DOI: 10.5061/dryad.kd51c5b91
title: Data for: Leaf N-S of wetland plants in western China

description: Salinization alters the elemental balance of wetlands and induces
 variations in plant survival strategies. Sulfur (S) plays vital roles in
 serving regulatory and catalytic functions in stress resistance of plants.
 Yet, how plant S and its relationships with nitrogen (N) vary across
 natural environmental gradients are not well documented. We collected 1366
 plant samples and 230 water and sediment samples from 230 wetlands in
 Tibetan Plateau and adjacent arid regions of western China, to analyze the
 effects of environmental variables on plant S accumulation and N-S
 correlations. We found that plant S correlated with N in unimodal
 patterns. Salinity, rather than temperature or nutrient supply, promoted
 disproportionate accumulation of S but limited N uptake, inducing
 decoupling of N-S correlation in plants. Towards high salinity, the faster
 increasing rates of total S than that of glutathione, the most abundant
 organic-S compound in plant resistance, provided potential evidences
 explaining the decoupled plant N-S correlation. A salinity of 3.9‰ was
 calculated to be a threshold at which substantial changes in plant N-S
 correlation occurred. We designed a conceptual model to illustrate the
 mechanisms driving variations of N-S correlation in plants and
 environments along salinity gradient. In addition, salinity reduced
 species richness and drove community reassembly by filtering species with
 high S concentrations at community scale. Our study addressed the critical
 roles of S in plant resistance under adverse conditions. Studies on
 biogeochemical cycles of S and N in wetland ecosystems will further
 enhance our understanding of plant responses to future climate change.
description: We focused on
 two plant forms: emergent plants and submerged plants. Emergent plants
 were defined as hydrophytes that grew in
 waterlogged soil with their roots submerged in water and their leaves in
 air. Submerged plants were those whose whole bodies were submerged in
 water with their roots in sediments. Using a uniform protocol, plant
 samples were collected across the study area in July and August of 2018
 and 2019. For emergent plants, 30-50 fully expanded and intact leaves were
 sampled randomly for each species. For submerged plants, we collected
 30-50 segments of plant shoots (20 cm from the tips) and then removed all
 the leaves from the segments. In total, we
 collected 82 species, belonging to 25 families and 37 genera from 230
 sites, for a total of 1366 samples (Dataset S1). The total 1366 samples
 consisted of two groups: 1019 samples from all 82 species in 230 sites for
 measuring concentrations of leaf N (LN) and leaf S (LS) and 347 samples
 from 44 common species in
 146 sites for measuring concentrations of leaf GSH. The 347 samples were
 collected simultaneously with the corresponding samples in the 1019
 samples, but was stored as fresh samples in liquid nitrogen during field
 investigation. The 1019 samples were oven-dried at 70℃ for 72 h and then
 ground into fine powder. Before sampling, the pH
 and salinity of the undisturbed water were measured <em style="color:#1c1d1e;font-family:'Times New Roman' , serif;font-size:11pt;">in situ</em> with a handheld
 multiparameter meter (PROPLUS, YSI, USA). Then, 500ml water samples were
 collected from midway between the water surface and the soil substrate.
 The total nitrogen contents of water were analyzed using a multiparameter
 portable colorimeter (DR900, HACH, USA) with a digestion solution, while
 the total SO<sub style="color:#1c1d1e;font-family:'Times New Roman' , serif;">4</sub><sup style="color:#1c1d1e;font-family:'Times New Roman' , serif;">2-</sup> contents of water were
 determined by ion chromatography (ICS-1000, DIONEX, USA). Three samples
 from the upper 0-20 cm of sediments were collected randomly at each site
 and then mixed, air dried, the roots and rocks removed, and then ground
 and sieved through a 0.15mm mesh for further analysis. The pH and
 conductivity of the sediments were measured by dissolving samples into a
 mass-based soil-water ratio of 1:5. Total N and S concentrations of both
 plants and sediments were measured from powdered samples by an elemental
 analyzer (UNICUBE, Elementar, Germany). According to the protocol of
 Cang and Zhao
 (2013), plant GSH
 concentrations were measured from fresh samples based on the
 5,5'-dithio bis-(2-nitrobenzoic acid) colorimetric (DNTB
 method).