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1.
Climate models predict drier conditions in the next decades in the Mediterranean basin. Given the importance of soil CO2 efflux in the global carbon balance and the important role of soil monoterpene and volatile organic compounds (VOCs) in soil ecology, we aimed to study the effects of the predicted drought on soil CO2, monoterpenes and other VOC exchange rates and their seasonal and interannual variations. We decreased soil water availability in a Mediterranean holm oak forest soil by means of an experimental drought system performed since 1999 to the present. Measurements of soil gas exchange were carried out with IRGA, GC and PTR-MS techniques during two annual campaigns of contrasting precipitation. Soil respiration was twice higher the wet year than the dry year (2.27±0.26 and 1.05±0.15, respectively), and varied seasonally from 3.76±0.85 μmol m−2 s−1 in spring, to 0.13±0.01 μmol m−2 s−1 in summer. These results highlight the strong interannual and interseasonal variation in CO2 efflux in Mediterranean ecosystems. The drought treatment produced a significant soil respiration reduction in drought plots in the wet sampling period. This reduction was even higher in wet springs (43% average reduction). These results show (1) that soil moisture is the main factor driving seasonal and interannual variations in soil respiration and (2) that the response of soil respiration to increased temperature is constrained by soil moisture. The results also show an additional control of soil CO2 efflux by physiology and phenology of trees and animals. Soil monoterpene exchange rates ranged from −0.01 to 0.004 nmol m−2 s−1, thus the contribution of this Mediterranean holm oak forest soil to the total monoterpenes atmospheric budget seems to be very low. Responses of individual monoterpenes and VOCs to the drought treatment were different depending on the compound. This suggests that the effect of soil moisture reduction in the monoterpenes and VOC exchange rates seems to be dependent on monoterpene and VOC type. In general, soil monoterpene and other VOC exchange rates were not correlated with soil CO2 efflux. In all cases, only a low proportion of variance was explained by the soil moisture changes, since almost all VOCs increased their emission rates in summer 2005, probably due to the effect of high soil temperature. Results indicate thus that physical and biological processes in soil are controlling soil VOC exchange but further research is needed on how these factors interact to produce the observed VOCs exchange responses.  相似文献   

2.
Leaf and berry transpiration ratio in grapevine (Vitis vinifera L.) was found to be affected by soil moisture. With the condition of diminished soil moisture, berry transpiration is higher prior to vèraison compared to conditions when the water content in the substrate is higher and berry transpiration decreases with an increase of leaf transpiration. Studies were conducted in 1993 and 1994 to investigate the link between soil moisture, traspiration, and accumulation of certain mineral elements in leaves and berries on plants of the Cabernet sauvignon cultivar grafted on Kober 5 BB rootstock. Leaf and berry transpiration and mineral accumulation were evaluated by gaseous exchange measurements, soil sampling and moisture analysis, and leaf and berry sampling and analysis of mineral content. Observations were repeated at about 15‐day intervals between full bloom and berry ripening. Transpiration per unit of surface area (mmol H2O m‐2 s‐1) was always higher in leaves than in berries. Leaf transpiration varied from 5.62 mmol H2O m‐2 s‐1 to 2.92 mmol H2O m‐2 s‐1 in 1993 in the period between the 8th and 86th day after full bloom (DAFB), and from 6.49 mmol H2O m‐2 s‐1 to 4.37 mmol H2O m‐2 s‐1 in 1994 between the 12th and 94th DAFB. Berry transpiration ranged between 3.86 mmol H2O m‐2 s‐1 and 1.04 mmol H2O m‐2 s‐1 in 1993 and between 4.34 mmol H2O m‐2 s‐1 and 0.5 mmol H2O m‐2 s‐1 in 1994. Leaf transpiration was not correlated with the mineral element content in the leaves, whereas berry transpiration was directly correlated with the nitrogen (N), calcium (Ca), potassium (K), and phosphorus (P) content in berries. Leaf mineral composition was affected only for iron (Fe) content by the variation on soil moisture, whereas the berry N, P, K, and Ca contents were positively correlated with soil water content. The leaf and berry Ca content appeared to be greater with high soil moisture, i.e., in conditions which favor intense metabolism of the whole plant.  相似文献   

3.

Purpose

Soil respiration (R s) is controlled by abiotic soil parameters interacting with characteristics of the vegetation and the soil microbial community. Few studies have attempted a comprehensive approach that simultaneously addresses the roles of all the major factors known to influence R s. Our goal was to explore the links between heterogeneity in R s, aboveground plant biomass and belowground properties in three representative land-use types in a dry Mediterranean ecosystem: (1) a 150-year-old mixed Aleppo pine-kermes oak open forest, (2) an abandoned agricultural field, which was cultivated with cereal for several years until abandonment in 1980, when establishment of typical Mediterranean shrubland vegetation started and (3) a rain-fed olive grove, which has been cultivated for 100 years.

Materials and methods

We selected two distinctive sampling periods coinciding with annual minimum or near minimum (December) and maximum (April) rates of R s in this dry Mediterranean ecosystem. In each sampling period, R s, temperature and moisture, aboveground plant biomass, carbon (C) and nitrogen (N) contents in both light and heavy soil organic matter fractions, extractable dissolved organic C (EDOC), as well as microbial and fine root biomass were measured within each land-use type.

Results and discussion

Across sites, R s rates were significantly higher in April (3.07?±?0.1 μmol?m?2?s?1) than in December (1.30?±?0.1 μmol?m?2?s?1). The labile soil organic matter fractions (light fraction C and N contents, microbial biomass C and EDOC) were consistently and strongly related to one another, and to a lesser extent, to the C and N contents in the heavy fraction across sites and seasons. Linear models adequately explained a large proportion of the within-site variability in R s (R 2 values ranged from 41 to 91 % depending on land use and season) but major controls on R s differed considerably between sites and seasons. Primary controls on spatial patterns in R s were linked to recent plant-derived C inputs in both forest and olive grove sites. However, in the abandoned agricultural field site R s appeared to be mainly driven by microbial activity, which could be sustained by intermediate or recalcitrant C and N pools derived from previous land use.

Conclusions

Conversion of native woodland to agricultural land and subsequent land abandonment leads to profound changes in the relationships between R s, aboveground biomass and belowground properties in this dry Mediterranean ecosystem. While above- and belowground vegetation are the primary controls on spatial variability in labile soil C pools and R s in the open forest and olive grove sites, a complete lack of influence of current vegetation patterns on soil C pools and respiration rates in the abandoned agricultural field was observed.  相似文献   

4.
Rates of C2H2-reduction in surface soil and litter from pine and eucalypt forests were measured for 1 yr. Rates of reduction increased significantly with moisture content, and mean rates (nmol kg?1 h?1) decreased in the order pine litter (339), eucalypt litter (220), eucalypt soil (54), pine soil (7). Asymbiotic N2-fixation in litter and surface soil was estimated to be 108 mg m?2 yr?1 in eucalypt forest and 64 mg m?2 yr?1 in pine forest. About 80% of total fixation in eucalypt was in the soil, while 80% of the total in pine was in the litter. N2ase was active in rotting wood but not in fresh foliage.  相似文献   

5.
Intensification of homegardens in the Nuba Mountains may lead to increases in C and nutrient losses from these small‐scale land‐use systems and potentially threaten their sustainability. This study, therefore, aimed at determining gaseous C and N fluxes from homegarden soils of different soil moisture, temperature, and C and N status. Emissions of CO2, NH3, and N2O from soils of two traditional and two intensified homegardens and an uncultivated control were recorded bi‐weekly during the rainy season in 2010. Flux rates were determined with a portable dynamic closed chamber system consisting of a photo‐acoustic multi‐gas field monitor connected to a PTFE coated chamber. Topsoil moisture and temperature were recorded simultaneously to the gas measurements. Across all homegardens emissions averaged 4,527 kg CO2‐C ha?1, 22 kg NH3‐N ha?1, and 11 kg N2O‐N ha?1 for the observation period from June to December. Flux rates were largely positively correlated with soil moisture and predominantly negatively with soil temperature. Significant positive, but weak (rs < 0.34) correlations between increasing management intensity and emissions were noted for CO2‐C. Similarly, morning emissions of NH3 and increasing management intensity were weakly correlated (rs = 0.17). The relatively high gaseous C and N losses in the studied homegardens call for effective management practices to secure the soil organic C status of these traditional land‐use systems.  相似文献   

6.
Abstract

The study aimed at quantifying the rates of soil CO2 efflux under the influence of common tillage systems of moldboard plow (PT), chisel plow (CT), rotary tiller (RT), heavy disc harrow (DT), and no-tillage (NT) for 46 days in October and November in a field left fallow after wheat harvest located in southern Turkey. The NT and DT plots produced the lowest soil CO2 effluxes of 0.3 and 0.7 g m?2 h?1, respectively, relative to the other plots (P < 0.001). Following the highest rainfall amount of 87 mm on the tenth day after the tillage, soil CO2 efflux rates of all the plots peaked on the 12th day, with less influence on soil CO2 efflux in the NT plot than in the conventional tillage plots. Soil evaporation in NT (64 mmol m?2 s?1) was significantly lower than in the PT (85 mmol m?2 s?1) and RT (89 mmol m?2 s?1) tillage treatments (P < 0.01). The best multiple-regression model selected explained 46% of variation in soil respiration rates as a function of the tillage treatments, soil temperature, and soil evaporation (P < 0.001). The tillage systems of RT, PT, and CT led, on average, to 0.23, 0.22, and 0.18 g m?2 h?1 more soil CO2 efflux than the baseline of NT, respectively (P≤0.001).  相似文献   

7.
Plants furnish soil with organic carbon (OC) compounds that fuel soil microorganisms, but whether individual plant species – or plants with unique traits – do so uniquely is uncertain. We evaluated soil microbial processes within a wetland in which areas dominated by a distinct plant species (cattail –Typha sp.; purple loosestrife –Lythrum salicaria L.; reed canarygrass –Phalaris arundinacea L.) co‐mingled. We also established an experimental plot with plant shoot removal. The Phalaris area had more acidic soil pH (7.08 vs. 7.27–7.57), greater amount of soil organic matter (19.0% vs. 9.0–11.5%), and the slowest production rates of CO2 (0.10 vs. 0.21–0.46 μmol kg−1 s−1) and CH4 (0.040 vs. 0.054–0.079 nmol kg−1 s−1). Nitrogen cycling was dominated by net nitrification, with similar rates (17.2–18.9 mg kg−1 14 days−1) among the four sampling areas. In the second part of the study, we emplaced soil cores that either allowed root in‐growth or excluded roots to evaluate how roots directly affect soil CO2 and CH4. The three plant species had similar amounts of root growth (ca 290 g m−2 year−1). Fungal biomass was similar in soils with root in‐growth versus root exclusion, regardless of dominant plant species. Rates of soil CO2 production did not differ with root in‐growth versus root exclusion, and added glucose increased CO2 production rates by only 35%. Root in‐growth did lead to greater rates of CH4 production; albeit, addition of glucose had much greater effect on CH4 production (1.24 nmol kg−1 s−1) compared with controls without added glucose (0.058 nmol kg−1 s−1). Our data revealed relatively few subtle differences in soil characteristics and processes associated with different plant species; albeit, roots had little effect, even inhibiting some microbial processes. This research highlights the need for both field and experimental studies in long‐established monocultures of plant species to understand the role of plant biodiversity in soil function.  相似文献   

8.
Fire affects large parts of the dry Mediterranean shrubland, resulting in erosion and losses of plant nutrients. We have attempted to measure these effects experimentally on a calcareous hillside representative of such shrubland. Experimental fires were made on plots (4 m × 20 m) in which the fuel was controlled to obtain two different fire intensities giving means of soil surface temperature of 439°C and 232°C with temperatures exceeding 100°C lasting for 36 min and 17 min. The immediate and subsequent changes induced by fire on the soil's organic matter content and other soil chemical properties were evaluated, together with the impact of water erosion. Seven erosive rain events, which occurred after the experimental fires (from August 1995 to December 1996), were selected, and on them runoff and sediment produced from each plot were measured. The sediments collected were weighed and analysed. Taking into account the variations induced by fire on the soil properties and their losses by water erosion, estimates of the net inputs and outputs of the soil system were made. Results show that the greatest losses of both soil and nutrients took place in the 4 months immediately after the fire. Plots affected by the most intense fire showed greater losses of soil (4077 kg ha?1) than those with moderate fire intensity (3280 kg ha?1). The unburned plots produced the least sediment (72.8 kg ha?1). Organic matter and nutrient losses by water erosion were related to the degree of fire intensity. However, the largest losses of N‐NH4+ and N‐NO3– by water erosion corresponded to the moderate fire (8.1 and 7.5 mg N m?2, respectively).  相似文献   

9.
Landfills are regarded as important sources of the atmospheric methane (CH4), one of the major greenhouse gases. In this study we investigated the CH4 dynamics of landfill cover soils in a long‐term field experiment. The CH4 emission rates were low, mostly ranging from —100 to 100 μmol m—2 h—1, with prevailing negative values. Higher values of up to 130,000 μmol m—2 h—1, obtained concurrently, were due to mice burrows, connecting the reduced soil sections with the aerated ones. Thus, the appearance of spatial dissimilarity was the most important factor influencing temporal variability. Reducing the soil cover from 120 cm to at least 60 cm caused a tendency of increased CH4 emission. The oxidation rates were also low and differed with low temporal variability from 1.0—11.9 nmol g—1 h—1 in 0—10 cm soil depth and 0—5.3 nmol g—1 h—1 in 40—50 cm, respectively. Highest rates were obtained at 25—30 % soil water content. A mapping of CH4 concentrations over the whole landfill showed a large spatial variation with values of 3.1—343 nmol g—1. Subsequent CH4 emission rates were between —0.2 and 120,000 mmol m—2 d—1 and showed a positive correlation to the CH4 concentrations (r = 0.993, P < 0.05). Thus, by a large scale mapping of CH4 concentrations a low‐cost procedure is proposed to identify the hot spots of CH4 release which should be treated with additional thick and well aerated cover soil materials.  相似文献   

10.
Extensive research has focused on the temperature sensitivity of soil respiration. However, in Mediterranean ecosystems, soil respiration may have a pulsed response to precipitation events, especially during prolonged dry periods. Here, we investigate temporal variations in soil respiration (Rs), soil temperature (T) and soil water content (SWC) under three different land uses (a forest area, an abandoned agricultural field and a rainfed olive grove) in a dry Mediterranean area of southeast Spain, and evaluate the relative importance of soil temperature and water content as predictors of Rs. We hypothesize that soil moisture content, rather than soil temperature, becomes the major factor controlling CO2 efflux rates in this Mediterranean ecosystem during the summer dry season. Soil CO2 efflux was measured monthly between January 2006 and December 2007 using a portable soil respiration instrument fitted with a soil respiration chamber (LI-6400-09). Mean annual soil respiration rates were 2.06 ± 0.07, 1.71 ± 0.09, and 1.12 ± 0.12 μmol m−2 s−1 in the forest, abandoned field and olive grove, respectively. Rs was largely controlled by soil temperature above a soil water content threshold value of 10% at 0-15 cm depth for forest and olive grove, and 15% for abandoned field. However, below those thresholds Rs was controlled by soil moisture. Exponential and linear models adequately described Rs responses to environmental variables during the growing and dry seasons. Models combining abiotic (soil temperature and soil rewetting index) and biotic factors (above-ground biomass index and/or distance from the nearest tree) explained between 39 and 73% of the temporal variability of Rs in the forest and olive grove. However, in the abandoned field, a single variable - either soil temperature (growing season) or rewetting index (dry season) - was sufficient to explain between 51 and 63% of the soil CO2 efflux. The fact that the rewetting index, rather than soil water content, became the major factor controlling soil CO2 efflux rates during the prolonged summer drought emphasizes the need to quantify the effects of rain pulses in estimates of net annual carbon fluxes from soil in Mediterranean ecosystems.  相似文献   

11.
Tree species can affect the sink and source strength of soils for atmospheric methane and nitrous oxide. Here we report soil methane (CH4) and nitrous oxide (N2O) fluxes of adjacent pure and mixed stands of beech and spruce at Solling, Germany. Mean CH4 uptake rates ranged between 18 and 48 μg C m?2 hour?1 during 2.5 years and were about twice as great in both mixed and the pure beech stand as in the pure spruce stand. CH4 uptake was negatively correlated with the dry mass of the O horizon, suggesting that this diminishes the transport of atmospheric CH4 into the mineral soil. Mean N2O emission was rather small, ranging between 6 and 16 μg N m?2 hour?1 in all stands. Forest type had a significant effect on N2O emission only in one mixed stand during the growing season. We removed the O horizon in additional plots to study its effect on gas fluxes over 1.5 years, but N2O emissions were not altered by this treatment. Surprisingly, CH4 uptake decreased in both mixed and the pure beech stands following the removal of the O horizon. The decrease in CH4 uptake coincided with an increase in the soil moisture content of the mineral soil. Hence, O horizons may maintain the gas diffusivity within the mineral soil by storing water which cannot penetrate into the mineral soil after rainfall. Our results indicate that conversion of beech forests to beech–spruce and pure spruce forests could decrease soil CH4 uptake, while the long‐term effect on N2O emissions is expected to be rather small.  相似文献   

12.
Soil respiration in forest plantations can be greatly affected by management practices. Irrigation is necessary for high productivity of poplar plantations in semi-arid northwest China. Moreover, plowing is essential for improving soil quality and reducing evaporation. In the present study, the influences of irrigation and plowing on soil carbon dioxide (CO2) efflux were investigated in poplar plantations in 2007 and 2008. The experiments included three stand age classes receiving three treatments: control, irrigation, and plowing. Mean soil respiration in irrigation treatment stands was 5.47, 4.86, and 4.43?µmol?m?2?s?1 in 3-, 8-, and 15-year-old stands, respectively, during the growing season. In contrast, mean soil respiration in control stands was 3.71, 3.83, and 3.98?µmol?m?2?s?1 in 3-, 8-, and 15-year-old stands, respectively. During the entire observation period, mean soil respiration in plowing treatment stands increased by 36.2% compared with that in the control stands. Mean soil respiration in irrigation treatment stands was significantly higher than that in the control stands; this was mainly because fine root growth and decomposer activities were greatly depressed by soil drought, since natural precipitation could not meet their water demands. The results also suggest that plowing management can greatly increase soil CO2 emission by modifying soil structure. After plowing, soil bulk density decreased and soil aeration was greatly improved, leading to greater rates of oxidation and mineralization.  相似文献   

13.
Abstract

Speciation study of microelements in soils is useful to assess their retention and release by the soil to the plant. Laboratory and greenhouse investigations were conducted for five soils of different agro‐ecological zones (viz., Bhuna, Delhi, Cooch‐Behar, Gurgaon, and Pabra) with diverse physicochemical properties to study the distribution of zinc (Zn) among the soil fractions with respect to the availability of Zn species for uptake by rice plant. A sequential extraction procedure was used that fractionated total soil Zn into water‐soluble (WS), exchangeable (EX), specifically adsorbed (SA), acid‐soluble (AS), manganese (Mn)‐oxide‐occluded (Mn‐OX), organic‐matter‐occluded (OM), amorphous iron (Fe)‐oxide‐bound (AFe‐OX), crystalline Fe‐oxide‐bound (CFe‐OX), and residual (RES) forms. There was a wide variation in the magnitude of these fractions among the soils. The studies revealed that more than 90% of the total Zn content occurred in the relatively inactive clay lattice and other mineral‐bound form (RES) and that only a small fraction occurred in the forms of WS, EX, OM, AFe‐OX, and CFe‐OX. Rice (Oryza sativa L.) cultivars differ widely in their sensitivity to Zn deficiency. Results suggested that Zn in water‐soluble, organic complexes, exchange positions, and amorphous sesquioxides were the fractions (pools) that played a key role in the uptake of Zn by the rice varieties (viz., Pusa‐933‐87‐1‐11‐88‐1‐2‐1, Pusa‐44, Pusa‐834, Jaya, and Pusa‐677). Isotopic ally exchangeable Zn (labile Zn) was recorded higher in Typic Ustrochrept of Pabra soil, and uptake of Zn by rice cultivars was also higher in this soil. The kinetic parameters such as maximum influx at high concentrations (Imax) and nutrient concentration in solution where influx is one half of Imax (Km) behaved differentially with respect to varieties. The highest Imax value recorded was 9.2×10?7 µmol cm?2 s?1 at the 5 mg kg?1 Zn rate for Pusa‐933‐87‐1‐11‐88‐1‐2‐1, and the same was lowest for Pusa‐44, being 4.6×10?7 µmol cm?2 s?1 at the 5 mg kg?1 Zn rate. The Km value was highest for Pusa‐44 (2.1×10?4µmol cm?2 s?1) and lowest for Pusa‐933‐87‐1‐11‐88‐1‐2‐1 (1.20×10?4µmol cm?2 s?1). The availability of Zn to rice cultivars in Typic Ustrochrepts of Bhuna and Delhi soils, which are characterized by higher activation energy and entropy factor, was accompanied by breakage of bonds or by significant structural changes.  相似文献   

14.
The methane dynamics of soils covering a landfill in Oldenburg, Lower Saxony, was investigated in 1996. The methane concentration was often < 20 nmol (dry g)?1 within the cover layer and up to 9950 nmol (dry g)?1 within the refuse body. The methane production rates correlated positively with the methane concentrations and were mostly < 10 nmol (dry g)?1 d?1 within the cover layer and up to 1090 nmol (dry g)_1 d_1 within the refuse body. The methane oxidation rates varied between 38.0–2310 nmol (dry g)?1 d?1. The methane emission rates showed values of up to 574 mol m?2 h?1, but in two cases no emission of methane was found. The data indicate that the methano-genesis of the deep refuse layers did not substantially affect the methane behaviour of the upper soil sections. It is likely that the emission of methane from landfills can be reduced by thick well aerated cover layers. The term “Reduktosol” for landfill soils is critically discussed.  相似文献   

15.
Nitric oxide (NO) plays a central role in the formation of tropospheric ozone, hydroxyl radicals, as well as nitrous and nitric acids. There are, however, large uncertainties around estimates of global NO emissions due to the paucity of data. In particular, there is little information on the rate of NO emission and its sensitivity to processes such as land use changes in dry environments. Here we report on a two-year study on the influence of afforestation on soil NO fluxes in the semi-arid afforestation system in Southern Israel (Yatir forest, mean annual precipitation ∼280 mm). Laboratory incubations were carried out under seasonally defined conditions of soil moisture and temperature using soils sampled in different seasons from the native shrubland (taken both under shrub canopy and in the inter-shrub areas), and from the adjacent ∼2800 ha, 40-year-old pine afforestation site. Combining laboratory results with field measurements of soil moisture and temperature, we up-scaled soil-atmosphere NO fluxes to the ecosystem level. The different microsites differed in their annual mean NO release rates (0.04, 0.14 and 0.03 mg m−2 d−1 for the shrubland under and between shrubs and for the forest, respectively), and exhibited high inter-seasonal variability in NO emission rates (ranging from zero up to 0.25 mg m−2 d−1 in the wet and dry-rewetting seasons, respectively), as well as in temperature responses. Up-scaling results to annual and ecosystem scales indicated that afforestation of the semi-arid shrubland could reduce soil NO emission by up to 65%.  相似文献   

16.
The effects of zeolite application (0, 4, 8 and16 g kg?1) and saline water (0.5, 1.5, 3.0 and 5.0 dS m?1) on saturated hydraulic conductivity (K s) and sorptivity (S) in different soils were evaluated under laboratory conditions. Results showed that K s was increased at salinity levels of 0.5‐1.5 dS m?1 in clay loam and loam with 8 and 4 g zeolite kg?1 soil, respectively, and at salinity levels of 3.0–5.0 dS m?1 with 16 g zeolite kg?1 soil. K s was decreased by using low and high salinity levels in sandy loam with application of 8 and 16 g zeolite kg?1, respectively. In clay loam, salinity levels of 0.5–3.0 dS m?1 with application of 16 g kg?1 zeolite and 5.0 dS m?1 with application of 8 g zeolite kg?1 soil resulted in the lowest values of S. In loam, all salinity levels with application of 16 g zeolite kg?1 soil increased S compared with other zeolite application rates. In sandy loam, only a salinity level of 0.5 dS m?1 with application of 4 g zeolite kg?1 soil increased S. Other zeolite applications decreased S, whereas increasing the zeolite application to 16 g kg?1 soil resulted in the lowest value of S.  相似文献   

17.
Abstract

To determine the means and variations in CH4 uptake and N2O emission in the dominant soil and vegetation types to enable estimation of annual gases fluxes in the forest land of Japan, we measured monthly fluxes of both gases using a closed-chamber technique at 26 sites throughout Japan over 2 years. No clear seasonal changes in CH4 uptake rates were observed at most sites. N2O emission was mostly low throughout the year, but was higher in summer at most sites. The annual mean rates of CH4 uptake and N2O emission (all sites combined) were 66 (2.9–175) µg CH4-C m?2 h?1 and 1.88 (0.17–12.5) µg N2O-N m?2 h?1, respectively. Annual changes in these fluxes over the 2 years were small. Significant differences in CH4 uptake were found among soil types (P < 0.05). The mean CH4 uptake rates (µg CH4-C m?2 h?1) were as follows: Black soil (95 ± 39, mean ± standard deviation [SD]) > Brown forest soil (60 ± 27) ≥ other soils (20 ± 24). N2O emission rates differed significantly among vegetation types (P < 0.05). The mean N2O emission rates (µg N2O-N m?2 h?1) were as follows: Japanese cedar (4.0 ± 2.3) ≥ Japanese cypress (2.6 ± 3.4) > hardwoods (0.8 ± 2.2) = other conifers (0.7 ± 1.4). The CH4 uptake rates in Japanese temperate forests were relatively higher than those in Europe and the USA (11–43 µg CH4-C m?2 h?1), and the N2O emission rates in Japan were lower than those reported for temperate forests (0.23–252 µg N2O-N m?2 h?1). Using land area data of vegetation cover and soil distribution, the amount of annual CH4 uptake and N2O emission in the Japanese forest land was estimated to be 124 Gg CH4-C year?1 with 39% uncertainty and 3.3 Gg N2O-N year?1 with 76% uncertainty, respectively.  相似文献   

18.
Increasing nitrogen deposition due to human activity might have a serious impact on ecosystem functions such as the nitrogen transformations conducted by microbes. We therefore focused on nitrous oxide (N2O) production as an indicator of soil microbial activity. The rates of N2O emission from the forest floor were measured every two weeks in two forest stands in the central part of Japan: a red pine stand at Kannondai and a deciduous stand at Yasato. Nitrogen deposition rates by throughfall were 30.6 kg N ha?1 y?1 at Kannondai and 15.7 at Yasato. The rates of N2O emission ranged from 0.5 to 14.2 µg N m?2 h?1 (mean 4.5) at Kannondai and from 0.2 to 7.0 µg N m?2 h?1 (mean 2.3) at Yasato. The N2O emission rate showed significant positive relationships with soil temperature and nitrogen deposition during the preceding two weeks. The annual emission rates of N2O were 0.38 kg N ha?1 y?1 at Kannondai and 0.20 at Yasato. As a the annual nitrogen deposition, these rates were 1.23% at Kannondai and 1.27% at Yasato.  相似文献   

19.
Land‐use change and soil management play a vital role in influencing losses of soil carbon (C) by respiration. The aim of this experiment was to examine the impact of natural vegetation restoration and long‐term fertilization on the seasonal pattern of soil respiration and cumulative carbon dioxide (CO2) emission from a black soil of northeast China. Soil respiration rate fluctuated greatly during the growing season in grassland (GL), ranging from 278 to 1030 mg CO2 m?2 h?1 with an average of 606 mg CO2 m?2 h?1. By contrast, soil CO2 emission did not change in bareland (BL) as much as in GL. For cropland (CL), including three treatments [CK (no fertilizer application), nitrogen, phosphorus and potassium application (NPK), and NPK together with organic manure (OM)], soil CO2 emission gradually increased with the growth of maize after seedling with an increasing order of CK < NPM < OM, reaching a maximum on 17 August and declining thereafter. A highly significant exponential correlation was observed between soil temperature and soil CO2 emission for GL during the late growing season (from 3 August to 28 September) with Q10 = 2.46, which accounted for approximately 75% of emission variability. However, no correlation was found between the two parameters for BL and CL. Seasonal CO2 emission from rhizosphere soil changed in line with the overall soil respiration, which averaged 184, 407, and 584 mg CO2 m?2 h?1, with peaks at 614, 1260, and 1770 mg CO2 m?2 h?1 for CK, NPK, and OM, respectively. SOM‐derived CO2 emission of root free‐soil, including basal soil respiration and plant residue–derived microbial decomposition, averaged 132, 132, and 136 mg CO2 m?2 h?1, respectively, showing no difference for the three CL treatments. Cumulative soil CO2 emissions decreased in the order OM > GL > NPK > CK > BL. The cumulative rhizosphere‐derived CO2 emissions during the growing season of maize in cropland accounted for about 67, 74, and 80% of the overall CO2 emissions for CK, NPK, and OM, respectively. Cumulative CO2 emissions were found to significantly correlate with SOC stocks (r = 0.92, n = 5, P < 0.05) as well as with SOC concentration (r = 0.97, n = 5, P < 0.01). We concluded that natural vegetation restoration and long‐term application of organic manure substantially increased C sequestration into soil rather than C losses for the black soil. These results are of great significance to properly manage black soil as a large C pool in northeast China.  相似文献   

20.
A field experiment was conducted to examine responses of soil respiration, nitrification, and denitrification to warming in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation cropland. The results showed that seasonal variations in soil respiration were positively related to seasonal fluctuations in soil temperature. Seasonal mean soil respiration rates for the experimental warming (EW) and control (CK) plots were 3.98 ± 0.43 and 2.54 ± 0.45 μmol m?2 s?1, respectively, in the winter wheat growing season, and they were 4.59 ± 0.16 and 4.36 ± 0.08 μmol m?2 s?1, respectively, in the soybean growing season. There was a marginally significant level (p = 0.097) for mean nitrification rates between EW and CK plots. Soil temperature and moisture accounted for 58.2% and 58.1% of the seasonal variations observed in the winter wheat and soybean plots, respectively.  相似文献   

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