Influence of salt stress on propagation, growth, and nutrient uptake of typical aquatic plant species

Authors: CHEN, XIN - Chinese Academy Of Sciences; CHENG, XIANWEI - Chinese Academy Of Sciences; ZHU, HUI - Chinese Academy Of Sciences; Banuelos, Gary; SHUTES, BRIAN - Chinese Academy Of Sciences; WU, HAITO - Chinese Academy Of Sciences

Submitted to: Nordic Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2019
Publication Date: 11/1/2019
Citation: Chen, X., Cheng, X., Zhu, H., Banuelos, G.S., Shutes, B., Wu, H. 2019. Influence of salt stress on propagation, growth, and nutrient uptake of typical aquatic plant species. Nordic Journal of Botany. 37(12). https://doi.org/10.1111/njb.02411.
DOI: https://doi.org/10.1111/njb.02411

Interpretive Summary: Wetlands in arid/semi-arid regions sometimes experience higher salinity periods and seasonal fluctuation of salinity levels due to both anthropogenic activities (e.g., land use change, water demand for irrigated agriculture) and natural causes (e.g., rising temperatures, decreases in precipitation, and the existence of naturally occurring salts in soils). Excessive salinity in wetland waters can threaten reproduction and growth of many wetland plant species, and thus decrease efficiency of a wetland treatment system to remove pollutants from saline wastewaters. To address potential threats to the sustainability of wetland treatment systems, we evaluated growth responses, asexual reproduction (e.g., tiller and cutting), nutrient absorption, and salt tolerance of seven aquatic plant species exposed to various levels of salinity in simulated wetland treatment systems. The experiments showed that salt tolerance among the seven species was correlated with the Na+ concentrations and Na+/K+ ratios in the plant tissues. As a salt-tolerance strategy, tolerant plant species controlled Na+ transport from root to shoot and regulated the Na+/K+ ratios during asexual reproduction and different plant growth stages. The results identified plant species - A. donax and A. philoxeroides - as the most tolerant aquatic species due to the ability to maintain better asexual reproduction and growth capacities under high salt input. The exhibited salt tolerance demonstrates that these two aquatic species will be effective in removing excessive nutrients, i.e., nitrogen, phosphorus, from a saline wetland environment. Including these two species as primary plant species in a wetland treatment system is key for restoring and sustaining degraded wetlands used for cleaning saline wastewater of different pollutants.

Technical Abstract: Excessive salinity can reduce the ability of plant species to survive in a wetland treatment systems to decontaminate saline wastewater of excessive pollutants. In wetlands, aquatic plants can absorb excessive nutrients and pollutants in wastewater and thereby play a vital role in the natural wastewater purification process created by wetlands. With increasing saline water, wetlands require salt tolerant plant species that can complete life cycles in hypersaline environments. Salt stress affects propagation and growth of plants primarily by means of osmotic and ionic impacts, which can be characterized by physiological drought and ionic toxicity. In aquatic plants, salt tolerance is mainly determined by controlled uptake and compartmentalization of ions like Na+, K+, and Cl-, and, consequently, the effects of salinity on reproduction and growth will vary among plant species. To assess salt tolerance of aquatic plant species, seven species were grown under varied levels of salinity and respective responses related to asexual propagation, growth, and nutrient absorption were evaluated. The salinity treatments consisted of five salinity levels with an electrical conductivity (EC) of 0.3 (referred to as control), 5, 10, 15, and 20 dS/m. The salt solution was prepared with only NaCl and deionized water, and no other salt ions were introduced in the simulated wetland beds. For each simulated wetland bed, there was a 10-cm depth of sediment and 10-cm depth of designated salt solution above the surface of sediment. Three plants (about two years old) were transplanted of each respective species with similar size and height into each simulated wetland at a planting density of 45 plants/m2. Results of this study demonstrated that A. donax and A. philoxeroides were the most salt-tolerant aquatic species and maintained better asexual reproduction and growth capacities when grown at a high salt level. Salt tolerance was correlated with the Na+ concentrations and Na+/K+ ratios in the plant tissue. Plants controlled the transport of Na+ from root to shoot and regulated Na+/K+ ratios during asexual reproduction and plant growth stages. In the other aquatic plant species, absorption of excessive nutrients (nitrogen and phosphorus) from wastewater was inhibited by high salinity treatment and stimulated under lower salinity levels. The results clearly showed that A. donax and A. philoxeroides were the most salt-tolerant and should be considered as potential aquatic plant species for use in the restoration of degraded saline wetlands. A long-term and large-scale field wetland experiment (e.g., in a natural saline wetland) is recommended to evaluate both salt tolerance and sustained ability of A. Donax and A. philoxeroides to remove pollutants from saline wastewater under field wetland conditions.