亚热带不同植被恢复阶段林地凋落物层现存量和养分特征

Stock and nutrient characteristics of litter layer at different vegetation restoration stages in subtropical region,China

为揭示亚热带森林植被自然恢复过程中,凋落物层现存量及其养分元素储存能力的演变,采用空间代替时间的方法,在位于亚热带丘陵区的长沙县选取地域相邻、生境条件基本一致的檵木+南烛+杜鹃灌草丛(Loropetalum chinense+Vaccinium bracteatum+Rhododendron simsii scrub-grass-land,LVR)、檵木+杉木+白栎灌木林(L.chinense+Cunninghamia lanceolata+Quercus fabri shrubbery,LCQ)、马尾松+柯+檵木针阔混交林(Pinus massoniana+Lithocarpus glaber+L.chinense coniferous-broad leaved mixed forest,PLL)、柯+红淡比+青冈常绿阔叶林(L.glaber+Cleyera japonica+Cyclobalanopsis glauca evergreen broad-leaved forest,LAG)作为一个恢复序列,设置固定样地,采集未分解层(U层)、半分解层(S层)、已分解层(D层)凋落物样品,测定凋落物层现存量和主要养分元素含量、储量及其释放率,分析植物多样性指数与凋落物层现存量、养分元素含量的相关性。结果表明:1)凋落物层及各分解层凋落物现存量随着植被恢复而增加;同一恢复阶段D层凋落物现存量最高,占凋落物层现存量的41.59%—51.02%,不同分解层凋落物现存量的差异随着植被恢复而增大;各恢复阶段凋落物分解率为0.44—0.61,周转期为1.65—2.28 a。2)凋落物层及各分解层凋落物主要养分元素含量均表现为:N>Ca>Mg>K>P,随着植被恢复呈现出不同的变化特征,其中N、P含量总体上呈增加趋势,K含量LAG(除U层外)最高,PLL最低,Ca含量LCQ最高,PLL最低,Mg含量LAG(除U层外)最高,LVR最低;同一恢复阶段N、P(除PLL、LAG外)、K、Ca、Mg含量随着凋落物的分解而下降。3)不同恢复阶段凋落物层主要养分元素的储量依次为:N>Ca>Mg>K>P;凋落物层及各分解层凋落物主要养分元素总储量及各种养分元素的储量总体上随着植被恢复而增加;同一恢复阶段随着凋落物的分解,N、P储量增加,而K、Ca、Mg储量变化不大;随着植被恢复,凋落物层养分元素储存能力和转化归还能力提高,特别是N,养分元素总释放率下降,有利于养分的固持。4)乔木层、灌木层、草本层的植物多样性指数对凋落物层现存量和主要养分元素含量的影响不同,其中乔木层的影响最明显。

This paper aims to investigate the evolution of litter stocks and its nutrient storage capacity along the natural restoration of subtropical forest vegetation.We used the space-for-time substitution method by selecting four adjacent vegetation communities with almost same habitat conditions in Changsha County,Hunan Province,China.The four communities are comprised of Loropetalum chinense+Vaccinium bracteatum+Rhododendron simsii scrub-grass-land(LVR),L.chinense+Cunninghamia lanceolata+Quercus fabri shrubbery(LCQ),Pinus massoniana+Lithocarpus glaber+L.chinense coniferous-broad leaved mixed forest(PLL),and L.glaber+Cleyera japonica+Cyclobalanopsis glauca evergreen broad-leaved forest(LAG)to represent the secondary forest successional sequence in this region.Permanent plots were established in each vegetation community.Litter samples were collected up into un-decomposed layer litter(U),semidecomposed layer litter(S)and decomposed layers(D).The standing crop of litter,the main nutrient elements content,reserves and release rates were measured.The correlation between plant diversity and litters stock,contents of main nutrients was analyzed.The results showed that:1)the stocks of litter layers and its different decomposed layers increased with the vegetation restoration.The stocks in the D layer were the highest,accounted for 41.59%—51.02% of stocks of litter layer at the same restoration stage.The difference between different decomposition layers increased with the vegetation restoration.The decomposition rates of litters were from 0.44 to 0.61 at different restoration stages,and the cycle time were 1.65 to 2.28 a.2)The contents of main nutrients in litters layer and its different decomposed layers were in the order of N>Ca>Mg>K>P,and presented different variations with vegetation restoration.With vegetation restoration,content of N and P increased on the whole,but K content was the highest in LAG(except U layer)and the lowest in PLL.Ca content was the highest in LCQ and the lowest in PLL,as well as Mg content was the highest in LAG(except U layer)and the lowest in LAG.Contents of N,P(except PLL and LAG),K,Ca and Mg decreased with the decomposition of litters at the same restoration stage.3)The storage of nutrient elements in litter layer followed the order of N>Ca>Mg>K>P at different restoration stages.The total amount of nutrient elements and various nutrient elements in litter layer and its different decomposed layers all increased with the restoration vegetation.At the same restoration stage,both N and P storage increased with the decomposition of litters,however neither K,Ca nor Mg storage changed.With the restoration vegetation,both the nutrient element storage capacity and the transformed-returned capacity of litters were improved,especially N.The release rate of nutrient elements decreased with restoration vegetation,indicating that it was beneficial to the fixation of nutrients.4)Effects of plant diversity index in arbor layer,shrub layer and herb layer on the stocks and nutrient element contents of litter were different,among which the effect of arbor layer was the most.