Invasive Plants and Species Richness Impact Litter Decomposition in Riparian Zones

Abstract

Natural ecosystems generally include litter decomposition as part of the natural cycle since the material properties and the environment greatly influence the decomposition rate. The invasion of exotic plants alters the species diversity and growth characteristics of plant communities, but its impact on litter decomposition is unknown in the riparian zone. This study examines how invasive plants affect the early stages of litter decomposition and how species richness impacts them. This experiment involved a random litter mixture of exotic (Alternanthera philoxeroides and Bidens pilosa) and native species in the riparian zone of the Three Gorges Dam Reservoir in China. There were 43 species mixture types, with various species richness ranging from 1 to 6. Litterbags were placed in the hydro-fluctuation zone and terrestrial zone, where they decomposed over the course of 55 days. Invasive plants decompose rapidly compared to native plants (35.71% of the remaining mass of the invasive plant). The invasive plant A. philoxeroides has the potential to accelerate native plant decomposition (0.29 of non-added synergetic effect), but Bidens pilosa cannot. Nonetheless, species richness had little effect on the decomposition rate. These effects are dependent upon differences in chemical functional characteristics among the species. The initial traits of the plants, specifically C, N, and C/N, were significantly and linearly correlated with the loss of mixed litter mass and mixing effect strength (P < 0.01). In addition, submergence decomposition conditions reduce the disturbance of invasive plants and predict decomposition rates based on litter characteristics. Invasive plants can therefore impact the material cycle of an ecosystem. There is a need to examine decomposition time, which may also involve considering other factors.

Keywords: Three Gorges Reservoir; exotic plants; hydro-fluctuation zone; plant traits; species diversity; submergence environment.

Figure 1

Bar charts show individual species' mass remaining litter rates within the hydro-fluctuation zone (S) and the terrestrial zone (CK). The y-axis shows the mean value (%). The vertical whisker represents the standard deviation. Paired tests were used to determine the differences between S and CK. ^*Indicates significant differences at P < 0.05.

Figure 2

The mean mixing effect intensity of litter mixture mass remaining in the hydro-fluctuation zone (A) and terrestrial zone (B). The Ap-group indicates litter mixtures of A. philoxeroides and native species, and the Bp-group represents litter mixtures of B. pilosa and native species. All data are presented as mean ± standard deviation. In the mean mixing effect intensity values, values above 0 indicate synergistic effects, and values below 0 indicate inhibitory effects. Xs, X. sibiricum; Pl, P. lapathifolium; Pa, P. alkekengi; Ha, H. altissima; Cd, C. dactylon; Ds, D. sanguinalis; Ap, A. philoxeroides; Bp, B. pilosa.

Figure 3

The litter remaining mass at different rates for different levels of species richness in the hydro-fluctuation zone (A) and terrestrial zone (B). The Ap-group indicates litter mixtures of A. philoxeroides and native species, and the Bp-group represents litter mixtures of B. pilosa and native species. Data are expressed as mean values.

Figure 4

The mean mixing effect intensity of litter mixture remaining mass on different species richness in the hydro-fluctuation zone (A) and terrestrial zone (B). The Ap-group indicates litter mixtures of A. philoxeroides and native species, and the Bp-group represents litter mixtures of B. pilosa and native species. Data are expressed as mean values. In the mean mixing effect intensity values, values above 0 indicate synergistic effects, and values below 0 indicate inhibitory effects.

Figure 5

The results of the paired t-test show the litter's remaining mass rate at observed and expected values for the hydro-fluctuation zone (A) and terrestrial zone (B). The Ap-group indicates litter mixtures of A. philoxeroides and native species, and the Bp-group represents litter mixtures of B. pilosa and native species. All data are presented as mean ± standard deviation. A paired t-test was used to test for significant differences between observed and expected values. NS, no significant difference; *P < 0.05; ***P < 0.001.

Figure 6

Linear regression relationships (A–F) between litter remaining mass rate and litter community weighted mean traits (CWM). S stands for litter that has been decomposed in the submergence environment, and CK stands for litter that has been decomposed in the terrestrial environment.

Figure 7

Linear regression relationships (A–F) between the mean mixing effect intensity of litter decomposition and community weighted mean traits (CWM) of litter mixture. S stands for litter that has been decomposed in the submergence environment, and CK stands for litter that has been decomposed in the terrestrial environment.

Figure 8

Linear regression relationships between litter remaining mass rate and litter functional dispersion (FDis). S stands for litter that has been decomposed in the submergence environment, and CK stands for litter that has been decomposed in the terrestrial environment.

Figure 9

Linear regression relationships between mean mixing effect intensity of litter decomposition andfunctional dispersion (FDis) of litter mixture. S stands for litter that has been decomposed in the submergence environment, and CK stands for litter that has been decomposed in the terrestrial environment.