The interactive effects of created salt marsh substrate type,hydrology, and nutrient regime on <Emphasis Type="Italic">Spartina alterniflora</Emphasis> and <Emphasis Type="Italic">Avicennia germinans</Emphasis> productivity and soil development

Recent salt marsh and barrier island restoration efforts in the northern Gulf of Mexico have focused on optimizing self-sustaining attributes of restored marshes to provide maximum habitat value and storm protection to vulnerable coastal communities. Salt marshes in this region are dominated by Spartina alterniflora and Avicennia germinans, two species that are valued for their ability to stabilize soils in intertidal salt marshes. We conducted a controlled greenhouse study to investigate the influences of substrate type, nutrient level, and marsh elevation on the growth and biomass allocation of S. alterniflora and A. germinans, and the consequent effects on soil development and stability. S. alterniflora exhibited optimal growth and survival at the lowest elevation (? 15 cm below the water surface) and was sensitive to high soil salinities at higher elevations (+ 15 cm above the water surface). A. germinans performed best at intermediate elevations but was negatively affected by prolonged inundation at lower elevations. We found that although there was not a strong effect of substrate type on plant growth, the development of stressful conditions due to the use of suboptimal materials would likely be exacerbated by placing the soil at extreme elevations. Soil shear strength was significantly higher in experimental units containing either S. alterniflora or A. germinans compared to unvegetated soils, suggesting that plants effectively contribute to soil strength in newly placed soils of restored marshes. As marsh vegetation plays a critical role in stabilizing shorelines, salt marsh restoration efforts in the northern Gulf of Mexico and other storm impacted coasts should be designed at optimal elevations to facilitate the establishment and growth of key marsh species.     

Functional and ecophysiological traits of <Emphasis Type="Italic">Halimione portulacoides</Emphasis> and <Emphasis Type="Italic">Sarcocornia perennis</Emphasis> ecotypes in Mediterranean salt marshes under different tidal exposures

The present paper aims to discuss the functional and ecophysiological traits of two abundant succulent halophytes in Mediterranean salt marsh systems, considering two ecotypes differing on their tidal exposure. In Halimione portulacoides the higher root/shoot (R/S) biomass ratio verified in low inundation frequency (LF) marshes, as compared with that in high inundation frequency (HF), indicates an optimal partitioning strategy, inducing differential allocation patterns along with varying environmental factors. Conversely, Sarcocornia perennis appear to have an isometric allocation strategy, based on intrinsic biomass allocation mechanisms independent from the surrounding environmental conditions. Similarly, the photosynthetic traits appear to reflect the intrinsic ecology of the species. Sarcocornia perennis habitat adaptation to HF conditions is clearly revealed by its high photosynthetic efficiency under HF conditions. On the other hand, the cosmopolitan H. portulacoides shows no differences between ecotypes, in which concerns this trait, mostly due to the high carotenoid content of the HF ecotype, which allows this specie to counteract the stress generated during submersion. Additionally, anti-oxidant enzymatic activities revealed that S. perennis presents a high degree of stress tolerance under HF conditions, while H. portulacoides is highly adapted to LF conditions. These functional (biomass-related) and physiological traits determine the optimal habitats for H. portulacoides and S. perennis. While H. portulacoides optimal biomass partitioning, along with its efficient anti-oxidant defence system, makes this species fitter to LF conditions, S. perennis isometric allocation strategy, along with a higher photosynthetic efficiency under frequent flooding conditions, provides this species the mechanisms to efficiently colonize the intertidal habitat.     

Field assessment of environmental factors constraining the development and expansion of <Emphasis Type="Italic">Schoenoplectus californicus</Emphasis> marsh at a California tidal freshwater restoration site

The effective restoration of wetland habitats requires understanding the establishment requirements, growth responses, and expansion dynamics of targeted plant species. This is particularly true when restoring areas that have been previously managed for other activities, such as agriculture, which can have legacy effects on the local environment. We investigated environmental factors (specifically hydrology and soil physicochemical conditions) that may influence the establishment, growth and expansion of Schoenoplectus californicus in a tidal freshwater marsh restoration site in the Sacramento–San Joaquin Delta, California, USA. This study site was previously leveed, drained, and utilized for agricultural production. A 1997 levee breach restored tidal connectivity and wetland vegetation has re-established in portions of the area. Our approach coupled an intensively-sampled transect study in S. californicus-dominated marshes with a spatially-extensive survey of S. californicus lateral expansion rates and elevation. Lateral expansion of S. californicus marsh edge was significantly less in lower elevation areas (0.61 ± 0.04 m NAVD88), whereas the marsh edge at higher elevations (0.84 ± 0.03 m NAVD88) exhibited greater expansion, often at rates greater than 1.0 m year^?1. These elevation means correspond to percentages of time that the marsh surface was flooded of 100 and 94 %, respectively. Although marsh edge expansion was influenced by elevation and the resultant hydrology, other factors, such as physical exposure of marsh shorelines and compacted agricultural soils also appear to be important. However, once established, S. californicus appears to be able to ameliorate high soil bulk densities over time as the advancing marsh platform develops.     

Nitrogen addition drives convergence of leaf litter decomposition rates between <Emphasis Type="Italic">Flaveria bidentis</Emphasis> and native plant

Evidence is growing that invasive species can change decomposition rates and associated nutrient cycling within an ecosystem by changing the quality of the litter entering a system. However, the relative contribution of their distinct litter types to carbon turnover is less understood, especially in the context of enhanced N deposition. The objective of this study was to investigate the whole-plant responses of an invasive plant Flaveria bidentis in litter decay to simulated N eutrophication. A 1-year study was conducted to assess if N enhancement influenced decomposition and nutrient dynamics of litters from foliage, fine roots and twigs of F. bidentis compared to co-occurring native species Setaria viridis. N fertilization significantly decreased the decomposition rate of the foliage of the invasive F. bidentis by more than 25% relative to the water control, but had relatively minor effects on decomposition of its twigs and fine root litter or leaf litter from the native species. Collectively, decomposition rates of foliar litters of the invasive and native species become convergent over time in the presence of N addition. Moreover, net N loss was predominately influenced by litter species, followed by the litter type, while N addition had little effect on net N loss. Our study showed that the variation in litter decomposition was much greater between litter types of the invasive F. bidentis than between different plant species under the N addition and that the litter of invasive species with higher inherent decomposability did not always decompose more rapidly than the litter of native species in response to predicted N deposition enhancement.     

Post-breeding densities,population sizes and lake size partitioning of loon species in western Chukotka,Russia

Loons (family Gaviidae) breed in small ponds and lakes across Arctic landscapes and are high level predators in the lake ecosystems. As such, they may serve as sentinel species, warning humans of alterations in habitat and ecosystem integrity in a region that is undergoing vast change due to climate warming. Here, we characterized the abundance and habitat use of four arctic breeding species of loons in the plains and surrounding mountains of western Chukotka, Russia. Loon surveys were conducted on foot and by boat from 2009–2015. Loon species differed in their use of the four lacustrine habitat types within the study area. In yedoma habitat, the yellow-billed loon (Gavia. adamsii) was the most abundant (0.593 birds/km²); on fluvial plain habitat, Pacific loons (G. pacifica) outnumbered other loons (0.701 birds/km²); mountain valleys were inhabited similarly by pacifica (0.354 birds/km²) and red-throated loons (G.stellata; 0.307); and maritime tundra was used only by pacifica (1.13) and Arctic loons (G. arctica; 0.553). G. adamsii was not observed in mountain valleys or maritime tundra. Mountainous portions of rivers were predominantly occupied by stellata and pacifica, and lowland rivers by stellata, pacifica and arctica. There was a significant difference in the size of lakes occupied by the four congeners. The largest loon, adamsii, occupied the largest lakes (0.69 km²), 80% larger than lakes utilized by pacifica (0.39 km²) and arctica (0.38 km²), and 35 times larger than stellata (0.02 km²). Most lakes were occupied by a single loon species (125/162, 77.2%).     

Long-term impact of elevated CO<Subscript>2</Subscript> on phosphorus fractions varies in three contrasting cropping soils

Background and aims

Leaf litters commonly interact during decomposition in ways that can synergistically increases rates of decay. These interactions have been linked to moisture availability, suggesting that drought could slow decomposition rates by disrupting litter interactions. Slowed decomposition may reduce competitive ability of exotic species that exploit rapid decomposition rates as part of niche construction mechanisms. Here, we evaluated the impacts of drought on interactions between native and exotic species’ litter decomposition.

Methods

We considered litter mixtures of Lupinus polyphyllus (exotic N-fixing forb), Trifolium pratense (native N-fixing forb), Senecio inaequidens (exotic non-N-fixing forb), and Senecio jacobaea (native non-N-fixing forb) with the native grass Alopecurus pratensis and evaluated the difference between the observed rate of decay and the one expected based on species decomposing in monocultures. Litters were deployed in Belgium and Germany and exposed to a 56 day drought, which resembled local millennium drought (statistical recurrence of duration in local precipitation series >1000 years).

Results

Litter interactions reduced mass remaining by 81% in Belgium and 15% in Germany, averaged across mixtures. Similarly, litter interactions reduced N remaining by 93% in Belgium and 14% in Germany. Drought consistently removed these interactions and resulted in additive litter decay. Litters of native and exotic species did not differ in their response to drought.

Conclusions

These findings support moisture availability as a key regulator of interactions between litters during decomposition. Thus, increasing frequency of drought may slow nutrient cycling to a greater extent than previously thought.

     

Litter Chemistry,Community Shift,and Non-additive Effects Drive Litter Decomposition Changes Following Invasion by a Generalist Pathogen

Forest pathogens have strong potential to shape ecosystem function by altering litterfall, microclimate, and changing community structure. We quantified changes in litter decomposition from a set of distinct diseases caused by Phytophthora ramorum, an exotic generalist pathogen. Phytophthora ramorum causes leaf blight and increased litterfall %N, but no mortality on California bay laurel (Umbellularia californica), a common overstory tree that accumulates high levels of infection. Lethal twig and bole cankers on tanoak (Notholithocarpus densiflorus) lead to the disease sudden oak death which creates canopy openings and alters litterfall in mixed-species forests dominated by redwood (Sequoia sempervirens) which is minimally susceptible. Species identity had the greatest effect on mass loss and N dynamics with the most rapid rates in bay laurel, slowest in redwood, and intermediate in tanoak. Decomposing litter from infected sources had increased N accumulation, and although these changes were of lower magnitude relative to species identity, the region-scale invasion of P. ramorum suggests that this effect could occur over an extensive area. Canopy mortality was a significant and slowing influence on litter N dynamics in all species and also dampened non-additive effects within mixed litter bags. Redwood—the lowest quality litter—demonstrated non-additive interactions with consistently lower C:N when decomposed in mixed litter bags, but this effect did not alter the entire mixture. Mortality and subsequent changes in community composition have the greatest magnitude effects on litter decomposition for sudden oak death, but our study implies that different and sometimes cryptic mechanisms will drive decomposition changes for other forest diseases.     

Leaf Litter Consumption by Macroarthropods and Burial of their Faeces Enhance Decomposition in a Mediterranean Ecosystem

In many terrestrial ecosystems, large amounts of leaf litter are consumed by macroarthropods. Most of it is deposited as faeces that are easily transferred into deeper soil layers. However, the decomposition of this large pool of organic matter remains poorly studied. We addressed the question of how leaf litter transformation into macroarthropod faeces, and their burial in the soil, affect organic matter decomposition in a Mediterranean dry shrubland. We compared mass loss of intact leaf litter of two dominant shrub species (Quercus coccifera, Cistus albidus) with that of leaf litter-specific faeces from the abundant millipede Ommatoiulus sabulosus. Leaf litter and faeces were exposed in the field for 1 year, either on the soil surface or buried at 5 cm soil depth. Chemical and physical quality of faeces differed strongly from that of leaf litter, but distinctively between the two shrub species. On the soil surface, faeces decomposed faster than intact leaf litter in Quercus, but at similar rates in Cistus. When buried in the soil, faeces and leaf litter decomposed at similar rates in either species, but significantly faster compared to the soil surface, most likely because of higher moisture within the soil enhancing microbial activity. The combined effects of leaf litter transformation into faeces and their subsequent burial in the topsoil led to a 1.5-fold increase in the annual mass loss. These direct and indirect macroarthropod effects on ecosystem-scale decomposition are likely more widespread than currently acknowledged, and may play a particularly important role in drought-influenced ecosystems.     

Responses of litter decomposition and nutrient release rate to water and nitrogen addition differed among three plant species dominated in a semi-arid grassland

Background and aims

Precipitation and nitrogen (N) deposition are predicted to increase in northern China. The present paper aimed to better understand how different dominant species in semi-arid grasslands in this region vary in their litter decomposition and nutrient release responses to increases in precipitation and N deposition.

Methods

Above-ground litter of three dominant species (two grasses, Agropyron cristatum and Stipa krylovii, and one forb, Artemisia frigida) was collected from areas without experimental treatments in a semi-arid grassland in Inner Mongolia. Litter decomposition was studied over three years to determine the effects of water and N addition on litter decomposition rate and nutrient dynamics.

Results

Litter mass loss and nutrient release were faster for the forb species than for the two grasses during decomposition. Both water and N addition increased litter mass loss of the grass A. cristatum, while the treatments showed no impacts on that of the forb A. frigida. Supplemental N had time-dependent, positive effects on litter mass loss of the grass S. krylovii. During the three-year decomposition study, the release of N from litter was inhibited by N addition for the three species, and it was promoted by water addition for the two grasses. Across all treatments, N and potassium (K) were released from the litter of all three species, whereas calcium (Ca) was accumulated. Phosphorus (P) and magnesium (Mg) were released from the forb litter but accumulated in the grass litter after three years of decomposition.

Conclusions

Our findings revealed that the litter decomposition response to water and N supplementation differed among dominant plant species in a semi-arid grassland, indicating that changes in dominant plant species induced by projected increases in precipitation and N deposition are likely to affect litter decomposition, nutrient cycling, and further biogeochemical cycles in this grassland. The asynchronous nutrient release of different species’ litter found in the present study highlights the complexity of nutrient replenishment from litter decomposition in the temperate steppe under scenarios of enhancing precipitation and N deposition.

     

Modeling the effect of water level on the Nueces Delta marsh community

Water resource development has decreased water delivery to marshes in the Nueces Delta, Corpus Christi, Texas, USA by 45% since 1983, which has led to marsh degradation. Recent management actions will allow for partial hydrological restoration of the marsh, but there is a need to understand the dynamics and the interactive roles of climate and water cycle changes in order to predict changes in salt marshes in the future. In this study, a model of multi-species competition with respect to hydrological change was developed to perform modeling experiments of the effects of water elevation on development of marsh plant species. Nueces Delta plants were divided into two functional groups: (1) clonal stress tolerant plants (Batis maritima, Distichlis spicata, Monanthcloe littoralis, and Salicornia virginica), and (2) clonal dominants (Borrichia frutescens and Spartina alterniflora). Growth rates were calculated for three climate regimes (wet, moderate, and dry), and in three elevation locations (low, mid, and high marsh). The model predicts reductions in plant cover in both drought and moderate conditions. Marsh plant coverage increases only during wet conditions and when there is space available for plant expansion. It is concluded that changes in areal extent of the marsh largely depend on water flow and elevation, which in turn depends on the quantity of fresh water flowing into the marsh. However, under current climate and water management conditions, the marsh will degrade further.     

First record of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> in southern Africa indicates adaptive potential of this saline grass

Spartina alterniflora was recorded in 2004 in the Great Brak Estuary, a system along the southern coast of South Africa that closes to the sea. This is alarming as this is a species with a known history as an aggressive invasive plant which has now been found 8000 km from its nearest known location and furthermore it is spreading under atypical conditions of submergence. This first recorded population in Africa indicates the adaptive potential of this invasive grass which survives inundation and non-tidal conditions for months at a time. Spartina alterniflora spread from 2566 m² in 2006 to a maximum area covered of 10,221 m² in 2011. There was an increase in silt, sediment organic matter and a significant reduction in sediment redox potential at sites invaded by S. alterniflora. When the estuary closes to the sea the water level rises and S. alterniflora is flooded, limiting opportunities for mechanical and chemical control. Application of a glyphosate-based herbicide in 2012 showed that chemical control was more effective in reducing the stands than mechanical removal. The additional use of imazapyr in 2014 significantly reduced stem density and the proportion of live stems. Spread of this invasive plant to the intertidal marshes in adjacent estuaries is a potential biodiversity threat although, fortunately, this population does not seem to produce viable seed. There is also the concern that hybridization with the resident S. maritima may occur. Important research and management questions remain i.e. how quickly will the natural marsh re-establish following eradication and how can we prevent movement of the grass to other estuaries?     

Effects of sediment-borne nutrient and litter quality on macrophyte decomposition and nutrient release

Macrophyte decomposition is a critical process that affects carbon and nutrient cycling, and energy flow, although the majority of the details involved in the process remain unclear. For the present study, a litter bag experiment was conducted to investigate the effects of sediment-borne nutrient and litter quality on the decomposition rates and nutrient release of four macrophyte life forms (emergent macrophyte: Phragmites australis, free-floating macrophyte: Hydrocharis dubia, floating-leaved macrophyte: Nymphoides peltata, submerged macrophyte: Ceratophyllum demersum), and a species mixture. Our results indicated that litter quality significantly influenced macrophyte decomposition and nutrient release. High-quality litter species (high initial nitrogen and phosphorus contents, as well as low C:N, C:P, and N:P ratios) decomposed more rapidly than low-quality litter species, and the initial C:N and C:P ratios, rather than the initial N and P contents, were effective indicators of the decomposition rate of macrophytes. Sediment-borne nutrients had little effect on the decomposition rate, yet a strong effect on the release of N and P, although the interactions between litter quality and sediment-borne nutrients significantly affected the decomposition rate. Three-way ANOVA analysis revealed that the litter quality imparted a more potent effect on the macrophyte decomposition rate and release of N and P than sediment-borne nutrients. These results implied that litter quality interacts with sediment-borne nutrients and may control macrophyte decomposition in shallow lakes.     

Direct and indirect effects of the fungal endophyte <Emphasis Type="Italic">Epichloë uncinatum</Emphasis> on litter decomposition of the host grass, <Emphasis Type="Italic">Schedonorus pratensis</Emphasis>

Microbial plant symbionts have been suggested to mediate plant-soil feedback and affect ecosystem functions. Systemic Epichloë fungal endophytes of grasses are found to mediate litter decomposition. These effects are often linked to alkaloids produced by Epichloë species, which are hypothesized to negatively affect decomposers. Although endophytes have been found to affect plant community and soil biota, direct (through litter quality) and indirect (through the environment) effects of fungal endophytes on litter decomposition have been scarcely scrutinized. We placed litterbags with endophyte-symbiotic (E+) and non-symbiotic (E?) Schedonorus pratensis plant litter in plots dominated by E+ or E? plants of the same species, and followed the dynamics of mass losses over time. We predicted the endophyte would hinder decomposition through changes in litter quality and that both types of litter would decompose faster in home environments. E+ litter decomposed faster in both environments. The mean difference between decomposition rate of E+ and E? litter tended to be higher in E? plots. Nitrogen and phosphorus, two elements usually associated with high decomposition rates, were significantly lower in E+ litter. We also detected a higher proportion of C in the cellulose form in E+ litter. Contrary to the general assumption, we found that symbiosis with Epichloë fungal endophytes can be associated with higher decomposition of plant litter. Since direct effects of Epichloë fungi were still stronger than indirect effects, it is suggested that besides the alkaloids, other changes in plant biomass would explain in a context-dependent manner, the endophyte effects on the litter decomposition.     

Rhizosphere processes induce changes in dissimilatory iron reduction in a tidal marsh soil: a rhizobox study

Background and aims

Although the role of microbial iron respiration in tidal marshes has been recognized for decades, the effect of rhizosphere processes on dissimilatory ferric iron reduction (FeR) is poorly known. Herein, we examined the FeR surrounding the root zone of three tidal marsh plants.

Methods

Using in situ rhizoboxes, we accurately separated rhizobox soil as one rhizosphere zone, and three bulk soil zones. Dissimilatory and sulfidic-mediated FeR were quantified by accumulation of non-sulfidic Fe(II) and Fe sulfides over time, respectively.

Results

The rates of dissimilatory FeR attained 42.5 μmol Fe g^?1 d^?1 in the rhizosphere, and logarithmically declined by up to 19.1 μmol Fe g^?1 d^?1 in the outer bulk soil. The rates of sulfidic-mediated FeR were less than 2 μmol Fe g^?1 d^?1 among all zones. Poorly crystalline Fe(III), DOC and DON, porewater Fe²⁺, and SO₄^2? were all enriched in the rhizosphere, whereas non-sulfidic Fe(II) and Fe sulfides gradually accumulated away from the roots. Iron reducers (Geobacter, Bacillus, Shewanella, and Clostridium) had higher populations in the rhizosphere than in the bulk soil. Higher rates of dissimilatory FeR were observed in the Phragmites australis and Spartina alterniflora rhizoboxes than in the Cyperus malaccensis rhizoboxes.

Conclusions

The radial change pattern of dissimilatory FeR rates were determined by allocation of poorly crystalline Fe(III) and dissolved organic carbon. The interspecies difference of rhizosphere dissimilatory FeR was associated with the root porosity and aerenchyma of the tidal marsh plants.

     

Pigment structure in the violaxanthin–chlorophyll-<Emphasis Type="Italic">a</Emphasis>-binding protein VCP

Salt-tolerant grasses of warm sub-tropical ecosystems differ in their distribution patterns with respect to salinity and moisture regimes. Experiments were conducted on CO₂ fixation and light harvesting processes of four halophytic C₄ grasses grown under different levels of salinity (0, 200 and 400 mM NaCl) under ambient environmental conditions. Two species were from a high saline coastal marsh (Aeluropus lagopoides and Sporobolus tremulus) and two were from a moderate saline sub-coastal draw-down tidal marsh (Paspalum paspalodes and Paspalidium geminatum). Analyses of the carbon isotope ratios of leaf biomass in plants indicated that carbon assimilation was occurring by C₄ photosynthesis in all species during growth under varying levels of salinity. In the coastal species, with increasing salinity, there was a parallel decrease in rates of CO₂ fixation (A), transpiration (E) and stomatal conductance (g _s), with no effect on water use efficiency (WUE). These species were adapted for photoprotection by an increase in the Mehler reaction with an increase in activity of PSII/CO₂ fixed accompanied by high levels of antioxidant enzymes, superoxide dismutase and ascorbate peroxidase. The sub-coastal species P. paspalodes and P. geminatum had high levels of carotenoid pigments and non-photochemical quenching by the xanthophyll cycle.     

Four novel <Emphasis Type="Italic">Talaromyces</Emphasis> species isolated from leaf litter from Colombian Amazon rain forests

Various Talaromyces strains were isolated during a survey of fungi involved in leaf litter decomposition in tropical lowland forests in the Caquetá and Amacayacu areas of the Colombian Amazon. Four new Talaromyces species are described using a polyphasic approach, which includes phenotypic characters, extrolite profiles and phylogenetic analysis of the internal transcribed spacer region (ITS) barcode, and beta-tubulin (BenA) and calmodulin (CaM) gene regions. Talaromyces amazonensis sp. nov., T. francoae sp. nov. and T. purgamentorum sp. nov. belong to Talaromyces section Talaromyces, and T. columbiensis sp. nov. is located in section Bacillispori. The new species produce several bioactive compounds: T. amazonensis produces the potential anticancer agents duclauxin, berkelic acid and vermicillin, and T. columbiensis produces the effective anticancer agent wortmannin (together with duclauxin). In addition to the new species, T. aculeatus and T. macrosporus were isolated during this study on leaf litter decomposition.     

Boreal peat properties link to plant functional traits of ecosystem engineers

Aims

Warming has the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how other factors such as litter species or substrate quality might modify the effects of increased temperature on decomposition. Meanwhile, the temperature sensitivity of plant litter decay in tropical and subtropical forest ecosystems remains poorly resolved.

Methods

This study was designed to assess the effects of experimental warming on litter decomposition and nutrient release of two contrasting tree species (Schima superba and Machilus breviflora) by translocating model forest ecosystems from the high-elevation sites to the lower-elevation sites in subtropical China. Translocating model mountain evergreen broad-leaved forest (MEBF) to the altitude of 300 m and 30 m increased the average monthly soil temperature at 5 cm depth by 0.88 and 1.84 °C, respectively during the experimental period. Translocating model coniferous and broad-leaved mixed forest (CBMF) to the altitude of 30 m increased the average monthly soil temperature at 5 cm depth by 0.85 °C.

Results

We found that experimental warming accelerated litter decomposition in both model forest types, and the promoting efficiency was greater when the temperature increased. The litter with high quality (Schima superba) had stronger response to warming than low quality litter (Machilus breviflora). Warming accelerated Na, K, Mg, P, N and Ca release from Schima superba litter, but only simulated Ca release from Machilus breviflora litter. Overall, litter decomposition was controlled by the order: soil temperature > litter quality > soil moisture > litter incubation forest type under experimental warming in the subtropical China.

Conclusion

We conclude that leaf litter decomposition was facilitated by experimental warming in subtropical China. Litter species might modify the effects of increased temperature on litter decomposition; however, forest type has no effect on litter decomposition.

     

Variation in tussock architecture of the invasive cordgrass <Emphasis Type="Italic">Spartina densiflora</Emphasis> along the Pacific Coast of North America

Some introduced species spread rapidly beyond their native range and into novel habitats mediated by a high degree of phenotypic plasticity and/or rapid evolutionary responses. In this context, clonality has been described as a significant factor contributing to invasiveness. We studied the abiotic environment and the responses of different tussock architecture traits of the invasive cordgrass Spartina densiflora Brongn. (Poaceae). A common garden experiment and field studies of S. densiflora in salt marshes across a wide latitudinal gradient from California (USA) to British Columbia (Canada) provided a model system for an integrated study of the potential mechanisms underlying the response of invasive S. densiflora populations to changes in environmental conditions. Our results showed that S. densiflora is able to adjust to widely variable climate (specifically, air temperature and the duration of the growing season) and sediment conditions (specifically, texture and hypoxia) through phenotypical plastic key functional tussock traits (e.g. shoot density, height, above- and below-ground biomass allocation patterns). Root biomass increased in coarser sediments in contrast to rhizomes, which were more abundant in finer sediments. Above-ground biomass and leaf area index increased mainly with air temperature during summer, and more robust (taller and wider) shoots were associated with more oxygenated sediments. In view of our results, S. densiflora appears to be a halophyte with a high degree of phenotypic plasticity that would enable it to respond successfully to changes in the abiotic conditions of salt marshes driven by global climate change, such as increasing salinity and temperatures.     

The Contribution of Photodegradation to Litter Decomposition in Semiarid Mediterranean Grasslands Depends on its Interaction with Local Humidity Conditions,Litter Quality and Position

Understanding how UV radiation interacts with prevailing climatic conditions and litter quality to determine leaf litter decomposition is fundamental for understanding soil carbon cycling pathways and ecosystem functioning in drylands. We carried out a field manipulative experiment to investigate how litter quality (labile and nitrogen-rich Retama sphaerocarpa vs. recalcitrant and nitrogen-poor Stipa tenacissima), position (on the ground vs. standing) and different UV radiation levels (UV pass vs. UV block) affect litter decomposition rates at two semiarid Mediterranean steppes with contrasting climates (continental vs. maritime) in a fully factorial experimental design. As expected, Retama litter decomposed faster than that of Stipa, and litter placed on the ground decayed faster than standing litter. However, and surprisingly, contrasting effects of UV radiation on litter decomposition were observed between the two sites. At the continental site, UV radiation increased litter decay constants by 21% on average, although the contribution of photodegradation was larger when litter was placed on the ground rather than in standing litter. At the maritime site, decay constants were 15% larger in the absence of UV radiation regardless of litter position. Significant litter type × UV exposure radiation and litter type × position interactions indicate that photodegradation contributes more to litter decomposition under less favorable moisture and substrate availability conditions for microbial decomposers. Our results emphasize the need to consider interactions between moisture availability, litter quality and UV radiation in litter decomposition models to fully understand litter decomposition impacts on soil carbon cycling and storage in drylands under climate change.     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.