Saline-alkaline Grassland Research Articles

Effect of mowing management on ecosystem stability response to different forms of nitrogen addition in a saline-alkaline grassland

Effect of mowing management on ecosystem stability response to different forms of nitrogen addition in a saline-alkaline grassland

Effects of Nitrogen Forms on Soil Enzyme Activities in a Saline-Alkaline Grassland.

Global climate change and agricultural practices have increased atmospheric nitrogen (N) deposition, significantly affecting the nitrogen cycling process in grasslands. The impact of different N forms on key soil enzyme activities involved in N nitrification, particularly in the saline-alkali grasslands of the Hexi Corridor, using natural grassland as a control (CK) and adding three N treatments: inorganic N (IN), organic N (ON) and a mixed N treatment (MN, with a 4:6 ratio of organic to inorganic N). Our study assessed the effects of these N forms on soil properties and enzyme activities crucial for N cycling. The findings indicate that different N forms significantly enhance soil mineral N content, with ON treatment leading to the highest increases in nitrate and ammonium content 92.44% and 35.6%, respectively, compared to CK. Both IN and ON treatments significantly boosted soil nitrate reductase and urease activities (p < 0.05), while MN treatment decreased nitrate reductase activity, with ON treatment showing the greatest sensitivity to enzyme activity changes. Soil pH slightly increased with N addition, but soil nitrite reductase activity remained relatively unchanged (0.372-0.385 mg g-1). Correlation analysis revealed that soil mineral N content and pH are key regulators of enzyme activities in saline-alkaline grasslands. These results suggest that different N forms should be considered in nutrient cycling models, with organic N addition potentially enhancing soil N conversion and mitigating nutrient limitations in grassland ecosystems.

Nutrient resorption exacerbates nitrogen–phosphorus imbalances in plants under increasing nitrogen addition in a saline-alkaline grassland

Abstract Reabsorbing nutrients from senescent tissues before leaf falling has been recognized as a strategy to adapt to nutrient deficiency. However, how nutrient resorption modulates the nitrogen (N)–phosphorus (P) balance inside plants remains unclear, especially under increased soil N availability. We examined the impacts of N addition at varying rates (0–32 g N m−2 yr−1) on nutrient resorption and the performance of nutrient resorption on controlling the internal N–P balance in the leaf and stem of a dominant grass species, Leymus secalinus, in a saline-alkaline grassland in northern China. After 6 years of N addition, N concentration and N:P ratio in green and senesced tissues (leaf and stem) rose with increasing N addition. The P concentration in green tissues decreased, but did not significantly change in senesced tissues with increasing N addition. The N resorption efficiency (NRE), P resorption efficiency (PRE) and NRE:PRE ratio significantly decreased along the N addition gradient. Moreover, we found more sensitive responses of N:P ratio in senesced tissues than in green tissues; such exacerbation of plant internal N–P imbalances mainly resulted from a disproportionate reduction in nutrient resorption, especially NRE. Overall, our study suggested that differences in NRE and PRE further exacerbated the internal N–P imbalances in plant litters.

Arbuscular mycorrhizal fungi communities and promoting the growth of alfalfa in saline ecosystems of northern China.

Arbuscular mycorrhizal fungi (AMF) are universally distributed in soils, including saline soils, and can form mycorrhizal symbiosis with the vast majority of higher plants. This symbiosis can reduce soil salinity and influence plant growth and development by improving nutrient uptake, increasing plant antioxidant enzyme activity, and regulating hormone levels. In this study, rhizosphere soil from eight plants in the Songnen saline-alkaline grassland was used to isolate, characterize, and screen the indigenous advantageous AMF. The promoting effect of AMF on alfalfa (Medicago sativa L.) under salt treatment was also investigated. The findings showed that 40 species of AMF in six genera were identified by high-throughput sequencing. Glomus mosseae (G.m) and Glomus etunicatum (G.e) are the dominant species in saline ecosystems of northern China. Alfalfa inoculated with Glomus mosseae and Glomus etunicatum under different salt concentrations could be infested and form a symbiotic system. The mycorrhizal colonization rate and mycorrhizal dependence of G.m inoculation were significantly higher than those of G.e inoculation. With increasing salt concentration, inoculation increased alfalfa plant height, fresh weight, chlorophyll content, proline (Pro), soluble sugar (SS), soluble protein (SP), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity while decreasing the malondialdehyde (MDA) content and superoxide anion production rate. The results highlight that inoculation with G.m and G.e effectively alleviated salinity stress, with G.m inoculation having a significant influence on salt resistance in alfalfa. AMF might play a key role in alfalfa growth and survival under harsh salt conditions.

Soil environment and annual rainfall co-regulate the response of soil respiration to different grazing intensities in saline-alkaline grassland

Grazing is a prevalent management strategy in grassland ecosystems that has profound effects on plants and soil microorganisms, consequently altering soil carbon (C) fluxes. However, the difference responses and regulatory mechanisms of soil autotrophic respiration (SRa) and heterotrophic respiration (SRh) to different grazing intensities remain unclear, especially in saline-alkaline grasslands. A six–year (2017–2022) field experiment involving four grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing) was conducted in a saline-alkaline grassland located in the agro-pastoral ecotone of northern China. Soil total respiration (SRtot) and its components (SRa and SRh), and the related biotic and abiotic factors (plants, soil microorganisms, and soil environment) were measured. The results showed that light grazing significantly decreased the mean SRh by 17.7% across six measuring years. The effects size of grazing on soil respiration fluctuated consistently with soil water content during the growing seasons (May–September), resulting in a neutral effect of grazing on the seasonal mean SRa. The cumulative soil C emissions of the current year varied with the seasonal precipitation in the previous year, whereas the changes in cumulative soil C emissions induced by grazing showed the same trends as annual precipitation. In addition, the key control factors for SRh and SRa differed and varied with grazing intensity and the soil environment played a critical role in regulating soil C fluxes. In conclusion, light grazing reduces soil microbial-driven C emissions and the soil environment and precipitation co-regulate the response of soil C fluxes to different grazing intensities in saline-alkaline grasslands.

Microbial community in the Leymus chinensis rhizosphere associates with its high production in mild saline–alkaline grassland

AbstractLeymus chinensis is a dominant grass widely distributed in Central Asia, in both saline−alkaline and non‐saline−alkaline grasslands. However, the mechanisms underlying its saline−alkaline tolerance have not been explored from the perspective of rhizosphere microbial communities. We investigated L. chinensis rhizosphere microbial communities in both saline–alkaline and non‐saline–alkaline grasslands. It was found that the biomass of L. chinensis was remarkably higher in saline–alkaline than in non‐saline–alkaline habitat and that changes in the rhizosphere bacterial and arbuscular mycorrhizal fungi (AMF) communities had a greater effect on biomass than climate, soil moisture, nutrients, and salinity. We demonstrated that the bacteria and AMF in the rhizosphere of L. chinensis grown in saline–alkaline grassland differed from those in non‐saline–alkaline grassland, and the differences were associated with soil salinity or alkalinity. The co‐occurrence networks of bacteria and AMF and bacteria–AMF interaction networks in rhizosphere were complex and connected, with more nodes and edges and a higher average degree of nodes and modularity in the saline–alkaline grassland. More complex networks promoted plant tolerance and growth under salt–alkali stress. High number of microbial keystone taxa was related to the nutrient concentration in the soil and L. chinensis leaves, and more remarkable direct effects of the bacterial and AMF keystone communities on plant nutrient concentrations were demonstrated in saline–alkaline grassland. This indicates that bacterial and AMF communities in saline–alkaline grasslands are favorable for plant growth and nutrient uptake. This study provides an accurate and beneficial source of soil microbial assemblages for future plant–microbial joint remediation of the saline–alkaline ecosystems.

Seasonal precipitation regulates magnitude and direction of the effect of nitrogen addition on net ecosystem CO2 exchange in saline-alkaline grassland of northern China

Increased nitrogen (N) deposition and altered precipitation regimes have profound effects on carbon (C) flux in semi-arid grasslands. However, the interactive effects between N enrichment and precipitation alterations (both increasing and decreasing) on ecosystem CO2 fluxes and ecosystem resource use efficiency (water use efficiency (WUE) and carbon use efficiency (CUE)) remain unclear, particularly in saline-alkaline grasslands. A four-year (2018–2021) field manipulation experiment was conducted to investigate N enrichment and precipitation alterations (decreased and increased by 50 % of ambient precipitation) and their interactions on ecosystem CO2 fluxes (gross- ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO2 exchange (NEE)), as well as their underlying regulatory mechanisms under severe salinity stress in northern China. Our results showed that N addition and precipitation alteration alone did not significantly affect the GEP, ER and NEE. While the interaction of N addition and increased precipitation over the four years significantly improved the mean GEP and NEE by 24.9 % and 15.9 %, respectively. The interactive effects of N addition and increased precipitation treatment significantly stimulated the mean value of WUE by 39.1 % compared with control, but had no significant effects on CUE over the four years. Based on the four-year experiment, the magnitude and direction of the effects of N addition on the NEE were related to seasonal precipitation. Nitrogen addition increased the NEE under increased precipitation and decreased it during extreme drought. Soil salinization (pH and base cations) could directly or indirectly affect GEP and NEE via plants productivity, plant communities, as well as ecosystem resource use efficiency (WUE and CUE) based on structural equation model. Our results address lacking investigations of ecosystem C flux in saline-alkaline grasslands, and highlight that precipitation regulates the magnitude and direction of N addition on NEE in saline-alkaline grasslands.

Spatial effects of nitrogen deposition on soil organic carbon stocks in patchy degraded saline-alkaline grassland

Soil organic carbon (SOC) represents the largest carbon sink and plays a critical role in mitigating global warming. Elevated nitrogen (N) deposition has substantial effects on soil carbon sequestration in grassland ecosystems. However, almost no study has examined the effects of N deposition in widely degraded saline-alkaline grasslands. This is a critical knowledge gap because saline-alkaline degradation is one of the key global threats to carbon sequestration services provided by grasslands. Here, we conducted a 3-year N addition experiment in a patchy degraded saline-alkaline grassland to examine the effects of simulated N deposition on SOC stocks, along with spatial effects for five types of saline-alkaline degraded patches (multi-species-mixture patches; Leymus chinensis patches; Puccinellia tenuiflora patches; Chloris virgata patches and Artemisia anethifolia patches). N addition had no overall effect on SOC stocks in the degraded saline-alkaline grassland, but showed pronounced spatial effects depending on the saline-alkaline characteristics of degraded patches. Specifically, SOC decreased in multi-species-mixture patches with low saline-alkaline stress (soil 7 < pH < 8), but no change was observed in other types of degraded patches with high saline-alkaline stress (soil pH > 9). Although N addition promoted plant growth and increased aboveground biomass in all degraded patches, the resulting aboveground carbon input did not further contribute to soil carbon sequestration. Rather than aboveground biomass, soil pH was the critical controlling factor for soil carbon in the saline-alkaline grassland. However, N addition did not alter soil pH in all degraded patches. In multi-species-mixture patches with lightly saline-alkaline soils, N addition reduced species richness and increased microbial C:N ratio, which could accelerate soil carbon decomposition, thereby decreasing SOC stocks. Our findings suggest that increased global N deposition would not restore natural soil carbon in degraded saline-alkaline grassland, and instead, may further deteriorate soil carbon sequestration in lightly degraded patches with high plant diversity and low saline-alkaline stress.

Study on Soil Desalination Process of Saline-Alkaline Grassland along the Yellow River in Western Inner Mongolia under Subsurface Drainage

This study aimed to explore the characteristics of water and salt transport in saline-alkali grassland, effectively guide the ecological construction of saline-alkali grassland along the Yellow River in western Inner Mongolia, and provide a theoretical basis and technical support for the ecological restoration of saline-alkali grassland and regional environmentally sustainable development. The desalination process of saline-alkali soil under the condition of subsurface pipe drainage was simulated using an indoor soil tank test. The variation in soil leaching water consumption, the salinity of the leaching filtrate with time, the accumulation of the filtrate, and the desalination rate of the filtrate under the condition of continuous leaching with a 25 mm head were analyzed. At the same time, the variation process of soil conductivity at 0~40 cm (upper layer), 40~80 cm (middle layer), and 80~120 cm (lower layer) was analyzed. Subsurface pipe drainage can reduce the soil salt content, while reducing the control area of the subsurface pipes can accelerate the soil desalination rate, thus improving the quality of saline-alkali soil. In addition, the leaching effect under 30 cm partition spacing was better than that under 35, 40, and 45 cm partition spacing, and the corresponding desalination rate was higher. Under stable continuous leaching with a 25 mm head, the entire leaching process can be divided into three stages: the rapid desalination, moderate desalination, and stable stages. During the desalination process, the upper, middle, and lower layers were desalinated synchronously, and the desalination rate of the upper layer was the highest, followed by the desalination rate of the middle and lower layers.

Plant community mediated methane uptake in response to increasing nitrogen addition level in a saline-alkaline grassland by rhizospheric effects

Methane (CH4) uptake in dryland ecosystems is a pathway in mitigating atmospheric CH4 concentrations. A number of studies have demonstrated that nitrogen availability is a key regulator of the CH4 oxidation process. However, how plants mediate soil CH4 oxidation in response to N addition, particularly in saline-alkaline grasslands in the vast regions of the northern China, has received little attention. We conducted a 3-yr (2017–2019) in-situ experiment with eight N addition levels to examine the effect of N on soil CH4 oxidation, and to explore the linkages between the N-induced changes of plant community and the seasonal dynamics of CH4 in a saline-alkaline grassland.We found that the saline-alkaline grassland was a weak CH4 sink displaying nonlinear CH4 uptake levels in response to N additions, possibly due to the nonlinear changes in the abundance of key functional genes (pmoA) that were responsible for CH4 oxidation. The changes in plant productivity and diversity that were induced by N additions explained 21 % of the variations in CH4 uptake. The N-induced increase in productivity indirectly enhanced CH4 uptake at N addition rates of <10 g m−2 yr−1, while the decrease in biodiversity indirectly inhibited CH4 uptake when N addition exceeded 10 g m−2 yr−1. The N-induced changes in the plant community can affect CH4 uptake, mainly through the rhizospheric effects of plants. In conclusion, our findings underscore the importance of rhizosphere when assessing the CH4 uptake in saline-alkaline grassland ecosystems.

Isolation and species diversity of arbuscular mycorrhizal fungi in the rhizosphere of Puccinellia tenuiflora of Songnen saline-alkaline grassland, China

Salinization has led to the deterioration of the ecological environment, affected the growth of plants, and hindered the development of agriculture and forestry. Arbuscular mycorrhizal (AM) fungi, as important soil microorganisms, play significant physiological and ecological roles in promoting plant nutrient absorption and improving soil structure. Puccinellia tenuiflora (Turcz.) Scribn. et Merr. in Songnen saline-alkaline grassland was selected as the research object to observe AM fungal colonization of the roots and explore the species and diversity of AM fungi in symbiotic association with P. tenuiflora. This study showed that AM fungi colonized in P. tenuiflora roots and formed a typical Arum–type mycorrhizal structure. A significant correlation was observed between vesicular abundance and the colonization intensity of mycorrhiza. Isolation and identification revealed 40 species of AM fungi in the rhizosphere of P. tenuiflora, belonging to 14 genera, of which two species could not be identified. The richness of the genus Glomus was the highest, accounting for 30% of the total species. Funneliformis mosseae and Rhizophagus intraradices were isolated from all the samples and were the species with the widest distribution in the rhizosphere of P. tenuiflora. Correlation analysis showed that pH only had a significant impact on the distribution of a few species, such as Glomus pustulatum, Diversispora spurca, Glomus aggregatum, Rhizophagus clarum, and Acaulospora foveata. The present study provides a theoretical basis for further exploring the resources of AM fungi in saline-alkaline soil.

Nitrogen Deposition Does Not Mitigate Soil Carbon Loss in Patchy Degraded Saline-Alkaline Grassland

Nitrogen Deposition Does Not Mitigate Soil Carbon Loss in Patchy Degraded Saline-Alkaline Grassland

Seasonal Precipitation Regulates the Magnitude and Direction of the Effect of Nitrogen Addition on Net Ecosystem Co 2 Exchange In A Saline-Alkaline Grassland of Northern China

Seasonal Precipitation Regulates the Magnitude and Direction of the Effect of Nitrogen Addition on Net Ecosystem Co 2 Exchange In A Saline-Alkaline Grassland of Northern China

Fire-Related Cues Significantly Promote Seed Germination of Some Salt-Tolerant Species from Non-Fire-Prone Saline-Alkaline Grasslands in Northeast China.

Seed germination in response to fire-related cues has been widely studied in species from fire-prone ecosystems. However, the germination characteristics of species from non-fire-prone ecosystems, such as the saline-alkaline grassland, where fire occasionally occurs accidentally or is used as a management tool, have been less studied. Here, we investigate the effects of different types of fire cues (i.e., heat and smoke water) and their combined effect on the seed germination of 12 species from the saline-alkaline grassland. The results demonstrated that heat shock significantly increased the germination percentage of Suaeda glauca and Kochia scoparia var. sieversiana seeds. Smoke water significantly increased the germination percentage of Setaria viridis and K. scoparia seeds. However, compared with single fire cue treatments, the combined treatment neither promoted nor inhibited seed germination significantly in most species. These results suggest that fire cues can be used as germination enhancement tools for vegetation restoration and biodiversity protection of the saline-alkaline grassland.

Effects of nitrogen addition and precipitation alteration on soil respiration and its components in a saline-alkaline grassland

The responses of soil total respiration (Rs) and its components (soil autotrophic respiration (Ra) and heterotrophic respiration (Rh)) to nitrogen (N) deposition have been widely evaluated in non-saline-alkaline grasslands. However, their responses to N addition under drought and wet conditions, especially in saline-alkaline grasslands, remain unclear. A two-factorial experiment involving N addition and precipitation changes (decreased or increased 50% precipitation relative to ambient) was conducted in a saline-alkaline grassland of Northern China, while soil respiration was measured in different treatment plots during two growing seasons (2018, 2019). Results showed that the addition of N or changes in precipitation alone had no significant effect on Rs, Ra or Rh in both years because root productivity and soil microbial biomass were not affected. However, N addition with increased precipitation synergistically augmented seasonal mean Rs and Ra by 25.7% and 46.8% in 2018, and by 42.4% and 89.3% in 2019, respectively, owing to the increase in plant productivity. The variation in Ra primarily contributed to variation in Rs, and the effect size of N addition on Rs and Ra were increased with precipitation. In addition, a structural equation model showed that the response of soil respiration to N addition and precipitation changes was regulated by soil salinization, in which the Ra was regulated by soil based cations while Rh was controlled by soil pH values. Our study highlights that N addition with increased precipitation preferentially affects plants rather than microorganisms, and that Rh was not sensitive to N addition and precipitation changes in saline-alkaline grassland.

Effects of precipitation change and nitrogen addition on soil net N mineralization in a saline-alkaline grassland of Northern Shanxi Province, China.

To explore the responses of soil net nitrogen (N) mineralization rate to precipitation varia-tion and nitrogen deposition in salinized grassland, we set precipitation manipulation and nitrogen addition experiments in the typical agro-pastoral ecotone saline-alkaline grassland of Northern Shanxi Province, China. The in situ soil net N mineralization rate was determined by top-cover buried PVC cylinder from May to September in 2019. The results showed that there were seasonal dynamics in soil net N mineralization rate. Soil net N mineralization rate was not affected by increase/decrease precipitation (±50%), nitrogen addition (10 g·m-2·a-1) or the combination of nitrogen addition and increase 50% precipitation treatments. The combination of nitrogen addition and 50% reduction of precipitation significantly improved soil net nitrification rate and net N mine-ralization rate by 10.8 and 8.6 times, respectively. Soil net nitrogen mineralization rate was positively related to soil water content, and negatively related to soil pH. The effects of nitrogen addition on soil nitrogen mineralization rate were dependent on precipitation conditions. Soil water content and pH were important factors regulating soil net nitrogen mineralization rate in the saline-alkaline grassland of Northern Shanxi Province. Therefore, to roundly assess the response model of soil N mine-ralization process to global change, it is necessary to consider the interaction of precipitation changes and nitrogen addition, and the soil physical and chemical properties of salinized grassland.

Effects of nitrogen addition at different levels on soil microorganisms in saline-alkaline grassland of northern China

Effects of nitrogen addition at different levels on soil microorganisms in saline-alkaline grassland of northern China

Response of soil net nitrogen mineralization to different levels of nitrogen addition in a saline-alkaline grassland of northern China

Response of soil net nitrogen mineralization to different levels of nitrogen addition in a saline-alkaline grassland of northern China

Nitrogen addition interacted with salinity-alkalinity to modify plant diversity, microbial PLFAs and soil coupled elements: A 5-year experiment

Atmospheric nitrogen (N) deposition has greatly increased in the past 50 years due to fossil fuel combustion and the use of synthetic fertilizers. Because N is the limiting nutrient for plant growth in terrestrial ecosystems, atmospheric deposition of N has the potential to increase biomass production, reduce species richness, inhibit microbial growth, and result in soil acidification. However, few studies have evaluated whether and how N inputs affect plant species diversity and the interactions among soil elements in saline-alkaline grassland ecosystems. The Songnen grassland of China is characterized by heterogeneous patches of saline-alkaline soils. A 5-year nitrogen deposition experiment was conducted in two contrasting saline-alkaline communities. Results showed that increasing N input increased the plant biomass production and reduced plant species richness in the low saline-alkaline stress community, but salinity-alkalinity was able to alleviate the negative effects of nitrogen input on community diversity. Plant communities were more sensitive to N addition than microbial communities. N addition induced a shift from N to P as the limiting factor in temperate grassland ecosystems. In particular, salinity-alkalinity in the high stress community increased the conversion rate from N to P limitation. These results highlight the importance of the integrative study of the plant-soil-microbe system in ecosystems under global N enrichment. Our study emphasizes the need for future research to understand the mechanisms that control biogeochemical cycling and maintain ecosystem stability under the combined conditions of N addition and other stress factors, such as saline-alkalinity.

Regenerative Role of Soil Seed Banks of Different Successional Stages in A Saline-alkaline Grassland in Northeast China

Soil seed banks can act as a potential seed source for natural revegetation and restoration. However, in a saline-alkaline grassland, it remains unclear how the stages of vegetation succession affect the characteristics of soil seed banks and the potential of soil seed banks of different successional stages for vegetation restoration. In this study, seasonal changes of the soil seed bank, and seed production and dispersal dynamics along degradation successional gradients were investigated in a saline-alkaline grassland in Northeast China, where the dominant grass during the 1960s, Leymus chinensis was replaced with the secondary successional order of Puccinellia chinampoensis, Chloris virgata, and Suaeda salsa, together with bare patches. It was found that the soil seed bank composition varied according to the changing vegetation and had the highest species richness (7–16) in the climax successional stage, but had a low Sorensen similarity (0.22–0.37) with the aboveground vegetation. There was a high seed density of the soil seed bank (21 062–62 166/m2 in August and December) and also high Sorensen similarity index values (0.47–0.60) in the secondary successional stages of P. chinampoensis, C. virgata, and S. salsa. In bare patches, there were many seeds in the soil seed bank and some seedlings also appeared in the aboveground vegetation, indicating the existence of a persistent soil seed bank. Seed density and species richness differed substantially among the different successional stages, which was related to the reproductive characteristics of the standing plants in vegetation communities. Due to the lack of propagules of perennial species, especially the climax species of L. chinensis, in the soil, the successful restoration of the degraded saline-alkaline grassland was not possible. The study proved that in a degraded saline-alkaline grassland dominated by biennial or annual species, the soil seed bank was important for the revegetation of the current dominant plants, but not for the restoration of the original target species. Therefore, it is necessary to induce seeds or other propagules of the target perennial species.