切枝对三峡库区两种榕属乔木生物量积累和枝供给的影响

榕（Ficusmicrocarpa L.）和黄桷树（Ficus virens Ait.var.sublanceolata（Miq.）Corner）是在三峡库区广泛栽植的优良绿化树种.在三峡库区诸多公路、铁路修建和移民搬迁城镇建设等工程建设后的生态恢复和环境改善中,需要大量的榕和黄桷树.榕和黄桷树的繁殖通常采用切枝扦插的营养繁殖方式进行.因种苗培育的需要,对榕和黄桷树进行切枝时常发生,并且为了尽快获得大的种苗,通常切取榕和黄桷树植冠下部的大枝条用于种苗培育.切枝导致植株大量光合叶组织损失,对榕和黄桷树的总体光合生产和生物量积累会发生影响,同时,也会影响新枝的生长和发生数量以及植株再次提供切枝的能力.为了明确切枝对榕和黄桷树生长的影响,对切枝后榕和黄桷树的生物量积累和枝供给进行了研究,目的在于阐明在三峡库区亚热带气候条件下,生长速度比较快的榕和黄桷树是否可以在每年1次的切枝后很好恢复,从而能够可持续地提供切枝用于种苗培育.实验中对榕和黄桷树1a切枝1次,连续进行了3a.实验共设置了4个切枝强度（从植冠下部开始,分别切去植冠长度0%（对照）、20%、50%和70%范围内的所有枝条）和两个切枝处理季节（春季切枝和秋季切枝）.实验结果表明,切枝会减少榕和黄桷树地上部分生物量增量,生物量增量减少的程度与切枝强度呈正相关;并且,每年连续进行的切枝使地上部分生物量增量减少加剧.实验发现,在20%、50%和70%的3个切枝强度中,高切枝强度可以保证在第1次切枝处理中获得高的枝收获量,但并不能保证在第2次和第3次切枝处理中也能获得高的枝收获量.与春季切枝处理相比,秋季切枝处理使榕和黄桷树获得更高的地上部分生物量增量,从而获得更高的枝收获量.就植株地上部分生物量增量和枝收获量而言,切枝强度对二者的影响并不因切枝季节不同而表现出差异.研究表明,对于本实验研究中采用的榕和黄桷树植株,当切枝强度高于20%时,每年1次的切枝不能使榕与黄桷树植株的生长完全恢复.如果切枝每年进行1次,为保证能够可持续地获得切枝并且对植株的生长不造成过大影响,对于本研究中所采用的榕和黄桷树植株而言,最适的切枝强度应低于20%.

Effects of branch removal on biomass production and branch availability of two fig tree species in Three Gorges reservoir region of China

In Three Gorges reservoir region of China, many roads, highways, railways, buildings and even new towns and cities have been constructed or are under construction. In this region, fig tree species Ficus microcarpa and Ficus virens are extensively planted for the ecological restoration and environmental improvement. Using branch cuttings to vegetatively cultivate saplings is a chief way of tree propagation for these two species in Three Gorges reservoir region, annual branch removal from trees of the two species for obtaining branch cuttings are common in the region. To evaluate the effects of annual branch removal on plant growth and subsequent harvest of branch cuttings, a branch removal experiment with four removal intensities (0%, 20%, 50%, and 70%), two removal seasons (spring and autumn) was carried out. Branch removal was conducted in three successive years. Aboveground biomass production of branch-removed Ficus microcarpa and Ficus virens trees decreased following treatment, and this reduction was correlated with branch-removal intensity. Annually repeated branch removal aggravated the decrease of aboveground biomass production. Among removal intensities of 20%, 50%, and 70%, higher removal intensities led to larger branch harvests in all species at the first pruning, but did not necessarily lead to larger branch harvests at the second and the third treatment. Trees subjected to branch removal in autumn produced higher aboveground biomass production, and resulted in a larger branch harvest than trees subjected to branch removal in spring. However, with respect to the aboveground biomass production and branch harvest, no interactions were found between treatment seasons and removal intensities. The results indicate that, in Three Gorges reservoir region, the annual branch removal regime can not provide enough time for these two fig trees to fully recover from removal intensities higher than 20%. The optimal removal intensity which ensures the largest sustainable harvest of branch cuttings from these trees under annual removal regime should be less than 20%.