DOI: 10.5061/dryad.dfn2z35f1
title: Different diversity mechanisms underlying drought resistance in native and invaded communities

description: The decline of global biodiversity and the increasing spread of invasive
 alien plants raise critical questions about how native species diversity
 and biological invasions interact to influence community resistance to
 disturbance, particularly global climate change.  To explore the
 effects of native species diversity and biological invasions on community
 resistance to drought, we established experimental plant communities with
 varying species richness levels (1, 2, 4, 8, and 16 species), introduced
 the invasive species Symphyotrichum subulatum into half of these
 communities, and then subjected all communities to no, moderate, or
 intense drought.  In both native and invaded communities,
 community resistance to drought was negatively correlated with biomass of
 the communities without drought, regardless of species richness.
 Additionally, lower biomass of the communities without drought was
 associated with smaller drought-induced increases in root:shoot ratio,
 which in turn conferred higher community drought resistance. However, the
 mechanisms underlying drought resistance differed between native and
 invaded communities: changes in biomass triggered by complementarity
 effects positively determined drought resistance in native communities,
 but those triggered by selection effects governed drought resistance in
 invaded communities.  Synthesis. These findings reveal distinct
 mechanisms governing drought resistance in native communities and those
 invaded by S. subulatum, offering valuable insights for managing the
 invasion of this species in the context of global climate change.
description: We constructed experimental plant communities with five levels of
 species richness (1, 2, 4, 8, and 16 species) on the campus of Taizhou
 University, Zhejiang Province, China (28°39’ N, 121°23’ E). The fieldwork
 did not need permission. We used a pool of 16 native plant species
 commonly found in areas of mixed brush and grassland in nearby valleys and
 hillsides in Taizhou. We established a total of 46 communities with
 different species compositions: one monoculture for each of the 16
 species, ten two-species mixtures, ten four-species mixtures, nine
 eight-species mixtures, and one 16-species mixture. Each mixture contained
 a unique combination of species randomly selected from the species pool.
 Monocultures and two-, four- and eight-species mixtures were replicated
 six times. The 16-species mixture was replicated 30 times, resulting in
 300 experimental communities. These replicates were randomly assigned to
 six treatment combinations consisting of three drought levels (no,
 moderate, and intense drought) and two invasion treatments (with or
 without the invasive species), as described below. Each of the six
 treatment combinations contained five replicates of the 16-species mixture
 and one replicate of the other 45 different communities.
 Experimental plant communities were established in plastic
 containers (72 × 64 × 42 cm) with five drainage holes at the bottom. Each
 container was filled with a 27 cm layer of soil from hillsides in Taizhou
 and then topped with a 10 cm layer of a 1:1 mixture of soil and
 nutrient-rich potting compost (Table S3). A target density of 32 seedlings
 per container was achieved through sowing (800 seeds per container) and
 subsequent thinning, retaining only vigorous seedlings of each species.
 Each species within a mixture was represented by an equal number of
 seedlings (e.g., eight seedlings per species in four-species mixtures).
 The 32 seedlings were evenly distributed within the container, avoiding
 adjacency of conspecific seedlings where possible. Additionally, seedlings
 that emerged after thinning were removed.
 <strong>Treatments</strong> All
 containers were randomly placed under a rain shelter at Taizhou
 University. Three drought treatments (no, moderate and intense drought)
 were implemented using automatic drip irrigation systems, controlling
 irrigation duration to achieve target soil moisture levels. Gravimetric
 soil water content was maintained at 15.5%-19.8% for the treatment with no
 drought (similar to ambient conditions in the surrounding hills),
 12.4%-15.4% for moderate drought, and 10.0%-12.6% for intense drought.
 Drought treatments began on March 12, 2015, 16 months after sowing the
 seeds of the native plant species. In December 2015,
 half of the experimental communities (150) were each sown with 50 seeds of
 the invasive annual herb Symphyotrichum subulatum, evenly distributed
 within the container. Four monoculture replicates of S. subulatum (50
 seeds per replicate) were also established under each drought treatment.
 Thus, our study simulated the invasion of the alien annual, which started
 from seeds and covered the entire growth cycle (seeds, seedlings, and
 adult plants). The density of the seeds of S. subulatum was within the
 range of the densities observed in the field. In each container with
 monocultures of the invasive species, the number of seedlings of S.
 subulatum emerged was 10–12 under no drought, 7–8 under moderate drought,
 and 3–4 under intense drought.
 <strong>Measurements</strong> We
 harvested all communities in October 2016, by which time plants of S.
 subulatum had reached the adult stage. Aboveground parts were sorted by
 species, dried to a constant mass at 80°C, and weighed. All six
 monocultures of the native species Medicago sativa failed to establish
 (one replicate in each of the six treatment combinations), and these
 containers were excluded from the analysis. The final sample size was,
 therefore, 49 communities (container) per treatment. Five soil cores (3 cm
 in diameter) were randomly collected from each container. Roots were
 extracted by rinsing the soil cores with water, dried to a constant mass
 at 80°C, and weighed. Total root biomass per container was estimated based
 on the area of the soil cores. The colonization rates
 of AMF in roots were quantified using the line-intersect method after
 clearing roots in 10% KOH and staining them in 0.05% trypan blue
 (Mcgonigle et al., 1990). For each native species in uninvaded and invaded
 communities with 16 native species, at least 200 intersects of root
 segments of ~1 cm long were scored under a light microscope at ×200
 magnification. The AMF colonization rate of a species was calculated by
 dividing the number of the infected intersects by the total number of
 intersects observed.
description: # Different diversity mechanisms underlying drought resistance in native
 and invaded communities Dataset DOI:
 [10.5061/dryad.dfn2z35f1](10.5061/dryad.dfn2z35f1) ## Description of the
 data and file structure 1\. Date of data collection: 2018 and 2019 2\.
 Geographic location of data collection: Taizhou, Zhejiang, China ### Files
 and variables #### File: Wang_2025_data.xlsx ##### Variables * plot code:
 Plot name. * richness: Species number in plot * invasion: 0 uninvaded, 1
 invaded * drought intensity: 1 moderate drought, 2 intense drought *
 species composition: Communities with different composition, 1-49 indicate
 49 types of communities with different compositions. * Dominant species: 0
 communities without dominant species, 1 community with dominant species. *
 Log original biomass: log (aboveground biomass of communities without
 drought). * CDR: log response ratio of biomass of the communities with
 drought (Biomasswith drought) to biomass of the communities without
 drought (Biomasswithout drought). * Root-shoot-ratio: the ratio of root
 biomass to shoot biomass. * Increase of root-shoot-ratio: The
 root-shoot-ratio of communities with drought is subtracted from that of
 communities without drought. * complementariychange: The complementarity
 effect of communities with drought subtracts that of communities without
 drought. * selectionchange: The selection effect of communities with
 drought subtracts that of communities without drought.