Seedbank persistence of four summer grass weed species in the northeast cropping region of Australia

Summer grass weed species are a particular problem in the northeast cropping region of Australia because they are prolific seeders and favor no-till systems. Information on weed seed persistence levels can be used for the development of effective and sustainable integrated weed management programs. A field study was conducted over 42 months to evaluate the seedbank persistence of Chloris truncata, C. virgata, Dactyloctenium radulans, and Urochloa panicoides as affected by burial depth (0, 2, and 10 cm). Regardless of species, buried seeds persisted longer than surface seeds and there was no difference in seed persistence between 2 and 10 cm depths. Surface seeds of C. truncata depleted completely in 12 months and buried seeds in 24 months. Similarly, C. virgata seeds placed on the soil surface depleted in 12 months. Buried seeds of this species took 18 months to completely deplete, suggesting that C. truncata seeds persist longer than C. virgata seeds. Surface seeds of D. radulans took 36 months to completely deplete, whereas about 7% of buried seeds were still viable at 42 months. U. panicoides took 24 and 42 months to completely exhaust the surface and buried seeds, respectively. These results suggest that leaving seeds on the soil surface will result in a more rapid depletion of the seedbank. Information on seed persistence will help to manage these weeds using strategic tillage operations.

Does the seed disperser matter? The influence of dispersal type on survival of Araucaria angustifolia seeds

Zoochoric dispersion is fundamental for the colonization of habitats by plants with large and heavy seeds such as the Paraná pine (Araucaria angustifolia). This is an endangered conifer from South America whose recruitment is heavily impacted by animals, but the way that different zoochoric dispersal modes and deposition sites can affect its successful establishment is not known yet. Thus, in this study, we aimed to evaluate the effect of dispersal mode (accordingly to the seed disperser), distance from adult conspecifics, and disposition site on long-term recruitment success. The experimental design included two environments (forest and open field) and each of them received 30 micro-habitat sampling stations (simulating deposition sites: 10 under conspecific; 10 far from conspecifics, next to a landmark; and 10 far from conspecifics, without a landmark), and each microhabitat had three levels of dispersal type simulating animal treatment (intact buried seed; intact seed over the ground; partially preyed seed over the ground), each with five seeds, totaling 900 seeds. In the forest environment, an experiment was also conducted to verify the fate of seeds using the spool and line technique. The environment and the micro-habitat alone did not explain seed survival, although the dispersal type given by the animal disperser was significant for survival and the buried seeds were the only ones that survived until the last survey. With the spool and line seed experiment, we attested that most of the Paraná pine seeds were preyed after removal (81.5%), and only buried seeds survived, reinforcing the role of scatter-hoarding animals as important agents in the Paraná pine dispersal. This way, our results showed that Paraná pine seeds suffer a very high predation rate, and that only a few seeds escape from predators and recruiting (only 1.1% of the all seeds used in the two experiments), indicating that the survival of seeds is a critical step in the life cycle of this plant, highlighting the role of dispersal mode in recruiting success.

“Active” Weed Seed Bank: Soil Texture and Seed Weight as Key Factors of Burial-Depth Inhibition

The ability of weeds to survive over time is highly dependent on an ecological strategy that ensures a high level of viable seed remains in the soil. Seed bank persistence occurs because of the specific characteristics of seed dormancy and longevity and the hypoxic microenvironment, which surrounds the buried seeds. These experiments investigate the role of soil texture, burial depth, and seed weight in seed bank dynamics. Seeds of twelve weed species are sown at increasing depths in various soil textures, and emergence data are used to detect the burial depth at which 50% and 95% inhibition is induced, using appropriate regressions. Clay soil is found to increase the depth-mediated inhibition, while it is reduced by sandy particles. In each soil texture, the highest level of inhibition is found for the smallest seeds. Seed weight is found to be closely related to the maximum hypocotyl elongation measured in vitro, and consequently, the seedlings are unable to reach the soil surface beyond a certain depth threshold. However, the threshold of emergence depth is always lower than the potential hypocotyl elongation. The depth-mediated inhibition of buried seeds is even more pronounced in clay soil, highlighting that the small size of clay particles constitutes a greater obstacle during pre-emergence growth. Finally, the role of soil texture and weed seed size are discussed not only in terms of evaluating the layer of “active” seed bank (soil surface thickness capable of giving rise to germination and emergence), but also in terms of developing a consistent and persistent seed bank. Finally, the role of soil texture and weed seed size are discussed, and the layer of “active” seed bank (the soil surface thickness that enables germination and emergence) is assessed with the aim of developing a consistent and persistent seed bank. Assessing seed bank performance when buried under different soil textures can help increase the reliability of the forecast models of emergence dynamics, thus ensuring more rational and sustainable weed management.

The role of seed water content for the perception of temperature signals that drive dormancy changes in Polygonum aviculare buried seeds

Seedling emergence in the field is strongly related to the dynamics of dormancy release and induction of the seed bank, which is mainly regulated by soil temperature. However, there is limited information on how temperature-driven effects on dormancy changes are modulated by the seed hydration-level. We investigated the effect of seed water content (SWC) on the dormancy release and dormancy induction in Polygonum aviculare L. seeds. We characterised quantitatively the interaction between seed water content (SWC) and temperature through the measurement of changes in the lower limit temperature for seed germination (Tl) during dormancy changes for seeds with different SWC. These relationships were inserted in existing population-based threshold models and were run against field obtained data. The model considering SWC was able to predict P. aviculare field emergence patterns. However, failure to consider SWC led to overestimations in the emergence size and timing. Our results show that in humid temperate habitats, the occurrence of eventual water shortages during late-winter or spring (i.e. short periods of water content below 31% SWC) can affect soil temperature effects on seed dormancy, and might lead reductions in the emergence size rather than to significant temporal displacements in the emergence window. In conclusion, SWC plays an important role for the perception of temperature signals that drive dormancy changes in buried seeds.

Biology of Brassica tournefortii in the northern grains region of Australia

Brassica tournefortii Gouan. (wild turnip, WT) has become a problematic weed in the no-till production systems of the northern grains region of Australia. Experiments were undertaken using different biotypes of B. tournefortii to examine its phenology, emergence and seedbank persistence. Biotypes were obtained from paddocks of barley (Hordeum vulgare L.) (WT1 and WT9) and chickpea (Cicer arietinum L.) (WT1/17 and WT2/17). Fresh seeds initially had high dormancy rates and persisted for a short period on the surface. Seedbank persistence increased with burial depth, with 39% of seeds remaining for WT1 and 5% for WT9 after 30 months at 2 cm depth. Persistence of buried seeds varied across biotypes; WT1/17 seedlings also emerged in the second growing season from 2 cm depth. Compared with buried seeds, seedlings readily emerged from the surface (in March–June following increased rainfall) within 6 months of planting. Emergence was greatest on the surface and varied between biotypes and tillage systems; the highest rate recorded was ~14%. Multiple cohorts were produced between February and October. No-till systems produced higher emergence rates than conventional tillage systems. Seedlings of B. tournefortii did not emerge from 5 cm soil depth; therefore, diligent tillage practices without seedbank replenishment could rapidly reduce the presence of this weed. A soil-moisture study revealed that at 25% of water-holding capacity, B. tournefortii tended to produce sufficient seeds for reinfestation in the field. Brassica tournefortii is a cross-pollinated species, and its wider emergence time and capacity to produce enough seeds in a dry environment enable it to become widespread in Australia. Early cohorts (March) tended to have vigorous growth and high reproduction potential. This study found B. tournefortii to be a poor competitor of wheat (Triticum aestivum L.), having greater capacity to compete with the slow-growing crop chickpea. Therefore, control of early-season cohorts and use of rotations with a more vigorous crop such as wheat may reduce the seedbank. The information gained in this study will be important in developing better understanding of seed ecology of B. tournefortii for the purpose of developing integrated management strategies.