Early allelopathic input and later nutrient addition mediated by litter decomposition of invasive Solidago canadensis affect native plant and facilitate its invasion

Abstract

Litter decomposition is essential for nutrient and chemical cycling in terrestrial ecosystems. Previous research on in situ litter decomposition has often underestimated its impact on soil nutrient dynamics and allelopathy. To address this gap, we conducted a comprehensive study involving both field and greenhouse experiments to examine the decomposition and allelopathic effects of the invasive Solidago canadensis L. in comparison with the native Phalaris arundinacea L. In the field, a 6-month litter bag experiment using leaf litter from S. canadensis and P. arundinacea was conducted across three community types: invasive, native, and mixed. Seed germination tests were also performed to investigate the allelopathic effects of decomposing litter. In the greenhouse, a pot experiment with lettuce as a bioindicator was performed to examine the allelochemical inputs from litter decomposition over various time intervals (0, 30, 60, 120, and 180 days). Subsequently, a soil-plant feedback experiment was carried out to further evaluate the effects of decomposing litter on soil biochemistry and plant dynamics. The findings of this study revealed that S. canadensis litter decomposed more rapidly and exhibited greater nitrogen (N) remaining mass compared with P. arundinacea in both single and mixed communities. After 180 days, the values for litter mass remaining for S. canadensis and P. arundinacea were 36% and 43%, respectively, when grown separately and were 32% and 44%, respectively, in mixed communities. At the invasive site, the soil ammonia and nitrate for S. canadensis increased gradually, reaching 0.89 and 14.93 mg/kg by day 120, compared with the native site with P. arundinacea. The soil organic carbon for S. canadensis at the invasive site also increased from 10.6 mg/kg on day 0 to 15.82 mg/kg on day 120, showing a higher increase than that at the native site with P. arundinacea. During the initial decomposition stages, all litters released almost all of their allelochemicals. However, at the later stages, litters continued to input nutrients into the soil, but had no significant impact on the soil carbon (C) and N cycling. Notably, litter-mediated plant-soil feedback facilitated the invasion of S. canadensis. In conclusion, this study highlights the significance of litter decomposition as a driver of transforming soil biochemistry, influencing the success of invasive S. canadensis.

Keywords: allelopathy; carbon and nitrogen cycle; invasion success; invasive species; plant-soil-feedback.

Figure 1

Experimental design. (A) The litter decomposition experiment was conducted from October 2018 to April 2019. The experiment was divided into in situ decomposition experiments and greenhouse supplement experiments. Three plant community plots for the in situ decomposition experiments were selected based on the degree of Solidago canadensis invasion. (B) Litter and soil samples were recovered for analysis in months 1, 2, 3, 4, and 6. At the same time, the allelopathic effect of the recovered litter extract was examined. In order to investigate the metabolic dynamics of litter allelochemicals entering the soil, litter decomposition was also carried out in the greenhouse, and litter was taken out at months 1, 2, 3, 4, and 6; lettuce was grown using the soil. In addition, after decomposing the litter in the greenhouse for 6 months, Solidago canadensis (Sc), Phalaris arundinacea (Pa), Solidago decurrens (Sd), and Pterocypsela laciniata (Pl) were planted to assess the soil feedback of the decomposition of Sc litter.

Figure 2

Lignin/nitrogen ratio (A), litter mass remaining (B), and carbon/nitrogen ratio of litter (C) (mean ± SE) of Solidago canadensis and Phragmites when each was decomposed alone or in mixed communities. Sc, Solidago canadensis at the invasive site; Pa, Phalaris arundinacea at the native site; MSc, S. canadensis in the mixed community at the co-exit site; MPa, P. arundinacea in the mixed community at the co-exit site.

Figure 3

Total phenol (A), total flavonoids (B), carbon loss (C), nitrogen loss (D), and indices of allelopathic effects (RIs) (E), (mean ± SE) of litter when each was decomposed alone or in mixed communities. Sc, S. canadensis at the invasive site; Pa, P. arundinacea at the native site; MSc, S. canadensis in mixed community at co-exit site; MPa, P. arundinacea in mixed community at co-exit site.

Figure 4

Linear fitting of ammonia nitrogen (A), nitrate nitrogen (B), soil inorganic nitrogen (C), and total organic carbon (D) (mean ± SE) of soil when litter was decomposed alone or in mixed communities. Sc, Solidago canadensis at the invasive site; Pa, Phalaris arundinacea at the native site; MSc, S. canadensis in the mixed community at the co-exit site; MPa, P. arundinacea in the mixed community at the co-exit site.

Figure 5

Plant height (A), plant biomass (B), root-to-shoot ratio (C), and plant–soil feedback (PSF) index plant biomass (D) (mean ± SE) of Solidago canadensis (Sc), Phalaris arundinacea (Pa), Solidago decurrens (Sd), and Pterocypsela laciniata (Pl) when grown in different feedback soils.

Figure 6

Result of redundancy analysis (RDA) (A) based on allelopathy, litter loss, soil nutrition, and impact factors (Cellulose, Lignin, Lignin/cellulose, Lignin/N, Quality loss, Total phenol, and Total flavon). Redundancy analysis (RDA) (B) based on litter decomposition days and plant communities. C/N is the litter carbon to nitrogen ratio, NH₄ ⁺–N is Ammonium nitrogen, NO₃ ^-–N is Nitrate, IN is Inorganic nitrogen, POA is Polyphenol oxidase, CA is Catalase, UA is Urease, SA is Sucrase, RL is Root Length, H is Plant height, LL is Leaf length, LW is Leaves wide, LSI is Leaf index, FBM is Fresh weight of seedlings, DBM is Dry weight of seedlings, MC is Water content, GFe is Germination rate, GPo is Germination potential, GI is Germination index, GVI is Germination vitality index, GRI is Germination speed index. Data were grouped according to the decomposition time (0 months, 2 months after the initial decomposition, and late decomposition).