[Variation of subtropical forest soil microbial biomass and soil microbial community functional characteristics along an urban-rural gradient]. / 亚热带森林土壤微生物生物量及群落功能特征的城乡梯度变化.

Soil microorganisms, which are sensitive to environmental changes, affect soil nutrient cycling and play an important role in the biogeochemical cycling. To understand the changes of soil microorganisms in subtropical forest across the urban-rural environmental gradient, we analyzed the differences in soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial community functional diversitiy in Dashu Mountain National Forest Park (urban forest), Zipeng Mountain National Forest Park (suburban forest) in Hefei and Wanfo Mountain(rural forest) in Luan City. Results showed that soil MBC followed an order of rural natural forest (115.07 mg·kg-1) > suburban forest (101.68 mg·kg-1) > urban forest (82.73 mg·kg-1), soil MBN followed an order of rural natural forest (57.73 mg·kg-1) > urban forest (31.57 mg·kg-1) > suburban forest (29.01 mg·kg-1), soil microbial metabolic activities (AWCD), McIntosh index (U) were shown as rural natural forest > suburban forest > urban forest. The main carbon sources used by soil microbial communities in those forests were carboxylic acids, amino acids and carbohydrates, with weak utilization capacity for polyamines and polyphenols. The utilization capacity of soil microorganisms to amino acids, carboxylic acids, polymers and polyphenols followed the order of rural natural forest > suburban forest > urban forest. There were significant spatial variations in the functional characteristics of soil microbial communities under urban-rural environmental gradient, with Tween 80 and ß-methyl-D-Glucoside being the characteristic carbon sources as the influencing factors. Soil pH was significantly positively correlated with the microbial McIntosh index and AWCD value, while soil ammonium nitrogen (NH4+-N) showed a significant positive correlation with microbial Shannon diversity index and AWCD value. There was a negative correlation between the microbial Simpson index and soil nitrate nitrogen (NO3--N). Soil pH, NH4+-N and NO3--N were the main factors affecting diversity index of microbial communities. The results suggested that there were significant differences in microbial community characteristics of forest soil in urban-rural environmental gradient forests, and that the metabolic potential and functional diversity of soil microbial community in urban forests were weaker than that of natural forests.

[Dynamics of soil respiration and its influencing factors in urban forests under nitrogen addition]. / æ°®æ·»åŠ ä¸‹åŸŽå¸‚æ£®æž—åœŸå£¤å‘¼å¸åŠ¨æ€å˜åŒ–åŠå ¶å½±å“å› ç´ .

Urban forest is an important carbon pool, soil respiration of which is an important part of terrestrial carbon cycle. To understand the dynamics and influencing factors of soil respiration in urban forest under the background of increasing nitrogen deposition, we conducted dynamic observation on soil respiration rate, temperature, moisture and chemical properties by adding 0 (CK), 50 (LN), 100 (HN) kg N·m-2·a-1 ammonium nitrate to a typical urban forest. The results showed that soil respiration had significant seasonal variation, which was not affected by nitrogen addition. Soil respiration was significantly correlated with soil temperature. The interaction between soil temperature and soil moisture could better explain the variation of soil respiration. Nitrogen addition changed temperature sensitivity of soil respiration, with the order of Q10 values as LN (2.12) > CK (2.10) > HN (2.05). Soil nitrate concentration, soil soluble organic carbon, pH, soil carbon to nitrogen ratio had significant correlation with soil respiration. The positive effect of nitrogen deposition on soil respiration was mainly in the growing season, with slightly inhibitive effect in the non-growing season.

Adsorption of Cd(II) by two variable-charge soils in the presence of pectin.

Batch experiments were conducted to investigate cadmium(II) (Cd(II)) adsorption by two variable-charge soils (an Oxisol and an Ultisol) as influenced by the presence of pectin. When pectin dosage was less than 30 g kg(-1), the increase in Cd(II) adsorption with the increasing dose of pectin was greater than that when the pectin dosage was >30 g kg(-1). Although both Langmuir and Freundlich equations fitted the adsorption isotherms of Cd(II) and electrostatic adsorption data of Cd(II) by the two soils well, the Langmuir equation showed a better fit. The increase in the maximum total adsorption of Cd(II) induced by pectin was almost equal in both the soils, whereas the increase in the maximum electrostatic adsorption of Cd(II) was greater in the Oxisol than in the Ultisol because the former contained greater amounts of free Fe/Al oxides than the latter, which, in turn, led to a greater increase in the negative charge on the Oxisol. Therefore, the presence of pectin induced the increase in Cd(II) adsorption by the variable-charge soils mainly through the electrostatic mechanism. Pectin increased the adsorption of Cd(II) by the variable-charge soils and thus decreased the activity and mobility of Cd(II) in these soils.

Effect of pectin on adsorption of Cu(II) by two variable-charge soils from southern China.

The influence of pectin on Cu(II) adsorption by two variable-charge soils (an Oxisol and an Ultisol) was investigated. Pectin increased the adsorption, and the extent of adsorption increased linearly with the dose of pectin, being greater in the Oxisol than that in the Ultisol because the adsorption of pectin by the Oxisol was greater. Both Langmuir and Freundlich equations fitted the adsorption isotherms of Cu(II) for both soils well. The fitting parameters of both equations indicated that pectin increased not only the adsorption capacity of the soils for Cu(II) but also the adsorption strength of Cu(II). The effect of pectin decreased with rising pH in the pH range 3.5-6.0, although the extent of electrostatic adsorption of Cu(II) by both soils was markedly greater over the pH range. Fourier-transformed infrared spectroscopy analysis and zeta potential measurement of soil colloids indicated that adsorption of pectin by the soils made the negative charge on both soils more negative, which was responsible for the increase in the electrostatic adsorption of Cu(II) induced by the addition of pectin. In conclusion, pectin-enhanced adsorption of Cu(II) especially at low pH would be beneficial to the soils as it would decrease the activity and mobility of Cu(II) in acidic variable-charge soils.

Subacute toxicity of copper and glyphosate and their interaction to earthworm (Eisenia fetida).

Glyphosate (GPS) and copper (Cu) are common pollutants in soils, and commonly co-exist. Due to the chemical structure of GPS, it can form complexes of heavy metals and interface their bioavailability in soil environment. In order to explore the interactions between GPS and Cu, subacute toxicity tests of Cu and GPS on soil invertebrate earthworms (Eisenia fetida) were conducted. The relative weight loss and whole-worm metal burdens increased significantly with the increasing exposure concentration of Cu, while the toxicity of GPS was insignificant. The joint toxicity data showed that the relative weight loss and the uptake of Cu, as well as the superoxide dismutase, catalase and malondialdehyde activities, were significantly alleviated in the present of GPS, which indicated that GPS could reduce the toxicity and bioavailability of Cu in the soil because of its strong chelating effects.

Does glyphosate impact on Cu uptake by, and toxicity to, the earthworm Eisenia fetida?

Glyphosate (GPS) is a wildly-used pesticide throughout the world. It affects metal behaviors in soil-water system as its functional groups such as amine, carboxylate and phosphonate can react with metal ions to form metal complexes. The reaction will result in the decreasing of heavy metal bioavailability. A laboratory experiment was conducted to investigate the interactions between GPS and copper (Cu) on the acute toxicity of soil invertebrate earthworm (Eisenia fetida), which was exposed to aqueous solutions for 48 h with different mixing concentrations of Cu and GPS (technical-grade Gly acid). The mortality rates, Cu uptake by earthworm, and some biomarkers such as superoxide dismutase (SOD) activity, glutathione (GSH) content, and acetylcholinesterase (AchE) activity were measured. The mortality rates and whole-worm metal burdens increased significantly with the increasing Cu concentration in solution. However, toxicity of GPS to earthworms was not observed in this study. Furthermore, the presence of GPS could significantly reduce the acute toxicity of Cu to earthworms. The mortality rates decreased sharply and the uptake of Cu was nearly halted in the presence of GPS. In addition, the SOD activity, GSH content, and AchE activity almost declined to the levels of the control. These results demonstrate that GPS could control the toxicity as well as the bioavailability of heavy metals in soil solutions where both GPS and heavy metals often coexist.

Persistence and dissipation of synthetic pyrethroid pesticides in red soils from the Yangtze River Delta area.

Laboratory incubation trials were conducted to investigate the effects of several factors on the persistence as well as the dissipation of three synthetic pyrethroid pesticides in red soils obtained from the Yangtze River Delta region in China. The pyrethroids selected for investigation were cypermethrin, fenvalerate, and deltamethrin, which continue to be used extensively to control pests on farmland in the region despite the concern that they are highly toxic to certain vertebrate and mammalian species. Data from this exploratory study showed that the dissipation half-lives (T (1/2)) tended to correlate with soil pH and soil organic matter contents, but not with soil cation-exchange capacity. The T (1/2) values were seen to be shorter in soil samples fertilized with glucose than without. The rates of pyrethroid dissipation also tended to increase with increasing initial soil concentration, but were largely unaffected by whether the pesticides were present in the soil separately or as a mixture. Another noteworthy observation is that microbial activity appeared to dominate the degradation process. Findings of this type could offer valuable clues for future research directions in reducing pesticide persistence in soil, which in turn could lead to the ultimate reduction of environmental pollution caused by pyrethroid application to farmland in the region.