Soil organic matter (SOM) and pH are key ecosystem drivers, influencing resilience to environmental change. We tested the separate effects of pH and SOM on nutrient availability, plant strategies, and soil community composition in calcareous and acidic Grey dunes (H2130) with low, intermediate, and/or high SOM, which differ in sensitivity to high atmospheric N deposition. Soil organic matter was mainly important for biomass parameters of plants, microbes, and soil animals, and for microarthropod diversity and network complexity. However, differences in pH led to fundamental differences in P availability and plant strategies, which overruled the normal soil community patterns, and influenced resilience to N deposition. In calcareous dunes with low grass‐encroachment, P availability was low despite high amounts of inorganic P, due to low solubility of calcium phosphates and strong P sorption to Fe oxides at high pH. Calcareous dunes were dominated by low‐competitive arbuscular mycorrhizal (AM) plants, which profit from mycorrhiza especially at low P. In acidic dunes with high grass‐encroachment, P availability increased as calcium phosphates dissolved and P sorption weakened with the shift from Fe oxides to Fe‐OM complexes. Weakly sorbed and colloidal P increased, and at least part of the sorbed P was organic. Acidic dunes were dominated by nonmycorrhizal (NM) plants, which increase P uptake through exudation of carboxylates and phosphatase enzymes, which release weakly sorbed P, and disintegrate labile organic P. The shifts in P availability and plant strategies also changed the soil community. Contrary to expectations, the bacterial pathway was more important in acidic than in calcareous dunes, possibly due to exudation of carboxylates and phosphatases by NM plants, which serve as bacterial food resource. Also, the fungal AM pathway was enhanced in calcareous dunes, and fungal feeders more abundant, due to the presence of AM fungi. The changes in soil communities in turn reduced expected differences in N cycling between calcareous and acidic dunes. Our results show that SOM and pH are important, but separate ecosystem drivers in Grey dunes. Differences in resilience to N deposition are mainly due to pH effects on P availability and plant strategies, which in turn overruled soil community patterns.

中文翻译：

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沿海沙丘草地的复原力：pH和土壤有机质对磷营养，植物策略和土壤群落的影响

土壤有机质（SOM）和pH值是生态系统的主要驱动力，影响着对环境变化的适应力。我们在低，中和/或高SOM的钙质和酸性灰沙丘（H2130）中测试了pH和SOM对养分有效性，植物策略和土壤群落组成的单独影响，这些对高大气氮沉降的敏感性不同。土壤有机质对于植物，微生物和土壤动物的生物量参数以及微节肢动物的多样性和网络复杂性至关重要。但是，pH值的差异导致了磷素有效性和植物策略的根本差异，从而推翻了正常的土壤群落模式，并影响了对氮沉降的适应能力。在草木入侵少的钙质沙丘中，尽管无机磷含量高，磷的利用率却很低，由于磷酸钙的溶解度低，并且在高pH下对Fe氧化物的P吸附能力强。钙质沙丘以低竞争性丛枝菌根（AM）植物为主，尤其是在低磷条件下，从菌根中获利。在草木高侵蚀的酸性沙丘中，磷的溶解度随磷钙的溶解而增加，磷的吸收随着铁氧化物的迁移而减弱。 Fe-OM复合物。弱吸附和胶体磷增加，并且至少一部分吸附的磷是有机的。酸性沙丘以非菌根（NM）植物为主，后者通过羧酸盐和磷酸酶的渗出增加P的吸收，释放出弱吸收的P，并分解不稳定的有机P。P有效性和植物策略的变化也改变了土壤群落。与期望相反，酸性环境中的细菌途径比钙质沙丘中的细菌途径更为重要，这可能是由于NM植物（作为细菌性食物资源）渗出的羧酸盐和磷酸酶所致。同样，由于AM真菌的存在，在钙质沙丘中真菌AM途径得以增强，真菌饲养者也更加丰富。土壤群落的变化反过来减少了钙质和酸性沙丘之间氮循环的预期差异。我们的结果表明，SOM和pH很重要，但在灰色沙丘中却是独立的生态系统驱动力。氮沉降抗逆性的差异主要归因于pH对磷有效性和植物策略的影响，从而反过来推翻了土壤群落格局。由于存在AM真菌，石灰性沙丘中的真菌AM途径得到增强，真菌饲养者数量也更加丰富。土壤群落的变化反过来减少了钙质和酸性沙丘之间氮循环的预期差异。我们的结果表明，SOM和pH很重要，但在灰色沙丘中却是独立的生态系统驱动力。氮沉降抗逆性的差异主要归因于pH对磷有效性和植物策略的影响，从而反过来推翻了土壤群落格局。由于AM真菌的存在，钙质沙丘中的真菌AM途径得到增强，真菌饲养者数量也更加丰富。土壤群落的变化反过来减少了钙质和酸性沙丘之间氮循环的预期差异。我们的结果表明，SOM和pH很重要，但在灰色沙丘中却是独立的生态系统驱动力。氮沉降抗逆性的差异主要归因于pH对磷有效性和植物策略的影响，从而反过来推翻了土壤群落格局。