模拟氮沉降对中亚热带杉木幼树根系生物量的影响

植物根系是全球陆地生态系统碳储量的重要组成部分，在全球生态系统碳循环中起着重要作用，日益加剧的氮沉降会影响根系生物量在空间和不同径级的分配，进而影响森林生态系统的生产力和土壤养分循环。以杉木幼树为研究对象，通过野外氮沉降模拟实验，研究氮沉降四年后对不同土层、不同径级根系生物量的影响。结果发现：（1）低氮和高氮处理总细根生物量较对照均无显著差异（P > 0.05），高氮处理粗根生物量及总根系生物量较对照分别增加45%和40%（P < 0.05）；（2）与对照相比，施氮处理显著增加20-40 cm与40-60 cm土层细根和粗根生物量，且在低氮处理下，20-40 cm土层细根、粗根在总土层细根与粗根生物量的占比显著提高。（3）与对照相比，高氮处理显著增加了2-5 mm、5-10 mm及10-20 mm径级的根系生物量，低氮处理显著增加2-5 mm、5-10 mm径级根系生物量，且显著降低20-50 mm径级根系生物量。综上所述表明：氮沉降后杉木幼树通过增加较粗径级根系来增加对养分及水分的输送，同时通过增加深层根系生物量及其比例的策略来维持杉木幼树的快速生长；而根系生物量的增加，在一定程度上会增加根系碳源的输入，影响土壤碳循环过程。

Effects of simulated nitrogen deposition on root biomass of subtropical Chinese fir saplings

Plant roots are an important part of global terrestrial ecosystem carbon storage and play an important role in global ecosystem carbon cycle. Increasing nitrogen deposition will affect the allocation of root biomass in different soil layers and diameter classes, and further affect the productivity of forest ecosystem and soil nutrient cycle. In this study, the effects of four-year nitrogen deposition on the root biomass of Chinese fir saplings in different soil layers and different diameter classes were investigated. The results showed that: (1) Fine root biomass in the low nitrogen (LN) and the high nitrogen (HN) treatments did not differ from that of the control (CT) (P > 0.05). The coarse roots and total root biomass in HN treatment were 45% and 40% higher than that of CT, respectively (P < 0.05). (2) The biomass of fine roots and coarse roots in 20-40 cm and 40-60 cm soil layers increased significantly after nitrogen addition. In addition, the proportions of fine root biomass and coarse root biomass increased in the 20-40 cm soil layer in LN treatment; (3) Compared with the CT, HN treatment significantly increased root biomass of 2-5 mm, 5-10 mm and 10-20 mm diameter classes, LN treatment significantly increased root biomass (2-5 mm and 5-10 mm in diameter), but reduced root biomass (20-50 mm in diameter). Overall, after nitrogen deposition, Chinese fir saplings could increase the transport of nutrients and water by increasing roots with larger diameter, and maintain the rapid growth by increasing the biomass and proportion of roots in deeper soil layer. To a certain extent, the increase of root biomass will increase carbon input through roots and affect the process of soil carbon cycle.