1,210 publications from this institution
There is a major knowledge gap concerning the extent of microplastic pollution in agronomic regions of China, which represent a plastic use hotspot. This study investigated the characteristics of microplastics distributed in agricultural soils of three typical regions (Beijing (BJ), Shandong (SD), and Xinjiang (XJ)) with two plastic film mulching modes (greenhouse (G) and conventional field-based film mulching (M)) in China. The average abundance of microplastic under G and M mode was 3.60×104 particles kg-1 and 3.01×104 particles kg-1, respectively; and the estimated weight of microplastics per kg of dry soils in BJ, SD, and XJ was 3.12 mg kg-1, 5.63 mg kg-1, and 7.99 mg kg-1, respectively. Microplastics in farmland were mainly of a small particle size (50 to 250 μm), with their abundance decreasing with increasing particle size. Among the microplastics detected, polyethylene and polypropylene were the two dominant types present, accounting for 50.0% and 19.7%, respectively. In addition, plastic film mulching mode (G vs. M) had a stronger effect on microplastic distribution than agronomic region. This research provides key data to support the development of guidelines for the sustainable use of agricultural plastic film and an assessment of the environmental risk of microplastics.
Summary The amount of carbon (C) stored in soil is an important regulator for the global climate and soil fertility and is the balance between formation and decomposition of soil organic matter ( SOM ). Decomposition of SOM can be powerfully affected by labile carbon (C) supplements in, for example, the rhizosphere. A stimulation of SOM mineralisation induced by labile C additions is termed ‘priming’, and the mechanisms for this phenomenon remain elusive. The most widely held explanation assigns priming to successional dynamics in r ‐ and K ‐selected groups within the microbial community; groups which have also been connected with fungal ( K ‐selected) and bacterial ( r ‐selected) decomposers. New evidence has also suggested that recently formed SOM is particularly sensitive to priming. We investigated (i) the labile C concentration dependence of SOM mineralisation, (ii) the susceptibility of differently aged SOM to priming and (iii) if priming is due to bacterial or fungal growth dynamics. To create an age gradient of traceable SOM , we spiked a pasture soil using 14 C glucose, and subsampled plots 1 day, 2 months, 5 months and 13 months after application (i.e. SOM aged 1 day – 13 months). Glucose (0–4000 μg C g −1 ) was added in subsequent laboratory experiments, and respiration, SOM mineralisation ( 14 CO 2 evolution), bacterial growth rates (leucine incorporation) and fungal biomass (ergosterol) were tracked during ca. 1 week. Mineralisation of SOM aged 2–13 months showed similar labile C concentration dependencies, and priming increased mineralisation of SOM systematically by up to 350%. The glucose treatments induced variable microbial growth responses for differently aged SOM , which were unrelated to the priming effect. That successional dynamics in microbial r ‐ and K ‐selected groups, or bacterial and fungal decomposers, respectively, underpinned priming was incompatible with the results obtained. An alternative explanation could be that SOM transformation by extracellular enzymes, for subsequent respiration, could be triggered by labile C. In conclusion, labile C primed the mineralisation of 2–13 months aged SOM , and the mechanism for this priming was unrelated to microbial growth dynamics.
The use of plastic much films has been fundamental to promoting food production in many regions of the world. However, concern is growing about the progressive accumulation of plastic residues in soil after crop harvest and its subsequent impact on soil health and potential to enter the food chain. Although biodegradable films have been developed to prevent these problems, it is still unclear whether they are environmentally benign. Here we evaluated the physical and chemical breakdown of four commercial poly(butylene adipate-co-terephthalate) based biodegradable mulch films (BMF1, BMF2, BMF3 and BMF4) in an agricultural soil over a 26-month period. Based on visual examination, degradation followed the series BMF4 > BMF1, BMF2 > BMF3. Importantly, microplastic residues (fragments <5 mm) still remained in the soil of all 4 plastic types after 2 years, suggesting that they are likely to accumulate over time if used on an annual basis. Viscosimetry, Fourier transform infrared (FTIR) spectroscopy and Thermogravimetric Analysis (TGA) were used to characterise the breakdown process. Our results indicated that the degradation of the mulch film after burial in agricultural soil may be linked to the nature of the polymer but also to its manufacturing formulation. Although the peak changes of polyester in the infrared spectrum were not distinct, the plastic films showed other signs of degradation including a reduction in intrinsic viscosity after burial in soil. The different degradation rates of BMF1 and BMF2 at the molecular level may be due to the different CaCO3 contents. In conclusion, under field conditions, we show that slight variations in the formulations of commercial biodegradable mulch films leads to very different persistence rates in soil. Further, we conclude that their slow rate of degradation will ultimately lead to their progressive accumulation in soil if used repeatedly.
Sustainable plant establishment on ore processing residues requires development of a functional soil, which includes the introduction of organic matter and reestablishment of active microbial communities. This study investigated the development of microbial diversity and function in residue sand generated from alumina refining of mined bauxite ore. The residue sand embankments underwent rehabilitation with native vegetation over time, allowing study of a 3‐year chronosequence using space‐for‐time substitution. A coastal dune ecosystem was used as a natural alkaline sand analog with which to compare residue properties. Microbial biomass carbon in the residue sands were typically well below that of the coastal sand analog (< 50 mg kg −1 in residue sand compared to circa 450 mg kg −1 in coastal sand). Although the size of the microbial biomass appeared to be limited by the low organic matter content of the residue sand, a decline in microbial metabolic quotient indicated a potential alleviation of microbial stress with rehabilitation age. Despite the low microbial biomass, the ability of the residue sand microbial community to function with respect to the metabolism of added amino acids developed rapidly. Contrary to our original hypothesis, the diversity of the bacterial and fungal community also developed rapidly, and was similar to, or higher than, the coastal sand analog in 0.5‐year‐old rehabilitation. However, the bacterial, and in particular the fungal, community structure within residue sands were significantly different to that of the coastal sand analog with shifts in community structure driven, in part, by changing physicochemical conditions.
The kinetics and characteristics of malate degradation were studied in four acid soils ranging in both pH (4.30 to 5.00) and vegetation type. The breakdown
Many temperate agricultural soils have prolonged periods in the winter when plant carbon inputs to the soil are low. Soil maintained at low temperature in the absence of plants was used to simulate the conditions in a vineyard soil during winter. In a four month simulated overwintering period we showed that the concentration of dissolved organic carbon and nitrogen in soil solution slowly declined alongside heterotrophic soil respiration. Measurements of free amino acid concentrations and turnover indicated that the amino acid pool in soil was rapidly depleted but readily replenished throughout the four-month period. This indicates that the soil contained intrinsic reserves of labile C that was capable of supporting the soil microbial community in times of reduced plant C inputs.
This encyclopedia is really two books: the first is a guide to the botany, cultivation, propagation, and pests and diseases of ferns; and the second half, Ferns to Grow, provides growing information for hundreds of species.
Simple laboratory methods have been developed for studying, under defined conditions, the colonization of cellulose substrata by soil micro-organisms. The substratum is placed on the surface of soil samples in Petri dishes and colonization followed by direct microscopic examination in situ and also by removing small pieces of colonized material for more critical study. Such factors as soil moisture, nutrient status and pH may be varied and their influence determined. In our studies the cellulose used was lens tissue and soil moisture was always maintained at ‘field capacity’. The factors varied were pH, nitrate and phosphate. The detailed effects of varying these factors depended on soil type but a striking feature was the small range of cellulolytic species found in any treatment. Generally, only one or two species were actively involved. The treatments all produced marked and consistent changes in the qualitative composition of the colonizing cellulolytic flora. These results emphasize the precise control of the environment in selecting individual members from a group of soil organisms all competent to degrade a particular substrate. They also have implications for the study of micro-environments in the soil. It is generally considered that the soil constitutes a mosaic of environments usually of too small a size for detailed analysis. By extension of the methods adopted here it appears that it would be possible to create on a sufficiently large scale a great many of the situations which occur naturally on only a micro-scale.
