Influence of vegetation factors on biological soil crust cover on rehabilitated grassland in the hilly Loess Plateau, China

Biological soil crusts (BSCs) perform essential ecosystem functions in arid and semi-arid ecosystems worldwide. The formation, development, and distribution of BSCs are influenced by changes in multiple environmental factors, including changes in the vascular plant community. The influence of changes in vegetation factors on BSC cover in 8-, 12-, and 16-year-old rehabilitated grasslands were studied in the hilly area of the Chinese Loess Plateau. The rate of degradation of BSCs underneath litter (P < 0.01) and the degradation cover of BSCs (P < 0.05) differed significantly between the 8- and 16-year-old successions. Stepwise multiple linear regression analysis showed that the main vegetation factors influencing the dynamics of BSC cover differed among the 8-, 12-, and 16-year-old rehabilitated grasslands. Basal cover, phytomass, and litter cover were the main vegetation factors influencing the dynamics of BSC cover on 8-year-old rehabilitated grassland. Phytomass, litter thickness, and litter cover were the main factors influencing the dynamics of BSC cover on 12-year-old rehabilitated grassland. On 16-year-old rehabilitated grassland, Pielou evenness index, litter thickness, and litter biomass were the main vegetation factors influencing degradation of BSC cover underneath litter, whereas basal cover, litter thickness, and litter biomass were the main vegetation factors influencing the degradation cover of BSCs. At particular stages of herbaceous succession, vegetation factors can have a large influence on changes in the community’s basal cover and litter, which are key factors influencing changes in BSC cover. The degradation of BSCs underneath litter may be a result of complicated eco-physiological processes.     

桂西南喀斯特季节性雨林凋落叶分解速率和养分含量特征分析

森林凋落物是森林生态系统极其重要的组成部分, 了解凋落物分解过程有助于理解森林生态系统的物质循环和养分平衡的机理。本研究以桂西南喀斯特季节性雨林凋落叶为研究对象, 将2018年全年收集的凋落叶混合均匀后采用分解袋法进行原位分解实验, 探讨桂西南喀斯特季节性雨林凋落物的分解特征。结果发现: 凋落叶在分解过程中整体失重模式呈现先快后慢的变化趋势, 且不同生境类型下凋落叶失重率为: 洼地＞坡地＞峰顶; 分解过程中C含量呈波动状态, 但总体表现为下降趋势, 而N含量呈无规则波动; 失重率与海拔呈显著负相关, 并在分解初期和中后期与坡度呈显著负相关, C含量变化同海拔呈显著正相关, 而与其他环境因子的相关性则随分解时间的变化而变化。桂西南喀斯特季节性雨林凋落叶分解速率低于亚热带常绿落叶阔叶混交林, 但与同类型的喀斯特森林退化区相当; 喀斯特季节性雨林不同生境类型代表的微环境因子对凋落叶的分解具有重要影响, 其中海拔引起的温度和湿度的差异是影响喀斯特季节性雨林凋落叶分解速率和C、N含量变化的主要因素。     

Controls on herbaceous litter decomposition in the estuarine ecotones of the Florida Everglades

The effects of nutrient availability and litter quality on litter decomposition were measured in two oligotrophic phosphorus (P)-limited Florida Everglades esturies, United States. The two estuaries differ, in that one (Shark River estuary) is directly connected to the Gulf of Mexico and receives marine P, while the other (Taylor Slough estuary) does not receive marine P because Florida Bay separates it from the Gulf of Mexico. Decomposition of three macrophytes.Cladium jamaicense, Eleochaaris spp., andJuncus roemerianus, was studied using a litter bag technique over 18 mo. Litter was exposed to three treatments: soil surface+macroinvertebrates (=macro), soil surface without macroinvertebrates (=wet), and above the soil and water (=aerial). The third treatment replicated the decomposition of standing dead leaves. Decomposition rates showed that litter exposed to the wet and macro treatments decomposed significantly faster than the aerial treatment, where atmospheric deposition was the only source of nutrients. Macroinvertebrates had no influence on litter decompostion rates.C. jamaicense decomposed faster at sites, with higher P, andEleocharis spp. decomposed significantly faster at sites with higher nitrogen (N). Initial tissue C:N and C:P molar ratios revealed that the nutrient quality of litter of bothEleocharis spp. andJ. roemerianus was higher thanC. jamaicense, but onlyEleocharis spp. decomposed faster thanC. jamaicense. C. jamaicense litter tended to immobilize P, whileEleocharis spp. litter showed net remineralization of N and P. A comparison with other estuarine and wetland systems revealed the dependence of litter decomposition on nutrient availability and litter quality. The results from this experiment suggest that Everglades restoration may have an important effect on key ecosystem processes in the estuarine ecotone of this landscape.     

原状枯落物覆盖对土壤温度及冻融过程的影响

为揭示枯落物在调节土壤温度及土壤冻融过程方面的作用, 对8 cm油松林原状枯落物覆盖(C8)、4 cm油松林原状枯落物覆盖(C4)、8 cm柞树林原状枯落物覆盖(B8)和裸地(CK)4种处理条件下10 cm、20 cm、30 cm、40 cm、50 cm和60 cm深度的土壤温度进行监测, 结果表明: (1) 枯落物覆盖可以延长观测层土壤冻结期, C8观测层完成冻结比CK滞后18 d. (2) 枯落物覆盖对观测层土壤温度的影响具有双重性, 始冻期和完全冻结期具有保温效应, 解冻期主要为隔热降温效应. (3) 枯落物覆盖对30 cm以上土壤影响强于深层, C8处理下仅20 cm以上土层对气温变化敏感. (4) 枯落物对土壤温度的调解作用与覆盖枯落物的厚度和结构有关, 枯落物越厚, 结构越完整, 其调节土壤温度的作用越明显, 不同枯落物覆盖下的土壤温度差异系数为CK > C4 > B8 > C8.     

石漠化区植被恢复过程凋落叶分解特征及其对土壤有机碳/氮的影响——以重庆中梁山为例

运用凋落物分解袋及样品室内分析的方法,研究了石漠化脆弱生态区植被恢复不同阶段主要建群种凋落叶分解及有机碳、氮释放动态及其与土壤团聚体有机碳、氮之间的关系。结果表明:(1)各植被恢复阶段凋落叶分解系数介于0.73～1.33之间,不同阶段之间表现为,草地<灌丛<乔木林<灌乔林,人工樟树林介于乔木林与灌乔林之间。(2)各植被恢复阶段凋落叶有机碳、氮净释放率介于58.5%～72.9%与21.2%～63.9%之间,有机碳在分解期间表现为净释放,有机碳、氮释放率随植被恢复年限的延长呈增加的趋势。(3)凋落叶分解与养分释放对土壤有机碳、氮含量的提高有促进作用。其中,凋落叶分解系数与0.25～1 mm、<0.25 mm粒径团聚体轻组有机碳、氮之间关系密切。在植被恢复过程中,凋落叶分解速率及有机碳、氮释放率随恢复年限延长而呈增加趋势,凋落叶分解对土壤有机碳、氮有重要影响,轻组有机碳、氮优先向小粒径团聚体输入,小粒径团聚体在土壤有机碳、氮积累中有重要作用。凋落叶分解一方面能为植物生长提供养分,同时也促进土壤有机质的形成与积累,植被恢复过程中应加强水土保持、提高土壤层的养分保蓄与抗水土流失能力。      

Salt marsh litter and detritivores: A closer look at redundancy

Most primary production of angiosperms in coastal salt marshes enters the detritivore food web; studies of this link have predominantly focused on one plant species (Spartina alterniflora) and one detritivore species (Littoraria irrorata). In mesocosm experiments, we studied the rates and pattern of decomposition of litter derived from four plant species common in southeastern United States coastal salt marshes and marsh-fringing terrestrial habitats. Crustanceans and gastropods were selected as detritivores feeding on, and affecting degradation of, the litter of two monocotyledons and two dicotyledons. Despite interspecific similarities in consumption, detritivores exhibited species-specific effects on litter chemistry and on the activity of litter-colonizing microbiota. The chemical composition of feces depended upon both the litter type and the detritivores’ species-specific digestive capabilities. Growth rates and survival of detritivores differed among litter species. Different salt marsh detritivores are likely to have different effects on decomposition processes in the salt marsh and cannot be regarded as functionally redundant nor can the litter of different plant species be regard ed as redundant as food for marsh detritivores.     

Effects of flooding regimes on the decomposition and nutrient dynamics of Calamagrostis angustifolia litter in the Sanjiang Plain of China

From May 2005 to September 2006, the potential effects of marsh flooding regimes on the decomposition and nutrient (N, P) dynamics of Calamagrostis angustifolia litter were studied in the typical waterlogged depression in the Sanjiang Plain, Northeast China. The decomposition of C. angustifolia litter was related to four sites with different hydrologic regimes [F1 (perennial flooding, average water depth of 480?days was 40.14?±?8.93?cm), F2 (perennial flooding 33.27?±?6.67?cm), F3 (perennial flooding 23.23?±?5.65?cm) and F4 (seasonal flooding 1.02?±?1.09?cm)]. Results showed that flooding regimes had important effects on the litter decomposition, the decomposition rates differed among the four sites, in the order of F3 (0.001820d^?1)?>?F1 (0.001210d^?1)?>?F2 (0.001040d^?1)?>?F4 (0.000917d^?1), and the values in the perennial flooding regimes were much higher. Flooding regimes also had significant effects on the N and P dynamics of litter in decomposition process. If the perennial flooding regimes were formed in C. angustifolia wetland due to the changes of precipitation in the future, the litter mass loss would increase 23.28?C48.88%, the decomposition rate would increase 13.41?C98.47%, and the t _0.95 would decrease 1.07 yr?C4.50 yr. In the perennial flooding regimes, the net N accumulated in some periods, while the net P released at all times. This study also indicated that the changes of N and P content in the litter of the four flooding regimes were probably related to the C/N or C/P ratios in the litter and the N or P availability in the decomposition environment. If the nutrient status of the decomposition environment did not change greatly, the decomposition rates depended on the substrate quality indices of the litter. Conversely, if the nutrient status changed greatly, the decomposition rates might depend on the supply status of nutrient in the decomposition environment.     

Relative contribution of foliar and fine root pine litter to the molecular composition of soil organic matter after in situ degradation

The influence of litter quality on soil organic matter (SOM) stabilization rate and pathways remains unclear. We used ¹³C/¹⁵N labeled litter addition and Curie-point pyrolysis gas chromatography–mass spectrometry combustion-isotope ratio mass spectrometry (Py–GC–MS–C–IRMS) to explore the transformation of litter with different composition and decay rate (ponderosa pine needle vs. fine root) to SOM during 18 months in a temperate conifer forest mineral (A horizon) soil. Based on ¹³C Py–GC–MS–C–IRMS the initial litter and bulk soil had ∼1/3 of the total pyrolysis products identified in common. The majority was related either to carbohydrates or was non-specific in origin. In bulk soil, carbohydrates had similar levels of enrichment after needle input and fine root input, while the non-specific products were more enriched after needle input. In the humin SOM fraction (260 yr C turnover time) we found only carbohydrate and alkyl C-derived compounds and greater ¹³C enrichment in the “carbohydrate” pool after fine root decomposition. ¹⁵N Py–GC–MS–C–IRMS of humic substances showed that root litter contributed more than needle litter to the enrichment of specific protein markers during initial decomposition.We found little evidence for the selective preservation of plant compounds considered to be recalcitrant. Our findings suggest an indirect role for decomposing plant material composition, where microbial alteration of fine root litter seems to favor greater initial stabilization of microbially derived C and N in SOM fractions with long mean turnover times, such as humin, compared to needles with a faster decay rate.     

喀斯特地区枯落物层对地表径流和土壤侵蚀的影响研究

以枯落物层质量和雨强为影响因素进行室内人工模拟降雨试验,探讨喀斯特地区枯落物层对地表径流和土壤侵蚀的影响规律。结果表明:(1)地表无枯落物覆盖的情形下,除雨强为40mm/h无地表径流外,其它雨强的情形均有产流;且均随着雨强的增加,初始产流时间提前,地表产流产沙量增大。(2)在有枯落物覆盖情形下,初始产流时间有所延缓,在40mm/h雨强下,枯落物层明显影响了地表径流的产生,但随着降雨强度的增加,减少径流效果越来越不明显;(3)枯落物覆盖对减少土壤流失效果显著,其中降雨强度为90mm/h时,枯落物保沙效率约99%,当降雨强度为140mm/h时,达到94%。研究表明,喀斯特地区枯落物层对延缓地表径流和减少土壤侵蚀具有重要作用。     

Effect of tidal flooding on mortality of juvenile muskrats

The effect of tidal flooding on survival of juvenile muskrats (Ondatra zibethicus) was investigated in a brackish marsh in Louisiana by examining 50 muskrat lodges each month from July 1984 to June 1985 and tidal data over a 19-yr period. Tide levels increased at a rate of 1.58 cm yr^?1 during the 19-yr period prior to the study, and during the study nest chambers in muskrat lodges were flooded on 43 d. Seventy-seven captured litters averaged 2.2±0.3 young per litter. older litters were less common than younger litters, but the number of young per litter did not differ among 5-d age classes, suggesting that mortality factors usually affected entire litters. The frequency of tidal flooding prior to opening of lodges each month was associated negatively with the number of litters and number of young per litter. If marsh subsidence and sea level rise continue, tidal flooding will become more prevalent and litter mortality will likely increase.     

森林凋落叶分解过程中单萜烯排放研究进展

对森林凋落叶分解过程中排放单萜烯气体的研究方法、种类、来源、排放量及影响因素进行综述。森林凋落叶分解过程中单萜烯气体排放的研究方法主要是在实验室控制条件下对凋落叶进行培养模拟分解并同步采集分析单萜烯气体样品,或者在野外采用分解袋法对凋落叶进行现场分解后带回实验室采集测定单萜烯气体样品;凋落叶排放的单萜烯目前检测到的有1...     

桂林毛村岩溶区与碎屑岩区檵木和马尾松凋落叶分解研究

为探究岩溶生态环境对凋落叶分解的影响,选用碎屑岩区相同树种作为对比,运用凋落物分解网袋法研究其凋落物分解初期动态,研究结果表明:（1）岩溶区檵木和马尾松凋落叶分解速率总体上均小于碎屑岩区相同树种凋落叶分解速率;（2）凋落叶分解速率k与凋落叶初始养分碳含量呈显著负相关（P<0.05）,与木质素含量呈极显著负相关（P<0.01）;（3）在凋落叶分解过程中,各养分释放规律具有一定的差异,凋落叶养分元素碳在分解过程中呈现出净释放;（4）岩溶区树种的碳释放速率比碎屑岩区慢,说明岩溶区两树种的凋落在一定程度上延长了C的循环周期      

A study of lignin degradation in leaf and needle litter using C-labelled tetramethylammonium hydroxide (TMAH) thermochemolysis: Comparison with CuO oxidation and van Soest methods

We studied the degradation of lignin in leaf and needle litter of ash, beech, maple, pine and spruce using ¹³C-labelled tetramethylammonium hydroxide (¹³C TMAH) thermochemolysis. Samples were allowed to decompose for 27 months in litter bags at a German spruce forest site, resulting in a range of mass loss from 26% (beech) to 58% (ash). In contrast to conventional unlabelled TMAH thermochemolysis, ¹³C-labelling allows thermochemolysis products from lignin, demethylated lignin and other polyphenolic litter compounds (e.g. tannins) to be distinguished. Proxies for lignin degradation (phenol yield; acid/aldehyde ratio of products) changed considerably upon correction for the contribution of non-lignin sources to the thermochemolysis products. Using the corrected values, we found increasing acid/aldehyde values as well as decreasing or constant yield of lignin derived phenols normalised to litter carbon, suggesting pronounced lignin degradation by wood-rotting fungi. No indication for build up of demethylated lignin through the action of brown rot fungi on ring methoxyls was found. The results were compared with those of other analytical techniques applied in previous studies. Like ¹³C-TMAH thermochemolysis, CuO oxidation showed increasing lignin oxidation (acid/aldehyde ratio) and no/little enrichment of lignin derived phenols in the litter. Molecular lignin degradation patterns did not match those from analysis of total acid unhydrolysable residues (AURs). In particular, the long assumed selective preservation of lignin during the first months of litter decomposition, based on AUR analysis, was not supported by results from the CuO and ¹³C TMAH methods.     

Loss and recycling of amino acids and protein from smooth cordgrass (Spartina alterniflora) litter

We investigated the source and composition of free and protein-bound amino acids during the decomposition ofSpartina alterniflora Loisel in laboratory percolators and in a field experiment in the Great Sippewissett Marsh (Falmouth, Massachusetts). In the percolator experiment, 50% of the nitrogen (N) could be extracted fromS. alterniflora litter in 16 d. This extract consisted of dissolved free amino acid N (28%), suspended protein amino acid N (16%), inorganic N (12%), and nitrogen from unidentified compounds (44%). Much of the free amino acid nitrogen was utilized by detrital microorganisms, resulting in a greater loss of suspended protein amino acid (SPAA) nitrogen from the biologically active percolator due to microbials biomass. Suspended microbial mass accounted for at least 50% of the SPAA washed out of the biologically active percolator. In the field study, 38% of the original litter nitrogen was leached fromS. alterniflora litter in litterbags during the first 13 d. After this initial leaching period, the concentration (41% to 69% of total nitrogen) and composition of most amino acids bound in the litter did not change over the 23-month period of the experiment. Increases in microbial protein did not account for increases in total nitrogen which occurred during the decomposition of the litter. Similarly, adsorbed ammonium did not appear to be responsible for this increase.     

积雪变化对中国森林凋落物分解影响研究进展

森林凋落物的分解对于维持生态系统物质循环和养分平衡具有重要意义,并受到不同积雪厚度下冻融格局的影响。冻融期（包括冻结过程期、完全冻结期、融化过程期）是冻土区凋落物分解的重要时期,该时期分解的凋落物量约占全年分解总量的一半。积雪减少通常会导致土壤温度降低、冻融循环次数增加,进而影响凋落物分解。通过综述近10年来积雪变化对我国森林凋落物分解影响的研究成果发现,积雪厚度减少在冻融期通常会抑制凋落物质量损失、碳元素释放和纤维素降解,生长季则起到促进作用,从全年来看多数表现为抑制作用。因此,冻融作用造成凋落物的物理破坏,对其分解的促进作用主要发生在后续生长季。积雪厚度减少在冻融期通常抑制氮元素释放,生长季和全年则无明显规律;磷元素和木质素目前研究还存在很大差异。最后,进一步阐述了积雪变化对凋落物分解影响研究存在的问题及未来研究发展方向。     

Release of arsenic and other trace elements from poultry litter: Insights from a field experiment on the Delmarva Peninsula,Delaware

A poultry litter application was conducted to examine field scale release and transport of trace elements from poultry litter into the subsurface. Field monitoring before and after litter application demonstrated increases in major ion, nutrient, and trace element concentrations in soil water after application, but concentrations of trace elements were all below regulatory standards. Using laboratory stepwise extractions of litter, calculated leaching rates of trace elements are fastest for As, followed by Cu and Zn. Comparison of the projected (from laboratory extractions) to actual (measured in the field) trace element concentrations in litter show that laboratory-derived rates generally over-predict leaching, but the long-term projections of Cu and Zn concentrations remaining in litter are within 20% of the field measurement. Arsenic leaching from litter was under-predicted by the laboratory leaching model by over 100%, suggesting that other processes (perhaps biological) occurring in the field allowed for additional As to be leached/removed. Mass balance coupled with conservative tracer calculations reveal that the vadose sediment was the main sink for the trace elements, with lesser uptake of Cu and Zn (not As) by orchard grass. Overall, results of this study showed that the fate and transport of trace elements from poultry litter are controlled by their leaching rate from litter, adsorption, uptake in vegetation and dilution. An additional process affecting As is biotransformation.     

In situ N and C labelling of indigenous and plantation tree species in a tropical mountain forest (Munessa, Ethiopia) for subsequent litter and soil organic matter turnover studies

We propose a novel pragmatic approach of in situ ¹⁵N and ¹³C isotope labelling of trees for subsequent litter decomposition and turnover studies under field conditions. Using this method the labelling of even large trees under natural conditions is possible and compared to tree labelling under artificial conditions in greenhouses the in situ approach is less expensive. ¹³C and ¹⁵N labelling were carried out simultaneously via photosynthesis by tree gassing with ¹³CO₂ and by stem injection of ¹⁵NH₄¹⁵NO₃. The aims of this study were: (i) to produce a sufficient quantity of labelled plant material for subsequent field incubation studies and (ii) to investigate the effectiveness and distribution of in situ ¹⁵N (¹⁵NH₄¹⁵NO₃) and ¹³C (¹³CO₂) labelling of Podocarpus falcatus, Croton macrostachys, Prunus africana and Cupressus lusitanica. The following targets need to be achieved: (i) Assuming almost natural litter fall conditions, enough labelled plant material must be produced in situ for the turnover experiment; (ii) intra-plant tracer enrichment shall be homogeneous; (iii) tracer enrichment should be comparable for different tree species; and (iv) tracer enrichment must be sufficient for subsequent litter turnover studies using the stable isotope approach. Our results clearly demonstrated that several kilograms of labelled plant material can be produced in situ. For many ecosystems, this amount is sufficient for a long term litter turnover experiment on a field scale under almost natural litter fall conditions. However, intra-plant label uptake of ¹³C and ¹⁵N was heterogeneous so that only leaves (litter) should be used for the turnover study. It could be shown that only a part of the labile C and N fraction in the leaves was labelled. Nevertheless, label uptake was sufficient for subsequent litter turnover studies.     

In situ 15N and 13C labelling of indigenous and plantation tree species in a tropical mountain forest (Munessa,Ethiopia) for subsequent litter and soil organic matter turnover studies

We propose a novel pragmatic approach of in situ ¹⁵N and ¹³C isotope labelling of trees for subsequent litter decomposition and turnover studies under field conditions. Using this method the labelling of even large trees under natural conditions is possible and compared to tree labelling under artificial conditions in greenhouses the in situ approach is less expensive. ¹³C and ¹⁵N labelling were carried out simultaneously via photosynthesis by tree gassing with ¹³CO₂ and by stem injection of ¹⁵NH₄¹⁵NO₃. The aims of this study were: (i) to produce a sufficient quantity of labelled plant material for subsequent field incubation studies and (ii) to investigate the effectiveness and distribution of in situ ¹⁵N (¹⁵NH₄¹⁵NO₃) and ¹³C (¹³CO₂) labelling of Podocarpus falcatus, Croton macrostachys, Prunus africana and Cupressus lusitanica. The following targets need to be achieved: (i) Assuming almost natural litter fall conditions, enough labelled plant material must be produced in situ for the turnover experiment; (ii) intra-plant tracer enrichment shall be homogeneous; (iii) tracer enrichment should be comparable for different tree species; and (iv) tracer enrichment must be sufficient for subsequent litter turnover studies using the stable isotope approach. Our results clearly demonstrated that several kilograms of labelled plant material can be produced in situ. For many ecosystems, this amount is sufficient for a long term litter turnover experiment on a field scale under almost natural litter fall conditions. However, intra-plant label uptake of ¹³C and ¹⁵N was heterogeneous so that only leaves (litter) should be used for the turnover study. It could be shown that only a part of the labile C and N fraction in the leaves was labelled. Nevertheless, label uptake was sufficient for subsequent litter turnover studies.     

The role of biodegradation and photo-oxidation in the transformation of terrigenous organic matter

Microbial and photochemical decomposition are two major processes regulating organic matter (OM) transformation in the global carbon cycle. However, photo-oxidation is not as well understood as biodegradation in terms of its impact on OM alteration in terrigenous environments. We examined microbial and photochemical transformation of OM and lignin derived phenols in two plant litters (corn leaves and pine needles). Plant litter was incubated in the laboratory over 3 months and compositional changes to OM were measured using nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry. We also examined the susceptibility of soil organic matter (SOM) to ultraviolet (UV) radiation. Solid-state ¹³C NMR spectra showed that O-alkyl type structures (mainly from carbohydrates) decreased during biodegradation and the loss of small carbohydrates and aliphatic molecules was observed by solution-state ¹H NMR spectra of water extractable OM from biodegraded litters. Photochemical products were detected in the aliphatic regions of NaOH extracts from both litter samples by solution-state ¹H NMR. Photo-oxidation also increased the solubility of SOM, which was attributed to the enhanced oxidation of lignin derived phenols and photochemical degradation of macromolecular SOM species (as observed by diffusion edited ¹H NMR). Overall, our data collectively suggests that while biodegradation predominates in litter decomposition, photo-oxidation alters litter OM chemistry and plays a role in destabilizing SOM in soils exposed to UV radiation.     

Conditional use of mangrove habitats by fishes: Depth as a cue to avoid predators

The flooded intertidal zone in coastal estuarine systems (e.g., mangroves and salt marshes) is thought to provide nekton with both food and refuge from predators. The primary aim of this study was to identify the relative contribution of root structure, shading, and leaf litter, all characteristic features of mangrove forests, in shaping the intertidal distribution of tidally migrating fishes. We manipulated the structure and shade in 9-m² sample plots in a shallow, mangrove-fringed, intertidal embayment in Tampa Bay, Florida. In a separate field experiment, we compared fish association with standing mangrove leaf litter and bare sand substrate. Shade and leaf litter had a water depthdependent effect on the distribution of the fish; no effect was associated with the presence of mangrove roots. In shallow water (<45 cm), fish were captured primarily in plots without shade, but this distribution shifted progressively with increasing water depth, so that when water was greater than 55 cm most fish were captured in shaded plots. Fish were more frequently associated with, and feeding in, plots covered in leaf litter than bare sand plots. This relationship did not persist at depths greater than 15 cm because fish abundance declined gratly. Tethering experiments usingCyprinodon variegatus demonstrated that predation pressure was quadratically correlated with water depth (inflexion point approximately 60 cm). Our results suggest that small fishes will abandon well-lighted foraging grounds in favor of the potential refuge of shaded waters as water depth increases. We suggest that studies of intertidal nekton should be carefully interpreted in the context of water depth.