Zavišić Aljosa, Yang Nan, Marhan Sven, Kandeler Ellen, Polle Andrea
Forest Botany and Tree Physiology, University of Göttingen, Göttingen, Germany.
Institute of Soil Science and Land Evaluation, Soil Biology, University of Hohenheim, Stuttgart, Germany.
Front Plant Sci. 2018 Apr 13;9:463. doi: 10.3389/fpls.2018.00463. eCollection 2018.
Phosphorus (P) is an important nutrient, whose plant-available form phosphate is often low in natural forest ecosystems. Mycorrhizal fungi mine the soil for P and supply their host with this resource. It is unknown how ectomycorrhizal communities respond to changes in P availability. Here, we used young beech ( L.) trees in natural forest soil from a P-rich and P-poor site to investigate the impact of P amendment on soil microbes, mycorrhizas, beech P nutrition, and photosynthesis. We hypothesized that addition of P to forest soil increased P availability, thereby, leading to enhanced microbial biomass and mycorrhizal diversity in P-poor but not in P-rich soil. We expected that P amendment resulted in increased plant P uptake and enhanced photosynthesis in both soil types. Young beech trees with intact soil cores from a P-rich and a P-poor forest were kept in a common garden experiment and supplied once in fall with triple superphosphate. In the following summer, labile P in the organic layer, but not in the mineral top soil, was significantly increased in response to fertilizer treatment. P-rich soil contained higher microbial biomass than P-poor soil. P treatment had no effect on microbial biomass but influenced the mycorrhizal communities in P-poor soil and shifted their composition toward higher similarities to those in P-rich soil. Plant uptake efficiency was negatively correlated with the diversity of mycorrhizal communities and highest for trees in P-poor soil and lowest for fertilized trees. In both soil types, radioactive P tracing (HPO) revealed preferential aboveground allocation of new P in fertilized trees, resulting in increased bound P in xylem tissue and enhanced soluble P in bark, indicating increased storage and transport. Fertilized beeches from P-poor soil showed a strong increase in leaf P concentrations from deficient to luxurious conditions along with increased photosynthesis. Based on the divergent behavior of beech in P-poor and P-rich forest soil, we conclude that acclimation of beech to low P stocks involves dedicated mycorrhizal community structures, low P reserves in storage tissues and photosynthetic inhibition, while storage and aboveground allocation of additional P occurs regardless of the P nutritional status.
磷（P）是一种重要的养分，其植物可利用形态的磷酸盐在天然森林生态系统中含量往往较低。菌根真菌从土壤中获取磷并为其宿主提供这种资源。目前尚不清楚外生菌根群落如何响应磷有效性的变化。在此，我们利用来自富磷和贫磷地点的天然森林土壤中的年轻山毛榉（Fagus sylvatica L.）树，研究磷添加对土壤微生物、菌根、山毛榉磷营养和光合作用的影响。我们假设向森林土壤中添加磷会提高磷的有效性，从而导致贫磷土壤中微生物生物量增加和菌根多样性提高，但富磷土壤中不会。我们预期磷添加会导致两种土壤类型中植物对磷的吸收增加以及光合作用增强。将来自富磷和贫磷森林且带有完整土芯的年轻山毛榉树置于一个共同花园实验中，并在秋季一次性施用重过磷酸钙。在接下来的夏天，响应肥料处理，有机层中但不是矿质表层土壤中的活性磷显著增加。富磷土壤中的微生物生物量高于贫磷土壤。磷处理对微生物生物量没有影响，但影响了贫磷土壤中的菌根群落，并使其组成向与富磷土壤中的群落更高的相似性转变。植物吸收效率与菌根群落多样性呈负相关，在贫磷土壤中的树木最高，在施肥树木中最低。在两种土壤类型中，放射性磷示踪（HPO42-）显示施肥树木中新磷优先向地上部分分配，导致木质部组织中结合磷增加以及树皮中可溶性磷增加，表明储存和运输增加。来自贫磷土壤的施肥山毛榉树叶片磷浓度从缺乏状态大幅增加到丰富状态，同时光合作用增强。基于山毛榉在贫磷和富磷森林土壤中的不同行为，我们得出结论，山毛榉对低磷存量的适应涉及特定的菌根群落结构、储存组织中低磷储备和光合作用抑制，而额外磷的储存和地上部分分配则与磷营养状况无关。
