I don’t know, you may be right. I was conflating ammonium and nitrates above because I have seen aphid appear when plant sap nitrates were low but ammonium was high. I agree about photorespiration, that’s definitely true and was part of my answer above. But regarding what I wrote about nitrates and magnesium, I got that from here: https://johnkempf.com/how-to-propagate-aphids/