Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 3: Ecosystem Effects <strong>of</strong> Invasive Spartina(e.g., mild temperature in summer) (Wang et al. 2008). Likenematodes, <strong>the</strong> relative abundance <strong>of</strong> major trophicfunctional groups <strong>of</strong> macrobenthic invertebrates was alsoaltered when S. mariqueter was replaced by S. alterniflora.Spartina alterniflora communities had a higher proportion <strong>of</strong>suspensivores but a lower proportion <strong>of</strong> herbivores anddetritivores than S. mariqueter communities (Chen et al.2005a).In addition, we compared <strong>the</strong> structure and diversity <strong>of</strong><strong>the</strong> bacterial communities in rhizosphere soils <strong>of</strong> S.alterniflora, P. australis and S. mariqueter throughconstructing 16S ribosomal DNA (rDNA) clone libraries.Our results showed that <strong>the</strong> shift <strong>of</strong> species composition <strong>of</strong>plant communities from native plants to S. alternifloracaused considerable changes in bacterial composition <strong>of</strong>rhizosphere soils in estuarine salt masrhes (Wang et al.2007).The above changes in soil biota caused by S.alterniflora invasions could have great effects on ecosystemprocesses in <strong>the</strong> soils that are associated with <strong>the</strong>seorganisms as decomposers.ARTHROPOD COMMUNITIESPlants serve as both food and habitats for manyarthropods, so subtle shifts in plant community compositionmay lead to considerable changes in <strong>the</strong> arthropodcommunity. In order to understand <strong>the</strong> possible effects <strong>of</strong> S.alterniflora invasions on arthropods, we examined <strong>the</strong>community structure and diets <strong>of</strong> arthropods in an estuarinesalt marsh previously dominated by native P. australis atChongming Dongtan through net sweeping and plantharvesting methods and stable isotope analysis (Wu et al.2009). We found that diversity indices were not significantlydifferent between exotic and native plant communities, but<strong>the</strong> total abundance <strong>of</strong> insects estimated through plantharvesting was found to be lower in S. alternifloramonocultures than that in P. australis monocultures.Community structure <strong>of</strong> insects in S. alternifloramonocultures was dissimilar to that in P. australismonocultures and P. australis–S. alterniflora mixtures.Moreover, stable isotope analysis showed that althoughsome native arthropods (perhaps generalists) shifted <strong>the</strong>irdiets, most native taxa did prefer P. australis to S.alterniflora even in S. alterniflora monocultures. Spartinaalterniflora invasions resulted in reduced abundances <strong>of</strong>some arthropds, and increased <strong>the</strong> dominance <strong>of</strong> o<strong>the</strong>rs thatfed preferentially on S. alterniflora. The experimentalevidence provided showed that invasive plants can change<strong>the</strong> community structure and diets <strong>of</strong> native arthropods,which will eventually alter arthropod food webs, and affect<strong>the</strong> integrity and functioning <strong>of</strong> native ecosystems within anature reserve that has been set aside for conserving <strong>the</strong>native biodiversity and maintaining <strong>the</strong> ecosystem integrity.BIRD COMMUNITIESThe conversion <strong>of</strong> mudflats to meadows resulting fromS. alterniflora invasions had significant impact on birds <strong>of</strong>Charadriidae and Scolopacidae, which might have beenattributable to <strong>the</strong> reduction in food resources and physicalalterations <strong>of</strong> habitats for birds (Li et al. 2009). Never<strong>the</strong>less,S. alterniflora may also provide habitat for certain landbirds.Recent bird surveys indicated that <strong>the</strong> Japanese marshwarbler Megalurus pryeri, a newly-recorded species in <strong>the</strong>Yangtze River estuary, nested exclusively in S. alternifloracommunities (Gan et al. 2006). This might be because <strong>the</strong>dense vegetation benefits <strong>the</strong> construction <strong>of</strong> nests. Inaddition, M. pryeri largely fed on <strong>the</strong> invertebrates in S.alterniflora communities (Gan 2009). It is likely that <strong>the</strong>rapid population increase <strong>of</strong> <strong>the</strong> Japanese marsh warbler wasrelated to <strong>the</strong> rapid spread <strong>of</strong> S. alterniflora in <strong>the</strong> YangtzeRiver estuary. However, <strong>the</strong> effects <strong>of</strong> S. alterniflora onlocal landbird communities still remain largely unexplored,and fur<strong>the</strong>r studies are needed.CARBON AND NITROGEN CYCLESS. alterniflora had great productive potential in <strong>the</strong>marshlands in <strong>the</strong> Yangtze River estuary. The results weobtained in Jiuduansha marshlands showed that exotic S.alterniflora had much greater primary productivity thannatives S. mariqueter and P. australis (Liao et al. 2007)because <strong>the</strong> exotic had greater leaf area index (LAI) and alonger photosyn<strong>the</strong>tic season than <strong>the</strong> native species (Jianget al. 2009). At <strong>the</strong> same time, decomposition rates <strong>of</strong> S.alterniflora litter, particularly <strong>the</strong> belowground litter, werelower than those <strong>of</strong> S. mariqueter and P. australis litter dueto <strong>the</strong> lower litter quality <strong>of</strong> S. alterniflora (Liao et al. 2008).Therefore, larger stocks <strong>of</strong> carbon and nitrogen were foundin <strong>the</strong> ecosystems dominated by S. alterniflora than in thosedominated by S. mariqueter and P. australis. Our fur<strong>the</strong>ranalysis <strong>of</strong> stable carbon isotopes also confirmed that <strong>the</strong>replacement <strong>of</strong> S. mariqueter by S. alterniflora significantlyincreased soil organic carbon and total soil nitrogen (Chenget al. 2006), especially soil labile carbon, recalcitrant carbon,and soil recalcitrant nitrogen contents in <strong>the</strong> upper soil layers(0–60 cm) (Cheng et al. 2008). The ecosystem carbon andnitrogen cycles altered by S. alterniflora invasions might be<strong>of</strong> limited significance on a large scale in relation to <strong>the</strong>range <strong>of</strong> S. alterniflora in <strong>the</strong> Yangtze River estuary, butmight have potentially far-reaching impact on <strong>the</strong> adjacentecosystems. In fact, S. alterniflora functioned as <strong>the</strong> primaryenergy source for certain nektons in <strong>the</strong> marshlands in <strong>the</strong>Yangtze River estuary (Quan et al. 2007). Potentialcascading effects on estuarine food webs <strong>of</strong> increasedecosystem productivity due to S. alterniflora invasions needsfur<strong>the</strong>r exploration.- 149 -