共查询到20条相似文献，搜索用时 46 毫秒
1.
《Applied soil ecology》2007,37(2-3):156-163
Wood ants (Formica rufa group) are ubiquitous in European boreal forests and their large long-lived mound nests, which mainly consist of forest litter and resin, accumulate carbon (C) and nutrients. The C and nutrient dynamics of wood ant mounds in response to forest succession have received minor attention in boreal forests. We aimed to study whether the C, nitrogen (N) and phosphorus (P) concentrations and the bulk density of ant mounds differ from those of the surrounding forest soil, to estimate the C, N and P pools in ant mounds, and to test whether the concentrations and pools change with forest age. Norway spruce (Picea abies (L.) Karst.) stands on medium-fertile sites in 5-, 30-, 60- and 100-year stand age classes were studied in eastern Finland. Carbon and P concentrations in the above-ground mound material were higher than those in the surrounding organic layer. The C, N and extractable P concentrations were higher in the soil under the ant mounds than in the surrounding mineral soil (0–21 cm). The low bulk densities in the ant mounds and the soil below them could be a result of the porous structure of ant mounds and the soil-mixing activities of the ants. The C/N ratios were higher in the mounds than in the organic layer. Carbon concentrations in the ant mounds increased slightly with stand age. Carbon, N and P pools in the ant mounds increased considerably with stand age. Carbon, N and P pools in ant mounds were <1% of those in the surrounding forest soil. Nevertheless, the above- and belowground parts of the ant mounds contained more C, N and P per sampled area than the surrounding forest soil. Wood ants therefore increase the spatial heterogeneity in C and nutrient distribution at the ecosystem level. 相似文献
2.
Red wood ants (Formica rufa group) are important elements in boreal forest ecosystems, where they occur in high abundance and build large and long-lasting, above-ground mounds of organic material. However, little is known on their role in the carbon (C) cycling in boreal forests. We measured temperature and carbon dioxide (CO2) efflux from three different-sized wood ant mounds and the surrounding forest floor from May 2004 to April 2005 in Norway spruce [Picea abies (L.) Karst.] dominated forests in eastern Finland. Additionally, mound and forest floor temperatures were measured continuously and CO2 effluxes at 2-4-week-intervals. During the ants’ active season (May-September), measurements were conducted in the morning, afternoon, evening and at night, while fluxes were measured once a day during the ants’ inactive season. CO2 emissions from the mounds were up to nearly eight times higher than those from the surrounding forest floor during the active season of the ants, but no statistically significant differences were observed during the period from October to February. Both mound and forest floor CO2 fluxes were highly correlated to mound or forest floor temperature. Based on our measurements, we are able to estimate the annual CO2 efflux from ant mounds and the surrounding forest floor, based on nonlinear regression analyses using CO2 flux as dependant and mound or forest floor temperatures as independent variables. Although red wood ant mounds were found to be “hot spots” for CO2 efflux, that increase the spatial heterogeneity of C emissions within a forest ecosystem, their annual emissions were only 0.30% of that from the forest floor. Thus, our results indicate that red wood ant mounds do not directly contribute significantly to the overall C budget of the boreal forest ecosystem studied. 相似文献
3.
Red wood ants (the Formica rufa group) build large nests which can last for many years. The ants often bring large quantities of conifer litter to their mounds. In this study we compared chemical properties of the forest floor and ant-nest materials of red wood ants at two different sites in Sweden. We also did an incubation study in the laboratory to determine C and N mineralisation rates of soil and nest materials at two moisture levels. Some chemical properties, e.g. pH and C/N ratio, differed between sites. Nests were always drier, had a higher C/N ratio and often had higher NH4+ concentrations than the surrounding forest floor. This indicates that the nests increase spatial heterogeneity of the forest floor not only because they contain large amounts of organic matter but also because of qualitative differences in nest composition. In the incubation study, experimentally increased moisture levels in the nest material resulted in net N immobilisation, while surrounding litter and humus materials showed net N mineralisation. The CO2 evolution was clearly increased by increased moisture. Dry conditions in the nest material prevented it from being decomposed and, since there were no plants to take up N, inorganic N accumulated. However, based on our results we hypothesise that ant nests do not produce large amounts of inorganic N as long as the ants bring fresh litter with high C/N ratio to the nests and keep the nests dry. However, the nests can be considered as potential "compost heaps" which probably decompose faster and will be a source of N leaching when the ants no longer maintain the specific dry conditions. 相似文献
4.
Wood ants (Formica rufa group) often bring large quantities of conifer resin to their mounds. The aim of this study was to test the hypothesis that
the resin acts as a fungicide and thereby reduces C and N mineralisation. Two laboratory incubation experiments were carried
out using two different materials: F/H layer from a Scots pine (Pinus sylvestris) stand and mixed litter from Scots pine and Norway spruce (Picea abies) stands. We estimated the effects of resin addition on fungal biomass and on the rates of C and N mineralisation. Addition
of resin to the F/H material caused an increase in fungal biomass and C mineralisation, whereas N mineralisation decreased.
Addition of resin to litter material did not significantly affect fungal biomass or C and N mineralisation. The results indicate
that rather than having a fungicidal effect, resin acts as a C source that increases C mineralisation (mainly from the resin
itself) and decreases net N mineralisation. The latter factor might be important in preventing plants dependent on inorganic
N from invading and covering the ant mounds.
Received: 17 December 1998 相似文献
5.
Recent studies suggest that wood ants (Formica rufa group) mounds are point sources of carbon dioxide (CO2), which increase the heterogeneity of soil carbon (C) emissions in forest ecosystems. However, little is known about the impact of anthropogenic activities, such as logging and subsequent forest succession, on these fluxes. In this study, we measured the CO2 efflux and temperature of wood ant mounds and the surrounding forest floor in managed Finnish boreal forests of different ages (5, 30, 60, and 100 years old) to assess how the effluxes vary with stand age. We conducted efflux measurements from the mounds and the surrounding forest floor throughout the ants' active season (May–September) and during the onset of hibernation (October). The annual CO2 efflux was then estimated using mound or forest floor temperatures, which were measured for one year. The average annual CO2 efflux from the ant mounds was 10.2 (±5.8 SD) kg m−2 year−1, increasing from 3.9 (±0.3 SD) kg m−2 year−1 in the 5 year-old stands to 14.3 (±3.0 SD) kg m−2 year−1 in the 100 year-old stands. Temperatures was significantly higher in the ant mounds than in the forest floor, and the average temperature difference between mounds and forest floor increased with stand age, being the lowest in the 5 year-old (4.1 (±3.1 SD) °C) and highest in the 100 year-old stands (10.3 (±5.2 SD) °C). There were no statistical differences in the mound CO2 efflux per volume among forest age classes, suggesting higher ant CO2 efflux in the older stands likely come from larger ant populations in the bigger mounts. The different mound temperature regimes among stand age classes indicates that the activity of wood ants changes with forest succession, particularly after clear-cutting, which alters CO2 efflux from the mounds. The impact of ant mounds on total CO2 efflux from the soil, estimated from mound area and volume, respectively, increased with forest age, from 0.05 (±0.05 SD) % to 0.31 (±0.18 SD) % and from 0.05 (±0.06 SD) % to 0.90% (±1.11 SD). 相似文献
6.
We conducted a study to determine why the pH of wood ant nest materials is typically higher than that of the surrounding forest soil. An experiment with litter bags demonstrated that the pH of litter increased significantly (after only 7 months) in ant nests. Because the food that foraging ants bring into the nest contains easily decomposed carbohydrates and basic cations (largely in the form of honeydew and prey) that can cause increases in pH, we then estimated the amount of this influ of basic cations and easily decomposed carbohydrates. Based on these estimates, we conducted a second experiment to determine whether addition of field-determined quantities of an easily decomposed carbohydrate (glucose) or a basic cation (Ca2+) would increase the pH of the litter in artificial ant nests in the forest. Both glucose and Ca2+ additions significantly increased the pH of the litter but the increase was greater with Ca2+. The rate of pH increase in the artificial nests was similar to the rate of increase in natural nests. According to our study, ants collect substantial amounts of mineral-enriched materials in this ecosystem, which collectively increase the pH of nest material. 相似文献
7.
P. Saetre P.-O. Brandtberg Heléne Lundkvist J. Bengtsson 《Biology and Fertility of Soils》1999,28(4):382-388
We examined how soil organisms and C, N and P mineralisation are affected by admixing deciduous tree species, silver birch
(Betula pendula) and woollen birch (B. pubescens), in managed Norway spruce (Picea abies) stands. Pure spruce and mixed spruce–birch stands were examined at four sites in southern and central Sweden. Soil macroarthropods
and enchytraeids were sampled in litter and soil. In the uppermost 5 cm of soil humus we determined microbial biomass and
microbial respiration; we estimated the rate of C, N and P mineralisation under laboratory conditions. The densities of Coleoptera,
Diptera and Collembola were larger in mixed stands than in spruce stands. Soil fauna composition differed between mixed and
spruce stands (as revealed by redundancy analysis). Staphyliniidae, Elateridae, Cecidiomyidae larvae and Onychiuridae were
the families that increased most strongly in mixed stands. There were no differences in microbial biomass and microbial respiration,
nor in the C, N and P mineralisation rates, between mixed and spruce stands. However, within mixed stands microbial biomass,
microbial activity and C mineralisation were approximately 15% higher under birch trees than under spruce trees. We propose
that the presence of birch leaf litter was likely to be the most important factor causing differences in soil fauna composition.
Birch may also influence the quality and the decomposition rate of humus in mixed stands. However, when the proportion of
birch trees is low, the short-term (decades) effect of this species on decomposition is likely to be small in mixed stands
on acid forest soils.
Received: 20 February 1998 相似文献
8.
川西亚高山人工云杉林地有机物和养分库的退化与调控 总被引：24，自引：0，他引：24
研究了川西亚高山云杉人工林地有机物和养分库状况 ,结果表明 :该区云杉人工林有机物和养分库严重退化 ,表现为 ,其凋落物的分解速率和周转期均较次生阔叶林和原始云杉林慢 ,致使地表枯枝落叶干物质和各种养分贮量滞留于凋落物层而不能进入土壤 ,土壤中有机质、全N、全P和碱解N含量随人工云杉林龄的增加而大幅度下降。人工云杉林份组成单一 ,其凋落物分解慢 ,归还土壤凋落物和养分数量少 ,是川西亚高山云杉人工林地土壤有机物和养分库退化的重要原因 ,人为收集凋落物积肥和人工抚育清灌 ,不断带走植被中养分是土壤有机物和养分库不断耗竭的另一重要原因。建议对该区人工成熟林抚育间伐和营造针阔混交林 ,改善成熟林下微环境和改变林份组成 ,可在很大程度上防治云杉人工林土壤有机物和养分库的退化 相似文献
9.
《Land Degradation \u0026amp; Development》2017,28(5):1538-1548
Ants are important soil engineers, affecting the structure and function of ecosystems. To address the impacts of ants (Camponotus herculeanus ) on the properties of an alpine meadow ecosystem of Qinghai–Tibet Plateau, we investigated the effects of ant mounds on plant biomass, soil physicochemical properties, microbial diversity, and functions. We found that the total biomass of plant community was significantly greater in ant mound periphery. Plant species richness in ant mounds was reduced compared with that of control plots without ant mounds. Significant changes in physicochemical properties of soil were also observed. Soil organic matter, total nitrogen, available phosphorous, total potassium, and available potassium increased in ant mound soil due to the excavation activities by ants as well as the accumulation of organic matter and other nutrients during mound construction. For example, roots/soil contents (g/g) and soil moisture in ant mound soils were lower than those in controls. Microbial community composition and microbial biomass were clearly changed in ant mound soils. BIOLOG analysis further indicated that the functional diversity of the microbial community of ant mound soil increased and differed from that of controls. This study indicates that ant‐induced modification of soil properties indirectly influences plant biomass and species composition, and ant mounds have different microbial communities from those of control soil. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
10.
Termite(Macrotermes spp.) mounds are complex biological habitats originated by the termite activity and possessing peculiar physical, chemical and biochemical properties. In this study we examined the concentration of nutrients and the biochemical activity of abandoned soil and mounds colonized by termites of the genera Macrotermes located in the Borana District, Ethiopia. To elucidate the magnitude and persistence of the termite-induced effects, we also studied an abandoned mound, previously colonized by termites of the same genera formed on the same soil. Results confirmed that termite-colonized mounds are ‘hot spots' of nutrient concentration and microbial activity in tropical soils. This is due to the termite driven litter input and decomposition. The abandoned mounds showed higher microbial biomass and activity and displayed a nutrient redistribution and a greater microbial activity than the adjacent soils. These findings allowed us to hypothesize a model of nutrient cycling in colonized soils and a partition of the relative roles of termites and soil microorganisms in nutrient location and turnover in tropical soils. These results may be also useful for the optimal management of termite-colonized soils. 相似文献
11.
Forest management practices often generate clear-cut patches, which may be colonized by ants not present in the same densities in mature forests. In addition to the associated changes in abiotic conditions ants can initiate processes, which do not occur in old-growth stands. Here, we analyse the effects of ants and aphid honeydew on litter solution of Norway spruce, microbial enzyme activities, and needle decomposition in a field and greenhouse experiment during summer 2003. In the field, low ant densities had relatively little effects on litter solution 30 cm away from a tree trunk, but significantly increased organic carbon concentrations and decreased inorganic nitrogen concentrations next to a trunk where ants tend to build their nests. In a greenhouse experiment, the addition of ants to lysimeters containing spruce litter significantly increased dissolved organic carbon (DOC), dissolved organic nitrogen (DON), NH4-N, NO3-N and K concentrations in litter solutions compared to the control treatment, while the simulation of aphid infestation (addition of honeydew) significantly increased DOC as a direct result of honeydew leaching, and decreased inorganic N concentrations in leachates. The presence of ants resulted in a changed composition of dissolved organic matter (DOM) with more aromatic and complex compounds, and microbial enzyme activity was significantly higher in litter extracts from the ant treatment compared to the honeydew and control treatment. However, mass loss, litter %C and %N were not affected by ants or honeydew. Our results suggest that ants have a distinct and immediate effect on solution composition and microbial activity in the litter layer indicating accelerated litter decay whereas the effect of honeydew was insignificant. 相似文献
12.
Petr Dostl Magdalena B&#x;eznov Vladimíra Kozlí
kov Tom&#x; Herben Pavel Kov&#x; 《Pedobiologia》2005,49(2):127-137
Lasius flavus is a dominant mound-building ant species of temperate grasslands that significantly modifies soil parameters. These modifications are usually the result of workers’ activities such as food accumulation and nest construction. An alternative hypothesis that could explain changes in soil is colony founding in areas of higher soil fertility.In our study we investigated several soil parameters sampled in 10 ant nests and adjacent (control) plots in mountain grassland in Slovakia. The alternative hypothesis was tested by comparing occupied and abandoned mounds. While we found increased concentrations of available P and K in the nests, concentrations of total C, total N, Ca2+ and Mg2+ were lower there. We propose that differences found between the soil of nests and control plots are entirely a product of ant activity during mound occupancy and not due to initial soil differences during nest establishment. This was confirmed by the comparison of occupied and abandoned nests in which the soil fertility of abandoned nests was similar to conditions in the surrounding soil.Along with the modification of soil chemistry, we recorded changes in soil physical properties and the vertical distribution of nutrients. Ant nests were characterized by the dominance of 0.02–0.1 mm particles and lower bulk density. In the same habitat, nutrient concentrations did not change along the vertical gradient in contrast to control plots where soil nutrients decreased and bulk density increased with depth. Root biomass followed the vertical pattern observed with nutrients: in control plots, most roots were concentrated in the uppermost layer (0–3 cm), whereas they were evenly distributed along the vertical gradient in the nests. We also found that rhizome internodes of Agrostis capillaris were thinner and longer in plants from the mounds. Changes in soil physical properties, vertical distribution of nutrients and root biomass in the nests are most probably a consequence of mounding and soil mixing (bioturbation), which has been less reported on in ant-soil studies. 相似文献
13.
The occurrence of aspen (Populus tremuloides Michx.) patches within stands dominated by black spruce (Picea mariana Mill. BSP) has been shown to increase litter decomposition and nutrient cycling rates by improving soil physical and chemical properties. It is well known, however, that these processes are also influenced by the structure of the soil biota, but this factor has received less attention. In this study, relationships between forest floor properties and soil invertebrates were studied along black spruce–trembling aspen gradients in three stands of the eastern boreal forest of Canada. The forest floor layer of 36 plots differing in aspen basal area was sampled and analyzed to determine physical and chemical properties, the rates of decomposition of standard substrates, net N mineralization, as well as microbial basal respiration and metabolic quotient. Soil invertebrates were also collected using funnel-extraction and pitfall trapping methods. Based on redundancy analyses, we found that forest floor properties, the abundance and composition of soil invertebrates, and the rates of belowground processes changed along the spruce–aspen gradient. The increase in aspen basal area was associated with a reduction in forest floor thickness, moisture content and microbial biomass, and with an increase in the concentration of nutrients. It was also accompanied by changes in soil faunal communities, as soil invertebrates were associated with specific soil properties. In general, macroinvertebrates (i.e., Lumbricidae, Formicidae, Carabidae, Staphylinidae and Gastropoda) were related to the nutrient-rich forest floor associated with aspen, whereas microarthropods and Enchytraeidae tended to be negatively related to aspen basal area. According to mixed linear models, decomposition rates of standard substrates and net ammonification significantly increased along the spruce–aspen gradient. Given the functional significance of macroinvertebrates in soils, these results suggest that aspen favours the elaboration of a macrofaunal community, which in turn accelerates the rate of soil processes by having either direct or indirect influence on microbial activity. Moreover, this study shows that the changes in soil processes and in the biodiversity of soil organisms related to the presence of mixed stands can operate only in the immediate surroundings of a given tree species. Therefore, coarse-scale tree species mixing in a forest stand may have a different effect on soil biodiversity and soil processes than fine-scale mixing. 相似文献
14.
The amounts of Ca, K, Mg and P were measured in leaf litter contained in litter bags in a southeastern United States deciduous forest. Half of the litter was treated with naphthalene, a chemical that reduced microarthropod densities to about 10% of those found in untreated litter. Phosphorus losses were significantly greater in untreated litter. After initial elemental losses, amounts of Ca, K and Mg generally increased in 9–12 month-old untreated litter, while naphthalene-treated litter generally showed no seasonal dynamics. Seasonal amounts of nutrients in forest litter depend upon elemental mobility, inputs of nutrients in rainfall, throughfall and particulates, and nutrient retention by forest floor biota. Microarthropods increase nutrient loss from forest litter by comminution; however, microbial stimulation as a result of microarthropod feeding activities appears to increase the nutrient retention capacities of forest litter. 相似文献
15.
Steven D. Allison David S. LeBauer Randy Reyes Tri M. Tran 《Soil biology & biochemistry》2009,41(2):293-302
Climate warming and associated increases in nutrient mineralization may increase the availability of soil nitrogen (N) in high latitude ecosystems, such as boreal forests. These changes in N availability could feed back to affect the decomposition of litter and organic matter by soil microbes. Since fungi are important decomposers in boreal forest ecosystems, we conducted a 69-day incubation study to examine N constraints on fungal decomposition of organic substrates common in boreal ecosystems, including cellulose, lignin, spruce wood, spruce needle litter, and moss litter. We added 0, 20, or 200 μg N to vials containing 200 mg substrate in factorial combination with five fungal species isolated from boreal soil, including an Ascomycete, a Zygomycete, and three Basidiomycetes. We hypothesized that N addition would increase CO2 mineralization from the substrates, particularly those with low N concentrations. In addition we predicted that Basidiomycetes would be more effective decomposers than the other fungi, but would respond weakly or negatively to N additions. In support of the first hypothesis, cumulative CO2 mineralization increased from 635 ± 117 to 806 + 108 μg C across all fungal species and substrates in response to 20 μg added N; however, there was no significant increase at the highest level of N addition. The positive effect of N addition was only significant on cellulose and wood substrates which contained very little N. We also observed clear differences in the substrate preferences of the fungal species. The Zygomycete mineralized little CO2 from any of the substrates, while the Basidiomycetes mineralized all of the substrates except spruce needles. However, the Ascomycete (Penicillium) was surprisingly efficient at mineralizing spruce wood and was the only species that substantially mineralized spruce litter. The activities of β-glucosidase and N-acetyl-glucosaminidase were strongly correlated with cumulative respiration (r = 0.78 and 0.74, respectively), and Penicillium was particularly effective at producing these enzymes. On moss litter, the different fungal species produced enzymes that targeted different chemical components. Overall, our results suggest that fungal species specialize on different organic substrates, and only respond to N addition on low N substrates, such as wood. Furthermore, the response to N addition is non-linear, with the greatest substrate mineralization at intermediate N levels. 相似文献
16.
《European Journal of Soil Biology》2002,38(1):97-102
Wood ants (Formica rufa group) normally feed on secretions of aphids to obtain carbohydrates, and on free-living invertebrates to obtain proteins. The availability of protein resources is usually unpredictable, and the demand for proteins is high during the period when ant larvae are developing. Thus, ants should select high quality food patches, i.e. patches with plenty of prey, when these are available. Foraging on the forest floor is seldom observed, but should be an alternative behaviour during periods of scarce food supply in the trees. To study the hunting behaviour of wood ants on soil invertebrates, ants were offered fly larvae (maggots) in two different quantities (six or two per pah) at two distances from an ant trail. Maggots exposed on the forest floor were found by randomly patrolling ant scouts regardless of bait quality. However, scouts that found the baits with six larvae recruited workers faster and, on average, four times as many workers were recruited to the six-larvae bait than to the bait with only two larvae. This indicates that ants can distinguish between poor and rich patches and that they are able to use this information to recruit more workers. Also, more workers were recruited and more maggots were carried away from patches nearby trails than from those far away. The results indicate that, during the warm season, ants explore and exhibit adaptive ‘foraging behaviour’ on the forest floor in the whole territory, not only close to trails. Consequently, wood ant feeding on soil invertebrates may be a common way for obtaining a large amounts of protein. 相似文献
17.
The forest floor was shown to be an effective sink of atmospherically deposited methylmercury (MeHg) but less for total mercury (Hgtotal). We studied factors controlling the difference in dynamics of MeHg and Hgtotal in the forest floor by doubling the throughfall input and manipulating aboveground litter inputs (litter removal and doubling litter addition) in the snow‐free period in a Norway spruce forest in NE Bavaria, Germany, for 14 weeks. The MeHg concentrations in the forest‐floor percolates were not affected by any of the manipulation and ranged between 0.03 (Oa horizon) and 0.11 (Oi horizon) ng Hg L–1. The Hgtotal concentrations were largest in the Oa horizon (24 ng Hg L–1) and increased under double litterfall (statistically significant in the Oi horizon). Similarly, concentrations of dissolved organic C (DOC) increased after doubling of litterfall. The concentrations of Hgtotal and DOC correlated significantly in forest‐floor percolates from all plots. However, we did not find any effect of DOC on MeHg concentrations. The difference in the coupling of Hgtotal and MeHg to DOC might be one reason for the differences in the mobility of Hg species in forest floors with a lower mobility of MeHg not controlled by DOC. 相似文献
18.
《Communications in Soil Science and Plant Analysis》2012,43(9):737-747
Abstract As a corollary of a detailed study on the ecology of the Harvester ants in soils of semi‐arid natural pastures, samples from a loessial Arid Brown soil were analyzed for the content of nitrogenous constituents (humic compounds, amino acids, nitrates, ammonia) as well as phenols and carbohydrates and the nutrient status of the soil. While there was a significant increase in fulvic and humic acids in the ant nests, the simultaneous decrease in amino acids ‐ in relation to the surrounding soil ‐ indicates that the humic substances have been synthesized from amino acids and the abundantly present phenols and possibly carbohydrates. The much higher concentration of nitrogen compounds in the ant mounds supports the idea that the soil mixing activity of the Harvester ants enhances microbiological processes and in turn the fertility of the mounds, as evident in the better growth of the pasture plants. 相似文献
19.
Organic mounds of the red wood ants (Formica rufa group; RWA) have been shown to be “hot spots” of carbon dioxide (CO2) efflux from the European forest soils. However, little information is available on the variability of CO2 effluxes from RWA mounds and on the factors regulating CO2 efflux. We assessed the seasonal and diurnal changes in CO2 effluxes, temperatures and volumetric water contents from mounds of Formica aquilona, the important RWA of the boreal forests in Finland. The daily average CO2 efflux from RWA mounds ranged 1.1-6.9 g CO2 m−2 h−1 during the active ant season (May-September), and from 0.2 to 1.1 g CO2 m−2 h−1 during their dormant period (October-April). Mound CO2 efflux from May to September was 3.6-6.0 times higher than from the surrounding forest floors, and most likely came from RWA respiration. Seasonal changes in mound CO2 effluxes were significantly correlated with mound temperature, but not with volumetric water content (7% on average). The high CO2 efflux associated with increased volumetric water content (up to 34%) after a RWA mound was abandoned indicated that these dry mound conditions restrict microbial decomposition of mound organic matter. CO2 effluxes were highest at night and lowest during the day, which is likely due to an increased ant activity or numbers in the mound at night. Diurnal changes in mound CO2 efflux were negatively correlated with air temperature, and positively correlated with the difference between the mound and air temperature. This suggests that thermal convection of warmer mound air to the colder outside air at night might be also a cause of the diurnal changes. We conclude that seasonal and diurnal variations in mound CO2 effluxes are dependent on RWA activities and fluctuation in RWA mound and outside temperatures. 相似文献
20.
Jarrah (Eucalyptus marginata Donn ex Smith) forest grows on poor soils with low stores of plant-available nutrients. We evaluated the impact of fertilizers on nutrient cycling in soil under Jarrah forest using a field study with three rates of P (0, 50, 200 kg P ha–1) and three rates of N (0, 100, 200 kg N ha–1) in a full factorial design. Litterfall was significantly increased by N application (30% relative to controls) in the first 2 years after treatment and by P application in the second year. The amounts of N, P, K, Ca and Mg in litterfall were also increased significantly by both N and P fertilizer. Although fertilizer treatments did not affect the total amount of litter accumulated on the forest floor over 4–5 years after application, there were large treatment differences in the amounts of N and P stored in the forest floor. Microbial respiration in litter was significantly greater (19%) on P-treated plots relative to controls, but this increase did not translate into increased decomposition rates as measured in long-term (5-year) mesh-bag studies. The results indicate that factors other than nutrition are mainly responsible for controlling the rate of decomposition in this ecosystem. Application of P, in particular, resulted in substantial accumulation of P in forest floor litter over 5 years. This accumulation was partly a result of the deposition of P in litterfall, but was also probably a result of translocation of P from the mineral soil. During the 5-year decomposition study, there was no net release of P from leaf litter and, at the highest rate of P application, the amounts of P stored in forest floor litter were more than four-fold greater than in fresh litter. Regular fire, a common phenomenon in these ecosystems, may be an important P-mobilizing agent for enhancing plant P uptake in these forests. 相似文献