DOI: 10.5061/dryad.qbzkh18r4
title: Cross-continental variation of herbivore resistance in a global plant invader

description: While successful plant invasions often occur in novel environments,
 invasive species usually occupy broad niches within their native and
 introduced ranges. A better understanding of the process of invasion
 therefore requires a wide sampling of ranges, and a good knowledge of
 introduction history. We tested for differentiation in herbivore
 resistance among 128 introduced (European, North American) and native
 (Chinese, Japanese) populations of the invasive Japanese knotweed
 (Reynoutria japonica) in two common gardens in the native range: one in
 Shanghai and the other in Yunnan. In both common gardens, we found that
 herbivore resistance of plants from introduced populations differed from
 that from native populations in China but not from native populations in
 Japan, the putative source of introduction. Compared to native Chinese
 populations, plants from native Japanese populations and introduced
 European and North American populations had thicker leaves in both common
 gardens, and a lower C: N ratio but higher flavonoids content in the
 Shanghai garden. Variation in herbivore resistance was more strongly
 associated with climate of collecting sites for populations from the
 native range than for those from introduced ranges. Our results support
 the hypothesis that introduction of particularly resistant plants from
 Japan may have played a key role in driving biogeographic variation in
 herbivore resistance. Our study demonstrates the importance of
 understanding introduction history to interpret the biogeographic
 divergence of global plant invaders.
description: In the middle of the growing season, we estimated herbivore
 damage—separately for beetle and caterpillar damage—as the percentage of
 leaf area eaten on each plant. Two days later, we sampled five fresh,
 fully developed leaves (the 1<sup>st</sup>,
 2<sup>nd</sup>, 4<sup>th</sup>,
 5<sup>th</sup>, and 6<sup>th</sup> leaves from the
 top) from the tallest shoot of each plant and measured the thickness of
 each leaf with a digital micrometer (Digimatic Outside Micrometer,
 Mitutoyo, Japan) in both gardens, and its toughness with a penetrometer
 (FA10, SAUTER, Balingen, Germany) in the Shanghai garden and with a
 mechanical testing machine (ZQ990A, Dongguan Zhiqu Precision Instrument
 Co., Ltd, China) in the Xishuangbanna garden. We then estimated the leaf
 thickness and toughness for each plant as the averages of the five
 measurements. We measured all plant traits in the Xishuangbanna and
 Shanghai common gardens from July 14 to 21, 2022, and July 24 to 31, 2022,
 respectively. Finally, we dried all leaves at 60 °C for
 72 h to analyze for leaf chemistry. After grinding samples to the required
 particle size with a ball mill (MM400, Retsch, Germany), we measured total
 C and N with an organic elemental analyzer (FlashSmart™ Elemental
 Analyzer, Thermo-Fisher Scientific, USA) via thermal combustion and TCD/IR
 detection of CO<sub>2</sub>/N<sub>2</sub>. Then,
 we measured leaf lignin, alkaloids, and total flavonoids using the
 MZS-1-G, SWJ-1-Y, and LHT-1-G test kits (Suzhou Comin Biotechnology Co.,
 Ltd., Suzhou, China), respectively. After acetylation, the phenolic
 hydroxyl group in lignin had a characteristic absorption peak at 280nm.
 Alkaloids can react with bromocresol green indicator to generate green
 compounds with a maximum absorption peak at 416nm. In alkaline nitrite
 solution, flavonoids can form red complexes with aluminum ions with a
 characteristic absorption peak at 510nm. Then, we used the photometric
 method to measure the absorbance of the sample solution at each wavelength
 using an enzyme-labeled instrument (Synergy2, Biotek Instrument Co., Ltd,
 Winooski, USA), and calculated the content of each chemical compound
 group.
description: # Cross-continental variation of herbivore resistance in a global plant
 invader
 [https://doi.org/10.5061/dryad.qbzkh18r4](https://doi.org/10.5061/dryad.qbzkh18r4) Contact Peipei Cao ([ppcao20@fudan.edu.cn](mailto:hahnp@ufl.edu)) with any questions. This manuscript has been accepted for publication (29-Jan-2025): Cao, P.P., Z.Y. Liao, S.Y. Wang, M. Parepa, L. Zhang, J.W. Bi, Y.J. Zhao, Y.L. Guo, T.T. Lin, S.B. Endriss, J.H. Wu, R.T. Ju, C.L. Richards, O. Bossdorf and B. Li. Cross-continental variation of herbivore resistance in a global plant invader. Ecography (accepted). 10.1111/ecog.07569 ## Data files include: ### herb-trait.csv This file contains data on leaf traits and phytochemistry. All data were collected by the authors. | variables | units | description | | :---------------- | :--------------------- | :-------------------------------------------------------------------------- | | Garden | categorical | Common garden, SH = Shanghai, YN = Yunnan | | Range | categorical | Geographic origins, US = North America, EU = Europe, JA = Japan, CN = China | | Population | number | numerical code for each maternal plant for where rhizome was collected | | Individual | categorical | Code for indivdual plants from each population | | Latitude | °N | latitude for each maternal plant for where rhizome was collected | | Longitude | °E | longitude for each maternal plant for where rhizome was collected | | Block | categorical | Block number assigned to each individual when planted | | Root\_weight | g | fresh weight of each rhizome before transplantation | | Source | categorical | Plant origin | | LeafThickness | mm | leaf thickness | | LeafToughness | N | leaf toughness | | LeafC/N | number | leaf C: N ratio | | Alkaloids | mg / g dry leaf tissue | concentration of chemical compound | | Flavonoids | mg / g dry leaf tissue | concentration of chemical compound | | Lignin | mg / g dry leaf tissue | concentration of chemical compound | | Herb\_beetle | % | leaf area eaten by beetles | | Herb\_Caterpillar | % | leaf area eaten by caterpillars | we obtained eight bioclimatic variables (1970–2000 averages at a spatial resolution of 30 seconds) from the WorldClim database (Fick and Hijmans 2017;  [https://www.worldclim.org/](https://www.worldclim.org/)) that seemed particularly meaningful for characterizing growing and overwintering conditions for knotweed plants: annual temperature (bio1), temperature seasonality (bio4), maximum temperature of the warmest month (bio5), minimum temperature of the coldest month (bio6), mean annual precipitation (bio12), precipitation of the wettest month (bio13), precipitation of the driest month (bio14), and precipitation seasonality (bio15). *The population number in the file is the original population number during field sampling. For the convenience of display, the population numbers in the manuscript are renamed according to the latitude value from small to large.