Growth of Gaeumannomyces graminis var. tritici in soil: Effects of temperature and water potential

The effects of temperature and water on the growth of the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt), were examined in two factorial experiments. The first examined the effects of temperature and water potential on the growth of two isolates of Ggt on agar media, using osmotically-adjusted water potentials. The second experiment was concerned with the growth of the Ggt isolates in one sterile and two natural soils at two water regimes in the absence of a living host. Three temperatures (10, 18 and 26°C) were used in these experiments. A third experiment determined growth through soil.Growth was greatest at high temperatures and low water potential in axenic culture, but in unsterile soil growth at different temperatures and water potentials was strongly influenced by competition from the soil biota. The best temperature for growth in unsterile soil was 18°C. Growth at 26°C in unsterile soil was greatly reduced, this being attributed to more intense microbial competition. In sterile soil Ggt grew equally well at 18 and 26°C. At 10°C, both isolates of Ggt grew better in unsterile soil than in sterile soil.Under suitable conditions Ggt grew out readily from infected straw into unsterile soil (up to 5 cm in 10 days) in the absence of a host plant, forming melanized, hyaline and branched hyphae. These hyphae were infectious after dry storage for 5 months in the laboratory. Ggt thus appears to be a more successful soil inhabitant than is widely believed. Our experiments could explain many of the host-based concepts related to field expression of disease.The technique presented here could be of value for testing the suppressiveness or conduciveness of soils by measuring fungal growth in soil.     

Temperature regime of some soil types in Georgia

The thermal regime of the different soil types of Georgia has been studied on the basis of soil temperature records obtained at 60 weather stations in 1947–1995. It is shown that the thermal conductivity and temperature gradients in the soil profiles depend on the soil type. In the upper 0–20 cm of the soils in the intermontane depressions, the lowest temperature gradients in the summer are typical of the red ferrallitic soils (0.5–1.1°C/dm), and the highest gradients are observed in the chernozems of eastern Georgia (1.0–1.3°c/dm). The soil temperature gradients are especially high in the late spring (1.4–1.8°c/dm), when the atmospheric convection is formed. In the mountains, the lowest gradients in the summer are observed in the cinnamonic soils (0.4–0.9°c/dm), and the highest gradients are established in the brown forest soils (0.5–1.3°c/dm). The redistribution of the temperatures in the deeper layers depends on the soil texture. The lowest temperature gradient is in the soils of Telavi (3.1°c/m), where a stony layer is found at the depth of 60 cm, which causes the good heating of the deep layers. The highest gradients are seen in the clayey and loamy soils of western (Chakva, 3.8°c/m) and eastern (Tbilisi, 3.9°c/m) Georgia. This is probably related to the high water content in the heavy-textured soils.     

Grazing intensity in subarctic tundra affects the temperature adaptation of soil microbial communities

Grazing by large ungulates, such as reindeer (Rangifer tarandus L.), in subarctic tundra exerts a considerable effect on the soil microclimate. Because of higher insulation by the aboveground vegetation in light versus heavily grazed areas, soil temperatures during the growing season are considerably higher under heavy grazing. Here, we hypothesized that these grazer-induced changes in soil microclimate affect the temperature sensitivity of soil microbial activity. To test this hypothesis, we conducted soil incubations at different temperatures (4 °C, 9 °C and 14 °C) for six weeks using soils from sites with contrasting long-term grazing intensities. Microbial respiration at low temperature (4 °C) was significantly higher in soils under light grazing than in soils under heavy grazing; however, grazing intensity did not affect respiration rates at 9 °C and 14 °C. In soils under light grazing, post-incubation β-glucosidase (BG) activity at 4 °C was higher in soils that had been incubated at 4 °C than in soils incubated at 14 °C, suggesting functional adaptation of the soil microbial community to low temperature. Similar adaptation was not detected in soils under heavy grazing. Ion Torrent sequencing of bacterial 16S rRNA genes showed major differences in the bacterial community composition in soils incubated at different temperatures. Overall, our results indicate that tundra soil microorganisms may be more cold-adapted under low than high grazing intensity. Due to this difference in temperature adaptation, the consequences of climate warming on soil microbial processes may be dependent on the grazing intensity.     

Does history matter? Temperature effects on soil microbial biomass and community structure based on the phospholipid fatty acid (PLFA) analysis

Background, aim, and scope

Temperature is an important environmental factor regulating soil microbial biomass, activity, and community. Soils from different climatic regions may have very different dominant soil microbes, which are acclimated to the local conditions like temperature. Changing soil temperature especially warming has been shown to increase the mortality rate of soil microbes. However, little is known about the responses of soil microbes coming from different climatic regions to different incubation temperatures. The objective of this study was to examine the temperature effects on microbial biomass and community of soils collected from cold, intermediate, and hot natural sites.

Materials and methods

Soils were collected from northern (Heilongjiang province), central (Jiangsu province), and southern (Guangxi province) China, these soils having very different temperature histories. The Heilongjiang soil was from the coldest region with a mean annual temperature of 1.2°C, the Jiangsu soil was intermediate with a mean annual temperature of 15.7°C, and Guangxi soil was from the hottest area, with a mean annual temperature of 21.2°C. These three soils were incubated at 4°C, 15°C, 25°C, and 35°C for up to 56 days. Phospholipid fatty acid (PLFA) analyses were conducted on days 0, 3, 7, 14, 28, and 56 to track the dynamics of soil microbes.

Results

Soil microbial biomass indexed by total phospholipid fatty acid concentration decreased with increasing incubation temperature, with that of the Heilongjiang soil decreasing most. At the end of incubation, the biomass at 35°C in the Heilongjiang, Jiangsu, and Guangxi soils had declined to 65%, 72%, and 96% of the initial biomass, respectively. The PLFA patterns shifted with increasing temperatures in all the soils, especially at 35°C; the change was biggest in the Heilongjiang soil.

Discussion

History does have effects on soil microbes responding to environmental stress. Soil microbial biomass and PLFA profiles shifted least in the Guangxi soil with the hottest temperature history and most in the Heilongjiang soil with the coldest temperature, indicating that the distribution of free-living microorganisms is influenced by climatic factors. The majority of soil microorganisms coming from the hot regions are more adapted to high temperature (35°C) compared to those from the cold area. There are some regular changes of PLFA profiles when increasing incubation temperature to 35°C. However, the effect of incubation temperature on soil microbial community structure was inconclusive. As PLFA profile community structure is the phenotypic community structure. Genotype experiments are required to be done in future studies for the better understanding of soil microbes in different climate regions with concerning temperature variation.

Conclusions

With the increasing incubation temperature, soil microbial biomass and PLFA profiles shifted most in the soil with the coldest temperature history and least in the soil with the hottest temperature. History does matter in determining soil microbial dynamics when facing thermal stress.     

Burn Effects on Soil Aggregate Stability and Water Repellency of Two Soil Types from East and North Tunisia

To date, evidence of the potential effects of burning practices on soil properties in Tunisia is limited. In order to address this issue, we carried out laboratory investigations of the effects of burning on soil aggregate stability (AS) and water repellency (WR) of a clayey and a sandy loam Fluvisol soils. The treatments included low (100°C, LT), medium (300°C, MT) and high (600°C, HT), heating temperatures. Unburned (0°C, UB) soil samples were used as a control. Two breakdown mechanisms, fast wetting (FW) and mechanical breakdown (MB), were used for the measurement of AS. The latter is expressed by calculating the mean weight diameter (MWD). The water drop penetration time (WDPT) was used to evaluate the soil WR. The results showed that the unburned clayey and sandy loam soils are poorly aggregated. The HT and MT treatments significantly (p < 0.05) increased MWD of both soils, compared to UB samples, following the FW stability test. A lesser increase of MWD was observed with the MB test. The LT treatment did not significantly (p < 0.05) affect the soils AS. For the unburned clayey soil, the FW and MB tests gave significantly (p < 0.05) different MWDs . In contrast, the unburned sandy loam soil had similar MWDs under both tests. As for water repellency, the sandy loam soil was initially wettable and the clayey soil slightly water repellent. Burning treatments did not affect the sandy loam soil behavior but caused a decrease of clayey soil WR.     

Verification of freezing point depression method for measuring matric potential of soil water

The matric potential of soil water was determined using the freezing point depression method for a range of soil types. Soil water characteristic curves of these soils were obtained and compared with those obtained by the pressure plate, psychrometer, and vapor pressure methods resulting in excellent agreement between the freezing point depression method and the other methods over the range of -10.0 to -0.1 MPa in matric potential (i.e., temperature range of -8.00 to -0.08°C for freezing point) in all soil types. Over those ranges of matric potentials and temperatures, the effect of temperature-dependence on the freezing point of soils both in terms of specific volume of water and latent heat of water freezing was negligibly small. Freezing point of soils was independent of the bulk density of soils due to the fact that soil water in the range of matric potentials less than -0.1 MPa was affected predominantly by adsorptive forces between water and the soil matrix. The results from this study indicate that the freezing point depression method is a simple and practical technique to determine the soil water content in the vicinity of the wilting point     

Soil chronosequences in Israel

Chronosequences of Israel soils are summarized. Soil development in the coastal plain is related to the time of the dune deposits while those of the inland valley is related to the formation of the sedimentological terraces. Soil development in the mountains is related to the features and stability of the slope.The properties of young soils resemble those of the parent material. With advancing development the soils are affected by various processes, among them also the accretion of aeolian dust. Leaching is significant already at early stages; in some cases like Hamra and Terra-rossa soils the leaching stage is more advanced in earlier stages than in the final stage of soil development.In advanced stages of soil development the effect of the underlying rock on soil properties is reduced. At the final stage soils on moderate relief in the same climatic zone on different bedrocks resemble each other. This is attributed mainly to the effect of the aeolian dust accretion. The final stage of soil development on moderate relief consists of Grumusols in the northern parts of Israel, grumic dark Brown soils in the semi-arid parts of central Israel, loessial light Brown clay loam and loessial Serozems in the arid parts of the northern Negev and Regs in the extremely arid areas of the Southern Negev and Sinai. Petrocalcic horizons are developed on slopes and terraces where the rate of soil erosion equals that of accumulation of aeolian dust. The formation of petrogypsic horizons in the extremely arid zones is restricted to areas where erosion is negligible.The final stages of soil development exhibit a clear climatic zonality. This zonality differs from the soil zonality in the USSR and the USA due to the special features of dust accretion on the soils of Israel.     

Temperature effect on seed germination,seedling root development and growth of several vegetables

Experiments were conducted to study the effect of temperature and nutrition on seed germination and plant growth of different plant species. The nutrition studies of vegetables showed a normal response to fertilization rates on deficient soils at temperatures above their critical minimum. At soil temperatures below this little or no response was obtained to increased P concentration. Plant growth as affected by soil temperature was studied on beans, corn, cucumber, eggplant, pea, pepper, radish, spinach, and watermelon. Growth of peas, radish and spinach was significantly reduced by soil temperatures 10°C or lower. Corn growth was restricted when soil temperatures were maintained in the range of 12.3–14.5°C or lower, while growth of bean, cucumber, eggplant, pepper and watermelon was limited when soil temperatures were maintained in the 16.7–18.9°C temperature range or lower.     

Temperature field of complex soilscapes (by the example of the Vladimir opolie region)

Problems of the assessment of soil temperature regime at the polypedon level have yet to be solved. An approach suggested by the authors consists of three stages: (1) the characterization and prediction of the soil water regime as a factor influencing the soil temperature regime, (2) the obtaining of thermophysical functions for the particular elements of complex soilscapes, and (3) the calculation and assessment of the temperature regime of complex soilscapes in the form of the functional fields of soil temperature isopleths. This approach has been applied to predict the soil temperature regime of an arable field in the Vladimir opolie region. The complex soilscape of the field consists of medium loamy agrogray soils, agrogray soils with the second humus horizon, and podzolized agrogray soils. At the beginning of the growing season, minimum temperatures are observed in the areas of agrogray soils with the second humus horizon; the difference in soil temperatures at a depth of 20 cm reaches 1°C, and the difference in the sum of active soil temperatures reaches 20°C. Then, this difference changes considerably, so that the agrogray soils with the second humus horizon become warmer than the agrogray soils. In general, the functional field of soil temperatures within the complex soilscape is highly dynamic and diverse, which is specified by the variability in the water-physical and thermophysical properties of particular soils.     

Effects of plant residues and environmental factors on phosphorus availability in soils

Abstract

Phosphorus availability is a major nutritional problem in several northern Idaho soils. Traditionally, fertilizers containing P have been applied to improve availability in soils; however, organic materials added to soils have the ability to provide large quantities of labile P via mineralization processes and to reduce sorption of P. Using this concept, plant residues applied to soils would increase P availability for future plant needs. This research evaluated the effect of plant residue, incorporated into a Northern Idaho soil, on P availability under controlled laboratory conditions. Alfalfa (Medicago sativa), pea (Pisum sativum) and wheat (Triticum aestivum) plant residues were incorporated into soil collected from the Ap horizon of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll) at rates of 0, 1, 5 and 10% (w/w). The soils were incubated at soil water potentials of ‐0.05, ‐0.15 and ‐0.40 MPa, and temperatures of 10, 20 and 30°C over a 20 week period. Soils were sampled at 2, 4, 8, 12, 16 and 20 weeks for determination of NaOAc extractable P. Data were analyzed by SAS‐GLM and Omega squared (ω²) values were used to identify the impact of each main effect and interaction. A significant 4‐factor interaction of plant residue x amendment rate x water potential x incubation time, four 3‐factor interactions, six 2‐factor interactions and four main effects were observed at each of the three incubation temperatures. Since all interactions and main effects significantly affected P availability, ω² values were used to assess their relative importance. Amendment rate was the most important factor and plant residue material was the second most important factor observed affecting extractable P levels. In general, NaOAc extractable P increased with increasing amendment rates and incubation time‐period. Increasing incubation temperature and soil water potential also positively affected the extracted P level. The greatest amount of P was mineralized from alfalfa residue material while the smallest amount was released from wheat residue. Pea residue contributed an intermediate quantity of extractable P. This study demonstrated that residues applied to northern Idaho soils have the ability to enhance P availability in addition to providing a usable N source.     

Size Characterization by Laser Granulometry of Colloids Extracted from Compost at Different Temperatures

The objective of this work was to characterize colloids extracted from composts and their potential retention in soils. Compost made of sludge and green wastes was sampled (i) during the fermentation phase and (ii) after maturation. The same kind of compost was used in a long-term field experiment at Feucherolles (France), near Paris where amended and nonamended soils were sampled. The colloidal fraction was extracted from composts in water at room temperature (20°C) and compared to the colloidal fraction extracted from the soil. Composts were also extracted by pressurized hot liquid water at 50, 125 and 175°C. The total organic carbon of the extracts was measured and the particle size distribution (PSD) of colloidal extracts was analyzed by laser granulometry. The diameters of the colloids extracted from the soil ranged between 0.040 and 0.300 μm, independently of the temperature. For composts, it varied from 0.040 to 3.200 μm when extraction was done at 20°C, while at higher temperatures, much more organic matter was extracted, and colloid diameters ranged from 0.040 μm to 0.200 μm. The water-soluble C decreased and the size of colloids recovered in water at temperatures below 50°C increased when compost maturity increased. The adsorption on soils of colloidal particles extracted from composts was characterized. The largest adsorption (up to 30% of the initial soluble C) occurred with the extracts recovered at high temperature, in relation to the more hydrophobic properties of the colloids extracted with hot water maintained in subcritical conditions. After adsorption, the particle size distribution in the colloidal fraction extracted at 20°C moved towards finer fractions; by contrast, the colloidal fraction extracted at 175°C moved towards coarser fractions. The coarsest colloids coming from the soil disappeared during the adsorption experiment, probably because of the coprecipitation with the finest colloids coming from compost.     

Stability of urease in soils

Studies with surface samples of Iowa soils selected to obtain a wide range in properties showed that the following treatments of field-moist soils had no effect on urease activity: leaching with water ; drying for 24 h at temperatures ranging from 30 to 60°C ; storage for 6 months at temperatures ranging from ?20 to 40°C; incubation under aerobic or waterlogged conditions at 30 or 40°C for 6 months. No loss of urease activity could be detected when field-moist soils were air-dried and stored at 21–23°C for 2yr, but complete loss of urease activity was observed when they were dried at 105°C for 24 h or autoclaved (120°C) for 2h. Inactivation of urease in moist soils was detected at temperatures above 60°C.Treatment of field-moist soils with proteolytic enzymes which cause rapid destruction of jackbean urease did not decrease urease activity, but jackbean urease was destroyed or inactivated when added to sterilized or unsterilized soils.Although no decrease in urease activity could be detected when field-moist soils were air-dried, an appreciable (9–33%) decrease in urease activity was observed when air-dried soils were incubated under aerobic or waterlogged conditions. This decrease occurred within a few days, and prolonged incubation or repetition of the drying-incubation treatment did not lead to a further decrease in urease activity. Treatment of incubated air-dried soil with urease or glucose initially increased urease activity to a level exceeding that of the undried soil, but this activity decreased with time and eventually stabilized at the level observed for the undried soil.The work reported supports the conclusions from previous work that the native urease in Iowa soils is remarkably stable and that different soils have different levels of urease activity determined by the ability of their constituents to protect urease against microbial degradation and other processes leading to inactivation of enzymes.     

Enzyme activity in soils at subzero temperatures

Urease activity, phosphatase activity, and sulfatase activity were detected in soils at ?10 and ?20°C. The occurrence of enzyme activity in soils at subzero temperatures is attributed to enzyme-substrate interaction in unfrozen water at the surfaces of soil particles. Support for this explanation was obtained from experiments showing that hydrolysis of urea by jackbean urease occurs at ?10 or ?20°C in the presence, but not in the absence, of clay minerals or autoclaved soils. No enzyme activity could be detected in soils at ?30°C.     

Temperature sensitivity of soil organic matter decomposition varies with biochar application and soil type

Biochar application has the potential to improve soil fertility and increase soil carbon stock, especially in tropical regions. Information on the temperature sensitivity of carbon dioxide(CO_2) evolution from biochar-amended soils at very high temperatures, as observed for tropical surface soils, is limited but urgently needed for the development of region-specific biochar management targeted to optimize biochar effects on soil functions. Here, we investigated the temperature sensitivity of soil respiration to the addition of different rates of Miscanthus biochar(0, 6.25, 12.5, and 25 Mg ha~(-1)) in two types of soils with contrasting textures. Biochar-amended soil treatments and their controls were incubated at constant temperatures of 20, 30, and 40℃. Overall, our results show that: i) considering data from all treatments and temperatures, the addition of biochar decreased soil CO_2 emissions when compared to untreated soils;ii) CO_2 emissions from biochar-amended soils had a higher temperature sensitivity than those from biochar-free soils; iii) the temperature sensitivity of soil respiration in sandy soils was higher than that in clay soils; and iv) for clay soils, relative increases in soil CO_2 emissions from biochar-amended soils were higher when the temperature increased from 30 to 40℃, while for sandy soils, the highest temperature responses of soil respiration were observed when increasing the temperature from 20 to 30℃. Together, these findings suggest a significantly reduced potential to increase soil organic carbon stocks when Miscanthus biochar is applied to tropical soils at high surface temperatures, which could be counteracted by the soil-and weather-specific timing of biochar application.     

ADAPTING TO CLIMATE CHANGE BY IMPROVING WATER PRODUCTIVITY OF SOILS IN DRY AREAS

Considering extreme events of climate change and declining availability of appropriate quality water and/or highly productive soil resources for agriculture in dryland regions, the need to produce more food, forage and fibre will necessitate the effective utilization of marginal‐quality water and soil resources. Recent research and practices have demonstrated that effective utilization of these natural resources in dry areas can improve agricultural productivity per unit area and per unit water applied. This paper focuses on the following three case studies as examples: (1) low productivity soils affected by high levels of magnesium in soil solution and on the cation exchange complex; (2) degraded sandy soils under rainfed conditions characterized by low water‐holding capacity, organic matter and clay content and (3) abandoned irrigated soils with elevated levels of salts inhibiting growth of income generating crops. The results of these studies demonstrate that application of calcium‐supplying phosphogypsum to high‐magnesium soils, addition of clays to light textured degraded soils and phytoremediation of abandoned salt‐affected soils significantly improved productivity of these soils. Furthermore, under most circumstances, these interventions were economically viable, revealing that the efficient use of marginal‐quality water and soil resources has the potential to improve livelihoods amid growing populations in dry areas while reversing the natural resource degradation trend. However, considerably more investment and policy‐level interventions are needed to tackle soil degradation/remediation issues across both irrigated and dryland agricultural environments if the major challenge of producing enough food, forage and fibre is to be met. Copyright © 2011 John Wiley & Sons, Ltd.     

Climatic conditions and crop‐residue quality differentially affect N,P, and S mineralization in soils with contrasting P status

The substitution of the widely practiced crop‐residue burning by residue incorporation in the subtropical zone requires a better understanding of factors determining nutrient mineralization. We examined the effect of three temperature (15°C, 30°C, and 45°C) and two moisture regimes (60% and 90% water‐filled pore space (WFPS)) on the mineralization‐immobilization of N, P, and S from groundnut (Arachis hypogae) and rapeseed (Brassica napus) residues (4 t ha^–1) in two soils with contrasting P fertility. Crop‐residue mineralization was differentially affected by incubation temperature, soil aeration status, and residue quality. Only the application of groundnut residues (low C : nutrient ratios) resulted in a positive net N and P mineralization within 30 days of incubation, while net N and P immobilization was observed with rapeseed residues. Highest N and P mineralization and lowest N and P immobilization occurred at 45°C under nearly saturated soil conditions. Especially net P mineralization was significantly higher in nearly saturated than in aerobic soils. In contrast, S mineralization was more from rapeseed than from groundnut residues and higher in aerobic than in nearly saturated soil. The initial soil P content influenced the mineralization of N and P, which was significantly higher in the soil with a high initial P fertility (18 mg P (kg soil)^–1) than in the soil with low P status (8 mg P (kg soil)^–1). Residue‐S mineralization was not affected by soil P fertility. The findings suggest that climatic conditions (temperature and rainfall‐induced changes in soil aeration status) and residue quality determine N‐ and S‐mineralization rates, while the initial soil P content affects the mineralization of added residue N and P. While the application of high‐quality groundnut residues is likely to improve the N supply to a subsequent summer crop (high temperature) under aerobic and the P supply under anaerobic soil condition, low‐quality residues (rapeseed) may show short‐term benefits only for the S nutrition of a following crop grown in aerobic soil.     

干湿循环条件下重庆地区三种土壤抗剪强度的动态变化

选择广泛分布于重庆丘陵山区的黄壤、钙质紫色土和中性紫色土3种土壤,通过对室内三轴剪切试验,测定含水率和干密度交互作用对土壤抗剪强度指标的影响,在含水率和干密度对土壤抗剪强度影响分析的基础上,3土壤按各自最优含水率和干密度制作干湿循环试验土样,进行干湿循环条件下土壤抗剪强度的动态变化分析。试验结果显示：(1)在相同干密度情况下,3种土壤粘聚力c值随着含水率的增加呈现出先增加后减小的趋势,在相同土壤含水率水平下,土壤粘聚力c值随干密度增大而增大,3种土壤内摩擦角φ值在各干密度条件下均随着含水率增加呈明显减小的趋势。(2)含水率和干密度的交互作用对土壤粘聚力c值有显著影响,粘聚力c值在1.3-1.7g/cm₃干密度范围内随着干密度的增大而增大,且每一个干密度都有一个含水率与之对应,在这样一个交互作用下粘聚力c值达到最大,含水率和干密度的交互作用对内摩擦角φ值影响相对较小,同一干密度下,其φ值差异不大,随干密度的增大缓慢增大。(3)3种土壤的粘聚力c值均随干湿循环次数的增加均呈减小趋势,且前两次循环c值衰减幅度都很大,从第三次干湿循环到第五次干湿循环粘聚力c值衰减幅度很小,趋于稳定。(4)3种土壤在干湿循环后内摩擦角φ值总体呈减小趋势,但不同土壤类型间存在差异,第五次循环结束后,黄壤为24.6?,中性紫色土为22.6?,钙质紫色土为19.3?。     

Changes in the temperature regime of podzolic soils in the course of natural forest restoration after clearcutting

The results of temperature monitoring in podzolic soils under the middle-taiga bilberry spruce forest and secondary mixed forest of the Komi Republic performed in 2008–2014 are presented. The changes in characteristics of soil temperature in the litter horizon and in the mineral horizons at the depths of 20 and 50 cm are outlined. It is shown that soil temperature regimes differ under the native spruce forest, young growth, and middle-aged secondary mixed forest. The soils of secondary phytocenoses are warmed up to a greater depth and are characterized by the higher heat supply. The differences are seen in a number of temperature parameters, such as the accumulated temperatures above 5°C and above 10°C at the depths of 20 and 50 cm. The most significant differences between the studied plots manifest themselves in the values of temperature amplitudes during the warm season. Maximum values of daily temperature amplitudes were obtained on the plot under young growth, whereas the soil under the middle-aged mixed forest was characterized by minimum values of daily temperature amplitudes.     

不同土壤坡面细沟侵蚀差异与其影响因素

采用室内纯净水人工模拟降雨试验,在坡度为10°、15°、20°、25°坡面,土槽为5 m、10 m两种规格,对两种土壤((土娄)土与黄绵土)分别进行雨强为1.5 mm min-1,的降雨实验,利用三维激光扫描仪对每一场降雨后的坡面进行监测,分析不同坡度对细沟侵蚀的影响,比较两种土壤坡面细沟侵蚀的差异,以及其差异的影响因子.结果表明:(土娄)土土壤颗粒以粉粒与黏粒为主,粉粒占总质量的64.12％,黏粒为28.42％.黄绵土的土壤颗粒以粉粒为主占总质量的67.95％,黏粒与沙粒含量较少,黏粒占14.52％,沙粒占17.53％.在相同条件下,(土娄)土降雨过程中人渗缓慢,产流时间、坡面流速均快于黄绵土,跌坎出现时间也较早,使其更容易产生细沟.(土娄)土的径流量高于黄绵土,在降雨过程中,径流稳定时间较早.(土娄)土侵蚀量高于黄绵土,(土娄)土产沙率呈增加趋势,黄绵土含沙量变化不明显.从坡面细沟发育来看,(土娄)土坡面细沟成平行状分布,黄绵土细沟为较宽树枝状.     

Effect of soil solarization on subsequent nitrification activity at elevated temperatures

Soil solarization is a nonchemical method of soil disinfection achieved by covering the soil surface with sheets of vinyl plastic to generate elevated soil temperature, generally over 45°C. Such elevated temperatures may be detrimental to some nitrifying microorganisms and favorable to others. However, little information exists to indicate how nitrification activity in soil is affected after solarization. We performed several experiments to investigate the effects of soil solarization on nitrification activity. We found that: (1) if a soil was subjected to pretreatment of 45 or 50°C for as little as 1 d, nitrification activity in a subsequent incubation at 30°C was less than that of a soil that did not receive any high-temperature pretreatment. However, if a soil received pretreatments of 45 or 50°C for more than 7 d, nitrification activity in a subsequent incubation at 45 or 50°C was greater than that of soil that did not receive high temperature pretreatment. (2) Nitrification activity in three kinds of soil taken from 0–5 cm depth after solarization treatment was greater at 45°C than 30°C. (3) Nitrification activity at 45°C in soil that had received solarization in the preceding year was greater than that in soil that had not been subjected to solarization. This was consistent with the fact that the population densities of ammonia oxidizers were greater in soils that had been subjected to solarization. These results suggest that soil solarization induces nitrifying microorganisms that are more active at 45–50°C than they are at 30°C, and that the effect of solarization on nitrification persists until the next crop season.