Reflectance, absorbance and transmittance spectra of bermudagrass and manilagrass turfgrass canopies
November
Reflectance, absorbance and transmittance spectra of bermudagrass and manilagrass turfgrass canopies
Marco Volterrani 0 1
Alberto Minelli 1
Monica Gaetani 0 1
Nicola Grossi 0 1
Simone Magni 0 1
Lisa Caturegli 1
0 Department of Agriculture , Food and Environment , University of Pisa , Pisa , Italy , 2 Department of Agricultural Sciences, University of Bologna , Bologna , Italy
1 Editor: Randall P. Niedz, United States Department of Agriculture , UNITED STATES
Leaves act as a primary organ for the interception of solar radiation and their spatial arrangement determines how the plant canopy interacts with light. Many studies have been carried out on the penetration of radiation into crops however to date, few results are available on turfgrasses, mainly due to the difficulties of introducing sensors into the turf without disturbing the natural position of the leaves. In the present research two warm season turfgrasses, hybrid bermudagrass (Cynodon dactylon × transvaalensis) 'Patriot' and manilagrass (Zoysia matrella) 'Zeon', were studied. The aim was to describe their canopy architecture grown with minimal disturbance to the natural arrangement of the leaves and stems, and to determine the potential effects of canopy architecture on light penetration and reflectance. Radiometric measurements were carried out at eight different profile levels of turfgrasses that were up to 12 cm tall. A LI-COR 1800 spectroradiometer with an optical fiber cable and a 7 mm diameter sensor was used. Measurements were carried out in the 390±1100 nm region at 5 nm intervals. The LAI value was higher for the manilagrass (9.0) than for the hybrid bermudagrass (5.6). The transmitted radiation was found to be closely dependent on downward cumulative LAI. Despite a more upright habit (mean insertion angle of 22.4Ê ±3.4), Zoysia matrella showed a higher NIR reflectance compared to Cdxt, which has a horizontal leaf arrangement (mean insertion angle 62.1Ê ± 9.6). The species studied showed substantial differences both in terms of phytometric characteristics and in the capacity to attenuate solar radiation.
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Data Availability Statement: All relevant data are
within the paper.
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
Introduction
Plants depend on solar radiation for the energy necessary to carry on photosynthesis and
photomorphogenesis. For the interception of incoming radiation leaves act as primary organ
and a number of properties have been reported to affect the leaf-light interaction such as cell
structure [
1
], pigment content [
2
], and surface characteristics [
3
]. Light reaching every point
within a canopy derives from two components: unfiltered radiation (direct or diffuse) and
filtered radiation which is modified and attenuated as it passes through the vegetation.
Incident radiation is only partially reflected by the external surface of a plant, while at the canopy
level, light interacts extensively with a plant community with a multitude of reflection,
refraction and diffusion phenomena which occur both within single leaves and the whole canopy.
Incident radiation is therefore partly absorbed, transmitted and subsequently redirected
outside the canopy as reflected light [
4
]. The radiation reflected by plant canopies brings a specific
ªspectral signatureº and the analysis of reflectance spectra provides valuable information on
the species [
5
] color [6; 7; 8] Leaf Area Index (LAI) [9; 10] chlorophyll content [
11
], drought
stress [12; 13] and nutritional status [14; 15] of many crops and turfgrasses. Based on the
interpretation of spectral reflectance instruments have been developed for the early detection of
stress in plants or for large scale data acquisition [16; 17; 18].
The canopy architecture, however, may lead to substantial variations in the plants ability to
interact with the incident radiation [
19
]. Canopy architecture is broadly defined as the amount
and spatial arrangement of the aboveground plant organs [20; 21]. Parameters such as the leaf
area index (LAI) [22; 23; 24], shoot density [
20
], specific leaf weight (SLW) [
25
], have been
used in previous studies to describe the amount of plant tissue over a given soil surface. On the
other hand, the spatial arrangement has often been described by the determination of leaf
angles, sometimes referred to as leaf orientation or leaf inclination [
26
]. Leaf biochemistry,
namely pigments, and canopy architecture, have been shown to be distinct sources of
variability in reflectance spectra. Pigment content and composition affect reflectance in the
photosynthetically active radiation (PAR) range (400±700 nm), whereas reflectance in the near infrared
(NIR) range (750±1100 nm) is governed mainly by canopy architecture, cell structure and leaf
inclination [
27
].
A large number of studies on the penetration of radiation into c (...truncated)