How Plants Make Flowers – Part 5: Photoperiod, Biological Clocks, and Florigen

It’s Time to Flower!

The correct timing of flowering is essential to maximize reproductive success in angiosperms.

And many flowering plants rely on the photoperiod (specifically, the relative night length) as an environmental signal to tell seasonal time. (To see how, please see previous posts about How Plants Tell Time and Why Plants Tell Time.)

As mentioned in the previous post, the so-called “flowering hormone”, historically known as florigen, is likely a small protein called FT.

Briefly, FT is produced in the leaves and is transported via the phloem to the shoot apical meristem (SAM). Here FT acts like a molecular “alarm-clock”, evoking a complex genetic scenario, which culminates in flower formation.

But what sets off this “alarm-clock”, i.e. the production of FT in the leaves?

Turns out the story involves red, far-red, and blue light, the length of the night, and the plant’s biological clock. (Please note: Why night length is more important than day length: animated explanation.)

First some caveats:

1. Most of this information is based on genetic research using the plant Arabidopsis thaliana. (Although specific genes and proteins vary, depending on plant species, it appears that the basic story presented below holds for most photoperiodic flowering plants.)

2. Arabidopsis is a so-called long-day (LD) flowering plant (in reality, a “short-night” plant, but don’t get me started). So, adjustments in the story need to be made for so-called short-day (SD) plants. (Yes, they really are “long-night” plants.)

3. In Arabidopsis florigen is likely the FT protein. In some SD cereals (such as rice), florigen is likely a protein called Hd3a, an ortholog of FT protein.

A Light-Sensitive, Flowering Alarm-Clock

The so-called biological clock in plants is set primarily in the leaves by phytochromes, which are sensitive to red and far-red light. They get help from blue-light-sensitive cryptochrome. These photoreceptors interact with “clock-genes” that cause some proteins in plant cells to cycle with a circadian rhythm.

One of these proteins regulates the gene that codes for florigen (FT in Arabidopsis and Hd3a in rice, for instance).

Thus, florigen cycles in the leaves also with a circadian rhythm.

Briefly, in LD (“short-night”) plants florigen apparently peaks not long after sundown, then slowly degrades during the night. If the nights are too long, the florigen level is below the threshold level to induce flowering at dawn, when the leaves begin to transport material to the SAM via the phloem. (Please note: florigen appears to be synthesized primarily by leaf vein cells adjacent to the phloem.)

Conversely, in SD (“long-night”) plants, the florigen apparently peaks long after sundown. So, if the night is too short, at dawn, the florigen hasn’t exceeded the threshold level to trigger flowering.

For more information, click on image below:

References:

1. Zeevaart, J.A.D. (2007) FT Protein, not mRNA, is the Phloem-Mobile Signal for Flowering. (see here)

2. Bäurle, I. and Dean, C. (2006) The Timing of Developmental Transitions in Plants. Cell, vol. 125, pp. 655-664 (see here)

3. Greenup, A., et al. (2009) The molecular biology of seasonal flowering-responses in Arabidopsis and the cereals. Annals of Botany, vol. 103, pp. 1165-1172. (see here)

How Plants Make Flowers – Part 4: Genetics of Flowering

The Long and Winding Road

So far, this journey through the subject of how plants make flowers has consisted of three parts:

Part 1, an introduction to the flowering hormone florigen,

…Part 2, how environmental cues affect flowering,

..and, Part 3, how the size and age of the plant itself may trigger flowering.

The Players

Because the genetic story of how plants flower turns out to involve many cellular “players”, as well as an intricate plot, perhaps it would be a good idea to first introduce the main “cast of characters”.

Let’s start with florigen.

As previously described, this is the so-called flowering hormone that can trigger the floral transition in plants.

The latest scientific evidence supports the hypothesis that florigen is actually a protein called FT coded for by the gene Flowering Locus T.

Most of the other key genetic “players” turn out to be proteins called transcription factors, which bind to specific DNA sequences and affect gene transcription.

Many of the flowering-related transcription factors (TFs) are members of a “family” called MADS-box TFs.

An especially interesting member of this MADS-box family with regard to flowering is the FLC protein. FLC (the product of a gene called Flowering Locus C) actually represses flowering.

The Genetics of Flowering (A Story in Three “Acts”)

Since flowering takes place in the shoot apical meristem (SAM) , let’s set the stage there. (And please keep in mind (1) that this is a very simplified version of a very complex, and as yet incomplete, story and (2) that most of this story is based on a single plant – Arabidopsis thaliana – though the basic storyline is likely the same for most flowering plants.)

Act 1 – Floral Initiation (From Vegetative To Inflorescence Meristem)

At center stage (currently), is SOC1 (Suppressor of Overexpression of Constans 1), a gene coding for a TF in the MADS-box family. SOC1 protein plays a pivotal roll in the great leap from vegetative meristem to inflorescence meristem (IM). The expression of SOC1 is effected, directly and indirectly, by factors known to induce flowering, such as the plant hormone gibberellin and FT protein (a.k.a., florigen).

FT gets into the act by first binding to a bZip TF called FD protein (gene product of Flowering Locus D). Together FT/FD promote SOC1 gene expression. (Though FT is not a transcription factor, it acts as a “key” to activate FD protein, which is a TF.)

Finally, the antagonist in “Act 1″ is the FLC protein (see above). It inhibits flowering by suppressing the expression of the SOC1 gene. (Further on down the trail, we’ll see how vernalization knocks off FLC and thus promotes flowering.)

Act 2 – “Arranging the Chairs” (From Inflorescence to Floral Meristem – Part 1)

The second act of the story involves the first step in the transition from the inflorescence meristem (IM) to the floral meristem (FM). What’s the difference? Well, think of the transition from vegetative to IM as “making the decision” to flower, without any overt signs of flowering. And the IM –> FM transition is actually starting to build a flower.

The first step in building a flower involves the spatial arrangement of the flower parts, sort of analogous to arranging the chairs in a room for a meeting.

This involves such TF genes as LEAFY (LFY) and APETAL1 (AP1), which are both activated by SOC1 and FT/FD.

Act 3 – “Seating the Guests” (From Inflorescence to Floral Meristem – Part 2)

There are four guests to be seated at the end of our story – sepal, petal, carpel, and stamen – the four basic floral organs.

The genes involved in floral organ identity are called homeotic genes. Together they are responsible for the so-called “ABC model” of floral organ development. (Though I think it’s the ABCD model now, but that’s for a later date.)

Bottom Line: For a visual summary of the above feel free to download and play this PowerPoint file: Flower_Genetics.ppt or see the corresponding YouTube video here.

Next Up: Making a Flower – Part 5: How does photoperiod induce florigen (FT protein) synthesis in leaves?

Life in the Phyllosphere: What Microbes Commonly Dwell on the Surface of Leaves?

Leaf Surfaces = Microbial Habitats

Imagine all the leaves of all the plants currently living on planet Earth.

Now, add up all the surface areas of all of those leaves.

And your answer is?… No idea?….

Luckily, some microbiologists have made an estimate, and it’s an astounding number.

According to a current review (see ref 1 below), the terrestrial leaf surface area that might be colonized by microbes is approximately 640,000,000 square kilometers or about 250 million square miles! (For perspective, consider that the total surface area of the Earth is 197 million square miles.)

From this, microbiologists have estimated that the planetary leaf-surface bacterial population on Earth may be as large as 10²⁶ cells! (Yes, that’s the numeral 1 with 26 zeros behind it.)

“Clearly, in aggregate, these bacteria are sufficiently numerous to contribute in many processes of importance to global processes, as well as to the behavior of the individual plants on which they live.”-(from ref 1 below).

In other words, the bacteria that live on the leaf surface are so numerous that they not only likely affect the plant on which they dwell but, collectively – on a planetary scale – they are so numerous as to significantly affect the global carbon and nitrogen cycles on Earth.

The Phyllosphere

The term “phyllosphere” was first published by Dr. Jakoba Ruinen in 1961 (see ref 2 below), who studied tropical ecology beginning in the 1950’s. She called the interface between leaves and air the “phyllosphere”, and said that this was a much neglected milieu, compared to studies of the rhizosphere.

“Under the microscope, aerial plant leaves resemble eerie landscapes, with deep gorges, tall peaks and gaping pits that riddle the waxy surface. [e.g., see photo below] Add to this scenery a climate that features temperature highs of 50 °C [122 °F] or more, exposure to harmful ultraviolet rays, erratic periods of drought and limited access to nutrients, and one gets the picture that this is a hostile environment. Still, many bacteria, fungi, yeast and other microorganisms dwell in great abundance in this ‘phyllosphere’…” (from ref 3 below).

Who Lives in the Phyllosphere?

“The microbial communities of leaves are diverse and include many different genera of bacteria, filamentous fungi, yeasts, algae, and, less frequently, protozoa and nematodes.” (from ref 1 below)

Most of what we know about these leaf “epiphytes” come from culturing (or trying to culture) representative isolates in the lab.

In a recent report (ref 4 below), the investigators have taken a 21^st-century approach to the question: “What bacteria live in the phyllosphere?”.

Using a new “metaproteogenomic” approach, they analyzed the bacteria associated with leaves of field-grown soybean and clover plants and wild populations of Arabidopsis thaliana plants. (This technique is related to proteogenomics.)

This study not only revealed “who” was there, but also provided clues to how such bacteria survive in the phyllosphere. Briefly, they discovered “…a high consistency of the communities on the 3 different plant species, both with respect to the predominant community members…” and with respect to the proteins that these bacteria apparently use to survive such a relatively hostile environment.

Photo Credit: Top two photos above by Koolpix/ Jay D., who has been awarded the Nature Photo of the Week by the Nature Conservancy. Twice! (please see here and here). Congratulations! And thank you!

Bottom Line: Using new molecular biology techniques, scientists have discovered important new information regarding not only what bacteria live in the phyllosphere but also how they do it.

References

1. Lindow, S. and Brandl, M.T. (2006) “Microbiology of the Phyllosphere”, Applied and Environmental Microbiology vol. 69, pp. 1875-1883. (full text)

2. Ruinen, J. (1961) “The Phylloshere. I. An Ecologically Neglected Mileau”, Plant and Soil vol. 15, pp. 81-106. (preview PDF)

3. Leveau, J. (2009) “Life on leaves.” Nature vol. 461, p. 741. (Abstract)

4. Delmotte, N., et al. (2009) “Community proteogenomics reveals insights into the physiology of phyllosphere bacteria” Proceedings of the National Academy of Sciences (USA) vol. 106, pp. 16428-16433. (full text).

How Plants Make Flowers – Part 3: Endogenous Cues

Is There a Single Flower-Inducing Hormone?

Florigen is the signal that triggers the transition from vegetative to reproductive development in plants that flower in response to photoperiod.

But some plants, that I’ll refer to “Night-Neutral” (a.k.a., “Day-Neutral”), apparently initiate flowering because of factors other than night length.

Such plants may flower after attaining a certain size or age, for example. Thus, floral induction in these plants may happen mainly in response to internal (endogenous) conditions rather than to environmental (external) conditions.

Some plants may not produce flowers until they are sufficiently robust enough to support the drain on resources required by flowering. In other words, a plant may not flower until it has enough leaves (photosynthetic sugar production) to build and support flowers.

This size-related competency to flower may also be gauged by the plant’s age, presuming that the older a plant is, the bigger it is.

But if one proposes that some plants flower in response to size or age, important questions arise, such as:

How does a plant “know” how big or how old it is?

In plants that flower in response to internal cues (such as size or age), does florigen still play a primary role?

How Do Plants “Know” How Big They Are?

One way plants may be able to determine their relative size is by “node counting”. That is, the more nodes (stem buds/leaves) the plant has, the bigger (more productive) it is. (For all you scholars out there, an exhaustive review of “node counting” can be found here.)

A plant may also gauge its size by how far the shoot apical meristem (SAM) is from the roots. Or a plant may determine its overall size by how big a root system it has.

There is scientific evidence for all of these possibilities. However, the key to all of them is that the nodes, the roots, or both produce chemical signals (likely one or more of the common plant hormones) that travel via the phloem to the SAM. (The SAM is where the floral transition will take place.)

Thus, flowering may be triggered at the SAM by a threshold amount of – or ratio of – one or more plant hormones.

How Do Plants “Know” How Old They Are?

It’s conceivable that a plant can obtain relative age info from the same ways it may estimate its size mentioned above.

It’s also been proposed that certain substances in plants (likely specific proteins) may start out at high levels in young seedlings, but then slowly decrease over the life of the plant (think sand through an hour-glass). Once the substance drops below a certain level in the SAM, the floral transition may then proceed.

Multiple Pathways Lead to Flowering

This, of course, is a big old subject in plant biology, with countless studies published over its hundred years of history. The past few years, however, have yielded much genetic insight into how plants make flowers.

From these genetic studies (mainly using the plant Arabidopsis thaliana) scientists have discovered the identity of florigen (much more on this later). These studies have revealed that the genetic mechanisms involved in floral induction are complex and are affected not only by florigen but by other plant chemical signals, such as gibberellins, as well as by environmental factors, such as temperature.

Indeed, a recently published genetic study has reported a newly discovered signaling pathway that ensures that a plant flowers, no matter what.

Bottom Line: There is likely a central genetic mechanism, common to all flowering plants, that initiates flowering. This mechanism is triggered not only by florigen but is also affected by other endogenous and environmental factors.

How Plants Make Flowers – Part 2: Environmental Cues

Many Plants Flower in Response to Night Length

For nearly 100 years scientists have been trying to identify the elusive flowering hormone called florigen.

Early in the last century two USDA researchers took a major step toward this by discovering how to induce flowering in plants under controlled conditions. In 1920, these two scientists, W.W. Garner and A.H. Allard, first published (PDF) their work on the effect of photoperiod on flowering in tobacco, soy bean, and many other plants. (Their findings are summarized here and nicely described with an historical perspective at a USDA webpage.)

At first, scientists thought that the day-length was the controlling factor in inducing flowering. Hence, plants were divided into three groups with regard to photoperiodic effects on flowering.

We now know that the night-length is more important than the day-length in inducing flowering in responsive plants. So, we can divide flowering plants into three groups – “Short-Night” plants, “Long-Night” plants, and “Night-Neutral” plants. (Unfortunately, most textbooks persist in using the old – and incorrect! – nomenclature. Sigh.)

Thus, many plants make the flowering transition from vegetative growth in response to a very dependable environmental cue, namely, the photoperiod.

But What Does This Have To Do With Florigen?

Firstly, by finding a way to induce many plants to flower at will by adjusting the photoperiod in the laboratory, Garner and Allard set the experimental stage for the eventual discovery of florigen.

In other words, this finding allowed other scientists to artificially induce the floral transition in some plants. Thus, by enabling them to initiate flowering at will, scientists began to study the sequence of events in how plants make flowers.

Secondly, it was discovered that plants sense the photoperiod in their leaves. (We’ll see how they do this later on.)

But the flower transition occurs, not in the leaves, but at the apical meristems.

Therefore, in plants that flower in response to photoperiod, some sort of flower-inducing signal must be sent from the leaves to the shoot apex.

This signal turned out to be florigen.

Are There Other Environmental Cues That Induce Flowering?

The short answer is: Yes.

The long answer is: Some biennial plants, such cabbage and carrots, require a long period (weeks) of “cold” (below 35^o to 40^o F) to become competent to flower. (Please note that this does not induce flowering but allows flowering to be induced.)

The story is a complex one, however. (See more about this here).

Bottom Line: By discovering a way to induce flowering via photoperiod, the first steps were taken toward the identifying a flowering hormone in plants.

Next-Time: Are there endogenous signals, other than florigen, that induce flowering in plants?

How Plants Make Flowers

The Mystery of the Flowering Hormone

What if you discovered a chemical that, when sprayed onto the leaves of plants, would induce them to flower?

How much do you think the patent on such a chemical would be worth? Especially to the agricultural and horticultural industries.

And what if I told you that scientific evidence for the existence of such a flower-inducing chemical has been known for nearly 100 years? And that whole scientific careers have been devoted to discovering this chemical…mostly in vain.

The story is true….and the hypothetical flowering hormone was even given a name in 1936 by the Russian scientist Mikhail Chailakhyan. He called it florigen* (derived from Latin for “flower-former”).

When did the story of the elusive flowering hormone florigen begin?

What Causes Plants to Flower?

As mentioned in a previous post, unlike animals, plants don’t start out with their “naughty bits” – they have no sexual organs, a.k.a., flowers.

Before flowering, plants grow “vegetatively”, that is, they produce just stems, leaves, and roots.

It’s a very big deal when the transition from a vegetative plant to a flowering plant occurs. This involves the “flipping” of some major genetic “switches”, that is, major changes in gene regulation.

Florigen is apparently the signal that “flips the switch”, that is, it’s the internal chemical signal that triggers the floral transition in plants.

But to understand the physiology of the floral transition, scientists first needed a way to be able to induce flowering in vegetative plants under controlled conditions.

A major breakthrough toward this goal was reported in 1920…and not long after, scientific evidence for the existence of a flowering-inducing signal emerged.

Next-Time: What environmental factors induce the flowering transition in plants?

*More information on florigen can be found at Wikipedia. And for a more scientific discussion of florigen, please see a 2007 review by Jan Zeevaart.

Does the Moon Affect Plants? Part 3: Gravitational Effects?

Does the Moon’s Gravity Affect Trees?

To me this sounds like a silly question.

Why?

Because I’d no more expect the moon’s gravity to affect trees than it affects the water in a pond or swimming pool.

If the moon doesn’t elicit tidal effects in such small bodies of water, then why would it’s gravity affect trees?

But, largely due to so-called “peasant beliefs” passed down through the ages, there are some who are convinced that the moon’s gravity does indeed have measurable effects on trees.

Do the Tides Correlate with Tree Rhythms?

In 1998, Ernst Zurcher and colleagues published this paper in the scientific journal Nature claiming that they had evidence that there was a correlation of tree stem diameters and the tides.

This, and other lunar effects on trees, was discussed by Zurcher in a subsequent publication (see ref. 1 below).

In 2000, a another team of scientists provided evidence against Zurcher’s conclusions (see ref. 2 below).

You Decide

From the physics of gravity explained by a fellow by the name of Isaac Newton, it seems obvious that the moon’s gravity is too weak, the distance from Earth to moon too large, and even a giant Sequoia’s mass is too small for the moon to have any significant gravitational effect on trees.

But the notion simply won’t die.

So you, dear reader, weigh the evidence – even do the calculation – and be the judge.

References
1. Zurcher, E. (1999) “Lunar Rhythms In Forestry Traditions – Lunar-Correlated Phenomena In Tree Biology And Wood Properties .” Earth, Moon, and Planets vol. 85-86, pp. 463-478. (PDF)

2. Vesala, T., et al. (2000) “Do tree rings shrink and swell with the tides?” Tree Physiology vol. 20, pp. 633-635. (PDF)

Bottom Line: Despite what we know about the laws of gravity and even direct scientific evidence to the contrary, some still believe that the moon affects trees as it does the tides. Oh well. Sigh.

Does the Moon Affect Plants? Part 2: Moonlight and Biorhythms

The Biology of Moonlight?

The moon may have effects on animal behavior (see here for example), but does it affect plants?

Last time I introduced the scientific literature on the subject by referring to a 1946 paper by Beeson (see ref. 1 below) published in the journal Nature. In this paper Dr. Beeson divided the information regarding the moon’s effects on plants into three categories: (a) myth or beliefs, (b) experiments by people believing in biodynamics, and (c) professional plant scientists with no ties to biodynamics.

Let’s see what’s out there from group (c), starting with the sunlight reflected by the moon.

Is Moonlight Bright Enough to Affect Plants?

From laboratory experiments, it’s known that light intensities as low as 0.1 lux (approximately 0.01 foot-candle) during the night can influence photoperiodic time measurement in some plants and animals.

Yet the intensity of light from a full moon on a cloudless night may reach 0.3 lux at latitude of 50′, and more than three times this value in tropical regions.

This fact led E. Bunning and his colleagues (ref 2 below) to inquire whether moonlight can disturb time measurement. Surprisingly, their investigations revealed that some plants have adaptive mechanisms that apparently prevent moonlight from interfering with photoperiodism.

Photoperiodic perception occurs in the leaves. In the leguminous plants soybean, peanut, and clover, “sleep movements” change the position of the leaves from horizontal during the, day to vertical at night. This behavior reduces the intensity of light falling on the leaf surface from an overhead lamp (an “artificial moon”) by 85% to 95%, to an intensity below threshold for interference with time measurement.

In some nyctinastic plants such as Albizzia, Sainanea, and Cassia, leaflets not only orient vertically at night, but also rotate on their axes so that paired leaflets fold together, with the upper surfaces shading each other, an interesting behavior in view of the fact that the upper surface is more sensitive to light breaks than is the lower surface.

Some long-night plants (a.k.a., short-day plants) flower most prolifically when grown with low intensity light (approximately 0.5 lux) rather than complete darkness during the night. In these plants, moonlight probably increases the number of flowers produced by a short-day regime.

However, flowering of Pharbitis nil (Morning Glory) plants was slightly inhibited by exposure to the light of the full moon for 8 or more hours with a single dark period of 16, 14 or 13 h. It is suggested that in the natural environment moonlight may have at most only a slight delaying effect on the time of flower induction in short-day plants (see ref. 3 below).

In a brief review, Wolfgang Schad (ref. 4) cites evidence for the effects of moonlight on biological rhythms in plants. He is co-author of the book Moon Rhythms in Nature: How Lunar Cycles Affect Living Organisms.

Bottom Line: Although it is not clear why low light intensities affect flowering more than darkness, these examples provide some rational basis for the belief of planting particular seeds by the light of the full moon. Another full moon one lunar cycle later could have effects on flowering.

References
1. Beeson, C.F.C. (1946) “The moon and plant growth.” Nature vol. 158, pp. 572-573. (PDF)

2. Bunning, E. and I. Moser (1969) “Interference of Moonlight with the
Photoperiodic Measurement of Time by Plants, and their Adaptive
Reaction.” Proceedings of the National Academy of Sciences (USA) vol. 62, pp. 1018-1022. (PDF)

3. Kadman-Zahavi, A. and D. Peiper (1987) “Effects of Moonlight on Flower Induction in Pharbitis nil, Using a Single Dark Period.” Annals of Botany vol. 60, pp. 621-623.

4. Schad, W. (1999) “Lunar influence on plants.”, Earth, Moon, and Planets vol. 85-86, pp. 405-411. (PDF)

Next Time: Does the moon’s gravity affect plants?

Does the Moon Affect Plants?

Walking on the Moon

On July 20, 1969 Apollo 11 crew members Neil Armstrong and Buzz Aldrin were the first humans to walk on the moon.

With the 40th anniversary of this first moon landing currently in news, I thought it would be interesting to investigate what’s known about the effects, if any, of the moon on plants….so that you don’t have to.

(By the way, if you haven’t seen In the Shadow of the Moon yet, it’s definitely worthwhile viewing.)

Planting and Gardening by the Moon: Legit or Lunacy?

Some people firmly believe that the phases of the moon affect seed germination, plant growth and flowering.

The effect of the moon on planting times is stated as a matter of fact in such popular publications as The Old Farmer’s Almanac and books such as Gardening and Planting by the Moon 2009: Higher Yields in Vegetables and Flowers, and, of course, calendars such as The Biodynamic Sowing and Planting Calendar 2009.

Others, however, consider such notions as prime examples of “New Age freakery”.

But is there any scientific evidence to support the idea that the moon elicits such effects on plants?

A few minutes with Google leads to sites such as this, this, and this. Such websites seem to be long on folklore and astrology and short on any scientific evidence, except for occasional vague references to university studies (unfortunately with no specific citations provided).

The Effects of the Moon on Plants webpage does, however, provide numerous explanations for reported lunar effects on plants. Here only the citations are provided, but that’s a start.

Delving into the Scientific Literature

A good place to start turned out to be a brief review on the subject written in 1946 by Dr. C.F.C. Beeson (see ref. 1 below).

Dr. Beeson introduced the subject this way:
“The literature on the moon and plants can be assigned to two groups: one comprising reiterations of peasant beliefs, myths and rules, both ancient and modern, and similar unsubstantiated statements; the other comprising experiments supported by numerical data capable of statistical analysis. This second group consists of (a) experiments mainly of the anthroposophical school, which demonstrate the existence of lunar effects on the growth of plants; and (b) experiments of professional horticulturists and foresters, which prove that there are no such effects, or that, if they do exist, they have no value in agricultural practice.“

The experiments Beeson reviewed from the so-called “anthroposophical school” (a.k.a., Biodynamics) were primarily those of Lily Kolisko, published in 1936.

More recent examples of work from biodynamic investigators include, for example: Evidence for Lunar-Sidereal Rhythms in Crop Yield: A Review (PDF) and Can lunar cycles affect the taste of wine?.

Obviously, the biodynamic folks have an axe to grind regarding lunar effects on plants. So, I can understand why scientists may be skeptical of their results. (see here, for example)

But is there recent research (since Beesons’ review) from professional plant scientists (non-biodynamic) that have studied the question of the moon’s effects on plants?

Yes!

Next Time: Scientific evidence regarding the effects of moonlight on plants. (The information may surprise some of you skeptics.)

References
1. Beeson, C.F.C. (1946) “The moon and plant growth.” Nature vol. 158, pp. 572-573. (PDF)

A Tale of Two Theories: The Mossy Earth and The Conquering Flowers

A Long, Long Time Ago on Planet Not So Far Away

What were the first plants to colonize the land on Earth? And when did this occur in the history of the biosphere?

Why did a burgeoning of flowering plant species come to dominate their gymnosperm and fern predecessors so quickly?

The Mossy (Algal and Fungal) Earth

Most biology textbooks state that plant life emerged on land about 450 million years ago (e.g, see p.4, The Biology of Plants by Raven, Evert & Eichhorn).

A new study suggests that plants colonized land much earlier than this.

As summarized here, the authors L. Paul Knauth and Martin J. Kennedy think that their geochemical data suggests that photosynthetic life forms (largely mats composed of mosses and algae, accompanied by fungi) carpeted the land over 800 million years ago.

Their evidence, albeit indirect, may help to explain the increase in atmospheric oxygen levels that allowed for the evolution of relatively large respirating animals about 600 MYA.

This green “welcome mat” may have set the stage for animal colonization of the land.

The “Abominable Mystery” of the Conquering Flowers

It’s been over 100 years since Charles Darwin described it as an “abominable mystery”.

What was perplexing Darwin was the fossil evidence that flowering plants (angiosperms) rapidly diversified and spread across the planet. (This was at odds with his belief that evolution was a gradual process.)

A new theory has been proposed in an attempt to solve this “mystery”.

As brilliantly summarized here, flowering plants may have taken advantage of changes in soil fertility, which were due largely to the higher growth and turnover rates of angiosperms compared to gymnosperms. Thus, a sort of positive feedback loop was created that allowed for the rapid proliferation of flowering plant species.

The originators of this theory, Frank Berendse and Marten Scheffer, published this ecological explanation of Darwin’s “abominable mystery” in Ecology Letters.

Bottom Line: Looks like studying the soil can provide answers to botanical questions.