川西亚高山天然次生林不同演替阶段土壤-微生物生物量及其化学计量特征

开展不同恢复演替阶段天然次生林土壤-微生物生物量及其化学计量特征关系的研究，可为有效和持续管理川西亚高山次生林提供科学依据。以川西亚高山米亚罗林区20世纪60、70、80年代3种采伐迹地经自然恢复演替形成的次生林（SF60、SF70和SF80）和岷江冷杉（Abies faxoniana）原始林（PF）为研究对象，探讨了表层（0-20 cm）土壤有机碳（C_soil）、全氮（N_soil）、全磷（P_soil）含量及微生物生物量碳（C_mic）、氮（N_mic）、磷（P_mic）含量随自然恢复演替的变化特征，分析了它们的化学计量比与微生物熵（qMB）之间的相互关系。结果表明：（1）随着恢复演替年限的增加，C_soil和N_mic含量显著降低，N_soil和P_soil及C_mic和P_mic含量呈现先升后降的显著变化趋势，且3种次生林的表层土壤碳、氮、磷及其微生物生物量的含量均低于PF。（2）次生林恢复年限对土壤微生物熵C（qMBC）和P（qMBP）没有显著影响，但对土壤微生物熵N（qMBN）存在显著影响。（3）土壤-微生物化学计量不平衡性C_imb：N_imb随自然恢复演替进程呈先降后升的显著变化趋势，C_imb：P_imb呈不显著的降低趋势，N_imb：P_imb呈现显著降低趋势。冗余分析显示，N_imb：P_imb和C_mic：N_mic是影响qMB变化的主导因子，其中N_imb：P_imb解释了qMB变化的62.6%，说明土壤氮磷及其活性组分（N_mic和P_mic）含量变化可能会影响到qMB变化。综上可知，次生林近60 年的自然恢复演替引起了土壤碳氮磷含量的显著变化；天然次生林土壤-微生物生物量碳氮磷化学计量比主要受到氮磷的协同影响，且SF60土壤质量状况较差，为此，对SF60林分可适当增加氮素供给以促进其林木生长，进而提升土壤质量。

Soil and soil microbial biomass contents and C:N:P stoichiometry at different succession stages of natural secondary forest in sub-alpine area of western Sichuan, China

The change characteristics of soil and soil microbial biomass contents of the natural secondary forests could significantly affect the soil organic carbon (C_soil), total nitrogen (N_soil), total phosphorus (P_soil), soil microbial biomass carbon (C_mic), microbial biomass nitrogen (N_mic), microbial biomass phosphorus (P_mic) contents, and their stoichiometry. To gain insights into the change characteristics of soil and soil microbial biomass contents and their stoichiometry along different successional stages of natural secondary forest, four forest types were selected in Miyaluo forest area of western Sichuan, China, which compose of three natural secondary forests (SF60, SF70 and SF80 from clear-logging area during the 1960s, 1970s and 1980s, respectively) and one Abies faxoniana primary forest (PF, 160 years old). C_soil, N_soil and P_soil, C_mic, N_mic and P_mic in 0-20 cm soil were measured. The results showed that contents of C_soil and N_mic marginally significantly decreased, whereas the contents of N_soil and P_soil, C_mic and P_mic increased initially but decreased over time late in the course of restorative succession of natural secondary forests. The contents of C_soil, N_soil, P_soil, C_mic, N_mic, and P_mic in the three natural secondary forests were lower than those in the PF, while the contents of C_soil, N_soil and soil microbial biomass had no significant changes between SF80 and SF70. The content of P_soil was significantly higher in SF70 than that in SF80. The soil C:N:P stoichiometry ratio was dominated by the synergy effect interaction of N_soil and P_soil contents. There was no obvious difference among forests of different successional stages for soil microbial nitrogen carbon quotient (qMBC) and phosphorus quotient (qMBP), but did exist for soil microbial nitrogen quotient (qMBN). qMBN was significantly greater in SF60 than that in the other two successional stages and PF. C_imb:N_imb ratio of the stoichiometric imbalances showed first decreased and then increased; C_imb:P_imb and N_imb:P_imb ratio of the stoichiometric imbalances showed a slightly and significantly gradual reduction, respectively. Redundancy analysis showed that soil microbial quotient (qMB) was significantly correlated with N_imb:P_imb and C_mic:N_mic ratio. N_imb:P_imb ratio revealed 62.6% of the variations in qMB, which implied that changes of qMB values were effected by the contents of N_soil, P_soil and their active components (N_mic and P_mic). Furthermore, our results revealed that nitrogen and phosphorus contribution could be an optimal strategy to meet the microbial stoichiometric demands and enhance nutrient availability for natural secondary forest at the early-successional stages (<60 a) in high-altitude sub-alpine forest ecosystems.