Is multiple nutrient addition affecting mesofauna-mediated litter decomposition in Patagonian woodlands?

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Margarita M. Fernandez, David M. Eissenstat and Margot W Kaye, Ecosystem Science and Management, The Pennsylvania State University, University Park, PA, Margarita M. Fernandez, David M. Eissenstat and Margot W Kaye, Intercollege Graduate Degree Program in Ecology, The Pennsylvania State University, University Park, PA, Margarita M. Fernandez and Lucas A. Garibaldi, Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural, Universidad Nacional de Río Negro, San Carlos de Bariloche, Río Negro, Argentina, Lucas A. Garibaldi, Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural, CONICET-Universidad Nacional de Río Negro, San Carlos de Bariloche, Río Negro, Argentina

Background/Question/Methods
Impacts of ecosystem nutrient enrichment on plant traits are well known, but cascading effects on secondary decomposers remain elusive. In temperate areas, microarthropods can contribute substantially to leaf litter decomposition. We tested the response of microarthropods litter decomposition to changes in litter quality resulting from multiple nutrient additions in temperate woodlands of NW Patagonia. We used a complete factorial experiment with N, P, and K, resulting in eight treatments in four randomized blocks (n=32). After two years, we installed a decomposition experiment in the same plots using senescent leaf litter from the dominant tree species Nothofagus antarctica. The four treatments resulted from the combination of two factors with two levels: litter from control plots (Q1) and from fertilized plots (Q2), and litterbag mesh size including microarthropods (2 mm) and excluding microarthropods (45 µm). Litterbags were collected at 40, 72, 180, and 376 days to estimate remanent organic matter (OM) and calculate the decomposition rate with the formula: k (year-1) = ln (OM)/t, where “t” is time. Since our site was limited by N and P, we expected multiple nutrient addition to decrease litter C/N ratio and accelerate decomposition in the presence of mesofauna. We used a two-way ANOVA to test the effect of blocks and fertilization treatments on litter C/N and a two-way nested ANOVA to test the effect of nutrient addition and decomposition treatments on the annual litter decay rate. We used a two-way ANOVA to test the effect of blocks and fertilization treatments on litter C/N and a two-way nested ANOVA to test the effect of nutrient addition and decomposition treatments on the annual litter decay rate.
Results/Conclusions
Litter C/N decreased between 15 and 40% among the different fertilization treatments compared to the control treatment. However, litter C/N declined significantly only with PK (p< 0.05) and NP addition (p< 0.01). For these treatments, however, the interaction between increased litter quality and mesofauna inclusion was not significant. In contrast, in control plots there was a significant increase in decomposition with mesofauna inclusion (p< 0.05). We conclude that: 1) NP and PK addition increase litter quality in N. antarctica; and 2) for both fertilization treatments, mesofauna relative contribution is not increased by changes in litter quality.