Fourteen Annually Repeated Droughts Suppressed Autotrophic Soil Respiration and Resulted in an Ecosystem Change

Predictions of future climate over the next 100 years show that the frequency of long periods of droughts in summer will increase in the Netherlands. This study investigated the effect of 14 annually repeated droughts on soil respiration at a Dutch heathland. Field measurements of total soil respiration (RS) and microbial respiration (RH) were modeled to determine annual C losses and to derive root respiration (RA) C losses. The application of repeated droughts resulted in suppression of the total soil C loss from 392 to 332 g C m-2 year-1 in 2010-2011 and from 427 to 358 g C m-2 year-1 in 2011-2012. The RH was the greatest contributor to heathland soil C loss (74-76%) and this was suppressed when directly exposed to drought conditions, although not significantly reduced on an annual basis. Annual RA was suppressed by 42% (2010-2011) and 45% (2011-2012) under repeated drought, indicating there was a greater effect of the repeated annual drought in roots than in microbes. Field observations of photosynthesis (PG) showed paradoxical results, with significantly greater ecosystem PG on the drought treatment than the control treatment. Inclusion of plant activity (PG) as a variable did not improve the fit of the models used in this study. However, other changes in plant composition and structure, such as increasing moss cover on the drought treatment, were noted to have occurred during the 14 years of annually repeated drought and these long term trends may help explain the effects of climate change (drought) on soil processes