Decomposition of mangrove leaf litter in Chunda Bay, north Queensland

Ageing yellow leaves, still attached to branches, but ready to abscise were collected from three mangrove species, Rhizophora stylosa, Avicennia marina and Ceriops tagal var. australis in Chunda Bay. Groups of leaves from each species were weighed and sewn into mesh bags of 2 mm² mesh size. Five leaf groups from each species were retained to derive fresh weight:dry weight:ash free dry weight (AFDW) conversion factors. The remaining bags were distributed in the field according to a combination of habitat (fully submerged in creek or mid-intertidal zone of forest) and site (two sites separated by 1 km of mangrove forest). For each species, 3 bags were removed on days 14, 40, 71, 112 and 156 of the study. Only leaves of Rhizophora and Ceriops from forest habitats remained after this time and were collected on day 348.In the laboratory, leaves from each bag, were rinsed, sieved and a subsample taken for analysis of bacterial densities. The remainder was dried, ground and subsamples were used to determine percent ash, percent carbon and nitrogen and percent soluble tannins. This field research was undertaken to:1. determine decay rates of leaf leaf litter due to bacterial action and leaching in the intertidal zone of mangrove forests and in the adjacent subtidal waters2. determine the nutritive value of different types of leaf detritus to consumers. This study is a component of a larger project to measure the inputs to mangrove detrital pools from a range of sources including turnover of litter by shredders and and the breakdown of wood.

本研究于春达湾（Chunda Bay）采集了三种红树植物的衰老黄叶：此类叶片仍附着于枝条且即将脱落。供试红树物种分别为柱果木榄（Rhizophora stylosa）、海榄雌（Avicennia marina）以及澳洲角果木（Ceriops tagal var. australis）。将各物种的叶片分组称重后，缝制于孔径为2 mm²的网袋中。保留每个物种的5组叶片，用于构建鲜重-干重-无灰干重（ash free dry weight, AFDW）的换算系数。剩余网袋则依据生境（完全浸没于潮沟或红树林潮间带中部）与样点（两个样点间隔1 km红树林距离）的组合设置，部署于野外样地。针对每个物种，分别于实验第14、40、71、112和156天取回3个网袋。直至实验第348天时，仅林生生境下的柱果木榄与角果木叶片残留，遂对其进行采集。在实验室中，对每个网袋内的叶片进行冲洗、过筛，随后分取子样本用于细菌密度分析。剩余样品经干燥、研磨后，再次分取子样本以测定灰分占比、碳氮占比以及可溶性单宁占比。本项野外研究旨在达成以下两个目标：1. 明确红树林潮间带及邻近潮下水域中，细菌作用与淋溶作用导致的叶片凋落物分解速率；2. 探究不同类型叶片碎屑对消费者的营养价值。本研究为一项大型项目的组成部分，该项目旨在量化多种来源向红树林碎屑库的物质输入，其中包括撕食者对凋落物的周转过程以及木质组织的降解过程。