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

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.

Dynamics of phosphorus nutrition, allocation and growth of young beech (Fagus sylvatica L.) trees in P-rich and P-poor forest soil.

To investigate how long-lived forest trees cope with low soil phosphorus (P) availabilities, we characterized P nutrition of beech (Fagus sylvatica, L.) in soils from P-rich and P-poor beech forests throughout an annual growth cycle. Young trees were excavated with intact soil cores in mono-specific beech forests, kept under common garden conditions, and used for 33P labeling, analyses of P uptake, P content and biomass during five phenological stages (dormancy in winter, bud swelling in early spring, mature leaves in early and late summer, and senescent leaves in fall). Seasonal allocation patterns showed that young, emerging leaves were preferred sinks for P under P-poor conditions, thereby keeping foliar P concentrations at levels similar to those of trees grown in P-rich soil. Phosphorus concentrations in stems and roots of trees from the P-poor conditions were lower than those from P-rich conditions. Coarse roots were the main P storage tissue, supplying inorganic P to newly formed leaves, originating from the inorganic and organic P pools under low and high P conditions, respectively. Beech trees in P-poor soil exhibited net biomass increment early in the annual growth along with a strong P deficit, which was replenished by enhanced uptake in late summer and fall. Trees in P-rich soil grew until late summer, and showed a moderate P decline in organic pools and recovery late in fall, which coincided with elevated P uptake from soil. Beech in P-poor soil produced more biomass per unit of P but at a slower growth rate than those in P-rich soil, thereby exhibiting similar P-use efficiencies. Temporal decoupling of growth and P acquisition in combination with internal P trade-off between storage tissues and leaves facilitated flexible acclimation of beech to a wide range of soil P availabilities.

Changes in the fine root proteome of Fagus sylvatica L. trees associated with P-deficiency and amelioration of P-deficiency.

Phosphorus is often the least available macronutrient in soil. Lack in phosphorus has detrimental effect on growth and biomass production of European Fagus sylvatica L., a major trees species in temperate forests. In contrast to leaf tissues, few studies have examined changes in the root system and no study has ever investigated the proteomic changes affected in beech roots by a lack in available phosphate (P). Here, we studied roots of young Fagus sylvatica L. trees in their native soils from two forests sites with contrasting availability of P: one P rich and P poor soil. To understand also the response to P fertilization, the trees were fertilized with triple superphosphate and the proteome of fine roots of all conditions was compared. Gel-free mass-spectrometry-based shotgun proteomics revealed that the proteome was differentially affected by diverging P availabilities. The proteomic changes that took place as the result of P fertilization were dependent on the supply level of P before the fertilization. When P was supplied to the P-rich soil proteins related to cell biogenesis exhibited increased abundances. Addition of P to soil that was strongly limited in P resulted in increased abundance of proteins associated with amino acid metabolism and transport. BIOLOGICAL SIGNIFICANCE: Beech (Fagus sylvatica L.) forests have a huge ecological and economic value across Europe. In recent years, however, these forest sites increasingly suffer under phosphorus (P) deficiency. As the consequence, growth and vitality of beech forests is impaired. For this reason, this study was conducted with the aim to identify and understand proteomic impairments and adjustments that evolve in the fine roots under both, a P deficiency and an amelioration thereof. For this, we analyzed (1) the fine root proteome of young beech trees grown (2) at two soil sites that contrast in their degree of availability P (low vs. high) in dependency (3) to a fertilization with P. This experiment revealed fundamental differences with respect to proteomic changes in dependency on the severity of P limitation and helped to identify processes that take place after amelioration of the deficiency. This information is useful to understand which physiological processes are impaired under P deficiency and, thus, impair growth. The fertilization experiment enabled to identify developmental processes that take place in fine roots when concentration of available P was increased. They are "cellular component organization and biogenesis" in the P rich soil and "synthesis of organonitrogen-containing compounds" in the P poor soil.