將下面一篇短文翻譯成通順的中文。
    However，there is difficulty in growing plants in space.Because of the lack of gravity in space，the oxygen that the plants produce stays around the plants.This can kill them，so fans are needed to circulate the air.Without gravity，roots don't "know" to grow down and leaves don't know to grow up.Specialized containers are being developed to help the plants grow correctly.There are problems with soil as well.As soil is too heavy to send to space，special liquid gels （凝膠） are used to support plant growth.These contain water and send it to the plants.