You need one of two things.

1. Better carbon storage and ability for dormancy in the plants. Then they can synthesize sugar when there is light, and respire when it is dark (as our plants do).

2. An organelle in the plants different from chloroplasts. They would use H2S (which has higher energy electrons that H2O) to provide the electrons to fix CO2 into sugar.

These plants will not be green, as the purpose of the green pigment is to collect light. If they conduct both types of autotrophy, which is certainly possible, some invertebrates have five symbionts, then they would be red or green again.

Indeed, this would be analogous to Riftia and similar tubeworms, or Bathymodiolus mussels, or other benthic invertebrates.

You need one of two things.

1. Better carbon storage and ability for dormancy in the plants. Then they can synthesize sugar when there is light, and respire when it is dark (as our plants do).

2. An organelle in the plants different from chloroplasts. They would use H2S (which has higher energy electrons that H2O) to provide the electrons to fix CO2 into sugar.

These plants will not be green, as the purpose of chlorophyll is to collect light. If they conduct both types of autotrophy, (which is certainly possible, some invertebrates have five organelle-like symbionts and plants have two), then they would be (red or) green again.

Indeed, this would be analogous to Riftia and similar tubeworms, or Bathymodiolus mussels, or other benthic invertebrates.

You need one of two things.

1. Better carbon storage and ability for dormancy in the plants. Then they can synthesize sugar when there is light, and respire when it is dark (as our plants do).

2. An organelle in the plants different from chloroplasts. They would use H2S (which has higher energy electrons that H2O) to provide the electrons to fix CO2 into sugar.

These plants will not be green, as the purpose of the green pigment is to collect light.

Indeed, this would be analogous to Riftia and similar tubeworms, or Bathymodiolus mussels, or other benthic invertebrates.

You need one of two things.

1. Better carbon storage and ability for dormancy in the plants. Then they can synthesize sugar when there is light, and respire when it is dark (as our plants do).

2. An organelle in the plants different from chloroplasts. They would use H2S (which has higher energy electrons that H2O) to provide the electrons to fix CO2 into sugar.

These plants will not be green, as the purpose of the green pigment is to collect light. If they conduct both types of autotrophy, which is certainly possible, some invertebrates have five symbionts, then they would be red or green again.

Indeed, this would be analogous to Riftia and similar tubeworms, or Bathymodiolus mussels, or other benthic invertebrates.