Toddler-led plant science

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Image credit: S. Shailes (CC BY 4.0)

Doesn’t time fly? My little baby is now a walking and talking toddler with a love of books and trains (and anything else on wheels!). Since my last post I have been busy trying to keep up with his ever-changing needs, alongside returning to part-time work and my volunteer role in Girlguiding.

I decided to leave my old job at the end of my maternity leave. I loved working for eLife, but the almost two-hour commute each way to the office no longer seemed compatible with my family life. I now do science writing and editing work on a freelance basis. This suits me really well at the moment as I can work when I like (or should I say when Sprog allows me to!).

I consider myself very fortunate to be able to spend most of my time at home looking after my son. We play games, read books (often the same ones “on repeat”), go for walks, meet friends at toddler groups or in parks, and do all sorts of silly things you don’t usually get to do as an adult (such as running around the dining table or rolling balls down a section of old drainpipe). We also do many jobs around the house together including cooking, gardening and laundry. These jobs take twice as long with my little helper and don’t always go to plan, but that’s all part of the fun, right?

I have to remind myself of these good times when one or more of us are unwell, very tired, or we are just having one of those days where even basic tasks (like getting dressed and out of the house) seem like insurmountable goals.

One of the most rewarding things about spending so much time with my son and other little people is observing how toddlers explore the world around them, often finding great joy from seemingly simple things. We have herbs growing in our garden and a few months ago I offered Sprog some herb leaves to sniff. He was captivated by the scents coming off the leaves and was keen to sniff the leaves of other plants. Weeks later, while preparing dinner in the kitchen, he picked up some basil we had just washed and sniffed it without any prompting from me.

As my son explores, he accidentally points out things that bring interesting scientific questions to my mind: how do plants produce fragrances? How do strawberries and other fruits change colour as they ripen? Why are there ants and aphids on the same branch of the apple tree? I’m going to try to harness his natural curiosity to help me write some new blog posts. Lead the way, son.

Guest post: Garlic mustard across the pond

 

By Mercedes Harris

Spring has finally sprung, and forests are coming to life again. Green leaves are starting to emerge along with the first colorful flowers of the season. But not all green is good. Odds are that much of the green you’re seeing this spring comes from non-native plants, especially in residential communities. At first glance, these “pretty” invaders may not appear destructive, but take a closer look and a different picture emerges.

Invasive species are non-native organisms whose introduction causes environmental or economic harm. An invasive herbaceous plant native to Europe and Asia called garlic mustard (Alliaria petiolata) spreads across North American forests causing multiple problems. Its presence inhibits the survival of butterflies, stops the growth of tree seedlings, and minimizes food sources for mammals. How does a 100 cm plant cause so much havoc?

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Figure 1: Garlic mustard sightings in the United States reported to Early Detection and Distribution Mapping System (EDDMapS) 

Garlic mustard uses a variety of techniques to persist for years once introduced into new areas. Fast growth, chemical compounds that make it bitter tasting to herbivores, a cryptic rosette plant form, and hefty seed production all give garlic mustard an advantage over native wildflowers, shrubs, and tree seedlings. Garlic mustard grows quicker and taller than native plants crowding the space on the forest floor. Its chemical compounds are toxic to native butterflies and cut off the supportive fungi networks necessary for native tree seedling growth. It has a two-year growing season consisting of a basal rosette during the first year’s growth, which can go unnoticed in this form, but over-winters and bears flashy flowers in the early spring of the second growth year.

It produces high volumes of seeds to spread across landscapes; from roadsides to backyards, pastures to wetlands, hillsides, and prairies. Left unchecked, this plant forms dense populations wherever it goes. One single plant can produce anywhere from 350-7,900 seeds!

So, what can we do about this rapidly spreading herbaceous threat? Land managers commonly use two options, and neither is perfect. First, they can apply herbicide routinely. But this comes with the risk of applying herbicide onto surrounding native plants too. Second, managers can put hours and hours of manual labor into removing existing plants by hand, but garlic mustard has a large root that, if left behind, will regenerate next year.

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Paul Henjum (public domain)

While land managers are still adjusting methods of garlic mustard removal and eradication, there are some things that everyone can do to limit the spread of garlic mustard and other invasive species. 1) When hiking, remain on marked trail ways to avoid spreading plant seeds. 2) In invaded areas, check shoes and clothing for seeds and remove them before leaving parks and trails. 3) Do not pick the flowers or open the seed pods as this will increase the seed dispersal range. 4) If spotted, report sightings of populations to land owners, or online invasive species detection databases such as EDDMapS.org.

About the author: Mercedes Harris is a recent graduate from the University of Massachusetts Amherst where she received a master’s degree in environmental conservation. She’s a biologist turned plant ecologist because the zoology courses always filled up too quickly during enrollment but the plant courses turned out to be great.

References:

EDDMapS. 2018. Early Detection & Distribution Mapping System. The University of Georgia – Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed May 31, 2018.

The rules of spacing

Guest post by Luke Simon

I was at a Christmas party in conversation with a local engineer who, hearing I design food forests, wanted to pick my brain on apple trees. He had six trees in two rows of three, well spaced in his backyard. He was throwing out terms about the mainstream organic sprays he was using, and framed his questions expecting me to know some super organic spray, or spray regimen, that would fix his problems of pests and low vigor in general. I don’t think he expected the answer I gave: ‘What’s planted around the trees?’

We often think of the rules of spacing as rules for keeping other plants away from each other. In practice I find the lines blur between species, and enters a much more broad science: it’s what should be included near the plant, as well as what shouldn’t. Between these two aspects, you make or break the majority of fruit tree problems.

The lines often blur between species because, let’s face it, plants don’t grow in a vacuum and always have something growing up against them. In this guy’s case, his trees were planted right into his lawn. They were in competition with the grass.

Looking at their history, grass and trees are in most cases nemesis of one another. Trees make forest; but grass needs open space. The setting in most yards of trees with grass between is quite artificial, and only exists because we keep the grass mowed. In any other situation, trees would take over.

The prairies are the kingdom of grass, and these occured because of rain shadows, or areas where circumstances such as the Rocky Mountain range messed with the winds that carry rain, creating droughts in one part of the year, and near flooding in another. Trees don’t like that, because most have relatively shallow roots, as much as 80 percent residing in the top three feet of soil depending on the kind and its conditions; but prairie plants, such as the grasses, and Nitrogen fixers like Senna hebecarpa, put roots down unusually deep, so reach the water table whether rain comes or not.

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An experiment showing the root growth of Red Delicious apple tree two years after planting.

Have you ever wondered as you pass woods how the trees survive so close? If you were planting an oak tree in your yard that would someday reach a hundred foot tall, can you imagine the spacing recommendations? They would be over fifty feet apart. Most yards couldn’t fit more than one tree. But in the woods they stand on top of each other, growing for hundreds of years, happy, and healthy.

Studies have shown that trees can grow their roots deep into the ground, but prefer to keep their roots higher in the soil if possible. There is more organic matter, hence nutrients and water, in this layer. If there isn’t, trees will try to put in the work to grow deeper. This is a lot more work, and certainly isn’t their first choice.

What trees really prefer is building networks in which they share and preserve resources. For instance, trees have what is called hydraulic redistibution, which is a fancy term for moving water not only up for their own use, but back down into the soil for storage, and horizontally to other plants. Peter Wholleben, in his book The Hidden Life of Trees recalls his surprise when he found a ring of roots from a beech tree that must have been cut down well over a century beforehand, but still had green, living roots showing above ground. It had no leaves, and the stump was gone. As he explained, citing various studies, the living trees around this ancient (should be dead) tree were feeding it sugars made in their leaves, keeping it alive. Likely, they got some kind of kickback from the extended root system because it allowed them access to more resources.

This is in ancient, established forests, so conditions aren’t quite the same for our young transplants. We can get some similar effects by growing fruit trees in more open settings, or riparian zones. These are zones similar to fencerows and overgrown fields where grasses are just converting to trees. These zones are iconically untidy and wild; but skillful gardeners know the elements of these zones, like clay in a potters hand, have the best potential to form the most beautiful, lush gardens.

Riparian zones have many layers, with notably high numbers of low growing herbaceous and woody shrubs, many of which are nitrogen fixers. The quickest way to simulate this ecology is making ‘guilds’ of plants right around your fruit trees. Here is my manual of bed building for info on quickly clearing grass without tillage. Plan on expanding these plantings every year until the beds around your trees meet. If the tree is older, and larger, the bed should extend at least a couple feet beyond its drip line.

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An example guild. 1. Fruit tree 2. Comfrey 3. Siberian Peashrub 4. Amorpha fruticosa 5. Japanese Wineraspberry 6. Honeyberry 7. Blueberry 8. Turkish Rocket 9. Crambe cordifolia 10. Stepping stones, (or in this case, stepping logs). The green base is a ground cover of mint.

Any guild should include at least 2 woody nitrogen fixing plants, about 5 plants that do not fix nitrogen but can be cut for mulch, such as comfrey, or a groundcover of something like mint, then several fruiting shrubs like raspberry or honeyberry, and some perennial vegetables.

This is the best method if you already have fruit trees in the ground, like our engineer friend. If you’re just planning your food forest, Robert Hart, the father of the northern food forests, recommended planting full size or standard fruit trees at recommended spacing for their size, in rows like any orchard, but then semi standard or medium trees, then dwarf trees, then shrubs, then herbaceous plants, then vines to climb and fill in the cracks between them.

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I’d recommend mulching as much as you can, and planting that area with a complete planting like this. The space should be completly filled with plants, and will establish faster with less work overall.

This system gives quite attractive results that are increasingly less cost and labor than serial applications of even organic, clay-based sprays, pyrethrums and neems, let alone harsher chemicals. There is work later on, but this is of course debatable, because its mostly harvests of fruit. Sounds like pleasant work to me.

This article was originally published on Mortal Tree on 24th February 2017.

About the author: Luke Simon is garden manager for Simon Certified Organic Family Farm, and on his own time a permanent edible landscape designer in Ohio, United States. He is the author of PASSIVE Gardening and Mastering the Growing Edge. Follow him on his blog, Mortal Tree, and his Instagram @mortal_tree.

 

How a virus gives back to its host

 

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Image by F_A (CC BY 2.0)

A study by UK scientists has shown that tomato plants infected with a virus are more attractive to bumblebees than healthy plants. Why would a plant virus want to change the behaviour of bumblebees?

The virus in question – cucumber mosaic virus (CMV) – can infect many different species of plant including tomatoes and a model plant called Arabidopsis thaliana. In tomatoes it causes many symptoms including yellowing, mottling, leaf distortion and can reduce the yield of seeds. As a result there is pressure for populations of plants to evolve better defences against the virus. Since CMV can only multiply within plant cells you might expect that, over time, CMV might become less common, but this doesn’t appear to be the case. One way the virus might be able to combat this problem is to compensate for the decrease in seed production in infected plants by encouraging pollinators, such as bumblebees, to visit the flowers.

Bumblebees fertilise tomato flowers by a process called buzz pollination, in which sounds produced by the bees shake the flowers to release pollen. Although tomato flowers can fertilise themselves without help from the bumblebees, buzz pollination makes the process more efficient and also leads to the transfer of pollen between flowers. Volatile compounds (molecules that easily become gases) released from the plants may help to guide the bees to the flowers. CMV infection can change the mix of volatile compounds that plants produce, but it was not clear whether this changes the behaviour of the bees.

Simon Groen, Sanjie Jiang, Alex Murphy, Nik Cunniffe et al. found that the bees are more attracted to the volatiles produced by CMV-infected tomato plants than those produced by healthy, uninfected plants. In the absence of buzz pollination, CMV-infected plants produce fewer seeds than healthy plants. However, mathematical modeling indicates that, in the “wild”, the bee’s preference for virus-infected flowers may help to compensate for this so that CMV-infected plants may produce more seeds than uninfected plants. Further experiments in A. thaliana suggest that molecules of micro ribonucleic acid (or miRNA for short) produced by the plants might regulate the mix of volatiles that plants produce.

These findings suggest that in some environments it may be in a virus’ interest to help its host plant by making the plant more attractive to bumblebees or other pollinators. Bumblebees are important pollinators for many crop plants so these findings may help us to develop new ways to increase crop yields in the future.

Reference: Groen SC, Jiang S, M, Murphy AM, Cunniffe N, Westwood JH, Davey MP, Bruce TJA,  Caulfield JA, Furzer O, Reed A, Robinson SI, Miller E, Davis CN, Pickett JA, Whitney HM,  Glover BJ, Carr JP. 2016. Virus Infection of Plants Alters Pollinator Preference: A Payback for Susceptible Hosts? PLOS Pathogens http://dx.doi.org/10.1371/journal.ppat.1005790

Bramble: friend or foe?

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Blackberries change colour from red to black as they ripen. Image by Thomas’ pics (CC BY 2.0 via Flickr)

In England at this time of year, the hedgerows along country lanes are full of delicious fruits called blackberries. Just last week I spent an enjoyable afternoon with friends gorging on blackberries along the route of an old railway line in Norwich (now a footpath and cycleway). The berries are a good source of vitamin C and antioxidants, and are commonly used in desserts and preserves. Although I love collecting and eating blackberries, I have a bit of a love-hate relationship with the plant that produces them, the bramble (Rubus fruticosus agg.).

Rubus fruticosus agg. isn’t a single species, but instead is a group (or aggregate; agg) of around 200-300 very similar species of shrub in the rose family that are very hard to tell apart (1). Like roses, brambles are covered in sharp thorns that help to protect the plant from herbivores (and humans). The thorns also help to make brambles a safe haven for many small birds and other wildlife.

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Brambles are pollinated by insects. Image by Roger Bunting (CC BY-NC-ND 2.0 via Flickr)

Brambles grow wild across most of Europe and in the UK they can thrive in most environments (1). The white or pinkish flowers are self-fertile and can still produce seeds even in the absence of fertilization (a process called apomixis) to produce an army of clone plants (2). Furthermore, brambles can produce suckers – new shoots from buds in the roots – which helps them rapidly cover an area of ground. As a result, brambles are often among the first plants to colonise abandoned plots of land. This is great for wildlife and the casual blackberry picker, but it’s not so helpful if you are trying to work on said piece of abandoned land…

When some friends and I took on an allotment this year, our plot had been neglected for a while and contained quite a lot of brambles. We removed a lot of the plants but have left some to be our own personal blackberry patch. Removing brambles is not a fun business as the thorns can cut through clothes (and gardening gloves). For several weeks in the spring my arms and legs were covered in scratches and I often found bramble thorns impaled in my fingers. If you don’t manage to completely remove the whole root, the bramble is quite capable of growing a fresh shoot so we’ve had a few cheeky brambles reappearing in the vegetable beds.

Despite my moaning about brambles I must say that the blackberry crop from the allotment has been great. It is kind of ironic that our most successful crop this year is something we weren’t deliberately growing. All in all, if I had to summarize my relationship with the bramble at the moment, I would say: “it’s complicated”.

 

References:

1) Wikipedia: Blackberry https://en.wikipedia.org/wiki/Blackberry

2) Brambles (Rubus fruticosus) http://www.woodlands.co.uk/blog/flora-and-fauna/brambles-rubus-fructicosus

Image links:

Bramble by Thomas’ pics

Canal: Morse to town 7 June ’11 by Roger Bunting

Poison in the garden

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The gates of Alnwick Poison Garden, north-east England. Image by Jacqui (CC BY-NC-ND 2.0) via Flickr

While giving my undergraduate class a tour of a botanic garden, a university professor said that “we should only eat the parts of a plant that the plant wants us to eat”. He was referring to the fruit, which many plants encourage animals to eat in order to spread their seeds in the environment (though not all fruits are edible). I don’t think he meant us to take his advice literally, but it is sensible to eat plants with caution. Alongside famous poisons including belladonna and hemlock, plants produce a variety of other molecules that aim to deter animals from eating them. Some of these molecules – such as ricin, which is produced by the castor oil plant – are so poisonous that tiny quantities can kill you. Others, like caffeine or the anti-malaria drug quinine, have less dramatic effects on the human body that we may find desirable or useful.

I recently visited The Alnwick Garden in north-east England, which has a special garden dedicated to educating visitors about the potential dangers of plants. In fact, some of the plants on display in the Poison Garden are so dangerous that visitors can only enter as part of a guided tour. I really enjoyed the tour and if you are ever in the area I recommend you pay the garden a visit.

The tour included some well-known poisonous plants, but the main message I took home from the tour was that many common garden plants are also potentially dangerous if they touch your skin or you accidently eat them. Below are a few examples of common plants that aren’t as benign as they might first seem:

Rhubarb (Rheum x hybridium)

While the pink fleshy stalks of the rhubarb plant are safe to eat and are commonly used in desserts, the leaves are highly toxic (1). This is thought to be due to the presence of high levels of oxalic acid, which can interfere with chemical reactions in the body by combining with calcium and other metals.

Common ivy (Hedera helix)

This rapidly growing vine is a haven for wildlife and attracts at least 70 species of nectar-feeding insects in its native range of Europe and Western Asia (2). Contact with ivy can cause an allergic skin reaction in some people, due to a natural pesticide in the leaves called falcarinol (3). Regardless of whether you are allergic to ivy or not, you should avoid eating this plant because its leaves contain saponins, which can cause vomiting, convulsions and even death.

Common nettle (Urtica dioica)

Children quickly learn that contact with common nettles results in a painful stinging sensation and skin inflammation. This is due to a cocktail of molecules including histamine, serotonin and oxalic acid, which is released from hairs on the surface of the leaves. For more information check out this cool infographic by Compound Interest.

Common laburnum (Laburnum anagyroides)

All parts of this small tree are poisonous, due to the presence of a molecule called cytisine, which has a similar structure to nicotine and has similar effects on the body. Laburnam is a member of the pea family and cases of laburnam poisoning are often caused by individuals mistaking laburnum seeds for peas and eating them (4). Mild cases may cause nausea and vomiting, but laburnum poisoning can also lead to insomnia, convulsions and coma.

These are just a few examples of common garden plants that can be harmful to humans and other animals. Fortunately, you can protect yourself against these and other poisonous plants by taking simple precautions, such as wearing gloves while gardening and carefully identifying edible plants when foraging.

Author’s note: Sorry for the long silence on this blog. My life has been quite chaotic in the last few months due to several events (expected/not expected, good/bad) and so the blog has had to take a back seat. Things are calming down a bit now so I’m hoping to get back into posting regularly, probably about twice a month. As ever, I’m always keen to receive guest posts so if you are interested in writing for Plant Scientist, please do get in touch.

References:

  1. The Poison Garden blog: Rheum x hybridium http://www.thepoisongarden.co.uk/atoz/rheum_x_hybridum.htm
  2. Wikipedia: Hedora helix https://en.wikipedia.org/wiki/Hedera_helix
  3. Compound interest advent calendar http://www.compoundchem.com/2014advent2/
  4. The Poison Garden blog: Laburnam anagyroides http://www.thepoisongarden.co.uk/atoz/laburnum_anagyroides.htm

Lab Girl by Hope Jahren

51miGrYIk-LIn Lab Girl, scientist Hope Jahren has cleverly weaves a memoir of her own life with passages about the lives of plants, her scientific passion. From her childhood in a small town in Minnesota to her current position as a Professor at the University of Hawai’i, she gives a candid account that includes some of the adventures, funny incidents, obstacles, and shifts in her scientific thinking that happened along the way. The book is a fascinating window into the life of a gifted, passionate, yet (reassuringly) human scientist. If you haven’t read it yet, then I highly recommend you get your hands on a copy.

If you aren’t convinced by my mini-review, then I suggest you check out this longer review from the NY times.