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Aims: Litter decomposition affects soil organic carbon storage, and nutrient addition alters exogenous nutrient availability in soil, thereby affecting the endogenous nutrient concentration and extracellular enzyme activity in litter. However, how above- and belowground litter decomposition responds to nutrient addition is not fully understood. Methods: We conducted a 7-yr field experiment with 5 levels (0, 1, 2.5, 5, and 12.5 g P m−2 yr−1) of phosphorus fertilization (P). Starting in the 6th year, we determine litter decomposition, nutrient elements, and enzyme activity to explore the response mechanisms of above- and belowground litter decomposition to P addition. Results: All levels of P addition increased the rate of aboveground litter decomposition, but only 2.5 g P m−2 yr−1 increased that of belowground litter. P addition increased the litter initial P and Mn contents, while decreased the C/P and N/P ratios of aboveground litter, which stimulated the activities of β-1,4-glucosidase and β-1,4-N-acetylglucosaminidase, thereby increasing the aboveground litter decomposition rate. The belowground litter decomposition was mainly inhibited by lignin content, and 2.5 g P m−2 yr−1 addition significantly decreased lignin content and increased the phenol oxidase activity, thereby accelerating the decomposition. P addition promoted the accumulation of P and the release of cellulose from aboveground litter and promoted the accumulation of calcium and the release of carbon from belowground litter. Conclusions: Different mechanisms of above- and belowground litter decomposition under P addition were driven by litter quality and enzyme activity, but moderate P addition increased semiarid grassland litter decomposition, which may contribute to low soil C sequestration. [ABSTRACT FROM AUTHOR]

• Decomposition rate of mixed forest is higher than that of pure forest. • Mixed forest and pure forest have the same dominant bacteria and fungi. • Mixed forests have more stable microbial alpha diversity index than pure forest. • TN, C:N and N:P ratio of litter affect soil microbial community structure. Soil microorganisms play an important role in the decomposition of litter. There stand structure and in-forest microenvironment of mixed forests and pure forests are different, and whether these differences affect the soil microbial community structure and further affect litter decomposition needs further research. In this paper, a mixed Quercus acutissima Carruth. and Robinia pseudoacacia L. (QR) forest and a pure Quercus acutissima Carruth. (QAC) forest were studied to analyse the compositions and influencing factors of soil bacterial and fungal communities during litter decomposition. Through field sampling and quantitative analysis performed in a laboratory, the results of this research were as follows: (1) During litter decomposition, the litter decomposition rate of the QR forest was higher than that of the QAC forest. (2) The dominant bacteria were Acidobacteria, Proteobacteria and Actinobacteria, and the dominant fungi were Basidiomycota and Ascomycota in the QR and QAC forests. (3) For litters decomposed from May to November, the soil bacterial alpha diversity index (richness index and evenness index) showed an increasing trend and the soil fungal alpha diversity index showed a decreasing trend in the QR and QAC forests, but the changes in the QR forest were smaller than those in the QAC forest. (4) Redundancy analysis (RDA) showed that the soil bacterial community structure was different between the QR and QAC forests, and the soil temperature, soil moisture, litter TN, C:N ratio, and N:P ratio were important factors affecting the soil microbial community structure. The results indicate that mixed forests have a more stable microbial alpha diversity index and that the TN, C:N ratio and N:P ratio of litter have important effects on soil microbial community structure; therefore, mixed forests should be given more priority in ecological restoration, and nitrogen regulation must be given attention during forest management. [ABSTRACT FROM AUTHOR]

Summary: Phosphorus (P) fertilization can alleviate a soil P deficiency in grassland ecosystems. Understanding plant functional traits that enhance P uptake can improve grassland management.We measured impacts of P addition on soil chemical and microbial properties, net photosynthetic rate (Pn) and nonstructural carbohydrate concentrations ([NSC]), and root P‐uptake rate (PUR), morphology, anatomy, and exudation of two dominant grass species: Leymus chinensis (C3) and Cleistogenes squarrosa (C4).For L. chinensis, PUR and Pn showed a nonlinear correlation. Growing more adventitious roots compensated for the decrease in P transport per unit root length, so that it maintained a high PUR. For C. squarrosa, PUR and Pn presented a linear correlation. Increased Pn was associated with modifications in root morphology, which further enhanced its PUR and a greater surplus of photosynthate and significantly stimulated root exudation (proxied by leaf [Mn]), which had a greater impact on rhizosheath micro‐environment and microbial PLFAs.Our results present correlations between the PUR and the Pn of L. chinensis and C. squarrosa and reveal that NSC appeared to drive the modifications of root morphology and exudation; they provide more objective basis for more efficient P‐input in grasslands to address the urgent problem of P deficiency. [ABSTRACT FROM AUTHOR]

The ability of plants to efficiently supply nitrogen (N) to their shoots is critical for reconstructing photosynthetic tissues after defoliation events. We conducted an indoor defoliation experiment and used 13C and 15 N labeling to investigate the photosynthetic carbon (C) allocation, the relationships between C allocation and N uptake, and the contribution of N reallocation for regrowth. Leymus chinensis increased the amount of belowground 13C to the low defoliation (LD) treatment, but allocated less 13C belowground in response to the medium (MD) and high defoliation (HD) treatments, these changes were related to photosynthetic C fixation. Moreover, there was no evidence of a trade-off in C allocation between root exudates and roots, because their direct sources of C differed. The uptake rate of 15 N was the greatest in the LD treatment, when the C invested belowground was maximal. MD treatment increased specific root length and specific root area, which augmented the N uptake. Crucially, defoliation increased the N reallocation from roots to shoots, likely due to the greater N demand of shoot. Altogether, our results show that N supply was governed by N uptake and reallocation for Leymus chinensis after low defoliation. [ABSTRACT FROM AUTHOR]

Aims: Phosphorus (P) addition can help restore degraded Chinese grasslands. Soil P-availability affects the plant niche dynamics. However, the dynamics of niche characteristics are not yet understood, particularly for above- and belowground differences between species and plant–microbe interactions that generate these dynamics.We conducted a long-term field P-fertilization experiment (0 to 12.5 g P m−2 year−1) to explore the impacts of P addition on the niche dynamics of a competitive forb (Chenopodium aristatum, a non-mycorrhizal C4 plant) and a dominant grass (Leymus chinensis, a mycorrhizal C3 plant) in a temperate grassland in Inner Mongolia, northern China.Phosphorus addition greatly changed the niche and exacerbated aboveground competition between C. aristatum and L. chinensis. Competitive exclusion of L. chinensis occurred at all levels, except P2.5. Photosynthesis and above- and belowground morphology of C. aristatum responded more to P1 due to its high photosynthetic plasticity and nutrient resorption, which was associated with its competitive advantage. Although NO peaked at P2.5, carbon assimilation and rhizosheath microbial biomass of L. chinensis were optimal. Alleviated NO at P5 and P12.5 was associated with segregation of root morphologies and rhizosheath microbial composition. However, surplus niches at P5 and P12.5 were occupied by invasive sub-shrubs, associating with the mismatched plant–microbe feedbacks of C. aristatum and L. chinensis.Our findings suggest that rhizosheath microbes mediate trade-offs between a host plant’s P-conservation and acquisition and highlight the importance of above- and belowground co-responses to community productivity and stability under P addition.Methods: Phosphorus (P) addition can help restore degraded Chinese grasslands. Soil P-availability affects the plant niche dynamics. However, the dynamics of niche characteristics are not yet understood, particularly for above- and belowground differences between species and plant–microbe interactions that generate these dynamics.We conducted a long-term field P-fertilization experiment (0 to 12.5 g P m−2 year−1) to explore the impacts of P addition on the niche dynamics of a competitive forb (Chenopodium aristatum, a non-mycorrhizal C4 plant) and a dominant grass (Leymus chinensis, a mycorrhizal C3 plant) in a temperate grassland in Inner Mongolia, northern China.Phosphorus addition greatly changed the niche and exacerbated aboveground competition between C. aristatum and L. chinensis. Competitive exclusion of L. chinensis occurred at all levels, except P2.5. Photosynthesis and above- and belowground morphology of C. aristatum responded more to P1 due to its high photosynthetic plasticity and nutrient resorption, which was associated with its competitive advantage. Although NO peaked at P2.5, carbon assimilation and rhizosheath microbial biomass of L. chinensis were optimal. Alleviated NO at P5 and P12.5 was associated with segregation of root morphologies and rhizosheath microbial composition. However, surplus niches at P5 and P12.5 were occupied by invasive sub-shrubs, associating with the mismatched plant–microbe feedbacks of C. aristatum and L. chinensis.Our findings suggest that rhizosheath microbes mediate trade-offs between a host plant’s P-conservation and acquisition and highlight the importance of above- and belowground co-responses to community productivity and stability under P addition.Results: Phosphorus (P) addition can help restore degraded Chinese grasslands. Soil P-availability affects the plant niche dynamics. However, the dynamics of niche characteristics are not yet understood, particularly for above- and belowground differences between species and plant–microbe interactions that generate these dynamics.We conducted a long-term field P-fertilization experiment (0 to 12.5 g P m−2 year−1) to explore the impacts of P addition on the niche dynamics of a competitive forb (Chenopodium aristatum, a non-mycorrhizal C4 plant) and a dominant grass (Leymus chinensis, a mycorrhizal C3 plant) in a temperate grassland in Inner Mongolia, northern China.Phosphorus addition greatly changed the niche and exacerbated aboveground competition between C. aristatum and L. chinensis. Competitive exclusion of L. chinensis occurred at all levels, except P2.5. Photosynthesis and above- and belowground morphology of C. aristatum responded more to P1 due to its high photosynthetic plasticity and nutrient resorption, which was associated with its competitive advantage. Although NO peaked at P2.5, carbon assimilation and rhizosheath microbial biomass of L. chinensis were optimal. Alleviated NO at P5 and P12.5 was associated with segregation of root morphologies and rhizosheath microbial composition. However, surplus niches at P5 and P12.5 were occupied by invasive sub-shrubs, associating with the mismatched plant–microbe feedbacks of C. aristatum and L. chinensis.Our findings suggest that rhizosheath microbes mediate trade-offs between a host plant’s P-conservation and acquisition and highlight the importance of above- and belowground co-responses to community productivity and stability under P addition.Conclusions: Phosphorus (P) addition can help restore degraded Chinese grasslands. Soil P-availability affects the plant niche dynamics. However, the dynamics of niche characteristics are not yet understood, particularly for above- and belowground differences between species and plant–microbe interactions that generate these dynamics.We conducted a long-term field P-fertilization experiment (0 to 12.5 g P m−2 year−1) to explore the impacts of P addition on the niche dynamics of a competitive forb (Chenopodium aristatum, a non-mycorrhizal C4 plant) and a dominant grass (Leymus chinensis, a mycorrhizal C3 plant) in a temperate grassland in Inner Mongolia, northern China.Phosphorus addition greatly changed the niche and exacerbated aboveground competition between C. aristatum and L. chinensis. Competitive exclusion of L. chinensis occurred at all levels, except P2.5. Photosynthesis and above- and belowground morphology of C. aristatum responded more to P1 due to its high photosynthetic plasticity and nutrient resorption, which was associated with its competitive advantage. Although NO peaked at P2.5, carbon assimilation and rhizosheath microbial biomass of L. chinensis were optimal. Alleviated NO at P5 and P12.5 was associated with segregation of root morphologies and rhizosheath microbial composition. However, surplus niches at P5 and P12.5 were occupied by invasive sub-shrubs, associating with the mismatched plant–microbe feedbacks of C. aristatum and L. chinensis.Our findings suggest that rhizosheath microbes mediate trade-offs between a host plant’s P-conservation and acquisition and highlight the importance of above- and belowground co-responses to community productivity and stability under P addition. [ABSTRACT FROM AUTHOR]

The extensive use of fossil fuels puts ecological and economic coordinated development at risk. Photovoltaic systems relieve the pressure of resource extraction and energy generation on climate change, and their installation and module operation affect vegetation productivity and grassland restoration by changing the microenvironment and ecosystem processes. However, it is still unclear whether plants adapt to these changes in photovoltaic systems to sustain their growth. Here, combined stable isotope techniques with plant traits, plant adaptations to photovoltaic systems at different scales were analyzed from the perspectives of water and nutrient sources, uptake, transport, and utilization. The results showed that photovoltaic systems increased water uptake by the dominant species Leymus chinensis from the top 10 cm of the soil and the aboveground biomass. This was associated with strong plasticity of roots and conduction tissues, which improved resource uptake from the fertile surface soil and transport within the plant, and promoted photosynthesis and leaf water loss by inducing stomatal opening. Different from fixed photovoltaic systems, tracking photovoltaic systems improved ecosystem water use efficiency and surface soil nutrient availability by reducing soil temperature. Tilting tracking photovoltaic systems especially promoted biomass accumulation and grassland restoration. The study suggested that photovoltaic systems promoted vegetation restoration of grassland ecosystem in semi-arid region through the water and nutrient coordination and the carbon-water coupling, and provides a solution for reasonable planning of photovoltaic industry and sustainable socio-economic development. • Photovoltaics changed plant water source and increased its water uptake of 0–10 cm. • Plant increased resource uptake and transportation by root traits in photovoltaics. • Plant in photovoltaic achieved carbon-water coupling by carbon gain and water loss. • Tracking photovoltaics improved ecosystem water use efficiency and biomass. • Tilting-tracking photovoltaics promoted power generation and grassland restoration. [ABSTRACT FROM AUTHOR]

Overgrazing and phosphorus (P) deficiency are two major factors limiting the sustainable development of grassland ecosystems. Exploring plant P utilization and acquisition strategies under grazing can provide a solid basis for determining a reasonable grazing intensity. Both foliar P allocation and root P acquisition are crucial mechanisms for plants to adapt to environmental P availability; however, their changing characteristics and correlation under grazing remain unknown. Here, we investigated foliar P fractions, root P-acquisition traits and gene expression, as well as rhizosphere and bulk soil properties of two dominant plant species, Leymus chinensis (a rhizomatous grass) and Stipa grandis (a bunchgrass), in a field grazing intensity gradient site in Inner Mongolia. Grazing induced different degrees of compensatory growth in the two dominant plant species, increased rhizosphere P availability, and alleviated plant P limitation. Under grazing, the foliar metabolite P of L. chinensis increased, whereas the nucleic acid P of S. grandis increased. Increased P fractions in L. chinensis were positively correlated with increased root exudates and rapid inorganic P absorption. For S. grandis , increased foliar P fractions were positively correlated with more fine roots, more root exudates, and up-regulated expression of genes involved in defense and P metabolism. Overall, efficient root P mobilization and uptake traits, as well as increases in leaf metabolic activity-related P fractions, supported plant compensatory growth under grazing, a process that differed between tiller types. The highest plant productivity and leaf metabolic activity-related P concentrations under medium grazing intensity clarify the underlying basis for sustainable livestock production. • Grazing induces plant compensatory growth and alleviates P limitation. • L. chinensis increases leaf metabolite P while S. grandis increases nucleic acid P. • Plant P-acquisition strategies differ between tiller types. • Root traits correlate with leaf P fractions by enhancing P mobilization and uptake. • Plant P utilization can be an important basis for sustainable grazing management. [ABSTRACT FROM AUTHOR]

The three-dimensional nature of agrophotovoltaic systems (APV) accounts for the needs of photovoltaic power generation and agricultural production. The combination can solve conflicts among utilization of resources, ecological protection, and agricultural production to achieve low-carbon economic development. However, the economically respond (crop yield and quality) of different species under the decreased light available system is still unclear. To provide insights, we compared agrophotovoltaic and traditional ecosystems to explore the economic feasibility of planting Bupleurum chinense (B. chinense) and Medicago sativa (M. sativa) from the perspectives of light utilization, photosynthetic responses, and land use. The combined system improved the land equivalent ratio, net income and species quality of B. chinense and M. sativa. Both species showed high plasticity, and maintained growth and development by regulating their morphology and photosynthetic parameters. B. chinense in the APV increased its light use efficiency, photosynthetic rate, and root biomass by increasing its height, electron transfer flux, and up-regulating a photosystem I protein (PsaA). M. sativa in the APV allocated more energy to photochemical reactions to improve photosynthetic capacity. It captured and utilized the limited light by reducing leaf mass per unit area and dark respiration, increasing the chlorophyll content, and down-regulating a photosystem II protein (PsbD). Our results showed the importance of species selection based on morphological and photosynthetic responses and provide insights into the selection of appropriate species, efficient resource utilization, and sustainable economic development based on APV. [Display omitted] • Bupleurum chinense and Medicago sativa maintained biomass accumulation and quality. • Bupleurum chinense increased photosynthesis by adjusting electron flux and PsaA. • Medicago sativa increased light capture area and protected photosystem II activity. • The agrophotovoltaic ecosystem increased the land use efficiency of both species. • Bupleurum chinense was more adaptable and improved economic benefits most. [ABSTRACT FROM AUTHOR]

Grazing has a profound impact on the availability of soil resources like carbon (C), nitrogen (N), and phosphorus (P) in grasslands. These changes can potentially make it difficult to meet microbial elemental demands, thus affecting microbial C use efficiency (CUE) and soil C dynamics. Nevertheless, it remains unclear how soil microbes respond to stoichiometric imbalances and their consequent effect on microbial CUE. In this study, we investigated the stoichiometry of soil labile resources, microbial biomass, extracellular enzymes, as well as the microbial community composition and microbial CUE, microbial respiration, microbial quotient (q MB), and soil organic carbon (SOC) changes, at sites with four grazing intensities (no grazing, light, medium, and heavy grazing) in a temperate steppe of northern China. Grazing led to decreased stoichiometric imbalances between soil labile resources and microbial biomass, thereby exacerbating limitations of available C on soil microbes. To alleviate this limitation of C, microbes raised the microbial threshold elemental ratios and microbial biomass, and increased fungi dominance rather than increased activities of C-, N-, and P- acquiring enzymes due to increased microbial own growth. Microbes also improved microbial CUE, q MB, and microbial respiration while decreasing SOC under increasing grazing intensity. These integrated adaptations denote that grazing can reduce SOC which is closely affected by soil microbial C utilization induced by resource change conditions despite the increased microbial biomass contribution to SOC. These findings illustrate the regulation of stoichiometric imbalances in soil C dynamics driven by microbes under grazing and improve our understanding of how stoichiometric changes influences soil C flows in semi-arid grassland. [Display omitted] • Grazing lowered stoichiometric imbalances but increased microbial C limitation. • Microbes decreased C-, N-, P-acquiring enzymes for limiting nutrients acquisition. • Microbes increased their biomass, threshold elemental ratios, and fungi:bacteria. • Aggravated grazing induced increased CUE, q MB, and microbial own growth. • Adaptative pathways of microbes resulted a decline of SOC. [ABSTRACT FROM AUTHOR]

Subsurface runoff is central to sloping land hydrology research. To explore the mechanism of nitrogen (N) and phosphorus (P) loss in surface and subsurface runoff in mountain forestland, we selected the typical tree species Quercus acutissima Carr. and Robinia pseudoacacia L. as our research objects and carried out simulated rainfall experiments to study the N and P loss characteristics of surface and subsurface runoff on different areas of slope land. Our results show that total N and total phosphorus P concentrations in surface runoff were initially high but tended to be stable as rainfall continued. Surface runoff accounted for most losses of both N and P, with a greater proportion found for forested land than for wasteland. Surface losses of N ranged from 70.8–88.8%, and those of P ranged from 82.2–87.5% of total losses in forest and wasteland, respectively. Our results show that the main pathway for N and P loss was surface runoff. However, N and P loss in subsurface runoff cannot be ignored in research on sloping land hydrology and the control by forestland of nonpoint source pollution in mountain forestland. Our research enriches sloping land hydrology research and provides a basis for the effective control of runoff, N, and P loss in forestland of the mountainous region of China and similar areas around the world. [ABSTRACT FROM AUTHOR]

Ecological security (ES) can express the health and integrity of regional ecosystems; hence, a better understanding of regional ES levels and their influencing factors can help to specify sustainable ecological management policies. Levels of ES in the West Liao River Basin were computed for the years of 2000 to 2020 at both the grid and county scale by using the pressure–state–response model, with ecosystem services also included in the assessment system. From 2000 to 2020, the area of both the forests and grasslands increased, due to the Grain for Green Project, which augmented net primary productivity (NPP), an ecosystem production service, and enhanced the overall habitat quality of the basin and promoted improvements to the regional ecological environment. The ES levels in most areas of the West Liao River Basin were improved over time, in that >90% of its area was above the middle level in 2020. The coordinates of "very insecure" moved to the basin's southeast, while "very secure" moved to its northwest, which indicated serious ES problems in the southeast of the basin. When compared with the most economically developed areas or remote areas having societal progress and human activities, generally the moderately developed areas have better ES levels. Further, human factors are more important to ES than natural factors, though all driving factors had enhanced impacts on the change in ES via their interactive effects. By determining the ES levels of the basin, four ecological management zones were then derived for it. We identified the main environmental problems in each ecological management zones and put forward the corresponding management measures, which would make the results more useful for supporting resource management and ecological protection of ecologically fragile areas in the agriculture and pasture interlaced landscape of northern China. • Ecological security levels were improved in most areas of the West Liao River Basin. • Moderately developed areas have better ecological security levels. • From 2000 until 2020, the gravity center of ecological security changed. • Human factors are more important to ecological security than natural factors. • Including ecosystem services can better quantify the ecological security status. [ABSTRACT FROM AUTHOR]

Panting protected forests to increase soil carbon sequestration is an effective means of reducing carbon emissions. Soil organic carbon (SOC) decomposition is one of the main indicators of soil carbon sequestration. However, SOC decomposition and its influencing factors in protected forests have not been fully characterized, especially in coastal zones. In this paper, coastal zone protected forest stands composed of Quercus acutissima Carruth (QAC), Pinus thunbergii Parl (PTP) and mixed PTP and QAC (MF) were selected as the research objects. The trends of the SOC decomposition rate were characterized by the beta (β) value, and the influencing factors were further explored with structural equation models. The results were as follows: The SOC content decreased from leaf to litter and then to the soil profile at all sites, while the δ13C value increased. The β value ranged from −3.12 to −5.76, with an average of −3.81. The β value was positively correlated with the diversity and richness of soil bacteria, supporting the hypothesis that the increase in δ13C with depth was mainly caused by isotope fractionation in the process of microbial SOC decomposition. The structural equation model showed that nitrogen and the availability of nitrogen have a strong ability to explain the value of β, which indicates that nitrogen-based edaphic variables play an important role in affecting SOC decomposition. The SOC decomposition rate in PTP was higher than that in QAC and MF. The results of this study indicate that the prediction of SOC decomposition based on the β value is suitable for coastal zone protected forests. The incorporation of edaphic variables into global carbon cycle models may enhance the predictions of SOC dynamics in coastal zone protected forests. [Display omitted] • δ13C enrichment along the soil depth profile was mainly due to selective utilization of carbon by bacteria. • Nitrogen availability and C:N have a strong ability to explain the SOC decomposition. • Tree species composition caused the significant change of SOC decomposition rate. • β value can be regarded as a good indicator of SOC decomposition in coastal zone. [ABSTRACT FROM AUTHOR]