Secondary metabolites ofPinus halepensisalter decomposer organisms and litter decomposition during afforestation of abandoned agricultural zones

Abstract

Summary1. Over a century of agricultural abandonment across the Mediterranean region has favoured the installation of the pioneer expansionist species Aleppo pine (Pinus halepensis Miller). This species synthesizes a wide range of secondary metabolites that are partially released during needle decomposition, and which can thus affect the 'brown food chain'. Litter decomposition is a key process connecting ecosystem structure and function, and involving microbial and faunal components. 2. The goal of this study was to determine the effect of chemical compounds from Aleppo pine needles on the litter decomposition process along a gradient of Mediterranean forest secondary succession. Using in situ litterbags, we compared the dynamics of decomposers, particularly the relative contributions of fungal and mesofauna biomass to litter mass loss (calculations based on the measured decomposer biomass, published fungal growth efficiency and mesofauna feeding rate), against the dynamics of secondary metabolites associated with decomposed needles in three successional stages (early, middle and late, i.e. pinewoods that were aged 10, 30 and over 60 years old). 3. Our first key finding was that fungi accounted for the largest portion of overall litter mass loss (60-79%) and detritivorous mesofauna contributed to 8-12%. In the early stage of succession, fungal biomass after 6 months of decomposition was lower than in middle and late stages, and may be responsible for the delay in litter colonization by mesofauna. We linked this result to a clearly longer residence time for phenolic compounds in young pine forest, leading to an overall slowdown in the decomposition process. 4. Synthesis. Litter phenolic content emerged as a key functional trait for predicting litter decomposition, delaying the colonization of litter by decomposers in Mediterranean forest ecosystems. Another key finding is that the relative contributions of fungi and detritivores to needle mass loss were different between the successional stages. From the food-web perspective, the organic matter available for higher trophic levels thus remains unchanged beyond 30 years after pine colonization.

Mediterranean forests, land use and climate change: a social-ecological perspective

“…• Between plants since chemicals present phytotoxic effects irrespective of their functional group (Bonanomi et al 2006;Fernandez et al 2013a, b), • Between plants and microorganisms because PSMs inhibit soil microorganisms involved in nitrogen cycling and forest regeneration (Pellissier et al 2002;Jonsson et al 2006;Chomel et al 2014).…”

“…For example, Pinus halepensis is rich in secondary metabolites (Pasqua et al 2002;Macchioni et al 2003;Fernandez et al 2009) particularly terpenoids but also phenolics that are thought to play a role in plant-plant and plant-microorganisms interactions through allelopathic processes (Fernandez et al 2006(Fernandez et al , 2008(Fernandez et al , 2009(Fernandez et al , 2013aChomel et al 2014). P. halepensis allelochemicals might drive plant biodiversity in Mediterranean, but their role in the variability of biodiversity has received little attention so far, particularly in stressful environments.…”

“…In summer, high temperature and low moisture, leading to persistent drought, can drastically limit microbial growth and activity (Criquet et al 2004;Fioretto et al 2005), whereas the milder and wetter spring and autumn seasons induce higher metabolic rates of microbes temporarily enhancing the litter decomposition rates (Coûteaux et al 1995). These markedly dry summer periods lead to a discontinuous decomposition process closely linked to water availability (Chomel et al 2014). …”

Litter chemistry prevails over litter consumers in mediating effects of past steel industry activities on leaf litter decomposition

“…Mixed-effects model, with "plot" specified as a random factor, was used for analyzing litter mass remaining (ln-transformed) and fungal biomass because measures were repeated on three occasions on the same plots and thus were not independent (Zuur et al, 2009). Time of exposure in the field was set as a covariate in the model for lntransformed litter mass remaining, so that the interactions between fixed factors and time elucidated differences in litter mass loss coefficients (Chomel et al, 2014). In the linear mixed effects model used for fungal biomass (ergosterol), time was set as a factor to detect potential non-linear changes through time.…”

Effects of leachate from understory medicinal plants on litter decomposition and soil enzyme activities of Betula albo-sinensis and Eucommia ulmoides

“…典型森林树种 (郭垚鑫等, 2011; 杨明琰等, 2012), (Hättenschwiler & Vitousek, 2000); 酚类物质可以抑 制土壤中真菌的定殖、孢子萌发和菌丝伸长并影响 细菌的粘附以及膜蛋白的转运 (Mierziak et al, 2014), 进而影响枯落物分解。然而, 目前关于该方面的研 究集中在来自植物自身或其枯落物的内源PSM (Chomel et al, 2014) 或 人 工 添 加 某 种 特 定 PSM (Hättenschwiler & Vitousek, 2000)对枯落物分解的 影响, 而很少关注在自然环境中普遍存在且种类组 成更加复杂的外源PSM (Zhang et al, 2016 Phytotoxic effect of Parthenium residues on the selected soil properties and growth of chickpea and radish. Weed Biology and Management, 2, 73-78.…”