Light-use Efficiency Research Articles

Higher plant photosynthetic capability in autumn responding to low atmospheric vapor pressure deficit

It has been long established that the terrestrial vegetation in spring has stronger photosynthetic capability than in autumn. However, this study challenges this consensus by comparing photosynthetic capability of terrestrial vegetation between the spring and autumn seasons based on measurements of 100 in situ eddy covariance towers over global extratropical ecosystems. At the majority of these sites, photosynthetic capability, indicated by light use efficiency (LUE) and apparent quantum efficiency, is significantly higher in autumn than in spring, due to lower atmosphere vapor pressure deficit (VPD) at the same air temperature. Seasonal VPD differences also substantially explain the interannual variability of the differences in photosynthetic capability between spring and autumn. We further reveal that VPD in autumn is significantly lower than in spring over 74.14% of extratropical areas, based on a global climate dataset. In contrast, LUE derived from a data-driven vegetation production dataset is significantly higher in autumn in over 61.02% of extratropical vegetated areas. Six Earth system models consistently projected continuous larger VPD values in spring compared with autumn, which implies that the impacts on vegetation growth will long exist and should be adequately considered when assessing the seasonal responses of terrestrial ecosystems to future climate conditions.

Canopy heterogeneity with border-row proportion affects light interception and use efficiency in maize/peanut strip intercropping

• Different border-row proportions (BRP) in maize/peanut intercropping were compared to mono crops. • Increasing BRP increased light interception (LI) of maize in the intercropping but not for light use efficiency (LUE). • Increasing BRP decreased LI but increased LUE of peanut in the intercropping. • LUE of both crops increased with leaf area index and decreased with light intensity. Intercropping usually plants two or more crop species, often with different canopy architectures by row configuration, creates spatial niche differentiation, changes light distribution and affects radiation utilization and yield. In this study, we investigated how row configuration (e.g. the proportion of border rows) affected light interception (LI) and light use efficiency (LUE) in maize ( Zea mays L.)/ peanut ( Arachis hypogaea Linn.) strip intercropping. Field experiments were carried out for two years in 2015 and 2016. Four intercropping treatments were set as M2P2 (two rows maize and two rows peanut), M4P4, M6P6 and M8P8, with border-row proportion (BRP) of 1, 0.5, 0.33 and 0.25 under an equal land use proportion (0.5 for each crop). Two monocultures, sole maize and sole peanut (with BRP of 0), were set as controls. The LI was estimated by a light interception model developed for strip intercropping. Both light capture and light use efficiency of intercropped crops were significantly affected by strip width. The LI of intercropped high-stalk maize was 23.4 % higher while LI of shaded peanut was 32.2 % lower than the control. The LI of intercropped maize increased with the increasing of BRP. The LI of peanut decreased with BRP but did not show significant difference in low BRP treatment (i.e. in M6P6 and M8P8). The LUE differed within treatments in dry 2015 but not in wet 2016. In dry 2015, LUE of intercropped maize on average 13.6 % lower than the sole crop (2.05 g MJ −1 ), while LUE of intercropped peanut especially in M2P2 was 23.9 % higher than the sole crop (0.73 g MJ −1 ). The LUE varied daily and was significantly correlated with leaf area index and incident radiation intensity in both intercropping and the sole crops. Both LI and LUE responded to BRP and the responses differed between intercropped crops. The result could be used as a basis for explaining the mechanism of strip intercropping on light utilization, optimizing row configuration of intercropping design and improving light use algorithm of crop simulation model.

Performance of Singular Spectrum Analysis in Separating Seasonal and Fast Physiological Dynamics of Solar‐Induced Chlorophyll Fluorescence and PRI Optical Signals

AbstractHigh temporal resolution measurements of solar‐induced chlorophyll fluorescence (F) and the Photochemical Reflectance Index (PRI) encode vegetation functioning. However, these signals are modulated by time‐dependent processes. We tested the applicability of the Singular Spectrum Analysis (SSA) for disentangling fast components (physiology‐driven) and slow components (controlled by structural and biochemical properties) from PRI, far‐red F (F760), and far‐red apparent fluorescence yield (Fy∗760). The proof of concept was developed on spectral and flux time series simulated with the Soil Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model. This allowed the evaluation of SSA decomposition against variables that are independent of physiology or are modified by it. Slow SSA‐decomposed components of PRI and Fy∗760 showed high correlations with the reference variables (R2 = 0.97 and 0.96, respectively). Fast SSA‐decomposed components of PRI and Fy∗760 were better related to the physiological reference variables than the original signals during periods when leaf area index (LAI) was above 1 m2 m−2. The method was also successfully applied to predict light‐use efficiency (LUE) from the fast SSA‐decomposed components of PRI (R2 = 0.70) and Fy∗760 (R2 = 0.68) when discarding data modeled with LAI < 1 m2 m−2 and short‐wave radiation Rin < 250 W m−2. The method was then tested on data acquired in a Mediterranean grassland. In this case, the fast SSA‐decomposed component of apparent LUE∗ showed a stronger correlation with the fast SSA‐decomposed component of Fy∗760 (R2 = 0.42) than with original Fy∗760 (R2 = 0.01). SSA‐based approach is a promising tool for decoupling physiological information from measurements acquired with automated proximal sensing systems.

MODIS PRI performance to track Light Use Efficiency of a Mediterranean coniferous forest: Determinants, restrictions and the role of LUE range

The relationship between the Photochemical Reflectance Index (PRI) and Light Use Efficiency (LUE) is well established at leaf and small canopy scales, but upscaling to ecosystem level is still a challenge. Only few studies have applied satellite-derived PRI to estimate LUE, mostly using MODIS, and although the results are promising, many external factors have been identified affecting PRI performance. The present study investigates determinants and restrictions of MODIS-derived PRI potential to follow the LUE variability of a Mediterranean coniferous forest.Daily and half-hour LUE values were calculated from eddy covariance measurements, dividing GPP by either Photosynthetically Active Radiation (PAR) or the absorbed fraction of PAR (APAR). Also, various PRI datasets were created based on different sensor (Terra, Aqua, Both), reference band (1, 12, 13) and observation/illumination angles. Overall, PRI correlated better with LUE calculated using PAR instead of APAR and Aqua PRI yielded better results than Terra. Restricting acquisitions according to observation/illumination angles improves the PRI:LUE relationship (maximum R2 = 0.512), with backscatter observations yielding the best correlations. Our findings suggest that MODIS-derived PRI is more sensitive to relatively large seasonal LUE changes, but is unable to closely follow severe drought events. Among the tested reference bands, the best results were derived using band 12 (546 - 556 nm), although the optimum reference band seems to depend on viewing conditions. The PRI:LUE relationship was further improved when half-hour LUE of the satellite overpass was used instead of daily LUE. However, it was found that the PRI:LUE relationships for the different datasets were strongly affected by the range of LUE values corresponding to each PRI group, with lower LUE variability resulting to weaker PRI:LUE correlations. LUE range effect should be accounted for in future studies, when different PRI datasets are compared and might explain the contradicting findings in the existing literature.

Aboveground Biomass Mapping of Crops Supported by Improved CASA Model and Sentinel-2 Multispectral Imagery

The net primary productivity (NPP) and aboveground biomass mapping of crops based on remote sensing technology are not only conducive to understanding the growth and development of crops but can also be used to monitor timely agricultural information, thereby providing effective decision making for agricultural production management. To solve the saturation problem of the NDVI in the aboveground biomass mapping of crops, the original CASA model was improved using narrow-band red-edge information, which is sensitive to vegetation chlorophyll variation, and the fraction of photosynthetically active radiation (FPAR), NPP, and aboveground biomass of winter wheat and maize were mapped in the main growing seasons. Moreover, in this study, we deeply analyzed the seasonal change trends of crops’ biophysical parameters in terms of the NDVI, FPAR, actual light use efficiency (LUE), and their influence on aboveground biomass. Finally, to analyze the uncertainty of the aboveground biomass mapping of crops, we further discussed the inversion differences of FPAR with different vegetation indices. The results demonstrated that the inversion accuracies of the FPAR of the red-edge normalized vegetation index (NDVIred-edge) and red-edge simple ratio vegetation index (SRred-edge) were higher than those of the original CASA model. Compared with the reference data, the accuracy of aboveground biomass estimated by the improved CASA model was 0.73 and 0.70, respectively, which was 0.21 and 0.13 higher than that of the original CASA model. In addition, the analysis of the FPAR inversions of different vegetation indices showed that the inversion accuracies of the red-edge vegetation indices NDVIred-edge and SRred-edge were higher than those of the other vegetation indices, which confirmed that the vegetation indices involving red-edge information can more effectively retrieve FPAR and aboveground biomass of crops.

Improved understanding of the spatially-heterogeneous relationship between satellite solar-induced chlorophyll fluorescence and ecosystem productivity

Satellite solar-induced chlorophyll fluorescence (SIF) is deemed as a good proxy for vegetation photosynthesis. To date, SIF has been shown to correlate strongly with gross primary productivity (GPP) at ecosystem scale and perform well in monitoring the impacts of extreme climate events on ecosystem productivity. However, the SIF-GPP relationship exhibits a spatially-heterogeneous pattern across ecosystems and produces both linear and nonlinear results at different spatiotemporal scales. Understanding of the different spatiotemporal SIF-GPP relationships is still incomplete and somewhat controversial in previous studies. Here, based on the light-use efficiency (LUE) models, this study investigated the spatially-heterogeneous SIF-GPP relationships across the conterminous United States (CONUS), and examined the possible drivers and mechanisms. Our results showed that SIF and GPP exhibited similar spatiotemporal patterns but responded differently to environmental factors (i.e., soil moisture, precipitation, photosynthetically active radiation, air temperature, and atmospheric vapor pressure deficit). The correlation analysis showed that the SIF-GPP relationships were spatially-heterogeneous across the CONUS both at monthly and annual scales. Moreover, our findings also indicated that different biome types could partly explain the spatial heterogeneity of SIF-GPP relationship. Different canopy structures and vegetation coverages across biomes could be primary drivers of the spatially-heterogeneous SIF-GPP relationship. In addition, the SIF-GPP relationships under the baseline and drought scenarios appeared to be similar and consistent. It implies that there could be an invariant SIF-GPP relationship under both drought and non-drought conditions, leading to a weak effect of interannual drought on the spatial heterogeneity. In summary, our results highlight that the effects of biome characteristics (Ωbiome) and environmental stresses (Φstress) on spatially-heterogeneous SIF-GPP relationship and further explore possible mechanisms of the linkage between SIF and GPP.

INTERCROPPING CHILLI WITH GROUNDNUT IN CHAR LAND

Intercropping is a farming practice involving two or more crop species, or genotypes, growing together and coexisting for a time. On the fringes of modern intensive agriculture, intercropping is important in many subsistence or low-input/resource-limited agricultural systems. Intercropping in order to improve land use efficiency, take advantage of intercropping facilitation and improve economic benefits. Also, linked with the higher yield, the associated higher amount of vegetables-legume by-product is preferred for animal feed or human consumption. The objective of this study is to find out the suitable groundnut – chilli intercropping system and increase productivity, economic and nutritional development of charland farmers of Bangladesh. In the experiment, intercropping system such as One row of chilli in between two normal rows of groundnut, two rows of chilli in between two normal rows of groundnut which was compared with sole groundnut and sole chilli production. Total yields of chilli /groundnut intercropping were higher than that of sole chilli and groundnut. chilli /groundnut intercropping is the efficient use of light because of complementary use of space between the chilli plants and the groundnut plants. Chilli /groundnut intercrop gross return and BCR per hectare were found higher than from sole crop system. The total yield of intercropped crops was greater than sole cropping shown by LER>1. The overall advantage of intercropping ranged from 71 to 81%. The highest land equivalent value of 81% was recorded from paired row chilli in between four normal rows of groundnut sowing arrangements indicated a yield advantage of 81% over sole crop.

A Method for Quantifying the Impacts of Human Activities on Net Primary Production of Grasslands in Northwest China

Accurately assessing the impact of human activities on net primary productivity (NPP) of vegetation is of great significance to the achievement of sustainable development. However, it is difficult to disentangle the effects of climate conditions and human activities on NPP, and bridging this knowledge gap largely depends on the calculation of the NPP under natural conditions. Here, we propose a method for calculating natural vegetation NPP (NNPP) based on non-human influence grids, which are obtained according to the consistent rate of climate and actual NPP (ANPP) temporal changes. We selected Northwest China as study area, and we used a light use efficiency (LUE) model to estimate ANPP and used the random forest algorithm (RF) to estimate the NNPP. The results show that NNPP is very close to ANPP, and the human activities on NPP (HNPP) based on NNPP is close to the actual situation of human activities on NPP. From 2001 to 2017, the positive HNPP accounts for 40.28% of the total grassland area, with an average value of 28.65 gC·m−2·yr−1, while the negative HNPP accounts for 59.72% of the total area, with an average value of −31.19 gC·m−2·yr−1. The grassland NPP shows an increasing trend, which is dominated by climate factors. Human activity is the dominant factor for the grassland degradation, accounting for 42.78% of the degraded area, but promoting grassland growth in 11.4% of the restored area. This study provides a new method to estimate the impacts of human activities on vegetation, and the results can be used to evaluate the effectiveness of ecological environmental governance, providing a quantitative basis for scientifically building the harmonious relationship between human and nature.

Van der Waals heterostructures based on SiC-BS: A promoted photocatalytic properties for water splitting

Motivated by the previous study of electronic properties of the two-dimensional (2D) hexagonal structure of group III-VI binary monolayers, this work further investigates the band edge alignment, charge transfer and strain response based on the density functional theory (DFT). We here combine monolayer SiC and BS through van der Waals (vdW) interaction to obtain a new heterostructure form with well-defined type-II alignment. Their potential applications for an efficient use of light have also been systematic studied. This work proves that SiC-BS heterostructures can fully meet all ideal criteria and have much better mobility priorities than that of pristine structures. The results indicate that the applied electric field can regulate the band alignment between type-I and type-II, while the applied strain can maintain three heterostructures in a relatively wide range of type-II character to effectively separate light induced carriers in space.

Continuous Lighting and High Daily Light Integral Enhance Yield and Quality of Mass-Produced Nasturtium (Tropaeolum majus L.) in Plant Factories.

Nasturtium (Tropaeolum majus L.), as a medicinal plant, has a high phenolic content in its leaves and flowers. It is often used in salads as a dietary vegetable. Attracting strong demand, it could be a good candidate crop for a plant factory with artificial lighting (PFAL) that can achieve the mass production of high-quality crops with high productivity by regulating environmental conditions such as light. In this study, two experiments were conducted to investigate the effects of continuous lighting (CL) and different daily light integrals (DLIs) under CL on the growth, secondary metabolites, and light use efficiency (LUE) of nasturtium, all of which are essential in the successful cultivation in PFALs. In Experiment 1, two lighting models, the same DLI of 17.3 mol m−2 d−1 but different light periods (24 and 16 h) with different light intensities (200 and 300 µmol m−2 s−1, respectively), were applied to nasturtium. The results showed that leaf production, secondary metabolites, and LUE were higher under the 24-h CL treatment than under the 16-h non-CL treatment. In Experiment 2, three DLI levels (17.3, 25.9, and 34.6 mol m−2 d−1) under the CL condition were applied. The results showed that the growth parameters were positively correlated with the DLI levels under CL. The lowest DLI had the highest LUE. We conclude that the mass production of nasturtium under CL in PFALs is feasible, and the yield increases as DLI increases from 17.3 to 34.6 mol m−2 d−1 under CL without causing physiological stress on plants.

Semi-Transparent Organic Photovoltaics Applied as Greenhouse Shade for Spring and Summer Tomato Production in Arid Climate

Recognizing the growing interest in the application of organic photovoltaics (OPVs) with greenhouse crop production systems, in this study we used flexible, roll-to-roll printed, semi-transparent OPV arrays as a roof shade for a greenhouse hydroponic tomato production system during a spring and summer production season in the arid southwestern U.S. The wavelength-selective OPV arrays were installed in a contiguous area on a section of the greenhouse roof, decreasing the transmittance of all solar radiation wavelengths and photosynthetically active radiation (PAR) wavelengths (400–700 nm) to the OPV-shaded area by approximately 40% and 37%, respectively. Microclimate conditions and tomato crop growth and yield parameters were measured in both the OPV-shaded (‘OPV’) and non-OPV-shaded (‘Control’) sections of the greenhouse. The OPV shade stabilized the canopy temperature during midday periods with the highest solar radiation intensities, performing the function of a conventional shading method. Although delayed fruit development and ripening in the OPV section resulted in lower total yields compared to the Control section (24.6 kg m−2 and 27.7 kg m−2, respectively), after the fourth (of 10 total) harvests, the average weekly yield, fruit number, and fruit mass were not significantly different between the treatment (OPV-shaded) and control group. Light use efficiency (LUE), defined as the ratio of total fruit yield to accumulated PAR received by the plant canopy, was nearly twice as high as the Control section, with 21.4 g of fruit per mole of PAR for plants in the OPV-covered section compared to 10.1 g in the Control section. Overall, this study demonstrated that the use of semi-transparent OPVs as a seasonal shade element for greenhouse production in a high-light region is feasible. However, a higher transmission of PAR and greater OPV device efficiency and durability could make OPV shades more economically viable, providing a desirable solution for co-located greenhouse crop production and renewable energy generation in hot and high-light intensity regions.

Impacts of Reduced Nitrate Supply on Nitrogen Metabolism, Photosynthetic Light-Use Efficiency, and Nutritional Values of Edible Mesembryanthemum crystallinum.

Mesembryanthemum crystallinum (common ice plant), as a nutritious ready-to-eat salad in Singapore, has become popular in recent years. However, basic data about the impacts of NO3– supply on its NO3– accumulation and nutritional quality are lacking. In this study, all plants were first grown indoor hydroponically in 10% artificial seawater (ASW) with modified full-strength Netherlands Standard Composition nutrient solution for 11 days, before transferring them to different reduced NO3– solutions. All plants grew well and healthy after 7 days of treatment. However, plants grown with 3/4 N and 1/2 N were bigger with higher shoot and root fresh weight (FW), greater leaf number, and total leaf area (TLA) than those grown with full nitrogen (N), 1/4 N, and 0 N. Mesembryanthemum crystallinum grown with full N, 3/4 N, and 1/4 N had similar specific leaf area (SLA), while 0 N plants had significantly lower SLA. All plants had similar leaf succulence (LS). However, leaf water content (LWC) was lower, while leaf dry matter accumulation (LDMC) was higher in 0 N plants after 7 days of treatment. Compared with plants grown with full N, shoot NO3– concentrations in 3/4 N, 1/2 N, and 1/4 N plants were constant or slightly increased during the treatments. For 0 N plants, shoot NO3– concentration decreased significantly during the treatment compared with other plants. Shoot NO3– accumulation was associated with nitrate reductase activity (NRA). For instance, after 7 days of treatment, shoot NO3– concentration and NRA on a FW basis in 0 N plants were, respectively, 45 and 31% of full N plants. After transferring full N to 0 N for 7 days, all M. crystallinum had higher chlorophyll (Chl) content coupled with higher electron transport rate (ETR) and higher effective quantum yield of PSII, while full N plants had higher non-photochemical quenching (NPQ). The 0N plants had much higher concentrations of proline, total soluble sugar (TSS), and total ascorbic acid (ASC) than other plants. In conclusion, totally withdrawing NO3– from the growth media prior to harvest could be one of the strategies to reduce shoot NO3– concentration. Reduced NO3– supply further enhanced nutritional values as concentrations of proline, TSS, and ASC were enhanced markedly in M. crystallinum plants after transferring them from full N to 0 N.

Threshold of vapour–pressure deficit constraint on light use efficiency varied with soil water content

AbstractUnderstanding the constraints on light‐use efficiency (LUE) induced by high evaporative water demand (vapour–pressure deficit; VPD) and soil water stress (soil moisture content; SMC) is crucial for understanding and simulating vegetation productivity, particularly in the arid and semi‐arid regions. However, the relative impacts of VPD and SMC on LUE are unclear, as we lack a mechanistic understanding of impacts and their interactions. In this study, we quantified the relative roles of VPD and SMC in limiting LUE and analysed the interactions among VPD, SMC and LUE using data from CO2 and water flux stations and weather stations along a climatic gradient in the Heihe River Basin, China. We found a threshold of VPD constraint on LUE; above the threshold, LUE decreased at only 3.6% to 23.1% of the rate below the threshold. As SMC decreased, however, the VPD threshold increased, and the reduction of LUE caused by VPD decreased significantly, which is more than half of that in moister regions. Therefore, both VPD and SMC played essential roles in LUE limitation caused by water stress. A threshold also existed for heat flux and the correlation between SMC and LUE; the strength of the correlation first decreased and then increased with increasing VPD. Our results clarified the relative impacts of VPD and SMC on LUE, and can improve simulation and prediction of plant productivity.

The role of Cytochrome b6f in the control of steady-state photosynthesis: a conceptual and quantitative model

Here, we present a conceptual and quantitative model to describe the role of the Cytochrome hbox {b}_{6}hbox {f} complex in controlling steady-state electron transport in hbox {C}_{3} leaves. The model is based on new experimental methods to diagnose the maximum activity of Cyt hbox {b}_{6}hbox {f} in vivo, and to identify conditions under which photosynthetic control of Cyt hbox {b}_{6}hbox {f} is active or relaxed. With these approaches, we demonstrate that Cyt hbox {b}_{6}hbox {f} controls the trade-off between the speed and efficiency of electron transport under limiting light, and functions as a metabolic switch that transfers control to carbon metabolism under saturating light. We also present evidence that the onset of photosynthetic control of Cyt hbox {b}_{6}hbox {f} occurs within milliseconds of exposure to saturating light, much more quickly than the induction of non-photochemical quenching. We propose that photosynthetic control is the primary means of photoprotection and functions to manage excitation pressure, whereas non-photochemical quenching functions to manage excitation balance. We use these findings to extend the Farquhar et al. (Planta 149:78–90, 1980) model of hbox {C}_{3} photosynthesis to include a mechanistic description of the electron transport system. This framework relates the light captured by PS I and PS II to the energy and mass fluxes linking the photoacts with Cyt hbox {b}_{6}hbox {f}, the ATP synthase, and Rubisco. It enables quantitative interpretation of pulse-amplitude modulated fluorometry and gas-exchange measurements, providing a new basis for analyzing how the electron transport system coordinates the supply of Fd, NADPH, and ATP with the dynamic demands of carbon metabolism, how efficient use of light is achieved under limiting light, and how photoprotection is achieved under saturating light. The model is designed to support forward as well as inverse applications. It can either be used in a stand-alone mode at the leaf-level or coupled to other models that resolve finer-scale or coarser-scale phenomena.

Impact of the facultative parasitic weed Rhamphicarpa fistulosa (Hochst.) Benth. on photosynthesis of its host Oryza sativa L.

Rhamphicarpa fistulosa is a facultative root parasitic annual forb, of the family Orobanchaceae that is native to sub-Saharan Africa. Parasitism results in yield reductions by the host plants but it is not known how exactly R. fistulosa affects its host or how the host responds physiologically. In three pot experiments, we investigated whether and when the parasite affects photosynthesis of rice, whether the level of impact was parasite density dependent and explored mechanisms underlying the response of rice photosynthesis to parasitism. Photosynthesis and related parameters were measured at a range of light use intensities. Host photosynthesis was negatively affected while light use efficiency was negatively affected only later on in the growth process. Except for dark respiration rates, which were never affected by parasite infection, suppression of host photosynthesis at light saturation, the initial light-use efficiency, chlorophyll content, specific leaf area and shoot weight were parasite density dependent with a stronger effect for higher parasite densities. Only at 56 days after sowing, the slope of the linear relationship between light adapted quantum efficiency of PSII electron transport (ΦPSII) and the quantum yield of CO2 assimilation (ΦCO2) of infected plants was less than those of un-infected plants. There was a considerable time lag between the parasite’s acquisition of benefits from the association, in terms of growth (previously observed around 42 DAS), and the reduction of host photosynthesis (around 56 DAS). Expression of relative reductions in host growth rates started at the same time as the relative suppression of host photosynthesis. This indicated that R. fistulosa affects host growth by first extracting assimilates and making considerable gains in growth, before impacting host photosynthesis and growth.

Drone-Based Hyperspectral and Thermal Imagery for Quantifying Upland Rice Productivity and Water Use Efficiency after Biochar Application

Miniature hyperspectral and thermal cameras onboard lightweight unmanned aerial vehicles (UAV) bring new opportunities for monitoring land surface variables at unprecedented fine spatial resolution with acceptable accuracy. This research applies hyperspectral and thermal imagery from a drone to quantify upland rice productivity and water use efficiency (WUE) after biochar application in Costa Rica. The field flights were conducted over two experimental groups with bamboo biochar (BC1) and sugarcane biochar (BC2) amendments and one control (C) group without biochar application. Rice canopy biophysical variables were estimated by inverting a canopy radiative transfer model on hyperspectral reflectance. Variations in gross primary productivity (GPP) and WUE across treatments were estimated using light-use efficiency and WUE models respectively from the normalized difference vegetation index (NDVI), canopy chlorophyll content (CCC), and evapotranspiration rate. We found that GPP was increased by 41.9 ± 3.4% in BC1 and 17.5 ± 3.4% in BC2 versus C, which may be explained by higher soil moisture after biochar application, and consequently significantly higher WUEs by 40.8 ± 3.5% in BC1 and 13.4 ± 3.5% in BC2 compared to C. This study demonstrated the use of hyperspectral and thermal imagery from a drone to quantify biochar effects on dry cropland by integrating ground measurements and physical models.

High Carotenoid Mutants of Chlorella vulgaris Show Enhanced Biomass Yield under High Irradiance.

Microalgae represent a carbon-neutral source of bulk biomass, for extraction of high-value compounds and production of renewable fuels. Due to their high metabolic activity and reproduction rates, species of the genus Chlorella are highly productive when cultivated in photobioreactors. However, wild-type strains show biological limitations making algal bioproducts expensive compared to those extracted from other feedstocks. Such constraints include inhomogeneous light distribution due to high optical density of the culture, and photoinhibition of the surface-exposed cells. Thus, the domestication of algal strains for industry makes it increasingly important to select traits aimed at enhancing light-use efficiency while withstanding excess light stress. Carotenoids have a crucial role in protecting against photooxidative damage and, thus, represent a promising target for algal domestication. We applied chemical mutagenesis to Chlorella vulgaris and selected for enhanced tolerance to the carotenoid biosynthesis inhibitor norflurazon. The NFR (norflurazon-resistant) strains showed an increased carotenoid pool size and enhanced tolerance towards photooxidative stress. Growth under excess light revealed an improved carbon assimilation rate of NFR strains with respect to WT. We conclude that domestication of Chlorella vulgaris, by optimizing both carotenoid/chlorophyll ratio and resistance to photooxidative stress, boosted light-to-biomass conversion efficiency under high light conditions typical of photobioreactors. Comparison with strains previously reported for enhanced tolerance to singlet oxygen, reveals that ROS resistance in Chlorella is promoted by at least two independent mechanisms, only one of which is carotenoid-dependent.

The Effect of Diffuse Film Covers on Microclimate and Growth and Production of Tomato (Solanum lycopersicum L.) in a Mediterranean Greenhouse

The efficient use of light is one of the most important factors for the development of greenhouse crops. It is increasingly necessary to use film covers that enhance transmittance and the proportion of diffuse light to generate a more homogeneous light distribution. The objective of this study was to evaluate the effect that an experimental film cover with high transmittance and high light diffusivity produces on the microclimate and the growth and yield of tomato crops (Solanum lycopersicum L.), compared with a commercial thermal film cover. The trial was developed during a spring–summer growing cycle in a multispan greenhouse divided into two compartments (sectors) separated by a vertical polyethylene sheet. In the East sector, a commercial film was installed (transmittance of 85% and diffusivity of 60%) and in the West sector, an experimental film was used (transmittance of 90% and diffusivity of 55%). The results show an increase in the marketable yield of 0.25 kg·m−2 in the sector with the experimental film, which represents 3.2% growth with respect to the commercial film. The photosynthetic activity measured in tomato leaves was 21.5% higher in plants growing in the sector with the experimental film, with had the highest transmittance. The increase in radiation transmittance of 14% produced greater photosynthetic activity without generating a higher inside air temperature at the crop level (at the height of 2 m above the floor). However, the mean temperature of the soil surface was statistically higher on the side with the diffuse experimental cover film, as a logical consequence of the higher level of intercepted solar radiation.

The application of EO-1 Hyperion hyperspectral data to estimate the GPP of temperate forest in Changbai Mountain, Northeast China

Flux tower is a link between ground measurements and large-scale remote sensing data. A large number of remote sensing model methods are used to estimate the regional scale Gross Primary Productivity (GPP) based on this principle. In this study, Vegetation Photosynthesis Model (VPM) and Vegetation Indexes (VIs) were used to estimate the GPP based on Earth Observing 1 (EO-1) Hyperion hyperspectral data in Changbai Mountain temperate forest. Result shows that the two different types of remote sensing input data of the VPM has similar result at the same level. For different time scope, 3-day flux data can better match remote sensing data. For different footprint, the effect of 500, 1000, 1500 m almost no difference in our area. Among the comparison of the four types of VIs, Bands Ratio (BR), Bands Subtraction (BS) and Bands Difference (BD) have a higher correlation significant than Single Band (SB). 457 nm is the optimum band for SB. The best bands combination of BR, BS, and BD mainly focus on near infrared region. Our research shows that for VPM, and other Light Use Efficiency (LUE) remote sensing model, the difference is not significant between multispectral data and hyperspectral data. At the comparison of VPM and VIs, although the estimation of former is more accurate, the latter is more convenient for that the establishment of VIs just need several bands of remote sensing data. Our findings will help to improve future research on GPP estimation based on hyperspectral observations, which is being more important with increasing availability of hyperspectral satellite data products.

Crop Yield Estimation at Gram Panchayat Scale by Integrating Field, Weather and Satellite Data with Crop Simulation Models

Advanced technologies can improve the operational implementation of the Indian national crop insurance scheme, the Pradhan Mantri Fasal Bima Yojana (PMFBY), particularly in terms of accuracy and timeliness of the crop yield estimates that are used to determine yield losses at the Gram Panchayat (GP) level. In this study, conducted as a pilot test for PMFBY during the kharif season of 2018, technologies based on the Terrestrial Observation and Prediction System (TOPS) were tested and implemented for estimating GP-level crop yields of bajra (pearl millet, Pennisetum glaucum) in Firozabad District of Uttar Pradesh and rice (Oryza sativa) in Kendujhar District of Odisha. A combination of Synthetic Aperture Radar and optical data was used to map crop extent. Daily 2-km grids of input weather conditions were generated using a machine learning algorithm that incorporated station observations, satellite data, and reanalysis model outputs. Required crop biophysical estimates of leaf area index (LAI) and the fraction of intercepted photosynthetically active radiation (FPAR) were derived using daily cloud-screened MODIS 250-m data from the Terra and Aqua satellites and a modified MOD15 LAI/FPAR backup algorithm. A light-use-efficiency (LUE) model adapted from the MODIS (Moderate Resolution Imaging Spectroradiometer) algorithm (MOD17-GPP/NPP) was then used to spatially estimate crop yields. Crop extent maps, daily climate and gap-filled FPAR and the LUE model were used to estimate above-ground biomass, which was accumulated over the growing season and converted to crop yields using a crop-specific harvest index. The estimated yields at 250 m were aggregated within each GP and compared with crop yield data from crop cutting experiments (CCEs) conducted in 142 GPs for rice and 42 GPs for bajra. Crop extent mapping was 96% accurate in rice and 80% in bajra when validated with field surveys. A comparison of modeled yields with CCE yields showed a promising performance by the model in both crops (rice: r = 0.80, root-mean-square error (RMSE) = 411 kg/ha, mean absolute error (MAE) = 359 kg/ha, percent error (PE) = 7, Observed mean = 1500 kg/ha; Bajra: r = 0.84, RMSE = 309 kg/ha, MAE = 262 kg/ha, PE = −12.8, Observed mean = 1859 kg/ha). Although the approach showed promising results for both crops, further progress is needed to ensure consistent and reliable results. Some of the needed improvements include incorporating a dynamic crop calendar, improved maximum LUE estimates, and harvest index values that represent crop varietals grown in India. Routinely conducted CCEs in different crops and seasons around the country could provide a valuable resource for improving these parameters and, ultimately, crop yield estimates.