The 141-year period for Dr. Beal's seed viability experiment: A hybrid surprise

Premise

In 1879, Dr. William Beal buried 20 glass bottles filled with seeds and sand at a single site at Michigan State University. The goal of the experiment was to understand seed longevity in the soil, a topic of general importance in ecology, restoration, conservation, and agriculture, by periodically assaying germinability of these seeds over 100 years. The interval between germination assays has been extended and the experiment will now end after 221 years, in 2100.

Methods

We dug up the 16th bottle in April 2021 and attempted to germinate the 141-year-old seeds it contained. We grew germinants to maturity and identified these to species by vegetative and reproductive phenotypes. For the first time in the history of this experiment, genomic DNA was sequenced to confirm species identities.

Results

Twenty seeds germinated over the 244-day assay. Eight germinated in the first 11 days. All 20 belonged to the Verbascum genus: Nineteen were V. blattaria according to phenotype and ITS2 genotype; and one had a hybrid V. blattaria × V. thapsus phenotype and ITS2 genotype. In total, 20/50 (40%) of the original Verbascum seeds in the bottle germinated in year 141.

Conclusions

While most species in the Beal experiment lost all seed viability in the first 60 years, a high percentage of Verbascum seeds can still germinate after 141 years in the soil. Long-term experiments such as this one are rare and invaluable for studying seed viability in natural soil conditions.     

Eco-evolution from deep time to contemporary dynamics: The role of timescales and rate modulators

Eco-evolutionary dynamics, or eco-evolution for short, are often thought to involve rapid demography (ecology) and equally rapid heritable phenotypic changes (evolution) leading to novel, emergent system behaviours. We argue that this focus on contemporary dynamics is too narrow: Eco-evolution should be extended, first, beyond pure demography to include all environmental dimensions and, second, to include slow eco-evolution which unfolds over thousands or millions of years. This extension allows us to conceptualise biological systems as occupying a two-dimensional time space along axes that capture the speed of ecology and evolution. Using Hutchinson's analogy: Time is the ‘theatre’ in which ecology and evolution are two interacting ‘players’. Eco-evolutionary systems are therefore dynamic: We identify modulators of ecological and evolutionary rates, like temperature or sensitivity to mutation, which can change the speed of ecology and evolution, and hence impact eco-evolution. Environmental change may synchronise the speed of ecology and evolution via these rate modulators, increasing the occurrence of eco-evolution and emergent system behaviours. This represents substantial challenges for prediction, especially in the context of global change. Our perspective attempts to integrate ecology and evolution across disciplines, from gene-regulatory networks to geomorphology and across timescales, from today to deep time.     

Stimulation of weed seed germination by 1–(3-chlorophthalirnido) cyclohexanecarboxamide (AC 94377)

The N-substituted phthalimide, AC 94377, promoted the germination of dry-stored seeds of 17 out of 24 weed species in Petri-dish tests maintained at 22°C. In a further test it was able to substitute for light and/or alternating temperatures in promoting the germination of some species. AC 94377 was more active than GA, in stimulating Solanum nigrum seed to germinate. When mixed with soil in the laboratory, AC 94377 again promoted germination of S. nigrum but the level and persistence of activity differed between soils. In the glasshouse, with soil containing a natural weed seed population, more seedlings emerged from treated than from untreated soil but this number represented fewer than half of the apparently viable seeds present. Field applications of AC 94377 promoted the germination of hand-sown seeds of certain weed species but did not increase the number of seedlings emerging from the natural weed seed bank.     

Effect of salinisation of soil on growth and macro- and micro-nutrient accumulation in seedlings of Acacia catechu (Mimosaceae)

The effects of salinisation of soil on Acacia catechu (Mimosaceae) were studied by means of emergence and growth of seedlings and pattern of mineral accumulation. A mixture of chlorides and sulphates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.1, 6.3, 8.2,10.1 and 12.2 dSm⁻¹. A negative relationship between proportion of seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.1 dSm⁻¹. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.1 dSm⁻¹, which suggests that this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. Among the tissues, young roots and stem were most tolerant to salt stress and were followed by old roots and leaves, successively. Leaf tissue exhibited maximum reduction in dry mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated “fine root turnover”, is of importance to the mechanisms of salt tolerance. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K was affected in response to salinity; it rapidly decreased in root tissues with increased salinisation. Nitrogen content decreased in all tissues (leaf, stem and root) in response to low water treatment and salinisation of soil. Phosphorus content significantly decreased, while Ca increased in leaves as soil salinity increased. Changes in tissue and whole plant accumulation patterns of the other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species during salinisation, are discussed.     

The applicability of the plant vigor and resource regulation hypotheses in explaining Epiblema gall moth–Parthenium weed interactions

A basic question in insect–plant interactions is whether the insects respond to, or regulate plant traits, or a complex mixture of the two. The relative importance of the directions of the influence in insect–plant interactions has therefore been articulated through both the plant vigor hypothesis (PVH) and the resource regulation hypothesis (RRH). This study tested the applicability of these hypotheses in explaining the interactions between Parthenium hysterophorus L. (Asteraceae) and its stem‐galling moth, Epiblema strenuana Walker (Lepidoptera: Tortricidae). Parthenium plants exposed to galling were sampled at three sites in north Queensland, Australia, over a 2‐year period, and the relationship between gall abundance and plant vigor (plant height, biomass, flowers per plant, and branches per plant) was studied. To test the predictions of PVH and RRH, the vigor of parthenium plants protected from galling using insecticides was compared to galled plants and plants that escaped from galling. The vigor of ungalled plants was less than the vigor of galled plants. The higher plant vigor in galled plants was not due to galling, as was evident from insecticide exclusion trials. The insect seemed to preferentially gall the more vigorous plants. These findings support the predictions of the PVH and are contrary to those of RRH. Since gall abundance is linked to plant vigor, galling may have only a limited impact on the vigor of parthenium. This has implications for weed biological control. If the objective of biological control is to regulate the population of a plant by a galling insect, a preference for more vigorous plants by the insect is likely to limit its ability to regulate plant populations. This may explain the paucity of successes against biocontrol of annual weeds using gall insects.     

Seasonal differences in mineral content, distribution and leakage of sweet pepper seeds

Pepper seed quality is sensitive to variations in climatic conditions during seed development, which might be associated with accumulation, distribution and leakage of mineral elements from the seeds. This was examined in hybrid seeds of sweet pepper (Capsicum annuum L. cv.‘Hazera’ 1195) in two experiments during two growing seasons. The mean daily temperature (day/night) and daily total radiation receipt during seed development were 27.9/23.2°C and 8.63 kW m^?2 in the summer and 18.3/ 14.9°C and 3.18 kW m^?2 in the winter, respectively. Seeds developed in the summer had lower percentage of seedling emergence and leaked a larger portion (45%) of their K content into the water medium than in winter‐developed seeds. Summer seeds accumulated more K and Cl, but less P, Mg, Ca and the weight ratio of linoleic acid to oleic acid was lower than in the winter seeds. The season did not significantly affect N, S and total fatty acids. The most abundant element on the seed coat surface was K in the summer and Ca in the winter seeds. The cotyledon and endosperm of the summer seeds contained relatively higher ratios of K and Ca and lower ratios of P and Mg than the winter seeds. Transportation of mineral nutrients appeared to be involved in the effect of heat and moisture stresses on emergence quality of the pepper seeds.     

Comparative seed ecology of the endangered shrub, Pimelea spicata and a threatening weed, Bridal Creeper: Smoke, heat and other fire-related germination cues

Summary Pimelea spicata R. Br. is a nationally listed endangered Australian shrub threatened with extinction by habitat fragmentation and environmental weed invasion. Bridal Creeper (Asparagus asparagoides L. W. Wight) is the primary weed threat to the largest remaining populations of P. spicata in the Cumberland Plain. Fire, as part of an integrated pest management program, offers the potential to stimulate P. spicata populations while controlling Bridal Creeper. It is important, therefore, to understand how the components of fire affect the germination and growth of both species. Using laboratory experiments we investigated the effects of smoke, heat, ash and/or light on the germination of P. spicata and Bridal Creeper. We found a significant promotive effect of smoke and indication of an inhibitory heat shock (90°C for 10 min) effect on the germination of P. spicata seeds. The response of Bridal Creeper seeds to the same factors was complex; while the results of one experiment suggested an inhibitory effect of smoke and a promotive effect of heat, subsequent trials were contradictory, implying that Bridal Creeper, like many weeds, is able to germinate under a wide range of environmental conditions. Other experiments investigated the optimal germination temperature and innate dormancy of P. spicata in the absence of fire‐related germination cues. Of the incubation temperatures investigated, the optimal diurnally fluctuating regime for P. spicata germinations was 10°C and 20°C in the night and day, respectively. The innate dormancy of freshly produced seeds disappeared after 3 months. In contrast to Bridal Creeper, we found a persistent germinable seed bank of about 97 P. spicata seeds/m² located in the top 5 cm of the soil profile. While fire alone is unlikely to kill Bridal Creeper plants, fire may help to manage local infestations of the weed by limiting germination and providing opportunity for herbicide treatment of regrowth.     

玉米种子萌发成苗不同阶段需水阈值的研究

用渗透势不同的聚乙二醇（ＰＥＧ）６０００模拟外界环境水分条件,对玉米不同品种的种子在萌动、萌发及成苗三个阶段需水的量化研究表明,种苗的抗旱性随吸水进程的推进而减弱;种子在萌动、萌发及胚芽伸长至一定长度的时间（ｔ）与外界环境水势（ｗ）之间存在着１／ｔ＝ａ＋ｂｗ的关系,据此推算出不同品种在不同成苗阶段的需水阈值,发现不同品种在同一成苗过程中对环境水分条件的反应不同,它们的抗旱性也不同。     

The effects of weed strips on aphids and aphidophagous predators in an apple orchard

Selected weeds were used to attract antagonists of apple aphids in an apple orchard near Berne, Switzerland. In the year before the experiment, in 1991, the apple aphidsDysaphis plantaginea (Pass.) andAphis pomi (DeGeer) and aphidophagous predators were homogenously distributed in the orchard. In April 1992, weed strips were sown between tree rows and along the border parallel to the first and the last row of trees in one part (the other part served as control). In both parts of the orchard, randomly chosen tress were controlled visually in weekly intervals in 1992 and 1993. During flowering of weeds more aphidophagous predators were observed on the apple trees within the strip-sown area than in the control area. The most abundant and permanent aphidophagous predators were spiders, predaceous Heteroptera, Coccinellidae, and Chrysopidae. Both species of aphids were significantly less abundant in the area with weed strips than in the control area during the vegetation period. The effects of the weed strips on aphidophagous predators, and those of predators on aphids, are discussed.     

Twin-screw extrusion of ‘Pesta’-encapsulated biocontrol agents

World Journal of Microbiology and Biotechnology -