Soil Stocks Research Articles

Evaluating the use of Ca/Sr and 87Sr/86Sr ratios to track Ca sources in sugar maple in Ontario

Decades of acidic deposition and timber harvesting have depleted calcium (Ca) stocks in soils, especially at base-poor soils characterized by low base cation weathering rates. One approach to tracking Ca sources from soil is by using Ca/Sr ratios in vegetation, while 87Sr/86Sr ratios have also been used to estimate mineral weathering rates. To evaluate the uses of Ca/Sr ratios and Sr isotopes in identifying Ca sources in sugar maple ( Acer saccharum Marsh.) trees, three base-poor sites on the Canadian Shield and three limestone sites in southern Ontario were sampled for Ca, Sr, and 87Sr/86Sr ratios. Higher Ca/Sr ratios in soil extracts and sugar maple tissues at base-rich sites compared with base-poor sites reflect different minerology among regions, while the Ca/Sr discrimination factor between roots and foliage indicated that internal cycling exerts a major control on Ca/Sr ratios in sugar maple. At the three off-shield sites, 87Sr/86Sr ratios in soil and tree tissues were higher than precipitation but were indistinguishable for off-shield sites. Mixing models using a 1.0 mol L−1 HCl soil extract as the weathering endmember indicated that a lower proportion of weathering Ca compared with other geochemical approaches. One potential explanation is that the extraction method dissolves more recalcitrant minerals to a greater extent than under field conditions, leading to a higher weathering rate endmember value used in the mixing model.

Soil Properties and Organic Carbon Stock of Soils under Arid Coastal Ecosystem Oasis in Southern East of Tunisia

Soil Properties and Organic Carbon Stock of Soils under Arid Coastal Ecosystem Oasis in Southern East of Tunisia

Investigating the potential for a blue carbon economy on Australia’s northern coastline

The term ‘Blue Carbon’ (BC) recognises the ability of mangroves, saltmarshes, and seagrasses to capture and store carbon in their soils and biomass. Given their anoxic sediment, BC ecosystems can sequester up to as much as four times more carbon per hectare, and store it 30–50 times faster, than terrestrial forests. Australia has some of the world’s largest BC storage capacity, with 5–11% of global BC soil stocks and 2–7% of annual BC sequestration, based on available global estimate. Evidence indicates that mangrove and saltmarsh degradation from cyclone damage, feral damage and disease, is occurring throughout the Northern Territory (NT). This is a growing issue with feral animal populations degrading Indigenous lands and areas of conservation significance. This cumulative pressure on BC habitat means that northern Australia is uniquely positioned to expand BC methods to also account for protection and restoration of degraded coastal habitats including freshwater wetlands that have been damaged by non-native feral animals. Researchers from Charles Darwin University (CDU), University of Queensland (UQ), and the Northern Australian Indigenous Land and Sea Management Alliance Ltd (NAILSMA) recently worked to explore the opportunity and potential for economically viable BC methods in the NT. The study had a particular focus on Aboriginal Land gazetted under the Aboriginal Land Rights (NT) Act (1976) (Cth). We present the research outcomes and identify the pathway to focused research on BC stores and tailored methods for generating Australian Carbon Credit Units (ACCUs) and potentially biodiversity credits, in the NT.

Can N2 fixation by forage legumes build soil organic matter to rival fertilizer N in a tropical forest biome?

Fertilization of pastures with nitrogen (N) can increase animal productivity and may also increase the stocks of soil carbon (C). Recently stoloniferous forage legumes have been used to develop productive sustainable mixed pastures in the Atlantic forest biome. The objective of this study was to compare the impact over 24 years on soil C and N stocks of a productive N-fertilized pasture of Urochloa brizantha cv. Marandu with a mixed forage peanut (Arachis pintoi)-Marandu grass pasture introduced 8 years after an N-fertilized elephantgrass (Pennisetum purpureum) pasture. The pastures were rotationally stocked by Nellore cattle a green-forage allowance equivalent to 4% of body weight and animal performance was continuously monitored. Soil samples were taken at the start of the study and after 8 and 24 years of grazing and analyzed for total C and N and 13C abundance. In 8 years, the stocks of soil organic matter (SOM – 0-30 cm) increased by 4.4 Mg C and 0.58 Mg N ha−1 under the elephantgrass pasture and by 10.4 Mg C and 1.23 Mg N ha−1 under the Marandu grass pasture, both fertilized with 160 kg N ha−1 yr−1. Over the subsequent 16 years, SOM stocks under the Marandu grass fertilized with 120 kg N ha−1 and the mixed forage peanut-Marandu pasture which replaced elephantgrass attained similar stocks of soil C of 51.8 and 52.5 Mg C ha−1 respectively, approximately 12 Mg C greater than under the native vegetation. The 13C abundance of the soil samples indicated that the C4 grass roots made an insignificant contribution to soil C below 30 cm depth. The results show that the N2-fixing forage peanut was just as effective in accumulating SOM as an annual application of 120 kg N fertilizer ha−1 and indicated that after 24 years of these pastures there was little further SOM accumulation.

Near-Term Effects of Perennial Grasses on Soil Carbon and Nitrogen in Eastern Nebraska

Incorporating native perennial grasses adjacent to annual row crop systems managed on marginal lands can increase system resiliency by diversifying food and energy production. This study evaluated (1) soil organic C (SOC) and total N stocks (TN) under warm-season grass (WSG) monocultures and a low diversity mixture compared to an adjacent no-till continuous-corn system, and (2) WSG total above-ground biomass (AGB) in response to two levels of N fertilization from 2012 to 2017 in eastern Nebraska, USA. The WSG treatments consisted of (1) switchgrass (SWG), (2) big bluestem (BGB), and (3) low-diversity grass mixture (LDM; big bluestem, Indiangrass, and sideoat grama). Soils were sampled at fixed depth increments (0–120 cm) in the WSG plots and in the adjacent corn experiment in 2012 and 2017. Soil stocks (Mg ha−1) of SOC and TN were calculated on an equivalent soil mass (ESM) basis and compared within the three WSG treatments as well as between experiments (corn compared to the mean of all WSGs). Soil organic C and TN stocks within soil layers and cumulative stocks responded to the main effect of WSG (PWSG < 0.05) but were no different when comparing the WSGs to corn (Pexpt = NS). Both SOC/TN stocks and cumulative stocks were generally greater in the LDM compared to the BGB. Neither SOC nor TN changed over time under either the WSGs or corn. Warm-season grass AGB responded to a three-way interaction of year, N rate, and WSG (p = 0.0007). Decreases in AGB over time were significant across WSGs and N levels except for SWG at 56 kg N ha−1 and LDM at 112 kg N ha−1. Above-ground biomass was generally greater in the LDM after the first harvest year (2013). Results suggest that incorporating WSGs into marginal cropland can maintain SOC and TN stocks while providing a significant source of biomass to be used in energy production or in integrated livestock systems.

Unearthing the importance of soil development in total phosphorus distribution in China’s mountains

Phosphorus (P) as an essential limiting nutrient for primary productivity has a far-reaching impact on ecosystem carbon sequestration. Increasing studies have evaluated the distribution and stock of soil P in natural terrestrial ecosystems, yet few studies explore the large-scale P distribution from the perspective of soil development in the mountain regions. In this study, 1254 soil samples, including organic soils (O horizon), surface mineral soils (A horizon) and parent materials (C horizon), were collected from twenty-nine mountains in China according to soil development conditions. The concentration and stock of total P in the soils were analyzed to decipher the effects of soil development along with other potential drivers on the P distribution. The results showed that total P concentration decreased significantly in the order of O horizon > A horizon > C horizon, whereas total P stock displayed an opposite trend. Spatially, soil total P concentration increased from South to North China and from West to East China, irrespective of soil horizons, whereas total P stock did not present a consistent spatial trend across the soil horizons. Climate, vegetation and atmospheric active nitrogen deposition exhibited negative effects on soil P distribution directly or indirectly by affecting pedogenesis, while soil organic carbon, pH and iron had distinctly positive effects on the P accumulation in specific horizon. The results highlight the importance of soil development on soil total P distribution in mountains, and this process should be considered when evaluating soil P dynamics in the P biogeochemical cycling models.

Limitations of farm management data in analyses of decadal changes in SOC stocks in the Danish soil‐monitoring network

AbstractChanges in soil organic carbon (SOC) storage in agricultural land are an important part of the Land Use, Land‐Use Change and Forestry component of national greenhouse gas emission inventories. Furthermore, as climate mitigation strategies and incentives for carbon farming are being developed, accurate estimates of SOC stocks are essential to verify any management‐induced changes in SOC. Based on agricultural mineral soils in the Danish soil‐monitoring network, we analysed management effects on SOC stocks using data from the two most recent surveys (2009 and 2019). Between 2009 and 2019, the average increase in SOC stock was 1.2 Mg C ha−1 for 0–50 cm despite a loss of 1.2 Mg C ha−1 from the topsoil (0–25 cm), stressing the importance of including deeper soil layers in soil‐monitoring networks. Comparing all four national surveys (1986, 1997, 2009, 2019), the mean SOC stock of mineral soils in Denmark appears stable. The change in SOC stock between 2009 and 2019 was analysed in detail in relation to management practices as reported by farmers. We found that the effects of single management factors were difficult to isolate from co‐varying factors including soil parameters and that the use of farm management data to explain changes in SOC stocks observed in soil‐monitoring networks appears limited. Uncertainty in SOC stock estimates also arises from low sampling frequency and statistical challenges related to regression to the mean. However, repeated stock measurements at decadal intervals still represent a benchmark for the overall development in regional and national SOC storage, as affected by actual farm management.

Distribution of Mercury in Drained Peatlands as the Effect of Secondary Transformation of Soil Organic Matter

Peat organic soils play a major role in the accumulation of soil organic matter (SOM) and the mercury (Hg) cycle. Large mercury resources in peatlands can be a source of methylmercury for many decades and centuries, even if deposition is significantly reduced. The organic matter of peatland soils drained for agricultural use is subject to secondary transformation, which may affect the accumulation and resources of mercury. The aim of our work is to assess the secondary transformation of organic matter in the soils of drained peatlands of the temperate climate zone and to examine whether it affects mercury resources and profile distribution in organic soils. Field research was conducted in peatlands located in eastern Poland. In the present study, evaluation of secondary transformations occurring after drainage was based on observations of soil morphological characteristics, physical and chemical properties as well as fractional composition of organic matter of the identified soil horizons (to depth 70 cm). Standard cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the total mercury content. In our research, we found a significant effect of the secondary transformation of organic matter occurring in drained peatlands of the temperate climate zone on the total mercury content and stock in soils. The highest content and differentiation of mercury occurred in murshic horizons (up to a maximum depth of 43 cm). The average mercury content of the distinguished soil horizons is grouped in the following series (in μg kg−1): M1 (212.0) > M2 (182.8) > M3 (126.3) > Pt (84.9). The mercury stock, up to a depth of 70 cm in the tested soils, ranged from 17.5 to 39.6 mg m−2. As much as 82.2% of soil mercury was found in the upper murshic horizons. We found strong correlations between soil properties characteristically variable in the secondary transformation process and total mercury content. The increased content of humic substances in murshic horizons caused a significant increase in the total mercury content. Our research is of great importance for soil monitoring, as the amount of determined mercury was greatly influenced by the depth of sampling (up to 25 cm). The results of the research should be taken into account when planning the restoration of peatlands of the temperate climate zone. There is a potential risk that elevated mercury concentrations in the upper murshic horizons may be a source of methylmercury for a long period of time. In peat soils with a high concentration of mercury, the risk of contamination with this toxic metal should be determined before re-irrigation.

Carbon stock, aggregate stability and hydraulic properties of soils under tillage, crop rotation and mineral fertiliser application in sub-humid Zimbabwe

Appropriate tillage and crop diversifications can improve soil quality leading to yield sustainability. Our objective was to quantify tillage, crop rotation and mineral fertiliser application effects on carbon sequestration, aggregation and soil water movement after two cropping cycles in the smallholder sector of Zimbabwe. Two split-plot experiments were set up at four sites on sandy, loamy and clayey soils. At experiment 1, crop rotation (maize-soya bean; continuous maize) was the main plot and mineral fertiliser ((NPKS (180 N + 30P2O5+30K2O+6.5SO3 kg ha−1); control (no fertiliser added)) was the sub-plot. At experiment 2, tillage (reduced, conventional) was the main plot and mineral fertiliser (NPKS; control) was the sub-plot. Soil samples collected from 0 to 0.2 m and 0.2–0.4 m layers were analysed for soil organic matter (SOM) content, bulk density and proportion of water stable aggregates. Saturated hydraulic conductivities (Ks), steady state infiltration rates (is) and soil sorptivities (Sp) were estimated from fitting field infiltration data into the Phillip model. SOM stocks (mean = 3.483 Mg ha−1) were significantly increased by reduced tillage at the sandy site and higher (p < 0.05) in 0–0.20 m than in 0.20–0.40 m layers at clayey sites. Proportion of water stable aggregates increased (p < 0.05) under reduced tillage compared with conventional tillage and under rotation compared with continuous maize system. Bulk densities were 11% lower (p < 0.05) in the 0–0.20 m than in 0.20–0.40 m layers. The estimated Ks(1 × 10−4-8x10−4 cm s−1) and is (7.08–55 × 10−4 cm s−1) were at least 100% higher (p < 0.05) under rotation compared with continuous maize whilst sorptivities (0.050–0.143 cm s−05) did not vary across the treatments. NPKS fertiliser reduced (p < 0.05) is by up to 1.8 fold compared with the control. Short term adoption of reduced tillage and maize-soya bean rotation can mitigate soil structural degradation; increase water recharging and increase carbon sequestration quicker in sands than in the buffering clays making the practices more relevant in the smallholder sector.

Pelletized Straw Incorporation in Sandy Soil Increases Soil Aggregate Stability, Soil Carbon, and Nitrogen Stocks

In China, increasing the quantity and quality of total carbon and nitrogen stocks in sandy soil used for crop production is an important research issue. Soil amendment with pelletized straw could improve both soil physical structure and fertility in sandy soils, but these aspects remain understudied. The present pot and field experiments examined the dynamic changes in sandy soil water holding capacity, soil bulk density, soil total carbon and nitrogen stocks, and the distribution of water-stable aggregates and soil total carbon stocks related to aggregates across the following treatments: no fertilization (i.e., study control (CK)), normal fertilizer rate (NM), soil amendment at 150 Mg ha−1 (S150), manure amendment at 150 Mg ha−1 (M150), pelletized straw amendment at 75 Mg ha−1 (PS75), and pelletized straw amendment at 150 Mg ha−1 (PS150). The results show that the pelletized straw incorporation significantly increased water holding capacity and decreased soil bulk density. PS150 notably increased the large macroaggregates (&gt;2000 μm) proportion and decreased the ratio of &lt;250 μm aggregate size fractions in comparison with CK, NM, S150, and M150 at 0–20 and 20–40 cm soil depths. Compared with the CK treatment, the bulk soil carbon and nitrogen stocks in the 0–20 cm layers under the PS150 treatment were significantly increased by 85.2% and 302.9%, and in the 20–40 cm layers those increased by 136.4% and 257.1%, respectively. The PS150 treatment resulted in higher soil organic carbon (SOC) and particulate organic carbon content than the CK and PS75 treatments, whereas the PS75 treatment achieved maximum soil inorganic carbon content. The pelletized straw treatment increased the large macroaggregate-associated soil total carbon content at 0–20 and 20–40 cm soil depths. The maximum soil total carbon stocks were in the small macroaggregates (250 &lt; WSA &lt; 2000 μm) rather than in the large macroaggregate and microaggregates under the PS75 and PS150 treatments. Additionally, the pelletized straw and manure amendments increased the yield of silage corn, which was dependent on the increase in soil total carbon and nitrogen content in the macroaggregates, whereas the soil and manure amendments did not facilitate sandy soil aggregation and soil total carbon stock increases. In conclusion, PS150 was found to be the optimal amendment for maintaining sandy soil profile physico-chemical properties through macroaggregate stabilization. These results will be beneficial for arid and semi-arid regions, thus contributing to soil carbon and nitrogen conservation.

How much carbon is stored in the terrestrial ecosystems of the Chilean Patagonia?

AbstractWe estimated the amount of carbon (C) stored in terrestrial ecosystems of the Chilean Patagonia and the proportion within protected areas. We used existing public databases that provide information on C stocks in biomass and soils. Data were analysed by ecosystem and forest type in the case of native forests. Our results show that some ecosystems have been more extensively studied both for their stocks in biomass and soils (e.g. forests) compared with others (e.g. shrublands). Forests and peatlands store the largest amount of C because of their large stocks per hectare and the large area they cover. The total amount of C stored per unit area varies from 261.7 to 432.8 Mg C ha−1, depending on the published value used for soil organic C stocks in peatlands, highlighting the need to have more precise estimates of the C stored in this and other ecosystems. The mean stock in national parks (508 Mg C ha−1) is almost twice the amount stored in undisturbed forests in the Amazon. State and private protected areas contain 58.9% and 2.1% of the C stock, respectively, playing a key role in protecting ecosystems in this once pristine area.

Ecosystem carbon and nitrogen gains following 27 years of grazing management in a semiarid alluvial valley

Soils in semiarid riparian ecosystems have large carbon (C) stocks that promote water and nutrient availability for productive plant communities consumed by grazing animals. Changes to riparian hydrologic conditions caused by channel incision result in different edaphic conditions and a greater abundance of upland plant species that may be associated with lower soil C stocks. Using riparian meadows alongside Maggie Creek in central Nevada, we show that 27 years of modified grazing practices can repair ecosystem processes and increase the C stocks. We compared C and nitrogen (N) stocks (of soils and plant biomass) on floodplains, terraces, and uplands of reaches where grazing was either modified or excluded to reaches where no changes to grazing practices were made. Grazing management allowed beaver to establish, improving hydrology and lengthening the growing season. These changes allowed C and N to accumulate on geomorphic surfaces that extended from the stream channel to the surrounding hillslopes. A stoichiometric relationship between C and N shows carbon sequestration can reduce nutrient runoff to nearby waterways and may depend on nitrogen availability. Gains in ecosystem carbon ranged from 93 to 452 g C m−2 y−1 and were dominated by increases in soil C. Gains in soil C occurred across the full depth range measured (0–45 cm) and were comparable to those found in restored wetlands and meadows located in more humid ecosystems. Carbon gains exhibited substantial variability caused by microtopography and plant community composition. While grazing exclusion resulted in the largest gains in ecosystem C, managed grazing that limited consumption of riparian plants increased ecosystem C relative to reaches where management wasn't changed. We demonstrate that managed grazing that maintains ecosystem process is compatible with projects aimed at increasing soil carbon in semiarid riparian rangelands.

Do Managed Hill Sal (Shorea robusta) Community Forests of Nepal Sequester and Conserve More Carbon than Unmanaged Ones?

Nepalese community forests are globally recognized for sustainable forest management and improving the livelihoods of forest-dependent communities, but their contribution to carbon sequestration in trees and soil is rarely studied. This study was performed to understand the effect of management practices on carbon stock of two community forests (CFs) - Taldanda (managed) and Dangdunge (unmanaged) - dominated by Sal (Shorea robusta) in the mid-hills of Nepal. Twenty-one concentric sample plots, each of 250 m2, were laid out in each forest to estimate different carbon pools and a stratified random sampling intensity of 0.5% used to collect data. Results showed significant (p&lt;0.05) differences in above and below-ground biomass and carbon sequestration potential between the two CFs. The managed and unmanaged forests had total carbon stock of 269.3±27.4 and 150.0±22.7 ton/ha, respectively, demonstrating 1.79 times higher carbon stock in the former than the latter. The managed forest had significantly (p&lt;0.05) greater mean soil organic carbon (SOC) stock than the unmanaged forest. The SOC was highest in the upper soil layer (0-10 cm), with a steady decrease as the soil depth increased. All other measured carbon pools values were higher in managed compared to unmanaged forest. The difference in carbon stock was due to the manipulation of different forest management activities, including thinning, timber extraction, fire control, grazing, and fuel wood/fodder extraction. The study suggests that the implementation of proper forest management would be necessary for enhancing carbon stock in forest trees and soils.

Difference in total N and its aggregate-associated N following cropland restoration in a karst region, Southwest China.

Cropland conversion has been cited as one of the most effective measures for increasing soil nitrogen pool in karst degraded regions. However, it is still unclear how N associated with aggregate patterns and their contribution to net soil N accumulation after cropland conversion. The experiment included four treatments with one control and three restoration strategies, that is, maize-soybean rotation cultivation (the control), sugarcane, mulberry, and forage grass cultivation. Soil samples were selected to determine the soil aggregate amount and its associated N content and stock across 0-30 cm soil layer. Macro-aggregate (> 2mm) was the predominant aggregate fraction in all cropland use types and had the largest N stock. Forage grass cultivation substantially increased N stocks in bulk soil and aggregate fractions. The N contents and stocks associated with aggregate were shown to be positively correlated with bulk soil N stocks. Furthermore, the increase in N stock in forage grass soil was largely caused by an increase in N stock within macro-aggregates (> 2mm), which is further attributed to the increased N content within macro-aggregates. Overall, forage grass cultivation replaced maize-soybean cultivation which was proposed as an ecological restoration model to improve soil N sequestration capacity due to its function in increasing the N stock of aggregate in the karst degraded region of Southwest China.

Soil organic carbon stocks by soil group for afforested soils in Ireland

Forest ecosystems are recognised as Natural Climate Solutions because forest soils are such important carbon stores, containing almost half of the total soil organic carbon of terrestrial ecosystems. Here we present the results of a synthesis of soil carbon stocks by World Reference Base soil group, and forest litter carbon stocks for afforested soils in the Republic of Ireland. We report soil carbon stocks of mineral soils separately from organo-mineral soils. We estimated mean soil carbon stocks in a 100 cm deep mineral soil to be between 162 ± 87 t C/ha (Gleysols) and 416 ± 0 t C/ha (Umbrisols, n = 1), and between 173 ± 65 t C/ha (Phaeozems) and 602 ± 226 t C/ha (Regosols) in a 100 cm deep organo-mineral soil; both less than the estimated soil carbon stocks in organic soils (Histosols): 645 ± 222 t C/ha. The entire soil carbon stocks in mineral Leptosols (100 ± 0 t C/ha, n = 1), Stagnosols (144 ± 39 t C/ha), Luvisols (159 ± 52 t C/ha) and Fluvisols (231 ± 0 t C/ha, n = 1) was contained in the upper 50 cm of soil. Based on a 100 cm deep soil, Histosols hold 1.6–4 times the amount of soil C than mineral soils and 1.1–3.7 times the amount in organo-mineral soils for the same profile depth. Certain mineral (e.g. Umbrisols) and organo-mineral soils (e.g Gleysols, Regosols) contain substantial soil carbon stocks relative to Histosols. We found considerable soil carbon stocks below 30 cm depth, which highlights the importance of depth extent for cumulative soil carbon stocks estimates. The upper third of the 100 cm profile contained 33% (Histosols) to 70% (Luvisols) of the soil carbon stocks and the upper half of a 100 cm profile contained the entire soil carbon stocks for Leptosols, Stagnosols, Luvisols and Fluvisols and organo-mineral Leptosols. Unfortunately, there were few samples available for mineral Leptosols, Umbrisols, Luvisols and Fluvisols, and the organo-mineral Stagnosols and Regosols, which precludes the drawing of conclusions for these groups. Relative to the soil carbon stocks, we found low mean forest litter stocks: 4.1 ± 5.5 t C/ha, 4.8 ± 3.3 t C/ha and 2.7 ± 2.9 t C/ha for broadleaf, coniferous and mixed forests respectively. Few exceptions existed for individual sites: 22.7 and 131.3 t C/ha for broadleaf forests. Our results are evidence that soil carbon stocks in mineral, organo-mineral and organic soils need to be protected, appropriately managed, and enhanced to be beneficial for greenhouse gas mitigation. Assessments are needed to identify which soil-site-management practice combinations risk soil carbon stock depletion. The large range observed in soil and litter carbon stocks stresses the importance of adequately accounting for soil group differences when GHG inventories are compiled. The synthesised dataset will contribute to improved SCS estimation for afforested lands in Ireland.

Potassium Fertilizer Rate Recommendations: Does Accounting for Soil Stock of Potassium Matter?

AbstractProfitability, yield, and fertilizer use are compared across three different potassium (K) fertilizer rate recommendation ideologies. Existing agronomic, “build and maintain” rate recommendations (KE) are compared to profit-maximizing rates with and without taking long-run soil-test K (STK) implications into account. Regardless of starting STK, K use equilibrated over the course of 3 years irrespective of ideology. Since taking long-run STK into account did not alter ending STK and only led to a miniscule yield effect, we encourage producers to use annual profit-maximizing K rates that were 3–11% lower than KE rates and generated more profit with minimal yield loss.

SOIL RESPIRATION AS MICROBIAL RESPONSE TO THE ENDOGEN INPUT OF BIO-SYNTHESIZED ORGANIC MATTER AND ITS IMPLICATION IN CARBON SEQUESTRATION

Active C, as a measure of the level of chemical oxidation of organic matter, reflects the carbon available to microorganisms. Soil respiration, as a direct way to estimate edaphic microbial activity, could be a measure of the fluctuations of carbon stocks in soils. To determine the ability of soil respiration to evaluate such fluctuations we used soils with an increased content of organic carbon, constant optimal conditions, to eliminate the disturbing factors, analyzed in a short period of time. The influence of the specific decomposition rates of these soils was assessed by both spot determinations of soil respiration and analyzing the flux of CO2 from ex situ soil samples, under standard experimental conditions, to highlight carbon storage in such soils. Reference data can be accumulated through the analysis of these parameters, which compared with the results of quantitative/qualitative determinations regarding the changes in the content of microbial biomass, the content of fulvic sub-fractions, the fluorescence of dissolved organic material and the evolution of the content of siderophores, could be considered, by their own evolutions, as arguments in sustaining the use of respiration in the efficient estimation of carbon storage evolution in the soils. The analyses of these parameters were carried out in two phases, for comparing initial and final data of experiment (after 30 days). The soils had different levels of the respiration potential between phases. The level of soil respiration was reduced in time between 4.27-14.60%, in each soil. The CO2 flux showed, in time, a continuous decreasing trend in both soils. In the case of Mollic Histic Gleysol (Salinic), the coefficient of determination has the value R2=0.92 for the flux determined in the final phase. The levels of microbial biomass of both soils were increased significantly at the end of the experiment. In the case of Mollic Histic Gleysol (Salinic), microbial biomass increased from 456±23.12 μgC∙g-1 to 514±24.57 μgC∙g-1 soil. The fulvic sub-fractions A-D of both soils revealed significant accumulates of soluble organic compounds, with different molecular weights and complexity levels, after 30 days of incubations in standard conditions. The fluorescent components present in the water-extractable organic matter were highlighted by imagistic method. The highest degree of storages of newly bio-synthesized compounds of carbon was registered in organic matter of Mollic Histic Gleysol (Salinic). The intensity of siderophores biosynthesis increased over time, starting from an initial lower presence in the Mollic Gleysol (Salinic) (with Ø 11 mm halo), which were followed by an increasing of siderophores content and availability of iron, at the end of the experimental period. Accumulations of siderophores in the Mollic Histic Gleysol (Salinic) determined a Ø 31 mm halo diameter.

Tree-size heterogeneity modulates the forest age-dependent carbon density in biomass and top soil stocks on Mediterranean woodlands

AimsCarbon accumulation in terrestrial ecosystems is inherent to the vegetation development and ageing process. Primary productivity synthetize biomass which is constantly incorporated to soil. Vegetation community composition, and other ecological drivers, are known to mediate biomass production. However, links between forest developmental stage and ecological drivers of carbon stocks are unexplored. We address this topic under the prediction that species-rich and uneven-sized forests can improve carbon storage potential in biomass and topsoil fraction across its development.MethodsThe study was carried in forest stands growing under Mediterranean conditions in Central Spain. Carbon content in both above- and below-ground tree biomass and in topsoil organic matter (0–40 cm) was measured in 30 sampling plots of variable size (900–3000 m2). We also assessed Shannon species diversity index, Gini tree-size inequality index and forest developmental stage using dendrochronological procedures to derive the mean age of the oldest trees. First-order interaction terms between diversity factors and forest age were regressed against carbon density in compartment-independent regressions.ResultsForest-age and tree-size heterogeneity coupling was the main factor driving carbon density of both compartments. The interaction showed that woodlands maximize density in aged forests composed by uneven-sized trees. Models gave not support to consider species diversity as a mediator of carbon stocks.ConclusionOur results shed light on how tree-size heterogeneity can regulate the temporal dimension of forest ageing to rise the carbon storage potential. Mature forests in semi-arid environments cannot store carbon due to their intrinsic ontogeny, they need to grow structurally diverse.

Forest liming in the face of climate change: the implications of restorative liming for soil organic carbon in mature German forests

Abstract. Forest liming is a management tool that has and continues to be used extensively across northern Europe to counteract acidification processes from anthropogenic sulfur and nitrogen (N) deposition. In this study, we quantified how liming affects soil organic carbon (SOC) stocks and attempt to disentangle the mechanisms responsible for the often contrasting processes that regulate net soil carbon (C) fluxes. Using a paired plot experimental design we compared SOC stocks in limed plots with adjacent unlimed control plots at 28 experimental sites to 60 cm soil depth in mature broadleaf and coniferous forests across Germany. Historical soil data from a subset of the paired experiment plots were analyzed to assess how SOC stocks in both control and limed plots changed between 1990 and 2019. Overall, we found that forest floor C stocks have been accumulating over time in the control plots. Liming however largely offset organic layer buildup in the L/Of layer, and forest floor C stocks remained unchanged over time in the limed plots. This, in turn, meant that nutrients remained mobile and were not bound in soil organic matter complexes. Results from the paired plot analysis showed that forest floor C stocks were significantly lower in limed plots than the control (−34 %, −8.4 ± 1.7 Mg C ha−1) but did not significantly affect SOC stocks in the mineral soil, when all sites are pooled together. In the forest floor layers, SOC stocks exhibited an exponential decrease with increasing pH, highlighting how lime-induced improvements in the biochemical environment stimulate organic matter (OM) decomposition. Nevertheless, for both forest floor and mineral soils, the magnitude and direction of the belowground C changes hinged directly on the inherent site characteristics, namely, forest type (conifer versus broadleaf), soil pH, soil texture, and the soil SOC stocks. On the other hand, SOC stock decreases were often offset by other processes that fostered C accumulation, such as improved forest productivity or increased carbon stabilization, which correspondingly translated to an overall variable response by SOC stocks, particularly in the mineral soil. Lastly, we measured soil carbon dioxide (CO2) and soil methane (CH4) flux immediately after a re-liming event at three of the experimental sites. Here, we found that (1) liming doubles CH4 uptake in the long-term; (2) soil organic matter mineralization processes respond quickly to liming, even though the duration and size of the CO2 flush varied between sites; and (3) lime-derived CO2 contributed very little to total CO2 emissions over the measurement period (determined using stable isotope approaches).

Enhancing assessments of blue carbon stocks in marsh soils using Bayesian mixed-effects modeling with spatial autocorrelation — proof of concept using proxy data

Our paper showcases the potential gain in scientific insights about blue carbon stocks (or total organic carbon) when additional rigor, in the form of a spatial autocorrelation component, is formally incorporated into the statistical model for assessing the variability in carbon stocks. Organic carbon stored in marsh soils, or blue carbon (BC), is important for sequestering carbon from the atmosphere. The potential for marshes to store carbon dioxide, mitigating anthropogenic contributions to the atmosphere, makes them a critical conservation target, but efforts have been hampered by the current lack of robust methods for assessing the variability of BC stocks at different geographic scales. Statistical model-based extrapolation of information from soil cores to surrounding tidal marshes, with rigorous uncertainty estimates, would allow robust characterization of spatial variability in many unsampled coastal habitats. In the absence of BC data, we consider a historical dataset (the best available) on soil organic matter (OM)—a close proxy of BC—on 36 tidal (fresh and salt) marshes in the Virginia portion of Chesapeake Bay (CBVA) in the USA. We employ Bayesian linear mixed(-effects) modeling to predict OM by marsh type, soil category, soil depth, and marsh site, whereby site effects are modeled as random. When the random site effects are additionally assumed to exhibit an intrinsic conditional autoregressive (ICAR) spatial dependence structure, this more complex model clearly suggests groupings of marsh sites due to their spatial proximity, even after adjusting for the remaining predictors. Although the actual membership of each group is not a focus of our proof-of-concept analysis, the clear presence of groupings suggests an underlying latent spatial effect at the localized-regional level within CBVA. In contrast, the non-spatially explicit model provides no clear indication of either spatial influence between sites or improvement in predictive power. The polar difference in conclusions between models reveals the potential inadequacy in relying on predictor variables alone to capture the spatial variability of OM across a geographic domain of this size or larger. We anticipate that spatially explicit models, such as ours, will be important quantitative tools for understanding actual carbon measurements and for assessing BC stocks in general.