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Leaf inclination and light interception of sunflower leaves. Leaf inclination and light interception of sunflower leaves. Importance of the petiole's mechanical and structural properties.
Luis F. Hernandez
Last modified: 2009-11-04
Abstract
The relationships between leaf biomass and morphology (lamina area and petiole and lamina inclination), petiole's mechanical and structural properties and the vertical light gradient inside the crop's canopy were studied in field grown sunflower plants (density=6 plants/sq meter), maintained at an optimum soil water and mineral status.
At flowering, incident PAR was measured at the top of the canopy and on individual leaves using a quantum sensor. The fraction of direct incident radiation that passes through the canopy reaching each individual leaf was then calculated.
Individual petiole and lamina inclination angles (iaP and iaL) were measured from orbital digital images taken from plants (n= 6) inside the crop. Petiole length and lamina area were measured after detaching the leaves from each plant.
Leaves were separated in petiole, lamina and main veins, and its dry weight (DWP, DWL, DWV, respectively) obtained. Petiole transverse cuts stained with acid fluoroglucinol were used to measure the relative area occupied by lignified and fibrous (supporting) tissue.
The petiole's Young's modulus (EP) for different leaves was calculated from a three-point bending test performed in petiole segments about 3.0 to 6.0 cm long. Petiole flexural rigidity (EIP) was calculated using elementary beam theory for homogenous materials.
Intercepted PAR in the canopy for individual leaves decreased basipetally. The iaP increased acropetally (from -9.0 deg. to +60.0 deg.) while the iaL increased basipetally (+1.0 deg. to -60.0 deg.) in concordance with increments in the intercepted PAR. Petiole specific weight (g/sq cm) did not change with leaf position whilst lamina specific weight decreased acropetally. Main veins dry weight increased basipetally. EP and EIP increased acropetally. The area covered by supporting tissue was significantly higher in upper petioles than in lower ones. The relationship between intercepted PAR and the ratio PDW/LDW was positively correlated.
The results obtained here suggest that, in order to optimize the interception of incident PAR, the sunflower plant invests more energy in differentiating supporting tissues in the petioles of the upper canopy. This results in the higher canopy strata having a preferentially planophyl to erectophyl leaf architecture.
At flowering, incident PAR was measured at the top of the canopy and on individual leaves using a quantum sensor. The fraction of direct incident radiation that passes through the canopy reaching each individual leaf was then calculated.
Individual petiole and lamina inclination angles (iaP and iaL) were measured from orbital digital images taken from plants (n= 6) inside the crop. Petiole length and lamina area were measured after detaching the leaves from each plant.
Leaves were separated in petiole, lamina and main veins, and its dry weight (DWP, DWL, DWV, respectively) obtained. Petiole transverse cuts stained with acid fluoroglucinol were used to measure the relative area occupied by lignified and fibrous (supporting) tissue.
The petiole's Young's modulus (EP) for different leaves was calculated from a three-point bending test performed in petiole segments about 3.0 to 6.0 cm long. Petiole flexural rigidity (EIP) was calculated using elementary beam theory for homogenous materials.
Intercepted PAR in the canopy for individual leaves decreased basipetally. The iaP increased acropetally (from -9.0 deg. to +60.0 deg.) while the iaL increased basipetally (+1.0 deg. to -60.0 deg.) in concordance with increments in the intercepted PAR. Petiole specific weight (g/sq cm) did not change with leaf position whilst lamina specific weight decreased acropetally. Main veins dry weight increased basipetally. EP and EIP increased acropetally. The area covered by supporting tissue was significantly higher in upper petioles than in lower ones. The relationship between intercepted PAR and the ratio PDW/LDW was positively correlated.
The results obtained here suggest that, in order to optimize the interception of incident PAR, the sunflower plant invests more energy in differentiating supporting tissues in the petioles of the upper canopy. This results in the higher canopy strata having a preferentially planophyl to erectophyl leaf architecture.