Climatic influences on active fractions of soil organic matter     

《Soil biology & biochemistry》2001,33(7-8):1103-1111

Biologically active fractions of soil organic matter are important in understanding decomposition potential of organic materials, nutrient cycling dynamics, and biophysical manipulation of soil structure. We evaluated the quantitative relationships among potential C and net N mineralization, soil microbial biomass C (SMBC), and soil organic C (SOC) under four contrasting climatic conditions. Mean SOC values were 28±11 mg g⁻¹ (n=24) in a frigid–dry region (Alberta/British Columbia), 25±5 mg g⁻¹ (n=12) in a frigid–wet region (Maine), 11±4 mg g⁻¹ (n=117) in a thermic–dry region (Texas), and 12±5 mg g⁻¹ (n=131) in a thermic–wet region (Georgia). Higher mean annual temperature resulted in consistently greater basal soil respiration (1.7 vs 0.8 mg CO₂–C g⁻¹ SOC d⁻¹ in the thermic compared with the frigid regions, P<0.001), greater net N mineralization (2.8 vs 1.3 mg inorganic N g⁻¹ SOC 24 d⁻¹, P<0.001), and greater SMBC (53 vs 21 mg SMBC g⁻¹ SOC, P<0.001). Specific respiratory activity of SMBC was, however, consistently lower in the thermic than in the frigid regions (29 vs 34 mg CO₂–C g⁻¹ SMBC d⁻¹, P<0.01). Higher mean annual precipitation resulted in consistently lower basal soil respiration (1.1 vs 1.3 mg CO₂–C g⁻¹ SOC d⁻¹ in the wet compared with the dry regions, P<0.01) and lower SMBC (31 vs 43 mg SMBC g⁻¹ SOC, P<0.001), but had inconsistent effects on net N mineralization that depended upon temperature regime. Specific respiratory activity of SMBC was consistently greater in the wet than the dry regions (≈33 vs 29 mg CO₂–C g⁻¹ SMBC d⁻¹, P<0.01). Although the thermic regions were not able to retain as high a level of SOC as the frigid regions, due likely to high annual decomposition rates, biologically active soil fractions were as high per mass of soil and even 2–3-times greater per unit of SOC in the thermic compared with the frigid regions. These results suggest that macroclimate has a large impact on the portion of soil organic matter that is potentially active, but a relatively small impact on the specific respiratory activity of SMBC.  相似文献   

Earthworm communities and soil properties in shaded coffee plantations with and without application of glyphosate     

《Applied soil ecology》2014

In central Veracruz, Mexico, many coffee plantations are managed using agrochemicals for weed control, with glyphosate-based herbicides (GBH) the most commonly used. To date, however, no studies in this region have characterized the soil biological and physicochemical properties in coffee plantations under such glyphosate application. In this study, earthworms were used as bioindicator organisms by measuring differences in the earthworm community in plots within shaded coffee plantations, with and without repeated applications of glyphosate. Differences in earthworm-induced soil processes, such as water infiltration rates, potential net carbon mineralization rates and soil physicochemical properties were also evaluated. Eight plots were selected in shaded coffee plantations; four had received regular applications of GBH over the preceding 22 years, while the other four had received no herbicides over the preceding 7 years. The earthworm species found in plots with no GBH treatment were Pontoscolex corethrurus (99%) and Amynthas corticis (1%), while A. corticis was absent in plots that had been treated with GBH. Significant differences (P < 0.01) in earthworm density (168 ± 16 and 353 ± 37 ind m⁻²) and biomass (22.7 ± 1.1 and 45.4 ± 6.9 g m⁻²) were observed in soils with and without GBH, respectively. No significant difference (P = 0.08) was observed in the water infiltration rate (2 × 10⁻⁴ ± 4 × 10⁻⁵ and 4 × 10⁻⁴ ± 1 × 10⁻⁴ cm s⁻¹ with and without GBH, respectively). Soil carbon flow was greater in plots with GBH (76 ± 7 μg dry soil⁻¹ d⁻¹) than in those without GBH (62 ± 1 μg dry soil⁻¹ d⁻¹, P < 0.005). Significant differences (P < 0.05) were found in pH and in the clay, silt and Ca content of the soil. Our findings indicated reduced species number, density and biomass of earthworms, and increased net carbon mineralization rate in plots with GBH. The plots managed with glyphosate presented a negative effect on the earthworm parameters measured, and we conclude that the earthworms therefore acted as indicators of perturbation. It is also possible that this effect could be due to factors unrelated to the glyphosate that were not considered in this study, such as chemical fertilization or legume litter spatial variability, among others.  相似文献   

Differences in soil respiration between different tropical ecosystems     

《Applied soil ecology》2007,35(2-3):258-265

We examined the relationship between soil respiration rate and environmental determinants in three types of tropical forest ecosystem—primary forest, secondary forest, and an oil palm plantation in the Pasoh Forest Reserve on the Malaysian Peninsula. In August 2000, the soil respiration rate and environmental factors (soil temperature, soil water content, soil C and N contents, biomass of fine roots, and microbes) were measured at 12–16 points in research quadrats. Soil respiration rates were 831 ± 480, 1104 ± 995, 838 ± 143, 576 ± 374, and 966 ± 578 (mean ± S.D.) mg CO₂ m⁻² h⁻¹ in the primary forest canopy and gap site, secondary forest canopy and gap site, and oil palm plantation, respectively. Although the mean soil respiration rates in the three forest ecosystems did not differ significantly, differences were evident in the environmental factors affecting the soil respiration. The major causes of spatial variation in soil respiration were fine root biomass, soil water content, and soil C content in the primary and secondary forests and oil palm plantation, respectively.  相似文献   

N2O emissions from humid tropical agricultural soils: effects of soil moisture,texture and nitrogen availability     

《Soil biology & biochemistry》2001,33(7-8):1077-1093

We studied soil moisture dynamics and nitrous oxide (N₂O) fluxes from agricultural soils in the humid tropics of Costa Rica. Using a split-plot design on two soils (clay, loam) we compared two crop types (annual, perennial) each unfertilized and fertilized. Both soils are of andic origin. Their properties include relatively low bulk density and high organic matter content, water retention capacity, and hydraulic conductivity. The top 2–3 cm of the soils consists of distinct small aggregates (dia. <0.5 cm). We measured a strong gradient of bulk density and moisture within the top 7 cm of the clay soil. Using automated sampling and analysis systems we measured N₂O emissions at 4.6 h intervals, meteorological variables, soil moisture, and temperature at 0.5 h intervals. Mean daily soil moisture content at 5 cm depth ranged from 46% water filled pore space (WFPS) on clay in April 1995 to near saturation on loam during a wet period in February 1996. On both soils the aggregated surface layer always remained unsaturated. Soils emitted N₂O throughout the year. Mean N₂O fluxes were 1.04±0.72 ng N₂O-N cm⁻² h⁻¹ (mean±standard deviation) from unfertilized loam under annual crops compared to 3.54±4.31 ng N₂O-N cm⁻² h⁻¹ from the fertilized plot (351 days measurement). Fertilization dominated the temporal variation of N₂O emissions. Generally fluxes peaked shortly after fertilization and were increased for up to 6 weeks (‘post fertilization flux’). Emissions continued at a lower rate (‘background flux’) after fertilization effects faded. Mean post-fertilization fluxes were 6.3±6.5 ng N₂O-N cm⁻² h⁻¹ while the background flux rate was 2.2±1.8 ng N₂O-N cm⁻² h⁻¹. Soil moisture dynamics affected N₂O emissions. Post fertilization fluxes were highest from wet soils; fluxes from relatively dry soils increased only after rain events. N₂O emissions were weakly affected by soil moisture during phases of low N availability. Statistical modeling confirmed N availability and soil moisture as the major controls on N₂O flux. Our data suggest that small-scale differences in soil structure and moisture content cause very different biogeochemical environments within the top 7 cm of soils, which is important for net N₂O fluxes from soils.  相似文献   

Emission of carbon dioxide and dynamics of inorganic N in a gradient of alkaline saline soils of the former lake Texcoco     

《Applied soil ecology》2007,35(2):390-403

A plan was developed to apply biosolid to soil of the former lake Texcoco to fertilize the pioneer vegetation. Because, no information exists about how differences in electrolytic conductivity (EC) might affect mineralization of biosolid and dynamics of C and N in soil, 20 soil samples forming a gradient in EC ranging from 22 to 150 dS m⁻¹ were characterized, amended with 500 mg biosolid C kg⁻¹ dry soil and incubated aerobically at 22 ± 2 °C while production of CO₂, concentrations of ammonium (NH₄⁺), nitrite (NO₂⁻), and nitrate (NO₃⁻), and NH₃ volatilization were monitored at 22 ± 2 °C for 70 days. Soil characteristics showed large variations with maximum values often >10-times larger than minimum values. The production of CO₂ in the unamended soil ranged from 25 to 159 mg CO₂-C kg⁻¹ day⁻¹ and NH₃ volatilization from 0 to 189 μg NH₃-N kg⁻¹ day⁻¹_. Application of biosolid increased production of CO₂ significantly 1.4-fold and volatilization of NH₃ 11.5-fold. The EC explained most of the variation in production of CO₂, while particle size distribution explained most of the variation in volatilization of NH₃. The concentration of NH₄⁺ in the biosolid-amended soil decreased sharply in the first 14 days, with the EC explaining most of the variation found, and remained constant thereafter with a small increase at day 70. Significant increases in the concentration of NO₃⁻ were generally found in soil with EC < 64 dS m⁻¹. The EC explained most of the variation in production of CO₂, and dynamics of NH₄⁺ and NO₃⁻ while clay positively and sand content negatively affected NH₃ volatilization. It was found that increases in EC inhibited C and N mineralization in soil of the former lake Texcoco.  相似文献   

Nitrous oxide production in turfgrass systems: Effects of soil properties and grass clipping recycling     

《Applied soil ecology》2013

Soil N₂O emissions can affect global environments because N₂O is a potent greenhouse gas and ozone depletion substance. In the context of global warming, there is increasing concern over the emissions of N₂O from turfgrass systems. It is possible that management practices could be tailored to reduce emissions, but this would require a better understanding of factors controlling N₂O production. In the present study we evaluated the spatial variability of soil N₂O production and its correlation with soil physical, chemical and microbial properties. The impacts of grass clipping addition on soil N₂O production were also examined. Soil samples were collected from a chronosequence of three golf courses (10, 30, and 100-year-old) and incubated for 60 days at either 60% or 90% water filled-pore space (WFPS) with or without the addition of grass clippings or wheat straw. Both soil N₂O flux and soil inorganic N were measured periodically throughout the incubation. For unamended soils, cumulative soil N₂O production during the incubation ranged from 75 to 972 ng N g⁻¹ soil at 60% WFPS and from 76 to 8842 ng N g⁻¹ soil at 90% WFPS. Among all the soil physical, chemical and microbial properties examined, soil N₂O production showed the largest spatial variability with the coefficient of variation ~110% and 207% for 60% and 90% WFPS, respectively. At 60% WFPS, soil N₂O production was positively correlated with soil clay fraction (Pearson's r = 0.91, P < 0.01) and soil NH₄⁺–N (Pearson's r = 0.82, P < 0.01). At 90% WFPS, however, soil N₂O production appeared to be positively related to total soil C and N, but negatively related to soil pH. Addition of grass clippings and wheat straw did not consistently affect soil N₂O production across moisture treatments. Soil N₂O production at 60% WFPS was enhanced by the addition of grass clippings and unaffected by wheat straw (P < 0.05). In contrast, soil N₂O production at 90% WFPS was inhibited by the addition of wheat straw and little influenced by glass clippings (P < 0.05), except for soil samples with >2.5% organic C. Net N mineralization in soil samples with >2.5% organic C was similar between the two moisture regimes, suggesting that O₂ availability was greater than expected from 90% WFPS. Nonetheless, small and moderate changes in the percentage of clay fraction, soil organic matter content, and soil pH were found to be associated with large variations in soil N₂O production. Our study suggested that managing soil acidity via liming could substantially control soil N₂O production in turfgrass systems.  相似文献   

Habitat use and activity patterns of larval and adult Cantharis beetles in arable land     

《European Journal of Soil Biology》2006,42(2):82-88

Generalist predators play a key role in agriculturally and environmentally sustainable systems of pest control. A detailed knowledge on their ecology, however, is needed to improve management practices to maximize their service of pest control. The present study examines the habitat use and activity patterns of larval and adult Cantharis beetles that are abundant predators in arable land. Laboratory experiments revealed that sixth instar larvae of Cantharis fusca and Cantharis livida significantly preferred high relative humidity levels of 85–90% to lower ones. This can explain their preference for meadows over fields due to the more favorable microclimatic conditions in the former habitats. Surface activity of sixth instar Cantharis larvae during autumn, winter and early spring occurred at soil temperatures above 0 °C. However, no correlation between surface activity and soil temperature, air temperature or relative humidity was found above 0 °C. Catches of sixth instar Cantharis larvae within fenced pitfall traps were higher in a meadow (Mean ± S.D.; 13.8 ± 7.63 individuals m⁻²) than in a field (4.60 ± 2.89 individuals m⁻²). Mark-recapture density estimations for sixth instar larvae indicated mean densities of 25.9 ± 5.63 (field) and 42.8 ± 16.0 individuals m⁻² (meadow). The same pattern was found for adult emergence rates in the field (0.17 ± 0.39 adults m⁻²) and meadow (1.83 ± 1.17 adults m⁻²) as well as for adult densities in the vegetation (field 4.89 ± 3.62 adults 60 m⁻²; meadow 12.5 ± 11.2 adults 60 m⁻²). It is concluded that especially in winter elements that provide plant cover should be incorporated in arable fields to enhance larval cantharid population densities and to attract them from their prime grassland habitats into arable sites.  相似文献   

Stability of soil organic matter under long-term biosolids application     

《Applied soil ecology》2013

Little is know on the impact of biosolids application on soil organic matter (SOM) stability, which contributes to soil C sequestration. Soil samples were collected in 2006 at plow layer from fields that received liquid and dry municipal biosolids application from 1972 to 2004 at the cumulative rate of 1416 Mg ha⁻¹ in mined soil and 1072 Mg ha⁻¹ in nonmined soil and control fields that received chemical fertilizer at Fulton County, western Illinois. The biosolids application increased the soil microbial biomass C (SMBC) by 5-fold in mined soil and 4-fold in nonmined soil. The biosolids-amended soils showed a high amount of basal respiration and N mineralization, but low metabolic quotient, and low rate of organic C and organic N mineralization. There was a remarkable increase in mineral-associated organic C from 6.9 g kg⁻¹ (fertilizer control) to 26.6 g kg⁻¹ (biosolids-amended) in mined soil and from 8.9 g kg⁻¹ (fertilizer control) to 23.1 g kg⁻¹ (biosolids-amended) in nonmined soil. The amorphous Fe and Al, which can improve SOM stability, were increased by 2–7 folds by the long-term biosolids application. It is evident from this study that the biosolids-modified SOM resists to decomposition more than that in the fertilizer treatment, thus long-term biosolids application could increase SOM stability.  相似文献   

Comparing net ecosystem exchange of carbon dioxide between an old-growth and mature forest in the upper Midwest,USA     

《Agricultural and Forest Meteorology》2005,128(1-2):33-55

Old-growth forests are often assumed to exhibit no net carbon assimilation over time periods of several years. This generalization has not been typically supported by the few whole-ecosystem, stand-scale eddy-covariance measurements of carbon dioxide exchange in old-growth forests. An eddy-flux tower installed in a >300-year-old hemlock–hardwood forest near the Sylvania Wilderness, Ottawa National Forest, MI, USA, observed a small annual carbon sink of CO₂ of −72 ± 36 g C m⁻² year⁻¹ in 2002 and −147 ± 42 g C m⁻² year⁻¹ in 2003. This carbon sink was much smaller than carbon sinks of −438 ± 49 g C m⁻² year⁻¹ in 2002 and −490 ± 48 g C m⁻² year⁻¹ in 2003 observed by a nearby flux tower in a 70-year-old mature hardwood forest (Willow Creek, WI). The mature forest had vegetation similar to the old-growth site prior to European settlement. Both sites had slightly larger carbon sinks in 2003, which was a drier and cooler year than 2002. However, the difference in sink strength between the two years was smaller than the uncertainty in the results arising from missing and screened data. Both sites also had significant systematic errors due to non-representative fluxes during certain micrometeorological conditions, which required careful screening. The difference in sink strength between the two sites was driven mainly by greater ER at the old-growth site (965 ± 35 g C m⁻² year⁻¹ in 2002 and 883 ± 69 g C m⁻² year⁻¹ in 2003) compared to the mature site (668 ± 21 g C m⁻² year⁻¹ in 2002 and 703 ± 17 g C m⁻² year⁻¹ in 2003). GEP was lower at the old-growth site (1037 ± 47 g C m⁻² year⁻¹ in 2002 and 1030 ± 41 g C m⁻² year⁻¹ in 2003) compared to the mature site (1106 ± 47 g C m⁻² year⁻¹ in 2002 and 1192 ± 51 g C m⁻² year⁻¹ in 2003), especially in 2003. Observations also suggested that growing season ER had greater interannual variability at the old-growth site. These results imply that old-growth forests in the region may be carbon sinks, though these sinks are smaller than mature forests, mostly likely due to greater ER.  相似文献   

Nitrogen mineralization in the ruderal sub-alpine communities in Mount Uludağ, Turkey     

《European Journal of Soil Biology》2008,44(4):408-418

Nitrogen mineralization and nitrification in the soil of sub-alpine ruderal community of Mount Uludağ, Bursa, Turkey was measured for 1 year, under field conditions with Verbascum olympicum and Rumex olympicus being the dominant pioneer species under dry and wet sites, respectively. Seasonal fluctuations were observed in N mineralization and nitrification. The net N mineralization and nitrification were high in early summer and winter, due to high moisture. The annual net N mineralization rate (for the 0–15 cm soil layer) was higher under R. olympicus (188 kg N ha⁻¹ yr⁻¹) than under V. olympicum (96 kg N ha⁻¹ yr⁻¹). A significant positive correlation between net N mineralization and soil organic C (r² = 0.166), total N (r² = 0.141) and water content (r² = 0.211) was found. Our results indicate that N mineralization rate is high in soils of ruderal communities on disturbed sites and varies with dominant species and, a difference in net N mineralization rate can be attributed to organic C, total N and moisture content of soils.  相似文献   

Overgrazing and soil carbon dynamics in the western Chaco of Argentina     

《Applied soil ecology》2001,16(3):243-249

Very little is known about the effect of overgrazing on carbon loss from soil in semi-arid savannas and woodlands of South America. Soil carbon parameters were measured in a 10,000 ha restoration project in the western Chaco of Argentina (24°43′S and 63°17′W). Three situations were compared: highly restored (HRS), moderately restored (MRS) and highly degraded (HDS). Soil and litter samples were recovered in the dry and wet seasons. SOC and CO₂–C values decreased from the HRS (7.0 kg m⁻² and 130 g m⁻²) to the HDS (1.5 kg m⁻² and 46 g m⁻²) whereas the C mineralization rate increased toward the less restored sites (0.96–2.29). Surface-litter C was similar in both sites under restoration (260 and 229 g m⁻²), being non-existent at the HDS. Leaves from woody species dominated surface-litter in the HRS, whereas grass material was predominant in the MRS. During the wet season, the SOC decreased, whereas both CO₂–C and C mineralization rate increased. The magnitude of the between-season differences was highest at the HDS (62% in SOC, 55% in CO₂, and 80% in C mineralization rate). We estimated that C loss since introduction of cattle into the forest was 58 Mg ha⁻¹, reaching a total of 2×10¹⁵ g at for the entire Chaco. These values are higher than those caused by the conversion of savannas and other ecosystems into agriculture or cultivated pastures. The amount of C fixed in the highly restored site (275 g ha⁻¹ per year) indicates that the Chaco soils have a significant potential as atmospheric carbon sinks.  相似文献   

Effects of cultivation on soil microbiological properties in a freshwater marsh soil in Northeast China     

《Soil & Tillage Research》2007,93(1):231-235

The Sanjiang Plain has become an intensive area of land use/cover change in China. However, little is known about the effect of cultivation on soil microbiological properties in this freshwater marsh ecosystem. Our objective was to evaluate the effect of cultivation on mineralizable, microbial biomass, and total C in the Sanjiang Plain of Northeast China. Soil microbial biomass C (MBC) was 4346 ± 309 mg kg⁻¹ in undisturbed marsh and 229 mg kg⁻¹ in soil cultivated for 15 years. Undisturbed marsh soil had the highest microbial quotient (3.64%), which declined with increasing cultivation time (R² = 0.97, p < 0.01). Metabolic quotient increased with increasing cultivation time. Soil C mineralization in undisturbed marsh was 3.5 times that in soil cultivated for 1 year, and was 12 times that in soil cultivated for 15 years. Cultivation strongly affected measured soil microbiological properties.  相似文献   

Testing the stability of carbon pools stored in tussock sedge meadows     

《Applied soil ecology》2013

Tussocks formed by Carex stricta are a relatively large carbon (C) pool in sedge meadows, but the stability of organic matter in these ecosystems is not well understood. We initiated year-long incubation experiments (22.5 °C) to evaluate the CO₂ and CH₄ production potentials of sedge meadow substrates under field moist and inundated treatments from five sites in the Upper Midwest, USA (4 reference, 1 restored). C mineralization potentials decreased with depth (tussocks > underlying soil), and were positively correlated with macro-organic matter content and negatively with lignin. Across sites, C stored in tussocks and soil at the restoration was the least stable, suggesting that the restoration of C-storage function may take decades. Mineralization potentials were similar between field moist and inundated treatments, but inundation resulted in higher methane production, accounting for 24–51% of total carbon mineralized from tussocks. In the field however, C. stricta tussocks emitted less methane (393 ± 76 mg CH₄ m⁻² d⁻¹) than tussock interspaces (1362 ± 371 mg CH₄ m⁻² d⁻¹) early in the growing season; we suggest that tussock tops oxidized methane produced from deeper anoxic horizons. Our results highlight the importance of considering how microtopography modulates greenhouse gas flux from wetlands and suggests that the C stored in the older, more decomposed C. stricta tussock sedge meadow substrates (both within and between sites) is relatively stable.  相似文献   

Carbon mineralization and properties of water-extractable organic carbon in soils of the south Loess Plateau in China     

《European Journal of Soil Biology》2008,44(2):158-165

Addition of organic manure over thousands of years has resulted in the development of very fertile soils in parts of the Loess Plateau in Northwest China. This region also suffers from serious soil erosion. For that reason, afforestation of arable soils has taken place. The dynamics of soil organic matter in these soils affected by a very specific management and by land use changes is largely unknown. Therefore, we measured C mineralization in a 35-days incubation experiment and analyzed amounts and properties of water-extractable organic carbon (WEOC) in 12 topsoils of this region. The soils differed in land use (arable vs. forest) and in amounts of added organic manure. Afforestation of arable soils resulted in a distinct stabilization of organic C as indicated by the smallest C mineralization (0.48 mg C g⁻¹ C d⁻¹) and the highest C content (2.3%) of the studied soils. In the soils exposed to intensive crop production without regular addition of organic manure we found the largest C mineralization (0.85 mg C g⁻¹ C d⁻¹) and the lowest contents of organic C (0.9%). Addition of organic manure over a time scale of millennia resulted in high organic C contents (1.8%) and small C mineralization (0.55 mg C g⁻¹ C d⁻¹). The content of WEOC reflected differences in C mineralization between the soils quite well and the two variables correlated significantly. Water-extractable organic C decreased during C mineralization from the soil illustrating its mainly labile character. Carbon mineralization from soils was particularly large in soils with small specific UV absorbance of WEOC. We conclude that amounts and properties of WEOC reflected differences in the stability of soil organic C. Both afforestation of arable land and the long-term addition of organic manure may contribute to C accumulation and stabilization in these soils.  相似文献   

Plant material addition affects soil nitrous oxide production differently between aerobic and oxygen-limited conditions     

《Applied soil ecology》2013

It is a common agricultural practice for crop residues to be plowed into the soil or left on the soil surface. Soil addition of crop residues can considerably modify soil microbial activity and net N mineralization, and in general such modifications are negatively related to the C:N ratios of crop residues. Yet, little is known on the impacts of crop residues of different C:N ratios on soil nitrous oxide (N₂O) production under different aeration conditions via nitrification and denitrification. In this study, an 84-day laboratory incubation was conducted under aerobic and O₂-limited conditions and soil N₂O production was measured every 3 days after the addition of plant materials with a wide range of C:N ratios from 14 to 297. Two aerobic conditions were created by adjusting the water content of soil at a bulk density of 1.1 g cm⁻³ to 30% water-filled pore space (WFPS) and 60% WFPS, and two O₂-limited conditions were made by 90% WFPS and fluctuation between 90% and 30% WFPS. Each fluctuation cycle lasted 9 days and soil water content was readjusted to 90% WFPS at the end of each cycle. We also measured microbial respiration activity and net N mineralization periodically (i.e., 3, 7, 14, 28, 42, 56, 70, and 84 days) during the incubation and microbial biomass C at the end of incubation. At aerobic conditions, soil amendments of plant materials, regardless of their C:N ratios, all enhanced soil N₂O production. However, net N mineralization was dependent on plant material C:N ratios, being significantly higher or lower than the control for C:N ratios ∼15 and C:N ratios ≥44, respectively. Such inconsistent responses indicated that nitrifiers mediating nitrification and therefore byproduct N₂O production could strongly compete with heterotrophic microbes for NH₄⁺ and therefore net N mineralization was not a good predictor for nitrification-associated N₂O production. Interestingly, plant material additions reduced soil N₂O production by up to ∼95% at O₂-limited conditions, perhaps due to NO₃⁻ limitation. Soil NO₃⁻ production via nitrification could be low at O₂-limited conditions, and soil NO₃⁻ availability could be further reduced due to increases in microbial biomass and thus microbial N assimilation after plant material additions. This NO₃⁻ limitation might enhance N₂O reduction to N₂, by which denitrifiers could harvest more energy from the consumption of limited NO₃⁻. Nonetheless, our results revealed contrasting differences in N₂O production between aerobic and O₂-limited conditions following soil amendments of plant materials.  相似文献   

An outline of soil nematode succession on abandoned fields in South Bohemia     

《Applied soil ecology》2011,47(3):355-371

Secondary succession of nematodes was studied in 1–48-year-old abandoned fields on cambisols in South Bohemia, Czech Republic, and compared with cultivated field and sub-climax oak forests. Bacterivores were the predominant group in the cultivated field whereas in forests root-fungal feeders (mainly Filenchus) were almost as abundant as bacterivores. The total abundance of nematodes in the cultivated field averaged 868 × 10³ ind m⁻². During the first three years of succession the abundance practically did not change (775 × 10³ ind m⁻²), the fauna was still similar to that in cultivated field but the biomass increased mainly due to Aporcelaimellus. Then the abundance increased up to 3731 × 10³ ind m⁻² in 7–8-year-old abandoned fields, plant parasites (Helicotylenchus) dominated and the fungal-based decomposition channel was activated. Later the abundance stabilised at between 1086 and 1478 × 10³ ind m⁻² in 13–25-year-old successional meadow stages with high population densities of omnivores and predators. The total abundance of nematodes was low in the 12–13-year-old willow shrub stage (594 × 10³ ind m⁻²), increased in the 35–48-year-old birch shrub stage (1760 × 10³ ind m⁻²) and the nematode fauna developed towards a forest community. The diversity and maturity of nematode communities generally increased with the age of abandoned fields but the highest values were in meadow stages (81–113 species, 57–68 genera, MI 2.73–3.30). The development of meadow arrested succession towards forests or diverted succession towards a waterlogged ecosystem. The succession of nematodes was influenced by the method of field abandonment (bare soil vs. legume cover, mowing) that affected the formation of either a shrub or meadow stage, and by the soil water status. The composition of the nematode fauna indicated that the soil food web could recover faster from agricultural disturbance under successive meadows than under shrubs.  相似文献   

Effect of freezing on soil nitrogen mineralization under different plant communities in a semi-arid area during a non-growing season     

《Applied soil ecology》2010,46(3):187-192

The influences of winter climate on terrestrial ecosystem processes have been the subject of growing attention, which is necessary to make the predictions about ecological responses to global warming in the future. However, little information can be found about the impacts of a large range of soil temperature fluctuation (e.g. −10 to 5 °C) over winter on the soil nitrogen (N) dynamics in the field. In the present study, we employed an intact soil core in situ incubation technique, and measured soil N mineralization and nitrification rates under three plant communities, i.e. a grassland, a shrub and a plantation, during the non-growing season (October 2004–April 2005) in Inner Mongolia, China. Our results demonstrate the significant effects of different plant communities on soil net N mineralization and the great temporal variations of soil N dynamics during the incubation period. The mean soil net N mineralization rates were 0.93, 0.77 and −1.28 mg N m⁻² d⁻¹, respectively, in the grassland, shrub and plantation. The mean soil NH₄⁺-N in the three plant communities declined by 40%, but the mean soil NO₃⁻-N increased by 190% by the end of the incubation compared with their initial concentrations at the beginning of incubation. The differences in plant communities significantly affected their soil N mineralization rates, accumulations and turnover rates, which followed the order: grassland > shrub > plantation. During the winter time, the studied soils experienced the three phases consisting of mild freezing (−7 to −2 °C soil), deep freezing (approximately −10 °C soil) and freeze–thaw (−2 to 5 °C soil). The results suggest that temporal variations of soil N mineralization are positively affected by the soil temperature and the soil nitrification is dominant in the N transformation process during the non-growing season. Our study indicates that the soil N mineralization over winter can make a substantial contribution to the mineral N pool that plants are able to utilize in the upcoming spring, but may also pose a great risk of mineral N leaching loss if great rainfalls occur during spring and early summer.  相似文献   

Compacted soil affects soil macrofauna populations in a semi-arid environment in central Queensland     

《Soil biology & biochemistry》2001,33(12-13):1869-1872

Population densities of soil macrofauna were assessed in a field experiment with annually compacted treatments (applied to whole plots) and management treatments to repair initially compacted soil. Earthworms accounted for about half the macrofauna recovered during the experiment. Compaction of wet surface soil (water content>plastic limit) by agricultural machinery generally reduced numbers of macrofauna and earthworms. Annual compaction with a 10 Mg axle load on wet soil reduced mean macrofauna numbers from 70 to 15 m⁻² and mean earthworm numbers from 41 to 2 m⁻². Annual compaction with 6 Mg on soil drier than the plastic limit to a depth of 0.08 m had no adverse effect on the soil macrofauna. A 3-year pasture ley had more macrofauna (211 m⁻²) than a control treatment under cropping (29 m⁻²) but numbers declined when cropping was resumed.  相似文献   

Soil compaction and poultry litter effects on factors affecting nitrogen availability in a claypan soil     

《Soil & Tillage Research》2007,92(1-2):109-119

Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m⁻³) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha⁻¹) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH₄⁺-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.  相似文献   

Can commercial mulches be reservoirs of invasive earthworms? Promotion of ligninolytic enzyme activity and survival of Amynthas agrestis (Goto and Hatai, 1899)     

《Applied soil ecology》2015

Amynthas agrestis is an exotic, invasive earthworm in North America that has been associated with horticulture settings as well as damage to forest soil. An experiment was conducted to find out whether A. agrestis, an earthworm commonly found in mulches in Vermont, stimulates ligninolytic enzymes in the presence of commercial wood mulches. Mesocosms filled with a sandy loam soil were topped with either spruce, cedar or pine mulch. Half of the mesocosms received juvenile A. agrestis, the other half did not. After 7 weeks soils were analyzed for phenoloxidase and peroxidase activity. Most A. agrestis survived and developed into adults during the incubation period. Significantly greater phenoloxidase activity was detected in soils with A. agrestis than without earthworms. Mean (standard deviation) phenoloxidase activities in the presence of A. agrestis were 0.15 (±0.10), 1.14 (±0.46), 2.71 (±0.98) μmol g⁻¹ h⁻¹ for pine, spruce and cedar respectively, and 0.012 (±0.023), 0.25 (±0.25), 0.78 (±0.45) μmol g⁻¹ h⁻¹ in the absence of A. agrestis. There was significantly greater peroxidase activity for the pine and spruce treatment when earthworms were present. Mean peroxidase activities were 0.47 (±0.21), 0.94 (±0.29), 1.20 (±0.77) μmol h⁻¹ g⁻¹ soil for pine, spruce and cedar, respectively for soils with A. agrestis and 0.15 (±0.10), 0.37 (±0.10), 0.63 (±0.30) μmol h⁻¹ g⁻¹ soil in the absence of earthworms. The increased ligninolytic activity in combination with successful maturation of juveniles into adult A. agrestis suggests that mulch can be habitat for these invasive earthworms. This finding is supported by a survey of master gardeners in Vermont and New Hampshire 20% of whom reported to have seen these earthworms mainly in their gardens and mulched beds.  相似文献