氮磷添加对高寒草甸植物群落根系特征的影响

全球变化背景下，持续的氮沉降加速了陆地生态系统的磷循环，进而引发了生态系统中潜在的磷限制，因此研究氮磷耦合对于植物应对环境变化导致的养分限制至关重要。以川西北高寒草甸为研究对象，通过微根管原位监测与室内分析相结合的方法探讨了青藏高原高寒草甸植物根系动态变化特征对不同梯度氮磷添加的响应机制及其与土壤理化特性间的相互关系。结果显示：氮磷（NP）添加增加了表层（0~10 cm）土壤全磷、速效磷以及速效氮含量，整体上降低了土壤pH和C∶P，但对土壤全氮和有机碳含量影响微弱；氮磷添加不仅延长了根系寿命，还使得表层根系现存量提高了8.79（NP₂₀）和13.21 mm·cm^-3（NP₃₀），生产量、死亡量分别提高了3.17（NP₃₀）和2.92 mm·cm^-3（NP₃₀），但深层（10~20 cm）根系现存量降低了8.85（NP₁₀）和5.37 mm·cm^-3（NP₃₀），生产量降低了1.63（NP₁₀）和1.43 mm·cm^-3（NP₂₀），死亡量降低了2.14（NP₁₀）和1.78 mm·cm^-3（NP₃₀）；另外，根系生产量、死亡量及现存量与土壤速效养分的相关性总体上达到了极显著水平（P<0.01）。综上可知，氮磷添加通过改变土壤可利用性氮磷含量，不仅使得植物根系分布浅层化，而且以延长根系寿命的方式减缓了根系周转，进而减少了根系对碳的消耗，增强了其碳汇功能，从而改变了高寒草甸生态系统的碳分配格局。

Effects of nitrogen and phosphorus addition on root characteristics of alpine meadow

This research studied root characteristics， including standing root biomass， root mortality， root production and root life span in alpine meadow in Northwest Sichuan. Our methodology combined ‘minirhizotron’ root viewing tubes and indoor analysis to evaluate effects of nitrogen and phosphorus （NP） addition. The fertilization gradients were 0 （CK）， 10 （NP₁₀）， 20 （NP₂₀） and 30 g·m^-2 （NP₃₀）， respectively. We also discuss the relationships between root characteristics and soil physical and chemical properties. It was found that nitrogen and phosphorus addition increased the levels of total phosphorus， available phosphorus and available nitrogen in the 0-10 cm soil layer， decreased the pH and C∶P， but had little effect on soil total nitrogen and organic carbon levels. Also， N and P addition prolonged root life. Compared to CK， standing root length increased by 8.79 and 13.21 mm·cm^-3 in NP₂₀ and NP₃₀ treatments， respectively and the production and mortality increased by 3.17 mm·cm^-3 and 2.92 mm·cm^-3， respectively， for NP₃₀. However， in the deep soil layer （10-20 cm）， the standing root length decreased by 8.85 mm·cm^-3 for NP₁₀ and 5.37 mm·cm^-3 for NP₃₀， the production decreased by 1.63 mm·cm^-3 for NP₁₀ and 1.43 mm·cm^-3 for NP₂₀， and the mortality decreased by 2.14 mm·cm^-3 for NP₁₀ and 1.78 mm·cm^-3 for NP₃₀. In addition， there was a significant correlation between standing root length， root production， root mortality and soil available nutrients （P<0.01）. In summary， NP addition made the distribution of plant roots shallower through change in the content of soil available nitrogen and phosphorus. Addition of NP slowed down root turnover by prolonging root life， reduced the carbon consumption of the root system and enhanced its carbon sink function， thus changing the carbon distribution pattern of the studied alpine meadow ecosystem.