Petal spur development in Centranthus

Petal spur development in <i>Centranthus</i>

Petal spur development in Centranthus

When concealed by petal spurs, nectar typically is restricted to flower-visiting animals possessing a sufficient tongue length to acquire it, and thus such spurs have evolutionary significance, often leading to speciation. Mack and Davis microscopically examine petal spur growth in Centranthus ruber and find that cell divisions dominate very early in development but it is cell elongation that leads to attainment of the spur’s final length. This pattern corroborates recent studies in Aquilegia and Linaria, inferring the existence of a common underlying mechanism for petal spur ontogeny in distant lineages of dicotyledons.

Climate change and wood formation

Tibetan Plateau In cold climates, seasonal changes in trees (phenology) is primarily controlled by temperature. Experiments inducing artificial heating of the stem in evergreen conifers during the quiescent stage showed that it is possible to induce reactivation of cell division, demonstrating that temperature is a trigger for the formation of wood (xylogenesis). The higher temperatures predicted for the future are expected to advance xylem formation in spring, although photoperiodic constraints could restrict the responses of some boreal and temperate species to climate warming. Most studies in temperate and cold climates have been performed in ecosystems in which snowmelt provides abundant water especially at the beginning of the growing seasons, precipitation is frequent in spring and summer, and water availability is not a limiting factor for xylem formation. Little is known about the effect of precipitation on the onset of xylogenesis in cold drought-prone areas.

A recent paper in Annals of Botany monitors xylogenesis in Juniperus przewalskii under extreme dry conditions on the north-eastern Tibetan Plateau and finds that precipitation in the early growing season can be a critical trigger of xylogenesis when the thermal conditions are favourable. Xylem growth shows a positive and significant response to precipitation but not to temperature. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure.

Rising temperatures since the late 1970s have increased aridity in many continental regions of the globe, exposing semi-arid forests in particular to additional stress. Such drought stress may postpone the initiation of xylogenesis, reduce cell production or contribute to radial growth decline. Long-term monitoring is necessary to detect potential thresholds in precipitation or soil moisture for the onset of xylogenesis.


Ren, P., Rossi, S., Gricar, J., Liang, E., & Cufar, K. (2015) Is precipitation a trigger for the onset of xylogenesis in Juniperus przewalskii on the north-eastern Tibetan Plateau? Annals of botany, 115(4): 629-639
A series of studies have shown that temperature triggers the onset of xylogenesis of trees after winter dormancy. However, little is known about whether and how moisture availability influences xylogenesis in spring in drought-prone areas.
Xylogenesis was monitored in five mature Qilian junipers (Juniperus przewalskii) by microcore sampling from 2009 to 2011 in a semi-arid area of the north-eastern Tibetan Plateau. A simple physical model of xylem cell production was developed and its sensitivity was analysed. The relationship between climate and growth was then evaluated, using weekly wood production data and climatic data from the study site.
Delayed onset of xylogenesis in 2010 corresponded to a negative standardized precipitation evapotranspiration index (SPEI) value and a continuous period without rainfall in early May. The main period of wood formation was in June and July, and drier conditions from May to July led to a smaller number of xylem cells. Dry conditions in July could cause early cessation of xylem differentiation. The final number of xylem cells was mainly determined by the average production rate rather than the duration of new cell production. Xylem growth showed a positive and significant response to precipitation, but not to temperature.
Precipitation in late spring and summer can play a critical role in the onset of xylogenesis and xylem cell production. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure. These findings could thus demonstrate an evolutionary adaptation of Qilian juniper to the extremely dry conditions of the north-eastern Tibetan Plateau.

Trees? Tibetan dendrochronologists don’t need trees!

Everyone knows that you can age a tree by counting its rings, and the width of those rings is a record of climate. But do you need trees to track the climate?

Tree rings

Tree rings. Photo: Katy / Flickr.

Climate isn’t the same everywhere. The forthcoming El Niño event threatens parts of the world with droughts and other parts with floods. So in recreating models of past climates it’s helpful to be able to check your work against a wide data set.

Dendrochronology, the study of tree rings, is a useful tool for doing this. A tree has annual growth and it’s visibly marked in the structure of the tree, making rings as the trunk grows bigger. The width of these rings is a record of the climate for that year. During a wet year a tree may be able to put on more growth than during a drought. So take a sample from a trees and the rings give you a very tight match between the year and its climate.

Of course, that does mean you’re reliant on the area you’re looking at having trees.

Eryuan Liang and Dieter Eckstein have looked at the Tibetan plateau, where there are few trees, and thhey’ve found an alternative. They published a paper in Annals of Botany, Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau, where they showed shrubs could be used instead.

Liang and Eckstein took samples from by the Zuoqiupu Glacier, between 4250 and 4500 metres above sea level. There air pressure at that height is so low that there’s a good chance you’d pass out without acclimatisation. They deliberately went this high, as human activity has affected the plants lower down. Rhododendrons are firewood, so the climate record could literally go up in smoke.

Rhododendron rings

(A) Cross-section of the oldest snowy rhododendron at the study site. The well-defined annual growth rings are shown in (B) and details of the wood anatomy in (C). Scale bar = 5 mm. Photos: Liang and Eckstein (2009).

You can see Liang and Eckstein found well-defined annual rings, and also no rotten core to the stem. They found the rings were wide enough to make dendrochronology practical.

They were also able to correlate the ring patterns in the rhododendrons with the rings in Georgei firs, so it looked like the rings were a reliable ecological indicator. The key period for ring width was the mean minimum temperature in July and in the November before. With rhododendrons being widespread in the Tibetan Plateau, they looked like a good source for climate data.

Interesting, but this was all in a paper in 2009, why does it matter now?

Liang and Eckstein got rings as far back as sixty years. It proved the concept, but it was limited in use. Now they’ve co-authored another paper, and the record goes back a lot further. The paper is Up to 400-year-old Rhododendron shrubs on the southeastern Tibetan Plateau: prospects for shrub-based dendrochronology (subscription required) in the journal Boreas.

This new study uses Rhododendron aganniphum. The plants in the new sample sites had a correlation with the July temperatures, but the relationship to the November temperatures seems a bit more murky. However, the samples they found enabled them to build one sequence from the year 1670 and four more from the eighteenth century. It seems more work could help flesh out the changing climate of the Himalayas.

Liang, E., & Eckstein, D. (2009). Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau. Annals of Botany, 104(4), 665-670. DOI: 10.1093/aob/mcp158

Lu, X., Camarero, J. J., Wang, Y., Liang, E., & Eckstein, D. (2015). Up to 400‐year‐old Rhododendron shrubs on the southeastern Tibetan Plateau: prospects for shrub‐based dendrochronology. Boreas. DOI:10.1111/bor.12122

Control of adventitious rooting and xylogenesis in arabidopsis

Control of adventitious rooting and xylogenesis in arabidopsis

Control of adventitious rooting and xylogenesis in arabidopsis

The Arabidopsis thaliana transcription factors SHORT ROOT (SHR) and SCARECROW (SCR) affect primary/lateral root development, as do the auxin-influx carriers LAX3 and AUX1. Della Rovere et al. study their involvement in adventitious root (AR) formation and xylogenesis using null-mutant seedlings grown with or without auxin-plus-cytokinin. They find that AR-formation and xylogenesis are developmental programmes that are inversely related, but which involve fine-tuning by the same proteins, namely SHR, SCR and AUX1. Pericycle activity is central for the equilibrium between xylary development and AR-formation in the hypocotyl, with a role for AUX1 in switching between, and balancing of, the two developmental programmes.

#SciFund is running a masterclass in poster design

Grab Attention

If you’re attending a conference any time soon, then you may want to look at #SciFund’s new course Mastering the art of poster design. Unlike MOOCs you do have to pay for this, but what you get for $50 is a five week course between Jun 7 and July 11, 2005.

If you want to see if if the course is likely to help you, you can get a preview of sorts. One of the course tutors is Zen Faulkes, who runs the Better Posters weblog. You can scroll through and read his critiques of other posters.

Like the FutureLearn courses, we have no affiliation with #SciFund, so you’ll need to contact them to register.

Drinking in the name of SCIENCE!

Pint of Science I’m used to Science driving people to drink, but next week it’s hoped that drink will drive people to Science. The Pint of Science festival is happening next week in Australia, France, Ireland, Italy, Spain, UK, USA and Berlin, Germany and São Carlos, Brazil. It’s the third iteration of the event, following work by Michael Motskin and Praveen Paul at Imperial College, London, to talk to people affected by Parkinson’s, Alzheimer’s, motor neurone disease and multiple sclerosis about their research.

Exactly what’s on depends on where you are. So if you’re in Los Angeles you can check out the Physics of Kung Fu Panda one night, while New York has a slate of talks, including Kevin Griffin on DIY Tree Science. In Brazil you get many mathematical talks, including Matemática e beleza. So, if you live somewhere where there’s a few events locally, it might well be worth looking around to see what’s on.

If you’d like to see if there’s something on near you, you can visit the website to find out. If there’s nothing near you, there are some soundfiles of recent talks below.

Why are carnivorous plants?

Carnivorous plants

Carnivorous plants have long fascinated scientists, and were described by Charles Darwin in the book Insectivorous plants (Darwin, 1875). Carnivorous plants typically attract, capture and digest animal prey by modified leaves called traps. No carnivorous plant is able to capture prey by its flower. Givnish et al. (1984) proposed that a plant must fulfil two basic requirements to be considered as carnivorous. First, it must be able to absorb nutrients from dead prey, and thereby obtain some increment to fitness in terms of increased growth, pollen production or seed set. Secondly, the plant must have some adaptation or resource allocation whose primary result is the active attraction, capture and/or digestion of prey. The first is needed to differentiate carnivory from defensive adaptation that immobilizes or kills animal enemies without leading to substantial nutrient absorption and thus increased plant survival. The second is required because many plants can passively profit by absorbing some nutrients from dead animals decomposing in the soil or on leaf surfaces. A plant must have at least one adaptation (i.e. active attraction, capture and digestion) in combination with nutrient absorption to be qualified as carnivorous, because many genera of carnivorous plants lack some of these attributes.

A long-standing problem in evolutionary biology, i.e. an explanation for the ecological conditions under which botanical carnivory is likely to evolve repeatedly, was resolved by Givnish et al. (1984). Several comprehensive reviews of the rise of carnivorous plants have been published over the past decade, all focusing on trade-offs among physiological and morphological traits. A new paper in Annals of Botany reviews the cost–benefit model for the evolution of botanical carnivory in view of new data on the molecular biology of trap leaves and highlights the importance of energetic costs of active trapping mechanisms. It also address the similarities between carnivory and plant defence mechanisms and the role of jasmonate signalling in carnivory and extends the intepretation of the cost–benefit model to alternative nutrient sequestration strategies in carnivorous plants.


Andrej Pavlovič and Michaela Saganová. A novel insight into the cost–benefit model for the evolution of botanical carnivory. Annals of Botany 06 May 2015 doi: 10.1093/aob/mcv050
The cost–benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (AN) in the microsites inhabited by carnivorous plants. This review summarizes results from the classical interpretation of the cost–benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost–benefit model. Traps of carnivorous plants have lower AN than leaves, and the leaves have higher AN after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, RD) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted.

Science, Politics and Evidence

Polling station

X marks the spot.

I write a few of these posts in advance. So this is being written the day before the General Election in the UK to come out the day after the election. I don’t know who has won at the moment, but if predictions are right it’s possible no one will know who’s won for a week or so after the result. We’re politically plural in the AoB Blog office so there’ll be a mix of emotions. For some of us it’ll be a day of exasperation or frustration, while the people who voted for the losers will deal with it in their own way.

But it’s not a foregone conclusion that politicians have to be disappointing.

Back in March last year a group of scientists decided that politicians could make better decisions if they had access to independent information. Instead of just setting up a unit, they chose to speak to politicians first to find out what would be most useful to them. They also wanted to know the best way an Evidence Information Service could deliver that information.

To get that information, they went to the public to ask for help. The idea was that each constituency would have its own champion who would interview an MP, and local representative for the devolved governments. I took part and spoke to my local MP and AM (Assembly Member) with a structured set of interview questions. The aim was to write a paper based on those responses. You can see the draft online.

Impressively, they’ve also released their raw data. Their conclusion is that the politicians who met with interviewers showed their human side in responding to questions. I don’t feel I can say exactly what my MP and AM said without breaching confidentiality, but I was impressed with both of them. It seems around the UK, politicians of all parties would like access to independent scientific information.

For most of the results announced today the winner will have been voted in by an overwhelming minority. Regardless of who wins, it would be helpful for the representatives to have somewhere they can get scientific information. Chris Chambers et al. might have a way to aid policymakers, even if the election results mean they’re not the ones I want.

You can read more about the proposed Evidence Information Service at the Guardian.

Biodiversity flourishes in an ancient rubbish tip

The preservation of archeological sites does not always overlap with the conservation of biodiversity. At the most basic level, the United Nations Educational, Scientific, and Cultural Organization separates cultural heritage sites and natural heritage sites: Of 981 heritage sites, 759 are cultural, 193 natural, and only 29 (2.65%) have mixed properties ( Cultural conservation and biodiversity conservation have overlapped in the sustainable use of natural resources (Timmer and Juma 2005), but shared targets of elevated conservation importance for both archeological and biodiversity priorities are still few.

Roots at Ta Prohm

Ta Prohm. Photo: Andrea Schaffer / Flickr.

The first archaeological dig I worked on, I could probably have used a little less biodiversity. Or at least fewer horseflies. And fewer trees. The site was a Gallo-Roman farmstead in what had become a forest. The roots of the trees were pulling apart the remains of the building. However, the trunks were thick and the roots had come to support parts of the walls, even as they were prising the bricks apart. A similar effect is even more visible in places like Ta Prohm. For archaeologists the natural environment can be a pest.

In their paper Biodiversity and Archeological Conservation Connected: Aragonite Shell Middens Increase Plant Diversity, Vanderplank et al. point out that an archaeological site is not always good news for biodiversity as humans tend to clear sites of anything they think gets in the way. Finding a site where the conservation priorities for archaeology assist biodiversity is rare, but it seems to be the case in Baja California.

Clam shell midden

Clam piles in Baja California Sur. Photo Sam Beebe / Flickr.

The archaeological sites might look dull at first sight. They’re piles of shells. In fact they’re piles and piles of shells. Masses of them. Once someone had eaten what was inside, the shell could be thrown away, so you get what are effectively rubbish dumps. One of the surprises about them is how old they are. The earliest sites are around ten thousand years old. This dates from close after the arrival of humans in the landscape Another surprise is how many people made the middens. Not as many as you might think.

It’s thought the groups of people occupying places would have been fairly small, maybe around thirty people closely connected as a family. They’d forage on the shore for food and move inland when the season was right to take advantage of food sources there. For small groups to make mounds this big, they’d have to be eating shellfish for a long time. Dates from the shells show this is what happened, with some sites being in use till the arrival of Europeans.

With occupation going on for so long, it’s not surprising that it has an effect, almost like geology and this is what Vanderplank et al. have found. Shells are becoming part of the local geology, in particular clam shells which degrade comparatively quickly compared to other species hunted for food. Vanderplank et al. decided to test to see if plant biodiversity could be an indicator of archaeological remains. The targets were middens by Colonet and San Quintín, Mexico.

It would have been neat if they could have shown a simple relationship between middens and biodiversity. Sadly, life’s not so considerate. There was quite a bit of difference in species between the two sites. They found that middens increased biodiversity at San Quintín, while biodiversity was greater away from the middens at Colonet.

While that’s slightly annoying, it shouldn’t be surprising. Obviously the local species will vary with the environment. Around San Quintín, the land is low-lying and often floods. The leaching of calcium from the shells allows plants to thrive that otherwise would not grow in the saline soils around the middens. Colonet had much less saline soils, so the effect there was somewhat different.

Vanderplank et al. argue that the effect of these middens makes them a marker of the Anthropocene. This is a proposed geological age that reflects humanity’s effect on the environment. Vanderplank et al’s paper would put the start of the Anthropocene somewhat early, but with things like the Ruddiman Hypothesis it’s not wildly out of step with some academics.

It certainly opens the possibility of using botanical survey as a means for prospecting for archaeological sites, not just in Mexico, but anywhere where humanity has had a major impact on sites.

Vanderplank S.E., Mata S. & Ezcurra E. (2014). Biodiversity and Archeological Conservation Connected: Aragonite Shell Middens Increase Plant Diversity, BioScience, 64 (3) 202-209. DOI:

The European Space Agency is offering a free course on climate observation


If you ever wonder where climate data comes from then ESA, the European Space Agency, might have the course for you. Monitoring Climate from Space is a free online course that looks at Earth Observation. The variety of instruments in space, and their wide coverage of the planet is creating an awful lot of data. How can you pull it all together to get a clear view of what’s happening? Over the five weeks they’ll cover Earth Observation from the basics to a look at how the various climate models are made.

The course is the product of CCI, the Climate Change Initiative, one of ESA’s many units and delivered by FutureLearn.

If space isn’t you’re thing and you’re looking for something closer to home then there’s also courses coming up on Our Hungry Planet: Agriculture, People and Food Security and Soils: Introducing the World Beneath Our Feet.

If you’re planning to take one of these courses, why not let us know below?