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1.
Many previous studies have demonstrated that heterotrophic nitrification processes play an important role in the production of NO3− in acidic soils. However, it is not clear whether a low concentration of nitrogenous organic compounds support heterotrophic nitrification processes in natural soils. In this study, we performed an 15N tracer experiment with a glycine concentration gradient (20, 40, 80, and 160 mg N kg−1) to investigate the effect of the organic nitrogen concentration on the heterotrophic nitrification rate and its relative contribution to the total nitrification of the studied acidic forest soil. This experiment demonstrated that 15N–NO3− accumulated over time with all nitrogen treatments in the presence of acetylene, confirming that heterotrophic nitrification occurred even at a low organic nitrogen concentration (20 mg kg−1) in the studied acidic forest soil. In the presence of acetylene, the 15N–NO3− concentration in the 20 and 40 mg kg−1 glycine-N treatments was significantly lower than in the 80 and 160 mg kg−1 glycine-N treatments (p < 0.05), indicating that a high organic nitrogen concentration stimulated the heterotrophic nitrification rate. There was no significant difference in the average contribution of heterotrophic nitrification to total nitrification among the different nitrogen treatments, suggesting that the organic nitrogen concentration did not affect the relative contribution of heterotrophic nitrification to total nitrification in the studied acidic soil. Our results confirmed that a low concentration of organic N (20 mg kg−1) supported heterotrophic nitrification in the studied soil. The organic nitrogen concentration stimulates the heterotrophic nitrification rate, but does not affect the relative contribution of heterotrophic nitrification to total nitrification in the studied acidic soil.  相似文献   

2.
For bioremediation of copper-contaminated soils, it is essential to understand copper adsorption and chemical forms in soils related to microbes. In this study, a Penicillium strain, which can tolerate high copper concentrations up to 150 mmol l?1 Cu2+, was isolated from a copper mining area. The objective was to study effects of this fungus on copper adsorptions in solutions and chemical forms in soils. Results from lab experiments showed the maximum biosorptions occurred at 360 min with 6.15 and 15.08 mg g?1 biomass from the media with Cu2+ of 50 and 500 mg l?1, respectively. The copper was quickly adsorbed by the fungus within the contact time of the first 60 min. To characterize the adsorption process of copper, four types of kinetics models were used to fit the copper adsorption data vs. time. Among the kinetics models, the two-constant equation gave the best results, as indicated by the high coefficients of determination (R 2?=?0.89) and high significance (p?<?0.01). The addition of the fungal strain to autoclaved soil facilitated increases in concentrations of acid-soluble copper, copper bound to oxides, and of copper bound to organic matter (p?<?0.05). However, the inoculation of Penicillium sp. A1 led to a decrease of water-soluble copper in the soil. The results suggested that Penicillium sp. A1 has the potential for bioremediation of copper-contaminated soils.  相似文献   

3.
《Soil & Tillage Research》2007,92(1-2):186-198
The influence of two organic wastes, cotton gin crushed compost (CC) and beet vinasse (BV) applied for 5 years on a Typic Xerofluvent under dryland conditions near to Sevilla city (Guadalquivir River Valley, Andalusia, Spain) on soil erodibility (K factor of the USLE and RUSLE) and soil loss was studied. CC and BV were applied at rates of 1780, 5340, and 10,680 kg ha−1 (expressed as organic matter content). When CC was applied to the soil, erodibility factor (K) is correlated with soil loss, highlighting a decrease in K and soil loss when increased the dose of CC applied to the soil. In this respect, K decreased 17% in CC-amended soils respect to control soil at the end of the experiment, and soil loss decreased 36% in CC-amended soils respect to control soil at the end of the experiment and for 45 min and 60 mm h−1. However, when BV was applied, soil physical and biological properties decreased. K decreased 6.4% in BV-amended soils respect to control soil at the end of the experiment, and soil loss increased 59.7% in BV-amended soils respect to control soil at the end of the experimental period and for 45 min and 60 mm h−1. We think that this is because the higher level of Na+ (and possibly of fulvic acids) in BV increased the exchangeable sodium percentage (ESP) and reduced structural stability of BV-amended soil, leading to higher soil loss. This explains the relatively higher soil loss in BV-amended soils. These results contradict many previous reports in which soil organic matter prevented soil loss. For this reason, the equation of soil erodibility (K factor of USLE and RUSLE) must have in consideration other aspects such as the chemical composition of the soil organic matter as well as the soil structural stability.  相似文献   

4.
In previous studies, Al extracted by acid ammonium acetate (Ala) or Na-pyrophosphate (Alp), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Ala is a comparable method (as much as CuCl2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Ala, Alp, oxalate (Alo, Sio and Feo), cold NaOH (Aln) and un-buffered salts, CuCl2 (AlCu), LaCl3 (AlLa) and KCl (Alk). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Ala had a good correspondence with Alp (R2 = 0.76) in the top soil with Ala/Alp ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R2 > 0.62). Acid ammonium acetate was as effective as AlCu to determine the Al-OM in allophanic soils. It is cheaper than AlCu and Alp and 0.5 h shaking is required compared to 2 h of AlCu and 16 h of Alp. The efficiency of the extraction was: Aln ≥ Alo > Alp > AlCu ≥ Ala > AlLa > Alk. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R2 = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R2 > 0.60) the largest proportion of variation of soil OC across studied soils.  相似文献   

5.
A 25-week laboratory study was carried out to determine sulfur, carbon, and nitrogen mineralization rates in soil samples obtained from representative soils in France. Their relationship with some of the soil properties was investigated to find a predictor of mineralized S in soils. At 20°C and 80% water-holding capacity, the S mineralization rate ranged from 0.02 to 0.16 mg kg−1 day−1. It was significantly positively related to soil organic C and N and to C and N mineralization rates. It was weakly related to total soil S. The results suggest that the S mineralization is predominantly driven by heterotrophic microbial activity. A predictive equation for S mineralization based on soil C content, soil pH, and clay content is proposed.  相似文献   

6.
To clarify the variation in soil microbial respiration (SMR) in Jiuduansha wetland during different succession stages, the SMR of five typical zones was evaluated. The results showed that the SMR during different successional stages of vegetation varied significantly (P < 0.05), with the SMR of the Spartina alterniflora zone (0.43 mg CO2 g−1 d−1) being the highest. These findings implied that S. alterniflora could enhance the SMR. Based on both the SMR and input of organic matter from plant decomposition, the Phragmites australis community likely possesses a higher organic carbon accumulation capability. In addition, the results of the present study implied that the difference in microbial characteristics among the wetland soils may be the primary reason for their different SMR. Path analysis indicated that the correlation between soil bacterial diversity and SMR was especially strong. Moreover, phylogenetic analysis showed that the bacterial community structure along the successional stages varied. Specifically, microbial species such as Acidobacteria, δ-Proteobacteria and Cytophaga belonging to Bacteroidetes, which have special heterotrophic metabolic capabilities or the ability to degrade cellulose, were the dominant soil bacterial flora in the S. alterniflora zone, which ultimately strengthened the SMR. Different elevations and vegetation types leading to a change in the wetland soil characteristics such as waterlogging time and inorganic nitrogen may be important factors resulting in the differences in soil microbial characteristics of different successional stages in Jiuduansha wetland.  相似文献   

7.
Anaerobic digestion of organic materials generates residues of differing chemical composition compared to undigested animal manures, which may affect the soil microbial ecosystem differently when used as fertilizers. This study investigated the effects of two biogas residues (BR-A and BR-B) and cattle slurry (CS) applied at rates corresponding to 70 kg NH4+-N ha−1 on bacterial community structure and microbial activity in three soils of different texture (a sandy, a clay and an organic clay soil). 16S rRNA genes were targeted in PCR reactions and bacterial community profiles visualized using terminal restriction fragment length polymorphism. General microbial activity was measured as basal respiration (B-resp), substrate-induced respiration (SIR), specific growth rate (μSIR), metabolic quotient (qCO2) and nitrogen mineralization capacity (NMC). Non-metric multidimensional scaling analysis visualized shifts in bacterial community structure related to microbial functions. There were significant differences in bacterial community structure after 120 days of incubation (+20 °C at 70% of WHC) between non-amended (control) and amended soils, especially in the sandy soil, where CS caused a more pronounced shift than biogas residues. Terminal-restriction fragment (TRF) 307, the predominant peak in CS-amended sandy soil, was identified as possibly Bacillus or Streptococcus. TRF 226, the dominant peak in organic soil amended with BR-B, was classified as Rhodopseudomonas. B-resp significantly increased and SIR decreased in all amendments to organic soil compared with the control, potentially indicating decreased efficiency of heterotrophic microorganisms to convert organic carbon into microbial biomass. This was also reflected in an elevated qCO2 in the organic soil. The μSIR level was higher in the sandy soil amended with BR-A than with BR-B or CS, indicating a shift toward species capable of rapidly utilizing glucose. NMC was significantly elevated in the clay and organic soils amended with BR-A and BR-B and in the sandy soil amended with BR-B and CS. Thus, biogas residues and cattle slurry had different effects on the bacterial community structure and microbial activity in the three soils. However, the effects of biogas residues on microbial activities were comparable in magnitude to those of cattle slurry and the bacterial community structure was less affected. Therefore, we do not see any reason not to recommend using biogas residues as fertilizers based on the results presented.  相似文献   

8.
Tree species have significant effects on the availability and dynamics of soil organic matter. In the present study, the pool sizes of soil dissolved organic matter (DOM), potential mineralizable N (PMN) and bio-available carbon (C) (measured as cumulative CO2 evolution over 63 days) were compared in soils under three coniferous species — 73 year old slash (Pinus elliottii), hoop (Araucaria cunninghamii) and kauri (Agathis robusta) pines. Results have shown that dissolved organic N (DON) in hot water extracts was 1.5–1.7 times lower in soils under slash pine than under hoop and kauri pines, while soil dissolved organic C (DOC) in hot water extracts tended to be higher under slash pine than hoop and kauri pines but this was not statistically significant. This has led to the higher DOC:DON ratio in soils under slash pine (32) than under hoop and kauri pines (17). Soil DOC and DON in 2 M KCl extracts were not significantly different among the three tree species. The DOC:DON ratio (hot water extracts) was positively and significantly correlated with soil C:N (R2 = 0.886, P < 0.01) and surface litter C:N ratios (R2 = 0.768, P < 0.01), indicating that DOM was mainly derived from litter materials and soil organic matter through dissolution and decomposition. Soil pH was lower under slash pine (4.5) than under hoop (6.0) and kauri (6.2) pines, and negatively correlated with soil total C, C:N ratio, DOC and DOC:DON ratio (hot water extracts), indicating the soil acidity under slash pine favored the accumulation of soil C. Moreover, the amounts of dissolved inorganic N, PMN and bio-available C were also significantly lower in soils under slash pine than under hoop and kauri pines. It is concluded that changes in the quantity and quality of surface litters and soil pH induced by different tree species largely determined the size and quality of soil DOM, and plantations of hoop and kauri pine trees may be better in maintaining long-term soil N fertility than slash pine plantations.  相似文献   

9.
Organic carbon (OC) is generally low in Alabama (U.S.A.) soils and varies considerably with cropping systems. Information on decomposition rates of the added C is a prerequisite to designing strategies that improve C sequestration in farming systems. Different models including exponential models have been used to describe OC mineralization in soils as well as to describe its potential as CO2 to be released into the environment. We investigated the decomposition of broiler litter added to ten non-calcareous soils (Appling, Troup, Cecil, Decatur, Sucarnoochee, Linker, Hartsells, Dothan, Maytag, and Colbert soils). A non-linear regression approach for N mineralization was used to estimate the potentially mineralizable OC pools (Co) and the first-order rate constant (k) in the soil samples. Results showed that the non-amended soils have distinct differences in their ability to release their native OC as CO2 and can be divided into four groups depending on their potentially mineralizable C (Co) and their ability to protect stable organic matter. Sucarnoochee soil represents the first group and contains a moderate amount of OC (11.4 g C kg−1) but had the highest Co (7.30 g C kg−1 soil). The second distinct group of soils has Co varying between 5.50 and 5.00 g C kg−1 soil (Decatur, Hartsells, Dothan, and Maytag). The third group has Co between 5.00 and 4.00 (Appling, Cecil, and Linker). The fourth group has Co less than 4.00 g C kg−1 soil (Troup and Colbert). Half-life of C remaining in non-amended soils varied from 26 days in Maytag soil to 139 days in Cecil soil. The OC in these non-amended soils represents a very stable form of organic C and thus, not easily decomposed by soil microorganisms. In the broiler litter-amended soils, the Co varied from 3.82 g C kg−1 in Appling soil amended with broiler litter 1-7.04 g C kg−1 soil in Maytag amended with broiler litter 2. Decomposition of the added OC proceeded in two phases with less than 31% decomposed in 43 days. Potentially mineralizable organic C (Co) was related to soil organic C (r = 0.661**) and soil C/N ratio (r = 0.819*).  相似文献   

10.
Getting a better understanding of CO2 efflux from forest soils is critical for increasing our comprehension of the global C cycle. We examined the influence of two common boreal tree species, either in pure stands (BS = black spruce; TA = trembling aspen) or in mixtures (MW = BS + TA mixedwood), on total (RS), heterotrophic (RH) and autotrophic soil respiration (RA) and their relationship with soil temperature and moisture, distance to the nearest tree, labile and total soil organic C (SOC), and root content. Stand-specific soil respiration–temperature models were developed to estimate annual soil CO2 efflux. Soil temperature was the main factor explaining RS and its components, followed by labile and total SOC. These three variables were significantly affected by forest composition, while no difference in soil moisture, distance to the nearest tree and root content was observed between stand types. A reciprocal forest floor transplant experiment showed that the influence of stand types on mineral soil temperature was due to a difference in light penetration rather than forest floor characteristics. Annual RS and RH were significantly greater in MW and TA than in BS, whereas annual RA was greater in BS and MW than in TA. Temperature sensitivity (Q10) of both RS and RH was significantly higher in BS than in MW and TA, suggesting that CO2 efflux from BS soils could be increased more under climate warming than that from the other stand types. Our results show evidence that boreal forest composition affects soil CO2 efflux and that litter quality is not the only factor explaining the differences between stand types. The influence of forest composition on soil CO2 efflux would be mediated through effects on soil temperature as well as on factors affecting the accumulation and the quality of SOC.  相似文献   

11.
The bacterium Wautersia [Ralstonia] basilensis has been shown to enhance the mycorrhizal symbiosis between Suillus granulatus and Pinus thunbergii (Japanese black pine). However, no information is available about this bacterium under field conditions. The objectives of this study were to detect W. basilensis in bulk and mycorhizosphere soils in a Japanese pine plantation in the Tottori Sand Dunes, determine the density of W. basilensis in soil, and determine the optimal cell density of W. basilensis for mycorrhizal formation in pine seedlings. We designed and validated 16S rRNA gene-targeted specific primers for detection and quantification of W. basilensis. SYBR Green I real-time PCR assay was used. A standard curve relating cultured W. basilensis cell density (103-108 cells ml−1) to amplification of DNA showed a strong linear relationship (R = 0.9968). The specificity of the reaction was confirmed by analyzing DNA melting curves and sequencing of the amplicon. The average cell density of W. basilensis was >4.8 × 107 cells g−1 of soil in the mycorrhizosphere and 7.0 × 106 cells g−1 in the bulk soil. We evaluated the W. basilensis cell density required for mycorrhizal formation using an in vitro microcosm with various inoculum densities ranging from 102 to 107 cells g−1 soil (104-109 cells ml−1). Cell densities of W. basilensis of >106 cells g−1 of soil were required to stimulate mycorrhizal formation. In vivo and in vitro experiments showed that W. basilensis was sufficiently abundant to enhance mycorrhizal formation in the mycorrhizosphere of Japanese black pine sampled from the Tottori Sand Dunes.  相似文献   

12.
《Soil & Tillage Research》2007,92(1-2):22-29
Sustainable agricultural use of cultivated desert soils has become a concern in Hexi Corridor in Gansu Province of China, because loss of topsoil in dust storms has been recently intensified. We chose four desert sites to investigate the effects of cultivation (cropping) on (i) soil organic C and its size fractions and (ii) soil aggregate stability (as a measure of soil erodibility). These parameters are of vital importance for evaluating the sustainability of agricultural practices.Total organic C as well as organic C fractions in soil (coarse organic C, 0.1–2 mm; young organic C, 0.05–0.1 mm; stable organic C, <0.05 mm) generally increased with the duration of the cultivation period from 0 (virgin soil, non-cultivated) to more than 30 years (p < 0.05). Compared to total organic C in virgin soils (2.3–3.5 g kg−1 soil), significantly greater values were found after 10 to >20 years of cultivation (6.2–7.1 g kg−1 soil). The increase in organic C in desert soils following prolonged cultivation was mainly the consequence of an increase in the coarse organic C. The increase in total organic C in soil was also dependent on clay content [total organic C = 0.96 + 0.249 clay content (%) + 0.05 cultivation year, R2 = 0.48, n = 27, p < 0.001]. This indicates that clay protected soil organic C from mineralization, and also contributed to the increase in soil organic C as time of cultivation increased.There was a significant positive correlation between aggregate stability and total organic C across all field sites. The water stability of aggregates was low (with water-stable aggregate percentage ∼4% of dry-sieved aggregates of size 1–5 mm). There was no consistent pattern of increase in the soil aggregate stability with time of cultivation at different locations, suggesting that desert soils might remain prone to wind erosion even after 50 years of cultivation. Alternative management options, such as retaining harvested crop residues on soil surface and excluding or minimizing tillage, may permit sustainable agricultural use of desert soils.  相似文献   

13.
Summary Topsoils (0–75 mm) from four soil types with different sulphate retention capacities were collected from stock camp and non-camp (main grazing area) sites of grazed pastures in New Zealand which had been annually fertilized with superphosphate for more than 15 years. These soils were analysed for different S fractions and incubated at 30°C for 10 weeks using an open incubation technique in order to assess the extent of S mineralization and the release of soluble soil organic S from camp and non-camp soils during incubation. The soils were preleached with 0.01 M KCl, followed by 0.04 M Ca(H2PO4)2 before being incubated. Pre-incubation leachates and weekly 0.01 M KCl leachates were analysed for mineralized S (i.e., hydriodic acid-reducible S) and total S. Soluble organic S was estimated as the difference between these two S fractions. Results obtained show higher cumulative amounts of all three S fractions in leachates over a 10-week incubation period in camp than in non-camp soils, suggesting that higher mineralization occurred in camp soils. Cumulative amounts of mineralized S from camp and non-camp soils showed a linear relationship with duration of incubation (R 20.985***), while the cumulative release of soluble organic S followed a quadratic relationship (R 20.975***). A significant proportion (14.6%–40.8%) of total S release in KCl leachates was soluble organic S, indcating that organic S should be taken into account when assessing S mineralization. Mineralized S and soluble organic S were best correlated with 0.01 M CaCl2-extractable soil inorganic S (R 2=0.767***) and 0.04 M Ca(H2PO4)2-extractable soil inorganic S(R 2=0.823***), respectively. Soil sulphate retention capacity was found to influence amounts of mineralized S and soluble organic S, and thus periodic leaching with KCl to remove mineralized S from soils may not adequately reflect the extent of soil S mineralization in high sulphate-retentive soils. In low (<10%) sulphateretentive soils, increasing the superphosphate applications from 188 to 376 kg ha–1 year–1 increased S mineralization but not amounts of C-bonded and hydriodic acid-reducible soil S fractions.  相似文献   

14.
《Applied soil ecology》2005,28(2):125-137
Microbial properties such as microbial biomass carbon (MBC), arylsulfatase, β-glucosidase and dehydrogenase activities, and microbial heterotrophic potential, together with several chemical properties such as pH, CaCl2 soluble heavy metal concentrations, total organic carbon and hydrosoluble carbon were measured to evaluate changes in soil quality, after “in situ” remediation of a heavy metal-contaminated soil from the Aznalcóllar mine accident (Southern Spain, 1998). The experiment was carried out using containers, filled with soil from the affected area. Four organic amendments (a municipal waste compost, a biosolid compost, a leonardite and a litter) and an inorganic amendment (sugarbeet lime) were mixed with the top soil at the rate of 100 Mg ha−1. Unamended soil was used as control. Agrostis stolonifera L. was sown in the containers. The soil was sampled twice: one month and six months after amendment application. In general, these amendments improved the soil chemical properties: soil pH, total organic carbon and hydrosoluble carbon increased in the amended soils, while soluble heavy metal concentrations diminished. At the same time, higher MBC, enzyme activities and maximum rate of glucose mineralization values were found in the organically amended soils. Plant cover was also important in restoring the soil chemical and microbial properties in all the soils, but mainly in those that were not amended organically. As a rule, remediation measures improved soil quality in the contaminated soils.  相似文献   

15.
Net carbon dioxide (CO2) emission from soils is controlled by the input rate of organic material and the rate of decomposition which in turn are affected by temperature, moisture and soil factors. While the relationships between CO2 emission and soil factors are well-studied in non-salt-affected soils, little is known about soil properties controlling CO2 emission from salt-affected soils. To close this knowledge gap, non-salt-affected and salt-affected soils (0-0.30 m) were collected from two agricultural regions: in India (irrigation induced salinity) and in Australia (salinity associated with ground water or non-ground water associated salinity). A subset (50 Indian and 70 Australian soils) covering the range of electrical conductivity (EC) and sodium adsorption ratio (SAR) in each region was used in a laboratory incubation experiment. The soils were left unamended or amended with mature wheat residues (2% w/w) and CO2 release was measured over 120 days at constant temperature and soil water content. Residues were added to overcome carbon limitation for soil respiration. For the unamended soils, separation in multidimensional scaling plots was a function of differences in soil texture (clay, sand), SOC pools (particulate organic carbon (POC) and humus-C) and also EC. Cumulative CO2-C emission from unamended and amended soils was related to soil properties by stepwise regression models. Cumulative CO2-C emission was negatively correlated with EC in saline soils (R2 = 0.50, p < 0.05) from both regions. In the unamended non-salt-affected soils, cumulative CO2-C emission was significantly positively related to the content of POC for the Indian soils and negatively related to clay content for the Australian soils. In the wheat residue amended soils, cumulative CO2-C emission had positive relationship with POC and humus-C but a negative correlation with EC for both Indian and Australian soils. SAR was negatively related (β = −0.66, p < 0.05) with cumulative CO2-C emission only for the unamended saline-sodic soils of Australia. Cumulative CO2-C emission was significantly negatively correlated with bulk density in amended soils from both regions. The study showed that in salt-affected soils, EC was the main factor influencing for soil respiration but the content of POC, humus-C and clay were also influential with the magnitude of influence depending on whether the soils were salt affected or not.  相似文献   

16.
Relationships between soil pH and microbial properties in a UK arable soil   总被引：1，自引：0，他引：1  
Effects of changing pH along a natural continuous gradient of a UK silty-loam soil were investigated. The site was a 200 m soil transect of the Hoosfield acid strip (Rothamsted Research, UK) which has grown continuous barley for more than 100 years. This experiment provides a remarkably uniform soil pH gradient, ranging from about pH 8.3 to 3.7. Soil total and organic C and the ratio: (soil organic C)/(soil total N) decreased due to decreasing plant C inputs as the soil pH declined. As expected, the CaCO3 concentration was greatest at very high pH values (pH > 7.5). In contrast, extractable Al concentrations increased linearly (R2 = 0.94, p < 0.001) from below about pH 5.4, while extractable Mn concentrations were largest at pH 4.4 and decreased at lower pHs. Biomass C and biomass ninhydrin-N were greatest above pH 7. There were statistically significant relationships between soil pH and biomass C (R2 = 0.80, p < 0.001), biomass ninhydrin-N (R2 = 0.90, p < 0.001), organic C (R2 = 0.83, p < 0.001) and total N (R2 = 0.83, p < 0.001), confirming the importance of soil organic matter and pH in stimulating microbial biomass growth. Soil CO2 evolution increased as pH increased (R2 = 0.97, p < 0.001). In contrast, the respiratory quotient (qCO2) had the greatest values at either end of the pH range. This is almost certainly a response to stress caused by the low p. At the highest pH, both abiotic (from CaCO3) and biotic Co2 will be involved so the effects of high pH on biomass activity are confounded. Microbial biomass and microbial activity tended to stabilise at pH values between about 5 and 7 because the differences in organic C, total N and Al concentrations within this pH range were small. This work has established clear relationships between microbial biomass and microbial activity over an extremely wide soil pH range and within a single soil type. In contrast, most other studies have used soils of both different pH and soil type to make similar comparisons. In the latter case, the effects of soil pH on microbial properties are confounded with effects of different soil types, vegetation cover and local climatic conditions.  相似文献   

17.
Partitioning the soil surface CO2 flux (RS) flux is an important step in understanding ecosystem-level carbon cycling, given that RS is poorly constrained and its source components may have different sensitivities to climate change. Trenched plots are an inexpensive but labor-intensive method of separating the RS flux into its root (autotrophic) and soil (heterotrophic) components. This study tested if various methods of plant suppression in trenched plots affected RS fluxes, quantified the RS response to soil temperature and moisture changes, and estimated the heterotrophic contribution to RS. It was performed in a boreal black spruce (Picea mariana) plantation, using a randomized complete block design, during the 2007 and 2008 growing seasons. Trenched plots had significantly lower RS than control plots, with differences appearing ∼100 days after trenching; spatial variability doubled immediately after trenching but then declined throughout the experiment. Most trenching treatments had significantly lower (by ∼0.5 μmol CO2 m−2 s−1) RS than the controls, and there was no significant difference in RS among the various trenching treatments. Soil temperature at 2 cm explained more RS variability than did 10-cm temperature or soil moisture. Temperature sensitivity (Q10) declined in the control plots from ∼2.6 (at 5 °C) to ∼1.6 (at 15 °C); trenched plots values were higher, from 3.1 at 5 °C to 1.9 at 15 °C. We estimated RS for the study period to be 241 ± 40 g C m−2, with live roots contributing 64% of RS after accounting for fine root decay, and 293 g C m−2 for the entire year. These findings suggest that laborious hand weeding of trenched plot vegetation may be replaced by other methods, facilitating future studies of this large and poorly-understood carbon flux.  相似文献   

18.
We studied a semi-natural forest in Northern Italy that was set aside more than 50 years ago, in order to better understand the soil carbon cycle and in particular the partitioning of soil respiration between autotrophic and heterotrophic respiration. Here we report on soil organic carbon, root density, and estimates of annual fluxes of soil CO2 as measured with a mobile chamber system at 16 permanent collars about monthly during the course of a year. We partitioned between autotrophic and heterotrophic respiration by the indirect regression method, which enabled us to obtain the seasonal pattern of single components.The soil pool of organic carbon, with 15.8 (±4.5) kg m?2, was very high over the entire depth of 45 cm. The annual respiration rates ranged from 0.6 to 6.9 μmol CO2 m?2 s?1 with an average value of 3.4 (±2.3) μmol CO2 m?2 s?1, and a cumulative flux of 1.1 kg C m?2 yr?1. The heterotrophic component accounted for 66% of annual CO2 efflux. Soil temperature largely controlled the heterotrophic respiration (R2 = 0.93), while the autotrophic component followed irradiation, pointing to the role of photosynthesis in modulating the annual course of soil respiration.Most studies on soil respiration partitioning indicate autotrophic root respiration as a first control of the spatial variability of the overall respiration, which originates mainly from the uppermost soil layers. Instead, in our forest the spatial variability of soil respiration was mainly linked to soil carbon, and deeper layers seemed to provide a significant contribution to soil respiration, a feature that may be typical for an undisturbed, naturally maturing ecosystem with well developed pedobiological processes and high carbon stocks.  相似文献   

19.
The intensive conversion from woodland to tea plantation in subtropical China might significantly change the potential supply processes and cycling of inorganic Nitrogen (N). However, few studies have been conducted to investigate the internal N transformations involved in the production and consumption of inorganic N and N2O emissions in subtropical soils under tea plantations. In a 15N tracing experiment, nine tea fields with different plantation ages (1-y, 5-y and 30-y) and three adjacent woodlands were sampled to investigate changes in soil gross N transformation rates in humid subtropical China. Conversion of woodland to tea plantation significantly altered soil gross N transformation rates. The mineralization rate (MNorg) was much lower in soils under tea plantation (0.53–0.75 mg N kg−1 d−1) than in soil sampled from woodland (1.71 mg N kg−1 d−1), while the biological inorganic N supply (INS), defined as the sum of organic N mineralized into NH4+ (MNorg) and heterotrophic nitrification (ONrec), was not significantly different between soils under woodland and tea plantation, apart from soil under 30-y tea plantation which had the largest INS. Interestingly, the contribution of ONrec to INS increased from 19.6% in soil under woodland to 65.0–82.4% in tea-planted soils, suggesting ONrec is the dominant process producing inorganic N in tea-planted soils. Meanwhile, the conversion from woodland to tea plantation destroyed soil NO3− retention by increasing ONrec, autotrophic nitrification (ONH4) and abiotic release of stored NO3− while decreasing microbial NO3− immobilization (INO3), resulting in greater NO3− production in soil. In addition, long-term tea plantation significantly enhanced the potential release of N2O. Soil C/N was positively correlated with MNorg and INO3, suggesting that an increase in soil C/N from added organic materials (e.g. rice hull) is likely to reduce the increased production of NO3− in the soils under tea plantation.  相似文献   

20.
This study characterizes the effects of water–soil flooding volume ratio and flooding time on copper (Cu) desorption and toxicity following multiple floodings of field-collected soils from agricultural sites acquired under the Comprehensive Everglades Restoration Plan (CERP) in south Florida. Soils from four field sites were flooded with three water–soil ratios (2, 4, and 6 [water] to 1 [soil]) and held for 14 days to characterize the effects of volume ratio and flooding duration on Cu desorption (volume ratio and flooding duration study). Desorption of Cu was also characterized by flooding soils four times from seven field sites with a volume ratio of 2 (water) to 1 (soil) (multiple flooding study). Acute toxicity tests were also conducted using overlying waters from the first flooding event to characterize the effects of Cu on the survival of fathead minnows (Pimephales promelas), cladocerans (Daphnia magna), amphipods (Hyalella azteca), midges (Chironomus tentans), duckweed (Lemna minor), and Florida apple snails (Pomacea paludosa). Acute tests were also conducted with D. magna exposed to overlying water from the second and third flooding events. Results indicate that dissolved Cu concentrations in overlying water increased with flooding duration and decreased with volume ratio. In the multiple flooding study, initial Cu concentrations in soils ranged from 5 to 223 mg/kg (dw) and were similar to Cu concentration after four flooding events, indicating retention of Cu in soils. Copper desorption was dependent on soil Cu content and soil characteristics. Total Cu concentration in overlying water (Cuw) was a function of dissolved organic carbon (DOC), alkalinity, and soil Cu concentration (Cus): log(Cuw)?=?1.2909?+?0.0279 (DOC)?+?0.0026 (Cus)???0.0038 (alkalinity). The model was validated and highly predictive. Most of the desorbed Cu in the water column complexed with organic matter in the soils and accounted for 99% of the total dissolved Cu. Although total dissolved Cu concentrations in overlying water did not significantly decrease with number of flooding events, concentrations of free Cu2+ increased with the number of flooding events, due to a decrease in DOC concentrations. The fraction of bioavailable Cu species (Cu2+, CuOH+, CuCO3) was also less than 1% of the total Cu. Overlying water from the first flooding event was only acutely toxic to the Florida apple snail from one site. However, overlying water from the third flooding of six out of seven soils was acutely toxic to D. magna. The decrease in DOC concentrations and increase in bioavailable Cu2+ species may explain the changes in acute toxicity to D. magna. Results of this study reveal potential for high Cu bioavailability (Cu2+) and toxicity to aquatic biota overtime in inundated agricultural lands acquired under the CERP.  相似文献   

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