Changes in dormancy and viability of weed seeds in soils.
TL;DR: Phy tochrome was important in controlling germination of the recovered weed seeds, and manifested itself as an acquired type of dormancy, as well as an initial one, but other factors in the soil environment appear to interact with the phytochrome system in the control of germinationof weed seeds in soils.
Abstract: Seeds of several weed species, each with initially known responses to light and temperature, were buried in soil in an open field at 2.5, 7.6, and 15.2-cm depths during November. At 3-month intervals during the following year, the seeds were recovered in the dark and reexamined for their response to light and temperature, and their viability. Loss in viability occurred fastest with seeds having little initial dormancy and with shallow placement of seeds. Phytochrome was important in controlling germination of the recovered weed seeds, and manifested itself as an acquired type of dormancy, as well as an initial one. However, other factors in the soil environment appear to interact with the phytochrome system in the control of germination of weed seeds in soils.
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TL;DR: The different factors that affect dormancy in weed seed banks in soil are discussed, aiming to set a conceptual basis that will facilitate the construction of predictive models and stress the importance of clarifying the interaction between soil thermal and hydric conditions in the modification of the degree of dormancy of seed populations.
520 citations
Cites background from "Changes in dormancy and viability o..."
...Examples of summer annuals presenting such a pattern of change are Cyperus in¯exus (Baskin and Baskin, 1978), Barbarea vulgaris (Taylorson, 1970), Stellaria faberi (Taylorson, 1972), P. aviculare (Courtney, 1968; Kruk and Benech-Arnold, 1998), P. persicaria (Karssen, 1980/81a,b; Bouwmeester and…...
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...Baskin, 1978), Barbarea vulgaris (Taylorson, 1970), Stellaria faberi (Taylorson, 1972), P....
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TL;DR: A view of the vegetative structure of a herb as the functional fruit ("bait" for the dispersal agent) confounds attempts at understanding leaf defensive chemistry and seed coat traits solely in the context of fitness-depressing herbivory or seed dormancy.
Abstract: Many species of herbs (including grasses) have some of their seeds dispersed by the large grazing mammals that consume the seeds along with foliage. This is an interaction that has probably been oc...
443 citations
TL;DR: Researchers have known for decades that many buried seeds need to be brought to the soil surface before they will germinate, and to understand how germination of buried seeds is controlled, plant biologists have studied the re.
Abstract: The classic studies of Brenchley and Warington (1930) and numerous other investigations have demonstrated that large reserves (pools) of weed seeds accumulate in arable soils. Work reviewed by Kropad (1966) and Roberts (1981) shows that the number of seeds per m2 in the upper 15-25 cm of soil in cultivated fields may be as high as 70,000-90,000, and up to 95% of these may be contributed by annuals. Soil samples collected under vegetation of known age and history suggest that buried seeds of some weedy species may remain viable for 50100 years or more (e.g., Livingston and Allessio 1968, Oosting and Humphreys 1940). Seeds of 3 of 21 species buried in 1879 by W. J. Beal were viable after 100 years (Kivilaan and Bandurski 1981). In another experiment started by J. W. T. Duvel in 1902, buried seeds of 36 of 107 species were viable after 39 years (Toole and Brown 1946). Researchers have known for decades that many buried seeds need to be brought to the soil surface before they will germinate. To understand how germination of buried seeds is controlled, plant biologists have studied the re-
419 citations
TL;DR: Each of the plant species studied was found to have its own survival strategies of seed dispersal and germination, which depends on the influences of maternal and environmental factors when the seeds are still on the mother plant, mostly during the final stage of seed maturation.
Abstract: Massive seed consumption is typical in many deserts. The “escape” or “protection” strategies of seed dispersal are important, as they prevent massive seed consumption. The more extreme the desert, the more unpredictable the low amounts and distribution of the rains as well as the beginning and length of the season or seasons with rains. Seeds, which have the highest resistance to extreme environmental conditions, develop during germination into seedlings, which are the most sensitive. Therefore, germination of parts of the seed population at their respective proper times spreads the risk over time and is thus very important for plant survival, especially in those plants inhabiting the more extreme deserts. Each of the plant species studied was found to have its own survival strategies of seed dispersal and germination. At least two extreme seed-dispersal and germination strategies have been observed: 1) the “escape” seed dispersal and “opportunistic” portioned seed-germination strategies, such as inSchismus arabicas andSpergularia
diandra, and 2) the “cautious” portioned dispersal by rain of the protected seeds, such as inAsteriscus hierochunticus and portioned dispersal and rapid germination strategies such as inBlepharis spp. The fate of future generations, as far as the germinability of seeds of some species is concerned, depends on the influences of maternal and environmental factors when the seeds are still on the mother plant, mostly during the final stage of seed maturation, as inTrigonella arabica. It may even depend on the position of the caryopsis from which the mother plant originated, as inAegilops geniculata.
The dry post-maturation conditions and the environmental factors during seed wetting and germination may also affect the percentage of seed germination, as inSchismus arabicus.
279 citations
TL;DR: Diverse crop production systems provide a wide range of examples to illustrate how recent advances in the understanding of the responses of weed seed germination can be used to develop new and sustainable cultural management of weeds.
Abstract: Weed seed banks reflect past weed populations and management practices and are the source of weed infestations to come. The factors affecting weed seed germination, however, are often poorly understood. Depleting the soil seed bank and influencing germination patterns are common goals of enduring cultural weed management practices. Greater understanding of the factors influencing the germination of weed seeds could facilitate the development of more effective cultural weed management practices through either suppressing germination or encouraging germination at times when seedlings can be readily controlled. Such cultural methods may contribute to overcoming problems such as feral crops (e.g., weedy rice), crop volunteers, and the evolution of herbicide resistance in weeds that have, in some systems, increased to a point where the lack of sustainable practices is a threat to productivity. Weed seed germination is commonly influenced by light exposure, soil moisture, burial depth through tillage, the use of mulches, fire for land clearance, and flooding of the soil. Harnessing these factors to influence germination can serve as major entry points for improved weed management. Diverse crop production systems provide a wide range of examples to illustrate how recent advances in the understanding of the responses of weed seed germination can be used to develop new and sustainable cultural management of weeds. Crop management practices, such as adopting no-till crops or delaying tillage, that increase weed seed exposure to predators (ants, beetles, etc.) could be incorporated into integrated weed management programs. Retention of crop residue on the soil surface under no-till systems can suppress weed seedling emergence, delay the time of emergence, and allow the crop to gain an advantage over weeds, and reduce the need for control. Rotation of tillage or crop establishment system could also be adopted to deflect the “trajectories” of likely weed population shifts. In rice, flooding after herbicide application or hand weeding can largely prevent the growth of weeds and reduce the need for further interventions.
272 citations
References
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301 citations
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152 citations
TL;DR: An effect of altered spectral quality of the leaf-filtered light on the ratio of inactive/active phytochrome (Pr/Pfr) in the underlying seeds is indicated and it is suggested that such phenomena could influence the germination of weed seeds in the fiell.
Abstract: Light fromii sunlight, incandescent, an(l fluorescent sources was filtered through fresh tobacco (Nicotiana tabaccuml L.), corn (Zea mays L.), anid soybean (Glycine max (L.) Merrill) leaves. The spectral quality of the leaf-filtered light showed that much more of the incident red energy was absorbed than the far-red. The effect of the leaf-filtered light on the phytochrome-controlled germination of six weed species was generally to inhibit germination of seeds given a stimulatory pre-irradiation of red light from a standard source. Germination of seeds with no pre-irradiation was either not promoted or promoted to various degrees. Unfiltered light, at intensities equivalent to those uinder the leaf filters, caused no comparable effects. These results indicate an effect of altered spectral quality of the leaf-filtered light on the ratio of inactive/active phytochrome (Pr/Pfr) in the underlying seeds. We suggest that such phenomena could influence the germination of weed seeds in the fiell.
133 citations
TL;DR: Unless fallowing operations can be carried out with a much greater degree of thoroughness than is usual, reduction of many weeds can be effected almost as well and more economically by intensified cultivation while the land is under crop.
Abstract: 1. The weed seed population of the soil is greatly influenced by the type of crop grown. Soil conditions being similar, the composition of the flora under continuous wheat and barley is very much the same, but the relative abundance of the constituent species varies greatly, some being favoured by the wheat crop and others by the barley. On the whole, the spring cultivation before barley sowing tends to keep the number of buried weed seeds below those occurring in the autumn ploughed wheat soil. 2. When fallowing operations are carried out the various species in the soil population are differently affected. Most species are reduced in number, but the degree of reduction ranges over a wide percentage, while a few species may even be increased. These variations seem to depend upon the correlation between the times of the fallowing operations and the periods of maximum germination of the different species, coupled with the length of their natural dormancy. 3. If the interval between processes of cultivations are too prolonged some species are able to reach maturity and replenish the soil with so many seeds that the beneficial effect of the fallowing is entirely lost. Weed species vary considerably in their ability to recolonise the soil in this way. 4. When land is cropped the processes of cultivation affect the weed flora more variably than is the case with fallowing. On the same area some species may be drastically reduced while others may be doubled or trebled in quantity. This again depends on the correlation between the data of sowing the crop, the method of cultivation, and the habits of the weed species as regards maximum period of germination and length of natural dormancy. 5. Some weed species respond to cropping and fallowing in the same general direction, being reduced by both methods of cultivation. Other species may be generally reduced by fallowing, but behave variably under crop, being increased or decreased in different seasons. 6. From the agricultural point of view it is apparent that unless fallowing operations can be carried out with a much greater degree of thoroughness than is usual, reduction of many weeds can be effected almost as well and more economically by intensified cultivation while the land is under crop. Other species, however, which tend to increase in some seasons under crop conditions, may be more effectively dealt with by fallowing if their predominance justifies the expense, which implies loss of crop as well as the cost of numerous cultivations.
113 citations
TL;DR: A light—flash mechanism for breaking dormancy is proposed as a possible adaptation aiding pioneer plants in exploitation of disturbed habitats.
Abstract: A connection is suggested between two well—known but hitherto unrelated phenomena: germination under field conditions of certain seeds following soil disturbance and germination in laboratory experiments of certain seeds following brief exposures to light. A light—flash mechanism for breaking dormancy is proposed as a possible adaptation aiding pioneer plants in exploitation of disturbed habitats. See full-text article at JSTOR
105 citations