Leaf Inclination Research Articles

Estimating near-infrared reflectance of vegetation from hyperspectral data

Disentangling the individual contributions from vegetation and soil in measured canopy reflectance is a grand challenge to the remote sensing and ecophysiology communities. Since Solar Induced chlorophyll Fluorescence (SIF) is uniquely emitted from vegetation, it can be used to evaluate how well reflectance-based vegetation indices (VIs) can separate the vegetation and soil components. Due to the residual soil background contributions, Near-infrared (NIR) reflectance of vegetation (NIRv) and Difference Vegetation index (DVI) present offsets when compared to SIF (i.e., the value of NIRv or DVI is non-zero when SIF is zero). In this study, we proposed a simple framework for estimating the true NIR reflectance of vegetation from Hyperspectral measurements (NIRvH) with minimal soil impacts. NIRvH takes advantage of the spectral shape variations in the red-edge region to minimize the soil effects. We evaluated the capability of NIRvH, NIRv and DVI in isolating the true NIR reflectance of vegetation using the data from both the model-based simulations and Hyperspectral Plant imaging spectrometer (HyPlant) measurements. Benchmarked by simultaneously measured SIF, NIRvH has the smallest offset (0–0.037), as compared to an intermediate offset of 0.047–0.062 from NIRv, and the largest offset of 0.089–0.112 from DVI. The magnitude of the offset can vary with different soil reflectance spectra across spatio-temporal scales, which may lead to bias in the downstream NIRv-based photosynthesis estimates. NIRvH and SIF measurements from the same sensor platform avoided complications due to different geometry, footprint and time of observation across sensors when studying the radiative transfer of reflected photons and SIF. In addition, NIRvH was primarily determined by canopy structure rather than chlorophyll content and soil brightness. Our work showcases that NIRvH is promising for retrieving canopy structure parameters such as leaf area index and leaf inclination angle, and for estimating fluorescence yield with current and forthcoming hyperspectral satellite measurements.

SDG128 is involved in maize leaf inclination.

Maize leaf angle (LA) is a complex quantitative trait that is controlled by developmental signals, hormones, and environmental factors. However, the connection between histone methylation and LAs in maize remains unclear. Here, we reported that SET domain protein 128 (SDG128) is involved in leaf inclination in maize. Knockdown of SDG128 using an RNA interference approach resulted in an expanded architecture, less large vascular bundles, more small vascular bundles, and larger spacing of large vascular bundles in the auricles. SDG128 interacts with ZmGID2 both invitro and invivo. Knockdown of ZmGID2 also showed a larger LA with less large vascular bundles and larger spacing of vascular bundles. In addition, the transcription level of cell wall expansion family genes ZmEXPA1, ZmEXPB2, and GRMZM2G005887; transcriptional factor genes Lg1, ZmTAC1, and ZmCLA4; and auxin pathway genes ZmYUCCA7, ZmYUCCA8, and ZmARF22 was reduced in SDG128 and ZmGID2 knockdown plants. SDG128 directly targets ZmEXPA1, ZmEXPB2, LG1, and ZmTAC1 and is required for H3K4me3 deposition at these genes. Together, the results of the present study suggest that SDG128 and ZmGID2 are involved in the maize leaf inclination.

OsRELA Regulates Leaf Inclination by Repressing the Transcriptional Activity of OsLIC in Rice.

Leaf angle is one of the most important agronomic traits in rice, and changes in leaf angle can alter plant architecture to affect photosynthetic efficiency and thus determine grain yield. Therefore, it is important to identify key genes controlling leaf angle and elucidate the molecular mechanisms to improve rice yield. We obtained a mutant rela (regulator of leaf angle) with reduced leaf angle in rice by EMS mutagenesis, and map-based cloning revealed that OsRELA encodes a protein of unknown function. Coincidentally, DENSE AND ERECT PANICLE 2 (DEP2) was reported in a previous study with the same gene locus. RNA-seq analysis revealed that OsRELA is involved in regulating the expression of ILI and Expansin family genes. Biochemical and genetic analyses revealed that OsRELA is able to interact with OsLIC, a negative regulator of BR signaling, through its conserved C-terminal domain, which is essential for OsRELA function in rice. The binding of OsRELA can activate the expression of downstream genes repressed by OsLIC, such as OsILI1, a positive regulator of leaf inclination in rice. Therefore, our results suggest that OsRELA can act as a transcriptional regulator and is involved in the regulation of leaf inclination by regulating the transcriptional activity of OsLIC.

A bHLH protein, OsBIM1, positively regulates rice leaf angle by promoting brassinosteroid signaling

Rice leaf angle is an important agronomic trait determining plant architecture and crop yield. Brassinosteroids (BRs) play crucial roles in controlling rice leaf angle, thus an increasing number of researches were focused on the BR signaling pathway in rice. However, the orthologs of some important components in Arabidopsis BR signaling have not yet been characterized in rice. In this study, we identified a rice bHLH transcription factor named OsBIM1, as the closest rice homolog of AtBIM1 (BES1-Interacting MYC-like Protein1). Overexpression of OsBIM1 significantly increases rice leaf angles, whereas the T-DNA knock-out mutant osbim1 and wide type (WT) showed similar leaf inclination. OsBIM1 overexpression enhances the sensitivity and response to BR treatment in rice. Gene expression analysis showed that the overexpression of OsBIM1 significantly increased the transcripts of INCREASED LEAF INCLINATION1 (OsILI1) that functions as a key transcription factor promoting BR signaling and response. Meanwhile, OsBIM1 inhibited the expression of DWARF2 (OsD2, a key enzyme in BR biosynthesis pathway). OsBIM1 can bind with OsILI1 promoter and enhance OsILI1 expression in response to BR treatment. The promoting effect of OsBIM1 overexpression on leaf angle can still be observed at harvest stage, but overexpression of OsBIM1 resulted in smaller grain size and reduced yield. These results indicate that OsBIM1 functions as a positive regulator in BR signaling, and its overexpression increases rice lamina inclination by promoting BR sensitivity and response.

OsWRKY108 is an integrative regulator of phosphorus homeostasis and leaf inclination in rice

ABSTRACT Phosphorus (P), which is taken up by plants as inorganic phosphate (Pi), is one of the most important macronutrients for plant growth and development. Meanwhile, it determines plant architecture in several ways, including leaf inclination. However, the molecular basis underlying the crosstalk between the signaling pathways of plant P homeostasis and architecture maintenance remains elusive. We recently characterized a WRKY transcription factor, OsWRKY108, in rice (Oryza sativa). It functions redundantly with OsWRKY21 to promote Pi uptake in response to Pi supply. Overexpression of either OsWRKY108 or OsWRKY21 led to up-regulation of Pi transporter genes and thus enhanced Pi accumulation. By contrast, transgenic rice plants expressing OsWRKY21-SRDX (a fusion protein transforming OsWRKY21 from an activator into a dominant repressor) but not the OsWRKY108-SRDX fusion showed decreased Pi accumulation under Pi-replete conditions. Here, we report that OsWRKY108 acts as a positive regulator of leaf inclination. OsWRKY108 overexpressors showed increased leaf inclination and OsWRKY108-SRDX plants showed an erect-leaf phenotype, irrespective of the Pi regimes. Nevertheless, the response of leaf inclination to Pi starvation was largely impaired upon OsWRKY108 overexpression. Moreover, in both OsWRKY108-SRDX plants and OsWRKY108 overexpressors, the ‘percentage of leaf angle alteration relative to wild-type’ under Pi-starvation condition was more significant than that under Pi-replete condition. These results suggest that the regulation of OsWRKY108 on leaf inclination is in part dependent on Pi availability. Altogether, our findings demonstrate that OsWRKY108 is an integrative regulator of P homeostasis and leaf inclination, serving as a link between plant nutrient signaling and developmental cues.

CRISPR/Cas9 mediated targeted mutagenesis of LIGULELESS-1 in sorghum provides a rapidly scorable phenotype by altering leaf inclination angle.

Sorghum (Sorghum bicolor L. Moench) is one of the world's most cultivated cereal crops. Biotechnology approaches have great potential to complement traditional crop improvement. Earlier studies in rice and maize revealed that LIGULELESS-1 (LG1) is responsible for formation of the ligule and auricle, which determine the leaf inclination angle. However, generation and analysis of lg1 mutants in sorghum has so far not been described. Here, we describe CRISPR/Cas9 mediated targeted mutagenesis of LG1 in sorghum and phenotypic changes in mono- and bi-allelic lg1 mutants. Genome editing reagents were co-delivered to sorghum (var. Tx430) with the nptII selectable marker via particle bombardment of immature embryos followed by regeneration of transgenic plants. Sanger sequencing confirmed a single nucleotide insertion in the sgRNA LG1 target site. Monoallelic edited plantlets displayed more upright leaves in tissue culture and after transfer to soil when compared to wild type. T1 progeny plants with biallelic lg1 mutation lacked ligules entirely and displayed a more severe reduction in leaf inclination angle than monoallelic mutants. Transgene-free lg1 mutants devoid of the genome editing vector were also recovered in the segregating T1 generation. Targeted mutagenesis of LG1 provides a rapidly scorable phenotype in tissue culture and will facilitate optimization of genome editing protocols. Altering leaf inclination angle also has the potential to elevate yield in high-density plantings.

Better revisiting chlorophyll content retrieval with varying senescent material and solar-induced chlorophyll fluorescence simulation on paddy rice during the entire growth stages

Solar-induced chlorophyll fluorescence at 760 nm (SIF) is a promising proxy of photosynthesis and can help improving plant stress monitoring. The Soil-Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model combines radiative transfer and enzyme kinetics of photosynthesis and is widely used to interpret SIF at different temporal and spatial scales. In this study, growing season canopy hyperspectral reflectance between 400 nm and 900 nm was used to retrieve chlorophyll content (Cab) and leaf inclination (LIDFa) using radiative transfer models (RTMs) combined with the shuffled complex evolution-University of Arizona (SCE-UA) method. These parameters were then used to simulate diurnal and seasonal trends of SIF for paddy rice. The results showed that the accuracy of Cab retrieval was improved when the variation in senescent material (Cs) was considered, especially in the later growth stages. The SCOPE model was able to reliably interpret the diurnal cycle and seasonal trend of SIF with a correlation coefficient of 0.92 and RMSE of 0.12 w m−2 sr-1 um−1. Our results revealed that the SCOPE model provides a promising method for interpreting SIF variations but its accuracy should be evaluated in different growth stages. This will serve as a significant reference for detecting plant photosynthetic activity and physiological traits at different growth stages.

Changes in peanut canopy structure and photosynthetic characteristics induced by an arbuscular mycorrhizal fungus in a nutrient-poor environment

A well-developed canopy structure can increase the biomass accumulation and yield of crops. Peanut seeds were sown in a soil inoculated with an arbuscular mycorrhizal fungus (AMF) and uninoculated controls were also sown. Canopy structure was monitored using a 3-D laser scanner and photosynthetic characteristics with an LI-6400 XT photosynthesis system after 30, 45 and 70 days of growth to explore the effects of the AMF on growth, canopy structure and photosynthetic characteristics and yield. The AMF colonized the roots and AMF inoculation significantly increased the height, canopy width and total leaf area of the host plants and improved canopy structure. AMF reduced the tiller angle of the upper and middle canopy layers, increased that of the lower layer, reduced the leaf inclination of the upper, middle and lower layers, and increased the average leaf area and leaf area index after 45 days of growth, producing a well-developed and hierarchical canopy. Moreover, AMF inoculation increased the net photosynthetic rate in the upper, middle and lower layers. Plant height, canopy width, and total leaf area were positively correlated with net photosynthetic rate, and the inclination angle and tiller angle of the upper leaves were negatively correlated with net photosynthetic rate. Overall, the results demonstrate the effects of AMF inoculation on plant canopy structure and net photosynthetic rate.

Modulation of Rice Leaf Angle and Grain Size by Expressing OsBCL1 and OsBCL2 under the Control of OsBUL1 Promoter.

Leaf angle and grain size are important agronomic traits affecting rice productivity directly and/or indirectly through modulating crop architecture. OsBC1, as a typical bHLH transcription factor, is one of the components comprising a complex formed with LO9-177 and OsBUL1 contributing to modulation of rice leaf inclination and grain size. In the current study, two homologues of OsBC1, OsBCL1 and OsBCL2 were functionally characterized by expressing them under the control of OsBUL1 promoter, which is preferentially expressed in the lamina joint and the spikelet of rice. Increased leaf angle and grain length with elongated cells in the lamina joint and the grain hull were observed in transgenic rice containing much greater gibberellin A3 (GA3) levels than WT, demonstrating that both OsBCL1 and OsBCL2 are positive regulators of cell elongation at least partially through increased GA biosynthesis. Moreover, the cell elongation was likely due to cell expansion rather than cell division based on the related gene expression and, the cell elongation-promoting activities of OsBCL1 and OsBCL2 were functional in a dicot species, Arabidopsis.

A biomechanical model of leaf inclination angle oscillations after raindrop impact

Raindrop impact exerts a force on the leaf resulting in a decaying oscillation of the leaf inclination angle. Nondestructive measurements of leaf oscillations is important for predicting changes in leaf angles in the field based on morphometric properties of leaves. The objectives of this study were to determine if a second order impulse response could describe experimentally observed changes in leaf inclination angle, to determine if field measurable, nondestructive leaf traits significantly correlate with model parameters, and to determine if the model parameters were species-specific. This study examined leaf oscillations for three common species in Colorado, USA (Acer saccharinum, Quercus gambelii, and Ulmus pumila) due to two different raindrop sizes. The drop impact was created by releasing a single drop of known size from a known height. The resulting leaf motion was recorded using a high-speed video camera. The images were then processed to measure the leaf inclination angle as a function of time, and a model was used to fit the data. The model was evaluated for quality of fit to the data. The experimental data closely fit the modeled data, indicating that the impulse response appropriately predicts leaf oscillations after raindrop impact. Strong linear relationships existed between leaf mass and maximum change in leaf inclination angle after drop impact for both the experimental and the modeled data. The model parameters were also found to be species-specific. The oscillations in leaf inclination angle are accurately described with a second order impulse response. The parameters of the impulse response correlate with field measurable leaf traits and the parameters are species-specific. The data and approach in this study provided a nondestructive tool for the prediction of changes in leaf inclination angle for many broad-leaved species with diverse leaf morphometric properties.

The Role of Spatial Averaging Scale in Leaf‐To‐Canopy Scaling of Non‐Linear Processes in Homogeneous Canopies

AbstractIn formulating canopy biophysical models of non‐linear processes like photosynthesis and stomatal conductance, it is necessary to average inputs over some representative spatial scale (sub‐leaf, leaf, sub‐crown, crown, whole‐canopy, etc.). The consequences of the choice of averaging scale is often unclear due to the inability of experiments to robustly quantify fluxes across the full range of relevant length scales. This study quantified errors in canopy‐level flux simulations due to input radiative flux averaging scale choice using a detailed leaf‐resolving biophysical model that represents three‐dimensional canopy geometry at the sub‐leaf level. Simulations were performed for an array of homogeneous canopies differing in leaf area index (LAI), canopy height, leaf inclination angle distribution, leaf size, leaf shape, and the size of leaf sub‐sections relative to total leaf size. Canopy fluxes based on a sub‐leaf averaging scale were compared with fluxes derived from averaging over single leaves, averaging sunlit and shaded portions of leaf area separately (i.e., two‐leaf model), and averaging multiple vertical layers and leaf angle classes separately (i.e., multi‐layer model). Canopy‐level fluxes were found to be influenced by the chosen averaging scale and other variables tested, especially LAI. Averaging approaches inherent in the two‐leaf and multi‐layer models currently used in most canopy models resulted in low or moderate over‐estimates of canopy‐level fluxes under many conditions tested. Surprisingly, averaging over entire leaves (i.e., leaf‐resolving model) had the potential to create the largest errors. This result underscored the need to sub‐divide leaves in leaf‐resolving models.

A method for calculating the leaf inclination of soybean canopy based on 3D point clouds

ABSTRACT In order to achieve high-efficiency, low-cost and non-destructive measurement of soybean leaf inclination, three soybean varieties (Fudou-6, Kangxian-9 and Kangxian-13) were taken as research objects, a calculation method of soybean leaf inclination based on 3D point clouds was proposed. First, the original 3D point cloud data of soybean plants were obtained by Kinect 2.0 depth camera. Second, the grid method, depth threshold filtering and statistical filtering were used to pre-process the original 3D point cloud data. Third, the k-means clustering algorithm was used to segment the leaf point clouds. Further, the Delaunay triangulation was applied in reconstructing the surface of discrete point clouds. Finally, the ratio of leaf area to projected area was obtained by calculating the area of triangular mesh, so as to realize the calculation of soybean leaf inclination. At the same time, the calculated values were compared with those obtained by multispectral three-dimensional laser scanning device. The average relative error of soybean leaf inclination was 3.21%. The coefficient of determination (R 2) of the three varieties were 0.8317, 0.9075 and 0.9186, respectively. The results showed that the proposed method could meet the needs of non-destructive and accurate measurement of soybean leaf inclination.

Effect of canopy condition on Machilus nanmu seedling configuration and biomass allocation

The adaptation strategy of seedlings plays a decisive role in population regeneration. Machilus nanmu is a tree species belonging to Lauraceae, which is national class Ⅱ protected species and one of the dominant species in the evergreen broadleaved forest in Jinyun Mountain, Chongqing. Therefore, it is of great significance to understand the adaptation strategies of M. nanmu seedlings to maintain population regeneration and protect the biodiversity of evergreen broadleaved forest. We studied the temporal dynamics of early adaptation strategy of M. nanmu in Jinyun Mountain in Chongqing and its response to heterogeneous habitats from the perspective of morphology and biomass allocation. The seedlings of M. nanmu were classified into different age stages (stage 1: 1-3 a; stage 2: 4-6 a; stage 3: 7-9 a) under different canopy environments (gap/understory). Stem configurations (except branch angle) and leaf inclination angle of M. nanmu seedlings in the gap were significantly greater than understory at stages 2 and 3. Root configurations (except root diameter) and leaf area were significantly greater than that in the understory at stages 1 and 2. Specific leaf area in the gap was significantly smaller than understory at all three stages. Across all the conditions, biomass distribution was dominated by leaves. From the stage 2, stem biomass distribution of M. nanmu seedlings in the gap was increased, while root biomass distribution was decreased. There was no significant variation in root biomass of M. nanmu seedlings in the understory. The coordination among different organs of M. nanmu seedlings would help their adaptation to different habitats. Root and leaf of M. nanmu seedlings in the gap were significantly correlated, with the correlation changing from positive to negative as the age increased. While in the understory, there was significant positive correlation between root and stem, but no correlation between root and leaf. The slope of SMA equation of branch weight and branch length had significant difference under different canopy environments only at stage 3, while the slope of SMA equation of leaf and root biomass and configuration had no significant difference. Most of the SMA equation intercepts between biomass and configuration differed significantly at stage 2.

Assessment of Five Thermal Infrared Kernel-Driven Models Using Limited Multiangle Observations

There are five widely used kernel-driven models in the thermal infrared domain designed for the angular correction of land surface temperature (LST), including three-parameter Roujean Lagouarde (RL), Vinnikov, RossThick-LiSparseR (Ross–Li), LiStrahlerFriedl-LiDenseR (LSF-Li), and four-parameter Vinnikov-RoujeanLagouarde (Vinnikov-RL). Their fitting accuracies with hundreds of observation angles (i.e., sufficient angle) were studied; however, the fitting ability of these five models with limited observation angles is unknown, which makes it difficult to choose the appropriate one in applications. To solve this problem, 30 600 groups of multiangle directional brightness temperature (DBT) datasets were simulated by the unified optical-thermal 4-stream model considering scattering by arbitrary inclined leaves (4SAIL) model considering ten different leaf area index values, three leaf inclination distribution functions, two hotspot factors, 17 different component temperatures, five solar zenith angles, and six solar azimuth angles. Each group contains DBT values in 21 960 viewing directions [i.e., 61 viewing zenith angle (VZA) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 360 viewing azimuth angle (VAA)]. We assume that all limited observations are in the plane with VAA = 180°/0° and VZA changing from −60° to 60° with a step of 10°. There are 13 candidate angles to be selected. Five, seven, nine, and 11 angle sampling schemes include 225, 400, 225, and 36 limited multiangle combinations, respectively. Each combination was used to drive these five kernel-driven models to fit 21 960 DBTs for 30 600 groups of 4SAIL simulations. The root-mean-square error (RMSE) of each combination and mean RMSE of all 886 combinations were used to assess the overall fitting ability of five kernel-driven models. In addition, 1 k errors were added to the driven DBTs to evaluate the models’ robustness. Four groups of airborne measured DBTs were adopted to validate the assessment conclusions. Results show that the recommended order of these five models driven by 5–11 multiangle DBTs is Vinnikov-RL, LSF-Li, Vinnikov, Ross–Li, and RL when the driven DBTs do not contain errors; Vinnikov-RL, Vinnikov, LSF-Li, Ross–Li, and RL when the driven DBTs contain 1k errors; and Vinnikov-RL, LSF-Li, Ross–Li, RL, and Vinnikov for four groups of airborne measured datasets.

Quantitative trait loci for leaf inclination angle in rice detected using reciprocal mapping populations

• Six Takanari alleles increased leaf inclination angle at least twice in four years. • No Koshihikari alleles consistently increased leaf inclination angle. • Takanari alleles decreased the length of lamina joint cells on the adaxial side. • Takanari alleles improved light penetration into the canopy. • The effects of Takanari alleles were not enhanced by pyramiding QTLs. The improvement of canopy architecture is a feasible way to increase rice productivity. However, its genetic control in rice cultivars in the field is not well understood. The high-yielding indica cultivar Takanari has more erect leaves (a larger leaf inclination angle: LIA) during ripening, and this contributes to its higher dry matter production than that of the widely grown but less productive japonica cultivar Koshihikari. To identify quantitative trait loci (QTLs) for increasing LIA, we used reciprocal mapping populations of backcross inbred lines (131 lines in 2009 and 143 lines in 2010) and chromosome segment substitution lines (80 lines in 2011 and 2012) derived from a cross between Takanari and Koshihikari. Six Takanari alleles increased LIA at least in two of the four years, but we could not detect any such Koshihikari alleles. Five QTLs for LIA were expressed in plants with both Koshihikari and Takanari genetic backgrounds. LIA of two near isogenic lines carrying only one Takanari allele reached the level of Takanari. The Takanari alleles of the QTLs decreased the length of parenchyma cells in the lamina joint on the adaxial side in plants with the Koshihikari background, decreasing the ratio of the lamina joint length on the adaxial side to that on the abaxial side (LJ ratio) and thus increasing LIA. Three Takanari alleles increased dry matter production in plants with Koshihikari background via decreasing the canopy extinction coefficient ( k ). However, any pyramiding effects of Takanari alleles on LJ ratio, LIA, k and dry matter production were not observed.

Error Analysis of LAI Measurements with LAI-2000 Due to Discrete View Angular Range Angles for Continuous Canopies

As a widely used ground-based optical instrument, the LAI-2000 or LAI-2200 plant canopy analyzer (PCA) (Li-Cor, Inc., Lincoln, NE) is designed to measure the plant effective leaf area index (Le) by measuring the canopy gap fraction at several limited or discrete view zenith angles (VZAs) (usually five VZAs: 7, 23, 38, 53, and 68°) based on Miller’s equation. Miller’s equation requires the probability of radiative transmission through the canopy to be measured over the hemisphere, i.e., VZAs in the range from 0 to 90°. However, the PCA view angle ranges are confined to several limited ranges or discrete sectors. The magnitude of the error produced by the discretization of VZAs in the leaf area index measurements remains difficult to determine. In this study, a theoretical deduction was first presented to definitely prove why the limited or discrete VZAs or ranges can affect the Le measured with the PCA, and the specific error caused by the limited or discrete VZAs was described quantitatively. The results show that: (1) the weight coefficient of the last PCA ring is the main cause of the error; (2) the error is closely related to the leaf inclination angles (IAs)—the Le measured with the PCA can be significantly overestimated for canopies with planophile IAs, whereas it can be underestimated for erectophile IAs; and (3) the error can be enhanced with the increment of the discrete degree of PCA rings or VZAs, such as using four or three PCA rings. Two corrections for the error are presented and validated in three crop canopies. Interestingly, although the leaf IA type cannot influence the Le calculated by Miller’s equation in the hemispheric space, it affects the Le measured with the PCA using the discrete form of Miller’s equation for several discrete VZAs.

Monitoring of leaf nitrogen content of winter wheat using multi-angle hyperspectral data

ABSTRACT Hyperspectral technology, which has been used in rapid and non-destructive monitoring of crop nitrogen status, is of great significance for the nitrogen fertilization management in modern agriculture. However, most researches collect hyperspectral data from the vertical angle, always leading to the inaccurate estimation of crop nitrogen. Studies have found that using multi-angle spectral data could improve the accuracy in estimating crop leaf nitrogen content (LNC). In this study, the LNC at different leaf positions of winter wheat under five nitrogen treatments was measured and the multi-angle spectral reflectance of leaves were collected. The results showed that the top third leaf were the most sensitive to nitrogen application rate. Correlation analysis showed that the correlation between LNC and spectral reflectance obtained at 0° was the highest, followed by that between LNC and spectral reflectance obtained at 10°, 30°, 40°, and 20°. Moreover, a model based on the multi-angle composite vegetation index (MACVI) for LNC estimation was constructed through combining the difference vegetable index (DVI), the normalized difference vegetable index (NDVI), and the ratio vegetable index (RVI) and using the spectral data obtained from multiple leaf inclination angles, finding that this model could improve the estimation accuracy. The accuracy of the model based on the spectral reflectance obtained at 0°, 10°, and 20° was higher than the others, and the coefficient of determination (R 2) for the MACVID,R-based model was the highest. The MACVI-based model proposed in this study could effectively improve the estimation accuracy of winter wheat nitrogen content, and provide scientific guidance for the nitrogen fertilization management in winter wheat cultivation.

Influence of the canopy structure of a birch forest on the visibility of the fires below

The work is aimed at studying the visibility of a flame through the canopy of a birch forest, depending on the structure of the latter, and providing support for decision-making on the choice of the optimal sensing geometry for solving the problem of detecting fires in birch forests when video shooting from low altitudes. For the site located in the Priozersk district of the Leningrad region, using photographic technology, data were obtained on the frequency distribution of birch leaf inclination angles (for a hybrid of two species). The information is compared with the results of the work of other researchers. On the basis of the collected data, three-dimensional models of the canopy of various structures were constructed, suitable for simulating the radiation transfer. A set of experiments has been carried out to estimate the values of the fraction of beam penetration for light emitted by the combustion center in the direction of the sensor at different viewing angles. For individual ratios of crown sizes and distances between them, the least informative ranges of viewing angles, which should be avoided when monitoring fires, have been determined. It has been confirmed that the visibility of the flame depends on the shape and closeness of the crowns, which determine the length of the radiation path in the vegetation layer, and, to a lesser extent, on the prevailing orientation of the leaves.

Application of Phenotyping Methods in Detection of Drought and Salinity Stress in Basil (Ocimum basilicum L.).

Basil is one of the most widespread aromatic and medicinal plants, which is often grown in drought- and salinity-prone regions. Often co-occurrence of drought and salinity stresses in agroecosystems and similarities of symptoms which they cause on plants complicates the differentiation among them. Development of automated phenotyping techniques with integrative and simultaneous quantification of multiple morphological and physiological traits enables early detection and quantification of different stresses on a whole plant basis. In this study, we have used different phenotyping techniques including chlorophyll fluorescence imaging, multispectral imaging, and 3D multispectral scanning, aiming to quantify changes in basil phenotypic traits under early and prolonged drought and salinity stress and to determine traits which could differentiate among drought and salinity stressed basil plants. Ocimum basilicum “Genovese” was grown in a growth chamber under well-watered control [45–50% volumetric water content (VWC)], moderate salinity stress (100 mM NaCl), severe salinity stress (200 mM NaCl), moderate drought stress (25–30% VWC), and severe drought stress (15–20% VWC). Phenotypic traits were measured for 3 weeks in 7-day intervals. Automated phenotyping techniques were able to detect basil responses to early and prolonged salinity and drought stress. In addition, several phenotypic traits were able to differentiate among salinity and drought. At early stages, low anthocyanin index (ARI), chlorophyll index (CHI), and hue (HUE2D), and higher reflectance in red (RRed), reflectance in green (RGreen), and leaf inclination (LINC) indicated drought stress. At later stress stages, maximum fluorescence (Fm), HUE2D, normalized difference vegetation index (NDVI), and LINC contribute the most to the differentiation among drought and non-stressed as well as among drought and salinity stressed plants. ARI and electron transport rate (ETR) were best for differentiation of salinity stressed plants from non-stressed plants both at early and prolonged stress.

PLASTOCHRON1 regulates leaf inclination through Brassinolide pathway in Oryza sativa

AbstractLeaf inclination directly affects the lamina angle of rice (Oryza sativa), which in turn affects the photosynthetic efficiency of the leaves and grain yield. A mutant s544 characterized by enhanced leaf inclination as well as small aerial organs was identified from the progeny of ethyl‐methanesulfonate treated seeds of Indica rice ‘Xida 1B’. Genetic analysis indicated that the mutant traits were controlled by a single recessive nuclear gene. Using a F2 population derived from ‘Jinhui 10’ and the mutant, the mutated gene was mapped on chromosome 10 between markers RM25367 and XJ‐1, with a physical distance of 246 kb, which included PLASTOCHRON1(PLA1). Sequencing revealed a C to A substitution at position 1489 of the coding region of PLA1, which caused conversion of the encoded amino acid from proline to threonine. The s544 mutant showed increased sensitivity to exogenous brassinolide (24‐eBL) compared with the wild type. QPCR revealed that the genes of s544 positively regulated brassinolide signal transduction, especially for BU1 and ILI1 with up‐regulated expression over seventy times, and that MDP1, a negative‐regulated gene, decreased significantly in the half of the wild type. Meanwhile, D4 and D11 involved into BR‐synthesis were up‐regulated in s544. These results suggested that PLA1 may regulate BR signaling and biosynthetic pathways in rice organ development.