Data from: Effect of plant root symbionts on performance of native woody species in competition with an invasive grass in multispecies microcosms

The majority of terrestrial plants form mutualistic associations with arbuscular mycorrhizal fungi (AMF) and rhizobia (i.e. nitrogen fixing bacteria). Understanding these associations has important implications for ecological theory and for restoration practice. Here we tested whether the presence of AMF and rhizobia influence the performance of native woody plants invaded by a non-native grass in experimental microcosms. We planted eight plant species (i.e. Acacia acuminata, A. microbotrya, Eucalyptus loxophleba subsp. loxophleba, E. astringens, Calothamnus quadrifidus, Callistemon phoeniceus, Hakea lissocarpha and H. prostrata) in microcosms of field-conditioned soil with and without addition of AMF and rhizobia in a fully factorial experimental design. After seedling establishment, we seeded half the microcosms with an invasive grass Bromus diandrus. We measured shoot and root biomass of native plants and Bromus, and on roots, the percentage colonization by AMF, number of rhizobia-forming nodules and number of proteaceous root clusters. We found no effect of plant root symbionts or Bromus addition on performance of myrtaceous, and as predicted, proteaceous species as they rely little or not at all on AMF and rhiozbia. Soil treatments with AMF and rhiozbia had a strong positive effect (i.e. larger biomass) on native legumes (A. microbotrya and A. acuminata). However, the beneficial effect of root symbionts on legumes became negative (i.e. lower biomass and less nodules) if Bromus was present, especially for one legume, i.e. A. acuminata, suggesting a disruptive effect of the invader on the mutualism. We also found a stimulating effect of Bromus on root nodule production in A. microbotrya and AMF colonization in A. acuminata which could be indicative of legumes’ increased resource acquisition requirement, i.e. for nitrogen and phosphorus, respectively, in response to the Bromus addition. We have demonstrated the importance of measuring belowground effects because the aboveground effects gave limited indication of the effects occuring belowground.绝大多数陆生植物与丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）和根瘤菌（rhizobia，即固氮细菌）形成互利共生关联。明晰这类共生关系对生态学理论与生态修复实践均具有重要价值。 本研究借助实验微宇宙系统，探究丛枝菌根真菌与根瘤菌的存在是否会影响被外来禾草入侵的本土木本植物的生长表现。我们采用完全因子实验设计，在经野外条件驯化的土壤微宇宙容器中，配置8种供试植物：细叶相思（Acacia acuminata）、微托相思（A. microbotrya）、直杆桉原亚种（Eucalyptus loxophleba subsp. loxophleba）、涩桉（E. astringens）、四叶卡氏木（Calothamnus quadrifidus）、红千层（Callistemon phoeniceus）、薄叶哈克木（Hakea lissocarpha）以及平卧哈克木（H. prostrata），并设置添加与不添加丛枝菌根真菌、根瘤菌的两组处理。在幼苗定植完成后，我们向半数微宇宙容器中播撒入侵禾草二芒雀麦（Bromus diandrus）的种子。 后续我们测定了本土植物与二芒雀麦的地上、地下生物量，同时检测了植物根系的丛枝菌根真菌侵染率、根瘤菌根瘤数量以及簇状根（proteaceous root clusters）数量。 研究发现，植物根系共生体与二芒雀麦的添加对桃金娘科植物的生长表现无显著影响，这与预期相符——山龙眼科植物几乎完全或完全不依赖丛枝菌根真菌与根瘤菌。施加丛枝菌根真菌与根瘤菌的土壤处理，对本土豆科植物（微托相思与细叶相思）具有显著的正向增益效果（即生物量更高）。然而，当二芒雀麦存在时，根系共生体对豆科植物的有益作用会转为负面（即生物量更低、根瘤数量更少），尤以细叶相思最为显著，这表明入侵植物会对这类互利共生关系产生干扰破坏作用。 我们还观测到，二芒雀麦的存在会促进微托相思的根瘤生成以及细叶相思的丛枝菌根真菌侵染，这或许暗示豆科植物在应对二芒雀麦入侵时，对氮与磷的资源获取需求分别有所提升。本研究证实了测定地下生态效应的重要性——仅通过观测地上效应，难以充分反映地下发生的实际生态影响。