高寒沙地两种柳树不同径级细根分解动态特征

Dynamic Characteristics of Fine Root Decomposition of Two Salicaceae Species with Different Diameters in Alpine Sandy Land

为了解高寒沙区杨柳科植物的细根分解特征,以青海共和的乌柳(Salix cheilophila)和沙柳(Salix psammophila)为研究对象,探讨不同径级细根(0~0.5、0.5~1和1~2 mm)的分解规律、养分释放规律及其影响因素,对评价两种杨柳科灌木人工林在共和盆地的长期适应性具有重要意义,为长期研究高寒沙区土壤碳循环和养分循环规律提供理论依据。利用埋袋法,比较不同径级细根在经历了489 d分解后的质量残留率、养分(C、N、P、K)释放率及分解速率与初始养分含量的相关性,总结乌柳和沙柳细根分解动态特征;运用非线性指数衰减模型拟合估算细根分解系数以及分解50%、95%所需的时间。结果表明,细根分解率表现为第一年生长季6—10月分解速率快,11月—次年6月分解速率缓慢,次年生长季6—10月分解速率加快的趋势。两种柳树在前120天均为快速分解阶段,各径级细根质量残留率为77.24%~85.26%,120~360 d为缓慢分解阶段,从第360天开始分解速率缓慢上升。经过489 d分解后,两种柳树细根质量显著下降,残留率为66.44%~82.23%,且分解速率随细根直径增大而增大。通过指数衰减模型拟合得到乌柳和沙柳细根分解极其缓慢,损失95%质量分别需要26 a和38 a。细根分解过程中,乌柳和沙柳不同养分的释放特征不同。细根C、N、P以释放为主,且养分释放速率总体上随细根直径增大而增大。细根质量残留率与初始C/N值呈显著负相关关系(P<0.01),即初始底物C/N值越大,细根初始分解速率越小。

In order to get a better understanding of fine roots decomposition characteristics of Salicaceae in alpine sandy land,fine roots decomposition law,nutrient release law and corresponding influence factors were investigated toward Salix cheilophila and Salix psammophila with fine roots(0~0.5,0.5~1 and1~2 mm)of different diameters,which contributed to the evaluation of long-term adaptability of these two Salicaceae plantations in Gonghe Basin,and further provided theoretical basis on long-term research of alpine sandy soil’s carbon and nutrient cycle.The buried bag method was adopted,and mass loss rate,nutrient(C,N,P,K)release rate,as well as correlation between initial concentrations and mass loss rates,were compared between two Salicaceae with fine roots of different diameters(0~0.5,0.5~1 and 1~2 mm)during 489 days’decomposition process.In addition,fine root decomposition coefficient and the time required for 50%and 95%decomposition were determined by nonlinear exponential regression.Results indicated that fine root decomposition rate performed a“fast-slow-relatively fast”tendency in the first growing seasons(from June to October),cold seasons(from this November to next June),and next growing seasons(from June to October),respectively.Mass residual rate was 77.24%~85.26%after 120 days’rapid decomposition process,followed by slow decomposition phase(120~360 d)and slowly speeding period(360~489 d).Fine root mass of two Salicaceae experienced a remarkable drop,and mass residual rate achieved 66.44%~82.23%after 489 days’decomposition,decomposition rate raised as fine root diameter increased.Nonlinear exponential regression indicated that the required time for 95%mass loss of Salix cheilophila and Salix psammophila were 26 a and 38 a,respectively,with extremely slow decomposition rates.During fine root decomposition process,nutrient release characteristics of Salix cheilophila and Salix psammophila were different.The nutrient C,N,P mainly performed releasing,and nutrient release rate generally raised with the increasing fine root diameter.Fine root mass loss rate was negatively correlated with initial C/N value significantly.The bigger the initial substrate C/N value,the smaller the initial decomposition rate of fine roots.