Evolution of nutrient limitation along a 60,000 yr forest soil chronosequence in Llaima Volcano, Chile

Background/Question/Methods

Few studies have investigated the evolution of nutrient limitation in ecosystems developed on volcanic soils. One-way to approach the problem is using “space for time substitution” to compare sites with the same state factors, except for the time elapsed since the disturbance. Forests of Conguillío National Park in southern Chile occur on volcanic soils that developed from lava flows and ashes of different ages, allowing the reconstruction of a long-term chronosequence. In this study we evaluate the patterns of change in total nutrients (carbon, nitrogen and phosphorous) in soils and leaves along a chronosequence of volcanic substrates from 50 to 60,000 years AP. We tested whether trends in nutrients agree with existing hypotheses for volcanic chronosequence from and Crews et al. and Walker & Syers in Hawaii and New Zealand, respectively. Six soil samples per site and fresh leaves from all plants in each successional site were collected and processed to obtain element concentrations. We also assessed the evolution of N and P limitation in plants by comparing the successional variation in N/P, C/P and C/N ratios.

Results/Conclusions

Results show almost negligible values of total C, N and P in surface soils in the first 250 years of succession, progressively increasing up to a maximum concentration at intermediate stages of succession (300-700 yr), to decline towards more advanced successional stages, a pattern also observed in the chronosequence from Hawaii. N and P concentrations in foliage from deciduous trees increase through the chronosequence, in contrast to evergreen foliage trees (conifers and angiosperms), which maintain fairly stable values in the entire chronosequence. Despite the retrogression phase documented by the decrease in the total contents of N and P in soils, we did not detected a similar decline in the foliar contents of N and P, which suggests that leaf and soil nutrient contents are decoupled. Foliar N/P ratios differed between functional groups (evergreen and deciduous trees), with values greater than 12.5 in evergreen trees, suggesting that the latter are P- limited. The chronosequence from Llaima volcano is of great importance because of its old age, which includes the period of retrogression, and provides clues to understanding current hypothesis on nutrient limitation forest through succession.