蚯蚓调控土壤微生态缓解连作障碍的作用机制

连作障碍不仅严重影响作物产量,而且会导致土壤生物多样性下降、有益微生物减少及病原菌增加等一系列微生态失衡问题。土壤微生态失衡反作用于植物,导致植物发生更严重的病害、减产等。作为土壤生态系统工程师,蚯蚓的取食、掘洞和爬行等活动对土壤微生态具有重要的调控作用,既可以改善土壤环境,又可以强化土壤生物群落功能,有望为缓解作物的连作障碍问题提供一条新途径。本文总结了土壤微生态与土壤功能维持及蚯蚓调控土壤生物作用的研究进展,在此基础上,结合蚯蚓对化感物质降解作用的研究,分析了蚯蚓通过调控土壤微生态缓解作物连作障碍的微生物作用机制的三条途径:直接调控微生物群落、通过改变化感物质组成以及通过调控土壤动物区系调控微生物群落。蚯蚓对微生物群落的调控可改善失衡的土壤根际微生态,有效缓解作物连作障碍。

Retrieval of global terrestrial solar-induced chlorophyll fluorescence from TanSat satellite

The first Chinese Carbon Dioxide Observation Satellite Mission(TanSat), which was launched on December 21, 2016, is intended to measure atmospheric CO_2 concentration.The high spectral resolution(0.044 nm) and high SNR(360 at 15.2 mW m^(-1) sr^(-1) nm^(-1)) measurements in the region of the O_2-A band of the Atmospheric Carbon dioxide Grating Spectroradiometer(AGCS) module onboard TanSat make it possible to retrieve solar-induced chlorophyll fluorescence(SIF) from TanSat observations at the global scale.This paper aims to explore the potential of the TanSat data for global SIF retrieval.A singular vector decomposition(SVD) statistical method was employed to retrieve SIF using radiance over a micro spectral window(～2 nm) around the Fe Fraunhofer lines(centered at 758.8 nm).The global SIF at 758.8 nm was successfully retrieved with a low residual error of 0.03 mW m^(-1) sr^(-1) nm^(-1).The results show that the spatial and temporal patterns of the retrieved SIF agree well with the global terrestrial vegetation pattern.The monthly SIF products retrieved from the TanSat data were compared with other remote sensing datasets, including OCO-2 SIF, MODIS NDVI, EVI and GPP.The overall consistency between TanSat and OCO-2 SIF products(R^2= 0.86) and the consistency of the spatial patterns and temporal variations between the TanSat SIF and MODIS vegetation indices and GPP enhance our confidence in the potential and feasibility of TanSat data for SIF retrieval.TanSat, therefore, provides a new opportunity for global sampling of SIF at fine spatial resolution(2 km × 2 km), thus improving photosynthesis observations from space.

Validation of Column-Averaged Dry-Air Mole Fraction of CO_2 Retrieved from OCO-2 Using Ground-Based FTS Measurements

In order to correctly use the column-averaged atmospheric COdry-air mole fraction(XCO) data in the COflux studies, XCOmeasurements retrieved from the Orbiting Carbon Observatory-2(OCO-2) in 2015 were compared with those obtained from the global ground-based high-resolution Fourier Transform Spectrometer(FTS) participating in the Total Carbon Column Observing Network(TCCON). The XCOretrieved from three observing modes adopted by OCO-2, i.e., nadir, target, and glint, were separately validated by the FTS measurements at up to eight TCCON stations located in different areas. These comparisons show that OCO-2 glint mode yields the best qualitative estimations of COconcentration among the three operational approaches. The overall results regarding the glint mode show no obvious systematic biases. These facts may indicate that the glint concept is appropriate for not only oceans but also land regions. Negative systematic biases in nadir and target modes have been found at most TCCON sites. The standard deviations of XCOretrieved from target and nadir modes within the observation period are similar, and larger than those from glint mode. We also used the FTS site in Beijing, China, to assess the OCO-2 XCOin 2016. This site is located in a typical urban area, which has been absent in previous studies. Overall, OCO-2 XCOagrees well with that from FTS at this site. Such a study will benefit the validation of the newly launched TanSat products in China.

Fast CO_(2) Retrieval Using a Semi-Physical Statistical Model for the High-Resolution Spectrometer on the Fengyun-3D Satellite

China’s Fengyun-3D meteorological satellite launched in December 2016 carries the high-resolution greenhouse-gases absorption spectrometer(GAS)aimed at providing global observations of carbon dioxide(CO_(2)).To date,GAS is one of the few instruments measuring CO_(2) from the near-infrared spectrum.On orbit,the oxygen(O_(2))A band suffers a disturbance,and the signal-to-noise ratio(SNR)is significantly lower than the nominal specification.This leads to difficulties in the retrieval of surface pressure and hence a degradation of the retrieval of the column-averaged CO_(2) dry air mole fraction(XCO_(2))if a full physics retrieval algorithm is used.Thus,a fast CO_(2) inverse method,named semi-physical statistical algorithm,was developed to overcome this deficiency.The instrument characteristics,the semi-physical statistical algorithm,and the results of comparison with ground-based measurements over land were introduced in this paper.XCO_(2) can be obtained from three bands,namely,the O_(2) A,weak CO_(2),and strong CO_(2) bands,with compensation from the Medium Resolution Spectral Imager-2(MERSI-2)products,ECMWF Reanaly-sis v5(ERA-5)data,and Total Carbon Column Observing Network(TCCON)data.The eigenvectors of covariance matrices and the least square fits were used to derive retrieval coefficients and yield cloud-free solutions.In addition to the GAS radiance,some key factors necessary for the accurate estimations of XCO_(2) were also taken as input information(e.g.,air mass,surface pressure,and a priori XCO_(2)).The global GAS XCO_(2) restricted over land was compared against the simultaneously collocated observations from TCCON.The retrieval algorithm can mitigate the issue caused by the low SNR of the O_(2) A band to a certain extent.Overall,through site-by-site comparisons,GAS XCO_(2) agreed well with the average precision(1σ)of 1.52 ppm and bias of−0.007 ppm.The seasonal variation trends of GAS XCO_(2) can be clearly seen at TCCON sites on the 1-yr timescale.