首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Sustainable cropping systems rely on a minimum of external inputs. In these systems N is largely acquired in animal manures and leguminous green manures. Little is known of how these organic forms of N fertilizer influence the presence and activity of free-living N2-fixing bacteria. High concentrations of inorganic N in soil inhibit N2-fixation in cyanobacteria and Azotobacter spp. It is likely that manure and fertilizer applications would result in concentrations of inorganic N capable of inhibiting N2 fixation and, ultimately, the presence of these organisms. We investigated the effect of synthetic and organic N fertilizer sources on the populations and N2-fixation potential of free-living N2-fixing bacteria in the Farming Systems Trial at the Rodale Research Institute. Field plots received the following N treatments prior to corn (Zea mays L.) production: (1) Legume rotations and green manures supplying about 165 kg N ha-1; (2) beef cattle manure applied at a rate of 220 kg N ha-1 (plus 60 kg N ha-1 from 1994 hay plow-down); or (3) fertilizer N (urea and NH4NO3) applied at a rate of 145 kg N ha-1. Soil samples were collected at two depths from corn plots four times during the growing season, and analyzed for soil moisture, soil pH, numbers of N2-fixing cyanobacteria and Azotobacter spp., extractable NH inf4 sup+ and NO inf3 sup- , and potentially mineralizable N. Soil samples collected in mid-July were analyzed for nitrogenase activity (by C2H2 reduction) and total C and N. Populations of Azotobacter spp. and cyanobacteria were influenced only slightly by treatment; however, cyanobacteria species composition was notably influenced by treatment. Nitrogenase activity in surface soils was greatest in legume-N plots and in subsurface plots levels were greatest in fertilizer-N plots. Populations and activity of free-living N-fixing bacteria appeared to be somewhat reduced in all plots as a result of low soil pH levels and high concentrations of inorganic N across all treatments. Annual applications of N to all plots resulted in high levels of potentially mineralizable N that in turn may have reduced non-symbiotic N2-fixation in all plots.  相似文献   

2.
N2-fixation by free-living (diazotrophic) microorganism is a key process affecting ecosystem functioning in soils. Understanding drivers affecting diazotrophic community assemblages and activities may lead to management practices to increase primary production and/or environmental sustainability. We used PCR-DGGE to determine the fundamental relationships between diazotrophic community structure and in a wide range of soils across southern Australia. In addition qPCR, RT-qPCR and N2-fixation (acetylene reduction) were used to investigate factors influencing gene abundance, expression and processes in similar soils with different agricultural inputs. Across 22 soils, the structural composition of the nifH community was significantly influenced by site (ANOSIM R = 0.876; P = 0.001). The effects of management practices were evident, and often larger than between-soil differences, but were only present at some sites. Differences in nifH communities between sites correlated to particulate organic carbon (POC; measured by mid-infrared spectroscopy) content of the soils (BIO-ENV test; ρ = 0.502; P = 0.001), but not other factors including total soil C. In 3 soils from the Murrumbidgee irrigation region of NSW, intensification of the farming systems was associated with increasing N2-fixation (P < 0.05), except where rice was cultivated. N2-fixation correlated either with nifH abundance or gene expression in soils, but not both. Our data shows that soil C is closely linked to diazotrophic ecology. Principally, the amount of C entering the soil system is directly related to the abundance and N2-fixation activity of free-living bacteria. However, we also show that C in the POC pool has associative links to the genetic diversity of the soil diazotroph community. Given the importance of diversity and abundance of functional organisms in supporting ecosystem processes, we suggest that soil C inputs should be considered for both qualitative and quantitative properties when considering impacts on diazotrophic bacterial ecology.  相似文献   

3.
The cryptogamic soil crusts of the Great Basin Artemisia, Ceratoides, and Atriplex plant communities contain a significant heterotrophic N2-fixing microbial population in addition to the predominating filamentous cyanobacteria. The bacterial association with the cyanobacteria exhibits a phycosphere-like effect. Heterotrophically fixed N gains reached 17.5 μg N· g?1 of soil (23.1% increase above the initial soil N content) and 45.9 μg N·g?1 of soil (57.4% increase) after 3 and 5 weeks, respectively. (NH4)2SO4 and native plant material amendments to soil resulted in a 41–100% reduction in N2-fixation. The potential input of N to soil crusts may be reduced in the presence of shrub-produced allelochemic agents and by concurrent denitrification.  相似文献   

4.
Summary A nitrogen balance study conducted in ceramic pots under net house conditions for four seasons showed that flooded rice soil leaves a positive nitrogen balance (N increase) in soil after rice cropping in both fertilized and unfertilized soil. Recovery of nitrogen from rice soil was more than its input in unfertilized soil, but it was reverse in fertilized soil. Incorporation of Azolla or BGA twice as basal and 20 days after transplanting (DAT) alone or in combination showed higher nitrogen balance and N2-fixation (N gain) in soil than in that where it was applied once either as basal or 20 DAT. Planted soil showed more N2-fixation than that of fallow rice, and flooded soil fixed more nitrogen in comparison to non-flooded soil in light but less in dark. Soil exposed to light fixed more nitrogen than that of unexposed soil in both flooded and non-flooded conditions.  相似文献   

5.
Dew is an important source of water in drylands, particularly for biological soil crusts (BSCs), which are soil communities dominated by lichens, mosses and cyanobacteria that are prevalent in these environments and play important roles in nutrient cycling. While BSCs can retain and use water from dew, the effects of dew events on the cycling of nitrogen (N) and carbon (C) in BSC-dominated ecosystems are largely unknown. We conducted an experiment to evaluate the effects of BSCs and dew on N and C cycling; intact soil cores from either bare ground or BSC-dominated microsites were incubated over 14 days under control and artificial dew addition treatments. A positive increment in the amount of total available N and phenols was observed in response to dew events under BSCs. We also found an increase in the concentration of dissolved organic N, as well as in the pentoses:hexoses ratio, under BSCs, suggesting that dew promoted an increase in the decomposition of organic matter at this microsite. The increase in the amount of available N commonly observed under BSCs has been traditionally associated with the fixation of atmospheric N2 by BSC-forming cyanobacteria and cyanolichens. Our results provide a complementary explanation for such an increase: the stimulation of microbial activity of the microorganisms associated with BSCs by dew inputs. These effects of dew may have important implications for nutrient cycling in drylands, where dew events are common and BSCs cover large areas.  相似文献   

6.
施肥对夏玉米季紫色土N2O排放及反硝化作用的影响   总被引：9，自引：0，他引：9  
采用原状土柱-乙炔抑制培养法研究了施肥对紫色土玉米生长季土壤N2O排放通量和反硝化作用的影响.结果表明:玉米季施肥显著增加土壤N2O排放和反硝化损失,同时,各施肥处理间N2O排放与反硝化损失量差异显著.猪厩肥、猪厩肥配施氮磷钾肥、氮肥、氮磷钾肥和秸秆配施氮磷钾肥等处理的土壤N,O排放量分别为3.01、2.86、2.51、2.19和1.88 kg hm-2,分别占当季氮肥施用量的1.63％、1.53％、1.30％、1.09％和0.88％,反硝化损失量分别为6.74、6.11、5.23、4.69和4.12 kg hm-2,分别占当季氮肥施用量的3.97％、3.55％、2.97％、2.61％和2.23％,不施肥土壤的N2O排放量和反硝化损失量仅为0.56和0.78 kg hm-2.施肥是紫色土玉米生长前期(2周内)土壤N2O排放和反硝化速率出现高峰的主要驱动因子,土壤铵态氮和硝态氮含量是影响土壤N2O排放、土壤硝化和反硝化作用的限制因子,土壤含水量是重要影响因子,降雨是主要促发因素.土壤N2O排放量与反硝化损失量的比值介于0.45 ～0.72之间,土壤反硝化损失量极显著高于土壤N2O排放量,说明土壤反硝化作用是紫色土玉米生长季氮肥损失的重要途径.  相似文献   

7.
Western Indian Himalaya is very rich in biodiversity. Being a cold climatic region, it possesses various psychrotolerant and psychrophilic microorganisms. Psychrotolerant bacterium Dyadobacter sp. was isolated from this region and studied for its plant growth promoting potential against four legumes and finger millet. This bacterium was able to grow at nitrogen (N) deficient medium at both 10°C and 28°C and gave positive nifH amplification that confirms the psychrotolerant and diazotrophic nature of this bacterium. Pot trial-based study showed that this bacterium was able to promote plant growth by fixing atmospheric nitrogen (N2) and making it available to plants. Agronomical parameters, leaf nitrate reductase activity, and total chlorophyll content were recorded at 30, 45, 60, and 90 days after sowing and found to be increased over their respective controls. The 16S rDNA and nifH genes were quantified by q-PCR to study the dynamics of total bacterial and diazotrophic abundance due to inoculation of Dyadobacter sp. in soil. Soil chemical properties related to soil fertility were also studied at different time intervals after sowing. We found positive correlation among soil pH, soil nifH gene abundance, soil nitrate concentration, and plant leaf nitrate reductase activity. PCR-DGGE was performed to study persistence of Dyadobacter sp. in soil after inoculation, which showed good persistence of plant growth promoting rhizobacteria (PGPR). Hence, it is concluded that Dyadobacter sp. has potential to promote plant growth by fixing atmospheric N2 and making it available to plant. Further, psychrotolerant nature of this bacterium can be exploited to enhance plant growth in cold climate agriculture due to its ability to fix atmospheric N2 at low temperature.  相似文献   

8.
Summary Nitrogen fixation in seven groundnut genotypes was measured by 15N-isotope dilution using a non-nodulating cultivar of groundnut as the nonfixing reference plant. Nitrogen fixation varied between 100 kg N ha–1 in genotype J-11 and 153 kg N ha–1 in Robut 33-1. The amount of plant-available soil N was small, so that 86%–92% of plant nitrogen was derived from N2-fixation. Thus differences in N2-fixation between genotypes closely reflected differences in their total N accumulation.ICRISAT Journal Article no. 600  相似文献   

9.
Abstract

Microbial nitrification and denitrification are responsible for the majority of soil nitrous (N2O) emissions. In this study, N2O emissions were measured and the abundance of ammonium oxidizers and denitrifiers were quantified in purple soil in a long-term fertilization experiment to explore their relationships. The average N2O fluxes and abundance of the amoAgene in ammonia-oxidizing bacteria during the observed dry season were highest when treated with mixed nitrogen, phosphorus and potassium fertilizer (NPK) and a single N treatment (N) using NH4HCO3as the sole N source; lower values were obtained using organic manure with pig slurry and added NPK at a ratio of 40%:60% (OMNPK),organic manure with pig slurry (OM) and returning crop straw residue plus synthetic NH4HCO3fertilizer at a ratio of 15%:85% (SRNPK). The lowest N2O fluxes were observed in the treatment that used crop straw residue(SR) and in the control with no fertilizer (CK). Soil NH4+provides the substrate for nitrification generating N2O as a byproduct. The N2O flux was significantly correlated with the abundance of the amoA gene in ammonia-oxidizing bacteria (r = 0.984, p < 0.001), which was the main driver of nitrification. During the wet season, soil nitrate (NO3?) and soil organic matter (SOC) were found positively correlated with N2O emissions (r = 0.774, p = 0.041 and r = 0.827, p = 0.015, respectively). The nirS gene showed a similar trend with N2O fluxes. These results show the relationship between the abundance of soil microbes and N2O emissions and suggest that N2O emissions during the dry season were due to nitrification, whereas in wet season, denitrification might dominate N2O emission.  相似文献   

10.
Nitrous oxide (N2O) flux in the semi-arid Leymus chinensis (Trin.) Tzvel. grassland in Inner Mongolia, China was measured for two years (from January 2005 to December 2006) with the enclosed chamber technique. The measurements were made twice per month in the growing season and once per month in the non-growing season. To evaluate the effect of aboveground vegetation on N2O emission, the ecosystem N2O flux over the grassland was measured, and concurrently soil N2O flux was measured after the removal of all the aboveground biomass. The possible effect of water-heat factors on N2O fluxes was statistically examined. The ecosystem N2O flux ranged from 0.21 to 0.26?kg nitrous oxide-nitrogen (N2O–N) ha? 1 year? 1, indicating that the Leymus chinensis grassland of Inner Mongolia was a source for the atmospheric N2O. There was no significant difference between the ecosystem N2O flux and the soil N2O flux. The ecosystem N2O flux was under similar environmental control as the soil N2O flux. Soil moisture was the primary driving factor of the N2O fluxes in the growing season of both years; the changes in water–filled pore space (WFPS) of soil surface layers could explain 45–67% of the variations in N2O fluxes. The high seasonal variation of the N2O fluxes in the growing seasons was regulated by the distribution of effective rainfall, rather than the precipitation intensity. While in the non-growing season, the N2O fluxes were restricted much more by air temperature or soil temperature, and 83–85% of the variations of the N2O fluxes were induced by changes in temperature conditions.  相似文献   

11.
The dynamics of nodulation, N2-fixation and N use in Leucaena leucocephala cv. K28 over time was investigated in a screenhouse at 4, 8, 12 and 16 months after planting (MAP) using the 15N-labelling method. Leucaena had a consistently increasing pattern of nodulation, dry biomass and nitrogen yield. A sharp rise in nodulation was observed between 12 and 16 MAP, whereas for biomass, N accumulation and N2-fixation, and N2-fixation, an upward surge occurred between 4 and 12 months. Nodulation, N accumulation, N2-fixation and biomass yield all peaked at 16 MAP. Along with the steady increase in N2-fixation throughout the 16-month growth period, the % N derived from the atmosphere rose from 17.9% to 61.5%, 70.1% and 74%, equivalent to 191, 1623, 2395 and 3385 mg N2 fixed plant-1 at 4, 8, 12 and 16 MAP, respectively. Nitrogen assimilation from soil and fertilizer decreased inversely to the increase in symbiotic nitrogen fixation with time.  相似文献   

12.
Topography and slope position influence the soil and environmental factors that affect N2 fixation by legumes. The present study was conducted to (1) estimate N2 fixation by field peas in a gently rolling farm field using the natural 15N abundance and the 15N-enriched isotope dilution techniques and (2) identify soil and environmental factors that influence N2 fixation at the landscape scale. Whereas soil available water capacity, available NH inf4 sup+ , total crop yield, and percent N derived from N2 fixation (% Ndfa) estimated using enriched N were significantly affected by landform patterns, soil NO inf3 sup- levels, seed yield, and the % Ndfa estimated using natural abundance did not follow landform patterns. The % Ndfa using natural abundance was correlated with NH inf4 sup+ but not with available soil water, pH, electrical conductivity, NO inf3 sup- , or particle size. Estimates of the % Ndfa using enriched 15N ranged from 0 to 92.8%. The highest median value (68.6%) for % Ndfa using enriched N occurred on the divergent footslopes, with the lowest value (28.1%) on the convergent shoulders. Estimates of % Ndfa using natural abundance ranged from 13.2% to 96.9%. Smaller fluctuations during the growing season in the 15N of the available N pool may have resulted in less variability for % Ndfa using natural abundance compared to enriched 15N. Despite similar mean values for % Ndfa using natural abundance (44.5) and enriched 15N (49.6), no significant correlation between the two estimates was found. These results suggest that although topography may exert gross controls on N2 fixation, large variations in N2 fixation at the microsite level may preclude correlations between individual estimates and limit detection of landscape scale patterns of N2 fixation.Contribution No. R754 of the Saskatchewan Center of Soil Research  相似文献   

13.
Residues from some tree species may contain allelopathic chemicals that have the potential to inhibit plant growth and symbiotic N2-fixing microorganisms. Soybean [Glycine max (L.) Merr] was grown in pots to compare nodulation and N2-fixation responses of the following soil amendments: control soil, leaf compost, red oak (Quercus rubra L.) leaves, sugar maple (Acer saccharum Marsh) leaves, sycamore (Platanus occidentalis L.) leaves, black walnut (Juglans nigra L.) leaves, rye (Secale cereale L.) straw, and corn (Zea mays L.) stover. Freshly fallen leaves were collected from urban shade trees. Soil was amended with 20 g kg-1 air-dried, ground plant materials. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage to determine N2-fixation by the difference method. Although nodulation was not adversely affected, soybean grown on leaf-amended soil exhibited temporary N deficiency until nodulation. Nodule number was increased by more than 40% for soybean grown on amended soil, but nodule dry matter per plant generally was not changed compared with control soil. Nonnodulating plants were severely N deficient and stunted as a consequence of N immobilization. Nodulating soybean plants grown on leaf or crop residue amended soil were more dependent on symbiotically fixed N and had lower dry matter yields than the controls. When leaves were composted, the problem of N immobilization was avoided and dry matter yield was not reduced. No indication of an allelopathic inhibition on nodulation or N2-fixation from heavy application of oak, maple, sycamore, or walnut leaves to soil was observed.  相似文献   

14.
Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO2 fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO2 efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO2 efflux to climate changes. In this study we measured winter soil CO2 efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO2 effluxes were 0.15-0.26 μmol m−2 s−1 and 2.65-4.61 μmol m−2 s−1, respectively, with significant differences in the growing season among the different ecosystems. Annual Q10 (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q10. Soil water content accounted for 84% of the variations in growing season Q10 and soil temperature range explained 88% of the variation in annual Q10. Soil organic carbon density to 30 cm depth was a good surrogate for SR10 (basal soil respiration at a reference temperature of 10 °C). Annual soil CO2 efflux ranged from 394.76 g C m−2 to 973.18 g C m−2 using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m−2 to 784.73 g C m−2 by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO2 efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO2 efflux continues throughout the winter and winter soil respiration is an important component of annual CO2 efflux.  相似文献   

15.
An experiment was conducted in an Andosol paddy field in Shizukuishi (Iwate Prefecture, Japan) to determine the effects of free-air CO2 enrichment (FACE) on biological N2-fixation activity and soil microbial biomass C at three levels of N application. Rice (Oryza sativa L. cv. Akitakomachi) plants were grown under ambient CO2 or FACE (ambient +200 µmol mol-1 CO2) conditions throughout the growing season with each treatment having four replicated plots. Three levels of N fertilizer (high, standard and low; 15, 9 and 4 g N m-2, respectively) were applied to examine the effect of different N availability under both CO2 conditions. Soil samples were collected at four different times from upper and lower soil layers (0-1-cm and 1-10-cm soil depths, respectively) and analysed for biological N2-fixation (BNF) activity and microbial biomass C (MBC) by the acetylene reduction and chloroform fumigation-extraction methods, respectively. The amounts of chlorophyll-type compounds (Chls), an index of algal growth, and soil available C were also determined. Compared to the ambient CO2 treatment, the FACE treatment had significantly higher BNF activity in both the upper and lower soil layers at ripening only in low-N soil and at harvest at all three levels of N fertilization rates. MBC was significantly increased by FACE in both the upper and lower soil layers from the middle to later period of the growing season compared to the ambient CO2 treatment. The FACE treatment increased the Chls in the upper soil layers at ripening only in low-N soil and at harvest at all three levels of N fertilization rates. The amount of soil available C was not significantly different between FACE and ambient CO2 treatments in both the upper and lower soil layers throughout the cropping season. From these results it can be concluded that the FACE treatment had a significantly positive influence on BNF activity, MBC and Chls at different levels of N fertilization rates in paddy field during the cropping season.  相似文献   

16.
As a result of intensive greenhouse vegetable production in northern China, the potential risk of nitrogen (N) fertilizer over-applied is increasingly apparent and is threatening ecosystem and the sustainability of food production. An experiment was carried out in Shouguang, Shangdong Province, China to evaluate agronomic benefit and soil quality under different N applications, including the conventional chemical N rate (1000 kg N ha-1 season-1, N1), 70% of N1 (N2), 70% of N1 + maize straw (N3), 50% of N1 + maize straw + drip irrigation (N4), and 0% of N1 (N0), during two successive growing seasons of autumn-winter (AW) and winter-spring (WS). The maximum yields for N4 were 1.1 and 1.0 times greater than those for N1 in the AW and WS seasons, respectively. N agronomic effciency (AEN) and apparent N recovery effciency (REN) were greatest with the N4. A significant relationship was found between soil NO-3 -N content and electrical conductivity (EC) (R2 = 0.61 in the AW season and R2 = 0.29 in the WS season). Reducing N fertilizer decreased soil NO-3 -N accumulation (20.9%-37.8% reduction in the AW season and 11.7%-20.1% reduction in the WS season) relative to the accumulation observed for N1 within the 0-100 cm soil layer. Soil urease and invertase activities were not significantly different among N treatments. The N4 treatment would be practical for reducing excess N input and maintaining the sustainability of greenhouse-based intensive vegetable systems in Shouguang.  相似文献   

17.
施氮和豌豆/玉米间作对土壤无机氮时空分布的影响   总被引：4，自引：1，他引：3  
为探明甘肃河西走廊绿洲灌区豌豆/玉米间作体系土壤无机氮时空分布现状和过量施用氮肥对环境的影响,2011年在田间试验条件下,采用土钻法采集土壤剖面样品,采用Ca Cl2溶液浸提、流动分析仪测定土壤无机氮含量的方法,研究了不同氮水平[0 kg(N)·hm?2、75 kg(N)·hm?2、150 kg(N)·hm?2、300 kg(N)·hm?2、450 kg(N)·hm?2]下豌豆/玉米间作体系土壤无机氮时空分布规律。结果表明:作物整个生育期内,灌漠土无机氮以硝态氮为主,其含量是铵态氮的7.55倍。在玉米整个生育期内,与不施氮相比,75 kg(N)·hm?2、150 kg(N)·hm?2、300 kg(N)·hm?2和450 kg(N)·hm?2处理的土壤硝态氮含量分别增加29.7%、67.5%、88.2%和134.3%。与豌豆收获期相比,在玉米收获时土壤硝态氮含量平均降低44.2%。间作豌豆和间作玉米分别比对应的单作在0~120 cm土层硝态氮含量降低6.1%和5.1%。豌豆/玉米间作体系土壤无机氮累积量在不同施氮量和不同生育时期都是表层(0~20 cm)最高。豌豆收获后,0~60 cm土层土壤无机氮累积量间作豌豆和间作玉米分别比相应单作降低4.9%和1.9%,60~120 cm土层降低10.8%和9.2%;玉米收获后0~60 cm土层平均降低28.2%和9.4%,60~120 cm土层平均降低23.5%和12.5%。土壤无机氮残留量间作豌豆比单作豌豆在0~60 cm土层降低4.9%,60~120 cm降低10.9%。因此,施用氮肥显著增加了土壤无机氮含量和累积量,且主要影响土壤硝态氮。过量的氮肥投入会因作物不能及时全部吸收而被大水漫灌和降雨等途径淋洗到土壤深层,造成氮肥损失和农田环境污染。间作能显著降低土壤无机氮浓度和累积量,特别在作物生长后期对土壤无机氮累积的降低作用更加明显。  相似文献   

18.
Elevated CO2 and defoliation effects on nitrogen (N) cycling in rangeland soils remain poorly understood. Here we tested whether effects of elevated CO2 (720 μl L−1) and defoliation (clipping to 2.5 cm height) on N cycling depended on soil N availability (addition of 1 vs. 11 g N m−2) in intact mesocosms extracted from a semiarid grassland. Mesocosms were kept inside growth chambers for one growing season, and the experiment was repeated the next year. We added 15N (1 g m−2) to all mesocosms at the start of the growing season. We measured total N and 15N in plant, soil inorganic, microbial and soil organic pools at different times of the growing season. We combined the plant, soil inorganic, and microbial N pools into one pool (PIM-N pool) to separate biotic + inorganic from abiotic N residing in soil organic matter (SOM). With the 15N measurements we were then able to calculate transfer rates of N from the active PIM-N pool into SOM (soil N immobilization) and vice versa (soil N mobilization) throughout the growing season. We observed significant interactive effects of elevated CO2 with N addition and defoliation with N addition on soil N mobilization and immobilization. However, no interactive effects were observed for net transfer rates. Net N transfer from the PIM-N pool into SOM increased under elevated CO2, but was unaffected by defoliation. Elevated CO2 and defoliation effects on the net transfer of N into SOM may not depend on soil N availability in semiarid grasslands, but may depend on the balance of root litter production affecting soil N immobilization and root exudation affecting soil N mobilization. We observed no interactive effects of elevated CO2 with defoliation. We conclude that elevated CO2, but not defoliation, may limit plant productivity in the long-term through increased soil N immobilization.  相似文献   

19.
Land-use type and nitrogen (N) addition strongly affect nitrous oxide (N2O) and carbon dioxide (CO2) production, but the impacts of their interaction and the controlling factors remain unclear. The aim of this study was to evaluate the effect of both factors simultaneously on N2O and CO2 production and associated soil chemical and biological properties. Surface soils (0–10 cm) from three adjacent lands (apple orchard, grassland and deciduous forest) in central Japan were selected and incubated aerobically for 12 weeks with addition of 0, 30 or 150 kg N ha–1 yr–1. Land-use type had a significant (p < 0.001) impact on the cumulative N2O and CO2 production. Soils from the apple orchard had higher N2O and CO2 production potentials than those from the grassland and forest soils. Soil net N mineralization rate had a positive correlation with both soil N2O and CO2 production rates. Furthermore, the N2O production rate was positively correlated with the CO2 production rate. In the soils with no N addition, the dominant soil properties influencing N2O production were found to be the ammonium-N content and the ratio of soil microbial biomass carbon to nitrogen (MBC/MBN), while those for CO2 production were the content of nitrate-N and soluble organic carbon. N2O production increased with the increase in added N doses for the three land-use types and depended on the status of the initial soil available N. The effect of N addition on CO2 production varied with land use type; with the increase of N addition doses, it decreased for the apple orchard and forest soils but increased for the grassland soils. This difference might be due to the differences in microbial flora as indicated by the MBC/MBN ratio. Soil N mineralization was the major process controlling N2O and CO2 production in the examined soils under aerobic incubation conditions.  相似文献   

20.
A great deal of uncertainty is associated with estimates of global nitrous oxide (N2O) emissions because emissions from arid and polar climates were not included in the estimates due to a lack of available data. In particular, very few studies have assessed the response of N2O flux to grazing under future warming conditions. This experiment was conducted to determine the effects of warming and grazing on N2O flux at different time scales for three years under a controlled warming-grazing system. A free-air temperature enhancement system (FATE) using infrared heaters and grazing significantly increased soil temperatures for both of growing (average 1.8 °C in 2008) and no-growing seasons (average 3.0 °C for 3-years) within 20-cm depth, but only warming reduced soil moisture at 10-cm soil depth during the growing season during the drought year of 2008. Generally, the effects of warming and grazing on N2O flux varied with sampling date, season, and year. No interactive effect between warming and grazing was found. Warming did not affect annual N2O flux when grazing was moderate during the growing season because the tradeoff of the effect of warming on N2O flux was observed between the growing season and no-growing season. No-warming with grazing (NWG) and warming with grazing (WG) significantly increased the average annual N2O flux (57.8 and 31.0%) compared with no-warming with no-grazing (NWNG) and warming with no-grazing (WNG), respectively, indicating that warming reduced the response of N2O flux to grazing in the region. Winter accounted for 36-57% of annual N2O flux for NWNG and NWG, whereas only for 5-8% of annual N2O flux for WNG and WG. Soil temperature could explain 5-35% of annual N2O flux variation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号