Woodland Soils Research Articles

Grassland to woodland transitions: Dynamic response of microbial community structure and carbon use patterns

AbstractWoodland encroachment into grasslands is a globally pervasive phenomenon attributed to land use change, fire suppression, and climate change. This vegetation shift impacts ecosystem services such as ground water allocation, carbon (C) and nutrient status of soils, aboveground and belowground biodiversity, and soil structure. We hypothesized that woodland encroachment would alter microbial community structure and function and would be related to patterns in soil C accumulation. To address this hypothesis, we measured the composition and δ13C values of soil microbial phospholipids (PLFAs) along successional chronosequences from C4‐dominated grasslands to C3‐dominated woodlands (small discrete clusters and larger groves) spanning up to 134 years. Woodland development increased microbial biomass, soil C and nitrogen (N) concentrations, and altered microbial community composition. The relative abundance of gram‐negative bacteria (cy19:0) increased linearly with stand age, consistent with decreases in soil pH and/or greater rhizosphere development and corresponding increases in C inputs. δ13C values of all PLFAs decreased with time following woody encroachment, indicating assimilation of woodland C sources. Among the microbial groups, fungi and actinobacteria in woodland soils selectively assimilated grassland C to a greater extent than its contribution to bulk soil. Between the two woodland types, microbes in the groves incorporated relatively more of the relict C4‐C than those in the clusters, potentially due to differences in below ground plant C allocation and organo‐mineral association. Changes in plant productivity and C accessibility (rather than C chemistry) dictated microbial C utilization in this system in response to shrub encroachment.

Comparative Analysis of Prokaryotic Communities Associated with Organic and Conventional Farming Systems

One of the most important challenges in agriculture is to determine the effectiveness and environmental impact of certain farming practices. The aim of present study was to determine and compare the taxonomic composition of the microbiomes established in soil following long-term exposure (14 years) to a conventional and organic farming systems (CFS and OFS accordingly). Soil from unclared forest next to the fields was used as a control. The analysis was based on RT-PCR and pyrosequencing of 16S rRNA genes of bacteria and archaea. The number of bacteria was significantly lower in CFS than in OFS and woodland. The highest amount of archaea was detected in woodland, whereas the amounts in CFS and OFS were lower and similar. The most common phyla in the soil microbial communities analyzed were Proteobacteria (57.9%), Acidobacteria (16.1%), Actinobacteria (7.9%), Verrucomicrobia (2.0%), Bacteroidetes (2.7%) and Firmicutes (4.8%). Woodland soil differed from croplands in the taxonomic composition of microbial phyla. Croplands were enriched with Proteobacteria (mainly the genus Pseudomonas), while Acidobacteria were detected almost exclusively in woodland soil. The most pronounced differences between the CFS and OFS microbiomes were found within the genus Pseudomonas, which significantly (p<0,05) increased its number in CFS soil compared to OFS. Other differences in microbiomes of cropping systems concerned minor taxa. A higher relative abundance of bacteria belonging to the families Oxalobacteriaceae, Koribacteriaceae, Nakamurellaceae and genera Ralstonia, Paenibacillus and Pedobacter was found in CFS as compared with OFS. On the other hand, microbiomes of OFS were enriched with proteobacteria of the family Comamonadaceae (genera Hylemonella) and Hyphomicrobiaceae, actinobacteria from the family Micrococcaceae, and bacteria of the genera Geobacter, Methylotenera, Rhizobium (mainly Rhizobium leguminosarum) and Clostridium. Thus, the fields under OFS and CFS did not differ greatly for the composition of the microbiome. These results, which were also confirmed by cluster analysis, indicated that microbial communities in the field soil do not necessarily differ largely between conventional and organic farming systems.

An improved method for qPCR detection of three Phytophthora spp. in forest and woodland soils in northern Britain

SummaryUsing TaqMan qPCR assays, DNA of P. ramorum, P. kernoviae and P. austrocedri was detected in 500 g soil samples collected from twelve infected forest and woodland sites in northern Britain. Phytophthora DNA was also amplified in soil adhering to boots after walking transects along footpaths or animal trails. At two sites, Phytophthora DNA was detected in soil over a 4‐year period following removal of infected hosts. This new method enabling assessment of larger quantities of soil demonstrates the contamination risk of these pathogens in soil at infected sites and improves our understanding of the mechanisms of persistence and spread.

Divergent responses of organic matter composition to incubation temperature

Increased or preferential decomposition of organic matter (OM) resulting from elevated global temperatures could have wide reaching impacts on ecosystem stability and function. The purpose of this experiment was to determine whether temperature and litter type interact to alter the chemical composition of OM decomposed during incubation. Either a higher-quality (fresh) eucalyptus leaf litter or a lower-quality (aged) eucalyptus leaf litter was mixed into a eucalyptus woodland soil. These soil and litter mixtures were incubated for 14days at 12°C or 32°C. The OM composition of the starting and ending mixtures were characterized with solid-state 13C cross polarisation magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. Despite significantly greater losses of CO2 at 32°C relative to 12°C in both litter mixtures, the OM composition of the fresh litter mixture was similar between the two temperatures, revealing compound classes were lost and gained in similar proportions. However, the OM composition of the aged litter mixture was significantly impacted by incubation temperature, with proportionately more lignin C and less lipid C at 32°C relative to 12°C. The differences in OM loss between the two litters in response to temperature (O-alkyl C in fresh litter; alkyl C in aged litter) reveal that there was not a consistent response of OM to elevated incubation temperature. Instead, the patterns of CO2 released during incubation were related to initial OM composition (r=0.76) and microbial community structure (r=0.74). In this experiment, the interacting effects of temperature, litter quality, and microbial community structure resulted in distinct decomposition trajectories for the two litter mixtures, and resulted (in the aged litter) in the enhanced loss of a compound considered to be relatively long-lived in soils. These results support the concept that in response to warming temperatures, the chemical composition of remaining OM will be impacted by both initial litter quality and microbial community structure.

Black Carbon Contribution to Organic Carbon Stocks in Urban Soil.

Soil holds 75% of the total organic carbon (TOC) stock in terrestrial ecosystems. This comprises ecosystem-derived organic carbon (OC) and black carbon (BC), a recalcitrant product of the incomplete combustion of fossil fuels and biomass. Urban topsoils are often enriched in BC from historical emissions of soot and have high TOC concentrations, but the contribution of BC to TOC throughout the urban soil profile, at a regional scale is unknown. We sampled 55 urban soil profiles across the North East of England, a region with a history of coal burning and heavy industry. Through combined elemental and thermogravimetic analyses, we found very large total soil OC stocks (31-65 kg m(-2) to 1 m), exceeding typical values reported for UK woodland soils. BC contributed 28-39% of the TOC stocks, up to 23 kg C m(-2) to 1 m, and was affected by soil texture. The proportional contribution of the BC-rich fraction to TOC increased with soil depth, and was enriched in topsoil under trees when compared to grassland. Our findings establish the importance of urban ecosystems in storing large amounts of OC in soils and that these soils also capture a large proportion of BC particulates emitted within urban areas.

Effect of orchard age on soil nitrogen transformation in subtropical China and implications

A better understanding of nitrogen transformation in soils could reveal the capacity for biological inorganic N supply and improve the efficiency of N fertilizers. In this study, a 15N tracing study was carried out to investigate the effects of converting woodland to orchard, and orchard age on the gross rates of N transformation occurring simultaneously in subtropical soils in Eastern China. The results showed that inorganic N supply rate was remained constant with soil organic C and N contents increased after converting woodland into citrus orchard and with increasing orchard age. This phenomenon was most probably due to the increase in the turnover time of recalcitrant organic-N, which increased with decreasing soil pH along with increasing orchard age significantly. The amoA gene copy numbers of both archaeal and bacterial were stimulated by orchard planting and increased with increasing orchard age. The nitrification capacity (defined as the ratio of gross rate of nitrification to total gross rate of mineralization) increased following the Michaelis–Menten equation, sharply in the first 10years after woodland conversion to orchard, and increased continuously but much more slowly till 30years. Due to the increase in nitrification capacity and unchanged NO3− consumption, the dominance of ammonium in inorganic N in woodland soil was shifted to nitrate dominance in orchard soils. These results indicated that the risk of NO3− loss was expected to increase and the amount of N needed from fertilizers for fruit growth did not change although soil organic N accumulated with orchard age.

Bioaugmentation and biostimulation as strategies for the bioremediation of a burned woodland soil contaminated by toxic hydrocarbons: A comparative study

In this work, the natural attenuation strategy (no soil amendments done) was compared with two different bioremediation approaches, namely bioaugmentation through soil inoculation with a suspension of Trichoderma sp. mycelium and biostimulation by soil addition with a microbial growth promoting formulation, in order to verify the effectiveness of these methods in terms of degradation efficiency towards toxic hydrocarbons, with particular attention to the high molecular weight (HMW) fraction, in a forest area impacted by recent wildfire in Northern Italy. The area under investigation, divided into three parcels, was monitored to figure out the dynamics of decay in soil concentration of C12-40 hydrocarbons (including isoalkanes, cycloalkanes, alkyl-benzenes and alkyl-naphthalenes besides PAHs) and low molecular weight (LMW) PAHs, following the adoption of the foregoing different remediation strategies. Soil hydrocarbonoclastic potential was even checked by characterizing the autochthonous microbial cenoses.Field experiments proved that the best performance in the abatement of HMW hydrocarbons was reached 60 days after soil treatment through the biostimulation protocol, when about 70% of the initial concentration of HMW hydrocarbons was depleted. Within the same time, about 55% degradation was obtained with the bioaugmentation protocol, whilst natural attenuation allowed only a 45% removal of the starting C12-40 hydrocarbon fraction. Therefore, biostimulation seems to significantly reduce the time required for the remediation, most likely because of the enhancement of microbial degradation through the improvement of nutrient balance in the burned soil.

Abiotic dissolution and biological uptake of nitrous oxide in Mediterranean woodland and pasture soil

Soil is generally regarded as a net emitter of nitrous oxide (N2O). However, there are numerous field studies showing net uptake of N2O from soil in different ecosystems. Consumption of N2O may be abiotic (absorption by water; adsorption by soil matrix) and biotic (microbial reduction of N2O). This study is the first using undisturbed soil cores to determine the capacity of soil to consume N2O and discuss the fate of N2O.We exposed the base of undisturbed soil cores from Mediterranean pasture and woodland soil to elevated concentrations of N2O and sulphur hexafluoride (SF6; as tracer gas). Headspace concentrations of N2O and SF6 were determined over time and consumption rates of N2O were calculated ranging from 148.8 ± 19.8 ng N2O min−1 g−1 to 163.8 ± 17.2 ng N2O min−1 g−1 in woodland soil and from 117.2 ± 36.1 ng N2O min−1 g−1 to 145.1 ± 19.4 ng N2O min−1 g−1 in pasture soil. Absorption of N2O by soil water contributed 17–49% of the total N2O consumption. The remaining N2O consumed by the cores was due to adsorbtion by the soil matrix and/or reduction by microbes.Mediterranean soil from different ecosystems with different nitrogen (N) loads has a great potential to store and consume N2O, if exposed to an N2O elevated atmosphere.

The Characteristics of Runoff and Sediment Yield in Different Land Use Types in Southwest Mountains of Henan Province

By indoor artificial rainfall simulator and slope plot test, the regularity of runoff and sediment yield of five types top soil— timber forest, shrubby grassland, terrace, slope cropland and waste-grassland under six kinds of rainfall intensity were studied in Danjiangkou Reservoir on southwest mountains of Henan Province to provide a scientific basis for comprehensive control of regional soil and water loss, to ensure the safety of water quality in the reservoir. The conclusions were that: (1) Land use types had less influence on the runoff comparing to sediment yield. (2) Sediment yield had obvious power function relationship with the runoff amount. (3) Bed load took up majority in the sediment yield of farmland soil while the bed load almost equaled to the value of silt load in woodland soil.

Microbial community structure mediates response of soil C decomposition to litter addition and warming

Microbial activity has been highlighted as one of the main unknowns controlling the fate and turnover of soil organic matter (SOM) in response to climate change. How microbial community structure and function may (or may not) interact with increasing temperature to impact the fate and turnover of SOM, in particular when combined with changes in litter chemistry, is not well understood. The primary aim of this study was to determine if litter chemistry impacted the decomposition of soil and litter-derived carbon (C), and its interaction with temperature, and whether this response was controlled by microbial community structure and function. Fresh or pre-incubated eucalyptus leaf litter (13C enriched) was added to a woodland soil and incubated at 12, 22, or 32 °C. We tracked the movement of litter and soil-derived C into CO2, water-extractable organic carbon (WEOC), and microbial phospholipids (PLFA). The litter additions produced significant changes in every parameter measured, while temperature, interacting with litter chemistry, predominately affected soil C respiration (priming and temperature sensitivity), microbial community structure, and the metabolic quotient (a proxy for microbial carbon use efficiency [CUE]). The direction of priming varied with the litter additions (negative with fresh litter, positive with pre-incubated litter) and was related to differences in the composition of microbial communities degrading soil-C, particularly gram-positive and gram-negative bacteria, resulting from litter addition. Soil-C decomposition in both litter treatments was more temperature sensitive (higher Q10) than in the soil-only control, and soil-C priming became increasingly positive with temperature. However, microbes utilizing soil-C in the litter treatments had higher CUE, suggesting the longer-term stability of soil-C may be increased at higher temperature with litter addition. Our results show that in the same soil, the growth of distinct microbial communities can alter the turnover and fate of SOM and, in the context of global change, its response to temperature.

Vertical profiles of soil water content as influenced by environmental factors in a small catchment on the hilly-gully Loess Plateau.

Characterization of soil water content (SWC) profiles at catchment scale has profound implications for understanding hydrological processes of the terrestrial water cycle, thereby contributing to sustainable water management and ecological restoration in arid and semi-arid regions. This study described the vertical profiles of SWC at the small catchment scale on the hilly and gully Loess Plateau in Northeast China, and evaluated the influences of selected environmental factors (land-use type, topography and landform) on average SWC within 300 cm depth. Soils were sampled from 101 points across a small catchment before and after the rainy season. Cluster analysis showed that soil profiles with high-level SWC in a stable trend (from top to bottom) were most commonly present in the catchment, especially in the gully related to terrace. Woodland soil profiles had low-level SWC with vertical variations in a descending or stable trend. Most abandoned farmland and grassland soil profiles had medium-level SWC with vertical variations in varying trends. No soil profiles had low-level SWC with vertical variations in an ascending trend. Multi-regression analysis showed that average SWC was significantly affected by land-use type in different soil layers (0–20, 20–160, and 160–300 cm), generally in descending order of terrace, abandoned farmland, grassland, and woodland. There was a significant negative correlation between average SWC and gradient along the whole profile (P<0.05). Landform significantly affected SWC in the surface soil layer (0–20 cm) before the rainy season but throughout the whole profile after the rainy season, with lower levels on the ridge than in the gully. Altitude only strongly affected SWC after the rainy season. The results indicated that land-use type, gradient, landform, and altitude should be considered in spatial SWC estimation and sustainable water management in these small catchments on the Loess Plateau as well as in other complex terrains with similar settings.

Spatial distribution of bowal and differences in physicochemical characteristics between bowal and woodland soils in Benin, West Africa

Bowal, is degraded land surface characterized by ferricrete exposure due to soil surface erosion. This study aims at assessing the spatial distribution of bowé in Benin and the physicochemical differences between bowé and soil of adjacent woodlands. Bowé surfaces were identified during field investigations and mapped. Soil samples were taken on the bowé surfaces and nearby woodland. Mann–Whitney test was applied to analyze the different physicochemical characteristics of bowé and woodland. The results show that bowé were directly related to ferruginous soils and rainfall regime. Bowé soils are characterized by significantly lower values of electrical conductivity, organic matter, extractable phosphorus, silt and total nitrogen than woodland soils, while potassium exchangeability of bowé soils is higher. Bowé can be expected wherever ferruginous soils and/or ferricretes are observed under unimodal rainfall regimes condition. The disaggregation of bowé ferricretes may improve the soil physicochemical characteristics and sustain the regrowth of forest under more humid conditions.

Soils and Surface Waters as Affected by Long-Term Swine Slurry Application in Oxisols of Southern Brazil

The accelerated expansion of swine production in Brazil has increased the generation of liquid wastes, which are usually applied to agricultural soils after a simplified treatment and pose potential environmental impacts. The objective of this study was to assess the agronomic and environmental impacts of long-term application of swine slurry (SS) on soil and stream water properties in watersheds dominated by Oxisols in Quinze de Novembro of Southern Brazil. Soil samples (0–30 cm) were collected from farms with continuous application of SS since 1990 at low (40–80 m3 SS ha−1 year−1) and high (120–300 m3 SS ha−1 year−1) rates of SS. Surface water samples were collected from streams adjacent to the farm fields. Long-term SS application did not change total organic C and particulate organic C compared to cropland and woodland soils without SS application. The high rates of SS increased total N, P, Cu, and Zn and available P and Cu in the topsoil (0–10 cm) compared to woodland and cropland soils without SS application. Surface water analyses showed that fecal coliform bacteria and biological oxygen demand exceeded the legal limits for high quality water (Class 1). Other water parameters (such as NO−3, phosphate and total suspended solids) were within the acceptable limits. Long-term disposal of SS in cropland under no-tillage had impaired water quality in Quinze de Novembro, especially biological parameters. Some best management practices should be adopted, including more rigorous control of SS application to cropland as well as requiring edge-of-field and riparian vegetative buffers.

Factors affecting uranium and thorium fractionation and profile distribution in contrasting arable and woodland soils

This work investigated the vertical distribution and fractionation of uranium and thorium in soils under contrasting arable and woodland sites based on the same parent material. The effect of long-term application of phosphate fertilizer on U and Th concentrations in the arable soil was also assessed. The arable surface soils contained higher amounts of U compared with underlying layers and the woodland soil profile; by contrast, the Th distributions were very similar in both arable and woodland soils. The U and phosphate concentration profiles within the arable soil were broadly similar; U was strongly associated with Ca (r=0.94) and soil P content (r=0.86) whereas the U concentration profile in the woodland soil was virtually uniform with depth. The ‘excess’ U in arable soil, associated with long term P fertilizer application, was approximately 2.5kgha−1 with 80% in the top 30cm of the soil profile. A sequential extraction technique was used to fractionate U and discriminate between ‘reactive’ (non-residual) and ‘residual’ forms of U. The reactive U was adsorbed, mainly by organic matter and Fe–Mn oxides in the arable topsoil and there was a very strong relationship between reactive U and soil phosphate content in the arable soil (r=0.99, P<0.001). The ‘excess’ U accumulated in the arable topsoil was also considerably more reactive than the co-existing native U. Thus the reactive fraction of the excess U ranged from 29 to 42% compared with 14 to 15% reactivity of the native U. Thorium in both soils showed a very consistent, and low, reactivity down the soil profile at about 4% of total soil Th content (96% residual), bound almost completely to humus.

Association between risk of birth defects occurring level and arsenic concentrations in soils of Lvliang, Shanxi province of China

The risk of birth defects is generally accredited with genetic factors, environmental causes, but the contribution of environmental factors to birth defects is still inconclusive. With the hypothesis of associations of geochemical features distribution and birth defects risk, we collected birth records and measured the chemical components in soil samples from a high prevalence area of birth defects in Shanxi province, China. The relative risk levels among villages were estimated with conditional spatial autoregressive model and the relationships between the risk levels of the villages and the 15 types of chemical elements concentration in the cropland and woodland soils were explored. The results revealed that the arsenic levels in cropland soil showed a significant association with birth defects occurring risk in this area, which is consistent with existing evidences of arsenic as a teratogen and warrants further investigation on arsenic exposure routine to birth defect occurring risk.

Cellulose decomposition rate and features of organic matter in forest soils in the Tatra mountains

The cellulose decomposition rate measurement and soil micromorphology have been used to determine the influence of parent material and tree species on mechanisms responsible for organic matter form differentiation in woodland soils in the Tatra Mountains in Poland. The study area is located in the lower montane belt of the Tatra Mountains. Investigated soils are developed on dolomites and shale. In the past, beech and beech-fir forests had been the dominant form of vegetation in the study area. Since the 16th century, these areas were deforested until the 19th century, when reforestation efforts were undertaken. Reforestation efforts provided mainly spruce; hence, it is the dominant species in the lower montane belt at the moment, although in some areas, natural or semi-natural beech and beech-fir forests have survived. Four plots were compared – two with soils developed on calcareous material (Rendzic Leptosols), one under beech forest and one under spruce forest, and two developed on shale (Haplic Cambisols), one under beech forest and one under spruce forest. Cellulose filters were placed in organic O-horizons and humus A-horizons in every plot to measure the cellulose decomposition rate. Before being placed in the soil, cellulose filters were boiled in KOH, rinsed in distilled water, dried, weighed, and set on glass plates in a nylon bag (1.5 mm mesh). The bags were placed in the soil vertically at approx. 15 cm intervals. After taken up, the filters were boiled in KOH, rinsed, dried, and weighed. The amount of ash was determined via combustion. The research was carried out during a period of 10 weeks between June and August as well as during a period of 1 year. Measurements were repeated ten times. A weighted average and standard deviation were calculated for every plot. The cellulose filter method is useful because of the homogeneity of the substrate, which helps to exclude differences connected with the chemical composition of the plant material, a factor that affects the decomposition rate. Undisturbed soil samples were taken from humus A-horizons in every soil profile. The thin sections were prepared and features of organic matter were described. It was concluded that the presence of calcarous material negatively affects organic matter decomposition rates which is pronounced in both: higher amount of organic matter residues in humus-A horizons and slower cellulose decomposition rates in Rendzic Leptosols than in Haplic Cabisols. The influence of tree species on organic matter features is observed only in Haplic Cambisols, where the cellulose decomposition rate under spruce is lower than under beech. This suggests that tree species indirectly affect the cellulitic microflora only in acidic soils.

Interactive effects of temperature and soil moisture on fungal-mediated wood decomposition and extracellular enzyme activity

Heterotrophic soil microbes regulate the rate-limiting step in soil organic matter decomposition via the production of hydrolytic and oxidative extracellular enzymes. The influence of climate change on heterotrophic microbial activity remains poorly understood, not least in terms of the differential sensitivity of microbial functional groups to warming and altered precipitation regimes. Cord-forming basidiomycete fungi dominate primary decomposition in temperate woodlands. We investigate the interactive influence of elevated temperature (3 °C), wetting and drying (6–9% increase and 5–6% decrease of soil moisture, respectively) on saprotrophic basidiomycete-mediated beech (Fagus sylvatica) wood decomposition, as well as on hydrolytic (β-glucosidase, cellobiohydrolase, β-xylosidase, N-acetyl-glucosaminidase, acid phosphatase and leucine aminopeptidase) and oxidative (peroxidase and phenoloxidase) enzyme potential activities, in woodland soil mesocosms. While drying decreased beech wood decomposition rate, warming resulted in an increased rate and compensated for the negative effect of drying. Moisture regulated the extracellular enzyme pool; all enzymes except leucine aminopeptidase had significantly greater potential activity under wetting than drying. Again, elevated temperature consistently compensated for the negative effect of drying, but did not increase extracellular enzyme potential activity, alone or in combination with wetting. This reflects microbial production (fungal biomass was not increased under these conditions) rather than in situ effects on enzyme kinetics. N-acetyl-glucosaminidase and acid phosphatase displayed differential responses to temperature and moisture in systems dominated by different fungi. Decomposer communities appear to be more functionally resilient to the combined effects of elevated temperature and altered moisture than is suggested based on the manipulation of single abiotic variables.

半干旱地区不同土地利用方式下土壤团聚体的微生物量属性

团聚体是土壤基本结构单元,是土壤质量和肥力的基础,研究了解不同土地利用方式下,不同团聚体的生物学属性,有助于深入了解土壤肥力本质,以及不同土壤肥力差异的根本原因.采集半干旱地区林地、旱地、灌溉耕地和草地4种土壤利用类型的表层土壤,用干筛法获得6级团聚体,测定微生物量碳(MBC)、三磷酸腺苷(ATP)含量、基础呼吸速率(BR)和基质诱导呼吸量(SIR)等指标.结果表明:土壤微生物量ATP浓度在7.79-9.26 μmol ATP/g C_mic,灌溉耕地最高、林地最低;微生物代谢熵(<em>q</em>CO₂)和SIR分别为0.35-0.69 μL CO₂ g^-1C_mic d^-1和88.7-132.2 μg CO₂ g^-1 d^-1,灌溉耕地最高、旱地最低.土壤团聚体的微生物量ATP浓度在6.54-9.32 μmol/g C_mic之间,平均值为8.22 μmol/g C_mic;<em>q</em>CO₂和SIR分别为0.29-0.71 μL/g C_mic和64-120 μg CO₂/g土,大团聚体含量总体上高于小团聚体,可能暗示不同团聚体土壤微生物群落活性及生理状态存在差异.土壤ATP含量、SIR和<em>q</em>CO₂与微生物量碳呈显著相关性 (<em>r</em>=0.929、0.865、0.885, <em>P</em> < 0.01),SIR和BR之间也有存在较高的相关性 (<em>r</em>=0.828、<em>P</em> < 0.01),说明尽管各级团聚体微生物学属性的绝对值存在很大的差异,但相互关系并未随团聚体大小而变化.;Soil aggregates are the basic units of soil structure and play an important role in soil quality and fertility. It is thus meaningful to investigate the natures and differences in biochemical properties of different soil aggregates. Moreover, it may be benefit to understand the essence of soil fertility and fundamental reason for the difference in fertility of different soils. In this study, 4 surface soils were sampled from woodland, none-irrigated cropland, irrigated cropland, and grassland in semi-arid region of Inner Mongolia. Six classes of soil aggregates with different diameters were collected with dry sieving method. The measured parameters included soil basic properties such as clay, organic matter, total nitrogen, K₂SO₄ extracted carbon, and soil microbial biomass C (MBC), ATP, basal respiration and substrate-induced respiration. The results showed that the irrigated soil had highest clay and organic matter contents, about 32.2 g/kg and 29.93 g/kg respectively, but lowest values in grassland soil, only 12.2 g/kg and 12.48 g/kg. The irrigated soil contained microbial biomass C of 336.03 mg/kg, but the woodland soil and none-irrigated cropland soil had about 207.53 mg/kg and 216.11 respectively. The ATP content in soils ranged 0.0016 - 0.0031 μmol/g soil, higher in the irrigated soil, lower in the woodland soil. The soil microbial biomass ATP concentration was the highest in the irrigated soil, about 9.26 μmol ATP/g C_mic, but lowest in the woodland soil, only 7.79 μmol ATP/g C_mic. The soil basal respiration and substrate-induced respiration were the highest in the irrigated soil, 10.31 μg CO₂-C g^-1soil d^-1 and 132.2 μg CO₂ g^-1 d^-1 respectively, but very low in the no-irrigated soil, only 3.33 μg CO₂-C g^-1soil d^-1 and 88.66 μg CO₂ g^-1 d^-1. The microbial biomass metabolic quotient (<em>q</em>CO₂) was high in the irrigated soil, about 0.69μg CO₂-C g^-1soil d^-1 but very low in the none-irrigated cropland soil, about 0.35 μL CO₂-C g^-1soil d^-1. The result showed that the microbial activity in the irrigated soil was higher than other soils, which might be linked with the quantity and quality of organic C input, water soluble carbon content and water content. Different soil aggregates had different natures of microbial biochemical properties. The basal respiration, <em>q</em>CO₂ and substrate-induced respiration in different soil aggregates were 0.29-0.71 μL/g C_mic, 0.29-0.71 μL/μg C_mic and 64-120 μg CO₂/g soil, respectively. The ATP content in soil aggregates changed among 0.83-3.02 nmol/g soil. The soil microbial biomass ATP concentration in soil aggregates were fallen within the range of 6.54-9.32 μmol/g C_mic. In general, the larger the soil aggregates, the higher values of those biochemical parameters were measured, which may imply the difference in microbial community and physiological activity among the soil aggregates. It may also indicate that microorganisms in larger aggregates (> 0.25 mm) have higher carbon utilization efficiency than those of smaller aggregates (< 0.25 mm). Soil microbial biomass ATP concentration, soil basal respiration and substrate-induced respiration were significantly and positively correlated with the soil microbial biomass C(<em>r</em>=0.929, 0.865, 0.885, <em>P</em> < 0.01). There was also a significant correlation between basal respiration and substrate-induced respiration (<em>r</em>=0.828, <em>P</em> < 0.01). It is evident that the relationships among the soil microbial parameters does not change with soil aggregates though dramatically different in the absolute values.

Impacts of landform, land use and soil type on soil chemical properties and enzymatic activities in a Loessial Gully watershed

Understanding the relationships among soil properties and, in turn, their relationships with landform, land use and soil type is essential for assessing soil quality and soil productivity. In this study, we examined the differences in the chemical properties and enzymatic activities of soils in a variety of landforms (plateau land, sloping land, terraced land and gully bottoms), land uses (woodland, grassland, cropland and orchard) and soil types (Chernozems, Cambisols and Regosols) in a gully watershed on the Loess Plateau, China. In total, 202 samples of surface soil (0–20 cm) were collected from different representative landscape units of the watershed. The chemical properties and enzymatic activities of the soils were measured. The results showed that chemical properties and enzymatic activities of the soils were all significantly influenced by landform, land use and soil type. There were interactive effects between landform and soil type. Soil pH varied the least, while invertase activity varied the most with landscape conditions. Soil pH, cation exchange capacity, organic carbon and total nitrogen contents, and enzymatic activities were all highest on plateau land and lowest on terraced land. Soil organic carbon and total nitrogen contents and alkaline phosphatase and invertase activities were higher in Chernozems than in Regosols, but the opposite trend was noted for pH, cation exchange capacity and catalase activity. Significantly higher values for most soil properties or enzymatic activities occurred in combinations including plateau land, Chernozems or Regosols. Soil pH was significantly lower in woodland soils than for other land uses, whereas the other properties had higher values in grassland and woodland soils than in orchard soils. The results from this study indicate the roles of landform, land use and soil type on the spatial patterns of chemical properties and enzymatic activities of soils and suggest that crops and orchards should be arranged on plateau land, and grasses and woodland on terraced and sloping land, respectively, for better economic and ecological efficiency in the area.

Empirical Analysis on the Influence of Different Land Use on Soil Organic Matter

In this paper, we take secondary forest, orchard, and woodland soils of rubber in different planting years as a research subject and analyze the influence of different land use on soil organic matter. The results show that land use has significant influence on soil organic matter components (p &lt;0.01). We conducted a survey and sampling on 10 age classes of Hainan Dongfang Daguangba (3, 8, 13, 18,23,29,33,35,38,42 years old) rubber plantation plots soil layer (0 cm-20 cm, 20 cm-40 cm), and conducted in-house testing analysis of its organic matter content, and achieved preliminary exploration that soil organic matter content of different land use patterns in Dongfang City in Hainan: secondary forest&gt; orchard&gt; rubber plantation. These differences are mainly due to the litter under different tillage quantity, quality and variety of management measures. While orchards and rubber plantation have used different tillage method, as a plantation by human, it was greatly influenced by human.