Abstract:

【Objective】 Salt stress seriously affects yield and fruit quality of fruit crops. Soil salinity is often heterogeneous in saline fields, and within the different root zones of single plant the salinity of the soil solution might vary widely. This paper was aimed to determine the injury extent of grapevine under the non-uniform salt treatment, and to disclose the corresponding mechanism through the determination of Na ⁺ flux and allocation of carbon and nitrogen in grapevine. 【Method】 Saline environment of vine roots was controlled through split-root system and five treatments with different NaCl concentration (mmol·L ^-1) were set: 0/0, 0/50, 50/50, 0/100, and 100/100. Grapevine injury was evaluated via determining content of chlorophyll and malondialdehyde (MDA) as well as the changes of chlorophyll fluorescence parameters. Na ⁺ transport was analyzed by the determination of Na ⁺ content, Na ⁺ flux and electrical conductivity of culture medium around roots. Nitrogen utilization efficiency and distribution rate of carbon and nitrogen were used to detect the changes of carbon and nitrogen in different tissues under different treatments.【Result】The uniform salt treatment of bilateral roots significantly reduced the content of chlorophyll and enhanced the MDA levels in roots and leaves at 15 and 30 days after treatment. In contrast, salt treatment of local roots alleviated the chlorophyll decrease and the MDA accumulation. Additionally, the determination of chlorophyll fluorescence parameters, such as Fv/Fm and ERT, showed the similar results. Therefore, the roots in the non-saline side could alleviate the grapevine injury in comparison to the uniform salt treatments. All of salt treatments increased Na ⁺ content in roots and leaves to varying extents at 15 days after treatment; particularly, the Na ⁺ content of the roots in the non-saline side was also enhanced; additionally, local root zone salinity significantly decreased the Na ⁺ content in leaves, and local treatment of 100 mmol·L ^-1NaCl significantly reduced the Na ⁺ content in saline side roots, compared to the uniform NaCl treatment. The Na ⁺ efflux was observed in non-treated roots, however, the Na ⁺ flux was reversed to influx in the non-saline side roots under non-uniform salt treatment. Additionally, the electrical conductivity of the culture medium around the roots in the non-saline side was significantly enhanced. Therefore, the Na ⁺ absorbed from the salt-treated side could be transported to the non-saline side roots and thereby expelled out of the roots. Nitrogen utilization efficiency was significantly reduced by the uniform salt treatment and the decline was associated with salt treatment concentration. In contrast, the non-uniform salt treatment alleviated the declines in nitrogen utilization efficiency and particularly, which was significantly enhanced in the non-saline side roots under the 0/100 mmol·L ^-1treatment. The uniform salt treatments and particularly 100 mmol·L ^-1NaCl decreased the distribution rate of nitrogen in roots and leaves and increased the values in the two-year-old shoots, favoring the storage of nitrogen. In contrast, the non-saline side roots alleviated the declines of nitrogen distribution rate in roots and leaves. The uniform salt treatment decreased carbon distribution rate in leaves and roots; in contrast, the non-saline side roots not only alleviated the declines of carbon distribution rate in leaves but also elevated carbon distribution rate in roots. It was noteworthy that 50 and 100 mmol·L ^-1 NaCl treatments imparted different effects on carbon distribution in new shoots and two-year-old shoots, i.e., the uniform and non-uniform treatments of 50 mmol·L ^-1 NaCl enhanced carbon distribution in the two-year-old shoots while the treatments of 100 mmol·L ^-1 NaCl produced the contrary results.【Conclusion】Compared with the uniform salt treatment, NaCl treatment of local roots produced the lesser injury for grapevines. Na ⁺ absorbed from the salt-treated side was transported to the non-treated side, expelled them from the roots, and thereby reduced Na ⁺ accumulation in leaves. The non-saline side roots alleviated the declines in carbon and nitrogen distribution rate of leaves and roots.

Key words: grapevine, salt treatment of local roots, injury extent, Na ⁺ flux, allocation of carbon and nitrogen