不同林龄马尾松凋落物基质质量与土壤养分的关系

Relationships between litter substrate quality and soil nutrients in different-aged Pinus massoniana stands

凋落物的质量、数量及分解速率在一定程度上代表了土壤的营养状况。为了精确估算凋落物分解对土壤碳库的年净归还量及凋落物-土壤生物化学连续体的深层理解,从凋落物基质质量的角度分析了三峡库区不同林龄马尾松凋落物基质质量与土壤养分的作用关系,结果表明:中龄林、近熟林、成熟林马尾松凋落物基质质量中的C、C/N比、C/P比、木质素/N比、木质素/P比差异显著,其中近熟林凋落物叶木质素/N分别比中龄林和成熟林的高33.65%、39.24%,N、P、K、木质素含量差异不显著;但各组织器官的N、P、K含量差异显著,均是皮<枝<叶<杂物,C/N比、C/P比的变化则相反。不同林龄马尾松0—20 cm(0—5cm、5—10 cm、10—20 cm)土壤有机质、总氮、有效磷含量均表现出近熟林<中龄林<成熟林,0—5 cm最大,10—20 cm最小,且随着土壤深度的增加而明显降低,总磷则是中林龄最低,成熟林最大,pH值则各土层均表现为中龄林<成熟林<近熟林,平均pH值为4.55—5.51。凋落物基质质量指标与土壤养分之间冗余分析(RDA)表明:马尾松凋落物基质质量和土壤养分之间关系紧密,N、P、纤维素、半纤维素、木质素、木质素/N比、C/N比对土壤养分影响比较大;凋落物中木质素/N比、C/N比与土壤有机质呈显著负相关,其含量越高越不利于土壤有机质的形成,土壤养分积累的越慢;凋落物基质质量氮含量与土壤氮含量呈显著正相关;土壤pH值、容重与N含量呈显著负相关,与凋落物C/N比、木质素/N比呈显著正相关。马尾松土壤表面有机质、N、P养分含量与凋落物基质质量对应养分含量变化规律一致,土壤养分高,凋落物基质质量相对较高,土壤贫瘠,凋落物基质质量相对较低。

The quality and quantity of litter and its decomposition rate represent,to some extent,the nutritional status of the soil.In order to accurately estimate the contribution of litter decomposition to the annual net return of soil carbon pool and understand the biochemistry of litter-soil continuum,the relationships between litter substrate quality and soil nutrients were studied for different-aged Pinus massoniana stands.The results showed that C,C/N ratio,C/P ratio,lignin/N ratio,lignin/P ratio of litter substrate collected from three different-aged P.massoniana stands were significantly different.The lignin/N ratio of leaf litter in nearly-mature P.massoniana stand was 33.65% and 39.24% higher than that in middle-aged and mature stands,respectively.However,N,P,K and lignin contents of litter substrate did not differ among the different-aged stands.The contents of N,P,and K varied with tissue types showing barkbranchesleafdebris,but the contents of C/N ratio and C/P ratio followed an opposite trend showing barkbranchesleafdebris.The contents of organic matter,total nitrogen,available phosphorus in 0—20 cm soil layer tended to increase from the nearly-mature,to the middle-aged,and mature stands and to decrease from 0—5 cm soil layer,to 5—10 cm,and 10—20 cm soil layer.The total phosphorus was lowest in the middle-aged stands and largest in the mature stand.The soil pH value varied from 4.55—5.55 showing middle-aged standmature standnearly-mature stand.Redundancy analysis（RDA） between litter substrate quality and soil nutrients indicated that the leaf litter substrate quality was significantly correlated with soil nutrients.The effects of litter nitrogen,phosphorus,cellulose,hemicellulose,lignin,lignin/N ratio,and C/N ratio on soil nutrients in different-aged P.massoniana stands were significant.Litter nitrogen content was significantly correlated with total soil nitrogen content.Soil pH,bulk density,and N content were significantly negatively correlated with litter C/N ratio,but positively correlated with lignin/N ratio.Soil surface organic matter,N and P contents were found to depend on nutrients contents in litter substrate.High litter substrate quality resulted in great soil nutrient contents.