Light Penetration and Light-induced Seed Germination in Soil

Abstract

Light penetration through a Drummer silty clay loam and a Broomfield sand was measured spectrophotometrically and biologically. The spectrophotometric measurements showed that less than 1% of the incident fight penetrated 2.2 millimeters at any wavelength between 350 and 780 nanometers for ped sizes up to 1 milimeter. Biological measurements with lightsensitive lettuce (Lactuca sativa) seeds In soil showed that an exposure to Ught equivalent to about I sunny day induced some germination of seeds which were 2 milmeters below the surface, but did not affect seeds 6 millimeters below the surface.The known light sensitivity of many seeds (11) has led to the hypothesis that light may be important in inducing the germination of weed seeds in cultivated fields. Dormant seeds, brought close to the surface by cultivation, could receive light, either directly during cultivation or later through the soil, and could therefore germinate. Experiments have tended to confirm this hypothesis (3,7,10,12). Still, there has been no attempt to measure light penetration into soil or to find out how near a seed must be to the surface to be affected. Nor has there been an attempt to consider the role of temperature in such germination, even though light sensitivity of seeds is known to be highly dependent on temperature (1-3, 6, 10, 11). We therefore measured light penetration through soil spectrophotometrically and also biologically, controlling temperature, and using light-sensitive lettuce seeds buried in the soil as our bioindicator. At temperatures below about 20 C, Grand Rapids lettuce (Lactuca sativa L.) seeds do not require light treatment for germination, and will germinate when allowed to imbibe water. At higher imbibition temperatures, some of the seeds will germinate without light, but others need a light treatment for germination. At field sand. The Drummer soil, when dry, is dark gray with a Munsell color notation of 5YR 4/1, and when moist is black (5YR 2.5/1). The two Drummer ped sizes, 0.42 to 0.50 mm and 0.84 to I mm, were separated by sifting. This soil maintains the integrity of its aggregates well through wetting and drying cycles. Dry Broomfield sand is yellowish brown (IOYR 5/4), and the moist sand is dark yellowish brown (IOYR 3/4). The sand grain size range was 0.3 to 0.5 mm.To determine light transmittance spectrophotometrically, we used a Beckman DK-2A spectroreflectometer, with soil samples in acrylic plastic cuvettes.To determine light transmittance through soils biologically, we placed light-sensitive lettuce seeds at various depths in the soils, then exposed the soils to light. Subsequent germination of the seeds indicated light penetration into the soil.In the preliminary experiment to determine the exact characteristics of our seeds and to establish the optimum temperature, time, and light regimes, we cultured seeds in Petri dishes, which were kept dark at the desired inbibition and incubation temperature for the desired time, then exposed to light and again placed in the dark at a desired tem...

Volatile organic compounds (VOCs) in soils

“…Anyway, Atkinson and Arey (2003) give a very detailed overview on physical-chemical degradation of VOCs in the atmosphere where photolysis and spontaneous reactions with OH radicals (under the presence of light), NO 3 radicals (under the absence of light), O 3 (under the presence of light), and Cl atoms (at coastlines) are the main processes responsible for abiotic VOC degradation. Considering the fact that light can only reach habitats located in the soil surface (Woolley and Stoller 1977;Ciani et al 2005), photolysis and other lightdriven reactions (with OH radicals and O 3 ) only occur in a thin surface zone (Konstantinou et al 2001). In this zone, OH radicals and O 3 are produced by microorganisms or they diffuse from the atmosphere.…”

A novel blue-light phototropic response is revealed in roots of Arabidopsis thaliana in microgravity

“…In addition to directing root growth towards the gravity vector, sunlight can penetrate the soil up to several millimeters beneath the soil surface, having a direct effect on the growth and development of roots (Woolley and Stoller 1978;Tester and Morris 1987). The red and farred part of the light spectrum can penetrate to greater depths than blue light (Mandoli and Briggs 1984) which has led to plants evolving blue-light receptors located near the upper portion of roots and red-light receptors near the apices due to this pattern of light penetration (Mo et al 2015).…”

The Effect of Temperature, Light and Calcium Carbonate on Seed Germination and Radicle Growth of the Polycarpic Perennial Galium cracoviense (Rubiaceae), a Narrow Endemic Species From Southern Poland

“…Seed germination is affected by many environmental factors, such as temperature, salt, light, soil moisture, oxygen concentration, and Ca 2+ ions (Harper, 1977;Woolley and Stoller, 1978;Baskin and Baskin, 1988;Benvenuti et al, 2001;Koyuncu, 2005;Travlos, 2009;Arslan et al, 2011). The temperature, which influences dormancy and germination, is the primary environmental factor regulating the latter process, and light and soil moisture are of secondary importance (Baskin and Baskin, 1988).…”