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1.
We examined effects of wetting and then progressive drying on nitrogen (N) mineralization rates and microbial community composition, biomass and activity of soils from spinifex (Triodia R. Br.) grasslands of the semi-arid Pilbara region of northern Australia. We compared soils under and between spinifex hummocks and also examined impacts of fire history on soils over a 28 d laboratory incubation. Soil water potentials were initially adjusted to −100 kPa and monitored as soils dried. We estimated N mineralization by measuring changes in amounts of nitrate (NO3−-N) and ammonium (NH4+-N) over time and with change in soil water potential. Microbial activity was assessed by amounts of CO2 respired. Phospholipid fatty acid (PLFA) analyses were used to characterize shifts in microbial community composition during soil drying. Net N mineralized under hummocks was twice that of open spaces between hummocks and mineralization rates followed first-order kinetics. An initial N mineralization flush following re-wetting accounted for more than 90% of the total amount of N mineralized during the incubation. Initial microbial biomass under hummocks was twice that of open areas between hummocks, but after 28 d microbial biomass was<2 μ g−1 ninhydrin N regardless of position. Respiration of CO2 from soils under hummocks was more than double that of soils from between hummocks. N mineralization, microbial biomass and microbial activity were negligible once soils had dried to −1000 kPa. Microbial community composition was also significantly different between 0 and 28 d of the incubation but was not influenced by burning treatment or position. Regression analysis showed that soil water potential, microbial biomass N, NO3−-N, % C and δ15N all explained significant proportions of the variance in microbial community composition when modelled individually. However, sequential multiple regression analysis determined only microbial biomass was significant in explaining variance of microbial community compositions. Nitrogen mineralization rates and microbial biomass did not differ between burned and unburned sites suggesting that any effects of fire are mostly short-lived. We conclude that the highly labile nature of much of soil organic N in these semi-arid grasslands provides a ready substrate for N mineralization. However, process rates are likely to be primarily limited by the amount of substrate available as well as water availability and less so by substrate quality or microbial community composition. 相似文献
2.
Forests naturally maintained by stand-replacing wildfires are often managed with clearcut harvesting, yet we know little about how replacing wildfire with clearcutting affects soil processes and properties. We compared the initial recovery of carbon (C) and nitrogen (N) pools and dynamics following disturbance in jack pine (Pinus banksiana) stands in northern Lower Michigan, USA, by sampling soils (Oa+A horizons) from three “treatments”: 3-6-year-old harvest-regenerated stands, 3-6-year-old wildfire-regenerated stands and 40-55-year-old intact, mature stands (n=4 stands per treatment). We measured total C and N; microbial biomass and potentially mineralizable C and N; net nitrification; and gross rates of N mineralization and nitrification. Burned stands exhibited reduced soil N but not C, whereas clearcut and mature stands had similar quantities of soil organic matter. Both disturbance types reduced microbial biomass C compared to mature stands; however, microbial biomass N was reduced in burned stands but not in clearcut stands. The experimental C and N mineralization values were fit to a first-order rate equation to estimate potentially mineralizable pool size (C0 and N0) and rate parameters. Values for C0 in burned and clearcut stands were approximately half that of the mature treatment, with no difference between disturbance types. In contrast, N0 was lowest in the wildfire stands (170.2 μg N g−1), intermediate in the clearcuts (215.4 μg N g−1) and highest in the mature stands (244.6 μg N g−1). The most pronounced difference between disturbance types was for net nitrification. These data were fit to a sigmoidal growth equation to estimate potential NO3− accumulation (Nitmax) and kinetic parameters. Values of Nitmax in clearcut soils exceeded that of wildfire and mature soils (149.2 vs. 83.5 vs. 96.5 μg NO3−-N g−1, respectively). Moreover, the clearcut treatment exhibited no lag period for net NO3− production, whereas the burned and mature treatments exhibited an approximate 8-week lag period before producing appreciable quantities of NO3−. There were no differences between disturbances in gross rates of mineralization or nitrification; rather, lower NO3− immobilization rates in the clearcut soils, 0.20 μg NO3− g−1 d−1 compared to 0.65 in the burned soils, explained the difference in net nitrification. Because the mobility of NO3− and NH4+ differs markedly in soil, our results suggest that differences in nitrification between wildfire and clearcutting could have important consequences for plant nutrition and leaching losses following disturbance. 相似文献
3.
To evaluate the pathways and dynamics of inorganic nitrogen (N) deposition in previously N-limited ecosystems, field additions of 15N tracers were conducted in two mountain ecosystems, a forest dominated by Norway spruce (Picea abies) and a nearby meadow, at the Alptal research site in central Switzerland. This site is moderately impacted by N from agricultural and combustion sources, with a bulk atmospheric deposition of 12 kg N ha−1 y−1 equally divided between NH4+ and NO3−. Pulses of 15NH4+ and 15NO3− were applied separately as tracers on plots of 2.25 m2. Several ecosystem pools were sampled at short to longer-term intervals (from a few hours to 1 year), above and belowground biomass (excluding trees), litter layer, soil LF horizon (approx. 5-0 cm), A horizon (approx. 0-5 cm) and gleyic B horizon (5-20 cm). Furthermore, extractable inorganic N, and microbial N pools were analysed in the LF and A horizons. Tracer recovery patterns were quite similar in both ecosystems, with most of the tracer retained in the soil pool. At the short-term (up to 1 week), up to 16% of both tracers remained extractable or entered the microbial biomass. However, up to 30% of the added 15NO3− was immobilised just after 1 h, and probably chemically bound to soil organic matter. 16% of the NH4+ tracer was also immobilised within hours, but it is not clear how much was bound to soil organic matter or fixed between layers of illite-type clay. While the extractable and microbial pools lost 15N over time, a long-term increase in 15N was measured in the roots. Otherwise, differences in recovery a few hours after labelling and 1 year later were surprisingly small. Overall, more NO3− tracer than NH4+ tracer was recovered in the soil. This was due to a strong aboveground uptake of the deposited NH4+ by the ground vegetation, especially by mosses. 相似文献
4.
Activated carbon amendments to soil alters nitrification rates in Scots pine forests 总被引：3，自引：0，他引：3
The influence of charcoal on biotic processes in soils remains poorly understood. Charcoal is a natural product of wildfires that burned on a historic return interval of ∼100 years in Scots pine (Pinus sylvestris L.) forests of northern Sweden. Fire suppression and changes in forest stand management have resulted in a lack of charcoal production in these ecosystems. It is thought that charcoal may alter N mineralization and nitrification rates, however, previous studies have not been conclusive. Replicated field studies were conducted at three late-succession field sites in northern Sweden and supporting laboratory incubations were conducted using soil humus collected from these sites. We used activated carbon (AC), as a surrogate for natural-occurring fire-produced charcoal. Two rates of AC (0 and 2000 kg ha−1), and glycine (0 and 100 kg N as glycine ha−1) were applied in factorial combination to field microplots in a randomized complete block pattern. Net nitrification, N mineralization, and free phenol concentrations were measured using ionic and non-ionic resin capsules, respectively. These same treatments and also two rates of birch leaf litter (0 and 1000 kg ha−1) were applied in a laboratory incubation and soils from this incubation were extracted with KCl and analyzed for NH4+ and NO3−. Nitrification rates increased with AC amendments in laboratory incubations, but this was not supported by field studies. Ammonification rates, as measured by NH4+ accumulation on ionic resins, were increased considerably by glycine applications, but some NH4+ was apparently lost to surface sorption to the AC. Phenolic accumulation on non-ionic resin capsules was significantly reduced by AC amendments. We conclude that charcoal exhibits important characteristics that affect regulating steps in the transformation and cycling of N. 相似文献
5.
Enchytraeids are involved both directly and indirectly in decomposition processes and nitrogen mineralization in soil. Their influence is especially important in nitrogen poor ecosystems such as heathland where the enchytraeid species, Cognettia sphagnetorum, is often abundant and playing a significant role in the N-cycling. The objective of this study was to quantify NH4+-N excretion of C. sphagnetorum at different temperatures. The results were combined with investigations of population dynamics during one year to estimate annual NH4+-N excretion of the population of C. sphagnetorum in a dry Danish heath soil. C. sphagnetorum significantly increased its NH4+-N excretion rate with increasing temperature. At 5 °C about 0.5 μg NH4+-N mg dry weight−1 day−1 was excreted increasing to about 3.3 μg NH4+-N mg dry weight−1 day−1 at 20 °C. Average enchytraeid biomass in the field was 2.5-3.5 g dry weight m−2 during cool and wet periods. Dry and warm conditions in May and June, 2008, had a drastic and long-term negative impact on the enchytraeid community. The excretion of NH4+-N by enchytraeids was therefore highest during the cool and moist months despite low temperatures (October 2007-May 2008) and amounted to about 2 mg NH4+-N m−2 day−1 during this period. The estimated annual NH4+-N excretion of the enchytraeid community was approximately 0.3 g N m−2 year−1. The results of the present study and the method described for estimation of N-excretion can increase our understanding of enchytraeids’ role in nitrogen mineralization. 相似文献
6.
Elevated enzyme activities in soils under the invasive nitrogen-fixing tree Falcataria moluccana 总被引：1，自引：0，他引：1
Like other N-fixing invasive species in Hawaii, Falcataria moluccana dramatically alters forest structure, litterfall quality and quantity, and nutrient dynamics. We hypothesized that these biogeochemical changes would also affect the soil microbial community and the extracellular enzymes responsible for carbon and nutrient mineralization. Across three sites differing in substrate texture and age (50-300 years old), we measured soil enzyme activities and microbial community parameters in native-dominated and Falcataria-invaded plots. Falcataria invasion increased acid phosphatase (AP) activities to >90 μmol g−1 soil h−1 compared to 30-60 μmol g−1 soil h−1 in native-dominated stands. Extracellular enzymes that mineralize carbon and nitrogen also increased significantly under Falcataria on the younger substrates. By contrast, total microbial biomass and mycorrhizal abundance changed little with invasion or substrate. However, fungal:bacterial ratios declined dramatically with invasion, from 2.69 and 1.35 to <0.89 on the 50- and 200-year-old substrates, respectively. These results suggest that Falcataria invasion alters the composition and function of belowground soil communities in addition to forest structure and biogeochemistry. The increased activities of AP and other enzymes that we observed are consistent with a shift toward phosphorus limitation and rapid microbial processing of litterfall C and N following Falcataria invasion. 相似文献
7.
Christoph Müller Ronald J. Laughlin Catherine J. Watson 《Soil biology & biochemistry》2011,43(6):1362-1371
The effects of repeated synthetic fertilizer or cattle slurry applications at annual rates of 50, 100 or 200 m3 ha−1 yr−1 over a 38 year period were investigated with respect to herbage yield, N uptake and gross soil N dynamics at a permanent grassland site. While synthetic fertilizer had a sustained and constant effect on herbage yield and N uptake, increasing cattle slurry application rates increased the herbage yield and N uptake linearly over the entire observation period. Cattle slurry applications, two and four times the recommended rate (50 m3 ha−1 yr−1, 170 kg N ha−1), increased N uptake by 46 and 78%, respectively after 38 years. To explain the long-term effect, a 15N tracing study was carried out to identify the potential change in N dynamics under the various treatments. The analysis model evaluated process-specific rates, such as mineralization, from two organic-N pools, as well as nitrification from NH4+ and organic-N oxidation. Total mineralization was similar in all treatments. However, while in an unfertilized control treatment more than 90% of NH4+ production was related to mineralization of recalcitrant organic-N, a shift occurred toward a predominance of mineralization from labile organic-N in the cattle slurry treatments and this proportion increased with the increase in slurry application rate. Furthermore, the oxidation of recalcitrant organic-N shifted from a predominant NH4+ production in the control treatment, toward a predominant NO3− production (heterotrophic nitrification) in the cattle slurry treatments. The concomitant increase in heterotrophic nitrification and NH4+ oxidation with increasing cattle slurry application rate was mainly responsible for the increase in net NO3− production rate. Thus the increase in N uptake and herbage yield on the cattle slurry treatments could be related to NO3− rather than NH4+ production. The 15N tracing study was successful in revealing process-specific changes in the N cycle in relationship to long-term repeated amendments. 相似文献
8.
An incubation experiment was conducted to study the response to sodium chloride (NaCl) salinity of microbial population immobilizing NH4+- and NO3−-N using glucose as an easily oxidizable C source. Immobilization of NH4+-N was faster than that of NO3−-N and was complete within 12 h of -incubation. Presence of NaCl retarded the process of N immobilization; that of NO3−-N being more affected. Remineralization of immobilized N started within 48 h in case of both NH4+- and NO3−-N and was faster for the latter. Both remineralization and nitrification were significantly delayed in the presence of NaCl; inhibition being more at 4000 mg NaCl kg−1 soil. The inhibitory effect of NaCl on remineralization of N was relatively more for NH4+-treated soil. The results of the study suggested a higher sensitivity to NaCl of microorganisms assimilating NO3−. However, remineralization of N from NO3−-assimilating microbial population was less affected by NaCl salinity compared to NH4+-assimilating population. 相似文献
9.
Woo-Jung ChoiHee-Myong Ro 《Soil biology & biochemistry》2003,35(3):483-486
Temporal variations in δ15N of NH4+ and NO3− in water-saturated and unsaturated soils were examined in a laboratory incubation study. Ammonium sulfate (δ15N=−2.6‰) was added to 25 g samples of soil at concentrations of 160 mg N kg−1. Soils were then incubated under unsaturated (50% of water holding capacity at saturation, WHC) or saturated (100% of WHC) water conditions for 7 and 36 d, respectively. During 7 d incubation of unsaturated soil, the NH4+-N concentration decreased from 164.8 to 34.4 mg kg−1, and the δ15N of NH4+ increased from −0.4 to +57.2‰ through nitrification, as evidenced by corresponding increase in NO3−-N concentration and lower δ15N of NO3− (product) than that of NH4+ (substrate) at each sampling time. In saturated soil, the concentration of NH4+-N decreased gradually from 162.4 to 24.2 mg kg−1, and the δ15N values increased from +0.8 to +21.0‰ during 36 d incubation. However, increase in NO3− concentration was not observed due to loss of NO3− through concurrent denitrification in anaerobic sites. The apparent isotopic fractionation factors (αs/p) associated with decrease in NH4+ concentration were 1.04 and 1.01 in unsaturated and saturated soils, respectively. Since nitrification is likely to introduce greater isotope fractionation than microbial immobilization, the higher value for unsaturated soil probably reflected faster nitrification under aerobic conditions. The lower value for saturated soil suggests that immobilization and subsequent remineralization of NH4+ were relatively more dominant than nitrification under the anaerobic conditions. 相似文献
10.
Argyro Zerva 《Soil biology & biochemistry》2005,37(11):2025-2036
We examined the effects of forest clearfelling on the fluxes of soil CO2, CH4, and N2O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO2, CH4, N2O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO2 efflux, with an average efflux rate of 4.0 g m−2 d−1 in the mature stand (40-year) and 2.7 g m−2 d−1 in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m−2 d−1) for CH4 to a net source (2.01 mg m−2 d−1). For the same period, soil N2O fluxes averaged 0.57 mg m−2 d−1 in the CF and 0.23 mg m−2 d−1 in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO2 remained the dominant greenhouse gas in terms of its greenhouse warming potential. 相似文献
11.
Emission of N2O and CH4 oxidation rates were measured from soils of contrasting (30-75%) water-filled pore space (WFPS). Oxidation rates of 13C-CH4 were determined after application of 10 μl 13C-CH4 l−1 (10 at. % excess 13C) to soil headspace and comparisons made with estimates from changes in net CH4 emission in these treatments and under ambient CH4 where no 13C-CH4 had been applied. We found a significant effect of soil WFPS on 13C-CH4 oxidation rates and evidence for oxidation of 2.2 μg 13C-CH4 d−1 occurring in the 75% WFPS soil, which may have been either aerobic oxidation occurring in aerobic microsites in this soil or anaerobic CH4 oxidation. The lowest 13C-CH4 oxidation rate was measured in the 30% WFPS soil and was attributed to inhibition of methanotroph activity in this dry soil. However, oxidation was lowest in the wetter soils when estimated from changes in concentration of 12+13C-CH4. Thus, both methanogenesis and CH4 oxidation may have been occurring simultaneously in these wet soils, indicating the advantage of using a stable isotope approach to determine oxidation rates. Application of 13C-CH4 at 10 μl 13C-CH4 l−1 resulted in more rapid oxidation than under ambient CH4 conditions, suggesting CH4 oxidation in this soil was substrate limited, particularly in the wetter soils. Application of and (80 mg N kg soil−1; 9.9 at.% excess 15N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N2O emissions. The highest N2O emission (119 μg 14+15N-N2O kg soil−1 over 72 h) was measured from the 75% WFPS soil and was mostly produced during denitrification (18.1 μg 15N-N2O kg soil−1; 90% of 15N-N2O from this treatment). Strong negative correlations between 14+15N-N2O emissions, denitrified 15N-N2O emissions and 13C-CH4 concentrations (r=−0.93 to −0.95, N2O; r=−0.87 to −0.95, denitrified 15N-N2O; P<0.05) suggest a close relationship between CH4 oxidation and denitrification in our soil, the nature of which requires further investigation. 相似文献
12.
Impact of land-use types on soil nitrogen net mineralization in the sandstorm and water source area of Beijing,China 总被引：1，自引：0，他引：1
Changes of land-use type (LUT) can affect soil nutrient pools and cycling processes that relate long-term sustainability of ecosystem, and can also affect atmospheric CO2 concentrations and global warming through soil respiration. We conducted a comparative study to determine NH4+ and NO3− concentrations in soil profiles (0–200 cm) and examined the net nitrogen (N) mineralization and net nitrification in soil surface (0–20 cm) of adjacent naturally regenerated secondary forests (NSF), man-made forests (MMF), grasslands and cropland soils from the windy arid and semi-arid Hebei plateau, the sandstorm and water source area of Beijing, China. Cropland and grassland soils showed significantly higher inorganic N concentrations than forest soils. NO3−-N accounted for 50–90% of inorganic N in cropland and grassland soils, while NH4+-N was the main form of inorganic N in NSF and MMF soils. Average net N-mineralization rates (mg kg−1 d−1) were much higher in native ecosystems (1.51 for NSF soils and 1.24 for grassland soils) than in human disturbed LUT (0.15 for cropland soils and 0.85 for MMF soils). Net ammonification was low in all the LUT while net nitrification was the major process of net N mineralization. For more insight in urea transformation, the increase in NH4+ and, NO3− concentrations as well as C mineralization after urea addition was analyzed on whole soils. Urea application stimulated the net soil C mineralization and urea transformation pattern was consistent with net soil N mineralization, except that the rate was slightly slower. Land-use conversion from NSF to MMF, or from grassland to cropland decreased soil net N mineralization, but increased net nitrification after 40 years or 70 years, respectively. The observed higher rates of net nitrification suggested that land-use conversions in the Hebei plateau might lead to N losses in the form of nitrate. 相似文献
13.
Soil organic-N dynamics, its controlling factors and its relationships with stand quality were studied in the 0-15 cm soil layer of 24 pinewoods with contrasting age, productivity and parent material (granite; acid schists), searching for N variables useful to predict stand growth and site quality. No significant differences were found between young and old stands for any of the N variables considered, nor two- or three-order interactions among stand age, site quality and parent material. The soil total-N content, which was correlated positively with the Al oxides content (a soil organic matter (SOM) stabilizing agent), did not vary significantly according to parent material, but it was lower (P≤0.02) in stands with high than with low site index (2.68±1.11 and 3.97±1.13 g N kg−1 soil, respectively). The soil δ15N ranged from +3.5 to +6.5 δ, without significant differences among stand groups, and it was negatively correlated with water holding capacity, exchangeable bases, Al oxides and N content, suggesting that: (i) N losses by NO3− leaching are the most important controlling factor of δ15N in these temperate humid region soils; and (ii) soil N richness is related with limited N losses, which discriminate against 15N. At any incubation time, no significant differences were found in soil inorganic-N content among stand groups (7.78±4.57, 39.33±16.20 and 67.80±26.50 mg N kg−1 soil at 0, 42 and 84 d, respectively). During the incubation, the relative importance of ammonification decreased and that of the nitrification increased. The net N mineralization rate (NNMR, in percentage of organic N) was significantly higher in granite than in schists soils at both 42 d (1.24±0.34 and 0.75±0.37%, respectively) and 84 d (2.18±0.56 and 1.53±0.66%, respectively). In high quality pinewoods, the NNMR at 42 and 84 d (1.16±0.45 and 2.12±0.79%, respectively) were significantly higher than in low quality stands (0.83±0.35 and 1.59±0.45%, respectively). This result, together with those on soil total-N and inorganic-N supply, suggests that soil N dynamics in low and high quality stands are different: in the former there is a bigger N pool with a slower turnover, whereas in the latter there is a smaller N pool with a faster turnover, both factors being nearly compensated, making the soil available N supply in both types of stand similar. After 42 and 84 d of incubation, the NNMR and the nitrification rates were higher in the coarse textured soils, likely due to the low physical and chemical protection of their SOM; both rates were positively correlated with available P, exchangeable K+ and CEC base saturation, suggesting strong relationships among the availabilities of the main plant nutrients, and they increased with SOM quality (low C-to-N ratio). The strong negative correlation of site index with soil total-N (r=−0.707; P≤0.005), and its positive correlations with NNMR after 42 and 84 d of incubation, suggested that site quality and potential productivity are closely related to soil organic-N dynamics. Half of the site index variation in the stands studied could be predicted with a cheap and easy analysis of soil N content, the prediction being slightly improved if soil δ15N is included and, more significantly, by including N mineralization measurements. 相似文献
14.
CH4 oxidation and emissions of CH4 and N2O from Lolium perenne swards under elevated atmospheric CO2
Emissions of N2O and CH4 and CH4 oxidation rates were measured from Lolium perenne swards in a short-term study under ambient (36 Pa) and elevated (60 Pa) atmospheric CO2 at the Free Air Carbon dioxide Enrichment experiment, Eschikon, Switzerland. Elevated pCO2 increased (P<0.05) N2O emissions from high N fertilised (11.2 g N m−2) swards by 69%, but had no significant effect on net emissions of CH4. Application of 13C-CH4 (11 μl l−1; 11 at.% excess 13C) to closed chamber headspaces in microplots enabled determination of rates of 13C-CH4 oxidation even when net CH4 fluxes from main plots were positive. We found a significant interaction between fertiliser application rate and atmospheric pCO2 on 13C-CH4 oxidation rates that was attributed to differences in gross nitrification rates and C and N availability. CH4 oxidation was slower and thought to be temporarily inhibited in the high N ambient pCO2 sward. The most rapid CH4 oxidation of 14.6 μg 13C-CH4 m−2 h−1 was measured in the high fertilised elevated pCO2 sward, and we concluded that either elevated pCO2 had a stimulatory effect on CH4 oxidation or inhibition of oxidation following fertiliser application was lowered under elevated pCO2. Application of 14NH415NO3 and 15NH415NO3 (10 at.% excess 15N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N2O emissions. Inhibition of CH4 oxidation in the high fertilised ambient pCO2 sward, due to competition between NH3 and CH4 for methane monooxygenase enzymes or toxic effects of NH2OH or NO2− produced during nitrification, was hypothesised to increase gross nitrification (12.0 mg N kg dry soil−1) and N2O emissions during nitrification (327 mg 15N-N2O m−2 over 11 d). Our results indicate that increasing atmospheric concentrations of CO2 may increase emissions of N2O by denitrification, lower nitrification rates and either increase or decrease the ability of soil to act as a sink for atmospheric CH4 depending on fertiliser management. 相似文献
15.
Long-term (13 years) measurements of SO2 fluxes over a forest and their control by surface chemistry
Long-term fluxes of sulphur dioxide (SO2) have been measured over a mixed suburban forest subjected to elevated SO2 concentrations. The net exchange was shown to be highly dynamic with substantial periods of both upward and downward fluxes observed in excellent conditions for flux measurement. Upward fluxes constituted 30% of selected fluxes and appeared more frequently when the canopy was acidic. Upward fluxes were shown to be due to desorption from a drying surface or when ambient levels declined after periods of increased SO2 exposure.The long term average SO2 flux (F) was −59 ng SO2 m−2 s−1 for the period 1997-2009 corresponding to an average SO2 concentration of 12.3 μg SO2 m−3 and a deposition velocity υd of 5 mm s−1. The smallest deposition fluxes and υd were measured in dry conditions (−42 ng m−2 s−1 and 3.5 mm s−1, resp.), which represented 57% of all cases. Wet canopies were more efficient sinks for SO2 and a dew-wetted canopy had a smaller υd (6 mm s−1) than a rain-wetted canopy (ca 10 mm s−1). Seasonal variability reflected differences in chemical climate or canopy buffering properties. During the summer half-year when surface acidity was low due to higher NH3/SO2 ratios, a higher deposition efficiency (υd/υdmax) and lower non-stomatal resistance (Rw) were observed compared to winter conditions. Comparisons of Rc for different combinations of canopy wetness and surface acidity categories emphasized the importance of both factors in regulating the non-stomatal sinks of SO2. Increased surface water acidity gradually led to a lower υd/υdmax and an increased Rc for all considered canopy wetness categories. The smallest υd/υdmax ratio and highest Rc were obtained for a dry canopy with high surface acidity. Conversely, a rain-wetted canopy was the most efficient sink for SO2. The canopy sink strength was further enhanced by high friction velocities (u*), optimizing the mechanical mixing into the canopy. Long-term trends were strongly coupled to changes in the NH3/SO2 ratio, which has clearly enhanced the deposition efficiency of SO2 in recent years. 相似文献
16.
Matthew P. Weand Mary A. Arthur Rebecca L. McCulley 《Soil biology & biochemistry》2010,42(12):2161-2173
Forest nitrogen (N) retention and soil carbon (C) storage are influenced by tree species and their associated soil microbial communities. As global change factors alter forest composition, predicting long-term C and N dynamics will require understanding microbial community structure and function at the tree species level. Because atmospheric N deposition is increasing N inputs to forested ecosystems across the globe, including the northeastern US, it is also important to understand how microbial communities respond to added N. While prior studies have examined these topics in mixed-species stands, we focused on the responses of different tree species and their associated microbial communities within a single forest type - a northern hardwood forest in the Catskills Mountains, NY. Based on prior studies, we hypothesized that N additions would stimulate extracellular enzyme activities in relatively labile litters, but suppress oxidative enzyme activities in recalcitrant litters, and tested for independent tree species effects within this context. During the 2007 growing season (May-June), we measured enzyme activities and microbial community composition (using phospholipid fatty acid analysis - PLFA) of the forest floor in single-species plots dominated by sugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), red oak (Quercus rubra), American beech (Fagus grandifolia) and eastern hemlock (Tsuga canadensis), species whose litters range from relatively labile to recalcitrant. Half the plots were fertilized with N by adding NH4NO3 (50 kg ha−1 y−1) from 1997 to 2009. Non-metric multidimensional scaling (NMS) and multi-response permutation procedures (MRPP) were used to examine microbial community structure and relationship to enzyme activities.We found that in response to N additions, both microbial community composition and enzyme activities changed; however the strength of the changes were tree species-specific and the direction of these changes was and not readily predictable from prior studies conducted in mixed-species stands. For example, in contrast to other studies, we found that N additions caused a significant overall increase in fungal biomass that was strongest for yellow birch (24% increase) and weakest for sugar maple (1% increase). Contrary to our initial hypotheses and current conceptual models, N additions reduced hydrolytic enzyme activities in hemlock plots and reduced oxidative enzyme activity in birch plots, a species with relatively labile litter. These responses suggest that our understanding of the interactions between microbial community composition, enzyme activity, substrate chemistry, and nutrient availability as influenced by tree species composition is incomplete. NMS ordination showed that patterns in microbial community structure (PLFA) and function (enzyme activity) were more strongly influenced by tree species than by fertilization, and only partially agreed with the structure-function relationships found in other studies. This finding suggests that tree species-specific responses are likely to be important in determining the structure and function of northeastern hardwood forests in the future. Enhanced understanding of microbial responses to added N in single and mixed-species substrates with varying amounts of lignin and phenols may be needed for accurate predictions of future soil C and N dynamics. 相似文献
17.
We evaluated the spatial structures of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) fluxes in an Acacia mangium plantation stand in Sumatra, Indonesia, in drier (August) and wetter (March) seasons. A 60 × 100-m plot was established in an A. mangium plantation that included different topographical elements of the upper plateau, lower plateau, upper slope and foot slope. The plot was divided into 10 × 10-m grids and gas fluxes and soil properties were measured at 77 grid points at 10-m intervals within the plot. Spatial structures of the gas fluxes and soil properties were identified using geostatistical analyses. Averaged N2O and CO2 fluxes in the wetter season (1.85 mg N m−2 d−1 and 4.29 g C m−2 d−1, respectively) were significantly higher than those in the drier season (0.55 mg N m−2 d−1 and 2.73 g C m−2 d−1, respectively) and averaged CH4 uptake rates in the drier season (−0.62 mg C m−2 d−1) were higher than those in the wetter season (−0.24 mg C m−2 d−1). These values of N2O fluxes in A. mangium soils were higher than those reported for natural forest soils in Sumatra, while CO2 and CH4 fluxes were in the range of fluxes reported for natural forest soils. Seasonal differences in these gas fluxes appears to be controlled by soil water content and substrate availability due to differing precipitation and mineralization of litter between seasons. N2O fluxes had strong spatial dependence with a range of about 18 m in both the drier and wetter seasons. Topography was associated with the N2O fluxes in the wetter season with higher and lower fluxes on the foot slope and on the upper plateau, respectively, via controlling the anaerobic-aerobic conditions in the soils. In the drier season, however, we could not find obvious topographic influences on the spatial patterns of N2O fluxes and they may have depended on litter amount distribution. CO2 fluxes had no spatial dependence in both seasons, but the topographic influence was significant in the drier season with lowest fluxes on the foot slope, while there was no significant difference between topographic positions in the wetter season. The distributions of litter amount and soil organic matter were possibly associated with CO2 fluxes through their effects on microbial activities and fine root distribution in this A. mangium plantation. 相似文献
18.
Zubin Xie Georg Cadisch Grant Edwards Elizabeth M. Baggs 《Soil biology & biochemistry》2005,37(7):1387-1395
Elevated pCO2 increases the net primary production, C/N ratio, and C input to the soil and hence provides opportunities to sequester CO2-C in soils to mitigate anthropogenic CO2. The Swiss 9 y grassland FACE (free air carbon-dioxide enrichment) experiment enabled us to explore the potential of elevated pCO2 (60 Pa), plant species (Lolium perenne L. and Trifolium repens L.) and nitrogen fertilization (140 and 540 kg ha−1 y−1) on carbon sequestration and mineralization by a temperate grassland soil. Use of 13C in combination with respired CO2 enabled the identification of the origins of active fractions of soil organic carbon. Elevated pCO2 had no significant effect on total soil carbon, and total soil carbon was also independent of plant species and nitrogen fertilization. However, new (FACE-derived depleted 13C) input of carbon into the soil in the elevated pCO2 treatments was dependent on nitrogen fertilization and plant species. New carbon input into the top 15 cm of soil from L. perennne high nitrogen (LPH), L. perenne low nitrogen (LPL) and T. repens low nitrogen (TRL) treatments during the 9 y elevated pCO2 experiment was 9.3±2.0, 12.1±1.8 and 6.8±2.7 Mg C ha−1, respectively. Fractions of FACE-derived carbon in less protected soil particles >53 μm in size were higher than in <53 μm particles. In addition, elevated pCO2 increased CO2 emission over the 118 d incubation by 55, 61 and 13% from undisturbed soil from LPH, LPL and TRL treatments, respectively; but only by 13, 36, and 18%, respectively, from disturbed soil (without roots). Higher input of new carbon led to increased decomposition of older soil organic matter (priming effect), which was driven by the quantity (mainly roots) of newly input carbon (L. perenne) as well as the quality of old soil carbon (e.g. higher recalcitrance in T. repens). Based on these results, the potential of well managed and established temperate grassland soils to sequester carbon under continued increasing concentrations of atmospheric CO2 appears to be rather limited. 相似文献
19.
《Soil biology & biochemistry》2007,39(8):1978-1989
Soil organic matter (SOM) quality and biodegradability the permafrost underlying Siberian wet tussock tundra (Kolyma river basin, northeast Siberia) were analyzed and compared to the characteristics of the contemporary active layer. For this purpose, three permafrost affected soil cores (down to 3 m depth) and seven active layer soil cores (down to 0.3 m depth) were sampled. The samples were divided into particular layers, which were analyzed separately. SOM stability was assessed using a simple chemical fractionation (sequential extraction by cold and hot water, and hot acid). SOM biodegradability and soil mineralization potentials were tested in short-term laboratory incubations. The active layer contained 24 kg C m−2 and 70 kg C m−2 was preserved in 3 m of permafrost. The chemical quality and biodegradability of permafrost SOM were very similar to that of the active layer mineral horizon, and independent from depth. The only exceptions were (1) higher solubility of permafrost SOM in water, indicating its higher mobility and potential leakage after permafrost thawing and (2) higher nutrient (N, P) concentrations available to a dense permafrost microbial community, which could support decomposition of more complex substrates under suitable temperature conditions after thawing. The mineralization potential of the upper 1 m deep permafrost, which could melt by 2100 according to permafrost degradation models, was 6.7 g C m−2 d−1 (optimum conditions of 20 °C, field water capacity), which is comparable to that of the contemporary active layer of 0.5 m depth (7.5 g C m−2 d−1). Under field conditions, SOM mineralization rate would reasonably be significantly lower due to prevailing anoxia (high water table) and diffusion constraints in the deep and flooded soil profile.We conclude from our results that the permafrost (1) cryopreserves a high SOM amount, which is distributed to considerable depths, being of similar chemical quality and biodegradability to that of the active layer mineral horizon SOM, and (2) contains a dense living microbial community, which is able to decompose the present SOM rapidly without any obvious chemical limitation under suitable conditions. 相似文献
20.
Impacts of anthropogenic N additions on nitrogen mineralization from plant litter in exotic annual grasslands 总被引：1，自引：0，他引：1
Urban regions of southern California receive up to 45 kg N ha-1 y-1 from nitrogen (N) deposition. A field decomposition study was done using 15N-labelled litter of the widespread exotic annual grass Bromus diandrus to determine whether elevated soil N is strictly from N deposition or whether N mineralization rates from litter are also increased under N deposition. Tissue N and lignin concentrations, which are inversely related in field sites with high and low N deposition, determine the rate at which N moves from plant litter to soil and becomes available to plants. The effect of soil N on N movement from litter to soil was tested by placing litter on high and low N soil in a factorial experiment with two levels of litter N and two levels of soil N. The litter quality changes associated with N deposition resulted in faster rates of N cycling from litter to soil. Concentrations of litter-derived N in total N, NH4+, NO3−, microbial N and organic N were all higher from high N/low lignin litter than from low N/high lignin litter. Litter contributed more N to soil NH4+ and microbial N in high N than low N soil. At the end of the study, N mineralized from high N litter on high N soil accounted for 46% of soil NH4+ and 11% of soil NO3−, compared to 35% of soil NH4+ and 6% of soil NO3− from low N litter on low N soil. The study showed that in high N deposition areas, elevated inorganic soil N concentrations at the end of the summer N deposition season are a result of N mineralized from plant litter as well as from N deposition. 相似文献