Complex vegetation patterns improve soil nutrients and maintain stoichiometric balance of terrace wall aggregates over long periods of vegetation recovery

Abstract

Steep terrace walls are the basis to guarantee the function of terraces, but due to the lack of vegetation cover, they are often exposed to serious erosion and soil degradation. Soil aggregate carbon, nitrogen, and phosphorus (C–N–P) contents and stoichiometry can provide a common framework for reflecting nutrient status, cycling, and limitation. However, the variability of C–N–P contents and stoichiometry of terrace wall soil aggregates and the path by which they are influenced have received little attention and are still uncertain. Soil samples were collected from terrace walls with four vegetation patterns, namely bare terrace wall (BTW), moss-covered terrace wall (MCTW), moss + grass-covered terrace wall (GCTW), and moss + grass + shrub-covered terrace wall (SCTW), at each vegetation recovery time (2, 5, 10, and 30 years) and at two soil depths (0–5 and 5–20 cm) in subtropical Camellia oleifera plantations. The results showed that the proportion of macroaggregates, the stability of aggregates, and the SOC, TN, C/P ratio, and N/P ratio in most aggregate sizes of terrace walls increased with increasing vegetation pattern complexity and recovery times. Compared to the vegetation patterns, the C–N–P contents and stoichiometry of aggregates were more influenced by vegetation recovery time through soil properties and aggregate size composition, respectively. Terrace walls are limited by soil C and N, but a complex SCTW vegetation pattern can effectively alleviate soil C limitation and improve nutrient content over long periods of vegetation recovery. Importantly, the colonization of mosses should be a priority on the bare terrace wall, allowing a more complex vegetation pattern that is beneficial to improve soil nutrients, maintain elemental balance, and form a more stable ecological environment. The results provide a theoretical basis for the ecological restoration of steep slopes and guarantee the function of terraces.