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 31 毫秒
1.

Purpose

Small but highly bioactive labile carbon (C) and nitrogen (N) pools are of great importance in controlling terrestrial C and N fluxes, whilst long-term C and N storage is determined by less labile but relatively large sizes of C and N pools. Little information is available about the effects of global warming and grazing on different forms of C and N pools in the Qinghai?CTibet Plateau of China. The aim of this study was to investigate the effects of warming and grazing on the sizes of different soil labile C and N pools and N transformation in this region.

Materials and methods

A free-air temperature enhancement system in a controlled warming?Cgrazing experiment had been implemented since May 2006. Infrared heaters were used to manipulate temperature, and a moderate grazing intensity was simulated by Tibetan sheep. After 3 years?? warming, soil samples were taken from the four treatment plots: no warming with no grazing; no warming with grazing; warming with no grazing; and warming with grazing. Concentrations of inorganic N in the 40?Ccm soil profiles were measured by a flow injection analyser. Microbial biomass C (MBC) and microbial biomass N (MBN) were measured by the fumigation?Cextraction method, and soluble organic C (SOC) and soluble organic N (SON) were determined by high-temperature catalytic oxidation. Total N (TN), C isotope composition (??13C) and N isotope composition (??15N) were determined using an isotope ratio mass spectrometer. Net N transformation under low temperature was studied in a laboratory incubation experiment.

Results and discussion

Warming and grazing treatments affected soil C and N pools differently, and these effects varied with soil depth. Warming significantly increased TN, MBC, MBN, and SON and decreased ??13C at the 10?C20 and 20?C30 cm soil depths, whilst grazing generally decreased SON at the 10?C20 and 20?C30 cm, and MBC at 20?C30 cm. At the 0?C10 cm depth, neither warming nor grazing alone affects these soil parameters significantly, indicating that there could be considerable perturbation on the soil surface. However, grazing alone increased NO 3 ? ?CN, total inorganic N, SOC and ??15N at the 0?C10 cm depth. Incubated at 4°C, warming (particularly with grazing) led to net immobilization of N, but no-warming treatments led to net N mineralization, whilst nitrification was strong across all these treatments. Correlations between MBC and SOC, and TN and MBN or SON were positive. However, SON was less well correlated with TN and MBN compared with the highly positive correlations between SOC and MBC.

Conclusions

It is clearly demonstrated that warming and grazing affected labile C and N pools significantly, but differently after 3 years?? treatments: Warming tended to enlarge labile C and N pools through increased litter inputs, whilst grazing tended to increase inorganic N pools, decrease SON and accelerate N cycling. Grazing might modify the mode that warming affected soil C and N pools through its strong impacts on microbial processes and N cycling. These results suggested that interactive effects of warming and grazing on C and N pools might have significant implications for the long-term C and N storage and productivity of alpine meadow ecosystem in the Qinghai?CTibet Plateau of China.  相似文献   

2.
Kobresia grasslands on the Tibetan Plateau comprise the world’s largest pastoral alpine ecosystem. Overgrazing-driven degradation strongly proceeded on this vulnerable grassland, but the mechanisms behind are still unclear. Plants must balance the costs of releasing C to soil against the benefits of accelerated microbial nutrient mineralization, which increases their availability for root uptake. To achieve the effect of grazing on this C-N exchange mechanism, a 15NH4+ field labeling experiment was implemented at grazed and ungrazed sites, with additional treatments of clipping and shading to reduce belowground C input by manipulating photosynthesis. Grazing reduced gross N mineralization rates by 18.7%, similar to shading and clipping. This indicates that shoot removal by grazing decreased belowground C input, thereby suppressing microbial N mining and overall soil N availability. Nevertheless, NH4+ uptake rate by plants at the grazed site was 1.4 times higher than at the ungrazed site, because plants increased N acquisition to meet the high N demands of shoot regrowth (compensatory growth: grazed > ungrazed). To enable efficient N uptake and regrowth, Kobresia plants have developed specific traits (i.e., efficient above-belowground interactions). These traits reflect important mechanisms of resilience and ecosystem stability under long-term moderate grazing in an N-limited environment. However, excessive (over)grazing might imbalance such C-N exchange and amplify plant N limitation, hampering productivity and pasture recovery over the long term. In this context, a reduction in grazing pressure provides a sustainable way to maintain soil fertility, C sequestration, efficient nutrient recycling, and overall ecosystem stability.  相似文献   

3.

Purpose

Alpine meadow soils are large carbon (C) and nitrogen (N) pools correlated significantly with global C and N cycling. Soil N transformations, including nitrification and N mineralization, are key processes controlling N availability. Alpine meadow degradations are common worldwide, and vegetation restorations have been widely implemented. However, grass species used for restorations may alter soil N transformations or their response to warming and N deposition due to divergent plant traits and their different effects on soil characteristic. To understand the effects of meadow restorations by non-historically dominant species on N transformations, we measured N transformation rates in restored soils and control soils under the context of warming and N deposition.

Materials and methods

We collected soils from plots restored by dominant (Miscanthus floridulus) and non-dominant species (including Carex chinensis and Fimbristylis dichotoma) and non-restored plots in alpine meadows of Wugong Mountain, China. We measured nitrification and N mineralization rates when soils were incubated at different temperature (15 or 25 °C) and N additions (control vs. 4 g m?2) to examine their responses to restoration species, warming, and N.

Results and discussion

Vegetation restored soils differed substantially from non-restored bare soils. Total N, total organic C, pH, and dissolved organic C contributed the most to the separation. Restoration altered soil N transformations substantially, even though the effects varied among restoration species. Specifically, non-historically dominant species accelerated N transformations, while the originally dominant species decreased N transformations. In addition, sensitivity of nitrification to warming in restored soils was decreased by restorations. Soils restored by originally dominant species were higher in sensitivity of N transformations to warming than those restored by the other two species. Warming increased nitrification rates by 45.5 and 17.4 % in bare soils and restored soils, respectively. Meanwhile, N mineralization rates were increased by 52.8 and 21.9 %, respectively.

Conclusions

Vegetation restoration of the degraded meadows impacted N transformations and their sensitivity to warming. The effects varied with identity of the restoration species, suggesting that grass species should be considered in future restorations of degraded meadows in terms of their divergent effects on N transformations and sensitivity to warming.
  相似文献   

4.

Purpose

Input of N as NH4 + is known to stimulate nitrification and to enhance the risk of N losses through NO3 ? leaching in humid subtropical soils. However, the mechanisms responsible for this stimulation effect have not been fully addressed.

Materials and methods

In this study, an acid subtropical forest soil amended with urea at rates of 0, 20, 50, 100 mg N kg?1 was pre-incubated at 25 °C and 60 % water-holding capacity (WHC) for 60 days. Gross N transformation rates were then measured using a 15N tracing methodology.

Results and discussion

Gross rates of mineralization and nitrification of NH4 +-N increased (P?<?0.05), while gross rate of NO3 ? immobilization significantly decreased with increasing N input rates (P?<?0.001). A significant relationship was established between the gross nitrification rate of NH4 + and the gross mineralization rate (R 2?=?0.991, P?<?0.01), so was between net nitrification rate of NH4 + and the net mineralization rate (R 2?=?0.973, P?<?0.05).

Conclusions

Stimulation effect of N input on the gross rate of nitrification of NH4 +-N in the acid soil, partially, resulted from stimulation effect of N input on organic N mineralization, which provides pH-favorable microsites for the nitrification of NH4 + in acid soils (De Boer et al., Soil Biol Biochem 20:845–850, 1988; Prosser, Advan Microb Physiol 30:125–181, 1989). The stimulated gross nitrification rate with the decreased gross NO3 ? immobilization rate under the elevated N inputs could lead to accumulation of NO3 ? and to enhance the risk of NO3 ? loss from humid forest soils.
  相似文献   

5.

Purpose

Initial soil pH determines the direction and magnitude of pH change after residue addition. This study aimed to evaluate the relative importance of initial soil pH and rate of residue application in determining subsequent pH change, nitrogen (N) mineralization, and soil-exchangeable aluminum (Al).

Materials and methods

An incubation experiment was conducted for 102 days on a Plinthudult soil and a Paleudalf soil, where pH gradients were produced after application of direct current (DC). Rates of vetch applications were 0, 5, 15, 30, and 50 g kg?1 soil.

Results and discussion

Increasing rates of vetch application caused greater increases in soil pH, but no consistent increase in soil pH at higher initial pH range (4.40～6.74), because of nitrification. There was a positive correlation between alkalinity production and the initial soil pH at day 14, while correlations became negative at days 56 and 102. Mineral N accumulated as NH4 +–N in low pH soils, due to limited nitrification, while NO3 ?–N dominated in higher pH soils. Application of vetch decreased KCl-extractable Al, probably because of complexation of Al by organic matter and precipitation of Al as a result of increased pH, reductions in Al concentration increased with increasing rates of vetch application. However, this amelioration effect on Al concentration weakened with time in higher pH soils.

Conclusions

Application of vetch residue can significantly increase soil pH and concentrations of mineral N and reduce exchangeable Al. These amelioration effects are enhanced with increased rate of vetch addition and vary with time depending on the initial pH of the soil.  相似文献   

6.

Purpose

Long-term manure applications can prevent or reverse soil acidification by chemical nitrogen (N) fertilizer. However, the resistance to re-acidification from further chemical fertilization is unknown. The aim of this study was to examine the effect of urea application on nitrification and acidification processes in an acid red soil (Ferralic Cambisol) after long-term different field fertilization treatments.

Materials and methods

Soils were collected from six treatments of a 19-year field trial: (1) non-fertilization control, (2) chemical phosphorus and potassium (PK), (3) chemical N only (N), (4) chemical N, P, and K (NPK), (5) pig manure only (M), and (6) NPK plus M (NPKM; 70 % N from M). In a 35-day laboratory incubation experiment, the soils were incubated and examined for changes in pH, NH4 +, and NO3 ?, and their correlations from urea application at 80 mg N kg?1(?80) compared to 0 rate (?0).

Results and discussion

From urea addition, manure-treated soils exhibited the highest acidification and nitrification rates due to high soil pH (5.75–6.38) and the lowest in the chemical N treated soils due to low soil pH (3.83–3.90) with no N-treated soils (pH 4.98–5.12) fell between. By day 35, soil pH decreased to 5.21 and 5.81 (0.54 and 0.57 unit decrease) in the NPKM-80 and M-80 treatments, respectively, and to 4.69 and 4.53 (0.43 and 0.45 unit decrease) in the control-80 and PK-80 treatments, respectively, with no changes in the N-80 and NPK-80 treatments. The soil pH decrease was highly correlated with nitrification potential, and the estimated net proton released. The maximum nitrification rates (K max) of NPKM and M soils (14.7 and 21.6 mg N kg?1 day?1, respectively) were significantly higher than other treatments (2.86–3.48 mg N kg?1 day?1). The priming effect on mineralization of organic N was high in manure treated soils.

Conclusions

Field data have shown clearly that manure amendment can prevent or reverse the acidification of the red soil. When a chemical fertilizer such as urea is applied to the soil again, however, soil acidification will occur at possibly high rates. Thus, the strategy in soil N management is continuous incorporation of manure to prevent acidification to maintain soil productivity. Further studies under field conditions are needed to provide more accurate assessments on acidification rate from chemical N fertilizer applications.  相似文献   

7.

Purpose

Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO3 ? leaching and soil acidification.

Materials and methods

We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg?1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied.

Results and discussion

During aerobic incubation, NO3 ? accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO3 ?, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N.

Conclusions

Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO3 ? leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N.  相似文献   

8.

Purpose

Carbon (C) dynamics in grassland ecosystem contributes to regional and global fluxes in carbon dioxide (CO2) concentrations. Grazing is one of the main structuring factors in grassland, but the impact of grazing on the C budget is still under debate. In this study, in situ net ecosystem CO2 exchange (NEE) observations by the eddy covariance technique were integrated with a modified process-oriented biogeochemistry model (denitrification–decomposition) to investigate the impacts of grazing on the long-term C budget of semiarid grasslands.

Materials and methods

NEE measurements were conducted in two adjacent grassland sites, non-grazing (NG) and moderate grazing (MG), during 2006–2007. We then used daily weather data for 1978–2007 in conjunction with soil properties and grazing scenarios as model inputs to simulate grassland productivity and C dynamics. The observed and simulated CO2 fluxes under moderate grazing intensity were compared with those without grazing.

Results and discussion

NEE data from 2-year observations showed that moderate grazing significantly decreased grassland ecosystem CO2 release and shifted the ecosystem from a negative CO2 balance (releasing 34.00 g C?m?2) at the NG site to a positive CO2 balance (absorbing ?43.02 g C?m?2) at the MG site. Supporting our experimental findings, the 30-year simulation also showed that moderate grazing significantly enhances the CO2 uptake potential of the targeted grassland, shifting the ecosystem from a negative CO2 balance (57.08?±?16.45 g C?m?2?year?1) without grazing to a positive CO2 balance (?28.58?±?14.60 g C?m?2?year?1) under moderate grazing. The positive effects of grazing on CO2 balance could primarily be attributed to an increase in productivity combined with a significant decrease of soil heterotrophic respiration and total ecosystem respiration.

Conclusions

We conclude that moderate grazing prevails over no-management practices in maintaining CO2 balance in semiarid grasslands, moderating and mitigating the negative effects of global climate change on the CO2 balance in grassland ecosystems.  相似文献   

9.

Purpose

Better understanding of N transformations and the regulation of N2O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies.

Materials and methods

15N tracer technique combined with acetylene (C2H2) method was used to measure gross N transformation rates and to distinguish pathways of N2O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C.

Results and discussion

Two tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (ntot) was 7.28 mg N kg?1 day?1 in TR soil () and 5.79 mg N kg?1 day?1 in GN soil. Heterotrophic nitrification rates (nh), which accounting for 50.8 and 41.9% of ntot, and 23.4 and 30.1% of N2O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N2O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg?1 day?1 under selected conditions but contributed more than 30% of N2O emissions.

Conclusions

Results demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO3?–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N2O emission in two pasture soils should be considered when developing mitigation strategies.
  相似文献   

10.
The aim of this study was to examine the effect of common diterpenes (colophony, abietic acid) and triterpene (beta-sitosterol) on carbon (C) and nitrogen (N) transformations in soil under birch (Betula pendula L.). Samples were taken from the organic layer at two study sites, Kivalo (N-poor soil) and Kerimäki (N-rich soil), and incubated with the above-mentioned terpenes in laboratory conditions. Carbon dioxide evolution (C mineralization), net N mineralization, nitrification, and N and C in microbial biomass were measured. All these terpenes increased C mineralization, but decreased net N mineralization. The potential to decrease net N mineralization depended on amount of terpenes, with a stronger effect at a higher amount. Net nitrification in Kerimäki soil (N-rich soil) decreased but was not completely inhibited by terpenes. Effect of terpenes on soil microbial biomass C and N was not so clear, but they tended to increase both. Our study suggests that higher terpenes can act as a carbon source for soil microbial communities.  相似文献   

11.
Previous studies have suggested grazing may alter nitrogen (N) cycling of grasslands by accelerating or decelerating soil net N mineralization. The important mechanisms controlling these fluxes remain controversial, and more importantly, the consequences on carbon storage and site productivity remain uncertain. Here we present results on the seasonal patterns of soil inorganic N pools and net N mineralization and their linkages to ecosystem functioning from a grazing experiment in the Inner Mongolia grassland, which has been maintained for five years with 7 levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep ha−1). Net N mineralization and nitrification rates were determined using an in situ soil core incubation method. Our findings demonstrated that, in the non-growing season, the net N mineralization rate was reduced by 181% in the lightly and moderately grazed plots (1.5-4.5 sheep ha−1) and by 147% in the heavily grazed plots (6.0-9.0 sheep ha−1), and the net N immobilization was observed in all grazed treatments. In the early growing season, however, it was increased by 107% in the lightly and moderately grazed plots and by 128% in the heavily grazed plots. In the peak growing season, grazing diminished the net mineralization rate by 71% in the lightly and moderately grazed plots and 108% in the heavily grazed plots. The seasonally dependent effects of grazing on soil inorganic N pools and net N mineralization were strongly mediated by grazing-induced changes in soil temperature and moisture, with soil moisture being predominant in the peak growing season. Grazing alterations of soil inorganic N and net N mineralization were closely linked to the changes in aboveground primary productivity, biomass N allocation, N use efficiency, and soil total nitrogen. Based upon the five year study, we conclude that grazing at moderate to high intensities is unsustainable in terms of productivity and soil N cycling and storage in these systems.  相似文献   

12.

Purpose

The aim of the research was to explore the effect of Chinese milk vetch (CM vetch) addition and different water management practices on soil pH change, C and N mineralization in acid paddy soils.

Materials and methods

Psammaquent and Plinthudult paddy soils amended with Chinese milk vetch at a rate of 12 g?kg?1 soil were incubated at 25 °C under three different water treatments (45 % field capacity, CW; alternating 1-week wetting and 2-week drying cycles, drying rewetting (DRW) and waterlogging (WL). Soil pH, dissolved organic carbon, dissolved organic nitrogen (DON), CO2 escaped, microbial biomass carbon, ammonium (NH4 +) and nitrate (NO3 ?) during the incubation period were dynamically determined.

Results and discussion

The addition of CM vetch increased soil microbial biomass concentrations in all treatments. The CM vetch addition also enhanced dissolved organic N concentrations in all treatments. The NO3–N concentrations were lower than NH4–N concentrations in DRW and WL. The pH increase after CM vetch addition was 0.2 units greater during WL than DRW, and greater in the low pH Plinthudult (4.59) than higher pH Paleudalfs (6.11) soil. Nitrogen mineralization was higher in the DRW than WL treatment, and frequent DRW cycles favored N mineralization in the Plinthudult soil.

Conclusions

The addition of CM vetch increased soil pH, both under waterlogging and alternating wet–dry conditions. Waterlogging decreased C mineralization in both soils amended with CM vetch. Nitrogen mineralization increased in the soils subjected to DRW, which was associated with the higher DON concentrations in DRW than in WL in the acid soil. Frequent drying–wetting cycles increase N mineralization in acid paddy soils.  相似文献   

13.

Purpose

The rate of litter decomposition can be affected by a suite of factors, including the diversity of litter type in the environment. The effect of mixing different litter types on decomposition rates is increasingly being studied but is still poorly understood. We investigated the effect of mixing either litter material with high nitrogen (N) and phosphorus (P) concentrations or those with low N and P concentrations on litter decomposition and nutrient release in the context of agroforestry systems.

Materials and methods

Poplar leaf litter, wheat straw, peanut leaf, peanut straw, and mixtures of poplar leaf litter-wheat straw, poplar leaf litter-peanut leaf, and poplar leaf litter-peanut straw litter samples were placed in litter bags, and their rates of decomposition and changes in nutrient concentrations were studied for 12 months in poplar-based agroforestry systems at two sites with contrasting soil textures (clay loam vs silt loam).

Results and discussion

Mixing of different litter types increased the decomposition rate of litter, more so for the site with a clay loam soil texture, representing site differences, and in mixtures that included litter with high N and P concentrations (i.e., peanut leaf). The decomposition rate was highest in the peanut leaf that had the highest N and P concentrations among the tested litter materials. Initial N and P immobilization may have occurred in litter of high carbon (C) to N or C to P ratios, with net mineralization occurring in the later stage of the decomposition process. For litter materials with a low C to N or P ratios, net mineralization and nutrient release may occur quickly over the course of the litter decomposition.

Conclusions

Non-additive effects were clearly demonstrated for decomposition rates and nutrient release when different types of litter were mixed, and such effects were moderated by site differences. The implications from this study are that it may be possible to manage plant species composition to affect litter decomposition and nutrient biogeochemistry; mixed species agroforestry systems can be used to enhance nutrient cycling, soil fertility, and site productivity in land-use systems.  相似文献   

14.

Purpose

Human disturbance is a major culprit driving imbalances in the biological transformation of nitrogen from the nonreactive to the reactive pool and is therefore one of the greatest concerns for nitrogen (N) cycling. The objective of this study was to compare potential nitrification rates and the abundance of ammonia oxidizers responsible for nitrification, with the amendment of external N in different agricultural soils.

Materials and methods

Three typical Chinese agricultural soils, QiYang (QY) acid soil, ShenYang (SY) neutral soil, and FengQiu (FQ) alkaline soil, were amended with 0, 20, 150, and 300 μg NH4 +-N g?1 soil and incubated for 40 days. The abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA) at the end of incubation in the soil microcosms was determined using the real-time PCR.

Results and discussion

There was a significant decrease in ammonium concentration in the QY soil from the highest to the lowest N-loading treatments, while no significant difference in ammonium concentrations was detected among the different N-loading treatments for the SY and FQ soils. A significantly higher potential nitrification rate (PNR) was observed in the FQ soil while lowest PNR was found in the QY soil. Quantitative PCR analysis of AOB amoA genes demonstrated that AOB abundance was significantly higher in the high N-loading treatments than in the control for the QY soil only, while no significant difference among treatments in the SY and FQ soils. A significant positive correlation between PNR and AOB amoA abundance, however, was found for the SY and FQ soils, but not for the QY soil. Little difference in AOA amoA abundance between different N-loading treatments was observed for all the soils.

Conclusions

This study suggested that ammonia oxidation capacity in the FQ and SY soils was higher than those in the QY soil with the addition of ammonium fertilizer for a short-term. These findings indicated that understanding the differential responses of biological nitrification to varying input levels of ammonium fertilizer is important for maximizing N use efficiency and thereby improving agricultural fertilization management.  相似文献   

15.
Intact soil cores from three adjacent sites (Site A: grazed, Site B: fenced for 4 years, and Site C: fenced for 24 years) were incubated in the laboratory to examine effects of temperature, soil moisture, and their interactions on net nitrification and N mineralization rates in the Inner Mongolia grassland of Northern China. Incubation temperature significantly influenced net nitrification and N mineralization rates in all the three grassland sites. There were no differences in net nitrification or N mineralization rates at lower temperatures (−10, 0, and 5 °C) whereas significant differences were found at higher temperatures (15, 25, and 35 °C). Soil moisture profoundly impacted net nitrification and N mineralization rates in all the three sites. Interactions of temperature and moisture significantly affected net nitrification and mineralization rates in Site B and C, but not in Site A. Temperature sensitivity of net nitrification and N mineralization varied with soil moisture and grassland site. Our results showed greater net N mineralization rates and lower concentrations of inorganic N in the grazed site than those in the fenced sites, suggesting negative impacts of grazing on soil N pools and net primary productivity.  相似文献   

16.

Purpose

Nitrogen (N) is one of the most important elements that can limit plant growth in forest ecosystems. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are considered as the key drivers of global N biogeochemical cycling. Soil ammonia-oxidizing microbial communities associated with subtropical vegetation remain poorly characterized. The aim of this study was to determine how AOA and AOB abundance and community structure shift in response to four typical forest vegetations in subtropical region.

Materials and methods

Broad-leaved forest (BF), Chinese fir forest (CF), Pinus massoniana forest (PF), and moso bamboo forest (MB) were widely distributed in the subtropical area of southern China and represented typical vegetation types. Four types of forest stands of more than 30 years grew adjacent to each other on the same soil type, slope, and elevation, were chosen for this experiment. The abundance and community structure of AOA and AOB were characterized by using real-time PCR and denaturing gradient gel electrophoresis (DGGE). The impact of soil properties on communities of AOA and AOB was tested by canonical correspondence analysis (CCA).

Results and discussion

The results indicated that AOB dominated in numbers over AOA in both BF and MB soils, while the AOA/AOB ratio shifted with different forest stands. The highest archaeal and bacterial amoA gene copy numbers were detected in CF and BF soils, respectively. The AOA abundance showed a negative correlation with soil pH and organic C but a positive correlation with NO3 ??N concentration. The structures of AOA communities changed with vegetation types, but vegetation types alone would not suffice for shaping AOB community structure among four forest soils. CCA results revealed that NO3 ??N concentration and soil pH were the most important environmental gradients on the distribution of AOA community except vegetation type, while NO3 ??N concentration, soil pH, and organic C significantly affected the distribution of the AOB communities.

Conclusions

These results revealed the differences in the abundance and structure of AOA and AOB community associated with different tree species, and AOA was more sensitive to vegetation and soil chemical properties than AOB. N bioavailability could be directly linked to AOA and AOB community, and these results are useful for management activities, including forest tree species selection in areas managed to minimize N export to aquatic systems.  相似文献   

17.
Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d−1 g−1 dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.

Purpose

Developing routine methods that accurately predict soil nitrogen (N) mineralization is essential for fertilization recommendation; thus, chemical soil testing has received worldwide attention. However, the optimal chemical soil test for predicting soil N mineralization is region specific. This study aimed to determine suitable chemical soil tests for predicting N mineralization in paddy soils of the Dongting Lake region, China.

Materials and methods

Composite surface samples (0–20 cm) of soils (n?=?30) with diverse inherent properties were collected from representative paddy fields across the region. The benchmark indices for soil N mineralization were the net mineralization rate of soil N in a 112-day anaerobic incubation under waterlogged conditions (NMRN112) and N mineralization potential (N o ) estimated using a modified double exponential model. Laboratory-based measurements of soil labile organic N (SLON) were conducted using chemical fractionation methods including 0.01 M NaHCO3 extraction, hot 2 M KCl hydrolysis, phosphate-borate (PB) buffer hydrolysis, acidic KMnO4 oxidation, and alkaline KMnO4 oxidation. These were compared with the benchmark indices to assess their suitability for use as indicators for N mineralization.

Results and discussion

Acidic KMnO4-oxidative organic N (acidic KMnO4-N) and PB buffer-hydrolysable organic N (PBHYDR-N) correlated strongly with NMRN112 and N o (r?=?0.825–0.884, P?<?0.001, n?=?30). Grouping of soils based on soil texture generally provided no improvement in the relationships of chemical soil tests with NMRN112 and N o . Multiple stepwise regression analysis indicated that combining acidic KMnO4-N and PBHYDR-N yielded the best prediction of soil N mineralization, explaining 86.1 and 85.5 % of the variation in NMRN112 and N o , respectively, of the 30 tested paddy soils.

Conclusions

The results of acidic KMnO4-N and PBHYDR-N as indicators for soil N mineralization were promising, and the operations of acidic KMnO4 oxidation and PB buffer hydrolysis procedures are simple and cost-effective. Therefore, a combination of acidic KMnO4-N and PBHYDR-N shows promise in predicting N mineralization in paddy soils of the Dongting Lake region. However, further calibration through field studies is required and the chemical characteristics of acidic KMnO4-N and PBHYDR-N needs to be further clarified.
  相似文献   

19.
《Applied soil ecology》2006,31(1-2):62-72
The aim of this study was to determine whether the spatial heterogeneity of grassland vegetation structure would lead to spatial heterogeneity in the net nitrogen mineralisation process in the soil and therefore in the quantity of mineral nitrogen available for the plants. The net nitrogen mineralisation in the soil was compared between different vegetation patches generated by grazing, on two different types of plant communities: mesophilous and meso-hygrophilous.In ungrazed conditions, the net soil nitrogen mineralisation rates did not vary significantly between the two plant communities and remained relatively constant with time. Grazing by cattle or horses appeared to have two effects on the process of net soil nitrogen mineralisation. Firstly, it significantly stimulated net nitrogen mineralisation compared to ungrazed conditions and secondly, it led to spatial heterogeneity in mineralisation rates in the grazed enclosures. This spatial heterogeneity of nitrogen available for plants occurred both between and within plant communities.In the meso-hygrophilous plant community, net nitrogen mineralisation increased with grazing pressure. We suggest that a decrease of C inputs to the soil, concomitant with increasing grazing pressure, could decrease microbial nitrogen immobilisation.By contrast, in the mesophilous plant community net nitrogen mineralisation did not vary with grazing pressure. These differences in the functional responsiveness to grazing and biomass between the two plant communities could be related to the differences in the functional traits characterizing their dominant species along the grazing gradient. In the meso-hygrophilous community, the species composition switch with grazing intensity gradient led to the replacement of the perennial plant species by annual plant species which could lead to an improvement in the litter nitrogen content and an acceleration in the litter decomposition rate. By contrast, in the mesophilous plant community, the perennial species remained dominant along the grazing intensity gradient and could explain the absence of effect on the net nitrogen mineralisation rates.We suggest that at the scale of the vegetation patch, the decrease in plant biomass linked to grazing could regulate soil microorganism activity, in relation with shift in plant functional traits which improve litter decomposability.  相似文献   

20.

Purpose

Soil water overconsumption is threatening the sustainability of regional vegetation rehabilitation in the Loess Plateau of China. In this study, two typical natural and artificial grasslands under different precipitation regimes were selected and the spatial variations in and the factors that impact the soil water content were investigated to provide support for vegetation restoration and sustainability management in the Loess Plateau.

Materials and methods

Soil samples were collected in May and September. Medicago sativa L. and Stipa bungeana Trin. were selected as representatives of natural and artificial grasslands, respectively. Soil measurements were conducted at the beginning and end of the rainy seasons at soil depths of 0 to 3 m in 0.2-m increments, and 147 undisturbed and 2205 disturbed soil samples were collected at 27 sampling sites with different precipitation gradients across the Loess Plateau. The plant height, the field capacity, the saturated hydraulic conductivity, the bulk density, and the slope gradient were considered as impact factors. Statistic methods included one-way ANOVA, correlation tests, significance tests, and redundancy analyses.

Results and discussion

Spatial variation trends indicated that the mean soil water content increased as the multi-year mean precipitation increased, and the soil water content was higher in the natural grassland of Stipa bungeana Trin. than in the artificial grassland of Medicago sativa L. in the same precipitation gradient zone. Vertical spatial variation trends indicated that the soil water content was higher in most surface layers than in the deep layer and lower at the end of the rainy season than at the beginning of the rainy season, when the mean annual precipitation was less than 510 mm. The soil water content of the Stipa bungeana Trin. grassland was significantly correlated with precipitation and plant height, whereas the soil water content of the Medicago sativa L. grassland only exhibited a significant correlation with precipitation. Thus, grasses with fine palatability, good adaptability, and low water consumption should be cultivated in the Loess Plateau.

Conclusions

The decreased soil water content is more obvious in the soil layers with active vegetation roots. In the areas with multi-year precipitation at 370–440 mm, natural grasslands are more suitable for restoration and these areas should be treated as key areas for vegetation restoration. With regard to the spatial distribution of vegetation restoration, the economic and ecological benefits must be balanced so that the ratio of artificial vegetation and natural restoration can be optimized to realize the continued sustainability of vegetation restorations.
  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