The air layers I have tried on JWP " Arakawa" so far have been unsuccessful ( five out of five) But I have not tried them on the young shoots which is what is done in Japan. I tried separating the dwarf JWP from the grafted root stock.
However the JWP cuttings are still showing promise with new buds extended, then stalled, new needles now turning green and standing away from the candles. I am pretty sure the reserves are used up by now and they must be taking in water and nutrients through roots. One that I checked had tiny hair roots only at this stage so I am leaving the rest before checking any further. Not confident that they would survive disturbance at this stage. Definitely less vigorous and slower than JBP.