Tree species effects on the distribution of carbon, nitrogen, and calcium in forest soils

Background/Question/Methods

While it is well recognized that different tree species are correlated with variation in soil properties and nutrient cycling rates, it remains unclear how intrinsic soil characteristics influence species distribution and to what degree soil properties are changed as a result of the species present. We are utilizing a common garden experiment to investigate how individual tree species influence the distribution of carbon (C), nitrogen (N), and calcium (Ca) within soils. The Turkey Hill Plantations in Dryden, NY consists of replicated, individual species plots that are now ~60 years old. Controlling for all abiotic soil forming factors, this site provides a unique opportunity to investigate differences in soil properties, and mechanisms which may regulate the distribution of C, N, and Ca within the soil profile. In this study, we are investigating how three tree species, sugar maple (Acer saccharum), red oak (Quercus rubra), and Norway spruce (Picea abies), influence the distribution of C, N, and Ca stocks. In summer 2006, forest floor and soils were collected from 2 plots of each species. The mineral soil profile was collected incrementally in depths 0-7cm, 7-14cm, 14-20cm and 20-40cm. Analysis included total C and N, δ¹³C and δ¹⁵N, and exchangeable Ca. 

Results/Conclusions

Results suggest that different tree species have varying effects on C and N stocks as well as δ¹³C and δ¹⁵N values. Carbon stocks were greatest in the soils beneath Norway spruce while total N varied little between species. There was also a greater percentage of both C and N in the Norway spruce soils and most of this difference was contained in the forest floor and 0-7cm of mineral soil. There was little difference between the deciduous species at any depth. δ¹³C values were greatest for Norway spruce throughout the soil profile. Red oak had a lower δ¹³C value than the other species in the top 0-7cm, exhibiting a δ¹³C value of -29.6‰. Sugar maple δ¹⁵N was extremely variable in the upper 0-7cm with values ranging from -2‰ to 5.8‰. Red oak showed the greatest change in δ ¹⁵N values with depth, with a mean of -1 ‰ in the upper 0-7cm and increasing to 5.2 ‰ in the deeper 20-40cm. Measurement of exchangeable Ca showed that Norway spruce had the greatest concentration in the top 0-7cm and red oak had the smallest. Deeper in the soil profile, sugar maple exhibits the greatest exchangeable Ca content.