Setaria Soil Seed Pools

Setaria spp. seed pool formation and initial assembly in agro-communities
Related Foxtail Seed Pool Information

Setaria spp. seed pool formation and initial assembly in agro-communities

Agroecosystem community assembly .  Community assembly of crops and weeds in agroecosystems, and its consequences, is a complex set of phenomena.  Accurate predictions of the time of weed interference, weed control tactic timing, crop yield losses due to weeds, and replenishment of weed seed to the soil seed pool, require information about how agricultural communities assemble and interact.  Despite attempts at description (e.g. Booth and Swanton, 2002), little is known about the rules of community assembly.  Their elucidation may remain an empirically intractable problem.

  Despite this, there exist two opportunities to understand agroecosystem community assembly during the recruitment phase (e.g. seedling emergence) that predicate future interactions with other plants.  The first advantage derives from the annual disturbance regime in agricultural fields that eliminates above ground vegetation (e.g. winter kill, tillage including seedbed preparation, early season herbicide use).  Understanding community assembly is most tractable when starting each growing year with a field barren of above-ground vegetation and possessing only dormant underground propagules (e.g soil seed and bud pools), a typical situation in much of world agriculture.

  The second advantage derives from the observation that the time of emergence of a particular plant from the soil relative to its neighbors (i.e. crops, other weeds) is the single most important determinate of subsequent weed control tactic use, competition, crop yield losses and weed seed fecundity.  Seedling recruitment is the first assembly step in these disturbed agricultural communities, and is therefore the foundation upon which all that follows is based.  Recruitment prediction information therefore may be the single most important life history behavior in weed management.

Setaria spp. soil seed pool formation.  The formation of weedy Setaria spp. (UK, bristlegrass; France, sétaire; U.S., foxtail; Minnesota, pigeongrass) soil seed pools is the inevitable consequence of dormancy induction in individual seeds (Dekker, 2003a, b).  Individual Setaria spp. panicles on a single parent plant produce a diverse array of seeds, each with potentially different dormancy states at abscission (heteroblasty; Dekker et al., 1996).  The subsequent behavior of an individual seed once it enters the soil is regulated by how this inherent dormancy responds to the amount of oxygen dissolved in water over time taken into the seed symplast, as well as temperatures favorable to germination (Dekker & Hargrove, 2002).  The dormancy state of an individual weedy Setaria sp. seed, interacting with its environment, determines when seedling recruitment occurs (Atchison, 2001).

  Morpho-physiological basis of weedy Setaria spp. seed dormancy .  There exists a cascade of three morpho-physiological mechanisms that act together to modulate received oxygen, water and heat and thereby constrain and control Setaria spp. seed embryo behavior.  The first is the seed hull and outer envelopes that act to attract and accumulate water, enhance gas solubility in that water by means of its surface rugosity, and channel that gas-laden water to the placental pore (the basal opening to the seed symplast; the only water entry point in the seed) (Donnelly et al., 2002).  The placental pore (PP) terminates with the transfer aleurone cell layer (TACL), a membrane whose diameter and function regulates diffusion of gas-laden water in and out of the symplast (Rost, 1971, 1972, 1973, 1975; Rost & Lersten, 1970, 1973).  The foxtail seed is gas- and water-tight except at this pore due to the enveloping caryopsis coat (CC).  Together the PP, TACL and CC provide the second controlling mechanism.  The third element is an oxygen-scavenging heme-containing protein ("X", fig. 1) in the symplast that acts to buffer the seed against premature germination by sequestering oxygen (Dekker & Hargrove, 2002; Sareini, 2002).  These controlling mechanisms are represented schematically in figure 1.

Figure 1.  Schematic diagram of the Setaria sp. seed and surrounding soil particles and water with dissolved oxygen (H₂O-O₂).  The symplast is surrounded by the glumes, hull, and the gas and water-impermeable caryopsis coat (apoplast);  the interior seed symplast consists of the aleurone layer, transfer aleurone cell layer (TACL), endosperm, oxygen-scavenging protein (X), and the embryo.

      The interaction of these three mechanisms in any individual seed defines its unique dormancy state at abscission.  The inherent dormancy state at abscission interacts with its immediate environment to define its subsequent behavior.  Environmental signals change the initial dormancy state of an individual seed over the course of its life history in the soil.  The quantity of these signals required to change behavior is an intrinsic quality of the individual and is retained for the entire life as a seed.  The dormancy state an individual living seed inherits from its parent plant is never lost or "broken".   The behavior of an individual seed in the soil during its life history is always a consequence of its current intrinsic state responding to its current extrinsic conditions.

Related Foxtail Seed Pool Information

Setaria spp. Seed Life History
      Seed germination process
      Seedling emergence

Setaria spp. Seed Morphology
      Seed hull topography
      Seed placental pore

Experimental Techniques
      Soil cores
      Germination techniques

Urban soil seed pool

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