Carbon flux from decomposing wood and its dependency on temperature,wood N2 fixation rate,moisture and fungal composition in a Norway spruce forest

Globally 40–70 Pg of carbon (C) are stored in coarse woody debris on the forest floor. Climate change may reduce the function of this stock as a C sink in the future due to increasing temperature. However, current knowledge on the drivers of wood decomposition is inadequate for detailed predictions. To define the factors that control wood respiration rate of Norway spruce and to produce a model that adequately describes the decomposition process of this species as a function of time, we used an unprecedentedly diverse analytical approach, which included measurements of respiration, fungal community sequencing, N₂ fixation rate, nifH copy number, ¹⁴C‐dating as well as N%, δ¹³C and C% values of wood. Our results suggest that climate change will accelerate C flux from deadwood in boreal conditions, due to the observed strong temperature dependency of deadwood respiration. At the research site, the annual C flux from deadwood would increase by 27% from the current 117 g C/kg wood with the projected climate warming (RCP4.5). The second most important control on respiration rate was the stage of wood decomposition; at early stages of decomposition low nitrogen content and low wood moisture limited fungal activity while reduced wood resource quality decreased the respiration rate at the final stages of decomposition. Wood decomposition process was best described by a Sigmoidal model, where after 116 years of wood decomposition mass loss of 95% was reached. Our results on deadwood decomposition are important for C budget calculations in ecosystem and climate change models. We observed for the first time that the temperature dependency of N₂ fixation, which has a major role at providing N for wood‐inhabiting fungi, was not constant but varied between wood density classes due to source supply and wood quality. This has significant consequences on projecting N₂ fixation rates for deadwood in changing climate.     

Effects of Forest Use on Aphyllophoraceous Fungal Community Structure in Sarawak, Malaysia

Aphyllophoraceous fungi are expected to reflect changes in the environmental conditions caused by forest use. To reveal the effects of forest uses on the fungal community structure, we performed a 3‐month survey of aphyllophoraceous species in five forest types (undisturbed primary forest, isolated patches of primary forest, old and young fallow forest, and rubber plantations) in Sarawak, Malaysia in 2005. We used a canonical correspondence analysis (CCA) to reveal the relationships between fungal community composition and the environmental variables (canopy openness, soil water potential, amount and composition of coarse woody debris, litter mass, basal area, plant species composition). A total of 155 samples from 67 species were collected during the study period. The fungal species density represented by the number of species in a transect differed significantly among forest types. The fungal species density increased significantly with increasing number of pieces of coarse woody debris (CWD), but decreased significantly with increasing the scores of second axis of principal component analysis (PCA) for plant species composition. In the CCA ordination, automatic forward selection revealed that only the number of pieces of CWD significantly affected the fungal species composition. The occurrences of Flabellophora licmophora, Coriolopsis retropicta, Microporus vernicipes, and Amauroderma subrugosum were positively correlated with the number of pieces of CWD. Our study clearly demonstrated that forest use negatively affected aphyllophoraceous fungal diversity and suggest that the quantity of CWD would be an important determinant of fungal diversity and composition.     

Plant traits and wood fates across the globe: rotted,burned, or consumed?

Wood represents the defining feature of forest systems, and often the carbon in woody debris has a long residence time. Globally, coarse dead wood contains 36–72 Pg C, and understanding what controls the fate of this C is important for predicting C cycle responses to global change. The fate of a piece of wood may include one or more of the following: microbial decomposition, combustion, consumption by insects, and physical degradation. The probability of each fate is a function of both the abiotic environment and the wood traits of the species. The wood produced by different species varies substantially in chemical, micro- and macro-morphological traits; many of these characteristics of living species have 'afterlife' effects on the fate and turnover rate of dead wood. The colonization of dead wood by microbes and their activity depends on a large suite of wood chemical and anatomical traits, as well as whole-plant traits such as stem-diameter distributions. Fire consumption is driven by a slightly narrower range of traits with little dependence on wood anatomy. Wood turnover due to insects mainly depends on wood density and secondary chemistry. Physical degradation is a relatively minor loss pathway for most systems, which depends on wood chemistry and environmental conditions. We conclude that information about the traits of woody plants could be extremely useful for modeling and predicting rates of wood turnover across ecosystems. We demonstrate how this trait-based approach is currently limited by oversimplified treatment of dead wood pools in several leading global C models and by a lack of quantitative empirical data linking woody plant traits with the probability and rate of each turnover pathway. Explicitly including plant traits and woody debris pools in global vegetation climate models would improve predictions of wood turnover and its feedback to climate.     

Ant colonization and coarse woody debris decomposition in temperate forests

Ants are ubiquitous, abundant and have widespread impacts on ecological communities and ecosystem processes. However, ant effects on coarse woody debris decomposition are unexplored. Several ant species colonize coarse woody debris for nesting, and this puts them in contact with fauna and microbes that utilize coarse woody debris as habitat and food, potentially influencing nutrient cycling and, ultimately, forest productivity. We report results from a field experiment employing 138 artificial ant nests (routed pine blocks) across five locations in southeastern US deciduous forests. We examine the correspondence between ant, termite and wood-eating fungi colonization and variation in coarse woody debris decomposition. After 1 year, nests colonized by ants had 5% more mass than those not colonized. Ant colonization corresponded with significantly less termite- and fungal-mediated decomposition of the nests. Without ants, termites removed 11.5% and fungi removed 4% more wood biomass. Ants, termites and wood-eating fungi all colonized pine nests where temperatures were highest, and ants also preferred higher soil moisture whereas termites and fungi responded negatively to high soil moisture when temperatures were higher. Ants reduce termite colonies through predation, and may inhibit fungi through the secretion of antimicrobial compounds. Our results indicate that interactions between forest understory ants, termites and fungi may influence the rate of coarse woody debris decomposition—biotic interactions that potentially influence forest structure and function.     

Biotic and Abiotic Factors Controlling Respiration Rates of Above- and Belowground Woody Debris of Fagus crenata and Quercus crispula in Japan

As a large, long-term pool and source of carbon and nutrients, woody litter is an important component of forest ecosystems. The objective of this study was to estimate the effect of the factors that regulate the rate of decomposition of coarse and fine woody debris (CFWD) of dominant tree species in a cool-temperate forest in Japan. Respiration rates of dead stems, branches, and coarse and fine roots of Fagus crenata and Quercus crispula felled 4 years prior obtained in situ ranged from 20.9 to 500.1 mg CO₂ [kg dry wood]^–1 h^–1 in a one-time measurement in summer. Respiration rate had a significant negative relationship with diameter; in particular, that of a sample of Q. crispula with a diameter of >15 cm and substantial heartwood was low. It also had a significant positive relationship with moisture content. The explanatory variables diameter, [N], wood density, and moisture content were interrelated. The most parsimonious path model showed 14 significant correlations among 8 factors and respiration. Diameter and [C] had large negative direct effects on CFWD respiration rate, and moisture content and species had medium positive direct effects. [N] and temperature did not have direct or indirect effects, and position and wood density had indirect effects. The model revealed some interrelationships between controlling factors. We discussed the influence of the direct effects of explanatory variables and the influence especially of species and position. We speculate that the small R ² value of the most parsimonious model was probably due to the omission of microbial biomass and activity. These direct and indirect effects and interrelationships between explanatory variables could be used to develop a process-based CFWD decomposition model.     

Species Composition of Saproxylic Fungal Communities on Decaying Logs in the Boreal Forest

Coarse woody debris supports large numbers of saproxylic fungal species. However, most of the current knowledge comes from Scandinavia and studies relating the effect of stand or log characteristics on the diversity and composition of decomposer fungi have not been conducted in Northeastern Canada. Logs from five tree species were sampled along a decomposition gradient in nine stands representing three successional stages of the boreal mixed forest of Northwestern Quebec, Canada. Using a molecular fingerprinting technique, we assessed fungal community Shannon–Weaver diversity index, richness, and composition. We used linear mixed models and multivariate analyses to link changes in fungal communities to log and stand characteristics. We found a total of 33 operational taxonomic units (OTUs) including an indicator species for balsam fir (similar to Athelia sp.) and one found only in aspen stands (similar to Calocera cornea). Spruce logs supported the highest fungal Shannon–Weaver diversity index and OTU number. Our results support the hypothesis that log species influences fungal richness and diversity. However, log decay class does not. Stand composition, volume of coarse woody debris, and log chemical composition were all involved in structuring fungal communities. Maintaining the diversity of wood-decomposing communities therefore requires the presence of dead wood from diverse log species.     

Global meta‐analysis of wood decomposition rates: a role for trait variation among tree species?

The carbon flux from woody debris, a crucial uncertainty within global carbon-climate models, is simultaneously affected by climate, site environment and species-based variation in wood quality. In the first global analysis attempting to explicitly tease out the wood quality contribution to decomposition, we found support for our hypothesis that, under a common climate, interspecific differences in wood traits affect woody debris decomposition patterns. A meta-analysis of 36 studies from all forested continents revealed that nitrogen, phosphorus, and C : N ratio correlate with decomposition rates of angiosperms. In addition, gymnosperm wood consistently decomposes slower than angiosperm wood within common sites, a pattern that correlates with clear divergence in wood traits between the two groups. New empirical studies are needed to test whether this difference is due to a direct effect of wood trait variation on decomposer activity or an indirect effect of wood traits on decomposition microsite environment. The wood trait–decomposition results point to an important role for changes in the wood traits of dominant tree species as a driver of carbon cycling, with likely feedback to atmospheric CO₂ particularly where angiosperm species replace gymnosperms regionally. Truly worldwide upscaling of our results will require further site-based multi-species wood trait and decomposition data, particularly from low-latitude ecosystems.     

Increased CO<Subscript>2</Subscript> evolution caused by heat treatment in wood-decaying fungi

Wood-decaying fungi are regarded as the main decomposers of woody debris in boreal forests. Given that fungal respiration makes a significant contribution to terrestrial carbon flows, it is important to understand how the wood-decaying fungal metabolism is regulated in relation to different environmental conditions and disturbances. In the present study, we investigated the effect of temperature stress on wood decomposition rate in 18 species of wood-decaying fungi, representing a broad range of species–habitat associations. Heat shock duration and temperature were calibrated to match the conditions of a forest fire. We found a general increase in fungal decay rate after heat shock; the response was more pronounced in species associated with fire-prone forests. The underlying mechanism is unclear, but possibly relates to an up-regulation at the cellular level in response to heat shock. Our results show that the decomposition rate of dead wood can be strongly affected by environmental triggers.     

Response of wood-inhabiting fungal community to fragmentation in a beech forest landscape

Fragmentation of natural habitats has become one of the main causes of the loss of biodiversity. To assess the effects of forest fragmentation on wood-inhabiting fungal community in a beech-dominated landscape, 15 differently shaped beech forest fragments were examined in northern Spain. This work covers all the wood-inhabiting macromycetes, including Basidiomycota and Ascomycota. A modelling approach was used to examine the predictability of the fungal community in a fragmented beech forest landscape. In the beech forest patches, a large proportion of edge, low tree densities and low levels of variety of woody debris caused a decrease of wood-inhabiting fungal richness. The fungal community composition proved complex to model due to its specific traits: it is made up of many species, most of which are rare, and each fungal group responds differently to environmental variables. Nevertheless, the dead wood availability and the exposure to light significantly affected the fungal community composition.     

八大公山亚热带森林木质残体中大型无脊椎动物群落特征

木质残体可为大型无脊椎动物提供重要栖息地、食物等资源, 并影响其生物多样性。目前针对不同树种、径级及分解阶段的木质残体如何调控土壤大型无脊椎动物群落结构尚不清楚, 相关研究在亚热带森林地区尤为稀缺。为此, 本文选取湖南省八大公山国家级自然保护区柳杉(Cryptomeria fortunei)、亮叶水青冈(Fagus lucida)及檫木(Sassafras tzumu) 3种树种为研究对象, 每种树种分别选取两类径级(直径分别为10 ± 2 cm、4 ± 2 cm)不同分解阶段的木质残体, 对其中的大型无脊椎动物进行调查。调查于2020年10-11月完成。结果显示: 共捕获大型无脊椎动物2,558只, 隶属4门10纲23目, 不同树种的优势类群、常见类群及稀有类群均存在差异。亮叶水青冈木质残体中大型无脊椎动物个体密度显著高于柳杉和檫木。亮叶水青冈和檫木大径级木质残体中大型无脊椎动物Shannon-Wiener多样性指数显著高于小径级, 3个树种大径级木质残体中大型无脊椎动物的类群数、特有类群数均大于小径级。木质残体中大型无脊椎动物的Shannon-Wiener多样性指数、Simpson优势度指数及Pielou均匀度指数与木材密度显著负相关, 表明随着分解的进行木质残体中大型无脊椎动物群落呈明显变化趋势。木质残体的理化性质(相对含水率、全氮、全碳及碳氮比)和土壤温度、湿度与木质残体中大型无脊椎动物群落特征具有相关性。研究初步表明, 大型无脊椎动物群落特征在所选树种、径级及分解阶段木质残体中具有差异, 在亚热带森林中同时保留不同树种、不同大小径级的木质残体或有利于增加大型无脊椎动物多样性。     

Effects of forest dieback on wood decay,saproxylic communities,and spruce seedling regeneration on coarse woody debris

Picea is one of the most dominant conifer genera in the Northern Hemisphere and includes species which require coarse woody debris (CWD) as a seedbed for regeneration. To understand the future of forest distribution under global climate change, it is important to investigate regeneration mechanisms in Picea forests on the borders of its distribution. In the present study, we evaluated the biotic factors affecting the establishment of Picea jezoensis var. hondoensis seedlings on CWD in one of its southernmost populations in central Japan, where there is dieback of Picea forest. Amplicon sequencing of the fungal ITS1 region of rDNA obtained from wood samples showed that forest dieback increased the frequency of brown rot fungi in CWD. The frequency of brown-rotted wood, in which wood holocellulose is decayed, increased with dieback intensity. The domination of brown-rotted wood in dieback forests was negatively associated with bryophyte cover which was positively associated with Picea seedling density. Forest dieback itself also had other strong negative effects on bryophytes. Thus, linkages between dead wood and spruce seedlings via bryophytes had collapsed after the dieback event, which may partly be a reason that the spruce forest shifted to and is staying as open grassland.     

Signature Wood Modifications Reveal Decomposer Community History

Correlating plant litter decay rates with initial tissue traits (e.g. C, N contents) is common practice, but in woody litter, predictive relationships are often weak. Variability in predicting wood decomposition is partially due to territorial competition among fungal decomposers that, in turn, have a range of nutritional strategies (rot types) and consequences on residues. Given this biotic influence, researchers are increasingly using culture-independent tools in an attempt to link variability more directly to decomposer groups. Our goal was to complement these tools by using certain wood modifications as ‘signatures’ that provide more functional information about decomposer dominance than density loss. Specifically, we used dilute alkali solubility (DAS; higher for brown rot) and lignin:density loss (L:D; higher for white rot) to infer rot type (binary) and fungal nutritional mode (gradient), respectively. We first determined strength of pattern among 29 fungi of known rot type by correlating DAS and L:D with mass loss in birch and pine. Having shown robust relationships for both techniques above a density loss threshold, we then demonstrated and resolved two issues relevant to species consortia and field trials, 1) spatial patchiness creating gravimetric bias (density bias), and 2) brown rot imprints prior or subsequent to white rot replacement (legacy effects). Finally, we field-tested our methods in a New Zealand Pinus radiata plantation in a paired-plot comparison. Overall, results validate these low-cost techniques that measure the collective histories of decomposer dominance in wood. The L:D measure also showed clear potential in classifying ‘rot type’ along a spectrum rather than as a traditional binary type (brown versus white rot), as it places the nutritional strategies of wood-degrading fungi on a scale (L:D=0-5, in this case). These information-rich measures of consequence can provide insight into their biological causes, strengthening the links between traits, structure, and function during wood decomposition.     

Linking wood-decay fungal communities to decay rates: Using a long-term experimental manipulation of deadwood and canopy gaps

Decomposition transfers carbon (C) from detrital organic matter to soil and atmospheric pools. In forested ecosystems, deadwood accounts for a large proportion of the detrital C pool and is primarily decomposed by wood-inhabiting fungi (WIF). Deadwood reductions linked to forest harvesting may alter WIF richness and composition, thus indirectly influencing the persistence of deadwood and its contribution to C and nutrient cycling. Forest structure was enhanced via canopy gap creation and coarse woody debris (CWD) addition that mimic natural disturbance by windfall within a deciduous northern hardwood forest (Wisconsin, USA) to examine its effect on deadwood-associated biodiversity and function. Experimental sugar maple (Acer saccharum) logs were sampled, for DNA extraction, ten years after placement to determine the assembly of fungal community composition and its relationship to wood decay rates.Our findings suggest that the WIF community responded to gap disturbance by favoring species able to persist under more extreme microclimates caused by gaps. CWD addition under closed canopy tended to favor a different species assemblage from gap creation treatments and the control, where canopy was undisturbed and CWD was not added. This was presumably due to consistent microclimatic conditions and the abundance of CWD substrates for host specialists. Fungal OTU richness was significantly and inversely related to CWD decay rates, likely due to competition for resources. In contrast, fungal OTU composition was not significantly related to CWD decay rates, canopy openness or CWD addition amounts. Our study site represents a diverse fungal community in which complex interactions among wood-inhabiting organisms and abiotic factors are likely to slow CWD decomposition, which suggests that maintaining a biodiverse and microsite-rich ecosystem may enhance the capacity for C storage within temperate forests.     

Postfire succession of saproxylic arthropods, with emphasis on coleoptera, in the north boreal forest of Quebec

Saproxylic succession in fire-killed black spruce [Picea mariana (Mill.) B.S.P.] coarse woody debris (CWD) in northern Quebec is estimated in this study using a 29-yr postfire chronosequence. Sampling was performed using both trunk-window traps and rearing from snag and log sections. A total of 37,312 arthropods (>220 taxa) were collected from both sampling methods. Two distinct colonization waves were identified. The onset of initial colonization occurs the year of the fire, whereas the second colonization phase begins only once debris falls to the ground. The initial colonization step is influenced by fire-associated species including subcortical predators, xylophages, and ascomycetes feeders. Abundance of most early colonizer species decline with time since fire with the disappearance of subcortical habitat. No noticeable species turnover occurred in snags thereafter. Lack of succession in snags is related to very low decomposition rates for postfire CWD because this substrate is unsuitable for species associated with highly decayed wood. Snag falling triggers fungal growth and concomitant saproxylic succession toward micro- and saprophagous species and increases accessibility for soil-dwelling organisms. Because the position of woody debris greatly influences overall physical properties of dead wood, the fall of burned CWD plays a major role in saproxylic community shift after fire.     

Fungal succession and decomposition of beech cupule litter

Beech cupule litter is the second largest (next to leaf litter) component of total annual litterfall in mast years, and makes an important contribution to carbon budgets in beech forest soils. We investigated the decomposition processes of beech cupule litter over a 30-month period with reference to the role of fungal succession in the decomposition of acid-unhydrolyzable residue (AUR) and holocellulose. During the study period, weight loss of holocellulose occurred, while there was little weight loss of AUR, and 77?% of the original cupule weight remained at the end of the study period. Xylaria sp.1, Geniculosporium sp. and Nigrospora sp. that can attack holocellulose selectively caused mass loss of holocellulose and were responsible for the cupule weight loss. Although the beech cupule is a woody phyllome and its lignocellulose composition is similar to that of coarse woody debris (CWD) rather than leaf litter of beech, the selective decomposition of holocellulose by fungi was similar to the decay process of leaf litter rather than CWD.     

Communities of wood-inhabiting fungi in dead pine logs along a geographical gradient in Japan

Fungi are the main agents of coarse woody debris decomposition in forest ecosystems. We examined the associations of environmental variables with fungal community structures in dead pine logs at 12 geographically distant sites using amplicon pyrosequencing of fungal ITS rDNA. A total of 575 operational taxonomic units (OTUs) were identified based on clustering at 97% similarity. Among the known fungal ecological groups, saprotrophic fungi generally showed highest frequency of occurrence and were positively associated with mean annual temperature (MAT) and log diameter. Wood decay fungi with unknown decay type were positively associated with pine wilt disease and negatively associated with log diameter. Ordination analysis of the 42 most prevalent OTUs showed that MAT and annual precipitation significantly explained the observed fungal community structure. These results suggested that climate conditions and site history differentially effect structure fungal communities in pine logs among different ecological groups.     

Influence of Forest Management on the Species Richness and Composition of Wood-inhabiting Basidiomycetes in Swiss Forests

In order to investigate the diversity of wood-inhabiting aphyllophoroid basidiomycetes in Swiss forests, 86 plots of 50 m ² were established. They harboured a total of 3339 samples of woody debris, classified according to three categories (coarse, fine, and very fine woody debris), yielding 238 species of wood-inhabiting fungi. The selected sites cover the main forest types of Switzerland and various degrees of management intensity. A multiple linear regression analysis showed that substrate variation, i.e. differences in the quality of dead wood, including volume, age, degree of decomposition and host tree species, are the most important factors influencing diversity of wood-inhabiting fungi. In addition, a Principle Coordinate Analysis highlighted differences in the fungal communities in the different forest types. The greatest fungal species richness is found on thermophilic deciduous tree and woody shrub species. Fine and very fine woody debris, even present in intensively managed forests, often serve as important refuges for many species. Forests with a recent management intervention were found to be either species poor or species rich. Possible reasons for these differences may lay in forest size and landscape fragmentation, the distance to the nearest species pool or microclimatic factors. In Switzerland intensively managed forests harbour significantly less wood-inhabiting, aphyllophoroid fungi than non-managed or extensively managed forests. This is the case in both deciduous forests and in conifer forests. However, occasionally intensively managed forest will also harbour rare and endangered species.     

Fungal decomposition of woody debris of Castanopsis sieboldii in a subtropical old-growth forest

Fungi, especially basidiomycetes, are the primary agents of woody debris decomposition in terrestrial forest ecosystems. However, quantitative data regarding the abundance and decay activity of wood-inhabiting fungi are lacking, especially for tropical and subtropical areas. This study demonstrates the dynamics of decay columns of wood-inhabiting fungi within decaying woody debris of Castanopsis sieboldii and the wood decay activities of those fungi in a subtropical natural forest. Among six basidiomycetes and two ascomycetes observed as sporocarps on fallen boles of C. sieboldii, Microporus affinis was most abundantly observed in terms of frequency of sporocarps and as percentage area of decay columns within cross-sections of boles, especially those in the early stages of decomposition. In decay columns of M. affinis, both acid-unhydrolyzable residue (AUR) and holocellulose decayed simultaneously, and wood relative density decreased to 45.8% of that of fresh C. sieboldii wood. A pure culture decay test under laboratory conditions showed that M. affinis was a strong decomposer of AUR and holocellulose. These results suggest that M. affinis has a central role in lignocellulose decomposition of wood of C. sieboldii in the early stages of decomposition.     

广西弄岗五桠果叶木姜子群落木质藤本空间格局及其与树种间的关系

木质藤本是生物多样性的重要组成,木质藤本通过影响支持木进而影响群落的结构和功能,但在生物多样性丰富的北热带喀斯特森林中,木质藤本与支持木的关系鲜为人知。以喀斯特季节性雨林的五桠果叶木姜子（Litsea dilleniifolia）群落为研究对象,对木质藤本的密度、分布格局及其与主要树种的关系进行调查研究,分析木质藤本对树木的影响。结果显示：（1）五桠果叶木姜子群落内木质藤本平均密度为0.0913株/m²,木质藤本在0-20m空间尺度整体表现为聚集分布,且随着尺度增大,聚集强度逐渐减弱;不同径级木质藤本在不同尺度上的分布格局不同。（2）木质藤本对不同径级、不同种类、不同聚集强度的支持木选择表现以下体征：随着支持木径级增加,木质藤本攀附的比例和每木藤本数有增加趋势,且木质藤本胸径与支持木胸径呈极显著正相关;附藤率较高的支持木有紫葳科（Bignoniaceae）种类和东京桐（Deutzianthus tonkinensis）,单木附藤数量多的是南方紫金牛（Ardisia thyrsiflora）;物种的聚集强度与附藤率、附藤数量呈负相关。（3）木质藤本的密度与支持木死亡率关系不显著,而物种的附藤率与死亡率呈极显著负相关。以上结果表明,木质藤本密度在原生性喀斯特季节性雨林中并不高,且木质藤本对支持木具有选择性,但其对五桠果叶木姜子群落的死亡率并未产生显著影响。该研究可为喀斯特原生性季节性雨林的物种共存、极小植物种群保育提供理论依据,也可为石漠化区域的植被修复提供科学参考。