DOI: 10.6084/m9.figshare.4239122.v3
title: Soil Respiration Rate from Mixed and Broadleaved forest sites from Bhutan, Eastern Himalayas for 2014 and 2015

description: <b>Field Rs , Soil Moisture and Soil Temperature</b>Soil Respiration (Rs) was measured regularly at the two sites (mixed, broadleaved) once every three weeks, from April 2014 to December 2015. We randomly set 10 plots (n = 10) at each site for Rs measurements. To cover the within-plot variability, Rs was measured at four positions within each plot (total 40 positions per site). We used a portable infrared gas analyzer (EGM-4, PP-Systems, Amesbury, USA) with an attached soil respiration chamber (SRC-1, PP-Systems, Amesbury, USA) for Rs measurements. Prior to measurements (March 2015), we installed permanent collars (total height 5 cm, 2-3 cm inserted into the soil, diameter 10 cm) at each plot which served as a base for Rs measurements. Rs was estimated by a linear fit to the increasing headspace CO2 concentration over time (chamber closure time 90 seconds). A soil respiration measurement campaign lasted for ~ 5 h at each site. Measurement order among plots and collars was fully random to avoid any error from temporal variations in Rs.We installed two trenching plots at each site in April 2014 (1 yr prior Rs measurements) to estimate the relative contributions of Ra and Rh. Trenches (1.5 x 1.5 m squares) were dug down ~ 1 m, and all the roots within the trenches were cut. The trenches were sealed with double layered plastic foil in order to restrict tree root ingrowth. Adjoining to each trenched plot, a corresponding control plot of the same size was established. Each trenched and control plot hosted three collars for Rs measurements. We measured Rs at trenched and corresponding control plots after finishing regular Rs measurements (same day).Volumetric soil water content (0 - 20 cm soil depth) was measured in the center of each plot (Rs plots, trenched plots, control plots) using a portable Field Scout TDR meter (Spectrum Technologies, Inc. Aurora, USA) during Rs measurements. Soil temperature at 5 cm soil depth was measured with a handheld thermometer probe (Hanna Instruments, Germany) at each Rs measurement location. Soil temperature and soil moisture were measured continuously at soil profile pits (two pits per site) with five combined soil temperature- moisture sensors (TM-5; Decagon Devices, Inc., Pullman, WA,  USA) at soil depths ranging from 5 to 120 cm. Data was recorded at 15 min intervals on Decagon-EM50 data loggers (Decagon Devices, Inc., Pullman, WA,  USA).<br><b>Laboratory Incubation</b><b><br></b>About 500 g of mineral soil (0-10 cm depth) and approximately 250 g of forest floor material were sampled at six random locations (n = 6) at each site in mid of September 2015. The mineral soil was homogenized and sieved (2 mm mesh) and stored at 4 °C, at field moisture for one week prior to transport from Bhutan to Austria for further processing. Forest floor material was not sieved. Upon arrival in Austria, samples from mineral soil were further divided into 3 sub-samples to account for potential soil heterogeneity at the individual sampling locations. Samples were filled into 200 cm3 stainless steel cylinders at approximate field bulk density (~ 0.5 g dry weight cm-3 for mineral soil; ~ 0.1 g dry weight cm-3 for forest floor). In total, we incubated 36 sub-samples (cylinders) for mineral soil and 12 sub-samples for the forest floor. Filled cylinders were kept at 4 °C for 5 days for equilibration before incubation. During incubation, CO2 efflux (= Rh) was measured using a fully automated incubation system. Samples were put into 2 l containers and their CO2 efflux was determined by a dynamic closed – chamber system (Pumpanen et al., 2009). For CO2 measurements, containers were sequentially connected to an infrared gas analyzer (SBA-4, PP Systems International Inc., Amesbury, MA, USA) by means of a tubing system. In the meanwhile, disconnected containers were ventilated in order to prevent internal CO<sub>2</sub> enrichment. CO<sub>2 </sub>concentration within connected containers were measured for 6 minutes with a recording interval of 10 sec. Rates of CO<sub>2</sub> efflux were calculated from the headspace CO<sub>2</sub> increase during 2 – 6 minutes, after Pumpanen et al. (2009).<br>