Effects of bannertail kangaroo rat mounds on small-scale plant community structure

The effects of bannertail kangaroo rat (Dipodomys spectabilis) mounds and associated soil-surface disturbance on plant species composition and diversity in the Chihuahuan Desert were examined with multivariate analysis. Kangaroo rat mounds created disturbance gaps and contributed to local species diversity by creating microhabitats that supported unique plant communities. These microhabitats supported populations of species that were relatively rare in surrounding areas. The diversity observed at the whole habitat level resulted from (1) local spatial heterogeneity, because the mounds offered microenvironments with distinctive nutrient, water, and light conditions; and (2) local patterning of disturbance, because the digging and traffic of the kangaroo rats maintained high levels of soil disturbance at and near the mounds. At a finer scale, species diversity was highest in the area immediately adjacent to active and inactive mounds, and was lower on both the highly disturbed soil of the mounds and in the relatively undisturbed area between mounds. Lowest species diversity occurred on inactive mounds. Annual plant biomass was much greater on mounds than in inter-mound areas. The results support the predictions that intermediate levels of disturbance and small-scale environmental heterogeneity contribute to supporting high species diversity.     

Nutrient dynamics and plant assemblages of Macrotermes falciger mounds in a savanna ecosystem

Termites through mound construction and foraging activities contribute significantly to carbon and nutrient fluxes in nutrient-poor savannas. Despite this recognition, studies on the influence of termite mounds on carbon and nitrogen dynamics in sub-tropical savannas are limited. In this regard, we examined soil nutrient concentrations, organic carbon and nitrogen mineralization in incubation experiments in mounds of Macrotermes falciger and surrounding soils of sub-tropical savanna, northeast Zimbabwe. We also addressed whether termite mounds altered the plant community and if effects were similar across functional groups i.e. grasses, forbs or woody plants. Mound soils had significantly higher silt and clay content, pH and concentrations of calcium (Ca), magnesium (Mg), potassium (K), organic carbon (C), ammonium (NH₄⁺) and nitrate (NO₃⁻) than surrounding soils, with marginal differences in phosphorus (P) and sodium (Na) between mounds and matrix soils. Nutrient enrichment increased by a factor ranging from 1.5 for C, 4.9 for Mg up to 10.3 for Ca. Although C mineralization, nitrification and nitrification fraction were similar between mounds and matrix soils, nitrogen mineralization was elevated on mounds relative to surrounding matrix soils. As a result, termite mounds supported unique plant communities rich and abundant in woody species but less diverse in grasses and forbs than the surrounding savanna matrix in response to mound-induced shifts in soil parameters specifically increased clay content, drainage and water availability, nutrient status and base cation (mainly Ca, Mg and Na) concentration. In conclusion, by altering soil properties such as texture, moisture content and nutrient status, termite mounds can alter the structure and composition of sub-tropical savanna plant communities, and these results are consistent with findings in other savanna systems suggesting that increase in soil clay content, nutrient status and associated changes in the plant community assemblage may be a general property of mound building termites.     

Accumulation and soil-to-plant transfer of radionuclides in the Nile Delta coastal black sand habitats

The radionuclide content was estimated in the soil of three black sand habitats in the Mediterranean coast of Egypt, namely, sand mounds and coastal sand planes and dunes. In addition, a total of 14 heavy minerals found in the soils were characterized. The soil to plant transfer of uranium and thorium was tested on three black sand species, namely, Cakile maritima Scop., Senecio glaucus L. and Rumex Pictus Forssk. The transfer of thorium and uranium radionuclides from the soil to plant is complex process that is subjected to many variables; among which are the organic matter and clay content of the soil, the type of radionuclides and plant species. The study revealed a strong negative relationship between uranium and thorium uptake by S. glaucus and R. pictus and the clay and organic matter content of soil. Concentration of thorium in the soil has a negative correlation with soil-to-plant transfer factor. The study results suggest the possibility of using black sand species for phytoremediation of soils contaminated with radioactive elements. The potentiality of S. glaucus as phytoremediator of radionuclides polluted soils is greater than R. pictus which in turn outweigh C. maritima.     

Adaptation of Pelage Color and Pigment Variations in Israeli Subterranean Blind Mole Rats,Spalax Ehrenbergi

Background

Concealing coloration in rodents is well established. However, only a few studies examined how soil color, pelage color, hair-melanin content, and genetics (i.e., the causal chain) synergize to configure it. This study investigates the causal chain of dorsal coloration in Israeli subterranean blind mole rats, Spalax ehrenbergi.

Methods

We examined pelage coloration of 128 adult animals from 11 populations belonging to four species of Spalax ehrenbergi superspecies (Spalax galili, Spalax golani, Spalax carmeli, and Spalax judaei) and the corresponding coloration of soil samples from the collection sites using a digital colorimeter. Additionally, we quantified hair-melanin contents of 67 animals using HPLC and sequenced the MC1R gene in 68 individuals from all four mole rat species.

Results

Due to high variability of soil colors, the correlation between soil and pelage color coordinates was weak and significant only between soil hue and pelage lightness. Multiple stepwise forward regression revealed that soil lightness was significantly associated with all pelage color variables. Pelage color lightness among the four species increased with the higher southward aridity in accordance to Gloger''s rule (darker in humid habitats and lighter in arid habitats). Darker and lighter pelage colors are associated with darker basalt and terra rossa, and lighter rendzina soils, respectively. Despite soil lightness varying significantly, pelage lightness and eumelanin converged among populations living in similar soil types. Partial sequencing of the MC1R gene identified three allelic variants, two of which were predominant in northern species (S. galili and S. golani), and the third was exclusive to southern species (S. carmeli and S. judaei), which might have caused the differences found in pheomelanin/eumelanin ratio.

Conclusion/Significance

Darker dorsal pelage in darker basalt and terra rossa soils in the north and lighter pelage in rendzina and loess soils in the south reflect the combined results of crypsis and thermoregulatory function following Gloger''s rule.     

The role of ant nest-mounds in maintaining small-scale patchiness in dry grasslands in Central Germany

Nest-mounds of Lasius flavus, Lasius alienus and Formica rufibarbis are mainly on north-facing slopes with a markedly patchy distribution at Gimritz, northwest of Halle (Saale). Nest-mound soils had higher sodium and potassium levels but lower phosphorus and nitrogen levels than soils away from mounds. Moisture content was lower but soil pH was significantly higher in nest-mound soils. However, there was no difference in the relative abundance of plants of alkaline or acid soils growing on mounds compared to plants off mounds and no significant difference between the numbers of nitrophilous plants on and off mounds. Fewer plant species (35 spp.) in total occurred on mounds than off mounds (42 spp.). Plant species richness and total plant cover was significantly less on the nest-mounds than off the mounds. Similarly, the mean number of grass (1.39 spp dm−2) and forb species (1.13 spp dm−2) on mounds was lower than the mean number of grass (1.99 spp dm−2) and forb species (1.91 spp dm−2) off mounds. Some shrubs and forbs had higher occurrence and cover on the mounds, although only in Calluna vulgaris, Thymus serpyllum and Cerastium arvense was this difference particularly marked. Ant nest-mounds may favour plant species that cannot compete with tall grasses on unmanaged, set-aside meadows. This revised version was published online in November 2006 with corrections to the Cover Date.     

Soil microorganisms as controllers of atmospheric trace gases (H2, CO, CH4, OCS, N2O, and NO).

Production and consumption processes in soils contribute to the global cycles of many trace gases (CH4, CO, OCS, H2, N2O, and NO) that are relevant for atmospheric chemistry and climate. Soil microbial processes contribute substantially to the budgets of atmospheric trace gases. The flux of trace gases between soil and atmosphere is usually the result of simultaneously operating production and consumption processes in soil: The relevant processes are not yet proven with absolute certainty, but the following are likely for trace gas consumption: H2 oxidation by abiontic soil enzymes; CO cooxidation by the ammonium monooxygenase of nitrifying bacteria; CH4 oxidation by unknown methanotrophic bacteria that utilize CH4 for growth; OCS hydrolysis by bacteria containing carbonic anhydrase; N2O reduction to N2 by denitrifying bacteria; NO consumption by either reduction to N2O in denitrifiers or oxidation to nitrate in heterotrophic bacteria. Wetland soils, in contrast to upland soils are generally anoxic and thus support the production of trace gases (H2, CO, CH4, N2O, and NO) by anaerobic bacteria such as fermenters, methanogens, acetogens, sulfate reducers, and denitrifiers. Methane is the dominant gaseous product of anaerobic degradation of organic matter and is released into the atmosphere, whereas the other trace gases are only intermediates, which are mostly cycled within the anoxic habitat. A significant percentage of the produced methane is oxidized by methanotrophic bacteria at anoxic-oxic interfaces such as the soil surface and the root surface of aquatic plants that serve as conduits for O2 transport into and CH4 transport out of the wetland soils. The dominant production processes in upland soils are different from those in wetland soils and include H2 production by biological N2 fixation, CO production by chemical decomposition of soil organic matter, and NO and N2O production by nitrification and denitrification. The processes responsible for CH4 production in upland soils are completely unclear, as are the OCS production processes in general. A problem for future research is the attribution of trace gas metabolic processes not only to functional groups of microorganisms but also to particular taxa. Thus, it is completely unclear how important microbial diversity is for the control of trace gas flux at the ecosystem level. However, different microbial communities may be part of the reason for differences in trace gas metabolism, e.g., effects of nitrogen fertilizers on CH4 uptake by soil; decrease of CH4 production with decreasing temperature; or different rates and modes of NO and N2O production in different soils and under different conditions.     

Geophagic termite mounds as one of the resources for African elephants in Ugalla Game Reserve,Western Tanzania

Knowledge of the distribution and nutrient values of key resources supporting the survival of wildlife species is integral for an effective conservation planning and management of the species. In the Miombo ecosystem of the Ugalla Game Reserve, African elephants (Loxodonta africana Blumenbach 1797), eat soil, that is geophagy, from certain termite mounds. We mapped that all the geophagic termite mounds are exclusively situated in the flood plain. To understand why soils from some termite mounds are eaten, we collected and analysed soil samples from 10 geophagic termite mounds, seven nongeophagic termite mounds and 13 samples from the surrounding flood plain. Percentage of clay content did not differ significantly among the soil samples. Soils from geophagic termite mounds were richer in mineral elements compared with other soil samples. The results demonstrate that the driver for geophagic behaviour is related to rich mineral element contents found in geophagic termite mounds made of the mineral‐enriching termites (Macrotermes). Thus, geophagic termite mounds play a role in elephant's dietary needs and possibly influence their movement patterns in Ugalla, as the elephants cannot obtain enough minerals from their feeds. Geophagic termite mounds should be protected from potential destructive land uses, such as airstrip construction.     

Disturbance by the mound-building termite,shape Trinervitermes trinervoides,and vegetation patch dynamics in a semi-arid,southern African grassland

Changes in the composition and abundance of grasses and shrubs, soil fertility, and the productivity and nutrition of the grass, Themeda triandra, were examined along an age gradient of Trinervitermes trinervoides mounds occurring in a semi-arid grassland of the Free State, South Africa. The composition and abundance of grasses and shrubs change alongside mounds as they become inactive and then erode away. The pioneer grass, Tragus koelerioides, and the climax grass, Themeda triandra, dominate around active mounds. As the mounds become inactive and erode away, these two grass species are replaced by the subclimax grass, Eragrostis lehmanniana, along with an increase in the cover of the unpalatable shrub, Walafrida saxatilis. Mound soils, in contrast, are sparsely vegetated and only change in composition, and the population abundance of T. triandra, on old active mounds compared to earlier or older mound age states. Soils on eroded mounds are more acidic, and contain higher concentrations of Mg, Ca, N, P, and total exchangeable cations (T.E.C.) than soils occurring 0.5 m from the margins of eroded, inactive and active mounds. A plant bioassay, using Lolium perenne, confirms the higher soil fertility on eroded mounds but also shows significant increases in soil fertility alongside inactive and eroded mounds. Pot experiments show an increase in the production of T. triandra plants grown on soils from eroded mounds, and those occurring alongside inactive and eroded mounds. Foliar protein and nitrogen increase when these plants are grown on soils from eroded mounds. Mounds of T. trinervoides are foci of biotic disturbance because they alter soil resources, and the population abundance and composition of grasses and shrubs in the first metre around their margins. Increases in soil fertility alongside inactive and eroded mounds, and the accompanying increase in the productivity of T. triandra, along with signs of its foliar nutrient enrichment, suggest the removal of this species through preferential grazing by animals as the mounds become inactive and erode away.Plant nomenclature: follows Gibbs Russell, G. E., Reid, C., Van Rooyen, J. & Smook, L. 1985. List of species of southern African plants. Mem. Bot. Surv. S. Afr. 51: 1-152, and Gibbs Russell, G. E., Welman, W. G., Retief, E., Immelman, K. L., Germishuizen, G., Pienaar, B. J., Van Wyk, M. & Nicholas, A. 1987. List of species of southern African plants. Mem. Bot. Surv. S. Afr. 56: 1–270.     

Heavy metal tolerance and accumulation in metallicolous and non-metallicolous populations of Thlaspi caerulescens from continental Europe

In continental Europe, the heavy metal hyperaccumulator Thlaspi caerulescens occurs both on heavy-metal polluted soils (subsp. calaminare) and on soils with normal heavy metal content (subsp. caerulescens). In order to assess the extent and partitioning of variation in heavy metal tolerance and foliar mineral composition, twelve families from two populations of each subspecies were grown in pots in four soil treatments differing in heavy metal (Zn, Pb) and macronutrient concentrations. The two subspecies differed systematically in many respects. Subsp. calaminare had a higher survival at high levels of heavy metals and a higher tolerance index in all treatments. It also had three times lower foliar zinc and lead concentrations when grown at moderate levels of heavy metals. This, together with a negative correlation of foliar Pb concentration with growth in subsp. caerulescens, suggests that heavy metal accumulation per se is not a mechanism of tolerance in this species. Variation among families within populations accounted for a larger proportion of total variance in growth and mineral composition than variation between populations. Additionally, within population variation in heavy metal tolerance and accumulation was significantly lower in subsp. calaminare. This suggests that, adding to a background constitutive tolerance at the species level, natural selection has increased heavy metal tolerance in metallicolous populations of Thlaspi caerulescens.     

Developmental stability and adaptive radiation in the Spalax ehrenbergi superspecies in the Near-East

Chromosomal species of the mole rat, Spalax ehrenbergi, in Israel have been shown to display distinct adaptive strategies to increasing aridity. This adaptive radiation appeared to be associated with an increase in allozymic heterozygosity. In the present study, the developmental stability (DS) estimated by fluctuating asymmetry (FA) of dental traits was used to assess the suitability of habitat and the efficiency of adaptation to local environmental conditions among populations and chromosomal species. Although FA levels were highly heterogeneous among populations, they were not found to differ between species. DS of populations appeared, however, to be impaired at higher altitudes and in indurate soils. Since these environmental features were largely covariant, the effect of each one could not be precisely determined. Interestingly, while aridity is considered as the major selective force acting on populations southwards, DS was not altered under arid conditions, suggesting that mole rat populations were adapted to their local conditions of aridity. However, the cline of aridity is matched to several environmental and genetic clines among which are the increasing heterozygosity and recombination rate among species southwards. In studies of natural populations, the potential complementary effects of environmental and genetics on DS have to be considered and hamper the interpretation of habitat suitability expressed by DS in terms of adaptive strategies.     

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.     

Is the population turnover of patchy‐distributed annuals determined by dormancy dynamics or dispersal processes?

In species with fragmented distribution, regional turnover dynamics is given by the processes of local population extinction and patch (re)colonization by migrants spreading from neighboring occupied patches. In plants with dormant stages (e.g. seeds) and limited dispersal capacity, regional dynamics based on dispersal processes can be overridden by pseudo-turnover determined by signals inducing or breaking dormancy (e.g. due to changes in habitat quality) resulting in a low importance of habitat configuration and size.
In this study, I investigated the turnover dynamics of 5 annual plant species growing on ant mounds of Lasius flavus over three years. I analyzed whether the grassland-scale dynamics of these annuals is influenced by dispersal processes, or alternatively, by pseudo-turnover of soil seed populations. For that purpose I 1) searched for populations formed from soil seeds only, 2) compared the relative contribution of the soil seed bank and seed rain for population restoration after disappearance from the vegetation and 3) investigated whether colonization and extinction events are affected by patch isolation. I assumed if population turnover was rather a result of the soil seed bank dynamics then spatial effects would be hard to detect.
In spite of the presence of populations formed from soil seed and the relatively more important soil seed bank for potential population reestablishment, turnover dynamics followed the predictions of metapopulation theory. Population appearance was more probable in larger and less isolated patches. Probability of disappearance increased with decrease of population size that was negatively influenced by the patch size and its isolation. These findings indicate dispersal processes to be important in the turnover dynamics and only limited contribution of soil seed populations. Their small effectiveness is probably related to the low chance of recurrent disturbance on the mound surface.     

多年冻土退化地区湿地土壤温室气体排放及其影响因子

采用野外原位实验静态箱-气相色谱法,研究了兴安岭多年冻土不同程度退化地区生长季湿地土壤温室气体CH₄、CO₂和N₂O的排放通量特征,同时分析了环境因子对土壤温室气体排放的影响。结果表明:1) 3种类型冻土区(季节性冻土区、岛状多年冻土区、连续多年冻土区,分别用D1、D2、D3表示)土壤在生长季时期表现为CO₂和N₂O的源; D1和D3为CH₄的源,D2为CH₄的汇。D1、D2、D3土壤在生长季中平均CH₄排放通量分别为(0.127±0.021)、(-0.020±0. 006)、(0. 082±0. 019) mg·m^-2·h^-1; CO₂排放通量分别为(371.50±66.73)、(318.43±55.67)、(213.19±37.05) mg·m^-2·h^-1; N₂O排放通量分别为...     

Comparison of ectomycorrhizas of Quercus garryana (Fagaceae) on serpentine and non-serpentine soils in southwestern Oregon

The diversity of ectomycorrhizal communities associated with Quercus garryana on and off serpentine soils was compared and related to landscape-level diversity. Serpentine soils are high in magnesium, iron, and heavy metals and low in fertility. In plant communities on serpentine soils, a high proportion of flowering plant species are endemic. At three sites with paired serpentine and nonserpentine soils in southwestern Oregon, we sampled Q. garryana roots and categorized ectomycorrhizas by morphotyping and by restriction fragment length patterns. Ectomycorrhizas were abundant at all sites; no single fungal species dominated in the ectomycorrhizas. Of 74 fungal species characterized by morphotype and pattern of restriction fragment length polymorphisms, 46 occurred on serpentine soils, and 32 were unique to serpentine soil. These species are potentially endemic to serpentine soil. Similarities in species composition between paired serpentine and nonserpentine soils were not significantly lower than among three serpentine sites or among three nonserpentine sites. We conclude that mycorrhizal communities associated with oaks on serpentine soil do not differ in species richness or species evenness from those on neighboring nonserpentine soil.     

祁连山东段高原鼢鼠(Eospalax baileyi)土丘空间分布格局及其与环境因子的空间关联性

高原鼢鼠推土造丘行为对高寒草地生态系统的生产和生态功能有重要影响,研究高原鼢鼠土丘空间分布格局及其与环境因子的关系,可以揭示高原鼢鼠栖息地利用和选择规律,为合理控制鼠害及保护草地生物多样性提供科学依据。于2014年8月在祁连山东段选取面积为140m×100m的高原鼢鼠栖息地,消除景观尺度取样带来的气候、地形和土壤的异质性,利用地统计学方法,分析高原鼢鼠土丘的空间分布格局、并揭示其与环境因子中土壤容重、土壤水分、植物地上、地下生物量、根系营养物质含量(可溶性糖、粗蛋白、粗脂肪)以及各功能群丰富度(禾本科、莎草科、杂类草)的空间关系。半方差函数及普通克里格插值表明,高原鼢鼠土丘存在中等程度的空间变异且呈现聚集分布,各环境因子均存在不同程度的空间异质性。交方差函数分析表明,高原鼢鼠分布虽与各环境因子在多种尺度下表现出复杂的空间关联性(正的或负的),但mantel检验发现土壤容重、莎草科丰富度与高原鼢鼠土丘分布呈现显著的负空间关联性,杂类草丰富度和根系粗脂肪含量与高原鼢鼠土丘分布存在显著正空间关联性。综上所述,高原鼢鼠主要栖息利用在土壤疏松、莎草科丰富度较低、杂类草较多和根系粗脂肪含量较高的地方。     

Mechanisms regulating proteostasis are involved in sympatric speciation of the blind mole rat,Spalax galili

Genome-wide analysis demonstrates extensive genomic adaptive complexes involved in sympatric speciation between blind mole rats (Spalax galili) in abutting populations living in basalt and chalk soils. Among the gene ontology (GO) enrichment, musculature and metabolism stood out in basalt dwellers while nutrition and neurogenetics were highlighted in chalk residents. Measurements of mechanisms regulating protein homeostasis inspired by these GO terms suggest that at the proteomic level there is also a habitat/soil-type driven divergence with the basalt residents exhibiting higher proteasome activity whereas elevated levels of markers of autophagy are evident in the chalk inhabitants.     

Hypoxia associated NMDA receptor 2 subunit composition: developmental comparison between the hypoxia-tolerant subterranean mole-rat, Spalax, and the hypoxia-sensitive rat

Vertebrate brains are sensitive to oxygen depletion, which may lead to cell death. Hypoxia sensitivity originates from the high intrinsic rate of ATP consumption of brain tissue, accompanied by the release of glutamate, leading to the opening of ionotropic glutamate receptors, such as N-methyl-D-aspartate (NMDA) receptors (NMDARs). The relative expression levels of the four NMDAR-2 (NR2) subunits change during mammalian development with higher levels of units NR2B and NR2D observed during early development and correlated with hypoxic tolerance during embryonic and neonatal stages of development. Higher levels of NR2D are also abundant in brains of hypoxia tolerant species such as the crucian carp. The subterranean mole-rat, Spalax spends its life underground in sealed burrows and has developed a wide range of adaptations to this special niche including hypoxia-tolerance. In this study, we compared the in vivo mRNA expression of NR2 subunits in the brains of embryonic, neonatal and adult Spalax and rat. Our results demonstrate that under normoxic conditions, mRNA levels of NR2D are higher in Spalax than in rat at all developmental stages studied and are similar to levels in neonatal rat and in other hypoxia/anoxia tolerant species. Furthermore, under hypoxia Spalax NR2D mRNA levels increase while no response was observed in rat. Similarly, hypoxia induces an increase in mRNA levels of Spalax NR2A, claimed to promote neuronal survival. We suggest that indeed the proportional combinations of NMDAR-2 subunits contribute to the ability of the Spalax brain to cope with hypoxic environments.     

Effect of some biological factors on soil variability in the tropics

Summary Observations of a selected area in the forest zone of south western Nigeria indicate that the distribution ofMacrotermes bellicosus (Smeathman) andMacrotermes subhyalinus (Rambur) mounds are mainly affected by the drainage conditions of the soils along a toposequence. Higher number of mounds are observed on the better drained soils, ranging from 35.4 to 17.2 mounds/ha covering an area of respectively 0.84 and 0.10 per cent. The shallow and poorly drained soils show lower mound density (<1 mound/ha). The mound soil bears close resemblance to the subsoil, has higher clay content, lower pH, organic C, CEC and extractable P, but higher P retentio than the adjacent surface soil. Growth of maize (Zea mays L.) and soybean (Glycine max. (L.) Merrill) was poorer in the mound soil than in the surface soil. The problem of increased soil variability when large number of mounds are encountered in the field is discussed.     

Plant Functional Type Effects on Trace Gas Fluxes in the Shortgrass Steppe

Plant community structure is expected to regulate the microbial processes of nitrification and denitrification by controlling the availability of inorganic N substrates. Thus it could also be a factor in the concomitant release of NO and N2O from soils as a result of these processes. C3 and C4 plants differ in several attributes related to the cycling of nitrogen and were hypothesized to yield differences in trace gas exchange between soil and atmosphere. In this study we estimated fluxes of NO, N2O and CH4 from soils of shortgrass steppe communities dominated by either C3 plants, C4 plants or mixtures of the two types. We collected gas samples weekly from two sites, a sandy clay loam and a clay, throughout the growing seasons of 1995 and 1996. Plant functional type effects on gas fluxes at the clay site were not apparent, however we found several differences among plant communities on the sandy clay loam. CH4 uptake from atmosphere to soil was significantly greater on C4 plots than C3 plots in both years. NO fluxes were significantly greater from C4 plots than from C3 plots in 1995. NO fluxes from C3 and mixed plots were not significantly different between 1995 and 1996, however fluxes from C4 plots were significantly greater in 1995 compared to 1996. Results indicate that under certain environmental conditions, particularly when factors such as moisture and temperature are not limiting, plant community composition can play an important role in regulating trace gas exchange.