Soil Respiration Along a Hydrological Gradient at Harvard Forest EMS Tower 2003-2006

Soil respiration is an important component of the terrestrial carbon budget. Spatial variation of organic matter and plant cover induce temperature and moisture gradations that obscure direct response of soil respiration to radiative forcing. Separation of spatial patterns from microclimate and substrate availability is vital to predict the response to global change. We are measuring temporal and spatial patterns of soil CO2 flux across a hydrological gradient from wetland to upland soils. A system of 8 automated opaque chambers were installed in 2003 along a hydrological gradient on the northeast margin of the "Beaver Swamp" north of the EMS tower (+42.537755,-72.171478). Two additional clear chambers were installed in the wetland in 2006. Each automated chamber closes for a measurement every four hours. The resulting semi-continuous data has been providing a high-temporal density characterization of soil flux during the growing season since 2003. Soil temperature and moisture were recorded in the litter, organic, and mineral soils during 2004 at three locations along the slope. These structures will provide a database of soil respiration flux, temperature, and soil moisture with both high spatial and temporal resolution, across multiple cover types and ground water levels. The analysis will seek to determine the appropriate spatial scale of soil respiration measurement in eastern hardwood forests.

土壤呼吸（soil respiration）是陆地碳收支（terrestrial carbon budget）的重要组成部分。有机质与植被覆盖的空间变异会引发温度与湿度梯度变化，进而掩盖土壤呼吸对辐射强迫（radiative forcing）的直接响应。将空间格局与微气候、底物有效性加以区分，对预测其对全球变化的响应至关重要。本研究测定沿湿地至旱地水文梯度的土壤CO₂通量时空分布格局。2003年，我们在EMS塔（+42.537755,-72.171478）北侧的“海狸沼泽（Beaver Swamp）”东北缘，沿水文梯度布设了8套自动不透明箱（automated opaque chambers）；2006年，又在该湿地内增设了2套透明箱（clear chambers）。每套自动箱每4小时关闭一次以完成一次通量测量。自2003年起，所获取的半连续数据已实现生长季内土壤通量的高时间分辨率表征。2004年，我们在沿坡度分布的3个点位同步记录了枯落物层、有机质层与矿质土壤层的土壤温度与湿度。该观测体系将构建一套兼具高空间与时间分辨率的数据库，涵盖不同植被覆盖类型与地下水位条件下的土壤呼吸通量、温度及土壤湿度数据。本研究旨在明确东部硬叶阔叶林土壤呼吸观测的适宜空间尺度。