脱落酸在林冠受损森林中的动态及对树种组成的影响

Exogenous abscisic acid (ABA) is an important allelochemical and it can accumulate in the soil through successional processes and have an important influence on forest succession. In present, extremely climate event become more frequently and can bring serious damage to forest and change its composition in abroad area. But the dynamic of ABA in a damaged forest community and its effect on forest composition is not be clearly researched. We hypothesized that the concentration of ABA in forest soil will degrade after forest damaged by extremely climate event and the low ABA level in soil is one of the driving factors of the increasing pioneer proportion in forest composition. To this end, we will use an artificial canopy trimming experimental plot on Nanling region to practice experiment. We will survey the dynamic of ABA in forest soil after canopy trimmed for three years to test if ABA concentration decreased. Then we will test the response of the seed germination and seedling growth of species from different successional stage to the inhibition of ABA. The vegetation censuses will be conduct to verify the theoretical deduction finally. We expect this research can consummate the theory about forest community dynamic and provide a new opinion on the technology of damaged forest quickly restoration.

土壤脱落酸浓度随着森林自然演替进程逐渐升高并能促进森林演替。森林演替进程在林冠受到极端气候事件损伤后会受到影响而发生改变，脱落酸在林冠受损森林群落中的动态及其对森林群落树种组成的影响尚不明确。本项目选择位于南岭地区的林冠损伤人工处理实验样地，跟踪监测森林林冠受损后林下土壤中脱落酸的变化动态，结合室内和野外的种子萌发实验研究变化的脱落酸环境对不同演替阶段树种的影响，通过与林冠受损后森林结构的群落调查结果对比分析，验证假说"森林林冠受损后土壤脱落酸浓度的降低是森林结构中先锋种比例上升的驱动因子之一"。研究结果可以完善森林群落动态相关理论，为解决灾后森林的快速健康恢复问题提供新思路。

本项目利用南岭生态定位站针对冰雪灾害建立的人工模拟森林林冠受损实验样地，监测了受损后林冠层的恢复动态，通过群落调查跟踪受损树木的生长情况和林下植被的结构变化，通过凋落物、穿透雨、树干流和林下土壤样品的采集与分析监测林冠受损后土壤脱落酸(ABA)输入量和留存量的变化与恢复动态，通过室内和野外的种子萌发实验研究变化的ABA环境对不同种类植物的影响，分析林冠受损后土壤ABA含量的变化对森林树种组成和演替过程的影响。研究结果表明，模拟损伤处理造成林冠郁闭度降至正常水平的63.6~67.4%，经三年时间即恢复至正常水平；受损后第2~4年ABA通过凋落物和淋溶作用进入土壤的量分别为正常水平的43.4%，62.2%，78.1%，土壤中ABA的含量则分别为正常水平的60.6%，77.2%和81.7%，表明林冠受损造成土壤ABA的输入量和留存量均大幅降低且恢复速度滞后于林冠郁闭度。林冠受损后，演替中前期树种的生长恢复慢于演替中后期树种，大径级树种的恢复慢于小径级树种，表明灾害会促进森林的正向演替。林冠受损造成了林下植被结构的较大变化，血桐(Macaranga tanarius)和山乌桕(Sapium discolor)等阳生树种大量萌生取代了藜蒴(Castanopsis fissa)和鸭公树(Neolitsea chui)成为乔木幼苗优势种，山苍子(Litsea cubeba)和野牡丹(Melastoma candidum)等阳生性灌木取代了鼠刺(Itea chinensis)和尖叶柃(Eurya acuminatissima)成为灌木层优势种，莎草(Cyperus rotundus)和淡竹叶(Lophatherum gracile)等阳生性草本取代了蕨类植物成为草本层优势种。随着林冠的恢复，阳生性植物的优势度逐渐降低，植被结构朝着受损前恢复，表明林冠受损后阳生性林下植物的入侵只是一个短期过程，不会改变森林固有的树种结构。阳生性植物的种子萌发一般比较容易被较低浓度的ABA所抑制，林冠受损造成的土壤ABA含量降低解除了这种抑制作用，一定程度上促进了这类植物的萌生。林冠受损后林下光照的增加和土壤ABA含量的降低是林下阳生植物大量萌生的原因。