At which latitude, heat gain through insolation approximately equals heat loss through terrestrial radiation?

A community which starts succession in a habitat is

Among bryophytes, lichens and fern which one is a pioneer species in a xeric succession ?

$A$ : Neither the community modifies environment nor the environment forces the community to leave the place in climax stage of succession.

$R$ : Climax community is xerophytic in most of the types of succession.

Green plants and green sulphur bacteria, prepare their organic food themselves with the help of sunlight, are known as