Stoichiometric characteristics of medium‐ and micro‐elements (Ca, Mg, Fe, and Mn) in soil aggregates as affected by stand age in Chinese fir plantations

In order to understand the fertility of soil comprehensively in Chinese fir plantations, the stoichiometric characteristics of soil nutrient elements should be paid more attention to. Despite the broad investigation of the stoichiometry regarding soil C, N, P, and K, the stoichiometry regarding soil Ca, Mg, Fe, and Mn remains unclear. Therefore, this research aimed at exploring how the medium- and micro-element (Ca2+, Mg2+, Fe2+, and Mn2+) contents, stocks, and their stoichiometric ratios (Ca2+/Mg2+ and Fe2+/Mn2+) in soil aggregates varied with Chinese fir-planting age (3, 9, 17, and 26 years) in the soil profile (0–40 cm). Our results showed that the stand age affected the stoichiometric characteristics of soil medium- and micro-elements in Chinese fir plantations, but such effects at the soil depth of 0–30 cm were more obvious compared with those at the 30–40 cm. At the soil depth of 0–30 cm, soil Fe2+ and Mn2+ were gradually accumulated over time, whereas soil Ca2+ and Mg2+ were susceptible to leaching and fir up taking. In the process of Chinese fir planting, decreasing soil Ca2+ and Mg2+, especially the Ca2+ (as demonstrated by decreasing soil Ca2+/Mg2+ ratio), could cause soil acidification. And then, soil acidification could lead to more Fe2+ and Mn2+ released by accelerated mineral collapse, especially the Fe2+ (as demonstrated by increasing soil Fe2+/Mn2+ ratio). Overall, the present research advances knowledge of soil nutrient dynamics in Chinese fir plantations and provides supplementary information for the ecological stoichiometry of soil in the terrestrial ecosystem elsewhere in the world.