Soil temperature and bacterial diversity regulate the impact of irrigation and fertilization practices on ecosystem respiration

Abstract

Understanding ecosystem respiration (R eco ) response to various management practices is important for the sustainable development of solar greenhouse systems, which represent a large and profitable industry in Northwest China. A tomato (Lycopersicon esculentum Mill.)-cucumber (Cucumis sativus L.)-tomato rotation experiment was conducted with four treatments including two irrigation levels (regular irrigation [RI] and low irrigation [LI]) and two N fertilizer sources (organic-N fertilizer [N1] and inorganic-N fertilizer [N2]). Ecosystem respiration and soil variables were measured multiple times. Mean R eco flux was 511, 319, and 437 mg m -2 h -1 for tomato-2016, cucumber-2016, and tomato-2017, respectively. Soil temperature was the most important factor affecting R eco magnitude. Tomato seasons with higher temperature had significantly greater R eco flux than the cucumber season. Organic-N fertilizer application can stimulate R eco flux, cumulative R eco , and R eco intensity mainly by providing favorable soil N and C condition for soil bacterial growth and activity, whereas the difference between irrigation levels was inconsistent. The fitted exponential function describing the relationship between R eco and soil temperature showed that the temperature sensitivity decreased from tomato-2016 to tomato-2017 for all treatments, corresponding to the continuously reduced soil bacterial alpha diversity. Soil bacterial Shannon index was an effective prediction factor for R eco in the relatively warmer and drier season, with an R 2 >.8 during tomato-2017. The RIN1 treatment consistently had the greatest cumulative R eco and the highest soil bacterial alpha diversity throughout the rotation. Further studies are needed on the mechanisms of how the change of soil properties would regulate the response of R eco to soil abiotic and biotic factors.