Where there’s muck there’s grass

The oldest ecological experiment in the world, set up almost 150 years ago to see whether inorganic fertilisers could produce more grass than traditional animal manures, is becoming an important source of evidence on the impact of climate change on genetic variation in plants.

Speaking at the British Ecological Society’s Annual Meeting, being held at Manchester Metropolitan University on 9-11 September 2003, Professor Jonathan Silvertown of the Open University will explain what the Park Grass Experiment has taught ecologists over the past century and how this uniquely long dataset has shed new light on many ecological problems, including the link between the genetics and population dynamics of species.

Set up in 1856, three years before Charles Darwin published his Origin of Species, the Park Grass Experiment is a hay meadow at Rothamsted Research to which a series of different fertiliser treatments have been applied annually. As well as measuring the yield of hay from each plot, ecologists have also measured the change in species composition in the meadow, and kept samples of the hay cut from it over the years.

Professor Silvertown will tell the meeting: “Long-term observations are increasingly important to understanding climate change and now show beyond any reasonable doubt that the warming of the Earth’s climate over the course of the 20th century has had detectable and widespread effects on the distribution, abundance and seasonal behaviour of plant and animal species. Climate change not only alters the abundance and behaviour of species, but also the evolutionary pressures acting upon them and so we can expect natural selection to alter the genetic composition of our native plants and animals.”

“Our best tool for predicting what may happen in the next 50 years is what has happened over that last 100 years in response to historical droughts etc. Apart from the Park Grass Experiment, very few natural habitats have been under continuous study for this length of time. By studying 20th century records of plant species found within the experiment and combining these with experiments on the population dynamics and genetics of plants growing there, we have found that species that have a self-fertilising mating system seem to be more prone to local extinction than species that reproduce by outcrossing. We think that this may be because populations of self-fertilising species have only limited genetic variation and that this makes it more difficult for them to adapt to changing conditions. This is some of the best evidence yet that the genetics of natural plant populations influences their ability to survive over the long term.”

Professor Silvertown is now planning to analyse the DNA of hay samples cut and stored more than 50 years before Crick and Watson discovered the structure of DNA. “We are now investigating the exciting possibility that we can look retrospectively at the genetics of plants that grew in the experiment over 100 years ago. This is being done by extracting DNA from old samples of hay that have been stored at Rothamsted. Our aim is to develop a genetic record for the plants at Park Grass that will parallel the 140 year-long ecological record which we already have. When we can compare the two records, we should be able to see how climatic changes that influence the abundance of species alter genetic variation, with possible consequences for the fate of plant species in the future,” he says.

Professor Silvertown will present his full findings at 10:20 on Thursday 11 September 2003.