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is no longer maintained by the ants, their decomposition is accelerated, and nutrients may be available for uptake by plants,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
Expansion of cropland involves immense land use changes, and the resulting intensified management practices have a strong influence on the functioning of the underlying soil. For instance, increased application of nitrogen (N) fertilizer is known to enhance fluxes of nitrous oxide (N2O) from the soil to the atmosphere. The emission factor (EF) proposed by the Intergovernmental Panel on Climate Change (IPCC) assumes a linear relationship between added N and N2O-N fluxes, but it does not account for environmental factors, such as soil properties or climate. Due to the high spatial and temporal variability of N2O-N fluxes, mechanistic models are preferable in terms of extrapolation to larger scales. In this study, we evaluated simulated N2O-N fluxes from soils under agricultural use in the Brazilian state, Mato Grosso, using the CANDY (Carbon and Nitrogen Dynamics) model. A control tool was developed in order to enable the simulation of 1 650 scenarios covering different sites (soil + climate) and management regimes (crop rotation + amount of applied fertilizer + sowing and harvesting dates). Results suggested that the sites had a very strong influence on calculated emissions, which is not accounted for by static EF. Furthermore, most fertilizer-induced N2O-N fluxes derived from the scenario simulations were best described by a non-linear function. For sounder budgeting on the federal and national scale, there is still a strong need for long-term observations of continuous crop rotations and spatial distribution of soil types and their specific characteristics. The presented results provide a valuable starting point for developing further scenario simulations and adapting experimental campaigns for N2O emission study. 相似文献