Ms Harper raised the need for an improved frequency of services to make them a more feasible public transport option with Transport Minister Graeme Day.
She also asked when the currently diesel lines will be decarbonised to help reduce emissions.
Mr Day responded: “The proposed May 2022 timetable seeks to improve services in the south west of Scotland by increasing the number of services and capacity.
"It’s proposed an additional six Ayr–Stranraer services compared to the current timetable and services from Glasgow to Dumfries and beyond will increase by five.
“Overall there will be an additional 1,000 seats on a daily basis across the south west service group to help encourage modal shift.
"75 per cent of all passenger services are currently undertaken by zero emission trains with the remainder to be decarbonised by 2035.
"Options to replace class 156 diesel which currently run on these south west Scotland routes are being considered, including self-powered fleets with battery or hydrogen fuel cells.”
Ms Harper was pleased by the Minister’s response, but will continue pushing for improvements.
She said: “I am regularly contacted about both the current infrequency of services on the Dumfries-Glasgow and Stranraer-Ayr lines and about the long journey times.
"I am therefore pleased to have received a commitment, from the Transport Minister, that both lines will have increased frequency as part of the new timetable.
“As well as improved journey frequency, the Scottish Government Scottish Strategic Transport Projects Review 2 is due to be published this autumn.
"I have been lobbying for this review to include further transport infrastructure upgrades for Dumfries and Galloway, including upgrades to the A75, A76 and A77 and improvements to bus and rail infrastructure.
"I have also made the case for this review to have commitments to decarbonised rail lines across our region which would quicken journeys.”