Rising atmospheric carbon dioxide (CO2) concentrations from agricultural activities prompted the need to quantify greenhouse gas emissions to better understand carbon (C) cycling and its role in environmental quality. The specific objective of this work was to determine the effect of no-tillage, deep plowing and wind speeds on the soil CO2 concentration in muck (organic) soils of the Florida Everglades. Miniature infrared gas analyzers were installed at 30 cm and recorded every 15 min in muck soil plowed with the Harrell Switch Plow (HSP) to 41 cm and in soil Not Tilled (NT), i.e., not plowed in last 9 months. The soil CO2 concentration exhibited temporal dynamics independent of barometric pressure fluctuations. Loosening the soil resulted in a very rapid decline in CO2 concentration as a result of “wind-induced” gas exchange from the soil surface. Higher wind speeds during mid-day resulted in a more rapid loss of CO2 from the HSP than from the NT plots. The subtle trend in the NT plots was similar, but lower in magnitude. Tillage-induced change in soil air porosity enabled wind speed to affect the gas exchange and soil CO2 concentration at 30 cm, literally drawing the CO2 out of the soil resulting in a rapid decline in the CO2 concentration, indicating more rapid soil carbon loss with tillage. At the end of the study, CO2 concentrations in the NT plots averaged about 3.3% while that in the plowed plots was about 1.4%. Wind and associated aerodynamic pressure fluctuations affect gas exchange from soils, especially tilled muck soils with low bulk densities and high soil air porosity following tillage. 相似文献
Effects of two tillage treatments, tillage (T) with chisel plough and no-till (NT), were studied under un-drained and drained soil conditions. Soil physical properties measured were bulk density (ρb), total porosity (ƒt), water stable aggregates (WSA), geometric mean diameter (GMD), mean weight diameter (MWD), organic carbon (OC) and total N concentrations in different aggregate size fractions, and total OC and N pools. The experiment was established in 1994 on a poorly drained Crosby silt loam soil (fine mixed, mesic, Aeric Ochraqualf) near Columbus, Ohio. In 2007, soil samples were collected (0–10, 10–20, and 20–30 cm) from all treatments and separated into six aggregate size classes for assessing proportions of macro (5–8, 2–5, 1–2, 0.5–1, 0.25–0.5) and micro (<0.25 mm) aggregates by wet sieving. Tillage treatments significantly (P ≤ 0.05) influenced WSA, MWD, and GMD. Higher total WSA (78.53 vs. 58.27%), GMD (0.99 vs. 0.68 mm), and MWD (2.23 vs. 0.99 mm) were observed for 0–10 cm depth for NT than T treatments. Relative proportion of macro-aggregates (>0.25-mm) was also more in NT than T treatment for un-drained plots. Conversely, micro-aggregates (<0.25-mm) were more in T plots for both drained and un-drained treatments. The WSA, MWD and GMD decreased with increase in soil depth. The OC concentration was significantly higher (P ≤ 0.05) in NT for un-drained (P ≤ 0.01) treatment for all soil depths. Within macro-aggregates, the maximum OC concentrations of 1.91 and 1.75 g kg−1 in 1–2 mm size fraction were observed in NT for un-drained and drained treatments, respectively. Tillage treatments significantly (P < 0.01) affected bulk density (ρb), and total porosity (ft) for all soil depths, whereas tillage × drainage interaction was significant (P < 0.01) for 10–20 and 20–30 cm depths. Soil ρb was negatively correlated (r = −0.47; n = 12) with OC concentration. Tillage treatments significantly affected (P ≤ 0.05) OC pools at 10–20 cm depth; whereas drainage, and tillage × drainage significantly (P ≤ 0.05) influenced OC pools for 0–10 cm soil layer. The OC pool in 0–10 cm layer was 31.8 Mg ha−1 for NT compared with 25.9 Mg kg−1 for T for un-drained treatment. In comparison, the OC pool was 23.1 Mg ha−1 for NT compared with 25.2 Mg ha−1 for T for the drained plots. In general, the OC pool was higher in NT system, coupled with un-drained treatment than in drained T plots. The data indicate the importance of NT in improving the OC pool. 相似文献
The knowledge about the relevance of physical and chemical fractionation methods to soil organic carbon (SOC) stabilization
mechanisms is fragmentary but needed to manage the SOC pool. Therefore, our objective was to compare the C contents of the
particle size fractions coarse and fine sand, silt, and clay of the two uppermost horizons of a soil under three different
management systems (meadow; no-till corn, NT; no-till corn with manure, NTm). The mineral composition was dominated by silt
(48–60%). However, coarse sand and clay showed the highest enrichment of C compared to the bulk soil. In spite of an enrichment
factor below 1, the high proportion of silt made this fraction the main C store. In the upper 30 cm, this fraction amounted
to 27.1 Mg C ha−1 in NTm and progressively less in NT (15.5 Mg C ha−1), and meadow (14.9 Mg C ha−1), representing 44%, 39%, and 39% of the total SOC pool, respectively. The C in the isolated particle size fractions was further
investigated by an oxidizing treatment with Na2S2O8 and a treatment with HF to solubilize the mineral phases. The pools of oxidizable C were comparable among particle size fractions
and pedons, as indicated by Na2S2O8 treatment. The pools of C preferentially associated with soil minerals were also comparable among pedons, as indicated by
HF treatment. However, NTm stored the largest pool (12.6 Mg ha−1) of mineral-associated C in 0–30 cm depth. The silt-associated and mineral-bound SOC pool in NTm was greater compared to
NT due to increased organic matter (OM) input. Thus, the silt particle size fraction at the North Appalachian Experimental
Watershed (NAEW) has the potential for SOC sequestration by stabilizing OM inputs. Mineralogical and molecular level analyses
on a larger set of fractions obtained from entire rooted soil profiles are required, however, to compare the SOC sequestration
capacity of the land uses. 相似文献
General concern about climate change has led to growing interest in the responses of terrestrial ecosystems to elevated concentrations
of CO2 in the atmosphere. Experimentation during the last two to three decades using a large variety of approaches has provided
sufficient information to conclude that enrichment of atmospheric CO2 may have severe impact on terrestrial ecosystems. This impact is mainly due to the changes in the organic C dynamics as a
result of the effects of elevated CO2 on the primary source of organic C in soil, i.e., plant photosynthesis. As the majority of life in soil is heterotrophic
and dependent on the input of plant-derived organic C, the activity and functioning of soil organisms will greatly be influenced
by changes in the atmospheric CO2 concentration. In this review, we examine the current state of the art with respect to effects of elevated atmospheric CO2 on soil microbial communities, with a focus on microbial community structure. On the basis of the existing information, we
conclude that the main effects of elevated atmospheric CO2 on soil microbiota occur via plant metabolism and root secretion, especially in C3 plants, thereby directly affecting the
mycorrhizal, bacterial, and fungal communities in the close vicinity of the root. There is little or no direct effect on the
microbial community of the bulk soil. In particular, we have explored the impact of these changes on rhizosphere interactions
and ecosystem processes, including food web interactions. 相似文献
Wood ants (Formica rufa group) are dominating ecosystem elements of the boreal region due to their wide and abundant occurrence. They collect and
concentrate organic material from the surrounding forest floor by building large above-ground mounds. These mounds have higher
temperature and lower water content than the surrounding forest floor. We studied how these peculiar environmental conditions
affected mass loss and carbon (C), nitrogen (N), phosphorus (P) and potassium (K) mineralisation of organic matter in boreal
Norway spruce (Picea abies L. Karst.)-dominated mixed forest stands of four different age classes (5-, 30-, 60-, and 100-year-old) situated in eastern
Finland using the litter bag technique. Norway spruce needle litter was incubated in inhabited and abandoned wood ant mounds
as well as on the surrounding forest floor. We expected decomposition to be extremely slow due to the dryness of the mounds.
Mass losses inside inhabited mounds were lower compared to the surrounding forest floor (on average 30 vs 50% after 2 years)
but not as low as we expected, which might be a result of ant and microbial activity in the mounds. Decomposition in the abandoned
mounds proceeded similarly as on the forest floor. Nutrient mineralisation proceeded more slowly in the ant mounds than on
the surrounding forest floor. Mineralisation occurred for all studied nutrients in the ant mounds, except for N, which net
amount remained stable during the years of the experiment. When wood ant mounds are abandoned and their porous and dry structure
is no longer maintained by the ants, their decomposition is accelerated, and nutrients may be available for uptake by plants,
although the nutrient mineralisation seems still to remain lower compared to the surrounding forest floor. However, eventually
the mound material will be decomposed and nutrients mineralised, thus providing a nutrient hot spot increasing the heterogeneity
of forest floor nutrient availability. 相似文献
It is shown that, for mineral soils, it is not the total amount of organic carbon (or organic matter) that controls soil physical behaviour but the amount of complexed organic carbon (COC). We assume that this complex is formed by the association of unit mass (i.e. 1 g) of organic carbon with n grams of clay. Analysis of data from two French and two Polish databases shows that, for these soils, n = 10. A consequence of this is that in soils with small contents of organic carbon (OC), such as arable soils, COC is proportional to OC. However, in soils with large contents of organic carbon, such as pasture soils, COC is proportional to the clay content. This explains why we find that soil bulk density is significantly correlated with OC in French arable soils but with the clay content in French pasture soils. The use of COC instead of OC enables the arable and pasture soils to be considered on the same scale.
Water retention data were fitted to a double-exponential equation which allows both the matrix and structural porosities to be estimated. It is shown that in soils with low contents of organic carbon, the carbon content is positively correlated with the matrix porosity. In contrast, in soils with high contents of organic carbon, the matrix porosity is constant at its maximum value and the structural porosity is not significantly correlated with either the total organic carbon or the non-complexed organic carbon (NCOC). It is suggested that the complexed organic carbon can be considered as being sequestered. The soil clay content can similarly be partitioned between clay that is complexed with organic carbon and clay that is not complexed. It is shown that non-complexed clay is more easily dispersed in water than clay that is complexed with organic carbon. These findings indicate how improved pedo-transfer functions for the prediction of soil physical properties may be produced. Such functions need to use the values of complexed and non-complexed organic carbon and clay which must be determined by algorithms. The values produced by the algorithms may then be used in the improved pedo-transfer functions. 相似文献
Net greenhouse gas (GHG) source strength for agricultural wetland ecosystems in the Prairie Pothole Region (PPR) is currently unknown. In particular, information is lacking to constrain spatial variability associated with GHG emissions (CH4, CO2, and N2O). GHG fluxes typically vary with edaphic, hydrologic, biologic, and climatic factors. In the PPR, characteristic wetland plant communities integrate hydropedologic factors and may explain some variability associated with trace gas fluxes at ecosystem and landscape scales. We addressed this question for replicate wetland basins located in central North Dakota stratified by hydropedologic vegetation zone on Jul 12 and Aug 3, 2003. Data were collected at the soil-atmosphere interface for six plant zones: deep marsh, shallow marsh, wet meadow, low prairie, pasture, and cropland. Controlling for soil moisture and temperature, CH4 fluxes varied significantly with zone (p < 0.05). Highest CH4 emissions were found near the water in the deep marsh (277,800 μg m− 2 d− 1 CH4), which declined with distance from water to − 730 μg m− 2 d− 1 CH4 in the pasture. Carbon dioxide fluxes also varied significantly with zone. Nitrous oxide variability was greater within zones than between zones, with no significant effects of zone, moisture, or temperature. Data were extrapolated for a 205.6 km2 landscape using a previously developed synoptic classification for PPR plant communities. For this landscape, we found croplands contributed the greatest proportion to the net GHG source strength on Jul 12 (45,700 kg d− 1 GHG-C equivalents) while deep marsh zones contributed the greatest proportion on Aug 3 (26,145 kg d− 1 GHG-C equivalents). This was driven by a 30-fold reduction in cropland N2O–N emissions between dates. The overall landscape average for each date, weighted by zone, was 462.4 kg km− 2 d− 1 GHG-C equivalents on Jul 12 and 314.3 kg km− 2 d− 1 GHG-C equivalents on Aug 3. Results suggest GHG fluxes vary with hydropedologic soil zone, particularly for CH4, and provide initial estimates of net GHG emissions for heterogeneous agricultural wetland landscapes. 相似文献
Laboratory and greenhouse experiments were conducted to study the effects of applications of rice residue and Pongamia pinnata and Azadirachta indica leaf litters on biochemical properties (extraction yield of humus, composition of humus, microbial biomass carbon, activities of urease and acid phosphatase) of a lowland rice soil under flooded conditions. Bulk soil sample collected from the Mandya paddy fields was used for the green house trials and the laboratory incubation studies. The organic materials were added at three rates – zero, 25.0 g carbon kg−1 (2.5% C) and 50.0 g carbon kg−1 dry soil (5.0% C). Results showed that tree leaf litter and rice residue at 5.0% C rate decreased instantaneous decay constant (k), there by retarded the rate of C mineralization. Carbon contents of HA increased with the rate of C added. Study of delta–log K values and C contents of humic acids revealed that greatest molecular weight of HA was in the pongamia litter treatment, followed by neem litter and rice residue. Grain and straw yields of rice crop in the pot culture study were statistically correlated to the soil quality parameters. Neem and pongamia tree litter incorporation at 2.5% C could be considered for improving soil health and crop yields of rice under flooded conditions; however, application at higher rates significantly (P ≤ 0.05) lowered total dry matter production in rice, despite favorable soil health parameters such as humic yields, microbial biomass – C content and acid phosphatase and urease activity. Among different soil health parameters, microbial quotient was found to be more sensitive indicator of decline in soil quality. 相似文献
Petrocalcic horizons are frequent in soils of semiarid landscapes. A survey of SIC and SOC contents made in Southern Spain in a pilot area with well defined geomorphological surfaces showed that topsoils overlying petrocalcic horizons are almost twice as rich in SOC as soil of similar depth without petrocalcic horizons. This could be due to impedance to root penetration, changes in redox potential and soil water availability caused by the presence of indurated crust. Soil age, on the contrary, seems not be an essential factor, since only a short time is required to reach a steady state in SOC in comparison to the time span available for soil formation on the different geomorphic surfaces. 相似文献