PRJNA841816
Data and Raw sequence reads for: Fate and stabilization of labile carbon in sandy soil - A question of nitrogen deficiency?
It has been assumed for a long time that stable soil organic carbon (SOC) results from selective preservation of plant residues. Yet, according to the recent paradigm of the microbial carbon pump, even labile C, such as sugars, may persist in soil due to their incorporation into microbial biomass and ultimately necromass with subsequent entombing. Here, we assumed (1) that the long-term stabilization of labile C is low in sandy soil where entombing mechanisms such as associations with clay minerals or aggregation are excluded. Further, (2) we hypothesized that differences in N supply and demand will change the functionality and composition of the microbial community, which will be reflected in the stabilization of microbial C in soil. (3) Specifically, we assumed that labile C does not accumulate under N deficient conditions as microbial residues may be intensely recycled for the N acquisition. To investigate these hypotheses, we conducted a greenhouse experiment including four treatments: bare soil, bare soil+N, tree, and tree+N. The soil was a sandy and nutrient poor forest soil from southern Finland and trees were 1 m high pines (Pinus Sylvestris). In order to follow the fate of labile C, we added 13C labeled glucose to the soil (4 replicates per treatment). Soil was regularly sampled within one year. Measurements of the 13C recovery in soil, microbial biomass, water extractable C, PLFA, amino sugars, and charcoal were conducted. In addition, we analyzed the microbial community structure and enzyme activities. Already within one day, around 40% of the added glucose was lost from the soil, i.e. it has been mineralized. A decrease in recovery mainly occurred within the first 6 months, but stabilized thereafter. After 1 year, the largest amount of glucose-derived C remained in the tree+N treatment (34%), whereas a smaller proportion remained in all other treatments (18%). The recovery in water extractable C was less than 0.8% from the 3rd day on but remained at an elevated level in living microbial biomass (2%) and microbial necromass (1.8%) after 1 year. Bacterial growth on 13C-glucose was higher in fertilized treatments compared to non-fertilized treatments. Overall, fertilization increased the abundance of gram-negative bacteria and trees increased the abundance of fungi, both known to have comparatively recalcitrant residues. Our study demonstrates that considerable amounts of labile C can become stabilized even in sandy soil but only in the absence of C and N limitation. The underlying mechanisms may be both, a small need of microbes to recycle microbial necromass but also the stimulation of a microbial community with more recalcitrant residues.