Plant invasions profoundly impact both natural and managed ecosystems, and removal of the invasive plants addresses only part of the problem of restoring impacted areas. The rehabilitation of diverse communities and their ecosystem functions following removal of invasive plants is an important goal of ecological restoration. Arthropod assemblages and trophic interactions are important indicators of the success of restoration, but have largely been overlooked in saltmarshes. We determined how arthropod assemblages and trophic interactions changed with the invasion of the exotic plant Spartina alterniflora and with the restoration of the native plant Phragmites australis following Spartina removal in a Chinese saltmarsh. We investigated multiple biotic and abiotic variables to gain insight into the factors underlying the changes in arthropod assemblages and trophic structure. We found that although Spartina invasion had changed arthropod diversity, community structure, feeding-guild composition, and the diets of arthropod natural enemies in the saltmarsh, these changes could be reversed by the restoration of native Phragmites vegetation following removal of the invader. The variation in arthropod assemblages and trophic structure were critically associated with four biotic and abiotic variables (aboveground biomass, plant density, leaf N, and soil salinity). Our findings demonstrate the positive effects of controlling invasive plants on biodiversity and nutrient cycling, and provide a foundation for assessing the efficacy of ecological restoration projects in saltmarshes.

Study site and plant communities

We collected this dataset in Dongtan wetlands on Chongming Island (31°27′–31°5l′ N, 121°09′–121°54′ E) in the Yangtze estuary. We sampled replicate transects of five types of plant communities in the Dongtan wetlands: 1) the original reference Phragmites monoculture that had never been affected by Spartina; 2) the Phragmites monoculture that had not yet been invaded by but was being threatened by Spartina (i.e, on periphery of the plant community where Spartina was encroaching with some number of meters); 3) the Phragmites–Spartina mixture in which Spartina was gradually displacing Phragmites; 4) the Spartina monoculture in which Spartina had completely displaced Phragmites; and 5) the restored Phragmites monoculture following Spartina removal.

Arthropod sampling

In each type of plant community, we randomly designated 15 replicate transects along the main creek channel. We used a vacuum suctioning method to collect arthropods on each transect on 22–25 June, 24–27 July, and 23–26 August in 2018. All arthropods were identified to the lowest taxonomic category possible and the number of individuals of each species on transects was counted. We followed several references to identify the arthropod taxa (Xin et al., 1985; Zhong, 1990; Zheng & Gui, 1999; Zhang & Li, 2011; Zhang & Wang, 2017). We also assigned these arthropods to trophic groups and feeding guilds according to Gratton and Denno (2005).

Arthropod natural enemy diets

We used stable isotopes to determine the diets of arthropod natural enemies collected from different types of plant communities. All arthropod and plant samples were dried, ground into powders and then subjected to the analysis using an isotope ratio mass spectrometer (DELTA V Advantage, Thermo, USA).

Environmental variables

We randomly designated five quadrats (0.5 m ´ 0.5 m) along each transect and extracted a soil core in each quadrat on 23–26 August 2018. All soil samples were weighted and then dried. Soil water was estimated from the weight of a soil core before and after drying. Soil pH and salinity were determined using a multi-function tester (S975-uMix SevenExcellence, Mettler-Toledo, Switzerland). Soil C and N were analyzed with an element analyzer (FlashEA1112 Series, Thermo, USA). Soil P was measured by molybdenum-antimony colorimetry using a microplate reader (Synergy 2, BioTek, USA). We counted plant (stem) density in each quadrat. All aboveground plant tissues in each quadrat were then dried and weighed to obtain their aboveground biomass. We measured leaf C, N, and P contents according to the same methods as used for soil samples. For each environmental variable, we used the average value in the five quadrats from one transect to represent the transect replicate.

Reference

    Gratton, C. & Denno R. F. Restoration of arthropod assemblages in a Spartina salt marsh following removal of the invasive plant Phragmites australis. Restoration Ecology 13, 358–372 (2005).

    Xin, J.L., Q.S. Yang, C.Y. Hu. 1985. Insect morphology taxonomy. Shanghai: Fudan University Press.

    Zhang, W.W., and Y.S. Li. 2011. Chinese insects illustrated. Chongqing: Chongqing University Press.

    Zhang, Z.S., and L.Y. Wang. 2017. Chinese spiders illustrated. Chongqing: Chongqing University Press.

    Zheng, L.Y., and H. Gui. 1999. Insect classification. Nanjing: Nanjing Normal University Press.

    Zhong, J.M. 1990. Taxonomy of insect larva. Beijing: Agriculture Press.

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