Evaluating leaf chlorophyll content prediction from multispectral remote sensing data within a physically-based modelling framework

Croft, Holly; Chen, J.M.; Zhang, Y.; Simic, A.; Noland, Thomas L.; Nesbitt, N.; Arabian, Jane M.

doi:10.1016/j.isprsjprs.2015.01.008

Cited by 95 publications

(44 citation statements)

References 50 publications

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“…The changes in Chl leaf may impact the amount of APAR distributed between leaves but the total APAR for the canopy is likely not sensitive to the changes in Chl leaf . It explains why most studies incorporating Chl leaf in TBMs only consider the impact of Chl leaf on

{V normalc}_{\max}^{25}

(Alton, ; Houborg et al, ; Luo, Croft, et al, ) and light use efficiency (Croft, Chen, Froelich, Chen, & Staebler, ; Croft, Chen, Zhang, et al, ; Houborg, Anderson, Daughtry, Kustas, & Rodell, ) and neglect the impact of Chl leaf on APAR. However, we acknowledge that the impact of Chl leaf on canopy fAPAR, though usually small, needs to be addressed in some special cases (i.e.…”

Section: Discussionmentioning

confidence: 99%

Improved estimates of global terrestrial photosynthesis using information on leaf chlorophyll content

Luo

Croft

Chen

et al. 2019

Global Change Biology

118

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The terrestrial biosphere plays a critical role in mitigating climate change by absorbing anthropogenic CO2 emissions through photosynthesis. The rate of photosynthesis is determined jointly by environmental variables and the intrinsic photosynthetic capacity of plants (i.e. maximum carboxylation rate; Vnormalcmax25). A lack of an effective means to derive spatially and temporally explicit Vnormalcmax25 has long hampered efforts towards estimating global photosynthesis accurately. Recent work suggests that leaf chlorophyll content (Chlleaf) is strongly related to Vnormalcmax25, since Chlleaf and Vnormalcmax25 are both correlated with photosynthetic nitrogen content. We used medium resolution satellite images to derive spatially and temporally explicit Chlleaf, which we then used to parameterize Vnormalcmax25 within a terrestrial biosphere model. Modelled photosynthesis estimates were evaluated against measured photosynthesis at 124 eddy covariance sites. The inclusion of Chlleaf in a terrestrial biosphere model improved the spatial and temporal variability of photosynthesis estimates, reducing biases at eddy covariance sites by 8% on average, with the largest improvements occurring for croplands (21% bias reduction) and deciduous forests (15% bias reduction). At the global scale, the inclusion of Chlleaf reduced terrestrial photosynthesis estimates by 9 PgC/year and improved the correlations with a reconstructed solar‐induced fluorescence product and a gridded photosynthesis product upscaled from tower measurements. We found positive impacts of Chlleaf on modelled photosynthesis for deciduous forests, croplands, grasslands, savannas and wetlands, but mixed impacts for shrublands and evergreen broadleaf forests and negative impacts for evergreen needleleaf forests and mixed forests. Our results highlight the potential of Chlleaf to reduce the uncertainty of global photosynthesis but identify challenges for incorporating Chlleaf in future terrestrial biosphere models.

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{V normalc}_{\max}^{25}

Section: Discussionmentioning

confidence: 99%

Improved estimates of global terrestrial photosynthesis using information on leaf chlorophyll content

Luo

Croft

Chen

et al. 2019

Global Change Biology

118

View full text Add to dashboard Cite

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“…The lack of progress at the global scale has largely been due to the lack of spectral bands sampled by existing satellite sensors that are sensitive to chlorophyll content, along the red‐edge portion of the electromagnetic spectrum. However, recent work has indicated that physically based radiative transfer models can accurately model leaf chlorophyll content using a reduced number of spectral bands [ Croft et al ., ]. Furthermore, an increasing number of sensors are beginning to contain the “red‐edge” bands that are highly sensitive to chlorophyll content, including Envisat MERIS (from 2002 to 2012), the forthcoming European Space Agency Sentinel‐2 mission, and the Vegetation and Environment monitoring New MicroSatellite (Venus) platform.…”

Section: Discussionmentioning

confidence: 99%

Seasonal controls of canopy chlorophyll content on forest carbon uptake: Implications for GPP modeling

et al. 2015

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Forested ecosystems represent an important part of the global carbon cycle, with accurate estimates of gross primary productivity (GPP) crucial for understanding ecosystem response to environmental controls and improving global carbon models. This research investigated the relationships between leaf area index (LAI) and leaf chlorophyll content (Chl Leaf ) with forest carbon uptake. Ground measurements of LAI and Chl Leaf were taken approximately every 9 days across the 2013 growing season from day of year (DOY) 130 to 290 at Borden Forest, Ontario. These biophysical measurements were supported by on-site eddy covariance flux measurements. Differences in the temporal development of LAI and Chl Leaf were considerable, with LAI reaching maximum values within approximately 10 days of bud burst at DOY 141. In contrast, Chl Leaf accumulation only reached maximum values at DOY 182. This divergence has important implications for GPP models which use LAI to represent the fraction of light absorbed by a canopy (fraction of absorbed photosynthetic active radiation (fAPAR)). Daily GPP values showed the strongest relationship with canopy chlorophyll content (Chl Canopy ; R 2 = 0.69, p < 0.001), with the LAI and GPP relationship displaying nonlinearity at the start and end of the growing season (R 2 = 0.55, p < 0.001). Modeled GPP derived from LAI × PAR and Chl Canopy × PAR was tested against measured GPP, giving R 2 = 0.63, p < 0.001 and R 2 = 0.82, p < 0.001, respectively. This work demonstrates the importance of considering canopy pigment status in deciduous forests, with models that use fAPAR LAI rather than fAPAR Chl neglecting to account for the importance of leaf photosynthetic potential.

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“…The absorption coefficients were recalculated to the corresponding Landsat bands using their respective spectral response functions. PROSPECT has previously been successfully used to model chlorophyll from multispectral data (Croft et al ., ).…”

Section: Methodsmentioning

confidence: 97%

Leaf chlorophyll content as a proxy for leaf photosynthetic capacity

Croft

Chen

Luo

et al. 2017

Global Change Biology

492

335

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Improving the accuracy of estimates of forest carbon exchange is a central priority for understanding ecosystem response to increased atmospheric CO levels and improving carbon cycle modelling. However, the spatially continuous parameterization of photosynthetic capacity (Vcmax) at global scales and appropriate temporal intervals within terrestrial biosphere models (TBMs) remains unresolved. This research investigates the use of biochemical parameters for modelling leaf photosynthetic capacity within a deciduous forest. Particular attention is given to the impacts of seasonality on both leaf biophysical variables and physiological processes, and their interdependent relationships. Four deciduous tree species were sampled across three growing seasons (2013-2015), approximately every 10 days for leaf chlorophyll content (Chl ) and canopy structure. Leaf nitrogen (N ) was also measured during 2014. Leaf photosynthesis was measured during 2014-2015 using a Li-6400 gas-exchange system, with A-Ci curves to model Vcmax. Results showed that seasonality and variations between species resulted in weak relationships between Vcmax normalized to 25°C (Vcmax25) and N (R = 0.62, P < 0.001), whereas Chl demonstrated a much stronger correlation with Vcmax25 (R = 0.78, P < 0.001). The relationship between Chl and N was also weak (R = 0.47, P < 0.001), possibly due to the dynamic partitioning of nitrogen, between and within photosynthetic and nonphotosynthetic fractions. The spatial and temporal variability of Vcmax25 was mapped using Landsat TM/ETM satellite data across the forest site, using physical models to derive Chl . TBMs largely treat photosynthetic parameters as either fixed constants or varying according to leaf nitrogen content. This research challenges assumptions that simple N -Vcmax25 relationships can reliably be used to constrain photosynthetic capacity in TBMs, even within the same plant functional type. It is suggested that Chl provides a more accurate, direct proxy for Vcmax25 and is also more easily retrievable from satellite data. These results have important implications for carbon modelling within deciduous ecosystems.

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Evaluating leaf chlorophyll content prediction from multispectral remote sensing data within a physically-based modelling framework

Cited by 95 publications

References 50 publications

Improved estimates of global terrestrial photosynthesis using information on leaf chlorophyll content

Improved estimates of global terrestrial photosynthesis using information on leaf chlorophyll content

Seasonal controls of canopy chlorophyll content on forest carbon uptake: Implications for GPP modeling

Leaf chlorophyll content as a proxy for leaf photosynthetic capacity

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