Soils contain biotic and abiotic legacies of previous conditions that may influence plant community biomass and associated aboveground biodiversity. However, little is known about the relative strengths and interactions of the various belowground legacies on aboveground plant-insect interactions. We used an outdoor mesocosm experiment to investigate the belowground legacy effects of range-expanding versus native plants, extreme drought, and their interactions on plants, aphids, and pollinators. We show that plant biomass was influenced more strongly by the previous plant community than by a previous summer drought. Plant communities consisted of four congeneric pairs of natives and range expanders, and their responses were not unanimous. Legacy effects affected the abundance of aphids more strongly than pollinators. We conclude that historical climate warming-induced plant latitudinal range expansion and extreme drought contingencies can be contained as soil ‘memories’ that influence plant performance and aboveground community interactions in the next growing season.

General introduction

The data was collected in 2019, in the experimental garden of the Netherlands of Ecology (NIOO-KNAW, Wageningen, the Netherlands). The semi-field experiment was a full-factorial design, containing 40 experimental units. Mesocosms were inoculated with northern soil (new range for range-expanders) and southern soil (original range for range-expanders). We created plant community-induced soil legacies (native vs. range-expander plant communities) and extreme summer drought-induced soil legacies (control vs. drought). In 2019, we grew natives and their congeneric range-expanders in mixed plant communities (each mesocosm considered as a plant community), to examine soil legacy effects on plant biomass production and the abundance of aboveground plant associated insects. 

Plant shoot biomass data collection

At the end of the experiment (i.e., end of the growing season), on September 18, 2019, the shoot biomass of each plant species was clipped and oven-dried at 60 ℃ until constant weight. In total, there were 1280 individuals harvested (few plant species were missing).

Flower numbers data collection

Between June 17 to August 27, flower numbers were counted weekly for 11 weeks.

Aphids number data collection

From the end of May until early September, aphids were counted once a week. There were possibly several aphid species on the plants, but only the total number of aphids associated with plant individuals was counted. When aphid densities were too high to count individuals, we counted the number of aphids on 1 cm of stem length and then multiplied this number by the length of stem (in cm) that was colonized by the aphids. Similarly, for aphids on leaves, we counted aphids on a 1 cm² leaf area and multiplied this by the total leaf area covered by aphids.

Pollinators richness and abundance 

We recorded pollinator visitation abundance and richness by observation, one day a week over 7 consecutive weeks. Every observation day, all mesocosms were observed in random order. The flowering stage and the fraction of ground covered by flowers of each plant species (named ‘flower proportion’) were also recorded. Consequently, the observation order, flowering stage, and flower proportion were included as random effects factors in the statistical analyses.

Plant height and width data collection

In order to know whether the sucking-aphids number was driven by plant size, we measured the plant height and width three times using a ruler, on 27/06/2019, 16/07/2019 and 05/08/2019, respectively.

The uploaded data and scripts can be opened using Excel and R studio.