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Background and aims Soil phosphorus (P) can often regulate plant productivity. However, the medium- to long-term effects of reforestation on P cycle within the continuum of plant, litter, and soil (including deep soil layers), and the subsequent regulation of soil P storage and its fractions, remain unclear. Methods We determined soil (0–100 cm) P fractions, acid phosphatase, stoichiometric ratios, root and leaf N/P ratios, leaf P resorption efficiency (PRE), and leaf-litter P concentration of 32-, 45-, and 60-year-old Pinus massoniana reforestation in southwest China. Results The storage of soil labile, moderately labile, and occluded P decreased with the increase of stand age. The concentration of NaHCO 3 -P i , NaHCO 3 -P o , and total labile P in top-soil layers decreased with the increase of stand age. The concentration of NaOH-P o and total moderately labile P in the entire soil profile declined over time. The concentration of C.HCl-P i and total occluded P in the 0–100 cm soil layer were lower in the 60-year-old stand than in the 32-year-old stand. The PRE, leaf N/P ratio, top-soil C/P ratio and acid phosphatase activity increased, and the leaf-litter P concentration decreased with the increase of stand age. Conclusions P. massoniana trees secreted more acid phosphatase and increased PRE to compensate for the decrease in soil P availability with stand development, which in turn decreased leaf-litter P concentration and thus resulted in a depletion of soil P. Overall, our results highlighted that P limitation of P. massoniana reforestation increased with stand development.

Phosphorus, as a key nutrient, plays an essential role in both algal growth in surface waters and crop development on land. Its presence in inorganic fertilizers is crucial for maximizing crop yields. However, an excessive accumulation of phosphorus in soils can lead to its loss and exacerbate eutrophication in water bodies. This study highlights the complex interplay among phosphorus management, agricultural productivity, and environmental health, particularly in the context of climate change’s influence on sediment transport and water pollution. We focus on the Poyang Lake Basin (PLB) and use a sophisticated process-based phosphorus model to forecast phosphorus load trends from 2020 to 2049. Our predictions indicate a significant increase in the total phosphorus load of the PLB due to the impact of climate change. To address these challenges, we explore a novel strategy combining organic and inorganic phosphorus fertilizers. This approach aims to improve crop yields while reducing non-point source phosphorus pollution through adjusted anthropogenic inputs. Our findings reveal that a synergistic application of these fertilizers, coupled with a controlled use of inorganic phosphate, can reduce its usage by more than 2.5% annually. This method not only contributes to a 2.2% average annual increase in livestock and poultry production but also promotes a 0.6% yearly growth in grain output. Consequently, it effectively diminishes non-point source phosphorus pollution, offering a sustainable solution to the dual challenge of enhancing agricultural productivity and protecting environmental health.

Riverine phosphorus (P) levels in headwaters are a worldwide concern for environmental management due to the sensitivity of freshwater ecosystems to phosphorus loads. Here, we evaluate P in the Huai River Basin of China, a watershed with one of the highest intensities of human-activity in the world. Estimates of net anthropogenic phosphorus inputs (NAPI) were obtained by accounting for the main anthropogenic phosphorus inputs in each watershed of the basin, including fertilizer application, net food and feed import, non-food P and seeding P. Multi-year average (2003–2010) anthropogenic inputs of P to the entire basin were 2700 kg P km⁻² year⁻¹, with an average amount of 1800 kg P km⁻² year⁻¹ entering its 17 headwater watersheds. Fertilizer application was the largest source of new P across the headwater watersheds (about 70 % of NAPI), followed by P content of imported food and feed (24 %) and non-food P (6 %). Riverine total phosphorus (TP) fluxes showed a significant linear relationship with NAPI, with an average 3.2 % of NAPI exported as riverine TP flux. Our result indicates that NAPI could be a good indicator for assessing the risk of regional P loss, as well as an excellent potential predictor of riverine TP flux. A comparison of our results with other similar analyses suggests that around 3 % of NAPI would be exported as riverine TP loads, although fractional export of P may vary significantly regionally. Corresponding P management should be targeted at the main anthropogenic sources and hot-spot areas.

Riverine nitrogen export (RNE) and riverine phosphorus export (RPE) are the cumulative results of regional anthropogenic nitrogen and phosphorus inputs combined with land use and hydrological changes that primarily drive the eutrophication of downstream water bodies. This study focuses on the characteristics of high nitrogen and phosphorus concentrations as well as low discharge in rivers in arid regions, using the Liao River in northern China as an example. The spatiotemporal patterns of net anthropogenic nitrogen input (NANI) and net anthropogenic phosphorus input (NAPI) in the Liao River Basin during 2010 to 2020 were investigated. Results indicated that the multi-year averages for NANI and NAPI were 9453 kg N km −2 yr −1 and 1916 kg P km −2 yr −1 , respectively. Our predictive models constructed based on the aforementioned influencing factors, explained 67% and 75% of the variations in RNE and RPE, respectively. Unlike previous studies, only a small portion of NANI and NAPI was exported through rivers. The RNE and RPE were 37 kg N km −2 ·yr −1 and 2 kg P km −2 ·yr −1 , accounting for 0.42% of NANI and 0.12% of NAPI. RNE and RPE were significantly influenced by discharge and precipitation. The cropland ratio influenced the output ratio of NANI, whereas RPE was mainly influenced by the NAPI of developed land.

Human activities have greatly influenced the inputs and cycling pathways of nitrogen (N) and phosphorus (P), causing dramatic environmental problems in the Pearl River Basin. In this study, the characteristics of net anthropogenic nitrogen and phosphorus inputs (NANI/NAPI) were analyzed in the Guangdong section of the Pearl River Basin from 2016 to 2020. NANI showed a very slight decrease trend from (1.51 ± 0.09) × 104 to (1.36 ± 0.08) × 104 kg·N·km−2·yr−1, while the average intensity of NAPI was 3.8 × 103 kg·P·km−2·yr−1. Both NANI and NAPI intensities were at high levels, resulting in the serious deterioration of water quality in the Pearl River Basin. Fertilizer input was the most important component for the intensities of NANI and NAPI, accounting for 38–42% and 53–56%. However, in the Pearl River Delta, the major components of NANI and NAPI were the human and animal consumption (food/feed) inputs and non-food net phosphorus input. The input of NANI and NAPI should be controlled for different areas, based on the differing driving forces, to alleviate the deterioration of water quality. This study of NANI and NAPI in the Pearl River Basin is one of the important prerequisites for clarifying the input and water quality, providing support for further effective control of nitrogen and phosphorus pollution in the Pearl River.

Nitrogen (N) deposition from human activities leads to an imbalance in the N and phosphorus (P) ratios of natural ecosystems, which has a series of negative impacts on ecosystems. In this study, we used 16s rRNA sequencing technology to investigate the effect of the N-P supply ratio on the bulk soil (BS) and rhizosphere soil (RS) bacterial community of halophytes in coastal wetlands through manipulated field experiments. The response of soil bacterial communities to changing N and P ratios was influenced by plants. The N:P ratio increased the α-diversity of the RS bacterial community and changed the structure of the BS bacterial community. P addition may increase the threshold, causing decreased α-diversity of the bacterial community. The co-occurrence network of the RS community is more complex, but it is more fragile than that of BS. The co-occurrence network in BS has more modules and fewer network hubs. The increased N:P ratio can increase chemoheterotrophy and denitrification processes in the RS bacterial community, while the N:P ratio can decrease the N-fixing processes and increase the nitration processes. The response of the BS and the RS bacterial community to the N:P ratio differed, as influenced by soil organic carbon (SOC) content in terms of diversity, community composition, mutualistic networks, and functional composition. This study demonstrates that the effect of the N:P ratio on soil bacterial community is different for plant roots and emphasizes the role of plant roots in shaping soil bacterial community during environmental change.

This study employed the Net Anthropogenic Phosphorus Inputs (NAPI) model to assess the impact of human activities on phosphorus input in a watershed, analyzing county-level statistical data and NAPI model parameters from 1991 to 2020. The Monte Carlo method was used for a quantitative analysis of the model parameters’ effects on each NAPI component and the overall simulation results. The sensitivity index method identified each component’s sensitive parameters. The study found that the lowest NAPI value was 454 kg/(km²·a) in 1991 and the highest was 1336 kg/(km²·a) in 2003. NAPI in Ningxia showed an overall upward trend from 1991 to 1999, a slight decrease from 1999 to 2003, and a slight increase from 2003 to 2020, with fertilizer being the main contributing factor, accounting for 77.4% of the total input. On a spatial scale, NAPI in Ningxia was significantly correlated with land use patterns, showing higher values in the northern and southern regions compared to the central part. The NAPI values derived from Monte Carlo simulations with appropriate parameters ranged from −24.83% to 31.49%. The study highlighted the net food and feed imports component as having the highest uncertainty, impacting simulation results within a range of −23.89% to 53.98%. It was observed that the larger a component’s proportion in the NAPI model, the more sensitive its parameters, with the phosphorus fertilizer (Pfer) component’s parameters being notably more sensitive than those of the food/feed phosphorus input and the non-food phosphorus input (Pnf) components. These findings can inform phosphorus pollution control policies in Northwest China, while the selection of sensitive parameters provides a useful reference for future NAPI research in other regions.

Responses of zooplankton, pelagic primary producers, planktonic bacteria, and CO2 exchange with the atmosphere were measured in four lakes with contrasting food webs under a range of nutrient enrichments during a seven-year period. Prior to enrichment, food webs were manipulated to create contrasts between piscivore dominance and planktivore dominance. Nutrient enrichments of inorganic nitrogen and phosphorus exhibited ratios of N:P > 17:1, by atoms, to maintain P limitation. An unmanipulated reference lake, Paul Lake, revealed baseline variability but showed no trends that could confound the interpretation of changes in the nearby manipulated lakes. Herbivorous zooplankton of West Long Lake (piscivorous fishes) were large-bodied Daphnia spp., in contrast to the small-bodied grazers that predominated in Peter Lake (planktivorous fishes). At comparable levels of nutrient enrichment, Peter Lake's areal chlorophyll and areal primary production rates exceeded those of West Long Lake by factors of approximately three and six, respectively. Grazers suppressed pelagic primary producers in West Long Lake, relative to Peter Lake, even when nutrient input rates were so high that soluble reactive phosphorus accumulated in the epilimnions of both lakes during summer. Peter Lake also had higher bacterial production (but not biomass) than West Long Lake. Hydrologic changes that accompanied manipulation of East Long Lake caused concentrations of colored dissolved organic carbon to increase, leading to considerable variability in fish and zooplankton populations. Both trophic cascades and water color appeared to inhibit the response of primary producers to nutrients in East Long Lake. Carbon dioxide was discharged to the atmosphere by Paul Lake in all years and by the other lakes prior to nutrient addition. During nutrient addition, only Peter Lake consistently absorbed CO2 from the atmosphere, due to high rates of carbon fixation by primary producers. In contrast, CO2 concentrations of West Long Lake shifted to near-atmospheric levels, and net fluxes were near zero, while East Long Lake continued to discharge CO2 to the atmosphere.

IntroductionThe effects of nitrogen (N) and phosphorus (P) addition on soil microbial diversity have been widely studied, however, the response of bacterial community to N and P imbalance input remains unclear.MethodsUsing a high-throughput Illumina Miseq sequencing platform, N and P imbalance addition experiment was conducted to characterize the rhizosphere and bulk soil bacterial community of Suaeda salsa (S. salsa) in the Yellow River Delta.ResultsThe results showed that the rhizosphere soil bacterial community α-diversity was significantly higher than bulk soil. The rhizosphere soil Bacteroidetes and Actinobacteria were higher and lower than bulk soil, respectively. N and P imbalance input had small effects on the composition and α -bacterial diversity of the rhizosphere soil, while significantly increasing the bulk soil bacterial diversity and remarkably changing the community composition. Differences in the response of rhizosphere and bulk soil bacterial community to N and P imbalance input were caused by soil organic matter (SOM) content. The N and P imbalance input increased the relative abundance of bulk soil Eutrophic bacteria and decreased the relative abundance of the predicted oligotrophic bacteria (Acidobacteria,Chorolflexi). Rhizosphere and bulk soil bacterial community α-diversity was significantly correlated with SOM, salt, total carbon (TC) and total N (TN) content, with SOM and salt having the greatest effect on bulk soil bacterial community composition.DiscussionThere may be a threshold N-P input ratio between 15:1 and 45:1. This threshold is the optimal ratio for increasing the diversity of bacterial community.

We analyzed management policies for ecosystems subject to alternate states, thresholds, and irreversible changes. We focused on the problem of lake eutrophication by excessive phosphorus (P) input. Eutrophic lakes may be classified, with respect to their response to reduced P input alone, as reversible (recovery is immediate and proportional to the reduction in P input), hysteretic (recovery requires extreme reductions in P input for a period of time), or irreversible (recovery cannot be accomplished by reducing P input alone). A model with one state variable and one control variable describes the responses of lake trophic state to changes in P input and other management interventions. Activities that generate P input to the lake are assumed to create profits, while the value of ecosystem services provided by the lake declines at high P levels. We then calculated P input policies that maximize the discounted net benefits from polluting activities and ecosystem services. If \"optimality\" is defined as maximizing this discounted criterion, then analyses based on deterministic lake dynamics usually lead to higher P input rates than analyses that assume various kinds of variability (e.g., inputs are affected by stochastic factors such as weather, policy is implemented with lags, or parameters of the limnological model are uncertain). In reality, all of these complications occur. Therefore, if maximum economic benefit is the goal of lake management, P input targets should be reduced below levels derived from traditional deterministic models. This pattern may apply to other situations where diffuse pollution causes nonlinear changes in ecosystem state, such as the greenhouse effect or acid deposition.