Nitrogen Stocks Research Articles

How hydrogen sulfide deposition from oil exploitation may affect bacterial communities and the health of forest soils in Congolese coastal plains?

The hydrogen sulfide (H2S) deposition from oil exploitation occurring since 1969 may potentially affect bacterial communities in acacia and eucalyptus plantations of the Congolese coastal plains. These plantations have been implemented on previous native savannas to use the unsuitable soils for agriculture, provide pulp wood and fuel wood energy, and preserve the natural forests. Increased carbon (C) and nitrogen (N) stocks in stands containing acacia relative to baseline (eucalyptus) stocks have been reported. Phosphorus availability also improved in coarse particulate organic matter (4,000–250 µm) in afforested stands as compared to natural savannas. Investigation of the abundance of bacterial phyla by metabarcoding of the 16S rRNA bacterial gene in different stands of monocultures and mixed-species stands reveals the prevalence of Actinobacteria in all stands. This phylum is generally associated with the presence of sulfur in industrial areas and has a crucial role in organic matter decomposition. This may be linked to improved soil attributes (C, N, and P) and related to oil exploitation in addition to natural processes. This review shows, therefore, how potentially human activities may impact bacterial community composition, which may further change other soil attributes. It also acknowledges that the sustainability of forest plantations on inherently nutrient-poor soils strongly relies on interactions between soil functions, the environment, and human activities driven by soil organisms.

Fire Impact on Carbon Pools and Basic Properties of Retisols in Native Spruce Forests of the European North and Central Siberia of Russia

Fires play an important role in the modern dynamics of boreal ecosystems. The article presents the results of studying the effect of old fires on soils and soil organic matter (SOM) of native spruce forests that were last affected by fires in the previous 100 to 200 years. The studies were carried out in the European north-east of Russia (Komi Republic) and Central Siberia (Krasnoyarsk region). The objects of the study were typical Glossic Stagnic Retisol (Siltic, Cutanic). The time after the fire was determined by dendrochronological methods. Data on the content of water-soluble organic matter and densimetric fractions of soils were obtained; carbon and nitrogen stocks were calculated. The content of polycyclic aromatic hydrocarbons (PAHs) was established to characterize the effect of fires. Pyrogenic carbonaceous inclusions were morphologically diagnosed 200 years after the fire. In this regard, it is proposed to distinguish a “pyrogenic” subtype for soils with pronounced signs of pyrogenesis. Carbon stocks in soils of the Komi Republic varied from 5.7 to 15.7 kg C m−2, and soils of the Krasnoyarsk region had an accumulation of 6.9–12.5 kg C m−2. The contribution of the pyrogenic horizon Epyr to the total carbon and nitrogen stocks was 9–45%. It is suggested that pyrogenic carbon (PyC) can accumulate in light densimetric fractions (fPOM<1.6 and oPOM<1.6). The analysis of PAH content showed their high concentrations in the organic and upper mineral horizons of the studied soils (24 to 605 ng g−1). The coefficient FLA (fluoranthene)/(FLA+PYR(pyrene)) was the most useful to diagnose the pyrogenic origin of PAHs in the studied Retisols.

Fungal biomass and microbial necromass facilitate soil carbon sequestration and aggregate stability under different soil tillage intensities

The aim of global carbon (C) neutrality brings soils and their potential for C storage into the spotlight. Improved agricultural management techniques such as minimum or no-tillage are thought to foster soil C sequestration. However, the underlying mechanisms are still not well understood. In this study, we investigated the inter-relations of soil organic C (SOC), fungal biomass, microbial necromass biomarkers, and aggregate stability in rhizosphere and bulk soil after thirteen years of reduced tillage intensities (reduced, minimum, and no-tillage). Overall, rhizosphere and bulk soil were indifferent in their response to reduced tillage. Reducing tillage intensity increased SOC and nitrogen stocks and dissolved organic C contents in the following order: minimum > no-tillage > reduced > conventional. Aggregate stability showed the strongest increase under no-tillage. Interestingly, ergosterol contents were highest under reduced and minimum tillage followed by no-tillage. The amino sugars muramic acid, galactosamine, and glucosamine – proxies for soil microbial-derived necromass – showed similar increases under all three tillage reduction systems. Structural equation modelling revealed that increased dissolved organic C contents under reduced tillage intensity facilitated SOC sequestration and aggregate stability through enhanced fungal biomass to necromass turnover. Thus, reducing soil tillage intensity is a valuable tool to facilitate microbial growth and hence to increase SOC sequestration in agricultural soils.

Short-Term Effects of Bamboo Plantation on Soil Carbon Fractions, Carbon and Nitrogen Stocks in Eastern Himalayas, India

Forest degradation and land-use change are considered as the major activities resulting in loss of carbon (C) from soil and both the issues are major concern in Eastern Himalayan region (EHR) of India. Apart from this, bamboo is a widely distributed species in tropical/sub-tropical forest ecosystems of EHR. The current study was planned to assess the impacts of bamboo plantation on carbon fractions, C and nitrogen (N) stocks in soil. For this, the selected site was revisited three times, before and after the bamboo plantation. It was found that the value of bulk density (BD) increased significantly (1.27 g cm−3) after the plantation of bamboo and was recorded after four years of plantation, while effect on soil organic carbon (SOC) was not significant. However, SOC stocks (54.23 t C ha−1) and C:N (5.15) ratio were increased significantly and both TN contents and stocks were decreased with bamboo age. Moreover, very labile and labile fractions were significantly influenced after bamboo plantation. In addition, accumulation of less labile (2.03 mg g−1) and non-labile (1.68 mg g−1) was also recorded under bamboo plantation. The results clearly reveal that the soil carbon pools increased under bamboo soils and their sequestration potential can be harnessed to combat the land degradation and soil rehabilitation issues, thus, plantation of bamboo under fallow lands can be recommended as sustainable land management practice.

The Distribution of Soil Carbon and Nitrogen Stocks Among Dominant Geomorphological Terrain Units in Qarlikturvik Valley, Bylot Island, Arctic Canada

AbstractSoils of circumpolar regions store large amounts of carbon (C) and are a crucial part of the global C cycle. Yet, little is known about the distribution of soil C stocks among geomorphological terrain units of glacial valleys in the Arctic. Soil C and nitrogen (N) content for the top 100 cm of the dominant vegetated geomorphological terrain units (i.e., alluvial fans, humid polygons, mesic polygons) at Qarlikturvik Valley, Bylot Island, Canada have been analyzed. Soil C content was greatest in humid low‐center ice‐wedge polygons (82 kg m−2), followed by mesic flat‐center ice‐wedge polygons (40 kg m−2), and alluvial fan area (16 kg m−2), due to prevailing geomorphological processes, differences in vegetation and soil characteristics, as well as permafrost processes. Soil N content was greatest in humid polygons (4 kg m−2), followed by mesic polygons (2 kg m−2), and alluvial fan area (1 kg m−2). Vertically, C and N decreased with increasing depth except for a peak in C at depth in humid polygons, a likely result of past changes in vegetation cover. At Qarlikturvik Valley, which has a size of 121.7 km2, alluvial fans store 0.226 Tg organic C and humid and mesic polygons store 1.643 and 0.218 Tg organic C, respectively in the top 100 cm of soil. Findings like these are important to further constrain pan‐Arctic soil C and N stock estimates and thus climate models.

Total Nitrogen Stock in Soil Profile Affected by Land Use and Soil Type in Three Counties of Mollisols

Soil total nitrogen is the major indicator of soil fertility and quality in agricultural ecosystems. However, few comparative studies investigated the spatial patterns of soil total nitrogen density (STND) in deep soils of different land uses and soil types. Therefore, our study aimed to identify the influence of environmental factors on spatial variability in STND by comparing the STND spatial patterns of different land uses and soil types in a typical Mollisols in northeast China. Results showed that land use types did not significantly affect STND, but the soil types did. The STND was more heterogeneous above 60 cm than that in subsoil, and no significant changes in STND were found in the same land use or soil type. The STND had a significant correlation with SOC, soil BD and pH regardless of land use or soil type. The STND in the soil profile (100 cm) and top 20 cm was fitted using a mathematical model. The results provided insights into nitrogen cycle and stock in similar areas in northeast China.

Effects of Sewage Sludge Application on Plant Growth and Soil Characteristics at a Pinus sylvestris var. mongolica Plantation in Horqin Sandy Land

The application of domestic sewage sludge (SS) may affect plant growth and soil quality through altering nutrient availability. However, the effect of SS application on the plant–soil system in sandy soils is poorly understood. In this study, we established SS application treatment plots (SL, 25 t ha−1) and control treatment plots without sewage sludge application (CK, 0 t ha−1). SS was applied to the soil surface of a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Horqin Sandy Land, Inner Mongolia, China, to assess its potential effects on plants and soil. We analyzed tree growth performances (tree height, basal diameter, and diameter at breast height), understory traits (species diversity, coverage, and aboveground biomass), soil physical and chemical parameters (nutrient content, dissolved organic carbon, soil water content, bulk density, pH), and proxies of ecosystem services (soil organic carbon and total nitrogen stocks). The results showed that SS addition not only significantly increased soil nutrient contents, but also markedly enhanced aboveground productivity and plant coverage. Specifically, SS addition decreased soil bulk density and increased concentrations of soil organic carbon, total nitrogen, and total phosphorus and mineral nitrogen, and it also increased soil carbon and nitrogen stocks. Furthermore, the addition of SS significantly increased soil dissolved organic carbon contents and enhanced the fluorescence intensities of dissolved organic carbon components (humic acid-like and UV fulvic acid-like) in the topsoil (0–5 cm). This study provides evidence that SS is an acceptable, and possibly preferred organic fertilizer for improving the soil quality and tree–grass growth of Mongolian pine plantations.

Microdosing of Compost for Sustainable Production of Improved Sorghum in Southern Mali

The depletion of soil organic matter is one of the major challenges constraining agricultural production in the southern zone of Mali. This study evaluated the effects of compost types, methods, and dose applications on the productivity and sustainability of sorghum. Two types of compost (farmer practice and cotton stems) were applied to sorghum at two rates (microdosing at 2.5 t ha−1 and broadcasting at 5 t ha−1) and evaluated on 30 farmer fields in 2019 and 2020. The treatments used included CPA (cotton stem compost at 5 t ha−1 + 100 kg ha−1 DAP), CPA (cotton stem compost at 2.5 t ha−1 + 100 kg ha−1 DAP), CP (farmer compost at 5 t ha−1 + 100 kg ha−1 DAP), CP (famer compost at 2.5 t ha−1 + 100 kg ha−1 DAP), control (100 kg ha−1 DAP), and control. The results showed that regardless of the compost type, applying a microdose of 2.5 t ha−1 improved the growth rate, plant height, grain yield, and biomass yield by 15%, 18%, 47%, and 27%, respectively, when compared to the control. No statistical difference was observed in the yield of 2061 kg ha−1 between applying compost by microdosing at 2.5 t ha−1 and broadcasting at 5 t ha−1. It can be inferred that the application of compost by microdosing makes it possible to achieve a 100% fertilized surface compared to broadcasting, with a nitrogen use efficiency of more than 55%. The application of compost by microdosing at 2.5 t ha−1 resulted in an economic gain of 334,800 XOF ha−1, which was 27% higher than that obtained with the application of compost by broadcasting at 5 t ha−1. Conversely, the contribution to the improvement of soil nitrogen stock varied from 12–20% with a microdose of 2.5 t ha−1 compared to 100% for broadcasting compost at 5 t ha−1 per application. Therefore, the availability of cotton stems in the southern zone of Mali presents an opportunity for farmers to implement compost microdose technology to double the fertilized area and improve sorghum productivity.

Alder-induced stimulation of soil gross nitrogen turnover in a permafrost-affected peatland of Northeast China

For the prediction of permafrost nitrogen (N) climate feedbacks, a better process-based understanding of the N cycle in permafrost ecosystems is urgently needed. Therefore, we characterized and quantified soil organic matter, gross soil microbial ammonification and nitrification and soil-atmosphere exchange of nitrous oxide (N2O) of boreal permafrost ecosystems on the southern edge of the Eurasian permafrost area in situ.Soil organic carbon (SOC) and total nitrogen (TN) stocks (top 0.5 m) of tree-free lowland peatland (LP) soils exceeded those of gravel-rich upland forest (UF) soils by an order of magnitude. Nuclear magnetic resonance spectroscopy revealed more recalcitrant organic matter at greater depth and more bioavailable organic matter substrates in upper peat horizons. In line with this result, gross ammonification and nitrification generally decreased with increasing sampling depth. Gross rates of mineral N turnover in active layers were comparable to those of temperate ecosystems. Despite substantial gross ammonification, the low nitrification:ammonification ratios and negligible soil N2O emissions depicted however a closed N cycle at UF and LP characterized by N limitation.In strong contrast, the lowland peat soils underneath alder trees (LA), being associated with diazotrophic bacteria in root nodules, showed an accelerated N turnover with very high gross rates of ammonification (3.1 g N m−2 d−1) and nitrification (0.5 g N m−2 d−1), exceeding those of UF and LP soils by an order of magnitude. This was accompanied by substantial N2O emissions comparable to temperate agricultural systems or tropical forests. The increase in gross soil microbial ammonification and nitrification was most pronounced in the rooted soil layer, where N inputs from biological N fixation almost doubled TN concentrations and halved SOC:TN ratios. The frozen ground of LA contained strongly increased ammonium concentrations that might be prone to release upon thaw via subsequent nitrification. This study shows that alder forests that further expand on permafrost-affected peatlands with global change create hot spots of soil mineral N turnover, thereby potentially enhancing permafrost N climate feedbacks via N2O emissions.

Direct and indirect plant-soil interactions in a semi-arid Mediterranean shrubland (NE Spain)

Dynamics between plants and soil control important processes such as community succession, nutrient cycling or resilience to environmental change. Until now, most research on plant-soil interactions has focused on uni-directional and species-specific effects of plants on soil and vice-versa, under controlled-conditions experiments, but little is known about the direct and indirect interactions between the plant community and the underlying soil under field conditions. We investigated these interactions in a semi-arid shrubland from NE Spain. We sampled plant biomass, nitrogen availability in soil, soil microbial biomass C, soil water infiltration capacity, soil bulk density and quality of plant tissue. These parameters were related to each other to build a statistical plant soil interaction model that was analyzed through regression and Structural Equation Modeling analyses. This statistical model was hypothesized to reveal important mechanisms for community regulation. Plant biomass was fundamentally dependent on water infiltration capacity and microbial biomass C was fundamentally dependent on nitrogen availability. Plant biomass interacted indirectly with microbial biomass C by directly affecting nitrogen stock and quality of plant tissue. Similarly, plant biomass modulated the soil bulk density. We demonstrated that vegetation has a preeminent role in the regulation of biological processes in this ecosystem through control on nutrient status, microbial biomass and mechanical soil conditions. Conclusions extracted from this study can be valuable in restoring and conserving similar ecosystems at risk of disappearing due to desertification.

Changes in Soil Properties and Scots Pine Tree Growth Induced by Different Soil Ploughing Prior to Afforestation: A Case Study

Numerous studies have confirmed that forests have the potential for a significant contribution to carbon sequestration, but afforestation of former agricultural land can be attempted to adopt technologies that further encourage carbon sequestration. The aim of this study was to evaluate the impact of different soil cultivation methods, including deep ploughing and soil cultivation by making microsites and furrows prior to afforestation of former agricultural land, on chemical soil properties and tree growth in 20 years old Scots pine plantations. A naturally regenerated Scots pine stand, representing the non-ploughed soil, was included as a control site. Deep ploughing, among other soil cultivation methods, significantly altered the chemical soil properties. Furthermore, significant effects were indicated in the sites afforested after cultivation by making furrows. A recent study found that, due to deep soil cultivation, higher stocks of soil organic carbon (SOC) and total nitrogen (N) were incorporated into deeper soil layers and were protected from direct environmental impact. Twenty years post afforestation in deeply ploughed sites, we still found a decreased C:N ratio and disbalanced relationship between the concentrations of SOC and total N. The SOC and total N stocks were higher in the subsoil than in the topsoil in the sites afforested after deep ploughing. Moreover, deep ploughing and soil cultivation by furrows prior to afforestation resulted in higher total SOC and total N stocks in the forest floor and mineral 0–80 cm soil layer. A higher total phosphorus (P) concentration in the subsoil and total potassium (K) in the upper mineral soil layer were obtained in the deep ploughing sites and the sites, cultivated by furrows, compared to the non-ploughed sites. Significantly higher total P stock per entire profile was found for the deep ploughing sites and the sites cultivated by furrows than in the naturally regenerated stand. Different soil cultivation methods caused no differences in tree diameter at breast height (DBH) in 20 years old Scots pine stands both in the afforested sites and in the naturally regenerated forest. However, significantly larger tree height in all afforested sites than in the naturally regenerated Scots pine stands was obtained. A lower differentiation in tree DBH was obtained in the deep ploughing sites.

Effect of site elevation and soil depth on the biomass and carbon, nitrogen, and phosphorus stocks of roots in planted Kandelia obovata mangrove forests

Site elevation is one of the most important factors for successful mangrove restoration. Understanding how site elevation influences mangrove roots is critical for evaluating mangrove primary productivity, carbon dynamics and nutrient cycles. Root biomass and organic carbon (OC), total nitrogen (N), and total phosphorus (P) stocks were compared through an in situ experiment among 11‐year‐old Kandelia obovata mangrove forests planted under three intertidal elevations. Compared with site upper elevation, biomass of total root, live root, dead root, fine root, and coarse root decreased approximately 74.62, 79.82, 26.65, 42.52, and 87.09%, respectively, but contribution rates of fine root to total root increased 35.40% at site lower elevation. Biomass of total root and fine root at the three sites decreased with soil depth increases. Stocks of OC, N, and P in the total root decreased approximately 70, 52.92, and 47.30% from site upper elevation to site lower elevation owing to decreases in the total root biomass. Stocks of OC, N, and P in the total root and fine root also decreased with soil depth increases, while only OC stock of coarse root had a decreasing trend with soil depth increases. These indicated that decreases in site elevation will reduce mangrove primary productivity, carbon dynamics, and nutrient cycles due to decreases in root biomass. For K.obovata forests, upper elevation should be used in the future mangrove forest restoration projects to improve mangrove blue carbon capability.

Biocrusts as a nature-based strategy (NbS) improve soil carbon and nitrogen stocks and maize productivity in semiarid environment

Biological soil crust (BSC) as a nature-based strategy has a great potential to restore soil and water in arid and semi-arid natural ecosystems. Yet, little is known about its effects on soil fertility and productivity as affected by the BSC inoculation in agroecosystems. We hypothesis that BSC inoculation can improve soil quality, while increasing crop productivity and economic benefits in semiarid rainfed region. To address this issue, we carried out field experiment using forage maize (Zea mays L.) from 2018 to 2019, with four treatments as follows: 1) conventional flat planting (control, CK), 2) flat planting with the inoculation of BSC (BSC), 3) ridge-furrow planting (RF), and 4) sectional ridge-furrow planting (SRF). The results showed that BSC inoculation significantly enhanced maize shoot and root biomass by 53–63 % and 30–67 % accordingly (P < 0.05), compared with CK in two growing seasons.Also, BSC treatment slightly increased soil water content and soil temperature, while significantly decreasing soil pH and soil bulk density, relative to CK, RF and SRF (P < 0.05). Compared with CK, the BSC inoculation markedly improved soil microbial biomass carbon by 54 % and nitrogen by 52%, soil organic carbon by 21 %, and total nitrogen by 30% respectively (P < 0.05) Critically, the contents of above four parameters were 42 %, 32 %, 19 % and 32 % greater in BSC than RF and SRF, respectively (P < 0.05). Simultaneously, the BSC significantly decreased soil C/N ratio by 7 %, while SRF and RF slightly decreased C/N ratio by 0.2 % and 2 % only, in comparison with CK. Interestingly, soil C&N mineralization efficiency were significantly greater in the BSC treatment than CK, RF and SRF (P < 0.05). In addition, the economic benefit under BSC was the highest relative to other three planting systems In conclusion, BSC can be used as a nature-based strategy (NbS) to improve soil properties, promote microbial C&N uptake and utilization via enhancing C&N mineralization and lowering C-N ratio. In conclusion, BSC can act as a green solution to achieve high productivity and promote soil fertility in semiarid agricultural ecosystem.

Carbon and nitrogen stocks in cultivation systems of a Quilombola community in the Brazilian Cerrado

Carbon and nitrogen stocks in cultivation systems of a Quilombola community in the Brazilian Cerrado

Fire in lichen-rich subarctic tundra changes carbon and nitrogen cycling between ecosystem compartments but has minor effects on stocks

Abstract. Fires are predicted to increase in Arctic regions due to ongoing climate change. Tundra fires can alter carbon and nutrient cycling and release a substantial quantity of greenhouse gases with global consequences. Yet, the long-term effects of tundra fires on carbon (C) and nitrogen (N) stocks and cycling are still unclear. Here we used a space-for-time approach to investigate the long-term fire effects on C and N stocks and cycling in soil and aboveground living biomass. We collected data from three large fire scars (&gt;44, 28, and 12 years old) and corresponding control areas and used linear mixed-effect models in a Bayesian framework to analyse long-term development of C and N stocks and cycling after fire. We found that tundra fires had no long-term effect on total C and N stocks because a major part of the stocks was located belowground in soils which were largely unaltered by fire. However, fire had a strong long-term effect on stocks in the aboveground vegetation, mainly due to the reduction in the lichen layer. Fire reduced N concentrations in graminoids and herbs on the younger fire scars, which affected respective C/N ratios and may indicate an increased post-fire competition between vascular plants. Aboveground plant biomass was depleted in 13C in all three fire scars. In soil, the relative abundance of 13C changed with time after fire. Our results indicate that in lichen-rich subarctic tundra ecosystems, the contribution of fires to the release of additional carbon to the atmosphere might be relatively small as soil stocks appear to be resilient within the observed time frame.

Micronutrient Content, Soil Carbon and Nitrogen Stocks in Forested and Deforested Sites

Summary The research examines micronutrient contents, soil carbon and nitrogen stocks of forested and deforested sites at Bobiri forest reserve in the Ashanti region, Ghana. Each site had 12 soil profiles excavated, six of which were from natural forest areas and six were from deforested areas. The samples were taken at 0-15 cm, 15-50 cm and 50-80 cm depths and repeated thrice. The contents of DTPA-extractable micronutrients in the forested sites were higher than in the deforested sites at all soil depths. There were significant differences between the forested and deforested sites. The soils at 0-15 cm depth in the forested sites showed improved micronutrient contents, which largely declined with the soil depth. At the same time, there was no consistent pattern of distribution in the deforested soil. According to the findings, all three depths and sites tested had enough extractable Fe, Mn and Cu, however only 15-50 cm depth of forested and deforested sites had sufficient Zn. All the soil depths except 50–80 cm showed significant differences in soil organic carbon and nitrogen stocks in the forested sites compared to the deforested sites. The forested sites had the largest amount of total soil organic carbon stocks (365 Mg ha−1), whereas the deforested sites had the lowest amount (181 Mg ha−1). It was found that micronutrient content and distribution in the soils at the research sites were influenced by organic matter, clay and soil pH.

Effects of whole-tree and stem-only clearcutting on forest floor and soil carbon and nutrients in a balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) dominated ecosystem

Intensive harvesting of forest biomass for bioenergy has the potential to degrade forest soils and productivity if ecosystem carbon and other nutrients are depleted faster than replenished naturally or by management inputs. Climate change mitigation potential associated with bioenergy may be threatened if forest management operations reduce soil carbon stocks. Research reported here was initiated in 1979 to determine the effects of whole-tree harvesting on long-term site productivity and ecosystem carbon and nutrient pools and fluxes in a northeastern North American temperate balsam fir-red spruce forest. A sequence of harvesting and silvicultural treatments were applied from 1981 to 1993 using a paired-watershed experimental design. Treatments included whole-tree clearcutting, stem-only harvesting, simulated by return of chipped or lopped delimbing residue, conifer release by applying herbicide, and pre-commercial thinning and fertilizer application. Quantitative samples of the forest floor were excavated in 2016. Quantitative soil pits were sampled in 2017 to a depth of 50 cm below the forest floor, where possible; the basal till subsoil was sampled to a depth of 100 cm with an auger. Forest floor samples were analyzed for total carbon, nitrogen, phosphorus, potassium, calcium, magnesium and aluminum. Organic and mineral soil layer samples from the quantitative pits were analyzed for pH, short and long-lived soil carbon via 13C cross polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR), total carbon and nitrogen and extractable phosphorus, potassium, calcium, magnesium and aluminum. Forest floor carbon and nitrogen on whole-tree harvested plots 35 years after harvest were about 50% of the amount on the unharvested watershed. Stem-only harvesting partially mitigated the reduction, and gross losses were apparently offset by increases in the mineral soil solum to depth 50 cm, suggesting that downward translocation of soil organic matter was a significant ecosystem process during the 35 years since harvest. Accumulated forest floor and mineral soil stock of total carbon and nitrogen and extractable nutrients to depth 100 cm did not differ significantly between the harvested and unharvested watershed. A corresponding similarity in mineral soil pools of extractable phosphorus and non-acid cations in the two watersheds suggests that inputs from atmospheric deposition, primary and secondary mineral weathering, organic matter mineralization and litterfall balanced exports including leaching and plant uptake. Ecosystem stocks of extractable phosphorus, base cations, and total organic carbon and nitrogen were maintained 35 years after whole-tree harvesting of a primary spruce-fir forest.

Soil dissolved carbon and nitrogen dynamics along a revegetation chronosequence of Caragana korshinskii plantations in the Loess hilly region of China

Widespread vegetation restoration is an effective measure used to control soil erosion and improve soil organic carbon (SOC) and total nitrogen (TN) storage; however, knowledge of soil dissolved carbon and nitrogen has not been well characterized. Caragana korshinskii plantations are valued for their critical role in soil and water conservation in the Loess Hilly Region. This study aimed to estimate the levels of soil carbon and nitrogen and their dissolved fractions in one farmland (Zea mays L.) and three C. korshinskii plantations at 15, 30 and 40 years; additionally, the distribution of soil carbon and nitrogen stocks among various soil depths were estimated. The results showed that afforestation with C. korshinskii resulted in a significant increase in the contents and stocks of SOC and TN and their dissolved fractions. At a depth of 0–10 cm, the 30-year-old C. korshinskii had the highest stocks of SOC and TN, but at depths of 40–100 and 100–200 cm, the highest SOC and TN stocks were found in the soil of 15-year-old C. korshinskii. The 15-year-old C. korshinskii had the highest stocks of SOC and TN at depths of 0–200 cm and the highest stocks of dissolved nitrogen across almost all soil layers. The soil at 100–200 cm contained 34%–54% of the total percentages of the cumulative stocks of SOC and TN and their fractions. The SOC stock was the most important factor affecting the variation in soil nitrogen fractions and contributed to more than 80% of the total variation; additionally, the nitrate (NO3-N) content and stock were the most important factors affecting the soil carbon fractions, contributing to 78% of the total variation. This study demonstrates that revegetation age and soil depth play important roles in determining carbon and nitrogen levels. The results also suggest that C. korshinskii plantations should be harvested and revegetated during the rapid growth period (∼15 years) during which they show the largest accumulations of soil carbon and nitrogen.

Soil carbon and nitrogen stocks in traditionally managed rangeland biomes in Karamoja sub-region, Uganda

Rangelands are known for their potential in mitigating rising atmospheric carbon dioxide (CO2) concentrations in the world. The objective of this study was to investigate the patterns of soil organic carbon (SOC) and nitrogen (N) in rangelands under traditional management systems in Karamoja sub-region in Uganda, with a view to facilitating the development of appropriate and strategic management practices for the rangeland resources. The study was conducted during the wet season of the sub-region. Four land use/cover types (cropland, grassland, woodland and thickets/shrubland) were laid out in a completely randomised design. Soil samples were collected from four plots each one measuring 50 m x 40 m in each land use/cover type. A diagonal design was used for sample collection at depths of 0 - 15 and 15 - 30 cm. Results showed that at both soil depths, croplands had the lowest mean SOC and highest N; while grasslands had the highest SOC. Also, cropland recorded the highest mean soil bulk density at both depths. Based on soil analysis only, this study showed that conversion to cropland over a specified period of time can considerably reduce the ability of rangelands to sequester carbon. Further studies to include assessment of carbon stocks in the respective vegetation biomass are recommended.

Biogeochemical and ecosystem properties in three adjacent semi‐arid grasslands are resistant to nitrogen deposition but sensitive to edaphic variability

AbstractDrylands have low nitrogen stocks and are predicted to be sensitive to modest increases in reactive nitrogen availability, but direct evidence that atmospheric nitrogen deposition will have sustained effects on dryland ecosystems is sparse and conflicting.We used three long‐running in situ nitrogen deposition simulation experiments and a complementary laboratory incubation experiment to address fundamental questions about how nitrogen inputs affect drylands: (1) What are the long‐ and short‐term consequences of nitrogen inputs for biogeochemical and ecosystem properties?; (2) Do these consequences depend on soil moisture availability?; and (3) Does soil texture modify the effects of nitrogen inputs and/or soil moisture availability?In 2011, we established three study sites along a soil texture gradient in Arches National Park with plots receiving 0, 2, 5 or 8 kg N ha−1annually (n = 5 per treatment per site). We assessed a suite of biogeochemical metrics over the long term and short term. To assess longer term effects, we sampled annually (2013–2019), just prior to spring nitrogen fertilization. To assess short‐term effects, we sampled immediately before and after spring nitrogen fertilization in 2013. Additionally, we compared foliar chemistry, soil extracellular enzyme activities, heterotrophic respiration rates, and nitrogen trace gas fluxes at select intervals during the study period (2011–2019). Finally, we conducted a laboratory incubation to measure the individual and interacting effects of soil moisture and nitrogen additions on soil microbial activity.We identified some short‐term effects in situ, but no lasting consequences of added nitrogen for any of the metrics measured. In the incubation, soil moisture treatments independently increased heterotrophic respiration rates but did not modify the effects of added nitrogen. In contrast to nitrogen treatments, soil texture was associated with large differences in biogeochemical cycling.Our results oppose the common prediction that coupled dryland biogeochemical cycles are sensitive to nitrogen inputs and suggest that fine‐scale edaphic heterogeneity is a key driver of dryland ecosystem properties.Synthesis. This study synthesizes a rare, long‐term dataset, which provides robust evidence that carbon and nutrient cycling and availability are resistant to realistic levels of atmospheric nitrogen deposition in remote dryland ecosystems.