Decomposition of Suaeda salsa and Phragmites australis in the degraded wetland of Shaohai: Species and tissue difference implications on ecosystem restoration

Abstract

Litter decomposition plays a key role in the recovery of wetlands, as it regulates the rate of soil organic matter (SOM) retention, fuels soil biota, and provides critical nutrients for plant growth. In natural plant succession, plant biological processes (especially litter decomposition) and soil chemistry can drive each other; therefore, the relationship between plant and soil can be used to restore the degraded wetlands without any side effect on the ecosystem. However, how litter decomposition influences soil chemistry and wetland restoration across species and tissues is not clear. We conducted a field litterbag study on decomposition of leaves, stems, roots, and fine roots of <i>Suaeda salsa</i> (<i>S. salsa</i>) and <i>Phragmites australis</i> (<i>P. australis</i>) in a degraded wetland of Shaohai in Qingdao near the Jiaozhou Bay, China. Results showed that litter decomposition is species and tissue specific. <i>S. salsa</i> had a higher decay rate and a larger amount of net nitrogen (N) release than <i>P. australis</i>, but the pattern was only limited in leaf litter; in stems and roots, the decomposition pattern was opposite. Leaf litter had a larger decay rate and amount of net N release than other tissues. Litter decay rates are positively related with initial N concentrations under low lignin concentrations (acid-insoluble carbon (C) fractions, “low” is &lt; 35%), confirming the interactive effect of lignin and N concentrations on litter decay rates. Litter N release pattern is controlled by the decomposition of N-rich C fractions. After 202 days of decomposition, <i>S. salsa</i> (especially stems and roots) contributed less SOM and N than <i>P. australis</i>, but <i>S. salsa</i> (especially leaves) released more N than <i>P. australis</i>, suggesting that <i>S. salsa</i> (especially its leaf) had an advantage to supply short-term N, while <i>P. australis</i> had an advantage to supply long-term N. Therefore, litter decomposition of <i>S. salsa</i> can be suggested for restoring degraded coastal wetlands because it can supply both short-term nutrients and long-term nutrients for new species settlement. Our study gave a further understanding of litter decomposition and suggested litter decomposition as the criterion to select plant species for the restoration of degraded wetlands, but long-term study should be continued to test the conclusion.