Soil-Weed Seed Communication Systems

The nature of weeds is a complex adaptive, soil-seed communication system. The nature of weedy Setaria life history is an adaptable, changeable system in which complex behaviors emerge when self-similar plant components self-organize into functional traits possessing biological information about spatial structure and temporal behavior. Setaria life history behavior is a Markov chain of irreversible and reversible processes regulated by morpho-physiological traits acting through environment-plant communication systems (environment-plant-seed, soil-seed). Heritable functional traits are the physical reservoirs of information guiding life history development, emergent behavior. The consequence of structural self-similarity and behavioral self-organization has been the evolution of a complex adaptive seed-soil communication system. Weedy Setaria life history is represented in algorithmic form as FoxPatch, a model to forecast seed behavior. Weedy Setaria seed life history behaviors are controlled by environmental information (signals) flowing from the soil to the seed embryo. The specific signal to which Setaria is tuned affecting seed behavior in the soil is the amount of oxygen and heat (T, thermal) in soil water over time, oxy-hydro-thermal time (O2-H2O-T-Time). The Shannon environmental-biological communication system between the soil and the Setaria seed contains the five elements (E) and components:E1, information source, soil; E2, transmitter, soil particle contact with seed surface water films; E3, channel, continuous soil particle-seed surface water films; E4, receiver, living seed interior from the transfer aleurone cell layer (TACL) membrane to aleurone layer to embryo; E5, destination, embryo. The signal is soil O2-H2O-T-Time; the message is O2-H2O-T stimulating embryo respiration. The Setaria soil-seed communication system seed behavior can be also expressed as operations (processes) computed by seed algorithms. Information is physical: memory resides in several locations in the Setaria seed. Memory is expressed in the long-term by responsiveness to O2-H2O-heat messages as determined by the morpho-physiological soil-seed communication system (hull, TACL membrane, scavenger protein). The message is remembered: plants pass on a range of heteromorphic seeds appropriate to continuing, successful local adaptation

Sustainable weed control system using natural product allelochemicals to replace conventional herbicides in maize

Weed control in crops should rely first on tillage and later on the crop as competition. But a window of opportunity still exists during which weeds are difficult to control without the use of herbicides. No dependable, long-term, sustainable weed control systems currently exist. The consequent widespread use of the herbicides atrazine and alachlor for corn production in Iowa poses a serious environmental concern because of their potential to pollute drinking water. Because of this possible hazard, an alternative weed control system is clearly desirable. However, any alternative practice must be developed in accordance with when yield losses due to weeds begin and when that weed interference end

Seed production in weedy Setaria spp.-gp

Seeds from Setaria faberi, S. viridis and S. pumila panicles in three Iowa crop fields were collected for the entire reproductive period. Seed number, panicle length, and seed number per panicle length varied among species, panicle types and sites. Greater numbers of seed per plant and per panicle were observed than previously reported. Setaria seed rain exhibited some stable, and many more plastic, responses. S. faberi panicles were consistently longer than those of S. viridis. S. viridis parameters were greater than S. pumila. Earlier panicles were greater than, or similar to, later ones for all parameters. More typically, tillers and panicles responded to local conditions in a plastic way, confounding the formulation of seed production generalizations. In S. faberi and S. viridis no consistent relationship between seed number and panicle length was observed among different tiller types. A more consistent relationship between parameters was observed for S. pumila compared to the others, making prediction possible for this species. The stability and plasticity of these relationships is partially due to the differences in S. faberi and S. viridis panicle, fascicle and spikelet morphology compared to S. pumila. These stable and plastic responses provide fine-scale adjustment to a locality, maximizing exploitation of local opportunity

Biologically intensive manipulation of foxtail seed banks for enhanced mortality

Studies were conducted at several Iowa locations to determine the fates and long-term carry-over of giant foxtail in agricultural soil weed seed banks, and the variability of these seed fates

Effect of Separating Giant Foxtail (Setaria faberi) Seeds from Soil Using Potassium Carbonate and Centrifugation on Viability and Germination

Changes in weed seedbank composition are often monitored by removing seeds from soil samples. One extraction method accomplishes this by creating a slurry of soil and a concentrated inorganic salt solution. Centrifugation is then used to separate constituents of differing densities. We have found that centrifugation of giant foxtail seeds in 3.2 M potassium carbonate solution as conducted in a centrifugation/flotation extraction method can reduce viability as measured by germination and tetrazolium tests. In one experiment, centrifugation/flotation separation reduced germination of giant foxtail seeds from 94 to 52%. The likely cause of seed damage was the high pH of the potassium carbonate solution in conjunction with the increased hydrostatic pressure due to centrifugation. While centrifugation affected quantitative measures of seed viability, it did not alter qualitative viability estimates using a pressure test

Setaria faberi Seed Heteroblasty Blueprints Seedling Recruitment: III. Seedling Recruitment Behavior

Seedling recruitment of heterogeneous Setaria faberi seed entering the soil post-abscission is elucidated herein. This is the third in a series of three articles providing evidence that weedy Setaria seedling recruitment behavior is predicated on dormancy state heterogeneity at abscission (seed heteroblasty), as modulated by environmental signals. Complex oscillating patterns of seedling emergence were observed during the first half of the growing season in all 503 soil burial cores of the 39 populations studied. These patterns were attributed to six distinct dormancy phenotype cohorts arising from inherent somatic polymorphism in seed dormancy states (canalized phenotypes). Early season cohorts were formalized using a mixture model consisting of four normal distributions. Two, numerically low, late season cohorts were also observed. Variation in emergence patterns among Setariapopulations revealed a fine scale adaptation to local conditions. Seedling recruitment patterns were influenced by both parental-genotypic (time of embryogenesis) and environmental (year, common nursery location, seed age in the soil) parameters. The influence of seed heteroblasty on recruitment behavior was apparent in that S. faberipopulations with higher dormancy at the time of dispersal had lower emergence numbers the following spring, and in many instances occurred later, compared to those less dormant. Heteroblasty was thus the first determinant of behavior, most apparent in recruitment number, less so in pattern. Environment modulated seedling numbers, but more strongly influenced pattern. The resulting pattern of emergence revealed the actual “hedge-bet” structure forSetaria seedling recruitment investment, its realized niche, an adaptation to the predictable mortality risks caused by agricultural production and interactions with neighbors. These complex patterns in seedling recruitment behavior support the conjecture that the inherent dormancy capacities of S. faberi seeds provides a germinability ‘memory’ of successful historical exploitation of local opportunity, the inherent starting condition that interacts in both a deterministic and plastic manner with environmental signals to define the consequential heterogeneous life history trajectories

Setaria faberi Seed Heteroblasty Blueprints Seedling Recruitment: II. Seed Behavior in the Soil

The fate of heteroblastic Setaria faberi seed entering the soil post-abscission is elucidated. Introduction of four populations of S. faberi seeds with heterogeneous dormancy capacities into the soil of a no-till Glycine max field resulted in the formation of enduring pools with varying cycles of dormancy, after-ripening, germination, dormancy reinduction and death. The buried seed rain of these highly dormant seed after-ripened with time and became highly germinable, awaiting favourable temperature and moisture conditions: the heterogeneous germination candidate pool. As this pool was depleted in the spring and early summer by seedling emergence and death, dormancy was re-induced in the living seeds that remained in the soil. These seeds remained dormant throughout the summer, then resumed after-ripening during late autumn. This dormancy-germinability cycle exhibited complexity both within and among S. faberi populations. Seed heteroblasty within S. faberi populations was retained, and germinability responses to the yearly seasonal environment varied among S. faberi populations. Further, local adaptation was shown by the differential germinability responses among S. faberi populations in common location agricultural nurseries. Seed mortality patterns also exhibited complexity within and among populations. Within an individual S. faberi population, mortality patterns changed as seeds aged in the soil. Among S. faberi populations differential mortality responses were observed in response to yearly seasonal environments and common nurseries. Observations of both germinability cycling and mortality are consistent with the hypothesis that S. faberi seed behaviour in the soil is predicated on dormancy capacity heterogeneity at abscission and modulated by the seasonal environmental conditions experienced in the field. The observations of seed fates obtained from heteroblastic seeds of four S. faberi populations buried at two common nurseries utilized a “bare core” technique. Cores were extracted periodically to determine seed fates. Inevitably, the fates of a fraction of those seeds could not be determined and were thus classified as unknown. Despite the equivocal nature of the unknowns they provided evidence that unaccounted seed losses were most likely not due to migration out of the core area. The lack of migration and high seed recovery (approximately 88.5%) emphasized the utility of the bare core technique in comparison to enclosed seed-soil cores

The Effects of Soil pH on Elymus Repens Growth and Tissue Nutrients

The perennial, graminaceous, plant quackgrass (Elymus repens (L.) Gould) is a serious weed problem. When corn is grown continuously, the high amounts of nitrogen fertilizer applied can alter the pH of the soil, and this decrease in soil pH with time may change the weed spectrum present in corn fields. Studies were conducted to determine the effect of four different pH soils (3.7, 4.3, 5.5, 6.2) on the growth of quackgrass rhizome fragments in terms of biomass accumulation and tissue nutrient content. As the soil pH decreased from 6.2 to 3.7, quackgrass plants accumulated less shoot, rhizome and root biomass, as well as less shoot height and numbers of main axis shoots, leaves and rhizome buds. This inhibitory effect of soil pH on quackgrass growth was most apparent in the later six weeks of development, until seedhead anthesis was apparent. In the first four weeks after planting the rhizomes, the reductions in quackgrass growth were best indicated by numbers of leaves and main axis shoots, as well as by shoot height. This reduction in growth associated with lower pH soils probably was due to two mechanisms. The first mechanism could be interference with uptake and incorporation of magnesium and phosphorus into both above and below ground plant parts, as well as with copper and calcium in shoots, and zinc in rhizome and root tissue. A second mechanism could be due to toxicity caused by excessive amounts of manganese in all plant parts, as well as excessive boron in shoot plant parts

Setaria faberi Seed Heteroblasty Blueprints Seedling Recruitment: I. Seed Dormancy Heterogeneity at Abscission

Studies were conducted to determine the relationship between weedy Setaria faberi seed dormancy and subsequent behaviors in the soil culminating in seedling recruitment.This is the first in a series of three articles demonstrating weedy Setaria seed dormancy capacity heterogeneity at abscission (seed heteroblasty) provides a “blueprint” for those subsequent behaviours. The objective for this present article was to provide a robust characterization of seed heteroblasty at the time of dispersal for 39 locally adapted S. faberi populations, as influenced by parental genotype (time of embryogenesis) and environment (year, location). The heteroblastic structure of each population was revealed by the germination response to increasing amounts of after-ripening (in “ideal” conditions). The majority of the populations were differentiated from each other; this variation indicated a fine scale adaptation to different local environments.Taken together, the 39 responses represented Setaria’s “seed dormancy phenotype space” and revealed three different generalized dormancy patterns. The first pattern, low dormancy populations, had high initial germination in response to low doses of after-ripening. The second, high dormancy populations, had no or low initial germination with little additional response to increased after-ripening. Most populations had the third pattern, intermediate to the others, with low initial germination and increasing germination with increasing after-ripening dose. Germination responses were also used to rank populations based on their dormancy level to facilitate later comparisons with emergence behavior. Heteroblasty at abscission, elucidated herein, is hypothesized to influence subsequent seed fates in the soil, the focus of the next two articles in this series