DOI: 10.5061/dryad.41ns1rnj0
title: Salinity effects on soil P cycling

description: Accelerated sea-level rise is expected to cause the salinization of
 freshwater wetlands, but the responses to salinity of the availability of
 soil phosphorus (P) and of microbial genes involved in the cycling and
 transformation of P remain unexplored. Our results suggest that the
 P-cycling microbial community abundance and P availability respond
 positively to moderate increases in salinity by promoting the microbial
 solubilization and mineralization of soil P in brackish wetlands. Changes
 in microbial communities and microbially mediated P cycling may represent
 microbial strategies to adapt to moderate salinity levels, which in turn
 control soil function and nutrient balance.
description: The field experiments were
 conducted in the growing (July) and non-growing seasons (January) in both
 the freshwater and brackish C. malaccensis wetlands. Three 1 × 1 m
 quadrats (5 m apart) were randomly established at each site, and three
 soil cores (0–20 cm) were randomly collected in each quadrat and pooled
 into one sample. All samples were then stored in a portable refrigerator
 and immediately transported to the laboratory. The samples
 were homogenized and
 then split into two
 subsamples: one subsample was air-dried for the determination of P
 fractions and physicochemical parameters, and the other subsample was
 frozen at −80°C for DNA extraction. Plant biomasses were also collected
 during each season. We used the Hedley scheme of sequential
 extraction to estimate the fractions and availabilities of soil P
 (Hedley et al.,
 1982), which can
 effectively distinguish between Pi and Po. Briefly, soil samples were
 successively extracted using an anion-exchange resin (resin-P), 0.5 M
 NaHCO3 (NaHCO3-Pi and NaHCO3-Po), 0.1 M NaOH (NaOH-Pi and NaOH-Po), 0.1 M
 NaOH with sonication (NaOHs-Pi and NaOHs-Po), and 1 M HCl (HCl-Pi). The
 residual soils were then digested with 4 mL of H2SO4 and 1 mL of HClO4
 (residual-P). The concentration of P was measured using a
 spectrophotometer. The P was further classified as labile P (resin-P,
 NaHCO3-Pi, and NaHCO3-Po), moderately labile P (NaOH-Pi and NaOH-Po), and
 stable P (NaOHs-Pi, NaOHs-Po, HCl-P, and residual-P) based on its
 availability to plants and microbes (Rodrigues et al., 2016). The salinity of the water was measured
 in situ using a salinometer (Oakton Instruments,
 Springfield, USA). Soil electric conductivity (EC) and pH were determined
 using a 2265FS EC meter (Spectrum Technologies Inc., Aurora, USA) and a pH
 meter (IQ Scientific Instruments, Carlsbad, USA), respectively. Soil
 moisture was evaluated by determining the amount of water lost at 105°C.
 Soil organic C (SOC) was analyzed using the dichromate oxidation method.
 Soil concentrations of total C (TC) and N (TN) were measured using
 an elemental analyzer (Elementar, Frankfurt,
 Germany). Soil concentrations of ammonium-N (NH4+-N) and nitrate-N
 (NO3−-N) were determined using flow-injection analysis (Skalar Analytical
 SAN++, Lachat, Netherland) and extraction with 2 M KCl. The soil texture
 was determined using a Mastersizer 2000 particle-size analyzer (Malvern
 Panalytical Ltd., Melvin, UK). Plant biomasses were measured by drying
 samples to constant weight at 70°C.
 Soil microbial DNA was
 extracted using an OMEGA DNA Kit following the manufacturer’s
 instructions. The quality and quantity of the extracted DNA were
 determined using a NanoDrop ND-1000 spectrophotometer (Thermo Fisher
 Scientific, Waltham, USA) and agarose gel electrophoresis, respectively.
 The extracted microbial DNA was processed, and metagenomic shotgun
 sequencing libraries were constructed with insert sizes of 400 bp using an
 Illumina TruSeq Nano DNA LT Library Preparation Kit. Each library was
 sequenced on an Illumina HiSeq X-ten platform (Illumina,
 San Diego, USA) using the PE150
 strategy at Personal Biotechnology Co., Ltd. (Shanghai, China). Please
 refer to the Supporting Information for more detailed descriptions
 (Appendix I). We obtained a total of 931
 million qualified sequences from 12
 metagenomes, ranging from 69 million to 88 million sequences per sample for downstream
 analyses (Table S1).
description: The dataset can be opened using regular Office software.