Nitrogen Gain and Loss Along an Ecosystem Sequence: From Semi-desert to Rainforest

Plants and microorganisms, besides the climate, drive nitrogen (N) cycling in ecosystems. Our objective was to investigate N losses and N acquisition strategies along a unique ecosystem-sequence (ecosequence) ranging from arid shrubland through Mediterranean woodland to temperate rainforest. These ecosystems differ in mean annual precipitation, mean annual temperate, and vegetation cover, but developed on similar granitoid soil parent material, were addressed using a combination of molecular biology and soil biogeochemical tools. Soil N and carbon (C) contents, δ15N signatures, activities of N acquiring extracellular enzymes as well as the abundance of soil bacteria and fungi, and diazotrophs in bulk topsoil and rhizosphere were determined. Relative fungal abundance in the rhizosphere was higher under woodland and forest than under shrubland. This indicates toward plants' higher C investment into fungi in the Mediterranean and temperate rainforest sites than in the arid site. Fungi are likely to decompose lignified forest litter for efficient recycling of litter-derived N and further nutrients. Rhizosphere—a hotspot for the N fixation—was enriched in diazotrophs (factor 8 to 16 in comparison to bulk topsoil) emphasizing the general importance of root/microbe association in N cycle. These results show that the temperate rainforest is an N acquiring ecosystem, whereas N in the arid shrubland is strongly recycled. Simultaneously, the strongest 15N enrichment with decreasing N content with depth was detected in the Mediterranean woodland, indicating that N mineralization and loss is highest (and likely the fastest) in the woodland across the continental transect. Higher relative aminopeptidase activities in the woodland than in the forest enabled a fast N mineralization. Relative aminopeptidase activities were highest in the arid shrubland. The highest absolute chitinase activities were observed in the forest. This likely demonstrates that (a) plants and microorganisms in the arid shrubland invest largely into mobilization and reutilization of organically bound N by exoenzymes, and (b) that the ecosystem N nutrition shifts from a peptide-based N in the arid shrubland to a peptide- and chitin-based N nutrition in the temperate rainforest, where the high N demand is complemented by intensive N fixation in the rhizosphere

Element contents and stable isotope analysis in plants from a nitrogen and potassium tracer experiment in the Chilean Coastal Cordillera

A tracer experiment was conducted in three study sites along a continental transect from arid to humid-temperate conditions in the Chilean Coastal Cordillera. The objective was to determine the short-term (<1 year) plant nitrogen (N) and potassium (K) acquisition from topsoil (A-Bw horizons), subsoil (Bw-BCw horizons), and saprolite (below BCw horizon). In February and March 2016, δ¹⁵N (as Na¹⁵NO₃, 99 at%) and the K analogs rubidium (as RbCl) and cesium (as CsCl) were injected in three soil depths around the focal plants: Gutierrezia resinosa (H.&A.) B. in the northernmost site (arid shrubland), Aristeguietia salvia (C.) K.&R. in the intermediate site (mediterranean woodland), and Araucaria araucana (M.) K. in the southernmost site (temperate rainforest). The injection holes were drilled with an auger and the excavated soil material was collected to determine soil N, K, Rb, and Cs contents. In November 2016, shoot and root material of labeled and unlabeled plants was collected. The N, K, Rb, and Cs contents and the stable isotope ratios of N (expressed as δ¹⁵N) in plant tissue were measured. The tracer recovery by plants was determined by the δ¹⁵N enrichment and the shift of Rb and Cs contents normalized to the K content between reference plants and labeled plants.The data set contains the N, K, Rb, and Cs contents as well as the stable isotope ratios of N in plant biomass

Potassium, rubidium, and cesium contents in soil along a continental transect in the Chilean Coastal Cordillera

A tracer experiment was conducted in three study sites along a continental transect from arid to humid-temperate conditions in the Chilean Coastal Cordillera. The objective was to determine the short-term (<1 year) plant nitrogen (N) and potassium (K) acquisition from topsoil (A-Bw horizons), subsoil (Bw-BCw horizons), and saprolite (below BCw horizon). In February and March 2016, ¹⁵N (as Na¹⁵NO₃, 99 at%) and the K analogs rubidium (as RbCl) and cesium (as CsCl) were injected in three soil depths around the focal plants: Gutierrezia resinosa (H.&A.) B. in the northernmost site (arid shrubland), Aristeguietia salvia (C.) K.&R. in the intermediate site (mediterranean woodland), and Araucaria araucana (M.) K. in the southernmost site (temperate rainforest). The injection holes were drilled with an auger and the excavated soil material was collected to determine soil N, K, Rb, and Cs contents. In November 2016, shoot and root material of labeled and unlabeled plants was collected. The N, K, Rb, and Cs contents and the stable isotope ratios of δ¹⁵N (expressed as δ¹⁵N) in plant tissue were measured. The tracer recovery by plants was determined by the ¹⁵N enrichment and the shift of Rb and Cs contents normalized to the K content between reference plants and labeled plants. The data set contains the K, Rb, and Cs contents in soil