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1.
Adenosine triphosphate (ATP) was measured in soil profiles taken from two areas of deciduous woodland on Rothamsted Farm, one near neutral, one acidic. Biomass carbon (C) was calculated from these measurements. Comparison of the results with others taken from the literature showed that an exponential function m=e−(rbd) gave a close fit to the assembled data for the top metre of mineral soil, where m is biomass C, expressed as a fraction of that in the topsoil, d the depth (in cm, measured downwards from the middle of the topmost sampling layer) and rb a constant, in cm−1. The mean value for rb for 12 soils (including our two) is 0.046 cm−1, with a SD of ±0.0078.  相似文献   

2.
The need to identify microbial community parameters that predict microbial activity is becoming more urgent, due to the desire to manage microbial communities for ecosystem services as well as the desire to incorporate microbial community parameters within ecosystem models. In dryland agroecosystems, microbial biomass C (MBC) can be increased by adopting alternative management strategies that increase crop residue retention, nutrient reserves, improve soil structure and result in greater water retention. Changes in MBC could subsequently affect microbial activities related to decomposition, C stabilization and sequestration. We hypothesized that MBC and potential microbial activities that broadly relate to decomposition (basal and substrate-induced respiration, N mineralization, and β-glucosidase and arylsulfatase enzyme activities) would be similarly affected by no-till, dryland winter wheat rotations distributed along a potential evapotranspiration (PET) gradient in eastern Colorado. Microbial biomass was smaller in March 2004 than in November 2003 (417 vs. 231 μg g−1 soil), and consistently smaller in soils from the high PET soil (191 μg g−1) than in the medium and low PET soils (379 and 398 μg g−1, respectively). Among treatments, MBC was largest under perennial grass (398 μg g−1). Potential microbial activities did not consistently follow the same trends as MBC, and the only activities significantly correlated with MBC were β-glucosidase (r = 0.61) and substrate-induced respiration (r = 0.27). In contrast to MBC, specific microbial activities (expressed on a per MBC basis) were greatest in the high PET soils. Specific but not total activities were correlated with microbial community structure, which was determined in a previous study. High specific activity in low biomass, high PET soils may be due to higher microbial maintenance requirements, as well as to the unique microbial community structure (lower bacterial-to-fungal fatty acid ratio and lower 17:0 cy-to-16:1ω7c stress ratio) associated with these soils. In conclusion, microbial biomass should not be utilized as the sole predictor of microbial activity when comparing soils with different community structures and levels of physiological stress, due to the influence of these factors on specific activity.  相似文献   

3.
In the desert areas of China investigated by the authors, various biological crusts were predominately associated with three blue-green algal (cyanobacterial) species, Microcoleus vaginatus Gom., Phormidium tenue (Menegh.) Gom. and Scytonema javanicum (Kütz.) Born et Flah. Their biomass and their compressive strength were measured simultaneously in the field in this study. It was also found that the compressive strength of algal crusts was enhanced with the increasing of algal biomass from an undetectable level to a value as high as 9.6 mg g−1 dry soil. However, when the algal biomass decreased, the compressive strength did not descend immediately, but remained relatively steady. The higher the algal biomass became, the thicker were the algal crusts formed. Given the same biomass, the highest compressive strength of man-made algal crusts in fields was found at an algal ratio of 62.5% M. vaginatus, 31.25% P. tenue and 6.25% S. javanicum, and it reached 0.89 kg cm−2. When the biomass of the crusts increased above the value of 8.16 mg chla g−1 dry soil, the compressive strength would not ascend easily. It indicated that the compressive strength of man-made algal crusts appeared temporarily saturated in the field.  相似文献   

4.
In this study we examined the effects of glucose-C on the activities of fungi and bacteria determined by the method of substrate-induced respiration (SIR) in combination with the selective inhibition technique, the immobilized-S and the arylsulphatase (ARS) activity in two calcareous arable and fallow soils. The amounts of glucose-C were added at six doses: 0, 125, 250, 500, 750 and 1000 mg kg− 1 soil to the soils and then incubated for one week with a Na235SO4 solution (518.9 kBq kg− 1 dry soil and 20 mg S kg− 1 dry soil) prior to analysis. At the highest dose of 1000 mg kg− 1 soil, fungal activity increased by 59.1% (of the dose 0) versus 45.5% for bacterial activity in the arable soil, while in the fallow soil the increases were more marked and corresponded to 69.9% and 71.1%, respectively. Largest increase in immobilized-S was observed in the arable soil (300.7%) compared with the fallow soil (153.1%). In contrast, the ARS activity increased by 16.4% in the arable soil versus 32.1% in the fallow soil. These results indicate that glucose proportionately affected more the intensities of immobilized-S than those of ARS. Strong positive correlation coefficients were found between fungal activities and immobilized-S in the arable soil (r = 0.96, P < 0.01) and in the fallow soil (r = 0.98, P < 0.001). However, non-significant correlations were observed between fungal activities and ARS in both studied soils. As to bacterial activities, positive significant correlation coefficients were found with immobilized-S in the arable soil (r = 0.95, P < 0.01) and in the fallow soil (r = 0.90, P < 0.05) as well as with ARS activities in the arable soil (r = 0.83, P < 0.05) and in the fallow soil (r = 0.97, P < 0.01). Overall, we also found positive and significant correlation coefficients of immobilized-S with ARS activities in the arable soil (r = 0.86, P < 0.05) and in the fallow soil (r = 0.83, P < 0.05). Accordingly, the results showed a presence of extracellular arylsulphatase activity of 38.7 mg p-nitrophenol kg− 1 soil h− 1 in the arable soil and of 63.5 mg p-nitrophenol kg− 1 soil h− 1 in the fallow soil. It was concluded that fallowing maintained larger activities of fungi, bacteria and arylsulphatase compared with the arable soil.  相似文献   

5.
To increase wetland acreage and biodiversity, Delaware agencies constructed >220 depressional wetlands. During construction, agencies included amendments thought to increase biodiversity. Because the efficacy of amendments is unknown, we investigated their effects on macroinvertebrate and vegetative communities. We selected 20 standardized wetlands (five contained coarse woody debris (CWD) and microtopography amendments (land surface ridges and furrows), five had neither, five had CWD only, and five had microtopography only). Additionally, 12 wetlands had received organic matter amendments (i.e., straw). Insect richness (P = 0.010; r2 = 0.16), insect biomass (P = 0.023; r2 = 0.13), intolerant insect biomass (P = 0.033, r2 = 0.03), Ephemeroptera biomass (P = 0.027; r2 = 0.12), and Odonata biomass (P = 0.046; r2 = 0.10) increased with CWD volume. Obligate plant percent cover increased with microtopographic variation (P = 0.029; r2 = 0.120). Although organic matter amendments did not increase percent soil organic matter (t13.7 = −1.16, P = 0.264), total (P = 0.027; r2 = 0.12), native (P = 0.036; r2 = 0.11), and facultative (P = 0.001; r2 = 0.24) plant richness increased with percent soil organic matter. To enhance biodiversity, constructed wetlands should contain CWD, but additional research is needed to understand the benefits of microtopography and organic matter amendments.  相似文献   

6.
A wheat seedling rhizobox approach was used to differentiate between the rhizosphere and non-rhizosphere (bulk) soil amended with low and high rates of biochar (20 and 60 t ha−1 vs. control). Nitrate (NO3−) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO3− loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct (P = 0.021), with greater soil-NO3− and biochar-NO3− contents in the high biochar treatment. Biochar addition increased wheat root length ratio (P = 0.053) and lowered root N uptake (P = 0.017), yet plant biomass and N content were similar between treatments. The results indicate localisation of NO3− within the rhizosphere of biochar-amended soils which has implications for NO3− loss and improved nitrogen use efficiency.  相似文献   

7.
Physiological groups of soil microorganisms, total C and N and available nutrients were investigated in four heated (350 °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g−1 soil or 3.0 μg chlorophyll a g−1 soil) with four cyanobacterial strains of the genus Oscillatoria, Nostoc or Scytonema and a mixture of them.Cyanobacterial inoculation promoted the formation of microbiotic crusts which contained a relatively high number of NH4+-producers (7.4×109 g−1 crust), starch-mineralizing microbes (1.7×108 g−1 crust), cellulose-mineralizing microbes (1.4×106 g−1 crust) and NO2− and NO3− producers (6.9×104 and 7.3×103 g−1 crust, respectively). These crusts showed a wide range of C and N contents with an average of 293 g C kg−1 crust and 50 g N kg−1 crust, respectively. In general, Ca was the most abundant available nutrient (804 mg kg−1 crust), followed by Mg (269 mg kg−1 crust), K (173 mg kg−1 crust), Na (164 mg kg−1 crust) and P (129 mg kg−1 crust). There were close positive correlations among all the biotic and abiotic components of the crusts.Biofertilization with cyanobacteria induced great microbial proliferation as well as high increases in organic matter and nutrients in the surface of the heated soils. In general, cellulolytics were increased by four logarithmic units, amylolytics and ammonifiers by three logarithmic units and nitrifiers by more than two logarithmic units. C and N contents rose an average of 275 g C kg−1 soil and 50 g N kg−1 soil while the C:N ratio decreased up to 7 units. Among the available nutrients the highest increase was for Ca (315 mg kg−1 soil) followed by Mg (189 mg kg−1 soil), K (111 mg kg−1 soil), Na (109 mg kg−1 soil) and P (89 mg kg−1 soil). Fluctuations of the microbial groups as well as those of organic matter and nutrients were positively correlated.The efficacy of inoculation depended on both the type of soil and the class of inoculum. The best treatment was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone. In the medium term there were not significant differences between the two inocula amounts tested.These results showed that inoculation of burned soils with alien N2-fixing cyanobacteria may be a biotechnological means of promoting microbiotic crust formation, enhancing C and N cycling microorganisms and increasing organic matter and nutrient contents in heated soils.  相似文献   

8.
Adenylate (i.e. adenosine tri- (ATP), di- (ADP) and monophosphates (AMP)) and microbial biomass C data were collected over a wide range of sites including forest floor layers and forest, grassland and arable soils. Microbial biomass C was measured by fumigation extraction and adenylates after alkaline Na3PO4/DMSO/EDTA extraction and HPLC detection. Our aims were (1) to test whether the sum of adenylates is a better estimate for microbial biomass than the determination of ATP, (2) to compare our conversion values with those proposed by others, and (3) to analyse whether soil properties or land use form affect the relationships between ATP, adenylates and microbial biomass C. A close relationship was found between microbial biomass C and ATP (r=0.96), but also with the sum of adenylates (r=0.96) within all appropriately conditioned soil samples (n=112). In the mineral soil (n=98), the geometric means of the ATP-to-microbial biomass C ratio and the adenylates-to-microbial biomass C ratio were 7.4 and 11.4 μmol g−1, respectively. The mean ratios did not differ significantly between the different texture classes and land use forms. In the forest floor, the ATP-to-microbial biomass C ratio and the adenylates-to-microbial biomass C ratio were both roughly two-thirds of those of the mineral soil. The average adenylate energy charge (AEC) of all soil samples was 0.79 and showed a strong negative relationship with the soil pH (r=−0.69). However, the AEC is presumably only indirectly affected by the soil pH.  相似文献   

9.
As a primary successional stage of biological soil crusts (BSCs), cyanobacterial crusts form firstly in the arid and semiarid areas. At the same time, they suffer many stress conditions, such as drought, salt, etc. In this study, we constructed man-made cyanobacterial crusts with Microcoleus vaginatus Gom. and comparatively studied the effects of drought and salt stresses on the crusts. The results showed that crust growth and photosynthetic activity was significantly inhibited by the stress conditions (P < 0.05), and inhibitory effect increased with the increasing stress intensity and treated time. Compared with salt stress, drought completely stopped crust metabolic activity, so the crust biomass was conserved at a higher level, which meant that drought itself might provide the crusts some protection, especially when the crusts simultaneously suffered drought and salt stresses. That is very important for the survival of crusts in the high-salt areas. In addition, to some extent the crusts could adapt to the stress conditions through metabolic adjustment. In our experiment, we found the accumulation of exopolysaccharides (EPS) increased under stress conditions within a certain threshold.  相似文献   

10.
A study was conducted in a Setaria italica (L.) Beauv. cropland on the Loess Plateau in order to partition total soil respiration (Rt) into microbial respiration (Rm) and root respiration (Rr) and to determine the carbon balance of the cropland ecosystem. A trenching method with micro-pore mesh was used to create root-free soil cores. Differences between mesh and non-mesh treatments were used to determine root respiration. Similar pattern was found in the diurnal variation of Rt and Rm with the minimum values at 3:00-6:00 h and the maximum at 13:00-15:00 h. The diurnal pattern of Rr was completely different, the minimum values appeared at 11:00-13:00 h and the maximum at 0:00-3:00 h. Soil temperature exerted predominant control over the diurnal variations of Rt and Rm. The daily mean values of Rt, Rm and Rr were close to the measurements taken at 9:00 h. On the seasonal scale, Rm was strongly dependent on soil temperature, with higher correlation with 2-cm-depth temperature (r2 = 0.79, P < 0.001) than with 5-cm-depth temperature. When the effects of both soil temperature and moisture were considered, a linear model provided more accurate prediction of Rm (r2 = 0.83, P < 0.0001). Root respiration (Rr) exhibited pronounced daily variation corresponding to changes in photosynthesis and seasonal variation related to crop phenological development. The seasonal variation in Rr was strongly correlated with leaf area index (LAI) (r2 = 0.85, P < 0.05), and also positively, but marginally correlated with root biomass (RB, P = 0.073). Contribution of root respiration to total soil respiration (Rr/Rt ratio) showed pronounced diurnal and seasonal variations. The daily mean values of Rr/Rt ratios were close to the values obtained at 9:00 h. In different phenological stages, Rr/Rt ratios ranged from 22.3% to 86.6%; over the entire growing season, the mean Rr/Rt ratio was 67.3%.Total annual loss of C due to Rm in 2007 was estimated to be 121.3 g C m−2 at the study site, while the annual NPP (net primary production) was 262.1 g C m−2. The cropland system thus showed net carbon input of 140.8 g C m−2.  相似文献   

11.
As saline soils dry, the salt in the remaining solution phase is concentrated and the microbes are subjected to both water and osmotic stress. However, little is known about the interactive effect of matric potential (MP) and osmotic potential (OP) on microbial activity and community structure. We conducted an experiment in which two non-saline soils, a sand and a sandy loam, were pre-incubated at optimal water content (for microbial activity) but different osmotic potentials achieved by adding NaCl. The EC of the saturated paste (ECe) ranged between 1.6 and 11.6 dS m−1 in the sand and between 0.6 and 17.7 dS m−1 in the sandy loam. After the 14-day pre-incubation, the soils were dried to different water contents: 25-35 g kg−1 in the sand and 95-200 g kg−1 in the sandy loam. Water potential (WP, the sum of osmotic + matric potential) ranged from −0.7 to −6.8 MPa in the sand and from −0.1 to −4.4 MPa in the sandy loam. After addition of ground pea straw to increase the concentration of readily available substrate, respiration was measured over 14 days and microbial community composition was assessed by phospholipid fatty acid analysis (PLFA) at the end of the experiment. In both soils, cumulative respiration at a given soil water content (WC) decreased with decreasing osmotic potential, but the effect of decreasing water content differed between the two soils. In the sand, cumulative respiration at the two lowest water contents (WC25 and WC28) was always significantly lower than that at the highest water content (WC35). In the sandy loam, cumulative respiration was significantly lower at the lowest water content (WC95) compared to the highest water content (WC200) only in treatments with added salt. The reduction of cumulative respiration at a given WP was similar in the two soils with a 50% reduction compared to the control (optimal water content, no salt added) at WP −3 MPa. In the sand at WP <−2 MPa, the reduction in fungal fatty acids was greater than that of bacterial fatty acids whereas in the sandy loam, the response of bacteria and fungi to decreasing WP was similar. In both soils, microbial biomass decreased by 35-50% as WP decreased to about −2 MPa but then remained stable with further decreases of WP. Microbial community composition changed with WP in both soils. Our results suggest that there are two strategies by which microbes respond to water potential. A decrease in WP up to −2 MPa kills a proportion of the microbial community, but the remaining microbes adapt and maintain their activity per unit biomass. At lower WP however, the adaptation mechanisms are not sufficient and although the microbes survive, their activity per unit biomass is reduced.  相似文献   

12.
To test the hypothesis that N isotope composition can be used as evidence of excessive compost application, we measured variation in patterns of N concentrations and corresponding δ15N values of plants and soil after compost application. To do so, a pot experiment with Chinese cabbage (Brassica campestris L. cv. Maeryok) was conducted for 42 days. Compost was applied at rates of 0 (SC0), 500 (SC1), 1000 (SC2), and 1500 mg N kg−1 soil (SC3). Plant-N uptake linearly increased with compost application (r2 = 0.956, P < 0.05) with an uptake efficiency of 76 g N kg−1 of compost-N at 42 days after application, while dry-mass accumulation did not show such linear increases. Net N mineralized from compost-N increased linearly (r2 = 0.998, P < 0.01) with a slope of 122 g N kg−1 of compost-N. Plant-δ15N increased curvilinearly with increasing compost application, but this increase was insignificant between SC2 and SC3 treatments. The δ15N of soil inorganic-N (particularly NO3−-N) increased with compost application. We found that plant-δ15N reflected the N isotope signal of soil NO3−-N at each measurement during plant growth, and that δ15N of inner leaves and soil NO3−-N was similar when initial NO3− in the compost was abundant. Therefore, we concluded that δ15N of whole plant (more obviously in newer plant parts) and soil NO3−-N could reveal whether compost application was excessive, suggesting a possible use of δ15N in plants and soil as evidence of excess compost application.  相似文献   

13.
干旱与重吸水对人工藻结皮光合特性的影响   总被引：2，自引：0，他引：2  
吴丽  杨红  兰书斌  张德禄  胡春香 《土壤学报》2015,52(5):1173-1179
通过接种蓝藻构建人工藻结皮促进荒漠地区生物结皮的生长发育以及整个荒漠生态系统的恢复,被认为是一种行之有效的荒漠化控制方法。在构建藻结皮过程中,接种的蓝藻以及形成的藻结皮,经常遭受干旱等环境条件的胁迫。本研究通过室内人工构建藻结皮,对形成的藻结皮进行干旱及重吸水处理,在此过程中监测结皮光合生物量、多糖含量以及结皮光合特性的变化规律。结果发现,干旱处理1d后,结皮蓝藻胞外多糖的分泌明显增加(p0.05);当结皮完全进入干燥状态后,结皮蓝藻停止所有代谢活动,结皮生物量及胞外多糖含量保持在一个相对稳定的水平。在结皮重吸水后,结皮初始荧光Fo能够迅速恢复,并在10 min内达到最大;之后Fo逐渐下降,同时结皮光合活性(Fv/Fm)按照函数y=ax/(b+x)逐渐上升并达到稳定。此外,在不同水分条件下,结皮光合活性随着水分的增加逐渐增加;然而结皮净光合速率(Pn)却随着水分的增加先增加后又下降,呈现单峰变化模式。该研究表明结皮蓝藻的代谢调节在人工藻结皮适应荒漠干旱环境中具有重要的作用,这对于进一步理解蓝藻乃至蓝藻结皮对干旱胁迫的适应,以及荒漠化防治中人工藻结皮的构建、维护、管理具有重要的理论与实践意义。  相似文献   

14.
Phosphomonoesterase (PMEase) activity plays a key role in nutrient cycling and is a potential indicator of soil condition and ecosystem stress. We compared para-nitrophenyl phosphate (pNPP) and 4-methylumbelliferyl phosphate (MUP) as substrate analogues for PMEase in 7 natural ecosystem soils and 8 agricultural top soils with contrasting C contents (8.0-414 g kg−1 C) and pH (3.0-7.5). PMEase activities obtained with pNPP (0.05-5 μmol g−1 h−1) were significantly less than activities obtained with MUP (0.9-13 μmol g−1 h−1), especially in soils with a high organic matter content (>130 g kg−1). Only PMEase activities assayed with MUP correlated significantly with total C and total N (r=0.7, P<0.01 all), and pH (r=−0.71, P<0.01). PMEase activities obtained with the two substrate analogues were correlated when expressed on a C-content basis (r=0.8, P<0.001), but not when expressed on an oven-dry soil weight basis. This indicated that interference by organic matter is related to the quantity rather than to the quality of organic matter. Overall, assaying with MUP was more sensitive compared to assaying with pNPP, particularly in the case of high organic and acid soils.  相似文献   

15.
To understand why anaerobic ombrotrophic peats can be very low in methane after drainage related afforestation, we analyzed the competition of sulfate reducing, humus reducing, and methanogenic microorganisms by incubating ombrotrophic peats of the Mer Bleue bog, Ontario. Sulfate, sulfide, and sulfate containing peat dissolved organic matter (DOM) from an afforested site were added in reduced and oxidized redox state. Sulfate and acetate concentrations were analyzed, bacterial sulfate reduction (BSR) and CO2 and CH4 production quantified, and results analyzed by ANOVA. DOM was characterized by Fourier transformed infrared and fluorescence spectroscopy and analyzed for trace elements. CH4 production (116 nmol cm−3 d−1) and BSR rate (102 nmol cm−3 d−1) were similar in ‘controls’. BSR in treatments ‘sulfate’ (73 nmol cm−3 d−1) and ‘sulfide’ (118 nmol cm−3 d−1) did not significantly differ from ‘controls’ but addition of DOM significantly diminished BSR down to 0.4 nmol cm−3 d−1 (Kruskal Wallis test, p < 0.05). CH4 production decreased with sulfate (16%, not significant) and sulfide addition (40%, p < 0.05) and CO2 production increased (treatment ‘sulfate’, p < 0.05). Addition of all DOM extracts (67 mg L−1) almost completely suppressed methanogenesis and CO2 production (p < 0.05), but acetate accumulated compared to the control (p < 0.05). The DOM applied contained carboxylic, aromatic and phenolic moieties and metal contents typical for peat humic substances. We conclude that a toxic effect of the intensely humified DOM occurred on both methanogenic and sulfate reducing bacteria (SRB) but not on fermenting microorganisms. As yet it is not clear what might cause such a toxic effect of DOM on SRB and archaea.  相似文献   

16.
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17.
Emissions of N2O were measured following addition of 15N-labelled (2.6-4.7 atom% excess 15N) agroforestry residues (Sesbania sesban, mixed Sesbania/Macroptilium atropurpureum, Crotalaria grahamiana and Calliandra calothyrsus) to a Kenyan oxisol at a rate of 100 mg N kg soil−1 under controlled environment conditions. Emissions were increased following addition of residues, with 22.6 mg N m−2 (124.4 mg N m−2 kg biomass−1; 1.1 mg 15N m−2; 1.03% of 15N applied) emitted as N2O over 29 d after addition of both Sesbania and Macroptilium residues in the mixed treatment. Fluxes of N2O were positively correlated with CO2 fluxes, and N2O emissions and available soil N were negatively correlated with residue lignin content (r=−0.49;P<0.05), polyphenol content (r=−0.94;P<0.05), protein binding capacity (r=−0.92;P<0.05) and with (lignin+polyphenol)-to-N ratio (r=−0.55;P<0.05). Lower emission (13.6 mg N m−2 over 29 d; 94.5 mg N m−2 kg biomass−1; 0.6 mg 15N m−2; 0.29% of 15N applied) after addition of Calliandra residue was attributed to the high polyphenol content (7.4%) and high polyphenol protein binding capacity (383 μg BSA mg plant−1) of this residue binding to plant protein and reducing its availability for microbial attack, despite the residue having a N content of 2.9%. Our results indicate that residue chemical composition, or quality, needs to be considered when proposing mitigation strategies to reduce N2O emissions from systems relying on incorporation of plant biomass, e.g. improved-fallow agroforestry systems, and that this consideration should extend beyond the C-to-N ratio of the residue to include polyphenol content and their protein binding capacity.  相似文献   

18.
Reactive forms of nitrogen (Nr) are accumulating at local, regional and global levels largely due to human activities, particularly N-fertilizer production and use as well as fossil fuel combustion. This has resulted in a change in the nitrogen (N) cycle and excess Nr in the environment, which has negative environmental effects. Therefore, characterizing denitrification and the edaphic variables controlling denitrification and its products is the first step in predicting the long-term effects of Nr accumulation. In the present study, six forest soil types in different climatic zones were collected from East China and evaluated for denitrification products following a K15NO3 amendment and subsequent incubation. The results showed that denitrification, indicated by production of nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2), was higher in the studied temperate forest soils than in the studied subtropical and tropical forest soils and was negatively correlated with soil redox potential at the beginning of incubation (r = −0.94, P < 0.01), but not with soil pH. The ratios of NO/total N gas and N2O/total N gas produced during denitrification varied among the soils, and were generally higher in the subtropical and tropical soils. Spearman's correlation analysis showed that the NO ratio was positively correlated with soil oxidation capacity (OXC) (r = 0.94, P < 0.01) and redox potential at the beginning of incubation (r = 0.86, P < 0.05), but negatively correlated with soil pH (r = −0.83, P < 0.05). The N2O ratio was not significantly correlated with these edaphic variables, but showed a significant correlation to NO ratio (r = 0.83, P < 0.05). These results suggested that the OXC value might be the key factor affecting denitrification rates in soils. One possible explanation for these effects is that large OXC values would result in a higher level soil redox potential, thus suppressing denitrification and enhancing NO and N2O ratios during denitrification.  相似文献   

19.
In the state of Tabasco, South-eastern, Mexico, land-use changes such as the conversion of natural into agricultural systems, modify soil quality and the abundance of soil macrofauna, including earthworms. The aim of this study was to characterize by near-infrared spectroscopy (NIRS) the earthworms’ fingerprint in soil, in six sites including natural and agricultural ecosystems with low and high earthworm biomass and low and high earthworm diversity, in order to identify specific wavelengths that discriminate the presence/abundance of earthworm species and functional groups. The spectral region of 1860–1870 nm was significantly correlated with total earthworm density, particularly at one of the sites (Cedar polyculture; r = 0.8, p < 0.05). Earthworm biomass had a specific NIRS wavelength according to the earthworm species and feeding category: 1820 and1860–1870 nm wavelengths were significantly correlated with Polypheretima elongata (r2 = 0.7, p < 0.05; mesohumic species) biomass and 2090 nm for biomass of all Lavellodrilus species (polyhumics). Two species had a much wider spectral range: L. bonampakensis and Dichogaster saliens (an epigeic worm; 1690–2300 nm, r2 = 0.7, p < 0.05). Biomasses of Periscolex brachysistis and Diplotrema murchiei were not significantly correlated with any near infrared wavelength spectra analyzed. Combining a maximum of 4 species per wavelength, mesohumic earthworms had a wider wavelength spectrum than polyhumics. Therefore, earthworm species diversity, biomass and abundance are associated with soil quality (as measured by NIR spectra) and this relationship varies with species and ecological category. Sites with lower and higher earthworm diversity have lower and higher soil organic matter quality, respectively, as observed by the wider or narrower spectral range with which earthworm biomasses are correlated.  相似文献   

20.
《Soil biology & biochemistry》2001,33(7-8):913-919
A reliable and simple technique for estimating soil microbial biomass (SMB) is essential if the role of microbes in many soil processes is to be quantified. Conventional techniques are notoriously time-consuming and unreproducible. A technique was investigated that uses the UV absorbance at 280 nm of 0.5 M K2SO4 extracts of fumigated and unfumigated soils to estimate the concentrations of carbon, nitrogen and phosphorus in the SMB. The procedure is based on the fact that compounds released after chloroform fumigation from lysed microbial cells absorb in the near UV region. Using 29 UK permanent grassland soils, with a wide range of organic matter (2.9–8.0%) and clay contents (22–68%), it was demonstrated that the increase in UV absorbance at 280 nm after soil fumigation was strongly correlated with the SMB C (r=0.92), SMB N (r=0.90) and SMB P (r=0.89), as determined by conventional methods. The soils contained a wide range of SMB C (412–3412 μg g−1 dry soil), N (57–346 μg g−1 dry soil) and P (31–239 μg g−1 dry soil) concentrations. It was thus confirmed that the UV absorbance technique described was a rapid, simple, precise and relatively inexpensive method of estimating soil microbial biomass.  相似文献   

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