Nitrogen Stocks Research Articles

Nitrogen distribution and forms in sediment cores of Daya Bay, China

Sediment was the hotspot of microbial nitrogen sink, affecting the biogeochemical cycle of nitrogen in aquatic ecosystems. However, the distribution and forms of nitrogen in coastal bay subsurface sediments are poorly understood, limiting our knowledge about nitrogen distribution characteristics in subsurface sediments and the implications for nitrogen sinks. Here, the spatial distribution of different forms of nitrogen was examined in the sediment cores of Daya Bay (DYB). The results showed that exchangeable nitrogen (Nex) with an average concentration of 13.14 ± 5.99 mg kg−1, mainly consisted of NO3− and NH4+, occupied only 1.88 ± 0.97% in the total nitrogen (Ntot) in the sediment cores. As the dominant nitrogen form, organic nitrogen (Norg) accounted for 50.52-94.29% in Ntot and displayed a similar decreasing trend with Ntot in sediment cores. No evident change was discovered in the vertical content of fixed ammonia (Nfix) in sediment cores, and the mean concentration of Nfix in the four sediment cores was 97.14 ± 29.08 mg kg−1. These results suggested that Nfix and Norg were the stable recalcitrant nitrogen stocks in the sediment cores, and the labile nitrogen input from anthropogenic activities was transformed by microbial processes, thus reducing the nitrogen pollution efficiently in DYB.

Carbon and nitrogen stocks and microbial indicators in tropical semiarid degraded Luvisols

Overexploitation of natural forest resources under the environmental conditions on the tropical semiarid region of Brazil is the main cause of soil degradation. This leads to insufficient restoration of both microbial and plant biomass and net loss of C and N from soils. In this study, we investigated degraded, partially degraded, and preserved Luvisols to quantify functional and total microorganisms and their activities and determine total C and N stocks. We hypothesize that degraded Luvisols have significant reduction in C and N stocks, abundance, and activity of total bacteria and fungi, diazotroph and phosphorus-mineralizing bacteria in relation to preserved or partially degraded Luvisols. We evaluated total C and N contents and stocks, microbial biomass (C, N and P), soil basal respiration, alkaline phosphatase activity, glomalin content, metabolic and microbial quotients and quantified 16S rRNA, 18S rRNA, nifH and phoD genes by real time quantitative PCR. C and N stocks of degraded Luvisols were a third of the stocks found in preserved soils. The values of soil microbial biomass and soil basal respiration on the degraded soils were ca. 1/5 and 1/20 in preserved soils; however, there was no indication of metabolic stress. The abundance of diazotrophic and phosphorus-mineralizing bacteria decreased in degraded Luvisols; nevertheless, total bacteria and fungi gene abundance as well as the glomalin content remained unchanged. The alkaline phosphatase activity indicated that mineralizing microorganisms could make phosphorus constantly available even in soils without vegetation cover.

Can an invasive African grass affect carbon and nitrogen stocks in open habitats of the Brazilian Cerrado?

Considering the emergence of ecosystems dominated by invasive species, there is growing interest in estimating the effect of biological invasions on ecosystem processes and provision of services. African grasses are the most invasive plants in the Cerrado (Brazilian savanna), but their impact on C and N stocks is poorly known. We compared patterns of C and N stocks in the aboveground biomass, root biomass and soil in open Cerrado (campo sujo) sites, both uninvaded and invaded by the African grass Urochloa decumbens. In both sites we estimated the aboveground biomass of U. decumbens and native grasses, as well as the root biomass up to 50 cm. We obtained C and N soil content and soil bulk density up to 1 m depth, which were used to obtain the overall soil C and N stocks; we also assessed the variation in soil δ13C and δ15N. Although invasion did not affect the aboveground biomass, it did affect belowground biomass, leading to more C stocked in fine roots and soil, higher N concentration close to soil surface, and also more C along the soil profile. C and N soil stocks, soil δ13C and δ15N values did not significantly differ between invaded and uninvaded site. Even a relatively low level of invasion by U. decumbens changed the root distribution pattern and increased C and N contents in the upper soil, which may promote ecosystem changes by altering nutrient dynamics. Although our study was conducted at a single site, it clearly shows effects of the invasive species on the belowground environment, and indicates the necessity of further studies.

The response of potato tuber yield, nitrogen uptake, soil nitrate nitrogen to different nitrogen rates in red soil

Nutrient-deficient red soil found in the southern region of China is increasingly being used for potato crops to meet the demand for this staple food. The application of nitrogen fertilizer is necessary to support the production of higher tuber yields; however, the links between nitrate nitrogen and the nitrogen balance in red soil are unknown. A field experiment was conducted in Jiangxi Province in 2017 and 2018 to determine the effects of different nitrogen application rates, 0 kg ha−1 (N0), 60 kg ha−1 (N60), 120 kg ha−1 (N120), 150 kg ha−1 (N150), 180 kg ha−1 (N180), 210 kg ha−1 (N210), and 240 kg ha−1 (N240, the highest rate used by local farmers), on potatoes growing in red soil. Data on tuber yield, crop nitrogen uptake, and the apparent nitrogen balance from the different treatments were collected when potatoes were harvested. Additionally, the content and stock of nitrate nitrogen at different soil depths were also measured. Nitrogen fertilization increased tuber yield but not significantly at application rates higher than 150 kg ha−1. We estimated that the threshold rates of nitrogen fertilizer application were 191 kg ha−1 in 2017 and 227 kg ha−1 in 2018, where the respective tuber yields were 19.7 and 20.4 t ha−1. Nitrogen uptake in potato in all nitrogen fertilization treatments was greater than that in N0 by 61.2–237% and 76.4–284% in 2017 and 2018, respectively. The apparent nitrogen surplus (the amount of nitrogen remaining from any nitrogen input minus nitrogen uptake) increased with increasing nitrogen application rates. The nitrate nitrogen stock at a soil depth of 0–60 cm was higher in the 210 and 240 kg ha−1 nitrogen rate treatments than in the other treatments. Moreover, double linear equations indicated that greater levels of nitrogen surplus increased the nitrate nitrogen content and stock in soils at 0–60 cm depths. Therefore, we estimate that the highest tuber yields of potato can be attained when 191–227 kg ha−1 nitrogen fertilizer is applied to red soil. Thus, the risk of nitrate nitrogen leaching from red soil increases exponentially when the apparent nitrogen balance rises above 94.3–100 kg ha−1.

The Impact of Sea Embankment Reclamation on Greenhouse Gas GHG Fluxes and Stocks in Invasive Spartina alterniflora and Native Phragmites australis Wetland Marshes of East China

The introduction of embankment seawalls to limit the expansion of the exotic C4 perennial grass Spartina alteniflora Loisel in eastern China’s coastal wetlands has more than doubled in the past decades. Previous research focused on the impact of sea embankment reclamation on the soil organic carbon (C) and nitrogen (N) stocks in salt marshes, whereas no study attempted to assess the impact of sea embankment reclamation on greenhouse gas (GHG) fluxes in such marshes. Here we examined the impact of sea embankment reclamation on GHG stocks and fluxes of an invasive Spartina alterniflora and native Phragmites australis dominated salt marsh in the Dongtai wetlands of China’s Jiangsu province. Sea embankment reclamation significantly decreased soil total organic C by 54.0% and total organic N by 73.2%, decreasing plant biomass, soil moisture, and soil salinity in both plants’ marsh. It increased CO2 emissions by 38.2% and 13.5%, and reduced CH4 emissions by 34.5% and 37.1%, respectively, in the Spartina alterniflora and Phragmites australis marshes. The coastal embankment wall also significantly increased N2O emission by 48.9% in the Phragmites australis salt marsh and reduced emissions by 17.2% in the Spartina alterniflora marsh. The fluxes of methane CH4 and carbon dioxide CO2 were similar in both restored and unrestored sections, whereas the fluxes of nitrous oxide N2O were substantially different owing to increased nitrate as a result of N-loading. Our findings show that sea embankment reclamation significantly alters coastal marsh potential to sequester C and N, particularly in native Phragmites australis salt marshes. As a result, sea embankment reclamation essentially weakens native and invasive saltmarshes’ C and N sinks, potentially depleting C and N sinks in coastal China’s wetlands. Stakeholders and policymakers can utilize this scientific evidence to strike a balance between seawall reclamation and invasive plant expansion in coastal wetlands.

Reducing soil organic carbon mineralization under moderate thinning magnifies the soil carbon sink in a Larix principis-rupprechtii plantation

How to reduce the rising carbon (C) in the atmosphere by enhancing forest soil C-holding capacity requires further research. Forest density via thinning has long been studied for this reason. However, how changes in density affect soil C sequestration is still uncertain for many other factors also affect soil C in open forest ecosystems. To measure the effect of thinning on soil organic carbon (SOC) stock relative to other contributing factors, we selected 12 25 × 25 m plots, and applied a series of thinning treatments: CK (control plots; 2173 ± 12 trees ha−1, which was how all plots started), LT (light thinning; 1834 ± 12 trees ha−1), MT (moderate thinning; 1418 ± 7 trees ha−1) and HT (heavy thinning; 1089 ± 13 trees ha−1). We measured the SOC stocks (kg C m−2) for 11 seasons crossing three years. In addition, soils of the four treatment plots (0–50 cm soil depth, 5 layers, 10 cm per layer) were collected once per season, and then the samples were incubated for 56 days before measuring their cumulate mineralized carbon (CMC). The temperature at 10 cm underground was measured every 60 min throughout two years. The active carbon (DOC (dissolved organic C) and MBC (microbial biomass C)) stocks were also measured. We found that soil in MT plots held more C overall, with more active carbon per unit of SOC. Soil temperatures were affected by the thinning as well as the C and N (nitrogen) stock. Soil temperatures and C, N stock alike rose from CK levels and peaked in MT, before decreasing in HT. However, SOC mineralization rate (mineralized-C) was reduced in MT across seasons, and mineralized-C varied seasonally. Soil C and N stocks were enhanced in MT plots, partly due to the increased soil temperatures and the reduced mineralized-C.

Changes in soil carbon and nitrogen stocks and microbial community after forest conversion in a subtropical region

ABSTRACT The quantitative understanding of different land use is still limited. We selected typical natural secondary forest (NSF) and Chinese-fir plantation (CPF) in southern China to quantify changes of soil carbon (C) and nitrogen (N) as well as microbial community composition after forest conversion in the soil profile up to 60 cm. The results showed that soil CN stocks and all functional microbial groups in CPF were significantly lower in the topsoil but did not change in the subsoil (10–60 cm) compared to those in NSF after 24 years conversion. Soil C/N ratio did not differ between the two forests for all soil depths. Correlation analysis showed that the abundance of microbial groups in the topsoil was significantly related to soil organic carbon, total nitrogen and forest floor N stock. Redundancy analysis showed that available N, especially NO3 −–N, was the most dominant factor influencing the microbial community composition. These findings suggest that the plantation could inhibit the accumulation of soil C and N, but the changes are primarily evident in surface soil after conversion. The study improves our understanding of soil C, N and microbial community changes under different land uses and provides insights into sustainable management of Chinese forests.

Biomass Mapping for an Improved Understanding of the Contribution of Cold-Water Coral Carbonate Mounds to C and N Cycling

This study used a novel approach combining biological, environmental, and ecosystem function data of the Logachev cold-water coral carbonate mound province to predictively map coral framework (bio)mass. A more accurate representation and quantification of cold-water coral reef ecosystem functions such as Carbon and Nitrogen stock and turnover were given by accounting for the spatial heterogeneity. Our results indicate that 45% is covered by dead and only 3% by live coral framework. The remaining 51%, is covered by fine sediments. It is estimated that 75,034–93,534 tons (T) of live coral framework is present in the area, of which ∼10% (7,747–9,316 T) consists of Cinorg and ∼1% (411–1,061 T) of Corg. A much larger amount of 3,485,828–4,357,435 T (60:1 dead:live ratio) dead coral framework contained ∼11% (418,299–522,892 T) Cinorg and <1% (0–16 T) Corg. The nutrient turnover by dead coral framework is the largest, contributing 45–51% (2,596–3,626 T) C year–1 and 30–62% (290–1,989 T) N year–1 to the total turnover in the area. Live coral framework turns over 1,656–2,828 T C year–1 and 53–286 T N year–1. Sediments contribute between 1,216–1,512 T C year–1 and 629–919 T N year–1 to the area’s benthic organic matter mineralization. However, this amount is likely higher as sediments baffled by coral framework might play a much more critical role in reefs CN cycling than previously assumed. Our calculations showed that the area overturns 1–3.4 times the C compared to a soft-sediment area at a similar depth. With only 5–9% of the primary productivity reaching the corals via natural deposition, this study indicated that the supply of food largely depends on local hydrodynamical food supply mechanisms and the reefs ability to retain and recycle nutrients. Climate-induced changes in primary production, local hydrodynamical food supply and the dissolution of particle-baffling coral framework could have severe implications for the survival and functioning of cold-water coral reefs.

A progressive simulation method to estimate the stocks of surface soil organic carbon and total nitrogen in an estuarine archipelago

Simulating the soil organic carbon (SOC) and total nitrogen (TN) stocks in estuarine areas is important for the development of digital soil mapping and the regional inventory of carbon and nitrogen, and simulation accuracy is the key issue. In this study, a progressive simulation method was proposed to further improve accuracy through the adequate utilization of the correlations among soil parameters and their relations with the comprehensive land surface factor system. Three soil parameters, namely, SOC, TN, and bulk density (BD), were simulated using the method for estimating SOC and TN stocks. The simulations were progressively conducted in three levels (Levels 1–3) by using partial least squares regression (PLSR) and cokriging. Each of the parameters was simulated separately in Level 1, one parameter was simulated based on each of the two other parameters in Level 2, and one parameter was simulated based on the two other parameters in Level 3. A typical estuarine archipelago in southern China was selected to demonstrate the performance of the method in surface soil (0–20 cm). Results showed the effectiveness of the progressive simulation in improving accuracy when the PLSR was used. The simulation results in Level 3 had the highest accuracy among the results in all levels, increasing the accuracies for SOC, TN, and BD by 54.35%, 57.24%, and 5.61%, respectively, compared with those in Level 1 and achieving high accuracies compared with those in similar studies. The SOC and TN stocks amounted to 270.66 and 26.96 Gg, respectively, and the mean values of SOC and TN densities were 2.65 and 0.26 kg/m2, respectively, which are lower than global values and those for China. The SOC and TN densities exhibited distinct spatial heterogeneities, which were fundamentally driven by different types of island exploitations and large-scale sea reclamation activities.

Soil carbon and nitrogen stock of the Japanese agricultural land estimated by the national soil monitoring database (2015–2018)

ABSTRACT Estimation of the soil organic carbon (SOC) stock based on the monitoring data is important to validate the carbon model estimates and provide the initial values of SOC stock to the model. The Japanese National Greenhouse Gas Inventory Report (NIR) has applied the RothC model since 2015 to report changes in SOC in agricultural land. This study estimated soil carbon and nitrogen stocks and C:N ratio of top 30 cm arable land in Japan using the 2015–2018 database of the national soil monitoring project. Estimates based on the stationary monitoring data from the top 30 cm of the soil layer arethe first public release. We modified categorization of the soil temperature regime and soil-type classification for estimation, expecting to mitigate the underestimation and overestimation of SOC stock in the areas of soil temperature 15–17°C and more than 17°C, respectively, and to optimize the soil classification to 16 fewer types to allow an appropriate estimation even in the current situation of decreasing number of survey sites. Statistical analysis to see the effects of land use and soil temperature on SOC stock, TN stock, and C:N ratio showed that soil types other than Andosols had an inverse temperature-dependent trend for all variables, while Andosols had an unclear trend in soil temperature, supporting existing studies. Also, when Lowland soils (Fluvisols or Anthrosols in the World Reference Base) were surrounded by Andosols, redeposition of volcanic ash could affect the temperature trend in SOC stock for Lowland soils. The distribution map of the SOC stock and C:N ratio across Japan visually showed a high value in the Andosols distribution areas and a temperature-dependent trend at the distribution areas of the other soil types. The total SOC stock estimated in this study was 176±12.8 TgC in paddy field, 100±8.6 TgC in upland field, 25±1.7 TgC in orchard, 78±8.9 TgC in grassland, and 379±17.9 TgC in total, the standard deviations of which were much smaller than those of the mean values for each land use calculated by the simple average method.

Chicken droppings influence on sod-podzolic soil fertility change studying experience

The aim of the research was to study the effect of fresh chicken droppings on the dynamics of the physical-chemical and agrochemical properties of sod-podzolic soil and the yield of grain crops. In the sod-podzolic light loamy soil of the Yaroslavl region in the layer of 0-0.20 m in May, fresh chicken droppings were embedded at the dose of 120 t/ha. By autumn, in the 0-0.40 m layer of pHKc1 increased from 4.53-4.99 to 5.38-7.09, the content of mobile phosphorus and exchangeable potassium increased by 2.0-2.4 times, nitrate and ammonium nitrogen - 3-5 times. The content of nitrates in the soil has exceeded the Maximum Allowable Concentration level. The grain yield of the spring wheat studied varieties, triticale and barley varied from 6.7 to 9.5 t/ha, chaffy oats - from 5.7 to 5.9, hulless oats - from 4.4 to 4.6 t/ha. At the beginning of the growing season of crops in the 0-0.40 m layer, the stocks of nitrate nitrogen were close to the stocks of the autumn observation period of 2019, and ammonium nitrogen decreased by 285 kg/ha.

Boreal tree species change as a climate mitigation strategy: impact on ecosystem C and N stocks and soil nutrient levels

AbstractTo increase the annual uptake of CO2 as well as the long‐term storage of carbon (C) in forests, the Norwegian government consider large‐scale replacements of native, deciduous forests with faster‐growing species like Norway spruce. To assess the effects of tree species change on ecosystem C and nitrogen (N) stocks and soil chemistry, we used a paired plot approach including stands of native downy birch and planted 45‐ to 60‐yr‐old Norway spruce. The birch stands were used as reference for the assessment of differences following the tree species change. We found significantly higher C and N stocks in living tree biomass in the spruce stands, whereas no significant differences were found for dead wood. The cover of understory species groups, and the C and N stocks of the aboveground understory vegetation were significantly higher in the birch stands. The tree species change did not affect the soil organic carbon (SOC) stock down to 1 m soil depth; however, the significantly higher stock in the forest floor of the spruce stands suggested a re‐distribution of SOC within the profile. There was a significant positive correlation between the SOC stock down to 30 cm soil depth and the total ecosystem C stock for the birch stands, and a negative correlation for the spruce stands. Significant effects of tree species change were found for C and N concentrations, C/N, exchangeable acidity, base saturation, and exchangeable Ca, K, Mg, Na, S, and Fe in the organic horizon or the upper mineral soil layer. The total ecosystem C stock ranged between 197 and 277 Mg/ha for the birch stands, and 297 and 387 Mg/ha for the spruce stands. The ecosystem C accumulation varied between 32 and 142 Mg/ha over the past 45–60 yr, whereas the net ecosystem C capture was considerably lower and potentially negative. Our results suggest that the potential to meet the governments' targets to increase C sequestration depend on the C debt incurred from the removed birch stands, the rotation length, and potentially also the susceptibility of the different stand types to future risk factors related to climate change.

Changes in soil carbon and nitrogen stocks after conversion of subtropical natural forest to loblolly pine plantations

Changes in soil carbon and nitrogen stocks after conversion of subtropical natural forest to loblolly pine plantations

Multi-trophic markers illuminate the understanding of the functioning of a remote, low coral cover Marquesan coral reef food web

We studied the food web structure and functioning of a coral reef ecosystem in the Marquesas Islands, French Polynesia, characterized by low coral cover, high sea surface temperature and meso- to eutrophic waters. The Marquesas constitute a relevant ecosystem to understand the functioning of low diversity reefs that are also subject to global change. A multi-tracer assessment of organic matter pathways was run to delineate ecosystem functioning, using analysis of fatty acids, bulk and compound specific stable isotope analysis and stable isotopes mixing models. Macroalgae and phytoplankton were the two major food sources fueling this food web with, however, some marked seasonal variations. Specifically, zooplankton relied on phytoplankton-derived organic matter and herbivorous fishes on macroalgae-derived organic matter to a much higher extent in summer than in winter (~ 75% vs. ~ 15%, and ~ 70 to 75% vs. ~ 5 to 15%, respectively) . Despite remarkably high δ15N values for all trophic compartments, likely due to local dynamics in the nitrogen stock, trophic levels of consumers were similar to those of other coral reef ecosystems. These findings shed light on the functioning of low coral cover systems, which are expected to expand worldwide under global change.

Plant invasion affects vegetation structure and sediment nitrogen stocks in subtropical mangroves

Plant invasion can primarily affect the structure and functioning of terrestrial and aquatic ecosystems. Although there is evidence that plant invasion can modify organic matter dynamics in mangroves, it is uncertain whether and to which extent these changes can affect carbon (C) and nitrogen (N) dynamics in the sediment-plant system. Here, we measured: (i) the structure of native vegetation and C and N in the sediment-plant system in subtropical mangroves subjected to aquatic macrophytes invasion in southeastern Brazil. We answered the following questions: i) Do invaded mangroves differ in aboveground biomass compared to non-invaded mangroves?; ii) Are there C4 macrophytes in these sites? iii) What are the C and N stocks in sediment of invaded mangroves? We quantified C and N concentrations and the isotopic signature of such elements (δ13C and δ15N) in the sediment-plant system, the C and N stocks in the sediment (0–20 cm depth), and mangrove aboveground biomass. Mangrove aboveground biomass was lower at invaded compared to non-invaded sites reflecting the species displacement in invaded sites. The sediment at invaded mangroves did not significantly contribute to C4 sources because of the large predominance of both mangrove and invasive C3 plants. While sediment C stocks were similar among study sites (∼47 Mg ha−1), N stocks were lower at invaded (2.7 Mg ha−1) comparing to non-invaded (3.2 Mg ha−1) mangroves. The lower N stocks at invaded sites can reflect the higher leaf N concentrations and lower C:N ratios of invasive plants compared to mangroves. Thus, the effects of macrophytes invasion in subtropical mangroves are more apparent for vegetation structure and N stocks. C stocks alteration is expected the be detectable in the future.

Spatial and temporal dynamics of soil organic carbon stock and carbon sequestration affected by major land-use conversions in Northwestern highlands of Ethiopia

Soil organic carbon (SOC) is the major component of the terrestrial carbon (C) budget, a key indicator of environmental sustainability. So, estimating SOC stock and soil carbon (C) sequestration dynamics is important for evidence-based and carbon-conscious decisions. Quantification of SOC stock and soil C sequestration affected by land-use changes (LUCs) have received much attention in addressing food and climate security. This study aims to estimate the dynamics of SOC stock, soil C sequestration and associated soil parameters affected by major LUCs from 2012 to 2021 in Awi highlands of Amhara Regional State of Ethiopia. The study area has experienced dramatic LUC, particularly plantation and growing of Acacia decurrens (J.C. Wendl.) tree followed by recurrent deforestation and then cropping and back to the plantation. The study quantified spatial and temporal dynamics of SOC stock, soil C sequestration and associated changes affected by the LUCs. A total of 22 topsoil (0–20 cm) legacy data was obtained from the Ethiopian Soil Information System (EthiSIS) database of 2012. The same number of samples were collected at the same locations in 2021 by using the same sampling procedure as that of 2012. In addition, the same number of core samples were collected in 2021 for bulk density analysis. To estimate the unmeasured bulk density of legacy data, we applied a pedotransfer function. We used empirical equations and basic statistics to assess changes in SOC stock and C sequestration rate between the two periods. Statistically significant variation (P < 0.01) in SOC stock and C sequestration was observed between the two periods. LUC from acacia plantation to croplands caused a decline of SOC stock by −30.16%, and it also caused the decline of total nitrogen stock, available phosphorus, cation exchange capacity (CEC). However, the reverse LUC caused an increase in SOC by 27.74% and the abovementioned soil parameters. LUC from plantation forest to cropland caused emission of 8.3 tons of CO2 year−1. Generally, overall LUCs caused the net negative change in SOC stock by (−2.42 %) and associated soil parameters in the last ten years. Our study provides evidence that overall LUCs in the current study site caused a decline in SOC stock, along with associated soil parameters with carbon emitted to the atmosphere. Hence, sustainable land-use management options which can offset losses in SOC stock should be implemented soon.

Stocks of organic carbon and nitrogen in dark serozems of the Chirchik river basin in Tashkent region of Uzbekistan

The reserves of SOC and TN were investigated in the profile of dark serozems of the river basinChirchik, Tashkent region of Uzbekistan, in connection with the exposure of slopes and use in agriculture. The highest stocks of SOC and TN (79.2 and 10.3 t/ha) are noted in the 1-meter layer of natural soil on the northern slope that is more abundant in moisture, relatively low temperature and thicker vegetation cover. And in a meter layer of a similar soil on the southern slope, the SOC and TN reserves were significantly lower and amounted to 75.5 and 9.7 t/ha. The use of these soils in agriculture led to significant losses of SOC and TN in the meter layer and in the soil profile as a whole. In the soil of the northern slope of agricultural use, the SOC and TN reserves were 76.7 t/ha and 10.3 t/ha, which is significantly lower compared to natural soil. Also, in the soil of agricultural use on the southern slope, the value of SOC and TN reserves in the meter layer of soil was 68 and 9 t/ha that is significantly lower than that in the natural soil of the slope developed in the same exposure. Thus, slope exposure and agricultural land use were the main factors affecting SOC and TN stocks in the profile of the studied soils.

Slope aspect and altitude effect on selected soil organic matter characteristics in Beskid Mountains forest soils

Abstract In the era of dynamic climate change, it is important to have knowledge on the interactions between climatic factors and processes occurring in the soil environment. The present study aimed to determine how slope aspect and altitude above sea level influence carbon and nitrogen accumulation and dehydrogenases activity of forest soils. The study was conducted in the Beskid Żywiecki in the south-facing part of Poland. Soils of the same texture, with similar vegetation species composition, in different altitude variants (600, 800, 1000 and 1200 m above sea level) and different north-facing and south-facing slope aspect were selected for the study. For each height and slope aspect variant, samples were collected from the surface horizons of soils for further analyses. The basic chemical properties and dehydrogenases activity of the soil samples were determined. Carbon and nitrogen stocks in the surface horizons of the soils were calculated. The analyses confirmed the influence of location conditions on the carbon and nitrogen stocks in mountain forest soils. The stock of carbon and nitrogen increased with the height up to 1000 m a.s.l. In the soils at the highest altitude, the reserve of carbon and nitrogen decreased regardless of the slope aspect variant. There were no statistically significant differences in carbon and nitrogen stocks between slope aspect variant. The highest dehydrogenases activity was associated with the organic horizons of the soils at the lowest altitude in height gradient. In our study, higher dehydrogenases activity was observed in the north-facing slope soils, and this finding can be explained by more stable thermal conditions.

Elevated temperature and nitrogen deposition did not affect the impacts of arbuscular mycorrhizal fungi on soil carbon or nitrogen stocks in atemperate meadow

Arbuscular mycorrhizal (AM) fungi are key players in the soil carbon (C) and nitrogen (N) cycles; on the one hand, AM fungi have been influenced by global changes, while on the other hand, they are involved in shaping the future climate. However, few field studies have combined AM fungi with both elevated temperatures and N deposition to examine their potential combined effects on the stocks of soil C and N in temperate meadow ecosystems. A 5-year experiment was conducted to explore the effects of AM fungal reductions on soil C and N stocks under elevated temperatures and N deposition. The stock of soil C and N and the C:N ratio were measured. The results showed that AM fungi significantly reduced soil C stocks by 8.5% across all treatment combinations compared to the AM fungi suppression treatment, and slight soil C accumulation was detected across the five years. The response of the soil C stocks was not influenced by elevated temperatures and N deposition simultaneously. The soil N stocks in the treatments without AM fungal suppression were, on average, 9.7% lower across all treatments than those in the AM fungal suppression treatment. AM fungi, elevated temperatures, and N deposition did not affect the soil C:N ratio. The robust decreases in soil C and N stocks caused by AM fungi observed here, even when combined with other global changes, suggest that AM fungi might accelerate soil C losses in temperate meadow ecosystems; however, there is a strong potential for reduced soil N accumulations to mitigate the negative impact of increasing N deposition on the stability of grassland ecosystems under future global changes. Overall, our results highlight that the effect of AM fungi on soil C and N stocks has a high resistance to global warming and N deposition in temperate meadow ecosystems.

Predictive Models to Estimate Carbon Stocks in Agroforestry Systems

This study aims to assess the carbon stock in a pasture area and fragment of forest in natural regeneration, given the importance of agroforestry systems in mitigating gas emissions which contribute to the greenhouse effect, as well as promoting the maintenance of agricultural productivity. Our other goal was to predict the carbon stock, according to different land use systems, from physical and chemical soil variables using the Random Forest algorithm. We carried out our study at an Entisols Quartzipsamments area with a completely randomized experimental design: four treatments and six replites. The treatments consisted of the following: (i) an agroforestry system developed for livestock, (ii) an agroforestry system developed for fruit culture, (iii) a conventional pasture, and (iv) a forest fragment. Deformed and undeformed soil samples were collected in order to analyze their physical and chemical properties across two consecutive agricultural years. The response variable, carbon stock, was subjected to a boxplot analysis and all the databases were used for a predictive modeling which in turn used the Random Forest algorithm. Results led to the conclusion that the agroforestry systems developed both for fruit culture and livestock, are more efficient at stocking carbon in the soil than the pasture area and forest fragment undergoing natural regeneration. Nitrogen stock and land use systems are the most important variables to estimate carbon stock from the physical and chemical variables of soil using the Random Forest algorithm. The predictive models generated from the physical and chemical variables of soil, as well as the Random Forest algorithm, presented a high potential for predicting soil carbon stock and are sensitive to different land use systems.