Archive for the ‘plants’ Category
deciduous and evergreen: pourquoi?
star magnolia (Magnolia stellata) – I think. Thank you, internet
It’s now more or less officially spring, and leafless trees are blossoming, like the one across the lane from my new home, as pictured. So I’m wondering how they have the energy, and more broadly, why do some trees lose their leaves seasonally, and others not? I’m no expert on trees, and I hope, before this piece is finished, to identify this one, but at least I know it’s deciduous, I think.
I also want to know how this deciduous and evergreen dichotomy relates to photosynthesis, as surely it does. So, of course, I must look it up. Surprisingly, Oliver Morton’s Eating the Sun makes no mention of the evergreen-deciduous thing, but then I likely wouldn’t comprehend his explanation…
But here’s a photosynthesis formula that I can more or less comprehend:
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Which can be roughly translated as: six lots of carbon dioxide (from the air) plus an equivalent lot of water (from the soil), plus solar energy, makes glucose, and starch. The starch, the carbohydrate, is stored in the roots, trunk and branches. Deciduous trees shed their leaves in autumn, and enter a period of dormancy – reduced metabolism, which slows or stops growth. Presumably energy is expended, though, in the production of blossoms. It’s a risk worth taking, however, because blossoms exposed to the open air can be seen and more easily approached by pollinators and can have their seeds blown by the wind.
I’m guessing that evergreen trees are mostly located in dense forests, which tend to create their own microclimates, less susceptible to seasonal change. And they’re more of a thing in the tropics, where the weather’s always – tropical, more or less. And the leaves of evergreens tend to be thicker and spinier. Ms AI tells me this:
Evergreen tree leaves—whether needle-like or broad—are uniquely adapted with thick, waxy outer layers and robust cellular structures that minimise water loss and resist freezing. Instead of shedding all foliage at once, these trees retain functional, chlorophyll-containing leaves year-round, slowly replacing them individually over several seasons.
I’m hopelessly ignorant about tree and plant types but I’ve found a website that will freely inform me (or try to) of the identity of any tree or plant I present to them via a photo I’ve taken. Instant learning! I’m quite excited.
Apparently some individual tree leaves can live for over twenty years, and these leaves ‘tend to be tougher and thicker, and more expensive to build’, according to a Macquarrie Uni article, referenced below. Other interesting facts are that ‘conifers and other evergreen trees make longer-living leaves the closer they are to the poles’, and ‘deciduous trees do the opposite. Their longest-lasting leaves are found at the tropics’. It’s all about maximising carbon absorption. If you’re an evergreen conifer in poor soil and facing a long harsh winter you’ll need to make a long-term investment in your leaves, but if you’re a deciduous maple you’re best to create new leaves quick-smart that will capture the summer sunlight before dropping in autumn, and that means investing in fast-growing, cheap but flimsy leaves. I’m more or less paraphrasing here.
So I’ll make this piece a short one, but I’ll be taking more photos in the neighbourhood and trying to learn more about blossoms and soil and climate and photosynthesis for future posts and my own delectation. I’m feeling Spring in my step!
References
A Tree Blooms Without Photosynthesis (Leaves)? The Science Behind Spring Blossoms
mostly about Ukraine and Russia and hopes for a better future
just some blokes
As a generalist sort of pseudo-intellectual in quiet and calm Australia, I’m tossed between the best and the worst stuff to focus on, mostly in the top hemisphere of our planet, as if I know which way is up. War and Russia and the USA under Frump (talk about the world’s worst-ever own goal), and the grim future with global warming, and the runaway rich-poor gap in so many countries, and the worries over the rapidity of AI developments and who’s controlling them, and then JWST (no longer Just Wonderful, it seems) and the future Nancy Grace Roman and all the exoplanets to come into our purview, and dark matter as structure or whatever, and the Hubble Tension, and gravitational lensing trickery, and then back down to Earth and its rubisco abundance….
So I’m re-reading with difficulty, but also great admiration tinged with annoyance, Eating the Sun, which I’m committed to finishing even without full comprehension, for who has such a thing, but I’m also reading a vastly different book, not as an antidote (for that would require some planning which I’m incapable of), but because I try to contain multitudes, as we all do to some degree (do we?).
The Story of Russia, by Orlando Figes, was published in 2022, so presumably was written, or mostly written, before the current attack on Ukraine, but is of course being read by me with that ‘special operation’ in mind. Needless to say, I despise Mr Pudding as much as I despise Frump, while also realising they can’t help but be who they are. They are the products of very different environments, and have both exploited those environments very effectively indeed.
What I’m learning from Figes, much of which I sort of knew already, is that Russia has long defined itself in opposition to Europe – or rather its leadership has. Russia is vast, and its multitudes contain vast differences, but they’ve never really had a voice, and it seems that they don’t want to, or they don’t know how to. It doesn’t really have a single definable ethnicity, and it defines itself more by class than anything else. The owner class, the worker/peasant class, the political class. It has never experienced anything remotely close to democracy, and I think it has, historically, been more open to, or more easily persuaded by, that vague, hopeful, egalitarian-sounding concept called ‘communism’, in which you don’t even have to vote to be part of the government, somehow or other. The people seem to have been convinced that Europe is their enemy – evil, presumably debauched, and rapacious. Out to get them, to steal their identity, to rub them out as a proud ethnicity. Certainly this is the kind of propaganda that Putin makes use of, but what does that bizarre much-murdering individual really think? For example, he never for a moment believed that Ukraine was full of Nazis, but he did believe that this line would work in Russia. So what does he think of the average Russian, then, and is he correct, or at least close to it? How popular is the bloke? Presumably not as popular as five years ago, but even so…
As I learn, through Figes, of Russia in 1917-1920, with Bolsheviks, Mensheviks, Social Revolutionaries (a different group apparently) and of course Germans, at a time when so much was up for grabs – Ukraine, Poland, Estonia, Finland – when Petrograd, that all-too-European city, was switched out for Moscow, the pride of Russia, as its capital – everything was changing, Tsars gone forever, and supposed freedoms being fought for with ever-increasing brutality by the new men, Lenin, Kerensky, Trotsky and the grotesque Stalin. All seeking to impose something entirely anti-European while looking over their shoulders at the European powers with a weird and dismal kind of love-hate. And that’s a theme, of course, that continues to this day. A kind of spurned lover’s hatred for the west, and a desperate need to find some superiority to cling to. This appears to be Mr Pudding’s obsession, and he really seemed to think that some weakness, or some Old Russian-ness in Ukraine would deliver it to him. He has under-estimated the depth of contempt that Ukraine has for him – for him personally, rather than Russia itself. And of course he has also under-estimated that country’s western advancements and passions, as well as the real difference that separation from the horrors of his regime has wrought. He has absolutely nothing positive to offer Ukrainians.
One can only hope, for Russia’s sake, that their 73-year-old dictator is their last. They deserve so much better than the thieving, murdering, backward-facing lot that finally emerged from the dissolution of the Soviet Union in the late 80s and early 90s. All that hopeful sense of glasnost and perestroika was brutally shattered. I’ll be interested to read what Figes thinks of Russia’s future in the final chapters of his book.
Reference
Orlando Figes, The story of Russia, 2022
Oliver Morton, Eating the Sun, 2007
more on photosynthesis: stuff about rubisco, or not
don’t ask
So in my wild wanderings on this topic I’ve been informed by a close friend that rubisco is key, and research is ongoing. So, starting off with my key text, Oliver Morton’s Eating the Sun, and a video on rubisco that’s been drawn to my attention, I’ll keep making attempts to educate myself.
So, nitrogen is essential to all living organisms, and our atmosphere is mostly nitrogen – just over 78%. It’s essential to proteins and DNA, but apparently it isn’t something we can directly access. There’s an enzyme complex called nitrogenase, which some bacteria and archaea can produce, which is able to convert inert nitrogen gas into ammonia (NH3). However, nitrogenase falls apart in the presence of oxygen, so atmospheric nitrogen can’t be used by virtually all living organisms. Only anoxic organisms – generally very basic microbes (spoiler alert – nitroplasts) – can make use of it. So, it has generally been a rule of biology that no complex organisms can utilise nitrogen, but a new bacterium was discovered quite recently, or rather its DNA. That’s to say, samples of seawater were examined for the presence of nitrogen-fixing bacteria. What was initially found, in the 1990s, in a search for a key nitrogen-fixing gene, was genetic material, without the organism it belonged to. The searcher, or researcher, felt that he had a good idea what the missing organism would look like. A hunt was on to find this organism, which left its ‘fingerprints’ everywhere, but it took years to find it, all they could find was DNA with a missing owner (I’m relying heavily on a video referenced below for all this). What they did find was quite strange – its DNA didn’t seem to contain the genes for photosynthesis. And this DNA turned up all over the place, ‘complete’ with missing genes – a lot of them, some 80% of its entire genome – which seemed to make its very survival questionable. But then it was worked out that the DNA was inside a species of algae which was hosting it. This algae, Braarudosphaera Bigelowii (Bigelowii for short), was being investigated in Japan by a female scientist, partly because of the symmetrical beauty of its shape at a particular developmental stage. She eventually managed to culture the algae (the video tells the story beautifully and movingly), and found something odd amongst the expected parts, almost like a separated container.
The Japanese researcher came across work from the team who had discovered the DNA with the missing host. It was generally a shock to both sides, but they were able to work together and discover what was effectively a symbiotic process, though the video on this suggests that the process goes beyond symbiosis, and is more like ‘two organisms fusing into one’, as with mitochondria and chloroplasts and their hosts. Bigelowii had become an organelle, dividing and growing at the same rate as its host. It was an important discovery, not only to add to the small family of organelles (it has been called a nitroplast), but to find an organism that effectively fed on nitrogen. Could this be used to produce nitrogen – which is currently produced in expensive and inefficient ways – out of the air?
So, this stuff about nitroplasts is quite recent, so it doesn’t get into Morton’s book to complexify it even further. And it’s the most complex book I’ve read – and I’ve read an awful lot of the bloody things. I can but give an example: this, about chloroplasts:
As they have spread out with and through their wormhole world, its chloroplast inhabitants have changed according to the requirements of the time-tunnels that they find themselves in; evolution applies in there just as it does out here. In some tunnels the chloroplasts are squadrons of small green capsules that still have the look of bacteria. In others they have evolved into swirling spirals pressed tight against the outer membrane like rifling in the barrel of a gun. Some are red five-pointed stars, one to a cell. But they are all descended from the same original ancestor.
There are many dead ends in the network – hundreds of thousands in every leaf that falls – billions of times as many in every fossil species bereft of descendants today. But the threads as yet unbroken are all but uncountable, and multiply still. All around us, moment by moment, the skein of wormholes pushes itself further into the future.
Oliver Morton, Eating the Sun, pp 209-10
Rifling in the barrel of a gun? I’ve managed to avoid going near such an item in the 70 years of my life. And I might know something about the look of love (or not), but the look of bacteria is well beyond me. Never owned a microscope, sadly. As for the rest, lovely writing but I can’t quite get a picture…. But, I will soldier on…
References
Oliver Morton, Eating the Sun, 2007
Animals r us, but also…
kinds of trunks
The video world that we now seem suddenly steeped in – I write from the perspective of someone who was almost 40 when the internet suddenly swept over us – has its pluses and minuses of course, and one definite plus for me is cute and often fascinating vids of non-human creatures doing smart stuff. I try not to get addicted, but it’s tough. I’m especially interested in ‘exotic’ creatures, which for me is anything I can’t encounter in my local park-lands or zoo. These videos bring such exotica into the living rooms of people like me, who worry about the time, effort and money involved in getting into the next suburb never mind darkest America or the hinterlands of Tunbridge Wells.
So I’m reading – slowly and savouringly, if that’s a word – Carl Safina’s Beyond Words, the first few pages of which – about elephants – literally brought tears to my eyes. Such exquisitely elegant and sensitive things – and that’s just the trunk.
Getting further into this inspiring book, it’s not just about elephants and other creatures whose superlative sensitivities, when brought more forcibly to our attention, are both exciting and mildly intimidating, it’s about the endless ways that complex lives can be lived. It even makes me think of the sudden surge in ‘AI’ over just the past few years, and where it will be in a few generations, as it adapts to ever more complex and challenging conditions. It ain’t going away.
But to return to conscious beings – assuming that AI hasn’t achieved consciousness quite yet – it wasn’t long ago that we preferred to believe we humans were the only ones. Safina looks at the issue early on in his book. It’s taken a long time for us to accept that we’re animals (millions, if not billions, refuse this label), and even those who have mostly believe that we’re massively exceptional, and consciousness, inter alia, is a thing that sets us apart. But what, exactly is consciousness? The neurologist Christof Koch calls it ‘the thing that feels like something’ [Safina, p21]. This subtle definition is certainly worth pondering. It doesn’t require language, it seems to me – language being another item we use to claim exceptionalism – even though we humans can name that thing – fear, anger, boredom, love, fatigue, hunger, pain etc – of which we are conscious. A hungry dog feels hungry. She’s conscious of her hunger, and that consciousness will make her start pestering her owner who’s late in feeding her.
These feelings are all in the mind. It follows that anything with a mind has consciousness. And yet we lose consciousness, when deeply asleep or under anaesthetic. Do we then lose our minds? A strange kind of thought experiment came to me recently when I noticed, without much originality, that upon waking up, it was somewhere between 6 and 7 in the morning, whereas the last time I was aware of myself it was around midnight. During that time I was ‘dead to the world’ as they say. My mind had ceased to exist. If someone had crept into my room during those hours, and gently slit my throat, would there be any real difference to my state?
Of course we know that deep sleep, or unconsciousness, isn’t the same as death, and some of us know a thing or two about REM and the three phases of non-REM sleep, but we don’t know it from experience. What we experience is the same – mostly nothingness. Non-experience. We know, because we have learned, that in those death-like states we still breathe, and blood is still pumped through our bodies. Our mind, though, has gone. We’ve ‘lost’ consciousness. It’s really quite bizarre.
Even so, it’s as common as life. Every animal sleeps, after all. Every animal loses consciousness, so every animal has a consciousness to lose. Fish sleep too, without closing their eyes, as they don’t have eye-shutters like we do. So do birds, insects, crustaceans, worms. They all lose, or greatly reduce, consciousness, so they all have consciousness to lose and recover. They all have experiences to be conscious of and learn from.
So what about plants? I mean, how low can you go? Most scientists today would agree that plant consciousness isn’t a thing, but the boundaries are certainly shifting. Early on in Daniel Dennett’s Kinds of minds he considers the development of consciousness in humans. A human’s life starts when she (or it?) becomes a fertilised egg – that’s to say, one single cell, known as a zygote. Just to confuse us, it’s also known as a diploid cell, as it contains the genetic material from two parents. Let’s accept that zygotes don’t have minds. What about blastulae? They’s mostly undifferentiated globs of cells which – well without getting into details, there’s no mind at this stage, so let’s go on to the foetal stage which starts at around eight weeks, and lasts until birth. That’s a lot of development, and presumably consciousness is one of the things that starts developing at this time, if not before…
Of course it all has to do with neural or brain development in animals. Yet many mysteries remain. Safina tells this story:
A thirty-year-old man named Roger lost about 95% of his cortex due to a brain infection. Roger can’t remember the decade before the infection, can’t taste or smell, and has great difficulty forming new memories. Yet he knows who he is, recognises himself in a mirror and in photographs, and generally acts normal around people. He can use humour and can feel embarrassed. All with a brain that does not resemble a human brain.
So it seems it doesn’t take as much as we think to make us conscious. And of course other consciousnesses, or minds, or even ways of living, can be just as impressively adaptive. Charles Darwin, in the feverish years after his Beagle adventure, was proudly intrigued by the subject, as his notebooks show:
It is absurd to talk of one animal being higher than another… People often talk of the wonderful event of intellectual Man appearing – the appearance of insects with other senses is more wonderful… Who with the face of the earth covered with the most beautiful savannahs & forests dare to say that intellectuality is only aim in this world…
Needless to say, Darwin was far more circumspect on these matters in his published work. Yet on the subject of plants he surely would’ve been chuffed to learn that, though they have no nervous system, they produce the same chemicals – including serotonin, dopamine and glutamate – essential for neurotransmission in animals like us (Safina, p23).
None of this should surprise us, I suppose, as we’ve come to learn that all life is connected. We have a relationship with every other living being on this planet, which we could trace, if we had all the time in the world…
References
Carl Safina, Beyond words: what animals think and feel, 2016
Daniel Dennett, Kinds of minds: towards an understanding of consciousness, 1996
Janet Browne, Charles Darwin, voyaging, 1995
How do plants transport water? Part 1: xylem, transpiration and a mysterious water potential difference
roots, xylem, upward flow, transpiration – but how does it work? Find out in the next thrilling episode, maybe.
Stolen from Nature Education, with apologies
This post could fit well in the ‘How Stuff Works’ series, always a useful resource, but I doubt if they’ve done a piece on today’s subject. Maybe I’ll check later.
I’ve been reading a book called The hidden life of trees, by Peter Wohlleben, a Chrissy present from a good friend. One of its shortest chapters is titled ‘The mysteries of moving water’. The reason for its brevity is essentially that there’s as yet no solution to the mystery of how water gets from the soil to the leaves of a tree, or any plant for that matter. At least, according to Wohlleben.
This strikes me as amazing, if true. After all, it’s a simple, everyday scenario for any home gardener. You notice on a hot summer day that the leaves of your capsicum plant are wilting. You apply a two-litre dose of H2O to the base, et voilà, within an hour or two (I don’t know, I’ve never timed it), those leaves have become as turgid as much of my writing. And it just may cross your mind that it’s pretty miraculous how plants can do that. But if it’s true that we don’t know how plants manage such an everyday miracle, surely working it out is Nobel Prizeworthy for any ambitious team of botanico-chemists out there, or whatever.
Of course it’s much more likely that botanists have been trying to solve this mystery for decades – isn’t it? But before I look into it, here’s what Wohlleben says in his book:
…water transport is a relatively simple phenomenon to research – simpler at any rate than investigating whether trees feel pain or how they communicate with one another – and because it appears so uninteresting and obvious, university professors have been offering simplistic explanations for decades… Here are the accepted answers: capillary action and transpiration.
Upon reading this I tried to recall what I knew of these terms. With capillary action I drew a blank, though I feel sure I knew about it once. Transpiration, though, was clear enough: it was like perspiration, the evaporation of water from the leaves, rather than the skin (or is perspiration the secretion of water through the pores rather than the evaporation? Later). So transpiration is only about the movement of water from the surface of a leaf to the atmosphere by means of solar energy; it surely has nothing to do with movement through the stem or trunk, though the loss of water from the leaves is presumably a signal to the plant to draw up more water from the earth, but how can we talk of signals when a plant has no brain or command centre to receive them? And how can water be ‘drawn up’ when it has no muscle power or other obvious energy source?
As to capillary action, Wohlleben explains:
Capillary action is what makes the surface of your coffee stand a few fractions of an inch higher than the edge of your cup. Without this force, the surface of the liquid would be completely flat. The narrower the vessel, the higher the liquid can rise against gravity. And the vessels that transport water in deciduous trees are very narrow indeed: they measure barely 0.02 inches across. Conifers restrict the diameter of their vessels even more, to 0.0008 inches. Narrow vessels, however, are not enough to explain how water reaches the crown of trees that are more than 300 feet tall. In even the narrowest of vessels, there is only enough force to account for a rise of 3 feet at most.
Needless to say, plenty of research has been done on the subject of water transport in plants, but I have to agree with Wohlleben that there’s a lot that’s missing. The key to the process is a material called xylem, a structure made from hollow, dead, reinforced cells. Here’s how a BBC science site tries to explain it:
Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump.
Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what’s lost.
As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.
Water doesn’t flow upwards, however. It has to be pumped up, or sucked, as we do when we apply our lips and energy to a straw. The BBC also describes the whole process as transpiration, which just seems wrong to me. Obviously much transpires here, but it isn’t just transpiration. What?
What obviously needs explaining is where the energy comes from to draw the water up against gravity, and how the plant ‘knows’ that water needs replenishing.
A more comprehensive, and richly referenced, attempt at an explanation is provided by Nature, the well-known science magazine, on one of its educational websites. There we’re told that ‘plants retain less than 5% of the water absorbed by roots for cell expansion and plant growth’. This is fascinating, as is the reason for the lack of retention – photosynthesis. Water is lost to the atmosphere from the leaves’ stomata, which are like our pores. These stomata are used to absorb CO2 for the photosynthesis of sugars, but their openness to CO2 increases the transpiration rate, so there’s a tricky balance between the two – water loss versus CO2 and sugar gain.
The xylem mentioned above doesn’t reach down all the way to the base of the root system. First the water must pass through several cell layers that act as a filtration system. But how does it do this? What is the force being applied and where does it come from? The Nature article gives this complex explanation:
The relative ease with which water moves through a part of the plant is expressed quantitatively using the following equation:
Flow = Δψ / R,
which is analogous to electron flow in an electrical circuit described by Ohm’s law equation:
i = V / R,
where R is the resistance, i is the current or flow of electrons, and V is the voltage. In the plant system, V is equivalent to the water potential difference driving flow (Δψ) and i is equivalent to the flow of water through/across a plant segment. Using these plant equivalents, the Ohm’s law analogy can be used to quantify the hydraulic conductance (i.e., the inverse of hydraulic R) of individual segments (i.e., roots, stems, leaves) or the whole plant (from soil to atmosphere).
Got that? I may be wrong, but isn’t this just an analogy? Don’t analogies tend to break down with a little bit of analytic pressure? The idea of hydraulic conductance is clearly drawn from electrical conductance, but electrical conductance relies on a power source, doesn’t it? What is the plant’s power source? Yes, I can see that certain parts of the plant have a greater resistance to the water’s mostly upward movement than others, and that this resistance is measurable by examining the time it takes for water to pass through the different parts with their particular structure and chemistry, but it says nothing about the energy source. In Ohm’s law, V, voltage is the amount of power, which comes from a source of that power, such as a battery. In the above analogy, Δψ is described as the water potential difference that drives flow. I’m possibly being dumb, but how does that happen? What’s meant by ‘water potential difference’?
The Nature article, I must say, is very good at telling us about the materials and obstacles negotiated by water molecules on their journey. First they pass through the root’s epidermis, then the cortex and the endodermis and then on to the xylem. They travel by an apoplastic pathway (more of that next time), or else a cell-to-cell pathway (C-C), and the role of ‘water-specific protein channels embedded in cell membranes (i.e., aquaporins)’ is mentioned, but this role is apparently still much of a mystery. Anyway, the xylem continues into the petiole, to which the leaves are attached, and then into the mid-rib, the main central vein of the leaf. From there the water passes into the smaller branching veins of a dicot leaf, which also contain tracheids – elongated xylem cells for the transport of water and mineral salts. It’s from this network of veins that transpiration takes place.
So I’m learning a lot, but the ‘water potential gradient’ and how it pulls or pushes water upwards, that’s still very much a mystery to me. But there’s more to come.
References
Peter Wohlleben, The hidden life of trees, Collins 2017
Ok, the usual update on Trump’s downfall. Some are saying that the Mueller enquiry is winding up (and I’m not talking about GOP hardheads), but I’m hoping not, because I reckon the financial stuff alone will take years to wade through properly. In the meantime though, I’m hoping that more really dramatic developments occur to light a fire under Trump’s capacious backside, sooner rather than later. The latest news is that the Mueller team are looking at the cover-up re Trump Jr’s meeting with Russian agents. So maybe the cover-ups and the endless obstructing will lead to some justice action soon, while the ‘follow the money’ aspect will continue for some time, and hopefully do the really lasting and permanent damage to the Trump horrorshow.