版纳植物园首次系统揭示林冠特殊生境下附生植物枯死物的分解规律

林冠附生植物及其枯死残留物是山地森林生态系统重要的结构性组分，在生态系统养分循环中具有重要的作用，尤其是对于营养来源匮乏、附生植物丰富的林冠环境而言，附生凋落物在林冠层通过分解和淋溶方式向周围环境输入养分的过程，对于整个森林与大气相互作用的关键生态界面层——冠层亚系统尤为重要。

尽管关于不同类型森林林地凋落物的分解作用已开展了大量研究，但目前对于不同附生植物类群的分解与养分动态及其机制，尤其是林冠层特殊生境条件下的植物分解研究鲜有报道。

中国科学院西双版纳热带植物园恢复生态研究组李苏博士及其导师刘文耀研究员以哀牢山亚热带山地湿性常绿阔叶林为对象，选择林冠附生蕨、苔藓、地衣和宿主树木叶片作为实验材料，开展了林冠和林地两种生境条件下的分解及养分动态的对比研究，首次系统揭示了林冠特殊生境下附生植物枯死物的分解规律。

研究结果表明，在林冠生境条件下，所有研究材料的分解速率均比林地面慢15-30%;不同功能团的分解速率和养分释放明显不同，呈现出附生地衣>乔木叶片>附生蕨类>附生苔藓的趋势。枝状地衣的分解速率快于叶状地衣，且其分解速率受其形态特征和初始N和P含量的显著影响;附生苔藓的分解速率最慢，但其N、P元素的释放较快，而附生蕨在分解过程中固定了较多的外源性N、P。

此外，分解中K元素迅速释放，Ca、Mg 最终释放但期间浓度多变。本研究还显示，附生非维管植物在增加森林冠层的有效性营养成分(尤其是N和P元素)方面具有重要作用，附生苔藓和蕨类植物在生物碳固定方面可能扮演着重要角色。

相关研究结果在国际土壤学学术期刊Soil BioLogy & Biochemistry(2014，70：211–220)上发表。研究得到NSFC—云南联合基金、中科院“135”项目及“西部之光”项目的资助。

原文摘要：

Slower rates of litter decomposition of dominant epiphytes in the canopy than on the forest floor in a subtropical montane forest, southwest China

Su Li, Wen-Yao Liu, Da-Wen Li, Ze-Xi Li, Liang Song, Ke Chen, Yun Fu

Epiphytes constitute a substantial proportion of the canopy biomass in subtropical montane forests, and their decomposition has not been adequately addressed, especially in the canopy relative to the forest floor compartments. The rates of litter decomposition and nutrient release of five epiphytes (macrolichensEverniastrum nepalense, Nephromopsis ornata and Usnea florida, moss Homaliodendron flabellatum, and fern Phymatopteris connexa) and two tree species (Castanopsis wattii and Lithocarpus xylocarpus) were quantified over a two-year period using litterbags in the canopy and on the forest floor in an evergreen broad-leaved forest in the subtropical Ailao Mountains in southwest China. After two years, all litter in the canopy decayed 15–30% slower than on the forest floor, with 17–69% and 2–51% of initial masses remaining respectively. Nutrient concentration varied regularly as decay proceeded in the canopy while nutrient amount underwent regular variation on the forest floor. Decay rate and nutrient release differed significantly among functional groups and the order of decay rate was lichen > tree > fern > bryophyte. Lichens had the fastest decay rates, and the fruticose U. florida decayed faster than the other two foliose species. The rate of lichen decomposition was significantly correlated with morphology and initial N and P concentrations. The bryophyte species had the lowest decay rate, but with relatively rapid release of N and P, while the fern had high net N and P immobilization. K was rapidly released from litter. Ca and Mg eventually decreased with variable concentrations during decomposition. Our results highlight the potential importance of nonvascular epiphytes in increasing nutrient availability, especially N and P, in the canopy soil environment, and the probable role of epiphytic bryophytes and ferns in accumulating organic matter.

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