Data from: Host phenology and potential saprotrophism of ectomycorrhizal fungi in the boreal forest

Phenology-induced changes in carbon assimilation by trees may affect carbon stored in fine roots and as a consequence, alter carbon allocated to ectomycorrhizal fungi. Two competing models exist to explain carbon mobilization by ectomycorrhizal fungi. Under the ‘saprotrophy model’, decreased allocation of carbon may induce saprotrophic behaviour in ectomycorrhizal fungi, resulting in the decomposition of organic matter to mobilize carbon. Alternatively, under the ‘nutrient acquisition model’, decomposition may instead be driven by the acquisition of nutrients locked within soil organic matter compounds, with carbon mobilization a secondary process. We tested whether phenology-induced shifts in carbon reserves of fine roots of aspen (Populus tremuloides) affect potential activity of four carbon-compound degrading enzymes, β-glucuronidase, β-glucosidase, N-acetylglucosaminidase and laccase, by ectomycorrhizal fungi. Ectomycorrhizal roots from mature aspen were collected across eight stands in north-eastern Alberta, Canada, and analysed during tree dormancy, leaf flush, full leaf expansion and leaf abscission. We predicted potential extracellular enzyme activity to be highest when root carbon reserves were lowest, should host phenology induce saprotrophism. Further, we anticipated enzyme activity to be mediated by invertase, a plant-derived enzyme which makes carbon available to fungal symbionts in the plant–fungus interface. Root carbon reserves were positively correlated with invertase, suggesting phenology may affect carbon allocation to ectomycorrhizal fungi. However, of the four enzymes, host phenology had the largest effect on β-glucuronidase, but activity of this enzyme was not correlated with root carbon reserves or invertase. Low-biomass ectomycorrhizas had greater potential laccase activity than high-biomass ectomycorrhizas, highlighting discrete functional traits in fungi for litter decomposition. Our results suggest that the decomposition of organic matter may be driven by foraging by fungi for nutrients locked within organic compounds rather than for mobilizing carbon. Furthermore, the potential ability to degrade lignin was more common in low-biomass ectomycorrhizas when compared to high-biomass ectomycorrhizas.树木碳同化过程随物候变化产生的改变，可能会影响细根储存的碳储量，并进而改变向外生菌根真菌（ectomycorrhizal fungi）分配的碳量。目前存在两种相互竞争的模型，用于解释外生菌根真菌的碳动员过程。在“腐生营养模型”下，碳分配的减少可能会诱导外生菌根真菌表现出腐生行为，进而通过分解有机质实现碳动员。而在“养分获取模型”中，分解过程的驱动因素实则为获取土壤有机质组分中结合的养分，碳动员仅为次要过程。 本研究针对颤杨（Populus tremuloides）细根碳储量因物候变化产生的波动是否会影响外生菌根真菌对四种碳组分降解酶——β-葡萄糖苷酸酶、β-葡萄糖苷酶、N-乙酰氨基葡萄糖苷酶与漆酶——的潜在活性展开了测试。研究人员于加拿大阿尔伯塔省东北部的8个样地采集成熟颤杨的外生菌根，并在树木休眠期、展叶初期、叶片完全展开期以及落叶期开展样本分析。我们提出如下假设：若宿主物候诱导真菌转为腐生营养型，则当根系碳储量最低时，胞外酶潜在活性应达到峰值。此外，我们推测酶活性会受到转化酶的调控——该酶为植物源酶，可在植物-真菌界面为真菌共生体提供可利用碳源。 根系碳储量与转化酶呈正相关，表明物候可能会影响向外生菌根真菌分配的碳量。不过在四种酶中，宿主物候对β-葡萄糖苷酸酶的影响最大，但该酶的活性与根系碳储量或转化酶均无相关性。低生物量外生菌根的漆酶潜在活性高于高生物量外生菌根，这凸显了真菌在枯落物分解过程中存在差异化的功能性状。 本研究结果表明，有机质的分解可能由真菌觅食以获取有机质组分中结合的养分所驱动，而非为了动员碳。此外，相较于高生物量外生菌根，低生物量外生菌根中降解木质素的潜在能力更为普遍。