So by "plant" you really meant a living plant and not the plant in process control. Those signals are rather DC or below 1Hz and in the millivolt range. Sound card will not pick it up, you need a precision low drift low noise DC amplifier with low pass filter. I assume you want something like in this article: https://dacemirror.sci-hub.se/journal-article/529a0faa05eb9b40c5e25b8331ccf9f3/fromm2006.pdf
There might be some signals in the audio range, but there would also likely be DC or very low frequency signals which would not be captured by the audio input on a PC.
