Research Article |
Corresponding author: Ivana Milakovic ( ivana.milakovic@boku.ac.at ) Academic editor: Marcel Rejmanek
© 2016 Ivana Milakovic, Gerhard Karrer.
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:
Milakovic I, Karrer G (2016) The influence of mowing regime on the soil seed bank of the invasive plant Ambrosia artemisiifolia L. NeoBiota 28: 39-49. doi: 10.3897/neobiota.28.6838
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Ambrosia artemisiifolia is an invasive annual herb infamous for the high allergenicity of its pollen, which is related to increasing medical costs. Additionally, it can cause serious yield losses as agricultural weed. Common ragweed seeds accumulate in the soil and can remain therein viable for decades, which poses a problem for the sustainable management of these populations. A long term management should thus target a reduction of the soil seed bank. We observed the influence of four different mowing regimes on the ragweed soil seed bank at six roadside populations in eastern Austria. The mowing regimes were based on methods from common roadside management practice and specifically adapted to reduce seed production. After three years of application, the soil seed bank was indeed reduced by 45 to 80 percent through three of the four mowing regimes tested. Therefore, we suggest that the best mowing regime for the most effective reduction of the size of the soil seed bank is the one consisting of one cut just after the beginning of female flowering (around the 3rd week of August in Eastern Central Europe), followed by a second cut 2–3 weeks later.
Common ragweed, invasive plant, management, mowing, roadside vegetation, seed bank, neophyte
Invasive alien species (IAS) are evident threats to local and regional biodiversity (
Common ragweed (Ambrosia artemisiifolia) is an annual IAS, growing on disturbed sites like roadsides, fields, riversides and gardens. It is feared for the allergenic properties of its pollen, as well as a weed in agriculture, in both instances related to high financial costs (
The plant reproduces exclusively by seeds. One individual can produce up to 62000 seeds in North-America (
The persistent soil seed bank of A. artemisiifolia compromises the efficacy of any kind of control measure. Even if a control option succeeds in killing green plants aboveground, some part of the population remains dormant in the soil awaiting more favorable conditions to germinate. Another disadvantage of a persistent soil seed bank is that it acts as a source of further spreading of the weed in soil containments (
Regrowth of ragweed after mowing is well-documented (
Soil seed bank of plants varies by year and season. On undisturbed soil, the annual seed production of ragweed germinates to high percentages in early next spring (
The effects of different tillage systems were analyzed with respect to the composition of the soil seed bank of arable fields (
We sampled the soil seed bank of six roadside populations in Eastern Austria before and after three years of application of management practices. Austrian arterial road verges are cut at least two times a year; a first cut in spring and a second cut between July and October. This resulted in a significant spread of common ragweed along arterial roads since 2000 (
The cutting experiment was set up in 2009 in the heavily infested parts of Austria (Lower Austria, Styria and Burgenland) (Table
Location (coordinate system WGS84) and habitat characteristics (road type, road orientation, initial ragweed coverage (%)) of the experimental sites along arterial roads in Austria.
Site ID | Longitude (E) | Latitude (N) | Altitude (m) | Road type | Road orientation | Initial ragweed coverage |
---|---|---|---|---|---|---|
3 | 15°57'21.21" | 46°42'59.81" | 212 | National | NW-SW | 15 |
4 | 16° 3'9.65" | 47°16'33.61" | 381 | Highway | SW-NE | 5 |
5 | 16°50'41.91" | 48°26'46.51" | 170 | National | N-S | 14 |
6 | 16° 5'31.96" | 47°42'17.61" | 379 | Highway | SW-NE | 25 |
7 | 15°40'4.61" | 48°10'54.87" | 296 | Highway | SW-NE | 17 |
8 | 16°36'18.83" | 48°18'40.06" | 162 | National | W-E | 5 |
Experimental design:
On each site, five experimental plots were installed on continuous spontaneous populations of A. artemisiifolia with coverages ranging from 5 to 25%. The plots were arranged along a line of 100 m, adjacent and parallel to the asphaltic surface of highways or arterial roads. Each plot sized 20 × 0.5 m and received one of the following treatments (mowing regimes), as defined in
Treatment 1: not mown (control),
Treatment 2: first cut before the start of flowering (the last week of June), and second cut at the beginning of seed set (second week of September). Treatment 2 resembles the common roadside cutting regime in eastern Austria.
Treatment 3: first cut after the beginning of female mass flowering (third week of August), and second cut at the beginning of seed set (second week of September),
Treatment 4: first cut before the start of flowering (last week of June), second cut before the onset of male mass flowering (last week of July), and third cut at the beginning of seed set (second week of September),
Treatment 5: first cut before the start of flowering (last week of June), second cut after the beginning of female mass flowering (third week of August) and third cut at the beginning of seed set (second week of September).
All sites have been sampled for soil seed bank before the start of the mowing experiment in spring 2009 and after three years of the experiment in spring 2012. The sampling was always performed just before or at the very start of the germination period in the field. First sampling was done in March 2009 preceding the different treatment of the plots: 20 soil cores (depth 7cm, 285cm³, equally distributed over 100m of the experiment plot) were taken at each site. After three years of applying the various treatments, in March 2012, 19 soil cores were taken per plot on each site.
The soil cores were analyzed for ragweed seed content using a wet sieving machine (Retsch). We counted all intact seeds and put them into wetted Petri dishes. In order to detect the proportion of viable seeds, first germination was induced by putting them into climate chambers at the following conditions: daylight for 8 hours at 30 °C and darkness for 16 hours at 15 °C. We stopped the germination trial after 4 weeks, left the dishes for drying out and stored them for 4 weeks at +4 °C in darkness, in order to overcome secondary dormancy by additional stratification. Afterwards, a second germination period was started at the same conditions like in the first session.
All seeds that did not germinate within the second germination session were tested for vitality by a standard staining (TTC-test with 1 % solution of 2,3,5 triphenyl tetrazolium chloride in pure water). For that, Ambrosia-achenes were first imbibed in tap water at room temperature for 24 hours. The achenes were then cut open with a scalpel to expose the embryo. The bigger part of the achene was used for testing, the other part was discarded. Achene halves were put into petri dishes, covered with TTC solution and left at 30 °C for 6 hours in absolute darkness. Finally seeds were evaluated under a dissecting microscope. All fully stained seeds were classified vital.
The soil seed bank samples in 2009 were taken from the whole sites that where covered consistently with A. artemisiifolia, and can therefore be used as baseline data for comparison to the soil seed bank counting at the differently treated plots three years later. That way, it is possible to observe the effect of the tested mowing regimes on the soil seed bank after three years of application.
Data were analyzed by GLM (generalized linear model) using Poisson distribution procedures and a log link in the package Statistica 10 (StatSoft 2011). Treatment was included in the model as independent categorical factor and seed number per m2 as dependent variable. Pairwise differences between treatments were judged at 95% confidence intervals. We compared the overall most effective treatment with the initial seed bank of the populations of each site by Kruskal-Wallis Tests.
In 2009, soil seed bank varied from 123 to 823 (522 in average) seeds per m² at all sites (Table
Number of Ambrosia artemisiifolia seeds per m2 (means and standard deviation (SD) calculated from 20 soil cores) in spring 2009 and in spring 2012 (calculated from 95 cores) at six experimental sites.
Site ID | Mean number of seeds/m2 in 2009 | SD | Germination rate (%) | Mean number of seeds/m2 in 2012 | SD | Germination rate (%) |
---|---|---|---|---|---|---|
3 | 467 | 652 | 66 | 1002 | 2069 | 98 |
4 | 467 | 699 | 53 | 394 | 1045 | 76 |
5 | 823 | 866 | 100 | 369 | 1102 | 98 |
6 | 541 | 702 | 77 | 1061 | 1181 | 98 |
7 | 123 | 246 | 90 | 205 | 565 | 86 |
8 | 713 | 836 | 95 | 0 | - | - |
After 3 years of applying different mowing regimes, significant differences in the soil seed bank under different treatments were found (Wald χ2 (5) = 188795; p ≤ 0,01). The soil seed bank of treatment 1 (control, unmown) was three times higher than the soil seed bank of the population before the experiment (Figure
Means and confidence intervals of the number of seeds of Ambrosia artemisiifolia per m² (depth 7cm) after 3 years of different mowing treatments (1–5) in 2012 compared to the soil seed bank of the population before the experiment in 2009 (“Treatment” 0 = baseline)
Mean numbers (and SE) of A. artemisiifolia seeds per m² (depth 7cm) in the plots of treatment 3 at six different sites in 2012 compared to the soil seed bank before the experiment in 2009
Kruskal-Wallis test for the differences between the soil seed bank (seeds per m2) in plots of treatment 3 in 2012 and the soil seed bank of the respective populations in 2009, differentiated by sites.
Site ID | H | p |
3 | 5.72 | <0.05 |
4 | 6.65 | <0.01 |
5 | 7.54 | <0.01 |
6 | 3.04 | 0.08 |
7 | 3.74 | 0.53 |
8 | 14.7 | <0.001 |
The number of ragweed seeds per m2 found in populations along Austrian roadsides before the start of treatments in 2009 indicate that those are all well-established populations that cannot be controlled by a one time management action. The aboveground assimilating part of the A. artemisiifolia population varied between the sites at the beginning of the experiment (Table
The seed bank densities of ragweed along Austrian highways are generally lower than in European arable fields (
Because most management options act on the green parts of the plant, they are not sustainable. The most desired aspect of ragweed control is the successful elimination of persistent seeds from the soil. The results of this long term experiment show, that the soil seed bank can be diminished vigorously by a sophisticated mowing management. The mowing regime should consist of a first cut in August, just at the first appearance of female flowers, and a second cut in early September, just before fertility of the female flowers on the regrowth from the base (
We advise analyzing the soil seed bank of ragweed before installing a field experiment or defining a management regime for ragweed control, as well as after the activity. Thus sustainability can be proven. The knowledge about the status of soil seed bank is particularly important for ragweed populations growing on roadsides, as the upper soil is prone to transportation elsewhere, which contributes to further dispersal of ragweed seeds and creates new populations.
We would like to thank the Austrian road authorities and ASFINAG for supporting us by co-operating in mowing of the experimental plots. Furthermore, we cordially thank Prof. Konrad Fiedler for statistical advice and Irene Karrer for language revising.
Financial support
The project was financially supported by the National Research Fund Luxembourg (I.M., Grant number PHD-09-010), the Austrian Ministry of Agriculture, Forestry, Environment and Water, eight Federal State Governments of Austria, as well as the European Commission, DG Environment (Grant Agreement No. 07.0322/2010/586340/SUB/B2). Additionally, we acknowledge support from EU COST Action FA1203 “Sustainable management of Ambrosia artemisiifolia in Europe” (SMARTER).