Abstract
The riparian zone can affect the degradation of foliar cellulose and lignin by changing the hydrological gradient of the foliage decomposition environment. However, their degradation dynamics during the process of foliage decomposition remain unclear in mixed plantation forests in a riparian zone. Herein, we explored degradation of cellulose and lignin for two dominant riparian species, bald cypress [Taxodium distichum (L.) Rich.] and Chinese willow (Salix matsudana Koidz.), and a combined treatment with equal proportions of foliar mass of these species, involving three water treatments [no submergence (CK), shallow submergence (SS), and deep submergence (DS)] in a riparian zone of the Three Gorges Dam Reservoir (TGDR), China. Throughout an entire year’s incubation, the degradation of cellulose and lignin was 55.57–97.76% and 79.87–93.82%, respectively. In the early stage of decomposition (i.e., the first 30 days), cellulose and lignin were rapidly degraded, and the mass loss of cellulose and lignin in water environments (SS and DS) was greater than that in a non-flooded environment (CK) regardless of the foliage type. The degradation of cellulose and lignin was mainly related to the quality of the leaf litter (as indicated by the concentrations of cellulose and lignin, and the contents of C, N, and P), decomposition period, and local environmental factors (temperature, water gradients, and dissolved oxygen). Our results will provide a clear insight into the material cycling process in a riparian zone of the TGDR and similar ecosystems in other regions.
Highlights
Riparian zones serve as crucial domains in watershed ecosystems, since they form transitional zones for the transfer of nutrients and the flow of energy between terrestrial and aquatic ecosystems (González et al, 2017; Zhang et al, 2020)
Water treatments significantly promoted the decomposition of various types of samples; approximately 79–90% of their initial mass was lost after one-year of decomposition in shallow submergence (SS) and deep submergence (DS) environments (Figure 1)
Cellulose and lignin degraded rapidly in the early phrase of decomposition (Figure 4), while during the entire decomposition period, the degradation rates of cellulose and lignin were always greater under SS and DS than CK treatment (Table 4), which indicated that this type of degradation occurs much earlier and at high rates in a riparian ecosystem as compared with previous findings in terrestrial ecosystems (Thevenot et al, 2010; Berg and McClaugherty, 2014; Yue et al, 2016)
Summary
Riparian zones serve as crucial domains in watershed ecosystems, since they form transitional zones for the transfer of nutrients and the flow of energy between terrestrial and aquatic ecosystems (González et al, 2017; Zhang et al, 2020). Few data are available on the dynamics of the relatively rapid decomposition of cellulose and lignin in leaf litter that occurs in riparian zones This prevents us from having a more-in-depth understanding of the changes in foliar cellulose and lignin degradation, as well as of the nutrient transportation and energy flow in riparian ecosystems. After completion of the Three Gorges Dam Reservoir (TGDR) in China, a water-level fluctuation zone covering an area of 349 km was created with an annual periodic water level change (Yuan et al, 2013) Such a dynamic hydrological regime in the TGDR has created a great challenge to understanding the process of nutrient cycling and energy flow associated with decomposition of plants, especially as it is related to the degradation of foliar cellulose and lignin (because of its total volume), in this newly created vast riparian zone. The results of the study will offer theoretical recommendations for the degradation of recalcitrant substances in reforestation tree species in the TGDR riparian zone and other similar regions, as well as the scientific plantation management of planted forests
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