Exploring the Potential of Gaofen-1/6 for Crop Monitoring: Generating Daily Decametric-Resolution Leaf Area Index Time Series

High spatiotemporal resolution time series of leaf area index (LAI) are essential for monitoring crop dynamics and validating coarse-resolution LAI products. The optical satellite sensors at decametric resolution have historically suffered from a long revisit cycle and cloud contamination issues that hampered the acquisition of frequent and high-quality observations. The 16-m/four-day resolution of the new-generation Gaofen-1 (GF-1) and Gaofen-6 (GF-6) satellites provide an unprecedented opportunity to address these limitations. Here, we developed an effective strategy to generate daily 16-m LAI maps combining GF-1/6 data and ground LAINet measurements. All high-quality GF-1/6 observations were utilized first to derive smoothed time series of vegetation indices (VIs). Second, a random forest regression (RF-r) model was trained to link the VIs with corresponding field LAI measurements. The trained RF-r was finally employed to generate the LAI maps. Results demonstrated the reliability of the reconstructed daily VIs (relative error (RE) < 1%) and the derived LAI time series, which greatly benefited from GF-1/6 high-frequency observations. The direct comparison with field LAI measurements by LAI-2200/LI-3000 showed the good performance of retrieved LAI maps, with bias, root mean square error (RMSE), and R2 of 0.05, 0.59, and 0.75, respectively. The LAI time series well captured the spatiotemporal variation of crop growth. Furthermore, the continuous GF-1/6 LAI maps outperformed Sentinel-2 LAI estimates both in terms of temporal frequency and accuracy. Our study indicates the potential of GF-1/6 to generate continuous decametric-resolution LAI maps for fine-scale agricultural monitoring

Microbe-induced phenotypic variation leads to overyielding in clonal plant populations

Overyielding, the high productivity of multispecies plant communities, is commonly seen as the result of plant genetic diversity. Here we demonstrate that biodiversity–ecosystem functioning relationships can emerge in clonal plant populations through interaction with microorganisms. Using a model clonal plant species, we found that exposure to volatiles of certain microorganisms led to divergent plant phenotypes. Assembling communities out of plants associated with different microorganisms led to transgressive overyielding in both biomass and seed yield. Our results highlight the importance of belowground microbial diversity in plant biodiversity research and open new avenues for precision ecosystem management

Polar-facing slopes showed stronger greening trend than equatorial-facing slopes in Tibetan plateau grasslands

The orientation of slopes in alpine zones creates microclimates, e.g. equatorial-facing slopes (EFSs) are generally drier and warmer than are polar-facing slopes (PFSs). The vegetation growing in these microhabitats responds divergently to climatic warming depending on the slope orientation. We proposed a spatial metric, the greenness asymmetric index (GAI), defined as the ratio between the average normalized difference vegetation index (NDVI) on PFSs and EFSs within a given spatial window, to quantify the asymmetry of greenness across aspects. We calculated GAI for each non-overlapping 3 × 3 km2 (100 × 100 Landsat pixels) grid, and seamlessly mapped it on Tibetan Plateau (TP) grassland using NDVI time series from the Landsat-5, -7 and -8 satellites. PFSs were greener than EFSs (GAI > 1) in warm and dry areas, and EFSs were greener than PFSs (GAI < 1) in cold and wet areas. We also detected a stronger greening trend (0.0040 vs 0.0034 y−1) and a higher sensitivity of NDVI to temperature (0.031 vs 0.026 °C−1) on PFSs than EFSs, leading to a significant positive trend in GAI (0.00065 y−1, P < 0.01) in the TP from 1991 to 2020. Our results suggest that global warming exacerbated the greenness asymmetry associated with the slope orientation: PFSs are more sensitive to warming and have been greening at a faster rate than EFSs. The gradient of EFSs and PFSs provided a “natural laboratory” to study interaction of water and temperature limitations on vegetation growth. Our study is the first to detect the effect of aspect on the greening trend in the TP. Future research needs to clarify the full biotic and abiotic determinants for this spatial and temporal asymmetry of greenness across aspects with the support of extensive field measurements and refined high-resolution NDVI products.This study was funded by the National Natural Science Foundation of China 42271323 and 41971282, the Sichuan Science and Technology Program 2021JDJQ0007, the Spanish Government project TED2021-132627B-I00 funded by the Spanish MCIN, AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR, the Fundación Ramón Areces project CIVP20A6621 and the Catalan government project SGR2021-1333.N

Genome Sequencing of Ralstonia solanacearum CQPS-1, a Phylotype I Strain Collected from a Highland Area with Continuous Cropping of Tobacco

Ralstonia solanacearum, an agent of bacterial wilt, is a highly variable species with a broad host range and wide geographic distribution. As a species complex, it has extensive genetic diversity and its living environment is polymorphic like the lowland and the highland area, so more genomes are needed for studying population evolution and environment adaptation. In this paper, we reported the genome sequencing of R. solanacearum strain CQPS-1 isolated from wilted tobacco in Pengshui, Chongqing, China, a highland area with severely acidified soil and continuous cropping of tobacco more than 20 years. The comparative genomic analysis among different R. solanacearum strains was also performed. The completed genome size of CQPS-1 was 5.89 Mb and contained the chromosome (3.83 Mb) and the megaplasmid (2.06 Mb). A total of 5229 coding sequences were predicted (the chromosome and megaplasmid encoded 3573 and 1656 genes, respectively). A comparative analysis with eight strains from four phylotypes showed that there was some variation among the species, e.g., a large set of specific genes in CQPS-1. Type III secretion system gene cluster (hrp gene cluster) was conserved in CQPS-1 compared with the reference strain GMI1000. In addition, most genes coding core type III effectors were also conserved with GMI1000, but significant gene variation was found in the gene ripAA: the identity compared with strain GMI1000 was 75% and the hrp(II) box promoter in the upstream had significantly mutated. This study provided a potential resource for further understanding of the relationship between variation of pathogenicity factors and adaptation to the host environment

Influence of the Cross-Sectional Shape and Corner Radius on the Compressive Behaviour of Concrete Columns Confined by FRP and Stirrups

Axial compression tests were carried out on 72 FRP (fiber reinforced polymer)–stirrup composite-confined concrete columns. Stirrups ensure the residual bearing capacity and ductility after the FRP fractures. To reduce the effect of stress concentration at the corners of the confined square-section concrete columns and improve the restraint effect, an FRP–stirrup composite-confined concrete structure with rounded corners is proposed. Different corner radii of the stirrup and outer FRP were designed, and the corner radius of the stirrup was adjusted accurately to meet the designed corner radius of the outer FRP. The cross-section of the specimens gradually changed from square to circular as the corner radius increased. The influence of the cross-sectional shape and corner radius on the compressive behaviour of FRP–stirrup composite-confined concrete was analysed. An increase in the corner radius can cause the strain distribution of the FRP to be more uniform and strengthen the restraint effect. The larger the corner radius of the specimen, the better the improvement of mechanical properties. The strength of the circular section specimen was greatly improved. In addition, the test parameters also included the FRP layers, FRP types and stirrup spacing. With the same corner radius, increasing the number of FRP layers or densifying the stirrup spacing effectively improved the mechanical properties of the specimens. Finally, a database of FRP–stirrup composite-confined concrete column test results with different corner radii was established. The general calculation models were proposed, respectively, for the peak points, ultimate points and stress–strain models that are applicable to FRP-, stirrup- and FRP–stirrup-confined concrete columns with different cross-sectional shapes under axial compression

Compressive behavior of BFRP-confined ceramsite concrete: An experimental study and stress–strain model

The novel structure of a basalt fiber reinforced polymer (BFRP)-confined ceramsite concrete column (BFCCC) reinforced with bamboo strips (BSs) was investigated. The characteristics of light weight, BSs and FRP reinforcement were reflected in the structure. Thirty-six BFCCCs and 18 unconfined ceramsite concrete columns were fabricated and subjected to axial compression tests, and the stress–strain curves were obtained. The research parameters included the number of BFRP layers and the volume content of BSs. Both types of specimens, with and without BFRP confinement, underwent brittle failure after reaching the ultimate bearing capacity. The increase in the number of BFRP layers had a positive effect on the bearing capacity and deformation capacity of the specimens. With the increase in the number of BFRP layers, the compressive strengths of BFCCCs were improved by 1.17–1.44 times, and the deformations were improved by 6.30–12.92 times, compared to the unconfined concrete. The addition of BSs could improve the ductility of the specimen, while the effect on the bearing capacity had an optimal value of 2.0%. The stress–strain curves of the BFCCCs showed obvious softening behavior after the peak point. Models were proposed to predict the axial stress–strain curves of BFCCCs reinforced with BSs

Compressive Behavior of Bamboo Sheet Twining Tube-Confined Concrete Columns

This study experimentally investigated various axial compressive parameters of a new type of confined concrete, which is termed bamboo sheet twining tube-confined concrete (BSTCC). This new composite structure was composed of an outer bamboo composite tube (BCT) jacket and a concrete core. Under axial compression, the parameters of thirty-six specimens include concrete strength (i.e., C30 and C50) and BCT thickness (i.e., 6, 12, 18, 24, and 30 layers). The mechanical properties of the BSTCC specimens from the perspective of the failure mode, stress-strain relationship, effect of BCT thickness and dilation behavior were analyzed. The results showed that, in compression, with an increase in BCT thickness in the range of 18-layers of bamboo sheets, the strength increased remarkably. When the strength of the concrete core was high, the confinement effect of the BCT was reduced. In addition, the BCT thickness relieved the dilation of the BSTCC specimens. Finally, the experimental results were compared with predictions obtained from 7 existing FRP-confined concrete models. All the predictions had good agreement with the test results, which further confirmed that the models developed for FRP-confined concrete can provide an acceptable approximation of the ultimate strength of the BSTCC specimens

Evaluation of the load-carrying effect of rectangular concrete-filled steel tubular columns under axial compression based on the multilevel extension method

The load-carrying effect of rectangular concrete-filled steel tubular (RCFST) columns under axial compression has complex influencing parameters. Previous relevant studies have mostly included experimental and modeling approaches, but there are few studies on evaluations based on multiple parameters. This study introduces the extension evaluation method, which is good at solving contradictory problems, and scientifically constructs a multilevel extension evaluation model of the load-carrying effect of RCFST columns. Key parameters such as the cross-sectional height-to-breadth ratio (Sr) and hoop confinement coefficient (ξs) that affect the load-carrying effect of RCFST columns are refined and converted into evaluation indices. The weights of the indices are calculated scientifically via the analytic hierarchy process (AHP). Through the extension evaluation of the tested RCFST columns, the accuracy and rationality of the proposed evaluation model are verified. The conclusion of the multilevel extension evaluation shows that for the fixed section tested in this study, the RCFST columns with moderately thick-walled steel tubes have the best load-carrying effect and economy among thin-walled, moderately thick-walled and very thick-walled steel tubes

Experimental and theoretical analysis of FRP-confined square lightweight aggregate concrete columns under axial compression

The structure of an FRP-confined square lightweight aggregate concrete (LWAC) column was investigated, and it was found to significantly decrease the self-weight while improving the deformation capacity and bearing capacity. Twelve FRP-confined LWAC columns and three unconfined LWAC columns underwent monotonic axial compression tests. The influences of the FRP thickness and type on the compressive performance, stressstrain relationship and strain cloud maps were investigated based on digital image correlation (DIC) technology. Both types of FRP materials demonstrated a noticeable enhancement in both the strength and deformation capacity of LWAC, with CFRP having the greatest effect on strength and BFRP having the greatest effect on ductility. Compared to LWAC columns without confinement, the compressive strength of LWAC confined by BFRP or CFRP increased by 9.4∼21.9% and 24.9∼53.3%, respectively, and the ultimate strain increased by 10.6–14.2 times and 8.0–10.9 times, respectively, with increasing the thickness of FRP. DIC technology was used to accurately measure changes in the strain and the crack development of the specimens, thereby obtaining an accurate rupture strain of the FRP material. The existing models were evaluated using test data, and new models were proposed for FRP-confined square LWAC

Exposure to Umbelliferone Reduces Ralstonia solanacearum Biofilm Formation, Transcription of Type III Secretion System Regulators and Effectors and Virulence on Tobacco

Ralstonia solanacearum is one of the most devastating phytopathogens and causes bacterial wilt, which leads to severe economic loss due to its worldwide distribution and broad host range. Certain plant-derived compounds (PDCs) can impair bacterial virulence by suppressing pathogenic factors of R. solanacearum. However, the inhibitory mechanisms of PDCs in bacterial virulence remain largely unknown. In this study, we screened a library of coumarins and derivatives, natural PDCs with fused benzene and alpha-pyrone rings, for their effects on expression of the type III secretion system (T3SS) of R. solanacearum. Here, we show that umbelliferone (UM), a 7-hydroxycoumarin, suppressed T3SS regulator gene expression through HrpG-HrpB and PrhG-HrpB pathways. UM decreased gene expression of six type III effectors (RipX, RipD, RipP1, RipR, RipTAL, and RipW) of 10 representative effector genes but did not alter T2SS expression. In addition, biofilm formation of R. solanacearum was significantly reduced by UM, though swimming activity was not affected. We then observed that UM suppressed the wilting disease process by reducing colonization and proliferation in tobacco roots and stems. In summary, the findings reveal that UM may serve as a plant-derived inhibitor to manipulate R. solanacearum T3SS and biofilm formation, providing proof of concept that these key virulence factors are potential targets for the integrated control of bacterial wilt