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Friday, 15 March 2013

The benefits of flowering early

Bristol was a swirl of snowflakes and blossoms earlier this week. Monday on my walk the cutting wind was relentless. Yet, despite my frozen nose and numb fingertips, I stopped to admire the many splashes of colour along my route – a street lined with blossom-laden plum trees, front gardens lined with daffodils, heather and crocuses, splashes of primulas and even some snow drops in the local woods. As my teeth chattered despite my thick down coat, I did marvel at these early spring bloomers that have clearly found it to their advantage to flower despite cold temperatures, relatively short days, and a paucity of pollinators. So, what exactly are the advantages of being the first blossoms of spring?

A robin and crocuses, both soaking up some sunshine
on Thursday at the Botanic Garden.

Early woodland blossoms have access to more light

The first and perhaps most obvious advantage is that these early blossoms appear before the deciduous trees come into leaf, which gives them more access to light. Many of these early blossoms are naturally woodland flowers and so as soon as conditions become tolerable, these flowers put all of their energy into producing foliage and flowers before the forest canopy has formed. If successfully pollinated, the plant will produce a seed for dispersal. Then, as the forest floor becomes shaded by the trees above, the flower and foliage die back and any unused nutrients are returned into the roots or bulb. There will be no sign of these plants above ground for the rest of the year.

Though this may sound very much like a ‘get-up-and-go’ approach to flowering, the timing of when each species, and indeed each plant, flowers is incredibly complex and scientists have yet to figure out all the intricacies. It is affected by physical factors, such as soil nutrients, water, sunlight, day length and temperature, but it is also affected by biological factors, such as abundance of pollinators, herbivorous predators, seed dispersers and competition from other plants.  All of these factors may ultimately affect the reproductive success of the plant; flower too early and there may not be sufficient to set seed, but flower too late and the bird species that normally disperse the seed may have already migrated to over-wintering grounds.

There is less competition for pollinators

Though there are fewer pollinators about in early spring, there are also fewer blossoms to compete for their attentions. Insects that emerge in early spring or that forage throughout the winter, such as some bumblebee species, do not have a plethora of blossoms to choose from, so this increases the likelihood that the flowers that are out will get a visit.

There is more time for seed maturation

For some early season blossoms, such as fruit trees, there is an enormous investment in seed production, which takes time. The benefit in the end, of course, is a rather extravagant and often delicious means of dispersing seed great distances.

Early blossoms favour out-crossing  (MunguĂ­a-Rosas et al., 2011)

Fewer blossoms in early spring also mean that pollinators will travel greater distances between flowers. As a result, a flower may receive pollen from a more distant flower, which may be less similar genetically. It’s the floral equivalent of “bringing in new blood”, also known as out-crossing.  Perhaps the genetic material carried in that pollen encodes some increased resistance to frost or disease...or perhaps not. Most importantly, it is adding diversity to the population, which is the foundation for adaptation.

The crocuses in my front garden are in full bloom.

The evolution of early bloomers

There are not only differences in the time that plants flower between species, but also between populations of the same species and between plants of the same population. For example, the crocuses at the front of my garden, which have been exposed to more direct sunlight, are much further along than those in my back garden, which are shaded by a cedar hedge. This is a clear example of differences in the resources available in these two different growing environments.

However, consider a woodland covered with bluebells, what drives those first few bluebells to burst out before the others? It might be slight differences in their growing environments, but it is also in part a result of their genetic makeup. A sort of bluebell “aptitude” if you will that predisposes them to go to flower quickly - two separate bluebells, under the same growing conditions, may still flower at different times. Of course, it is therefore inevitable that those bluebells that are first to bloom will be pollinated by others that are in blossom, giving rise to new generations of early bloomers.

It might also be that environmental conditions are such that early bloomers are for some reason more successful in reproducing, perhaps because pollinators favour early bloomers (Munguia-Rosas et al., 2011). This will eventually drive the flowering time of entire populations earlier each season and over time this will become fixed within the genetic makeup of that population, in as few as three generations for some species (Galloway and Burgess, 2012).

Temperate plants tend to be more flexible with their flowering times

In temperate climates, there are much bigger differences in variables such as frost, temperature and day length across the landscape, between the seasons and between years. As a result, flowering plants in these regions exhibit tremendous variability in their flowering time – it is an adaptive flexibility that enables them to take advantage of the best growing conditions possible regardless of when they might happen (within reason of course).

If you’re going to be a risk-taker, be sure and have a plan B

Of course, many of these early spring blossoms have what could be considered a back-up plan. Snowdrops, crocuses, and daffodils are all capable of both sexual and asexual reproduction. So, if there is a prolonged heavy frost after these flowers have emerged or they are not successfully pollinated for any other reason during the season, then the bulbs will still form new small bulbs that are genetically identical to the parental bulbs. However, it is sexual production that brings genetic diversity to a population and this is what will allow a population to adapt to changing environmental conditions and resist disease.

There is a lovely clip here from the BBC’s Private Life of Plants on their website showing the progression of early blossoms as a British woodland bursts to life in the spring.

Well, I hope you are getting the opportunity to enjoy these early spring blossoms! Also, be sure to come out to the Botanic Garden over the Easter weekend to enjoy the Easter Sculpture Exhibition – amazing art, refreshments, and garden tours sounds like an ideal way to spend a weekend to me, I’m definitely going to be there!

Here are the references used above:
Galloway LF and Burgess KS. 2012. Artificial selection on flowering time: influence on reproductive phenology across natural light environments. Journal of Ecology 100: 852-861.

MunguĂ­a-Rosas MA, Ollerton J, Parra-Tabla V, De-Nova JA. 2011. Meta-analysis of phenotypic selection on flowering phenology suggests that early flowering plants are favoured. Ecology Letters 14 (5):511-521.

Friday, 8 March 2013

Students set to tell the story behind the ballast seed collection

Guest post by Rhiannon Williams & Alex Learmont

The seeds of some plants can survive for many years lying dormant, waiting for improved environmental conditions to germinate. Seeds can withstand extreme drought or cold; some dry seeds can be stored at -150 degrees Celsius without harm, and still be induced to germinate!  Some seeds can be transported around the globe in the hulls of ships, immune to the storms and scurvy, only to one day be dumped on the banks of a foreign river, which may or may not provide the conditions it needs to grow and flourish.

We are biology students at the University of Bristol and for our dissertation we are creating interpretation boards for one of the Botanic Garden’s newer collections – the ballast seed collection. Our boards will be displayed at the Botanic Garden next to the ballast seed flower bed, which can be found near the glasshouses. This summer, once the flower bed has been planted up, it will be a joy to come and visit.

Alex Learmont and Rhiannon Williams are
preparing interpretation boards and
other materials on the ballast seed project
as part of their dissertation.
Our aim is to provide visitors of the gardens and the public with accessible and interesting information about the ballast seed project and the plants found within the collection. In addition to the interpretation boards, we are making A4 cards with information for each plant species and leaflets that will be available at the Garden and on tours of the floating garden at the harbourside. Visitors will even be able to scan QR codes placed beside some of the plants with their smartphones and access informative websites for some of the species. This collection is unique to the Botanic Garden and we’re looking forward to telling the remarkable story behind it.

The project began as part of the ‘Port City’ exhibition at the Arnolfini

The ‘Seeds of Change’ project is an on-going exploration of the ballast flora of European port cities by the artist Maria Thereza-Alves. Empty or lightly loaded ships carry low-value materials such as earth, stones and gravel, or sea water as ballast to weigh them down, giving improved manoeuvrability and stability. This ballast was emptied into the river Avon and onto ballast dumps that used to be present around Bristol. For centuries, exotic plant species have been transported to Bristol in the ballast of trading ships coming from countries all over the world.

The project began in 2007 as a part of the international Arnolfini exhibition entitled ‘Port City’ and was part of the London 2012 Festival. With the help of Botanic Garden curator Nick Wray, a list was composed of exotic plants found growing on ballast dumps throughout the UK, including the local port of Avonmouth. The full collection of these seeds was germinated in the University of Bristol Botanic Garden. Then with the support of the Arnolfini, the Botanic Garden and Bristol City Council, designer Gitta Gschwendtner used a condensed version of this collection to transform a disused grain barge on Bristol’s floating harbour into a ballast seed garden.

The floating garden can be viewed from Castle Park, but visitors can only reach it by boat. The next set of boat tours begin this spring. For a small fare, visitors can book onto them through the Arnolfini. Some of the tours focus particularly on the design and artistic concepts of the project whereas others are aimed more at those with a botanical interest. For example, last summer a micro-sound tour allowed visitors to listen to the sounds of plants growing.

Exotic plants reflect Bristol’s rich maritime history

The idea behind the project was to draw links between Bristol’s floral history and the social and economic history of Bristol’s trading past. Human dispersal of plants often follows routes of transportation, and the ballast of ships was a route into Bristol for invasive plant species. Some of the plants are native to the Mediterranean, West Asia, North Africa, and even South America. Ships would have been trading back and forth to these places over the past few hundred years. The plants in the collection convey a living history of Bristol’s rich maritime past.

Relatively few seeds in the ships ballast would have survived the long sea journeys, but some were able to germinate or lie dormant in the ballast dumps around Bristol for many years. In the late 1800s ballast became a more important aid to invasion when the new generation of metal ships changed from solid to liquid ballast. Ballast water can contain hundreds of species including bacterial, microbes, small invertebrates and seeds. Now, ballast is a major source of invasive species to port’s and in coastal freshwater and marine ecosystems. The International MaritimeOrganization (IMO) has developed a Convention aimed at preventing these harmful effects, this involves “Ballast water exchange”. The water taken up at the port of departure is replaced during the voyage with water from the deep sea. The organisms in the deep sea water are far less likely to survive when the water is discharged at the port of arrival, hence reducing the impact of invasive species in ballast water.

Most exotic seeds never establish themselves

In 1996, Williamson and Fitter proposed a ‘tens rule’. The rule states that only 10% of non-native species imported into a region will appear in the wild. Of these, only 10% will become established, and 10% of the establishing species may become invasive. Therefore, only 1 in a thousand imported species will cause problems.

An important message the ballast seed garden conveys is that most non-native flora does not become established or invasive. Even if the plants survived the long journey, the environment where they were unloaded from the ships (such as a ballast dump) was likely to be unsuitable for growth, or the number of plants of the same species was too small to result in a viable breeding population. However, some of the species on the ballast seed display are capable of survival and reproduction in the wild. Many of these naturalized species exist alongside British flora causing no obvious damage to habitats and ecosystems.  The Garden promotes the idea for multihorticulturalism: the view that migrations of species are natural and trying to stop them is futile.

New projects bring ‘Seeds of Change’ to schools and communities

During spring and summer 2013 a new project, “Seeds of Change: Growing a Living History of Bristol”, will provide the opportunity for Bristol schools and community groups to grow ballast seed gardens of their own. The project was set up by The University of Bristol Centre for Public Engagement and the Botanic Garden in partnership with the Arnolfini, and with funding provided by the Heritage Lottery Fund. Academics, artists and student volunteers from the university will be working together to lead a programme of activities and workshops exploring themes of history, botany and art; making the original themes of the “Seeds of Change” project exciting and accessible to school children and community groups.

For more information on the Heritage Lottery Funded schools and community programme you can visit the University website: or contact Martha Crean by email: or phone: 0117 3318313.

Monday, 4 March 2013

Re-potting lotus ready for the new growing season

The lotus plant is a symbol of friendship, family, rejuvenation, hope, rebirth, fortune, purification and positivity. The rhizomes of the plant lie buried in the sludgy, smelly mud on the bottom of lakes and ponds. Rising up from the mud are the leaves and the strong stems, which come up through the water to support the heavily scented, beautiful flowers. This pattern of growth makes the lotus a very important and powerful symbol in Buddhism. It signifies the progress of the soul as the flower rises from the primeval mud of materialism, through the waters of experience, and into the bright sunshine of enlightenment (source). Though most water plants send blooms to the surface in this way, only the lotus flower sits up to one metre above the water’s surface, truly rising above it all (source).

Lotus are a primitive plant. The fossil record shows that 15 million years ago there were eight different species of lotus, which were later reduced to only two species – the Asian lotus (Nelumbo nucifera) and the American lotus (Nelumbo lutea). The spiritual, nutritional and medicinal importance of this plant in Chinese, Vietnamese and Indian cultures has made it the focus of extensive research and breeding programs. There are over 500 different cultivars of lotus in the world and the University of Bristol Botanic Garden has carefully chosen cultivars that show the range of flower forms and colours for its small collection.

Last week I met Penny Harms, Glasshouse Coordinator at the Botanic Garden, in the potting shed to see what she’s doing to prepare the Garden’s lotus collection for the next growing season. Penny and her team pulled the lotus plants out of the pond in October, where they have been sitting dormant in their pots ever since. Now, it’s time to give them some attention and get them ready to go back into the pond.

Penny is very careful when cleaning
the lotus rhizomes as any damage will
affect its growth.

Looking after Lotus

First, Penny tips the pots out, getting rid of all the old soil and gently collecting the lengths of rhizomes that wind around in circles within the pots. The rhizomes are then placed into plastic trays with lids that have holes to ensure they don’t get moldy. Over several days, Penny then sorts through each of the trays and pulls off any of last year’s rhizomes, which are brown and rotten compared with the cream-coloured healthy rhizomes.

“You have to be really careful,” explained Penny. “These are the growing shoots – this is a leaf here – so if you damage these, the plant won’t grow very well this year.”

Once the rhizomes have been cleaned they are potted up. Penny has prepared a special mix which is a loam-based potting mix to which she adds Bracken Down – a mixture of thoroughly composted bracken, bark and manure – and Osmocote – a controlled release fertilizer.

“Osmocote releases its nutrients over 18 months in a normal pot,” said Penny, “but because the pots are going into a really warm tropical environment, this will speed up considerably. It will release the nutrients over the summer, which is quite handy as these are quite hungry plants.”

Bonemeal is also added to the soil to give added support to the roots and chicken manure pellets are also added to provide more food. The lotus plants replenish themselves each year, so all of the rhizomes Penny showed me will be completely replaced by new growth this year. If the soil doesn’t have enough food and the temperature isn’t warm enough, the plants get weak and don’t really do anything.

“Last summer was quite poor,” said Penny “which meant there was less light and the glasshouse didn’t get as hot. We noticed that the quality of the rhizomes has gone down this year. I record the quality of the rhizomes when I pot them up and we’ve had some really strong rhizomes in the past. But this year, they don’t seem to have done anything – it’s as though they reached a growth plateau.”

Trays of lotus rhizomes. The tray on the left hasn't had
the old material removed yet, but the one on the right has
been cleaned and is ready to be potted up.

Placing lotus by the poolside

After the lotus have been potted up into clean pots with all new soil, Penny will write new labels and bring them into the tropical house. The pots then stand in trays of water along the side of the pool. This keeps the soil constantly wetted and after about a week of being in 25oC temperatures, the plants come into growth.

Once the leaves are 3-4” high and there are enough of them that Penny knows the rhizomes are growing, she raises the water level of the pool and moves the pots down onto a lower edge along the pool. This keeps the pots submersed in the warmest upper layer of water.
For the final phase, the pots are moved into the main pool where they sit on top of a stack of mesh trays. The water level is raised again so that it covers the top of the pots, but this has to be timed as well with the growth of the giant water lilies (Victoria) that occupy the large planters in the pond.

“Then that’s it for spring and summer,” said Penny “and I have to just cross my fingers that they do their stuff and produce beautiful flowers.”

The many uses of lotus

The rhizomes of lotus are rich in sugar and starches and contain up to 2% protein. They are sliced and roasted, dried or pickled. For medicinal purposes the rhizome is made into a juice or steeped in a tea and taken topically or ingested to stop bleeding.
The disc-shaped leaves and stems are eaten raw or used to wrap other foods, such as rice, for cooking. Medicinally they are taken to clear fever.

The flower has many uses. The outer covering of the flower – the calyx – is used in medicine. The petals of the flower are eaten and the male stamens are used to flavour tea and also contain the fragrant essential oil, which is extremely coveted. Lotus oil is three times more expensive than gold weight for weight. The receptacle, which houses the female parts of the flower and eventually the seeds, is aged and used for medicinal purposes.

The young green seeds have up to 16% protein content and are considered quite a delicacy. They can also be ground into flour to make bread or used medicinally to stop incontinence and digestive problems. The green shoots from the seed – known as the plumule – can also be removed and used for medical purposes.

There’s a lot in a name

When you visit the lotus display in the tropical glasshouse, you will notice that each of the labels has a series of names. At the top is the latin name (e.g., Nelumbo nucifera), then beneath that is the Chinese name (e.g., Xiao Foushou) and the translation (e.g., Small Buddha’s hand). Finally, along the bottom of the label is a description of the flower type (e.g., pink cup lotus). Chinese lotus flowers range from pink to white and some are cream or with a hint of green, but there are no yellow flowers in the Chinese lotus species. Yellow flowered cultivars, originate from the American lotus lineage.

The Botanic Garden has recently ordered some new cultivars from China to expand their lotus collection, including a yellow-flowered cultivar of the American lotus.

Date holder: Mark the 19th of May in your calendars as the Botanic Garden will be hosting a Fascination of Plants Day event

Friday, 1 March 2013

An update on Victoria!

So much can change within a week at the Botanic Garden it can make your head spin. When I spoke to Penny about the giant water lily, she informed me that she wasn't going to be trying to germinate Victoria seeds yet as they didn't have the facilities. However, within a week, that has all changed. Penny received some seeds from Oxford and is currently putting together the pot and water heater she will need to keep the seeds at a balmy 30oC to germinate. Along with that, the Paignton Zoo has managed to overwinter a small plant, which is a Victoria Longwood hybrid that they are giving to the Botanic Garden along with some young germinated Victoria cruziana. Suddenly, Penny has gone from having no seeds to having seeds, young plants and old’s lily overload!