Biotic homogenization of wetland nematode communities by exotic Spartina alterniflora in China

Abstract

Introduced species may homogenize biotic communities. Whether this homogenization can erase latitudinal patterns of species diversity and composition has not been well studied. We examined this by comparing nematode and microbial communities in stands of native Phragmites australis and exotic Spartina alterniflora in coastal wetlands across 18°of latitude in China. We found clear latitudinal clines in nematode diversity and functional composition, and in microbial composition, for soils collected from native P. australis. These latitudinal patterns were weak or absent for soils collected from nearby stands of the exotic S. alterniflora. Climatic and edaphic variables varied across latitude in similar ways in both community types. In P. australis there were strong correlations between community structure and environmental variables, whereas in S. alterniflora these correlations were weak. These results suggest that the invasion of S. alterniflora into the Chinese coastal wetlands has caused profound biotic homogenization of soil communities across latitude. We speculate that the variation in P. australis nematode and microbial communities across latitude is primarily driven by geographic variation in plant traits, but that such variation in plant traits is largely lacking for the recently introduced exotic S. alterniflora. These results indicate that widespread exotic species can homogenize nematode communities at large spatial scales.

Contrasting latitudinal clines of nematode diversity in Spartina alterniflora salt marshes between native and introduced ranges

“…In striking contrast, this study, together with our previous work in China (Zhang, Pennings, et al, 2019), found no latitudinal pattern in richness or diversity for nematodes sampled from the salt marshes in China that were dominated by introduced S. alterniflora . As a result, beta diversity increased with geographic distance (latitude) in the United States, but not in China.…”

“…This pattern is also consistent with the general trend of decreased diversity of species overall, and of richness within most taxa, at higher latitudes (Gaston, 2000; Hillebrand, 2004; Mannion et al, 2014). Previous work along the East Coast of China found that soil nematode richness and diversity decreased with increasing latitude within wetland habitats dominated by the native grass Phragmites australis , with nematode richness about twice as high at low (22°) versus high (39°) latitudes (Zhang, Pennings, et al, 2019). Thus, this pattern of decreasing nematode diversity with increasing latitude appears to be consistent for nematode in native plants dominating coastal wetlands as well as for nematodes in terrestrial habitats (Nielsen et al, 2014; Song et al, 2017; Wu et al, 2016).…”

“…Samples from China were collected in June 2015 ( n = 24) and June 2017 ( n = 17). The 2015 data were previously published (Zhang, Pennings, et al, 2019). In both countries, individual sites were at least 1 km apart.…”

“…One of important global change factors is the introduction of species to areas outside their historic geographic ranges (Alba, Fahey, & Flory, 2019; van der Putten, 2012). Species that spread rapidly may not be well adapted to their new geographic ranges or to the species in their new communities (Allen et al, 2017; Zhang, Pennings, Li, & Wu, 2019). One of the consequences may be that the invasive species may not show the same latitudinal clines in traits or species interactions that are often found in native species (Bhattarai et al, 2017; Liu, Strong, Pennings, & Zhang, 2017).…”

“…Also, because plants are one of the major factors affecting nematode communities, introduced species may alter natural patterns of nematode diversity and distribution. In China, the nematode communities associated with native P. australis show a geographic pattern of decreasing genus‐level diversity with increasing latitude; however, the nematode communities associated with introduced S. alterniflora do not show similar patterns, which may be related to the edaphic parameters and plant traits (Zhang, Pennings, et al, 2019). This finding suggests that the introduced S. alterniflora has homogenized the native nematode community across latitude; however, results were not compared with the native range of S. alterniflora .…”