桂西北不同林龄秃杉人工林土壤碳氮储量

Storage of Soil Carbon and Nitrogen in Taiwania flousiana Plantation at Different Stand Ages

依据广西南丹县山口林场秃杉人工林的栽植和分布状况,于2018年3—4月份在广西南丹县山口林场9、17、25、37年生秃杉(Taiwania flousiana)人工林中,分别选择邻近分布、立地条件基本一致地段,各设置3块20 m×30 m的标准样地;在每块标准样地内按S形随机设置5个代表性采样点,按照土层深度(h)0<h≤20 cm、20 cm<h≤40 cm、40 cm<h≤60 cm、60 cm<h≤80 cm分别采集土壤样品,将同一样地同一土层样品混合均匀,自然风干并粉碎过筛后,测定土壤有机碳质量分数、全氮质量分数;用环刀法采集各土层原状土,测定土壤密度、自然含水量;依据试验测定结果,采用单因素方差分析法、邓肯多重比较法,分析不同林龄秃杉人工林0~80 cm土层土壤有机碳储量、全氮储量及其变化规律。结果表明:①土壤有机碳质量分数、全氮质量分数,随土壤深度加深而下降、随林龄增加而增大。②9、17、25、37年生秃杉人工林土壤(0~80 cm土层),有机碳储量分别为142.47、144.42、151.90、160.64 t·hm-2,全氮储量分别为12.34、12.92、14.41、15.11 t·hm-2,均随林龄增加而增加。③不同林龄土壤,土壤碳质量分数(w(C))∶土壤氮质量分数(w(N))在8.23~13.43之间,随林龄增长而减少、随土壤深度增加而下降。④土壤有机碳质量分数、全氮质量分数、w(C)∶w(N)、土壤密度4个指标之间,均存在密切的相关性,其中土壤有机碳质量分数与全氮质量分数间呈极显著正相关,两者也均与w(C)∶w(N)呈现极显著正相关,但两者与土壤密度呈极显著负相关。⑤综合试验测定结果,秃杉人工林的生长过程,有利于土壤有机碳和全氮的生物积累,从而提高土壤有机碳和全氮储量。

With the planting and distribution status of Taiwania flousiana plantations in Shangkou Forest Farm,Nandan County,Guangxi,three plots of 20 m×30 m were set in adjacent areas with similar site conditions in 9,17,25 and 37-year-old T.flousiana plantations in Shankou Forest Farm,Nandan County,Guangxi from March to April 2018.Five representative sampling points were randomly set in an S-shaped pattern in each plot.Soil samples were collected according to the soil depth(h)categories:0<h≤20 cm,20 cm<h≤40 cm,40 cm<h≤60 cm,and 60 cm<h≤80 cm.The soil samples from the same plot and the same soil depth were mixed uniformly,naturally air-dried,and sieved after crushing.The soil organic carbon and total nitrogen contents were determined.Undisturbed soil samples were collected using volumetric soil samplers for each soil layer,and soil density and natural moisture content were measured.Based on the experimental results,One-way analysis of variance and Duncan’s multiple comparison were used to analyze the soil organic carbon storage,total nitrogen storage,and their variations in the 0-80 cm soil layers of T.flousiana plantations of different ages.Soil organic carbon and total nitrogen contents decreased with increasing soil depth and increased with increasing forest age.The soil organic carbon storage in the 0-80 cm soil layers of 9,17,25 and 37-year-old T.flousiana plantations were 142.47,144.42,151.90 and 160.64 t·hm^(-2),respectively,and the total nitrogen storage were 12.34,12.92,14.41,and 15.11 t·hm^(-2),respectively,both increasing with forest age.The C/N ratio of different forest ages ranged from 8.23 to 13.43,decreasing with increasing forest age and soil depth.There was a close correlation between soil organic carbon mass fraction,total nitrogen mass fraction,C/N ratio,and soil bulk density.The soil organic carbon content was significantly positively correlated with the total nitrogen mass fraction,both of which were also significantly positively correlated with the C/N ratio,but negatively correlated with soil density.Based on the comprehensive experimental results,the growth process of T.flousiana plantations promoted the biological accumulation of soil organic carbon and total nitrogen,thereby increasing soil organic carbon and total nitrogen storage.