The role of litter in an old-field community: impact of litter quantity in different seasons on plant species richness and abundance

Summary We studied the effect of removing and adding plant litter in different seasons on biomass, density, and species richness in a Solidago dominated old-field community in New Jersey, USA. We removed all the naturally accumulated plant litter in November (658 g/m²) and in May (856 g/m²) and doubled the amount of litter in November and May in replicated plots (1 m²). An equal number of plots were left as controls. Litter removal and addition had little impact on total plant biomass or individual species biomass in the growing season following the manipulations. Litter removal, however, significantly increased plant densities but this varied depending upon the season of litter removal, species, and life history type. Specifically, the fall litter removal had a much greater impact than the spring litter removal suggesting that litter has its greatest impact after plant senescence in the fall and prior to major periods of early plant growth in spring. Annual species showed the greatest response, especially early in the growing season. Both spring and fall litter removal significantly increased species richness throughout the study. Litter additions in both spring and fall reduced both plant densities and species richness in June, but these differences disappeared near the end of the growing season in September. We concluded than in productive communities where litter accumulation may be substantial, litter may promote low species richness and plant density. This explanation does not invoke resource competition for the decline in species richness. Finally, we hypothesize that there may be broad thresholds of litter accumulation in different community types that may act to either increase or decrease plant yield and diversity.     

Effects of leaf litter on woody seedlings in xeric successional communities

We investigated the effect of leaf litter on the establishment of Eucalyptus incrassata, a mallee eucalypt. It has been suggested that litter accumulation may hinder seedling establishment, and that the removal of litter may be one of the mechanisms through which fire enhances recruitment. We conducted factorial experiments testing the effects of three kinds of leaf litter on E. incrassata seeds and seedlings at three contiguous sites with different land use histories. One site was an uncleared E. incrassata open mallee woodland (Mallee site), one a cleared area that had been ungrazed for about five years (Pasture site) and the third an area of mallee rolled some 40 years ago and permitted to regenerate (Regrowth site). Litter had no effect on emergence of planted E. incrassata seeds, but emergence differed between sites. Overall, the percentage of seeds that germinated and emerged was substantial (mean 35.2% ± 25.9%). Seedling shoot biomass did not differ between sites or litter treatments. Although seedlings grown in Pasture litter suffered higher mortality rates, overall mortality rates were low (mean 13.2% ± 15.5%), suggesting that leaf litter has little effect on recruitment rates during winter and spring. We conclude that leaf litter does not affect emergence or growth in young E. incrassata seedlings during winter and spring, when most establishment occurs. Our results emphasize the difficulty in predicting litter effects on recruitment.     

A more detailed seasonal division of the energy balance and the protein balance of Japanese macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>) on Kinkazan Island,northern Japan

Nakagawa (Am J Primatol 41:267–288, 1997) reported that both the gross energy and gross protein intakes of an adult female Japanese macaque (Macaca fuscata) on Kinkazan Island, northern Japan, were high in spring (March–May) and fall (September–November) and low in summer (June–August) and winter (December–February), and that these values reflected the seasonal differences in nutritional conditions (defined as whether the intakes of energy and protein satisfy the requirements). We estimated the energy balance (energy intake minus its expenditure) and the protein balance (protein intake minus its requirement) of the monkeys on Kinkazan Island every month over the course of 1 year (2004–2005) in order to verify Nakagawa’s conclusions. Like Nakagawa, we found that the energy balance of the monkeys in the fall was higher than in the summer and winter, whereas the protein balance in the fall was higher than in the winter. However, we did not find that spring energy and protein values were greater than summer and winter values. We also did not find that summer protein values were low. Both the energy balance and the protein balance changed rapidly within the same season. The energy intakes and the energy balances were higher in mid-spring and mid- and late fall and lower in late spring and early summer, whereas the protein intakes and the protein balances were higher in mid-spring and mid-summer and lower in early and mid-winter. Since Japanese macaques respond to seasonal changes in food supply by changing their foods, continuous data collection with short intervals is recommended in order to accurately document the energy and protein balances of the monkeys.     

Effect of cultural methods on leaf spot (<Emphasis Type="Italic">Mycosphaerella fragariae</Emphasis>) and gray mold (<Emphasis Type="Italic">Botrytis cinerea</Emphasis>) damage in strawberries

Damage of leaf spot, caused by Mycosphaerella fragariae and gray mold also called Botrytis fruit rot, caused by Botrytis cinerea, average fruit weight and yield were evaluated with regard to cultural methods over 2years. Leaf spot damage decreased significantly by around 90% due to leaf sanitation (removal of dead and leaf spot infected leaves in early spring) and by 50% due to plantation in a one-row-system instead of a two-row-system. When all leaves including the healthy green ones were removed in early spring, average fruit weight decreased significantly by 10%. Fruit sanitation – the third treatment – did not influence any of the measured parameters. Neither leaf sanitation nor fruit sanitation (removal of damaged fruits during harvest) reduced B. cinerea damage significant. Only the combination of a one-row-system, leaf sanitation and fruit sanitation almost halved (not significantly) B. cinerea damage in the first crop year compared to a two-row-system without leaf and fruit sanitation. B. cinerea damage correlated significantly and positively with the biomass of plants by R²= 0.47. According to this study and the cited literature it is suggested for humid Central European conditions to apply a one-row-system combined with leaf sanitation in early spring and fruit sanitation during harvest if fruit density is high, to reduce the risk of damages in larger dimension caused by M. fragariae and B. cinerea.     

东祁连山灌丛凋落叶水浸提液对垂穗披碱草种子萌发和幼苗生长的影响

为了解灌丛凋落叶在灌草群落结构维持中可能存在的潜在化感作用,以东祁连山3种优势灌木和灌下优势草种垂穗披碱草(Elymus nutans)为供试材料,分析了不同浓度(0.01 g/L、0.025 g/L、0.05 g/L、0.075 g/L、0.1 g/L)的金露梅(Potentilla fruticosa)、川滇柳(Salix rehderiana)、头花杜鹃(Rhododendron capitatum)及灌间草本的凋落叶水浸提液,对垂穗披碱草种子萌发、幼苗形态和生理指标的影响。结果表明：(1)垂穗披碱草种子发芽率与发芽势在金露梅与川滇柳凋落叶浸提液处理下呈“低促高抑”的浓度效应,在灌间草本凋落叶浸提液处理时表现为先升后降,而头花杜鹃凋落叶浸提液处理时均下降,并在浓度超过0.075 g/L时种子不发芽。(2)灌丛凋落叶浸提液对垂穗披碱草幼苗根长与干重均表现出抑制作用,且随浓度增大而增强;金露梅、川滇柳与灌间草本凋落叶浸提液对垂穗披碱草幼苗苗高表现出“低促高抑”的浓度效应;而头花杜鹃凋落叶浸提液处理对垂穗披碱草幼苗鲜重与苗高均呈抑制作用。(3)垂穗披碱草幼苗CAT、SOD活性随着浸提液...     

Tree leaf litter composition and nonnative earthworms influence plant invasion in experimental forest floor mesocosms

Dominant tree species influence community and ecosystem components through the quantity and quality of their litter. Effects of litter may be modified by activity of ecosystem engineers such as earthworms. We examined the interacting effects of forest litter type and earthworm presence on invasibility of plants into forest floor environments using a greenhouse mesocosm experiment. We crossed five litter treatments mimicking historic and predicted changes in dominant tree composition with a treatment of either the absence or presence of nonnative earthworms. We measured mass loss of each litter type and growth of a model nonnative plant species (Festuca arundinacea, fescue) sown into each mesocosm. Mass loss was greater for litter of tree species characterized by lower C:N ratios. Earthworms enhanced litter mass loss, but only for species with lower C:N, leading to a significant litter × earthworm interaction. Fescue biomass was significantly greater in treatments with litter of low C:N and greater mass loss, suggesting that rapid decomposition of forest litter may be more favorable to understory plant invasions. Earthworms were expected to enhance invasion by increasing mass loss and removing the physical barrier of litter. However, earthworms typically reduced invasion success but not under invasive tree litter where the presence of earthworms facilitated invasion success compared to other litter treatments where earthworms were present. We conclude that past and predicted future shifts in dominant tree species may influence forest understory invasibility. The presence of nonnative earthworms may either suppress of facilitate invasibility depending on the species of dominant overstory tree species and the litter layers they produce.     

Effects of simulated feeding by snow geese on Scirpus americanus rhizomes

Summary We simulated the feeding of Greater Snow Geese (Chen caerulescens atlantica) on the rhizomes of three-square bulrush (Scirpus americanus) in a tidal marsh along the St. Lawrence River estuary in Québec. During the spring staging period, aboveground biomass is unavailable and geese feed solely on rhizomes and overwintering buds. An experiment was designed to test the effect of three factors on subsequent growth of Scirpus: the intensity of removal (3 to 77% removal of belowground biomass), the number of bites (1, 2 or 3 sections removed) and the number of adventitious buds removed (1, 2 or 3). Rhizomes were dug out in May, treated and transplanted into 85-1 basins sunk in the marsh and filled with marsh soil freed of all plant material. Growth was observed weekly until the end of the growing season in August. Shoots and rhizomes were then collected, dried and weighed to obtain biomass estimates. The net above- and belowground production of Scirpus was inversely related to the initial rhizome biomass removed. At a high level of removal (>35%), the cumulative number of shoots was significantly reduced as early as two weeks after transplantation. The relative reduction in production of the treated rhizomes compared to the control plants was also related to the intensity of removal. An increased number of bites reduced production and the removal of an increased number of adventitious buds further amplified the effect of removal on rhizome production. These experimental results show that even low intensity of feeding by Snow Geese can reduce the production of Scirpus marshes.     

Relative effects of nutrient enrichment and grazing on epiphyte-macrophyte (Zostera marina L.) dynamics

The independent and interactive effects of nutrient concentration and epiphyte grazers on epiphyte biomass and macrophyte growth and production were examined in Zostera marina L. (eelgrass) microcosms. Experiments were conducted during early summer, late summer, fall, and spring in a greenhouse on the York River estuary of Chesapeake Bay. Nutrient treatments consisted of ambient or enriched (3× ambient) concentrations of inorganic nitrogen (ammonium nitrate) and phosphate. Grazer treatments consisted of the presence or absence of field densities of isopods, amphipods, and gastropods. epiphyte biomass increased with both grazer removal and nutrient enrichment during summer and spring experiments. The effect of grazers was stronger than that of nutrients. There was little epiphyte response to treatment during the fall, a result possibly of high ambient nutrient concentrations and low grazing pressure. Under low grazer densities of early summer, macrophyte production (g m^–2 d^–1) was reduced by grazer removal and nutrient enrichment independently. Under high grazer densities of late summer, macrophyte production was reduced by enrichment only with grazers absent. During spring and fall there were no macrophyte responses to treatment. The relative influence of epiphytes on macrophyte production may have been related to seasonally changing water temperature and macrophyte requirements for light and inorganic carbon.     

Colonization and hyperparasitism ofCotesia rubecula (Hym.: Braconidae), a newly introduced parasite ofPieris rapae,in Virginia

A Yugoslavian strain ofCotesia rubecula (Marshall) (Hymenoptera: Braconidae) was released in spring broccoli for control of the imported cabbageworm,Pieris rapae (L.), in Montgomery Co., Virginia, in 1987.C. rubecula reproduced and parasitized imported cabbageworm larvae in fall broccoli in 1987. It was found in moderate numbers in the summer and fall crops in 1988, and by fall had dispersed 0.8 km from the original release site. However, noC. rubecula were detected in our broccoli plots in Montgomery Country in 1989 or 1990. The hymenopteran hyperparasitesIsdromas lycaenae (Walker)(Ichneumonidae), Spilochalcis torvina (Cresson) (Chalcididae), andTetrastichus galactopus (Ratzeburg) (Eulophidae) were found attackingC. rubecula. Hyperparasites emerged from 31.8% and 41.1% of theC. rubecula cocoons in 1987 and 1988, respectively.T. galactopus was the most numerous hyperparasite in 1987, butS. torvina was dominant in 1988. Hyperparasite activity was low during early spring, but increased in July in both years. By August 1988, only hyperparasites emerged from theC. rubecula cocoons collected in the field. In spite ofC. rubecula's success in overwintering, hyperparasites, especiallyS. torvina, may be a limiting factor in the establishment ofC. rubecula in southwestern Virginia.      

Upward cascading effects of nutrients: shifts in a benthic microalgal community and a negative herbivore response

We evaluated the effects of nutrient addition on interactions between the benthic microalgal community and a dominant herbivorous gastropod, Cerithidea californica (California horn snail), on tidal flats in Mugu Lagoon, southern California, USA. We crossed snail and nutrient (N and P) addition treatments in enclosures on two tidal flats varying from 71 to 92% sand content in a temporally replicated experiment (summer 2000, fall 2000, spring 2001). Diatom biomass increased slightly (~30%) in response to nutrient treatments but was not affected by snails. Blooms of cyanobacteria (up to 200%) and purple sulfur bacteria (up to 400%) occurred in response to nutrient enrichment, particularly in the sandier site, but only cyanobacterial biomass decreased in response to snail grazing. Snail mortality was 2–5 times higher in response to nutrient addition, especially in the sandier site, corresponding to a relative increase in cyanobacterial biomass. Nutrient-related snail mortality occurred only in the spring and summer, when the snails were most actively feeding on the microalgal community. Inactive snails in the fall showed no response to nutrient-induced cyanobacterial growths. This study demonstrated strongly negative upward cascading effects of nutrient enrichment through the food chain. The strength of this upward cascade was closely linked to sediment type and microalgal community composition.     

Litter fall and litter layer decay in coastal scrub at Sydney,Australia

Summary Seasonal litter fall and changes in dry weight and minerals within the litter layer were sampled throughout one year. The annual total litter fall was 4.9 t per hectare of which 70% was leaf fall. Litter fall was highest in spring and early summer, the falls of each component (leaf, wood, etc.) and species being markedly seasonal but not all in phase. The annual amounts of minerals cycling as litter fall ranged from 44 kg N to 2 kg P per hectare. Mineral concentrations of the litter fall underwent seasonal variation and in the case of potassium were related to rainfall. The litter layer, mean biomass 19 t ha^-1, declined in weight at a rate of 2.4% per week between spring and summer. The mean turnover time for the dry weight of the litter layer was 3.8 years and for the mineral approx. 1 year (K, Cl) or in excess of 3 years (P, Ca, S, Mg and N).     

Linking community and ecosystem development on Mount St. Helens

In the two decades following the 1980 eruption of Mount St. Helens in Washington State, the N₂-fixing colonizer Lupinus lepidus is associated with striking heterogeneity in plant community and soil development. We report on differences in nutrient availability and plant tissue chemistry between older, dense patches (core) of L. lepidus and more recently established low density patches (edge). In addition, we conducted a factorial nitrogen and phosphorus fertilization experiment in core patches to examine the degree of N and P limitation in early primary succession. We found that there were no significant differences in N or P availability between core and edge L. lepidus patches during the dry summer months, although nutrient availability is very low across the landscape. In the high density patches we found lower tissue N content and higher fiber content in L. lepidus tissue than in the younger edge patches. The addition of nutrients substantially altered plant community composition, with N addition causing an increase in other forb biomass and a corresponding competition-induced decline in L. lepidus biomass. The majority of the positive biomass response came from Hypochaeris radicata. In the second year of the fertilization experiment, the addition of N significantly increased total community biomass while L. lepidus biomass declined by more than 50%. The response of every species other than L. lepidus to N additions suggests that N may be the macronutrient most limiting plant production on Mount St. Helens but that the gains in productivity were somewhat offset by a decline of the dominant species. By the third year of the experiment, L. lepidus began to increase in abundance with P addition. This result suggests co-limitation of the community by N and P.     

Spatial and temporal dynamics of phytoplankton communities along a regulated river system, the Nakdong River, Korea

The longitudinal distribution and seasonal fluctuation of phytoplankton communities was studied along the middle to lower part of a regulated river system (Nakdong River, Korea). Phytoplankton biomass decreased sharply in the middle part of the river (182 km upward the estuary dam), and then increased downstream reaching a maximum at the last sampling station (27 km upward the estuary dam). In contrast, there was little downstream fluctuation in species composition, irrespective of pronounced differences in nutrient concentrations (TN, TP, NO₃, NH₄, PO₄) as well as in algal biomass. In the main river channel, small centric diatoms (Stephanodiscus hantzschii, Cyclotella meneghiniana) and pennate diatoms (Synedra, Fragilaria, Nitzschia) were dominant from winter to early spring (November–April). A mixed community of cryptomonads, centric and pennate diatoms, and coenobial greens (Pediastrum, Scenedesmus) was dominant in late spring (May–June). Blue-green algae (Anabaena, Microcystis, Oscillatoria) were dominant in the summer (July–September). A mid-summer Microcystis bloom occurred at all study sites during the dry season, when discharge was low, though the nutrient concentration varied in each study site. Nutrients appeared everywhere to be in excess of algal requirement and apparently did not influence markedly the downstream and seasonal phytoplankton compositional differences in this river.     

Dispersal and predation in alien Acacia

Summary I investigated seed removal in the litter layer of alien Acacia stands at bimonthly intervals throughout one year. Both ants (dispersers) and rodents (predators) removed significant quantities of seeds and may compete for seeds in low density Acacia stands. Seed removal from depots was greatest prior to seed-fall (Sept.–Nov.) and lowest during seed-fall (Jan.–Mar.). As rodents may consume a large proportion of the annual seed production at low Acacia densities, I propose that ants have played a critical role in accumulating Acacia seed banks.     

Effects of invasive species on plant communities: an example using submersed aquatic plants at the regional scale

Submersed aquatic plants have a key role in maintaining functioning aquatic ecosystems through their effects on the hydrological regime, sedimentation, nutrient cycling and habitat of associated fauna. Modifications of aquatic plant communities, for example through the introduction of invasive species, can alter these functions. In the Sacramento-San Joaquin River Delta, California, a major invasive submersed plant, Brazilian waterweed Egeria densa, has become widespread and greatly affected the functionality of the submersed aquatic plant community. Rapid assessments of the distribution and abundance of this species are therefore crucial to direct management actions early in the season. Given the E. densa bimodal growth pattern (late spring and fall growth peaks), summer assessments of this species may indicate which and where other submersed species may occur and fall assessments may indicate where this and other species may occur in the following spring, primarily because the Delta’s winter water temperatures are usually insufficient to kill submersed aquatic plant species. We assessed community composition and distribution in the fall of 2007 and summer of 2008 using geostatistical analysis; and measured summer biomass, temperature, pH, salinity, and turbidity. In the fall of 2007, submersed aquatic plants covered a much higher proportion of the waterways (60.7%) than in the summer of 2008 (37.4%), with a significant overlap between the seasonal distribution of native and non-native species. Most patches were monospecific, and multispecies patches had significantly higher dominance by E. densa, co-occurring especially with Ceratophyllum demersum. As species richness of non-natives increased there was a significant decrease in richness of natives, and of native biomass. Sustained E. densa summer biomass negatively affected the likelihood of presence of Myriophyllum spicatum, Potamogeton crispus, and Elodea canadensis but not their biomass within patches. Depth, temperature and salinity were associated with biomass; however, the direction of the effect was species specific. Our results suggest that despite native and invasive non-native submersed plant species sharing available niches in the Delta, E. densa affects aquatic plant community structure and composition by facilitating persistence of some species and reducing the likelihood of establishment of other species. Successful management of this species may therefore facilitate shifts in existing non-native or native plant species.     

Effects of two contrasting hemiparasitic plant species on biomass production and nitrogen availability

Hemiparasitic plants can substantially change plant community structure; the drainage of host resources has a direct negative effect on host biomass and, as a consequence, promotes non-host biomass production (parasitism pathway); on the other hand, hemiparasitic litter inputs can enhance nutrient cycling which may have an indirect positive effect on both host and non-host biomass production (litter pathway). We evaluated the net effect of both pathways on total shoot biomass (with and without the hemiparasite) and shoot biomass of graminoids, forbs and ericaceous shrubs using a removal experiment in three sites infested with the annual Rhinanthus angustifolius, and three sites infested with the biennial Pedicularis sylvatica. We addressed the potential importance of litter effects by determination of litter quantity and quality, as well as modeling N release during decomposition. In the second year after removing the hemiparasites, total plant biomass at Rhinanthus sites was 24 % higher in weeded plots than in control plots, while weeding had no significant effect at Pedicularis sites. The increase in total biomass following Rhinanthus removal was mainly due to a higher biomass of graminoids. The amount of litter produced by Rhinanthus was only half of that produced by Pedicularis; N contents were similar. The amount of N in the litter was 9 and 30 % of the amount removed by mowing for Rhinanthus and Pedicularis sites, respectively. Within 2 months, about 45 % of the N in both hemiparasitic litter types was released by decomposition. Our results suggest that in addition to the suppression of host biomass due to parasitism, positive litter feedbacks on host and non-host biomass—via an increase in nutrient availability—also affect plant community structure. We propose that, depending on the particular hemiparasite and/or site conditions, these positive litter feedbacks on shoot biomass can compensate for the negative effect of parasitism.     

Due to symbiotic N2 fixation,five years of elevated atmospheric pCO2 had no effect on the N concentration of plant litter in fertile,mixed grassland

Experimental findings indicate that, in terrestrial ecosystems, nitrogen cycling changes under elevated partial pressure of atmospheric CO₂ (pCO₂). It was suggested that the concentration of N in plant litter as well as the amount of litter are responsible for these changes. However, for grassland ecosystems, there have been no relevant data available to support this hypothesis. Data from five years of the Swiss FACE experiment show that, under fertile soil conditions in a binary plant community consisting of Lolium perenne L. and Trifolium repens L., the concentration of litter N does not change under elevated atmospheric pCO₂; this applies to harvest losses, stubble, stolons and roots as the sources of litter. This is in strong contrast to the CO₂ response of L. perenne swards without associated legumes; in this case the above-ground concentration of biomass N decreased substantially. Increased symbiotic N₂ fixation in T. repens nodules and a greater proportion of the N-rich T. repens in the community are regarded as the main mechanisms that buffer the increased C introduction into the ecosystem under elevated atmospheric pCO₂. Our data also suggest that elevated atmospheric pCO₂ results in greater amounts of litter, mainly due to increased root biomass production. This study indicates that, in a fertile grassland ecosystem with legumes, the concentration of N in plant litter is not affected by elevated atmospheric pCO₂ and, thus, cannot explain CO₂-induced changes in the cycling of N. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparison of insect,fungal, and mechanically induced defoliation of larch: effects on plant productivity and subsequent host susceptibility

Summary Larch sawfly, Pristiphora erichsonii Hartig, and larch needlecast fungus, Mycosphaerella laricinia (R. Hartig) Neg., are early season defoliators restricted only to Larix host trees. Larch defoliation (100%) by either the fungus or insect, but not mechanical removal, induced systemic responses that reduced sawfly consumption and digestion rates one year later. In a feeding behavior assay, larvae quickly abandoned seedlings previously defoliated by M. laricinia. Adult female oviposition choice and egg deposition were unaffected. Seedling growth was not affected during the year of defoliation by M. laricinia, but was significantly reduced one year later. Defoliation by M. laricinia reduced stem volume, radial growth, root biomass and new shoot production. The latter tissue is the only oviposition resource for larch sawfly, and, in contrast, is not influenced by sawfly feeding. We hypothesize that M. laricinia infection may limit larch sawfly populations where both species coexist. However, this reduction is at a substantial net cost to larch productivity.     

氮肥添加对高寒藏嵩草(Kobresia tibetica)沼泽化草甸和土壤微生物群落的影响

以藏嵩草沼泽化草甸为研究对象,利用磷脂脂肪酸(PLFA)技术,研究连续6年N素添加对地上植被群落数量特征、土壤微生物群落结构的影响。结果表明:①藏嵩草沼泽化草甸群落生物量、枯枝落叶对施肥处理无明显响应,且莎草科植物对土壤氮素的吸收和利用率较低。②施肥增加了0-10 cm土壤微生物类群PLFAs丰富度尤其细菌和革兰氏阳性菌PLFAs,降低了10-20 cm PLFAs丰富度;③磷脂脂肪酸饱和脂肪酸/单烯不饱和脂肪酸、细菌PLFAs/真菌PLFAs的比值随土壤层次增加而增加;④0-10 cm土层革兰氏阳性菌、真菌PLFAs含量与pH、土壤速效磷、速效氮、土壤有机质显著正相关(P0.05或P0.01);10-20 cm土层,细菌、革兰氏阳性菌、真菌和总PLFAs含量与土壤有机质含量显著正相关(P0.05或P0.01)。表明藏嵩草沼泽化草甸微生物PLFAs含量和丰富度对施肥的响应存在明显的土层梯度效应,土壤微生物PLFAs含量和丰富度主要受表层土壤初始养分含量的影响。     

Mangrove litter dynamics in La Mancha Lagoon,Veracruz, Mexico

In the mangrove surrounding the coastal lagoon of La Mancha, Veracruz, Mexico, we studied litter fall, litter standing crop, and turnover rates in four different mangrove settings, based on the ecological classification of Lugo and Snedaker (1974). We studied those three prominent ecological processes at the basin, fringe and riverine mangrove settings, being the last one a relict riverine stand. The aim was to describe and compare litter dynamics among mangrove types in a lagoon with an ephemeral inlet, as a way of understanding functional heterogeneity within this coastal ecosystem. The daily average values of litter fall were different (P < 0.01) among mangrove site basin I, formed by Avicennia germinans and Rhizophora mangle (2.35 g/m²/day); basin II, formed by Laguncularia racemosa, Avicennia germinans, and Rhizophora mangle (2.93 g/m²/day); fringe with Rhizophora mangle (2.13 g/m²/day); and relic riverine, also with R. mangle (4.70 g/m²/day). The amount of litter standing crop was different among sites (P < 0.001), and also between the dry and rainy season, for each mangrove type (P < 0.001). Turnover ratios were higher in basin I and basin II sites (6.34 and 7.44 times per year) than in relic riverine and fringe mangroves (1.49 and 2.39 times per year). Interstitial salinity and sediment nutrients varied among mangrove types and could influence litter production. Since this lagoon has an ephemeral inlet, continuous inundation throughout 7–8 months per year has an important effect on litter dynamics.