Modeling N_2O Emissions from Agricultural Fields in Southeast China

DNDC, a rainfall-driven and process-oriented model of soil carbon and nitrogenbiogeochemistry, is applied t0 simulate the nitrous oxide emissions from agricultural ecosystem inSoutheast China. We simulated the soil N2O emission during a whole rice-wheat rotation cycle(from Nov. 1, 1996 to Oct. 31, 1997) under three different conditions, which are A) no fertilizer, B)both chemical fertilizer and manure and, C) chemical fertiliser only. The processes ofN2O emission were discussed in detail by comparing the model outputs with the results from fieldmeasurement. The comparison shows that the model is good at simulating most of theNzO emission pulses and trends. Although the simulated N2O emission fluxes are generally lessthan the measured ones, the model outputs during the dryland period, especially during the wheatreviving and maturing stages in spring, are much better than those during the paddy field period.Some sensitive experiments were made by simulating the N2O emissions in spring, when there is asmallest gap between the simulated fluxes and the measured ones. Meanwhile, the effects of someimportant regulating factors, such as the rainfall N deposition by rainfall, temperature, tillage, nitrogen fertilizer and manure application on N2O emission during this period were analyzed. Fromthe analysis, we draw a conclusion that soil moisture and fertilization are the most important regulating factors while the N2O emission is sensitive to some other factors, such as temperature, manure, tillage and the wet deposition of atmospheric nitrate.

A Review of Research on Agroecosystem Services Based on Bibliometric Analysis

Agricultural ecosystem is one of the most important ecosystems in the world,which provides multiple ecosystem services such as grain produc­tion,climate regulation,water conservation and biodiversity.The degrada­tion of ecosystem services has become an important factor that severely re­stricts the sustainable development of agriculture.Agroecosystem services have become the core and hot topic of ecological research.In recent years,countries and related institutions have been increasing their research on agricultural ecosystem service.Based on Web of Science(WoS)and China Knowledge Resource Integrated(CNKI)databases,the development char­acteristics and trends of agroecosystem services research were analyzed by bibliometric methods.The results show that:(1)The number of papers on agroecosystem services is increasing,which shows that the research on it is developing.(2)Developed countries are the main research forces in the field of ecosystem services,and the developed countries in Europe and the United States occupy the absolute leading position;China Agricultural Uni­versity and the University of California in the United States are the main research institutions.(3)At present,eight research hotspots in this field are the study of ecosystem services mechanism,protection management and sustainability,sustainable development,biodiversity,land use and land­scape change,value assessment,climate change,sustainable development of agriculture,ecological compensation.From the overall distribution of research hotspots in each period,the international research focuses more on the interdependence between ecosystem services and ecosystem services and human well-being,while the research in China focuses more on eco­system services assessment.(4)In recent years,there is a big gap between China and foreign countries in the field of ecosystem services research.It is necessary to strengthen cooperation with research institutions in developed countries in Europe and the United States,and further improve the research content,research vision and research methods.

Precipitation regulated soil nematode community and footprint in cropland ecosystems

●Nematode abundance and footprint show unimodal patterns with precipitation levels.●MAP governed nematode diversity along the precipitation gradient of agroecosystem.●Soil pH determined nematode abundance and footprint in low precipitation levels.Precipitation plays a crucial role in global biodiversity change across terrestrial ecosystems.Precipitation is proven to affect soil organism diversity in natural ecosystems.However,how precipitation change affects the function of the soil nematode community remains unclear in cropland ecosystems.Here,we tested soil nematode communities from different precipitation sites(300 mm to 900 mm)of the agricultural ecosystem.The abundance of total nematodes,fungivores,and plant parasites,together with the footprint of fungivores was significantly affected by mean annual precipitation(MAP)in cropland ecosystem.Plant parasites diversity and footprint showed negative relationships with MAP.The random forest suggested plant parasite footprint was the most responsive to MAP.The structural equation model revealed that MAP affected nematode abundance and footprint indirectly via soil pH;nematode diversity was affected by MAP directly.We conclude that precipitation could act as the main selection stress for nematode diversity among the large gradient of agricultural ecosystems.However,the soil pH may act as a stress factor in determining nematode community and carbon flow in the soil food web.Our study emphasized that using nematode value by trophic group would provide a deep understanding of nematode response to precipitation in cropland ecosystems.

Heavy metals potentially drive co-selection of antibiotic resistance genes by shifting soil bacterial communities in paddy soils along the middle and lower Yangtze River

Heavy metals(HMs)and antibiotic resistance have become serious environmental problems affecting soil and human health.Soil microorganisms play key roles in pollutant degradation and biogeochemical cycling processes;however,the interactions among HMs,soil microbial communities,and antibiotic resistance genes(ARGs)in agricultural soils remain unclear.Using quantitative real-time polymerase chain reaction and NovaSeq sequencing,we evaluated heavy metal contents,abundances of ARGs,soil bacterial community structure and functions,and their correlations in paddy soils at 43 sampling sites along the middle and lower reaches of the Yangtze River,central and eastern China.Our results showed the co-occurrence of HMs,ARGs,and HM resistance genes across all paddy soils.Additionally,significant positive associations were detected between HMs and resistance genes.Cadmium,czcA,and int1 were positively correlated with bacterial community diversity.The Mantel test showed that bacterial community composition and functions were significantly associated with HMs and resistance genes,such as Cd,Cr,Zn,copA,czcA,int1,and sul1.Moreover,HMs and ARGs were the major factors shaping soil bacterial communities;thus,HMs triggered proliferation of HM and antibiotic resistances by influencing the mobile genetic element(int1)and soil microbial communities.Our study revealed that HMs potentially drive the co-selection of ARGs by shifting soil bacterial community structure and functions,thereby increasing the potential risks to human health as well as ecological environment in the paddy soils along the middle and lower reaches of the Yangtze River.