Liu, your question is little confusing? You can not calculate sugar accumulation. It can be either sugar content or sugar concentration. Is that sugar concentration that you want to calculate? OR, if you sugar accumulation, you need to estimate sugar deposition in a tissue, monitoring by labelling studies.
So, sugar accumulation in a plant tissue can be expressed on two ways: content basis and concentration basis. You can choose which way you want to express and follow the formula accordingly. It should be easy.
Yes, you are right. but now what made me confusing is that how to get sugar concentration, as we don't know the consumption of sugar and actual production. I saw some references they used dry biomass and nitrogen content to calculate nitrogen accumulation, so I was wondering whether I can use this way or not. Do you have some good idea? I really appreciate it.