Removes the phosphate from trehalose 6-phosphate to produce free trehalose. Trehalose accumulation in plant improves abiotic stress tolerance. alpha,alpha-trehalose 6-phosphate + H2O = alpha,alpha-trehalose + phosphate Optimum pH is 6.5-7.0. Glycan biosynthesis; trehalose biosynthesis. Expressed in roots and shoots. By cold, drought, salt stress and abscisic acid (ABA). Over-expression of TPP1 increases trehalose levels and enhances tolerance to salt and cold stresses. Belongs to the trehalose phosphatase family.