Growth dynamics of Tamarix chinensis plantations in heavy-saline coastal lands and related ecological effects

Tamarix chinensis, a pioneering native salt-tolerant plant in abandoned coastal saline lands, has high potential as eco-engineering plant species for re-vegetation and soil quality improvement. However, field experiments on the effectiveness of T. chinensis in re-restoration of saline lands along the coastal areas of China have been largely lacking. T. chinensis was planted in 2005, 2007 and 2009 to assess the effectiveness of plants on vegetation and saline soil restoration in this study. The individual biomass, sequenced carbon amount, herb species diversity and soil characteristics of T. chinensis plantations with different planting years and of adjacent abandoned lands without T. chinensis were investigated. The results showed that T. chinensis grew well in the research area and with increasing individual biomass during the experimentation period. T. chinensis plantations produced significant ecological benefits which increased plot vegetation carbon density from 4.78 t(C)·hm^-2 in 3-year plots to 5.56 t(C)·hm^-2 in 5-year plots and then to 6.89 t(C)·hm^-2 in 7-year plots. On the average, there was only 0.98 t(C)·hm^-2 in abandoned lands without T. chinensis. Significant soil quality improvement was indicated by lower saltiness and higher organic matter and available N and K in T. chinensis plantation lands. Salt content in the 0 10 cm soil layer of abandoned lands was 10.53 g·kg^-1. It was 3.35 g·kg^-1 in the 3-year plots, 1.86 g·kg^-1 in the 5-year plots and 5.54 g·kg^-1 in the 7-year plots with T. chinensis. Compare with abandoned lands, soil available K in the 0 5 cm and 5 15 cm soil layer in the 7-year plots respectively increased by 65.59% and 28.90%. In addition, T. chinensis played a significant "eco-engineering" role in terms of increasing volume and species of grass during T. chinensis plant development. Whereas only 8 grass species existed in the abandoned lands without T. chinensis, a total of 15 grass species existed in the 7-year plot with T. chinensis plantation. However, other important salt-tolerant species decreased in T. chinensis plots. Colon plants like Aeluropus sinensis and Ixeris polycephala became more dominant than seed plants such as Suaeda salsa after planting T. chinensis. This suggested that T. chinensis plant progressively alleviated salt stress in the coastal environments. The study demonstrated via field experiments that T. chinensis was effective in vegetation regeneration, soil enhancement and carbon sequestration in saline lands.