Submitted to: Plant and Soil Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/24/2001
Publication Date: N/A
Interpretive Summary: Measurements of root and soil respiration rates are required for a broad range of applications, including monitoring root and microbial activity and assessing plant productivity. However, there is no detailed information available on how soil texture affects estimates of root and soil respiration. It is likely that soil texture will have strong effects CO2 movement in the soil because of its influence on soil porosity. Small pores, for instance, hold water well, but large interconnecting pores are needed for water and air to move freely into and out of the soil. Hence, the present study examines the dynamic relationship between CO2 produced during respiration and subsequent CO2 flux from the soil surface for soils of different textures following wetting and drying cycles. We compared root respiration, soil water content, water uptake and soil CO2 concentrations of citrus growing in three different soil mixtures varying in their ratios of sand, silt and clay. We found that although the different textured soils differed in their soil-plant water relation characteristics, root and soil respiration rates were similar under most soil moisture conditions for soils varying widely in percentages of sand, silt and clay. Only following irrigation did respiration rates vary with soil type, where flux of CO2 from the soil surface was much more restricted after watering in finer textured soils (therefore rendering the respiration measurements inaccurate).
Technical Abstract: Estimates of root and soil respiration are becoming increasingly important in agricultural and ecological research, but there is little understanding how soil texture and water content may affect these estimates. We examined the effects of soil texture on i) estimated rates of root and soil respiration and ii) soil CO2 concentrations, during cycles sof soil wetting and drying in the citrus rootstock, Volkamer lemon. Plants were grown in soil columns filled with three different soil mixtures varying in their sand, silt and clay content. Root and soil respiration rates, soil water content, plant water uptake and soil CO2 concentrations were measured, and, dynamic relationships among these variables were developed for each soil texture treatment. We found that although the different soil textures differed in their plant-soil water relation characteristics, plant growth was only slightly affected. Root and dsoil respiration rates were similar under most soil moisture conditions for soils varying widely in percentages of sand, silt and clay. Only following irrigation did observed respiration rates vary among soils. Efflux of CO2 from the soil surface was much more restricted after watering (therefore rendering any respiration measurements inaccurate) in finer textured soils than sandy soils because of reduced porosity in the finer textured soils. Accordingly, CO2 reached and maintained the highest concentrations in finer textured soils (> 40 mmol). This study revealed that changes in soil moisture can affect interpretations of root and soil measurements based on CO2 efflux, particularly in fine textured soils. The implications of the present findings on field soil CO2 flux measurements are discussed.