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.

Influence of Long Term Fertilization and Manures on Soil Physical and Chemical Properties of Udorthentic Chromusterts

To study the effect of different nutrient management practices on different soil physical and chemical properties in the permanent manurial experiment field of Tamil Nadu Agricultural University, which was established during 1982 at Agriculture Research Station, Kovilpatti. Soil physical and chemical properties are mainly affected by the continuous application of fertilizers or manures from years together. To study the above mentioned properties of soil the soil samples were collected from the permanent manurial experiment of kovilpatti where the Randomized Block Design (RBD) was followed with nine different treatments viz., T1- Control; T2- 100 % RDF (40:20:40 NPK kg ha-1); T3- 50% RDF (20:10:20 NPK kg ha-1); T4- 50% N (Crop residues); T5- 50 % N (FYM); T6- 50 % Inorganic N+ 50% organic N (crop residues) + P (50%) + K (50%) ; T7- 50 % Inorganic N+ 50% organic N (FYM) + P (50%) + K (50%); T8- 100 % RDF + 25 kg ZnSO4 ha-1; T9- FYM - 12.5 t ha-1. The effect of these treatments along with the depth (0-15 cm; 15-30 cm and 30-45 cm) was compared. The treatment receiving organics viz., T9- FYM - 12.5 t ha-1 was observed to be the best in all the physical and chemical properties which was then followed by INM viz., T7- 50 % Inorganic N+ 50% organic N (FYM) + P (50%) + K (50%) and T6- 50 % Inorganic N+ 50% organic N (crop residues) + P (50%) + K (50%).

Different Relationships of Fine Root Traits With Root Ammonium and Nitrate Uptake Rates in Conifer Forests

Purpose: Nitrogen (N) uptake by fine roots of trees is important for understanding the root physiological function in forest ecosystems, but a direct investigation of in situ rate of ammonium and nitrate uptake is limited. Thus, we aimed to clarify the inorganic N uptake rates among tree species and to determine the factors controlling N uptake through relationships with fine root traits in cool temperate forests.Methods: Using a solution depletion method for measuring N uptake, we observed the relationship of N uptake rate in the form of NH4+ and NO3– by an intact root system with root morphological traits, such as root diameter, specific root length (SRL), and root tissue density (RTD), and chemical traits, including root nitrogen (N) content. Results: The coniferous roots in this study preferred NH4+ form more than NO3– form. Across species, there were significant relationships between NH4+ uptake and diameter, SRL, and RTD, while these were significant only for RTD in NO3– form. Relationships between N uptake rates and root morphological traits differed between NH4+ and NO3–. Conclusions: We found that the relationship of inorganic N uptake with the morphological traits depends on the characteristics of the N form adsorbed through soil and tree N assimilation efficiency. An approach on the relationships of in situ N uptake with root traits will provide a breakthrough in our understanding of the root physiological function and the prediction of fundamental N acquisition strategies.

Too Much of a Good Thing? Inorganic Nitrogen (N) Inhibits Moss-Associated N2 Fixation But Organic N Can Promote It

Moss-associated nitrogen (N2) fixation is one of the main inputs of new N in pristine ecosystems that receive low amounts of atmospheric N deposition. Previous studies have shown that N2 fixation is inhibited by inorganic N (IN) inputs, but if N2 fixation in mosses is similarly affected by organic N (ON) remains unknown. Here, we assessed N2 fixation in two dominant mosses in boreal forests (Pleurozium schreberi and Sphagnum capillifolium) in response to different levels of N, simulating realistic (up to 4 kg N ha−1 yr−1) and extreme N deposition rates in pristine ecosystems (up to 20 kg N ha−1 yr−1) of IN (NH4NO3) and ON (alanine and urea). We also assessed if N2 fixation can recover from the N additions. In the realistic scenario, N2 fixation was inhibited by increasing NH4NO3 additions in P. schreberi but not in S. capillifolium, and alanine and urea stimulated N2 fixation in both moss species. In contrast, in the extreme N additions, increasing N inputs inhibited N2 fixation in both moss species and all N forms. Nitrogen fixation was more sensitive to N inputs in P. schreberi than in S. capillifolium and was higher in the recovery phase after the realistic compared to the extreme N additions. These results demonstrate that N2 fixation in mosses is less sensitive to organic than inorganic N inputs and highlight the importance of considering different N forms and species-specific responses when estimating the impact of N inputs on ecosystem functions such as moss-associated N2 fixation.

Phosphorus Losses to Surface Runoff Waters After Application of Digestate to a Soil Over Fertilised with Phosphorus

Anaerobic digestates from biogas plants can be used as agricultural fertilisers providing recycling nitrogen (N) and other nutrients for crop needs. It is still unclear the impact on phosphorus (P) losses to runoff waters of digestates as sources of N instead of inorganic N fertilisers in over fertilised soils with P. A field experiment was done in a sandy and acidic soil high in P. The experimental design was completely randomised with five treatments. The inorganic N fertilisation (90 kg ha−1) was done in four treatments, those with past P inputs of the following: (i) inorganic N and P fertilisers (Ni/MF), (ii) organic amendments (pig or duck dry slurry-Ni/PS and Ni/DS or cattle manure compost-Ni/CM). Digestate was applied in plots with past P input of cattle slurry (DG/CS) providing also 90 kg N ha−1. Ryegrass was sowed as cover crop. The concentration of total dissolved P in runoff waters was high in all treatments and ranged between 0.5 (Ni/PS) and 2.6 mg L−1 (DG/CS). These runoff waters pose a risk of non-source P pollution for fresh waters. In soils with low P sorption capacity and over fertilised with P, the fertilisation with anaerobic digestate as the only source of N to crops increased the risk of P losses to runoff waters compared with inorganic N fertilisation. Therefore, the amount of digestate applied to soil must be calculated considering its N:P ratio in order to not exceed the crop P requirement.

Ectomycorrhizal access to organic nitrogen mediates CO2 fertilization response in a dominant temperate tree

Plant–mycorrhizal interactions mediate plant nitrogen (N) limitation and can inform model projections of the duration and strength of the effect of increasing CO2 on plant growth. We present dendrochronological evidence of a positive, but context-dependent fertilization response of Quercus rubra L. to increasing ambient CO2 (iCO2) along a natural soil nutrient gradient in a mature temperate forest. We investigated this heterogeneous response by linking metagenomic measurements of ectomycorrhizal (ECM) fungal N-foraging traits and dendrochronological models of plant uptake of inorganic N and N bound in soil organic matter (N-SOM). N-SOM putatively enhanced tree growth under conditions of low inorganic N availability, soil conditions where ECM fungal communities possessed greater genomic potential to decay SOM and obtain N-SOM. These trees were fertilized by 38 years of iCO2. In contrast, trees occupying inorganic N rich soils hosted ECM fungal communities with reduced SOM decay capacity and exhibited neutral growth responses to iCO2. This study elucidates how the distribution of N-foraging traits among ECM fungal communities govern tree access to N-SOM and subsequent growth responses to iCO2.

Nitrogen species specific phosphorus mineralization in temperate floodplain soils

As an essential component of enzymes, higher N availability from agricultural runoff to forest soils may boost the activity of phosphatase, increasing the bioavailability of phosphate. The objective of this study was to evaluate P mineralization rates in temperate floodplain soils as a function of inorganic N species (i.e., ammonium and nitrate) and amendment rate (1.5–3.5 g N kg−1). Accordingly, the soil was amended with nitrate and ammonium, and P dynamics were monitored during a 40-day incubation. The addition of ammonium significantly boosted acid and alkaline phosphatase activity by 1.39 and 1.44 µmol p-nitrophenol P (pNP) g−1 h−1, respectively. The degree of increase was positively correlated with the amendment rate. Likewise, the P mineralization rate increased by 0.27 mg P kg−1 in the 3.5 g N kg−1 ammonium treatment. 31P nuclear magnetic resonance spectroscopic analysis further supported the reduction in organic orthophosphate diesters on day 30. Meanwhile, the addition of nitrate promoted P mineralization to a lesser degree but did not increase phosphatase activity. While floodplain soils have great potential to sequester anthropogenic P, high availability of inorganic N, especially ammonium, could promote P mineralization, potentially increasing P fertility and/or reducing P the sequestration capacity of floodplain soils.