Gram positive or negative is just the way to group bacteria or classify them. The functions of bacterium does not relate to whether it is gram positive or negative.

The gram positive and gram negative classification is irrelevant when looking at the functional role of microorganisms in soils. There are multiple metabolisms and biochemical processes which relates to these bacteria. You should look into specific microbial communities in soils, identifying main components and their functional role. Then you can see if they are gram positive or negative.

It is difficult to answer the question by listing the various function/role played by these broad categories.

Have a look at this useful link.

https://www.nature.com/articles/s41598-020-72696-y

Dear Md. Abul Kalam Azad thank you for your interesting technical question. In addition to the valuable link provided by Arvind Singh please also have a look at the following potentially useful articles:

1. Role of Soil Bacteria

https://ohioline.osu.edu/factsheet/anr-36

2. The ratio of Gram-positive to Gram-negative bacterial PLFA markers as an indicator of carbon availability in organic soils

Article The ratio of Gram-positive to Gram-negative bacterial PLFA m...

3. Litter fingerprint on microbial biomass, activity, and community structure in the underlying soil

Article Litter fingerprint on microbial biomass, activity, and commu...

The last article is freely available as public full text on RG.

Bacteria are important in producing polysaccharides that cement sand, silt, and clay particles together to form microaggregates and improve soil structure.

https://ohioline.osu.edu/factsheet/anr-36

Gram negative bacteria are well known for their nitrogen fixing ability in the soil.

in accordance with Harasit Kumar Paul