CA-TP4 Soil Respiration Data 2008-2018

Soil CO2 emissions or soil respiration (Rs) data were measured at an eastern white pine forest (Pinus strobus L.) planted in 1939 as monoculture stands north of Lake Erie in southern Ontario, Canada. The forest site is part of the Turkey Point Observatory and has been associated with AmeriFlux and global Fluxnet initiatives, where it is known as CA-TP4. The forest is dominated (&gt;82%) by eastern white pine, while other tree species include 11% balsam fir (Abies balsamea L. Mill) and species native to the hardwood forests of North American Eastern Temperate Forest Ecoregion, including 4% Oak (Quercus velutina L., Q. alba L.), 2 % Red Maple (Acer rubrum L.) and some wild black cherry trees (Prunus serotina Ehrh). The forest was thinned in 1983 and winter of 2012, where one-third of trees were randomly removed. <br><br>Soil CO2 efflux was measured using an automated non-steady state chamber system developed by the University of British Columbia in a 50 m × 50 m area located 100 m north from the eddy covariance flux tower at the site from June 2008 to October 2018. Initially four chambers were installed. One measured heterotrophic respiration (FRT1) in the trenched plot whereby live tree roots were removed from surrounding area and other three as controls. chambers and measured total soil CO2 efflux (FS: FS1, FS2, and FS22). One of the control chambers (FS22) was altered in May 2009 to measure the contributions from the mineral-soil horizon (FLR) to total soil respiration, by removing the litter layer. In May 2009, two more control chambers (FS3 and FS4) were added to the chamber system to measure total soil respiration. Finally, in May 2010, two additional chambers were installed, one as a control (FS5) and an additional chamber to measure heterotrophic respiration (FRT2); increasing the total number of chambers in the chamber system to eight. In total, five chambers were measuring total soil CO2 efflux, two chambers measured heterotrophic soil CO2 efflux and one chamber measured contributions from the mineral-soil horizon. Each chamber consisted of a PVC collar and a chamber lid that fit onto the collar. The collars were inserted approximately 2 to 4 cm into the ground. The chamber lid consisted of a transparent plastic dome fixed to a metal frame. Each chamber closed individually for a one-minute interval, where the CO2 concentration was sampled and measured by an infrared gas analyzer (model LI-840, Li-COR Inc.). Measurements were cycled through the eight collars for a total of three cycles per half-hour period. Each half-hour average consisted of three, minute-long CO2 concentration measurements per chamber. One half-hourly value was produced for each collar by averaging the three measurements taken during that half-hour. The measurement chambers remained open when not taking measurements. Throughout the growing season, any vegetation growth was removed from inside the collars to eliminate potential photosynthesis effects. <br>Chamber 1: Reference plot (then converted to litterless in May 8, 2009) <br><br>Chamber 2: Reference plot <br><br>Chamber 3: Heterotrophic plot (trenched at the time of instalation in 2008 to exclude live roots). <br><br>Chamber 4: Drought plot (90% rainfall exclusion from 1 April to 3 July, 2009 in a 20m x 20m plot) <br><br>Chamber 5: Reference plot (installed in May 2009) <br><br>Chamber 6: Drought plot (installed in May 2009) (90% rainfall exclusion from 1 April to 3 July, 2009 in a 20m x 20m plot). <br><br>Chamber 7: Reference plot (installed in May 2010 ) <br><br>Chamber 8: Reference plot (converted to heterotrophic in May 2010 by trenching and excluding live roots)<br><br>Tree density is 413 (321) tree per ha, Leaf Area Index is 8.5 (5.3), tree heigh 23.4 (22.9) m, and diamter at breat heigh is 39 (37.2) m. Numbers in paranthesis show vales after 2012 thinning. Topography in the area is predominantly flat with occasional 0.5-3.0% undulating slopes. The soil at the site is well drained with a low water holding capacity and classified as brunisolic grey-brown luvisols in the Canadian System of Soil Classification and is composed of ~98% sand. The climate in the region is cool temperate with a 30-year mean annual temperature of 8.0 °C and mean annual precipitation of 1036 mm.

土壤CO₂排放（或称土壤呼吸，soil respiration, Rs）数据采自加拿大安大略省南部伊利湖以北的一片1939年营造的纯林东部白松（Pinus strobus L.）林分。该森林样地属于土耳其角观测站（Turkey Point Observatory），并参与了AmeriFlux与全球通量网（Fluxnet）计划，编号为CA-TP4。林分优势种为东部白松，占比超过82%，其余树种包括11%的香脂冷杉（Abies balsamea L. Mill），以及北美东部温带森林生态区硬木林原生树种：4%的黑栎（Quercus velutina L.、Q. alba L.）、2%的红枫（Acer rubrum L.），还有少量野生黑樱桃（Prunus serotina Ehrh）。该林分曾于1983年和2012年冬季进行疏伐，每次随机移除三分之一的林木。

2008年6月至2018年10月，研究团队于该样地涡度协方差通量塔（eddy covariance flux tower）以北100米处的50 m × 50 m区域内，采用不列颠哥伦比亚大学研发的自动非稳态箱法系统，测定土壤CO₂排放通量。最初布设4个箱室：1个用于测定异养呼吸（heterotrophic respiration, FRT1），对应根际去除的切根样地；其余3个为对照样地，用于测定总土壤CO₂排放通量（FS：FS1、FS2、FS22）。2009年5月，对其中1个对照箱室（FS22）进行改造，移除枯落物层以测定矿质土壤层（mineral-soil horizon, FLR）对总土壤呼吸的贡献。同年5月，新增2个对照箱室（FS3、FS4）用于总土壤呼吸测定。2010年5月，再次新增2个箱室：1个为对照箱（FS5），另1个用于测定异养呼吸（FRT2），至此总箱室数量增至8个。最终，5个箱室用于测定总土壤CO₂排放通量，2个箱室测定异养土壤CO₂排放通量，1个箱室测定矿质土壤层的呼吸贡献。每个箱室由PVC套管和适配的箱盖组成，套管插入土壤约2~4 cm。箱盖为固定于金属框架上的透明塑料穹顶。每个箱室单独闭合1分钟，在此期间通过红外气体分析仪（infrared gas analyzer，型号LI-840，Li-COR公司）采集并测定CO₂浓度。每半小时内循环测定8个套管共3轮，每个箱室的半小时均值由该时段内3次1分钟的CO₂浓度测定结果平均得到。非测定时段箱室保持开放。在整个生长季，定期清除套管内部的植被，以消除潜在的光合作用干扰。

1号箱室：对照样地（2009年5月8日改造为无枯落物样地）

2号箱室：对照样地

3号箱室：异养呼吸样地（2008年布设时即进行切根，排除活根影响）

4号箱室：干旱胁迫样地（2009年4月1日至7月3日，在20m × 20m样地内排除90%的降雨）

5号箱室：对照样地（2009年5月布设）

6号箱室：干旱胁迫样地（2009年5月布设，2009年4月1日至7月3日在20m × 20m样地内排除90%的降雨）

7号箱室：对照样地（2010年5月布设）

8号箱室：对照样地（2010年5月通过切根排除活根，改造为异养呼吸样地）

林分密度为413（321）株/公顷，叶面积指数为8.5（5.3），树高23.4（22.9）m，胸径为39（37.2）cm（原文标注单位为米，结合专业常识修正为厘米）。括号内的数值为2012年疏伐后的对应指标。该区域地形以平坦为主，偶有0.5%~3.0%的起伏缓坡。样地土壤排水良好，持水能力低，按加拿大土壤分类系统归类为灰棕暗棕淋溶土（brunisolic grey-brown luvisols），砂粒含量约占98%。该区域气候为冷温带气候，30年平均年温为8.0 ℃，年平均降水量为1036 mm。