量化多样性对木质残体分解的影响

Given high rates of global biodiversity loss, the relationship between diversity and ecosystem functioning is of critical concern and an active area of theoretical enquiry. Dead wood accounts for a significant proportion of forest carbon pools (up to 40%) and wood decomposition is a non-trivial component of the global carbon cycle. However, the decomposition of woody debris is poorly understood and one of the largest remaining sources of uncertainty in global climate models. Wood decomposition is predominantly mediated by fungi, and the rate of decomposition is influenced by climate, substrate quality, and the responses of the decomposer community to these factors. Hence, diversity may affect wood decomposition through (i) habitat structure and its effect on microclimatic conditions on the ground, (ii) the chemical and physical properties of the wood, and (iii) the composition of the decomposer community. Moreover, the decomposition of woody debris is a successional process with different species performing distinct roles in the decomposition of substrates. We have established three complementary field experiments to assess the role of diversity in the decomposition of woody debris. In Experiment 1, we are incubating logs of two species, with low and high density wood, respectively, across a natural disturbance gradient from mature forest to degraded grassland. In Experiment 2, we are incubating the same two species in a mesocosm experiment designed to separate the effects of habitat structure and litter conditions. We used shade-cloth to simulate three levels of canopy cover and six litter-bed treatments were constructed from soil and leaf litter collected from plots selected from across the disturbance gradient. In Experiment 3, we are incubating logs of 25 tree species selected from across the higher plant phylogeny to assess the effects of wood traits and phylogeny on decomposition. In these experiments, we are monitoring mass (density) loss over 4 years. In addition, we measure respiration monthly. To monitor the composition of the decomposer community, we collect wood samples from each log and soil samples from the litter-beds every six months. These samples will be analysed using next generation sequencing to determine the fungal communities and soil mesofauna. As novel experiments on the role of biodiversity in an important and poorly understood ecosystem process, we expect these results to generate several important publications. This will be the first study to investigate wood decomposition at a landscape scale, the first study to use a shade house/litter-bed mesocosm to experimentally separate abiotic and biotic factors affecting decomposition, and the first study to quantify the effects of wood traits on decomposition across a wide functional and phylogenetic sample of species.

随着全球生物多样性加速丧失，多样性和生态系统功能之间的关系日益成为人们研究的热点。枯木是森林碳库的重要组成部分,其分解在全球碳循环中发挥着不容忽视的作用,而目前人们对木材分解作用还知之甚少。多样性主要通过生境结构、木材的化学和物理性质、分解者群落三个方面影响木材分解。本研究拟开展三种互补的野外实验。实验1：自然监测两种木材，分别估测其在不同自然干扰梯度下的分解率；实验2：人工模拟自然环境，监测与实验1同种木材，区分林层和凋落物对分解的影响；实验3：人工监测25种木材，量化木材性质和系统发育对分解的影响。另外，土壤分解者群落（真菌群落和中型动物群）构成将通过DNA第二代测序获得。本研究从生物多样性角度探讨其对木材分解的影响。首次从景观尺度研究木材分解，首次利用遮阴棚凋落物床组区分生物和非生物因子在分解中的作用，并首次量化了多样性对木材分解的影响。研究结果将大大加深人类对相关领域的认识。

生态系统服务是大自然的馈赠，生物多样性的丧失改变了生态系统的功能。然而人们并不了解两者之间复杂多变的关系，尤其是多样性如何影响分解这样复杂的功能。分解在营养元素从地上植被到土壤的转移过程起着关键作用。森林生态系统中的分解速率通常被认为随着干扰的增加而增加，但是之前并没有研究过完整退化过程中木材分解速率的干扰梯度变化，随着树冠开放度增加，表面土壤水分预计会随干扰梯度下降，反过来会降低分解速率。 .这项研究包括以下几种多样性变量对于木材分解的影响：（i）基质材料的质量，（ii）分解者群落的组成，（iii）影响分解的小气候条件。该项目通过自然样地测量和遮荫室实验来量化多样性在木质碎片分解中的作用。主要研究结果如下：（i）确定了如何正确计算木质碎片分解的CO2流出量（ii）木质碎片分解不随扰动梯度变化（iii）栖息地对木材碎片分解损失没有显著影响，但对真菌组成有显著影响（iv）叶片凋落物分解速率沿着干扰梯度下降（v）发酵时间和木材种类同一性是真菌多样性的重要预测因子（vi）真菌多样性在发酵后18个月达到峰值，之后下降（vii）树皮对木质碎片分解的影响是具有物种和木材尺寸特异性的（viii）树皮可以增强某些物种中木材分解难度（ix）森林退化对凋落物分解的影响主要来源于微气候条件的变化导致的冠层开放性增加（x）土壤腐殖性真菌丰富度随着森林干扰的增加而下降。因此，这些结果有助于通过精确量化CO2来改善气候变化模型的参数。更好的理解在景观尺度上影响木材分解的因素，这将有利于土地管理实践。.这是第一项调查景观尺度木质碎片分解的研究，第一项同时量化基质质量和木材分解者群体组成的作用的研究，第一项使用中型砂岩床平台实验来确定影响木材分解的非生物和生物因素的相对贡献的研究。此外我们的研究调查了木材功能性状对不同物种的木材分解的影响，并首次在系统发育控制的背景下进行调查研究。我们的结果有可能帮助校准短期呼吸测量值与质量损失值，建立了一个基线，让未来的研究人员能够只通过短期呼吸测量就能够单独评估木材分解率（Dossa等2015）。我们在项目期间也表明了树木在木材分解中的重要性（Dossa等2016，Dossa等2018）。这项工作一直是Dossa博士和E.Paudel博士论文的核心内容。Dossa博士还以此项目开展了博士后研究工作。