365
physiological functions and as shown in the TRY leaf trait database (Kattge et al.
2011). Studies show loose stoichiometric relationships between different biochemical elements such as C, N, and phosphorus and growth rates and biomass accumulation. Although the relationships vary with conditions and species, typically, C shows
relationships with X (biochemical) where the C/X ratio increases under nutrientlimited growth, increasing light intensity, and partial pressure of CO 2 and as a function the species (Sterner et al. 2002).
We expect that to maintain high levels of productivity, leaf chemistry associated
with light harvesting and reduction of CO 2 must be correlated, such as chlorophyll
a and b and N concentrations, and correlations with other nutrients and water content are all available at appropriate levels for leaves to achieve high productivity.
This is formulated in concepts of plant functional morphology (Tilman 1985;
Chapin et al. 1993), which emphasize trade-offs in allocation of resources. For
example, allocation should shift to shoots under low light and high nutrient conditions and to roots under high light and low nutrient conditions. Ackerly (1999) show
that under conditions of high fertility, high rates of growth produce self-shading in
older leaves that are lower in the canopy. This limits available light and results in
declining rates of assimilation for older leaves. Field (1983) reported that older
leaves had reduced N concentrations and photosynthetic potential. Other studies
have shown that canopies with steep light gradients exhibit greater declines in photosynthetic capacity than those with small gradients (Mooney et al. 1981). These
relationships result in high nutrient environments being favorable to deciduous trees
with high growth rates, low C/N ratios, and high rates of leaf and root turnover.
Under low nutrient conditions and high light environments, plants exhibit slower
growth rates and higher root/shoot ratios. Competition would favor slow growth and
low stature species with high nutrient retention and higher C/N ratios. The ratio of
leaf dry mass per unit leaf area seems to be highly correlated with growth potential,
and species with low mass per unit area have high potential growth rates and high
rates of C uptake, while species with high leaf mass area have low growth potential
but are generally more stress tolerant (Wright et al. 2004). Of course, all species fall
somewhere on this range, but annuals are expected to be at the higher growth end,
deciduous woody species are expected to have higher values than evergreen species,
and those with thick leathery evergreen leaves are expected to score among the lowest values.
Today, with the development of imaging spectrometry, there is active research
aimed at understanding the significance of different assemblages of leaf traits (and
their associated chemistry), the roles they play in adaptation for specific habitats,
and how they can be detected from spectral patterns measured with optical sensors
(Féret and Asner 2014a; Asner et al. 2014b, 2015; Serbin et al. 2015; Singh et al.
2015; Couture et al. 2016). The concept of detecting plant traits has jumped from
RS and ecological research to rapid testing of crop breeding of new genotypes
through high-throughput phenotyping (Araus and Cairns 2014; Li et al. 2014). The
current procedures are derived from precision farming but involve high spatial resolution (using differential GPS) multiple RS inputs, commonly including lidar, thermal infrared, imaging spectrometers, fluorescence imagers, and multiband imagery
14 How the Optical Properties of Leaves Modify the Absorption and Scattering…
physiological functions and as shown in the TRY leaf trait database (Kattge et al.
2011). Studies show loose stoichiometric relationships between different biochemical elements such as C, N, and phosphorus and growth rates and biomass accumulation. Although the relationships vary with conditions and species, typically, C shows
relationships with X (biochemical) where the C/X ratio increases under nutrientlimited growth, increasing light intensity, and partial pressure of CO 2 and as a function the species (Sterner et al. 2002).
We expect that to maintain high levels of productivity, leaf chemistry associated
with light harvesting and reduction of CO 2 must be correlated, such as chlorophyll
a and b and N concentrations, and correlations with other nutrients and water content are all available at appropriate levels for leaves to achieve high productivity.
This is formulated in concepts of plant functional morphology (Tilman 1985;
Chapin et al. 1993), which emphasize trade-offs in allocation of resources. For
example, allocation should shift to shoots under low light and high nutrient conditions and to roots under high light and low nutrient conditions. Ackerly (1999) show
that under conditions of high fertility, high rates of growth produce self-shading in
older leaves that are lower in the canopy. This limits available light and results in
declining rates of assimilation for older leaves. Field (1983) reported that older
leaves had reduced N concentrations and photosynthetic potential. Other studies
have shown that canopies with steep light gradients exhibit greater declines in photosynthetic capacity than those with small gradients (Mooney et al. 1981). These
relationships result in high nutrient environments being favorable to deciduous trees
with high growth rates, low C/N ratios, and high rates of leaf and root turnover.
Under low nutrient conditions and high light environments, plants exhibit slower
growth rates and higher root/shoot ratios. Competition would favor slow growth and
low stature species with high nutrient retention and higher C/N ratios. The ratio of
leaf dry mass per unit leaf area seems to be highly correlated with growth potential,
and species with low mass per unit area have high potential growth rates and high
rates of C uptake, while species with high leaf mass area have low growth potential
but are generally more stress tolerant (Wright et al. 2004). Of course, all species fall
somewhere on this range, but annuals are expected to be at the higher growth end,
deciduous woody species are expected to have higher values than evergreen species,
and those with thick leathery evergreen leaves are expected to score among the lowest values.
Today, with the development of imaging spectrometry, there is active research
aimed at understanding the significance of different assemblages of leaf traits (and
their associated chemistry), the roles they play in adaptation for specific habitats,
and how they can be detected from spectral patterns measured with optical sensors
(Féret and Asner 2014a; Asner et al. 2014b, 2015; Serbin et al. 2015; Singh et al.
2015; Couture et al. 2016). The concept of detecting plant traits has jumped from
RS and ecological research to rapid testing of crop breeding of new genotypes
through high-throughput phenotyping (Araus and Cairns 2014; Li et al. 2014). The
current procedures are derived from precision farming but involve high spatial resolution (using differential GPS) multiple RS inputs, commonly including lidar, thermal infrared, imaging spectrometers, fluorescence imagers, and multiband imagery
14 How the Optical Properties of Leaves Modify the Absorption and Scattering…