There are several factors that effect the rates of photosynthesis:
Light intensity - the more light, the faster the rate (more O2 produced, and CO2 absorbed)
Carbon dioxide concentration - more CO2 the faster the rate
Temperature - the colder it is the slower the rate (if negative, O2 is absorbed, and CO2 released)
Availability of water - the less water available the more likely the plant will wilt loosing some of its ability to absorb sunlight
Availability of nutrients - the amount of chlorophyll, and magnesium for instance or important for the conversion of sunlight, the less of them there are, the slower the rate of photosynthesis.