DOI: 10.5061/dryad.mkkwh715f
title: Eutrophication decreases ecological resilience by reducing species diversity and altering functional traits of submerged macrophytes

description: Positive feedback is key to producing alternative stable states and
 largely determines ecological resilience in response to external
 perturbations. Understanding the positive feedback mechanisms in
 macrophyte-dominated lakes is crucial for resilience-based management and
 restoration. Based on the field investigation of submerged macrophyte
 communities in 35 lakes in China, we found that morphological complexity
 (MC) and morphological plasticity (MP) are correlated with the
 stoichiometric homeostasis of phosphorus (HP) and are related to ecosystem
 structure, functioning, and stability. We also found that the positive
 feedback strength of lakes dominated by macrophytes is biomass- and
 diversity-dependent. Eutrophication can decrease the community biomass by
 decreasing community MC, MP, and HP and the species diversity through
 low-light availability, ultimately decreasing the positive feedback
 strength and resilience of clear-water states. We argue that functional
 traits and species diversity should be considered to build more resilient
 ecosystems in future changing environment scenarios.
description: Submerged macrophyte communities from 35
 subtropical lakes in China were investigated between 2014–2021. 534 sites
 were sampled among those lakes distributed in the middle and lower reaches
 of the Yangtze Plain (2014 and 2018; an average of 16 sampling sites for
 each lake), Sichuan Basin (2020; an average of 11 sampling sites for each
 lake), and Yunnan Plateau (2021; an average of 17 sampling sites for each
 lake) . Water clarity was measured by a Secchi disc
 (Secchi depth, SD). Ten species of submerged macrophytes widely
 distributed in subtropical lakes were studied: <em>Potamogeton
 maackianus, Potamogeton malaianus, Ceratophyllum demersum, Hydrilla
 verticillata, Vallisneria natans, Myrophyllum verticillatum, Potamogeton
 pectinatus, Potamogeton perfoliatus, Najas marina, and Potamogeton
 lucens.</em> We measured
 the surface area of plants above the sediment level by portable leaf area
 meter .  An electronic balance was used to weigh the wet biomass. Plant
 height was defined as the length (cm) of the aboveground part. The
 phosphorus in plants and sediments was first digested using concentrated
 sulfuric acid and hydrogen peroxide, and the amount was determined using
 the ammonium molybdate-ascorbic acid method (Sparks <em>et
 al</em>.,1996). Total phosphorus (TP) in the water
 sample was digested with potassium persulfate (Sigma Aldrich, Germany) in
 a sterilization pot at 120 ℃ for 30 min. We caculated
 P stoichiometric homeostasis (Sterner
 & Elser, 2002) by P concentration in sediments and
 plants and quantized morphological complexity and plasticity by specific
 surface area. Community trait is the overall mean of functional traits
 across all species weighted by the relative
 biomass.  The community biomass of a lake is defined as
 the mean total biomass of all submerged macrophyte species in a quadrat,
 and community stability is indicated by the mean biomass to standard
 deviation ratio. Species diversity here is indicated by the H-Shannon
 diversity, which is calculated as the exponential of Shannon entropy. We
 define positive feedback strength as the ability of plants to improve
 water clarity per unit biomass. Finally,
 general linear model and piecewise SEM were used to explored the
 relationships of TP, MC, MP, H, community biomass, stability, species
 diversity and positive feedback strength. Sparks, D.L.,
 Page, A.L., Helmke, P.A., Loeppert, R.H., Soltanpour, P.N. Tabatabai, M.A.
 et al. (1996). Methods of Soil Analysis. Part 3-Chemical Methods. Soil
 Science Society of America Inc. http://refhub.elsevier.com/S0043-1354(21)00590-X/sbref0043 Sterner, R.W. & Elser, J.J. (2002). Ecological stoichiometry: the Biology of Elements from Molecules to the Biosphere. Princeton University Press, Princeton. http://refhub.elsevier.com/S0043-1354(21)00590-X/sbref0046