Coconut coir does have some antimicrobial properties, mainly for fungal pathogens such as damping off fungus. Coconut coir is even used against oral pathogens in humans. Peat, on the other hand is known for its ability to destroy all microbes even the good ones. A case in point are the human bodies found in peat bogs which are basically mummified. This state of the bodies is only possible by the lack of any fungal or bacterial activity. I don't really know all that much about the differences between the two, I just know that by using coconut coir my seedling loss due to damping off as dropped to zero, for years. Depending on what I am seeding I usually sterilize my seed starting mix. I use the coconut coir about 50% coconut, 50% sifted leaf mold. The leaf mold I rake up is really just compost that is so composted it is almost soil. There are good and bad microbes. Thankfully most soil microbes are beneficial . And yes, plants need microbes. Soil microbes do many different things. Some soil microbes break down organic matter in to form plants can uptake. Others attack and kill harmful microbes. Only when bad microbes outnumber good microbes does a plant get a bacterial disease or even a fungal disease. Fungal pathogens are, by far, the most common, but fungal pathogens are usually caused by events such as overwatering, watering at the wrong time of the day or splashing. Even these avoidable events can be mitigated by growing more beneficial microbes, thus the use of whole ground cornmeal which enables many more trichoderma to grow. I could go on but this old man is tired and going to bed.
