Identify six things that will slow down the rate of photosynthesis in a plant

As we know photosynthesis is a process that the plant do it to make its own food 
1- decrease amount of co2 in atmosphere 
2-decrease the temperature of the earth 
3- decrease the amount of light the plant absorb it
4- decrease amount of water  the plant absorb it 
5- decrease amount of nitrates 
6- distribution of an ecosystem  
 

Where are the options?