Projected Elevated [CO2] and Warming Result in Overestimation of SPAD-Based Rice Leaf Nitrogen Status for Nitrogen Management

Nitrogen (N) has a unique place in agricultural systems with large requirements. To achieve optimal nitrogen management that meets the needs of agricultural systems without causing potential environmental risks, it is of great significance to increase N use efficiency (NUE) in agricultural systems. A chlorophyll meter, for example, the SPAD-502, can provide a simple, nondestructive, and quick method for monitoring leaf N status and NUE. However, the SPAD-based crop leaf’s N status varies greatly due to environmental factors such as CO2 concentration ([CO2]) or temperature variations. In this study, we conducted [CO2] (ambient and enriched up to 500 μmol moL1) and temperature (ambient and increased by 1.5~2.0 °C) controlled experiments from 2015 to 2017 and in 2020 in two Free-Air CO2 Enrichment (FACE) sites. Leaf characters (SPAD readings, chlorophyll a + b, N content, etc.) of seven rice cultivars were measured in this four year experiment. Here, we provide evidence that SPAD readings are significantly linearly correlated with rice leaf chlorophyll a + b content (chl a + b) and N content, while the relationships are profoundly affected by elevated [CO2] and warming. Under elevated [CO2] treatment (E), the relationship between chl a + b content and N content remains unchanged, but SPAD readings and chl a + b content show a significant difference to those under ambient (A) treatment, which distorts the SPAD-based N monitoring. Under warming (T), and combined elevated [CO2] and warming (ET) treatments, both of the relationships between SPAD and leaf a + b content and between leaf a + b content and N content show a significant difference to those under A treatment. To deal with this issue under the background of global climate change dominated by warming and elevated [CO2] in the future, we need to increase the SPAD reading’s threshold value by at least 5% to adjust for applying N fertilizer within the rice cropping system by mid-century.

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Responses of rice leaf thickness, SPAD readings and chlorophyll a/b ratios to different nitrogen supply rates in paddy field

Field Crops Research ◽

10.1016/j.fcr.2009.09.009 ◽

2009 ◽

Vol 114 (3) ◽

pp. 426-432 ◽

Cited By ~ 36

Author(s):

Li Jinwen ◽

Yang Jingping ◽

Fei Pinpin ◽

Song Junlan ◽

Li Dongsheng ◽

...

Keyword(s):

Chlorophyll A ◽

Paddy Field ◽

Nitrogen Supply ◽

Leaf Thickness ◽

Rice Leaf ◽

Spad Readings

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Effect of Initial Phosphorus Concentration on Chlorophyll a Contents and Extracellular Polysaccharides Contents of Scenedesmus quaclricauda in TGR

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.971-973.53 ◽

2014 ◽

Vol 971-973 ◽

pp. 53-58

Author(s):

Qiang An ◽

Sha Wang ◽

Ce Wang ◽

Niu Qiu Huang ◽

Byebirooha Justus

Keyword(s):

Chlorophyll A ◽

Growth Period ◽

Inhibitory Effect ◽

Extracellular Polysaccharides ◽

Phosphorus Concentration ◽

Lag Phase ◽

Chl A ◽

The Three Gorges ◽

Significant Difference ◽

In The Beginning

An experiment was carried out to evaluate the effects of initial phosphorus concentration (0, 0.54, 2.7, 5.4, 10.8and 16.2mg/L) on chlorophyll a (chl-a) contents and extracellular polysaccharides (EPS) contents of Scenedesmus quaclricauda, which was separated and purified from the Three Gorges reservoir (TGR). The different conditions of initial phosphorus concentration have different volumetric meanings. 0mg/L, 0.54mg/L and 2.7mg/L are P-limited, 5.4mg/L is P-standard, 10.8mg/L as well as 16.2mg/L, is P-rich. Results showed that the growth period of Scenedesmus quaclricauda was shortened, and the stationary phase happened earlier than usual in the condition of P-limited. However, the growth period of Scenedesmus quaclricauda got a proceeding extension in the condition of P-rich. The condition of P-rich had an inhibitory effect on the growth of Scenedesmus quaclricauda during lag phase and exponential phase. It seemed that there was an inhibition threshold of initial phosphorus concentration, which was between 5.4mg/L and 10.8mg/L. And the inhibitory effect decreased with the initial increasing phosphorus concentrations from 10.8mg/L to 16.2mg/L. One-way analysis of variance (ANOVA) was used to compare the effects of both P-limited and P-rich and their impact on sEPS contents and bEPS contents of Scenedesmus quaclricauda in the cultured time segments. The results showed that there was no significant difference at sEPS contents or bEPS contents either in P-limited or P-rich. In the whole culture period, the sEPS contents of Scenedesmus quaclricauda had small fluctuations but kept nearly unchanged. Whereas, the bEPS contents increased in the beginning 8 days, and then dropped to the level, which is slightly higher than the initial contents, and keep fluctuating steadily. The EPS contents were just floating up and down at the initial value and had not shown a trend of rising or falling precisely. Our results suggest that phosphorus concentration could change chl-a contents but have no significant effect on EPS contents.

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Chlorophyll content of Thalassia hemprichii (Ehrenberg) Ascherson leaves in some coastal areas of Cebu Island, Central Philippines

Annals of Tropical Research ◽

10.32945/atr4023.2018 ◽

2018 ◽

pp. 35-44

Author(s):

Lorenzo Halasan ◽

Danilo Dy

Keyword(s):

Chlorophyll Content ◽

Chlorophyll A ◽

Biomass Productivity ◽

Nonparametric Tests ◽

Coastal Areas ◽

Light Limitation ◽

Thalassia Hemprichii ◽

Chl A ◽

Pigment Extraction ◽

Significant Difference

Variations in the chlorophyll concentrations in seagrass leaves can be used to indicate biomass, productivity and overall ecosystem condition in coastal areas. In this study, we determined the chlorophyll content (ie chl a and b) of Thalassia hemprichii from selected coastal areas in Cebu Island, Central Philippines to determine if there were spatial variations between intertidal (0m) and subtidal (1.5m) sections, and in the five geographically separate coastal areas of the island. Pigment extraction was done using 95% acetone, the solution analyzed via spectrophotometry and quantified using the equation of Ritchie (2006). The values were statistically compared using nonparametric tests. Mean chlorophyll content and chlorophyll a/b ratio of T. hemprichii showed no significant variations between intertidal and subtidal sections: F(4,45)=27.75, p=0.192 for mean chlorophyll content and F(4,45)=18.28, p=0.116 for chlorophyll a/b ratio. However, there was significant difference between geographic areas (p=0.000). Although T. hemprichii tend to display a physiological response to shading and light limitation, the difference in depth (≈ 1.5m) between intertidal and subtidal sections did not produce a statistically meaningful difference. However, the significant differences between sites for the chlorophyll content and chlorophyll a/b ratio of T. hemprichii could guide future decision in seagrass transplantation of specific localities.

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Chloroplastid pigment contents and chlorophyll a fluorescence in Amazonian tropical three species

Revista Árvore ◽

10.1590/s0100-67622007000500020 ◽

2007 ◽

Vol 31 (5) ◽

pp. 959-966 ◽

Cited By ~ 14

Author(s):

Ronaldo Ribeiro de Morais ◽

José Francisco de Carvalho Gonçalves ◽

Ulysses Moreira dos Santos Júnior ◽

Oliver Dünisch ◽

André Luis Wendt dos Santos

Keyword(s):

Chlorophyll A ◽

Chlorophyll A Fluorescence ◽

Plant Biomass ◽

Wet Season ◽

Chl A ◽

Carapa Guianensis ◽

Significant Difference ◽

Pigment Contents ◽

Chloroplastidic Pigments ◽

Shade Leaves

Plants react to changes in light and hydrological conditions in terms of quantity and composition of chloroplastidic pigments, which affects the photosynthetic properties and consequently the accumulation of plant biomass. Thus, the chloroplastidic pigment concentration and chlorophyll a fluorescence of three Amazonian species (Bertholletia excelsa, Carapa guianensis e Dipteryx odorata) were investigated in sun and shade leaves form the tree crown collected during two distinct periods of precipitation (dry and rainy seasons). Pigment contents were determined by spectrophotometry and fluorescence variables were determined using a portable fluorometer. The results demonstrated that the species showed high concentrations of Chl a, Chl b e Chl total during the wet season in relation to the dry season, especially in shade leaves. A higher concentration of carotenoids was found in B. excelsa, when compared with leaves of C. guianensis and D. odorata. In leaves of B. excelsa and D. odorata no significant difference was found in relation to the photochemistry of photosystem II (Fv/Fm) between the wet and dry seasons. In conclusion, the three species react differently to variations in the light and precipitation conditions regarding light capture, aspects that might be considered in the management of forest plantations.

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Spatiotemporal Variability of Surface Phytoplankton Carbon and Carbon-to-Chlorophyll a Ratio in the South China Sea Based on Satellite Data

Remote Sensing ◽

10.3390/rs13010030 ◽

2020 ◽

Vol 13 (1) ◽

pp. 30

Author(s):

Wenlong Xu ◽

Guifen Wang ◽

Long Jiang ◽

Xuhua Cheng ◽

Wen Zhou ◽

...

Keyword(s):

South China Sea ◽

Chlorophyll A ◽

South China ◽

Satellite Data ◽

Phytoplankton Biomass ◽

The South China Sea ◽

Spatiotemporal Variability ◽

The South ◽

Chl A ◽

China Sea

The spatiotemporal variability of phytoplankton biomass has been widely studied because of its importance in biogeochemical cycles. Chlorophyll a (Chl-a)—an essential pigment present in photoautotrophic organisms—is widely used as an indicator for oceanic phytoplankton biomass because it could be easily measured with calibrated optical sensors. However, the intracellular Chl-a content varies with light, nutrient levels, and temperature and could misrepresent phytoplankton biomass. In this study, we estimated the concentration of phytoplankton carbon—a more suitable indicator for phytoplankton biomass—using a regionally adjusted bio-optical algorithm with satellite data in the South China Sea (SCS). Phytoplankton carbon and the carbon-to-Chl-a ratio (θ) exhibited considerable variability spatially and seasonally. Generally, phytoplankton carbon in the northern SCS was higher than that in the western and central parts. The regional monthly mean phytoplankton carbon in the northern SCS showed a prominent peak during December and January. A similar pattern was shown in the central part of SCS, but its peak was weaker. Besides the winter peak, the western part of SCS had a secondary maximum of phytoplankton carbon during summer. θ exhibited significant seasonal variability in the northern SCS, but a relatively weak seasonal change in the western and central parts. θ had a peak in September and a trough in January in the northern and central parts of SCS, whereas in the western SCS the minimum and maximum θ was found in August and during October–April of the following year, respectively. Overall, θ ranged from 26.06 to 123.99 in the SCS, which implies that the carbon content could vary up to four times given a specific Chl-a value. The variations in θ were found to be related to changing phytoplankton community composition, as well as dynamic phytoplankton physiological activities in response to environmental influences; which also exhibit much spatial differences in the SCS. Our results imply that the spatiotemporal variability of θ should be considered, rather than simply used a single value when converting Chl-a to phytoplankton carbon biomass in the SCS, especially, when verifying the simulation results of biogeochemical models.

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Research on Inversion Mechanism of Chlorophyll—A Concentration in Water Bodies Using a Convolutional Neural Network Model

Water ◽

10.3390/w13050664 ◽

2021 ◽

Vol 13 (5) ◽

pp. 664

Author(s):

Yun Xue ◽

Lei Zhu ◽

Bin Zou ◽

Yi-min Wen ◽

Yue-hong Long ◽

...

Keyword(s):

Neural Network ◽

Regression Model ◽

Convolutional Neural Network ◽

Chlorophyll A ◽

Language Processing ◽

Water Bodies ◽

Inversion Effect ◽

Least Squares Regression ◽

Chlorophyll A Concentration ◽

Chl A

For Case-II water bodies with relatively complex water qualities, it is challenging to establish a chlorophyll-a concentration (Chl-a concentration) inversion model with strong applicability and high accuracy. Convolutional Neural Network (CNN) shows excellent performance in image target recognition and natural language processing. However, there little research exists on the inversion of Chl-a concentration in water using convolutional neural networks. Taking China’s Dongting Lake as an example, 90 water samples and their spectra were collected in this study. Using eight combinations as independent variables and Chl-a concentration as the dependent variable, a CNN model was constructed to invert Chl-a concentration. The results showed that: (1) The CNN model of the original spectrum has a worse inversion effect than the CNN model of the preprocessed spectrum. The determination coefficient (RP2) of the predicted sample is increased from 0.79 to 0.88, and the root mean square error (RMSEP) of the predicted sample is reduced from 0.61 to 0.49, indicating that preprocessing can significantly improve the inversion effect of the model.; (2) among the combined models, the CNN model with Baseline1_SC (strong correlation factor of 500–750 nm baseline) has the best effect, with RP2 reaching 0.90 and RMSEP only 0.45. The average inversion effect of the eight CNN models is better. The average RP2 reaches 0.86 and the RMSEP is only 0.52, indicating the feasibility of applying CNN to Chl-a concentration inversion modeling; (3) the performance of the CNN model (Baseline1_SC (RP2 = 0.90, RMSEP = 0.45)) was far better than the traditional model of the same combination, i.e., the linear regression model (RP2 = 0.61, RMSEP = 0.72) and partial least squares regression model (Baseline1_SC (RP2 = 0.58. RMSEP = 0.95)), indicating the superiority of the convolutional neural network inversion modeling of water body Chl-a concentration.

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Response of Total Suspended Sediment and Chlorophyll-a Concentration to Late Autumn Typhoon Events in the Northwestern South China Sea

Remote Sensing ◽

10.3390/rs13152863 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2863

Author(s):

Junyi Li ◽

Huiyuan Zheng ◽

Lingling Xie ◽

Quanan Zheng ◽

Zheng Ling ◽

...

Keyword(s):

South China Sea ◽

Continental Shelf ◽

Suspended Sediment ◽

Chlorophyll A ◽

South China ◽

Total Suspended Sediment ◽

Offshore Area ◽

Chl A ◽

Late Autumn ◽

China Sea

Strong typhoon winds enhance turbulent mixing, which induces sediment to resuspend and to promote chlorophyll-a (Chl-a) blooms in the continental shelf areas. In this study, we find limited Chl-a responses to three late autumn typhoons (typhoon Nesat, Mujigae and Khanun) in the northwestern South China Sea (NWSCS) using satellite observations. In climatology, the Chl-a and total suspended sediment (TSS) concentrations are high all year round with higher value in autumn in the offshore area of the NWSCS. After the typhoon passage, the Chl-a concentration increases slightly (23%), while even TSS enhances by 280% on the wide continental shelf of the NWSCS. However, in the southern area, located approximately 100 km from the typhoon tracks, both TSS and Chl-a concentrations increase 160% and 150% after typhoon passage, respectively. In the deeper area, the increased TSS concentration is responsible for the considerable increase of the Chl-a. An empirical analysis is applied to the data, which reveals the TSS and Chl-a processes during typhoon events. The results of this study suggest a different mechanism for Chl-a concentration increase and thus contribute toward further evaluation of typhoon-induced biological responses.

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Temporal Variation of Chlorophyll-a Concentrations in Highly Dynamic Waters from Unattended Sensors and Remote Sensing Observations

Sensors ◽

10.3390/s18082699 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2699 ◽

Cited By ~ 2

Author(s):

Jian Li ◽

Liqiao Tian ◽

Qingjun Song ◽

Zhaohua Sun ◽

Hongjing Yu ◽

...

Keyword(s):

Remote Sensing ◽

Water Quality ◽

Chlorophyll Fluorescence ◽

Chlorophyll A ◽

Temporal Variations ◽

Lake Area ◽

Short Term ◽

Chl A ◽

Spatio Temporal

Monitoring of water quality changes in highly dynamic inland lakes is frequently impeded by insufficient spatial and temporal coverage, for both field surveys and remote sensing methods. To track short-term variations of chlorophyll fluorescence and chlorophyll-a concentrations in Poyang Lake, the largest freshwater lake in China, high-frequency, in-situ, measurements were collected from two fixed stations. The K-mean clustering method was also applied to identify clusters with similar spatio-temporal variations, using remote sensing Chl-a data products from the MERIS satellite, taken from 2003 to 2012. Four lake area classes were obtained with distinct spatio-temporal patterns, two of which were selected for in situ measurement. Distinct daily periodic variations were observed, with peaks at approximately 3:00 PM and troughs at night or early morning. Short-term variations of chlorophyll fluorescence and Chl-a levels were revealed, with a maximum intra-diurnal ratio of 5.1 and inter-diurnal ratio of 7.4, respectively. Using geostatistical analysis, the temporal range of chlorophyll fluorescence and corresponding Chl-a variations was determined to be 9.6 h, which indicates that there is a temporal discrepancy between Chl-a variations and the sampling frequency of current satellite missions. An analysis of the optimal sampling strategies demonstrated that the influence of the sampling time on the mean Chl-a concentrations observed was higher than 25%, and the uncertainty of any single Terra/MODIS or Aqua/MODIS observation was approximately 15%. Therefore, sampling twice a day is essential to resolve Chl-a variations with a bias level of 10% or less. The results highlight short-term variations of critical water quality parameters in freshwater, and they help identify specific design requirements for geostationary earth observation missions, so that they can better address the challenges of monitoring complex coastal and inland environments around the world.

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Can chlorophyll-a in meso-oligotrophic shallow waters be estimated using statistical approaches and empirical models from MODIS imagery?

RBRH ◽

10.1590/2318-0331.231820170106 ◽

2018 ◽

Vol 23 (0) ◽

Author(s):

Andres Mauricio Munar ◽

José Rafael Cavalcanti ◽

Juan Martin Bravo ◽

David Manuel Lelinho Da Motta Marques ◽

Carlos Ruberto Fragoso Júnior

Keyword(s):

Linear Regression ◽

Spatial Heterogeneity ◽

Multiple Linear Regression ◽

Chlorophyll A ◽

Linear Regression Analysis ◽

Multiple Linear Regression Analysis ◽

Accurate Estimation ◽

Shallow Waters ◽

Chl A ◽

Input Variables

ABSTRACT Accurate estimation of chlorophyll-a (Chl-a) concentration in inland waters through remote-sensing techniques is complicated by local differences in the optical properties of water. In this study, we applied multiple linear regression (MLR), artificial neural network (ANN), nonparametric multiplicative regression (NPMR) and four models (Appel, Kahru, FAI and O14a) to estimate the Chl -a concentration from combinations of spectral bands from the MODIS sensor. The MLR, NPMR and ANN models were calibrated and validated using in-situ Chl -a measurements. The results showed that a simple and efficient model, developed and validated through multiple linear regression analysis, offered advantages (i.e., better performance and fewer input variables) in comparison with ANN, NPMR and four models (Appel, Kahru, FAI and O14a). In addition, we observed that in a large shallow subtropical lake, where the wind and hydrodynamics are essential factors in the spatial heterogeneity (Chl-a distribution), the MLR model adjusted using the specific point dataset, performed better than using the total dataset, which suggest that would not be appropriate to generalize a single model to estimate Chl-a in these large shallow lakes from total datasets. Our approach is a useful tool to estimate Chl -a concentration in meso-oligotrophic shallow waters and corroborates the spatial heterogeneity in these ecosystems.

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Analysis of within- and between-day chlorophyll-a dynamics in Mantua Superior Lake, with a continuous spectroradiometric measurement

Marine and Freshwater Research ◽

10.1071/mf12229 ◽

2013 ◽

Vol 64 (4) ◽

pp. 303 ◽

Cited By ~ 27

Author(s):

M. Bresciani ◽

M. Rossini ◽

G. Morabito ◽

E. Matta ◽

M. Pinardi ◽

...

Keyword(s):

Chlorophyll A ◽

Continuous Monitoring ◽

Phytoplankton Growth ◽

Key Factors ◽

Eutrophic Lakes ◽

Chl A ◽

Metabolic Adaptations ◽

Horizontal Migration ◽

Radiometric System ◽

Growth Distribution

Eutrophic lakes display unpredictable patterns of phytoplankton growth, distribution, vertical and horizontal migration, likely depending on environmental conditions. Monitoring chlorophyll-a (Chl-a) concentration provides reliable information on the dynamics of primary producers if monitoring is conducted frequently. We present a practical approach that allows continuous monitoring of Chl-a concentration by using a radiometric system that measures optical spectral properties of water. We tested this method in a shallow, nutrient-rich lake in northern Italy, the Mantua Superior Lake, where the radiometric system collected data all throughout the day (i.e. every 5 min) for ~30 days. Here, specifically developed algorithms were used to convert water reflectance to Chl-a concentration. The best performing algorithm (R2 = 0.863) was applied to a larger dataset collected in September 2011. We characterised intra- and inter-daily Chl-a concentration dynamics and observed a high variability; during a single day, Chl-a concentration varied from 20 to 130 mg m–3. Values of Chl-a concentration were correlated with meteo-climatic parameters, showing that solar radiance and wind speed are key factors regulating the daily phytoplankton growth and dynamics. Such patterns are usually determined by vertical migration of different phytoplankton species within the water column, as well as by metabolic adaptations to changes in light conditions.

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