Abstract
Background Soil moisture is a key factor limiting vegetation growth on the Loess Plateau, and it further influences the effectiveness of regional ecological restoration by regulating the uptake of soil elements by plants. Methods This study investigated the coupling relationships between soil moisture and macronutrients (N, P, K, Ca, Mg), micronutrients (Fe, Cu, Mn, Zn, Ni), and non-essential elements (Cr, Pb, Cd, Al, Na) in soils and needles across Pinus tabulaeformis forests of different ages (8, 10, 12, and 16 years) in rocky mountain area of Loess Plateau. Results The results indicated that (1) soil moisture content in Pinus tabulaeformis forests showed an initial increase followed by a decline with stand development. Additionally, the 0-10cm soil layer generally maintained higher moisture levels (9.52%-13.59%) than the 10-20cm layer (7.84%-12.23%) across all stand ages. (2) Soils of different stand ages contained relatively high proportions of macroelements K (19%-69%), Ca (10%-69%), and Mg (10%-23%), as well as the micronutrient Fe (97%-99%) and non-essential elements Al (68%-89%) and Na (11%-32%). Significant differences in elemental concentrations were observed both among stand ages and between soil layers. The element contents showed no consistent trend with stand age, but their concentrations in the 0-10cm soil layer were generally higher than those in the 10-20cm layer. (3) Needles of Pinus tabulaeformis contained substantial amounts of macronutrients N (32%-43%), P (4%-32%), K (11%-26%), and Ca (6%-34%), as well as micronutrients such as Fe (76%-90%) and Mn (4%-18%), and non-essential elements Na (68%-83%) and Al (16%-31%). Among these, the concentrations of certain elements were more sensitive to stand age variations. For example, the concentrations of P and Ca exhibited unimodal patterns, reaching their peak values at 12 and 16 years, respectively. Mn showed a gradual decline with increasing stand age, while Cd and Na displayed decreasing and increasing trends, respectively. (4) Pinus tabulaeformis exhibited higher bioconcentration factor (BCF) for N (6.09–68.02) and P (1.46–21.21) in soil, followed by Cu (0.15–0.37), Zn (0.34–0.65), Ni (0.29–0.48) and Cr (0.29–0.68), whereas the uptake of K, Ca, Mg, Fe, Mn, Pb, Cd, Al, and Na was relatively weak. Among them, Cu, Zn, Ni, and Cr can impose negative effects on plant growth when present at high concentrations. Additionally, Pinus tabulaeformis showed pronounced enrichment of N, Mg, Mn, and Na under drought conditions, suggesting a certain degree of drought tolerance. In addition, the BCF values of N in the 10-20cm soil layer were generally higher than those in the 0-10cm layer, indicating a stronger uptake and utilization of N from the surface soil. In contrast, Pinus tabulaeformis exhibited a higher absorption capacity for P in the 10-20cm soil layer. Conclusions Soil moisture exerts a substantial influence on the elemental accumulation processes of Pinus tabulaeformis forests.Therefore, the proper regulation of soil moisture and elemental levels is essential for maintaining the health and long-term stability of Pinus tabulaeformis forest ecosystems.
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