Research Article |
Corresponding author: Gerhard Karrer ( gerhard.karrer@boku.ac.at ) Academic editor: Sven Jelaska
© 2024 Gerhard Karrer, Felicia Lehner, Nina Waldhaeuser, Bence Knolmajer, Rea M. Hall, Judit Poór, Ildikó Jócsák, Gabriella Kazinczi.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Karrer G, Lehner F, Waldhaeuser N, Knolmajer B, Hall RM, Poór J, Jócsák I, Kazinczi G (2024) Long-term seed survival of common ragweed (Ambrosia artemisiifolia L.) after burial. NeoBiota 96: 363-379. https://doi.org/10.3897/neobiota.96.130750
|
Ambrosia artemisiifolia is a serious threat to human health and agricultural yield. Due to its annual growth form management should focus on the prevention of seed production in the long run. The long-term survival of ragweed seeds depends on the implementation of viable seeds to the persistent soil seed bank. In a field study, we tried to find out how long this species must be surveyed/managed to reach the goal of complete eradication after burial of seeds into mineral soil. We tested for the influence of different seed sources (origin), different soil depths of burial, different experimental sites in Middle Europe (labs), and duration of burial on the viability of seeds by germination test plus TTC-test. In our study, seed origin had a highly significant influence on the seed survival. In all the 10 years of the experiment, seeds sampled from a rural stand in Austria showed significantly lower viability rates than seeds from Hungary. The Hungarian seeds from arable fields had viability rates of up to 90% even after 10 years’ burial. Burial depth (7 cm/25 cm) had no significant influence on the viability rates but we detected a serious influence of the experimental sites which can be caused either by the burial site conditions (differences in soil and climate) or by different implementation of the manuals for germination tests and colouration test using 2,3,5-triphenyltetrazolium chloride. The decline of viability within the 10-year period differed by seed origin, but was generally faster in the first few years but relatively low in the following years. Due to the fact that we found 30 to 90% viable seeds after 10 years burial there is substantial evidence that soil perturbation (digging animals, ploughing) should be avoided for even more than ten years in habitats that are highly infested with ragweed.
Control measures, dormancy, germination, invasive species, soil seed bank, weed management
Common ragweed (Ambrosia artemisiifolia L.) is considered one of the most dangerous invasive alien weed species in Europe (
The invasiveness of common ragweed was documented for Europe but also for other continents, i.e., Asia (
In agroecosystems the average seed production is around 4000 achenes (
Long-term experiments showed that the survival rates of weed seeds under field conditions were best in deeper soil layers.
However, ragweed seeds deposited on the soil surface under field conditions were found viable for 4 only years (
Soil perturbation by ploughing incorporates weed seeds like those of ragweed to deeper soil horizons where weed seed survival rates increase with burial depth (
Two populations of ragweed seeds were sampled in autumn 2011 from arable fields in Hungary (Kaposvár: 46.368608, 17.851789; 148 m a.s.l.) and from ruderal arable fields in Austria (Hagenbrunn: 48.343333, 16.466278; 178 m a.s.l.). Seeds were air dried and stored at room temperature (± 20 °C).
Field experiments were established in the experimental farm areas of Kaposvár University (Kaposvár: 46.368608, 17.851789; 148 m a.s.l.) and of BOKU University (Groß-Enzersdorf: 48.199417, 16.557611; 154 m a.s.l.). Seeds were buried in winter 2011/2012 at two soil depths (upper layer (5−8 cm), and lower soil layer (25 cm).
In a pre-trial, another seed lot from Austria (Styria, Unterpurkla: 46.731500, 15.901528; 229 m a.s.l.) was sampled in 2010 and buried in the botanical garden of the BOKU University (Vienna: 48.237194, 16.332361; 236 m a.s.l.) in winter 2010/2011 at a soil depth of about 10 cm. This pre-trial gave us some valuable technical and practical experiences for the main trial.
Portions of 50 seeds were enclosed each in polyester mash before burial (Fig.
The buried seed lots represent spatially independent replicates (Fig.
Excavation of the seeds of the pre-trial (7 bags each year) started in 2012 and ended by 2021. In the main experiment, excavation of 10 bags per year (5 from each layer) ranged from the year 2013 until 2022. Excavated seed bags were transferred to the lab for immediate germination tests.
Seed viability was tested by both labs following the manuals of
Before burial the sampled seeds from 2010 and 2011 were also tested in Vienna for germinability, and viability by TTC-test, after 6 weeks of vernalisation in darkness at 4 °C (n = 100 each seed lot).
In parallel to the burial trial, seeds from the Kaposvár seed lots were stored for 10 years in dry conditions at room temperature and tested for germinability and viability annually following the same procedure as administered to the buried seeds.
Analysis of the data were performed either on the number of germinated seeds, or on the number of TTC-positive seeds, or on the number of viable seeds from both subsequent tests. „Viable” seeds comprise therefore finally the germinated seeds plus TTC-positive seeds from the TTC-test that was applied to the non-germinated seeds. Statistical analysis of germinability and final viability was applied to arcsin-transformed data. GLMM and ANOVA was used to describe differences of viability with respect to the independent factors ‘seed origin’, ‘burial depth’, ‘burial site’ (lab, resp.) and ‘year of excavation’. For fine-tuning the results of multiple regression analysis we constructed generalised linear mixed models (GLMM) using R packages lme4 (
As ragweed seeds are known to stay dormant under specific conditions we tested the initial germinability and viability rates of the seed lots before burial. The seeds from Unterpurkla used in the pre-trial in Vienna were germinable at an average of 72% and finally viable (germinated and TTC-positive) at an average of 82%, before burial. Pre-burial-tests of the seed lots from Hagenbrunn and Kaposvár in the lab in Vienna gave 14% and 76% germinability, and 18% and 85% viability, respectively. In general, the seeds started with less than 100% viability due to some dead embryos, which could not be detected from outside the obviously intact seeds.
For the trial at the BOKU-garden in Vienna with seeds from Unterpurkla, excavated seeds started with very low mean viability rates of 43% after the first year of burial (2012). After two years’ burial seed viability was measured at 73% which was about the same values as the seeds before burial (2011: 72%). In subsequent years the viability rates dropped to a level of ≥ 40%. Only in the very last year (2021) ragweed seeds showed a marked further viability decrease to 30%. (Fig.
The trial gave results for germination rates as well as for total viability rates (including TTC-positive seeds). Viability rates are generally equal to or higher than the germination rates. Both rates are positively correlated (R = 0.884, p < 0.001). But there is a difference between the places of burial/analysing labs. The germinability rates were almost as high as the viability rates and reached a perfect linear correlation for the Austrian labs whereas for the Hungarian data the linear regression coefficient was less positive but nevertheless significant (Suppl. material
In the main burial experiment four influential factors on germinability and viability were tested.
The ANOVA with all four factors showed a significant influence of ‘seed origin’, ‘year of excavation’, and ‘burial site/laboratory’ (p < 0.001) on the viability rates of buried ragweed seeds (Suppl. material
The GLMM analysis started with the calculation of the explanatory power of each stand-alone factor, indicating that seed viability was particularly affected by the factor „seed origin”. As null model we used the factor „burial site/laboratory” to test if results are influenced by site specific conditions and/or lab conditions but this could be mainly excluded. However, when calculating the models, it became obvious that seed viability of common ragweed was mainly explained by the interaction of the factors „seed origin”, „year of excavation” and „burial site”, indicating that there is some influence of site/lab specific conditions. Additive effects of the factors showed only very low AICc values (not shown in Table
Summary of AICc values used for model selection of dependent variable seed survival rate; number of estimated explanatory parameters and parameter combinations = 8; AICc = Second order Akaike Information Criterion; ΔAICc = difference between AICc to the next most parsimonious model; R² = proportion of variance explained by the factors on the (arcsin-transformed) viability rates of buried ragweed seeds.
Explanatory model | AICc | ΔAICc | R 2 | |
Viability of seeds | Null Model: Burial site (Laboratory) | 433.5 | ||
Seed origin * Year of excavation * Burial site | -206.2 | 0.0 | 0.86 | |
Seed origin * Year | -45.2 | 161.0 | 0.81 |
Years of excavation significantly affected seed viability rates in general (Fig.
Seed viability rate (box-plots, percentages of viable ragweed seeds per bag) from 2013 to 2022.
In general, seeds originating from Kaposvár/Hungary had significantly higher viability rates than the seeds from Hagenbrunn/Austria (means at 89.45 and 47.92, resp.; Mann-Whitney-U-Test: p < 0.001). This significant difference in viability rates was detected for all years (evident from Fig.
Seed viability rate (box-plots, percentages of viable ragweed seeds per bag) from 2013 to 2022 with respect to seed origin.
Interestingly, the burial site/testing lab showed also significant influence on the viability rates of ragweed seeds (Fig.
Seed viability rate (box-plots, percentages of viable ragweed seeds per bag) from 2013 to 2022 with respect to burial site (AT = Groß-Enzersdorf in Austria, HU = Kaposvár in Hungary).
When seed viability rates were compared with respect to year of excavation and burial depth no significant difference was found (F = 1.478; p = 0.155, Fig.
Seed viability rate (box-plots, percentages of viable ragweed seeds per bag) from 2013 to 2022 with respect to burial depth of seeds.
But when the data are presented in groups by seed origin and burial site (Fig.
Seed viability rate (box-plots, percentages of viable ragweed seeds per bag) with respect to seed origin (Ha=Hagenbrunn/Ka=Kaposvár) and burial site (AT=Austria/HU=Hungary); letters correspond to significant group differences in means.
Seeds of common ragweed are known to stay dormant when the conditions (i.e., burial in deeper soil horizons, long dry periods, missing stratification by several weeks of low temperature after seed ripening) do not allow germination (
Viability rates comprised of germinated seeds and subsequent TTC-test on the non-germinated seeds. Therefore, germination rates were somehow lower than rates of viability, but the burial and test conditions in Hungary differed obviously to those in Austria. This confirmed the fact that all germinating seeds are viable but not all viable seeds germinate – due to seed dormancy – similar to the majority of any weed seeds (
Our experimental design did not allow to clarify the role of potential factors that may cause some of the differences in the viability results. Climatic conditions during burial (Suppl. material
Viability values of the pre-trial in Vienna indicated a significant decrease in the first 3 years from 72% to about 40%. In subsequent years there was no further loss of viability except for the last year (30%). This result runs contrary to the main experiment results (Fig.
Several factors may influence the germinability and viability in burial experiments like ours: When seeds are sampled in the field seed sizes and ripening stage may vary to some extent. The conditions of storage or transportation of weed seeds may have an influence on their viability (
Obviously, the burial of ragweed seeds at seven or more centimetres of soil depth is deep enough to stop initiation of germination. We found only a slightly higher (but not significant viability of seeds buried deeper into the soil at 25 cm. This is in line with the results of
Our results confirmed the fact that under field conditions ragweed seeds can remain viable for a long time, especially in the deeper soil layers, so its seeds can enrich the persistent soil seed bank in habitats with regular soil perturbance as in arable fields. Seeds that are deposited on the soil surface or beneath shallow litter layers undergo the dormancy/non-dormancy environmental influences in temperate regions every year. They are prone to germinate easily due to nice water and light supply after having experienced break of dormancy until early spring. In such populations the soil seed bank is lower in numbers of viable seeds (
In our experiment it became evident that the exactness of sticking to the experimental protocols is essential to gain comparable data.
So from the point of integrated weed management in arable fields we suggest to prefer preventive control procedures, primarily to prevent the flowering and seed production of ragweed (
To conclude, we found significant differences in the viability of ragweed seeds with respect to seed origin which was interestingly negatively correlated to seed weight. Effects of burial site/lab conditions were also significantly different over the whole duration of the experiment, but towards the end (after 8 years) the differences collapsed. Our tested soil depths had no significant influence on viability, indicating that burial at ±7 cm fulfils the need of ragweed seeds for continuation of innate dormancy. The loss of viability with ageing of buried seeds was expected although this effect was less prominent in the Hungarian seed origin. Hungarian seed populations from Kaposvár experienced a far longer period, by about 70 years, of successful invasion and establishment of common ragweed compared to the Austrian population with about 10 years. This might have promoted the development of a segetal weed population with prolonged buried seed survival rates adapted to the local agricultural regimes in Hungary whereas the ruderal population in Austria was far younger and still not adapted so much to burial processes.
Many thanks to several persons who contributed additional data about ragweed germination and TTC-testing; at the BOKU University: Melinda Vitalos, Martin Karrer, Maximilian Ferner, Hansjörg Wieser, Elisabeth Fasching, Michaela Teufner, Valentin Rakos, Fabian Bartusel, Jasmin Gierlinger, Carina Habel, Belinda Krammer, Nora Durec, Peter Rojacz, Sarah Schwarzl; at Kapsovár University: Ildikó Kerepesi, Sándor Máté.
The authors have declared that no competing interests exist.
No ethical statement was reported.
We greatly appreciate funding of this work by the EU-project HALT Ambrosia (Complex research on methods to halt the Ambrosia invasion in Europe; 07.0322/2010/586350/SUB/B2) and the EU COST Action FA1203 ‘Sustainable management of Ambrosia artemisiifolia in Europe (SMARTER)’.
Conceptualisation, resources, project administration and supervision: GKAR, GKAZ. Formal analysis: GKAR, GKAZ, RH, JP. Investigation: GKAR, FL, NW, RH, BK, JP, IJ. Methodology: GKAR, GKAZ. Writing – original draft: GKAR, GKAZ. Writing – review and editing: GKAR, GKAZ, RH.
Gerhard Karrer https://orcid.org/0000-0001-5172-2319
Rea M. Hall https://orcid.org/0000-0001-5823-2507
Judit Poór https://orcid.org/0009-0007-0176-823X
Ildikó Jócsák https://orcid.org/0000-0002-1958-6377
Gabriella Kazinczi https://orcid.org/0000-0002-8081-7824
All of the data that support the findings of this study are available in the main text or Supplementary Information.
Supplementary data
Data type: pdf
Explanation note: figure S1. Discolouration and viability stage after TTC-test of common ragweed seeds; figure S2. Linear correlation of germinability and total viability of ragweed seeds buried in Austria and in Hungary; figure S3. Synoptic boxplots of viability rates of ragweed seeds with respect to seed origin, burial site/lab, year of excavation, and grouped by burial depth; table S1. ANOVA results about the influence of the factors seed origin, year of excavation, place of burial/lab, and burial depth on the viability rates of buried ragweed seeds; table S2. ANOVA results about the influence of the factors seed origin, year of excavation, place of burial/lab, and burial depth on the germination rates of buried ragweed seeds; table S3. Viability rates of ragweed seed lots originating from Hagenbrunn or Kaposvár, buried in Austria or Hungary and excavated from 2013 to 2022; table S4. Differences of means of ragweed seed germination and viability rate in the burial experiment performed in Hungary; table S5. Climatic variables in the 10 years of the experiment at the burial sites Kaposvár and Groß-Enzersdorf.