请大神帮忙分析一下下面这个句子。

Question

The bacteria that legumes host within their root nodules (small swellings on the root) change nitrogen gas from the atmosphere into nitrogen compounds that plants are able to metabolize, a process, known as nitrogen fixation, that makes the soil more fertile.

1. 想问主句是什么？
2. 最后的 that makes the soil more fertile 修饰的是什么？是修饰 nitrogen compounds 吗？还是别的？

Answer 1

主句是：The bacteria change nigrogen gas from the atmosphere into nitrogen compounds.
that make the soil more fertile 是指：a process, know as nigrogen fixation.
翻译：寄宿在豆类根瘤中的细菌把大气中的氮气变成含氮化合物，使植物能够新陈代谢这个过程被称作固氮作用，这（个过程）使得土壤更肥沃。

Answer 2

The bacteria that legumes host within their root nodules (small swellings on the root) change nitrogen gas from the atmosphere into nitrogen compounds是主句。
that makes the soil more fertile修饰 nitrogen fixation或者process