Net, sure, but it's actually really really complex when you look at point in time numbers.

> Carbon dioxide is not released during photosynthesis, but small amounts of that gas are emitted both day and night as a by-product of cellular respiration. It is worth noting that the majority of plants absorb carbon dioxide during the day for photosynthesis and do so in greater amounts than they release for cellular respiration.

So depending on the time plants could easily be pushing out more CO2 than they are pulling it at that time, which could result in CO2 concentrations increasing during that time.

Time dependent, plants give off O2 in the evening. The co2 is released by the micro organisms which are bacterial and fungal and breathe O2 just like us.