Carbon versus nitrogen release from root and leaf litter is modulated by litter position and plant functional type

Litters of leaves and roots of different qualities occur naturally above‐ and below‐ground, respectively, where they decompose in contrasting abiotic and biotic environments. Therefore, ecosystem carbon (C) and nitrogen (N) dynamics can be strongly affected by the combination of litter position and quality. However, it is poorly understood how C versus N turnover of litters depend on the interplay among plant functional type (PFT), organs, traits and litter position. In a semi‐arid inland dune, soil surface and buried leaf litters and buried fine roots of 25 species across three PFTs (herbs, legume shrubs and nonlegume shrubs) were incubated for 3, 6, 9, 12, 18 and 24 months to investigate litter decomposition and C and N dynamics. Morphological and chemical (nutrient and NMR carbon) traits of initial litters of leaves and fine roots were determined. The litter decomposition rates (k values) of surface leaves and buried fine roots did not differ, but buried fine roots and buried leaf litter decomposed faster than surface leaf litter. Ratios of k values of surface leaves to buried leaves decreased with leaf C:N ratio. Herbs and legume shrubs decomposed faster than nonlegume shrubs for buried fine roots, but not for leaves. At given C loss, buried fine roots had higher N loss than leaf litters; legume shrubs with relatively higher N or lower C:N ratio had higher N loss than nonlegume shrubs. Stronger positive relationships between C and N losses were shown in leaves and legume shrubs than in fine roots and nonlegume shrubs respectively. Synthesis. The generality of faster N release of legume litters at given C release highlights the importance of legumes in N cycling in semi‐arid ecosystems where N is the limiting factor. The dynamics and coordination of C versus N release as a function of litter quality are modulated by litter position and PFT. These findings have important implications for the development of process‐based models on C and N cycles in the context of on‐going global change potentially altering the functional composition of plant communities and the relative quantities and qualities of above‐ground versus below‐ground litter. 摘要 不同质量的叶和细根凋落物分别位于地表和地下，它们在截然不同的非生物和生物环境中分解。因此，凋落物位置和质量对生态系统碳(C)和氮(N)动态具有很强的影响。然而，有关凋落物碳氮周转如何依赖于植物功能型、器官、性状和凋落物位置之间的相互作用的认识仍不清楚。 在半干旱区毛乌素沙地，选择代表三类植物功能型(草本、豆科灌木和非豆科灌木)的25种植物，将叶凋落物(地表和沙埋)和细根(沙埋)分别进行3、6、9、12、18和24个月的原位分解，研究其分解和碳氮动态。测定叶片和细根初始凋落物的形态和化学性状。 地表叶和沙埋细根凋落物的分解速率(k值)没有差异，但沙埋细根和沙埋叶凋落物的分解速率快于地表叶凋落物。地表叶凋落物与沙埋叶凋落物的k值比随叶片