生機勃勃：It can also be used to describe the phenomenon in nature (originally) or the society. Such as a particular industry or city is very active. 生機勃勃的城市、生機勃勃的花園 勃勃 itself means very active, full of energy. 生機勃勃/生氣勃勃 is basically the same meaning. 野心勃勃 is the same as you said, very ambitious. Hope that helps :)

勃勃 mean thriving / vigorous / exuberant. It is used as a final particle to emphasis the preceeding action. Therefore it can be translated as "very". 生机勃勃 = zest for life, thriving to live is great or even penchant for hatching out ideas. 生气勃勃 = the aura of life is great/exuberating etc, (here 生气 does not mean "to get angry") 野心勃勃 = great ambitions but in a negative sense. Use 志向 or 雄心 instead for a positive manner.

野心勃勃—— This phrase is used to describe someone who wants to get a higher position or the top position in the work,in a company or any other organization or field. It is negative.It seems like the person who is 野心勃勃 is really hard to satisfied with what he already got.He desires more and more. Hope you can understand.

还有"兴致勃勃"。

the first question：we don't just use this word on rank plant . we can use it on every plants. the second Q：this words is describe a people or society are full of energy the third Q : It is really translated as ambitious. you should use it in a man .this words have some bad meanings but not at all my english is very poor .but i still hope you can understand it