Ecophysiology of salt excretion in the xero‐halophyte Reaumuria hirtella

Abstract

Different aspects of salt excretion from leaves of the xero-halophyte Reaumuria hirtella Jaub. et Sp. (Tamaricaceae) were investigated under the extremely arid conditions of the desert. The diurnal excretion pattern, which gradually decreased toward midday, showed a negative correlation with the daily transpiration pattern. The relative excretion, which is the ratio between the absolute excretion of Na + and the change in its internal content, was maximal at sites with low salinity, and decreased when the concentration of NaCl in the root environment increased. By contrast, the absolute excretion increased from 253 to 323 mmol Na + g −" f. wt per 12 h with increase in the total soil salinity from 0n24 to 1n23 %, respectively. Water stress conditions, caused either by increasing soil salinity or by dryness of the atmosphere, greatly influenced the efficiency of excretion process.Six ions : Na + , K + , Ca# + , Mg# + , Cl − and SO % #− constituted 96n8 % of the d. wt of the field-collected secreted salts. Na + and Cl − , which were the predominating ions in the soil solution of the root environment, were also the predominantly secreted, constituting c. 89 % of salts secreted. The proportion of Na + which was prevented from entry into the roots increased with increasing Na + concentration in the soil solution. More than 67 % of the absorbed NaCl was secreted by leaves during the day. However, the accumulated salts contributed to the osmotic potential (ψ s ) and improved the plant water status. The osmotic potential of the plant sap at the end of the day or during periods of low excretion rates was shown to be decreased k7n3 to k13n7 bar from that in the morning. The fraction of osmotic potential decreased during the day (∆ψ s ) was positively correlated with the soil salinity. These retained salts are expelled from the leaves by increased efficiency of extraction during the night and early morning, so that the plant begins the day with low internal salt content, and the leaf reservoirs become suitable for a new supply. The rejection mechanism at the plant roots and the secretion mechanism at shoots allow the plant to maintain its internal salt content at an approximately constant level despite the great variation in soil salinity.

Species, types, distribution, and economic potential of halophytes in China

“…The classification of Chinese halophytes into three physiological types is based on salt uptake and storage, as described by Breckle (1995 Wang and Li 1993, and b from Chen et al 1990Chen et al , 1997; Desert Institute of Lanzhou in China Academy of Science 1986; Li and Wang 1990;Li and Zheng 1997;Li et al 2001;Lin 1990Lin , 1993Lin and Fu 1995;Ninxia Agriculture Prospesting College 1990;Ramadan 1998;Shao et al 2004;The Biology, Soils and Desert Institute of Xinjiang 1981;Wu 1980;Wu and Wang 1983;Xi et al 2006;Xiong and Li 1990;Zhao and Li 1999 mum, Halostachys, Suaeda, Glycyrrhiza, and Zygophyyllum. Hydrohalophytes are divided into emergent halophytes and submerged halophytes.…”

Effects of salinity and benzyl adenine on development and function of microhairs of Zea mays L

“…These structures, one of the forms of trichome found on the surface of the leaves of grasses, are termed 'microhairs' or 'salt glands' (Amarasinghe 1990; Amarasinghe andWatson 1988, 1989;Marcum and Murdoch 1992;Ramadan 1998). These microhairs are (with one exception amongst the grasses, see Flowers et al 1990) bicellular.…”

Role of Na+/H+Antiporters in Na+Homeostasis in Halophytic Plants

“…Salt glands also secrete considerable amounts of fluid in Limonium latifolum; under certain conditions the leaf discs secrete fluid up to half their weight in a 24-h period [38]. It has been reported that in Sporobolus spicatus the molar ratio of K þ /Na þ in the plant leaves was more than 10-fold that in the interstitial soil solution and 13 times that in the secreted salts, indicating the high selectivity of the secretion mechanism for sodium [39]. In addition to salt gland secretion, salts are also released through the cuticle or by guttation fluid, and they can be retransported back to the roots and soil via the phloem, or become concentrated in the salt hairs [40].…”