Short- and long-term effects of the endogeic earthworm Millsonia anomala (Omodeo) (Megascolecidæ, Oligochæta) of tropical savannas,on soil organic matter

Summary This study aimed to establish the effects of Millsonia anomala, a tropical geophagous earthworm common in the humid savannas of Lamto (Ivory Coast), on soil organic matter dynamics over different time scales under laboratory conditions. The texture of casts produced by the worms fed on a shrub savanna soil was not significantly different from that of the soil, which showed that M. anomala ingested soil particles without selection. Physical fractionation of soil organic matter showed that the coarse organic fraction (250–2000 m) was depleted by 25–30% in fresh casts compared to the control noningested soil; this was mainly due to a fragmentation of coarse organic debris. Incubation of casts and a 2-mm sieved control soil under laboratory conditions for more than 1 year showed that the C mineralisation rate was almost four times lower in the casts (3% year^-1) than in the control soil (11% year^-1). We therefore concluded that on a long time scale M. anomala populations may significantly reduce the decomposition rate of soil organic matter in Lamto savannas.     

The microbial diversity and structure in peatland forest in Indonesia

The microbial community structure and function under forest in tropical peatlands are poorly understood. In this study, we investigated the microbial community structure and diversity in natural peat swamp forest soil, disturbed peat soil and mineral soil in Central Kalimantan, Indonesia, using 454 pyrosequencing. The results showed that the natural peat soil had the greatest fungal species richness (Chao1), which was significantly (p < .05) larger than that in the other two soils. Community structure of both fungi and bacteria in natural peat soil differed significantly from that in the disturbed peat soil (p = .039 and p = .045, respectively). Ascomycota (40.5%) was the most abundant phylum across the three soils followed by Basidiomycota (18.8%), Zygomycota (<0.1%) and Glomeromycota (<0.1%). The linear discriminant analysis with effect size (LEfSe) showed that Ascomycota (p < .05) and genus Gliocephalotrichum (p < .05) dominated in natural peat soil. Functionally, pathotrophs were more abundant in disturbed peat soil (p < .05). Proteobacteria (43.8%) were the most abundant phylum followed by Acidobacteria (32.6%), Actinobacteria (9.8%), Planctomycetes (1.7%). Methylocystis, Telmatospirillum, Syntrophobacter, Sorangium and Opitutus were the more abundant genera in disturbed peat soil, whereas Nevskia and Schlesneria were more abundant in mineral soil and natural peat soil, respectively. The natural peat forest soil supported a more diverse microbiology; however, the land use of such a soil can change its microbial community structure. The results provide evidence that the disturbance of tropical peat land could lead to the introduction and spread of a large number of fungal diseases     

广西十万大山自然保护区外来植物的初步研究

十万大山地处北热带山地,有着丰富的生物多样性,但定居的外来种在不断增多,有的外来种成了入侵种,如飞机草等,给该自然保护区带来了严重威胁。通过实地调查以及查证文献,全面整理了十万大山国家级自然保护区的外来植物,并分析了外来种的类型、原产地、引种原因及引入途径,确认：①迄今为止共计99种（含亚种）外来植物,隶属于38科83属,其中菊科最多（10种）,占10．1％,其次为禾本科（6种）,占6．1％;②栽培种56种,逸生种20种,入侵种23种,分别占56．6％、20．2％和23．2％;③外来植物的原产地主要是热带美洲（有54种,占54．5％）,其次是印度（10种）、非洲（9种）和地中海地区（7种）;④人为有意引入有87种,占87．9％。最后对保护区内外来植物的危害预测和防治策略做了分析。     

Ten-year evapotranspiration estimates in a Bornean tropical rainforest

This study was undertaken to quantify interannual variations of total evaporation (ET) in a tropical rainforest in Sarawak, Malaysia. To this end, we conducted 10-year meteorological measurements and formulated a simplified big-leaf model that reproduces transpiration (Et), rainfall interception (Ei), and ET as the sum of these. The model was validated independently using eddy covariance fluxes, rainfall interception based on throughfall and stemflow measurements, and sap flow measurements conducted for more than 2 years. Using the model, Et, Ei, and ET were estimated for the period 2000-2009. Annual Et, Ei, and ET averaged over 10 years were estimated as 1114, 209, and 1323 mm, respectively, with small seasonal fluctuations. The derived estimates showed conservative year-to-year variations in annual Et, Ei, and ET (CV = 5-7%) in contrast to considerable year-to-year variations in annual rainfall (CV = 11%). Specific rainfall characteristics (e.g. intense short duration storms) at this site can explain the conservative year-to-year Ei variations. Small interannual variations in meteorological conditions and absence of severe drought during the study period can explain the small year-to-year Et variations. To characterize ET at our site, we also compared Ei and ET at our site with those of other tropical forests. Based on the derived ET characteristics, we discuss possible ET changes in response to changes in rainfall regime at this site.     

热带地区时间序列土壤中伊利石类矿物的演化——P.Barré假设在热带地区土壤中也存在吗?

P.Barré等认为温带地区自然土壤中,由于植物根系将下层土壤中的钾和硅向上搬运,减缓了上层土壤中伊利石类矿物(混层伊利石/蒙皂石+伊利石)脱钾和脱硅过程,致使其长时间地存在较多的伊利石类矿物。本文旨在了解热带地区土壤中这一假设是否也存在,以海南琼北地区发育于由不同年代火山喷发形成的玄武岩所构成的时间序列土壤(1×104a,(9.0±2.0)×104a,(14.6±0.9)×104a,64×104a,(133±18)×104a,(181±8)×104a)为对象,利用X-射线衍射(XRD)技术分析了其黏土矿物的变化情况,结合土壤钾、硅、活性硅的分析结果,发现伊利石类矿物仅存在于(133±18)×104a以前的土壤中,表层土壤中钾和硅的含量高于下层的土壤,活性硅含量随成土年龄而降低。为此,我们认为:P.Barré假设在热带土壤形成发育过程中,在具有一定的生物复钾和复硅条件下,在成土初期也会存在,但最终会由于土壤强烈的脱钾和脱硅作用而逐步消失。     

Biosorption of macronutrients by Brazilian tropical peats

The objective of this work was to evaluate the adsorption of macronutrients calcium, potassium, magnesium, nitrogen, and phosphorus in two Brazilian tropical peat samples, investigating the effect of pH and determining the kinetics of the adsorption process. Two different Brazilian tropical peat samples were characterized using FTIR, TG, and SEM techniques. Different pH conditions were tested, as well as different mass concentrations of the peats. Differences in the chemical structures of the peat samples directly influenced the adsorptive capacities for the macronutrients. The adsorptive capacity for nitrogen was highest at pH 3, while the best adsorption of calcium and potassium was obtained at pH 6. The best fit to the data was provided by the pseudo-second-order model, which confirmed the rapid adsorption of calcium by both peats.     

Geochemical Fractionation and Adsorption Characteristics of Zinc in Thai Major Calcareous Soils

Zinc (Zn) is a vital plant nutrient that is widely deficient in Thai cultivated calcareous soils. The chemical fractionation and adsorption of Zn are among the most important solid- and liquid-phase interactions that determine the retention of Zn in the soils. This study aimed to investigate the fractionation and adsorption isotherms of Zn in cultivated Thai calcareous soils. The results of sequential extractions showed that Zn is mainly distributed in residual fractions followed by organic-bound, iron and manganese oxides-bound, carbonate-bound, and exchangeable Zn, respectively. Zinc adsorption was well fitted by the Langmuir and Freundlich isotherms. Thai calcareous soils had high Zn adsorption capacity. Soil pH, organic carbon, calcium carbonate, cation exchange capacity, and extractable calcium were the major soil properties that affected the Zn adsorption isotherms in these soils. Zinc hydroxide was the solid precipitate and the Zn hydroxide ion (ZnOH⁺) was the dominant Zn ion in alkaline equilibrium solution.