长期氮添加对杉木人工林土壤碳、氮含量及细根分布的影响

Effect of long-term nitrogen addition on soil C,N and distribution of fine roots of Chinese fir plantation

对福建沙县24a生,经12a氮添加处理的杉木(Cunninghamialanceolata)人工林细根分布进行研究。氮添加量分别为对照N0(0 kg·hm^-2·a^-1)、低氮N1(60 kg·hm^-2·a^-1)、中氮N2(120 kg·hm^-2·a^-1)和高氮N3(240kg·m^-2·a^-1)4种处理,重复次数为3。结果表明中氮(N2)和高氮处理(N3)使杉木人工林表层土壤(0~10 cm)碳(C)含量显著增加(P<0.05),而土壤氮(N)和碳氮比(C/N)各处理间无显著差异。杉木人工林的细根分布也受到长期氮添加影响:在0~10 cm土层,中氮处理(N2)促进细根生长,杉木1级根生物量密度显著增加,而高氮处理(N3)则抑制细根的生长,0~10 cm土层1级根生物量密度显著降低(P<0.05)。在10~20 cm土层,中氮处理(N2)和高氮处理(N3)均使1级根的生物量密度增加(P<0.05)。2~5级根和灌草根生物量密度在低、中、高氮处理(N1-N3)均表现为增加。以上结论表明适当的氮添加可以促进植物细根的增长,而过量氮添加则抑制植物细根的生长。总之,人工林的施肥除了考虑到树种特性和土壤状况,还应考虑到当地的氮沉降量,以便进行合理施肥。

This study investigated the distribution of the fine roots of 24 year-old Chinese fir( Cunninghamia lanceolata)plantation after twelve years’ nitrogen addition. The nitrogen addition amount were CK( N0,0 kg·hm^-2. a^-1),low nitrogen( N1,60 kg·hm^-2. a^-1),medium nitrogen( N2,120 kg·hm^-2. a^-1) and high nitrogen( N3,240 kg·hm^-2. a^-1),respectively,with three replicas of each treatment. The results show that mid-nitrogen( N2) and high-nitrogen( N3) addition increased the soil C concentration of the 0 ~ 10 cm soil layer( P < 0. 05). There were no significant differences between the 4 treatments of soil N and C/N. Long-term nitrogen addition can affect the distribution of fine roots: mid-nitrogen addition( N2) increased while high-nitrogen addition( N3) decreased the biomass of the 1 storder roots of the 0 ~ 10 cm soil layer. All of the three nitrogen additions( N1-N3) increased the biomass of the 2 ndto 5 thorder roots and understory fine roots in both0 ~ 10 and 10 ~ 20 cm soil layers. This study indicates that appropriate nitrogen addition can accelerate the growth of tree fine roots while high nitrogen addition decreases the growth of tree fine roots. Thus,reasonable fertilization of plantation should take into account not only soil conditions and plant species,but also nitrogen deposition.