Pine Litter Research Articles

Tracking Replicate Divergence in Microbial Community Composition and Function in Experimental Microcosms.

The study of microbial community functions necessitates replicating microbial communities. Variation in community development over time renders this an imperfect process. Thus, anticipating the likely degree of variation among replicate communities may aid in experimental design. We examined divergence in replicate community composition and function among 128 naturally assembled starting communities obtained from soils, each replicated three times, following a 30-day microcosm incubation period. Bacterial and fungal communities diverged in both composition and function among replicates, but remained much more similar to each other than to communities from different starting inocula. Variation in bacterial community composition among replicates was, however, correlated with variation in dissolved organic carbon production. A smaller-scale experiment testing nine starting communities showed that divergence was similar whether replicates were incubated on sterile or non-sterile pine litter, suggesting the impact of a pre-existing community on replicate divergence is minor. However, replicates in this experiment which were incubated for 114days diverged more than those incubated for 30days, suggesting experiments that run over long time periods will likely see greater variation among replicate community composition. These results suggest that while replicates diverge at a community level, such divergence is unlikely to severely impede the study of community function.

Postpyrogenic Variability of Litter in Mountain Forests of Baikal Region

The data of experimental studies on the postpyrogenic dynamics of the litter in mountain taiga cedar (Pinus sibirica), pine (Pinus sylvestris) and subtaiga forest-steppe pine (Pinus sylvestris) forests in the Baikal region are analyzed. Ground fires prevailing in this region transform the surface organic diagnostic horizons of soils and result in the formation of new pyrogenic organic horizons (Opir, OLpir, OL/Opir, OApir). The adverse impact of ground fires on the thickness, reserves, moisture capacity and fractional composition of forest litters is shown. The data on the chemical ash composition of litters, as well as the content of mobile microelement compounds is also given. The tendency of reducing the concentration of mobile elements in the organic horizons of soils from the taiga Siberian pine (cedar) altitudinal zonal complex (AZC) to the subtaiga forest-steppe pine AZCC of forest types was revealed. Forest fires were found to cause great quantitative and qualitative changes in the chemical composition of surface organic pyrogenic horizons; they are especially manifested in the transformation of their labile properties (рН, exchangeable cations, total and mobile nitrogen, etc.).

The effect of fire affected Pinus radiata litter and char addition on soil nitrogen cycling

In pine forest litters, decomposition rate is directly affected by the pathway the needle followed to the ground, whether that was via programmed apoptosis and abscission or via stress induced loss through branch damage or tree death. Stress induced losses may occur due to fire damage, which leads to a post-fire litter layer composed of non-senescent debris that fell during or after the event. This study investigates decomposition and nitrogen cycling in soils amended with two litters from Pinus radiata plantations that had different recent fire histories. Litters were incubated in the presence or absence of field collected char for up to 94 days. These soil treatments were analysed for microbial activity (soil respiration) and N pools (microbial, mineral, and potentially mineralisable). Soil and litter treatments were additionally incubated in the presence of ammonium nitrate solution to determine N absorption potential of the litters. Respiration was greatest in soils that received fire affected (FA) litter regardless of the presence or absence of char. Nitrogen pools were largely similar between the control (no litter) treatment and not fire affected (NFA) litter treatments. Measured N pools were exceedingly low (92% of samples <2 μg-N g soil−1 where detected) or not detectable (37% of samples below detection limits) in all FA litter treatments at most times. Char appeared inert throughout and had no effects on microbial activity or nitrogen cycling. This study indicates that fire affected pine litter collected four months post fire has strong N absorption properties with or without the presence of char. The presence of fire affected litter is likely to affect N availability for regeneration of forest growth.

Tree litter identity and predator density control prey and predator demographic parameters in a Mediterranean litter-based multi-trophic system

Plant litter decomposition is an essential process of ecosystem functioning, driven by a complex soil food web. The identity and density of the predators, as well as the quality and quantity of litter, could conjointly affect the strength of trophic interactions within a soil food web. Pine and oak are dominant tree species in temperate and Mediterranean forests and, although they exhibit distinct litter characteristics, no previous study attempted to decipher how these two litters can affect a litter-based multi-trophic system with varying predator density. Using a microcosm experiment, we aimed at understanding how different densities of a predatory Acari (Stratiolaelaps scimitus) and two Mediterranean litter species (Quercus pubescens and Pinus halepensis) may impact the demographic parameters of the predatory Acari, its Collembola prey (Folsomia candida) and the fungal biomass associated with litter. We did not observe any interactive effect of litter identity and predator density on both predator and prey demographic parameters. Survival and fecundity rates of the predator and its prey decreased at high predator density. However, demographic parameters of the predator and its prey were differentially affected by litter identity, with greater prey demographic parameters in Quercus litter and, in the opposite, greater predator demographic parameters in Pinus litter, probably due to differences in physical characteristics providing more or less refuge for the prey. We also observed a higher increase in fungal biomass in Pinus compared to Quercus litter, i.e. the litter with the fungivorous Collembola abundance reduced by the predatory Acari. Litter identity could thus strongly regulate these tri-trophic interactions (Fungi – fungivorous Collembola – predatory Acari) in forest ecosystems. Finally, the implications of our findings could be important as the distribution area of oak and pine forests may be altered in response to climate change with then potentially strong cascading effects on soil organisms and the processes they drive.

EXPERIMENTAL STUDIES OF FIRE HAZARD OF PINE NEEDLES IN LABORATORY AND FIELD CONDITIONS

Introduction. The fire hazard analysis of young pine stands was carried out. There are listed the most common sources of ignition as factors of influence on the occurrence of a fire. There is described the examples of studies on solid combustible materials` ignition, particularly, forest litter. The device developed is proposed for studying the process of forest fuels combustion.&#x0D; The aim of the work is determine the time to ignition of pine needles, as well as the forest litter in young pine stands by using a Device for the study of flammable material combustion using an electric heating element.&#x0D; Material statement. Laboratory studies have been done to ignite three types of needles of young pine plantations: fresh, inherent in the composition of forest underlay and dried needles. There was conducted an experimental studies of the time interval to the ignition of pine stands forest litter in the field condition with the use of the proposed device.&#x0D; Scientific novelty. It for the first time was established that the time interval before ignition of freshly cut needles exceeds by almost 4 times the meaning of this value in comparison with the dried needles. It was established that the value of the time to ignition of pine needles fallen in the forest litter, obtained from the results of field studies, with a slight deviation of its moisture, is almost the same with the values obtained in laboratory conditions.&#x0D; The results indicate that the forest litter in pine stands is fire-hazardous and can deal with a frequency close to ½ of a source with a temperature of 450°C, on average 25,7 seconds. There has been substantiated the expediency of using the device for the study of flammable material combustion using an electric heating element for investigating indicators of forest combustible materials` fire hazard.

О некоторых факторах, лимитирующих почвообразовательную роль дождевых червей в европейской части таежной зоны России

The aim of the study: In order to study the factors limiting soil-forming activity of various earthworm species most common for the European part of the taiga zone of Russia. Location and time of the study. The study was conducted, in the period 2017-2018 in the European part of Russia. Methodology. Model experiments in standardized laboratory conditions were carried out in plastic trays to examine the influence of mineral subsoil acidity and plant litter composition on the survival and preferences of representatives of different ecological groups of earthworms (Oligochaeta, Lumbricidae): Dendrobaena octaedra, Lumbriscus rubellus, Aporrectodea caliginosa (epigeic, epigeic-endogeic and endogenic, respectively), differently involved in mixing of soil mineral and organic layers. Main results. For D. octaedra, which is not involved in the mixing of soil layers, the limiting factors (among the studied combinationst of mineral subsoil and litter properties) were not revealed. For L. rubellus, the most pedoturbation-effective of the studied species, the effect of litter chemistry on their integument was found to be the limiting factor in spruce forests. The A. caliginosa and D. octaedra were not sensitive to the chemical stimuli of the spruce litter F-layer. The substrates, which were apparently toxic for L. rubellus, were found to be suitable for D. octaedra, but not for A. caliginosa nutrition. L. rubellus was shown to useas food decomposition products of spruce, fir, juniper, cowberry, moss (Sphagnum) litter, enriched with carbonate-containing coprolites. The decomposition products of spruce litter, also enriched in coprolites, or in deciduous tree litter, were suitable for consumption by L. rubellus and A. caliginosa. The decomposition products of pine and cedar litter, including those enriched in coprolites, were not attractive as a food source for L. rubellus. Conclusion. It was concluded that active relocation of mineral particles to the fresh litter surface is an evolutionarily developed type of L. rubellus behavior, leading to decreased litter acidity and increased decomposition rate, and that L. rubellus participates in the formation of coarse-humus soils. However, the decomposition of coniferous litter accelerates acidification of mineral soil layers, precluding even limited vermopedoturbation from soil-forming processes. Among the studied earthworm species D. octaedra (the least effective n pedoturbation) is the most fit to the habitat formed by climax taiga vegetation, whereas the most effective L. rubellus is the least fit.

The influence of forest-forming tree species on diversity and spatial distribution of algae in forest litter

Abstract The forest litter plays a significant role in forest ecosystems. The composition of the litter biota comprises micro- and mesofauna, and a great diversity of microorganisms, including unrecognized algae (eukaryotic representatives and Cyanoprokaryota). The aim of this work was to study the diversity of algae in the different types of forest litters and to clarify the relationship between the algae composition and the forest-forming tree species. Our results show that the pine forest litter is the most appropriate habitat for the development of green and yellow-green algae and that this litter type limits the variety of blue-green ones. The admixture of deciduous leaf litter to pine litter caused an increase in the species richness of blue-green algae and diatoms. The algae were unevenly distributed across the sub-horizons of pine litter. The highest species richness of algae was identified in the enzymatic sub-horizon of litter. The peculiarity of the composition of leaf litter algae was a significant variety of green, yellow-green and blue-green algae. The spatial organization of algae communities in the leaf litter was characterized by equal distribution of algae species in the litter-subhorizons.

Surface fuel accumulation and decomposition in old-growth pine-mixed conifer forests, northwestern Mexico

BackgroundStand-level forest structure varies spatially and surface fuels would be expected to vary as well. We measured surface fuel deposition and decomposition within old-growth Jeffery pine (Pinus jeffreyi Balf.)-mixed conifer forests to quantify rates of change and examine relationships with overstory structure and composition.ResultsAnnual fuel deposition ranged from 0.7 to 20.1 Mg ha−1 for litter and 0.2 to 0.8 Mg ha−1 for woody fuels, exhibiting large temporal and spatial variation, and corresponded with annual precipitation during the study period. Surface fuel deposition had high spatial heterogeneity and was predicted by stand structure such as basal area and canopy cover, particularly for litter deposition, which was the main contributor to total fuel loadings in this system. Jeffery pine litter decomposition rate of 7 to 11% yr−1 over the six-year study period is among the lowest compared to other conifer forests in western North America.ConclusionsTwo sites were distinguished by edaphic and structural characteristics, but exhibited similarities in fuels dynamics. Incorporating within-stand variation into fuel modeling could improve the accuracy in predicting fire behavior, fire effects, and stand progression.

Decomposition of Pine and Oak Litters as Affected by Their Lignin and Mineral Concentrations

Tree litter chemistry such as lignin, nitrogen (N), calcium (Ca), phosphorus (P) and manganese (Mn) affects litter decomposition and ultimately alters the soil carbon (C) and nutrient dynamics. Specifically, it is well known that the ratio of lignin to N (lignin/N) is a key factor affecting litter decomposition; i.e., litter with low lignin and high N concentrations decomposes fast as compared to litter with high lignin and low N. However, no comprehensive study on the effects of various chemistry as well as lignin/N on the litter decomposition is available. To fill the research gap, this study investigated the variations in the decomposition of pine and oak litters with different chemistry. Split plot design with tree species as a main plot (pine and oak) and litter chemistry (e.g., low vs. high lignin/N) as a sub-plot were laid out in triplicates. Litter samples (1.5 g on the dry basis) were mixed with soils (30 g) and incubated for 45 days, and CO2 emission was monitored periodically. Litter addition increased the cumulative CO2 emissions (Ccum) by 16 times over the control soil without litter regardless of litter species and chemistry. The litters applied to the soil were decomposed by more than 20% of the initial during the incubation period. Regardless of species, the Ccum was higher for litter with high lignin/N than with low lignin/N in contradiction to the previous studies. These results suggest that CO2 emissions from litter decomposition may not be explained solely by the lignin/N of litters but should be deciphered by considering mineral concentration as well as lignin/N. Comparing two pine litter with different chemistry, decomposability of pine litter with high Ca and Mn concentration was greater than the other one due to the role of essential co-factor of Ca and Mn in ligninolytic enzyme. However, for two oak litter with different chemistry, P rather than Ca and Mn found to contribute to litter decomposition. Therefore, this study highlights the necessity of comprehensive understanding of the effects of various chemistry as well as lignin/N of litter on the decomposition of litter. Daily CO2 emission rate (large figures) and cumulative CO2 emission (small figures) of soils amended with litters of pine and oak with different litter chemistry during 45-days incubation.

Effects of solar heating on the moisture dynamics of forest floor litter in humid environments: composition, structure, and position matter

Much of fire behavior is driven by fine-scale patterns of fuel moisture; however, moisture predictions typically occur over large scales. The source of fine-scale variation in moisture results from a combination of fuelbed properties and overstory forest structure that influences water movement and distribution of solar radiation. Fine-scale moisture variation is of particular relevance in humid forests managed with frequent prescribed fire where fire behavior variation is tightly linked to differential fire effects. Results of a three-tiered experiment combining laboratory and field methods demonstrated that solar radiation exerted a strong influence on fuel moisture patterns in a temperate humid pine forest. Infrared radiation more rapidly dried Quercus and Pinus litter in laboratory experiments compared with controls. Litter exposed to sunlight during small-scale outdoor experiments was significantly drier than shaded litter. Quercus litter was wetter than Pinus on mornings, but dried more rapidly, becoming drier than Pinus litter by mid-day when exposed to sunlight. Field observations validated small-scale outdoor and laboratory results but also revealed the influence of fuel position: elevated litter was wetter than ground-level litter at peak burning time. Results provide insight into how overstory structure and composition may influence fine-scale heterogeneity of surface moisture dynamics and fire behavior.

Moving away from the native forest edge: Changes in ecosystem processes towards the interior of Pinus taeda plantations

Tree plantations are considered as strategic systems for climate change mitigation and economic development. However, their establishment in subtropical areas frequently involves the replacement of a species-rich forest by a tree monoculture with exotic species, which may be functionally different from native species. The impact of this change on ecosystem processes is still widely unknown. In Argentina, large portions of the Semideciduous Atlantic Forest were replaced by non-native Pinus taeda monocultures. The P. taeda litter has lower quality and a slower decomposition rate than native plant litter. Therefore, this replacement would change the characteristic of the litter that reaches the ground. Litter quality is one of the major drivers of decomposition. In the transitional area between two different environments, the edge effect influences populations and communities and could affect ecosystem processes due to changes in its drivers. We wonder how ecosystem processes, as litter decomposition and litterfall production, will respond from the forest edge into the exotic pine monocultures. In five P. taeda plantations and five sites in native forest, we established litter traps to estimate litterfall and litterbags to estimate pine litter decay rate. Litter layer thickness and necromass were also estimated. The change of these variables along a distance gradient from the forest edge into the pine plantation was studied in 10 points at different distances from the edge (0–300 m). Comparisons of these variables between P. taeda plantations and native forest were also done. Native forest replacement by P. taeda monocultures changed the litter identity that reached the ground and decreased the pine litter decomposition rate. The litter layer necromass increased towards the interior of P. taeda plantations, consistently with the increase in pine litterfall. Within the pine plantation, the distance to the native forest edge had no effect on the litterfall neither on pine litter decomposition rates. However, the increase in litter layer necromass towards the interior of plantations suggests that the presence of native forest contiguous to pine plantations in the Semideciduous Atlantic Forest favors litter layer decomposition. Litter from native species, with higher quality than pine litter, decomposes faster in the litter layer and would drive to a more efficient stabilization of soil organic matter. Accordingly, management techniques promoting the increase in the abundance of native species inside pine plantations would improve nutrient cycling and monoculture sustainability.

Characterization of pyrolysis products from slow pyrolysis of live and dead vegetation native to the southern United States

Prescribed (i.e., controlled) burning is a common practice used in many vegetation types in the world to accomplish a wide range of land management objectives including wildfire risk reduction, wildlife habitat improvement, forest regeneration, and land clearing. To properly apply controlled fire and reduce unwanted fire behavior, an improved understanding of fundamental processes related to combustion of live and dead vegetation is needed. Since the combustion process starts with pyrolysis, there is a need for more data and better models of pyrolysis of live and dead fuels. In this study, slow pyrolysis experiments were carried out in a pyrolyzer apparatus under nitrogen atmosphere in two groups of experiments. In the first group, the effects of temperature (400–800 °C), a slow heating rate (5–30 °C min−1), and carrier gas flow rate (50–350 ml min−1) on yields of tar and light gas obtained from pyrolysis of dead longleaf pine litter were investigated to find the optimum condition which results in the maximum tar yield. The results showed that the highest tar yield was obtained at a temperature of 500 °C, heating rate of 30 °C min−1, and sweep gas flow rate of 100 ml min−1. In the second group of experiments, 14 plant species (live and dead) native to forests in the southern United States, were heated in the pyrolyzer apparatus at the optimum condition. A gas chromatograph equipped with a mass spectrometer (GC–MS) and a gas chromatograph equipped with a thermal conductivity detector (GC-TCD) were used to study the speciation of tar and light gases, respectively. The results showed that the tar composition is dominated by oxygenated aromatic compounds consisting mainly of phenols. The light gas analysis showed that CO and CO2 were the dominant light gas species for all plant samples on a dry wt% basis, followed by CH4 and H2.

Carabids benefit more from pine stands with added understory or second story of broad-leaved trees favored by climate change than from one-storied pine stands

The released excess anthropogenic nitrogen and carbon produces habitat enrichment, as exemplified by the modification of one-storied pine stands by introducing deciduous species into the understory or second story. In this study, we discuss the validity of pine stand modification by pitfall-trapping epigeic carabid beetles. Two hypotheses were formulated: (1) proportion of late-successional species is higher in assemblages inhabiting pine stands with understory or a second story than in one-storied pine stands; (2) plant litter composition affects carabid beetle assemblages more than other environmental variables. Additionally, characteristic carabid species of the respective pine stand types were identified. GLMM analysis revealed a higher proportion of late-successional species in pine stands with understory or a second story than in one-storied ones. NMDS separated those pine stand types. RDA analysis indicated that pine litter and humus had the strongest effect on carabid beetle assemblage structure in one-storied stands, being drier and thicker in this stand type than in the others. Indicator value analysis identified two characteristic non-forest species in one-storied stands The study revealed that the introduction of understory and particularly a second story into pine stands increased carabid beetle diversity and the proportion of late-successional species, confirming the validity of pine stand modification.

Transformation of Water-Soluble Organic Substances in Litters of Podzols in the Background and Technogenic Areas of the Kola Peninsula

Mineralization of water-soluble organic substances in forest litters of different compositions under conditions of their pollution with heavy metals from aerogenic emissions is considered. Water-soluble organic substances of the pine forest litters are shown to be less stable than that under the spruce forests irrespective of their pollution; the portion of mineralized at 20°C carbon for a month reached 40%. In the spruce litters, mineralizable amounts of carbon are related to their pollution: in the technogenic areas, compared to the background ones, carbon losses from the litters are twice greater. In the course of decomposition, in the spruce and pine litters, phenol compounds accumulate among the water-soluble organic compounds, and this process is more intense in the contaminated areas. After the decomposition of all the litters, irrespectively of their composition and the distance from the pollution sources, the water-soluble organic substances are characterized by higher indices of humification (HIX), more intense fluorescence, and greater coefficients of specific extinction (E260). In the ultraviolet spectra, bands appear in the region of aromatic amines absorption. These changes indicate the transformation of water-soluble organic substances: the degrees of their condensation and aromaticity increase and nitrogen-containing aromatic compounds are formed.

Comprehensive Study of Reclaimed Soil, Plant, and Water Chemistry Relationships in Highly S-Contaminated Post Sulfur Mine Site Jeziórko (Southern Poland)

The aim of the work was a comprehensive study of the soils (pH, EC, SOC, NT, ST), surface waters (pH, EC, Ca2+ Mg2+, Na+, NO3−, SO42−, Cl−, HCO3−), and reactions of trees and herbaceous plants in the restored forest ecosystem of a former sulfur mine. Common birch and Scots pine growth reaction, vitality (according to IUFRO standards- International Union of Forest Research Organizations), nutrient supply (Na, K, P, Ca, Mg, K), and Calamagrostis epigejos (L.) Roth chemical composition (Na, K, P, Ca, Mg, K) were assayed. The chemistry dynamics (pH, EC, DOC, NT, Ca, Mg, and S at the beginning and end of the experiment) of soil leaching and the sulfur load leached from the sulfur-contaminated soil substrates were evaluated. The remediation effects of birch and pine litter were assayed in an experiment under controlled conditions. It was found that reclamation was effective in the majority of the post-mining site; however, hotspots with sulfur contamination reaching even 45,000 mg kg−1, pH &lt; 2.0 and electrical conductivity (EC) of 6500 µS cm−1 were reported. Surface waters typically displayed elevated concentrations of sulfate ions (average 935.13 mg L−1), calcium ions (up to 434 mg L−1), and high EC (average 1797 µS cm−1), which was related both to sulfur contamination and the sludge lime that was used in neutralization. Calamagrostis epigejos was found to be a species that adapted well to the conditions of elevated soil salinity and sulfur concentration. It was observed that the application of organic matter had a significant beneficial impact on the chemistry of soil solutions, but did not show a remediation effect by increased sulfur leaching in a short-term study.

Rapid Microbial Community Changes During Initial Stages of Pine Litter Decomposition

Plant litter decomposition is a process enabling biogeochemical cycles closing in ecosystems, and decomposition in forests constitutes the largest part of this process taking place in terrestrial biomes. Microbial communities during litter decomposition were studied mainly with low-throughput techniques not allowing detailed insight, particularly into coniferous litter, as it is more difficult to obtain high quality DNA required for analyses. Motivated by these problems, we analyzed archaeal, bacterial, and eukaryotic communities at three decomposition stages: fresh, 3- and 8-month-old litter by 16/18S rDNA pyrosequencing, aiming at detailed insight into early stages of pine litter decomposition. Archaea were absent from our libraries. Bacterial and eukaryotic diversity was greatest in 8-month-old litter and the same applied to bacterial and fungal rDNA content. Community structure was different at various stages of decomposition, and phyllospheric organisms (bacteria: Acetobacteraceae and Pseudomonadaceae members, fungi: Lophodermium, Phoma) were replaced by communities with metabolic capabilities adapted to the particular stage of decomposition. Sphingomonadaceae and Xanthomonadaceae and fungal genera Sistotrema, Ceuthospora, and Athelia were characteristic for 3-month-old samples, while 8-month-old ones were characterized by Bradyrhizobiaceae and nematodes (Plectus). We suggest that bacterial and eukaryotic decomposer communities change at different stages of pine litter decomposition in a way similar to that in broadleaf litter. Interactions between bacteria and eukaryotes appear to be one of the key drivers of microbial community structure.

Elevated CO2 concentration affected pine and oak litter chemistry and the respiration and microbial biomass of soils amended with these litters

Elevated atmospheric CO2 concentration ([CO2]) may change litter chemistry which affects litter decomposability. This study investigated respiration and microbial biomass of soils amended with litter of Pinus densiflora (a coniferous species; pine) and Quercus variabilis (a deciduous species; oak) that were grown under different atmospheric [CO2] and thus had different chemistry. Elevated [CO2] increased lignin/N through increased lignin concentration and decreased N concentration. The CO2 emission from the soils amended with litter produced under the same [CO2] regime was greater for oak than pine litter, confirming that broadleaf litter with lower lignin decomposes faster than needle leaf litter. Within each species, however, soils amended with high lignin/N litter grown under elevated [CO2] emitted more CO2 than those with low lignin/N litter grown under ambient [CO2]. Such contrasting effects of lignin/N on inter- and intra-species variations in litter decomposition should be ascribed to the effects of other litter chemistry variables including nonstructural carbohydrate, calcium and manganese as well as inhibitory effect of N on lignin decomposition. The microbial biomass was also higher in the soils amended with high lignin/N litter than those with low lignin/N litter probably due to low substrate use efficiency of lignin by microbes. Our study suggests that elevated [CO2] increases lignin/N for both species, but increased lignin/N does not always reduce soil respiration and microbial biomass. Further study investigating a variety of tree species is required for more comprehensive understanding of inter- and intra-species variations of litter decomposition under elevated [CO2].

Effects of ultraviolet (UV) radiation and litter layer thickness on litter decomposition of two tree species in a semi-arid site of Northeast China

Forests and grasslands in arid and semi-arid regions receive high-intensity ultraviolet (UV) radiation year-round. However, how the UV radiation affects the litter decomposition on the forest floor remains unclear. Here, we conducted a field-based experiment in 2011 in the southeastern Horqin Sandy Land, Northeast China, to investigate the effects of UV radiation, litter layer thickness, and their interaction on the mass loss and chemical properties of decomposing litter from Xiaozhuan poplar (Populus × xiaozhuanica) and Mongolian pine (Pinus sylvestris var. mongolica) plantation trees. We found that UV radiation accelerated the decomposition rates of both the Xiaozhuan poplar litter and Mongolian pine litter. For both species, the thick-layered litter had a lower mass loss than the thin-layered litter. The interaction between UV radiation and litter layer thickness significantly affected the litter mass loss of both tree species. However, the effects of UV radiation on the chemical properties of decomposing litter differed between the two species, which may be attributed to the contrasting initial leaf litter chemical properties and morphology. UV radiation mostly had positive effects on the lignin concentration and lignin/N ratio of Xiaozhuan poplar litter, while it had negative effects on the N concentration of Mongolian pine litter. Moreover, litter layer thickness and its interaction with UV radiation showed mostly positive effects on the N concentration and lignin/N ratio of Xiaozhuan poplar litter and the ratios of C/N and lignin/N of Mongolian pine litter, and mostly negative effects on the C/N ratio of Xiaozhuan poplar litter and the N concentration of Mongolian pine litter. Together, these results reveal the important roles played by UV radiation and litter layer thickness in the process of litter decomposition in this semi-arid region, and highlight how changes in the litter layer thickness can exert strong influences on the photodegradation of litter in tree plantations.

Soil C and N isotope composition after a centennial Scots pine afforestation in podzols of native European beech forests in NE-Spain

The replacement of native European beech forests (Fagus sylvatica) with Scots pine (Pinus sylvestris) afforestation may exert changes in soil properties, particularly with respect to soil organic matter (SOM). Stable isotope composition of light elements (δ13C, δ15N) in soils are known proxies for the characterisation of SOM genesis and dynamics. In this research, C and N isotope composition of organic layers, classified as OL (fresh litter), OF (fragmented litter) and OH (humified litter), and the first mineral horizon (Ah) from what was, originally, a beech domain and from a domain of afforestation with pine were analysed by using EA–IRMS. Additionally, C and N isotope signatures were studied in complete soil profiles that were representative of each forest. Pine OL was found to be 13C enriched (δ13C = −28.08 ± 0.49‰) compared with beech (−29.87 ± 0.27‰). Along the soil profile, C isotope composition mirrors that of the standing vegetation down to the first mineral Ah horizon, with significantly higher δ13C in pine than in beech. Deeper in the soil, from the eluvial E horizon, no significant δ13C differences were found between soils, indicating a limited pine influence in depth, years after afforestation. Pine litter tended to be 15N enriched (δ15N = 4.43 ± 2.65‰) compared to beech (1.43 ± 2.80‰). Along the soil profile, a consistent 15N enrichment was observed with depth in the organic layers (O–layers) down to OH. No significant δ15N differences were found in the mineral horizons between soils, except for the E horizon that showed a lower δ15N in the beech than in the pine profile. This N trend could be explained by 1) a progressive biomass alteration and a concomitant 15N–enrichment being, in general, more pronounced in O–layers under alien pine than under beech, and 2) migration of more humified SOM forms from eluvial to deeper Bhs horizons, causing a relative accumulation of 15N–depleted SOM in the beechwood E horizon. The accumulation of fungal and root biomass in pinewood OF horizons could be reflected in its 15N–depleted signature.

Patch size, isolation, and matrix effects on biodiversity and ecosystem functioning in a landscape microcosm

AbstractThe amount and arrangement of habitat is a fundamental determinant of biodiversity and ecosystem processes in a landscape. Biodiversity is expected to decline following habitat loss and isolation, potentially impeding ecosystem function. But because greater isolation usually accompanies habitat loss, the effects of habitat amount and isolation can be confounded. Moreover, the type or quality of the intervening matrix habitat can mediate amount and isolation effects on biodiversity. We used a landscape microcosm of oak leaf litter patches to examine the responses of bacterial communities and the ecosystem function of oak leaf decomposition to patch size, degree of isolation, and matrix habitat type (pine litter or bare ground). We found that oak patch size had no significant effect on bacterial communities or decomposition rates. However, bacterial richness increased with greater patch isolation and when oak litter patches were surrounded by a matrix of pine litter, rather than bare ground. The benefit of patch isolation for biodiversity runs counter to that expected by island biogeography theory, suggesting that spatially dependent interspecific interactions, such as predation or competition, may override direct dispersal effects. Higher bacterial richness in oak litter patches surrounded by a pine litter matrix indicated that spillover from neighboring matrix habitat can increase local richness. Instead of greater bacterial richness enhancing ecosystem functioning, leaf litter decomposition was negatively correlated with bacterial richness: Decomposition was slower in isolated oak litter patches and patches surrounded by a pine litter matrix. This negative relationship may be a result of spatial dynamics that can promote the persistence of bacteria from pine litter habitats that are not well suited to oak litter decomposition. Overall, our experiment indicates that effects of habitat loss, isolation, and matrix quality on richness and composition may depend on spatially constrained interspecific interactions, which can determine the functional ability of communities.