Periodic Flooding Decoupled the Relations of Soil C, N, P, and K Ecological Stoichiometry in a Coastal Shelterbelt Forest of Eastern China

Understanding the variation in soil nutrients found in coastal shelterbelt forests in response to periodic flooding is crucial for restoring the soil quality of flooded stands. In this study, we examined soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK) contents and their ecological stoichiometry, as well as soil organic matter and soil-available N, P, and K contents at three soil depths (0–10, 10–20 and 20–30 cm), in a shelterbelt forest of eastern China that was affected by periodic flooding. Results showed that soil C, N, and P contents all had a clear decreasing trend after being flooded, with significant decreases in SOC, TN and hydrolyzable N of 0–10 cm soil, as well as TP of 10–20 cm soil. Soil K content, however, had minimal changes after flooding across different soil layers. Soil C:N ratio increased significantly in 0–10 cm layer, while soil C:P, C:K, N:P, N:K, and P:K ratios decreased notably in both 0–10 cm and 20–30 cm layers following the flooding. Additionally, periodic flooding partially decoupled the correlations among SOC, TN, TP, TK and their ratios. For example, the connection between TK and N:P reversed into a negative correlation in 10–20 cm soil, while SOC and TK became negatively correlated with TP and P:K in the 20–30 cm layer. Principal component analysis revealed the effects of periodic flooding on soil C, N, P, and K availability, in which the total explained variance was decreased from 94% to 86.6%. Specifically, flooding significantly reduced the SOC and soil TN contents on the first axis, influencing C- and N-related ratios. On the second axis, flooding mainly affected soil TK content, which subsequently influenced the correlation between SOC and TK. Thus, periodic flooding notably affected the soil C, N, P, and K ecological stoichiometries of the coastal forest, but the variation patterns were depth-dependent. The insights gained from these results can contribute to the restoration of soil quality in degraded stands caused by flooding in the coastal shelterbelts regions of Eastern China.