Host effects in high ectomycorrhizal diversity tropical rainforests on ultramafic soils in New Caledonia

Tropical rainforests have been thought to have low prevalence and diversity of ectomycorrhizal symbioses. However, to date, tropical regions have been poorly sampled for ectomycorrhizal fungi. Here, we investigated ectomycorrhizal fungal community diversity and the role of host plants in shaping this diversity in three main ultramafic rainforests in New Caledonia, an archipelago renowned for its exceptional plant diversity and recognized as a biodiversity hotspot. Sampling of ectomycorrhizal root tips and fruit bodies in Nothofagus aequilateralis-dominated, Arillastrum gummiferum-dominated and mixed rainforests showed high fungal diversity with, in total, 28 lineages and 311 operational taxonomic units (OTUs), of which 95% might be endemic. We also found that host preference and host density influenced ectomycorrhizal community composition and contributed to the high fungal diversity of New Caledonian rainforests. Finally, the /cortinarius lineage dominated the below- and above-ground communities, which suggests that this lineage plays a central role in ultramafic ecosystems functioning.     

Bioaccumulation of mercury,arsenic, cadmium,and lead in plants grown on coal mine soil

Mercury (Hg), arsenic (As), cadmium (Cd), and lead (Pb) are the major toxic metals released by coal mining activities in the surrounding environment. These metals get accumulated in the soils. The plants grown on the contaminated soil uptake these toxic metals in their roots and aerial parts. This study monitored the bioaccumulation of Hg and other three toxic metals in coal mine soil. The pot study of Hg accumulation in Brassica juncea showed that the extent of Hg uptake by roots and shoots of the plants grown on was high in the mature plant and Hg content in root was higher than the shoot. In the soil of unreclaimed overburden (OB) dump, the toxic metal content was higher than that of reclaimed OB dump which posed high ecological risk in the soil of unreclaimed OB dump. Bioaccumulation coefficient (BAC) value showed that Hg was not accumulated in the leaves of Dalbergia sissoo L., Gmelina arborea, Peltaphorum inerme L., Cassia seamea L, and Acacia mangium L grown on coal mine soil.     

Tree identity and diversity directly affect soil moisture and temperature but not soil carbon ten years after planting

1. Soil C is the largest C pool in forest ecosystems that contributes to C sequestration and mitigates climate change. Tree diversity enhances forest productivity, so diversifying the tree species composition, notably in managed forests, could increase the quantity of organic matter being transferred to soils and alter other soil properties relevant to the C cycle.
2. A ten‐year‐old tree diversity experiment was used to study the effects of tree identity and diversity (functional and taxonomic) on soils. Surface (0–10 cm) mineral soil was repeatedly measured for soil C concentration, C:N ratio, pH, moisture, and temperature in twenty‐four tree species mixtures and twelve corresponding monocultures (replicated in four blocks).
3. Soil pH, moisture, and temperature responded to tree diversity and identity. Greater productivity in above‐ and below‐ground tree components did not increase soil C concentration. Soil pH increased and soil moisture decreased with functional diversity, more specifically, when species had different growth strategies and shade tolerances. Functional identity affected soil moisture and temperature, such that tree communities with more slow‐growing and shade‐tolerant species had greater soil moisture and temperature. Higher temperature was measured in communities with broadleaf‐deciduous species compared to communities with coniferous‐evergreen species.
4. We conclude that long‐term soil C cycling in forest plantations will likely respond to changes in soil pH, moisture, and temperature that is mediated by tree species composition, since tree species affect these soil properties through their litter quality, water uptake, and physical control of soil microclimates.

     

A comparison of the ability of forest and agricultural soils to mineralize chlorinated aromatic compounds

Soils were sampled from two agricultural fields, two relatively pristine forests, and one suburban forest in Ontario, Canada. The ability of these soils to mineralize 2,4-dichlorophenoxyacetate, 3-chlorobenzoate, 4-chlorophenol, 2,4-dichlorophenol, pentachlorophenol, and atrazine was determined using ¹⁴C-labeled substrates. Direct preexposure was necessary before atrazine mineralization could be detected; however, it was not necessary for degradation of any of the other chemicals. 2,4-dichlorophenoxyacetate and pentachlorophenol mineralization was much higher in the agricultural soils relative to the pristine forest soils, but 3-chlorobenzoate and 2,4-dichlorophenol mineralization rates showed the opposite trend. Mineralization of 4-chlorophenol was about equivalent in all soils. Suburban forests soils were indistinguishable from agricultural soils with respect to their degradation of 2,4-dichlorophenoxyacetate and chlorobenzoate. Additionally, they were better able than any of the soils to withstand the toxic effects of pentachlorophenol. Pentachlorophenol mineralization was highly variable in the pristine forest soils, ranging from about 6 to 50%. Abiotic factors such as pH, soil type, and organic and moisture content did not account for these significant site differences. The selective forces responsible for these differences, and the possible differences in microbial populations are discussed.     

Arbuscular mycorrhizas in a valley-type savanna in southwest China

The arbuscular mycorrhizal (AM) status of 67 plant species in a savanna community in the hot, dry valley of Jinsha River, southwest China was surveyed. It was found that about 95% of the plant species formed AM and 5% possibly formed AM. The composition of AM fungi (AMF) in the rhizosphere soils was also investigated. The AMF spore density ranged from 5 to 6,400 per 100 g soil, with an average of 1,530, and these spores/sporocarps were identified as belonging to six genera. Fungi belonging to the genera Glomus and Acaulospora were the dominant AMF. High densities of AMF spores in the rhizosphere soils, and the intensive colonization of the plant roots, indicated that plants grown in this valley-type savanna may be highly dependent on AM.     

Composition and mean residence time of molecular weight fractions of organic matter extracted from two soils under different forest species

The organic matter extracted from various mineral horizons of two forest soils, one under silver fir (Abies alba Mill.), the other under European beech (Fagus sylvatica L.), was fractionated by dialysis into three fractions, 100–1000, 1000–8000, and >8000Da. On a C basis, in all horizons the recovered organic matter amounted to less than a half of the total and was mainly composed of molecules >8000Da. The 100–1000Da fraction had a principal elemental composition profoundly different from the other two fractions, which, instead differed from each other significantly only for the S content and the molar ratio of C with N. No significant difference in this regard was found between soils. The richness in O and some typical absorption bands in the FT-IR spectra indicated that the 100–1000Da fraction had a lot of carboxyl moieties. The spectroscopic (¹³C NMR) investigation showed that the 1000–8000 and >8000Da fractions had a prevalently aliphatic nature and signals attributable to polysaccharides (O-alkyl C) revealed overall a high presence of non-humic biopolymers. These latter were significantly more abundant, suggesting a lower degree of humification, in the >8000Da fraction than in the 1000–8000Da fraction. Comparing soils, that under beech appeared significantly richer in O-alkyl C than that under fir. The organics extracted from the A horizon of both soils had positive ¹⁴C values, indicating recent synthesis mainly due to the present forest cover. The mean residence time (MRT) of the combined 100–1000Da and 1000–8000Da fractions and the >8000Da fraction increased with depth, even to about 5000 years in the more than 1-m deep BC horizons under beech. In some cases, and especially in the soil under fir, despite higher values of ¹³C denoting stronger microbial decomposition, the 100–8000Da fraction showed a higher MRT than that of the >8000Da fraction, perhaps due to its ascertained lower content of non-humic biopolymers.     

人扁桃体中应激免疫抑制蛋白的初步观察

以前的实验证明,在应激条件下,外周淋巴组织中产生一种蛋白质,具有抑制某些免疫功能的作用,称为应激免疫抑制蛋白（immune suppressive protein of stress,ISPS）。本实验用人外周淋巴器官扁桃体进行了研究,证明扁桃体的提取物能抑制小鼠由Con A诱导的淋巴细胞转化,而且这种抑制作用可被ISPS单克隆抗体（2C4）部分翻转。间接ELISA法证明人扁桃体提取物能与2C4单克隆抗体相结合。以ISPS单克隆抗体（2C4）作免疫组织化学研究,证明人扁桃体中有很多染色呈阳性的细胞。这些结果从不同角度提示,人外周淋巴组织中存在一种与ISPS相类似的免疫抑制物质。     

Spatial variation in pyritization of trace metals in salt-marsh soils

In the present study, the pyritization of trace metals was studied in 12soils from 3 salt marshes in the Ría of Ortigueira (NW Spain). Theconcentrations of trace metals in the pyrite fraction were related tophysicochemical conditions, physiographical position in the salt marsh, and thepresence or absence and type of vegetation. Redox conditions in soils from thelow-salt marsh and from the creek bottom were strongly reducing throughout theprofile, and there were higher concentrations of Fe and some trace metals (Cuand Mn) in the pyrite fraction (soluble in HNO₃) than in thereactivefraction (soluble in 1N HCl). In contrast, the trace-metal content in pyritefraction in the surface layers of the high-salt marsh was low. In some of thesoils, there was a significant increase in the pyrite content below 25cm, and levels of Fe, Mn and Cu incorporated into this fractionwere similar to those in the reactive fraction. The degree of pyritizationvaried greatly among metals in the order: CuFe-1NHCl>dithionite-Fe>NiMn>>Zn>Cr, although when we consideredonly the amorphous forms (ascorbate-Fe) as reactive-Fe, the order was:ascorbate-Fe>>Cu>NiMn>>Zn>Cr. These differences appearedto be a consequence of the different geochemical behaviour of each metal(mainlyin terms of the thermodynamic stability of sulfides and reaction kinetics),except for Zn. The low concentrations of Zn obtained may have been due to thesolubility of ZnS in 1N HCl, which meant that it was extracted with thereactivefraction. Finally, we observed a direct relationship between DOP and DTMP,whichwas independent of the geochemical behaviour of each metal and of itsconcentration in the soil. Thus, the strong correlation between pyrite-Fe andthe metals associated with this fraction appears to indicate that these metalscoprecipitate with pyrite rather than form metal sulfides.     

Effects of Canopy Gaps,Topography, and Soils on the Distribution of Woody Species in a Central Brazilian Deciduous Dry Forest1

The interrelationships between the distribution of woody species and environmental variables were investigated in an area of deciduous dry forest in Santa Vitöria, central Brazil. This is the first study of a vanishing type of dry forest which grows on base-rich soils originating from the basalt bedrocks of southern Goiás and western Minas Gerais. A survey of topography, soil properties, canopy gaps and woody plants (≥5 cm diameter at the base of the stem) was conducted in 50–15 × 15 m quadrats. The soils were classified into the following soil series: Hapludolls → Haplustolls → Haplustolls → Ustropepts → Rhodustalfs. This series corresponded to a gradient of increasing elevation and effective soil depth and decreasing slope gradient, soil organic matter and total exchangeable bases. A canonical correspondence analysis and a detrended correspondence analysis indicated that plant species’abundance distribution was significantly correlated with both the relative area of canopy gaps in the quadrats and the soil-topography gradient. Presumably, the critical factors involved in these two gradients are, respectively, light and ground water regimes. The influence of canopy gaps (i.e., light) was surprising and has not been documented previously for tropical deciduous dry forests.