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

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.