On the assessment of root and soil respiration for soils of different textures: interactions with soil moisture contents and soil CO2 concentrations

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 respira tion and (ii) soil CO2 concentrations, during cycles of soil wetting and dr ying in the citrus rootstock, Volkamer lemon (Citrus volkameriana Tan. and Pasq.). Plants were grown in soil columns filled with three different soil mixtures varying in their sand, silt and clay content. Root and soil respir ation rates, soil water content, plant water uptake and soil CO2 concentrat ions were measured and dynamic relationships among these variables were dev eloped for each soil texture treatment. We found that although the differen t soil textures differed in their plant-soil water relations characteristic s, plant growth was only slightly affected. 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 CO2 ef flux from the soil surface vary among soils. That is, efflux of CO2 from th e soil surface was much more restricted after watering (therefore rendering any respiration measurements inaccurate) in finer textured soils than in s andy soils because of reduced porosity in the finer textured soils. Accordi ngly, CO2 reached and maintained the highest concentrations in finer textur ed soils (> 40 mmol CO2 mol(-1)). 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 pr esent findings for field soil CO2 flux measurements are discussed.