The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.     

Inundation,Vegetation, and Sediment Effects on Litter Decomposition in Pacific Coast Tidal Marshes

The cycling and sequestration of carbon are important ecosystem functions of estuarine wetlands that may be affected by climate change. We conducted experiments across a latitudinal and climate gradient of tidal marshes in the northeast Pacific to evaluate the effects of climate- and vegetation-related factors on litter decomposition. We manipulated tidal exposure and litter type in experimental mesocosms at two sites and used variation across marsh landscapes at seven sites to test for relationships between decomposition and marsh elevation, soil temperature, vegetation composition, litter quality, and sediment organic content. A greater than tenfold increase in manipulated tidal inundation resulted in small increases in decomposition of roots and rhizomes of two species, but no significant change in decay rates of shoots of three other species. In contrast, across the latitudinal gradient, decomposition rates of Salicornia pacifica litter were greater in high marsh than in low marsh. Rates were not correlated with sediment temperature or organic content, but were associated with plant assemblage structure including above-ground cover, species composition, and species richness. Decomposition rates also varied by litter type; at two sites in the Pacific Northwest, the grasses Deschampsia cespitosa and Distichlis spicata decomposed more slowly than the forb S. pacifica. Our data suggest that elevation gradients and vegetation structure in tidal marshes both affect rates of litter decay, potentially leading to complex spatial patterns in sediment carbon dynamics. Climate change may thus have direct effects on rates of decomposition through increased inundation from sea-level rise and indirect effects through changing plant community composition.     

Monitoring the abundance of plastic debris in the marine environment

Plastic debris has significant environmental and economic impacts in marine systems. Monitoring is crucial to assess the efficacy of measures implemented to reduce the abundance of plastic debris, but it is complicated by large spatial and temporal heterogeneity in the amounts of plastic debris and by our limited understanding of the pathways followed by plastic debris and its long-term fate. To date, most monitoring has focused on beach surveys of stranded plastics and other litter. Infrequent surveys of the standing stock of litter on beaches provide crude estimates of debris types and abundance, but are biased by differential removal of litter items by beachcombing, cleanups and beach dynamics. Monitoring the accumulation of stranded debris provides an index of debris trends in adjacent waters, but is costly to undertake. At-sea sampling requires large sample sizes for statistical power to detect changes in abundance, given the high spatial and temporal heterogeneity. Another approach is to monitor the impacts of plastics. Seabirds and other marine organisms that accumulate plastics in their stomachs offer a cost-effective way to monitor the abundance and composition of small plastic litter. Changes in entanglement rates are harder to interpret, as they are sensitive to changes in population sizes of affected species. Monitoring waste disposal on ships and plastic debris levels in rivers and storm-water runoff is useful because it identifies the main sources of plastic debris entering the sea and can direct mitigation efforts. Different monitoring approaches are required to answer different questions, but attempts should be made to standardize approaches internationally.     

鄱阳湖水体淹没频率变化及其湿地植被的响应

湖水淹没频率是影响湿地植被生态系统的最重要的水文因素。基于地物波谱特征的MODIS混合像元分解模型,分析了2000—2015年退水期鄱阳湖水体淹没频率的时间变化和空间规律,并在此基础上探讨了湿地植被的空间响应。研究结果表明:(1)鄱阳湖退水期水体的淹没频率总体呈"南低北高",同时具有大小不一的"斑块式"空间分布特征;(2) 15年内湖水的淹没频率经历了先急剧缩减然后恢复到相对稳定的状态,并且不同空间段的变化差异明显:北部河道的淹没频率先急剧降低后回升,中部洲滩不如北部河道段剧烈但大面积的淹没频率下降,南部子湖泊的淹没频率则基本没变;(3)植被丰度对淹没频率具有密切的响应关系,两者呈中间高两边低的"n"形分布,当淹没频率为40%时高植被丰度的像元数最多。(4)淹没频率与植被丰度的关系指示着鄱阳湖湿生植被在空间上的积极演变。     

The effects of agricultural management on the reproductive activity of female rodents in Argentina

The aim of this study was to test if female rodents in border habitats of organic farms have higher reproductive activity than those of conventional farms in south-east Córdoba province, Argentina. The study was conducted in field borders of organic and conventional farms in 2012 and 2013 during the summer months, the time of the year when reproductive activity is more likely. We sampled field borders through a CMR trapping session and recorded vegetation cover, plant litter, vegetation volume, bare ground cover and land use of the field on both sides of the border (crop/crop or crop/pasture). We recorded the number of reproductive females and the rate of postpartum estrus. Green vegetation cover was higher in organic borders whereas plant litter was higher in borders of conventional farms. We used Generalized Linear Mixed Models (GLMM) to determine the factors that influence the number of reproductive females in borders of organic and conventional farms. The number of reproductive females was mainly determined by agriculture management and field type. There were more reproductive females in organic than in conventional borders, and borders associated with crop fields at both sides supported the highest number of reproductive females. The rate of postpartum estrus was higher in organic than in conventional borders. Our results showed that in border habitats of farms under organic management reproductive activity of female rodents was higher than in borders of conventional farms. Organic farm borders may provide high quality habitats that provide resources for reproduction and persistence of rodent populations.     

Exploration and exploitation of foraging patches by desert sparrows: environmental indicators and local evaluation of spatially correlated costs and benefits

Conventional evolutionary and behavioral reasoning expects foragers to show strong spatial preferences in environments with heterogeneous resource distribution. Moreover, consumers should benefit from exploiting the information embedded in environmental features that indicate resource abundance. In desert soils seed abundance associates strong and reliably with vegetation and litter cover at small spatial scales. However, other spatially correlated factors (substrate complexity, temperature, predation risk) may affect foraging costs, benefits and decisions by ground‐feeding granivores. We used a sequence of three semi‐controlled field experiments of binary spatial choice within a portable aviary to identify the main cause of foraging microhabitat selection by the most abundant postdispersal granivorous bird in the central Monte desert (Argentina). In the first experiment we placed the aviary at field to offer pairs of adjacent microhabitats of unmodified, naturally‐contrasting substrates and environmental conditions to single, untrained rufous‐collared sparrows Zonotrichia capensis. Birds selected covered microhabitats in winter and summer, ruling out substrate complexity or thermoregulation as main single causes of patch selection. The other two experiments dissociated seed abundance, tree cover and litter to reveal their effects on patch selection. The results indicate that 1) sparrows do not restrict microhabitat exploration relying on environmental indicators, 2) distance to tree cover influences the order of patch exploration, probably in association with apprehension or risk‐assessment behavior, and 3) patch exploitation is determined by short‐term local estimation of seed abundance. The integration of these with previous results obtained under variable degrees of realism and experimental control allows for a better explanation of the spatial component of postdispersal granivory and its consequences on plants. The unconstrained selective foraging strategy of these sparrows would allow them to detect sporadic or ephemeral rich patches with structural characteristics indicating ‘low‐quality’, should promote the spatial homogenization of the palatable seed bank, and would favor indirect interactions between plants.     

Indirect effects of habitat disturbance on invasion: nutritious litter from a grazing resistant plant favors alien over native Collembola

Biological invasions are major threats to biodiversity, with impacts that may be compounded by other forms of environmental change. Observations of high density of the invasive springtail (Collembola), Hypogastrura manubrialis in heavily grazed renosterveld vegetation in the Western Cape, South Africa, raised the question of whether the invasion was favored by changes in plant litter quality associated with habitat disturbance in this vegetation type. To examine the likely mechanisms underlying the high abundance of H. manubrialis, cages with three types of naturally occurring litter with different nutrient content were placed out in the area and collected after different periods of time. Hypogastrura manubrialis was mainly found in the nutrient‐rich litter of the yellowbush (Galenia africana), which responds positively to disturbance in the form of overgrazing. This suggests that invasion may have been facilitated by a positive interaction with this grazing resistant plant. By contrast, indigenous Collembola were least abundant in yellowbush litter. Negative correlations between high abundance of H. manubrialis and the abundance and diversity of other species suggest that competitive interactions might underlie low abundance of these other species at the patch level. Group behavior enables H. manubrialis to utilize efficiently this ephemeral, high quality resource, and might improve its competitive ability. The results suggest that interactions among environmental change drivers may lead to unforeseen invasion effects. H. manubrialis is not likely to be very successful in un‐grazed renosterveld, but in combination with grazing, favoring the nutrient‐rich yellowbush, it may become highly invasive. Field manipulations are required to fully verify these conclusions.     

Dynamics of Organic Matter Decomposition and Microflora Composition of Forest Litter in Artificial Biogeocenoses

The dynamics of litter stock, microbial biomass, and composition and structure of microbial communities, were studied in the course of soil organic matter transformation during vegetation season. The dynamics of litter stock in coniferous and deciduous forests proved to correlate with the biomass and total abundance of microorganisms, particularly, with the proportion of microfungi in the microbial community.     

Effects of the litter layer of Pteridium aquilinum on seed banks under experimental restoration

Questions: Does the litter layer of Pteridium aquilinum (bracken) act as a barrier to certain species in the seed bank? Does bracken control/restoration treatment affect seed transfer through the litter layer? Location: Five experiments at three sites across the UK covering two major vegetation types; acid‐grassland and heath‐land. Methods: At each experiment a range of bracken control and vegetation restoration treatments were applied for about ten years. The seed bank was sampled in both the bracken litter and the soil. The cover (%) of each species in the vegetation and the bracken litter abundance (cover and depth) was also estimated. Results: The bracken litter layer acts as an inert barrier as it contained a large proportion of seeds available in the litter‐soil profile (38%– 67% of the total). Bracken litter depth and cover also influenced significantly the seed bank composition in both the bracken litter and the soil. These effects were site‐specific, and species‐specific. The application of treatments changed significantly the balance between seed inputs and outputs in the bracken litter layer for some species. This was either a positive or negative response relative to the untreated control plots. Conclusion: For heathland and acid‐grassland restoration, the bracken litter layer may be an important seed source, but it must be disturbed particularly before seed addition.     

三江平原典型湿地枯落物早期分解过程及影响因素

枯落物分解是湿地物质循环和能量流动的关键环节,是维持湿地功能的重要过程之一。采用分解袋法对三江平原3种典型湿地植物枯落物分解过程及影响因素进行了研究。研究表明,在164d实验过程中乌拉苔草分解速率始终最快;在分解前103d中毛果苔草分解速率大于小叶章,但在103~164d间小叶章分解速率大于毛果苔草;分解164d,小叶章、乌拉苔草和毛果苔草枯落物的失重率分别为初始重的31.98%、32.99%和28.91%。分解过程中小叶章和毛果苔草枯落物中有机碳浓度波动较大,而乌拉苔草枯落物中持续下降;3种枯落物有机碳绝对含量都表现为净释放。小叶章枯落物中N浓度波动较大,绝对含量发生净释放;毛果苔草枯落物N浓度持续增加,绝对含量净增加;乌拉苔草枯落物N浓度先增加后减少,绝对含量发生净释放。3种枯落物中P浓度都先迅速下降后缓慢上升,绝对含量都表现为净释放。3种枯落物中C/N和C/P也相应的发生变化。小叶章和乌拉苔草枯落物分解速率与枯落物C/P显著相关,而毛果苔草枯落物与枯落物N浓度显著相关;对应3种枯落物分解速率的主要环境因子分别为土壤含水量、土壤容重和土壤温度。3种枯落物分解速率和营养物质含量动态受到枯落物自身质量和温湿条件、周围环境营养状况等自然环境条件的共同影响,相比而言,受枯落物质量的影响更大。     

Riparian leaf litter decomposition on pond bottom after a retention on floating vegetation

Allochthonous (e.g., riparian) plant litter is among the organic matter resources that are important for wetland ecosystems. A compact canopy of free‐floating vegetation on the water surface may allow for riparian litter to remain on it for a period of time before sinking to the bottom. Thus, we hypothesized that canopy of free‐floating vegetation may slow decomposition processes in wetlands. To test the hypothesis that the retention of riparian leaf litter on the free‐floating vegetation in wetlands affects their subsequent decomposition on the bottom of wetlands, a 50‐day in situ decomposition experiment was performed in a wetland pond in subtropical China, in which litter bags of single species with fine (0.5 mm) or coarse (2.0 mm) mesh sizes were placed on free‐floating vegetation (dominated by Eichhornia crassipes, Lemna minor, and Salvinia molesta) for 25 days and then moved to the pond bottom for another 25 days or remained on the pond bottom for 50 days. The leaf litter was collected from three riparian species, that is, Cinnamomum camphora, Diospyros kaki, and Phyllostachys propinqua. The retention of riparian leaf litter on free‐floating vegetation had significant negative effect on the carbon loss, marginal negative effects on the mass loss, and no effect on the nitrogen loss from leaf litter, partially supporting the hypothesis. Similarly, the mass and carbon losses from leaf litter decomposing on the pond bottom for the first 25 days of the experiment were greater than those from the litter decomposing on free‐floating vegetation. Our results highlight that in wetlands, free‐floating vegetation could play a vital role in litter decomposition, which is linked to the regulation of nutrient cycling in ecosystems.     

Effects of environmental factors on the ant fauna of restinga community in Rio de Janeiro, Brazil

The effects of environmental factors on the richness, diversity and abundance of ants were studied in the Restinga da Marambaia, south coast of Rio de Janeiro State, Brazil. The samples were taken using pitfall traps in August/2004 (winter) and March/2005 (summer) in three different vegetation types: (1) herbaceous ridge palmoid (homogeneous habitat); (2) shrub dune thicket and (3) ridge forest (heterogeneous habitats). At each habitat a range of environmental attributes was recorded: soil temperature and humidity, percentage of soil covering by litter and litter depth. Ninety-two ant species belonging to 36 genera and eight subfamilies were recorded. Density of ant species and abundance varied significantly between habitats and seasons; ant diversity varied only between habitats. Homogeneous habitat had lower ant species density, abundance and diversity than heterogeneous habitats. The two first variables were positively correlated with litter depth and both were higher in summer than in winter samples. There were more species of Ponerinae and Ectatomminae in heterogeneous than in the homogeneous habitat, whereas the Formicinae species were more abundant in the later.     

Accumulation rates of soil organic matter in wet dune slacks on the Dutch Wadden Sea islands

Background and aims

A long-term monitoring program (ranging from 16 to 77 years) on the Dutch Wadden Sea Islands provided well-documented examples of vegetation succession in wet dune slacks. We used this opportunity to study soil organic matter (SOM) accumulation in relation to vegetation succession. The aim of this paper is to identify the factors which regulate accumulation rates of SOM in wet dune slacks.

Methods

We used several soil chronosequences using data from the monitoring program together with data from a long-term research activity and more recent measurements. We used several soil chronosequences using data from the monitoring program together with data from a long-term research (up to 150 years) and more recent measurements. Field measurements included pH, soil organic matter, above ground standing crop and water levels. Water level regimes (inundation duration and mean minimum water level), were simulated using a hydrological model. Capable of simulating inundation duration and water-level fluctuations, this model used field measurements collected over more than 5 years, as well as precipitation and evapotranspiration data collected over a period of 25 years.

Results

Sampling two synchronic chronosequences showed that SOM accumulations increased linearly during the first 50–60 years and then levelled off. Sampling various diachronic chronosequences over time showed a wide variation in accumulation rates. Slacks with low productive species, such as Littorella uniflora, showed low accumulation rates (0.02–0.08 kg/m²/year), and persisted even over a period of more than 90 years. In contrast, slacks dominated by high productive species, such as Phragmites australis, showed ten times higher accumulation rates (0.17–0.26 kg/m²/year) over a similar time period and comparable annual inundation periods (176–240 days). A multiple linear regression showed that variation in SOM accumulation rates was best explained by above-ground biomass of the vegetation.

Conclusions

We conclude that the rate of SOM accumulation in wet dune slacks is primarily controlled by plant above-ground biomass. Both above-ground biomass and SOM accumulation can remain very low over a long period of time when dune slacks are flooded during most of the year and plants with adaptive traits are able to maintain vegetation succession at a pioneer stage.     

Anthropogenic ecological change and impacts on mosquito breeding and control strategies in salt-marshes, Northern Territory, Australia

Darwin, in the tropical north of Australia, is subject to high numbers of mosquitoes and several mosquito-borne diseases. Many of Darwin's residential areas were built in close proximity to tidally influenced swamps, where long-term storm-water run-off from nearby residences into these swamps has led to anthropogenic induced ecological change. When natural wet-dry cycles were disrupted, bare mud-flats and mangroves were transformed into perennial fresh to brackish-water reed swamps. Reed swamps provided year-round breeding habitat for many mosquito species, such that mosquito abundance was less predictable and seasonally dependent, but constant and often occurring in plague proportions. Drainage channels were constructed throughout the wetlands to reduce pooled water during dry-season months. This study assesses the impact of drainage interventions on vegetation and mosquito ecology in three salt-marshes in the Darwin area. Findings revealed a universal decline in dry-season mosquito abundance in each wetland system. However, some mosquito species increased in abundance during wet-season months. Due to the high expense and potentially detrimental environmental impacts of ecosystem and non-target species disturbance, large-scale modifications such as these are sparingly undertaken. However, our results indicate that some large scale environmental modification can assist the process of wetland restoration, as appears to be the case for these salt marsh systems. Drainage in all three systems has been restored to closer to their original salt-marsh ecosystems, while reducing mosquito abundances, thereby potentially lowering the risk of vector-borne disease transmission and mosquito pest biting problems.     

Seasonal flooding,topography, and organic debris interact to influence the emergence and distribution of seedlings in a tropical grassland

In seasonally flooded wetlands, inundation and associated organic debris deposition followed by a drawdown period can promote plant community diversity across space and time. Post‐flood regeneration might be influenced by the direct effect of flooding on seed dispersal and seedling emergence, as well as the indirect effect of organic debris on seed trapping and germination. Our objective was to examine the influence of seasonal flooding, topography, and organic debris cover on seedling distribution in a seasonally flooded grassland. We measured species richness, seedling abundance, and organic debris cover for 3 yr in a seasonally flooded grassland in the Pantanal, Brazil, at three topographic levels at the end of the flood season and during the dry season when there was no debris deposition. A total of 43 species were recorded, with no difference in species richness detected between seasons. However, the abundance of some species was higher post‐flood than during the dry period. The greatest seedling abundance and richness were found post‐flood at intermediate elevations, followed by high and the lowest elevations. Seed germination and seedling establishment were likely suppressed at low topographic positions due to shading from organic debris and poor drainage. Therefore, areas with predictable annual floods promote diversity by creating spatial and temporal variations in environmental conditions.     

Contrasting responses of web-building spiders to deer browsing among habitats and feeding guilds

We examined web-building spider species richness and abundance in forests across a deer density gradient to determine the effects of sika deer browsing on spiders among habitats and feeding guilds. Deer decreased the abundance of web-building spiders in understory vegetation but increased their abundance in the litter layer. Deer seemed to affect web-building spiders in the understory vegetation by reducing the number of sites for webs because vegetation complexity was positively correlated with spider density and negatively correlated with deer density. In contrast, the presence of vegetation just above the litter layer decreased the spider density, and deer exerted a negative effect on this vegetation, possibly resulting in an indirect positive effect on spider density. The vegetation just above the litter layer may be unsuitable as a scaffold for building webs if it is too flexible to serve as a reliable web support, and may even hinder spiders from building webs on litter. Alternatively, the negative effect of this vegetation on spiders in the litter may be as a result of reduced local prey availability under the leaves because of the reduced accessibility of aerial insects. The response to deer browsing on web-building spiders that inhabit the understory vegetation varied with feeding guild. Deer tended to affect web-invading spiders, which inhabit the webs of other spiders and steal prey, more heavily than other web-building spiders, probably because of the accumulated effects of habitat fragmentation through the trophic levels. Thus, the treatment of a particular higher-order taxon as a homogeneous group could result in misleading conclusions about the effects of mammalian herbivores.     

Microbial Community Composition and Denitrifying Enzyme Activities in Salt Marsh Sediments

Denitrifying microbial communities and denitrification in salt marsh sediments may be affected by many factors, including environmental conditions, nutrient availability, and levels of pollutants. The objective of this study was to examine how microbial community composition and denitrification enzyme activities (DEA) at a California salt marsh with high nutrient loading vary with such factors. Sediments were sampled from three elevations, each with different inundation and vegetation patterns, across 12 stations representing various salinity and nutrient conditions. Analyses included determination of cell abundance, total and denitrifier community compositions (by terminal restriction fragment length polymorphism), DEA, nutrients, and eluted metals. Total bacterial (16S rRNA) and denitrifier (nirS) community compositions and DEA were analyzed for their relationships to environmental variables and metal concentrations via multivariate direct gradient and regression analyses, respectively. Community composition and DEA were highly variable within the dynamic salt marsh system, but each was strongly affected by elevation (i.e., degree of inundation) and carbon content as well as by selected metals. Carbon content was highly related to elevation, and the relationships between DEA and carbon content were found to be elevation specific when evaluated across the entire marsh. There were also lateral gradients in the marsh, as evidenced by an even stronger association between community composition and elevation for a marsh subsystem. Lastly, though correlated with similar environmental factors and selected metals, denitrifier community composition and function appeared uncoupled in the marsh.     

Distribution and microhabitats of freshwater mussels in waterbodies in the terrestrialized floodplains of a lowland river

Even when anthropogenically altered, river floodplains continue to contribute to biodiversity. This study examined the distribution of freshwater mussels in relation to environmental factors in waterbodies in the terrestrialized floodplain of a lowland river. Mussels were captured, and environmental measurements were taken in November of 2013 and 2014 in quadrats established in three floodplain waterbodies (FWBs), which were isolated from the main river channel. Among the three FWBs, mussel abundance was highest in a shallow FWB (depth range 18–45 cm) that had intermediate conditions of mud depth and fine sediment rate. Mussel abundance showed a hump-shaped relationship with water depth (the peak 45–50 cm) and mud depth (the peak 8–12 cm). Mussel abundance was also negatively related to the abundance of benthic litter. Litter abundance was positively related to branch abundance and the presence of tree cover, and negatively related to the distance to tree cover, indicating that benthic litter was derived from riparian trees. Our results indicate that relatively shallow (≤ 50 cm) FWBs with moderately accumulated mud, which are not scoured even during flooding, appear to be suitable habitats for mussels. Moreover, it is possible that riparian trees negatively impact mussel distribution in FWBs. Possible short-term measures for improving mussel habitat in FWBs may include the elimination of riparian trees and benthic litter.     

Do non-native Platanus hybrida riparian plantations affect leaf litter decomposition in streams?

In forest headwater streams where the riparian canopy limits autochthonous primary production, leaf litter decomposition is a key process controlling nutrient and carbon cycling. Any alteration of the riparian vegetation may influence litter decomposition and detrital food webs. We evaluated the effect of non-native Platanus hybrida riparian plantations on leaf litter decomposition in Mediterranean streams. The experiment was conducted in six headwater streams; three lined by native riparian vegetation and three crossing P. hybrida plantations. We have characterized the processing rates of alder leaves and the assemblages of shredder macroinvertebrates and fungi. Litter decomposition was significantly faster in the P. hybrida than in the reference streams. Although the dissolved inorganic nitrogen concentration was higher in P. hybrida, no significant effect was observed in decomposition rates. Differences in decomposition rates reflected the macroinvertebrate and shredder colonization in alder litter, with higher abundance and richness in the P. hybrida streams. However, aquatic hyphomycete sporulation rate was higher in reference streams, suggesting that the variation in decomposition rates is a direct consequence of shredder abundance. Our findings support part of the substrate quality-matrix quality (SMI) hypothesis, which expects that high-quality litter will show increased decomposition rates in a low-quality litter matrix.     

Litter decomposition in a sandy Monte desert of western Argentina: Influences of vegetation patches and summer rainfall

Abstract: We tested the hypothesis that shrub canopies interact with monthly rain pulses to control litter decomposition in a sandy Monte desert, in Argentina. We assessed (i) the potential for litter decomposition of soils beneath the canopies of two dominant shrub species (Larrea divaricata and Bulnesia retama, Zygophyllaceae R. Br.) and from bare‐ground microsites or ‘openings’; (ii) litter decomposition at different spatial patches over the summer rainy season; and (iii) the interaction between vegetation patches and monthly rain pulses on short‐term litter decomposition, or decomposition pulses. In a greenhouse experiment, we found buried litter decomposition to be higher in soils from under the canopies of a dominant shrub species compared with soils from openings and sterilized controls. This, and higher nutrient concentration under shrub soils, suggest undercanopy soils may support a microbial community capable of decomposing litter at higher rates than soils in bare openings. However, ?eld trials showed that shrub patches did not affect leaf litter decomposition over the rainy season, at least for short periods. We found an interaction between shrub patches and incubation time at the end of the ?eld experiment, with higher litter decomposition rates under B. retama canopies. In a monthly ?eld experiment, we found monthly rain pulses signi?cantly explained decomposition pulses, irrespective of patch type. Our ?ndings support the hypothesis that shrub soils have a greater potential for litter decomposition, but this is not directly translated to the ?eld possibly due to interactions with abiotic factors. Rain pulses create conditions for decomposition pulses to occur at shorter time scales, whereas rainfall may interact with a dominant shrub undercanopy to control litter mass loss over longer time scales.