小兴安岭次生林细根及枯落物分解影响因素的预测及对不同抚育间伐强度的响应

Prediction of factors affecting fine root and litter decomposition of secondary forests in Lesser Khingan and their responses to different thinning intensities

【目的】探讨抚育间伐对细根及枯落物分解的影响,同时对细根及枯落物分解过程中养分释放的驱动因素进行预测,为研究森林生态系统内的养分循环奠定基础。【方法】在小兴安岭带岭林业实验局东方红林场,设置30 m×30 m的固定样地7块,分别为:A(间伐强度10%)、B(15%)、C(20%)、D(25%)、E(30%)、F(35%),以未间伐样地作为对照样地,记为CK。于2021年7月进行细根及枯落物分解实验,使用Olson衰减模型来表征细根及枯落物分解的质量损失模式,研究不同抚育间伐强度下细根及枯落物的分解情况。同时调查并测定林分因子、土壤理化性质、土壤微生物的相关指标,运用随机森林(Random forest)模型对细根及枯落物养分释放(C释放、N释放、P释放、K释放)进行,确定影响养分释放最主要的因素。【结果】细根分解50%的时间在1.57~2.44 a,分解95%的时间6.8~19.6 a。枯落物分解50%的时间在0.94~1.24 a,分解95%的时间在4.05~4.06 a。枯落物分解速率显著快于细根分解速率。随机森林拟合模型对细根C释放的总方差解释率为67.42%,对细根N释放的总方差解释率为44.71%,对细根P释放的总解释率为79.43%,对细根K释放总方差解释率为73.96%。随机森林拟合模型对枯落物C的总方差解释率为60.61%,对枯落物N释放的总方差解释率为83.97%,对枯落物P释放的总解释率为60.21%,对枯落物K总方差解释率为82.98%。枯落物和细根养分释放主要受其初始的化学基质及化学计量比、微生物碳、氮及碳氮比的驱动。此外,乔木生物量对细根分解有显著的驱动效果;土壤容重及土壤速效钾对枯落物分解有显著的驱动效果。【结论】通过对不同抚育间伐强度下的细根及枯落物分解研究,林内养分循环主要受细根和枯落物本身性质及土壤微生物量的影响。

【Objective】To investigate the effect of tending thinning on the decomposition of fine roots and litter,and to predict the driving factors of nutrient release during the decomposition of fine roots and litter,so as to lay a foundation for studying nutrient cycling in forest ecosystems.【Method】In the Dongfang Red forest farm of Xiaoxing’anling Daling Forestry Experimental Bureau,7 fixed plots of 30 m×30 m were set up,which were A(thinning intensity 10%),B(15%),C(20%),D(25%),E(30%),F(35%),and the unthinned sample plot was used as the control plot and recorded as CK.In July 2021,the decomposition experiment of fine roots and litter was carried out,and the Olson decay model was used to characterize the mass loss mode of fine root and litter decomposition,and the decomposition of fine roots and litter under different thinning intensities was studied.At the same time,the relevant indicators of stand factor,soil physical and chemical properties and soil microorganisms were investigated and measured,and the nutrient release(C release,N release,P release,K release)of fine roots and litter was carried out by random forest model to determine the most important factors affecting nutrient release.【Result】The time of decomposition of fine roots was 1.57-2.44 years,and the time of decomposition of 95%was 6.8-19.6 years.50%of litter decomposition time was 0.94-1.24 years,and 95%decomposition time was 4.05-4.06 years.The rate of litter decomposition was significantly faster than that of fine roots.The total variance interpretation rate of fine root C release by random forest fitting model was 67.42%,the total variance interpretation rate of fine root N release was 44.71%,the total interpretation rate of fine root P release was 79.43%,and the total variance interpretation rate of fine root K release was 73.96%.The total variance interpretation rate of litter C was 60.61%,the total variance interpretation rate of litter N release was 83.97%,the total interpretation rate of litter P release was 60.21%,and the total variance interpretation rate of litter K was 82.98%.The release of litter and fine root nutrients was mainly driven by their initial chemical matrix and stoichiometric ratio,microbial carbon,nitrogen and carbonnitrogen ratio.In addition,arbor biomass had a significant driving effect on fine root decomposition.Soil bulk density and soil available potassium have significant driving effects on litter decomposition.【Conclusion】Nutrient cycling in forest is mainly affected by the properties of fine roots and litter and soil microbial mass.