Reproductive significance of feeding on saprobic and arbuscular mycorrhizal fungi by the collembolan, Folsomia candida

1. Collembolans have often been credited with negatively affecting arbuscular mycorrhizal (AM) symbioses, mainly by grazing and severing the associated external fungal network from host roots. However, most previous experiments were performed using relatively 'clean' systems where other, non-mycorrhizal, fungi were largely excluded. Yet, plant rhizospheres harbour a wide variety of highly palatable non-AM fungi, most of which have saprobic lifestyles.
2. In this study we isolated and cultured several rhizosphere fungi, and the collembolan , Folsomia candida , from the Long-Term Mycorrhiza Research Site, University of Guelph, Canada, to test the hypothesis that, given a choice, collembolans would prefer to feed on saprobic fungi and that such a choice is of adaptive significance to the animals.
3. A laboratory food preference experiment revealed that F. candida favours common saprobic fungi over a variety of AM fungi. Coincidentally, fecundity levels across two Folsomia generations were higher when animals fed exclusively on the preferred fungus, Alternaria alternata . When fed less palatable fungi, fecundity was greatly reduced; in fact animals from the F1 generation were unable to produce any eggs when placed on an exclusive diet of one of the following three AM fungi, Acaulospora spinosa, Scutellospora calospora and Gigaspora gigantea .
4. These results indicate that a strict diet of AM fungi by collembolans has reproductive consequences. Therefore, we propose that under natural conditions these animals spend more time feeding on common saprobic fungi rather than their AM counterparts. This suggests that previous 'clean' studies that investigated the interactions between collembolans and AM fungi may have reported exaggerated effects of animal grazing. The influence of collembolans on the functioning of AM symbioses, under more natural conditions, remains not well understood.     

Hydrogen bond analysis of confined water in mesoporous silica using the reactive force field

ABSTRACT

The structural and dynamical properties of water confined in nanoporous silica with a pore diameter of 2.7?nm were investigated by performing large-scale molecular dynamics simulations using the reactive force field. The radial distribution function and diffusion coefficient of water were calculated, and the values at the centre of the pore agreed well with experimental values for real water. In addition, the pore was divided into thin coaxial layers, and the average number of hydrogen bonds, hydrogen bond lifetime and hydrogen bond strength were calculated as a function of the radial distance from the pore central axis. The analysis showed that hydrogen bonds involving silanol (Si–OH) have a longer lifetime, although the average number of hydrogen bonds per atom does not change from that at the pore centre. The longer lifetime, as well as smaller diffusion coefficient, of these hydrogen bonds is attributed to their greater strength.     

Lanthanum relieves salinity-induced oxidative stress in <Emphasis Type="Italic">Saussurea involucrata</Emphasis>

Changes in growth, physiological and biochemical characteristics under salt stress with or without La³⁺ treatment in Saussurea involucrata Kar. et Kir. were investigated. The results showed that La³⁺ relieved the plant growth inhibition, improved the leaf water potential and water content, increased the soluble protein and the proline contents and decreased malondialdehyde content under salt stress. Further, addition of La³⁺ significantly increased the activities of superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase, decreased the photosynthetic pigment decomposition and increased the ratio of total chlorophyll to carotenoids under salt stress.     

Species Traits as Practical Tools for Ecological Restoration of Marly Eroded Lands

Plant functional traits are increasingly used in restoration ecology because they have the potential to guide restoration practices at a broad scale. This article presents a trait‐based multi‐criteria framework to evaluate and predict the performance of 17 plant seedlings to improve ecological restoration of marly eroded areas in the French Southern Alps. The suitability of these species to limit soil erosion was assessed by studying both their response to erosive forces and their effect on erosion dynamics. We assumed that species efficiency could be explained and predicted from plant traits and we looked for trait‐performance relationships. Our results showed that root slenderness ratio, the percentage of fine roots and root system topology, were the three root morphology traits best describing anchorage strength. Root system characterized by a long and thin tap root and many fine lateral ramifications would be the best to resist concentrated runoff. Species response to burial mainly depended on growth form and morphological flexibility. The abilities of species in reinforcing the soil and reducing erosion rates were negatively correlated to root diameter and positively to the percentage of fine roots. Moreover, root system density and root tensile strength also influenced root reinforcement. Finally, the ability to trap sediment was positively correlated to leaf area and canopy density. Species were then scored and classified in four clusters according to their global performance. This method allows identifying species that possess both response and effect traits related to the goal of preventing erosion during ecological restoration.     

Understorey plant community assemblage of Australian Eucalyptus woodlands under elevated CO2 is modulated by water and phosphorus availability

水分和磷调控的澳大利亚桉树林林下植物群落组合对二氧化碳浓度升高的响应 鉴于林下植物群落具有的关键性功能作用和全球范围内巨大的森林覆盖面积,研究林下群落对 CO₂浓度升高(eCO₂)的响应以及土壤资源在这些响应中的作用,对于了解CO₂浓度升高对森林生态系统造成的影响非常重要。本研究评估了在澳大利亚东部磷有限的桉树林林下群落中,两种限制性的资源(即水分和磷)在发芽、物候、覆盖率、群落组成和叶片性状等方面对eCO₂响应的作用。我们收集了含有当地土壤种子库的土壤,在温室条件下种植实验性的林下植物群落。研究结果表明,添加磷提高了植物的总体覆盖率,特别是在生长期的最初4 周以及水分含量高的条件下,而且该响应是由植物群落中的类禾本科植物所驱动。然而,随着实验的进行,不同处理方法之间的差异逐渐减小,所有处理在大约11周后均达到了80%左右的植物覆盖率。相反,植物覆盖率并未受到eCO₂ 的影响。多元分析结果反映出植物群落组成随时间的变化,盆栽从以裸土为主变为以高覆盖率的多样化群落为主。但是在实验过程中,磷的添加以及水分可利用性和CO₂之间的相互作用都对植物群落随时间的变化轨迹有所影响。CO₂浓度的升高也增加了群落水平的比叶面积,这表明植物群落对eCO₂的功能适应可能发生在成分响应开始之前。鉴于我们用种子库培育的林下群落对eCO₂ 的响应随着时间的推移而有 所变化,并且受到与磷和水分可利用性的相互作用的调节。我们的结果表明,在水分含量有限的系统中, 特别是在土壤养分可利用性低所导致的生产力响应受限的情况下,CO₂浓度的升高在塑造植物群落方面作用有限。     

Production of cellulolytic enzymes from theXylaria andHypoxylon species of xylariaceae

Eighteen strains of xylariaceous fungi have been screened for higher activities of cellulolytic enzymes,Trichoderma reesei QM 9414 was also examined for comparison. Strains ofXylaria anisopleura andX. regalis had higher endocellulase (CMCase) and exocellulase (Avicelase) activities after 2 weeks' incubation.Hypoxylon stygium produced the highest activity of -glucosidase 3 days after inoculation. The optimum pH for these cellulolytic enzymes was approx. 5.0 and the optimum temperatures ranged from 37 to 50°C. A mixed culture process usingT. reesei QM 9414 andH. stygium was developed to obtain enhanced synthesis of cellulase. -Glucosidase activities in the mixed culture increased within 48h whenH. stygium was introduced after 24h.     

Leaf characteristics and optical properties of different woody species

 Light partition has been examined and evaluated on five woody species (Olea europaea, Ficus carica, Pittosporum tobira, Hedera helix maculata, Persica vulgaris) in relation to their leaf morpho-histological characteristics, water and chlorophyll contents. Leaf parameters and optical properties (reflectance, transmittance, absorbance) in PAR, FR and NIR wavebands (400–1100 nm) were preliminarily submitted to a canonical correlation analysis where lamina thickness and water content showed a leading role in determining all the optical properties, while chlorophyll, influential in the PAR region, was remarkably effective only in an extreme pigment situation when green and albino patches of ivy leaves were compared. Transmittance appeared inversely related to lamina thickness in accordance with the Lambert Beer law. Significant correlations were found also between mesophyll water content and both transmittance (positive) and reflectance (negative). Olive leaves showed peculiar optical patterns because of the dense and continuous trichome layer on their abaxial surface. Received: 3 January 1997 / Accepted: 5 May 1997