Effects of pH in irrigation water on plant growth and flower quality in herbaceous peony (Paeonia lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) is an excellent landscape plant because of its great ornamental values. The objective of this study was to determine if plant growth and flower quality of P. lactiflora were affected by extreme pH in irrigation water. Compared with the control (pH 7.0), P. lactiflora exhibited a decrease in all morphological parameters except leaf number when irrigated with pH 4.0 and 10.0 waters. Physiological indices including chlorophyll a, chlorophyll b, chlorophyll a+b, soluble protein, malondialdehyde (MDA), soluble sugar, hydrogen peroxide (H2O2) and free proline were increased in response to irrigation with waters at pH 4.0 and 10.0, while the decline was occurred in chlorophyll a/b. Moreover, activities of three protective enzymes were also decreased in response to pH 4.0 and 10.0 treatments. These results indicated that the growth of P. lactiflora was significantly affected by extreme pH in irrigation water, and the most serious stress to P. lactiflora was caused under pH 10.0 treatment. Compared with plants irrigated with water at pH 7.0, 26.78% and 27.82% reduction were found in flower diameter and flower fresh weight of plants irrigated with water at pH 4.0. Likely, flower color fade under pH 4.0 treatment was attributed to decreased anthocyanin content and increased pH value of petal, which were coordinately regulated by nine anthocyanin biosynthetic genes and a vacuolar Na+/H+ antiporter1 gene (NHX1), respectively. The results would provide a theoretical guidance for the use of irrigation water in practical production of P. lactiflora.

► Morphological parameters were reduced except leaf number under pH treatments.
► Physiological indices and enzymes activities reflected plants stress under pH treatments.
► Flower quality was adversely affected by pH4.0 treatment.
► Flower color fade was attributed to decreased anthocyanin content and increased pH value.