Effects of salt and water stress on plant biomass and photosynthetic characteristics of Tamarisk (Tamarix chinensis Lour.) seedlings

Abstract

Tamarix chinensis Lour. (Tamarisk) is regarded as a potential shrub that improves the marginal lands, and is conversely considered as an invasive species in many areas. This study conducted controlled experiments to investigate the biomass accumulation, allocation and photosynthetic responses of T. chinensis seedlings to different salt and water conditions. The results showed that T. chinensis seedlings died when soil salt content attained 16 to 20 g kg^-1; total biomass, root biomass, shoot biomass and leaf biomass decreased by 63.3, 56.3, 70.6 and 62.4% respectively, from 0 to 16 g kg^-1 (added NaCl content), and decrease by 37.9, 25.3, 48.4 and 37.9%, respectively, from 60 to 20% field capacity (FC, soil moisture). Water deficit led to earlier peaks of net photosynthetic rate (P_N) during the day. Relative rate of electron transport (ETR) decreased, but optimal quantum yield of photosystem II (F_v/F_m) showed no significant difference (P<0.05) with water deficit (from 60 to 20% FC); soil salt significantly decreased P_N and transpiration rate (E), and also decreased ETR and F_v/F_m when soil moistures was 40 or 20% FC. Increased soil salt content had no significant effect (p>0.05) on biomass allocation of T. chinensis seedlings, while water deficit significantly favoured root biomass accumulation. T. chinensis seedlings were able to maintain high leaf gas exchange rates under 20% FC, but water use efficiency (WUE) decreased and sufficient water supply may increase the ability of T. chinensis to survive in higher soil salinity conditions.

Keywords: Salt cedar, biomass allocation, gas-exchange, fluorescence, photosystem II.