Changes in Community Composition Following Secondary Succession of a Temperate Oak-hornbeam Forest After Grassland Abandonment and Their Effect on Soil Carbon and Nutrient Pools

To date, changes in C and nutrient cycling during succession are somewhat studied, however, results are often contrasting for different nutrients and successional sequences. Generally, due to increment of litter rich in lignocellulosic components during late succession, mineralization of nutrients is expected to decelerate, and large amounts of nutrients become captivated within tree biomass. We investigated the changes in community composition following secondary succession of oak-hornbeam forest after grassland abandonment, along with the differences in soil chemistry between early- and late- successional stages. We aimed to discover whether late succession increases soil organic C and total N and S pool, but decreases the pools of plant available P and K, and that of micronutrients due to their captivation within the tree biomass.The successional sequence studied had a following pathway: Helictotrichon pubescens haypastures à Brachypodium pinnatum successional grasslands à Cornus sanguinea scrubs à late-successional Populus tremula forests à late-successional oak-hornbeam (Quercus-Carpinus) forests. Total species number was highest in haypastures and lowest in late-successional P. tremula forest. Species richness of haypastures was higher from that of mid-successional scrub and late-successional forest stages. Species richness did not differ between mid-successional scrub and late-successional forest stages. Occurrences of plant species throughout secondary succession was mostly stage-specific; only Fragaria vesca, Ajuga reptans, Cornus sanguinea, Prunus spinosa, and Viola hirta showed survival ability throughout almost all stages. Late-successional forest stages had a higher soil organic carbon (SOC), soil organic matter (SOM), and KA concentration, along with the higher soil C:N and C:S ratio in A horizon compared to early-successional grassland stages, whereas concentrations of plant available P and total N, S, Mn, Zn, Ni, Cu, and Fe remained unaltered.Even though late-successional forest stages tighten the nutrient cycles through nutrient captivation within the tree biomass, we found that late succession efficiently retained PA and micronutrient pools and even increased KA concentration in the A horizon, despite the fact that great amounts of these nutrients were already excluded from the nutrient cycle. Despite the contradicting C inputs, soil total N and S concentration did not differ between late-successional forest and early-successional grassland stages.

Changes in Community Composition Following Secondary Succession of a Temperate Oak-hornbeam Forest After Grassland Abandonment and Their Effect on Soil Carbon and Nutrient Pools

BackgroundTo date, changes in C and nutrient cycling during succession are somewhat studied, however, results are often contrasting for different nutrients and successional sequences. Generally, due to increment of litter rich in lignocellulosic components during late succession, mineralization of nutrients is expected to decelerate, and large amounts of nutrients become captivated within tree biomass. We investigated the changes in community composition following secondary succession of oak-hornbeam forest after grassland abandonment, along with the differences in soil chemistry between early- and late- successional stages. We aimed to discover whether late succession increases soil organic C and total N and S pool, but decreases the pools of plant available P and K, and that of micronutrients due to their captivation within the tree biomass. ResultsThe successional sequence studied had a following pathway: Helictotrichon pubescens haypastures à Brachypodium pinnatum successional grasslands à Cornus sanguinea scrubs à late-successional Populus tremula forests à late-successional oak-hornbeam (Quercus-Carpinus) forests. Total species number was highest in haypastures and lowest in late-successional P. tremula forest. Species richness of haypastures was higher from that of mid-successional scrub and late-successional forest stages. Species richness did not differ between mid-successional scrub and late-successional forest stages. Occurrences of plant species throughout secondary succession was mostly stage-specific; only Fragaria vesca, Ajuga reptans, Cornus sanguinea, Prunus spinosa, and Viola hirta showed survival ability throughout almost all stages. Late-successional forest stages had a higher soil organic carbon (SOC), soil organic matter (SOM), and KA concentration, along with the higher soil C:N and C:S ratio in A horizon compared to early-successional grassland stages, whereas concentrations of plant available P and total N, S, Mn, Zn, Ni, Cu, and Fe remained unaltered.ConclusionsEven though late-successional forest stages tighten the nutrient cycles through nutrient captivation within the tree biomass, we found that late succession efficiently retained PA and micronutrient pools and even increased KA concentration in the A horizon, despite the fact that great amounts of these nutrients were already excluded from the nutrient cycle. Despite the contradicting C inputs, soil total N and S concentration did not differ between late-successional forest and early-successional grassland stages.

Forest Soil Colloids Enhance Delivery of Phosphorus Into a Diffusive Gradient in Thin Films (DGT) Sink

Phosphorus (P) is preferentially bound to colloids in soil. On the one hand, colloids may facilitate soil P leaching leading to a decrease of plant available P, but on the other hand they can carry P to plant roots, thus supporting the P uptake of plants. We tested the magnitude and the kinetics of P delivery by colloids into a P sink mimicking plant roots using the Diffusive Gradients in Thin-Films (DGT) technique. Colloids were extracted with water from three forest soils differing in parent material using a method based on dispersion and sedimentation. Freeze-dried colloids, the respective bulk soil, and the colloid-free extraction residue were sterilized and mixed with quartz sand and silt to an equal P basis. The mixtures were wetted and the diffusive fluxes of P into the DGTs were measured under sterile, water unsaturated conditions. The colloids extracted from a P-poor sandy podzolic soil were highly enriched in iron and organic matter compared to the bulk soil and delivered more P at a higher rate into the sink compared to bulk soil and the colloid-free soil extraction residue. However, colloidal P delivery into the sink was smaller than P release and transport from the bulk soil developed on dolomite rock, and with no difference for a soil with intermediate phosphorus-stocks developed from gneiss. Our results provide evidence that both the mobility of colloids and their P binding strength control their contribution to the plant available P-pool of soils. Overall, our findings highlight the relevance of colloids for P delivery to plant roots.

Changes and Interactions between Grassland Ecosystem Soil and Plant Properties under Long-Term Mineral Fertilization

Grasslands intensification by use of mineral fertilization has contributed substantially to the increase in forage production. Intensification, however, can degrade the other beneficial functions or soil properties. The effects of mineral fertilization on soil and plant chemical qualities of a permanent wet grassland (Festucetum pratense association) were investigated in Slovakia. The grassland was treated using 3 different N, P, and K rates of mineral fertilizers in kg. ha−1. yr−1 plus the Control (0NPK) almost over 60-year period (1961–2017). The N, P, and K rates in low NPK treatment (LNPK) were N50, P15.4, and K 41.5, in the medium NPK treatment (MNPK) were N100, P30.8, and K83, and in the high NPK treatment (HNPK) were N200, P 61.6, and K 166, respectively. Overall, soil variables (pH, soil organic carbon, plant-available K) showed the most significant changes. A more balanced development was observed in case of soil total nitrogen, C:N ratio, and plant-available P. ANOVA revealed a significant effect between treatments only on plant-available P. In the case of plant functional group development, long-term mineral addition significantly disfavors legumes and forbs. However, analyses of the botanical composition over the last 5 years showed that legume cover significantly differs only in the HNPK treatment. Plant C:P, N:P, and N:K ratios were significantly reduced when fertilizers were added. In terms of grasslands yields, the highest biomass and content of macronutrients were obtained under the HNPK rates. However, with regard to the quality and quantity of the soil organic matter, the most appropriate treatment has been with the MNPK rates. Our findings demonstrate that medium fertilization seems to be an acceptable compromise to meet both productivity and environmental aspects and to connect ecological benefits with social benefits in the long term.

Depletion, accumulation and availability of soil phosphorus in the Askov long-term field experiment

Soil phosphorus (P) reserves, built up over decades of intensive agriculture, may account for most of the crop P uptake, provided adequate supply of other plant nutrients. Whether crops grown on soils with reduced supply of other nutrients obtain similar use-efficiency of soil P reserves remains unclear. In treatments of the Askov Long-Term Experiment (initiated in 1894 on light sandy loam), we quantified changes in soil total P and in plant-available P (Olsen P, water extractable P and P offtake in wheat grains) when P-depleted soil started receiving P in rock phosphate and when P application to soil with moderate P levels ceased during 1997–2017. Additionally we studied treatments with soil kept unfertilised for >100 years and with soil first being P depleted and then exposed to surplus dressings of P, nitrogen (N) and potassium in cattle manure. For soil kept unfertilised for >100 years, average grain P offtake was 6 kg ha–1 and Olsen P averaged 4.6 mg kg–1, representing the lower asymptotic level of plant-available P. Adding igneous rock phosphate to severely P-depleted soil with no N fertilisation had little effect on Olsen P, water extractable P (Pw), grain yields and P offtake. For soils with moderate levels of available P, withholding P application for 20 years reduced contents of Olsen P by 56% (from 16 to 7 mg P kg–1) and of Pw by 63% (from 4.5 to 1.7 mg P kg–1). However, the level of plant-available P was still above that of unfertilised soil. Application of animal manure to P-depleted soil gradually raised soil P availability, grain yield and P offtake, but it took 20 years to restore levels of plant-available P. Our study suggests symmetry between rates of depletion and accumulation of plant-available P in soil.

Sensitivity of Three Phosphate Extraction Methods to the Application of Phosphate Species Differing in Immediate Plant Availability

Extractive tests for determining the plant-availability of soil phosphorus (P) give varying results due to the inherently different characteristics of the extraction solution. Generally, classical soil P tests such as the Olsen or calcium acetate/lactate (CAL) method do not give an indication on the total amount of plant available P, but merely give an indication of the equilibrium between soil and extraction solution. It is also not entirely clear which fractions of P are directly determined through the various methods of extraction, i.e., determined P must not be immediately plant available, as is the case for rock phosphate. It is therefore possible that extraction methods either over or under estimate the amount of P available for plant consumption. In this research, we compared three methods of soil P determination (CAL, Olsen and diffusive gradients in thin films (DGT)) with regards to their ability to determine P species (Ca(H2PO4)2, CaHPO4, Ca3(PO4)2 and Inositol-6-hexakisphosphate) added to soils of high sorption capacity, immediately after as well as two weeks after application. For each of the methods, it could be shown that sorption processes in the soil immediately (0 days incubation) fix P to a point where it is not extractable through any of the described methods. These sorption processes continue over time, leading to a further decrease of determined P. The acidic CAL extraction method gives higher results of extractable P compared to the Olsen method. Due to the extraction of Ca3(PO4)2, the CAL method may overestimate immediately plant-available P. The most suitable methods for the determination of immediately plant available P may therefore be the Olsen and DGT methods. Organic IP6 is not determined by any of the extraction methods. At low concentrations of soil P, the DGT method may fail to give results.

The use of isometric log ratios to classify phosphorus attributes in composts

This research aimed to classify 16 horticultural composts collected across Canada into management group according to their phosphorus (P) fractions and carbon (C) content using isometric log ratio (ilr) and to interpret the clusters against the total P content and C-to-P ratio indices. The ilr approach was found to be more discriminant for grouping the composts compared with the conventional statistical analysis. The C-to-P ratio index was representative of cluster 1 only. This cluster included organic amendments with C-to-P ratios higher than 100 and high capacity to increase soil organic matter content without excessive P dosage. Total P separated clusters 2 and 3 despite the amalgamation of P forms into total P. Cluster 2 showed high total P (>10 g P kg−1) and low C-to-P ratios (24–38), whereas cluster 3 showed variable C-to-P ratios (18–78) and total P <9 g kg−1after excluding one compost close to cluster 2. Clusters 2 and 3 were considered as potential sources of plant-available P. The ilr approach suggests that composts made of municipal biosolids and poultry manures in cluster 2 have the highest potential as plant-available P source compared with those made of other livestock manures or food processing wastes.

What is the P value of Siberian soils? Soil phosphorus status in south-western Siberia and comparison with a global data set

Climate change is particularly strong in northern Eurasia and substantial ecological changes are expected in this extensive region. The reshaping and migration northwards of bioclimatic zones may offer opportunities for agricultural development in western and central Siberia. However, the bioclimatic vegetation models currently employed for projections still do not consider soil fertility, in spite of this being highly critical for plant growth. In the present study, we surveyed the phosphorus (P) status in the south-west of Siberia where soils have developed on loess parent material. We selected six sites differing in pedoclimatic conditions and the soil was sampled at different depths down to 1 m in aspen (Populus tremula L.) forest as well as in grassland areas. The P status was assessed by conventional methods and by isotope dilution kinetics. We found that P concentrations and stocks, as well as their distribution through the soil profile, were fairly homogeneous on the regional scale studied, although there were some differences between sites (particularly in organic P). The young age of the soils, together with slow kinetics of soil formation processes have probably not yet resulted in a sufficiently wide range of soil physico-chemical conditions to observe a more diverging P status. The comparison of our data set with similar vegetation contexts on the global scale revealed that the soils of south-western Siberia, and more generally of northern Eurasia, often have (very) high levels of total, organic and inorganic P. The amount of plant-available P in topsoils, estimated by the isotopically exchangeable phosphate ions, was not particularly high but was intermediate on the global scale. However, large stocks of plant-available P are stored in subsurface layers which currently have low fine-root exploration intensities. These results suggest that the P resource is unlikely to constrain vegetation growth and agricultural development under the present conditions or in the near future.