No, conifers generally are at an advantage in dry conditions because they depend on tracheids which provide a safer path for water transport. Sap tends not to be flowing in the winter, although the first rise of sap in the spring may have a similar mechanism to guttation. When transpiration stops and there is no tension in the xylem, its water potential can be lower than the soil solution's so water is taken in and forced up the plant.
Materials can move up the plant in the phloem.
Yes water flows in one direction only in the xylem, whereas material can flow in either direction in the phloem, depending on source-sink relations.