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Understanding the growth adaptive strategies of Amorpha fruticosa in response to the changes of saline soil environment under different mulch types (plastic mulch [PM]; sand mulch [SM]; rice straw mulch [RSM]; and control with non-mulching [CK]) is very important, as this determines afforestation success in a moderately saline soil. The species' soil microenvironments, fine root traits, and biomass allocation patterns were investigated in 2016 and 2017. Compared to CK, electrical conductivity of saturated paste extracts (EC e) reduced significantly under the mulching treatments especially under PM. Both PM and SM effectively increased soil temperature (T soil) and available nitrogen (AN), but reduced soil organic carbon (SOC) in 2016; while RSM increased soil nutrients, but reduced T soil. The A. fruticosa under RSM (following PM and SM) invested more biomass, to shoots relative to roots, to coarse roots relative to fine roots, and to stems and leaves at the expense of coarse roots and fine roots from 2016 to 2017, as its saline soil environment especially the low T soil improved. In both years, the fine roots of A. fruticosa under PM employed exploitation potential or 'extensive strategy' (fine root mass density; fine root length density) more successfully at the 0-40 cm, while the fine roots under CK used higher exploitation efficiency or 'intensive strategy' (specific root length; and specific root area). The indicators of intensive strategy at the 40-60 cm were higher under PM than SM and RSM. Therefore, PM will better help A. fruticosa adapt to the harsh soil environment during afforestation in a moderately saline wasteland.

A. fruticosa (Amorpha fruticosa L.) is widely used for revegetation in semiarid lands that undergo secondary salinization. Understanding A. fruticosa plants response to soil water and salt stress is essential for water irrigation management and proper revegetation practices. In this study, we measured sap flow, stomatal conductance, meteorological and soil characteristics in an A. fruticosa community that recently experienced secondary salinization in northwestern China. Results of our study showed that daytime and nocturnal sap flows averaged 804.37 g•cm −2 •day −1 and 46.06 g•cm −2 •day −1 , respectively, during the growing season. Within individual days, the highest sap flow appeared around noon local time and followed a similar pattern of photosynthetically active radiation (PAR). Despite the significant effect of meteorological factors on the characteristics of sap flow, our study highlighted that the sap flow of A. fruticosa is strongly regulated by the availability of soil relative extractable water (REW). The daytime sap flow, which is predominant compared to nocturnal sap flow, was strongly affected by PAR, air temperature and vapor-pressure deficit. With water stress in the top 40 cm of the soil (REW 0-40 cm < 0.4), daytime sap flow displayed a strong relationship with soil water content (SWC) (positive) and soil electrical conductivity (EC) (negative) in the relatively shallow soil profile (up to 40 cm). For the nocturnal sap flow, our results suggest that in the absence of soil water stress (REW 0-40 cm > 0.4), the nocturnal sap flow is mainly used to replenish the stem water content and sustain nocturnal transpiration. Under soil water stress, nocturnal sap flow is mainly used to replenish stem water content. The results of our study indicate that it is necessary to shorten the irrigation cycle during the primary growing period (May-July) of A. fruticosa. Moreover, in the absence of soil water stress (REW 0-40 cm > 0.4), A. fruticosa can survive well in an saline environment with soil EC < 5 mS•cm −1. Secondary salinization is the presence of high salts in soil, which has occurred widely in the semi-arid regions of northwestern China due to the poor irrigation management 1. To manage both problems of secondary salinization and land degradation, a series of ecological revegetation projects have been implemented in this region in the past few decades. The shrub Amorpha fruticosa L. (A. fruticosa) is an important species for the revegetation projects because of its drought and salt tolerance 2. Understanding plant responses to water and salt stress is essential for water irrigation management and proper revegetation practices 3. However, information about the water use characteristics of A. fruticosa remains limited. The responses of plants to water and salt stress can be evaluated by sap flow, as this is the mechanism of water movement in soil-plant-atmosphere continuum 4. For many trees and shrubs, daytime sap flow is the most important part of sap flow, but nocturnal sap flow may account for up to 4-...