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

Author:
Kang, Jianjun, Zhao, Wenzhi, Zheng, Ying, Zhang, Dong Mei, Zhou, Hong, Sun, Pengcheng
Source:
Plant growth regulation 2017 v.82 no.3 pp. 467-478
ISSN:
0167-6903
Subject:
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
Abstract:
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.
Agid:
5750811