DOI: 10.5061/dryad.3j9kd51rm
title: Divergent geographic variation in above- versus belowground secondary metabolites of Reynoutria japonica

description: Secondary metabolites play an important role in plant adaptation because
 they can mitigate biotic and abiotic environmental stresses. However,
 their production and allocation incur different costs and benefits and are
 therefore subject to trade-offs, which are less studied. To understand
 large-scale geographic patterns of secondary metabolites, and their
 environmental drivers and trade-offs, we studied 39 natural populations of
 the perennial herb Japanese knotweed (Reynoutria japonica) along a large
 latitudinal gradient in China. We measured the concentrations of six
 polyphenols in leaves and rhizomes of R. japonica and associated the
 variation in these metabolites with biotic and abiotic environmental
 factors as well as with functional plant traits and putative costs of
 secondary metabolites. We found that climate was an important driver of
 variation in secondary metabolites, both above- and belowground.
 Remarkably, the patterns of association differed between leaves and
 rhizomes, as well as between putative low-cost vs. high-cost compounds.
 While annual mean temperature was a stronger predictor of aboveground
 metabolites, annual precipitation was more frequently associated with
 variation in belowground metabolites. Moreover, annual temperature was
 positively associated with high-cost metabolites, but negatively with
 low-cost metabolites. Aboveground secondary metabolites were generally
 more strongly associated with functional traits (e.g., specific leaf area)
 than belowground metabolites, and in all cases, the directions of
 correlation were opposite for low-cost versus high-cost metabolites
 aboveground. The patterns of association also varied with latitude such
 that leaf concentrations of low-cost metabolites (quercetin) increased but
 those of high-cost metabolites (resveratrol, piceid and emodin) decreased
 at higher latitudes. In rhizomes, in contrast, the concentrations of
 high-cost metabolites (piceid and emodin) increased with latitude.
 Synthesis. Our findings indicate that allocation strategies differ between
 above- and belowground tissues of R. japonica. As latitude increases, R.
 japonica invests relatively more into belowground metabolites. We propose
 that reduced high-cost metabolites in the leaves at higher latitudes may
 help to conserve nutrients after defoliation, while maintaining high-cost
 metabolites in rhizomes may be important for persistent allelopathic
 effects and resource conservation belowground. The divergent patterns of
 above- and belowground metabolite allocation thus likely reflect the
 multiple functions of metabolites and the plants’ adaptation to different
 environments.
description: # Divergent geographic variation in above- versus belowground secondary
 metabolites of *Reynoutria japonica*
 Secondary metabolites,
 trait and environmental data for this study are available. ## Datasets
 included: # Divergent geographic variation in above- versus belowground
 secondary metabolites of Reynoutria japonica
 Secondary metabolites,
 trait and environmental data for this study are available. We sampled R.
 japonica populations at 39 sites along a latitudinal gradient from 23.29°N
 to 31.40°N during peak growing season in July 2020. ## Datasets included:
 1. Carbon and Nitrogen (TC, TN): Measured total carbon and nitrogen (mg/g)
 in leaf and rhizome samples using an elemental analyzer to calculate their
 C:N ratios. 2. Secondary Metabolites: Analyzed concentrations of six
 polyphenol metabolites (Quercetin, Ellagic acid, Piceid, Emodin and
 Catechin;μg/mL). We employed a triple quadrupole mass spectrometer with
 multiple reaction monitoring (MRM) capabilities. Upon obtaining mass
 spectrometry data for various samples, we integrated the chromatographic
 peaks of the different target compounds and conducted quantitative
 analysis using internal/external standards. 3. Plant Functional Traits:
 Recorded five key traits: measured the diameter (10 cm above the ground;
 mm) and number of branches of each selected R. japonica stem. We then
 collected five healthy leaves (the third to the eighth fully developed
 leaves from the top of each stem) to determine leaf toughness (N) with a
 SAUTER FA10 mechanical dynamometer, and to measure leaf chlorophyll
 content using a SPAD-502Plus chlorophyll meter. We also estimated leaf
 area using ImageJ on photos of these leaves and calculated specific leaf
 area (SLA; mm²/mg) as the leaf area divided by leaf dry mass. 4. Enemy
 Pressure: we primarily focused on chewing herbivores and pathogens. To
 quantify variation in leaf damage reflecting average natural herbivory, we
 collected four kinds of data using the selected five R. japonica stems at
 each site. Quantified herbivory and disease impact by (i) relative
 abundance of knotweed, (ii) percentage of leaves damaged by herbivores
 (Proportion_damaged; %), (iii) proportion of individuals with disease
 (LAL.TLA; %), and (iv) percentage of leaf area lost to herbivores
 (Pathogens), using ImageJ analysis of leaf photographs. 5. Environmental
 Variables: we measured soil pH using a 1:5 soil-water suspension (IQ
 Scientific Instruments, CA, USA). The soil samples were ground, sieved
 through a 2 mm mesh sieve, oven-dried at 60°C for 72 hr, weighed into tin
 capsules and measured for total carbon and nitrogen contents (S_TN, S_TC;
 mg/g) with an elemental analyzer (Vario MACRO cube, Elementar, Germany).
 Soil organic carbon content (SOC; mg/g) was measured based on the ignition
 loss method. In addition, we measured microbial biomass carbon (SMC;
 mg/kg) content using the chloroform fumigation-extraction method. We
 obtained climate data (BIO1/Annual Mean Temperature, C; BIO2/Mean Diurnal
 Range; BIO12/Annual Precipitation, mm; and solar_annual.mean, kJ/m2/d) for
 all study sites from http://worldclim.org/version2v.