How do some plant roots cause chemical weathering?

Question

How do some plant roots cause chemical weathering?

Answer 1

In addition to chemical weathering, plant roots also cause mechanical weathering by growing into cracks in the rocks and breaking them apart.

Lichens and mosses growing on the rocks surfaces and in cracks also cause chemical weathering by releasing acid which assists in the breakdown and alteration of rocks, and by holding water on the rock surface for longer.  Also all plant material helps the soil retain moisture, and it that moisture which is the primary agent in chemical weathering.

Answer 2

A few plants can produce acidic secondary compounds that are exuded from their roots into the soil.  This increase in H+ cations increases phosphorous weathering in soils.  This is believed to be a mechanism of phosphorous uptake in nonmycorrhizal plants.

If you can get the full text of the article below, they briefly describe this process and have references to other articles.