Aboveground fungal lethal effects of local plants on invasive plant Ageratina adenophora seedlings

We measured the effects of the aboveground and belowground microbes of 25 native plant species and Ageratina adenophora on the germination and survival of invader A. adenophora in this study. We isolated fungi from dead seedlings 7 d after inoculated 0.1 g of plant tissue fragments with 21-day-age seedlings (G21 experiment), and we tested the lethal effects of these strains on A. adenophora seedling survival. Some statistical analyses were performed in R. Thus, we provided two tables and R code files, including data of germination seedling survival.csv, lethal effect of 70 fungi on seedlings.txt, Script20250119. The file of data of germination seedling survival.csv provide the germination time, number of germinated seeds and survival seedling of G0 and G21 inoculation when inoculated aboveground tissue from 26 plant species, and the germination time, number of germinated seeds and survival seedling of G0 inoculation when inoculated soils from 26 plant species. The file of lethal effect of 70 fungi on seedlings.txt provide the seedling mortality of A. adenophora caused by 70 fungal strains.

Methods
To quantify the effects of plant tissue and soil microbes of A. adenophora or different local native plant species on A. adenophora seed germination and seedling survival, we placed 16 surface-sterilized A. adenophora seeds on petri dishes and kept them as controls or inoculated them with 0.1 g of plant tissues or rhizosphere soil of a single species from a single site that were live or sterilized (hereafter referred to as G0 inoculation), resulting in a total of 525 plates (species [26] * soil vs.tissue [2] * sterile vs. unsterilized [2] * replicate [5] + control [5]). All petri dishes were randomly placed in a growth chamber (RXZ-380D, Ningbo Southeast Instrument Co., Ltd., Ningbo, China) and rearranged every week to mitigate potential positional effects. Petri dishes were kept at a temperature of 25/20°C (day/night), a light intensity of 12 000 lux (12h / 12h) and a humidity of 65%. The number of germinated seeds was recorded for the first 14 days then again on the 21st day to calculate germination time (GT) and germination rate (GR). GT was calculated by the formula GT= Σ(Gi×i)/ΣGi (i: number of days between seed sowing (day 0) and seed germination; Gi: number of seeds germinated on day i). GR was calculated as the proportion of seeds germinated by the 21st day. The number of survival seedlings on the 28th day was used to calculate the seedling survival rate (named SSR_G0). Because we observed high seedling mortality with unsterilized tissue inoculation, we performed an additional inoculation on 21-day-old control seedlings to explore resistance of A. adenophora to plant tisses microbes across seedling ontogeny, resulting in a total of 265 plates (species [26] * sterile vs. unsterilized [2] * replicate [5] + control [5]). We used the proportion of seedlings alive 7 days later to calculate SSR (hereafter referred to as SSR_G21).

Furthermore, we tested the effect of 70 fungal strains on A. adenophora seedling survival. Sixteen surface-sterilized A. adenophora seeds were sown in a water agar petri dish. All 21-day-old seedlings in one petri dish were inoculated with one fungal strain by touching 3 mm diameter agar discs with fungal mycelia to the leaves and stems. Five petri dishes were used as five replicates for each strain. Fungi were grown on PDA for 7 days in an incubator at 25°C in the dark before inoculation. Seedlings were regarded as dead when the leaf and stem became brown and rotten. We calculated mortality rate as the proportion of seedlings that died in a dish 14 d after inoculation.