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1.
Nests of the yellow meadow ant (Lasius flavus) occur at high densities in grasslands worldwide. Although many studies have shown that L. flavus nests influence soil nutrient contents, little is known about their effect on soil nutrient cycling rates. The aim of this study was to examine the role of nest-mounds inhabited by L. flavus as potential ‘hot spots’ for soil nutrient cycling. Six pairs of nest-mounds and control soils were selected at a grassland site at the plateau of the Alter Gleisberg (Thuringia, Central Germany). L. flavus significantly modified the soil environment within the nest. In comparison to the control soils, nest-mounds were characterized by slightly higher soil temperatures during the summer months. In addition, we found that nests were related to decreased potential C mineralization rates and increased potential net N mineralization rates. Nest-mound soil exhibited lower amounts of SOC, hot-water extractable DOC and DN, and higher concentrations of leachable DOC and DN. Moreover, ants promoted the enrichment of base cations in the nest. Differences in the soil environment between nests and control soils were possibly a result of the burrowing activity of ants, soil mixing, accumulation of aphid honeydew, and decreased plant-derived nutrient inputs into the nest-mound soil. In conclusion, L. flavus nest-mounds had a significant but element dependent effect on the soil nutrient cycling and may represent cold spots for C cycling and hot spots for N cycling. Thus, L. flavus nests increase the spatial heterogeneity of soil properties and create unique micro-sites within grassland ecosystems.  相似文献   

2.
A study was carried out during 2001 on mine tailings in NW Bohemia aimed at describing the spatial patterns of nests distribution and epigeic activity of ants in relation to the vegetation mosaic. Lasius niger was the most abundant species of ant and its nest mounds were significantly more numerous in patches with sparse vegetation than inside dense Calamagrostis epigejos vegetation; this was particularly true for small and medium-sized nests. Small and medium nests also occurred more frequently near the edges of a given patch than in the center. Large and medium nests were randomly distributed in the area, whereas small nests had an aggregated distribution. Pitfall trapping reveal significantly higher activity of L. niger workers in tall and dense vegetation stands in comparison with low and sparse vegetation. This pattern was particularly pronounced during the peak of foraging activity in summer and was not so significant in spring or autumn. We expect that ant preferentially forage in shaded habitats during the summer months when bare soil may be too hot. The results indicated that nesting and foraging may differ in their microclimatic requirements and the formation of vegetation mosaics may be important to changes in the ant population during succession.  相似文献   

3.
Leaf-cutting ants consume up to 10% of canopy leaves in the foraging area of their colony and therefore represent a key perturbation in the nutrient cycle of tropical forests. We used a chronosequence of nest sites on Barro Colorado Island, Panama, to assess the influence of leaf-cutting ants (Atta colombica) on nutrient availability in a neotropical rainforest. Twelve nest sites were sampled, including active nests, recently abandoned nests (<1 year) and long-abandoned nests (>1 year). Waste material discarded by the ants down-slope from the nests contained large concentrations of nitrogen and phosphorus in both total and soluble forms, but decomposed within one year after the nests were abandoned. Despite this, soil under the waste material contained high concentrations of nitrate and ammonium that persisted after the disappearance of the waste, although soluble phosphate returned to background concentrations within one year of nest abandonment. Fine roots were more abundant in soil under waste than control soils up to one year after nest abandonment, but were not significantly different for older sites. In contrast to the waste dumps, soil above the underground nest chambers consistently contained lower nutrient concentrations than control soils, although this was not statistically significant. We conclude that the ‘islands of fertility’ created by leaf-cutting ants provide a nutritional benefit to nearby plants for less than one year after nest abandonment in the moist tropical environment of Barro Colorado Island.  相似文献   

4.
利用黔东南16个气象观测站1971-2000年的气象资料,结合兔眼蓝浆果正常生长发育对光、温、水等气象条件的要求,对黔东南种植兔眼蓝浆果气候资源的优劣进行了分析,得出:海拔高度在300m以下地区兔眼蓝浆果打破休眠期的需寒条件不够,不宜种植;700-1000m的高度层上,虽然可以种植,但受冬末春初低温天气影响较大,产量不稳定;300-700m高度层是黔东南种植兔眼蓝浆果的高产、稳产区。研究结果可为黔东南扩大兔眼蓝浆果种植面积提供气候依据。  相似文献   

5.
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   

6.
Tropical ecosystems play a key role in the global carbon cycle, but their response to global warming is not well understood. Altitudinal gradients offer the unique possibility of undertaking in situ experimental studies of the influence of alterations in climate on the carbon (C) cycle. In a soil‐translocation experiment we took replicate soil cores at 3030 m, 1500 m, 1000 m and 200 m above sea level along an altitudinal gradient in tropical forest in Peru, and exchanged (i.e. translocated) them among these sites to observe the influence of altered climatic conditions on the decomposition of soil organic matter under natural field conditions. Soil respiration rates of the translocated soil cores and adjacent undisturbed soils were measured twice a month from April 2007 to October 2007. The temperature sensitivity of heterotrophic respiration in each core was examined using a Lloyd & Taylor function and a simple modified third‐order polynomial fit. Calculated Q10 values decreased with decreasing altitude using both mathematical functions (2.53–1.24 according to the Lloyd & Taylor function, and 2.56–0.63 using the polynomial fit). Soil organic C‐stocks increased markedly and linearly with altitude, but surprisingly the average total soil respiration rate did not vary significantly with altitude along the transect (3.98–4.31 μmol CO2 m−2 s−1). This implies an increase with elevation of absolute C allocation to below‐ground allocation.  相似文献   

7.
The main reason for meadow bird declines is supposed to be the intensification of grassland management with earlier first harvest dates and more frequent harvests, resulting in high nest destruction rates. To increase productivity of meadow bird populations in intensified grassland areas a delay of mowing date and individual nest protection measures have been proposed. However, for ground-nesting songbirds such as the whinchat (Saxicola rubetra) the effectiveness of such measures remains widely unknown. In particular, if nest predation rate is high, measures to protect nests from agricultural destruction alone might be questionable. Here, we quantify whinchat nest survival of (1) unprotected nests situated in early mown meadows, (2) protected nests situated in early mown meadows, and (3) nests situated in late mown meadows. Analyses considered the fact that successful and unsuccessful nests are not found with equal probabilities. Periods of reduced nest survival were associated with mowing periods in the different types of meadows. In early mown meadows nest survival rates were low (S < 0.1), and both conservation measures, individual nest protection and delayed mowing, resulted in significantly increased nest survival rates (S > 0.7). Individual nest protection cannot avoid changes in habitat quality of intensively managed meadows, and therefore is only suitable as small-scale and short-term measure to increase nest success until a high portion of late mown meadows is established. Thus, we suggest that a combination of the two measures applied to intensified grassland fields should be provided to maintain viable sizes of endangered meadow bird populations.  相似文献   

8.
Ants significantly change the soil environment within the nest. The aim of this study is to contribute to ecology and thus the importance of two ant species Lasius niger and Lasius flavus in a post-mining landscape near the town of Sokolov in northwest Bohemia where both species are common. Chemical (total C, N, and available P) and microbiological parameters (respiration, cellulose decomposition and direct counts of bacteria) were investigated in both ant species in two different habitats: a tertiary clay heap after brown coal mining with a weakly developed organic layer and semi natural meadows with well developed organic horizons. Total C and N in the L. flavus mound was lower than in the surrounding soil in both stands, the same was true for total N in L. niger on the heaps. L. niger nests in both sites were significantly enriched by available P. A litter bag test with cellulose indicated lower decomposition in the ant nest in comparison with the surrounding soil. Respiration seems to be limited by lower soil moisture in the nest. However, microbial respiration, even in suitable moisture conditions, did not differ between the nest and soil (on heaps) or nest respiration was significantly lower (in L. flavus nests in the meadow). In meadow soil both species had a lower bacteria count than the surrounding soil, but the L. niger nest on the heap had higher bacterial numbers. Both species significantly alter soil conditions, although the effect on selected parameters is variable. Moreover, the result with lower nest moisture and lower decomposition rate in ant mounds indicates that soil moisture should be the next important factor limiting soil processes inside ant mounds.  相似文献   

9.
We investigated microbial biomass, fungal biomass and microbial community structure at three altitudes (1000, 2000 and 3000 m) and in two soil layers [L/F layer (Layer I) and underlying H/Ah layer (Layer II)] of tropical mountain rain forests in southern Ecuador. Basal respiration, microbial biomass and concentration of ergosterol generally declined from Layer I to Layer II and peaked at 2000 m. Compared to temperate forest ecosystems microbial biomass and ergosterol concentrations were generally low. Patterns in phospholipid fatty acids indicated that the composition of microbial communities markedly changed from Layer I to Layer II. These differences between layers decreased with increasing altitude. The concentration of the arbuscular mycorrhizal fungal marker PLFA 16:1ω5c decreased with altitude in Layer I but increased in Layer II. The fungal-to-bacterial ratio increased with altitude and was higher in Layer I than in Layer II. Presumably, low microbial biomass in soils of tropical forest ecosystems is due to high temperature associated with high respiration but also low litter quality, with the latter declining with altitude. These conclusions are supported by the fact that at higher altitude the microbial community changed from a bacterial-dominated to a fungal-dominated system. CCA showed that microbial biomass correlated closely with density of a number of putatively bacterial feeding testate amoeba species including Corythion dubium Taranek, 1871, Euglypha cristata Leidy, 1879, Trigonopyxis arcula Penard, 1912, Tracheleuglypha dentata Deflandre, 1928 and Trinema lineare Penard, 1890. Ergosterol concentrations, but not the PLFA 18:2ω6c, strongly correlated with the putatively fungal feeding species Phryganella acropodia (Hertwig, Lesser, 1874) Hopkinson, 1909. Generally, parallel to microbial biomass and ergosterol concentrations the density of testate amoebae peaked at 2000 m. However, compared to microbial parameters changes in testate amoebae communities between two layers were less pronounced. The data suggest that density and community structure of testate amoebae are driven by the availability of food resources (bacteria and fungi) which at high altitude decrease with increasing moisture and decreasing pH.  相似文献   

10.
Respiration of a soil used for vegetable crops at the beginning of the vegetation period Soil respiration was measured with a new portable soil respiration system (PP Systems, Hitchin, England) in vegetable plots in the greenhouse and field near Bonn from January to May 1996 with the following results:
  • 1 The equipment proved suitable for the purpose over a wide range of temperatures.
  • 2 Soil respiration ranged from less than 26 mg CO2 in winter, 30–180 mg CO2 in spring to 700 mg CO2 m?2 h?1 in summer with large variations.
  • 3 The largest soil respiration was recorded from peat-based commercial potting compost with small variations between measurements.
  • 4 The Q10 was 2,5 (±0,6) in the field for temperatures between 5–25°C.
  • 5 The rate of soil respiration was affected by soil cultivation with the effect declining with temperature: Ploughing, which unveiled cold and produced a coarse soil surface, reduced soil respiration, whereas soil respiration was increased by fine soil cultivation.
  • 6 In vegetable plots, soil respired 6–12 kg in cold (4°C), 40–50 kg CO2 in cool (14°C) conditions in April and 170–210 kg CO2/ha and 24 hours in warm (27°C) weather.
  相似文献   

11.
The attributes of roadside vegetation, an important bird habitat in grassland ecosystems, have been shown to affect bird abundance, distribution composition, and diversity, yet there are relatively few works on reproductive success of birds nesting along roadsides. Because roadsides are linear habitats, management at the landscape scale can affect nest success in roadsides through bottom-up and top-down effects. In northeastern Oklahoma tallgrass prairie is subjected annually to prescribed spring fires. In the short term fires can alter both arthropod abundance and predator access to nests. We explored effects of burning on bird nest success with a five-year study along roads that traversed tallgrass prairie habitat. Using data from ∼1400 nests of 23 species, we generated nest survival curves for groups of altricial species defined by nest substrate (ground, shrub, tree, or culvert). We then determined if these curves were affected by management practice (spring burning), food abundance (arthropod biomass), and habitat attributes (tree density and height). Nest substrate had a large effect on nest success: despite their shorter nest exposure period, ground nests were least successful and culvert nests were most successful. An increase in arthropod biomass following burning was possibly the cause for the increased nest success in burned plots, regardless of substrate, suggesting bottom-up control. Tree height and nest height were correlated positively with nest success, whereas tree density had no effect. Conversely, nest predation rates were correlated negatively with nest success, with ground nests experiencing the highest predation, culvert nests the lowest. Our results suggest that burning may increase nest success through bottom-up processes, but some species may not benefit from the increase in food abundance as a result of a concomitant increase in predation.  相似文献   

12.
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   

13.
Waders leave nests and conduct distractive displays when approached by people. The time taken for waders to return to nests depends on numerous factors that affect the costs and benefits of incubation and anti-predator behavior. Understanding this trade-off may help assess the reproductive consequences of different nest return times and identify variables to consider in breeding disturbance studies. We subjected 73 Malaysian plover (Charadrius peronii) nests to standardized human disturbances and an analysis of covariance was used to determine how weather, time of day, embryonic age, weeks into breeding season and nest attendance (proportion of time adults incubated nests) influence nest return times. Egg temperatures were estimated using a regression model that predicted the temperature inside unshaded eggs from air temperature, cloud cover and time of day (r2 = 0.88). We assessed the relationship between nest return times and hatch success. Plovers returned to nests faster at higher modeled egg temperature (P = 0.010), in the morning (P = 0.003), if they had younger clutches (P = 0.038), and if they had high nest attendance prior to the disturbance (P = 0.015). Pairs that returned to nests faster had lower hatch success (P = 0.021). This may be because pairs that spend more time distracting humans may also do so for predators. These results suggest that short nest return times may not indicate low fitness costs of disturbance. The thermal and predation environment in addition to nest return times should be taken into account when assessing the deleterious effects of human disturbance.  相似文献   

14.
Soil respiration (CO2 evolution), soil temperature (1 dm) and water content (0–1dm) were determined over a 2 yr period in a grassland soil of the arid shrub-steppe. Respiration was due primarily to decomposition of plant roots by soil organisms. Although respiration rate was generally limited by soil temperature in the fall, winter and early spring and by soil water content in the late spring and summer, temperature and water content were interdependent in their effects on soil respiration rate. Soil organisms responded to changes in soil temperatures at water contents as low as 1–2 per cent (106-88 bar suction). Above approximately 6° C, increased soil water content resulted in increased soil respiration rate. but the extent of the increase was non-linear and dependent upon soil temperature. Respiration rate approached a maximum at soil water contents of 6–10 per cent (35-13 bar suction) depending upon soil temperature and was generally optimum at temperatures above 15° C. The mutual regulation of soil respiration rate by temperature and moisture during this study was best described by a soil temperature-water interaction or multiplicative term, and regression equations which included this term served to accurately predict seasonal changes in soil respiration rate. Using a simple regression equation which included only the interaction term, it was possible to account for 70 per cent of the total variation in soil respiration rate during the monitoring period.  相似文献   

15.
Soil respiration is an important component of terrestrial carbon cycling and can be influenced by many factors that vary spatially. This research aims to determine the extent and causes of spatial variation of soil respiration, and to quantify the importance of scale on measuring and modeling soil respiration within and among common forests of Northern Wisconsin. The potential sources of variation were examined at three scales: [1] variation among the litter, root, and bulk soil respiration components within individual 0.1 m measurement collars, [2] variation between individual soil respiration measurements within a site (<1 m to 10 m), and [3] variation on the landscape caused by topographic influence (100 m to 1000 m). Soil respiration was measured over a two-year period at 12 plots that included four forest types. Root exclusion collars were installed at a subset of the sites, and periodic removal of the litter layer allowed litter and bulk soil contributions to be estimated by subtraction. Soil respiration was also measured at fixed locations in six northern hardwood sites and two aspen sites to examine the stability of variation between individual measurements. These study sites were added to an existing data set where soil respiration was measured in a random, rotating, systematic clustering which allowed the examination of spatial variability from scales of <1 m to 100+ m. The combined data set for this area was also used to examine the influence of topography on soil respiration at scales of over 1000 m by using a temperature and moisture driven soil respiration model and a 4 km2 digital elevation model (DEM) to model soil moisture. Results indicate that, although variation of soil respiration and soil moisture is greatest at scales of 100 m or more, variation from locations 1 m or less can be large (standard deviation during summer period of 1.58 and 1.28 μmol CO2 m−2 s−1, respectively). At the smallest of scales, the individual contributions of the bulk soil, the roots, and the litter mat changed greatly throughout the season and between forest types, although the data were highly variable within any given site. For scales of 1-10 m, variation between individual measurements could be explained by positive relationships between forest floor mass, root mass, carbon and nitrogen pools, or root nitrogen concentration. Lastly, topography strongly influenced soil moisture and soil properties, and created spatial patterns of soil respiration which changed greatly during a drought event. Integrating soil fluxes over a 4 km2 region using an elevation dependent soil respiration model resulted in a drought induced reduction of peak summer flux rates by 37.5%, versus a 31.3% when only plot level data was used. The trends at these important scales may help explain some inter-annual and spatial variability of the net ecosystem exchange of carbon.  相似文献   

16.
Knowledge about soil formation in tropical montane rainforests is scarce and patchy. We examined the altitudinal change of soils in a Bolivian tropical montane rainforest, aiming to illuminate the contribution of podzolization and hydromorphic processes to soil formation. In three transects from 1700 m to 3400 m a.s.l. we determined the pH, exchangeable cation exchange capacity, carbon and nitrogen stocks, and iron and aluminium fractions from 26 soil profiles. Three zones of different dominant soil forming processes were found: In the lower montane forest (LMF, 1700–2200 m a.s.l.), Dystropepts with high nutrient concentration and acidity were common. The pronounced change to the upper montane cloud forest (UMCF, 2200–2700 m a.s.l.) coincided with the appearance of Placorthods with more acidic conditions, deep ectorganic horizons and increasing translocation of sesquioxides. In the sub-alpine forest (SCF, 2700 m–3400 m a.s.l.), hydromorphic processes dominated over podzolization, resulting in Placaquods with low mineralization rate and nutrient concentration. This shows that due to increasing wetness and colder temperatures at high altitudes, dominant soil forming processes change from podzolization to hydromorphism soils with increasing altitude.  相似文献   

17.
Climate change scenarios predict increases in temperature, changes in precipitation patterns, and longer drought periods in most semi-arid regions of the world. Ecosystems in these regions are prone to land degradation, which may be aggravated by climate change. Soil respiration is one of the main processes responsible for organic carbon losses from arid and semi-arid ecosystems. We measured soil respiration over one year in two steppe ecosystems having different degrees of land degradation under three ground-covers: with vegetation, bare soil, and an intermediate situation between plants and bare soil.The largest differences in soil respiration rates between the sites were observed in spring, coinciding with the highest level of plant activity. The degraded site had drier and hotter soils with less soil water availability and a longer drought period. As a result, vegetation on the degraded site did not respond to spring rainfall events. Soil respiration showed a strong seasonal variability, with average annual rates of 1.1 and 0.8 μmol CO2 m−2 s−1 in the natural and degraded sites, respectively. We did not observe significant differences in soil respiration rates associated with ground-cover i.e., the temporal variation was much larger than the spatial variation. At both sites, soil moisture was the controlling driver of soil respiration for most of the year, when temperatures were above 20 °C and constrained the response to temperature for the few months when the temperature was below 20 °C. An empirical model based on soil temperature and soil moisture explained 90% and 72% of the seasonal variability of soil respiration on the natural and degraded sites, respectively. For the first time, this study suggests that land degradation may alter the carbon balance of these ecosystems through changes in the temporal dynamics of soil respiration and plant productivity, which have important negative consequences for ecosystem functioning and sustainability.  相似文献   

18.
[目的]探讨不同植被类型土壤呼吸特征及其温度敏感性,为陆地生态系统碳循环研究提供理论支持.[方法]以太行山南麓裸地、草地、灌丛、林地为研究对象,采用长期定位观测和室内化验分析相结合的方法,研究不同季节土壤水热因素、呼吸特征及其温度敏感性.[结果]不同植被类型的土壤温度变化较大,均表现为1月初最低,8月下旬最高,8月以后...  相似文献   

19.
The effects of harvester ant (Pogonomyrmex rugosus) nests on the density and cover of spring annual plants and on soil characteristics were measured at three locations characterized by different soils and dominant vegetation on a desert watershed. There were few differences in vegetation and soils associated with harvester ant nests at locations at the base of the watershed where brief periods of flooding and sediment deposition occur at periodic intervals. At mid-slope locations, there were significant increases in total nitrogen, inorganic phosphorus, and cover (biomass) of four species of spring annuals at the edges of nest disks when compared with reference sites. The spring annuals that exhibited increased cover were species that increase biomass as a function of available nitrogen. At a clay-loam, Scleropogon-Hilaria, grassland site, there were significant reductions in the concentrations of Ca2+ and Mg2+, significant increases in nitrate and total nitrogen, but a significant increase in cover in only one species of annual plant. The data demonstrate that the effects of ants on soil properties and vegetation vary with site location and soil type.  相似文献   

20.
The aim of our studies was to determine the relation between temperature and the respiration rate of the forest soil organic layer along an altitudinal gradient while controlling the effects of the soil characteristics. The respiration rate was measured in laboratory conditions at different temperatures, 0, 10, 20, and 30°C, in samples collected in the Polish part of the Western Carpathians at 600, 800, 1,000, and 1,200 m above sea level from four different mountains, which were later treated as replicates. The increase in the average respiration rate between two consecutive temperatures was expressed as Q 10 coefficients. Among the nutrients measured in the soil organic layer, only the total organic N concentration significantly increased with elevation. The temperature effect was significant for both the respiration rate and the Q 10 values. The calculated Q 10 values were highest for the temperature range between 10 and 20°C, and the lowest values were obtained from the highest temperature range (20–30°C). The altitude effect was significant for the respiration rate but not for the Q 10 values, indicating that the temperature sensitivity of the soil respiration did not change much along the studied altitudinal gradient.  相似文献   

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