Predicting the Stability of Organic Matter Originating from Different Waste Treatment Procedures.

Recycling organic wastes into farmland faces a double challenge: increasing the carbon storage of soil while mitigating CO2 emission from soil. Predicting the stability of organic matter (OM) in wastes and treatment products can be helpful in dealing with this contradiction. This work proposed a modeling approach integrating an OM characterization protocol into partial least squares (PLS) regression. A total of 31 organic wastes, and their products issued from anaerobic digestion, composting, and digestion-composting treatment were characterized using sequential extraction and three-dimension (3D) fluorescence spectroscopy. The apportionment of carbon in different fractions and fluorescence spectra revealed that the OM became less accessible and biodegradable after treatments, especially the composting. This was proven by the decrease in CO2 emission from soil incubation. The PLS model successfully predicted the stability of solid digestate, compost, and compost of solid digestate in the soil by using only the characterized variables of non-treated wastes. The results suggested that it would be possible to predict the stability of OM from organic wastes after different treatment procedures. It is helpful to choose the most suitable and economic treatment procedure to stabilize labile organic carbon in wastes and hence minimize CO2 emission after the application of treatment products to the soil.

Response of Bacterial Community to the Occurrence of Clubroot Disease in Chinese Cabbage.

Clubroot disease is a common soilborne disease caused by Plasmodiophora brassicas Wor. and widely occurs in Chinese cabbage. Soil microorganisms play vital roles in the occurrence and development of plant diseases. The changes in the soil bacterial community could indicate the severity of plant disease and provide the basis for its control. This study focused on the bacterial community of the clubroot disease-infected soil-root system with different severity aiming to reveal the composition and structure of soil bacteria and identified potential biomarker bacteria of the clubroot disease. In the clubroot disease-infected soil, the bacterial community is mainly composed of Actinobacteria, Gammaproteobacteria, Alphaproteobacteria, Bacilli, Thermolrophilia, Bacteroidia, Gemmatimonadetes, Subgroup_6, Deltaproteobacteria, KD4-96, and some other classes, while the major bacterial classes in the infected roots were Oxyphotobacteria, Gammaproteobacteria, Alphaproteobacteria, Actinobacteria, Bacilli, Bacteroidia, Saccharimonadia, Thermoleophilia, Clostridia, Chloroflexia, and some other classes. The severe clubroot disease soil-root system was found to possess a poorer bacterial richness, evenness, and better coverage. Additionally, a significant difference was observed in the structure of the bacterial community between the high-severity (HR) and healthy (LR) soil-root system. Bacillus asahii and Noccaea caerulescens were identified as the differential bacteria between the LR and HR soil and roots, respectively. pH was demonstrated as a vital factor that was significantly associated with the abundance of B. asahii and N. caerulescens. This study provides novel insight into the relationship between soil bacteria and the pathogen of clubroot disease in Chinese cabbage. The identification of resistant species provides candidates for the monitoring and biocontrol of the clubroot disease.

Characterizing ammonia emissions from water bodies using dynamic floating chambers.

Ammonia (NH3) is the most important alkaline gas in the atmosphere and plays a central role in atmospheric pollution and the global N cycle. Water bodies receive increasing nitrogen inputs from effluents and atmospheric deposition due to anthropogenic activities and are regarded as the major natural NH3 and NH4+ sinks. In this work, floating dynamic flux chambers were deployed at four types of freshwater (rivers, large reservoirs, medium-sized reservoirs and ponds) systems and a coastal seawater system to estimate the water-air NH3 emission fluxes. The NH3 emission fluxes of rivers (26.4 µg NH3 m-2 h-1) were significantly higher than those of other types of freshwater systems, and the NH3 flux of offshore water was unexpectedly high (3.9 µg NH3 m-2 h-1). The ammonium content and water temperature were the most important factors driving NH3 emissions from water bodies. The global NH3 emissions from water bodies reached 8.88 TgN a-1, and this value will increase persistently with global warming and water quality deterioration. Water bodies that are relatively eutrophic and directly affected by anthropogenic activities should be considered reservoirs of inputted N instead of permanent sinks.