Field experiments were conducted to evaluate the effects of wheat straw return methods, which included the use of surface straw mulch and a buried straw layer, on soil water content, electrical conductivity (EC), and sodium adsorption ratio (SAR) of saline sodic soils in an effort to identify useful ways for reducing soil salt accumulation and enhancing soil water content. The results showed that the straw return treatments were effective for inhibiting salt accumulation and soil water loss, resulting in a reduction of EC and SAR but an enhancement of soil water content. After a year-long experiment, compared with the treatment with no straw return, the straw burial and straw mulching treatments decreased the EC by 10.5% and 3.5%, reduced the SAR by 7.4% and 21.5%, and increased the soil water by 0.9% and 4.4%, respectively. Furthermore, the combined application of straw layer burial and surface straw return had a more significant effect than the individual treatments; the positive effect of straw return occurred mainly focused in the topsoil (0–40 cm) and decreased with increasing soil depth. Our results allowed us to conclude that burial of the straw layer was necessary to enhance the effects of surface mulch, and the combination of surface mulch (3.0 t ha−1 of wheat straw) and straw layer burial (6.0 t ha−1 of wheat straw) proved to be a better straw return method than the others.

Background Predicting relationships between plant functional traits and environmental effects in their habitats is a central issue in terms of classic ecological theories. Yet, only weak correlation with functional trait composition of local plant communities may occur, implying that some essential information might be ignored. In this study, to address this uncertainty, the objective of the study is to test whether and how the consistency of trait relationships occurs by analyzing broad variation in eight traits related to leaf morphological structure, nutrition status and physiological activity, within a large number of plant species in two distinctive but comparable harsh habitats (high-cold alpine fir forest vs. north-cold boreal coniferous forest). Results The contrasting and/or consistent relationships between leaf functional traits in the two distinctive climate regions were observed. Higher specific leaf area, photosynthetic rate, and photosynthetic nitrogen use efficiency (PNUE) with lower N concentration occurred in north-cold boreal forest rather than in high-cold alpine forest, indicating the acquisitive vs. conservative resource utilizing strategies in both habitats. The principal component analysis illuminated the divergent distributions of herb and xylophyta groups at both sites. Herbs tend to have a resource acquisition strategy, particularly in boreal forest. The structural equation modeling revealed that leaf density had an indirect effect on PNUE, primarily mediated by leaf structure and photosynthesis. Most of the traits were strongly correlated with each other, highlighting the coordination and/or trade-offs. Conclusions We can conclude that the variations in leaf functional traits in north-cold boreal forest were largely distributed in the resource-acquisitive strategy spectrum, a quick investment-return behavior; while those in the high-cold alpine forest tended to be mainly placed at the resource-conservative strategy end. The habitat specificity for the relationships between key functional traits could be a critical determinant of local plant communities. Therefore, elucidating plant economic spectrum derived from variation in major functional traits can provide a fundamental insight into how plants cope with ecological adaptation and evolutionary strategies under environmental changes, particularly in these specific habitats.

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