On my journey to understanding my sandy soil from the plant to the soil, we have already found that the plant pretty much sucks up the water from the soil and releases it out of the leaves as water vapour in some kind of super pump delivering the nutrients along the way. There are other uses for the water in the plant, but we’re just interested in the bit that connects it to the soil.
The common line is ‘water and nutrients are absorbed from the soil’ but that isn’t good enough for me – I want to know how. Some soils are better hosts to this process than others and so if we understand how this happens then we can treat our soils in ways that can help and not harm the process.
This means we are still looking at the structure of the plant down in the roots, but there is also some chemistry in there and other complex scary sciency stuff, but if we step back and look at it in a more user-friendly way, it might make more sense. If we think of it in a space type action adventure, then it is even more interesting.
In the centre of the roots is the up and down elevators to the plant above with the phloem bringing the manufactured sugars down and if they are bringing them as far down as the roots it is likely to be stored for future use, like in spuds, carrots or turnips. Beside that is the xylem which whisks the water upward taking with it any nutrients that have been ‘absorbed’. This is wrapped with the endodermis that has within it the ultimate gate keeper as to who can enter the xylem and who can leave the phloem – the Casparian Strip. Like some kind of bouncer protecting the VIP area in a nightclub. And there goes my space analogy already… maybe it is like some kind of specialist Storm Trooper protecting the access way to the heart of the Death Star? I don’t know – my kids are the Star Wars experts. But the endodermis with its embedded Casparian Strip wraps around the pipes to create what is known as the vascular bundle and you can only get in if you’re on the list.
Beyond this central core is the cortex which has large cells that can be thought of like some kind or foyer or waiting room. The sugars from above can be stored here as starches but it is also where incoming waters and absorbed nutrients are escorted across the root as they make their way across the cortex to the vascular bundle as they await permission to head on up into the interior of the plant. In my head I see some kind of secure government department that once you clear the front doors you need some kind of staff member with a clipboard and a name tag dangling from their neck to take you to where you need to be. (I’ve never been in a place like that but seem something similar in the movies.)
Beyond the cortex is the epidermis that wraps around the whole lot in a waterproof layer in a single layer of cells. But not just any kind of protective layer – it has special cells with special jobs. Like the leaves it has stomata cells that open and close to allow gas exchange. But it is the root hairs we are interested in as these are the ones that do the ‘absorbing’.
The root hairs are single cells that elongate out from the epidermis along the length of the root and its branches and are the ones responsible for the all-important water and nutrient absorption. These cells are the hunters and gatherers of the plant cell community. They are microscopic, fragile and only last a few weeks, but the epidermis cells are constantly being replaced.
And that is the biology bit of understanding the soil. Giving myself an overview in my head I see these intrepid individuals (root hairs) risking life and limb going out to seek out the essential elements for life for their civilisation. These nutrients are then thoroughly checked for suitability and demand and then whisked up into the heart of the community on a wave transportation not dissimilar to being teleported to where it needs to be in some hi tech mail room organisational system, with the water being little more than the mechanics of the transport rather than essential in great quantities for hydration – although it does have essential for life uses for a portion of it.
So, you can sort of see some kind of space action movie thing going on… well it is a bit weak, you hopefully you get the picture. There are so many more amazing things going on in the plant to make it the functioning being that it is. But I’m just focusing on how it is connected to the soil.
Come again soon – because we now know how – but want to find out more about this ‘how’ business as ‘absorb’ seems a bit wishy washy to me.
Sarah the Gardener : o)