Forest Soil Phosphorus Resources and Fertilization Affect Ectomycorrhizal Community Composition, Beech P Uptake Efficiency, and Photosynthesis

Abstract

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 (Fagus sylvatica 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 (H333PO4) 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.

Plant Nutritional Status Explains the Modifying Effect of Provenance on the Response of Beech Sapling Root Traits to Differences in Soil Nutrient Supply

“…The beech saplings from natural rejuvenation used in our experiment were of similar age to those investigated by Yang et al (2016) and Zavišić et al (2018). In contrast to the strong influence of "current soil" on the N, Mg, and K concentrations in the second year, P concentrations in different plant compartments were still similar to P concentrations of saplings from the two sites when grown in their natural soil (Zavišić et al, 2018).…”

“…Comparing foliar nutrient concentrations and nutrient ratios with threshold values by Mellert and Göttlein (2012); ratios) and Göttlein (2015); concentrations in mature trees), the mature beeches at BBR exhibited a balanced nutrition except for a latent deficiency in K and N/K ratios above the normal range, while the trees at LUE showed a latent deficiency in P and N/P, N/Mg, and N/Ca ratios above the normal range. A lower P nutritional status of juvenile beech trees from LUE than from BBR was documented by Zavišić et al (2018). They found a respective difference in P concentration for all plant compartments.…”

“…The beech saplings from natural rejuvenation used in our experiment were of similar age to those investigated by Yang et al (2016) and Zavišić et al (2018). In contrast to the strong influence of "current soil" on the N, Mg, and K concentrations in the second year, P concentrations in different plant compartments were still similar to P concentrations of saplings from the two sites when grown in their natural soil (Zavišić et al, 2018). In the following, we assess the relative nutritional status of the saplings and its change during the experiment (i) by evaluating the foliar nutrient concentrations based on threshold values for juvenile beech trees by Göttlein (2015) and foliar N-to-nutrient ratios based on threshold values by Mellert and Göttlein (2012) and (ii) by comparing the average concentrations in the whole plant among the treatments.…”

“…These adaptations are expressed in a slower growth of the mature beeches at LUE than at BBR, as is indicated by a smaller stem diameter. When grown under identical climatic conditions in undisturbed soil cores from their own site, saplings from natural rejuvenation at LUE produced smaller leaves with a lower photosynthetic activity and stomatal conductance than saplings from natural rejuvenation at BBR (Yang et al, 2016;Zavišić et al, 2018). In particular, FIGURE 3 | Nitrate (A), phosphate (B), oxalate (C), and citrate (D) collected with anion exchange membranes in the rhizosphere in a rhizobox experiment with beech (Fagus sylvatica L.) saplings originating from the sites Bad Brückenau (BBR) and Unterlüss (LUE).…”

Response of Soil Nematode Community to Phosphorous Amendment in a Subalpine Spruce Plantation

“…Numerous studies confirmed that P addition influenced fine root biomass, leaves and litter‐fall quantity and quality, tree growth, aboveground primary production, the rate of succession for plants and for microbial phototrophs, soil nutrient status, soil microbial biomass, and community composition . Collectively, the direction and magnitude of P addition on these variables range from negative to positive.…”