Selenium uptake by plants as a function of soil type,organic matter content and pH

In pots containing sandy soils at two levels (pH 5 and 7) to which 0.5 mg Se L^-1 soil had been added, an increase in the proportion of clay soil or peat soil led to a decrease in the uptake of Se by spring wheat grain (Triticum aestivum L., var. Drabant) and winter rape plants (Brassica napus L., var. Emil). The effect was most pronounced for the smallest additions of clay and peat soils. Differences in Se uptake between the two pH levels were greatest in treatments where the additions of clay and peat soils were small. At the high pH, an increase in clay content from 7% to 39% resulted in a decrease in Se uptake of 79% for wheat and 70% for rape. At the low pH, the uptake decreased by 72% and 77%, respectively. At the higher pH, an increase in the content of organic matter from 1.4% to 39% resulted in decreases in Se uptake of 88% for wheat grain and 69% for rape. At the low pH, Se uptake decreased by 63% and 48%, respectively. Adding peat soil to clay soil had little effect on Se uptake. Among the limed, unmixed clay, sand and peat soils to which Se had not been added, uptake was highest from the sandy soil, i.e. 8.3 ng Se/g wheat grain and 42 ng Se/g rape. The lowest uptake rates were obtained in the clay soil, i.e. 3.0 ng Se/g for wheat grain and 9.0 ng Se/g for rape.     

Factors affecting the occurrence and distribution of entomopathogenic fungi in natural and cultivated soils

Factors affecting the occurrence and distribution of entomopathogenic fungi in 244 soil samples collected from natural and cultivated areas in Spain were studied using an integrated approach based on univariate and multivariate analyses. Entomopathogenic fungi were isolated from 175 of the 244 (71.7 %) soil samples, with only two species found, Beauveria bassiana and Metarhizium anisopliae. Of the 244 soil samples, 104 yielded B. bassiana (42.6 %), 18 yielded M. anisopliae (7.3 %), and 53 soil samples (21.7 %) harboured both fungi. Log-linear models indicated no significant effect of habitat on the occurrence of B. bassiana, but a strong association between M. anisopliae and soils from cultivated habitats, particularly field crops. Also, irrespective of habitat type, B. bassiana predominated over M. anisopliae in soils with a higher clay content, higher pH, and lower organic matter content. Logistic regression analyses showed that pH and clay content were predictive variables for the occurrence of B. bassiana, whereas organic matter content was the predictive variable for M. anisopliae. Also, latitude and longitude predicted the occurrence of these same species, but in opposite directions. Altitude was found to be predictive for the occurrence of B. bassiana. Using principal component analysis, four factors (1 to 4) accounted for 86 % of the total variance; 32.8, 22.9, 19.6 and 10.4 % of the cumulative variance explained, respectively. Factor 1 was associated with high positive weights for soil clay and silt content and high negative weights for soil sand content. Factor 2 was associated with high positive weights for soil organic matter content and high negative weights for soil pH. Factor 3 was associated with high positive weights for latitude and longitude of the sampled localities and factor 4, had high positive weights only for the altitude. Bi-plot displays representing soil samples were developed for different factor combinations and indicated that, irrespective of geographical location, absence of both fungal species was determined by alkaline sandy soils with low organic matter content, whereas heaviness of soil texture, acidity and increasing organic matter content led to progressively higher percentages of samples harbouring entomopathogenic fungi. These results could aid decision-making as to whether or not a particular cultivated or natural soil is suitable for using entomopathogenic fungi as a pest control measure and for selecting the fungal species best suited to a particular soil.     

Quantification and correlation of vesicular-arbuscular mycorrhizal propagules with soil properties of some mollisols of northern India

The populations of vesicular-arbuscular mycorrhizae (VAM) propagules by the most probable number method in some mollisols and their correlations with some important soil properties were determined. On average, the six soils, Phoolbagh clay loam, Beni silty clay loam, Haldi loam, Nagla loam, Khamia sandy loam and Patherchatta sandy loam contained 4.9, 4.0, 7.9, 7.9, 3.3 and 13.0 propagules/g soil, respectively, i.e. none of the soils was found to be high in VAM. The size of the VAM population was compared to soil properties such as pH, organic carbon, sand content, available phosphorus and available potassium, cation-exchange capacity, silt and clay contents. A significant positive correlation (r=0.586) was only found with available soil phosphorus (P<0.05) and a significant negative correlation (r=-0.555) with soil clay content (P<0.05).Directorate research paper series No. 7862     

Interactive response of herbivores,soils and vegetation to annual burning in a South African savanna

Abstract Despite decades of research, the primary factors determining savanna structure remain elusive – a conundrum termed ‘the savanna problem’. After 47 years of annual burning in Terminalia woodland and Acacia/Combretum savanna on sandy, granite‐derived soils in the southern Kruger National Park, South Africa, a dense cover of trees and shrubs persists on some burnt plots and is largely absent from others. We postulated that intense browsing pressure by antelope and other herbivores prevents recruitment of trees in burnt plots and that herbivores concentrate on plots that are richest in nutrients. Herbivore abundance did not show a relationship with soil macronutrients and we consequently investigated micronutrient status. The reduction in tree cover as a result of annual burning was positively correlated with mass of herbivores (15–1500 kg) (r ² = 0.61, n = 8). This index of herbivore abundance was in turn positively correlated with total Zn (r ² = 0.64, n = 8). Other indices of herbivore abundance showed significant relationships with total clay content and total Mn. We suggest that herbivores concentrate on sites with greater clay content (possibly due to a greater availability of micronutrients), and that tree cover can remain relatively dense under a regime of annual burning if browsing pressure is not intense. The long‐term burn experiments in the Kruger National Park savanna provide a platform for unravelling the savanna problem. Determining possible interactions between soil properties, herbivory and fire is a step in this direction.     

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.     

荒漠草原区土壤粒径组成对柠条根际土壤微生物数量及酶活性的影响

柠条(Caragana korshinskii)是荒漠草原区主要的造林绿化树种,研究其根际土壤微生物和酶活性与不同土壤类型土壤粒径组成的关系有重要意义,然而土壤粒径对荒漠草原柠条根际土壤微生物数量和酶活性的影响知之甚少,探讨土壤颗粒组分与微生物数量、土壤酶活性之间的关系,以及土壤颗粒组成对荒漠草原区固沙灌木植物柠条根际土壤微生物数量及酶活性的影响,可为揭示荒漠草原土壤退化及生态修复提供参考。以宁夏荒漠草原区土壤粒径组成差异显著的灰钙土、红黏土、风沙土环境下栽植的柠条为研究对象,研究不同土壤颗粒组成对根际土壤微生物数量及酶活性的相互关系与影响。结果表明:土壤微生物的数量表现为细菌放线菌真菌。根际土壤中的细菌、真菌数量显著高于非根际,且在3种不同类型的土壤中随着细砂粒的增多,真菌和放线菌数量逐渐降低,而细菌数量呈先增大后减小的趋势;根际与非根际土壤的蔗糖酶、碱性磷酸酶及过氧化氢酶活性均呈现出灰钙土红黏土风沙土的趋势,红黏土根际土壤中的脲酶活性显著高于灰钙土与风沙土;除过氧化氢酶外,土壤酶活性表现为根际高于非根际,在3种不同类型的土壤中随着细砂含量的增加,土壤酶活性均呈递减趋势。土壤颗粒组成与微生物数量之间没有明显的相关性,而与土壤酶活性之间显著相关,土壤酶活性与黏粒、粉粒呈正相关,与细砂、中砂呈负相关关系,根际土壤中酶活性更高,能够为植物及微生物提供更多的营养。     

The reserve of weatherable primary silicates impacts the accumulation of biogenic silicon in volcanic ash soils

Banana plantlets (Musa acuminata cv Grande Naine) cultivated in hydroponics take up silicon proportionally to the concentration of Si in the nutrient solution (0–1.66 mM Si). Here we study the Si status of banana plantlets grown under controlled greenhouse conditions on five soils developed from andesitic volcanic ash, but differing in weathering stage. The mineralogical composition of soils was inferred from X-ray diffraction, elemental analysis and selective chemical/mineralogical extractions. With increasing weathering, the content of weatherable primary minerals decreased. Conversely, clay content increased and stable secondary minerals were increasingly dominant: gibbsite, Fe oxides, allophane, halloysite and kaolinite. The contents of biogenic Si in plant and soil were governed by the reserve of weatherable primary minerals. The largest concentrations of biogenic Si in plant (6.9–7 g kg⁻¹) and soil (50–58 g kg⁻¹) occurred in the least weathered soils, where total Si content was above 225 g kg⁻¹. The lowest contents of biogenic Si in plant (2.8–4.3 g kg⁻¹) and soil (8–31 g kg⁻¹) occurred in the most weathered desilicated soils enriched with secondary oxides and clay minerals. Our data imply that soil weathering stage directly impacted the soil-to-plant transfer of silicon, and thereby the stock of biogenic Si in a soil–plant system involving a Si-accumulating plant. They further imply that soil type can influence the silicon soil–plant cycle and its hydrological output.     

Holocene boundary dynamics of a northern Australian monsoon rainforest patch inferred from isotopic analysis of carbon, (14C and δ13C) and nitrogen (δ15N) in soil organic matter

Abstract Soil organic matter (SOM) was sampled from lateritic soil profiles across an abrupt eucalypt savanna–monsoon rainforest boundary on the north coast of Croker Island, northern Australia. Accelerator mass spectrometry dating revealed that SOM that had accumulated at the base of these 1.5 m profiles had a radiocarbon age of about 5000 years. The mean carbon and nitrogen stable isotope composition of SOM from 10 cm deep layers from the surface, middle and base of three monsoon rainforest soil profiles was significantly different from the means for these layers in three adjacent savanna soil profiles, suggesting the isotopic ‘footprint’ of the vegetation boundary has been stable since the mid Holocene. Although there were no obvious environmental discontinuities associated with the boundary, the monsoon rainforest was found to occur on significantly more clay rich soils than the surrounding savanna. Tiny fragments of monsoon rainforest and abandoned ‘nests’ (large earthen mounds) of the orange‐footed scrubfowl, an obligate monsoon rainforest species, occurred in the savanna, signalling that the rainforest was once more extensive. Despite episodic disturbances, such as tropical storm damage and fires, the stability of the boundary is probably maintained because clay rich soils enable monsoon rainforest tree species to grow rapidly and achieve canopy closure, thereby excluding grass and reducing the risk of fire. Conversely, slower tree growth rates, grass competition and fire on the savanna soils would impede the expansion of the rainforest although high rainfall periods with shorter dry seasons may enable rainforest trees to grow sufficiently quickly to colonize the savanna successfully.     

Potato bacterial wilt suppression and plant health improvement after application of different antioxidants

Bacterial wilt caused by Ralstonia solanacearum is a devastating disease that often threatens potato production and exportation. The potential of four antioxidants (seaweed extract (SWE), yeast, chitosan and ascorbic acid (ASA)) in controlling the disease was evaluated in vitro, under glasshouse and field conditions. The field experiment was conducted in two naturally infested locations: Wardan, Giza (sandy soil), and Talia, Minufiya (silty clay soil). Only chitosan showed antibacterial properties against the pathogen in vitro. SWE, yeast and chitosan showed disease suppression under both glasshouse and field conditions. The disease suppression was accompanied by an increase in the ratio of soil copiotrophic to oligotrophic bacteria. The three antioxidants increased plant nitrogen content, decreased soil OM content and decreased C/N ratio. Disease suppression after chitosan application was clearly observed only in Wardan area, which was characterized by a higher soil alkalinity. A high percentage of antagonistic fluorescent strains similar to Pseudomonas putida group were detected for chitosan‐treated plants in Wardan area (sandy soil). ASA drastically decreased the count of the pathogen in soil, but was conducive to the pathogen in plant tissues. A remarkable increase in microbial (bacterial and fungal) soil and rhizosphere diversity as indicated by PCR‐DGGE analysis for bacterial 16S rRNA and fungal 18S rRNA was recorded. In Talia area (silty clay soil), the soil microbial community was more stable and was in general resistant to the disease where the soils were characterized by high electrical conductivity. SWE, yeast and ASA significantly increased crop production in Talia area only.     

Floristic composition,plant species abundance,and soil properties of montane savannas in the Gran Sabana,Venezuela

Floristic composition, species abundance, and soil properties were studied in slope, flat and disturbed savannas in the northern part of the Gran Sabana, Venezuela. All savannas presented shallow soils (<30 cm depth) with high content of sand and low content of clay. In general, the soils were poor in nutrients and strongly acidified. The major difference between the soils was the content of the stony fraction, which was significantly higher (P<0.05) in the slope savannas than in the flat savannas. A total of 57 dicot, 42 monocot, and 7 fern species were recorded in all studied savannas. In the flat and slope savannas predominated the monocot species, while in the disturbed savanna predominated the dicots. The families with the largest number of species were Poaceae (19.8%), Cyperaceae (13.2%), Asteraceae (10.4%) and Melastomataceae (8.5%). The number of species in the flat savannas was higher than that of the slope savannas. The lowest plant species richness was associated to slope savannas and their high content of stony fraction of the soils. The highest floristic similarity was found between slope savannas, and the lowest between disturbed savanna and slope savannas. The most abundant life forms in the studied savannas were perennial (42.4%) and annual (24.5%) herbs, followed by suffruticoses (16.0%) and shrubs (12.3%), and the less frequent was lianas (4.7%). The disturbed savanna showed the higher richness and diversity index. Trachypogon plumosum (Poaceae) was the most abundant species in all studied savanna.     

Changes in soil associated with continuous growth of some vegetation

Summary and conclusions From a study of the composition of the soil and the subsoil under three grasses,Imperata cylindrica, Pennisetum orientale, Pennisetum polystachyum and three legumesTephrosia candida, Medicago sativa andPueraria hirsuta and of those of natural bare soil in the neighbourhood of each, it could be observed that the soils under vegetation contained more moisture, organic matter, organic nitrogen clay and soluble salts but had lower pH values than the bare soils. The soils under grasses had less moisture, lower pH and lower salinity but higher clay content and exhibited greater aggregation than the soils under legumes. Though the soils under grasses had significantly higher quantities of organic matter than the soils under legumes there was no significant difference in the organic nitrogen contents between them.     

Soil type, microsite, and herbivory influence growth and survival of Schinus molle (Peruvian pepper tree) invading semi-arid African savanna

Naturalization of Schinus molle (Anacardiaceae) has been observed in semi arid savanna of the Northern Cape Province of South Africa. However, with high dispersal ability, the species is expected to achieve greater densities and invade more widely. The study involved a field manipulation experiment over 14 months using a factorial block design to examine transplanted seedlings in different savanna environments. The experiments examine the effects of soil type (sandy and clay), microsite, and herbivores on seedling performance (establishment, growth and survival). Seedlings were grown in a greenhouse and individually transplanted into four treatment groups: in open grassland, under tree canopies, and with and without cages to exclude large herbivores (cattle and game). The same experiment was repeated in two different soil types: coarse sand and fine-textured clay soil. Results suggest that protection provided by canopies of large indigenous Acacia trees facilitates S. molle invasion into semi-arid savanna. In the field, S. molle seedlings performed considerably better beneath canopies of indigenous Acacia trees than in open areas regardless of soil type. Whether exposed or protected from large herbivores, no seedlings planted in open grassland survived the first winter. Although, seedlings grew better and had higher survival rates beneath tree canopies than in the open sites, exposure to large herbivores significantly decreased heights and canopy areas of seedlings compared with those protected from large herbivores. The effect was greater on clay soil than on sandy soil. The results suggest that low temperature (frost), and possibly inter-specific competition with grasses, may limit S. molle seedling establishment, survival and growth away from tree canopies in semi arid savannas. Low soil nutrient status and browsing may also delay growth and development of this species. The invasive potential of S. molle is thus greatest on fertile soils where sub-canopy microsites are present and browsing mammals are absent.     

Distribution of soil fractions and location of soil bacteria in a vertisol under cultivation and perennial grass

Effects of soil management on soil characteristics were investigated on the rhizosphere (RPP) and the nonrhizosphere (NRPP) soil of a re-grass vertisol underDigitaria decumbens and in the soil under continuous cultivation (CC). A low energy technique allowed to separate eight size and density fractions, including macro- and micro-aggregates while preserving soil bacteria. Organic C and N, microbial biomass C and the number of total bacteria (AODC) and ofAzospirillum brasilense and their distribution were determined in soil fractions isolated from the CC, NRPP and RPP soils. Soil macroaggregates (>2000 m) were similarly predominant in the NRPP and RPP soils when the dispersible clay size fraction (<2 m) respresented more than 25% of the CC soil mass. The main increase of C content in RPP originated from the macroaggregates (> 2000 m) and from the root fraction, not from the finer separates. The proportion of organic C as microbial biomass C revealed the low turnover of microbial C in the PP situations, especially in the clay size fraction of the NRPP soil. A common shift of AODC toward the finer separates from planted soils (CC and RPP) revealed the influence of living plants on the distribution of soil bacteria. The relative abundance ofA. brasilense showed the presence of the active roots ofDigitaria in the macroaggregates and their contact with the dispersible clay size fraction of the rhizosphere soil.     

溶解性有机碳在红壤水稻土中的吸附及其影响因素

吸附作用是影响土壤中溶解性有机碳(DOC)迁移转化及生物有效性的重要反应过程,研究DOC在土壤中的吸附行为,对正确阐明土壤有机碳的循环和转化特征以及进行污染风险评估有重要意义.采用平衡法研究了红壤水稻土对DOC的吸附特征,并分析土壤有机质、粘粒含量及pH值与DOC吸附量之间的关系.结果表明,供试土壤对DOC的吸附等温线符合Freundlich和Linear方程.不同土壤对DOC的吸附能力有明显差异.在相同浓度下,DOC吸附量以第四纪红色粘土发育的低肥力水稻土最大,第三纪红砂岩风化物发育的低肥力水稻土次之,两种高肥力水稻土最小.土壤对DOC的吸附过程分为快、慢两个阶段,0-0.25 h内DOC的吸附速率最大,随着时间的推移,吸附速率渐小,2-4 h后基本达到吸附平衡.描述供试土壤对DOC吸附动力学过程的最优模型为一级扩散方程,其次为Elovich方程和抛物扩散方程.粘粒含量和有机质是影响土壤DOC吸附量的重要因素,随着粘粒含量的增加,有机质含量的降低,DOC的吸附量增大.     

Forces affecting water imbibition inMacrotermes workers (Termitidae,Isoptera)

Summary Observations of putative drinking behaviour at soil surfaces by major workers ofMacrotermes subhyalinus andM. bellicosus suggested that unidirectionally arranged trichomes on the anterior hypopharynx exert capillarity on water in soil pores. To test this hypothesis thirsty major workers were placed on soil of relatively low water content. From the soil types tested we determined soil-moisture retention curves which represent graphically the water content of the soil and its corresponding capillary potential. The termites were able to obtain water from different types of clay soil against potentials in the range – 1.6 to – 1.9 bar. On sandy soil the capillary potential was found to be much higher (– 0.18 bar), i.e. closer to zero. Sandy soil has a very unfavourable water retention capacity, i.e. its water content is very low at low capillary potential, whereas clay soil retains much more water at low capillary potential. The ability of the termites to gain water from soils with relatively low water content is an important adaptive feature for survival in semi-arid areas.     

Termitaria vs. mistletoe: Effects on soil properties and plant structure in a semi-arid savanna

Termite mounds by creating patches of increased resource availability (e.g. water and nutrients) are a major source of spatial heterogeneity in savannas. Likewise, mistletoes via input of nutrient-rich litter alter nutrient and water availability increasing environmental heterogeneity in semi-arid savanna. Despite this recognition, the influence of termitaria and mistletoe on soil properties and plant community have not been investigated together. We established eight 100 m² plots each on termitaria, under mistletoe-infected trees and in the surrounding savanna and examined the soil properties and the structure of Securinega virosa (Euphorbiaceae) and Euclea divinorum (Ebenaceae) in semi-arid savanna, southwest Zimbabwe. Soil properties significantly differed among the sampling sites (p = 0.001) with soils of increasing clay, soil moisture, pH and phosphorus, calcium and ammonium concentrations occurring on termite mounds. Soils under mistletoe-infected trees were associated with silt, organic matter, sodium, potassium, magnesium and nitrate and the surrounding savanna was associated with soils of increasing sand content. Plant structure also differed significantly between sites with greater basal area of both S. virosa and E. divinorum on termitaria relative to mistletoe-infected trees and the surrounding savanna. However, the stem density of S. virosa was greater under mistletoe-infected trees than on termitaria and in the surrounding savanna. Plant structural variables of individuals of the same species were affected by different soil properties across treatments. The major patterns showed that plant structure was influenced positively by soil moisture and nitrate and negatively by phosphorus on termitaria; positively by clay, soil moisture and ammonium and negatively by potassium under mistletoe-infected trees; and by phosphorus and calcium in the surrounding savanna. These findings show that soil properties, plant structure and their relationships differ between termitaria, mistletoe-infected trees and surrounding savanna, and these differences are suggested to increase heterogeneity in soil resources availability and vegetation structure in semi-arid savanna.     

Competition of strains of Rhizobium of the cowpea group in two soil types

Summary Competition of five strains of Rhizobium of the cowpea group, onVigna radiata (L) Wilcjeck variety ML 5, was tested in loamy clay and loamy sand soils. Strains RM 6 and RM 5 were effective nodulators in loamy clay soil, and strains MNH, M 20 and RM 6 were effective nodulators in loamy sand soil. Strains RM 6 and MNH predominated nodule formation in loamy clay and loamy sand soils respectively.     

Shewanella putrefaciens CN32对粘土附着态铵氮释放的影响

【目的】研究产胞外分泌物微生物Shewanella putrefaciens CN32对土壤中常见粘土矿物附着态NH_4~+的释放效果及影响机制。【方法】以吸附NH_4~+的蒙脱石、蛭石、伊蒙混层矿物和黑云母为对象,通过监测S. putrefaciens CN32作用下不同粘土释放的NH_4~+含量及过程,以及监测微生物量及释放的胞外聚合物(Extracellular Polymeric Substances,EPS)的含量变化,研究S. putrefaciens CN32作用下不同粘土矿物类型附着态NH_4~+释放的差异性。【结果】粘土矿物附着态NH_4~+含量从高到低依次为蒙脱石蛭石伊蒙混层矿物黑云母(黑云母NH_4~+吸附量极低,会在非生物作用下几乎完全释放),CN32作用下粘土附着态NH_4~+相对释放量依次为蒙脱石伊蒙混层矿物蛭石;然而,尽管CN32有效促进了粘土附着态NH_4~+释放,但释放的NH_4~+并未在溶液中大量累积,而是多被微生物同化吸收转化为生物有机氮(EPS为主)并吸附在粘土表面,且粘土对EPS的吸附能力表现为蒙脱石伊蒙混层矿物蛭石黑云母;由于粘土吸附NH_4~+及EPS都与矿物中的羟基(结构水或层间水)关系密切,推测EPS对矿物羟基的竞争吸附可能是CN32促进NH_4~+释放的重要原因之一。【结论】以上结果表明,产EPS微生物S. putrefaciens CN32能够促进各类粘土矿物的附着态NH_4~+释放,但释放的NH_4~+可以通过微生物作用转化为有机氮,从而在减少NH_4~+流失的同时增加土壤氮肥的生物可利用性,因此微生物在降低土壤氮肥流失、转化土壤氮肥污染过程中可能起到了重要作用,也揭示了深入系统地分析不同类型土壤(粘土类型不同)中粘土附着态NH_4~+在不同功能微生物作用下的迁移转化过程,是精准评估土壤氮肥施用效率及流失风险的前提之一。     

Geophagy by the bonnet macaques (Macaca radiata) of southern India: A preliminary analysis

Bonnet macaques (Macaca radiata) in the Marakkanam Reserved Forest of southern India consume termitaria soils. Samples from the ingested termite mounds are compared with samples taken from the surrounding uneaten soils in an attempt to determine why the termitaria soils are eaten. Particle size, clay and primary mineral composition, geochemistry, and scanning electron microscopic analyses are used to search for a possible explanation for geophagy among the bonnet macaques. Kaolin minerals abound throughout the Marakkanam soil sample suite. But the termitaria soils are distinguished by the presence of small amounts of smectite. An abundance of kaolin minerals in combination with small amounts of smectite strongly resembles the mineralogy ofeko, a traditional African remedy for stomach ailments, and Kaopectate™, a western anti-diarrhoeal preparation. The percentage of mature leaves and fruits ofAzadirachta indica consumed by the bonnet macaques is relatively high. Plant feeding deterrents, such as, acid detergent fibre (ADF) and the inherent nature of the fruits ofAzadirachta indica, when consumed in large quantities to act as a purgative, could cause gastrointestinal upsets and diarrhoea. At Marakkanam, bonnet macaques ingest termitaria earth that would act as a pharmaceutical agent to alleviate gastrointestinal upsets and control diarrhoea.     

三种苦苣苔对石灰土和红壤的适应性分析

为探讨苦苣苔科植物对其岩溶生境的适应性,该研究选取黄花牛耳朵(Primulina lutea)、紫花报春苣苔(Pri.purpurea)和桂林蛛毛苣苔(Paraboea guilinensis)三种苦苣苔科植物,将其栽种在石灰土及红壤两种不同类型的土壤中,观测记录其生长性状并对其叶片元素含量进行测定和比较。植株采集过程中,同时采集自然生境中三种苦苣苔科植物叶片及取样植物基部土壤,并对叶片及土壤元素的含量进行测定,作为今后苗圃试验的参照。结果表明:三种苦苣苔科植物在两种土壤上的生长状况及适应性具有差异,其在石灰土上生长良好,在红壤上生长较差;在两种不同土壤中,除N外,桂林蛛毛苣苔的叶片其他元素(P、K、Mn、Mg、Ca、Zn、Cu)差异极显著(P0.01);除P外,紫花报春苣苔的叶片其他元素(N、K、Mn、Mg、Ca、Zn、Cu)差异极显著(P0.01);除N、Cu、Ca外,黄花牛耳朵的叶片元素(P、K、Mn、Mg、Zn)差异极显著(P0.01);三种植物的叶片元素比值,除少数值没有差异外,大部分指标差异都极显著;对叶片元素与栽培土壤元素的相关性分析,发现植物叶片Mn元素与土壤中N、Ca、Mg、Zn、Mn、有机质含量等呈正相关,土壤P元素与叶片中N、P元素呈正相关,而与叶片中Zn元素呈负相关关系。在其他栽培条件一致的条件下,土壤因素及物种差别是造成黄花牛耳朵、紫花报春苣苔和桂林蛛毛苣苔适应性产生差异的主要原因。