Cross‐biome transplants of plant litter show decomposition models extend to a broader climatic range but lose predictability at the decadal time scale

We analyzed results from 10‐year long field incubations of foliar and fine root litter from the Long‐term Intersite Decomposition Experiment Team (LIDET) study. We tested whether a variety of climate and litter quality variables could be used to develop regression models of decomposition parameters across wide ranges in litter quality and climate and whether these models changed over short to long time periods. Six genera of foliar and three genera of root litters were studied with a 10‐fold range in the ratio of acid unhydrolyzable fraction (AUF, or ‘lignin’) to N. Litter was incubated at 27 field sites across numerous terrestrial biomes including arctic and alpine tundra, temperate and tropical forests, grasslands and warm deserts. We used three separate mathematical models of first‐order (exponential) decomposition, emphasizing either the first year or the entire decade. One model included the proportion of relatively stable material as an asymptote. For short‐term (first‐year) decomposition, nonlinear regressions of exponential or power function form were obtained with r² values of 0.82 and 0.64 for foliar and fine‐root litter, respectively, across all biomes included. AUF and AUF : N ratio were the most explanative litter quality variables, while the combined temperature‐moisture terms AET (actual evapotranspiration) and CDI (climatic decomposition index) were best for climatic effects. Regressions contained some systematic bias for grasslands and arctic and boreal sites, but not for humid tropical forests or temperate deciduous and coniferous forests. The ability of the regression approach to fit climate‐driven decomposition models of the 10‐year field results was dramatically reduced from the ability to capture drivers of short‐term decomposition. Future work will require conceptual and methodological improvements to investigate processes controlling decadal‐scale litter decomposition, including the formation of a relatively stable fraction and its subsequent decomposition.     

The potential for forest canopy litterfall interception by a dense fern understorey, and the consequences for litter decomposition

Most studies on litter decomposition have assumed that all falling plant litter reaches the ground where it then decomposes. In many forests a proportion of this litter may in fact be intercepted by understorey vegetation, but the ecological significance of this remains poorly understood. We performed two experiments in a temperate rainforest in southern New Zealand, in which there was a dense understorey of the crown fern Blechnum discolor. The fronds of this fern originate from a crown, and have a funnel‐like arrangement that can trap falling litter and prevent it from reaching the ground. The first experiment measured the effects of ferns on the spatial distribution of litter accumulation over one year. The ferns intercepted a substantial proportion of the total litterfall, and the fern crowns (from which the fronds originate) retained 10% of the total incoming litterfall (despite occupying only 2% of the ground area). The retained litter had a substantially higher ratio of twig to foliar litter than did the incoming litterfall. Further, much of the litter not retained on the crowns of the ferns accumulated at the base of the fern trunks. The second experiment considered litter decomposition in fern crowns versus the ground under the ferns. The litter that had accumulated in the crowns was characterized by higher microbial basal respiration and active microbial biomass than was the litter that had accumulated on the ground. The use of litterbags revealed that litter decomposition rates were significantly higher on the fern crowns than on the ground at 30 cm and 60 cm from the fern trunks. These results show that litter interception ameliorates the decomposer environment and increases the rate of litter decomposition. In total, this study provides evidence for understorey ferns greatly influencing both the spatial distribution of litterfall and the decomposition of plant litter. Although the ecological role of understorey vegetation in forested ecosystems has received little attention to date, our results point to understorey species as an important driver of forest ecosystem processes.     

三个亚热带森林优势种凋落物非结构性碳水化合物含量的季节动态

非结构性碳水化合物(NSC)是凋落物中的易分解组分,在凋落物分解早期快速释放进入土壤并被微生物利用,参与森林土壤生物地球化学循环,因此新鲜凋落物中NSC变化规律是认识森林土壤碳和养分循环的关键之一。选取亚热带常绿阔叶林优势树种米槠(Castanopsis carlesii)和主要造林树种杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)为研究对象,分析其新鲜凋落叶和凋落枝中NSC(可溶性糖和淀粉)含量的动态变化规律。结果表明：凋落物中NSC含量在不同月份表现出明显的时间动态,米槠、杉木和马尾松凋落叶和凋落枝中NSC含量总体上在11—12月呈上升趋势,而在2—6月呈缓慢下降趋势。不同类型的凋落物NSC含量存在显著差异,米槠、杉木和马尾松凋落叶中NSC含量分别为3.03%—3.56%、2.18%—4.37%、3.38%—4.89%,凋落枝中NSC含量分别为1.87%—4.22%、2.88%—4.28%、2.75%—5.27%,米槠和马尾松凋落叶中NSC含量高于凋落枝,而杉木凋落枝中NSC含量高于凋落叶。不同树种凋落物NSC含量差异显著,米槠和...     

Context dependency of litter‐mixing effects on decomposition and nutrient release across a long‐term chronosequence

Litter decomposition is an important driver of terrestrial systems, and factors that determine decomposition rate for individual litter species have been widely studied. Fewer studies have explored the factors that regulate how mixing litters of multiple species affects litter decomposition and nutrient dynamics, and only a handful of studies have investigated how litter‐mixing effects may differ among different habitats or ecosystems, or how they respond to environmental gradients. We used a well‐established retrogressive chronosequence involving thirty lake islands in northern Sweden in which time since fire disturbance increases with decreasing island size; smaller islands therefore have reduced rates of aboveground and belowground ecosystem processes. On each of these islands we utilized plots with and without the long‐term experimental removal of shrubs. Litters from the six most common plant species on the islands were prepared in single‐, three‐ and six‐species litterbags, and placed on both the shrub‐removal and non‐removal plots on each island to decompose for one year. We found significant non‐additive effects of litter mixing on litter decomposition rates, on final litter N and P concentrations, and on litter N loss, but these non‐additive effects varied both in direction and magnitude with changed number of species, and even among litter mixtures with the same number of species. Further, the magnitude of non‐additive effects of litter mixing on both litter decomposition and nutrient dynamics was significantly influenced by both island size and the interaction between island size and shrub‐removal treatment. When shrubs were present, there was a U‐shaped relationship between these non‐additive effects and island size, while the relationship was positive when shrubs were removed. Hence, our results support previous findings that litter mixing may produce non‐additive effects on litter decomposition and nutrient dynamics, and that these effects tend to be idiosyncratic due to the importance of effects of individual species in the mixture. Most importantly, our results show that non‐additive litter‐mixing effects change greatly across environmental gradients, meaning that the biotic and abiotic characteristics of an ecosystem can be a powerful driver of the magnitude and even the direction of litter‐mixing effects on ecosystem processes.     

Litter decomposition rate is dependent on litter Mn concentrations

A statistically significant linear relationship was found between annual mass loss of foliar litter in the late stages of decomposition and Mn concentration in the litter. We used existing decomposition data on needle and leaf decomposition of Scots pine (Pinus sylvestris L.), lodgepole pine (Pinus contorta var. contorta), Norway spruce (Picea abies (L.) Karst.), silver birch (Betula pendula L.), and grey alder (Alnus incana L.) from Sweden and Aleppo pine (Pinus halepensis Mill.) from Libya, to represent boreal, temperate, and Mediterranean climates. The later the decomposition stage as indicated by higher sulfuric-acid lignin concentrations, the better were the linear relationships between litter mass loss and Mn concentrations. We conclude that Mn concentrations in litter have an influence on litter mass-loss rates in very late decomposition stages (up to 5 years), provided that the litter has high enough Mn concentration. The relationship may be dependent on species as the relationship is stronger with species that take up high enough amounts of Mn.     

森林凋落物研究进展

对森林凋落物的概念、研究方法及主要研究内容作了阐述,特别就凋落物收集面积和分解袋孔径大小、凋落量时空动态和凋落物分解速率等问题进行了综合分析。目前森林凋落物研究的重要结论有：海拔和纬度因子是通过对光、温、水等生态因子的再分配来影响凋落量,其中主导气候因子是年均温。凋落物的分解与化学组成和环境因子有关,C／N和N含量在凋落物分解过程中起着重要作用。土壤水分是影响凋落物分解主要环境因子之一;土壤微生物对凋落物的影响,前期是通过真菌破碎凋落物表层使内居性动物得以侵入凋落物内部,后期则以细菌降解有机物为主。凋落量、凋落物分解的影响因子,以及凋落物的生态作用等内容应是凋落物研究的重要方向。     

四川红杉-岷江冷杉原始林凋落物K和Na的归还动态

以凋落物为载体的养分归还是生态系统物质循环的主要过程,也是林木生长所需养分的重要来源。相对于其他元素,钾(K)和钠(Na)在调节渗透压方面有着极其重要的作用,且淋溶作用强烈,极易流失,但缺乏必要关注。因此,以海拔3589 m高山峡谷区典型的四川红杉(Larix mastersiana)-岷江冷杉(Abies faxoniana)原始林为研究对象,在2015年9月到2016年8月期间调查了不同类型凋落物中K和Na元素在不同时期的归还特征。结果表明:1)凋落物K和Na元素年归还量分别为25.34和4.44 kg·hm^-2,表现为:凋落叶>凋落枝>其他凋落物>凋落皮>附生植物>繁殖器官。其中,凋落叶和枝占总凋落物K和Na元素归还的85%以上;2)总凋落物、凋落叶和枝的K、Na元素归还动态呈现"双峰型",最大值出现在5月和10月;凋落皮和繁殖器官K、Na元素归还动态呈现"单峰型",最大值出现在5月;3)乔木层树种凋落物的K和Na元素呈现"双峰型"的归还模式,最大值在5月和10月,灌木树种凋落物的K和Na元素呈现"单峰型"归还模式,最大值在9-10月。这些结果说明了高山峡谷区典型针叶林不同类型凋落物元素归还的季节性特征,为进一步认识区域森林物质循环及相关的生态学过程提供了基础数据。     

冬季雪被对青藏高原东缘高海拔森林凋落叶P元素释放的影响

雪被是影响高海拔森林凋落物分解的重要生态因子,其是否影响到生长季节与非生长季节凋落物中的P元素释放,尚未量化。为了量化季节性雪被对高海拔森林凋落物分解过程中P元素释放的影响,于2010年10月至2012年10月间,在青藏高原东缘川西高海拔森林不同厚度冬季雪被斑块下,设置凋落物分解袋实验。检测该地区代表性树种岷江冷杉(Abies faxoniana)、红桦(Betula albo-sinensis)、四川红杉(Larix mastersiana)和方枝柏(Sabina saltuaria)凋落叶在雪被覆盖不同关键时期(雪被形成前期、完全覆盖期和消融期)以及生长季节的P元素动态。结果表明,凋落物质量与雪被厚度均显著影响了P元素的释放过程。雪被覆盖时期凋落物P元素释放率表现为有雪被覆盖大于无雪被覆盖,而生长季节中除岷江冷杉外的其他3种凋落物P元素释放率均为无雪被覆盖下最大。相对于无雪被覆盖斑块,冬季雪被的存在提供了保护绝缘层,促进凋落物P元素释放,提高了各物种冬季P元素释放贡献率。这些结果表明,全球变化情景下的雪被减少可能减缓高海拔森林凋落物P元素的释放过程,改变森林土壤P元素水平。所以在研究高寒、高海拔地区全球气候变化下生态系统功能的工作中,应注重雪被这一异质性环境因子对生态系统功能的影响。     

Decomposition dynamics in mixed-species leaf litter

Literature on plant leaf litter decomposition is substantial, but only in recent years have potential interactions among leaves of different species during decomposition been examined. We review emerging research on patterns of mass loss, changes in nutrient concentration, and decomposer abundance and activity when leaves of different species are decaying in mixtures. Approximately 30 papers have been published that directly examine decomposition in leaf mixtures as well as in all component species decaying alone. From these litter‐mix experiments, it is clear that decomposition patterns are not always predictable from single‐species dynamics. (Characteristics of decomposition in litter‐mixes that deviate from responses predicted from decomposition of single‐species litters alone are designated "non‐additive"; "additive" responses in mixes are predictable from component species decaying alone.) Non‐additive patterns of mass loss were observed in 67% of tested mixtures; mass loss is often (though not always) increased when litters of different species are mixed. Observed mass loss in some mixtures is as much as 65% more extensive than expected from decomposition of single‐species litter, but more often mass loss in mixtures exceeds expected decay by 20% or less. Nutrient transfer among leaves of different species is striking, with 76% of the mixtures showing non‐additive dynamics of nutrient concentrations. Non‐additive patterns in the abundance and activity of decomposers were observed in 55% and 65% of leaf mixes, respectively. We discuss some methodological details that likely contribute to conflicting results among mixed‐litter studies to date. Enough information is available to begin formulating mechanistic hypotheses to explain patterns in litter‐mix experiments. Emerging patterns in the mixed‐litter decomposition literature have implications for relationships between biodiversity and ecosystem function (in this case, the function being decomposition), and for potential mechanisms through which invasive plant species could alter carbon and nutrient dynamics in ecosystems.     

Litterfall Dynamics Under Different Tropical Forest Restoration Strategies in Costa Rica

In degraded tropical pastures, active restoration strategies have the potential to facilitate forest regrowth at rates that are faster than natural recovery, enhancing litterfall, and nutrient inputs to the forest floor. We evaluated litterfall and nutrient dynamics under four treatments: plantation (entire area planted), tree islands (planting in six patches of three sizes), control (same age natural regeneration), and young secondary forest (7–9‐yr‐old natural regeneration). Treatments were established in plots of 50 × 50 m at six replicate sites in southern Costa Rica and the annual litterfall production was measured 5 yr after treatment establishment. Planted species included two native timber‐producing hardwoods (Terminalia amazonia and Vochysia guatemalensis) interplanted with two N‐fixing species (Inga edulis and Erythrina poeppigiana). Litter production was highest in secondary forests (7.3 Mg/ha/yr) and plantations (6.3), intermediate in islands (3.5), and lowest in controls (1.4). Secondary forests had higher input of all nutrients except N when compared with the plantation plots. Inga contributed 70 percent of leaffall in the plantations, demonstrating the influence that one species can have on litter quantity and quality. Although tree islands had lower litterfall rates, they were similar to plantations in inputs of Mg, K, P, Zn, and Mn. Tree islands increased litter production and nutrient inputs more quickly than natural regeneration. In addition to being less resource intensive than conventional plantations, this planting design promotes a more rapid increase in litter diversity and more spatial heterogeneity, which can accelerate the rate of nutrient cycling and facilitate forest recovery.     

Litter decomposition of a pine plantation is affected by species evenness and soil nitrogen availability

Background and aims

Litter decomposition is a key process controlling flows of energy and nutrients in ecosystems. Altered biodiversity and nutrient availability may affect litter decomposition. However, little is known about the response of litter decomposition to co-occurring changes in species evenness and soil nutrient availability.

Methods

We used a microcosm experiment to evaluate the simultaneous effects of species evenness (two levels), identity of the dominant species (three species) and soil N availability (control and N addition) on litter decomposition in a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Northeast China. Mongolian pine needles and senesced aboveground materials of two dominant understory species (Setaria viridis and Artemisia scoparia) were used for incubation.

Results

Litter evenness, dominant species identity and N addition significantly affected species interaction and litter decomposition. Higher level of species evenness increased the decomposition rate of litter mixtures and decreased the incidence of antagonistic effects. A. scoparia-dominated litter mixtures decomposed faster than P. sylvestris var. mongolica- and S. viridis-dominated litter mixtures. Notably, N addition increased decomposition rate of both single-species litters and litter mixtures, and meanwhile altered the incidence and direction of non-additive effects during decomposition of litter mixtures. The presence of understory species litters stimulated the decomposition rate of pine litters irrespective of N addition, whereas the presence of pine litters suppressed the mass loss of A. scoparia litters. Moreover, N addition weakened the promoting effects of understory species litters on decomposition of pine litters.

Conclusions

Pine litter retarded the decomposition of understory species litters whereas its own decomposition was accelerated in mixtures. Nitrogen addition and understory species evenness altered species interaction through species-specific responses in litter mixtures and thus affected litter decomposition in Mongolian pine forests, which could produce a potential influence on ecosystem C budget and nutrient cycling.     

The Effects of Exotic Grasses on Litter Decomposition in a Hawaiian Woodland: The Importance of Indirect Effects

Exotic grasses and grass-fueled fires have altered plant species composition in the seasonal submontane woodlands of Hawaii Volcanoes National Park. These changes have altered both structural and functional aspects of the plant community, which could, in turn, have consequences for litter decomposition and nitrogen (N) dynamics. In grass-invaded unburned woodland, grass removal plots within the woodland, and woodland converted to grassland by fire, we compared whole-system fluxes and the contributions of individual species to annual aboveground fine litterfall and litterfall N, and litter mass and net N loss. We assessed the direct contribution of grass biomass to decomposition and N dynamics, and we determined how grasses affected decomposition processes indirectly via effects on native species and alteration of the litter layer microenvironment. Grasses contributed 35% of the total annual aboveground fine litterfall in the invaded woodland. However, total litterfall mass and N were not different between the invaded woodland and the grass removal treatment because of compensation by the native tree Metrosideros polymorpha, which increased litter production by 37% ± 5% when grasses were removed. The 0.3 g N m^–2/y^–1 contained in this production increase was equal to the N contained in grass litter. Litter production and litterfall N was lowest in the grassland due to the loss of native litter inputs. Decomposition of litterfall on an area basis was highest in the grass-invaded woodland. We attributed this effect to increased inherent decomposability of native litter in the presence of grasses because (a) the microenvironment of the three vegetation treatments had little effect on decomposition of common litter types and (b) M. polymorpha litter produced in the invaded woodland decomposed faster than that produced in the grass removal plots due to higher lignin concentrations in the latter than in the former. Area-weighted decomposition was lowest in the grassland due to the absence of native litter inputs. Across all treatments, most litter types immobilized N throughout the incubation, and litter net N loss on an area basis was not different among treatments. Our results support the idea that the effects of a plant species or growth form on decomposition cannot be determined in isolation from the rest of the community or from the direct effects of litter quality and quantity alone. In this dry woodland, exotic grasses significantly altered decomposition processes through indirect effects on the quantity and quality of litter produced by native species.     

Do physical plant litter traits explain non‐additivity in litter mixtures? A test of the improved microenvironmental conditions theory

The decomposition rates of plant litter mixtures often deviate from the averaged rates of monocultures of their component litter species. The mechanisms behind these non‐additive effects in decomposition of litter mixtures are lively debated. One plausible explanation for non‐additive effects is given by the improved microenvironmental condition (IMC) theory. According to this theory, plant litter species, whose physical characteristics improve the microclimatic conditions for decomposers, will promote the decomposition of their co‐occurring litter species. We tested the IMC theory in relation to leaf litter and soil moisture in two contrasting moisture conditions in a dry subarctic mountain birch forest with vascular plant leaf litters of poor and high quality. The non‐additive effects in mass loss of litter mixtures increased when moisture conditions in litter and soil became more favourable for plant litter decomposition. The sign of this increase (antagonistic or synergistic) in non‐additive effects was more predictable for litter mixtures of poor litter quality. Although the specific mechanisms underlying the IMC theory depended on the litter quality of the litter mixtures, a standardized water holding capacity (WHC) was the litter trait most closely related to the non‐additive effects in mixtures of both poor and high quality litter types. Furthermore, we found that higher dissimilarity in WHC traits between the component litter species in a mixture increased synergistic effects in litter mixtures under limiting moisture conditions. However, under improved moisture conditions, increased antagonistic effects were observed. Thus, we found clear support for the IMC theory and showed that climatic conditions and leaf litter physical traits determine whether the non‐additive effects in litter mixtures are antagonistic or synergistic. Our study emphasizes the need to include litter physical traits into predictive models of mixing effects on plant litter decomposition and in general suggests climate specificity into these models.     

Decomposition Patterns of Foliar Litter and Deadwood in Managed and Unmanaged Stands: A 13-Year Experiment in Boreal Mixedwoods

Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability.     

Survival ofSclerotinia minor Jagger sclerotia in solarized soil

Calcium, magnesium and potassium dynamics in decomposing litter of three tree species were measured over a two-year period. The speices studied were flowering dogwood (Cornus florida), red maple (Acer rubrum) and chestnut oak (Quercus prinus). The order of decomposition was:C. florida>A. rubrum>Q. prinus.Calcium concentrations increased following any initial leaching losses. However, there were net releases of Ca from all three litter types since mass loss exceeded the increases in concentration. Net release of Ca by the end of two years from all three species combined was 42% of initial inputs in litterfall. Magnesium concentrations increased in the second year, following decreases due to leaching during the first year inC. florida andA. rubrum litter. Net release of Mg by the end of two years was 58% of initial inputs. Potassium concentrations decreased rapidly and continued to decline throughout the study. Net release of K by the end of two years was 91% of initial inputs.These data on cation dynamics, and similar data on N, S and P dynamics from a previous study, were combined with annual litterfall data to estimate the release of selected nutrients from foliar litter of these tree species at the end of one and two years of decomposition. The relative mobility of all six elements examined in relation to mass loss after two years was; K>Mg>mass>Ca>S>P>N.     

Litter decomposition and nitrogen and phosphorus dynamics in peatlands and uplands over 12 years in central Canada

The large accumulation of organic matter in peatlands has been partially attributed to litter decomposition rates, which are slowed by a high water table. To test this, we examined whether there were significant differences in the decomposition and N and P dynamics of ten foliar litters and wood blocks at three pairs of upland forest and peatland sites in the transitional grassland, high boreal and low subarctic regions of central Canada, using litterbags collected over a 12-year period. At two of the three pairs, the decomposition rate, as determined by proportion of the original mass remaining after 12 years and by the exponential decay coefficient (k), was faster overall at the upland than at the peatland. In the third pair, there was no significant difference, despite the water table being close to the peat surface; warmer soil temperatures in the peatland than the upland may be the cause. In general, there were small losses or gains of N in the litters after 12 years, compared to the original litter, though there were some differences among litter types and sites, net gains in N likely reflecting the higher exogenous N availability. P was lost from most litters at the two northern pairs of sites, but at the transitional grassland pair, there were large net gains in P and greater variation among litters. The N:P ratio in the original litters ranged from 5 to 26 and after 12 years the ratio narrowed, with the site average of the ten litters ranging from 13 to 22, varying with the soil ratio. Decomposition rates and N and P dynamics after 12 years are different between upland and peatland sites: although the water table is a primary control on these differences, other factors such as temperature and soil nutrient status are also important.     

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.     

The Contribution of Litterfall to Net Primary Production During Secondary Succession in the Boreal Forest

Litterfall is a fundamental process in the nutrient cycle of forest ecosystems and a major component of annual net primary production (NPP). Despite its importance for understanding ecosystem energetics and carbon accounting, the dynamics of litterfall production following disturbance and throughout succession remain poorly understood in boreal forest ecosystems. Using a replicated chronosequence spanning 209 years following fire and 33 years following logging in Ontario, Canada, we examined the dynamics of litterfall production associated with stand development, overstory composition type (broadleaf, mixedwood, and conifer), and disturbance origin. We found that total annual litterfall production increased with stand age following fire and logging, plateauing in post-fire stands approximately 98 years after fire. Neither total annual litterfall production nor any of its constituents differed between young fire- or logging-originated stands. Litterfall production was generally higher in broadleaf stands compared with mixedwood and conifer stands, but varied seasonally, with foliar litterfall highest in broadleaf stands in autumn, and epiphytic lichen litterfall highest in conifer stands in spring. Contrary to previous assumptions, we found that the contribution of litterfall production to net primary production increased with stand age, highlighting the need for modeling studies of net primary productivity to account for the effects of stand age on litterfall dynamics.     

Litterfall and nutrient dynamics shift in tropical forest restoration sites after a decade of recovery

Multi‐year studies comparing changes in litterfall biomass and nutrient inputs in sites under different restoration practices are lacking. We evaluated litterfall dynamics and nutrient inputs at 5 yr and after a decade of recovery in four treatments (natural regeneration—no planting, plantation—entire area planted, tree islands—planting in patches, and reference forest) at multiple sites in an agricultural landscape in southern Costa Rica. We inter‐planted two native species (Terminalia amazonia and Vochysia guatemalensis) and two naturalized N‐fixing species (Inga edulis and Erythrina poeppigiana) in plantation and island treatments. Although litterfall N was higher in plantations in the first sampling period, litter production and overall inputs of C, N, Ca, Mg, P, Cu, Mn, and Fe did not differ between island, plantation, or reference forest after a decade; however, all were greater than in natural regeneration. Potassium inputs were lower in the natural regeneration, intermediate in island and plantation, and greater in reference forest. The percentage of litterfall comprised by the N‐fixing planted species declined by nearly two‐thirds in both plantations and islands between sampling periods, while the percentage of V. guatemalensis more than doubled, and the percentage from naturally regenerated species increased from 27 to 47 percent in islands. Island and plantation treatments were equally effective at restoring litterfall and nutrient inputs to levels similar to the reference system. The nutrient input changed substantially over the 7‐yr interval between measurements, reflecting shifts in vegetation composition and demonstrating how rapidly nutrient cycling dynamics can change in recovering forests.     

Changes in Soil Fungal Communities, Extracellular Enzyme Activities, and Litter Decomposition Across a Fire Chronosequence in Alaskan Boreal Forests

Wildfires are a pervasive disturbance in boreal forests, and the frequency and intensity of boreal wildfires is expected to increase with climate warming. Boreal forests store a large fraction of global soil organic carbon (C), but relatively few studies have documented how wildfires affect soil microbial communities and soil C dynamics. We used a fire chronosequence in upland boreal forests of interior Alaska with sites that were 1, 7, 12, 24, 55, ~90, and ~100 years post-fire to examine the short- and long-term responses of fungal community composition, fungal abundance, extracellular enzyme activity, and litter decomposition to wildfires. We hypothesized that post-fire changes in fungal abundance and community composition would constrain decomposition following fires. We found that wildfires altered the composition of soil fungal communities. The relative abundance of ascomycetes significantly increased following fire whereas basidiomycetes decreased. Post-fire decreases in basidiomycete fungi were likely attributable to declines in ectomycorrhizal fungi. Fungal hyphal lengths in the organic horizon significantly declined in response to wildfire, and they required at least 24 years to return to pre-fire levels. Post-fire reductions in fungal hyphal length were associated with decreased activities of hydrolytic extracellular enzymes. In support of our hypothesis, the decomposition rate of aspen and black spruce litter significantly increased as forests recovered from fire. Our results indicate that post-fire reductions in soil fungal abundance and activity likely inhibit litter decomposition following boreal wildfires. Slower rates of litter decay may lead to decreased heterotrophic respiration from soil following fires and contribute to a negative feedback to climate warming.