Butterfly Identification Course; Yellow Rattle Interactions with Meadow Plants

Many thanks to Dr. Deborah Sazer for organising the following event :

The Butterflies of Carmarthenshire

Learn how to identify butterflies and their food plants, and how to manage their habitats.

Indoor morning presentation, and afternoon butterfly walk with Dr Deborah Sazer.

Saturday 29th July 2017 10:30am to 3:30pm

Carmel Village Hall, Carmel, Carmarthenshire SA14 7TL

£20 per person

Special offer: £15 Carmarthenshire Meadows Group members

Booking essential

Indoor session in the morning at Carmel Village Hall, then we will walk a short distance to Carmel National Nature Reserve (South and West Wales Wildlife Trust Reserve) in the afternoon for an outdoor practical session.

Note that this will involve walking over some rough ground, so unfortunately not suitable for wheelchairs.

Tea and coffee provided, please bring lunch

Please wear suitable footwear and clothing

Contact: Wild Gower / Gŵyr Gwyllt

email: ecoleg.sazer@gmail.com

Phone: 07703 343597

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I’ve mentioned before how quickly Lousewort, Pedicularis sylvatica, has become really well established, from an initial small scattering of seed collected from a friend’s local meadow just 4 years ago…This perennial hemi-parasite has been a really popular early season nectar flower with at least 3 species of bumblebees visiting the flowers, which have opened over several weeks from early April. (I incorrectly identified it as Marsh Lousewort before – sincere apologies…) Lousewort is a much shorter plant, than Marsh Lousewort.With the first flowers of annual Yellow rattle (Rhinanthus minor) opening this year by May 9th, it dovetails very nicely to give a much longer reliable nectar supply for these tough pollinators.

But how do both these hemi-parasitic plants fit into the ecology of meadows? I struggled to find much about studies on Lousewort interactions with roots, although did discover that both the genus Pedicularis, of which there are several hundred species worldwide (many in China) and Rhinathus have recently been switched from the Scrophulariaceae and into the Orobanchaceae, or Broomrapes. Broomrapes generally are obligate parasites – lacking any chlorophyll, and so are entirely dependent upon penetrating other green plant root systems and obtaining their nutrition by stealing it from them.

Both Yellow Rattle and Lousewort do contain chlorophyll, so can photosynthesise but can still penetrate other plants’ root systems to obtain certain nutrients from them. I discovered that much work has been done on Yellow rattle, since as many will already know, it is frequently recommended as an aid to restoration of wildflower meadows, by reducing the vigour of otherwise dominant grasses. Indeed this is why we first imported local seeds of yellow rattle onto our meadow about 5 years ago.

My first discovery was that it doesn’t parasitise just grasses, but a range of more than 50 different potential host plant species, all of which might be found in a typical meadow – though it’s not apparently capable of damaging any native Orchid species.

It does this by developing its own root system on germination of the overwintered seed in spring, and this root system then develops special structures designed as transfer organs called haustoria (single – haustorium), which connect the host and parasite root tissues. The haustorium surrounds the host root, crushes the outer layers, and then forms a penetration peg to tap into the host’s xylem channels which distribute fluids and nutrients up through the host’s tissues. Once it has done this successfully, secondary xylem channels develop and the parasitic rattle root can then begin the process of sucking out fluids, and more particularly nutrients including carbon and nitrogen from the host. It does this by having higher transpiration rates, in turn because the stomata or pores on the leaves of the rattle are relatively insensitive to water loss. So the water potential of the parasite tissues is kept below that of the host, and creates an effective gradient which ensures materials flow in one direction – away from the host and into the yellow rattle.

But this sophisticated process doesn’t work equally well on all the plant species which yellow rattle will attack.

Meadows being the diverse communities that they are, means that a single small rattle plant can have simultaneous links into up to 7 different plants at the same time – and remember this is an annual plant which only has a few months to grow, flower, set seed and then die. Grasses and legumes like the trefoils, seem to be its most useful hosts whereas many other dicotyledenous flowering plants (or forbs) can be attacked, but have developed quite sophisticated defence mechanisms.

Quite recent work has shown that in some plants, like the Ribwort, or lanceolate plantain, (Plantago lanceolata) this defence entails hypersensitive host cell death at the point of  attempted penetration by the rattle’s haustoria. Essentially the plantain’s root cells are intentionally sacrificed and killed ( by the plantain) at an early stage of interaction with the Rattle’s attack, so that the Rattle root can never form a viable peg penetration into the plantain’s xylem system, and the attack fails. Though at what cost to the plantain?This year I’ve noticed a few plantain in our meadow which seem very aetiolated. Are these plants which have suffered so much root damage from this defence strategy that their own viability has been affected? Or is something else completely unrelated affecting them? I just don’t know.

In Ox-eye daisies, Leucanthemum vulgare, the plant’s defence is different and involves sealing off the attacking peg of the rattle’s haustorium with lignin, to completely prevent penetration of its xylem. A wooden wall, to repel invaders.

It clearly is a battlefield beneath the soil’s surface.

All of this suggests one would expect variation within a meadow of the impact of Yellow Rattle, in part depending on the actual range of plant species present in it. Some more recent work has also looked at the impact of genetic variation within populations of Yellow rattle itself to try to explain the quantified difference in impact of yellow rattle on some meadows where it’s been introduced. In one study, grass biomass suppression induced by adding rattle seeds ranged from a small 8% to a whopping 84%, whilst at the same time, the abundance of forbs increased by anything between a miserly 5% to an impressive 57%.

The concept of the impact of community genetics is a new one to me, but makes empirical sense having observed the variability in spread of Yellow Rattle in our own and other meadows. In our case the source seed was from a local meadow in which Rattle seemed to be quite a dominant force, and I’ve probably layered on an anthropogenic genetic shift by consciously hand harvesting and scattering saved seed from just the earliest flowering, and therefore seeding, plants in the meadow. (For the first 2 years, until the plant became so widely distributed that hand scattering was unnecessary). This was motivated by our need to cut the meadow in stages, some quite early, since we currently do mainly manual hay making, so it’s impossible to clear the field in one session. We have to pace ourselves.

And this is just considering the impact of Rattle genetic variation. A lab study involving parasitism of 4 different strains of Barley showed big variations in how much the same strain of Yellow Rattle impacted on the different Barleys’ productivity, and indeed how the different parasitised Barleys created bigger, (or smaller), and therefore more fecund in term’s of seed production, Yellow Rattle plants.

Our meadow has now morphed to a majority of Sweet Vernal Grass (Anthoxanthum odoratum) flowers at this time of the year. Does it have greater resistance to Yellow Rattle? Or just thrive better, since it’s quicker off the mark in spring? We don’t know and we’re not complaining, since it’s this plant more than any other that gives meadow hay its fantastic scent.

Add in the impacts from mycorrhizal and other fungi which are also key beneath-ground components of a meadow, linking up plant roots and  involved in mineral and nutrient exchanges, and one begins to understand that never mind how complex a diverse hay meadow might seem visually above ground, what’s going on below the surface is mind boggling in its complexity.If I took one message away from this brief foray into what is clearly now a hot area of research, it is that genetic diversity within plant populations in a meadow is a very good thing for long term species viability. Given the now extremely diminished and fragmented distribution of such meadow communities, perhaps there are great benefits in the intentional local exchange of seed material between meadow owners, to help maintain such species genetic diversity, and consequent species resilience. In the past, the natural wandering of sheep, and their seed carrying fleeces, would have ensured this was a constant low frequency process, and plant populations made up from those individuals best suited to local growing conditions would have slowly evolved.

One final point. A recent review article by Ken Thompson, click here, referenced a pan European study highlighting just how variable germination rates for meadow plant seeds like Yellow Rattle were, when obtained across Europe from commercial suppliers. (Apparently 3 out of 17 samples of Yellow Rattle contained no viable seeds!) In addition many samples were contaminated with other species, so again hand collected, and locally sourced seeds have real advantages when it comes to adding species, or extending genetic diversity, in our native hay meadows.

Julian Wormald

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Thanks for reading, and remember I’m always happy to receive any suitable articles or photos to include as blog posts. Please send them to me…

Julian Wormald… website@carmarthenshiremeadows.com

4 thoughts on “Butterfly Identification Course; Yellow Rattle Interactions with Meadow Plants

  1. Fascinating. A lot of new information about yellow rattle to me, especially their effect on plants other than grasses. Sweet vernal seems unaffected here at Waun Las NNR but another early flowerer, meadow foxtail (Alopecurus pratensis), has been virtually wiped out wherever rattle has spread – so I suspect it’s not about timing. All makes me think of yellow rattle as the Dracula plant.

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