Fumiko Iwanaga

Inorganic and organic osmolytes accumulation in five halophytes growing in saline habitats around the Aiding Lake area in Turpan Basin, Northwest China

ABSTRACT Halophytes dominate the plant community in saline soils. Here, osmoregulation via the accumulation of osmolytes is the basic strategy by which plants survive salinity stress. We investigated the accumulation of inorganic and organic osmolytes in the leaves of five halophytes (Tamarix hispida, Halocnemum strobilaceum, Kalidium foliatum, Karelinia caspica, and Phragmites australis) growing in the dry lakebed of Aiding Lake, Xinjiang, China. The succulent euhalophytes (H. strobilaceum and K. foliatum) accumulated large amounts of Na+, whereas other species had low Na+ concentrations. P. australis contained high concentrations of soluble carbohydrates, mainly sucrose, and amino acids, such as proline and alanine. K. caspica accumulated large quantities of mannitol. H. strobilaceum and K. foliatum had high glycine betaine contents. Only T. hispida accumulated γ-butyro betaine, which was found in high concentrations. Our findings indicate that at least four types of osmolytes (carbohydrates, polyols, amino acids, and betaines) function either alone, or in combination in the osmoregulation of these halophytes.

Effect of soil salinity and nutrient levels on the community structure of the root-associated bacteria of the facultative halophyte, tamarix ramosissima, in southwestern united states

Tamarix ramosissima is a tree species that is highly resistant to salt and drought. The Tamarix species survives in a broad range of environmental salt levels, and invades major river systems in southwestern United States. It may affect root-associated bacteria (RB) by increasing soil salts and nutrients. The effects of RB on host plants may vary even under saline conditions, and the relationship may be important for T. ramosissima. However, to the best of our knowledge, there have been no reports relating to T. ramosissima RB and its association with salinity and nutrient levels. In this study, we have examined this association and the effect of arbuscular mycorrhizal colonization of T. ramosissima on RB because a previous study has reported that colonization of arbuscular mycorrhizal fungi affected the rhizobacterial community (Marschner et al., 2001). T. ramosissima roots were collected from five locations with varying soil salinity and nutrient levels. RB community structures were examined by terminal restriction fragment (T-RF) length polymorphism, cloning, and sequencing analyses. The results suggest that RB richness, or the diversity of T. ramosissima, have significant negative relationships with electrical conductivity (EC), sodium concentration (Na), and the colonization of arbuscular mycorrhizal fungi, but have a significant positive relationship with phosphorus in the soil. However, at each T-RF level, positive correlations between the emergence of some T-RFs and EC or Na were observed. These results indicate that high salinity decreased the total number of RB species, but some saline-tolerant RB species multiplied with increasing salinity levels. The ordination scores of nonmetric multidimensional scale analysis of RB community composition show significant relationships with water content, calcium concentration, available phosphorus, and total nitrogen. These results indicate that the RB diversity and community composition of T. ramosissima are affected by soil salinity and nutrient levels. Sequence analysis detected one Bacteroidetes and eight Proteobacteria species. Most 16S rRNA gene sequences had high similarities with the bacteria isolated from saline conditions, indicating that at least a portion of the RB species observed in T. ramosissima was halotolerant.

Effects of Irregular Saltwater Submergence on Taxodium distichum Seedlings

Abstract The growth response and photosynthetic activity of Taxodium distichum in relation to the leaf and root Na+ content was assessed with the use of 2-year-old seedlings submerged in saline. Seedlings were submerged in water containing 0, 4000, and 8000 ppm NaCl during May, July, and September, respectively. Submergence and soil flooding with fresh water (control) did not inhibit vertical or lateral seedling growth. No morphological changes were observed during submergence in salt water; however, in July and September, leaf injury and shoot dieback were observed in the drained seedlings. Saline submergence in July and September inhibited photosynthesis and decreased the leaf and stem biomass but did not affect the root biomass. The seedling Na+ and K+ ion contents increased with increases in salt concentration; however, in May, the ion contents did not increase significantly. Such seasonal differences in ion content might lead to variations in the extent of leaf damage and growth inhibition after saline submergence in T. distichum seedlings.

Osmolyte accumulation in leaves of Tamarix ramosissima growing under various soil conditions in the Colorado River basin

Tamarixramosissima is a dominant species in desert riparian ecosystems in the western USA. It is a phreatophytic halophyte, with salt glands on the leaves. While osmoregulation is essential for turgor maintenance under high salinity, the dose–response relationship to salinity of various osmolytes in plants with salt glands is still unknown. We profiled crude leaf extracts of T. ramosissima to identify the metabolic compounds that contribute to its salt tolerance. We compared leaf cation, soluble sugar, amino acid, and betaine content among T. ramosissima samples from five points along the Colorado River. The leaf sodium content of T. ramosissima trees increased with increasing soil salinity. Under high salinity conditions, soluble sugar and betaine content did not increase, but amino acids did. The increase in proline accumulation was highly and positively correlated with leaf sodium content. Thus, proline appears to be the essential osmolyte that T. ramosissima accumulates in response to severe salt stress in desert riparian areas of the USA.

Flooding adaptations of wetland trees

A reduction in gas exchange between the air and the rhizosphere causes a major problem for terrestrial plants (Jackson & Drew 1984; Visser & Vosenek 2004). Soil flooding or submergence sets in motion a series of physical, chemical, and biological processes that profoundly influence the quality of soil as a medium for plant growth (Ponnam peruma 1984). In well-drained soils, the stability of the gas composition is maintained by rapid gas exchange between the soil and air, despite oxygen consumption, carbon dioxide production, and nitrogen fixation by soil organisms. In contrast, soil flooding or submergence causes oxygen depletion and carbon dioxide accumulation in the rhizosphere and plants (Jackson & Drew 1984; Ponnamperuma 1984; Greenway et al. 2006). These events lead to an energy deficit in plants through the inhibition of aerobic respiration and disturbance of photosynthetic processes. The accumulation of phytotoxic compounds, including reduced forms of iron and manganese, ethanol, lactic acid, acetaldehyde, aliphatic acids, and cyanogenic compounds, is also a major problem for plants (Ponnamperuma 1984). The effects of such compounds on root metabolism cause the inhibition of root growth and development (Jackson & Drew 1984; Ponnamperuma 1984; Armstrong et al. 1996; Armstrong & Armstrong 1999; Pezeshki 2001; Greenway et al. 2006). Thus, vegetation in the peripheral zone of lakes and swamps typically consists of flood-tolerant species that have specific mechanisms to tolerate excessive water.