氮添加对川西高寒灌丛凋落枝化学计量特征及养分归还的影响

氮(N)是陆地生态系统初级生产力的重要限制因子，大气N沉降的增加将会对植物的化学元素含量和生物量产生重要影响，进而影响凋落物的化学计量特征及其养分归还。高寒灌丛是陆地生态系统的重要组成部分，但有关N沉降对高寒灌丛凋落物尤其是凋落枝的化学元素和生物量的研究还较为缺乏，难以深入揭示N沉降对高寒灌丛土壤碳(C)和养分循环的影响机理。基于此，以青藏高原东部地区的优势高寒灌丛类型—窄叶鲜卑花(Sibiraea angustata(Rehd.) Hand.-Mazz.)灌丛为研究对象，连续4年人工模拟N沉降，分析了凋落枝C、N、磷(P)、木质素和纤维素化学计量特征及其归还量对不同N添加浓度(0、20、50、100 kg hm^-2 a^-1)的响应趋势。结果表明：(1)N添加对凋落枝C、N含量无显著性影响(P>0.05),而对P、木质素和纤维素含量有显著性影响(P<0.05),但不同年份间的影响趋势不一致；(2)4年的N添加并未改变凋落枝的C/N、N/P,但显著降低了凋落枝的木质素/N(第3年)、C/P(第1年和第4年)和C/N/P(第1年);(...

Effects of nitrogen addition on stoichiometric characteristics and nutrient return of twig litter in an alpine shrubland of western Sichuan Plateau, China

Nitrogen (N) is an important limiting factor affecting net primary productivity in terrestrial ecosystems. Consequently, increasing N deposition would profoundly affect litter chemical properties and biomass production, which further affect litter nutrient inputs to soil. However, how long-term N addition influence twig litter nutrients and biomass production is poorly understood. This is especially true for the alpine shrublands, which are important component of terrestrial ecosystems. To fill this gap, we examined N effects on the twig litter stoichiometric properties and nutrient return in an alpine shrubland dominated by Sibiraea angustata of western Sichuan Plateau, China. This shrubland received four levels of N input (N₀, control; N₂₀, 20; N₅₀, 50; N₁₀₀, 100 kg hm^-2 a^-1) during four growing seasons from 2012 to 2015. Our results showed that N addition did not significantly affect total C and N concentrations in the twig litter (P>0.05), but did significantly affect total P, lignin, and cellulose concentrations (P<0.05). The ratios of C/N and N/P did not change significantly after N addition, while the ratios of lignin/N, C/P and C/N/P significantly decreased in the third, first and fourth, and first year of N addition, respectively. Cumulative production of the twig litter biomass, C, N, P, lignin and cellulose (g m^-2 a^-1) from 2012 to 2015 showed a significant quadratic response to increasing N (P<0.05), with the largest value observed for N₅₀ treatment. Our results indicated that the effects of N on the twig litter stoichiometric properties showed a largely annual variation, and appropriate N input promoted carbon and nutrients return to soil by increasing twig litter biomass rather than altering litter chemistry.