The nutritional status of the young generation of trees growing on a landslide was dependent on the soil properties. In the course of this analysis, we identified the soil properties that had the largest impact on the nutritional status of birch and fir trees growing on a landslide. The first group of properties is related to soil acidification. In places with higher soil pH and lower acidity, higher Ca, Mg, and P was found in birch leaves and fir needles. The importance of pH for the availability and plant absorption of macro and microelements, has been well documented [1
]. The uptake of macro- and microelements reaches the highest level from slightly acidic to neutral pH and decreases in both strong acidic and alkaline pH [2
]. Soils with a strongly acidic pH dominated the landslide. Only at a few points located in the depletion zone of the landslide, a weak acidic pH was found, and the supply of microelements proved to be the best. The formation of places with higher soil pH in the landslide is usually associated with the exposure of deeper, less leached soil horizons with lower acidity [4
]. The C&RT approach confirms the importance of pH in the nitrogen nutrition of the tested species. In the case of birch and fir, low nitrogen concentration in leaves and needles was noted below 4.2 pH. The second group of properties that appear to be important for the nutritional status of the young generation of trees was soil organic matter and biochemical activity in the soil. This is for the reason that, as microorganisms lead to the decomposition of organic matter, carbon dioxide is produced, it equilibrates with soil water and releases hydrogen ions, affecting soil pH. Through this mechanism, microorganisms affect soil enzyme activities and regulate the speed of organic matter decomposition [32
]. Birches and firs were characterized by significantly increased nitrogen supply on landslide sites with greater organic matter content (accumulation zone). The importance of soil organic matter as a source of the basic macroelements, particularly nitrogen, has long been evidenced in the literature [33
]. Furthermore, organic matter stimulates the activity of microorganisms by being a source of energy for microorganisms and a primary source of nitrogen, carbon, and phosphorus. A close relationship between the content of organic carbon in soils and the activity of enzymes participating in the C, N and P cycle, the decomposition of cellulose and amino acids, was demonstrated in the examined landslide. Sample points with higher biochemical activity were characterized by increased nitrogen, which was taken up by plants. The level of nitrogen supply, particularly for birch trees, depended on the amount of nitrate nitrogen contained in the soil. The relationship between enzyme activity involved in the C, N and P transformations and organic matter, has been repeatedly observed [5
]. Moreover, in previous studies on the recovery of soil cover following landslides, organic matter has been identified as a key factor determining the rate of soil recovery [5
]. The accumulation zone, in which material had slipped from higher parts of the landslide, was characterized by increased organic matter and greater presence of tree species with greater nitrogen demands. In addition, greater variety of species and with improved nutritional development, were found in sections of the landslide characterized by high soil organic matter [11
Higher contents of phosphorus were found in young generation trees growing in soil with high pH and simultaneously low levels of organic matter. It should be noted that the phosphorus measured in this study was the total pool of the component, of which only a small part is available for plants [1
]. The quantity of phosphorus available for plants depends on the degree of decomposition of soil organic matter, soil microbiological activity and relations with other ions. For example, while aluminium and iron compounds form insoluble phosphates in a strongly acidic pH, in a strongly alkaline environment, phosphorus assimilability may be reduced by calcium excess [36
]. In the accumulation zone, despite higher levels of total phosphorus and higher biochemical activity that favors the release of phosphorus, a strongly acidic pH and high concentration of aluminium limits its uptake by plants.
During this study, various ecological characteristics of the analyzed species were confirmed. Birch is considered a relatively robust pioneer species with relatively low requirements, only being intolerant to soil phosphorus and nitrogen deficiency [39
]. In our study birch accumulated significant amounts of nitrogen, magnesium, phosphorus and zinc, compared to those accumulated by fir. In depletion zone, birch accumulated twice as much nitrogen and phosphorus as well as three times more magnesium compared to fir. In the accumulation zone, as in the depletion zone, birch accumulated twice as much nitrogen and phosphorus as well as three times more magnesium compared to fir. The literature review determined the quantities of macroelements collected by the species under study [40
]. Fir is a species with a particularly low nitrogen demand (2–5 times lower than species such as pine, spruce, oak and ash). Birch on the other hand, is reported in the literature to provide optimal contents of basic macroelements in leaves, as follows: N 1.9–2.3% dm, P 0.18–0.28% dm, K 0.7–1.6% dm, Mg 0.15–0.25% dm. In the analyzed landslide, birch leaves accumulated P and K in quantities corresponding to the lower limit of the range; magnesium aligned with the range reported in the literature; while nitrogen accumulation exceeded the upper limit of the range determined as the optimum supply of N. The intensive uptake of N and Mg and their return to the soil makes birch trees particularly valuable for accelerating the circulation of these elements, which may be key to soil cover recovery following landslides. This aligns with the findings of previous studies [42
] that confirm that large quantities of K, N, Ca, Mg, and P are leached from birch leaves per unit of leaf area. In previous studies, high biomass of birch growing on the landslide was indicated [14
]. Birch had six times higher biomass compared to fir of the same age. Considering our results with better nitrogen, magnesium and phosphorus supply of birch and higher birch biomass, it can be assumed that this species will have a more beneficial effect on nutrient circulation in the landslide.