Hello everyone, 
I have started growing different species of bonsai from seedlings. These are the species I choose:

• Acer palmatum
• Juniper chinensis
• Larix decidua 
• Pinus ponderosa 
• Pinus thumbergi
• Cryptomeria japonica 

Most of them already sprouted!

Because I don't have any experience with these young trees, I would like to know if now I should put them on full sun or on the sun just for few hours per day. Probably every species will require a different treatment...

Allo of them is full sun species except acer.

Even now that they are only one week old?

When thinking about care of any plant or animal I always think about how they live in nature. Under what conditions and environment.

It may sounds like a weird to say, but trees in nature do not move. What can we learn from this information?

Ok, thank you very much for your advice! 

Hello again,

I have seen this video on how to create cuttings from pine seedlings:

Rooting Black Pine Seedling Cuttings

It looks quite intersting and I would like to experiment that technique on some of my seedlings. Which ones of the species I elencated above do fit better for this technique?

I am quite sure the pines Jelle was cutting is pinus thunbergii.

I have never seen that method before and I am supriced that it works. To me it looks like a very risky method for a result that can be achieved a few years down the lane with pruning and backbudding. Japanese black pines is very strong backbudders where I live. It may be different at your or Jelles location (I think he is in northern Germany close to Netherlands in zone 7).

Some of these techniques are done by the pros who work them on a hundred trees and don't particularly care if they kill 90. I would think about the risk involved before I tried something. 

Hi everyone,

Most of my pine seeds sprouted, but the mortality rate was quite high. Even now, at almost six months old, some are still dying. I noticed that the taproot has grown significantly: could this be normal, or might it be linked to their deaths?

 
 

Hello!

About the seedling cutting technique, it's quite common for Japanese Black Pines in order to get a better root system, but like Ivan said, people do that when they have a good ammount of seedlings, it's expected to lose a few, and as you can see in Jelle's video, using hormone is important to raise your success rate.

That being said, long taproot might be a clue to a not too granular substrate, so when you separate them (late winter), you might think about making a more aerated substrate, that will help you on getting more thin roots... But for now, be carefull not to allow the soil to stay too damp, I'm asuming you're entering in autumn at the moment...

Are those 4 all of them now?
They don't look that bad, it's expected for those old needles to fall off, some of them might not even be actual needles.

Edit:
Oh, and no, the long taproot itself wouldn't be the cause for a tree to die, it's natural for trees to grow a long taproot in order to be stable on the ground... But like I said, can be a clue for a soil that is too compact, not allowing the roots to grow that freely tru' the substrate, and the more feeder roots you get, better your tree will be able to absorb water and nutrients...