This is not Adobe, this is a user community. We are here for helping out to interpret the refusals, but we do not issue the refusals. You need to tell us Adobe's rejection reason. But I suppose, looking at your picture, the reason is "Technical issues".
I've identified the following problems:
Sharpness: the picture is out of focus, or your camera moved during taking the picture.
Exposure: the mushroom is overexposed and is missing structure.
Composition: the picture is not well composed. You should have taken away that wittered plant at the left and that yellow fruit (or compose such that the fruit is completely in the image)
In-camera post-processing introduced a fake DOF. The processing does not do that with the same quality as a real lens does that. You have to avoid such features.
Examine your pictures at 100% and 200%, and if you see artefacts, correct them before submission. If you can't correct them, don't submit.