Global patterns and drivers of soil total phosphorus concentration

Soil represents the largest phosphorus (P) stock in terrestrial ecosystems. Determining the amount of soil P is a critical first step in identifying sites where ecosystem functioning is potentially limited by soil P availability. However, global patterns and predictors of soil total P concentration remain poorly understood. To address this knowledge gap, we constructed a database of total P concentration of 5275 globally distributed (semi-)natural soils from 761 published studies. We quantified the relative importance of 13 soil-forming variables in predicting soil total P concentration and then made further predictions at the global scale using a random forest approach. Soil total P concentration varied significantly among parent material types, soil orders, biomes, and continents and ranged widely from 1.4 to 9630.0 (median 430.0 and mean 570.0) mg kg−1 across the globe. About two-thirds (65 %) of the global variation was accounted for by the 13 variables that we selected, among which soil organic carbon concentration, parent material, mean annual temperature, and soil sand content were the most important ones. While predicted soil total P concentrations increased significantly with latitude, they varied largely among regions with similar latitudes due to regional differences in parent material, topography, and/or climate conditions. Soil P stocks (excluding Antarctica) were estimated to be 26.8 ± 3.1 (mean ± standard deviation) Pg and 62.2 ± 8.9 Pg (1 Pg = 1 × 1015 g) in the topsoil (0–30 cm) and subsoil (30–100 cm), respectively. Our global map of soil total P concentration as well as the underlying drivers of soil total P concentration can be used to constraint Earth system models that represent the P cycle and to inform quantification of global soil P availability. Raw datasets and global maps generated in this study are available at https://doi.org/10.6084/m9.figshare.14583375 (He et al., 2021).

Effect of biochar applications on soil phosphorus availability under different soil moisture levels

Soil moisture level is crucial to soil phosphorus (P) availability. However, there is no quantitative research on the relation between soil P availability and moisture level. In addition, biochar application could also alter soil P availability at different moisture levels. In this study, a 16-day soil incubation experiment was conducted at a laboratory-scale to analyze the effects of soil moisture and P fertilization regimes (P-laden biochar fertilizer and conventional mineral P fertilizer) on soil P availability and fractionation. The results showed that soil P availability was positively correlated with soil moisture level (Pearson coefficients ranged from 0.46 to 0.91). High moisture level would lead to less amount of P in readily available fractions under P-laden biochar application. However, even with less P in readily available fractions, P-laden biochar could maintain soil P availability (117.7 mg P m-2) at a similar level as the conventional P fertilizer (116.1 mg P m-2).

Enhancement of Soil Phosphorus Bioavailability by Arbuscular Mycorrhizae and Earthworms Through Regulating Soil Bacterial Community and Plant Nutrient Balance Under Salt Stress

Aims Soil salinization is an important factor limiting plant phosphorus (P) uptake and crop production. This study aimed to investigate the effects of arbuscular mycorrhizal fungi (AMFs) and earthworms in enhancing soil P bioavailability by regulating soil salt ions and altering the soil bacterial community under salt stress. Methods Treatments with or without earthworms and with or without AMFs in a high-salinity soil were applied. Results The results showed that the maize biomass and plant P, Ca and Mg contents were significantly increased by earthworms and AMF inoculation, and the highest plant P, Ca and Mg contents were observed with earthworm application alone. Earthworms and AMFs significantly decreased the soil stable inorganic P (hydroxyapatite) proportion and increased the soil available dicalcium phosphate proportion. AMFs significantly increased soil phosphatase activity and inorganic P fraction contents. Earthworms and AMFs significantly increased soil bacterial Chao1 and phylogenetic diversity. Structural equation model analysis showed that the most important driver of soil P mineralization was soil bacterial diversity, followed by soil Ca2+ and total salt concentration. Network analysis suggested that the response of bacteria to soil Ca2+ but not salt concentration positively correlated with soil P availability. Earthworms and AMFs could stimulate certain bacteria harbouring the phoX alkaline phosphatase gene to increase soil phosphatase activity and soil P availability. Conclusions In conclusion, earthworms and AMFs could enhance soil P bioavailability by stimulating soil P-cycling bacteria to activate soil stable inorganic P and by improving the plant cation nutrient balance under salt stress.

Phosphorus regulates ecosystem carbon dynamics after permafrost thaw

<p>The ecosystem carbon (C) dynamics after permafrost thaw depends on more than just climate change since soil nutrient status may also impact ecosystem C balance. It has been advocated that the potential nitrogen (N) release upon permafrost thaw could promote plant growth and thus offset soil C loss. However, compared with the widely accepted C-N interactions, little is known about the potential role of soil phosphorus (P) availability. Here we combined two-year field observations along a permafrost thaw sequence (constituted by four thaw stages, <em>i</em>.<em>e</em>., non-collapse and 5, 14, and 22 years since collapse) with an in-situ fertilization experiment (included N and P additions at the level of 10 g N m<sup>-2</sup> yr<sup>-1</sup> and 10 g P m<sup>-2</sup> yr<sup>-1</sup>, respectively) in a Tibetan swamp meadow to evaluate ecosystem C-nutrient interactions upon permafrost thaw. Our results showed that changes in soil P availability rather than N availability played an important role in regulating the increases in gross primary productivity and the decreases in net ecosystem exchange along the thaw sequence. The fertilization experiment further confirmed that P addition had stronger effects on plant growth than N addition in this permafrost ecosystem. These two lines of evidence highlight the crucial role of soil P availability in altering the trajectory of permafrost C cycle under climate warming.</p>

Foliar nutrient-allocation patterns in Banksia attenuata and Banksia sessilis differing in growth rate and adaptation to low-phosphorus habitats

Background and aims Phosphorus (P) and nitrogen (N) are essential nutrients that frequently limit primary productivity in terrestrial ecosystems. Efficient use of these nutrients is important for plants growing in nutrient-poor environments. Plants generally reduce foliar P concentration in response to low soil P availability. We aimed to assess ecophysiological mechanisms and adaptive strategies for efficient use of P in Banksia attenuata (Proteaceae), naturally occurring on deep sand, and B. sessilis, occurring on shallow sand over laterite or limestone, by comparing allocation of P among foliar P fractions. Methods We carried out pot experiments with slow-growing B. attenuata, which resprouts after fire, and faster-growing opportunistic B. sessilis, which is killed by fire, on substrates with different P availability using a randomised complete block design. We measured leaf P and N concentrations, photosynthesis, leaf mass per area, relative growth rate, and P allocated to major biochemical fractions in B. attenuata and B. sessilis. Key results The two species had similarly low foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with concentrations of both foliar nucleic acid P and total N, but there was no correlation with other P fractions. Faster-growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar. Conclusions The nutrient-allocation patterns in faster-growing opportunistic B. sessilis and slower-growing B. attenuata revealed different strategies in response to soil P availability which matched their contrasting growth strategy.