Over the last week we got a bit side tracked from the study of the soil, what with Easter and April Fools – I think my 24 carrot gold seeds were a bit too subtle… maybe I should have spray painted 24 carrots gold! Anyway…. The other exciting distraction over the last week is the house has arrived, but I’ll share more of that with you later, because I really need to press on with this soil science stuff. The arrival of the house has tightened the timeline, because as soon as they have finished sticking it all back together and council signs it off, then we can move in. That will mean the caravan and the container can go, and I can start my garden. So, I’d better know as much as I can about the soil before I get started. So where were we…
In order to understand my new sandy soil, I have been trying to understand how the plant works and how the soil works so I can make sense of it all and be a better gardener in less than ideal conditions. Last time was like the bit in a scary movie, where they are crossing a dangerous rope bridge and the hero wants to go fast to get across as quickly as they can, but needs to go slow and examine each tread so they don’t fall through. I feel like we have made it passed the horrible bits and are now safe of solid ground.
So, we know water is a great carrier of nutrients up into the plant, through the xylem, and the root cells have good systems for managing the nutrients once they get in. And we now know the nutrients need to be tiny – on a molecular level to get in. But the question remains: how do they get in? They don’t have arms and they’re not a sponge and don’t go about sucking up everything arbitrarily. It turns out the plant is very particular as to who and what it invites inside.
There are a couple of ways this happens down deep in the soil. One method is passive, and the other is active. The passive process occurs through a process called osmosis which is a kind of popularity contest for ions (the molecules with the electrical charge). Basically, they want to be at the exclusive party and all mill about outside the cell in high numbers, being absorbed through the semi-permeable cell wall into the cell where there are low numbers. The numbers are kept low as once inside the ions that are needed are escorted off into the heart of the root, across the cortex and beyond the casparian strip, and are locked into the plant and able to be used where needed.
However, the water is trying to control this movement and prefers things to be balanced on both sides so won’t let everyone in. If too many ions get in, it becomes too concentrated and the process reverses and the ions leave the cell like it is yesterday’s news. So, there can be a lot of coming and going in the root hair cell.
This is all very well if there are large concentrations of the ions needed lingering in the soil the roots are sitting in. But not all of the ions are there in large enough numbers to just drift in and have to be delivered into the cell like a VIP in an active system. The cool thing about plants is they have a process for everything they need and even create their own energy currency ATP (adenosine triphosphate for those who want to know). It is made in the respiration process up in the leaves.
Apparently, it is not known exactly how this works, but the cell walls of the root hairs have different carrier molecules embedded in them that recognise specific nutrients. Sort of like secret entrance ways and the energy from the ATP is used to bring in these nutrients against the concentration flow so the plant can get what it needs specifically.
I sort of see it like the DJ and the magician turn up to the party and is stuck in among all the party goers out the front. The party goers are having their tickets checked and allowed in so long as the party isn’t overcrowded on the inside. But the DJ and the magician are special and need priority treatment to get in and with the assistance of some currency to grease the wheels (ATP) they are whisked in through their own separate entrances.
However, this system has its limitations. If the temperature isn’t right and it is too cold or too hot, then the doors don’t open, so the DJ and the Musician have to wait outside for it to warm up. Meanwhile the party goes on without the talent. This can be seen in many common plant problems – if it is too cold phosphorus can’t get in and without it the plant turns purple. Or blossom end rot in tomatoes – it is due to a calcium deficiency and in most circumstances, it isn’t because it isn’t in the soil, but it is too cold to get into the plant and so the nasty rot problem occurs. This is why it is more common earlier in the season, when it is still a little cool and then comes right.
But even the passive system has something to teach us… if there aren’t enough nutrients in the soil, the ones already in the root hair cells have no choice but to leave, so they can hang out with their friends until the numbers become more concentrated that they can flow back in the other direction back into the cell. It would seem balance is the key to ensure the plant stays consistently well fed, not yo-yoing between feast and famine.
And that seems like enough to take on today. It would seem information uptake into my head is also limited by concentration levels.
Come again soon – I think we need to find out more about these all important nutrients.
Sarah the Gardener : o)