Search

Aims: Plant and soil nitrogen (N) isotope ratios (δ15N) have been used as indicators of N cycling processes of ecosystems. However, the effects of N and Phosphorus (P) addition on δ15N values and their indicative roles in N-cycling in legume-dominated tropical forests remain poorly understood. Methods: We compared leguminous (Acacia auriculiformis) and non-leguminous (Eucalyptus urophylla) forests in terms of N concentration and δ15N in the leaf–litter–soil continuum under long-term N and P addition. Typical soil N-cycling processes, including rates of mineralization, nitrification, and N loss, were also examined to determine the differences between the corresponding 15N signatures observed in the leguminous and non-leguminous forests. Results: The plants in both tropical forests were found to be 15N-depleted. N addition significantly increased the foliage δ15N in understorey species in the non-leguminous but not the leguminous forest. In both forests, the addition of N resulted in an increase in nitrate (NO3−) leaching and nitrous oxide (N2O) emission. Conversely, P addition led to a decrease in NO3− leaching and N2O emission. Additionally, foliage δ15N was positively correlated with soil N loss rates (N2O emission and NO3− leaching) in the non-leguminous forest but showed no correlation in the leguminous forest. Conclusions: In contrast to the traditional convention derived from non-leguminous forests, our results suggest that foliar 15N isotope signals are not applicable for indicating the soil N dynamic status of leguminous forests. This study highlights the importance of distinguishing legumes from other plant species in terrestrial N-cycling models when incorporating 15N isotope signals. [ABSTRACT FROM AUTHOR]

Background and aims: Increased nitrogen (N) deposition may exacerbate soil phosphorus (P) deficiency, which alters soil greenhouse gas (GHG) emissions by changing soil properties and understory vegetation in subtropical forests. However, the effects of N addition, P addition, and understory vegetation interactions on soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions in forest ecosystems and their underlying mechanisms remain unclear. Methods: We conducted a continuous N and P addition experiment in a subtropical Chinese fir plantation. The effects of N and P addition on soil CO2 and N2O emissions with different understory vegetation were examined using a structural equation model. Results: The addition of N and P did not directly affect soil CO2 emission of the understory, which was affected by understory species (F = 2.86; p = 0.05). N indirectly and positively affects soil CO2 emission through plant elements, and directly affect N2O emission of understory soil. Compared with CK, the addition of N2 promoted the N2O cumulative emission by 74.3%. N has a direct positive effect on soil N2O emissions, while P addition indirectly exerts a negative influence on N2O emissions through its impact on soil properties. Plant elements and soil properties were explained in 26.3% of soil CO2 emissions, of which 17.6% and 16.0% variations were explained by plant elements and soil properties, respectively. Leaf total N was the most important factor for predicting CO2 emissions. Conclusions: Our results suggested that soil CO2 emission was more dependent on plant elements, and soil N2O emission was directly dependent on N addition rather than plant elements. Thus, different patterns of soil GHG emissions and associated controls following N and P addition provided novel insights into predicting the effects of understory vegetation on climate change mitigation outcomes. [ABSTRACT FROM AUTHOR]

Increasing nitrogen (N) deposition alters the availability of soil nutrients and is likely to intensify phosphorus (P) limitations, especially in P-limited tropical and subtropical forests. Soil microorganisms play vital roles in carbon (C) and nutrient cycling, but it is unclear whether and how much N and P imbalances affect the soil's microbial metabolism and mechanisms of nutrient limitations. In this study, a 3-year field experiment of N and P addition (control (CK), 100 kg N ha−1 yr−1 (N), 50 kg P ha−1 yr−1 (P), and NP) was set up to analyze the extracellular enzyme activities and stoichiometry characteristics of the top mineral soils in Chinese fir plantations with different stand ages (7, 20, and 33 years old). The results showed that the enzyme activities associated with the acquisition of C (β-1,4-glucosidase (BG) and β-d-cellobiohydrolase (CBH)) and P (acid phosphatases (APs)) in the N treatment were significantly higher than those in the CK treatment. Moreover, vector analysis revealed that both the vector's length and angle increased in stands of all ages, which indicated that N addition aggravated microbial C and P limitations. The P and NP treatments both significantly decreased the activity of AP and the enzymes' N:P ratio, thereby alleviating microbial P limitations, as revealed by the reduction in the vector's angle. Stand age was found to promote all enzymatic activities but had no obvious effects on the limitation of microbial metabolism with or without added nutrients in the soils under Chinese fir. Available N, Olsen-P, and pH were the main drivers of microbial metabolic limitations related to C nutrients. These results provide useful data for understanding the change in soil microbial activity in response to environmental changes, and suggest that P fertilization should be considered for management to improve productivity and C sequestration in Chinese fir plantation in the context of increased deposition of N. [ABSTRACT FROM AUTHOR]

The phenomenon of nitrogen deposition resulting in species loss in terrestrial ecosystems has been demonstrated in several experiments. Nitrogen (N) and phosphorus (P), as major nutrients required for plant growth, exhibit ecological stoichiometric coupling in many ecosystems. The increased availability of nitrogen can exacerbate the ecological effects of phosphorus. To reveal the ecological effects of phosphorus under nitrogen-limiting and non-limiting conditions, we conducted a controlled N-P interaction experiment over 5 years in the Hulunbuir meadow steppe, where two nitrogen addition levels were implemented: 0 g N·m-2·a-1 (nitrogen-limiting condition) and 10 g N·m-2·a-1 (nitrogen-non-limiting condition), together with six levels of phosphorus addition (0, 2, 4, 6, 8, and 10 g P·m-2·a-1). The results showed that nitrogen addition (under nitrogen-non-limiting conditions) significantly decreased species diversity in the steppe community, which was exacerbated under phosphorus addition. Under nitrogen-limiting conditions, phosphorus addition had no marked impact on species diversity compared to the control; however, there were substantial differences between different levels of phosphorus addition, exhibiting a unimodal change. Under both experimental nitrogen conditions, the addition of 6 g P·m-2·a-1 was the threshold for affecting the community species diversity. Nitrogen addition reduced the relative biomass of legumes, bunch grasses, and forbs, but substantially increased the relative biomass of rhizomatous grasses. In contrast, phosphorus addition only markedly affected the relative biomass of forbs and rhizomatous grasses, with the former showing a unimodal pattern of first increasing and then decreasing with increasing phosphorus addition level, and the latter exhibiting the opposite pattern. The different responses of rhizomatous grasses and other functional groups to nitrogen and phosphorus addition were observed to have a regulatory effect on the changes in grassland community structure. Phosphorus addition may increase the risk of nitrogen deposition-induced species loss. Both nitrogen and phosphorus addition lead to soil acidification and an increase in the dominance of the already-dominant species, and the consequent species loss in the forb functional group represents the main mechanism for the reduction in community species diversity. [ABSTRACT FROM AUTHOR]

Abiotic resource limitation presents organisms with a dilemma about how to use resources when they become available. Characterizing how resource allocation affects investment in growth or defensive traits that affect organismal survival strategies allows us to understand the environmental contexts in which species interact. Our goal was to measure how macronutrient availability drives nitrogen and phosphorus allocation towards functional growth and defensive chemical traits of the Neotropical passion vine, Passiflora biflora.We investigated this question with a paired field study in La Selva, Costa Rica and a full factorial greenhouse experiment to determine whether the concentration of a key secondary chemical defence is driven by nitrogen availability. We correlated defensive chemical concentration with soil nitrogen availability in naturally occurring plants, measured the effects of nitrogen and phosphorus availability on growth and secondary chemical defence traits in the greenhouse and characterized the P. biflora leaf metabolome to assess how nutrient availability affected shifts in metabolism related to plant fitness.We found that nutrient allocation increased the magnitude of both growth and defence traits. Increased nitrogen availability resulted in higher concentrations of toxic leaf secondary chemicals, longer vines, greater biomass and more leaves with a superior ability to capture sunlight. In addition, plants from high nitrogen environments had metabolomes with significantly greater secondary metabolite richness and biochemical pathway diversity, as well as increases in the number of metabolites from several chemical classes related to basic cell function and defence. Nutrient availability had no significant effect on the richness and diversity of primary metabolites involved in basic cell functions. A direct comparison of the relative strength of quantitative growth and secondary defence traits indicated that P. biflora favours nutrient allocation to growth at low nitrogen levels but invests in both strategies more evenly as nitrogen availability increases.These findings lead us to predict that passion vines are better prepared to tolerate and resist herbivory when nutrients are plentiful and experience a trade‐off between growth and chemical defence against natural enemies when they are scarce. These findings are consistent with both the 'escape' and 'defend' syndromes that are often used to describe tropical plant survival strategies. This is one of the only studies to measure nutrient allocation in vines, a group comprising a significant percentage of global plant diversity. Moreover, this work demonstrated the power of leveraging untargeted metabolomics to characterize how nutrient addition affects plant growth and defence, highlighting its potential for understanding functional trait variation. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the response of cross-domain co-occurrence networks of soil microorganisms to phosphorus stability and the resulting impacts is critical in ecosystems, but the underlying mechanism is unclear in artificial grassland ecosystems. Methods: In this study, the effects of four phosphorus concentrations, P0 (0 kg P ha-1), P1 (15.3 kg P ha-1), P2 (30.6 kg P ha-1), and P3 (45.9 kg P ha-1), on the cross-domain co-occurrence network of bacteria and fungi were investigated in an artificial Leymus chinensis grassland in an arid region. Results and discussion: The results of the present study showed that phosphorus addition significantly altered the stem number, biomass and plant height of the Leymus chinensis but had no significant effect on the soil bacterial or fungal alpha (ACE) diversity or beta diversity. The phosphorus treatments all increased the cross-domain co-occurrence network edge, node, proportion of positively correlated edges, edge density, average degree, proximity to centrality, and robustness and increased the complexity and stability of the bacterial-fungal cross-domain co-occurrence network after 3 years of continuous phosphorus addition. Among them, fungi (Ascomycota, Basidiomycota, Mortierellomycota and Glomeromycota) play important roles as keystone species in the cooccurrence network, and they are significantly associated with soil AN, AK and EC. Finally, the growth of Leymus chinensis was mainly due to the influence of the soil phosphorus content and AN. This study revealed the factors affecting the growth of Leymus chinense in artificial grasslands in arid areas and provided a theoretical basis for the construction of artificial grasslands. [ABSTRACT FROM AUTHOR]

Introduction: Phosphorus (P), which plays a vital role in plant growth, is continually added to soil to maximize biomass production, leading to excessive P accumulation and water eutrophication. Results: In this study, a pot experiment using a subtropical tobacco-growing soil fertilized with four P levels—no P, low P, medium P, and high P—was conducted and rhizosphere and bulk soils were analyzed. Results: P addition significantly increased tobacco biomass production (except under low P input) and total soil P and available P content (P<0.05), whereas total nitrogen content decreased in the rhizosphere soils, although this was only significant with medium P application. P fertilization also significantly altered the bacterial communities of rhizosphere soils (P<0.05), but those of bulk soils were unchanged (P>0.05). Moreover, a significant difference was found between rhizosphere soils with low (LR) and high (HR) P inputs (P<0.05). Additionally, compared with rhizosphere soils with no P (CKR), Shannon diversity showed a declining trend, which was significant with LR and HR (P<0.05), whereas an increasing tendency was observed for Chao1 diversity except in LR (P>0.05). Functional prediction revealed that P application significantly decreased the total P and N metabolism of microorganisms in rhizosphere soils (P<0.05). Discussion: Collectively, our results indicate that maintaining sustainable agricultural ecosystems under surplus P conditions requires more attention to be directed toward motivating the potential of soil functional microbes in P cycling, rather than just through continual P input. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) addition is considered key factor in soil organic carbon (SOC) cycle. The potential impact mechanisms of P addition on SOC stability and sequestration were explored in saline-alkali soil. Methods: A 9-year field experiment was arranged in the Yellow River Delta, which included (i) CK, no fertilization; (ii) NK, N and K fertilizer application; (iii) NP1K and (iv) NP2K, NK plus 28 and 56 kg P ha−1 year−1 application, respectively. Results: Compared with NK, the content of particulate OC (POC) was significantly increased by 29.9% and 26.8% in NP1K and NP2K treatments, respectively. The variation trend of aromatic-C and microbial biomass C (MBC) was similar to that of POC, which were positively corelated with SOC sequestration. Meanwhile, C and specific C mineralization rate (CMR, SCMR) were increased with P addition, which might be due to the decrease of carboxyl or amidogen-C. Moreover, owing to the increase in root biomass, SOC sequestration was significantly increased by more than 9.3% with P addition. Redundancy analysis further indicated that root biomass was the main factor in regulating SOC. While the CMR and SCMR were higher of NP2K treatment than those of NP1K treatment, this might result in SOC sequestration was no significant change between the two treatments. Conclusion: Long-term low-level P fertilization is a preferable practice to increase POC, stable chemical composition and MBC, and then SOC sequestration. These findings provide important insights into how long-term different levels of P application regulate soil C cycling in saline-alkali paddy soil. [ABSTRACT FROM AUTHOR]

The escalation of global nitrogen deposition levels has heightened the inhibitory impact of phosphorus limitation on plant growth in subtropical forests. Plant roots area particularly sensitive tissue to nitrogen and phosphorus elements. Changes in the morphological characteristics of plant roots signify alterations in adaptive strategies. However, our understanding of resource-use strategies of roots in this environment remains limited. In this study, we conducted a 10-month experiment at the Castanopsis kawakamii Nature Reserve to evaluate the response of traits of seedling roots (such as specific root length, average diameter, nitrogen content, and phosphorus content) to nitrogen and phosphorus addition. The aim was to reveal the adaptation strategies of roots in different nitrogen and phosphorus addition concentrations. The results showed that: (1) The single phosphorus and nitrogen–phosphorus interaction addition increased the specific root length, surface area, and root phosphorus content. In addition, single nitrogen addition promotes an increase in the average root diameter. (2) Non-nitrogen phosphorus addition and single nitrogen addition tended to adopt a conservative resource-use strategy to maintain growth under low phosphorus conditions. (3) Under the single phosphorus addition and interactive addition of phosphorus and nitrogen, the roots adopted an acquisitive resource-use strategy to obtain more available phosphorus resources. Accordingly, the adaptation strategy of seedling roots can be regulated by adding appropriate concentrations of nitrogen or phosphorus, thereby promoting the natural regeneration of subtropical forests. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) not only contributes to maintain soil health, but is also important in regulating global climate change. How atmospheric nitrogen (N) deposition and phosphorus (P) addition affects SOC dynamics remains unclear, especially in subtropical forests. The response of SOC in three layers to N deposition and P addition in this study is estimated by analyzing the soil aggregates and C chemical stability composition fertilized with N (100 kg N hm−2 a−1) and/or P (50 kg P hm−2 a−1) over 9 years in a Chinese fir (Cunninghamia lanceolata) plantation. Treatments involving N deposition increased the SOC concentration, while P addition alone decreased the SOC concentration in soil layers above 10 cm. The addition of N significantly increased the mean diameter of topsoil aggregates, macroaggregates SOC concentration, and the contribution of N to total SOC. P addition decreased the relative abundances of aromatic and aliphatic functional groups while decreasing the chemical stability of SOC in the topsoil. A structural equation model indicated that N deposition promoted SOC concentration by mainly improving the physical protection of soil aggregates, while P addition reduced SOC sequestration by decreasing the chemical stability of SOC. Our research suggested that elevated N deposition might promote the soil C sink, while P fertilization would not be recommended under increased N deposition to protect soil C storage in subtropical forests. [ABSTRACT FROM AUTHOR]

Increasing nitrogen (N) deposition alters the availability of soil nutrients and is likely to intensify phosphorus (P) limitations, especially in P-limited tropical and subtropical forests. Soil microorganisms play vital roles in carbon (C) and nutrient cycling, but it is unclear whether and how much N and P imbalances affect the soil’s microbial metabolism and mechanisms of nutrient limitations. In this study, a 3-year field experiment of N and P addition (control (CK), 100 kg N ha−1 yr−1 (N), 50 kg P ha−1 yr−1 (P), and NP) was set up to analyze the extracellular enzyme activities and stoichiometry characteristics of the top mineral soils in Chinese fir plantations with different stand ages (7, 20, and 33 years old). The results showed that the enzyme activities associated with the acquisition of C (β-1,4-glucosidase (BG) and β-d-cellobiohydrolase (CBH)) and P (acid phosphatases (APs)) in the N treatment were significantly higher than those in the CK treatment. Moreover, vector analysis revealed that both the vector’s length and angle increased in stands of all ages, which indicated that N addition aggravated microbial C and P limitations. The P and NP treatments both significantly decreased the activity of AP and the enzymes’ N:P ratio, thereby alleviating microbial P limitations, as revealed by the reduction in the vector’s angle. Stand age was found to promote all enzymatic activities but had no obvious effects on the limitation of microbial metabolism with or without added nutrients in the soils under Chinese fir. Available N, Olsen-P, and pH were the main drivers of microbial metabolic limitations related to C nutrients. These results provide useful data for understanding the change in soil microbial activity in response to environmental changes, and suggest that P fertilization should be considered for management to improve productivity and C sequestration in Chinese fir plantation in the context of increased deposition of N.

Abstract Introduction Fungal communities are key players in the soil biogeochemical processes of forest ecosystems. Although it has been illustrated that soil fungi are susceptible to environmental changes, little is known about the interactive effects of nitrogen (N) and phosphorus (P) enrichment on the soil fungal functional guild. Materials and Methods Here, a 5‐year N and P addition manipulation experiment was conducted in two growing stages (i.e., tree ages 80 years) of a subtropical forest, in which soil fungal diversity and functional guilds were investigated using a multiple‐time sampling strategy. Results Fungal species richness and Shannon indices were significantly different across sampling times. Fungal community composition was significantly affected by both N and P addition but not by forest age. Old forest had a higher fungal network complexity than young forest, and fertilisation decreased soil fungal network complexity and generated looser and more random networks in comparison with the control. The community composition of symbiotrophic and saprotrophic fungi was significantly impacted by N and P addition and correlated with soil available P and total P contents and soil C:P and N:P. Conclusions Our findings highlight that soil P availability has a strong effect on soil fungal communities and their functional guild composition in the subtropical forest.

Nitrogen (N) and phosphorus (P) are key components in biogeochemical cycling and considerable efforts have been made to understand the effects of their availability on microbial biomass. Nevertheless, the interplay between N and P supply in modulating soil microbes remains unclear. We conducted a comprehensive global analysis of 108 studies spanning boreal to tropical regions to evaluate their interactive impacts on microbial biomass. The findings revealed a significant decrease in microbial biomass with N addition, whereas P supplementation resulted in a notable increase in microbial biomass. Among the observed interactive effects, additive effects were predominant. More importantly, we found that among all of the assessed factors, the impacts of N-P interaction on soil microorganisms are dependent on changes in soil pH. In conclusion, our findings provide valuable insights into the interactive effects of N and P enrichment on microbial biomass. These findings will contribute to the development of global models that predict the impacts of N and P enrichment on soil microbes and ecosystem functions.

The escalation of global nitrogen deposition levels has heightened the inhibitory impact of phosphorus limitation on plant growth in subtropical forests. Plant roots area particularly sensitive tissue to nitrogen and phosphorus elements. Changes in the morphological characteristics of plant roots signify alterations in adaptive strategies. However, our understanding of resource-use strategies of roots in this environment remains limited. In this study, we conducted a 10-month experiment at the Castanopsis kawakamii Nature Reserve to evaluate the response of traits of seedling roots (such as specific root length, average diameter, nitrogen content, and phosphorus content) to nitrogen and phosphorus addition. The aim was to reveal the adaptation strategies of roots in different nitrogen and phosphorus addition concentrations. The results showed that: (1) The single phosphorus and nitrogen–phosphorus interaction addition increased the specific root length, surface area, and root phosphorus content. In addition, single nitrogen addition promotes an increase in the average root diameter. (2) Non-nitrogen phosphorus addition and single nitrogen addition tended to adopt a conservative resource-use strategy to maintain growth under low phosphorus conditions. (3) Under the single phosphorus addition and interactive addition of phosphorus and nitrogen, the roots adopted an acquisitive resource-use strategy to obtain more available phosphorus resources. Accordingly, the adaptation strategy of seedling roots can be regulated by adding appropriate concentrations of nitrogen or phosphorus, thereby promoting the natural regeneration of subtropical forests.

Soil organic carbon (SOC) not only contributes to maintain soil health, but is also important in regulating global climate change. How atmospheric nitrogen (N) deposition and phosphorus (P) addition affects SOC dynamics remains unclear, especially in subtropical forests. The response of SOC in three layers to N deposition and P addition in this study is estimated by analyzing the soil aggregates and C chemical stability composition fertilized with N (100 kg N hm−2 a−1) and/or P (50 kg P hm−2 a−1) over 9 years in a Chinese fir (Cunninghamia lanceolata) plantation. Treatments involving N deposition increased the SOC concentration, while P addition alone decreased the SOC concentration in soil layers above 10 cm. The addition of N significantly increased the mean diameter of topsoil aggregates, macroaggregates SOC concentration, and the contribution of N to total SOC. P addition decreased the relative abundances of aromatic and aliphatic functional groups while decreasing the chemical stability of SOC in the topsoil. A structural equation model indicated that N deposition promoted SOC concentration by mainly improving the physical protection of soil aggregates, while P addition reduced SOC sequestration by decreasing the chemical stability of SOC. Our research suggested that elevated N deposition might promote the soil C sink, while P fertilization would not be recommended under increased N deposition to protect soil C storage in subtropical forests.

Phosphorus (P) is considered to be one of the most limiting elements in terrestrial ecosystems, especially in the subtropical forests in China. However, little is known about how rhizosphere soil bacterial communities and functions, especially at the level of functional genes abundance, respond to P inputs. Herein we conducted a P addition experiment and treatments included 80 g m−2 yr−1 (P1), 160 g m−2 yr−1 (P2), 240 g P m−2 yr−1 (P3), 320 g P m−2 yr−1 (P4) and the control without any fertilizer application (CK) in the Phoebe bournei young plantations. This study used the quantitative microbial element cycling (QMEC) smart chip technology and 16S rRNA gene sequencing to investigate changes in the relative abundance of C-, N-, and P-cycle genes and rhizosphere soil bacterial community that received various inputs of P nutrients. Soil bacterial diversity showed a progressively decreased trend with increasing of P fertilizer, accompanied by significant differences in bacterial community structure between CK and P4 treatment. The relative abundance of N- and P-cycle genes were increased by P addition, and the highest relative abundance was observed in P3 treatment among the five P addition treatments. The relative abundance of C-cycle genes was significantly enhanced by P4 treatment, promoting C fixation, degradation, and methane metabolism. Random forest model indicated that invertase activity was the most important predictor for the relative abundance of C-, N-, and P-cycle genes. Partial least squares path modeling analysis revealed that the predominant effect of P fertilizer in driving the relative abundance of functional genes was maintained when accounting for multiple abiotic factors (total P, available P, available potassium, soil organic carbon and soil pH) drivers and there was a strong relationship between the relative abundance of functional genes and catalase, invertase and urease activities. Overall, our findings confirm that high P addition significantly altered rhizosphere soil bacterial community composition in the Phoebe bournei young plantations, and significantly enhanced the relative abundance of C-, N- and P-cycle genes. These results suggest that sufficient P fertilizer benefits to improve the nutrients cycle processes mediating by soil bacteria in Phoebe bournei young plantations. [Display omitted] • Soil bacterial diversity showed a progressively decreased trend with increasing of P fertilizer. • High P addition increased the relative abundance of functional genes involving in C-, N- and P-cycle genes. • TP, AP, AK, SOC and pH had significant effects on the relative abundance of functional genes. • Enzyme activities were significantly correlated with the relative abundance of functional genes. • Invertase activity was the most important predictor for the relative abundance of functional genes. [ABSTRACT FROM AUTHOR]

The phenomenon of nitrogen deposition resulting in species loss in terrestrial ecosystems has been demonstrated in several experiments. Nitrogen (N) and phosphorus (P), as major nutrients required for plant growth, exhibit ecological stoichiometric coupling in many ecosystems. The increased availability of nitrogen can exacerbate the ecological effects of phosphorus. To reveal the ecological effects of phosphorus under nitrogen-limiting and non-limiting conditions, we conducted a controlled N-P interaction experiment over 5 years in the Hulunbuir meadow steppe, where two nitrogen addition levels were implemented: 0 g N·m -2 ·a -1 (nitrogen-limiting condition) and 10 g N·m -2 ·a -1 (nitrogen-non-limiting condition), together with six levels of phosphorus addition (0, 2, 4, 6, 8, and 10 g P·m -2 ·a -1 ). The results showed that nitrogen addition (under nitrogen-non-limiting conditions) significantly decreased species diversity in the steppe community, which was exacerbated under phosphorus addition. Under nitrogen-limiting conditions, phosphorus addition had no marked impact on species diversity compared to the control; however, there were substantial differences between different levels of phosphorus addition, exhibiting a unimodal change. Under both experimental nitrogen conditions, the addition of 6 g P·m -2 ·a -1 was the threshold for affecting the community species diversity. Nitrogen addition reduced the relative biomass of legumes, bunch grasses, and forbs, but substantially increased the relative biomass of rhizomatous grasses. In contrast, phosphorus addition only markedly affected the relative biomass of forbs and rhizomatous grasses, with the former showing a unimodal pattern of first increasing and then decreasing with increasing phosphorus addition level, and the latter exhibiting the opposite pattern. The different responses of rhizomatous grasses and other functional groups to nitrogen and phosphorus addition were observed to have a regulatory effect on the changes in grassland community structure. Phosphorus addition may increase the risk of nitrogen deposition-induced species loss. Both nitrogen and phosphorus addition lead to soil acidification and an increase in the dominance of the already-dominant species, and the consequent species loss in the forb functional group represents the main mechanism for the reduction in community species diversity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Wang, Chen, Pan, Zhao, Yang, Li and Wang.)

• N addition had a negative effect on soil microbial biomass. • P addition had a positive effect on soil microbial biomass. • The additive effect dominated the interactive effects on soil microbial biomass. • The responses to interactive effects were largely dependent on changes in soil pH. Nitrogen (N) and phosphorus (P) are key components in biogeochemical cycling and considerable efforts have been made to understand the effects of their availability on microbial biomass. Nevertheless, the interplay between N and P supply in modulating soil microbes remains unclear. We conducted a comprehensive global analysis of 108 studies spanning boreal to tropical regions to evaluate their interactive impacts on microbial biomass. The findings revealed a significant decrease in microbial biomass with N addition, whereas P supplementation resulted in a notable increase in microbial biomass. Among the observed interactive effects, additive effects were predominant. More importantly, we found that among all of the assessed factors, the impacts of N-P interaction on soil microorganisms are dependent on changes in soil pH. In conclusion, our findings provide valuable insights into the interactive effects of N and P enrichment on microbial biomass. These findings will contribute to the development of global models that predict the impacts of N and P enrichment on soil microbes and ecosystem functions. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the response of cross-domain co-occurrence networks of soil microorganisms to phosphorus stability and the resulting impacts is critical in ecosystems, but the underlying mechanism is unclear in artificial grassland ecosystems., Methods: In this study, the effects of four phosphorus concentrations, P0 (0 kg P ha -1 ), P1 (15.3 kg P ha -1 ), P2 (30.6 kg P ha -1 ), and P3 (45.9 kg P ha -1 ), on the cross-domain co-occurrence network of bacteria and fungi were investigated in an artificial Leymus chinensis grassland in an arid region., Results and Discussion: The results of the present study showed that phosphorus addition significantly altered the stem number, biomass and plant height of the Leymus chinensis but had no significant effect on the soil bacterial or fungal alpha (ACE) diversity or beta diversity. The phosphorus treatments all increased the cross-domain co-occurrence network edge, node, proportion of positively correlated edges, edge density, average degree, proximity to centrality, and robustness and increased the complexity and stability of the bacterial-fungal cross-domain co-occurrence network after 3 years of continuous phosphorus addition. Among them, fungi (Ascomycota, Basidiomycota, Mortierellomycota and Glomeromycota) play important roles as keystone species in the co-occurrence network, and they are significantly associated with soil AN, AK and EC. Finally, the growth of Leymus chinensis was mainly due to the influence of the soil phosphorus content and AN. This study revealed the factors affecting the growth of Leymus chinense in artificial grasslands in arid areas and provided a theoretical basis for the construction of artificial grasslands., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Zhou, Hu, Li, Sheng, Cheng, Zhao and Zhang.)

Introduction: Phosphorus (P), which plays a vital role in plant growth, is continually added to soil to maximize biomass production, leading to excessive P accumulation and water eutrophication., Results: In this study, a pot experiment using a subtropical tobacco-growing soil fertilized with four P levels-no P, low P, medium P, and high P-was conducted and rhizosphere and bulk soils were analyzed., Results: P addition significantly increased tobacco biomass production (except under low P input) and total soil P and available P content ( P <0.05), whereas total nitrogen content decreased in the rhizosphere soils, although this was only significant with medium P application. P fertilization also significantly altered the bacterial communities of rhizosphere soils ( P <0.05), but those of bulk soils were unchanged ( P >0.05). Moreover, a significant difference was found between rhizosphere soils with low (LR) and high (HR) P inputs ( P <0.05). Additionally, compared with rhizosphere soils with no P (CKR), Shannon diversity showed a declining trend, which was significant with LR and HR ( P <0.05), whereas an increasing tendency was observed for Chao1 diversity except in LR ( P >0.05). Functional prediction revealed that P application significantly decreased the total P and N metabolism of microorganisms in rhizosphere soils ( P <0.05)., Discussion: Collectively, our results indicate that maintaining sustainable agricultural ecosystems under surplus P conditions requires more attention to be directed toward motivating the potential of soil functional microbes in P cycling, rather than just through continual P input., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Zhou, Cheng, Peng, Li, Li, Wang, Wang and Guo.)