Makela, MinnaKabir, Kazi Md JahangirKanerva, SannaYli-Halla, Markku...
13页
查看更多>>摘要：Factors limiting the production of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated in three incubation experiments conducted with soil from top- and subsoil horizons of a peatland which had an acid sulphate mineral subsoil derived from black schists. The effect of moisture was investigated by equilibrating undisturbed soil samples from three horizons (H-2, Cg and Cr) at -10, -60 or -100 cm matric potential and measuring the gas production. In the second experiment, the effects of temperature and various substrates were studied by incubating disturbed soil samples in aerobic conditions at 5 or 20 degrees C, and measuring basal respiration and N2O production before and after adding water, glucose or ammonium into the soil. In the third experiment, the effects of added glucose and/or nitrate on the denitrification in soil samples from four horizons (H1, H2, Cg and Cr were investigated by acetylene inhibition and monitoring of N2O production during a 48-h anaerobic incubation. The production of CO2 in the topmost peat horizon was largest at -10 cm matric potential, and it was larger than those in the mineral subsoil also at -60 and -100 cm potentials. In contrast, drainage seemed to increase N2O production, whereas in the wettest condition the production of N2O in the mineral subsoil was small and the peat horizon was a sink of N2O. Lowering of temperature (from 20 degrees C to 5 degrees C) decreased CO2 production, as expected, but it had almost no role in the production of N2O in aerobic conditions. Glucose addition increased the aerobic production of CO2 in peat, but it had a minor effect in the mineral horizons. Lack of C source (glucose) was limiting anaerobic N2O production in the uppermost peat horizon, while in all other horizons, nitrate proved to be the most limiting factor. It is concluded that peatlands with black schist derived acid sulphate subsoil horizons, such as in this study, have high microbial activity in the peaty topsoil horizons but little microbial activity in the mineral subsoil. These findings are contrary to previous results obtained in sediment-derived acid sulphate soils.
查看更多>>摘要：The rapid and accurate determination of soil chromium (Cr) is crucial for preventing toxic element pollution in soils and ensuring ecological security. Proximal sensing technology uses visible and near-infrared (Vis-NIR) diffuse reflectance spectroscopy, which has been demonstrated to be a viable approach for monitoring soil Cr concentrations. However, at trace levels, soil Cr is not especially spectrally active, thus limiting the practical application of using corresponding spectral data for quantifying soil Cr concentrations. In this study, we hypothesized that fused proximal sensing and soil auxiliary attributes (including organic matter (OM) and pH) could improve estimation of Cr concentrations in the soil. Additionally, the introduction of best-fit variogram models was theoretically possible to improve spatial visualization. To address these hypotheses, we collected 168 soil samples from the open coal mine area in the Eastern Junggar Basin, China. Fractional-order derivative (FOD) pretreatment and optimal band combination methods were implemented for spectral data mining and the derivation of spectral parameters, respectively. Soil Cr estimation models were calibrated with a partial least squares (PLS) approach through four designed strategies with different predictors: (I) full Vis-NIR variables, (II) effective three-band spectral indices (TBIs), (III) the effective TBIs and OM, and (IV) the effective TBIs, OM, and the pH. The results suggest that FOD could identify abundant spectral variability. Compared with full Vis-NIR variables, the effective TBIs can effectively magnify the subtle spectral signals concerning soil Cr. The optimal estimation model was determined as Strategy IV, indicating that the introduction of soil auxiliary attributes (pH and OM) can improve the estimation performance of the model; notably, the coefficient of determination (R-2) and ratio of performance to interquartile distance (RPIQ) were 0.87 and 2.68, respectively. Based on the optimal semivariance model, we used kriging interpolation to map regional soil Cr. In the study area, the soil Cr distribution features strong spatial dependence and strong associations. Our study might inspire further research on soil contamination mapping based on proximal Vis-NIR sensors.
查看更多>>摘要：The intermediate-disturbance hypothesis (IDH) posits that more species will be found under moderate disturbance in an ecosystem. We found that moderate disturbance improved the microbial community structure in biocrusts in a one-year field experiment in a dryland ecosystem. However, whether the improvement of microbial community structure in biocrusts can be sustained for a long time is unclear. Here, considering microorganisms as indicators, we used the phospholipid fatty acid (PLFA) method to examine changes in the microbial communities of biocrusts under varying disturbance intensities from 2016 to 2019. We found that under moderate disturbance, the total microbial PLFAs of biocrusts increased by 11 similar to 94% in the 4 years of disturbance, and the microbial community in biocrusts was more abundant under such disturbance than under no disturbance over time. The ratios of fungal to bacterial PLFAs (F/B) and gram-negative to gram-positive bacterial PLFAs (G-/G+) under moderate disturbance increased over time. However, these variables decreased over time under low- and high-intensity disturbances. The alterations were related to improvements in cyanobacterial biomass, available N, soil moisture, and vegetation coverage and a reduction in the C/N ratio. Through a long-term experiment, we demonstrated that improvements in microbial community in biocrusts under moderate disturbance can be maintained over the long term. Our study provides insights into the sustainability of biocrust systems under moderate disturbance in drylands.
查看更多>>摘要：Dryland ecosystems can be constrained by low soil fertility. Within drylands, the soil nutrient and organic carbon (C) cycling that does occur is often mediated by soil surface communities known as biological soil crusts (biocrusts), which cycle C and nutrients in the top ca. 0-2 cm of soil. However, the degree to which biocrusts are influencing soil fertility and biogeochemical cycling in deeper, subsurface mineral soils is unclear. The movement of dissolved resources from biocrusts to deeper soil layers in leachate may be one of the main mechanisms through which biocrust fertility is transferred downward towards deeper microbial communities and plant roots occurring within mineral soil. Here we examined the role of biocrust leachate in contributing to subsurface nutrient and soluble C pools and subsurface microbial cycling. We collected biocrusts from three biocrust successional stages and explored resource pools in situ at multiple soil depths, while collecting leachate and measuring nutrient and organic C concentrations and metabolite composition from each successional stage in the laboratory. After four leachate collections, we conducted an incubation of mineral soil collected from below each biocrust successional stage to measure heterotrophic microbial CO2 flux and biomass. Overall, our findings observed that the degree of nutrient and C connectivity between biocrusts and the sub-crust mineral soil depended on the biocrust successional stage and the element being considered, and the influence of biocrust successional stage on mineral soil CO2 flux is likely related to long-term resource build up. Together, our results suggest that the influence of biocrust leachate on subsurface mineral soil is complex and context dependent, but, over longer time periods and at later successional stages, can have measurable effects on dryland soil biogeochemical cycling with feedbacks to resource availability and CO2 flux.
查看更多>>摘要：Phosphorus (P) availability in calcareous forest soils is commonly low compared to siliceous soils. The main reason for this is that phosphate ions tend to precipitate with calcium (Ca). Weathering of calcareous rocks and the potential of microorganisms to dissolve calcareous parent material is not fully understood. Therefore, we examined microbial carbonate dissolution and the abundance of phosphorus-solubilizing bacteria in temperate forest soils with contrasting calcareous parent materials. We incubated soil extracts with weathered parent materials (i.e., dolomite and limestone) from two calcareous forest soils differing in P content and determined the rates of P and Ca solubilization. In addition, we determined the abundance of phosphorus-solubilizing bacteria (PSB). We found that the net Ca solubilization rate ranged from 8.8 to 511.1 nmol m(-2) d(-1) across both soils and depths. Calcium dissolution rates were negatively related to pH and positively related to the concentration of organic acids. The gross P solubilization rates were on average 63.6% higher from dolomite (P-poor soil) than from limestone (P-rich soil). The abundance of soil PSB ranged from 3.8 % at the limestone site (P-rich soil) to 24.4 % at the dolomite site (P-poor soil). The higher abundance of PSB in the soil derived from dolomite is in line with the high Ca and P solubilization rates at this site, indicating that PSB abundance is related to rock weathering rates from calcareous soils. Pseudomonadales and Enterobacteriales were by far the two most abundant bacterial orders in the PSB community of both soils and soil depths. In conclusion, this study shows, first, that weathering of calcareous bedrocks is strongly affected by the activity of soil microorganisms, and second, that there is likely a selective pressure in P-poor soils towards a higher abundance of PSB.
查看更多>>摘要：Performing laboratory measurement of saturated hydraulic conductivity, K-s, of sieved soil is important for many scientific purposes such as testing theories and methods to determine K-s. A given soil mass can be used only once or it can be reused after a previous use. Little is known on the dependence of the K-s measurements on both the applied packing method and the reuse of the same soil mass. This lack of knowledge makes comparisons among different investigations more or less uncertain. Four packing methods were tested on an initially dry loam soil by measuring K-s with the simplified falling head (SFH) technique. The four methods differed by the used compacting procedure (dropping from a given height, pestle imparting vertical and radial forces on the pressed soil surface) and the number of soil layers disposed at each step of the procedure. Changes in K-s due to the reuse of the same soil mass were also determined. Depending on the packing method and the number of times a given soil mass was used, the means of K-s varied from 51 to 110 mm h(-1), with a ratio between these two extremes of 2.2, and the coefficients of variation, CVs, ranged between 10 and 36%, depending on the developed dataset (sample size, N = 15 for each dataset). Therefore, the packing method and the reuse of the same soil had a moderate effect on determination of K-s. For a given pre-treatment of the soil mass, the lowest variability of K-s was detected by using the pestle, probably because this simple device favored homogenization of the soil and enhanced the contact with the walls of the cylinder. With the pestle, reusing the soil once was enough to pass from a medium (CV = 23-27%) to a low (CV = 12%) variation of K-s. Taking into account that the best procedure yields the lowest variability of the individual K-s measurements, the conclusion was that the pestle and a previously wetted soil should be used. In the future, additional experiments should be carried out on other soils, in different antecedent soil water conditions and with other laboratory measurement methods of K-s. This study provided new information on soil sample preparation methods and it showed that simple procedures could be applied for preparing different samples with similar K-s values.
查看更多>>摘要：Spectral-based models extracted from laboratory reflectance in the 400-2500 nm spectral range to predict soil attributes may not be applicable to soil spectra acquired in the field. This is because laboratory sampling procedures disturb the natural soil surface's status. We investigated this issue by using the soil surface-dependent property of water-infiltration rate (WIR). We created a dataset with 114 samples collected from six fields with varying textures located in three different Mediterranean countries (Israel, Greece, Italy). Using the field and laboratory spectral datasets, we demonstrated that WIR is better predicted by field vs. laboratory measurements (R-2 = 0.92 and 0.56, respectively). We also developed a transfer function (TF) to predict the field spectral measurements from the laboratory spectra. Use of the TF-processed dataset considerably improved the WIR prediction using laboratory information (from R-2 = 0.56 to 0.76). It was concluded that soil surface reflectance values can be estimated based on laboratory spectra using a TF. The generated TF enables exploiting soil spectral libraries for remote-sensing views and for assessing surface-related soil properties.
查看更多>>摘要：In dryland ecosystems, soil erosion poses severe threats to ecosystem productivity and human well-being. Biological soil crusts (biocrusts) are ubiquitous living covers in these ecosystems and play an important role in soil stabilization and erosion prevention. However, the quantitative relationship between biocrust coverage and soil water erosion as well as the driving mechanism have not yet been fully discussed, which hinders the development of soil erosion models that consider the effect of biocrusts. Accordingly, we set up 19 biocrust plots (10 m x 2.1 m) with coverage ranging from 9.3% to 80.0% on the Loess Plateau of China and conducted a series of simulated rainfall experiments. The quantitative relationship between runoff and sediment yield and biocrust coverage was assessed, and further complex correlations among these variables were analyzed using structural equation modeling (SEM). We found that (1) the runoff rates and sediment yield were significantly related to biocrust coverage. The runoff rates and sediment yield decreased with increasing biocrust coverage via a logarithmic function and an exponential function, respectively. The runoff rate and sediment yield rate from the plot with 9.3% biocrust coverage were 3.2 and 51.5 times higher, respectively, than those from the plot with 78.4% biocrust coverage. (2) The flow pattern and regime of overland flow were significantly affected by biocrust coverage. The overland flow was shifted from tranquil flow to supercritical flow when the biocrust coverage declined to 12.3%. The flow velocity, stream power, Darcy-Weisbach resistance coefficient, Froude number, and Reynolds number were strongly correlated with biocrust coverage (R-2 = 0.548-0.830). (3) Biocrust coverage both directly and indirectly affected sediment yield. The anchoring effect of biocrusts directly protected the surface soil from raindrop impacts and runoff scouring (direct effect = -0.59). Additionally, biocrust cover had an indirect negative effect (-0.38) on sediment yield by decreasing the flow velocity and runoff rate with path coefficients of -0.81 and -0.78, respectively. Our results confirm that soil hydrological and erosive behavior have nonlinear relationships with biocrust coverage at the hill-slope scale, and they also reveal that variation in biocrust coverage is one of the main driving factors affecting soil hydrological and erosive behaviors. These results would improve soil water erosion estimation on biocrust-covered slopes and provide guidance for revising soil erosion models to include the effectiveness of biocrusts.
Roy, DibakarDatta, AshimJat, H. S.Choudhary, Madhu...
13页
查看更多>>摘要：Soil quality is of utmost essential for yield sustainability of intensive cereal based cropping system in North West Indo Gangetic plains of India. Hence, we evaluated long-term (10 years) effect of conservation agriculture (CA) practices on soil quality improvement under six different cropping scenarios (Sc), i.e. Sc1-represented by transplanted puddled rice (TPR) followed by conventional tilled broadcasted wheat (CT-wheat) with residue removal, Sc2-TPR rice followed by zero tillage (ZT) wheat and ZT-mung bean with partial residue retention, Sc3-direct seeded rice (DSR) followed by ZT-wheat and ZT-mung bean with full residue retention, Sc4-DSR is replaced by ZT-maize followed by ZT-wheat and ZT-mung bean, Sc5 and Sc6 were - Sc3 integrated with sub surface drip irrigation (SDI) and Sc4 + SDI, respectively. Soil samples were collected from 0 to 5, 5-15 and 15-30 cm soil depth from each scenario after harvesting of wheat in 2019. Results showed that, reduction in bulk density (BD), soil penetration resistance (SPR) and enhancement of water holding capacity and infiltration were associated with CA based scenarios (Sc3-Sc6). Scenario 3 recorded lowest BD of 1.39 and 1.58 g cm(-3) at 0-5 and 5-15 cm soil depth, respectively. CA based Sc6 recorded highest infiltration rate (1.48 cm hr(-1)) and lowest was associated with Sc1 (0.5 cm hr(-1)). The enrichment of soil organic carbon (SOC) content, stock, available nitrogen and potassium was mainly confined to upper surface soil layer (0-5 cm). The SOC content and stock in CA based scenarios (average of Sc3 to Sc6) was 41-57 and 69-94% higher than Sc1 at 0-5 cm soil layer. Available nitrogen was increased by 23-50 and 64-98% and available potassium increased by 13-28 and 42-71% in 0-5 and 5-15 cm soil depth, respectively in CA based scenarios over Sc1. Similarly, microbial biomass carbon (MBC) and dehydrogenase (DHA) activity in top soil layer under CA based scenarios was increased by 177-195 and 67-107% over Sc1, respectively. The maximum SQI was registered with Sc6 (0.91) followed by Sc4 (0.89) and least was recorded in Sc1 (0.65) at 0-5 cm soil depth. Maize-wheat based cropping system recorded higher SQI over rice-wheat based cropping system. Sustainable yield index was strongly related with key soil quality indicators and also positively correlated with SQI. Thus our study suggests that CA based maize-wheat-mung bean cropping system should be recommended for better soil quality and yield sustainability in North West India.
查看更多>>摘要：Climate warming can enhance the decomposition of soil organic matter (SOM), thereby increasing the rate of carbon release from soils. In permafrost regions, climate warming alters the nature of freeze-thaw cycles by affecting sub-surface hydrology and soil temperature, thereby impacting the decomposition of SOM. However, this process is rarely considered in projections of the long-term dynamics of soil organic carbon (SOC) on the Tibetan Plateau (TP) in response to climate change. Here, we employ the CENTURY-FTC model, which implements a freeze-thaw module in the CENTURY model, to simulate the response of top soil organic carbon density (SOCD) at 0-20 cm depth to climate change in the permafrost region of Northern Tibet. Our findings suggest that (i) the average SOCD was 2.123 kg C m(-2) in 2015; (ii) the SOCD decreased at an average rate of 0.7 x 10(-3) kg C m(-2) year(-1) for the period 1961-2015; and (iii) SOCD decreases spatially from south to north across Northern Tibet. Under various climate scenarios, the SOCD is projected to decrease significantly throughout Northern Tibet from 2016 to 2050, with the decline being most pronounced under the representative concentration-pathway (RCP) 8.5 scenario, which projects an increase in global mean surface temperature of 4.5 degrees C by 2100. Superimposed on this pattern, regional differences might be driven by vegetation type, with the largest decrements occurring in southern, alpine-meadow-dominated areas and the smallest in the northern alpine desert. We propose that this declining trend will be enhanced as climate warming continues and might be amplified by the increase in freeze-thaw processes. The addition of a freeze-thaw module to the CENTURY model changes projections of SOCD change due to climate. Whereas the freeze-thaw cycle has had little impact during the baseline period, its influence is likely to increase as climate warming continues. By 2050, freeze-thaw processes are projected to contribute 3% to SOCD decline under the RCP2.6 scenario, which projects a rise in global mean surface temperature of 1.5 degrees C by 2100, and as much as 10% under the RCP8.5 scenario. In general, future warming is likely to result in declining SOCD throughout Northern Tibet and a reduction in the capacity of alpine soils to sequester carbon.
NSTL
Elsevier