Ectomycorrhizal (EM) fungi can acquire phosphorus (P) through the production of extracellular hydrolytic enzymes (exoenzymes), but it is unclear as to the manner and extent native EM fungal communities respond to declining soil P availability. We examined the activity of six exoenzymes (xylosidase, N-acetyl glucosaminidase, β-glucosidase, acid phosphomonoesterase, acid phosphodiesterase [APD], laccase) from EM roots of Pseudotsuga menzesii across a soil podzolization gradient of coastal British Columbia. We found that APD activity increased fourfold in a curvilinear association with declining inorganic P. Exoenzyme activity was not related to organic P content, but at a finer resolution using ³¹P-NMR, there was a strong positive relationship between APD activity and the ratio of phosphodiesters to orthophosphate of surface organic horizons (forest floors). Substantial increases (two- to fivefold) in most exoenzymes were aligned with declining foliar P concentrations of P. menzesii, but responses were statistically better in relation to foliar nitrogen (N):P ratios. EM fungal species with consistently high production of key exoenzymes were exclusive to Podzol plots. Phosphorus deficiencies in relation to N limitations may provide the best predictor of exoenzyme investment, reflecting an optimal allocation strategy for EM fungi. Resource constraints contribute to species turnover and the assembly of distinct, well-adapted EM fungal communities.

外生菌根真菌可通过产生细胞外水解酶（外切酶）来获取磷（P），但尚不清楚原生EM真菌群落对土壤磷有效性下降的反应方式和程度。我们在不列颠哥伦比亚省沿海地区的土壤过土壤化梯度中检测了来自假单胞菌（Pseudotsuga menzesii）EM根的六个外切酶（木糖苷酶，N-乙酰氨基葡萄糖苷酶，β-葡萄糖苷酶，酸性磷酸单酯酶，酸性磷酸二酯酶[APD]，漆酶）的活性。我们发现，APD活性与无机P下降呈曲线关系增加了四倍。外酶活性与有机P含量无关，但使用^31时分辨率更高。通过P-NMR，APD活性与表面有机层（森林地面）中磷酸二酯与正磷酸盐的比率之间存在很强的正相关关系。大幅增加（两轮至五倍）在大多数胞外酶与叶面磷浓度下降对齐P。Menzesii，但相对于叶面氮（N）：P的比例，响应在统计上更好。Podzol地块专有的关键外酶始终高产的EM真菌物种。与N限制相关的磷缺乏可能是外酶投资的最佳预测指标，反映了EM真菌的最佳分配策略。资源限制促进了物种周转以及独特的，适应性强的EM真菌群落的聚集。