[Effects of Long-term Biochar Addition on Denitrification N2O Emissions from Bacteria and Fungi in Paddy Soil].

Denitrification driven by bacteria and fungi is the main source of nitrous oxide （N2O） emissions from paddy soil. It is generally believed that biochar reduces N2O emissions by influencing the bacterial denitrification process, but the relevant mechanism of its impact on fungal denitrification is still unclear. In this study, the long-term straw carbonization returning experimental field in Changshu Agricultural Ecological Experimental Base of the Chinese Academy of Sciences was taken as the object. Through indoor anaerobic culture and molecular biology technology, the relative contributions of bacteria and fungi to denitrifying N2O production in paddy soil and the related microorganism mechanism were studied under different long-term biochar application amounts （blank, 2.25 t·hm-2, and 22.5 t·hm-2, respectively, expressed by BC0, BC1, and BC10）. The results showed that compared with that in BC0, biochar treatment significantly reduced N2O emission rate, denitrification potential, and cumulative N2O emissions, and the contribution of bacterial denitrification was greater than that of fungal denitrification in all three treatments. Among them, the relative contribution rate of bacterial denitrification in BC10 （62.9%） was significantly increased compared to BC0 （50.8%）, whereas the relative contribution rate of fungal denitrification in BC10 （37.1%） was significantly lower than that in BC0 （49.2%）. The application of biochar significantly increased the abundance of bacterial denitrification functional genes （nirK, nirS, and nosZ） but reduced the abundance of fungal nirK genes. The contribution rate of fungal denitrification was significantly positively correlated with the N2O emission rate and negatively correlated with soil pH, TN, SOM, and DOC. Biochar may have inhibited the growth of denitrifying fungi by increasing pH and carbon and nitrogen content, reducing the abundance of related functional genes, thereby weakening the reduction ability of NO to N2O during fungal denitrification process. This significantly reduces the contribution rate of N2O production during the fungal denitrification process and the denitrification N2O emissions from paddy soil. This study helps to broaden our understanding of the denitrification process in paddy soil and provides a theoretical basis for further regulating fungal denitrification N2O emissions.

[Effects of Low-density Polyethylene Microplastics on the Growth and Physiology Characteristics of Ipomoea aquatica Forsk].

Microplastic pollution in soil and its toxicological effects have attracted increasing attention from researchers, but the mechanisms of microplastics affecting crop growth and physiology remain unclear. A pot experiment was conducted to evaluate the impacts of various mass concentrations (0%, 0.2%, 5%, and 10%) of low-density polyethylene microplastics (LDPE MPs) on the germination rate, photosynthetic pigment content, biomass, antioxidant enzyme activity, soluble protein, and soluble sugar content of water spinach (Ipomoea aquatica Forsk). The results showed that LDPE MPs significantly inhibited (P<0.05) the seed vigor of water spinach, and the inhibitory effect increased with increasing concentration of LDPE MPs. However, the 5% LDPE MPs significantly promoted the aboveground biomass of water spinach. The 0.2% and 10% LDPE MPs significantly improved the superoxide dismutase (SOD) activity and catalase (CAT) and peroxidase (POD) activities, respectively. Further, malondialdehyde (MDA) content decreased with increasing concentration of LDPE MPs, and the reductions reached 15.53%-27.39% in comparison to that in the control. The LDPE MPs also significantly increased the soluble sugar content of water spinach leaves. In summary, LDPE MPs could inhibit the seed vigor and promote biomass accumulation in water spinach. Water spinach could relieve the oxidative stress caused by LDPE MPs by regulating antioxidant enzyme activity and soluble protein content. Therefore, this study may provide basic information for assessing the influences of microplastics on vegetables.

Effects of maize straw and its biochar application on soil organic carbon chemical composition and carbon degradation genes in a Moso bamboo forest.

We investigated the effects of maize straw and its biochar application on soil organic carbon chemical composition, the abundance of carbon degradation genes (cbhI) and the composition of cbhI gene community in a Moso bamboo forest, to provide the theoretical and scientific basis for enhancing carbon sequestration. We conducted a one-year field experiment in a subtropical Moso bamboo forest with three treatments: control (0 t C·hm-2), maize straw (5 t C·hm-2), and maize straw biochar (5 t C·hm-2). Soil samples were collected at the 3rd and 12th months after the treatment. Soil organic carbon chemical composition, the abundance and community composition of cbhI gene were determined by solid-state 13C NMR, real-time fluorescence quantitative PCR, and high-throughput sequencing, respectively. The results showed that compared with the control, maize straw treatment significantly increased the content of O-alkyl C and decreased aromatic C content, while maize straw biochar treatment showed an opposite effect. Maize straw treatment significantly increased the abundance of cbhI gene and the relative abundance of Penicillium, Gaeumannomyces and Marasmius. However, maize straw biochar treatment reduced the abundance of this gene. The relative abundance of dominant cbhI in soils was positively correlated with the content of O-alkyl C and negatively correlated with the content of aromatic C. Results of redundancy analysis showed that maize straw treatment had a significant effect on the microbial community composition of cbhI gene by changing soil O-alkyl C content, while maize straw biochar affected the microbial community composition of cbhI gene by changing soil pH, organic carbon, and aromatic C content. Maize straw biochar treatment was more effective in increasing soil organic carbon stability and reducing microbial activity associated with carbon degradation in the subtropical Moso bamboo forest ecosystem compared with maize straw treatment. Therefore, the application of biochar has positive significance for maintaining soil carbon storage in subtropical forest ecosystems.

Effects of plant residues on C:N:P of soil, microbial biomass, and extracellular enzyme in an alpine mea-dow on the Qinghai-Tibetan Plateau, China.

Plant residues can affect C:N:P of soil, microbial biomass, and extracellular enzyme, but the effects are still unclear. We conducted a field experiment in an alpine meadow on the eastern part of the Qinghai-Tibetan Plateau to explore the effects of removing aboveground plant or roots and adding plant residues on the C:N:P of soil, microbial biomass, and extracellular enzyme. The results showed that removing aboveground plant biomass significantly decreased soil C:N (the change was -23.7%, the same below) and C:P (-14.7%), microbial biomass C:P and N:P, while significantly increased microbial biomass C:N, and enzyme C:N:P compared with meadow without human disturbance. Removing all plant biomass (aboveground and roots) significantly reduced soil C:N (-11.6%), C:P (-24.0%), N:P (-23.3%) and microbial biomass C:N in comparison to removing aboveground plant, while significantly improved microbial biomass N:P and enzyme N:P. Adding plant residues after removing aboveground plant significantly increased microbial biomass C:N and C:P, enzyme C:N compared with removing aboveground plant, while significantly decreased enzyme N:P. Compared with removing all the plant, adding plant residues after removing whole plant significantly reduced soil C:N (-16.4%), microbial biomass C:P, N:P and enzyme N:P, while significantly increased enzyme C:N. Our results suggest that removal of plants could have a strong effect on C:N:P of soil, microbial biomass, and extracellular enzyme, and C:N:P of microbial biomass and that extracellular enzyme woule be more sensitive to plant residues. Roots could play a key role in stabilizing C:N:P of soil, microbial biomass, and extracellular enzyme under plant residues addition. Adding plant residues could be a suitable solution for restoring alpine meadows under the circumstance of intact roots, which was conducive to soil C storage, but might not be suitable for alpine meadows with serious root damage, which would increase soil CO2 emission.

[Short-term nitrogen deposition changes chemical composition of litter and soil organic matter in a Moso bamboo forest]. / 短期氮沉降改变毛竹林凋落物和土壤有机质化学组成.

To investigate the effects of short-term nitrogen (N) deposition on organic matter composition of litter and soil in Moso bamboo (Phyllostachys edulis) forests, we established a N-addition treatments (50 kg N·hm-2·a-1) to simulate the ambient and N deposition in a subtropical Moso bamboo forest from July 2020 to January 2022. We analyzed the organic matter composition of Moso bamboo leaf/root litter and soil by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique. The results showed that short-term N deposition significantly increased the relative content of soil phenols by 50.9%, while significantly decreased fatty acids by 26.3%. The rela-tive content of alkanes & alkenes and lignin in leaf litter was significantly increased by 51.9% and 33.5%, respectively, while that of phenols and polysaccharides significantly decreased by 52.2% and 56.3%. In root litter, eleva-ted N significantly decreased the relative content of polycyclic aromatic hydrocarbons by 16.6%. Moreover, the relative content of fatty acids in soil organic matter was significantly positively correlated with the relative content of poly-saccharides in leaf litter. The relative content of phenols in soil organic matter was significantly positively correlated with the relative content of lignin, and negatively correlated with the relative content of polysaccharides in leaf litter. Our results demonstrated that short-term N deposition did not change the concentration of total organic carbon, total nitrogen, and C/N of the soil, leaf litter, and root litter, but significantly altered the chemical composition of organic matter. In addition, the changes in chemical composition of organic matter in soil under short-term N deposition were affected by the composition of organic matter in leaf litter.

[Effects of the removal of invasive Moso bamboo on soil microbial biomass and enzyme activities in subtropical forests]. / å ¥ä¾µæ¯›ç«¹çš†ä¼å¯¹äºšçƒ­å¸¦æ£®æž—åœŸå£¤å¾®ç”Ÿç‰©ç”Ÿç‰©é‡å’Œé ¶æ´»æ€§çš„å½±å“.

Removal of invasive plant species is the first step to restoring the invaded ecosystems. The soil microbial biomass and extracellular enzyme activities were measured in Moso bamboo (Phyllostachys edulis) pure forest (completely invasion), invasive P. edulis removal forest (secondary succession 5 years after clear cutting), and the evergreen broadleaved forest (no invasion) in Tianmu Mountain. The results showed that compared with P. edulis pure forest, invasive P. edulis removal significantly increased the contents of soil organic carbon (SOC), nitrate nitrogen, available phosphorus and potassium, as well as microbial biomass carbon (MBC) and microbial biomass phosphorus (MBP), while significantly decreased microbial biomass nitrogen (MBN). The activities of α-glucosidase (AG), ß-glucosidase (BG), leucine aminopeptidase (LAP) and phenol oxidase (POX) in the forest with removal of invasive P. edulis were significantly higher than those in P. edulis pure forest, while invasive P. edulis removal did not change the activities of cellodisaccharide hydrolase (CBH), ß-N-acetyl-glucosaminopeptidase (NAG), acid phosphatase (ACP) and peroxidase (PER). Furthermore, the activities of AG, BG and LAP were positively correlated with SOC and MBC, while the increase in POX activity was positively correlated with soil nitrate content. In addition, MBC, MBN and MBP, and activities of AG, BG, NAG, LAP and ACP in P. edulis removal forest forest were significantly higher than those in evergreen broadleaved forests. Taken together, the removal of invasive P. edulis could increase soil nutrient contents, microbial biomass and extracellular enzyme activities, thus could be considered as an effective way to restore the invaded forests. Our results provide important theoretical basis for controlling P. edulis invasion in subtropical forests.

[Characteristics and Drivers of Dissolved Carbon Dioxide and Methane Concentrations in the Nantiaoxi River System in the Upper Reaches of the Taihu Lake Basin During Summer-Autumn].

Inland waters are vital sinks for active carbon (C) and potential sources of greenhouse gas emissions. In this study, the characteristics of dissolved carbon dioxide (CO2) and methane (CH4) concentrations in the Nantiaoxi River system in the upper reaches of the Taihu Lake basin were observed between Jul. 2019 and Nov. 2019 (summer and autumn) using headspace equilibration-gas chromatography. Simultaneously, physical and chemical parameters were also determined to understand the factors influencing dissolved CO2 and CH4 concentrations. The results showed that the mean dissolved CO2 concentrations and saturation levels in water were (505.47±16.99) µg·L-1 and (256.31±8.32)%, respectively, and the corresponding values for CH4 were (1.88±0.09) µg·L-1 and (5218.74±264.30)%, respectively. The saturation levels of dissolved CO2 and CH4 at all observation points were greater than 100%, indicating that the Nantiaoxi River system is a potential source of CO2 and CH4. The highest mean dissolved CO2 concentrations in water were found in agricultural areas followed by residential and forest areas, and there were significant differences among the three land-use types. The mean dissolved CH4 concentrations in the water in residential areas were significantly higher than those in agricultural area forest areas. The dissolved CO2 concentrations, saturation levels of CO2, dissolved CH4 concentrations, and saturation levels of CH4 in water were all negatively correlated with oxidation reduction potential (ORP) (P<0.01) and positively correlated with electrical conductivity (EC) (P<0.01). The discrepancies in chlorophyll (Chl-a), nitrate (NO3--N), total nitrogen (TN), and EC were the main reasons for differences in dissolved CO2 concentrations among the different land use types. Phytoplankton growth could be promoted by the higher input of nitrogen pollutants into rivers in agricultural and residential areas, and respiration could be also enhanced, resulting in higher dissolved CO2 concentrations. The higher concentrations of dissolved organic carbon (DOC) and ammonium nitrogen (NH4+-N) in the water, and the water temperature in residential areas, were probably the main causes of the higher dissolved CH4 concentrations. Rainfall also had some influence on dissolved CO2 and CH4 concentrations in the water associated with the different land use types. Specifically, higher concentrations of nitrogen pollutants and the enhancement of DOC were the main drivers of high dissolved CO2 concentrations in agricultural areas as well as the higher dissolved CH4 concentrations in residential areas following rainfall events.

[Soil denitrifying enzyme activity and its influencing factors in a bamboo forest riparian zone in the upper reaches of the Taihu Lake Basin, China]. / å¤ªæ¹–æµåŸŸä¸Šæ¸¸ç«¹æž—æ²³å²¸å¸¦åœŸå£¤åç¡åŒ–é ¶æ´»æ€§åŠå ¶å½±å“å› ç´ .

Soil denitrifying enzyme activity (DEA) was measured by acetylene inhibition technique, along with exploration of factors influencing DEA in a bamboo forest riparian zone in the upper reaches of the Taihu Lake Basin during summer. Our aim was to provide important insights into the assessment of ecological functions of bamboo forest riparian zone on reducing nitrogen pollution in rivers. The results showed that the riparian soil DEA ranged from 6.32 to 23.22 µg N·kg-1·h-1, with a mean value of 14.65 µg N·kg-1·h-1. The vertical distribution (0-40 cm soil profile) of DEA was affected by several factors, such as soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO3--N), soil water content, and activity of carbon and nitrogen hydrolase, which resulted in decreased DEA with increasing soil depth. The horizontal changes in DEA (at the same soil depth but at different distances from river) was mainly governed by the variation in SOC concentration. In this area, the concentration of soil dissolved organic carbon was relatively low, which might inhibit the soil DEA during summer.

[Effects of nitrogen deposition and biochar application on soil N2O fluxes in a Moso bamboo plantation]. / 氮沉降和施生物质炭对毛竹林土壤N2O通量的影响.

In July 2019-July 2020, we conducted a field trial to examine the effects of nitrogen addition (60 kg N·hm-2·a-1), biochar application (10 t·hm-2), and their combination on soil N2O emission and the relationship between soil N2O emission and environmental factors in a typical Moso bamboo (Phyllostachys edulis) plantation in Hangzhou City of Zhejiang Province. Soil N2O flux of Moso bamboo plantation was measured by the static chamber-gas chromatography technique. The results showed that nitrogen addition treatment increased the annual cumulative N2O emission by 14.6%, while biochar application and the combination treatment reduced it by 20.8% and 10.6%, respectively. Soil N2O flux rate was significantly correlated with soil temperature, NO3--N concentration, urease and protease activities, and soil NH4+-N concentration across all treatments. In conclusion, under the background of nitrogen deposition, the application of biochar would have a significant reduction effect on soil N2O fluxes in Moso bamboo plantations.

[Relationships of soil physical and microbial properties with nitrous oxide emission under effects of freezing-thawing cycles].

Freezing-thawing cycles often occurs in the regions of mid-high latitude and high altitude. This process can affect soil physical and biological properties, e.g., soil water status, aggregate stability, and microbial biomass and community structure. Under its effects, the bio-indicators of soil microbes, i.e., the kinds and quantities of some specific amino sugars varied, and the course and intensity of soil nitrogen transformation changed, which resulted in an increase of nitrous oxide (N2O) production and emission, and made the soil be a major source of N2O emission. This paper summarized the research progress on the aspects mentioned above, with the further research directions on the theoretical problems of soil N2O production and emission under effects of freezing-thawing suggested.