Leaf anatomical structure of dominant shrubs and their influencing factors across habitats in hyper-arid region.

We analyzed the drought adaptation mechanism of shrub species in three typical habitats (oasis, transition zone, and desert) of the extremely arid area in the lower reaches of the Heihe River, with 15 species as the objects. Using paraffin sectioning technology combined with microscopic observation, we measured 14 anatomical traits, including leaf epidermal thickness, total leaf thickness, palisade tissue thickness, spongy tissue thickness, and main vein vascular bundle thickness, etc. The results showed that leaf thickness, palisade tissue thickness, and leaf structure compactness (palisade tissue thickness/total leaf thickness) significantly varied among different habitats, and increased with the aggravation of drought degree. The other anatomical traits showed no differences among the three habitats. The contribution rate of soil nutrient heterogeneity to the variations of anatomical traits reached 44.4% to 85.2%, being significantly higher than that of soil water availability (5.8% to 32.8%) and salinity-alkalinity (8.0% to 33.9%). The collaborative adaptation strategies of leaf anatomical structures were manifested as: thickening leaves and epidermal cells to reduce water transpiration loss, increasing palisade tissue thickness to improve photosynthetic efficiency, decreasing main vein vascular bundle thickness to sacrifice part of water transport efficiency, thereby enhancing salt secretion capacity, and finally forming a multi-dimensional environmental adaptation mechanism. The shrubs in the arid area formed a stable adaptation mechanism through the systematic reconstruction of leaf anatomical structures. Their trait differentiations were mainly driven by soil nutrients such as total nitrogen and total phosphorus.