Seasonal variations of soil inorganic nitrogen contents and their responses to changing grazing intensity in grasslands of an agro-pastoral ecotone in northern Shanxi, China

Livestock grazing is an important component and driver of biodiversity in grassland ecosystems. While numerous studies and a few meta-analyses had been conducted on the response of single taxon diversity to grazing in grasslands, a synthesis of how multi-taxa diversity is affected has been largely missing, especially reflecting its changes along a grazing intensity gradient. We performed a comprehensive meta-analyses of 116 published studies on the species richness (SR) and Shannon−Wiener index (H′) of plants, arthropods, and microbes to examine the response of biodiversity to grazing intensity in temperate grasslands globally. This quantitative assessment showed that the response of SR and H′ to grazing intensity agreed with the intermediate disturbance hypothesis in grasslands; SR and H′ increased with light and moderate grazing intensities, while they decreased at heavy intensity. In addition, plant SR increased markedly with light and moderate grazing and declined with heavy grazing intensity; however, H′ increased at light intensity and declined at moderate and heavy intensities. Moreover, the SR and H′ of microbes were enhanced at light and moderate grazing and were significantly reduced with heavy intensity. The SR and H′ of arthropods monotonously declined with increasing grazing intensity. Importantly, structural equation modeling showed that grazing resulted in enhanced plant SR mainly through its negative effects on plant biomass. Grazing had negative effects on plant coverage and arthropod abundance so that arthropod SR declined with increased grazing intensity. Moreover, increased grazing intensity caused an increase in soil pH, decrease in soil moisture, and then a decrease in microbe SR. Our findings confirm that different taxa exhibit diverse responses to changes in grazing intensity, and the way that grazing intensity affects diversity also varied with different taxa. We strongly recommend considering the requirements of multi-taxa diversity when applying grazing management and including arthropods and microbes in monitoring schemes.

Land use change is a considerable representation of mutual effect between human and natural activities. Northern Shanxi is located in the northern agro pastoral ecotone, which the land use pattern changes violently. This paper focuses on the dynamic change characteristics of cultivated land and grassland in the agro pastoral ecotone of northern Shanxi from 2000 to 2015, and explores the main driving factors of their change. It can provide support for land planning and management and relevant policy-making in northern Shanxi and promote regional sustainable development. The results showed that: ➀ There was a close interrelation between the change of cultivated land and grassland I n northern Shanxi, and the whole showed the opposite dynamic change trend. ➁The main land transfer type of cultivated land and grassland is construction land. And grassland is also the main transfer type of cultivated land. And cultivated land contributes greatly to the growth of grassland area. ➂Economic factors are the main driving force which affecting the area change of cultivated land and grassland, followed by the benefit factors of agricultural development, and finally the labor factors. ➃Economic factors can explain the shift of cultivated land and grassland in different districts and counties in northern Shanxi. The benefit factor of cultivated land development plays a negative driving role on cultivated land, the benefit of grassland development plays a promoting role on the growth of grassland area, and the driving force of labor factor is relatively small.

We explored the impacts of nitrogen (N) inputs and the rhizosphere effect on the properties of rhizosphere and bulk soils in a salinized grassland in Northern Shanxi under N addition rates of 0, 1, 2, 4, 8, 16, 24 and 32 g N·m-2·a-1. The results showed that N addition significantly decreased soil pH, but significantly increased Ca2+, NO3--N and inorganic nitrogen contents in rhizosphere and bulk soil. With the increases of N addition rates, the contents of Ca2+, NO3--N, inorganic nitrogen in rhizosphere and bulk soils and total nitrogen in rhizosphere soil increased gradually, whereas the contents of Na+, K+, Mg2+, NH4+-N and amino acid in rhizosphere soil, and total nitrogen in bulk soil first increased and then decreased. Results of the principal component analysis showed that the responses of soil properties to low (≤8 g·m-2·a-1) and high nitrogen addition rates (>8 g·m-2·a-1) were significantly different. Compared with bulk soil, soil pH, the contents of organic acids and amino acids in rhizosphere soil were significantly lower by 0.71 units, 44.3% and 9.8%, respectively, while the contents of K+, Ca2+, Mg2+, NH4+-N, inorganic nitrogen, total carbon and total nitrogen in rhizosphere soil were significantly higher by 51.0%, 47.6%, 20.8%, 215.5%, 139.3%, 31.7% and 65.3%, respectively. These results indicated that rhizosphere effect on soil properties was stronger than that of nitrogen addition.

The changes in soil nitrogen mineralization rate induced by litter input can determine the availability of nitrogen for plant growth in the soil. In forest ecosystems, the mixing of different species of litter can alter the chemical properties of the litter, ultimately affecting the rates of soil nitrogen transformation and cycling. In this study, litters with Fraxinus mandshurica Rupr. and Larix gmelinii (Rupr.) Kuzen. and mixed litter with Fraxinus mandshurica and Larix gmelinii were added to dark brown soil and incubated in the lab for 175 days at 25 °C. NH4+-N and NO3−-N contents and nitrogen mineralization rates were periodically measured to explore the effect of mixed litter addition on soil nitrogen mineralization. The results showed that compared to Larix gmelinii litter, Fraxinus mandshurica litter demonstrates higher carbon, nitrogen, and phosphorus contents while exhibiting lower lignin and cellulose contents and lower C/N and lignin/N ratios. Soil inorganic nitrogen content showed a trend of initial decrease followed by an increase. At the end of the incubation, soil NH4+-N and NO3−-N and the total inorganic nitrogen contents were 4.6–7.8 times, 2.2–3.4 times, and 2.9–4.3 times higher than the initial value, respectively. The soil nitrogen mineralization rate exhibited an initial rapid increase followed by stabilization. During days 7–28 of incubation, the nitrogen mineralization rates in litter addition treatments were lower than that in the control, while they were higher than that in the control during days 42–175. The soil nitrogen mineralization rate in the treatments with Fraxinus mandshurica litter and mixed litter were higher than those in the treatment with Larix gmelinii litter. The cumulative net nitrogen mineralization amounts in the Fraxinus mandshurica litter and mixed litter treatments were higher than those in the Larix gmelinii litter treatment, being 1.5 and 1.2 times those of the Larix gmelinii litter treatment, respectively. MBC and MBN presented a trend of first increasing and then decreasing, peaking on days 7 and 14 of incubation, respectively. Correlation analysis revealed that soil inorganic nitrogen content and nitrogen mineralization rate were positively correlated with the litter total nitrogen and soil microbial carbon and nitrogen and negatively correlated with litter C/N and lignin/N. The changes in soil inorganic nitrogen and nitrogen mineralization are primarily associated with soil microbial immobilization. Initially, in the treatments with litter addition, an increase in microbial biomass enhanced the immobilization of soil inorganic nitrogen. Subsequently, as litter mineralization progressed, the amount of litter decreased, leading to reduced microbial biomass and weakened immobilization. This study indicates that the interaction between litter types and soil microorganisms is the key factor affecting soil nitrogen mineralization process and soil mineral nitrogen content. These findings provide a scientific basis for soil fertility management in the forest ecosystems of Northeast China.

Soil nitrogen cycling in forests may be accelerated or inhibited by global warming, with consequences on forest productivity. Such an impact will be more complicated with extending period of warming. We examined the effects of warming on soil inorganic nitrogen content in the young and mature Cunninghamia lanceolata plantations. Warming was simulated by means of soil cable warming, simulating a future climate change scenario of 4 ℃ warming. The results showed that after three years warming, both total soil inorganic nitrogen and ammonium contents in the young and mature plantations were significantly reduced. The sharp decline occurred in the young plantation, with soil ammonium content in 0-10, 10-20, 20-40, 40-60 cm soil layers decreased by 32.1%, 37.1%, 20.8% and 19.9%, respectively. Dissolved organic nitrogen was reduced and N2O emission was accelerated in the both plantations. The main reasons for the reduction of soil inorganic nitrogen concentration were lower input of organic nitrogen substrate and higher gaseous nitrogen loss. The decrease in soil organic nitrogen substrate and increase in gaseous nitrogen emissions in the young plantation were larger than those in the mature plantation, indicating that soils in the young plantation were more sensitive to increasing temperature. The 3-year warming decreased soil inorganic nitrogen contents in the two C. lanceolata plantations, which might negatively affect productivity of the C. lanceolata plantations in subtropic China.

Abstract. The application of nitrification inhibitors together with ammonium-based fertilizers is proposed as a potent method to decrease nitrous oxide (N2O) emission while promoting crop yield and nitrogen use efficiency in fertilized agricultural fields. To evaluate the effects of nitrification inhibitors, we conducted year-round measurements of N2O fluxes, yield, aboveground biomass, plant carbon and nitrogen contents, soil inorganic nitrogen and dissolved organic carbon contents and the main environmental factors for urea (U), urea + dicyandiamide (DCD) and urea + 3,4-dimethylpyrazol phosphate (DMPP) treatments in a wheat–maize rotation field. The cumulative N2O emissions were calculated to be 4.49 ± 0.21, 2.93 ± 0.06 and 2.78 ± 0.16 kg N ha−1 yr−1 for the U, DCD and DMPP treatments, respectively. Therefore, the DCD and DMPP treatments significantly decreased the annual emissions by 35% and 38%, respectively (p < 0.01). The variations of soil temperature, moisture and inorganic nitrogen content regulated the seasonal fluctuation of N2O emissions. When the emissions presented clearly temporal variations, high-frequency measurements or optimized sampling schedule for intermittent measurements would likely provide more accurate estimations of annual cumulative emission and treatment effect. The application of nitrification inhibitors significantly increased the soil inorganic nitrogen content (p < 0.01); shifted the main soil inorganic nitrogen form from nitrate to ammonium; and tended to increase the dissolved organic carbon content, crop yield, aboveground biomass and nitrogen uptake by aboveground plant. The results demonstrate the roles the nitrification inhibitors play in enhancing yield and nitrogen use efficiency and reducing N2O emission from the wheat–maize cropping system.

The single‐year response of soil inorganic nitrogen (N) content and indices of red raspberry (Rubus ideaus L.) yield, vigor, and N status to rate and source of fertilizer N were determined. Twenty‐nine trials were conducted in commercial plantings from 1994 to 1996. Treatments were 0, 55, or 110 kg N ha−1 as ammonium nitrate or 55 kg N ha−1 as a slow‐release fertilizer product containing 60% polycoated sulfur‐coated urea and 40% urea. Soil nitrate (NO3) content frequently increased during the growing season, indicating that soil N supply was nonlimiting. The plant indices were generally insensitive to fertilizer‐N rate under these high‐N fertility conditions. Soil nitrate content measured after berry harvest was frequently excessive even at the recommended N rate and can be used to identify fields with excess N fertility. The slow‐release N fertilizer provided limited benefits compared with use of ammonium nitrate.

晋北地区土地利用覆被格局的演变与模拟

Question: How is grazing intensity associated with species and morpho‐functional traits (MFTs) composition, productivity and richness of annual dominated grasslands? Have native and exotic species similar associations to this gradient?Location: Anthropogenic grassland in the Espinal vegetation in the sub‐humid area of the mediterranean type climate region of Chile (35°58’ S, 72°17’ W).Methods: Data were obtained from a long‐term (eight years) experiment with six stocking rates (1 to 3.5 sheep/ha). Detrended Correspondence Analysis (DCA) and regression analysis were used to determinate the relationship between grazing intensity and biomass, richness, abundance and traits of the species.Results: The first DCA axis was related to grazing intensity and explained most of the floristic variation (69.3%); the abundance of some non‐native species, e.g. Vulpia megalura were highly correlated with this axis. In the DCA for MFTs the first axis explained 87% of the variance and was also related to grazing intensity; the abundance of small size plants and shallow roots increased with grazing intensity. The relative abundance of grasses and composites, but not of legumes, changed with stocking rate: as grazing intensity increased composites became the predominant species to the detriment of grasses. The above‐ground biomass measured in exclusion cages declined with increasing grazing pressure. The richness of exotic species was greater compared to native ones at low stocking rates, but they converge to similar values at higher stocking rates. However, the relative abundance of exotic species was greater than 75% in all stocking rates.Conclusions: Grazing intensification has large effects in the structure of grassland in central Chile. With grazing intensities greater than 1 sheep/ha species characteristics change; evolving in a few years (6–8) towards a similar community regardless of the stocking rate. The overgrazed community has more native than exotic species richness, possibly due to greater defence traits against herbivory of this group of species.

Arbuscular mycorrhizal fungi (AMF) taxa, glomalin protein, and hyphal density are potential indicators of soil functionality of temperate grasslands in marginal environments subject to grazing over the years. This study evaluated how the AMF community composition, glomalin protein, and hyphal density vary in response to grazing intensity (low or high) and seasonality (spring and autumn) in sodic soils of Argentinian temperate grasslands. The AMF community was dominated by Glomeraceae species. Funneliformis geosporus and Glomus brohultii were the most abundant in both seasons and all grasslands. No AMF species were associated with a particular grazing intensity. However, Entrophospora etunicata, Glomus fuegianum, Septoglomus constrictum, and Acaulospora sp. occurred only in spring, and no species were exclusive to autumn. Hyphal density was highest in grasslands with low grazing intensity and can be considered an indicator of soil functionality. Glomalin protein was the highest in spring in all grasslands. The lower grazing intensity in grasslands with poor livestock control showed no changes in AMF diversity. The AMF community showed high adaptation to soil conditions, indicating high resilience. We concluded that longer periods of controlled grazing management are needed to improve soil conditions and, consequently, change the AMF species composition.

Litter amendment rather than phosphorus can dramatically change inorganic nitrogen pools in a degraded grassland soil by affecting nitrogen-cycling microbes

Zunehmende Landnutzungsintät ist eine der Hauptursachen für den weltweiten Biodiversitätsverlust. Die Zahl der gefährdeten Arten steigt stetig an und nur wenige Arten - meist Generalisten - profitieren von der Landnutzungsintensivierung. Folglich beeinträchtigt steigende Landnutzungsintensität Arten mit bestimmten „life-history traits“ stärker als andere. Durch unterschiedlich intensive Landnutzung unterscheiden sich die biotischen und abiotischen Gegebenheiten für interagierende Arten und können deshalb multitrophische Interaktionen beeinflussen. Landnutzungsintensität beeinflusst viele Bereiche in der Ökologie, aber diese Effekte können in Regionen mit unterschiedlichen Umweltbedingungen verschieden ausfallen. In meiner Arbeit stellte ich die Frage, wie Landnutzungsintensität ökologische Aspekte wie Artenvielfalt und –abundanz und das Vorkommen gefährdeter Arten (Kapitel II), ökologische und „life-history traits“ (im Weiteren als „Traits“ abgekürzt) von Lebensgemeinschaften (Kapitel III) und multitrophische Interaktionen (Kapitel IV), beeinflusst. Mich interessierte, ob sich Effekte zwischen Regionen unterscheiden. In meiner Studie in Kapitel II habe ich Tagfalter und tagaktive Nachtfalter (im Weiteren als Schmetterlinge bezeichnet) als Zielgruppe ausgewählt. Aus Roten Listen Deutschlands habe ich die Gefährdungssituation von Arten erhalten. Ich erwartete einen Rückgang der Schmetterlingsarten, ihrer Abundanz und des Vorkommens gefährdeter Arten mit zunehmender Landnutzungsintensität in Abhängigkeit von der Region. In Kapitel III habe ich die tagaktiven Nachtfalter aus dem Datensatz des Kapitels II herausgenommen, da nur für Tagfalter verlässliche Daten zu zehn ausgewählten „Traits“ in der Literatur verfügbar sind. Ich erwartete, dass sich „Traits“ mit zunehmender Landnutzungsintensität von für Spezialisten typischen hin zu für Generalisten typischen verschieben. Weiterhin erwartete ich, dass Arten, die überwiegend „Traits“ von Spezialisten aufweisen, gefährdet sind. Um dies zu untersuchen, habe ich Schmetterlinge auf Transekten auf 137 Graslandflächen in drei verschieden Regionen Deutschlands gefangen. Die ausgewählten Graslandflächen zeigten in jeder Region einen Gradienten von sehr extensiver bis sehr intensiver Landnutzungsintensität. Um die Landnutzungsintensität zu berechnen, habe ich einen Landnutzungsintensitätsindex verwendet, der sich aus der Menge Dünger, Mahdhäufigkeit und der Beweidungsintensität zusammensetzt. In Kapitel IV behandle ich ein multitrophisches System, das aus vier Stufen besteht: Endophyten der Gattung Neotyphodium, die sich asexual in Gräsern vermehren („Bottom-up“-Kontrolle), der Wirtspflanze, an der Pflanze saugenden Blattläusen und deren natürlichen Feinden („Top-down“-Kontrolle). Frühere Feldstudien führten zu kontroversen Schlüssen bezüglich des Charakters der Symbiose zwischen Endophyten und ihren Wirtspflanzen, da einige Studien negative Wirkungen (Mutualismus), andere positive Wirkungen auf Herbivore (Parasitismus) zeigten. Ich nahm an, dass Effekte von Endophyten auf Blattlausabundanzen von Umweltbedingen in unterschiedlichen Regionen und unterschiedlich intensiv genutzten Graslandflächen und von Prädatoren, die eventuell Blattläuse von Endophyten-freien Pflanzen bevorzugen, beeinflusst werden. Für diese Studie habe ich in zwei Regionen 40 Graslandflächen ausgewählt, von denen in jeder Region zehn intensiv und zehn extensiv genutzt waren, um auf die damit einhergehenden unterschiedlichen Umweltbedingungen zu testen. Auf jede Graslandfläche habe ich vier Grastöpfe (Lolium perenne) mit Blattläusen (Rhopalosiphum padi) ausgebracht. Die Blattlauspopulationsgröße wurde regelmäßig aufgenommen. Das Gras war a) entweder mit Endophyten (Neotyphodium lolii) infiziert oder nicht und b) Prädatoren wurden ausgeschlossen oder hatten freien Zugang zu den Töpfen. In allen drei Studien (Kapitel II-IV) konnte ich einen starken Effekt der Landnutzungsintensität auf die getesteten Variablen feststellen und einige Effekte unterschieden sich zwischen den Regionen. Die Schmetterlingsartenvielfalt und -abundanz, die in Kapitel II untersucht wurden, nahmen nur in zwei Regionen signifikant ab, aber nicht der dritten. Ähnlich war das Vorkommen gefährdeter Schmetterlingsarten durch die Landnutzungsintensität beeinflusst. Der Regionenunterschied des Landnutzungseffekts ist wahrscheinlich durch die Größe der unterschiedlichen regionalen Artenpools und der korrelierenden Anzahl gefährdeter Arten und des Vorhandenseins von Kalkmagerrasen in nur zwei Regionen bedingt. In artenreichen Regionen mit vielen gefährdeten Arten sind Landnutzungsintensitätseffekte stark ausgeprägt im Gegensatz zu artenarmen Regionen, in denen es meist nur gewöhnliche Arten gibt, die nicht stark auf intensive Landnutzung reagieren. Zudem stellen Kalkmagerrasen, die in der artenarmen Region fehlen, ein wichtiges Habitat für Schmetterlinge dar. Ich konnte zeigen, dass Düngung und steigende Beweidungsintensität, aber nicht die Mahdfrequenz die Artenvielfalt signifikant verringerten. In Kapitel III zeigte ich, dass sich acht der zehn getesteten „Traits“ von Tagfaltergemeinschaften mit steigender Landnutzungsintensität von Spezialisten-typischen hin zu Generalisten-typischen „Traits“ veränderten (breitere Nahrungsnische, höhere Ausbreitungsfähigkeit, stärkeres Wanderverhalten, größeres Verbreitungsgebiet, geringere Populationsdichte, Schlupf von mehr als einer Generation pro Jahr, Überwinterung in einem höher entwickelten Raupenstadium und eine längere Flugzeit). Ein Vergleich des Gefährdungsgrades der Arten in der Roten Liste 2008 und einer Kombination von „Traits“ für jede Art zeigte, dass Arten mit mehreren „Traits“, die typisch für extensiv genutzte Graslandflächen und damit für Spezialisten sind, gefährdet sind. Das weist darauf hin, dass nur Arten mit „Traits“ von Generalisten in der Lage sind, mit häufigen Störungen im Habitat und unbeständiger Futterpflanzenverfügbarkeit, welches beides durch hohe Landnutzung verursacht ist, umgehen können. In dem multitrophischen System in Kapitel IV konnte ich starke Effekte durch Landnutzungsintensität und Prädatoren auf die Blattlausabundanz feststellen. Der Effekt der Endophyten dagegen war schwach und Regionen-abhängig. Endophyten verringerten die Blattlausabundanz nur in einer der beiden Regionen. Prädatoren und Landnutzungsintensität hatten keinen zusätzlichen Einfluss auf den Effekt der Endophyten. Insgesamt weist dies darauf hin, dass Effekte von Endophyten auf Herbivore eine geringere Bedeutung in natürlichen Systemen haben, wenn sie mit anderen Herbivoren-beeinflussenden Faktoren wie Region, Landnutzungsintensität oder Räubern verglichen werden, und dass die Effekte der Endophyten abhängig von den Umweltbedingungen sind. In Kapitel II und III wurde die Bedeutung von Kalkmagerrasen und anderen Graslandflächen mit extensiver Landnutzungsintensität in Regionen mit einem hohen Artenpool für den Schutz hoher Schmetterlingsartenvielfalt, -abundanz, gefährdeter Arten und spezialisierter Arten gezeigt. „Trait“-Daten von Arten können herangezogen werden, um den Gefährdungsgrad einer Art zu bewerten, und sind daher höchst wertvoll für den Naturschutz. Im vierten Kapitel habe ich gezeigt, dass der Effekt von Endophyten auf Herbivore von Umweltbedingungen abhängig ist, was in zukünftigen Feldstudien berücksichtigt werden muss. Die Bedeutung von Endophyten in Gräsern im Vergleich zu anderen Herbivoren-beeinflussenden Faktoren muss für Feldstudien überdacht werden. Zusammenfassend konnte ich zeigen, dass die Landnutzungsintensität in allen Studien die Untersuchungsobjekte beeinflusst hat. Daher gilt Landnutzung als ein wichtiger Faktor, der in zukünftigen ökologischen Studien berücksichtigt werden muss. Manche Effekte unterschieden sich zwischen den Regionen, weshalb Beobachtungen und Experimente in verschiedenen Regionen zu wiederholen sind, um generelle Aussagen über Ergebnisse machen zu können oder um regional bedingte Unterschiede aufzudecken.

ABSTRACTSolarization makes a great impact on the abundance of ammonia oxidizers and nitrifying activity in soil. To elucidate fluctuations in the abundance of ammonia oxidizers and nitrification in solarized soil, copy numbers of amoA gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA), viable number of ammonia oxidizers and inorganic nitrogen contents were investigated in greenhouse experiments. The copy number of amoA gene and the viable number of ammonia oxidizers were determined by the quantitative polymerase chain reaction and most probable number methods, respectively. Abundance of AOB based on the estimation of amoA gene copy numbers and viable counts of ammonia oxidizers was decreased by the solarization treatment and increased during the tomato (Solanum lycopersicum L.) cultivation period following the solarization. Effect of solarization on the copy number of amoA gene of AOA was less evident than that on AOB. The proportion of nitrate in inorganic nitrogen contents was declined by the solarization and increased during the tomato cultivation period following the solarization. Positive correlations were found between the proportion of nitrate in inorganic nitrogen content and the copy number of bacterial or archaeal amoA gene or the viable number of ammonia oxidizers; the copy number of bacterial amoA gene showed a strong correlation with the viable number of ammonia oxidizers. The present study revealed influences of solarization on the fluctuation in the abundance of ammonia oxidizers and dynamics of inorganic nitrogen contents in soil and the results indicate that the determination of amoA gene of AOB is possibly a quick and useful diagnostic technique for evaluating suppression and restoration of nitrification following solarization.

The ability to acclimate quickly to changing environmental conditions is important for sessile organisms that cannot move to areas with more favourable conditions. Sponges are known to exhibit considerable phenotypic plasticity in response to environmental variability. However, most studies examining differences in sponge morphology have looked at spatial variation in morphological characteristics by comparing sponges at sites with differing environmental conditions. Here we explored the potential of two intertidal sponge species (Halichondria panicea and Hymeniacidon perlevis) to show seasonal acclimation to changing environmental conditions at two sites on the Welsh coast, UK. Both species had a higher proportion of inorganic tissue content in winter months, which correlated with higher levels of wave action and lower temperature, representing either an increase in spicule size/number or a loss of organic material. We also detected rapid decreases in organic content in some months, which corresponded with previously reported reproductive timings for the two species, and likely represent gamete release events. While the increased inorganic content in winter months may be a secondary consequence of reduced food and the sponges having to rely on organic reserves to meet metabolic demand, the higher level of inorganic material in winter likely makes sponges stiffer and stronger, and better able to deal with higher levels of wave action during winter months.

Here we investigated the potential impacts of soil inorganic nitrogen (SIN) content on the phylogenetic characteristics and ecological functions of soil bacterial communities in estuarine intertidal zones in China, aiming to comprehend the response mechanism of soil microorganisms to variations in SIN content within estuarine wetlands. Our results show that SIN in estuarine areas has a significant spatiotemporal variation on spatial and seasonal scales, in this study and is significantly associated with the phylogenetic diversity and phylogenetic turnover of soil bacterial communities. In addition, the results of the metagenomic analysis showed that the relative abundance of nitrogen-cycling functional genes in bacterial communities did not differ significantly in sampling sites and seasons, and weakly correlated with SIN content. Further, the results based on structural equation modeling (SEM) analysis showed that SIN directly and significantly regulated the phylogenetic characteristics of bacterial communities, thereby indirectly affecting the potential of bacterial nitrogen metabolism. This study emphasizes the key influence of SIN variations on the phylogenetic dissimilarity in soil bacterial communities. Moreover, although there was a weak direct relationship between the functional characteristics of the bacterial nitrogen metabolism and SIN content, the spatiotemporal variation of bacterial nitrogen metabolic potential may be indirectly regulated by SIN content by influencing the phylogenetic diversity in bacterial communities. Our study unravels the pivotal mechanisms through which SIN content influences bacterial communities, thereby offering novel insights into the microbial intricacies governing nitrogen metabolism within estuaries.