Methods Samples were collected from normal grassland, moderate degraded grassland and severe degraded grassland, respectively. Plant height, shoot dry mass, and nutrient elements at different leaf positions of reeds were measured.

Important findings The Na⁺ content, total salt content and pH value of soil are important factors that determine soil salinity in the Songnen grassland. The degree of soil salinity was aggravated stepwise from the single dominant reed communities to the reed coexisted with Suaeda salsa communities. Height and shoot dry mass decreased with increased salinity. The profiles of 10 key nutrient elements were measured, namely, K, Na, Ca, Mg, Fe, Cu, Zn, Mn, P, and B. Results from the principal component analysis indicated that all samples were distributed within the 95% confidence interval. The results showed that K and P contents decreased with lowered leaf positions; while Na, Ca, and Mg showed the opposite distribution trends. Fe and Cu contents were less in young leaves than in the other leaves, Mn accumulated in the old leaves. However, a large amount of Zn accumulated in the young leaves. No obvious change in B was observed. Thus, salinity stress produced a small effect on the distribution of nutrients in young leaves, but strongly affected the older leaves. Under salinity stress, old leaves accumulated more Na⁺ to protect the young leaves from ion harm. High accumulation of Ca, Mg, Fe, and Cu in mature and old leaves was more beneficial to maintain and protect the function of photosynthesis. The increased K and P contents in the young leaves could provide the necessary nutrition and improve the salinity resistance of reed. This process contributes to the physiological response strategy of reed under salinity stress.