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Aims: Moso bamboo (Phyllostachys pubescens) invasions into native forest cause a series of ecological problems, including the alteration of soil microorganism community composition. Additionally, it has been established that variation changes in leaf litter types can drive changes in soil microorganism communities. We have previously demonstrated distinct differences in nutrient composition between bamboo leaf litter and leaf litter of native plants. Yet to date, we lack a comprehensive understanding of how Moso bamboo leaf litter inputs change soil microorganism community composition in native forests. Methods: We conducted an in-situ decomposition experiment to examine the response of soil bacterial and fungi phyla to Moso bamboo leaf litter addition in three native forest soils. Results: Bamboo leaf litter had higher quality (low lignin content and low C:N) and higher decomposition rates compared to native forest plants. Bamboo leaf litter additions did not change the richness and diversity of soil bacterial and fungi in the Broadleaf forest and Chinese fir forest. Additionally, bamboo leaf litter additions only affected the soil microorganisms in the Cryptomeria japonica var. Sinensis forest with low-quality litter; Principal Component Analysis (PCA) further supported this result. Conclusions: Our results demonstrate that the soil microbial community has resilience to chemical and biotic inputs from foreign leaf litter. This study helps soil ecologists better understand the impacts of Moso bamboo invasions into native forests, including the weak effects of its litter input on soil microorganisms. [ABSTRACT FROM AUTHOR]

Background and aims: Subtle morphological traits, such as leaf litter curling, may have unexpected legacy effects on ecosystems. We tested the hypotheses that litter curling is influenced by plant species, hybridization and genotype, and has extended consequences for associated organisms and soil processes. Methods: A novel litter curling index (LCI) was used to characterize the curling of leaf litter from 11 plant species (including shrubs, trees and a forb) in natural field sites and of two Populus species (P. fremontii James, P. angustifolia S. Watson), their F1 hybrids and replicated P. angustifolia genotypes from a common garden. Surveys of dominant, litter-dwelling spiders (Agelenidae), and a soil drying experiment, were used to test the potential extended ecological consequences of litter curling. Results: Five results emerged. (1) LCI ranged 15-fold among plant species in natural sites. (2) LCI nearly doubled from P. fremontii to P. angustifolia, while average LCI for F1 hybrids was intermediate (although not statistically different from P. fremontii). (3) LCI exhibited broad-sense heritability (H2 = 0.42) among P. angustifolia genotypes. (4) Abundance of spider webs was positively associated with increasing litter curl across the Populus hybrid system (R2 = 0.35). (5) After 57 days of drying, flat litter contained 1.4 times higher moisture than curled litter, which translated to wetter soil beneath flat litter. Conclusion: Litter curling has a genetic basis, which has legacy effects on other trophic levels and soil moisture dynamics that may shape the ecology and evolution of complex communities. [ABSTRACT FROM AUTHOR]

Efforts to maintain the function of critical ecosystems under climate change often begin with foundation species. In the southwestern United States, cottonwood trees support diverse communities in riparian ecosystems that are threatened by rising temperatures. Genetic variation within cottonwoods shapes communities and ecosystems, but these effects may be modified by phenotypic plasticity, where genotype traits change in response to environmental conditions. Here, we investigated plasticity in Fremont cottonwood (Populus fremontii) leaf litter traits as well as the consequences of plasticity for riparian ecosystems. We used three common gardens each planted with genotypes from six genetically divergent populations spanning a 12°C temperature gradient, and a decomposition experiment in a common stream environment. We found that leaf litter area, specific leaf area, and carbon to nitrogen ratio (C:N) were determined by interactions between genetics and growing environment, as was the subsequent rate of litter decomposition. Most of the genetic variation in leaf litter traits appeared among rather than within source populations with distinct climate histories. Source populations from hotter climates generally produced litter that decomposed more quickly, but plasticity varied the magnitude of this effect. We also found that hotter growing conditions reduced the variation in litter traits produced across genotypes, homogenizing the litter inputs to riparian ecosystems. All genotypes in the hottest garden produced comparatively small leaves that decomposed quickly and supported lower abundances of aquatic invertebrates, whereas the same genotypes in the coldest garden produced litter with distinct morphologies and decomposition rates. Our results suggest that plastic responses to climate stress may constrict the expression of genetic variation in predictable ways that impact communities and ecosystems. Understanding these interactions between genetic and environmental variation is critical to our ability to plan for the role of foundation species when managing and restoring riparian ecosystems in a warming world. [ABSTRACT FROM AUTHOR]

Despite abounding evidence that leaf litter traits can predict decomposition rate, the way these traits influence trophic efficiency and element transfer to higher trophic levels is not resolved. Here, we used litter labeled with 13C and 15N stable isotopes to trace fluxes of litter C and N from four leaf types to freshwater invertebrate communities. We measured absolute (mg C or N) and relative assimilation (percentage of litter C or N incorporated into invertebrate biomass relative to C and N lost during decomposition). Four patterns emerged: (1) Invertebrate communities assimilated more C and N from slowly decomposing litter than communities feeding on rapidly decomposing litter; (2) absolute assimilation of both C and N in leaf packs was positively correlated with the relative biomass of invertebrate taxa in leaf packs; (3) Chironomidae larvae, which colonize packs in the early decomposition stages, assimilated the most C and N by the end of the 35-day experiment; and (4) most taxa, spanning five functional feeding groups (collector–gatherers, shredders, collector–filterers, scrapers, and predators), showed similar patterns in both absolute and relative assimilation across leaf types. These results challenge traditional views of litter quality by demonstrating that trophic efficiency is negatively associated with decomposition rate across these four leaf types. [ABSTRACT FROM AUTHOR]

Summary: Litter decomposition plays a key role in nutrient cycling across ecosystems, yet to date, we lack a comprehensive understanding of the nonadditive decomposition effects in leaf litter mixing experiments.To fill that gap, we compiled 69 individual studies with the aim to perform two meta‐analyses on nonadditive effects.We show that a significant synergistic effect (faster decomposition in mixtures than expected) occurs at a global scale, with an average increase of 3–5% in litter mixtures. In particular, low‐quality litter in mixtures shows a significant synergistic effect, while additive effects are observed for high‐quality species. Additionally, synergistic effects turn into antagonistic effects when soil fauna are absent or litter is in very late stages of decomposition (near‐humus). In contrast to temperate and tropical areas, studies in boreal regions show significant antagonistic effects.Our two meta‐analyses provide a systematic evaluation of nonadditive effects in mixed litter decomposition studies and show that litter quality alters the effects of litter mixing. Our results indicate that nutrient transfer, soil fauna and inhibitory secondary compounds can influence mixing effects. We also highlight that synergistic and antagonistic effects occur concurrently, and the final litter mixing effect results from the interplay between them. [ABSTRACT FROM AUTHOR]

Abstract: Leaf litter provides an important nutrient subsidy to headwater streams, but little is known about how tree genetics influence energy pathways from litter to higher trophic levels. Despite the charge to quantify carbon (C) and nitrogen (N) pathways from decomposing litter, the relationship between litter decomposition and aquatic consumers remains unresolved. We measured litter preference (attachments to litter), C and N assimilation rates, and growth rates of a shredding caddisfly (Hesperophylax magnus, Limnephilidae) in response to leaf litter of different chemical and physical phenotypes using Populus cross types (P. fremontii, P. angustifolia, and F1 hybrids) and genotypes within P. angustifolia. We combined laboratory mesocosm studies using litter from a common garden with a field study using doubly labeled litter (13C and 15N) grown in a greenhouse and incubated in Oak Creek, Arizona, USA. We found that, in the lab, shredders initially chose relatively labile (low lignin and condensed tannin concentrations, rapidly decomposing) cross type litter, but preference changed within 4 d to relatively recalcitrant (high lignin and condensed tannin concentrations, slowly decomposing) litter types. Additionally, in the lab, shredder growth rates were higher on relatively recalcitrant compared to labile cross type litter. Over the course of a three‐week field experiment, shredders also assimilated more C and N from relatively recalcitrant compared to labile cross type litter. Finally, among P. angustifolia genotypes, N assimilation by shredders was positively related to litter lignin and C:N, but negatively related to condensed tannins and decomposition rate. C assimilation was likewise positively related to litter C:N, and also to litter %N. C assimilation was not associated with condensed tannins or lignin. Collectively, these findings suggest that relatively recalcitrant litter of Populus cross types provides more nutritional benefit, in terms of N fluxes and growth, than labile litter, but among P. angustifolia genotypes the specific trait of litter recalcitrance (lignin or tannins) determines effects on C or N assimilation. As shredders provide nutrients and energy to higher trophic levels, the influence of these genetically based plant decomposition pathways on shredder preference and performance may affect community and food web structure. [ABSTRACT FROM AUTHOR]

Terrestrial leaf litter provides aquatic insects with an energy source and habitat structure, and species differences in litter can influence aquatic insect emergence. Emerging insects also provide energy to riparian predators. We hypothesized that plant genetics would influence the composition and timing of emerging insect communities among individual genotypes of Populus angustifolia varying in litter traits. We also compared the composition and timing of emerging insect communities on litter from mixed genotypes of three cross types of a hybridizing cottonwood complex: P. angustifolia, P. fremontii, and their F1 hybrids. Using litter harvested from an experimental common garden, we measured emerging insect community composition, abundance, and production for 12 weeks in large litter packs affixed with emergence traps. Five major findings emerged. (1) In support of the genetic similarity hypothesis, we found that, among P. angustifolia tree genotypes, litter from more closely related genotypes had more similar litter thickness, nitrogen concentrations, decomposition rates, and emerging insect communities. (2) Genetic similarity was not correlated with other litter traits, although the litter fungal community was a strong predictor of emerging insect communities. (3) Litter decomposition rate, which was the strongest predictor of emerging aquatic insect communities, was influenced by litter thickness, litter N, and the litter fungal community. (4) In contrast to strong community composition differences among P. angustifolia genotypes, differences in community composition between P. fremontii and P. angustifolia were only marginally significant, and communities on F1 hybrids were indistinguishable from P. angustifolia despite genetic and litter trait differences. (5) Mixed litter packs muted the genetic effects observed in litter packs consisting of single genotypes. These results demonstrate that the genetic structure of riparian forests can affect the composition and timing of aquatic insect emergence. Because many riparian trees are clonal, including P. angustifolia, large clone size is likely to result in patches of genetically structured leaf litter that may influence the timing and composition of insect emergence within watersheds. Riparian restoration efforts incorporating different tree genotypes could also influence the biodiversity of emerging aquatic insects. Our work illustrates the importance of plant genes for community and ecosystem processes in riparian corridors. [ABSTRACT FROM AUTHOR]

Dissolved organic C (DOC) leached from leaf litter contributes to the C pool of stream ecosystems and affects C cycling in streams. We studied how differences in leaf-litter chemistry affect the optical properties and decomposition of DOC. We used 2 species of cottonwoods (Populus) and their naturally occurring hybrids that differ in leaf-litter phytochemistry and decomposition rate. We measured DOC and nutrient concentration in leaf leachates and determined the effect of DOC quality on heterotrophic respiration in 24-h incubations with stream sediments. Differences in DOC composition and quality were characterized with fluorescence spectroscopy. Rapidly decomposing leaves with lower tannin and lignin concentrations leached ∼40 to 50% more DOC and total dissolved N than did slowly decomposing leaves. Rates of heterotrophic respiration were 25 to 50% higher on leachate from rapidly decomposing leaf types. Rates of heterotrophic respiration were related to metrics of aromaticity. Specifically, rates of respiration were correlated negatively with the Fluorescence Index and positively with Specific Ultraviolet Absorbance (SUVA254) and T280 tryptophan-like fluorescence peak. These results reveal that leaf-litter DOC is distinctly different from ambient streamwater DOC. The relationships between optical characteristics of leaf leachate and bioavailability are opposite those found in streamwater DOC. Differences in phytochemistry among leaf types can influence stream ecosystems with respect to DOC quantity, composition, and rates of stream respiration. These patterns suggest that the relationship between the chemical structure of DOC and its biogeochemistry is more complex than previously recognized. These unique properties of leaf-litter DOC will be important when assessing the effects of terrestrial C on aquatic ecosystems, especially during leaf fall. [ABSTRACT FROM AUTHOR]

Few investigators have examined simultaneous bacterial and fungal responses to leaf-litter chemistry in fresh water. We tested the hypothesis that bacteria would be more abundant on labile litter with lower concentrations of defensive compounds, whereas fungi would be more abundant on recalcitrant litter. We used quantitative-polymerase chain reaction (qPCR) to measure the abundance of bacterial 16S and fungal 18S ribosomal ribonucleic acid (rRNA) genes and found that these groups responded differently to leaf chemistry. Bacterial 16S rRNA genes were 43 more abundant on labile than on recalcitrant litter. In contrast, fungal 18S rRNA genes were 83 more abundant on recalcitrant than on labile litter. Peak bacterial gene abundances on day 6 were related to leaf-litter % bound condensed tannin (r2 = 0.38), and peak fungal gene abundances on day 14 were related to % soluble condensed tannin (r2 = 0.49), % bound condensed tannin (r2 = 0.34), and % lignin (r2 = 0.33). Leaf-litter C:N ratios were not associated with microbial gene abundance. The ratio of fungal 18S:bacterial 16S genes also increased along the 1st axis in a principal components analysis of phytochemical variables. The early peak in bacterial rRNA gene abundance may indicate the role of bacteria in the early decomposition of leaf litter. rRNA gene abundance patterns demonstrate that bacteria and fungi have different patterns of growth and productivity in response to leaf-litter chemistry. [ABSTRACT FROM AUTHOR]