Phosphorus fluxes in two contrasting forest soils along preferential pathways after experimental N and P additions

The assessment of impacts of an altered nutrient availability, e.g. as caused by consistently high atmospheric nitrogen (N) deposition, on ecosystem phosphorus (P) nutrition requires understanding of P fluxes. However, the P translocation in forest soils is not well understood and soil P fluxes based on actual measurements are rarely available. Therefore, the aims of this study were to (1) examine the effects of experimental N, P, and P+N additions on P fluxes via preferential flow as dominant transport pathway (PFPs) for P transport in forest soils; and (2) determine whether these effects varied with sites of contrasting P status (loamy high P/sandy low P). During artificial rainfall experiments, we quantified the P fluxes in three soil depths and statistically analyzed effects by application of linear mixed effects modeling. Our results show that the magnitude of P fluxes is highly variable: In some cases, water and consequently P has not reached the collection depth. By contrast, in soils with a well-developed connection of PFPs throughout the profile fluxes up to 4.5 mg P m−2 per experiment (within 8 h, no P addition) were observed. The results furthermore support the assumption that the contrasting P nutrition strategies strongly affected P fluxes, while also the response to N and P addition markedly differed between the sites. As a consequence, the main factors determining P translocation in forest soils under altered nutrient availability are the spatio-temporal patterns of PFPs through soil columns in combination with the P nutrition strategy of the ecosystem.

Effects of short-term nitrogen and phosphorus addition on leaf stoichiometry of a dominant alpine grass

The effects of increasing nitrogen (N) and phosphorus (P) deposition on the nutrient stoichiometry of soil and plant are gaining improving recognition. However, whether and how the responses of N cycle coupled with P of the soil–plant system to external N and P deposition in alpine grassland is still unclear. A short-term external N and P addition experiment was conducted in an alpine grazing grassland in the KunLun Mountain to explore the effects of short-term N and P addition on the nutrient stoichiometry in soil and plant. Different rates of N addition (ranging from 0.5 g N m−2 yr−1 to 24 g N m−2 yr−1) and P addition (ranging from 0.05 g N m−2 yr−1 to 3.2 g P m−2 yr−1) were supplied, and the soil available N, P, leaf N and P stoichiometry of Seriphidium rhodanthum which dominant in the alpine ecosystem were measured. Results showed that N addition increased soil inorganic N, leaf C, leaf N, and leaf N:P ratio but decreased soil available P and leaf C:P. Furthermore, P addition increased soil available P, leaf P, soil inorganic N, leaf N, and leaf C and reduced leaf C:N, C:P, and N:P ratios. Leaf N:P was positively related to N addition gradient. Leaf C:P and leaf N:P were significantly negatively related to P addition gradient. Although external N and P addition changed the value of leaf N:P, the ratio was always lower than 16 in all treatments. The influences of P addition on soil and plant mainly caused the increase in soil available P concentration. In addition, the N and P cycles in the soil–plant system were tightly coupled in P addition but decoupled in N addition condition. The nutrient stoichiometry of soil and leaf responded differently to continuous N and P addition gradients. These data suggested that the alpine grazing grassland was limited by P rather than N due to long-term N deposition and uniform fertilization. Moreover, increasing P addition alleviated P limitation. Therefore, the imbalanced N and P input could change the strategy of nutrient use of the grass and then change the rates of nutrient cycling in the alpine grassland ecosystem in the future.

Evaluation of phosphorous fixation capacity on river alluvium, beach ridge and coastal plain sand of Akwa ibom state, Nigeria

Phosphorous fixation capacities of selected parent materials in Akwa Ibom State were assessed. The soils used were those derived from river alluvium, beach ridge sand and coastal plain sand. These soils were incubated with four rates of P ranging from 0, 20, 40, 80 mgl-l prepared from KH2PO4 and incubated for 1, 7, 30, 60 and 90 days. The design was 3 x 4 factorial experiment (3 soil types and 4 rates of P) fitted into Completely Randomized Design (CRD) with three replications. At a set day, the exchangeable and water-soluble (available) P were extracted with Bray P – I extractant and P not extracted by this extractant was considered fixed in the soils, using fractional recovery of P to obtained. The results showed that the available P in the soils decrease with days of incubation. Beach ridge sand had the highest fractional recovery of P while river alluvium had the least. The trend were beach ridge sand (5.04 gkg-1) > coastal plain sand (2.34 gkg-1) > river alluvium (1.07 gkg-1). The recovery of P increase with increasing P addition. The fixing capacity of the soils increased in this order: river alluvium (97%) > coastal plain sand (92%) > beach ridge sand (84%). The result also revealed that the amount of P fixed increases with increasing rates of P addition.

Soil Respiration and N-Mineralization Processes in the Patagonian Steppe Are More Responsive to Nutrient Than to Water Addition

Aims: Soil respiration and N-mineralization are key processes in C and N cycling of terrestrial ecosystems. Both processes are limited by soil temperature, moisture and nutrient content in arid and cold ecosystems, but how nutrient addition interacts with water addition requires further investigation. This study addresses the effects of water and N+P additions on soil respiration and mineralization rates in the Patagonian steppe.Methods: We measured soil respiration and N-mineralization throughout seasons in control, fertilized, irrigated and irrigated-fertilized plots. We also analyzed root density and soil physico-chemical properties.Results: The soil CO2 effluxes in the Patagonian steppe were controlled by soil temperature, soil water content and root density. Increases in water addition had no effects on soil respiration, except when combined with N+P addition. However, soil nutrient enrichment without water addition enhanced soil respiration during the plant growing season. We found a linear positive relationship between root density and soil respiration, without interaction with treatments. N+P addition had negative impacts on N-mineralization, resulting in a strong N-immobilization. However, soil ammonium and nitrate content increased with N+P addition all over the seasons.Conclusion: Moderate increases in the precipitation through small pulses lead to no long-term response of soil processes in arid and cold Patagonian ecosystems. However, soil CO2 effluxes are likely to increase with nutrient additions, such as anthropogenic N deposition, and microbial biomass could retain more nutrients in the soil. Therefore, high levels of N enrichment in arid ecosystems may strengthen the positive feedback between C cycle and climate change.

Soil microbes influence nitrogen limit on the plant biomass of the alpine steppe, North Tibet

It is uncertain that plant biomass of grassland was co-limited by nitrogen (N) and phosphorus (P) or only limited by N or P. Moreover, it is also unclear why plant biomass was not limited by the P when the N was added at grassland ecosystem. The N and P additional experiment was conducted at the alpine steppe from 2013 to 2017. Results from analyzing response ratio of shoot biomass and leaf N and P concentration to N and P addition suggested that N is the main limiting factor for plant biomass of alpine steppe, and P is synergistic with N in contributing to biomass. Based on the N:P stoichiometry, plants have to increase P absorption due to N addition. Results of SEM analysis showed plant and fungi promoted the activity of phosphatase. At the same time, the abundance of fungi and saprotrophic group associated with decomposition were increased due to N addition, which would provide more P for plant. Those results suggested P deficit of plant due to N addition would be alleviated. Similarly, plant have to increase the N absorption when P was added. Although activity of urease was enhanced by soil microbes and plant, there was a little substrate for microbes because plant biomass was not increased due to P addition. Therefore, composition and function of soil microbes were affected by plant and soil N:P due to N addition, and then delivered P for plant, which will influence the effect of N on plant biomass at alpine steppe.

Responses of Root Endophytes to Phosphorus Availability in Peach Rootstocks With Contrasting Phosphorus-Use Efficiencies

Phosphorus (P) is an important macronutrient for all lives, but it is also a finite resource. Therefore, it is important to understand how to increase the P availability and plant uptake. The endophytes can help host plants to improve P uptake and will be apparently affected by plant genotypes. To investigate the mechanism of root endophytes in promoting P uptake of peach rootstocks, we analyzed the variations of the root endophytic fungal and bacterial communities of peach rootstocks with different P efficiencies under high or low level of P addition. Results showed that Proteobacteria was the dominant bacterial phylum in the roots of all rootstocks under the two levels of P addition. At low P level, the abundance of Actinoplanes in phosphorus-inefficiency root system was apparently higher than that at high P level. Actinoplanes produced important secondary metabolites, improving the stress resistance of plants. Under high P condition, the abundance of Ferrovibrio was higher in Qing Zhou Mi Tao than in Du Shi. Fe oxides considerably reduced the availability of applied P, which partially explained why the P utilization in Qing Zhou Mi Tao is inefficient. Further, Ascomycota was the dominant fungal phylum in the roots of all rootstocks under different levels of P addition. The fungi community of roots varied in different rootstocks at each P level, but was similar for the same rootstock at different P levels, which indicated that genotype had a greater effect than P addition on the fungal community of peach rootstocks.

Impact of nitrogen and phosphorus addition on resident soil and root mycobiomes in beech forests

N and P are essential macronutrients for all organisms. How shifts in the availability of N or P affect fungal communities in temperate forests is not well understood. Here, we conducted a factorial P × N fertilization experiment to disentangle the effects of nutrient availability on soil-residing, root-associated, and ectomycorrhizal fungi in beech (Fagus sylvatica) forests differing in P availability. We tested the hypotheses that in P-poor forests, P fertilization leads to enhanced fungal diversity in soil and roots, resulting in enhanced P nutrition of beech, and that N fertilization aggravates P shortages, shifting the fungal communities toward nitrophilic species. In response to fertilizer treatments (1 × 50 kg ha−1 P and 5 × 30 kg ha−1 N within 2 years), the labile P fractions increased in soil and roots, regardless of plant-available P in soil. Root total P decreased in response to N fertilization and root total P increased in response to P addition at the low P site. Ectomycorrhizal species richness was unaffected by fertilizer treatments, but the relative abundances of ectomycorrhizal fungi increased in response to P or N addition. At the taxon level, fungal assemblages were unaffected by fertilizer treatments, but at the order level, different response patterns for saprotrophic fungi among soil and ectomycorrhizal fungi on roots were found. Boletales increased in response to P, and Russulales decreased under N + P addition. Our results suggest that trait conservatism in related species afforded resistance of the resident mycobiome composition to nutritional imbalances.

Microstructural evolution of an Al–Mg–Si–Mn– Fe alloy due to Ti and P addition

This paper presents the results of research on material and microstructural effects in a hypoutectic Al–Mg– Si–Mn–Fe alloy, modified by the addition of Ti and Ti + P, in two series of castings, gravity and pressure. It has been found that the use of high pressure die casting technology allows for significant improvement of mechanical properties, especially tensile strength and plasticity of the examined alloy. On the other hand, the addition of Ti and Ti + P caused different material effects. In gravity castings, the addition of Ti and Ti + P caused a decrease in strength and plasticity, while in high-pressure castings, an increase in the values of these parameters was observed. The microstructural effects related to the foundry technology and those caused by Ti and P additions were revealed, such as differences in the phase composition of the interdendritic eutectics and in the morphology and dispersion of their phase constituents: Mg2Si and α-Al(Fe,Mn)Si.