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1.
Ji Young Jung  Rattan Lal 《Geoderma》2011,166(1):145-152
Growing switchgrass (Panicum virgatum, L.), a promising bioenergy crop, needs finely-tuned nitrogen (N) fertilization to improve biomass yields depending on soil types and site characteristics. N fertilization can also affect the soil organic carbon (SOC) pool. Therefore, this study was conducted to assess the effects of N fertilization on switchgrass biomass production and the SOC stock in Ohio. Switchgrass was established at three research stations (Northwest, Jackson, and Western sites) of the Ohio Agricultural Research and Development Center (OARDC) in spring 2004. N fertilizer was applied at four different rates (0, 50, 100, and 200 kg N ha−1) in 2008 and 2009. Aboveground and root biomass and the carbon (C) and N concentrations in plant tissues, SOC concentrations up to 30 cm depth were measured at the end of the growing season in 2009. Aboveground biomass at the Western site was the highest as 26 Mg ha−1 with 200 kg N ha−1 application, but there were no significant effects of N fertilization on aboveground biomass at two other sites and on root biomass across all sites. The amount of N export due to harvesting aboveground biomass increased with increase in N rates but did not vary among sites. With increasing N rates, the SOC stock linearly increased from 102 to 123 and from 55 to 70 Mg C ha−1 at the Northwest and the Jackson sites, respectively. However, this positive correlation was not observed for the Western site (a range of 59 to 67 Mg C ha−1). This study showed a potential of growing switchgrass as a bioenergy crop in Ohio and positive responses of the SOC stock to N fertilization.  相似文献   

2.
Little work has been done to quantify annual soil CO2 effluxes in the High Arctic region because of the difficulty in taking winter measurements. Since the effects of climate change are expected to be higher in Arctic than in temperate ecosystems, it is important that summer measurements are extended to cover the entire year. This study evaluates the quantity and quality of soil organic C (SOC) and seasonal controls of soil CO2 effluxes in three soils under three dominating types of vegetation (Dryas, Cassiope, and Salix) at Svalbard. Measurements included soil CO2 effluxes in the field and the laboratory, temperature, water content, and snow thickness. About 90% of the variation in soil respiration throughout 1 year was due to near-surface soil temperatures which ranged from −12 to +12 °C. Total annual soil CO2 effluxes varied from 103 g C m−2 at soils under Cassiope, 152 g C m−2 under Dryas sites, and 176 g C m−2 under Salix, with 20%, 14%, and 30%, respectively, being released during a 6-month winter period. The sensitivity of soil respiration with respect to soil temperature was the same year round and differences in winter CO2 effluxes at the three vegetation types were mainly related to subsurface soil temperatures controlled by snow depth. The quantity and quality of soil organic matter varied under the different vegetation types. Soils under Salix had the largest and most labile pool of SOC and were characterized by a long period of snow cover. In contrast, soils under Cassiope were more nutrient-poor, more acidic and held the smallest amount of total and labile SOC, whereas soils under Dryas remained snow-free most of the winter and therefore had the coldest winter conditions. Thus, winter soil respiration rates under Dryas and Cassiope were significantly lower than those under Salix; under Dryas this was mainly due to snow depth, under Cassiope this was a combination of snow depth and poor litter quality. It is concluded that winter respiration is highly variable across Arctic landscapes and depends on the spatial distribution of snow, which acts as a direct control on soil temperatures and indirect on vegetation types and thereby, the amount and quality of soil organic matter, which serve as additional important drivers of soil respiration.  相似文献   

3.
Spartina alterniflora is an invasive C4 perennial grass, native to North America, and has spread rapidly along the east coast of China since its introduction in 1979. Since its intentional introduction to the Jiuduansha Island in the Yangtze River estuary, Spartina alterniflora community has become one of the dominant vegetation types. We investigated the soil carbon in the Spartina alterniflora community and compared it with that of the native C3Scirpus mariqueter community by measuring total soil carbon (TC), soil organic carbon (SOC), total soil nitrogen (TN), and the stable carbon isotope composition (δ13C) of various fractions. TC and SOC were significantly higher in Spartina alterniflora in the top 60 cm of soil. However, there was no significant difference in soil inorganic carbon (IC) between the two communities. Stable carbon isotopic analysis suggests that the fraction of SOC pool contributed by Spartina alterniflora varied from 0.90% to 10.64% at a soil depth of 0-100 cm with a greater percentage between 20 and 40 cm deep soils. The δ13C decreased with increasing soil depth in both communities, but the difference in δ13C among layers of the top 60 cm soil was significant (p<0.05), while that for the deeper soil layers (>60 cm) was not detected statistically. The changes in δ13C with depth appeared to be associated with the small contribution of residues from Spartina alterniflora at greater soil depth that was directly related to the vertical root distribution of the species.  相似文献   

4.
Alkaline soils are considered much less prone to developing water repellency induced by fire than acidic soils. Here we report on the persistence of water repellency present in calcareous soils immediately after wildfires in 10 burned areas in SE Spain, its distribution in different aggregate size fractions (< 2, 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm) and on results from aggregate stability tests. We also distinguished between soil samples taken beneath pine (Pinus halepensis) and beneath understory vegetation.  相似文献   

5.
Experimentation with dynamics of soil carbon pools as affected by elevated CO2 can better define the ability of terrestrial ecosystems to sequester global carbon. In the present study, 6 N HCl hydrolysis and stable-carbon isotopic analysis (δ13C) were used to investigate labile and recalcitrant soil carbon pools and the translocation among these pools of sorghum residues isotopically labeled in the 1998-1999 Arizona Maricopa free air CO2 enrichment (FACE) experiment, in which elevated CO2 (FACE: 560 μmol mol−1) and ambient CO2 (Control: 360 μmol mol−1) interact with water-adequate (wet) and water-deficient (dry) treatments. We found that on average 53% of the final soil organic carbon (SOC) in the FACE plot was in the recalcitrant carbon pool and 47% in the labile pool, whereas in the Control plot 46% and 54% of carbon were in recalcitrant and labile pools, respectively, indicating that elevated CO2 transferred more SOC into the slow-decay carbon pool. Also, isotopic mixing models revealed that increased new sorghum residue input to the recalcitrant pool mainly accounts for this change, especially for the upper soil horizon (0-30 cm) where new carbon in recalcitrant soil pools of FACE wet and dry treatments was 1.7 and 2.8 times as large as that in respective Control recalcitrant pools. Similarly, old C in the recalcitrant pool under elevated CO2 was higher than that under ambient CO2, indicating that elevated CO2 reduces the decay of the old C in recalcitrant pool. Mean residence time (MRT) of bulk soil carbon at the depth of 0-30 cm was significantly longer in FACE plot than Control plot by the averages of 12 and 13 yr under the dry and wet conditions, respectively. The MRT was positively correlated to the ratio of carbon content in the recalcitrant pool to total SOC and negatively correlated to the ratio of carbon content in the labile pool to total SOC. Influence of water alone on the bulk SOC or the labile and recalcitrant pools was not significant. However, water stress interacting with CO2 enhanced the shift of the carbon from labile pool to recalcitrant pool. Our results imply that terrestrial agroecosystems may play a critical role in sequestrating atmospheric CO2 and mitigating harmful CO2 under future atmospheric conditions.  相似文献   

6.
Soil organic carbon (SOC) sequestration by vegetation restoration is the theme of much current research. Since 1999, the program of “Grain for Green”has been implemented in the semi-arid Loess Plateau, China. Its scope represents the largest vegetation restoration activity in China. However, it is still unclear for the SOC sequestration effects of vegetation cover change or natural succession promoted by the revegetation efforts at different scales under the semi-arid conditions. In this study, the changes in SOC stocks due to the vegetation restoration in the middle of Loess Plateau were estimated at patch, hill slope transect and small watershed scale from 1998 to 2006. Soil samples were taken from field for the determination of cesium-137 (137Cs) and SOC contents. Vegetation cover change from 1998 to 2006 at the small watershed scale was assessed using Geographic Information System. The results showed that cropland transforming to grassland or shrubland significantly increased SOC at patch scale. Immature woodland, however, has no significant effect. When vegetation cover has no transformation for mature woodland (25 years old), SOC has no significant increase implying that SOC has come to a stable level. At hill slope scale, three typical vegetation cover patterns showed different SOC sequestration effects of 8.6%, 24.6%, and 21.4% from 1998 to 2006, and these SOC increases mainly resulted from revegetation. At the small watershed scale, SOC stocks increased by 19% in the surface soil layer at 0–20 cm soil depth from 1998 to 2006, which was equivalent to an average SOC sequestration rate of 19.92 t C y− 1 km− 2. Meanwhile, SOC contents showed a significant positive correlation (P < 0.001) with the 137Cs inventory at every soil depth interval. This implied significant negative impacts of soil erosion on SOC sequestration. The results have demonstrated general positive effects of vegetation restoration on SOC sequestration at multiple scales. However, soil erosion under rugged topography modified the spatial distribution of the SOC sequestration effects. Therefore, vegetation restoration was proved to be a significant carbon sink, whereas, erosion could be a carbon source in high erosion sensitive regions. This research can contribute to the performance assessment of ecological rehabilitation projects such as “Grain to Green” and the scientific understanding of the impacts of vegetation restoration and soil erosion on soil carbon dynamics in semi-arid environments.  相似文献   

7.
Scanty information on long-term soil organic carbon (SOC) dynamics hampers validation of SOC models in the tropics. We observed SOC content changes in a 16-year continuously cropped agroforestry experiment in Ibadan, south-western Nigeria. SOC levels declined in all treatments. The decline was most pronounced in the no-tree control treatments with continuous maize and cowpea cropping, where SOC levels dropped from the initial 15.4 to 7.3-8.0 Mg C ha−1 in the 0-12 cm topsoil in 16 years. In the two continuously cropped alley cropping (AC) systems, one with Leucaena leucocephala and one with Senna siamea trees, SOC levels dropped to 10.7-13.2 Mg C ha−1. Compared to the no-tree control treatments, an annual application of an additional 8.5 Mg ha−1 (dry matter) of plant residues, mainly tree prunings, led to an extra 3.5 Mg C ha−1 (∼0.2% C) in the 0-12 cm top soil after 11 years, and 4.1 Mg C ha−1 after 16 years. The addition of NPK fertilizer had little effect on the quantities of above-ground plant residues returned to the soil, and there was no evidence that the fertilizer affected the rate of SOC decomposition. The fact that both C3 and C4 plants returned organic matter to the soil in all cropping systems, but in contrasting proportions, led to clear contrasts in the 13C abundance in the SOC. This 13C information, together with the measured SOC contents, was used to test the ROTHC model. Decomposition was very fast, illustrated by the fact that we had to double all decomposition rate constants in the model in order to simulate the measured contrasts in SOC contents and δ13C between the AC treatments and the no-tree controls. We hypothesized (1) that the pruning materials from the legume trees and/or the extra rhizodeposition from the tree roots in the AC treatments accelerated the decomposition of the SOC present at the start of the experiment (true C-priming), and/or (2) that the physical protection of microbial biomass and metabolites by the clay fraction on this site, having a sandy top soil in which clay minerals are mainly of the 1:1 type, is lower than assumed by the model.  相似文献   

8.
The location of soil organic matter (SOM) within the soil matrix is considered a major factor determining its turnover, but quantitative information about the effects of land cover and land use on the distribution of SOM at the soil aggregate level is rare. We analyzed the effect of land cover/land use (spruce forest, grassland, wheat and maize) on the distribution of free particulate organic matter (POM) with a density <1.6 g cm−3 (free POM<1.6), occluded particulate organic matter with densities <1.6 g cm−3 (occluded POM<1.6) and 1.6-2.0 g cm−3 (occluded POM1.6-2.0) and mineral-associated SOM (>2.0 g cm−3) in size classes of slaking-resistant aggregates (53-250, 250-1000, 1000-2000, >2000 μm) and in the sieve fraction <53 μm from silty soils by applying a combined aggregate size and density fractionation procedure. We also determined the turnover time of soil organic carbon (SOC) fractions at the aggregate level in the soil of the maize site using the 13C/12C isotope ratio. SOM contents were higher in the grassland soil aggregates than in those of the arable soils mainly because of greater contents of mineral-associated SOM. The contribution of occluded POM to total SOC in the A horizon aggregates was greater in the spruce soil (23-44%) than in the grassland (11%) and arable soils (19%). The mass and carbon content of both the free and occluded POM fractions were greater in the forest soil than in the grassland and arable soils. In all soils, the C/N ratios of soil fractions within each aggregate size class decreased in the following order: free POM<1.6>occluded POM<1.6-2.0>mineral-associated SOM. The mean age of SOC associated with the <53 μm mineral fraction of water-stable aggregates in the Ap horizon of the maize site varied between 63 and 69 yr in aggregates >250 μm, 76 yr in the 53-250 μm aggregate class, and 102 yr in the sieve fraction <53 μm. The mean age of SOC in the occluded POM increased with decreasing aggregate size from 20 to 30 yr in aggregates >1000 μm to 66 yr in aggregates <53 μm. Free POM had the most rapid rates of C-turnover, with residence times ranging from 10 yr in the fraction >2000 μm to 42 yr in the fraction 53-250 μm. Results indicated that SOM in slaking-resistant aggregates was not a homogeneous pool, but consisted of size/density fractions exhibiting different composition and stability. The properties of these fractions were influenced by the aggregate size. Land cover/land use were important factors controlling the amount and composition of SOM fractions at the aggregate level.  相似文献   

9.
Dehesa ecosystems are open woodlands with scattered oak trees as their main component. As a result of differing land-uses, the structure of vegetation found within dehesas varies between: (i) oak trees and intercropped cereals (cropped), (ii) oak trees and native grass vegetation (grazed), and (iii) oak trees with abundant understorey shrubs (encroached). The aim of this study is to investigate whether land-use influences the water dynamics of dehesas by measuring available soil water content (AWC) in the upper 250 cm of the soil at different distances from tree trunks (maximum 30 m) at four Quercus ilex dehesas in Central–Western Spain. The technique used was Time Domain Reflectometry and the study was undertaken between May of 2002 and December of 2005. Leaf water potential (Ψ) was also measured on trees at one site by mean of a pressure chamber. Within the upper meter of the soil, it appears that trees, grasses and shrubs extracted soil water resources in a similar way from both beneath and beyond the tree canopy. However, encroached plots in general showed lower average AWC values than cropped or grazed plots (3.7, 5.6, and 6.2% in encroached, cropped and grazed, respectively). Cereal crops do not compete more strongly than grasses with trees for available soil water resources. The similar Ψ values found at cropped and grazed plots supported these results. From our results, it could be hypothesized that ploughed dehesas could facilitate soil re-watering in the plots with pronounced slopes. The decrease of AWC values at encroached plots with respect to the cropped and grazed plots was found mostly beyond the tree trunk at deeper soil layers, indicating that shrubs use water partly not accessible to trees. The presence of an understory of shrubs seems to have slightly increased the water constraints on trees during the summer period (Ψd values of − 0.5, − 0.5, and − 0.8 MPa in cropped, grazed, and encroached plots, respectively). In cropped and grazed plots, an important amount of water seems to have remained unused for trees and grasses.  相似文献   

10.
The effects of tillage on the interaction between soil structure and microbial biomass vary spatially and temporally for different soil types and cropping systems. We assessed the relationship between soil structure induced by tillage and soil microbial activity at the level of soil aggregates. To this aim, organic C (OC), microbial biomass C (MBC) and soil respiration were measured in water-stable aggregates (WSA) of different sizes from a subtropical rice soil under two tillage systems: conventional tillage (CT) and a combination of ridge with no-tillage (RNT). Soil (0–20 cm) was fractionated into six different aggregate sizes (> 4.76, 4.76–2.0, 2.0–1.0, 1.0–0.25, 0.25–0.053, and < 0.053 mm in diameter). Soil OC, MBC, respiration rate, and metabolic quotient were heterogeneously distributed among soil aggregates while the patterns of aggregate-size distribution were similar among properties, regardless of tillage system. The content of OC within WSA followed the sequence: medium-aggregates (1.0–0.25 mm and 1.0–2.0 mm) > macro-aggregates (4.76–2.0 mm) > micro-aggregates (0.25–0.053 mm) > large aggregates (> 4.76 mm) > silt + clay fractions (< 0.053 mm). The highest levels of MBC were associated with the 1.0–2.0 mm aggregate size class. Significant differences in respiration rates were also observed among different sizes of WSA, and the highest respiration rate was associated with 1.0–2.0 mm aggregates. The Cmic/Corg was greatest for the large-macroaggregates regardless of tillage regimes. This ratio decreased with aggregate size to 1.0–0.25 mm. Soil metabolic quotient (qCO2) ranged from 3.6 to 17.7 mg CO2 g− 1 MBC h− 1. The distribution pattern of soil microbial biomass and activity was governed by aggregate size, whereas the tillage effect was not significant at the aggregate scale. Tillage regimes that contribute to greater aggregation, such as RNT, also improved soil microbial activity. Soil OC, MBC and respiration rate were at their highest levels for 1.0–2.0 mm aggregates, suggesting a higher biological activity at this aggregate size for the present ecosystem.  相似文献   

11.
Carbon isotopic composition of soils subjected to C3-C4 vegetation change is a suitable tool for the estimation of C turnover in soil organic matter (SOM) pools. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability. Soil samples from a field plot with 10.5 years of cultivation of the C4 plant Miscanthus×gigantheus and from a reference plot under C3 grassland vegetation were analysed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). According to differential weight losses (dTG) and energy release or consumption (DSC), five SOM pools with increasing thermal stability were distinguished: (I) 20-190 °C, (II) 190-310 °C, (III) 310-390 °C, (IV) 390-480 °C, and (V) 480-1000 °C. Their δ13C values were analysed by EA-IRMS. The weight losses in pool I were connected with water evaporation, since no significant C losses were measured and δ13C values remained unchanged. The δ13C of pools II and III in soil samples under Miscanthus were closer to the δ13C of the Miscanthus plant tissues (−11.8‰) compared to the thermally stable SOM pool V (−19.5‰). The portion of the Miscanthus-derived C4-C in total SOM in 0-5 cm reached 55.4% in the 10.5 years. The C4-C contribution in pool II was 60% and decreased down to 6% in pool V. The mean residence times (MRT) of SOM pools II, III, and IV were similar (11.6, 12.2, and 15.4 years, respectively), while pool V had a MRT of 163 years. Therefore, we concluded that the biological availability of thermal labile SOM pools (<480 °C) was higher, than that of the thermal stable pool decomposed above 480 °C. However, the increase of SOM stability with rising temperature was not gradual. Therefore, the applicability of the TG-DSC for the separation of SOM pools with different biological availability is limited.  相似文献   

12.
This work investigated the effects of land cover and land-use change (LUC) on the ability of a soil to store carbon (C) and reduce carbon dioxide (CO2) emissions, in a Mediterranean area. Using a paired-site approach, we estimated the effect of land-cover change on the C stock from 1972 to 2008 in a natural reserve (Grotta di Santa Ninfa) in western Sicily. We selected 15 paired sites representative of five LUCs. We studied the effect of land use on soil organic C (SOC) content in bulk soil and in different particle-size fractions (2000-1000 μm, 1000-500 μm, 500-250 μm, 250-63 μm, 63-25 μm, and < 25 μm). Laboratory incubation of the soil samples was conducted to measure CO2 evolution in bulk soil collected at two different depths from each paired site. We found that the conversion of natural vegetation to orchards (vineyards and olive groves) resulted in SOC decreases ranging from 27% to 50%. The conversion from vineyards to arable land led to a 9% decrease in SOC, whereas the opposite caused a 105% gain. When arable land was replaced by Eucalyptus afforestation, a 40% increase in SOC was observed. SOC decline occurred mainly in coarser soil fractions, whereas the finest fractions were not influenced by land use. We calculated an overall SOC reduction of 63% in the study area, corresponding to a 58 Mg ha− 1 SOC loss in less than 30 years. Our results indicate that land-use conversion, vegetation type, and management practices that control the biogeochemical and physical properties of soil could help reduce CO2 emissions and sequester SOC.  相似文献   

13.
Soil respiration (SR) is highly sensitive to future climate change, and particularly to global warming. However, considerable uncertainties remain associated with the temperature sensitivity of SR and its controlling processes. Using 384 field measurement data from 114 published papers and one book, this study quantifies the variation in the seasonal Q10 values of soil respiration, the multiplier by which respiration rates increase for a 10 °C increase in temperature, and its drivers across different sites. No significant correlation between Q10 and mean annual temperature or mean annual precipitation is found when statistically controlling seasonal changes in vegetation activity, deduced from satellite vegetation greenness index observations (normalized difference vegetation index, or NDVI). In contrast, the seasonal amplitude of NDVI is significantly and positively correlated with the apparent Q10 of SR. This result indicates that the variations of seasonal vegetation activity exert dominant control over the variations of the apparent Q10 of SR across different sites, highlighting the ecological linkage between plant physiological processes and soil processes. It further implies that the seasonal variation of vegetation activity may thus dominate the apparent seasonal temperature sensitivity. We conclude that the apparent Q10 value of SR estimated from field measurements is generally larger than the intrinsic temperature sensitivity of soil organic matter decomposition, and thus cautions should be taken when applying apparent Q10 values directly in ecosystem models. Our regression analysis further shows that when the amplitude of NDVI variation approximates 0 (and thus when the seasonality in vegetation activity is marginal), the residual Q10 of SR for soil temperature measured at 5 cm depth is about 1.5.  相似文献   

14.
In order to assess its potential for estimating soil redistribution rates, the naturally occurring fallout radionuclide 210Pbex has been used in parallel with 137Cs, derived from the atmospheric testing of nuclear weapon testing in the 1950s to 1970s, to estimate rates of soil redistribution on a sloping field with traditional erosion control measures located near Jiajia Village, Jianyang County, in the Sichuan Hilly Basin of China. The local 210Pbex reference inventory of 12,860 Bq m− 2 is higher than those reported for many other areas of the world and may reflect the influence of cloudy weather in preventing 210Pb released to the atmosphere across the local region moving up into the upper troposphere, where is would be more widely dispersed. The mean 210Pbex and 137Cs inventories measured in cores collected from the upper part of the field with an average slope of 10° were 8028 Bq m− 2 and 993 Bq m− 2, respectively, and the equivalent values for the lower part of the field, where the slopes are steeper (20°) were 11,388 Bq m− 2 and 1299 Bq m− 2. The pattern of post-fallout 210Pbex and 137Cs redistribution on the sloping field reflects not only the effects of water erosion and redistribution by tillage, but also the local traditional practice of “Tiaoshamiantu”, whereby sediment trapped in the ditches is returned to the fields by the farmer. The estimates of annual rates of soil loss provided by the 210Pbex measurement are closely comparable with those derived from the 137Cs measurements and are consistent with existing knowledge for the study area. The results obtained from this study confirm the potential for using 210Pbex measurement to estimate soil erosion rates over medium-term timescale of 50–100 years. By combining the estimates of erosion rates provided by the 210Pbex and 137Cs measurements, the weighted mean net soil loss was estimated to be 48.7 t ha− 1 year− 1 from the upper subfield and 16.9 t ha− 1 year− 1 from the lower subfield. These rates are considerably lower than the erosion rates obtained from runoff plot measurements in the local area. It is suggested that the traditional erosion control practices and the practice of “Tiaoshamiantu” have a significant effect in reducing soil loss and conserving valuable cultivated soil on sloping fields in the Sichuan Hilly Basin.  相似文献   

15.
Soil compaction and soil moisture are important factors influencing denitrification and N2O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N2O, N2 and CO2 from undisturbed soil cores fertilized with (150 kg N ha−1) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρD=1.03 g cm−3), the interrow area (ρD=1.24 g cm−3), and the tractor compacted interrow area (ρD=1.64 g cm−3), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N2O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N2 production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N2O-N emission in most cases. There was no soil moisture effect on CO2 emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N2O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O2 consumption induced by soil drying and rewetting for the emissions of N2O.  相似文献   

16.
In this study the estimation of reflectivity at 1730 MHz (l-band), measured with a microwave digital cordless telephony (DCT) patch antenna, is presented as an easy-to-handle and non-destructive new method to assess the relative water content (RWC) of poplar leaves and filter discs at different levels of dehydration. The accuracy of this new method has been contrasted with the R1300/R1450 index, determined by a portable near infrared (NIR) spectrometer. The close correlations found between RWC and the reflectivity at a frequency of 1730 MHz, both for filters and leaves, indicate that microwave determinations are rather independent of the physical properties of the material analysed. On the contrary, the differences found between poplar leaves and leaf filters in the relationships established between RWC and the R1300/R1450 index demonstrate a strong influence of the properties of the material in NIR reflectance measurements, specifically as they relate to changes in leaf thickness during dehydration. It should be noted that the amount of energy received by the leaf for the microwave technique (0.1 mW) was much lower than that received for the measuring of the R1300/R1450 index (2.5 W). Moreover, R-square coefficients were higher for microwaves than for the R1300/R1450 index. The use of a technologically simple, low cost and portable device, based on a microwave DCT patch antenna, could yield a solid support for the development of a commercial apparatus enabling the determination of plant water status under field conditions.  相似文献   

17.
The effects of elevated CO2 supply on N2O and CH4 fluxes and biomass production of Phleum pratense were studied in a greenhouse experiment. Three sets of 12 farmed peat soil mesocosms (10 cm dia, 47 cm long) sown with P. pratense and equally distributed in four thermo-controlled greenhouses were fertilised with a commercial fertiliser in order to add 2, 6 or 10 g N m−2. In two of the greenhouses, CO2 concentration was kept at atmospheric concentration (360 μmol mol−1) and in the other two at doubled concentration (720 μmol mol−1). Soil temperature was kept at 15 °C and air temperature at 20 °C. Natural lighting was supported by artificial light and deionized water was used to regulate soil moisture. Forage was harvested and the plants fertilised three times during the basic experiment, followed by an extra fertilisations and harvests. At the end of the experiment CH4 production and CH4 oxidation potentials were determined; roots were collected and the biomass was determined. From the three first harvests the amount of total N in the aboveground biomass was determined. N2O and CH4 exchange was monitored using a closed chamber technique and a gas chromatograph. The highest N2O fluxes (on average, 255 μg N2O m−2 h−1 during period IV) occurred just after fertilisation at high water contents, and especially at the beginning of the growing season (on average, 490 μg N2O m−2 h−1 during period I) when the competition of vegetation for N was low. CH4 fluxes were negligible throughout the experiment, and for all treatments the production and oxidation potentials of CH4 were inconsequential. Especially at the highest rates of fertilisation, the elevated supply of CO2 increased above- and below-ground biomass production, but both at the highest and lowest rates of fertilisation, decreased the total amount of N in the aboveground dry biomass. N2O fluxes tended to be higher under doubled CO2 concentrations, indicating that increasing atmospheric CO2 concentration may affect N and C dynamics in farmed peat soil.  相似文献   

18.
Elevated pCO2 increases the net primary production, C/N ratio, and C input to the soil and hence provides opportunities to sequester CO2-C in soils to mitigate anthropogenic CO2. The Swiss 9 y grassland FACE (free air carbon-dioxide enrichment) experiment enabled us to explore the potential of elevated pCO2 (60 Pa), plant species (Lolium perenne L. and Trifolium repens L.) and nitrogen fertilization (140 and 540 kg ha−1 y−1) on carbon sequestration and mineralization by a temperate grassland soil. Use of 13C in combination with respired CO2 enabled the identification of the origins of active fractions of soil organic carbon. Elevated pCO2 had no significant effect on total soil carbon, and total soil carbon was also independent of plant species and nitrogen fertilization. However, new (FACE-derived depleted 13C) input of carbon into the soil in the elevated pCO2 treatments was dependent on nitrogen fertilization and plant species. New carbon input into the top 15 cm of soil from L. perennne high nitrogen (LPH), L. perenne low nitrogen (LPL) and T. repens low nitrogen (TRL) treatments during the 9 y elevated pCO2 experiment was 9.3±2.0, 12.1±1.8 and 6.8±2.7 Mg C ha−1, respectively. Fractions of FACE-derived carbon in less protected soil particles >53 μm in size were higher than in <53 μm particles. In addition, elevated pCO2 increased CO2 emission over the 118 d incubation by 55, 61 and 13% from undisturbed soil from LPH, LPL and TRL treatments, respectively; but only by 13, 36, and 18%, respectively, from disturbed soil (without roots). Higher input of new carbon led to increased decomposition of older soil organic matter (priming effect), which was driven by the quantity (mainly roots) of newly input carbon (L. perenne) as well as the quality of old soil carbon (e.g. higher recalcitrance in T. repens). Based on these results, the potential of well managed and established temperate grassland soils to sequester carbon under continued increasing concentrations of atmospheric CO2 appears to be rather limited.  相似文献   

19.
Understanding the sensitivity of soil respiration to temperature change and its impacting factors is an important base for accurately evaluating the response of terrestrial carbon balance to future climatic change, and thus has received much recent attention. In this study, we synthesized 161 field measurement data from 52 published papers to quantify temperature sensitivity of soil respiration in different Chinese ecosystems and its relationship with climate factors, such as temperature and precipitation. The results show that the observed Q10 value (the factor by which respiration rates increase for a 10 °C increase in temperature) is strongly dependent on the soil temperature measurement depth. Generally, Q10 significantly increased with the depth (0 cm, 5 cm, and 10 cm) of soil temperature measuring point. Different ecosystem types also exhibit different Q10 values. In response to soil temperature at the depth of 5 cm, alpine meadow and tundra has the largest Q10 value with magnitude of 3.05 ± 1.06, while the Q10 value of evergreen broadleaf forests is approximately half that amount (Q10 = 1.81 ± 0.43). Spatial correlation analysis also shows that the Q10 value of forest ecosystems is significantly and negatively correlated with mean annual temperature (R = −0.51, P < 0.001) and mean annual precipitation (R = −0.5, P < 0.001). This result not only implies that the temperature sensitivity of soil respiration will decline under continued global warming, but also suggests that such acclimation of soil respiration to warming should be taken into account in forecasting future terrestrial carbon cycle and its feedback to climate system.  相似文献   

20.
We measured methane (CH4) emissions from the stem surfaces of mature Fraxinus mandshurica var. japonica trees in a floodplain forest. Flux measurements were conducted almost monthly from May to October 2005, and positive CH4 fluxes were detected throughout the study period, including the leafless season. The mean CH4 flux was 176 and 97 μg CH4 m−2 h−1 at the lower (15 cm above the ground) and upper (70 cm above the ground) stem positions, respectively. The CH4 concentration was lower in soil gas than in ambient air to a depth of at least 40 cm. One possible source of CH4 emitted from the stems might be the dissolved CH4 in groundwater; maximum concentrations were 10,000 times higher than atmospheric CH4 concentrations. Our results suggest that CH4 transport from the submerged soil layer to the atmosphere may occur through internal air spaces in tree bodies.  相似文献   

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