Main content area

Calcium chloride improves photosynthesis and water status in the C4 succulent xerophyte Haloxylon ammodendron under water deficit

Kang, Jianjun, Zhao, Wenzhi, Zheng, Ying, Zhang, Dong Mei, Zhou, Hong, Sun, Pengcheng
Plant growth regulation 2017 v.82 no.3 pp. 467-478
Haloxylon ammodendron, calcium, calcium chloride, chlorophyll, drought tolerance, dry environmental conditions, greenhouses, osmotic pressure, photochemistry, photosystem II, plant growth, potassium, sand, sandy soils, sodium, turgor, water potential, xerophytes
Our results showed that in addition to sodium (Na⁺), succulent xerophyte Haloxylon ammodendron was more inclined to absorb and accumulate large amount of calcium (Ca²⁺) than potassium (K⁺) as an important osmotica for osmotic adjustment (OA) under arid environments. To further reveal the possible physiological mechanisms of Ca²⁺ accumulation involved in drought resistance of H. ammodendron, 8-week-old plants were treated with a series concentration of external Ca²⁺ (calcium chloride, 1 × 10⁻⁴ to 8 × 10⁻⁴ g CaCl₂ g⁻¹ dry soil) by potted sandy soil culture experiments in field. Plants were also subjected to water deficit (30% of field water capacity) in the presence or absence of Ca²⁺ (4 × 10⁻⁴ g CaCl₂ g⁻¹dry soil) by potted sand culture experiments in greenhouse. The results showed that 4 × 10⁻⁴ g CaCl₂ g⁻¹ soil resulted in optimal plant growth and effectively mitigated harmful impacts of water deficit on the growth of H. ammodendron, by inducing a significant drop in PB water potential and, concomitantly, increasing PB turgor pressure and chlorophyll concentration resulting in an enhancement of overall plant photosynthetic activity. Furthermore, 4 × 10⁻⁴ g CaCl₂ g⁻¹ soil had no effects on the photosystem II photochemistry, but mitigated the inhibitory effect of water deficit on the activity of photosystem II in H. ammodendron. The contribution of Ca²⁺ to the total osmotic potential varied from 6.2% in the control to 11.4% in plants subjected to water deficit and, surprisingly, to 21.6% in plants grown in the presence of 4 × 10⁻⁴ g CaCl₂ g⁻¹ soil under water deficit; however, the contribution of K⁺ significantly decreased from 12.1 to 7.0%. These findings suggest that, under arid environments, H. ammodendron is able to accumulate high concentration of Ca²⁺ in its PB and use it directly for OA, which was coupled with an improvement in PB hydration and photosynthetic activity.