You can use some of qualitative method for same.

For pH: You can use different dye in media which changes color upon pH change (methyl red turns from yellow to red from alkaline to acid pH), will be easy to measure the pH chang during incubation.

For Microbial activities: Depend on you project you have to decide.

For example referred article :Organic-acid-producing, phytate-mineralizing rhizobacteria and their effect on growth of pigeon pea"

Best

Hello Xiaoyan,

I recommened technologies such as zymography (see Spohn et al.) for detecting enzyme activities. For pH measurements I recommend (no surprise) the use of planar optodes.

I attached some examples.

Best regards

Article Spatial and temporal dynamics of hotspots of enzyme activity...

Article Soil zymography - A novel in situ method for mapping distrib...

Article Distribution of microbial- and root-derived phosphatase acti...

Article Light for the dark side of plant life: —Planar optodes visua...

Dear Xiaoyan Tang,

it depends upon your specific area of the research, In the rhizosphere, In this crucial pocket of the plant there are various processes and mechanisms are going on.e.g. root exudate biology,unseen and unexplored microbial world, elemental cycling effects, plant defense molecule, plant microbe intercaction  

You could look Into the PGPR induced defense proteins. Mechanism of antagonism including production of antagonistic metabolites. Nutrient solubilization and no ilization.

Dear Xiaoyan

If you wanted to study rhizosphere microorganisms at the transcriptional level you could perform metagenomics and metatranscriptomics. I have attached a couple of recent reviews on the topic for you to get a better idea of the approach. I hope this helps....

Hi

Rhizosphere is a wide topic.

You may find a useful information in the following attached files.

Hi Xiaoyan

Many useful references on attachment 1

https://www.wsl.ch/dienstleistungen/publikationen/pdf/7762.pdf

2

https://onlinelibrary.wiley.com/doi/10.1111/ejss.3_12398/pdf

3

https://aem.asm.org/content/73/19/6001.full

4

https://www.wsl.ch/dienstleistungen/publikationen/pdf/7762.pdf

5

https://www.plantpath.cornell.edu/labs/enelson/PDFs/Hill_et_al_2000.pdf

6

http://wwwuser.gwdg.de/~kuzyakov/SBB_2013_Blagodatskaya_Active-MO-Microorganisms_Review.pdf

7

https://cjsbs.sljol.info/article/download/5896/4764/

8

https://www.wsu.edu/~mavrodi/antibiotics.htm

9

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0146558

10

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3706808/

11

https://publishup.uni-potsdam.de/opus4-ubp/files/6517/rudolph_moor_diss.pdf

12

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4320215/

13

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3105091/

14

https://academic.oup.com/femsec/article/42/2/187/595231

15

https://www.sciencedirect.com/science/article/pii/S2095177915300150

16

https://academic.oup.com/aob/article/116/6/987/161798/The-impact-of-elevated-carbon-dioxide-on-the

17

https://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162015000200014

18

https://www.helmholtz-muenchen.de/inet/forschung/arbeitsgruppen/molekulare-mikrobenoekologie/publikationen/index.html

19

https://www1.montpellier.inra.fr/rhizosphere-2/book_of_abstracts/

20

https://www.esciencecentral.org/ebooks/enzymes/pdf/soil-enzymes.pdf