Carbon dioxide and methane chamber flux data from temperate S. alterniflora salt-marsh

A collection of carbon dioxide (CO2), methane (CH4) gas flux and leaf area index (LAI) datasets from a temperate salt-marsh with S. alternifloria vegetation cover (39.09 ˚N, 75.44 ˚W). Measurements were collected from May 2020 through December of 2020 with 2 separate collection times per month for a total of 16 field sampling campaigns. Measurements were performed on 5 plots located within the footprint of an eddy covariance tower which collects ecosystem scale CO2 and CH4 fluxes (Ameriflux Site ID: StJ). Supporting measurements were also performed for leaf-level photosynthesis rates and plot LAI during each chamber campaign. 

The dark and light flux chambers each occupied 1.0 m2 ground area and the vegetation stand was fully enclosed by the chambers. The sediment chambers each occupied 0.025 m2 ground area and the vegetation stand was excluded from the chambers. CO2 and CH4 fluxes from all chambers were measured with a portable greenhouse gas analyzer (LGR  Los Gatos Research, Model 915-0011, San Jose, CA) for approximately 2-3 min after chamber closure. The dark and soil chambers were 100% opaque while the light chamber allowed for 90% transmission of photosynthetically active radiation. Sediment fluxes and leaf-level photosynthesis was measured from 2 points within each of the larger chamber plots. Leaf-level photosynthesis was measured with a  portable photosynthesis meter (Li-6400, Licor, Lincoln, NE) and LAI was measured with a ceptometer (Accupar LP80, Meter Inc, Pullman, WA, USA). All measurements were made consecutively over the span of 2-3 hours with leaf-level measurements preformed first, followed by light chambers, dark chambers, sediment chambers and plot LAI.

本数据集采集自北纬39.09°、西经75.44°的一处覆盖互花米草（S. alternifloria）的温带盐沼，包含二氧化碳（carbon dioxide, CO₂）、甲烷（methane, CH₄）气体通量及叶面积指数（leaf area index, LAI）相关数据。观测时段为2020年5月至2020年12月，每月开展2次采样，累计完成16次野外采样作业。观测在涡度协方差塔（eddy covariance tower）的通量足迹区内的5个样地开展，该塔用于采集生态系统尺度的CO₂与CH₄通量（美国通量网Ameriflux站点编号：StJ）。每次箱式采样作业期间，还同步开展了叶片级光合速率及样地LAI的辅助测量。

暗通量箱与光照通量箱的占地面积均为1.0 m²，可完全包围植被群落。沉积物采样箱占地面积为0.025 m²，且不包含植被群落。所有箱式装置测得的CO₂与CH₄通量，均使用便携式温室气体分析仪（portable greenhouse gas analyzer, LGR Los Gatos Research, 型号915-0011, 加州圣何塞）在箱室密闭后约2~3分钟内完成测定。暗通量箱与沉积物采样箱完全不透明，而光照通量箱可透过90%的光合有效辐射（photosynthetically active radiation）。每个大型通量箱样地内选取2个测点，开展沉积物通量与叶片级光合速率测量。叶片级光合速率采用便携式光合仪（portable photosynthesis meter, Li-6400, Licor, 内布拉斯加州林肯市）测定，LAI则使用冠层分析仪（ceptometer, Accupar LP80, Meter Inc, 华盛顿州普尔曼市，美国）测定。

所有测量作业均在2~3小时内连续完成，测量顺序依次为叶片级光合速率、光照通量箱、暗通量箱、沉积物采样箱，最后测定样地LAI。