Changes In Soil Conditions Research Articles

Feasibility of coupled empirical and dynamic modeling to assess climate change and air pollution impacts on temperate forest vegetation of the eastern United States.

Changes in climate and atmospheric nitrogen (N) deposition caused pronounced changes in soil conditions and habitat suitability for many plant species over the latter half of the previous century. Such changes are expected to continue in the future with anticipated further changing air temperature and precipitation that will likely influence the effects of N deposition. To investigate the potential long-term impacts of atmospheric N deposition on hardwood forest ecosystems in the eastern United States in the context of climate change, application of the coupled biogeochemical and vegetation community model VSD+PROPS was explored at three sites in New Hampshire, Virginia, and Tennessee. This represents the first application of VSD+PROPS to forest ecosystems in the United States. Climate change and elevated (above mid-19th century) N deposition were simulated to be important factors for determining habitat suitability. Although simulation results suggested that the suitability of these forests to support the continued presence of their characteristic understory plant species might decline by the year 2100, low data availability for building vegetation response models with PROPS resulted in uncertain results at the extremes of simulated N deposition. Future PROPS model development in the United States should focus on inclusion of additional foundational data or alternate candidate predictor variables to reduce these uncertainties.

Change to ecosystem properties through changing the dominant species: Impact of Pteridium aquilinum-control and heathland restoration treatments on selected soil properties

It is well known that soils are influenced by the plant species that grow in them. Here we consider the effects of management-induced changes to plant communities and their soils during restoration within a 20-year manipulative experiment where the aim was to change a late-successional community dominated by the weed, Pteridium aquilinum, to an earlier-successional grass-heath one. The ecological restoration treatments altered the above- and below-ground components of the community substantially. Untreated plots maintained a dense Pteridium cover with little understory vegetation, cutting treatments produce significant reductions of Pteridium, whereas herbicide (asulam) produced significant immediate reductions in Pteridium but regressed towards the untreated plots within 10 years. Thereafter, all asulam-treated plots were re-treated in year 11, and then were spot-sprayed annually. Both cutting and asulam treatments reduced frond density to almost zero and resulted in a grass-heath vegetation. There was also a massive change in biomass distribution, untreated plots had a large above-ground biomass/necromass that was much reduced where Pteridium was controlled. Below-ground in treated plots, there was a replacement of the substantive Pteridium rhizome mass with a much greater root mass of other species. The combined effects of Pteridium-control and restoration treatment, reduced soil total C and N as and available P concentrations, but increased soil pH and available N. Soil biological activity was also affected with a reduction in soil N mineralization rate, but an increased soil-root respiration. Multivariate analysis showed a clear trend along a pH/organic matter gradient, with movement along it correlated to management intensity from the untreated plots with low pH/high organic matter and treated plots with to a higher pH/lower organic matter in the sequence asulam treatment, cut once per year to cut twice per year. The role that these changed soil conditions might have in restricting Pteridium recovery are discussed.

Will CO2 Emissions from Drained Tropical Peatlands Decline Over Time? Links Between Soil Organic Matter Quality, Nutrients, and C Mineralization Rates

Conversion, drainage, and cultivation of tropical peatlands can change soil conditions, shifting the C balance of these systems, which is important for the global C cycle. We examined the effect of soil organic matter (SOM) quality and nutrients on CO2 production from peat decomposition using laboratory incubations of Indonesian peat soils from undrained forest in Kalimantan and drained oil palm plantations in Kalimantan and Sumatra. We found that oil palm soils had higher C/N and lower SOM quality than forest soils. Higher substrate quality and nutrient availability, particularly lower ratios of aromatic/aliphatic carbon and C/N, rather than total SOM or carbon, explained the higher rate of CO2 production by forest soils (10.80 ± 0.23 µg CO2–C g C h−1) compared to oil palm soils (5.34 ± 0.26 µg CO2–C g C h−1) from Kalimantan. These factors also explained lower rates in Sumatran oil palm (3.90 ± 0.25 µg CO2–C g C h−1). We amended peat with nitrogen (N), phosphorus (P), and glucose to further investigate observed substrate and nutrient constraints across the range of observed peat quality. Available N limited CO2 production, in unamended and amended soils. P addition raised CO2 production when substrate quality was high and initial P state was low. Glucose addition raised CO2 production in the presence of added N and P. Our results suggest that decline in SOM quality and nutrients associated with conversion may decrease substrate-driven rates of CO2 production from peat decomposition over time.

Effects of fire frequency on litter decomposition as mediated by changes to litter chemistry and soil environmental conditions.

Litter quality and soil environmental conditions are well-studied drivers influencing decomposition rates, but the role played by disturbance legacy, such as fire history, in mediating these drivers is not well understood. Fire history may impact decomposition directly, through changes in soil conditions that impact microbial function, or indirectly, through shifts in plant community composition and litter chemistry. Here, we compared early-stage decomposition rates across longleaf pine forest blocks managed with varying fire frequencies (annual burns, triennial burns, fire-suppression). Using a reciprocal transplant design, we examined how litter chemistry and soil characteristics independently and jointly influenced litter decomposition. We found that both litter chemistry and soil environmental conditions influenced decomposition rates, but only the former was affected by historical fire frequency. Litter from annually burned sites had higher nitrogen content than litter from triennially burned and fire suppression sites, but this was correlated with only a modest increase in decomposition rates. Soil environmental conditions had a larger impact on decomposition than litter chemistry. Across the landscape, decomposition differed more along soil moisture gradients than across fire management regimes. These findings suggest that fire frequency has a limited effect on litter decomposition in this ecosystem, and encourage extending current decomposition frameworks into disturbed systems. However, litter from different species lost different masses due to fire, suggesting that fire may impact decomposition through the preferential combustion of some litter types. Overall, our findings also emphasize the important role of spatial variability in soil environmental conditions, which may be tied to fire frequency across large spatial scales, in driving decomposition rates in this system.

Long-term deer exclosure alters soil properties, plant traits, understory plant community and insect herbivory, but not the functional relationships among them

Evidence of the indirect effects of increasing global deer populations on other trophic levels is increasing. However, it remains unknown if excluding deer alters ecosystem functional relationships. We investigated how sika deer exclosure after 18 years changed soil conditions, the understory plant community, the traits of a dominant understory plant (Sasa palmata), herbivory by three insect-feeding guilds, and the functional relationships between these properties. Deer absence decreased understory plant diversity, but increased soil organic matter and ammonium concentrations. When deer were absent, S. palmata plants grew taller, with more, larger, and tougher leaves with higher polyphenol concentrations. Deer absence led to higher leaf area consumed by all insect guilds, but lower insect herbivory per plant due to increased resource abundance (i.e., a dilution effect). This indicates that deer presence strengthened insect herbivory per plant, while in deer absence plants compensated losses with growth. Because plant defenses increased in the absence of deer, higher insect abundances in deer absence may have outweighed lower consumption rates. A path model revealed that the functional relationships between the measured properties were similar between deer absence versus presence. Taken together, deer altered the abiotic and biotic environment, thereby changing insect herbivory, which might impact upon nutrient cycling and primary productivity. These results provide evidence that deer can alter interactions between trophic levels, but that functional relationships between certain ecosystem components may remain constant. These findings highlight the need to consider how increasing global deer populations can have cascade effects that might alter ecosystem dynamics.

Harvest date of Miscanthus x giganteus affects nutrient cycling, biomass development and soil quality

Anaerobic digestion is the most advanced technology allowing the production of methane as flexible energy carrier. Recently, in view of mitigating the ecological drawbacks of maize as predominantly used feedstock, perennial energy crops were introduced in European agriculture, which implicated reduced resource input and improved landscape diversity. The biogas potential of Miscanthus x giganteus is high when harvested in autumn, prior to lignification. However, the effects of autumn harvest on carbon and nutrient recycling depict a gap of research. A two-year field experiment was conducted to compare autumn harvest with the commonly conducted harvest date in spring. Below and aboveground plant fractions were analysed to quantify pathways of nutrient recycling and contrasting different harvest dates. Additionally, crop biomass development and soil quality parameters were monitored.This study indicates that autumn harvest increase biomass yields by up to 30%, whilst nutrient exports were several times higher than in spring. Our results further show that pathways of nutrient recycling were element-specific and that recycling of specific elements was influenced to a varying extent by autumn harvest. Significantly reduced deposition of storage proteins in rhizomes resulted in weaker biomass development in subsequent years. The degradation of the mulch layer, resulting from drastically reduced input of organic material to the soil, led to changed soil conditions, which were reflected in reduced soil microbial biomass and activity.Consequently, the ecological benefits of Miscanthus cultivation, such as low nutrient demands, perennial soil cover and high potential for carbon sequestration, would be distinctly reduced.

Species-specific effects of leaf litter on seedling emergence and growth of the invasive Flaveria bidentis and its co-occurring native species: a common garden test

The amount of litter and its type can affect seedling establishment and species richness in plant communities. However, little is known about the species-specific effects of litter, especially in the presence of a competitor. We conducted a common garden test to examine the combined effects of competition and plant litter from conspecific versus heterospecific species on the emergence and early growth of the invasive plant Flaveria bidentis and the co-occurring native plant Amaranthus retroflexus. The litter of native species reduced the rate of seedling emergence of F. bidentis; this effect was stronger in the presence of a competitor. Litter addition reduced the seedling emergence rate of A. retroflexus, but had a neutral to positive effect on its early growth, indicating a clear species-specific pattern. Litter addition, combined with interspecific competition, facilitated growth of A. retroflexus; this species seemed to perform better in changing soil conditions than did F. bidentis. Consequently, a habitat-specific adaptation might be involved in this interspecific plant–soil feedback. Our results contribute our understanding of how to suppress F. bidentis in disturbed sites without herbicide application. Manipulating litter cover could be used to manage this invader; such addition would either affect emergence or the belowground competition for soil resources.

Contrasting elevational diversity patterns for soil bacteria between two ecosystems divided by the treeline.

Above- and below-ground organisms are closely linked, but how elevational distribution pattern of soil microbes shifting across the treeline still remains unknown. Sampling of 140 plots with transect, we herein investigated soil bacterial distribution pattern from a temperate forest up to a subalpine meadow along an elevational gradient using Illumina sequencing. Our results revealed distinct elevational patterns of bacterial diversity above and below the treeline in responding to changes in soil conditions: a hollow elevational pattern in the forest (correlated with soil temperature, pH, and C:N ratio) and a significantly decreasing pattern in the meadow (correlated with soil pH, and available phosphorus). The bacterial community structure was also distinct between the forest and meadow, relating to soil pH in the forest and soil temperature in the meadow. Soil bacteria did not follow the distribution pattern of herb diversity, but bacterial community structure could be predicted by herb community composition. These results suggest that plant communities have an important influence on soil characteristics, and thus change the elevational distribution of soil bacteria. Our findings are useful for future assessments of climate change impacts on microbial community.

Biesterfeld to sell Heroc aseptic/antimicrobial masterbatches worldwide

Designing support structures for offshore wind turbines is a complex task as these are highly dynamic systems subjected to long-term cyclic loads with variable amplitude. Long-term cyclic loading may cause stiffening or softening of the soil around the pile foundation of an offshore wind turbine, which leads to variations in the foundation stiffness and accumulated permanent rotation of the pile. Although variations in the foundation stiffness can negatively impact the fatigue life, the long-term variability of the soil conditions is normally not considered in the fatigue damage assessment. The main objective of this study is the investigation of the impact of changes in soil parameters on the fatigue lifetime for an offshore wind turbine founded in loose sand. For this purpose, a generic monopile based offshore wind turbine with flexible foundation model was used. The soil-pile interaction was modeled with a distributed spring model using nonlinear API p-y curves. Integrated analyses in the time domain were performed and fatigue damage was assessed in terms of a damage equivalent bending moment at mudline. The fatigue lifetime varies between -9 percent and +4 percent when considering changes in soil conditions, depending on the assumption of soil softening or stiffening, respectively. These results indicate that changes in soil parameters should be taken into account in the fatigue damage calculations of offshore wind turbines for more precise fatigue lifetime estimation. Moreover, it is emphasized that more accurate modeling of soil-pile interaction is required in the design and optimization of offshore wind turbines.

Brazil: Evonik – precipitated silica

Designing support structures for offshore wind turbines is a complex task as these are highly dynamic systems subjected to long-term cyclic loads with variable amplitude. Long-term cyclic loading may cause stiffening or softening of the soil around the pile foundation of an offshore wind turbine, which leads to variations in the foundation stiffness and accumulated permanent rotation of the pile. Although variations in the foundation stiffness can negatively impact the fatigue life, the long-term variability of the soil conditions is normally not considered in the fatigue damage assessment. The main objective of this study is the investigation of the impact of changes in soil parameters on the fatigue lifetime for an offshore wind turbine founded in loose sand. For this purpose, a generic monopile based offshore wind turbine with flexible foundation model was used. The soil-pile interaction was modeled with a distributed spring model using nonlinear API p-y curves. Integrated analyses in the time domain were performed and fatigue damage was assessed in terms of a damage equivalent bending moment at mudline. The fatigue lifetime varies between -9 percent and +4 percent when considering changes in soil conditions, depending on the assumption of soil softening or stiffening, respectively. These results indicate that changes in soil parameters should be taken into account in the fatigue damage calculations of offshore wind turbines for more precise fatigue lifetime estimation. Moreover, it is emphasized that more accurate modeling of soil-pile interaction is required in the design and optimization of offshore wind turbines.

Influence of Soil Parameters on the Fatigue Lifetime of Offshore Wind Turbines with Monopile Support Structure

Designing support structures for offshore wind turbines is a complex task as these are highly dynamic systems subjected to long-term cyclic loads with variable amplitude. Long-term cyclic loading may cause stiffening or softening of the soil around the pile foundation of an offshore wind turbine, which leads to variations in the foundation stiffness and accumulated permanent rotation of the pile. Although variations in the foundation stiffness can negatively impact the fatigue life, the long-term variability of the soil conditions is normally not considered in the fatigue damage assessment. The main objective of this study is the investigation of the impact of changes in soil parameters on the fatigue lifetime for an offshore wind turbine founded in loose sand. For this purpose, a generic monopile based offshore wind turbine with flexible foundation model was used. The soil-pile interaction was modeled with a distributed spring model using nonlinear API p-y curves. Integrated analyses in the time domain were performed and fatigue damage was assessed in terms of a damage equivalent bending moment at mudline. The fatigue lifetime varies between -9 percent and +4 percent when considering changes in soil conditions, depending on the assumption of soil softening or stiffening, respectively. These results indicate that changes in soil parameters should be taken into account in the fatigue damage calculations of offshore wind turbines for more precise fatigue lifetime estimation. Moreover, it is emphasized that more accurate modeling of soil-pile interaction is required in the design and optimization of offshore wind turbines.

Applying an artificial neural network approach to the analysis of tractive properties in changing soil conditions

For better performance of a micro-tractor during agricultural operations, it is necessary to select the optimal tractor configuration for the operation. The purpose of this study was to analyse the effects of soil texture, soil moisture and compaction as well as horizontal deformation and vertical load on traction force and traction efficiency. Analysis and mathematical modelling were performed with the use of artificial neural networks (ANN). Accurate mathematical models were obtained with high values of coefficient of determination R2 for the validation data set (R2=0.945 for traction force and R2=0.963 for traction efficiency). Based on neural models, analysis of the contribution of independent input variables was performed. Soil texture and soil moisture had the highest influence on traction force and traction efficiency; vertical load significantly affected traction force. Horizontal deformation and soil compaction had minor influences on both dependent variables. Evolutionary algorithm was used for the determination of soil conditions and vertical load which produce high traction force and traction efficiency. The vertical load is considered as an easily managed parameter during agricultural operations. Since the increase in vertical load results in increasing traction force and, at the same time, in decreasing traction efficiency, the appropriate vertical load value was calculated for optimization of traction force and traction efficiency in changing soil conditions, which is crucial for tillage management.

The Effects of Coal Seam Gas Infrastructure Development on Arable Land in Southern Queensland, Australia: Field Investigations and Modeling

<abstract> <b><sc>.</sc></b> The production of coal seam gas (CSG) in Australia is set to increase, driven by increasing global demand for energy and in response to the transition to a lower carbon economy through greater use of gas for electricity generation. Despite the many economic benefits delivered by the CSG industry, concerns have been raised over the potential environmental impacts associated with CSG production, particularly the long-term effects on the soil resource. Therefore, this work was conducted to: (1) assess the extent of damage to agricultural soil caused by the various elements of CSG development and (2) estimate the likely impact of soil compaction, caused during establishment of CSG infrastructure, on crop productivity. The study was undertaken using a paired-sites approach by comparing measurements conducted on selected soil properties in areas around and including well-head sites with measurements in neighboring agricultural fields. These spatial areas are referred to as “lease” and “field” areas, respectively. Measurements were used to guide parameterization and application of the Agricultural Production Systems Simulator (APSIM) model to assess the likely effects of changed soil conditions on crop productivity. To achieve this, the APSIM model was used to simulate wheat ( L.) yields for 115 years on Grey Vertosols in the Darling Downs region of Queensland. Simulations were conducted with soil properties representing: (1) field area conditions not affected by CSG activities, (2) lease area conditions in which soil had been impacted by CSG activities during the development phase, and (3) lease area conditions where soils had been rehabilitated. Results showed that soil compaction within lease areas in the top 300 mm of the profile was approximately 15% higher compared with field areas (p < 0.05). The modeling work suggested that near-surface (0 to 300 mm depth) soil compaction within affected areas can lead to significant losses in crop productivity due to adverse effects on soil hydraulic properties. The simulation analyses predicted a 53% reduction in median wheat yields compared with simulated results in neighboring agricultural fields. For the bottom and top deciles, predicted relative yields were up to 60% and 32% lower, respectively. Practical solutions for management of such compaction are presented and discussed. Soil cultivation of the top 300 to 350 mm will ensure sufficient soil water storage in most years, thereby reducing the risk of crop failure. Progressive soil loosening techniques for alleviation of deeper compaction were reviewed; however, their cost-effectiveness under Australian soil conditions requires further investigation. Limit bulk density values of 1.45 and 1.60 g cm^-3 for the 0 to 350 mm and 350 to 700 mm depth intervals, respectively, are suggested as references for CSG-rehabilitated soil. These critical values may be used as guidance until further studies are undertaken. The assessment of soil chemical properties indicated that these were affected to a lesser extent by the establishment of CSG infrastructure. However, a general requirement is careful manipulation of sodium-rich subsoil and avoidance of soil blending during reinstatement operations. The dataset acquired and the simulation approach employed in this study can be used to further develop soil management guidelines relevant to the Australian CSG industry. Cost-benefit analyses of soil management practices for reinstatement, development of soil quality standards, and industry best management practices are required.

Effects of long-term continuous cropping on soil nematode community and soil condition associated with replant problem in strawberry habitat.

Continuous cropping changes soil physiochemical parameters, enzymes and microorganism communities, causing “replant problem” in strawberry cultivation. We hypothesized that soil nematode community would reflect the changes in soil conditions caused by long-term continuous cropping, in ways that are consistent and predictable. To test this hypothesis, we studied the soil nematode communities and several soil parameters, including the concentration of soil phenolic acids, organic matter and nitrogen levels, in strawberry greenhouse under continuous-cropping for five different durations. Soil pH significantly decreased, and four phenolic acids, i.e., p-hydroxybenzoic acid, ferulic acid, cinnamic acid and p-coumaric acid, accumulated with time under continuous cropping. The four phenolic acids were highly toxic to Acrobeloides spp., the eudominant genus in non-continuous cropping, causing it to reduce to a resident genus after seven-years of continuous cropping. Decreased nematode diversity indicated loss of ecosystem stability and sustainability because of continuous-cropping practice. Moreover, the dominant decomposition pathway was altered from bacterial to fungal under continuous cropping. Our results suggest that along with the continuous-cropping time in strawberry habitat, the soil food web is disturbed, and the available plant nutrition as well as the general health of the soil deteriorates; these changes can be indicated by soil nematode community.

Analyzing load response and load sharing behavior of piled rafts installed with driven piles in sands

In this study, the load carrying behavior of piled rafts embedded in sand were investigated using the 3-D finite element analysis. Focus was given on piled rafts installed with driven piles. Various foundation and soil conditions were considered in the analyses. To simulate driven piles, the soil influence zone around driven pile was set where the relative density and lateral stress were increased to reflect the changes in soil condition and stress state due to pile driving. For both bored- and driven-pile cases, the values of load sharing ratio showed non-linear variation with settlement. The load sharing ratios for driven piles were higher than for bored piles within a certain settlement range. With further increasing settlement, however, the values of load sharing ratio for driven piles became similar to those of bored piles with limited variation. This indicates that load-sharing model can be applied for both cases to estimate the load capacity of piled rafts.

Effect of artificial shade and grazing removal on degraded grasslands: Implications of woody restoration for herbaceous vegetation

SummaryExtensive degraded short tussock grasslands of New Zealand's eastern South Island were dominated by woody vegetation prior to burning and livestock grazing associated with human settlement starting 800 years ago. There is increasing interest in restoring some of these grasslands back to a woody state. However, because of the long time frames involved in establishing a woody cover, it is difficult to predict the impacts that woody restoration will have on the extant herbaceous flora. Using a factorial trial with artificial shade and grazing exclusion, we assessed the potential impact of woody restoration on the structure and composition of the herbaceous flora over a six‐year period. The imposition of artificial shade resulted in significant increases in total species richness and the total cover of herbaceous vegetation, increases in cover of several individual forb and grass species and decreases in the cover of bare ground, moss and lichen in shade treatments. There were also changes in the overall community composition of shaded treatments reflecting these changes in vegetation cover and species richness. We found no statistically significant effects of grazing exclusion. We suggest that increased soil moisture resulting from shade addition plays an important role in increasing the herbaceous component of the flora. While woody restoration will have a range of effects on the herbaceous understorey, for example through competition and changes in soil conditions, our findings are important for planning future woody restoration in these degraded tussock grasslands. In particular, our results suggest that the best approach to ensure the persistence of herbaceous vegetation in woody restorations might be to ensure that restoration plantings result in a spatially heterogeneous vegetation arrangement.

Impacts of the alien trees Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. on soil nutrients and microbial communities

Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. are two aggressive invasive trees in riparian areas in Central Spain. We aim to test whether soil properties, nutrient mineralization rates and soil bacterial communities of riparian forest dominated by the native Populus alba L. can be altered by the presence of A. altissima or R. pseudoacacia. In autumn 2011 and spring 2012 we conducted a field soil sampling in three sites where invasive and native trees were paired. In addition, in a 6-month greenhouse experiment (GHE), we grew A. altissima, R. pseudoacacia and P. alba from seeds in a soil collected from a native area. We quantified soil organic matter (OM), nitrogen (N), phosphorous (P), nitrate (NO3−–N), ammonium (NH4+–N), pH, potential net ammonification and nitrification rates, phosphomonoesterase (PME) activity and the composition of soil bacterial community in soils from the field study and from the GHE. Both the field and the GHE results showed the capability of A. altissima to decrease soil total N and of R. pseudoacacia to increase soil mineral N. In the field, all invaded soils had greater NO3−–N than P. alba soils. R. pseudoacacia field soils had greater PME activity, total N and net ammonification rates while A. altissima soils had lower OM, NH4+–N, net nitrification and total N mineralization rates than those of P. alba. Differences in the composition of soil bacterial communities were only found in the field, being more evident between A. altissima and P. alba than between R. pseudoacacia and P. alba field soils. Symbiotic N2 fixation could explain the capability of R. pseudoacacia to increase soil mineral N, while the potential of A. altissima to decrease total soil N may be attributed to changes in the balance between N input and losses from the soil. Although the GHE results indicated that the invasive trees can start changing soil conditions during early stages of establishment, more impacts found in the field study suggests that several soil properties, the composition of soil bacteria communities and microbial activities need longer time since invasion to be altered.

Influence of atmospheric stability and transport on CH4 concentrations in northern Spain

Continuous methane (CH4) concentrations were measured in Northern Spain over two years (2011–2012) by multi-point sampling at 1.8, 3.7 and 8.3m using a Picarro analyser. The technique is based on cavity ring-down spectroscopy. The contrast in mean concentrations was about 1.2ppb, with 95th percentiles differing by 2.2ppb and mean minimum concentrations proving similar. Temporal variations of CH4 were also analysed, with a similar seasonal variability being found for the three heights. The highest CH4 concentrations were obtained in late autumn and winter and the lowest in summer, yielding a range of 52ppb. This variation may depend on the active photochemical reaction with OH radical during a period of intense solar radiation and changes in soil conditions together with variations in emissions. Peak concentration levels were recorded at night-time, between 5:00–7:00 GMT, with mean values ranging between 1920 and 1923ppb. The lowest value, around 1884ppb, was obtained at 16:00 GMT. This diurnal variation was mainly related to vertical mixing and photochemistry. Therefore, CH4 concentrations were also examined using the bulk Richardson number (RB) as a stability indicator. Four groups were distinguished: unstable cases, situations with pure shear flow, transitional stages and drainage flows. The highest contrast in mean CH4 concentrations between lower and upper heights was obtained for the transition and drainage cases, mainly associated to high concentrations from nearby sources. The impact of long range transport was analysed by means of 3-day isobaric backward air mass trajectories, which were calculated taking into account origins from Europe, Africa, the Atlantic Ocean and Local conditions. Assessment of the results showed the influence of S and SE wind sectors, especially with Local conditions associated with low winds. Finally, an estimation of the background CH4 concentration in the study period provided an average value of about 1892ppb.

Stand scale variability of topsoil organic matter composition in a high-elevation Norway spruce forest ecosystem

Our knowledge about the effect of single-tree influence areas on the physicochemical properties of the underlying mineral soil in forest ecosystems is still limited. This restricts our ability to adequately estimate future changes in soil functioning due to forest management practices. We studied the stand scale spatial variation of different soil organic matter species investigated by 13C NMR spectroscopy, lignin phenol and neutral sugar analysis under an unmanaged mountainous high-elevation Norway spruce (Picea abies L.) forest in central Europe. Multivariate geostatistical approaches were applied to relate the spatial patterns of the different soil organic matter species to topographic parameters, bulk density, oxalate- and dithionite-extractable iron, pH, and the impact of tree distribution. Soil samples were taken from the mineral top soil. Generally, the stand scale distribution patterns of different soil organic matter compounds could be divided into two groups: Those compounds, which were significantly spatially correlated with topography/altitude and those with small scale spatial pattern (range≤10m) that was closely related to tree distribution. The concentration of plant-derived soil organic matter components, such as lignin, at a given sampling point was significantly spatially related to the distance of the nearest tree (p≤0.05). In contrast, the spatial distribution of mainly microbial-derived compounds (e.g. galactose and mannose) could be attributed to the dominating impact of small-scale topography and the contribution of poorly crystalline iron oxides that were significantly larger in the central depression of the study site compared to crest and slope positions.Our results demonstrate that topographic parameters dominate the distribution of overall topsoil organic carbon (OC) stocks at temperate high-elevation forest ecosystems, particularly in sloped terrain. However, trees superimpose topography-controlled OC biogeochemistry beneath their crown by releasing litter and changing soil conditions in comparison to open areas. This may lead to distinct zones with different mechanisms of soil organic matter degradation and also stabilization in forest stands.

石羊河下游退耕地土壤微生物变化及土壤酶活性

PDF HTML阅读 XML下载 导出引用 引用提醒 石羊河下游退耕地土壤微生物变化及土壤酶活性 DOI: 10.5846/stxb201412282593 作者: 作者单位: 甘肃农业大学 草业学院,甘肃农业大学 草业学院,甘肃省荒漠化与风沙灾害防治国家重点实验室培育基地,甘肃省荒漠化与风沙灾害防治国家重点实验室培育基地,甘肃省荒漠化与风沙灾害防治国家重点实验室培育基地,甘肃省荒漠化与风沙灾害防治国家重点实验室培育基地,甘肃省荒漠化与风沙灾害防治国家重点实验室培育基地 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41161049，31360584，31160264） Soil microbial and soil enzyme activity in a discontinued farmland by the Lower Shiyang River Author: Affiliation: Gansu Desert Control Research Institute,Pratacultural College of Gansu Agricultural University,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用时空替代法，对石羊河下游不同年限（1，2，3，4，5，8，15，24、31 a）退耕地土壤微生物（细菌、真菌和放线菌）数量、生物量（碳、氮和磷）及土壤酶（过氧化氢酶、蔗糖酶、脲酶和磷酸酶）活性变化及三者的相关性进行了测定和分析。结果表明，在退耕1-31 a的9个样地样方中土壤三大类微生物数量以细菌最高，放线菌次之，真菌最低。总体来看，三大土壤微生物数量的加权平均值最大值均在退耕后的前8 a。土壤微生物生物量碳在退耕初期随着退耕年限的增加而减小，退耕4 a后逐渐增大，退耕24 a期间达到了加权平均值的最大，最后趋于稳定；土壤微生物生物量氮在退耕初期随着退耕年限的增加而增加，退耕4 a加权平均值的最大值出现，随后逐渐减小的趋势，并且不同退耕年限土壤微生物生物量氮差异显著；土壤微生物生物量磷在退耕初期随着退耕年限的增加而增加，退耕8 a前后加权平均值达到最大值，随后逐渐减小，最终趋于稳定。土壤酶活性总趋势随着退耕地自然演替时间的增加呈波动式下降。不同土壤层次（0-10 cm，10-20 cm，20-30 cm及30-40 cm），土壤微生物数量、生物量及土壤酶活性随土层深度显著降低，并且表层土壤微生物生物量及土壤酶活性占有较大比例。土壤微生物及土壤酶活性的变化是一个极其缓慢的互动过程，存在着互相回馈的响应，特别是真菌与放线菌、微生物量氮及蔗糖酶，放线菌与过氧化氢酶、蔗糖酶，微生物量碳与磷酸酶，微生物量氮与脲酶，微生物量磷与蔗糖酶均存在极显著的相关性。总体来看在退耕年限4-5 a前，有利于土壤发育，退耕后期土壤肥力呈下降的趋势。 Abstract:To better understand the changes in soil conditions after agriculture use ceases, we measured and analyzed the changes in three components-soil microbial quantity, soil microbial biomass, and soil enzyme activity-in sample sites where farming had been discontinued for different periods (1, 2, 3, 4, 5, 8, 15, 24 and 31 years), in the lower Shiyang River area. By using the data, the correlations between the three components were also studied in 2012. The three components, respectively, contained 1) bacteria, fungi, and actinomycetes; 2) microbial biomass carbon, microbial biomass nitrogen, and microbial biomass phosphorus; and 3) catalase, sucrase, urease, and phosphatase. Synchronic space investigation was adopted instead of diachronic temporal investigation. Results showed that bacteria were the most abundant of the three soil microorganisms in the nine soil samples taken 31 years after farming ceased, followed by actinomycetes and fungi. Overall, the maximum weighted average of the three soil microbial quantities all occurred in the first 8 years after farming ceased. The quantity of soil microbial biomass carbon initially decreased with increasing time since farming ceased. It gradually increased starting in the 4th year and reached the peak in the 24th year, after which it became stable. The soil microbial biomass nitrogen appeared to increase with time. After the maximum weighted average in the 4th year, there was a steady reduction with large significant differences in soil microbial biomass nitrogen among soil sites of various ages. The weighted average soil microbial biomass phosphorus increased at the same pace as nitrogen at the beginning of the soil restoration period. The biomass phosphorus level climaxed at the 8th year, after which it tended to decline gradually before finally stabilizing. The general trend of soil enzyme activity decreased, but with fluctuations, with increasing soil succession age. Moreover, soil microbial quantity, soil microbial biomass, and soil enzyme activity declined dramatically in all restoration ages with soil depth from 0 to 10 cm, 10 to 20 cm, and 20-30 to 30-40 cm. In addition, the surface soil microbial biomass and soil enzyme activity were the largest among the four soil levels. The changes in soil microbial quantity, soil microbial biomass, and soil enzyme activity were extremely slow. In addition, an interactive process and a feedback response between the three components was observed. Highly significant correlations were found, especially between fungi and actinomycetes, microbial biomass nitrogen and sucrase, actinomycetes and catalase and sucrase, microbial biomass carbon and phosphatase, microbial biomass nitrogen and urease, and microbial biomass phosphorus and sucrose. To summarize, we noted an improvement in the soil conditions in the initial 4-5 years after ceasing agricultural practice, followed by a declining trend in soil fertility. 参考文献 相似文献 引证文献