lambsquarters seeds

Two publications provide insight into the germination structure of common lambsquarters seed rain arising from seed morphology and environment, with implications for the patterns of seedling recruitment.

• The effects of light, temperature, after-ripening, nitrate and water on Chenopodium

Chenopodium album flowers are arranged in glomerules, forming spikes at a terminal panicle (Gleason and Cronquist, 1963). Seeds appear to be disk-shaped with two convex sides. Detailed seed morphology and classification is not agreed upon in published literature, but similarities are evident among descriptions as illustrated herein. As described by Delorit (1970), seeds of C. album are black, with a glossy surface and enclosed in a semi-translucent granular pericarp. The five-parted perianth may also be attached to the seed, but is often detached during collection and subsequent handling. The seeds of C. album have been described by Williams and Harper (1965) as having four distinct forms at maturity: brown-reticulate, brown-smooth, black-reticulate and black-smooth. Additionally, all of these seed types may be present on the same plant. Chu, Sweet and Ozbun (1978) described seed as having four color morphs: brown, deep brown, brown-black and black but they did not distinguish between smooth or reticulate. Wentland (1965) described the variation in color as yellow, orange, and dark red being characteristic of immature seed, whereas mature seeds are dark in color. A few studies considered here (Henson, 1970; Moravcova and Dostalek, 1989) stated that they used only black seed while most studies did not specify seed morphology.

The study reported herein used only seed which appeared to be brown to dark brown in color, with pericarp intact or nearly complete, as this was the state of seed when collected. A perianth was present on roughly half of seeds used, in an open or closed formation, as collected in the field. Immature, yellow, orange or red seeds were omitted from experiments.

Germination tests were conducted in the light on the several morphological types of C. album seed present in Ames, Iowa populations (October 5, 2007 harvest; Table 1). The structure of C. album seed variability, seed heteroblasty, was revealed in the differences among seed morphological phenotypes to alternating temperature.

Table 1. Structure of Chenopodium album seed germination (%) in response to seed hull morphology (color, structure, maturity), alternating temperature (5-15; 15-25; 25-35° C), and chilling pretreatment (4° C-wet-dark after-ripening; 0-35 days).

Seed Hull Phenotype		Alternating Temperature	Maximum % Germination
Color	Morphology	Alternating Temperature	Maximum % Germination
Red	immature	5-15° C	15
		15-25° C	5
		25-35° C	20

Dark	sepals and perianth present	5-15° C	5
		15-25° C	20
		25-35° C	10
	reticulate (net-like) hull	5-15° C	10
		15-25° C	15
		25-35° C	5
	smooth hull	5-15° C	35
		15-25° C	45
		25-35° C	15

The greatest germination was observed with dark-smooth seeds, which also were the most responsive to cool (5-15° C) and warm (15-25° C) temperatures. Immature red seed were the most readily germinable (data not presented) and most responsive to hot (25-35° C) temperatures. Among dark seeds, germination was less with reticulate relative to smooth seeds.

The structure of C. album seed variability, seed heteroblasty, was revealed by conducting germination assays on propagules collected in Ames, Iowa in 2007 (October 5) and 2008 (October 11). These seed germination assays were organized as a factorial arrangement of treatments to understand the complex interactions of 6 parameters:

2] Chilling after-ripening (4° C-wet-dark) pretreatment (0-10 weeks) prior to the germination assay,

All six parameters affected C. album seed germination, but groups of seeds within each population responded to these stimulatory factors differently (Table 2). The germination structure, seed heteroblasty, was made apparent in different combinations of these factors. There exist different germination fractions in C. album seed populations: the seed rain consists of different groups, each of which is stimulated by different sets of germination conditions. Germination was stimulated primarily by light, but a small fraction was revealed in dark germination. Germination was greatest in warm (15-25° C) alternating temperatures, but other fractions responded to hot (25-35° C) conditions. Nitrate stimulated germination significantly, but some fractions responded well to just water. In fact the 2008 population germination increased with increasing water quantity (warm; nitrate), a fractional response not observed in the 2007 population. Fine scale germination structure was revealed in many factor combinations with increasing dosages of pre-chilling (oxygenation): each week (0-4 or 5) more germination sub-fractions were revealed.

Table 2. Structure of Chenopodium album seed germination in response to year of embryogenesis, photoperiod (light, dark), alternating temperature (5-15; 15-25; 25-35° C), nitrate(0.01 M), water quantity (0.75, 1.0, or 1.25 ml), 4° C-wet-dark after-ripening (chilling) duration (weeks) and percent seed germination; ‘-‘, averaged over this parameter of the interaction.

Year	Light-Dark	Alternating Temp	Nitrate (0.01 M)	Water Amount	Chilling Time to Max Germ	% Seed Germ
2007	Dark	-	-NO₂	-	-	0-2
	Light		-	H₂O	0-4 weeks	2-7
			-NO₂	-	0-4 weeks	7-22
		25-35° C	-		0-5 weeks	5-20
		15-25° C	-		0-5 weeks	5-25

2008	Dark	-	-	-	-	0-2
	Light	25-35° C		H₂O	=	0-4
		15-25° C		H₂O	0-4 weeks	4-19
		25-35° C	-NO₂	-	0-4 weeks	3-38
		15-25° C		-	0-5 weeks	6-50
				0.75 ml	-	27
				1.00 ml		33
				1.25 ml		38

The complexity of C. album seed germination structure may provide some insight into the complexity of recruitment patterns revealed in the research conducted by the European Weed Research Society, Working group on germination and early growth, on this species.

Altenhofen, L.A. 2009. The effects of light, temperature, after-ripening, nitrate and water on Chenopodium album seed germination. M.S. Thesis; Ecology and Evolutionary Biology, Iowa State University.

Chu, C. C., R. D. Sweet, and J. L. Ozbun. 1978. Some germination characteristics in common lambsquarters (Chenopodium album). Weed Sci. 26:255-258.

Delorit, R. J. 1970. An illustrated taxonomy manual of weed seeds. Agronomy Publications, River Falls, Wisconsin. p 76.

Gleason, H. A. and A. Cronquist. 1963. Manual of vascular plants of northeastern United States and adjacent Canada. D. Van Nostrand Company, New York, New York. p 274.

Henson, I. E. 1970. The effects of light, potassium nitrate, and temperature on the germination of Chenopodium album L. Weed Res. 10:27-39.

Moravcova, L. and J. Dostalek. 1989. Contribution to the biology of germination of four species of Chenopodium album agg. under different conditions. Folia Geobot. Phytotx. 24:431-439.

Seed germination

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