varied from 29%-46% in Scots pine stands and from 41%-44% in Scleroderma ectomycorrhizae in sessile oak stands. The concentration of carbon in both Xerocomus and Scleroderma ectomycorrhizae was significantly higher in the fertile horizons (organic and uppermost mineral) compared to the brunic (infertile) horizon. In summary, the analysis conducted in the present study indicates that the LDET ectomycorrhizae, Xerocomus and Scleroderma, possess inherent variations in C and N content to manage soil resources.

Differences in microbial community response to nitrogen fertilization result in unique enzyme shifts between arbuscular and ectomycorrhizal-dominated soils.

While the effect of nitrogen (N) deposition on belowground carbon (C) cycling varies, emerging evidence shows that forest soils dominated by trees that associate with ectomycorrhizal fungi (ECM) store more C than soils dominated by trees that associate with arbuscular mycorrhizae (AM) with increasing N deposition. We hypothesized that this is due to unique nutrient cycling responses to N between AM and ECM-dominated soils. ECM trees primarily obtain N through fungal mining of soil organic matter subsidized by root-C. As such, we expected the largest N-induced responses of C and N cycling to occur in ECM rhizospheres and be driven by fungi. Conversely, as AM trees rely on bacterial scavengers in bulk soils to cycle N, we predicted the largest AM responses to be driven by shifts in bacteria and occur in bulk soils. To test this hypothesis, we measured microbial community composition, metatranscriptome profiles, and extracellular enzyme activity in bulk, rhizosphere, and organic horizon (OH) soils in AM and ECM-dominated soils at Bear Brook Watershed in Maine, USA. After 27years of N fertilization, fungal community composition shifted across ECM soils, but bacterial communities shifted across AM soils. These shifts were mirrored by enhanced C relative to N mining enzyme activities in both mycorrhizal types, but this occurred in different soil fractions. In ECM stands these shifts occurred in rhizosphere soils, but in AM stands they occurred in bulk soils. Additionally, ECM OH soils exhibited the opposite response with declines in C relative to N mining. As rhizosphere soils account for only a small portion of total soil volume relative to bulk soils, coupled with declines in C to N enzyme activity in ECM OH soils, we posit that this may partly explain why ECM soils store more C than AM soils as N inputs increase.

Geospatial Modeling of Nitrogen and Carbon Content and Stock in the Forest Litter Horizons Based on Sentinel-2 Multi-Seasonal Satellite Imagery

The capabilities of Sentinel-2 optical multispectral satellite data for modeling nitrogen (N) and carbon (C) contents, their ratio (C : N), and stocks in the litter horizons of forest soils were assessed. The study was conducted in the Bryansk Forest Nature Reserve and its buffer zone. The organic horizon samples were taken on 33 plots selected with due account for the tree species diversity of the reserve’s forests. Two layers of the organic horizon—L and FH—were sampled separately. The main variables for geospatial modeling were derived from a time series of eight Sentinel-2 multi-seasonal satellite images. Basic terrain characteristics and pixel coordinates were also added to variables’ stack. We used random forest to build regression models and the corresponding standard methods to assess their performance. The best results were obtained for the C : N ratio: the coefficient of determination R2 = 0.71 with a scaled root-mean-square error RMSE = 12.5% in the L layer, and R2 = 0.83 with RMSE = 10.6% in the FH layer. For other models, the values of R2 ranged from 0.23 to 0.61, and the RMSE ranged from 15.8 to 48.6% with the least reliable results for the N and C stocks. Satellite-based variables were most informative for the contents of N and C, and, notably, for the C : N ratio. The most significant periods in the time series were early spring, summer, and snowy winter. To conclude, Sentinel-2 satellite imagery can be successfully used for estimation and mapping the contents and stocks of N and C in the forest soil organic horizon as a free and relevant alternative to thematic data on the species composition and related properties of stands.

Differences in phenolics produced by invasive Quercus rubra and native plant communities induced changes in soil microbial properties and enzymatic activity

Invasive trees can alter soil properties and ecosystem functioning by producing phenolic compounds. Phenolics can influence carbon and nitrogen availability as well as enzymatic activity or act as signaling molecules. In plant-microorganism interactions, species-specific phenolics can be the source of food or toxicity. They may have antimicrobial, stimulatory or both (ambiguous) properties and thus affect soil microbial properties, enzymatic activity, and plant-soil feedbacks differently. We hypothesized that phenolic compounds with antimicrobial properties produced by invasive Quercus rubra would reduce soil microbial biomass and enzymatic activity, and alter microbial community structure. We expected these changes to be most pronounced in the soil organic horizon as they are driven by litter chemistry. We tested changes, potentially associated with the concentrations of 12 phenolic compounds in Q. rubra litter and soil, in microbial properties (respiration rate, bacterial and fungal biomass), enzymatic activity, and microbial community structure in organic and mineral soil horizons as well as in arbuscular mycorrhizal fungi (AMF) spore number and species richness in mineral soil horizon. We found that Q. rubra reduced several soil parameters, namely respiration rate, phosphatase activity, total microbial biomass, bacterial (both G + and G–) biomass, and 16:1ω5 NLFA AMF storage lipid marker as well as changed microbial community structure, which supports our hypothesis that the phenolics produced by Q. rubra have mostly toxic effect on native soil communities. However, Q. rubra did not affect arylsulfatase and urease activity, saprotrophic fungi population, and the number of AMF spores and species. The changes in soil microbial properties and enzymatic activity may be related to high amounts of ellagic acid, ferulic acid, phloridzin, and syringic acid provided with newly shed Q. rubra litter to the soil surface. Some phenolics found in soil, i.e., phloridzin and (–)-epicatechin, correlated negatively, while others, i.e., quercetin and chlorogenic acid, correlated positively with soil microbial parameters and/or enzymatic activity, which suggest either antimicrobial or stimulatory properties of these compounds. Our study demonstrated that invasive Q. rubra has multiple potential effects on soil microbial communities, which can mediate plant-soil feedbacks. Future research should address the long-term consequences of these changes for forest ecosystems and the fitness of native flora.

Geochemical Features of Cryogenic and Al–Fe-Humus Soils of Mountainous Taiga in Northern Mongolia

Geochemical features of permafrost-affected (Folic Protic Leptic Cryosols, Histic Protic Leptic Cryosols) and Al-Fe-humus soils (Folic Leptic Entic Podzols, Histic Leptic Entic Podzols) have been studied. These soils are widespread in taiga forests of Khentei, Eastern Sayan, and Khangai mountains. Data on the microelemental composition of parent rocks are given. The dispersion coefficients of most of the studied microelements in parent rocks relative to the lithosphere exceed 1.0, which indicates the predominance of processes of material removal. Differences in the concentrations of microelements in soils largely depend on the texture of parent rocks. Data on the morphology, physicochemical and chemical properties of soils and on the distribution of microelements in the soil profiles are discussed. The studied soils differ both in the absolute contents of microelements involved in the biological cycle and the intensity of their biogenic migration. The intensive biogenic migration of elements results in their accumulation in organic and raw-humus soil horizons and in the accumulative patterns of element distribution in the soils of the altitudinal zones of forest vegetation. In contrast to Cryosols, the organic and raw-humus horizons of Entic Podzols are characterized by a less intensive accumulation of microelements. In the Al–Fe-humus (spodic) horizon of Podzols, the concentrations of Pb, Cr, Mo, and B are above the clarke level. Spodic horizons of the studied soils act as chemosorption geochemical barrier for some biophilous elements and elements of the iron group.

A New Approach Using Modeling to Interpret Measured Changes in Soil Organic Carbon in Forests; The Case of a 200 Year Pine Chronosequence on a Podzolic Soil in Scotland

Scotland is continuing to afforest land in order to combat climate change, but the long-term capacity for carbon sequestration in forest soils is still uncertain. Soil organic carbon stock changes were studied in a >120 year-old Scots pine chronosequence and adjacent grassland sites on podzolic soils. Significant differences were observed in the top organic soil horizons, while no changes were noted in the deeper mineral soil horizons. Simulations with the RothC-26.3 model revealed that pine forests could lose a significant amount of soil organic carbon through management operations. The lowest modelled stocks of soil organic carbon were not in the young sites (0-25 years old), but at 43 years since reforestation. Using measured data from our study site, simulations of grassland afforestation suggested that accumulation of organic carbon under forest is mainly in the organic horizons, while the deeper mineral soil horizons are likely to become depleted in soil organic carbon compared to grasslands. Our simulations suggest that afforestation of grasslands would increase overall soil carbon stocks but deplete the more stable carbon pools in the deeper mineral soils, which is not a desirable outcome in the context of climate change. The measurements provide comparative estimates of SOC in grassland and forestry sites at steady state; few studies provide these comparative measures. This study presents a new method for simulating soils that are accumulating carbon using the assumption of steady state with respect to the rate of accumulation. The approach has never been presented before and could have important implications for estimates of impacts of land use and climate change on the large SOC stocks held in highly organic soils. Subsequent simulations provide a new method for interpolating measurements that allow the losses due to management operations to be determined.

Removing riparian Rhododendron maximum in post-Tsuga canadensis riparian forests does not degrade water quality in southern Appalachian streams

In the past century, the evergreen woody shrub, Rhododendron maximum, has experienced habitat expansion following foundational tree species die-off in eastern US deciduous forests. Rhododendron can potentially alter stream chemistry, temperature, trophic dynamics, and in-stream decomposition rates, given its dominance in riparian areas. Here we conducted two operational-scale (3 ha) riparian treatments that removed rhododendron through cutting alone (CR, canopy removal), or removing both the rhododendron canopy and forest floor using cutting and prescribed fire (CFFR, canopy and forest floor removal). We expected that rhododendron shrub removal, with or without soil organic horizon removal, would increase soil nutrient availability and subsequently alter stream pH, acid neutralizing capacity (ANC), inorganic nitrogen (NO3-N, NH4-N), total dissolved inorganic nitrogen, dissolved organic carbon (DOC), calcium (Ca), potassium (K), and magnesium (Mg). We hypothesized that responses would occur more quickly in the CFFR treatment. Treatments reduced shrub-, but not tree basal area. Treatments lowered soil N, but not C. Stream chemistry responses to treatments varied between CR and CFFR and were transient, generally with pH, N, and some cations declining, and aluminum (Al) and DOC showing a pulse increase. By removing rhododendron, the remaining deciduous trees likely accelerated N uptake as soil moisture availability increased. This could partially explain why we observed lower than expected stream nutrients (NO3-N, Ca, and Mg) after treatments. Initial rhododendron slash on the forest floor coupled with incomplete consumption of the O-horizon on the CFFR treatment likely elevated DOC in the upper soil horizons and mobilized Al. From a management perspective, using these treatments to restore structure and function to riparian forests in the wake of eastern hemlock mortality, with or without fire, would most likely not result in short-term diminished water quality that is common when overstory trees are harvested and may even lower stream NO3-N concentrations long term.

Effects of plant functional group removal on CO2 fluxes and belowground C stocks across contrasting ecosystems.

Changes in plant communities can have large effects on ecosystem carbon (C) dynamics and long‐term C stocks. However, how these effects are mediated by environmental context or vary among ecosystems is not well understood. To study this, we used a long‐term plant removal experiment set up across 30 forested lake islands in northern Sweden that collectively represent a strong gradient of soil fertility and ecosystem productivity. We measured forest floor CO2 exchange and aboveground and belowground C stocks for a 22‐yr experiment involving factorial removal of the two dominant functional groups of the boreal forest understory, namely ericaceous dwarf shrubs and feather mosses, on each of the 30 islands. We found that long‐term shrub and moss removal increased forest floor net CO2 loss and decreased belowground C stocks consistently across the islands irrespective of their productivity or soil fertility. However, we did see context‐dependent responses of respiration to shrub removals because removals only increased respiration on islands of intermediate productivity. Both CO2 exchange and C stocks responded more strongly to shrub removal than to moss removal. Shrub removal reduced gross primary productivity of the forest floor consistently across the island gradient, but it had no effect on respiration, which suggests that loss of belowground C caused by the removals was driven by reduced litter inputs. Across the island gradient, shrub removal consistently depleted C stocks in the soil organic horizon by 0.8 kg C/m2. Our results show that the effect of plant functional group diversity on C dynamics can be relatively consistent across contrasting ecosystems that vary greatly in productivity and soil fertility. These findings underline the key role of understory vegetation in forest C cycling, and suggest that global change leading to changes in the relative abundance of both shrubs and mosses could impact on the capacity of boreal forests to store C.

Elemental composition of soils of the Pur-Taz interfluve

In order to evaluate the chemical composition of natural background environments of Pur-Taz interfluve (Western Siberia), the mineral components of soils, peats, lichens, and sphagnum mosses have been analyzed. The samples were tested using X-ray fluorescence technology. The average contents of hazardous metals in the soils of the Pur-Taz interfluve are either lower (for Cu, Pb, Zn, Ni, Sr) or equal to (for Hg, Co) the average values of these elements in the Earth's crust. This finding corresponds to the commonly held view that the contents of elements in the soils located in the north of Western Siberia are lower than the world averages. Additionally, in our samples low concentrations of copper and zinc have been observed. Since these microelements are important for soil physiology, this finding indicates unfavorable biochemical conditions in the research area. On the other hand, high concentrations are observed for inactive elements such as Mo, Sn and Zr. The significant differences have been identified in the composition of mineral and organic soil horizons. For instance, the average concentrations of P, Zn and S in organic horizons are 7.1, 8.1 and 18 times greater than in the illuvial mineral horizons, respectively. The intense accumulation of Zn, Cu, Cd, Hg has been recorded, all of them are chalcophiles in the ombrotrophic peat. This means that the chemical composition of soil is largely determined by biological accumulation of chalcophile elements. The content of lithophilic Al, Si, Ti and Zr, coming with dust precipitation from the atmosphere increases in the peat of dwarf shrub-moss-lichen tundras and larch woodlands. The revealed values of the elemental composition of soils can be recommended as background in the course of the environmental monitoring.

Effects of elevated pH and phosphorus fertilizer on soil C, N and P enzyme stoichiometry in an acidic mixed mesophytic deciduous forest

Long-term additions of lime and/or phosphate fertilizer caused an indirect and/or direct increase in the availability of P in mixed mesophytic deciduous forest soil on the unglaciated portion of the Allegheny Plateau, southeast Ohio, USA. As expected, the activities of extracellular phosphatases declined across all treatments (by 23–65%), in both organic and mineral soil horizons. In contrast, there were few effects of P availability on either C or N acquiring extracellular enzyme activities. However, enzyme vector analysis showed the relative activity of phosphatases decreased with respect to N-acquiring enzymes (vector angles fell 4–30%) and the relative activity of C acquisition increased (vector lengths rose 9–51%) relative to the activities of both N and P acquiring enzymes. Thus, the overall ecoenzymatic stoichiometry of extracellular enzymes was altered by P availability. Also, the relative contribution of phosphodiesterase declined relative to phosphomonoesterase by an average of 16 ± 16% as overall phosphatase activity declined, suggesting a reduction in the relative contribution of the less efficient enzyme as P demand decreased. Finally, contrary to expectations, the relative contribution of leucine aminopeptidase to total N acquiring enzyme activity did not increase with pH, but showed a bimodal relationship to soil NH4+ concentration. In summary, phosphatase activity declined with increased P availability but with little response in C or N acquiring activity suggesting emerging co-limitations by C and/or N in this ecosystem.

Air moisture and soil texture are crucial for the water dynamics of riparian bamboo in a subtropical region

This study investigated the influence of soil properties and plant age on the water use pattern of Bambusa rigida at different distances from a river during the dry season. The oxygen and hydrogen isotope compositions (δ18O and δ2H) of soil water and culm water in B. rigida forests from sites located at different distances from a river (site A: beside the river with high air moisture; site B: 200 m from the river with high clay content; site C: 400 m from the river with low clay content) were measured. Water uptake was not affected by plant age during early summer. Bambusa rigida at site A were able to use water from the soil organic horizon and moist air contributed 26% and 16% of soil water in this layer during winter and early summer. Bambusa rigida mainly took up water from soil layers with a high clay content at a depth < 50 cm due to the high water storage of these layers, although a high clay concentration weakened water uptake of bamboo roots at greater depths. This study is the first to identify the importance of air moisture for water dynamics of riparian bamboo and offers new insights into water use strategies of riparian B. rigida.

Generalized models to estimate carbon and nitrogen stocks of organic soil horizons in Interior Alaska

Abstract. Boreal ecosystems comprise one-tenth of the world's land surface and contain over 20 % of the global soil carbon (C) stocks. Boreal soil is unique in that its mineral soil is covered by what can be quite thick layers of organic soil. These organic soil layers, or horizons, can differ in their state of decomposition, source vegetation, and disturbance history. These differences result in varying soil properties (bulk density, C concentration, and nitrogen concentration) among soil horizons. Here we summarize these soil properties, as represented by over 3000 samples from Interior Alaska, and examine how soil drainage and stand age affect these attributes. The summary values presented here can be used to gap-fill large datasets when important soil properties were not measured, provide data to initialize process-based models, and validate model results. These data are available at https://doi.org/10.5066/P960N1F9 (Manies, 2019).

Carbon sequestration and storage in Norwegian Arctic coastal wetlands: Impacts of climate change

Coastal wetlands contain some of the largest stores of pedologic and biotic carbon pools, and climate change is likely to influence the ability of these ecosystems to sequester carbon. Recent studies have attempted to provide data on carbon sequestration in both temperate and tropical coastal wetlands. Alteration of Arctic wetland carbon sequestration rates is also likely where coastal forcing mechanisms interact directly with these coastal systems. At present there are no data available to provide a detailed understanding of present day and historical carbon sequestration rates within Arctic coastal wetlands.In order to address this knowledge gap, rates of carbon sequestration were assessed within five Arctic coastal wetland sites in Norway. This was undertaken using radiometric dating techniques (210Pb and 137Cs) to establish a geochronology for recent wetland development, and soil carbon stocks were estimated from cores.Average carbon sequestration rates were varied, both between sites and over time, ranging between 19 and 603 g C m2 y−1, and these were correlated with increases in the length of the growing season. Stocks ranged between 3.67 and 13.79 Mg C ha−1, which is very low compared with global average estimations for similar coastal systems, e.g. 250 Mg C ha−1 for temperate salt marshes, 280 Mg C ha−1 for mangroves, and 140 Mg C ha−1 for seagrasses. This is most likely due to isostatic uplift and sediment accretion historically outpacing sea level rise, which results in wetland progradation and thus a continuous formation of new marsh with thin organic soil horizons. However, with increasing rates of sea level rise it is uncertain whether this trend is set to continue or be reversed.