The Role of Litter Quality Feedbacks in Terrestrial Nitrogen andPhosphorus Cycling

摘要

Many studies in ecosystem ecology argue for strong control of litter quality over nitrogen (N) cycling. Wedeveloped a model for temperate grasslands to test the importance of litter quality in decomposition for N and phosphorus(P) cycling based on the following premises. First, terrestrial N and P cycling differ fundamentally because N is astructural component of the soil organic matter (SOM), whereas P is not. Secondly, SOM has a much lower C:N ratio thanlitter inputs. Thirdly, litter decomposition follows an exponential decay with 20% of the original litter mass turning intoSOM. Fourth, litter N concentration shows an exponential increase during decomposition, whereas P does not change andis released proportionally to the litter mass. Based on these premises we constructed a model which shows that 0.75% N isa critical initial litter concentration at which concentration all N is immobilized and no N is released from the litter. Thusat 0.75% N of the litter all net N mineralization is through SOM decomposition and not through litter decomposition.Phosphorus, in contrast, is primarily released in the early stages of litter decomposition. Empirical tests of these modelpredictions support the applicability of the model to temperate grassland ecosystems. This model predicts that Nmineralization from SOM is much more important than mineralization from litter and that plant litter quality differencesalone cannot explain ecosystem N cycling patterns. Phosphorus, in contrast, does cycle largely through litterdecomposition, and plant litter quality differences are the dominant factor in determining ecosystem P cycling feedbacks.