Analysis of Land Use Change and Associated Implications on Soil Ecosystem Functions in South Eastern Nigeria

Land use change affects soil functions and its capacity to provide ecosystem services. Though much of the tropics are experiencing accelerated increases in land use change, associated impacts of such changes are poorly understood and studied. This study assessed the extent to which land use changes affect the soil ecosystem functions in a rainforest zone of south eastern Nigeria. Soil samples were collected from 24 sample locations in selected natural forest, cashew and palm plantations. Samples were analyzed in triplicate in the laboratory for geochemical analysis, after which the result was subjected to statistical analysis—ANOVA, correlation and regression. Forest carbon had higher % mean carbon content;though there was no significant difference (F (2, 21) = .246, p = .784) in carbon level across land uses. R value of .301 showed low correlation between % carbon, organic matter and % loss in ignition. Furthermore, R2 value of 9.1% total variation in the dependent variable could only be explained by the independent variables. CEC, Nitrogen, Potassium and Phosphorus content of the land uses did not differ significantly: CEC (F (2, 21) = .844, p (.44);Nitrogen (.243), p (.79), Potassium (.140), p (.87), Phosphorus (.783), p (.47). This showed that there was no significant variation in soil fertility of the land uses, although natural forest had higher concentrations for these variables. Across the land uses, soil texture equally had no significant variations: % sand (F (2, 21) = .320, p (.729) % clay (.430), p (.656), % silt (.043), p (.958). Soil carbon was seen to be more enhanced in natural forest ecosystems than other land uses. Though plantations had reduced capacities to provide ecosystem functions, establishing such in modified landscapes is still advocated as they can coexist with such and yet ensure ecosystem functions.

IMPACTS OF DIFFERENT TYPES OF LAND USE ON PROCESSES OF SOIL AND WATER LOSS OVER PURPLE SOIL SLOPELAND

Based on natural precipitation observations, impacts of different types of land use on processes of soil and water loss over purple soil related slopeland were studied by simulated rainfall experiments. Measurement data revealed that rainstorms and slope length are the essential factors accountable for soil and water loss on purple soil slopeland for intense rill erosion can be caused on 10 meter long purple soil slopes by high intensity rainfall. Under circumanstances of rainstorms, annual hedge plants grown on slopeland of 25 degrees can cause a reduction of runoff by 22 43 percent and that of erosion induced sand content by 94 98 percent. Stone bund horizontal terraces can lead to a runoff reduction by 62 67 percent in comparison with steep slopelands and that of erosion induced sediment by 97.8 99 percent. Soil and water loss can be substantially decreased on steep slopes by hedge plants with a cost of only 10 20 percent that of the stone bund horizontal terraces. Hence it is an effective way to control soil and water loss in terms of slopeland amelioration and utilization in the Three Gorges Reservoir Area.

How freezing and thawing processes affect black-soil aggregate stability in northeastern China

Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size groups, different water contents, various freeze-thaw cycles, and various freezing temperatures. The results showed that, when at suitable water content, aggregate stability was enhanced, aggregate sta-bility will be disrupted when moisture content is too high or too low, especially higher water content. Temperature also had a significant ef-fect, but moisture content determined the suitable freezing temperatures for a given soil. Water-stable aggregate （WSA〉0.5）, the total aggre-gate content, and mean weight diameter decreasing with the freeze-thaw cycles increase, reached to 5 percent significance level. The reason for crumbing aggregates is the water and air conflict, thus raising the hypothesis that water content affects the aggregate stability in the process of freezing and thawing.

Coupling changes of soil functional gene abundances and extracellular enzyme activities across the diagnostic horizons of agricultural Isohumosols

Soil functional microbial taxa and extracellular enzymes are involved in a variety of biogeochemical cycling processes.Although many studies have revealed the vertical change patterns of microbial communities along soil profile,the general understanding of the coupling changes in the functional gene abundances(FGAs)and extracellular enzyme activities(EEAs)in soil profiles is still limited,which hinders us from revealing soil ecosystem processes.Herein,we comparatively investigated the FGAs and EEAs in the diagnostic A,B,and C horizons of soil profiles obtained from two suborders of Isohumosols(Mollisols),Ustic and Udic Isohumosols,in Northeast China based on quantitative real-time polymerase chain reaction and standard fluorometric techniques,respectively.The distribution patterns of both FGAs and EEAs significantly distinguished by the two soil suborders and were also separated from A to C horizon.Additionally,the variations of EEAs and FGAs were greater in Udic Isohumosols compared to Ustic Isohumosols along soil profiles,and greater changes were observed in C horizon than in A horizon.Both FGAs and EEAs correspondently decreased along the soil profiles.However,when normalized by soil organic carbon,the specific EEAs significantly increased in deep soil horizons,suggesting that microorganisms will input more resources to the production of enzymes to ensure microbial nutrient requirements under resource scarcity.More importantly,we revealed that soil microbial nutrient demands were limited by carbon(C)and phosphorus(P),and the C and P limitations significantly increased along soil profiles with a greater C limitation observed in Ustic Isohumosols than in Udic Isohumosols.Overall,our findings provided solid evidence showing the links between FGAs,EEAs,and microbial nutrient limitations,which would be helpful for a better understanding of the ecosystem processes in soil profiles.

A comprehensive review on coupled processes and mechanisms of soil-vegetation-hydrology, and recent research advances

Research on the coupling of soil,vegetation,and hydrological processes is not only a research hotspot in disciplines such as pedology,ecohydrology and Earth system science but also important for achieving sustainable development.However,scientists from different disciplines usually study the coupling mechanism of soil-vegetation-hydrological processes at very different space and time scales,and the mechanistic connections between different scales are quite few.This article reviewed research advances in coupled soil-vegetation-hydrological processes at different spatial scales—from leaf stomata to watershed and regional scales—and summarized the spatial upscaling methods and modeling approaches of coupled soil-vegetationhydrological processes.We identify and summarize the following coupling processes:(1)carbon-water exchange in leaf stomata and root-soil interface;(2)changes in soil aggregates and profile hydraulic properties caused by plant roots and water movement;(3)precipitation and soil moisture redistribution by plant canopy and root;(4)interactions between vegetation patches and local hydrological process;(5)links between plant community succession and soil development;and(6)links between watershed/regional water budget and vegetation phenology and production.Meanwhile,the limitations and knowledge gaps in the observations,mechanisms,scaling methods,and modeling approaches of coupled soil-vegetation-hydrological processes were analyzed.To achieve a deep integration of various coupling processes across different spatiotemporal scales,future work should strengthen multiscale,multifactor and multiprocess soil-vegetation-hydrology coupling observations and mechanism studies,develop new scaling methods,identify different feedback pathways,and take time-variable plant behavior and soil hydraulic properties into account during modeling.

Comparing surface erosion processes in four soils from the Loess Plateau under extreme rainfall events

This research aims to improve erosion control practice in the Loess Plateau,by studying the surface erosion processes,including splash,sheet/interrill and rill erosion in four contrasting soils under high rainfall intensity(120 mm h^(−1))with three-scale indoor artificial experiments.Four contrasting soils as sandy loam,sandy clay loam,clay loam and loamy clay were collected from different parts of the Loess Plateau.The results showed that sediment load was significantly impacted by soil properties in all three sub-processes.Splash rate(4.0-21.6 g m^(−2∙)min^(−1))was highest in sandy loam from the north part of the Loess Plateau and showed a negative power relation with the mean weight diameter of aggregates after 20 min of rainfall duration.The average sediment load by sheet/interrill erosion(6.94-42.86 g m^(−2∙)min^(−1))was highest in clay loam from middle part of the Loess Plateau,and the stable sediment load after 20 min showed a positive power relation with the silt content in soil.The average sediment load increased dramatically by rill and interrill erosion(21.03-432.16 g m^(−2∙)min^(−1)),which was highest in loamy clay from south part of the Loess Plateau.The average sediment load after the occurrence of rill showed a positive power relation with clay content and a negative power relation with soil organic matter content.The impacts of slope gradient on the runoff rate and sediment load also changed with soil properties.The critical factors varied for different processes,which were the aggregate size for splash erosion,the content of silt particles and slope gradient for sheet/interrill erosion,and the content of clay particles,soil organic matter and slope gradient for rill erosion.Based on the results of the experiments,specific erosion control practices were proposed by targeting certain erosion processes in areas with different soil texture and different distribution of slope gradient.The findings from this study should support the improvement of erosion prediction and cropland management in different regions of the Loess Plateau.

The principles and guidelines for designing long-term agronomic experiments

Many of the important questions facing farming systems in the world today require long-term studies to provide meaningful information and answers. A long-term agronomic experiment (LTAE) should (1) have long-term objectives; (2) study important soil processes or ecological processes; and (3) be related to the productivity and sustainability of systems. A well established LTAE can provide both insights into how the system operates and foresight into where the system goes. The prerequisites for setting up a LTAE are the secured land, continuous funding and dedicated scientists. A number of principles must be considered carefully when establishing a LTAE, (1) the site must be representative of large areas; (2) the treatments should be simple, but focusing on the big questions; (3) the plots should be large enough to allow subsequent modification of the experiment if this becomes necessary; (4) crop rotations should minimise, wherever possible, the risk of build-up of pests and diseases, and rotational phase should be considered in a rotational experiment; (5) a clearly defined experimental protocol should be developed to ensure data collected is scientifically valid and statistically analysable, but with flexibility to allow essential changes; (6) soil samples, possibly plant samples, should be achieved to provide better answer to the original questions when new, perhaps more accurate analytical techniques are developed, or answer new research questions that were not considered in the original design. The MASTER experiment in Australia was used as a case study to demonstrate how these principles are implemented in practice.

Ground temperature variation and its response to climate change on the northern Tibetan Plateau

Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP).Under the background of temperature warming,the TP has witnessed an accelerated warming trend in frozen ground temperature,an increasing active layer thickness,and the melting of underground ice.Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP,the trend of ground temperature at each observation site and its response to climate change were analyzed.The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period,the warming in winter is more significant than that in summer.The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites.During the study period,thawing occurred earlier,whereas freezing happened later,resulting in shortened freezing season and a thinner frozen layer at the BJ site.And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn.From 1997 to 2012,the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend,with a more significant temperature increase in winter than in summer.The ground temperature showed an obvious response to air temperature warming,but the trend varied significantly with soil depths due to soil heterogeneity.

The removal of trimethoprim and sulfamethoxazole by a high infiltration rate artificial composite soil treatment system

Sulfamethoxzole （SMX） and trimethoprim （TMP）, two combined-using sulfonamide antibiotics, have gained increasing attention in the surface water, groundwater and the drinking water because of the ecological risk. The removal of TMP and SMX by artificial composite soil treatment system （ACST） with different infiltration rates was systematically investigated using K＋, Na＋, Ca2＋, Mg2＋ hydrogeochemical indexes. Batch experiments showed that the sorption onto the low-cost and commercially available clay ceramsites was effective for the removal of SMX and TMP from water. The column with more silty clay at high infiltration rate （1.394 m·d^-1） had removal rates of 80% to 90% for TMP and 60% to 70% for SMX. High SMX and TMP removal rates had a higher effluent concentration of K＋, Ca2＋ and Mg2＋ and had a lower effluent Na＋ concentration. Removal was strongly related to sorption. The results showed that the removal of SMX and TMP was related to hydrogeochemical processes. In this study, ACST is determined to be applicable to the drinking water plants.

The influence of desiccation on the recovery process of nitrogenase activity in restored biological soil crusts

Dear Editor,Biological soil crusts(BSCs),a layered structure formed by associations of soil organisms and topsoil,dominate arid and semiarid areas and serve important ecological functions in these areas(Eldridge and Greene,1994).Nitrogen fixation by BSCs is the main source of N in arid and semi-arid ecosystems.Desiccation is the most notable factor that influences BSCs,which recover physiological activity only after moistening.By influencing the amount of carbohydrates,