ACROSS the Australian outback, when the heavy rains come and droughts break, new seedlings sprout and the dry landscape comes alive with new growth. High up on the slopes of our mountains when the spring thaw comes and the snows retreat, dormant seeds germinate, green shoots emerge from the frozen ground and white snow gives way to green plants.
But how do these seeds know when to sprout, and how do they survive dormant in the soil for so long in the first place, often for years or decades at a time?
An international team of twenty-nine scientists from 13 institutions around the world — including the US, UK, Australia, Brazil, Germany and France — have joined forces to argue that we need to do more to study seeds and their features. This information could then be stored in a central database to help conservation and restoration efforts across the globe.
Every species of plant has unique seeds, and the traits of these seeds effect how the seeds are spread and how they survive and grow. These traits and functions influence how plants evolve, how ecosystems develop, how plant species survive environmental hazards and ultimately how we can improve conservation efforts.
Traditionally plant research has focussed on mature plants. It is only now that researchers are beginning to examine seed traits in great detail and how the beginning of a plant’s life affects everything which comes after.
Until now seed researchers have focused mainly on the sizes of seeds, particularly their weight and length. These are important metrics which affect nearly every function of a seed, but they do not capture everything. Comparing seeds only by size and weight is like judging a book by its cover; you might be right, but you’re missing most of the story.
“While seed size is useful it is like a Jack of all trades and master of none, as one of my collaborators puts it. Seed size is important, but there are actually hundreds of different traits we should be analysing to better understand seed functions,” says Dr Lydia Guja, seed conservation biologist and National Seed Bank Manager at CSIRO and the Australian National Botanic Gardens.
Dr Guja and her colleagues propose that all seed traits can be linked to four basic functions: seeds need to be spread (dispersal), they need to survive in the soil (persistence), they need to germinate at the right time (germination), and they need to progress from germination and grow into a seedling (seedling establishment).
One prominent example of the importance of these basic functions is a common occurrence in Australia – bushfires.
Scientists have known for decades that some Australian ecosystems rely on regular bushfires to rejuvenate the environment. Bushfires are catastrophic and often tragic events, but Australian plants have evolved to respond to them and stimulate new growth.
After a bushfire, most of the smaller plants and shrubs are destroyed, and the larger trees are often damaged severely. This leaves an opening for many plant seeds which lie dormant in the soil, often for decades, to germinate.
This is one of the only ways in which young plants can have an opportunity to grow in an environment which is well-established with mature plants. Without these events it is almost impossible for a young plant to establish itself.
How a seed takes advantage of such an opportunity is determined by a combination of many traits. It is only recently that scientists have begun examining the combination of seed traits that make these various processes possible.
Seeds need to be dispersed widely and be able to survive deep in the soil, often for decades until the next major bushfire. The seeds also need to be able to survive the fire itself, which burns hot enough to destroy plants and the upper layers of soil. The seeds also need to have a timing mechanism so that they will begin to germinate after the fire has passed.
All of these processes require a complex network of traits, unique to each species. By examining many species we can begin identifying patterns in these seed traits. For example, plants which need their seeds to survive for long periods of time in the soil tend to have larger seeds. To survive hot temperatures seeds tend to have thick protective coatings on their seeds.
“Some of the trait links that have been made to date are very specific,” says Dr Guja, “For example, research has shown that in bushfires, larger seeds don’t need to have as hot a fire as small seeds to allow them to germinate.”
“Even in related species like Pomaderris adnata and Pomaderris walshii, the P. walshii seeds are double the size of P. adnata and their dormancy is alleviated by a higher temperature, 108 degrees versus 98 degrees respectively.”
“This is likely because larger seeds have the energy reserves to germinate from deeper down where it is not as hot, but smaller seeds need to be closer to the surface of the soil where the temperature from the fire happens to be hotter.”
Various studies look at specific environments and groups of species, and by bringing that information together we can gain a global understanding of these patterns in seed traits.
A better understanding of seed traits and the specific effects they have will help researchers, conservationists and ecological restorer in many areas, and could have impacts for agriculture or understanding the effects of climate change.
Global seed trait database
Many researchers across the globe are beginning to look at seed traits and their functions, but Dr Guja and her colleagues argue that we need to start working on a standardised database.
Such an electronic database would collect and store data from researchers across the globe, and allow researchers and conservationists to easily access and share data.
Some such databases already exist, but they all have different limitations. Some are limited to a specific geographic area, and others might include some seed information but not the full range of seed traits which are known or believed to be important.
“Right now, we’re often using the same terminology but don’t necessarily agree on what we mean,” says Dr Guja, “For instance, I might measure germination from a different starting point to another researcher, or we might summarise our results in a very different way.”
“Some scientists have also developed their own ways of measuring or classifying traits which can make it difficult to compare their data with others. If we want global collaboration on this research, we need to agree on trait definitions and measurement standards and work together on a global database.”
To be truly useful in the way that researchers hope for and need, this database must contain a wide variety of information from many species and environments regarding seed traits and how they impact individual plants, plant species and wider ecology.
Similar databases exist already in many areas of science, such as genetic research. Standardised databases allow researchers across the world to easily share their findings and build on each other’s work. It would also encourage standardisation across this field.
Such databases will also help conservation and restoration efforts across the globe.
“Seed use efficiency can be dramatically improved by understanding dormancy and germination. For instance, other studies have shown that in many cases of mine site restoration only 10 per cent of the seeds used will germinate and emerge as seedlings,” says Dr Guja, “but we think that could be improved to 80-90 per cent with a better understanding of seed functional traits.”
This has significant impacts in the costs of conservation and restoration efforts. A standardised global database will help conservationists assess the traits of the seeds they are dealing with and see how those seeds will likely behave as a result.