Study

Effects of turf removal on leopard's bane Arnica montana regeneration is mediated by arbuscular mycorrhizal fungi at Schapedobbe and Havelte, Overijssel Netherlands

  • Published source details Vergeer P., van den Berg L.J.L., Baar J., Ouborg N.J. & Roelofs J.G.M. (2006) The effect of turf cutting on plant and arbuscular mycorrhizal spore recolonisation: Implications for heathland restoration. Biological Conservation, 129, 226-235

Summary

Many semi-natural habitats of conservation value in western Europe have declined in species richness due to soil acidification and nutrient enrichment. Attempts to restore such habitats have focussed on reducing soil nutrients and frequently involve removal of eutrophied and/or acidified soil. Recolonisation by desirable herbaceous plants after turf-cutting is largely dependent upon seed availability. However, even if seeds are present either in the seed bank or artificially sown, changes in physical and chemical conditions can prevent successful re-establishment. It has been suggested that soil organisms, such as arbuscular mycorrhizal fungi (AMF), are adversely affected by soil removal. AMF have been shown to promote recovery of herbaceous plants by increasing essential nutrient uptake, reducing pathogens and increasing tolerance to drought, aluminium and soil acidity. This case describes the effects of turf cutting on AMF spore numbers and the concomitant effect this has on leopard's bane Arnica montana. Leopard's bane is a herbaceous perennial characteristic of nutrient-poor grassland and dry heathlands. It is threatened due to habitat loss and degradation.

Study site: The study was conducted at two locations in the north of the Netherlands: Schapedobbe (52º57'N, 6º16'E) and Havelte (52º48'N, 6º13'E). Both areas are nutrient poor, species-rich heathland with an abundance of herbaceous species, including leopard's bane Arnica montana, an uncommon and local species.

Field experimental design: The experimental design to assess spore recolonisation consisted of two treatment types:

1) Three experimental fields from which the top 15-20 cm of soil had been removed to expose the mineral layer in April 2002 - One of the fields (400 m2 in size) was at Schapedobbe and the remaining two in Havelte (80 m2 and 200 m2 in size). At each, three soil samples were randomly taken using an auger (depth 0-5 cm, diameter 3 cm) 1 week before and 1, 3, 7, 13, 18 and 30 months after turf removal.

2) One control area at Schapedobbe and one at Havelte, both in natural non-declining populations of leopard's bane - In each area three soil samples were taken with a 3 cm diameter augur and the samples divided into five equal depth classes spanning the range of 0-25 cm. The first set of samples were taken in May 2001 and repeats samples taken every four months.

The recolonisation rate of AMF after turf cutting was analysed from April until October 2002 by measuring the increased number of spores per gram dry soil (in soil samples) through time. Spores were extracted by wet sieving and sucrose centrifugation and then counted by using a microscope by placing them in a gridded petri dish.

Laboratory experimental design: To investigate factors affecting leopard's bane regeneration, 48 soil cores (16 cm in diameter, 20 cm in depth) were collected from Schaopedobbe in May 2001. All soil cores were watered three times a week with distilled water and kept in a climate room with a day (16 hours, 20ºC, 150 μE m-2 light intensity) and night (8 hours, 15ºC, 0 μE m-2 light intensity) regime. Germination was recorded every two days. Five weeks after the start of the experiment, when germination had ceased, the total number of seedlings was counted, and again counted at ten weeks. The effects of three factors were determined using a fully factorial design in which all combinations of factors were investigated:

1) Effects of turf-cutting - Regeneration in samples in which all organic material was removed was compared to regeneration in samples in which vegetation was clipped every two weeks (thus excluding the effects of resource competition by original vegetation).

2) Seedlings versus seeds - Regeneration in samples planted with seeds (50/core) was compared to regeneration in samples planted with seedlings (9/core) grown for four weeks on sterilised (by γ-irradiation) quartz sand. Seeds were obtained from 15 randomly selected Leopard's Bane flowering plants at Schaopedobbe.

3) Effects of AMF. Regeneration in samples inoculated with 10 g of AMF was compared to regeneration in samples in which no inoculum was added. AMF spores were obtained from additional soil samples within 30 cm of randomly selected leopard's bane plants at Schaopedobbe. Spores were extracted by wet-sieving and sucrose centrifugation and then propagated on ribwort plantain Plantago lanceolata to produce the inoculum. In half of the samples inoculated with AMF, the inoculum was first sterilised by γ-irradiation.

Thus the experiment comprised a total of eight treatments replicated six times to investigate the effects of the three main factors. Two of these were subdivided into four treatments with three replicates to determine the effect of sterilising the AMF inoculum.

Effects of turf/soil removal on spore abundance: Turf-cutting significantly reduced total AMF spore counts. One week prior to cutting, in experimental and control plots, 100-125 spores/g were counted in each. After turf removal spore counts fell to only 19-39 spores/g during the first 13 months but by 30 months had risen to 60-95 spores/g. Spore abundances were positively correlated with length of time after turf removal. The recolonisation rates in the different experimental fields varied slightly, being slightly greater in the smallest field.

Laboratory experiments: Overall, turf-cutting significantly reduced the percentage of leapard's bane seeds that germinated after five weeks, with the degree of reduction unaffected by other factors. Turf-cutting also reduced the percentage of seedlings that had established after 10 weeks, but only in AMF treated samples that had not been sterilised. Treatment with AMF inoculum increased the percentage of seeds that established themselves after 10 weeks, with the effect being stronger in samples in which turf had been removed and stronger still in samples in which the AMF inoculum had been irradiated. Sterilisation of AMF inoculum reduced the percentage of seeds that germinated after five weeks and also reduced maximum germination rates and the percentage of seedlings that established themselves after 10 weeks. The effects of turf-removal, AMF inoculum treatment and sterilisation on germination, germination rates and establishment are shown in Table 1 (attached).

Conclusions: Turf-cutting has a substantial influence on soil characteristics and below ground soil fungi communities, which in turn appears to have a pronounced effect on the success of leopard's bane recolonisation after turf removal. In a natural setting, turf-removal reduces the abundance of AMF spores for longer than 30 months. Laboratory experiments reveal that turf removal has a detrimental impact on leopard's bane regeneration but the addition of AMF spores to samples in which turf had been removed appears to have assisted regeneration. However, sterilising spores prior to adding them appears to negate their positive impact. This case shows that turf-cutting has a deleterious impact on the abundance of soil micro-fungi, which in turn could have a negative effect on the recolonisation and establishment of herbaceous plant species.

Output references

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