1 INTRODUCTION

Globally, forests act as “carbon sinks” by absorbing more than 1 Pg C per year (Pan et al., 2011). Most of the stored carbon will be slowly released to the atmosphere as CO₂ once the trees die and subsequently decompose. The dynamic in the carbon- and nutrient cycling process in forest ecosystems depends on the speed of deadwood decomposition. Stem decay process is determined by both intrinsic and extrinsic drivers (Cornwell et al., 2009; Kahl et al., 2017) and can strongly differ between tree species (Villéger et al., 2008; Yang, Sterck, et al., 2022). Species-specific anatomical and chemical wood and bark traits are documented to have strong afterlife effects (Freschet et al., 2012). Stem traits can shape the richness and composition of wood-inhabiting fungi (Yang et al., 2021), bacteria and arthropods (Andringa et al., 2019), thus affecting wood decomposition rate and biogeochemical cycling (Kahl et al., 2017; Zuo et al., 2016). Wood decomposition is also driven by biotic interactions between stem traits, the different decomposers and their priority effects (van der Wal et al., 2016; Weedon et al., 2009), and by abiotic conditions (temperature, moisture and light) that determine the decomposer abundance and activity (Edman et al., 2021; Hu et al., 2017). However, we still have little knowledge of the combined and relative effects of these multiple drivers in determining wood decomposition rate and outcomes throughout the decomposition trajectory (but see Kahl et al., 2017; Zuo et al., 2021).

Physical, chemical and anatomical traits of different stem compartments (bark and wood) determine the accessibility and substrate quality for different wood decomposers (Baldrian et al., 2016; Rajala et al., 2012). Bark represents the first line of defence; it comprises up to 20% of above-ground tree biomass, differs greatly from wood in terms of physical–chemical traits (Yang, Sterck, et al., 2022), and serves as an environmental filter for the decomposer community assembly (Ulyshen et al., 2016). Bark can inhibit decomposers' access because of the high content of defence compounds (Jones et al., 2020) or, alternatively attracting decomposers by its high nutrient and by creating locally favourable conditions for wood decomposition (Wu et al., 2021). As a result, the effect of bark on wood decay is often tree species- and stem size-specific (Dossa et al., 2016; Tuo et al., 2021). Nutritional stem traits, like high nutrient and non-structural carbohydrate concentrations, generally stimulate fungal growth (Sinsabaugh et al., 1993), whereas a high C/N ratio or low initial N concentration may cause microbial N limitation and reduce microbial metabolic activity and wood decomposition rate (Bonanomi et al., 2021; Weedon et al., 2009). Chemical defence traits such as toxic phenols and tannins reduce the decomposability of stem cells (Kahl et al., 2017; Viotti et al., 2021). Physical defence traits, such as bark physical toughness, wood density and lignin concentration also determine fungal richness and community composition (Hoppe et al., 2016; Krah et al., 2018). Less attention has been paid to anatomical traits such as parenchyma fraction and conduit size, which may increase access and spread of wood-decaying organisms, thereby regulating nutrient and carbon availability (Lee & Hawkes, 2021; Zanne et al., 2015). Therefore, how this complex of stem traits, in combination with fungi infestation, drives wood decay over time and differs across tree species remains poorly studied.

Fungi are the primary decomposers of dead wood because they can actively decompose lignin and other recalcitrant compounds (Boddy, 2001; Stokland et al., 2012). Three main wood decomposing fungal functional groups are known to break down the major wood polymers cellulose, hemi-cellulose and lignin (Kirk et al., 1987; van der Wal et al., 2013). White-rot Basidiomycetes degrade cellulose, hemicelluloses and recalcitrant lignin with the aid of extracellular lignocellulolytic enzymes; brown-rot Basidiomycetes degrade cellulose and hemicelluloses by depolymerisation while partially modifying lignin through non-enzymatic process, e.g. by demethoxylation (Niemenmaa et al., 2008); and soft-rot Ascomycetes degrade cellulose and hemicelluloses by secreting cellulase (Schmidt, 2006). Fungal richness can increase wood decomposition via increased niche partitioning, or facilitative interactions among fungal species (Tiunov & Scheu, 2005; Van Der Wal et al., 2015). Yet, this positive richness effect can saturate at rather low fungal richness because of redundancy in metabolic abilities of fungi (Dang et al., 2005; van der Wal et al., 2013) or because of intense competition among fungi (Fukami et al., 2010; Nielsen et al., 2011). Therefore, further studies are necessary to fully understand the effects of fungi on wood decomposition and their role in maintaining the balance of forest ecosystems and the carbon cycle.

We examined the relative importance of stem traits and fungal decomposer community structure, as well as their interactions, on wood density loss over 4 years of decay in the field. We sought to address three hypotheses. First, wood density loss will be positively correlated with anatomical trait values that increase accessibility for decomposers (e.g. larger conduit size) and nutritional quality (i.e. N, P), and negatively correlated with values for physical (e.g. high wood density) and chemical defence traits (e.g. high lignin and phenolic concentrations) that inhibit the activity of wood decomposers (Cornwell et al., 2009; Lee et al., 2020). Moreover, the importance of initial stem traits may decrease with ongoing decay as many metabolites of the substrate may be decomposed or have changed. Second, Basidiomycete white-rot and brown-rot fungi will become more important in wood degradation later in the decomposition trajectory, owing to their ability to degrade recalcitrant polymers that remain after initial decomposition stages (Blanchette, 2000; Boddy, 2001). Third, based on the two commonly tested mechanisms: niche complementary (Loreau & Hector, 2001; Tilman et al., 1997) and the mass ratio hypothesis (Grime, 1998), we expect that fungal richness is correlated with wood density loss in the early decay period, because the fungal species that are initially present may be complementary in their niches, while later stages are likely dominated by a narrow range of specialists, thereby eliminating any expected effects of fungal richness (Tiunov & Scheu, 2005; van der Wal et al., 2013). For testing these hypotheses, we took advantage of a common garden experiment (LOGLIFE), in which similar-sized coarse logs of 13 temperate tree species were placed in a Dutch forest and monitored for 4 years (Cornelissen et al., 2012). This design allows for showing the potential effects of species-specific stem traits and their interactions with fungi on wood decay, largely without confounding effects of environmental conditions.

中文翻译：

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温带树种的茎分解由早期茎腐烂过程中的茎性状和真菌群落组成决定

 1 简介

在全球范围内，森林每年吸收超过 1 Pg C，充当“碳汇”（Pan 等，2011）。一旦树木死亡并随后分解，大部分储存的碳将以 CO ₂ 的形式缓慢释放到大气中。森林生态系统中碳和养分循环过程的动态取决于枯木分解的速度。茎腐烂过程由内在和外在驱动因素共同决定（Cornwell et al., 2009；Kahl et al., 2017），并且树种之间存在很大差异（Villéger et al., 2008；Yang, Sterck, et al., 2022） ）。据记录，特定物种的木材和树皮的解剖和化学特征具有强烈的来世影响（Freschet 等，2012）。茎性状可以塑造木材栖息真菌（Yang等，2021）、细菌和节肢动物（Andringa等，2019）的丰富度和组成，从而影响木材分解速率和生物地球化学循环（Kahl等，2017；左等人，2016）。木材分解还受到茎性状、不同分解者及其优先效应之间的生物相互作用的驱动（van der Wal et al., 2016; Weedon et al., 2009），以及决定木材分解的非生物条件（温度、湿度和光照）。分解者丰度和活性（Edman 等人，2021；Hu 等人，2017）。然而，我们对这些多重驱动因素在确定木材分解速率和整个分解轨迹结果方面的综合和相对影响仍然知之甚少（但参见 Kahl 等人，2017 年；Zuo 等人，2021 年）。

不同茎室（树皮和木材）的物理、化学和解剖特征决定了不同木材分解剂的可及性和基质质量（Baldrian 等，2016；Rajala 等，2012）。树皮代表第一道防线；它占地上树木生物量的 20%，在物理化学特性方面与木材有很大不同（Yang，Sterck 等人，2022），并且可作为分解者群落组装的环境过滤器（Ulyshen 等人）等，2016）。由于防御化合物含量高，树皮可以抑制分解者的进入（Jones 等人，2020），或者通过其高营养成分和为木材分解创造当地有利的条件来吸引分解者（Wu 等人，2021）。因此，树皮对木材腐烂的影响通常因树种和茎的大小而异（Dossa 等人，2016 年；Tuo 等人，2021 年）。营养茎性状，如高营养和非结构碳水化合物浓度，通常会刺激真菌生长（Sinsabaugh 等，1993），而高 C/N 比或低初始氮浓度可能会导致微生物氮限制并降低微生物代谢活动和木材分解率（Bonanomi 等人，2021 年；Weedon 等人，2009 年）。有毒酚和单宁等化学防御特性会降低干细胞的分解性（Kahl et al., 2017；Viotti et al., 2021）。物理防御特征，如树皮物理韧性、木材密度和木质素浓度也决定真菌丰富度和群落组成（Hoppe等，2016；Krah等，2018）。 人们对薄壁组织分数和导管尺寸等解剖特征的关注较少，这些特征可能会增加木材腐烂生物的进入和传播，从而调节养分和碳的可用性（Lee＆Hawkes，2021；Zanne等人，2015）。因此，这种复杂的茎性状与真菌侵扰相结合如何随着时间的推移导致木材腐烂，并且在不同树种之间存在差异，这一点仍然缺乏研究。

真菌是死木的主要分解者，因为它们可以主动分解木质素和其他顽固化合物（Boddy，2001；Stokland 等，2012）。已知三种主要的木材分解真菌官能团可分解主要的木材聚合物纤维素、半纤维素和木质素（Kirk 等，1987；van der Wal 等，2013）。白腐担子菌借助胞外木质纤维素分解酶降解纤维素、半纤维素和顽固木质素；褐腐担子菌通过解​​聚降解纤维素和半纤维素，同时通过非酶促过程部分改性木质素，例如通过去甲氧基化（Niemenmaa 等，2008）；软腐子囊菌通过分泌纤维素酶降解纤维素和半纤维素（Schmidt，2006）。真菌丰富度可以通过增加生态位分配或真菌物种之间的促进相互作用来增加木材分解（Tiunov＆Scheu，2005；Van Der Wal等人，2015）。然而，由于真菌代谢能力的冗余（Dang等，2005；van der Wal等，2013）或由于真菌之间的激烈竞争（Fukami等，2013），这种积极的丰富度效应可能会在相当低的真菌丰富度下饱和。 ，2010；尼尔森等人，2011）。因此，有必要进一步研究以充分了解真菌对木材分解的影响及其在维持森林生态系统和碳循环平衡中的作用。

我们研究了茎性状和真菌分解者群落结构及其相互作用对田间腐烂 4 年期间木材密度损失的相对重要性。我们试图解决三个假设。首先，木材密度损失将与增加分解者可及性（例如更大的管道尺寸）和营养质量（即N、P）的解剖特征值呈正相关，并与物理（例如高木材密度）和化学防御值呈负相关抑制木材分解剂活性的特性（例如高木质素和酚类浓度）（Cornwell 等人，2009 年；Lee 等人，2020 年）。此外，初始茎性状的重要性可能会随着持续腐烂而降低，因为底物的许多代谢物可能会分解或发生变化。其次，担子菌白腐真菌和褐腐真菌在分解轨迹后期的木材降解中将变得更加重要，因为它们能够降解初始分解阶段后残留的顽固聚合物（Blanchette，2000；Boddy，2001）。第三，基于两种常用的测试机制：生态位互补（Loreau & Hector，2001；Tilman 等人，1997）和质量比假设（Grime，1998），我们预计真菌丰富度与木材密度损失相关。早期腐烂期，因为最初存在的真菌物种可能在其生态位中互补，而后期阶段可能由一小部分专家主导，从而消除了真菌丰富度的任何预期影响（Tiunov＆Scheu，2005；van der Wal）等人，2013）。 为了检验这些假设，我们利用了一个常见的花园实验 (LOGLIFE)，其中将 13 种温带树种的大小相似的粗原木放置在荷兰森林中并监测了 4 年（Cornelissen 等人，2012 年）。这种设计可以显示物种特定的茎特征及其与真菌的相互作用对木材腐烂的潜在影响，很大程度上不会混淆环境条件的影响。