Interactive effects of soil-dwelling ants, ant mounds and simulated grazing on local plant community composition

Interactions between aboveground vertebrate herbivores and subterranean yellow meadow ants (Lasius flavus) can drive plant community patterns in grassland ecosystems. Here, we study the relative importance of the presence of ants (L. flavus) and ant mounds under different simulated grazing regimes for biomass production and species composition in plant communities. We set up a greenhouse experiment using intact soil cores with their associated vegetation.We found that plant biomass production in the short term was affected by an interaction between simulated grazing (clipping) and ant mound presence. Clipping homogenized production on and off mounds, while in unclipped situations production was higher off than on mounds. During the experiment, these differences in unclipped situations disappeared, because production on unclipped mounds increased. Plant species richness was on average higher in clipped treatments and patterns did not change significantly over the experimental period. Plant community composition was mainly affected by clipping, which increased the cover of grazing-tolerant plant species. The actual presence of yellow meadow ants did not affect plant community composition and production.We conclude that the interaction between ant mounds and clipping determined plant community composition and biomass production, while the actual presence of ants themselves was not important. Moreover, clipping can overrule effects of ant mounds on biomass production. Only shortly after the cessation of clipping biomass production was affected by ant mound presence, suggesting that only under low intensity clipping ant mounds may become important determining plant production. Therefore, under low intensity grazing ant mounds may drive the formation of small-scale plant patches.     

热带森林不同演替阶段蚂蚁巢穴的分布特征及其影响因素

为探明热带森林蚂蚁巢穴的分布特征及其影响因素, 采用样方法研究了西双版纳不同演替阶段热带森林定居巢穴蚂蚁的种类及其巢穴的密度、盖度和空间分布特征, 并分析了土壤理化环境与蚂蚁种类总数、巢穴密度及盖度的相关性。结果表明, 不同演替阶段热带森林蚂蚁种类总数、巢穴的密度及盖度大小顺序为: 小果野芭蕉 (Musa acuminata)群落>白背桐(Mallotus paniculatus)群落>思茅崖豆(Mellettia leptobotrya)群落, 并且热带森林的演替类型显著影响蚂蚁种类总数及巢穴密度, 而对巢穴盖度的影响未达到显著水平; 蚂蚁种类总数、巢穴密度与土壤总有机碳和水解氮显著正相关, 与土壤容重和土壤含水率显著负相关, 但所选择的土壤理化指标与巢穴盖度的相关性均未达到显著水平; 蚂蚁巢穴的空间分布呈随机分布格局。我们的数据表明, 不同演替阶段热带森林所形成的植被类型及土壤环境状况共同影响定居的蚂蚁种类总数与筑巢密度。     

Vegetation of ant-hills in a mountain grassland:effects of mound history and of dominant ant species

Vegetation in grasslands with well-developed long-lastingant-hills in the Slovenské Rudohorie Mts., Slovakia, was studiedin relation to (i) position on the mound, (ii) ant speciesforming the mound, and (iii) history of the mound. Permanent plotrecordings of mound size and dominant ant species started fifteen years priorthe study began provided information on the history of individual mounds.The mound vegetation bears a striking similarity to vegetation insimilar habitats across a large part of Europe due to presence of species suchas Agrostis capillaris, Dianthusdeltoides, Polytrichum commune agg.,Thymus pulegioides, and Veronicaofficinalis. Out of the three major ant species-groups presentat the site (Lasius flavus, Tetramoriumcaespitum and Formica spp.), L.flavus had the most pronounced and the most lasting effect on themound vegetation. The dominance of the plant species listed above increased withthe time span over which the mound was inhabited by L.flavus. The effects of other species on vegetation composition,though discernible from short-term observation, disappeared over severalyears. The mounds proper did not differ from the undisturbed grassland in theproportion of myrmecochorous plants or plants with specific seed size ordormancy type. However, there was a highly significant concentration ofmyrmecochorous plants in the grassland patches immediately neighbouring themounds; this is likely to be due to seeds deposited there by the workers fromthe nest after the elaiosomes had been consumed. The mound vegetation wascomposed mainly of species with long stolons or rhizomes; however, there was nosignificant difference in formation type or length of stolons/rhizomesbetween mounds and the rest of the grassland or among mounds formed by differentant species.     

Changes of soil organic carbon,nitrogen and phosphorus concentrations under different land uses in marshes of Sanjiang Plain

Wetlands provide a large pool of organic matter and nutrients, and are important for maintaining material cycle balances in terrestrial ecosystems, and also help retard climate change. Land use changes in wetlands have greatly disturbed the natural evolution of wetland ecosystems. Wetland drainage and reclamation alters the physical, chemical and biological conditions of the wetland, thus significantly disturbing the material cycles, leading to significant changes in the biogeochemical processes of carbon, nitrogen and phosphorus in the wetland. The wetlands in the Sanjiang Plain are the largest area of fresh wetlands in China. However, the area has experienced major land uses changes since the 1950s; areas of the wetland have been drained and converted to arable land. Some studies have been conducted into the effects of land use change on material cycles in the Sanjiang Plain wetlands but few reports have discussed the C/N and C/P ratios and pH values as indicators of wetland degradation due to land use changes. We selected eight land uses: humus marsh (HM), marshy meadow (MM), drained humus marsh (DHM), drained marshy meadow (DMM), tillage land (TL), abandoned land (AL), natural secondary forest (NSF) and artificial forest (AF), in the Honghe area of the Sanjiang Plain. We studied changes in the total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), C/N and C/P ratios and pH values in topsoil (0–20 cm) of these eight different land uses. The possible mechanisms underlying the changes, and the significance of the C/N and C/P ratios as indicators of soil quality were also discussed. In the natural wetland, the TOC, TN and TP concentrations in the soil were high, with values of 203.5 g/kg, 20.2 g/kg and 1.44 g/kg, respectively, in HM; and 59.2 g/kg, 5.28 g/kg and 0.83 g/kg, respectively, in MM. Drainage of the HM has led to decreases in the TOC, TN and TP concentrations of about 50%. Significant decreases were also observed in TOC, TN and TP for NSF and AF compared to HM. Drained MM led to decreases in the TOC and TN of about 45%, but had little effect on TP. Marshy meadow that had been drained for more than 10 years experienced an exponential decline in TOC, TN and TP, with decreases of more than 60% for TOC and TN, and 20% for TP. However, after being abandoned for a short time (5 years), the TOC, TN and TP concentrations in soil experienced little change because poor water conditions combined with low productivity led to a large loss of soil organic matter. Land use change in the marsh areas has led to a decrease in C/N and C/P ratios of the soil, which are positively related to TOC and TN with different land uses (P < 0.05). Marsh reclamation has led to decreasing C/N and C/P ratios in soil and increasing pH values, which are negatively related to TOC, TN and TP (P < 0.05). Changes in carbon, nitrogen and phosphorus in soil with different land uses were mainly regulated by water-heat conditions and microbial activity, while the C/N and C/P ratios were mainly regulated by substrate availability. Our results suggest that C/N and C/P ratios and the pH value could be used as indicators to evaluate the quality and nutrient status of wetland soil under different land uses.     

Soil bacterial community structure and physicochemical properties in mitigation wetlands created in the Piedmont region of Virginia (USA)

Wetland creation is a common practice for compensatory mitigation in the United States. Vegetation attributes have been used as a quick measure of mitigation success in most post-creation monitoring, while little attention has been paid to soils that provide the substrate for flora and fauna to establish and develop. Created wetland soils are often found not indicative of ‘hydric soil’ with a lack of development of physicochemical properties (i.e., bulk density, moisture content, and carbon and nitrogen contents) comparable to those in natural wetlands. Moreover, soil bacterial communities are rarely examined though they are integrally involved in biogeochemical functions that are critical for ecosystem development in created wetlands. We analyzed soil physicochemistry and profiled soil bacterial community structure using amplicon length heterogeneity polymerase chain reaction (LH-PCR) of 16S ribosomal DNA in three relatively young wetlands (<10 years old) created in the Piedmont region of Virginia. We examined the data by site and by specific conditions of each site (i.e., induced microtopography and hydrologic regime). Multidimensional scaling (MDS) and analysis of similarity (ANOSIM) showed clear clustering and significant differences both in soil physicochemistry (Global R = 0.70, p = 0.001) and in soil bacterial community profiles (Global R = 0. 77, p = 0.001) between sites. Soil physicochemistry (Global R = 1, p = 0.005) and bacterial community structure (Global R = 0.79, p = 0.005) of soils significantly differed by hydrologic regime within a wetland, but not by microtopography treatment. A significant association was found between physicochemistry and bacterial community structure in wetland soils, revealing a close link between two attributes (ρ = 0.39, p = 0.002). C/N (carbon to nitrogen) ratio was the best predictor of soil bacterial community patterns (ρ = 0.56, p = 0.001). The diversity of soil bacterial community (Shannon's H′) differed between sites with a slightly higher diversity observed in a relatively older created wetland, and seemed also fairly determined by hydrologic regime of a site, with a relatively dry site being more diverse.     

Impact of Formica exsecta Nyl. on seed bank and vegetation patterns in a subalpine grassland ecosystem

The mound building ant Formica exsecta Nyl. is widely distributed in grassland ecosystems of the Central European Alps. We studied the impact of these ants on seed bank and vegetation patterns in a 11 ha subalpine grassland, where we counted over 700 active ant mounds. The mounds showed a distinct spatial distribution with most of them being located in tall‐grass, which was rarely visited by ungulates (red deer; Cervus elaphus L.). Heavily grazed short‐grass, in contrast, seemed to be completely avoided by ants as only few mounds were found in this vegetation type. The species composition of the ant mound and grassland seed banks was quite similar, i.e. from 15 common plant species 12 were found in both seed bank types. We found the same proportions of myrmecochorous seeds in ant mound and grassland soil samples. In contrast, the number of seeds was 15 times higher in mound compared with the grassland soil samples. Also, the vegetation growing on ant mounds significantly differed from the vegetation outside the mounds: graminoids dominated on ant mounds, herbaceous and myrmecochorous species in the grassland vegetation. We found significant continuous changes in vegetation composition on gradients from the ant mound centre to 1 m away from the mound edge. Overall, F. exsecta was found to have a considerable impact on seed bank and vegetation patterns in the grassland ecosystem studied. These insects not only altered grassland characteristics in the close surrounding of their mounds, but also seem to affect the entire ecosystem including, for example, the spatial use of the grassland by red deer.     

Social structure in the ant Lasius flavus: multi-queen nests or multi-nest mounds?

Abstract.

• 1 The yellow subterranean ant Lasius flavus is generally considered to have a single queen in mature nests. Yet, many anecdotal observations have suggested that the conspicuous earth mounds of this ant may, at least occasionally, contain several queens and their offspring.
• 2 To estimate the number of matrilines per mound, samples for horizontal starch gel electrophoresis were collected from a total of thirty-seven mounds in three sites of old chalk-grassland in southern England.
• 3 Allozymatic variation at an esterase and hexokinase locus showed that probably more than 50% of the mounds contained more than one queen and that the mean number of queens per mound is at least 1.5–2.
• 4 Further results strongly suggested that workers from different matrilines may share the same galleries, at least in the top of the mound.
• 5 The apparently variable social structure of Lasius flavus colonies is discussed, both technically and with reference to ecological processes related to the presence of ants in the nest mounds.

     

Community congruence of plants,invertebrates and birds in natural and constructed shallow open-water wetlands: Do we need to monitor multiple assemblages?

Biomonitoring is a common means of evaluating wetlands. It is based on the premise that the community composition of one taxonomic group is indicative of overall biology and the underlying environmental conditions at a wetland. To be a good bioindicator, there must be adequate concordance between the indicator group and other biotic assemblages. Otherwise, multi-assemblage monitoring is necessary to glean a complete picture of wetland condition. In 32 sites ranging from reference wetlands to stormwater retention ponds, we evaluated concordance in community composition among the six most commonly monitored wetland assemblages: waterfowl, wetland dependent songbirds, aquatic macroinvertebrates, and plants in the wet meadow, emergent, and open-water vegetation zones. We also assessed agreement in environmental correlates among these six assemblages and investigated the impact of human disturbance on cross-assemblage concordance. We found that cross-assemblage concordance was positive (p < 0.03 in 14 of 15 pair-wise comparisons, p = 0.06 in 15th case), but relatively low (Mantel R values 0.11–0.37), suggesting that the assemblages are mediocre surrogates for one another. Yet, we found very strong agreement among environmental correlates of the six assemblages, especially along the first axis of assemblage-specific ordinations (mean Spearman rho = 0.923), indicating that despite low concordance, the six assemblages are likely responding to the same environmental gradients. Thus, while a single assemblage may not serve as a surrogate for the other assemblages, it should yield an adequate estimate of underlying environmental conditions and the degree of disturbance. Most important among the environmental correlates were sediment and water nutrient levels, shoreline slope, and the size of wet meadow and emergent vegetation zones. Perhaps most interestingly, we found that the strength of cross-assemblage concordance was greatest in reference wetlands and was lower (p ≤ 0.05) in constructed wetlands. This implies that cross-assemblage concordance present in undisturbed sites may not persist in disturbed wetlands where several of these cross-assemblage relationships deteriorate. Furthermore, a general change in cross-assemblage concordance may itself be indicative of human disturbance in wetlands.     

Soil quality assessment of coastal wetlands in the Yellow River Delta of China based on the minimum data set

Little information is available to assess the dynamic changes in wetland soil quality in coastal regions, though it is essential for wetland conservation and management. Soil samples were collected in Suaeda salsa wetlands (SWs), Tamarix chinensis wetlands (TWs), Suaeda salsa–Tamarix chinensis wetlands (STWs), freshwater Phragmites australis wetlands (FPWs) and saltwater Phragmites australis wetlands (SPWs) in three sampling periods (i.e., summer and autumn of 2007 and spring of 2008). According to the flooding characteristics of these wetlands, the study area could be grouped into three sub-regions: short-term flooding region (STFR), seasonal flooding region (SFR) and tidal flooding region (TFR). Soil quality was evaluated using the soil quality index (SQI), which was calculated using the selected minimum data set (MDS) based on principal components analysis (PCA). Our results showed that soil salt content (SSC), total carbon (TC), magnesium (Mg), nitrate nitrogen (NO₃⁻-N) and total sulfur (TS) consisted of a MDS among 13 soil properties. The SQI values varied from 0.18 to 0.66 for all soil samples, of which the highest and lowest SQI values were observed in TFR. The average SQI values were significantly higher in summer (0.50 ± 0.13) than in spring (0.37 ± 0.13) and autumn (0.36 ± 0.11) in the whole study area (p < 0.05). The average SQI values followed the order STFR (0.44 ± 0.12) > TFR (0.41 ± 0.15) > SFR (0.35 ± 0.09) although no significant differences were observed among the three regions (p > 0.05). SPWs and SWs soils showed higher SQI values (0.50 ± 0.10 and 0.47 ± 0.15, respectively) than TWs (0.30 ± 0.08) soils (p < 0.05). The SSC was the dominant factor of soil quality with its proportion of 34.1% contributing to the SQI values, followed by TC (24.5%) and Mg (24.1%). Correlation analysis also showed that SQI values were significantly negatively correlated with SSC. SSC might be a characteristic indicator of wetland soil quality assessment in coastal regions. The findings of this study showed that the SQI based on MDS is a powerful tool for wetland soil quality assessment.     

沙丘微地形生境蚁丘分布特征及其对恢复过程的响应

为了阐明沙丘微地形生境蚁丘特征及分布规律对沙丘固定过程的响应规律,以科尔沁沙地为研究区,选择不同固沙阶段沙丘的4个方位（西北、东南、西南、东北）布设调查样地,测定了不同样地的蚁丘密度、直径和高度,分析了不同样地蚁丘特征及空间分布规律。结果表明：（1）流动沙丘背风向（即东南方位）蚁丘密度显著高于其他方位,但从流动沙丘到半流动沙丘,背风向（即东南方位）蚁丘密度显著低于其他方位;从半固定沙丘开始,半固定和固定沙丘微地形对蚁丘密度分布的影响较小。（2）在流动沙丘、半流动沙丘、半固定沙丘,不同微地形生境中蚁丘直径和高度均呈现出相似的分布规律,即东南方位均小于其他方位。在固定沙丘,蚁丘高度表现为东南方位亦较低,但蚁丘直径表现为西南和东北方位显著小于西北方位。（3）在流动沙丘,西北、西南和东南方位上蚁丘空间分布均表现为均匀分布型,而在半流动、半固定和固定沙丘,4个方位上蚁丘空间分布均表现为聚集分布型。（4）相关性分析表明,不同固沙阶段不同微生境下蚁丘密度、高度、直径与植物密度、多样性间的相关性不同。随着固沙阶段演替,不同微生境下蚁丘特征与植物密度、多样性的相关性增强。研究表明,在科尔沁沙地,随着流动沙丘固定和生境逐渐恢复,沙丘不同空间方位上蚁丘密度分布差异缩小,而蚁丘直径和高度仍存在沙丘微地形间显著差异性,并且蚁丘空间方位上均呈现聚集分布状态。     

Distribution of ant species and mounds (Formica) in different-aged managed spruce stands in eastern Finland

Mound‐building ants (Formica spp.), as key species, have large impacts on organisms and ecosystem functions in boreal Eurasian forests. The density, sizes and locations of ant mounds determine the magnitude and the spatial distribution of ant activities in forest ecosystems. Clear‐cutting can destroy wood ant colonies, and the species, abundance, dimensions and locations of ant mounds may change as forest stand structure changes with stand age. We compared ant species composition, ant mound numbers and dimensions, and the spatial distribution of mounds in Norway spruce [Picea abies (L.) Karst.] stands of different age (5, 30, 60 and 100 years) in eastern Finland. The mound density of Formica aquilonia Yarr. was greater in the two oldest stand age classes, while most mounds of Formica rufa L., Formica polyctena Först., Formica lugubris Zett., Formica exsecta Nyl. and Formica pressilabris Nyl. were found in the two youngest age classes. The mean volume, the volume per area and height/diameter ratio of F. aquilonia mounds increased with stand age. In the oldest stand age class, mounds were slightly smaller in well‐lit locations than in shade and near stand edges than further from the edges indicating that new mounds are established in well‐lit locations. Similarly, the longest slopes of the mounds faced south, indicating the importance of exposure to the sun. F. aquilonia mounds were concentrated near stand edges, and the spatial distribution of the mounds was aggregated in some stands. At the ecosystem level, the aggregation of ant mounds near stand edges may increase the edge productivity, as mounds concentrate resources to the edges and release nutrients after abandonment.     

Selection of incubation mound sites by the Australian Brush-turkey Alectura lathami

Environmental characteristics associated with siting of the incubation mounds of the megapode, the Australian Brush-turkey Alectura lathami were investigated in three rainforest locations in southeast Queensland. Seventeen environmental variables were measured for 52 mounds and 137 non-mound sites. Most mounds were constructed on top of old mounds which had not been used during the previous year. A Discriminant Function Analysis obtained a clear separation between mound and non-mound sites, based primarily on three variables: (1) the number of saplings growing within the mound or centre of the site: this was considered to be a result of the germination of seeds raked in earlier years; (2) the proportion of Lantana camara thicket occupying the site. Approximately half of the mounds constructed during a season were abandoned by their constructor due to expulsion by a neighbouring male. Brush-turkeys could more easily establish mounds next to thickets since the efficiency of defence by other males was reduced in these areas; and (3) the openness of the canopy. Areas with greater canopy cover provided two important mound resources: a good supply of leaf litter, and protection of the mound from dessication.     

Soil phosphorus flux from emergent marsh wetlands and surrounding grazed pasture uplands

Phosphorus (P) release from wetland soils to overlying waters is important to consider when restoring wetland hydrology. Soil physicochemical characteristics influence P dynamics between underlying soil and overlying water. Our study initially characterized wetland and surrounding upland soils prior to flooding. Deep marsh wetland soils had greater moisture content, soil organic matter, nitrogen (N), P, and lower bulk density than surrounding upland pasture soils, which indicates a nutrient concentration gradient between wetland and upland soils. To determine the short-term P dynamics between soils and overlying water, we conducted four laboratory soil water core studies during a 15-month period. Surface soils (0-10 cm) collected October 2005, February 2006, October 2006 and December 2006 from wetlands and their surrounding uplands within cow-calf grazed pastures were flooded for 7 days, and we measured P release from soil to overlying water. Phosphorus release rates from wetland (deep marsh and shallow marsh) and upland soils were similar. Values ranged between ?20 mg m^?2 d^?1 (retention) and 77 mg m^?2 d^?1 (release). There was a significant, although weak, negative linear relationship between P release from deep marsh soils and hydroperiod. Thus, it may be important for land managers to consider increasing hydroperiod of wetland soils to decrease P release and increase retention. In addition, there was a significant negative exponential relationship between P release and days since deep marsh soil inundation. This suggests that to decrease P release from soils, soils should be wet rather than dry for prolonged periods, prior to flooding. We found significant relationships between P release from upland soils and their nutrient content (N, P and carbon). Reducing nutrient content in upland soils may help reduce the magnitude of P release from soil.     

Comparative study of ecological indices for assessing human-induced disturbance in coastal wetlands of the Laurentian Great Lakes

Several ecological indices have been developed to evaluate the wetland quality in the Laurentian Great Lakes. One index, the water quality index (WQI) can be widely applied to wetlands and produces accurate measurements of wetland condition. The WQI measures the degree of water quality degradation as a result of nutrient enrichment and road runoff. The wetland fish index (WFI), wetland zooplankton index (WZI), and the wetland macrophyte index (WMI), are all derived from the statistical relationships of biotic communities along a gradient of deteriorating water quality. Compared to the WQI, these indices are less labor-intensive, cost less, and have the potential to produce immediate results. We tested the relative sensitivity of each biotic index for 32 Great Lakes wetlands relative to the WQI and to each other. The WMI (r² = 0.84) and WFI (r² = 0.75) had significant positive relationships (P < 0.0001) with the WQI in a linear and polynomial fashion. Slopes of the WMI and WFI were similar when comparing the polynomial regressions (ANCOVA; P = 0.117) but intercepts were significantly different (P = 0.004). The WZI had a positive relationship with the WQI in degraded wetlands and a negative relationship in minimally impacted wetlands. The strengths and weaknesses of each index can be explained by the interactions among fish, zooplankton, aquatic plants and water chemistry. The distribution of different species indicative of low and high quality in each index provides insight into the relative wetland community composition in different parts of the Great Lakes and helps to explain the differences in index scores when different organisms are used. Our findings suggest that the WMI and WFI produce comparable results but the WZI should not be used in the minimally impacted wetlands without further study.     

PTP1B inhibitors from the seeds of Iris sanguinea and their insulin mimetic activities via AMPK and ACC phosphorylation

To find PTP1B inhibitors from natural products, two new compounds (1 and 2), along with nine known compounds (3–11), were isolated from a methanol-soluble extract of Iris sanguinea seeds. The structures of compounds 1 and 2 were determined based on extensive spectroscopic data analysis including UV, IR, NMR, and MS. The IC₅₀ value of compound 5 on protein tyrosine phosphatase 1B (PTP1B) inhibitory activity is 7.30 ± 0.88 µM with a little activity compared to the IC₅₀ values of the tested positive compound. Compound 5 significantly enhanced glucose uptake and activation of pACC, pAMPK and partially Erk1/2 signaling. These results suggest that compound 5 from Iris sanguinea seeds are utilized as both PTP1B inhibitors and regulators of glucose uptake. These beneficial effects could be applied to treat metabolic diseases such as diabetes and obesity.     

Ants accelerate succession from mountain grassland towards spruce forest

Question: What is the role of mound‐building ants (Lasius flavus) in successional changes of a grassland ecosystem towards a spruce forest? Location: Slovenské Rudohorie Mountains, Slovakia; ca. 950 m a.s.l. near the Obrubovanec point (1020 m a.s.l.; 48°41′N, 19°39′E). Methods: Both chronosequence data along a successional gradient and temporal data from long‐term permanent plots were collected on ants, spruce establishment, and vegetation structure, together with additional data on spruce growth. Results: There are more spruce seedlings on ant mounds (4.72 m^?2) than in the surrounding vegetation (0.81 m^?2). Spruce seedlings grow faster on these mounds compared to surrounding areas. The first colonization wave of seedlings was rapid and probably occurred when grazing prevailed over mowing. Ant colony presence, mound volume, and plant species composition change along the successional gradient. Mounds become bigger when partly shaded but shrink in closed forest, when ant colonies disappear. Shade‐tolerant acidophylic species replace grassland plants both on the mounds and in surrounding areas. Conclusions: The massive occurrence of Lasius flavus anthills contributes to a runaway feedback process that accelerates succession towards forest. The effect of ants as ecosystem engineers is scale‐dependent: although they stabilize the system at the scale of an individual mound, they may destabilize the whole grassland system over a longer time scale if combined with changes in mowing regime.     

Characterization of N<Subscript>2</Subscript>O emissions and associated microbial communities from the ant mounds in soils of a humid tropical rainforest

Tropical rainforest soils harbor a considerable diversity of soil fauna that contributes to emissions of N₂O. Despite their ecological dominance, there is limited information available about the contribution of epigeal ant mounds to N₂O emissions in these tropical soils. This study aimed to determine whether ant mounds contribute to local soil N emissions in the tropical humid rainforest. N₂O emission was determined in vitro from individual live ants, ant-processed mound soils, and surrounding reference soils for two trophically distinct and abundant ant species: the leaf-cutting Atta mexicana and omnivorous Solenopsis geminata. The abundance of total bacteria, nitrifiers (AOA and AOB), and denitrifiers (nirK, nirS, and nosZ) was estimated in these soils using quantitative PCR, and their respective mineral N contents determined. There was negligible N₂O emission detected from live ant individuals. However, the mound soils of both species emitted significantly greater (3-fold) amount of N₂O than their respective surrounding reference soils. This emission increased significantly up to 6-fold in the presence of acetylene, indicating that, in addition to N₂O, dinitrogen (N₂) is also produced from these mound soils at an equivalent rate (N₂O/N₂?=?0.57). Functional gene abundance (nitrifiers and denitrifiers) and mineral N pools (ammonium and nitrate) were significantly greater in mound soils than in their respective reference soils. Furthermore, in the light of the measured parameters and their correlation trends, nitrification and denitrification appeared to represent the major N₂O-producing microbial processes in ant mound soils. The ant mounds were estimated to contribute from 0.1 to 3.7% of the total N₂O emissions of tropical rainforest soils.     

Effect of natural maize phytochemicals on Aspergillus section Flavi sclerotia characteristics under different conditions of growth media and water potential

The effects of the natural phytochemicals trans-cinnamic acid (CA) and ferulic acid (FA) at concentrations of 1–20 mM (CA) and 1–25 mM (FA) on sclerotial production by Aspergillus flavus and Aspergillus parasiticus were evaluated. Studies on sclerotium number and size were carried out in different growth media and water potentials (MPa). High concentrations of CA (20 mM, ?0.75 MPa; 10 mM, ?3.5 MPa) and FA (10, 20, 25 mM, ?0.75 and ?3.5 MPa) significantly reduced sclerotial production of Aspergillus strains. Overall, CA at concentrations of 10 and 20 mM on Czapek Dox medium (CD), maize meal extract agar (MMEA) and maize meal extract agar with sucrose and NaNO₃ (MMEA S/N) inhibited sclerotium most in the four species assayed. The data show that the sclerotia characteristics of A. flavus and A. parasiticus were influenced by natural phytochemicals and modifications of growth media and water potential. CA and FA could be used at high concentrations to prevent the survival of Aspergillus species in grain.     

若尔盖湿地退化过程中土壤水源涵养功能

若尔盖湿地是青藏高原上面积最大的沼泽湿地,也是长江、黄河两大河流的水源区,对区域水循环起重要调节作用。近年来在全球变化及放牧的影响下,若尔盖湿地出现了不同程度的退化。为了查明若尔盖湿地退化过程中水源涵养功能的变化趋势,2009年8月对该区域的沼泽草甸、草原草甸和沙化草甸3个阶段的土壤水源涵养功能进行了调查。结果为:若尔盖湿地由沼泽草甸向草原草甸和沙化草甸的退化过程中,土壤容重显著增加(P<0.01),毛管孔隙度和总孔隙度显著下降(P<0.01),且容重和孔隙度在土壤剖面自然分布规律也发生变化;沼泽草甸的土壤自然含水量、毛管持水量、最小持水量和最大持水量均显著高于草原草甸和沙化草甸(P<0.01);0-100 cm 深度范围内的沼泽草甸土壤的最大持水量(8486.27 t/hm²)显著高于草原草甸(4944.98 t/hm²)和沙化草甸(4637.96 t/hm²)(P<0.01)。土壤持水量与有机质含量、毛管孔隙度和总孔隙度有显著正相关(P<0.01),与土壤容重呈显著负相关(P<0.01),并受植被盖度和泥炭层厚度的影响。研究结果表明,若尔盖湿地退化过程中植被盖度、土壤有机质含量及泥炭层厚度的下降和土壤质地沙化是导致若尔盖湿地水源涵养功能下降的主要原因。     

Two-decade wetland cultivation and its effects on soil properties in salt marshes in the Yellow River Delta,China

Wetland cultivation and its effects on soil properties in salt marshes in the Yellow River Delta, China were examined by using a combination of the satellite imageries and field experiments. Results showed that the conversions mainly occurred between dry lands and Phragmites australis–Suaeda salsa–Tamarix chinensis marshes (PSTMs). The total area of marsh wetland was reduced by 65.09 km² during the period from 1986 to 2005, and these conversions might be attributed to a combination of farming, oil exploration and water extraction, as well as soil salinization. Significant differences were observed in bulk density, pH, salinity and NO₃⁻-N between different land-use types (P < 0.05). After the conversions from marsh wetlands to dry lands, bulk density, pH, salinity and NH₄⁺-N decreased slightly, while a significant increase in NO₃⁻-N, TN (total nitrogen), and AP (available phosphorus) (P < 0.05) was observed. The more loss of soil nutrient storage also occurred after the maximal area conversion from PSTMs to dry lands compared to other conversions during the study period. The storages of soil organic matter, NH₄⁺-N and total phosphorus decreased greatly under the conversion from three types of marshes to dry lands, while those of NO₃⁻-N, AP and TN showed an obvious increase during the whole study period.