Variation In Decomposition Rates Research Articles

Variability in terrestrial litter decomposition can be explained by nutrient allocation strategies among soil decomposer communities

Abstract Leaf litter decomposition is a key process for nutrient cycling with broad ecosystem‐level consequences. However, we still cannot explain an important amount of the observed variability in decomposition rates. Therefore, a mechanistic model of how litter quality impacts the metabolic capacity of microbial decomposers to degrade litter at a given rate could improve our understanding of litter decomposition. Elemental imbalances between leaf litter and microbial decomposers can lead to nutrient‐limited decomposition. Microbial decomposers can deal with elemental imbalances via three main physiological mechanisms; by adjusting their carbon use efficiency (i.e. the proportion of assimilated carbon that is not respired), accumulating nitrogen or adjusting extracellular enzyme allocation between carbon (C) and nitrogen (N). Therefore, decomposer communities that adjust to elemental imbalances using these strategies should decompose litter faster than those unable to adjust. In this study, in a reciprocal transplant microcosm, we experimentally evaluated whether differences in the capacity of decomposers to reduce elemental imbalances help explain variability in decomposition rates. We used litter and soils from three coexisting woody species with contrasting litter C:N. Throughout the decomposition experiment, we quantified litter biomass loss, the allocation to β‐1,4‐glucosidase and β‐N‐acetylglucosaminidase (i.e. C and N degrading enzymes), and N accumulation. These data allowed us to identify the main strategies through which decomposers deal with elemental imbalances and their concomitant effects on litter decomposition rates. Our results confirm that litter decomposition rates are strongly controlled by litter quality, but differences in decay rates are a function of C and N demands of decomposers. Here, decomposers dealt with elemental imbalances mainly through N accumulation and, to a lesser extent, through extracellular enzyme allocation and lower carbon use efficiency. However, when enzymatic allocation and N accumulation were insufficient to reduce elemental imbalances, decomposition rates were slower irrespective of litter quality. Finally, we show that the effectiveness of physiological strategies used by decomposers to reduce elemental imbalances will affect decomposition rates, a key ecosystem process. Read the free Plain Language Summary for this article on the Journal blog.

How detritivores, plant traits and time modulate coupling of leaf versus woody litter decomposition rates across species

Abstract Plant functional traits are increasingly used to understand ecological relationships and (changing) ecosystem functions. For understanding ecosystem‐level biogeochemistry, we need to understand how (much) traits co‐vary between different plant organs across species and its implications for litter decomposition. However, we do not know how the degree of synchronous variation in decomposition rates between organs across species could be influenced by different keystone invertebrates decomposing different senesced plant organs, especially in warm‐climate forests. Here we asked whether interspecific patterns in wood and leaf decomposition rates and in the spectra of resource economics traits underpinning them, co‐vary across woody species; and how (much) the keystone invertebrate decomposers of the litter of these organs enhance or lower such co‐variation of decomposition rates through time. We addressed these questions through an 18‐month ‘common‐garden’ decomposition experiment using leaf, twig and branch litter of 41 woody species in two distant subtropical forest sites in east China. We quantified the effects of leaf, twig and branch functional traits and their respective key invertebrates (moth larvae, termites) on the decomposition rates of those organs. Interspecific variation in wood traits was partly decoupled from that in leaf traits across species, while strong coupling was found between twigs and branches. The co‐variation between leaf and woody organ decomposition rates was altered dynamically through the shifting activities of the key decomposers, which created nonlinear relationships of invertebrate litter consumption as a function of species rankings along the resource economic trait spectra of leaves and branches. The deviations from coupling of decomposition rates between organs were likely caused by combinations of three mechanisms: (1) (de‐)coupling between organs of other traits, not commonly considered in resource economics spectra (e.g. resins) (2) leaf and wood decomposers having specific diet requirements and (3) temporal patterns of the decomposers' activity. Synthesis. Our study highlights the importance of considering the different ways by which invertebrate detritivores drive decomposition processes through time. Under the ongoing biodiversity decline, future research would benefit from a better understanding of the role of the dynamic interactions between detritivore activities and plant functional traits on the carbon turnover in ecosystems.

Parsing spatial and temporal variation in stream ecosystem functioning

AbstractThe decomposition of organic matter is a fundamental ecosystem‐level process that governs nutrient cycling, fuels ecosystems, and impacts our global climate. Despite the central importance of this process for ecosystems across the planet, little is known about how the capacity of ecosystems to decompose organic matter—that is, their decomposition potential—varies across time and space. Closing this gap is needed to provide baseline information on the dynamics of ecosystems, for tracking anthropogenic impacts, and for development of practical and efficient sampling procedures. For nine consecutive years during the months of July–August, we deployed an identical organic‐matter decomposition assay in the same 26 temperate deciduous‐forest streams (234 stream‐years total) to evaluate the interannual and among‐stream variation in the decomposition of organic matter. Decomposition rates (as k values) ranged widely across all stream‐years (mean = 0.026, SD = 0.018, range = 0.0020–0.094). Interestingly, among‐stream variation, expressed on a per‐stream basis, was more than three times greater than interannual variation (expressed on a per year basis), explaining 75% and 22% of the overall variation in our dataset, respectively. Removing the effects of temperature by adjusting decomposition rates for degree days did not substantially impact this pattern (stream: 80% of variation, year: 17% of variation). Surprisingly, despite large differences in temperature among streams, temperature explained little variation in decomposition rates, pointing to the importance of other factors. When compared to the decomposition rates from stream sites across the planet, the rates presented here spanned 27.3% of this range, highlighting the diversity of decomposition rates that can be found in a relatively compact geographic area. From the perspective of using organic‐matter decomposition as a bioassessment tool, this variation could limit the sensitivity of decomposition‐based assays to human impacts, although study designs could be utilized to ameliorate this problem (e.g., those that stratify by geology). The results and dataset presented here are a needed step toward a more complete understanding of how ecosystem processes vary across time and space.

Seasonal variation in the coupling of microbial activity and leaf litter decomposition in a boreal stream network

Abstract Most stream networks are characterised by spatial and temporal variability in the physico‐chemical conditions that regulate microbial processing of particulate organic matter. How these patterns control the turnover of particulate organic matter via altered activity of leaf‐associated microbes has rarely been studied in high‐latitude landscapes, particularly throughout long (i.e., up to 6 months) ice‐ and snow‐covered periods. We investigated development of fungal biomass, enzyme activity, microbial respiration, and birch leaf litter decomposition from autumn to early summer in 11 nested streams in a boreal catchment that encompass a gradient in wetland (mire) cover. We observed relatively low variability in decomposition rates across the network, despite differences in key physical and chemical variables (e.g. temperature, pH, and dissolved organic carbon [DOC] concentrations) over time and space. Microbial enzymatic activity and respiration were positively related to leaf litter decomposition rates during early stages of decomposition (i.e., up to c. 30% loss of initial ash‐free dry mass). Thereafter, variation in microbial activity and respiration was decoupled from leaf litter mass loss, as enzymatic activity and respiration instead became positively related to DOC concentrations and upstream mire (wetland) cover among streams. Our results suggest that leaf‐associated microbes increase their reliance on external sources of energy over time. This switch in resource use was more evident in streams with higher DOC concentration, which in boreal landscapes is largely determined by mire cover. Hence, variation in DOC concentration, linked to landscape configuration, or from intensified land use and climate change, could affect how different carbon sources are used by stream microbial communities, with consequences for overall carbon cycling in boreal headwaters.

Low-decomposition rates of riparian litter in a North Patagonian ultraoligotrophic lake

Littoral zones of lakes are important for carbon and nutrient recycling because of the accumulation and decomposition of organic matter (OM) coming from terrestrial and aquatic plants. Here, we aimed to study OM decomposition from the most abundant riparian trees (Nothofagus dombeyi and Myrceugenia exsucca), and an emergent macrophyte (Schoenoplectus californicus), in the littoral zone of an ultraoligotrophic North-Patagonian Andean lake. We analysed the initial 2-days leaching, and litter mass loss and litter nutrient changes after one year of decomposition in a litter-bag experiment. The three studied species had very slow decay rates (k < 0.005 day−1), and initial nutrient release by leaching was not related to differences in decomposition rates. However, differences in leaf traits (lignin content) were related to interspecific variation in decomposition rates. The highest decomposition rates were observed for the macrophyte S. californicus, the species with the lower lignin content, while the opposite was observed in the Myrtaceae M. exsucca. In the three studied species, nitrogen content increased during decomposition. Our results indicated that in the shore of ultra-oligotrophic lakes, litter remains for long periods with net nutrient immobilization, thus OM of the riparian vegetation represents a carbon and nutrient sink.

Effects of dams and reservoirs on organic matter decomposition in forested mountain streams in western Japan

AbstractDamming of streams and rivers alters downstream ecosystem processes, and understanding its effects is essential in managing forested mountain streams. This study examined the effects of dams with a reservoir on organic matter decomposition and its seasonality in two neighbouring mountain streams over five seasons. The cotton‐strip assay and measurement of tensile strength loss were used to evaluate decomposition rates. In addition, the environmental factors, such as water level, water temperature, inorganic nitrogen concentrations and contribution of macro invertebrates were measured. The dams with a reservoir lowered decomposition rates downstream compared to upstream and unregulated sites, in all seasons. The decomposition rates also varied by season at all sites, with higher rates in summer and lowest in winter, and the seasonal variation was larger than the effects by the reservoirs in both streams. Seasonal variation in decomposition rates coincided with water temperature variation, suggesting strong influence of water temperature. However, the temperature differences did not explain the effects of reservoirs because water temperature was always higher at downstream sites. The downstream sites had lower nitrate concentrations and contribution of macroinvertebrates, and these factors may have greater effects than water temperature. Thus, damming of streams may lower the decomposition rates at downstream sites due to altered nutrient and biological effects. However, seasonal variation in water temperature may have more pronounced effects, resulting in greater seasonal variation than the difference among sites.

Seasonal patterns of Phragmites australis breakdown in a karstic freshwater system (Doberdò Lake, Northeast Italy) in relation to water level fluctuations, environmental features, and macrobenthic invertebrate communities

We investigated the main seasonal drivers of Phragmites australis decomposition dynamics in a freshwater karst lake subject to water level fluctuations. Physical and chemical parameters were monitored every two weeks for one year and P. australis decomposition rates were measured using the leaf bag technique during two seasons (autumn and spring). Decomposition dynamics were analyzed for the contribution of macrobenthic invertebrate colonizers and the influence of intermittent water level variations. Seasonal trends for changes in physical and chemical parameters were observed in relation to the underground origin of the water supply, which also affected the macrobenthic invertebrate communities. Decomposition rates k differed significantly between seasons (k = 0.0131 in autumn and k = 0.0115 in spring) but remained within a narrow range, reflecting the trend for changes in water temperature. Our findings show that the variability in decomposition rates was largely due to water level fluctuations (46.7% relative importance), rainfall (12.4% relative importance) and macrobenthic invertebrate communities dominated by shredders (23.9% relative importance; 40.9–93.7% of the collected samples). The influence of physical and chemical changes, particularly water temperature, was less important (relative importance 1.82%).

Leaf litter traits predominantly control litter decomposition in streams worldwide

AbstractAimLeaf litter decomposition in freshwater ecosystems is a vital process linking ecosystem nutrient cycling, energy transfer and trophic interactions. In comparison to terrestrial ecosystems, in which researchers find that litter traits predominantly regulate litter decomposition worldwide, the dominant factors controlling its decomposition in aquatic ecosystems are still debated, with global patterns not well documented. Here, we aimed to explore general patterns and key drivers (e.g., litter traits, climate and water characteristics) of leaf litter decomposition in streams worldwide.LocationGlobal.Time period1977–2018.Major taxa studiedLeaf litter.MethodsWe synthesized 1,707 records of litter decomposition in streams from 275 studies. We explored variations in decomposition rates among climate zones and tree functional types and between mesh size groups. Regressions were performed to identify the factors that played dominant roles in litter decomposition globally.ResultsLitter decomposition rates did not differ among tropical, temperate and cold climate zones. Decomposition rates of litter from evergreen conifer trees were much lower than those of deciduous and evergreen broadleaf trees, attributed to the low quality of litter from evergreen conifers. No significant differences were found between decomposition rates of litter from deciduous and evergreen broadleaf trees. Additionally, litter decomposition rates were much higher in coarse‐ than in fine‐mesh bags, which controled the entrance of decomposers of different body sizes. Multiple regressions showed that litter traits (including lignin, C:N ratio) and elevation were the most important factors in regulating leaf litter decomposition.Main conclusionsLitter traits predominantly control leaf litter decomposition in streams worldwide. Although further analyses are necessary to explore whether commonalities of the predominant role of litter traits in decomposition exist in both aquatic and terrestrial ecosystems, our findings could contribute to the use of trait‐based approaches in modelling the decomposition of litter in streams globally and exploring mechanisms of land–water–atmosphere carbon fluxes.

Litter decomposition: effects of temperature driven by soil moisture and vegetation type

We examined the importance of litter quality and microclimate on early-stage litter mass loss, analysed the importance of interactions among environmental factors in determining key decomposition parameters and compared the variation in decomposition rates in vegetation types and sites with similar climate. Following the Tea-Bag Index approach, 464 tea-bags were incubated in the soil in 79 sites, distributed across Italy, which included six vegetation types and a broad range of microclimatic conditions. Litter type exerted a stronger control on mass loss compared to climatic factors. The effects of soil moisture were not the same for high and lower quality litter. In addition, the effects of temperature on the decomposition rate depended on soil moisture. The stabilization factor was strongly temperature-dependent, but the influence of temperature differed among vegetation types: those dominated by small-size plants showed a strong decrease in the potential amount of plant material entering into the soil stock under warmer temperatures. The lowest variation in decomposition rate was found in sites characterised by low temperatures, and, among the vegetation types, in alpine snowbeds. The role of litter quality and of the interactions among environmental conditions can potentially determine significant shifts in the expected patterns of ecosystem carbon fluxes.

Depth dependence of soil carbon temperature sensitivity across Tibetan permafrost regions

Permafrost regions with high soil organic carbon (SOC) storage are extremely vulnerable to global warming. However, our understanding of the temperature sensitivity of SOC decomposition in permafrost regions remains limited, leading to considerable uncertainties in predicting carbon-climate feedback magnitude and direction in these regions. Here, we investigate general patterns and underlying mechanisms of SOC decomposition rate and its temperature sensitivity (Q10) at different soil depths across Tibetan permafrost regions. Soils were collected at two depths (0–10 and 20–30 cm) from 91 sites across Tibetan permafrost regions. SOC decomposition rate and Q10 value were estimated using a continuous-flow incubation system. We found that the SOC decomposition rate in the upper layer (0–10 cm) was significantly greater than that in the lower layer (20–30 cm). The SOC content governed spatial variations in decomposition rates in both soil layers. However, the Q10 value in the upper layer was significantly lower than that in the lower layer. Soil pH and SOC decomposability had the greatest predictive power for spatial variations in Q10 value within the upper and lower layers, respectively. Owing to the greater temperature sensitivity in the lower layer, our results imply that subsurface soil carbon is at high risk of loss, and that soil carbon sequestration potential might decrease in these regions in a warming world.

Traits drive global wood decomposition rates more than climate.

Wood decomposition is a major component of the global carbon cycle. Decomposition rates vary across climate gradients, which is thought to reflect the effects of temperature and moisture on the metabolic kinetics of decomposers. However, decomposition rates also vary with wood traits, which may reflect the influence of stoichiometry on decomposer metabolism as well as geometry relating the surface areas that decomposers colonize with the volumes they consume. In this paper, we combined metabolic and geometric scaling theories to formalize hypotheses regarding the drivers of wood decomposition rates, and assessed these hypotheses using a global compilation of data on climate, wood traits, and wood decomposition rates. Our results are consistent with predictions from both metabolic and geometric scaling theories. Approximately half of the global variation in decomposition rates was explained by wood traits (nitrogen content and diameter), whereas only a fifth was explained by climate variables (air temperature, precipitation, and relative humidity). These results indicate that global variation in wood decomposition rates is best explained by stoichiometric and geometric wood traits. Our findings suggest that inclusion of wood traits in global carbon cycle models can improve predictions of carbon fluxes from wood decomposition.

Plant traits related to leaf decomposition processes in arid ecosystems of northern Patagonia

Plants play an important role in ecosystem processes. Functional meaning of trait variation in wide environmental gradients is well known but is scarcely known across narrow gradients. We analyze the variation of morphological, physical and chemical traits of dominant plant species and the potential rates of dry mass loss and N release/immobilization during senesced leaf decomposition of these species across a narrow aridity gradient, and to identify indicative traits useful to set species functional groups sharing decomposition patterns. We analyzed the variation of morphological, physical and chemical traits (specific leaf area, seed mass, N and soluble phenols in green and senesced leaves, plant height) in dominant plant species at 12 sites across an aridity gradient in northern Patagonia, Argentina. We collected senesced leaves of each plant species at each site and used them to estimate the potential rates of dry mass loss and N release/immobilization from decomposing senesced leaves in a microcosm experiment. We analyzed the variation of plant traits and decomposition rates across the aridity gradient. We grouped plants species according to growth forms (perennial grasses, deciduous shrubs, evergreen shrubs) and different combinations of morpho-physical and chemical traits of green and senesced leaves and compared the potential rates of dry mass loss and N release/immobilization during leaf decomposition among these groups delimited by each grouping criteria. Plant traits did not vary across the aridity gradient. The potential rate of dry mass loss was positively related to aridity, while the potential rate of N release/immobilization did not vary across the gradient. Grouping species by separately morpho-physical and chemical traits resulted in a large overlapping in mean values of decomposition rates among groups. In contrast, plant groupings based on growth forms and those including all morpho-physical and chemical traits of green or senesced leaves yielded groups with differentiated rates of decomposition processes. The two latter groupings clustered species from more than one growth form indicating some overlapping in the rates of decomposition processes among species of different growth forms. Among traits, N concentration in senesced leaves and plant height explained the highest variation in decomposition rates being positively related to potential rates of dry mass loss and N release/immobilization. We concluded that plant groupings based on morpho-physical and chemical traits of either green or senesced leaves may be more powerful to differentiate functional species groups sharing decomposition patterns than the growth form grouping. Moreover, plant height and N concentration in senesced leaves may be considered relevant synthetic functional traits in relation to decomposition processes in narrow aridity gradients.

Species associations overwhelm abiotic conditions to dictate the structure and function of wood-decay fungal communities.

Environmental conditions exert strong controls on the activity of saprotrophic microbes, yet abiotic factors often fail to adequately predict wood decomposition rates across broad spatial scales. Given that species interactions can have significant positive and negative effects on wood-decay fungal activity, one possibility is that biotic processes serve as the primary controls on community function, with abiotic controls emerging only after species associations are accounted for. Here we explore this hypothesis in a factorial field warming- and nitrogen-addition experiment by examining relationships among wood decomposition rates, fungal activity, and fungal community structure. We show that functional outcomes and community structure are largely unrelated to abiotic conditions, with microsite and plot-level abiotic variables explaining at most 19% of the total variability in decomposition and fungal activity, and 2% of the variability in richness and evenness. In contrast, taxonomic richness, evenness, and species associations (i.e., co-occurrence patterns) exhibited strong relationships with community function, accounting for 52% of the variation in decomposition rates and 73% in fungal activity. A greater proportion of positive vs. negative species associations in a community was linked to strong declines in decomposition rates and richness. Evenness emerged as a key mediator between richness and function, with highly even communities exhibiting a positive richness-function relationship and uneven communities exhibiting a negative or null response. These results suggest that community-assembly processes and species interactions are important controls on the function of wood-decay fungal communities, ultimately overwhelming substantial differences in abiotic conditions.

Impact of an invasive alien plant on litter decomposition along a latitudinal gradient

AbstractInvasive alien plant effects on ecosystem functions are often difficult to predict across environmental gradients due to the context‐dependent interactions between the invader and the recipient communities. Adopting a functional trait‐based framework could provide more mechanistic predictions for invasive species' impacts. In this study, we contrast litter decomposition rates among communities with and without the invasive plant Impatiens glandulifera in five regions along a 1600 km long latitudinal gradient in Europe. Across this gradient, four functional traits, namely leaf dry matter content (LDMC), specific leaf area (SLA), stem‐specific density (SSD), and plant height, are correlated to rates of litter decomposition of standardized rooibos (labile), green tea (recalcitrant), and I. glandulifera litter. Our results show that both invaded and non‐invaded plant communities had a higher expression of acquisitive traits (low LDMC and SSD, high SLA) with increasing temperature along the latitudinal gradient, partly explaining the variation in decomposition rates along the gradient. At the same time, invasion shifted community trait composition toward more acquisitive traits across the latitudinal gradient. These trait changes partly explained the increased litter decomposition rates of the labile litter fraction of rooibos and I. glandulifera litter in invaded communities, a shift that was most evident in the warmer study regions. Plant available nitrogen was lower in invaded communities, likely due to high nutrient uptake by I. glandulifera. Meanwhile, the coldest study region was characterized by a reversed effect of invasion on decomposition rates. Here, community traits related to low litter quality and potential allelopathic effects of the invader resulted in reduced litter decomposition rates, suggesting a threshold temperature at which invader effects on litter decomposition turn positive. This study therefore illustrates how functional trait changes toward acquisitive traits can help explain invader‐induced changes in ecosystem functions such as increased litter decomposition.

Specific leaf area predicts dryland litter decomposition via two mechanisms

Abstract Litter decomposition plays important roles in carbon and nutrient cycling. In dryland, both microbial decomposition and abiotic degradation (by UV light or other forces) drive variation in decomposition rates, but whether and how litter traits and position determine the balance between these processes is poorly understood. We investigated relationships between litter quality and their decomposition rates among diverse plant species in a desert ecosystem in vertically contrasting positions representing distinct decomposition environments driven by different relative contributions of abiotic and microbial degradation. Thereto, leaf litter samples from 17 desert species were sealed into litterbags and placed on the soil surface under strong solar exposure vs. shade conditions, or buried in the soil at 10 cm depth, for a whole year. Litter decomposition rates were 21% and 17% higher in burial and light‐exposed treatments, respectively, than those in shade. Leaf traits, i.e. specific leaf area (SLA), litter C:N ratio and lignin concentration could predict litter decomposition to some degree, but their predictive power was dependent on litter position. However, multiple linear regressions showed that SLA, litter C and P significantly affected k values for leaf litter decomposition besides litter position, with SLA standing out as a strong determinant of litter decomposition rate as related either to solar radiation or the environment below the soil surface. Furthermore, the interspecific differences in litter decomposition rates decreased over time, implying that afterlife effects of leaf traits on decomposition were attenuated. Synthesis. These findings suggest that abiotic photodegradation and soil burial mediated microbial decomposition could be responsible for higher than expected litter turnover in dryland. They point to a dual role of specific leaf area (SLA) as a promotor of decomposition rates: via relative exposure of the leaf surface to abiotic factors such as UV light vs. to soil moisture and microbes under soil burial.

The Effect of Body Mass on Outdoor Adult Human Decomposition

Forensic taphonomy explores factors impacting human decomposition. This study investigated the effect of body mass on the rate and pattern of adult human decomposition. Nine males and three females aged 49-95years ranging in mass from 73 to 159kg who were donated to the Complex for Forensic Anthropology Research between December 2012 and September 2015 were included in this study. Kelvin accumulated degree days (KADD) were used to assess the thermal energy required for subjects to reach several total body score (TBS) thresholds: early decomposition (TBS ≥6.0), TBS ≥12.5, advanced decomposition (TBS ≥19.0), TBS ≥23.0, and skeletonization (TBS ≥27.0). Results indicate no significant correlation between body mass and KADD at any TBS threshold. Body mass accounted for up to 24.0% of variation in decomposition rate depending on stage, and minor differences in decomposition pattern were observed. Body mass likely has a minimal impact on postmortem interval estimation.

English

Sustaining the productive capacity of soils has raised interest in the maintenance of soil organic matter through management practices and use of crop residues. While the impact of management practices has been studied, little is done to understand how the charateristics of the residue itself impact the decomposition at the soil surface. This study relates the chemical composition and the surface area of the aboveground residue to the decomposition rates for three cultivars each of three crops: cotton, peanut and sorghum. The rates were determined by mass loss. Change in the residue specific surface area to mass loss was also measured. Findings show that after 14 days, the aboveground residue for the three crops were from the most rapid loss to the slowest: cotton (43%) > peanut (32%) > sorghum (24%). Changes in the specific surface area-to-mass ratio were from the slowest to the most rapid loss: cotton (1.60×10-4) > peanut (1.50×10-4> sorghum (1.20×10-4). Since varietal differences within crops have led to variation in decomposition rates, cultivars with slower decaying residues might be recommended for C sequestration and for erodible lands in semi-arid zones of the Sahel. Likewise, crop residues with faster decomposition rates can be recommended for soil fertility improvement. Key words: Decomposition rate, crop type, crop residue, chemical composition, specific surface area-to-mass ratio.

Genotypic variability in Populus tremula L. affects how anthropogenic nitrogen enrichment influences litter decomposition

Background and aimsBoreal forests can receive substantial nitrogen (N) enrichment via atmospheric N deposition and industrial forest fertilization. While it is known that N enrichment can impact ecosystem properties, such as litter decomposition, it remains poorly understood how genetic variability within plant species modifies these impacts.MethodsWe grew replicates of ten Populus tremula L. genotypes (GTs) under 3 N conditions; ambient, and levels representing atmospheric N deposition and industrial forest fertilization. We measured leaf and litter physical and chemical traits, and conducted a litter decomposition assay.ResultsLeaf traits varied due to N treatment, GT, and constitutive tannin levels. Leaf traits were in some cases correlated with litter traits, and decomposition was influenced by single and interactive effects of N and GT. Nitrogen addition unexpectedly decelerated decomposition, potentially due to changes in specific leaf area (SLA). Variation in decomposition rates among the GTs was best explained by their differences in SLA, and lignin:N ratio. Nitrogen addition also caused a shift in which traits most strongly influenced decomposition.ConclusionsOur findings highlight that the considerable diversity present in tree species can have a strong influence on ecosystem processes, such as decomposition, and how these processes respond to environmental change.

Decay rates of leaf litters from arbuscular mycorrhizal trees are more sensitive to soil effects than litters from ectomycorrhizal trees

Summary While it is well established that leaf litter decomposition is controlled by climate and substrate quality at broad spatial scales, conceptual frameworks that consider how local‐scale factors affect litter decay in heterogeneous landscapes are generally lacking. A critical challenge in disentangling the relative impacts of and interactions among local‐scale factors is that these factors frequently covary due to feedbacks between plant and soil communities. For example, forest plots dominated by trees that associate with ectomycorrhizal (ECM) fungi often differ from those dominated by trees that associate with arbuscular mycorrhizal (AM) fungi in terms of their litter quality, microbial community structure and inorganic nutrient availability. Here, we evaluate the extent to which such factors alter leaf litter decomposition rates. To characterize variations in decomposition rates, we compared decay rates of high‐quality litter (maple; AM) and low‐quality litter (oak; ECM) across forest plots representing a gradient in litter matrix quality and nitrogen (N) availability driven by the relative proportions of AM and ECM trees in each plot. In experiment two, we added litter from two AM and three ECM tree species to forest plots with either a high‐quality litter matrix and high N availability (i.e. AM‐dominated plots) or a low‐quality litter matrix and low N availability (i.e. ECM‐dominated plots). In both experiments, we found that AM litter decomposed more rapidly than ECM litter, and this effect was enhanced in AM‐dominated plots. Then, to separate the contributions of litter matrix effects from N availability effects, we added N fertilizer to a subset of plots from experiment two. Nitrogen addition increased decay rates of high‐quality litter across all sites, but had no effect on low‐quality litter, suggesting that low N availability, not litter matrix quality, constrains decomposition of high‐quality litters. Hence, N availability appears to alter litter decomposition patterns independently of litter matrix properties. Synthesis. Our results indicate that shifts in the relative abundance of ECM‐ and AM‐associated trees in a plot or stand have the potential to affect litter decay rates through both changes in litter quality as well as through alterations of the local‐scale soil environment.

Understanding litter decomposition in semiarid ecosystems: linking leaf traits, UV exposure and rainfall variability.

Differences in litter quality, microbial activity or abiotic conditions cannot fully account for the variability in decomposition rates observed in semiarid ecosystems. Here we tested the role of variation in litter quality, water supply, and UV radiation as drivers of litter decomposition in arid lands. And show that carry-over effects of litter photodegradation during dry periods can regulate decomposition during subsequent wet periods. We present data from a two-phase experiment, where we first exposed litter from a drought-deciduous and an evergreen shrub to natural UV levels during five, rainless summer months and, subsequently, in the laboratory, we assessed the carry-over effects of photodegradation on biomass loss under different irrigation treatments representing the observed range of local rainfall variation among years (15–240 mm). Photodegradation of litter in the field produced average carbon losses of 12%, but deciduous Proustia pungens lost >25%, while evergreen Porlieria chilensis less than 5%. Natural exposure to UV significantly reduced carbon-to-nitrogen and lignin:N ratios in Proustia litter but not in Porlieria. During the subsequent wet phase, remaining litter biomass was lower in Proustia than in Porlieria. Indeed UV exposure increased litter decomposition of Proustia under low and medium rainfall treatments, whereas no carry-over effects were detected under high rainfall treatment. Consequently, for deciduous Proustia carry-over effects of UV exposure were negligible under high irrigation. Litter decomposition of the evergreen Porlieria depended solely on levels of rainfall that promote microbial decomposers. Our two-phase experiment revealed that both the carry-over effects of photodegradation and litter quality, modulated by inter-annual variability in rainfall, can explain the marked differences in decomposition rates and the frequent decoupling between rainfall and litter decomposition observed in semiarid ecosystems.