Nature repeating itself

It was Georgia O’Keefe who said, ‘When you take a flower in your hand and really look at it, it’s your world for the moment’. It’s worth doing this, nature is captivating close up; perfectly packaged and clinically efficient, each flower has an adapted shape and look gleaned over hundreds of thousands of years for maximum productivity. This economy of engineering uses patterns and shapes that are repeated again and again throughout the natural world and dotted all around the Botanic Garden. (more…)

Tea, thatch and early spring

Crocus appearing in the Garden.

Today as I write this the sun is shining, the birds are in full voice singing, cawing and screeching around the Garden. Bulbs are popping up, crocus are the first with daffodils a week away from carpeting the ground with yellow. Primroses are dotting grassy areas and bees are beginning to forage in the middle of the day; the minimum temperature that a bee can fly is said to be 13 degrees, so when you see one out and about you know the season is changing. (more…)

Keeping your head above water: plants coping with waterlogging

By Helen Roberts

Flooding on the Somerset Levels.
Photo credit: Nigel Mykura [CC BY-SA 2.0],
via Wikimedia Commons

Britain has had its fair share of flooding over the last couple of years. In 2014, the Somerset Levels was under water for weeks and 2015 saw some truly devastating flooding occurring in the northwest of England. Flooding can have detrimental effects on our own lives, but also on plant communities.

Waterlogging of plants can cause chlorosis (loss of the normal green colour) of the leaves, root rot and eventually death. It’s a common problem that many gardeners face every day and there are different techniques to cope with this ever persistent problem on our shores. Precautions are even taken at the University of Bristol Botanic Garden during this wet weather.

“As far as the garden borders go, we’re very careful about never walking on them when there’s been heavy rain,” explained Andy Winfield, horticultural technician at the Botanic Garden. “If we have to get on a border for any reason, we use a board and then fork over where it was to prevent compaction and a pan forming. When a pan forms, then water is more likely to sit on the surface and create problems.”

How does waterlogging affect soils and plants?

The profile of a soil will greatly affect its interaction with water. Soils are composed of solid material with spaces filled with water, gases, roots and other living organisms – these attributes impact water retention and drainage. For example, clay soils have small pore spaces and so retain more water compared with sandy loams.

Subsoils can also influence soil structure and its interaction with water. Waterlogged soils are not only affected by the amount of water coming into the system, but by the soil’s ability to disperse and absorb that water.

When soils are waterlogged, the air spaces between the particles are filled with water and the movement of gases within the soils is inhibited preventing the roots from respiring properly. Gases such as ethylene and carbon dioxide begin to accumulate, which leads to further negative impacts on root growth. Anaerobic processes begin to changes the soil biochemistry, which leads to plant death through the build up of toxins within soils.

What is happening to plants at a cellular level when faced with anoxic or hypoxic conditions? 

When plants are waterlogged, they are not getting enough oxygen via the roots for cellular respiration and energy production. Because the plants cannot obtain oxygen via the roots, plants turn on their own energy reserves. This is much like when we use our muscles during strenuous exercise and we can’t get sufficient oxygen to the hard working cells – the cells undergo anaerobic respiration, which produces lactic acid. Plants can also undergo anaerobic respiration, but it is not sustainable and eventually, the plant dies as the demand for energy exceeds the supply.

Until recently little was known about how some plants cope with the stress of waterlogging. However, researchers from the Max Planck Institute of Molecular Plant Physiology, with colleagues from Italy and the Netherlands, have discovered a protein that triggers the activation of stress response genes when oxygen levels drop due to waterlogging. This protein is attached to the cell membrane under normal aerobic conditions, but when levels drop it detaches from the membrane and relocates to the nucleus where it switches on the stress genes. When oxygen levels return to normal, the protein degrades and the stress response genes switch off again.

How some plants have evolved to cope with anoxic and hypoxic conditions

When out walking as a child on Exmoor, I would often pick the stems of the soft rush, Juncus effusus, and peel back the green outer coating to reveal the soft, husky white pith inside. I was amazed when an adult told me this material was once used for making rush lights. The pith would be extracted from the rush leaves and combined with fat or grease to provide a source of artificial light. This pithy material is interesting though in this context as it contains a tissue called aerenchyma, which is usually found in the roots and stems of many hydrophytes (plants adapted for living in water). The tissue has large interconnected intercellular gas spaces that help to oxygenate the roots and increase buoyancy.

Other plants adapted to soggy conditions will produce fine surface roots called adventitious roots. These roots scavenge oxygen from the surface where there is a thin aerobic layer. Many of the Melaleuca species, mostly from Australia, use this way of coping with water hypoxia.

Some plants are adapted to rise above it all; they elongate their shoots to get above the water, as is the case with some floodplain Rumex species (docks and sorrels). Nymphaea species (the water lilies) – which you can see in the Botanic Garden glasshouses –  have a hugely elongated petiole, often more that two metres long, to keep their leaves and flowers at the water surface.

Arial roots (pneumatophores) of the grey mangrove
(Avicennia marina var resinifera) from South Australia.
Photo Credit: Peripitus (Own work) [GFDL, CC-BY-SA-3.0 )
or CC BY-SA 2.5-2.0-1.0 ], via Wikimedia Commons

Large tree species have also adapted their roots to cope with swamp-like conditions. These strange looking roots are known as pneumatophores – woody extensions that grow vertically upwards from the underground root syste
m to reach above water and capture that much needed oxygen. The bald cypress, Taxodium distichum, which is found in the southern USA in lowland river floodplains and swamps, forms these roots that look like knees sticking up out of the water. The actual surface of the root is pockmarked with many lenticels, which are small stomata-like pores found in the bark that allow gaseous exchange. Other swamp and mangrove species have variations of these root adaptations to cope with low oxygen levels including pencil and cone roots (which belong to the pneumatophore group) and other types of aerial roots like knee, stilt, peg and plank roots. These roots differ in both their morphology and function, but are ultimately adapted to cope with waterlogging and often saline conditions.

The importance of wetlands as carbon sinks

Waterlogged lands are not all doom and gloom, in fact, bogginess is vitally important in terms of the Earth’s climate. Peatlands fall into that category. They act as important carbon sinks and currently cover about four per cent of the Earth’s land surface. Drainage of these areas of peatlands and wetlands for agricultural use leads to increases in greenhouse gas emissions. Researchers are actively trying to understand the effects of climate change on peatlands globally and there have been pushes to effectively  conserve and manage these precious ecosystems.

Sources:

Guillermina M. Mendiondo, Daniel J. Gibbs, Miriam Szurman-Zubrzycka, Arnd Korn, Julietta Marquez, Iwona Szarejko, Miroslaw Maluszynski, John King, Barry Axcell, Katherine Smart, Francoise Corbineau, Michael J. Holdsworth. Enhanced waterlogging tolerance in barley by manipulation of expression of the N-end rule pathway E3 ligasePROTEOLYSIS6. Plant Biotechnology Journal, 2015; DOI: 10.1111/pbi.12334

Francesco Licausi, Monika Kosmacz, Daan A. Weits, Beatrice Giuntoli, Federico M. Giorgi, Laurentius A. C. J. Voesenek, Pierdomenico Perata, Joost T. van Dongen. Oxygen sensing in plants is mediated by an N-end rule pathway for protein destabilization. Nature, 2011; DOI: 10.1038/nature10536

Daniel J. Gibbs, Seung Cho Lee, Nurulhikma Md Isa, Silvia Gramuglia, Takeshi Fukao, George W. Bassel, Cristina Sousa Correia, Françoise Corbineau, Frederica L. Theodoulou, Julia Bailey-Serres, Michael J. Holdsworth. Homeostatic response to hypoxia is regulated by the N-end rule pathway in plants. Nature, 2011; DOI: 10.1038/nature10534

Children take a 'walk through time' at the Bristol Botanic Garden

It’s 1 pm, the sun is shining and the volunteer guides are starting to gather near the welcome lodge in anticipation of 60 Year 4 children arriving at the Botanic Garden for a tour. It’s my son’s school, Horfield CEVC Primary School, and so I’ve decided to come along for the tour and get a glimpse into how the Garden is viewed through the eyes of eight and nine year olds.
Anne is one of the volunteer guides at the garden and she and I get chatting while we await the children’s arrival. She was a teacher for 40 years – teaching at GCSE and A levels. She laughs as she tells me she was a bit nervous she would find touring younger children challenging when she started giving these school tours at the Garden. She soon found, however, that though it was different from teaching upper level students, it was also just good fun.
Volunteer guide Tony gives a talk to Year 4 students
from Horfield CEVC Primary School prior to their tour.
“I’m not responsible for making sure they learn the curriculum, I’m here to entertain them with interesting stories about the plants we have here in the garden – to get them excited and inspired by what they see,” Anne says from a shady bench.
The guides have come prepared; they know the Horfield children have been learning about Egypt and different habitat types. As well as discussing the logistics of touring sixty children around the garden in small groups, they check in with each other about plants that might be important to point out that will link to the topics and themes they’ve been learning in the classroom.
Then the coach arrives.

A tour through the glasshouses

Before the children break into small groups to go around the garden, volunteer guide Tony gives a very brief talk about what plants need to survive. The children enthusiastically put up their hands in response to Tony’s question of what plants need to grow. Horfield Primary is lucky enough to have a garden and most of the children will have grown plants in the classroom at some stage (my son brought a runner bean home from school a few weeks back that’s doing splendidly). So, although photosynthesis hasn’t been taught by Year 4, there are other opportunities where the children are learning the basic needs and processes of plant growth.
Students have a look in the pitcher plants in the sub-tropical
zone of the glasshouses.
Baking sun and a tight schedule keeps the introductory talk brief and I follow Anne’s small group down into the glasshouses. She points out the Deadly Nightshade along the way and talks about the large black poisonous berries – a good wow factor for the kids right off the start!
In the sub-tropical zone, the children talk about the challenges of plants growing in a rainforest beneath a heavily shaded canopy and some of the adaptations they’ve made to get alternate sources of food. They have a look into the pitcher plants to see whether any wayward insects have fallen into the plant’s pitcher-shaped trap. As Anne walks by the lichen, she talks about how lightning changes the nitrogen in the air into a form that’s easier for plants to use – lichens need a continual supply of nitrogen to survive. Lightning helps feed plants? This has the children’s attention.
Having a look at the giant lily pads in the pond in the
tropical zone of the glasshouses.
In the tropical zone the giant lily pads (Victoria) impress the children immediately. Then Anne points out the papyrus that’s growing at the corner of the pond and the children quickly make the link between this plant and the papyrus paper that they’ve been learning about in their Egyptian studies. As I switch between the different groups I hear one of the other guides tell a story from Egyptian Mythology about how the Scorpion-godess, Selkis, protects the child Horus by hiding him in a papyrus thicket.
The lotus plants (Nelumbo nucifera) are also linked to Egypt as there is a Nymphaea lotus that grows in the Nile. Anne encourages the children to splash some of the pond water onto the leaves of the lotus plant and I watch as two girls are astonished at how the leaves repel the water.
Water beads off the leaf of the lotus plant.
Some of the other highlights in the tropical zone were the cocoa plant, vanilla and cotton. The Madagascar periwinkle (Catharanthus) is also pointed out for its utility in treating leukaemia.
As the children stand beside the cacti in the glasshouses, they are told that some of these plants will go 10 years without ever experiencing rainfall – longer than these children have been alive. Anne and the other guides talk about all the adaptations these plants have made to go for long periods without water.
Students are given an opportunity to experience what
happens to Mim
osa plants when you touch their leaves.

Time travel through the evolutionary dell

I leave the heat of the glasshouses to join Tony’s group as they begin their walk through the evolutionary dell. Tony is telling the children about horsetails (no friend of the gardener) and pointing out the nodes of the plants. He tells them that 350 million years ago this little snippet of a plant would have been the size of a tree! The kids crane their necks up imagining and as we walk toward the tree ferns one of the girls says “It feels like time travelling!”
Tony takes the children on a walk through time in
the evolutionary dell.
Indeed it is like time travelling in the dell. In the 100 m span of the dell, we travel 200 million years from the horsetails (350 mya) to the first flowering plants (150 mya), such as the magnolia that’s on the left as you leave the dell. Surrounded by ferns, moss, horsetails, Wollemia and other conifers, the guides tell the children about how plants reproduced before the evolution of flowers and pollinators.

It’s never long enough

Somehow an hour seemed to fly by and before long the guides were rushing through the last few displays before sending the children off on their coach. As I had the opportunity to hop between the different groups I got the great sense that each group would have left the garden with a different experience as each guide has their own style and favourite stories associated with the garden. It’s never possible to see everything, but hopefully that means some of the children will encourage their parents and guardians to bring them back for another visit!
Tony holds up a horsetail and talks about plant nodes.

Linking to the curriculum

Mrs Amy Parkin, one of the Year 4 teachers at Horfield Primary, was kind enough to speak with me the next day after the tour about how tours such as this link with the classroom curriculum. This is the first time Horfield Primary has done the tour at the Botanic Garden and it was prompted by Curator Nick Wray giving a talk earlier this year to the Key Stage 2 children.
“We had two weeks where we talked about prehistoric Bristol, dinosaurs and fossils,” said Mrs Parkin. “Each class did a science trail with various outside activities and we also had speakers come in to talk to the children. Nick spoke about what plants would have been around 160 million years ago and he brought in some different species to show the children.”
As well as learning about Egypt, the Year 4 children have also covered the topic of habitats under their science curriculum and there are also cross-curricular links with their geography topic of water.
“The tour at the Botanic Garden helped extend the children’s knowledge on habitats,” said Mrs Parkin. “We focused on animals in different habitats in the classroom and in the tour we saw how plants adapt to different habitats as well.”
This tour will also give the Year 4 students a taste of what lies ahead as they will have plants as a topic in Year 5.

Talking with the students after the tour

After the tour I had a chance to speak with Megan and Henry about what they thought of the Botanic Garden. Megan said “I really liked the giant lily pads, especially since a small child could sit on one!”, while Henry really liked the giant lemon that was in the glasshouse.
When I asked Megan and Henry what the most interesting thing they learned was, Megan said she couldn’t believe that some plants can live for 10 years without water. Henry, on the other hand, learned something new about pollination, “There are lots of different bugs that pollinate plants – blowflies and beetles – and birds too!”
The Botanic Garden will run about 15 school tours during the months of June and July, with the help of their dedicated volunteer guides. These tours are in keeping with the Garden’s mission to promote education and awareness as well as to encourage and foster interest in plants within the Bristol community. In fact, the garden would like to run more school tours, so if you are involved with a local school and are interested in a trip to the Botanic Garden, please contact them via:   www.bristol.ac.uk/botanic-garden