Contribution of periphytic biofilm of paddy soils to carbon dioxide fixation and methane emissions

Rice paddies are major contributors to anthropogenic greenhouse gas emissions via methane(CH_(4))flux.The accurate quantification of CH_(4)emissions from rice paddies remains problematic,in part due to uncertainties and omissions in the contribution of microbial aggregates on the soil surface to carbon fluxes.Herein,we comprehensively evaluated the contribution of one form of microbial aggregates,periphytic biofilm(PB),to carbon dioxide(CO_(2))and CH_(4)emissions from paddies distributed across three climatic zones,and quantified the pathways that drive net CH_(4)production as well as CO_(2)fixation.We found that PB accounted for 7.1%-38.5%of CH_(4)emissions and 7.2%-12.7%of CO_(2)fixation in the rice paddies.During their growth phase,PB fixed CO_(2)and increased the redox potential,which promoted aerobic CH_(4)oxidation.During the decay phase,PB degradation reduced redox potential and increased soil organic carbon availability,which promoted methanogenic microbial community growth and metabolism and increased CH_(4)emissions.Overall,PB acted as a biotic converter of atmospheric CO_(2)to CH_(4),and aggravated carbon emissions by up to 2,318 kg CO_(2)equiv ha^(-1)season^(-1).Our results provide proof-of-concept evidence for the discrimination of the contributions of surface microbial aggregates(i.e.,PB)from soil microbes,and a profound foundation for the estimation and simulation of carbon fluxes in a potential novel approach to the mitigation of CH_(4)emissions by manipulating PB growth.

Bacterial biogeography in China and its association to land use and soil organic carbon

●6102 high-quality sequencing results of soil bacterial samples were re-analyzed.●The type of land use was the principal driver of bacterial richness and diversity.●SOC content is positively correlated with key bacteria and total nitrogen content.Soil organic carbon(SOC)is the largest pool of carbon in terrestrial ecosystems and plays a crucial role in regulating atmospheric CO_(2) concentrations.Identifying the essential relationship between soil bacterial communities and SOC concentration is complicated because of many factors,one of which is geography.We systematically re-analyzed 6102 high-quality bacterial samples in China to delineate the bacterial biogeographic distribution of bacterial communities and identify key species associated with SOC concentration at the continental scale.The type of land use was the principal driver of bacterial richness and diversity,and we used machine learning to calculate its influence on microbial composition and their co-occurrence relationship with SOC concentration.Cultivated land was much more complex than forest,grassland,wetland and wasteland,with high SOC concentrations tending to enrich bacteria such as Rubrobacter,Terrimonas and Sphingomona.SOC concentration was positively correlated with the amounts of soil total nitrogen and key bacteria Xanthobacteraceae,Streptomyces and Acidobacteria but was negatively correlated with soil pH,total phosphorus and Micrococcaceae.Our study combined the SOC pool with bacteria and indicated that specific bacteria may be key factors affecting SOC concentration,forcing us to think about microbial communities associated with climate change in a new way.

破碎化景观格局中热带干旱森林的结构、多样性与保护价值

尽管热带干旱森林是世界上退化和破碎化程度最严重的生物群落之一,但我们对它们的基本生态特征和保护状况仍然知之甚少,尤其是在新热带地区。在本研究中,我们对尼加拉瓜破碎化景观格局中的热带干旱森林的多样性、组成、结构和保护价值进行了评估。我们在河流廊道、次生林、绿篱和林间牧地之中和沿线地区建立了31处样地和样带。我们使用希尔数(Hill number)对胸高处直径≥2.5 cm的所有树木进行了记录,并对每种森林类型中树木的丰富性和多样性进行了估算,接着计算了种级分类和科级分类上的重要值指数(Importance Value Index,IVI),最后则使用Bray-Curtis相似性指数进行了非度量多维标度(Non-Metric Multidimensional Scaling,NMDS)排序和相似性分析(Analysis of Similarities,ANOSIM)。不同森林类型之间在多样性上存在差异,但物种丰富度却不存在差异。豆科植物的IVI值最高,其次是桑科植物和锦葵科植物。Vachellia pennatula、Guazuma ulmifolia和Bursera simaruba的IVI值都>30%,其中前两种是所有森林类型中最为丰富的树木。对群落的相似性进行分析后可知每种森林类型都有着不同的组成,从而凸显了对所有这些不同类型的土地覆盖开展保护的重要性。

土壤水分胁迫制约全球植被变绿和初级生产力持续增加

大尺度的研究表明全球植被光合能力和生产力自20世纪80年代以来持续增加,但是很少有研究关注到其时空异质性.本研究将全球植被绿度变化趋势分为持续变绿、由变绿转为变棕、持续变棕以及不显著变化等不同类型,发现全球植被绿度变棕区域持续增加.到2010年以后逐渐超过持续变绿的区域(27.8×10^(6)km^(2),26.4%),达到了39.0×10^(6)km^(2)(全球植被面积的35.9%).这一现象抵消了2010年前12.0%±3.1%(0.019±0.004 NDVI a^(-1))植被绿度增加(2010~2016,P<0.05).全球陆地生态系统初级生产力也表现为类似的变化特征.这种变化主要是由于土壤水对于植被胁迫的负向作用,在部分地区超过了温度和辐射对于植被光合的积极作用.目前地球系统模型中的相关模块并不能反映这一正在增加的植被土壤水分胁迫.研究提示随着全球升温作用进一步加强,目前的地球系统模型土地模块可能会高估全球陆地生态系统碳固持能力.

Daily CO_(2) Emission Reduction Indicates the Control of Activities to Contain COVID-19 in China

Lockdown measures are essential to containing the spread of coronavirus disease 2019(COVID-19),but they will slow down economic growth by reducing industrial and commercial activities.However,the benefits of activity control from containing the pandemic have not been examined and assessed.Here we use daily carbon dioxide(CO_(2))emission reduction in China estimated from statistical data for energy consumption and satellite data for nitrogen dioxide(NO_(2))measured by the Ozone Monitoring Instrument(OMI)as an indicator for reduced activities consecutive to a lockdown.We perform a correlation analysis to show that a 1%day-1 decrease in the rate of COVID-19 cases is associated with a reduction in daily CO_(2) emissions of 0.22%±0.02%using statistical data for energy consumption relative to emissions without COVID-19,or 0.20%±0.02%using satellite data for atmospheric column NO_(2).We estimate that swift action in China is effective in limiting the number of COVID-19 cases<100,000 with a reduction in CO_(2) emissions of up to 23%by the end of February 2020,whereas a 1-week delay would have required greater containment and a doubling of the emission reduction to meet the same goal.By analyzing the costs of health care and fatalities,we find that the benefits on public health due to reduced activities in China are 10-fold larger than the loss of gross domestic product.Our findings suggest an unprecedentedly high cost of maintaining activities and CO_(2) emissions during the COVID-19 pandemic and stress substantial benefits of containment in public health by taking early actions to reduce activities during the outbreak of COVID-19.

种间相互作用影响植物氮和磷的吸收量而不是氮磷比

量化不同农艺措施下作物氮和磷吸收量(即从农田中移除的量)的化学计量特征对理解农田生态系统中的养分收支和优化氮、磷肥施用至关重要。目前还不清楚在不同的氮肥和覆膜措施下,单作和间作体系作物氮和磷吸收量以及氮磷化学计量特征随整个生长季的变化。本研究探讨了植物种间养分竞争如何对(1)5种种植模式(小麦、玉米和大麦单作、小麦/玉米和大麦/玉米间作),(2)两种施氮水平(0和225 kg N ha^(−1))和(3)两种玉米覆膜处理(覆膜和不覆膜)下的作物氮、磷吸收量(以及氮磷比)时间动态的影响。研究结果表明,小麦和大麦的氮、磷竞争能力强于玉米,导致间作体系共生期的小麦和大麦氮、磷吸收量相比于单作增加,而玉米氮、磷吸收量相比于单作减少。3种作物植株氮磷比随作物生长而降低。作物氮磷比不受间作的影响,也不随施氮呈现一致的变化,覆膜降低了玉米的氮磷比。两种间作体系群落水平的氮磷比在成熟期与相应单作不同。由于(1)间作从土壤移除的氮和磷的比例不同于单作,以及(2)作物对氮和磷的吸收在施氮和覆膜下均是不耦合的,这些发现可能对间作系统的养分收支有启示意义。

A Broadband Green-Red Vegetation Index for Monitoring Gross Primary Production Phenology

The chlorophyll/carotenoid index(CCI)is increasingly used for remotely tracking the phenology of photosynthesis.However,CCI is restricted to few satellites incorporating the 531nm band.This study reveals that the Moderate Resolution Imaging Spectroradiometer(MODIS)broadband green reflectance(band 4)is significantly correlated with this xanthophyll-sensitive narrowband(band 11)(R^(2)=0:98,p<0:001),and consequently,the broadband green-red vegetation index GRVI—computed with MODIS band 1 and band 4—is significantly correlated with CCI—computed with MODIS band 1 and band 11(R^(2)=0:97,p<0:001).GRVI and CCI performed similarly in extracting phenological metrics of the dates of the start and end of the season(EOS)when evaluated with gross primary production(GPP)measurements from eddy covariance towers.For EOS extraction of evergreen needleleaf forest,GRVI even overperformed solar-induced chlorophyll fluorescence which is seen as a direct proxy of plant photosynthesis.This study opens the door for GPP and photosynthetic phenology monitoring from a wide set of sensors with broadbands in the green and red spectral regions.