title: Effects of Low pH on Photosynthesis, Related Physiological Parameters, and Nutrient Profiles ofCitrus.
abstract: Seedlings of "Xuegan" (Citrus sinensis) and "Sour pummelo" (Citrus grandis) were irrigated daily with a nutrient solution at a pH of 2.5, 3, 4, 5, or 6 for 9 months. Thereafter, the following responses were investigated: seedling growth; root, stem, and leaf concentrations of nutrient elements; leaf gas exchange, pigment concentration, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and chlorophyll a fluorescence; relative water content, total soluble protein level, H2O2production and electrolyte leakage in roots and leaves. This was done (a) to determine how low pH affects photosynthesis, related physiological parameters, and mineral nutrient profiles; and (b) to understand the mechanisms by which low pH may cause a decrease in leaf CO2assimilation. The pH 2.5 greatly inhibited seedling growth, and many physiological parameters were altered only at pH 2.5; pH 3 slightly inhibited seedling growth; pH 4 had almost no influence on seedling growth; and seedling growth and many physiological parameters reached their maximum at pH 5. No seedlings died at any given pH. These results demonstrate that citrus survival is insensitive to low pH. H+-toxicity may directly damage citrus roots, thus affecting the uptake of mineral nutrients and water. H+-toxicity and a decreased uptake of nutrients (i.e., nitrogen, phosphorus, potassium, calcium, and magnesium) and water were likely responsible for the low pH-induced inhibition of growth. Leaf CO2assimilation was inhibited only at pH 2.5. The combinations of an impaired photosynthetic electron transport chain, increased production of reactive oxygen species, and decreased uptake of nutrients and water might account for the pH 2.5-induced decrease in CO2assimilation. Mottled bleached leaves only occurred in the pH 2.5-treatedC. grandisseedlings. Furthermore, the pH 2.5-induced alterations of leaf CO2assimilation, water-use efficiency, chlorophylls, polyphasic chlorophyll a fluorescence (OJIP) transients and many fluorescence parameters, root and leaf total soluble proteins, H2O2production, and electrolyte leakage were all slightly greater inC. grandisthan inC. sinensisseedlings. Hence,C. sinensiswas slightly more tolerant to low pH thanC. grandis. In conclusion, our findings provide novel insight into the causes of low pH-induced inhibition of seedling growth and leaf CO2assimilation.
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: An
authors.initials: A
authors.lastname: Long
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: Lin-Tong
authors.initials: LT
authors.lastname: Yang
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Ye
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: Ning-Wei
authors.initials: NW
authors.lastname: Lai
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: Ling-Ling
authors.initials: LL
authors.lastname: Tan
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry University Fuzhou, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Lin
authors.affiliation: Institute of Plant Nutritional Physiology and Molecular Biology, College of Resources and Environment, Fujian Agriculture and Forestry UniversityFuzhou, China; Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry UniversityFuzhou, China; The Higher Educational Key Laboratory of Fujian Province for Soil Ecosystem Health and Regulation, Fujian Agriculture and Forestry UniversityFuzhou, China.
authors.forename: Li-Song
authors.initials: LS
authors.lastname: Chen
keywords: Citrus grandis; Citrus sinensis; OJIP transient; chlorophyll a fluorescence; low pH; photosynthesis; uptake of nutrient and water