Spatial and temporal variability of soil respiration in an irrigated olive grove in southeastern Spain

Olive grove management entails environmental and socio-economic repercussions for the Mediterranean region. Maintaining bare soil in alleys is the most common management in this crop, but its implications for soil respiration (Rsoil) are not well understood. Although previous studies have quantified Rsoil at specific moments, soil respiration has not yet been continuously measured in olive groves. In this study a complete year of Rsoil measurements was taken in an irrigated olive grove in southeast of Spain. To avoid spontaneous weed growth a glyphosate-based herbicide was periodically applied. Six automated soil CO2 efflux chambers with additional sensors of soil temperature (T) and soil water content (SWC) were controled by a multichamber monitoring system (Li-8100A, Li-cor). With the aim of know the spatial variability in Rsoil and facilitate scaling up to estimate ecosystem soil respiration, 3 chambers were installed under the olive tree canopy and 3 chambers in the alleys.Preliminary results show that Rsoil increased in the warmer months and decreased in the colder months as expected. Also, daily Rsoil values under the trees are normally several times higher than in the alleys but this ratio changed with the seasons. In warm months, daily Rsoil under the tree was 2-3 times higher than daily Rsoil in the alley, while in cold months (like January) it was 6 times higher. In the alleys, diurnal variability was detected in Rsoil except in winter. While Rsoil under the trees was practically constant throughout the day during the year except in summer when there appears to be a relationship with the decrease in the flux of photosynthates in environments with high VPD. In spring Rsoil-alleys was double at midday versus night-time. Additionally, a positive and a negative relationship was established with temperature and SWC respectively. On the other hand, we found no clear relationship for Rsoil under the tree with respect to T or SWC. These preliminary results suggest a considerable Rsoil component of total ecosystem respiration influenced by the tree which does not depend on changes in T and SWC and that should be included in the partition models.