Nutrients (N, P, K, Na) and warming affect heterotrophic respiration in temperate forest litter

Abstract

At present, ecosystems are facing changes caused by global warming and anthropogenic impacts on geochemical cycles. Both temperature and nutrient availability affect litter decomposition; however, little is known about their simultaneous effect on litter decomposition in temperate forests, especially for nutrients such as Na and K. To address this perspective, we investigated how changes in N, P, Na and K supply and increased temperature affect litter decomposition measured as respiration. Moreover, the study determines what changes can be expected in the functioning of two forest types of different fertility (deciduous and coniferous). The respiration measurements were conducted in the laboratory in mesocosms filled with litter from deciduous (oak-hornbeam) and coniferous (mixed pine-oak) forests fertilized by N, P, K, and Na. The experiment was conducted at ambient (14 °C; oak-hornbeam and mixed pine-oak litter) and increased temperatures (22 °C; oak-hornbeam litter). The respiration of oak-hornbeam litter increased with increasing temperature, with Q10 values ranging from 1.49 to 2.14. Our results showed different responses of respiration to nutrient addition between temperatures and litter types. In oak-hornbeam, at 14 °C, the addition of N, P and K decreased respiration, whereas at 22 °C, such an effect was noted only under N application, and P and Na addition increased respiration. In mixed pine-oak litter at 14 °C, respiration decreased after Na addition, and other nutrients had no effect. Together, our results suggest that forecasting the impact of nutrient deposition on ecosystem functioning should consider temperature rise as a factor altering ecosystem responses to fertilization in future research.