Effects of Epigeic Earthworms on Decomposition of Wheat Straw and Nutrient Cycling in Agricultural Soils in a Reclaimed Salinity Area:A Microcosm Study

Earthworms,one of the most important macroinvertebrates in terrestrial ecosystems of temperate zones,exert important influences on soil functions.A laboratory microcosm study was conducted to evaluate the influence of the earthworm Eisenia fetida on wheat straw decomposition and nutrient cycling in an agricultural soil in a reclaimed salinity area of the North China Plain.Each microcosm was simulated by thoroughly mixing wheat straw into the soil and incubated for 120 d with earthworms added at 3 different densities as treatments:control with no earthworms,regular density(RD)with two earthworms,and increased density(ID)with six earthworms.The results showed that there was no depletion of carbon and nitrogen pools in the presence of the earthworms.Basal soil respiration rates and metabolic quotient increased with the increase in earthworm density during the initial and middle part of the incubation period.In contrast,concentrations of microbial biomass carbon and microbial biomass quotient decreased in the presence of earthworms.Earthworm activity stimulated the transfer of microbial biomass carbon to dissolved organic carbon and could lead to a smaller,but more metabolically active microbial biomass.Concentrations of inorganic nitrogen and NO₃^--N increased significantly with the increase in earthworm density at the end of the incubation(P<0.05),resulting in a large pool of inorganic nitrogen available for plant uptake.Cumulative net nitrogen mineralization rates were three times higher in the ID treatment than the RD treatment.     

黄土高原某些耕作土壤中土壤微生物生物量C、N与矿化N的关系

The chloroform fumigation-incubation method was used to measure the soil microbial biomass C (SMBC) and N (SMBN) in 16 loessial soils sampled from Ansai, Yongshou and Yangling in Shaanxi Province. The SMBC contents in the soils ranged from 75.9 to 301.0 μg C g^-1 with an average of 206.1 μg C g^-1, accounting for 1.36%~6.24% of the total soil organic C with an average of 3.07%, and the SMBN contents from 0.51 to 68.40 μg N g^-1 with an average of 29.4 μg N g^-1, accounting for 0.20%~5.65% of the total N in the soils with an average of 3.36%. A close relationship was found between SMBC and SMBN, and they both were positively correlated with total organic C, total N, NaOH hydrolizable N and mineralizable N. These results confirmed that soil microbial biomass had a comparative role in nutrient cycles of soils.     

Effect of indaziflam on microbial activity and nitrogen cycling processes in an orchard soil

Indaziflam is a preemergent herbicide widely used for the control of weeds in pecan (Carya illinoinensis) orchards in the southwestern region of the United States. Given the paucity of data regarding the effect of indaziflam on the biochemical properties of soils supporting pecan production, this study was conducted to evaluate the effects of different application rates of indaziflam on soil microbial activity, diversity, and biochemical processes related to nitrogen (N) cycling. During two consecutive growing seasons (2015 and 2016), soil samples were obtained from experimental mesocosms consisting of soil-filled pots where pecan saplings were grown and treated with indaziflam applied at two different rates (25 and 50 g active ingredient (ai) ha^-1, with the higher rate being slightly lower than the recommended field application rate of 73.1 g ai ha^-1). Soil samples were collected approximately one week before and one week after herbicide application for determination of soil microbial biomass and diversity, N mineralization, and β-glucosaminidase activity. Soil samples collected from the control mesocosms without herbicide application were treated in the laboratory with two rates of indaziflam (75 and 150 g ai ha^-1) to determine the immediate effect on microbial activity. No significant effect of herbicide treatment on soil respiration and microbial biomass was detected. The results showed a slight to moderate decrease in microbial diversity (7% in 2015 and 44% in 2016). However, decreased β-glucosaminidase activity with herbicide treatment was observed in soils from the mesocosms (33%) and soils treated with indaziflam in the laboratory (45%). The mineral N pool was generally dominated by ammonium after indaziflam application, which was consistent with the drastic decrease (75%) in nitrification activity measured in the laboratory experiment. The results of this study indicate that indaziflam, even when applied at higher than recommended rates, has limited effects on soil microbial activity, but may affect N cycling processes.     

玉米秸秆应用和腐化对钙质苏打土改良的影响: 实验室试验研究

A laboratory lysimeter experiment was conducted to investigate the effects of forage corn (Zea mays L.) stalk application on the CO₂ concentration in soil air and calcareous sodic soil reclamation. The experimental treatments tested were soil exchangeable sodium percentage (ESP) levels of 1, 11, and 19, added corn stalk contents of 0 to 36 g kg^-1, and incubation durations of 30 and 60 days. The experimental results indicated that corn stalk application and incubation significantly increased CO₂ partial pressure in soil profile and lowered pH value in soil solution, subsequently increased native CaCO₃ mineral dissolution and electrolyte concentration of soil solution, and finally significantly contributed to reduction on soil sodicity level. The reclamation effciency of calcareous sodic soils increased with the added corn stalk. When corn stalks were added at the rates of 22 and 34 g kg^-1 into the soil with initial ESP of 19, its ESP value was decreased by 56% and 78%, respectively, after incubation of 60 days and the leaching of 6.5 pore volumes (about 48 L of percolation water) with distilled water. Therefore, crop stalk application and incubation could be used as a choice to reclaim moderate calcareous sodic soils or as a supplement of phytoremediation to improve reclamation effciency.     

用熏蒸提取法校正酸性红壤的KEC值

Commonly used K_EC value (0.45) of the fumigation-extraction (FE) method was obtained on the basis of temperate neutral soils. To ascertain its applicability to acidic red soils widespread in southern China and other subtropical regions, the K_EC value was investigated based on 8 acidic red soils by in situ labelling of native soil microorganisms using ¹⁴C-labelled glucose. Realistic K_EC value for red soils could be obtained by in situ ¹⁴C-labelling as long as an incubation period of 72 h is adopted after addition of ¹⁴C glucose to soil. The single K_EC values for the eight red soils ranged from 0.27 to 0.35 and averaged 0.31. Lower K_EC value obtained in red soils probably resulted from different soil quality, compared with other types of soil, which causes possible changes in microbial community structure and extractability of cellular component. Microbial biomass C contents of the eight red soils measured using a unique and constant K_EC value of 0.45 decreased by 22.2%~40% in comparison to those using variable K_EC values. The results suggest that microbial biomass C would be significantly underestimated using the present K_EC value and a calibration of the K_EC value is necessary for red soils.     

Soil Erosion as A ffected by Polyacrylamide Application Under Simulated Furrow Irrigation with Saline Water

The reduction of soil and water losses under furrow irrigation with saline water is important to environmental protection and agricultural production.The objective of this study was to determine the effect of polyacrylamide(PAM)application on soil infiltration and erosion under simulated furrow irrigation with saline water.Polyacrylamide was applied by dissolving it in irrigation water at the rates of 1.5,7.5,and 15.0 mg L^-1 or spreading it as a powder on soil surface at the rates of 0.3,1.5,3.0,and 6.0 g m^-2,respectively.The effectrolyte concentration of tested irrigation water was 10 and 30 mmolc L^-1 and its sodium adsorption ratio(SAR)was 0.5,10.0,and 20.0(mmol_c L^-1)_0.5.Distilled water was used as a control for irrigation water quality.Results indicated that the effectrolyte concentration and SAR generally did not significantly affect soil and water losses after PAM application.Infiltration rate and total infiltration volume decreased with the increase of PAM application rate.Polyacrylamide application in both methods significantly reduced soil erosion,but PAM application rate did not significantly affect it.The solution PAM application was more effective in controlling soil erosion than the powdered PAM application,but the former exerted a greater adverse influence on soil infiltration than the latter.Under the same total amounts,the powdered PAM application resulted in a 38.2%-139.6% greater infiltration volume but a soil mass loss of 1.3-3.4 times greater than the solution PAM application.     

施入粉煤灰和污泥对酸性淋溶土镉和铅吸附的影响

The safe recycling of fly ash (FA) and sewage sludge (SS) in the agricultural processes comprises an important environmental technology on waste management. Soils amended with FA and SS may change their ability to adsorb heavy metals due to either increase of soil pH or decomposition of sludge-borne organic matter. Thus, Cd and Pb sorption was investigated by 1-month incubation under soil moisture content at field capacity and room temperature with an acidic Typic Haploxeroalf from central Greece amended with varying amounts of FA and SS. Batch experiments were conducted by equilibrating the soil samples with CaCl₂ solutions containing 0-400 mg Pb L^-1 or 0-100 mg Cd L^-1. The results showed that the Freundlich equation described well the Cd and Pb sorption. Distribution coefficient (K_d) values of Pb were higher than those of Cd in all the treatments of this study. Application of FA increased K_d values for Cd and Pb to 8.2 and 2.3 times more than the controls, respectively. Simultaneous applications of FA and SS caused a K_d increase of 3.8 and 2.1 times compared to the treatments that received only SS for Cd and Pb, respectively. Treatment of SS alone did not significantly change Cd and Pb sorption compared to the controls. The sorption reactions seemed to be mainly affected by soil pH, which was revealed by the significant correlations of Cd and Pb sorption with soil pH. These suggested that fly ash was very useful as a low-cost adsorbent for Cd and Pb and could be used as an ameliorant for biosolid-amended acidic soils.     

Wheat yield prediction by zero sink and equilibrium-type soil phosphorus tests

Diffusive gradients in thin films (DGT) measurements have been shown to outperform other phosphorus (P) tests in soils with strong P sorption, but this has not been confirmed for moderately weathered European soils. We compared the performance of DGT in predicting wheat grain yield in Swedish long-term fertility experiments with those of standard intensity (water-extractable P (P-H₂O)) and quantity (ammonium lactate-extractable P (P-AL)) tests. A Mitscherlich-type model was used to fit wheat yield response to P application rates (0, 15, 30 or 35, and 45 kg P ha^-1 year^-1) in each individual trial replicate to estimate the maximum yield. For trials with clear plateau-type yield responses and the goodness of fit (R²) > 0.75, relative yields (RYs) were calculated for each P treatment and plotted against the soil P test results (n=143). The goodness of the Mitscherlich-type fits decreased in the following order:DGT-measured P (P-DGT) (R²=0.35) > P-H₂O (R²=0.18) > P-AL (R²=0.13). When excluding soils with P-AL:P-DGT ≥ 0.1 L g^-1, R² was considerably improved to 0.55 for P-AL, 0.46 for P-H₂O, and 0.65 for P-DGT (n=61). At 95% of maximum yield, the upper limit of P deficiency for P-DGT was 44.8 (the soils with P-AL:P-DGT < 0.1 L g^-1) and 61.9 μg L^-1 (all soils), falling within the range reported for other European and Australian soils (6.0-142 μg L^-1). We show that in the investigated Swedish soils, DGT performed better than the quantity and intensity tests, which is attributed to its ability to capture P diffusion and resupply from the soil solid phase, similar to plant roots in the rhizosphere.     

中国亚热带耕作雏形土及强酸土的可蚀性与渗透性关系

To evaluate the validity of different indices in estimating soil readily mineralizable N, soil microbial biomass (Nmic), soil active N (SAN), soluble organic N (SON), net N mineralization rate (NNR) and gross N mineralization rate (GNR) in mineral soils (0-10 cm) from six forest stands located in central Germany were determined and compared with two sampling times: April and November. Additionally, soil density fractionation was conducted for incubated soils (with addition of ¹⁵NH₄-N and glucose, 40 days) to observe the sink of added ¹⁵N in different soil fractions. The study showed that Nmic and NNR in most stands differed significantly (P ≤ 0.05) between the two sampling times, but not GNR, SAN and SON. In November, no close relationships were found between GNR and other N indices, or between Nmic, SON, and SAN and forest type. However, in April, GNR was significantly correlated (P ≤ 0.05) with Nmic, SAN, and NNR along with Nmic under beech being significantly higher (P ≤ 0.05) than under conifers. Furthermore, density fractionation revealed that the light fraction (LF, 0.063-2 mm, > 1.7 g cm^-3) was not correlated with the other N indices. In contrast, results from the incubation study proved that more ¹⁵N was incorporated into the heavy fraction (HF < 0.063 mm, > 1.7 g cm^-3) than into LF, indicaing that more labile N existed in HF than in LF. These findings suggested that attention should be paid to the differences existing in N status between agricultural and forest soils.     

水培和土培条件下氮素供应对燕麦生长和磷素吸收的影响

Plants show different growth responses to N sources supplied with either NH₄⁺ or NO₃^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavailability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat (Avena nuda L.) grown in hydroponics and in soil culture were investigated under supply with sole NH₄⁺-N, sole NO₃^--N, or a combination. Sole NO₃^--fed oat plants accumulated more biomass than sole NH₄⁺-fed ones. The highest biomass accumulation was observed when N was suppliedw ith both NH₄⁺-N and NO₃^--N. Growth of the plant root increased with the proportion of NO₃^- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO₃^--fed plants. However, root vigor was the highest when N was supplied with NO₃^-+NH₄⁺. NH₄⁺ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO₄ added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg^-1. P uptake was increased when N was supplied partly or solely as NO₃^--N, similarly as biomass accumulation. The results suggested that oat was an NO₃^--preferring plant, and NO₃^--N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH₄⁺-N did not improve P nutrition, which was most likely due to the absence of P deficiency.     

Microbial response to bensulfuron-methyl treatment in soil.

A laboratory incubation study was conducted to evaluate the effect of bensulfuron-methyl treatment on soil microbial biomass and N-mineralization of a loamy sand soil. The herbicide was applied at 0 (control), 0.01 (field rate), 0.1, and 1.0 microg g(-1), and soil microbial biomass carbon (C(mb)), soil microbial biomass nitrogen (N(mb)), and N-mineralization rate (k) were measured at different times after herbicide treatment. Compared to the untreated soil, C(mb) and N(mb) decreased significantly (p < or = 0.05) within the first 7 days after herbicide treatment at 0.1 and 1.0 microg g(-1), and the impact was greater for N(mb) than for C(mb). Nitrogen mineralization was significantly suppressed during the first 5 days of incubation when the soil was treated with bensulfuron-methyl at 0.1 and 1.0 microg g(-1). The overall impact of bensulfuron-methyl to the soil microbial communities was closely related to the application rate in the range of 0.01-1.0 microg g(-1). This effect, however, was found to be transitory, and significant impact occurred only at high application rates.     

A field study of gross rates of N mineralization and nitrification and their relationships to microbial biomass and enzyme activities in soils treated with dairy effluent and ammonium fertilizer

Abstract. Gross N mineralization and nitrification rates were measured in soils treated with dairy shed effluent (DSE) (i.e. effluent from the dairy milking shed, comprising dung, urine and water) or ammonium fertilizer (NH₄Cl) under field conditions, by injecting ¹⁵N-solution into intact soil cores. The relationships between gross mineralization rate, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) as affected by the application of DSE and NH₄Cl were also determined. During the first 16 days, gross mineralization rate in the DSE treated soil (4.3–6.1 μg N g^?1 soil day^?1) were significantly (P 14;< 14;0.05) higher than those in the NH₄Cl treated soil (2.6–3.4 μg N g^?1 soil day^?1). The higher mineralization rate was probably due to the presence of readily mineralizable organic substrates in the DSE, accompanied by stimulated microbial and extracellular enzyme activities. The stable organic N compounds in the DSE were slow to mineralize and contributed little to the mineral N pool during the period of the experiment. Nitrification rates during the first 16 days were higher in the NH₄Cl treated soil (1.7–1.2 μg N g^?1 soil day^?1) compared to the DSE treated soil (0.97–1.5 μg N g^?1 soil day^?1). Soil microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) increased after the application of the DSE due to the organic substrates and nutrients applied, but declined with time, probably because of the exhaustion of the readily available substrates. The NH₄Cl application did not result in any significant increases in microbial biomass C, protease or urease activities due to the lack of carbonaceous materials in the ammonium fertilizer. However, it did increase microbial biomass N and deaminase activity. Significant positive correlations were found between gross N mineralization rate and soil microbial biomass, protease, deaminase and urease activities. Nitrification rate was significantly correlated to biomass N but not to the microbial biomass C or the enzyme activities. Stepwise regression analysis showed that the variations of gross N mineralization rate was best described by the microbial biomass C and N.     

有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮

土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。     

Mobile and readily available C and N fractions and their relationship to microbial biomass and selected enzyme activities in a sandy soil under different management systems

Within different land‐use systems such as agriculture, forestry, and fallow, the different morphology and physiology of the plants, together with their specific management, lead to a system‐typical set of ecological conditions in the soil. The response of total, mobile, and easily available C and N fractions, microbial biomass, and enzyme activities involved in C and N cycling to different soil management was investigated in a sandy soil at a field study at Riesa, Northeastern Germany. The management systems included agricultural management (AM), succession fallow (SF), and forest management (FM). Samples of the mineral soil (0—5, 5—10, and 10—30 cm) were taken in spring 1999 and analyzed for their contents on organic C, total N, NH₄⁺‐N and NO₃^—‐N, KCl‐extractable organic C and N fractions (Corg_(KCl) and Norg_(KCl)), microbial biomass C and N, and activities of β‐glucosidase and L‐asparaginase. With the exception of Norg_(KCl), all investigated C and N pools showed a clear relationship to the land‐use system that was most pronounced in the 0—5 cm profile increment. SF resulted in greater contents of readily available C (Corg_(KCl)), NH₄⁺‐N, microbial biomass C and N, and enzyme activities in the uppermost 5 cm of the soil compared to all other systems studied. These differences were significant at P ≤ 0.05 to P ≤ 0.001. Comparably high C_mic:C_org ratios of 2.4 to 3.9 % in the SF plot imply a faster C and N turnover than in AM and FM plots. Forest management led to 1.5‐ to 2‐fold larger organic C contents compared to SF and AM plots, respectively. High organic C contents were coupled with low microbial biomass C (78 μg g^—1) and N contents (10.7 μg g^—1), extremely low C_mic : C_org ratios (0.2—0.6 %) and low β‐glucosidase (81 μg PN g^—1 h^—1) and L‐asparaginase (7.3 μg NH₄‐N g^—1 2 h^—1) activities. These results indicate a severe inhibition of mineralization processes in soils under locust stands. Under agricultural management, chemical and biological parameters expressed medium values with exception for NO₃^—‐N contents which were significantly higher than in SF and FM plots (P ≤ 0.005) and increased with increasing soil depth. Nevertheless, the depth gradient found for all studied parameters was most pronounced in soils under SF. Microbial biomass C and N were correlated to β‐glucosidase and L‐asparaginase activity (r ≥ 0.63; P ≤ 0.001). Furthermore, microbial biomass and enzyme activities were related to the amounts of readily mineralizable organic C (i.e. Corg_(KCl)) with r ≥ 0.41 (P ≤ 0.01), suggesting that (1) KCl‐extractable organic C compounds from field‐fresh prepared soils represent an important C source for soil microbial populations, and (2) that microbial biomass is an important source for enzymes in soil. The Norg_(KCl) pool is not necessarily related to the size of microbial biomass C and N and enzyme activities in soil.<?show $6#>     

不同施肥处理对黄泥土微生物生物量碳氮和酶活性的影响

通过室内培育实验,研究了不同施肥处理对黄泥土微生物生物量C、N和脲酶、酸性磷酸酶、蔗糖酶活性的影响。培养过程中,单施化肥处理土壤微生物生物量C、N均呈下降趋势,施用有机肥处理的土壤微生物量C前期升高至一定水平后或保持稳定、或呈下降趋势,而微生物生物量N总体均呈下降趋势;不同施肥处理的脲酶活性呈前期上升后期下降趋势,而酸性磷酸酶和蔗糖酶则单施化肥处理呈上升趋势、配施有机肥处理呈下降趋势。与对照处理相比,单施化肥处理显著降低土壤微生物生物量C、N,高量施用化肥处理还显著降低土壤脲酶活性,但对酸性磷酸酶和蔗糖酶活性的影响并不明显。秸秆施用可显著提高土壤微生物生物量C、N和酶活性,特别是高量施用秸秆的效果更明显。施用猪粪由于同时带入了大量的活性养分,对土壤微生物生物量C、 N和酶活性的影响尚难评价。在高度集约农业利用下,继续保持较高的化肥施用量并不利于土壤生物质量的维护和提高,而秸秆直接还田才是保持土壤健康状态的有效措施。     

半干旱农田生态系统作物根系和施肥对土壤微生物体氮的影响

盆栽和大田试验表明,作物根系显著影响土壤微生物体氮的含量。在田间试验条件下,根际土壤微生物体氮比非根际土壤平均高出N54.7μg/g;盆栽试验中,根际土壤微生物体氮平均含量为N77.1±13.6μg/g,而非根际土壤为N65.2±17.0μg/g,差异达显著水平,根际微生物体氮含量为非际根际土壤的1.10～2.04倍。施肥能明显增加土壤微生物体氮含量,但影响程度因肥料种类而不同。秸秆和富含有机物质的厩肥对土壤微生物体氮的影响远大于化学肥料,而且土壤微生物体氮含量随秸秆施用量增加而增加。在红油土上进行的20年长期田间定位试验结果表明,对不施肥和施氮磷处理,0—20cm土层的微生物体氮分别是N102.2和110.4μg/g;在施氮磷的基础上,每公顷配施新鲜玉米秸秆9375kg、18750kg、37500kg和厩肥37500kg时,相应土层微生物体氮分别是N147.5、163.2、286.4和265.3μg/g。培养条件下,当有效能源物质缺乏时,微生物对NH4+-N的同化固定能力远大于NO3--N,但在加入有效能源物质葡萄糖后,微生物对2种形态氮的固定量大幅度增加,且对2种形态氮的固定量趋于一致。     

氮沉降增加和人类干扰对半干旱草地土壤呼吸的影响

土壤呼吸是全球碳循环的主要流通途径,但半干旱草地土壤呼吸对全球变化和人类干扰的响应机制尚不清楚。该研究以科尔沁沙质草地为研究对象,研究氮沉降增加、人类干扰(火烧、刈割)及其交互作用对沙质草地整个植物生长季(2017年5-9月)土壤呼吸的影响。结果表明,土壤呼吸呈明显的季节动态变化,在7月最高。氮沉降增加使根呼吸显著提高42%,土壤呼吸显著增加17%(P0.001),但对微生物呼吸无显著影响。火烧使根呼吸显著提高25%(P0.01),但使微生物呼吸降低13%(P0.001),从而导致土壤呼吸未显著增加(P0.05)。刈割显著降低了土壤温度,诱导微生物呼吸和根呼吸分别降低13%(P0.001)和20%(P0.05),从而显著抑制土壤呼吸(P0.001)。氮沉降增强了火烧对土壤呼吸的促进作用,但未显著影响刈割对土壤呼吸的抑制作用。氮沉降、火烧和刈割对土壤呼吸的不同影响可对全球变化背景下沙质草地土壤碳循环的预测和天然草地的科学管理提供参考。     

氮素和水分对贝加尔针茅草原土壤酶活性和微生物量碳氮的影响

在内蒙古贝加尔针茅草原,分别设对照(N0)、1.5 g·m-2(N15)、3.0 g·m-2(N30)、5.0 g·m-2(N50)、10.0 g·m-2(N100)、15.0 g·m-2(N150)、20.0 g·m-2(N200)和30g·m-2(N300)(不包括大气沉降的氮量)8个氮素(NH4NO3)梯度和模拟夏季增加降水100 mm的水分添加交互试验,研究氮素和水分添加对草原土壤养分、酶活性及微生物量碳氮的影响。结果表明:氮素和水分添加对草原土壤理化性质和生物学特性有显著影响。随施氮量的增加土壤总有机碳、全氮、硝态氮、铵态氮含量呈增加的趋势,相反,土壤pH值呈降低的趋势。土壤脲酶和过氧化氢酶的活性随施氮量的增加而升高,多酚氧化酶则随施氮量的增加呈下降的趋势。氮素和水分添加对草原土壤微生物量碳氮含量有显著影响,高氮处理(N150、N200和N300)显著降低了微生物碳含量,微生物氮含量随施氮量的增加呈上升趋势。水分添加能够减缓氮素添加对微生物的抑制作用,提高微生物量碳、微生物量氮含量。草原土壤养分、土壤酶活性及土壤微生物量碳氮含量间关系密切,过氧化氢酶与全氮、总有机碳、硝态氮呈显著正相关,多酚氧化酶与铵态氮、硝态氮、全氮呈显著负相关。微生物量氮含量与土壤全氮、铵态氮、硝态氮含量以及过氧化氢酶和磷酸酶活性呈显著正相关,与多酚氧化酶呈负相关;微生物量碳与过氧化氢酶呈负相关,与多酚氧化酶活性呈正相关。     

Effect of phosphate rock, lime and cellulose on soil microbial biomass in acidic forest soil and its significance in carbon cycling

Phosphate rock (PR), limestone, coal combustion by-product (CCBP) high in Ca and high organic manures are potential amendments for increasing agricultural production in the acidic soils of the Appalachian region. The objective of this study was to examine effects of PR, CCBP and cellulose addition on soil microbial biomass in an acidic soil based on the measurement of soil microbial biomass P (P _mic) and on the mineralization of organic matter. Application of PR alone or in combination with CCBP increased P _mic. The P _mic was far less when the soil received PR in combination with limestone than with PR application alone or PR in combination with CCBP. Either CCBP or limestone application alone considerably decreased P _mic in the soil due to reduced P solubility. Cellulose addition alone did not increase P _mic, but P _mic was significantly increased when the soil was amended with cellulose in combination with PR. The decomposition of added cellulose was very slow in the soil without PR amendment. However, mineralization of both native organic matter and added cellulose was enhanced by PR application. Mineralization of organic matter was less when the soil was amended with PR in combination with high rates of CCBP (> 2.5%) because PR dissolution varied inversely with amount of CCBP addition. Overall, CCBP had no detrimental effect on soil microbial biomass at low application rates, although, like limestone, CCBP at a high rate may decrease P _mic in P-deficient soils through its influence on increased soil pH and decreased P bioavailability in the soil. Application of PR to an acidic soil considerably enhanced the microbial activity, thereby promoting the cycling of carbon and other nutrients. Received: 11 December 1995     

Application of eco-physiological quotients (qCO2 and qD) on microbial biomasses from soils of different cropping histories

Metabolic quotients for CO₂C (qCO₂C) and microbial-C-loss (qD) were studied on soil microbial communities under long-term monoculture (M) or continuous crop rotations (CR). Under defined laboratory conditions the mean qCO₂C (unit CO₂C unit⁻¹ C_mic h⁻¹) of different microbial biomasses from 17 M systems amounted to 1.097 μg CO₂qCO₂CC as compared to 0.645 μg CO₂C of microbial biomasses from 19 CR systems. The 1.7 times higher CO₂C release per unit biomass and time of microbial biomasses from M systems was significantly different at the P =0.001 level.In addition, microbial C-loss in samples from M or CR plots was followed for 5 weeks. Again, mean qD per unit microbial biomass and time was 1.6 times higher (P = 0.01) for microbial biomasses from M systems (0.301 μg C, 14 soils) when compared with CR systems (0.188μg C, 14 soils).These differences were not related to soil texture, C_org or pH of these soils. The effects of environmental influences (soil management) on the microbial pool in terms of a changing energy demand are discussed.