Climate change can pose a significant threat to terrestrial ecosystems by disrupting the circulation of soil nitrogen. However, experimental analyses on the effect of climate change on soil nitrogen cycles and the implications for the conservation of key wildlife species (i.e., the giant panda, Ailuropoda melanoleuca) remain understudied. We investigated the effects of a 1.5 °C, 3 °C, and 4.5 °C temperature increase on nitrogen distribution in different soil layers of bamboo forest via an in-situ experiment and assessed the implications for the growth and survival of arrow bamboo (Bashania faberi), a critical food resource for giant pandas. Our results showed that warming treatments generally increased soil N content, while effects differed between surface soil and subsurface soil and at different warming treatments. Particularly an increase of 1.5 °C raised the subsurface soil NO3-N content, as well as the content of N in bamboo leaves. We found a significant positive correlation between the subsurface soil NO3-N content and the N content of arrow bamboo. An increase of 3-4.5 °C raised the content of total N and NO3-N in the surface soil and led to a reduction in the total aboveground biomass and survival rate of arrow bamboo. Limited warming (e.g., the increase of 0-1.5 °C) may promote the soil N cycle, raise the N-acetylglucosaminidase (NAG) enzyme activity, increase NO3-N in subsurface soil, increase the N content of bamboo, and boost the biomass of bamboo - all of which could be beneficial to giant panda survival. However, higher warming (e.g., an increase of 3-4.5 °C) resulted in mass death of bamboo and a large reduction in aboveground biomass. Our findings provide a cautiously optimistic scenario for bamboo forest ecosystems under low levels of warming over a short period of time, but risks from higher levels of warming may be serious, especially considering the unpredictability of global climatic change.

Lead (Pb) and cadmium (Cd) have been identified as the primary contaminants in soil, posing potential health threats. This study aimed to examine the effects of applying a nitrogen fertilizer and a fungal agent Trichoderma harzianum J2 (nitrogen alone, fungi alone, and combined use) on the phytoremediation of soils co-contaminated with Pb and Cd. The growth of Leucaena leucocephala was monitored in the seedling, differentiation, and maturity stages to fully comprehend the remediation mechanisms. In the maturity stage, the biomass of L. leucocephala significantly increased by 18% and 29% under nitrogen-alone (NCK+) and fungal agent-alone treatments (J2), respectively, compared with the control in contaminated soil (CK+). The remediation factors of Pb and Cd with NCK+ treatment significantly increased by 50% and 125%, respectively, while those with J2 treatment increased by 73% and 145%, respectively. The partial least squares path model suggested that the nitrogen-related soil properties were prominent factors affecting phytoextraction compared with biotic factors (microbial diversity and plant growth). This model explained 2.56 of the variation in Cd concentration under J2 treatment, and 2.97 and 2.82 of the variation in Pb concentration under NCK+ and J2 treatments, respectively. The redundancy analysis showed that the samples under NCK+ and J2 treatments were clustered similarly in all growth stages. Also, Chytridiomycota, Mucoromucota, and Ciliophora were the key bioindicators for coping with heavy metals. Overall, a similar remediation mechanism allowed T. harzianum J2 to replace the nitrogen fertilizer to avoid secondary pollution. In addition, their combined use further increased the remediation efficiency.

The investigation into trade-offs among plant functional traits sheds light on how plants strategically balance growth and survival when facing environmental stress. This study sought to evaluate whether trade-offs observed at both community and individual species levels could indicate adaptive fitness across an intensity of flooding intensity. The study was conducted at 25 sampling sites spanning approximately 600 km along the riparian zone in the Three Gorges Reservoir area, China. The findings revealed that, along the flooding gradient, the overall riparian community did not exhibit significant trade-offs between leaf and root traits. Examining three broadly distributed dominant species (Cynodon dactylon, Xanthium strumarium, and Abutilon theophrasti), perennial plants showed pronounced trade-offs under low flooding intensity, while annuals exhibited trade-offs under moderate and low flooding intensity. The trade-offs were evident in traits related to nitrogen-carbon resources, such as specific leaf area, root tissue density, and photosynthetic rate. However, under strong flooding intensity, the relationship between leaf and root traits of the species studied was decoupled. Furthermore, the study identified a significant correlation between soil nitrogen and the trade-off traits under moderate and low flooding intensity. Integrating results from the CSR (Competitors, Stress-tolerators, Ruderals) strategy model, species niche breath analysis, and nitrogen-regulated trade-off, the study revealed that, in the face of high flooding intensity, perennial species (C. dactylon) adopts an S-strategy, demonstrating tolerance through a conservative resource allocation that decouples leaf-root coordination. Annual species (X. strumarium and A. theophrasti), on the other hand, exhibit niche specialization along the flooding gradient, employing distinct strategies (R- and C-strategy). As flooding stress diminishes and soil nitrogen level decreases, plant strategies tend to shift towards an R-strategy with a competition for reduced N resources. In conclusion, the study highlighted the pivotal roles of soil nitrogen and flooding intensity acting as the dual determinants of species growth and tolerance. These dynamics of growth-tolerance balance were evident in the diverse trade-offs between leaf and root traits of individual plant species with different life histories, underscoring the array of adaptive strategies employed by riparian plants across the flooding intensity gradient.

Partial replacement of mineral fertilisers (MF) with animal manures is a good alternative to reduce MF use and increase both nutrient cycling in agriculture and soil organic matter. However, the adoption of this practice must not lead to increased environmental impacts. In this two-year study conducted in an apple orchard, MF were partially replaced with various animal manures, including cattle slurry (CS), acidified cattle slurry (ACS), solid cattle manure (CsM), or poultry manure (PM), and their impacts on greenhouse gas emission (GHG: CO2, N2O and CH4) were examined. A control (CTRL) receiving only MF served as the baseline, representing the conventional scenario in orchard fertilisation. Overall, replacing MF with manures increased GHG emissions, with the magnitude of the impacts depending on the specific characteristics of the manures and the amount of nutrients and organic matter applied. Comparing to the CTRL, application of ACS and CS led to higher CH4 and N2O emissions, while PM application increased both N2O and CO2 emissions. In contrast, replacement with PM and CsM decreased CH4 emissions. Nevertheless, results varied between the two years, influenced by several factors, including soil conditions. While acidification showed potential to mitigate CH4 emissions, it also led to increased N2O emissions compared to CS, particularly in 2022, suggesting the need for further investigation to avoid emission trade-offs. Replacement with CS (20.49 t CO2-eq ha-1) and CsM (20.30 t CO2-eq ha-1) showed comparable global warming potential (GWP) to the conventional scenario (CTRL, 19.49 t CO2-eq ha-1), highlighting their potential as viable MF substitutes.

Nitrogen (N) and phosphorus (P) are the two most important macronutrients supporting forest growth. Unprecedented urbanization has created growing areas of urban forests that provide key ecosystem services for city dwellers. However, the large-scale patterns of soil N and P content remain poorly understood in urban forests. Based on a systematic soil survey in urban forests from nine large cities across eastern China, we examined the spatial patterns and key drivers of topsoil (0-20 cm) total N content, total P content, and N:P ratio. Topsoil total N content was found to change significantly with latitude in the form of an inverted parabolic curve, while total P content showed an opposite latitudinal pattern. Variance partition analysis indicated that regional-scale patterns of topsoil total N and P contents were dominated by climatic drivers and partially regulated by time and pedogenic drivers. Conditional regression analyses showed a significant increase in topsoil total N content with lower mean annual temperature (MAT) and higher mean annual precipitation (MAP), while topsoil total P content decreased significantly with higher MAP. Topsoil total N content also increased significantly with the age of urban park and varied with pre-urban soil type, while no such effects were found for topsoil total P content. Moreover, topsoil N:P ratio showed a latitudinal pattern similar to that of topsoil total N content and also increased significantly with lower MAT and higher MAP. Our findings demonstrate distinct latitudinal trends of topsoil N and P contents and highlight a dominant role of climatic drivers in shaping the large-scale patterns of topsoil nutrients in urban forests.

Intercropping is a widely recognised technique that contributes to agricultural sustainability. While intercropping leguminous green manure offers advantages for soil health and tea plants growth, the impact on the accumulation of theanine and soil nitrogen cycle are largely unknown. The levels of theanine, epigallocatechin gallate and soluble sugar in tea leaves increased by 52.87% and 40.98%, 22.80% and 6.17%, 22.22% and 29.04% in intercropping with soybean-Chinese milk vetch rotation and soybean alone, respectively. Additionally, intercropping significantly increased soil amino acidnitrogen content, enhanced extracellular enzyme activities, particularly β-glucosidase and N-acetyl-glucosaminidase, as well as soil multifunctionality. Metagenomics analysis revealed that intercropping positively influenced the relative abundances of several potentially beneficial microorganisms, including Burkholderia, Mycolicibacterium and Paraburkholderia. Intercropping resulted in lower expression levels of nitrification genes, reducing soil mineral nitrogen loss and N2 O emissions. The expression of nrfA/H significantly increased in intercropping with soybean-Chinese milk vetch rotation. Structural equation model analysis demonstrated that the accumulation of theanine in tea leaves was directly influenced by the number of intercropping leguminous green manure species, soil ammonium nitrogen and amino acid nitrogen. In summary, the intercropping strategy, particularly intercropping with soybean-Chinese milk vetch rotation, could be a novel way for theanine accumulation.

The number of forest fires has increased globally, together with considerable smoke emission that significantly impacts the atmospheric environment and associated ecosystems. Most current studies have focused on the in situ effects of fire on the forest ecosystem. However, the mechanisms by which smoke particles affect adjacent ecosystems are largely unexplored. In this study, a simulated forest fire combustion system was developed to evaluate the effect of different smoke concentrations (control, low and high) on soil physico-chemical properties of adjacent farmland at two soil depths. The abundance and diversity of bacterial community were also determined. The results showed that smoke deposition increased the contents of total carbon (TC), total nitrogen (TN), and total phosphorus (TP) in the 0-10 cm soil layer; however, no significant changes in soil water content (SWC) and pH values was observed. The ACE(Abundance Coverage-based Fastimator) and Chao1 diversity indices of bacterial community generally showed a downward trend whereas the PD_whole_ tree diversity index increased after 180 d of smoke deposition. The relative abundance of Proteobacteria remained stable, while abundance of Firmicutes in soil decreased after 180 d of smoke deposition. Smoke deposition slightly affected the physical and chemical properties of the 10-20 cm soil, but the range of variation of the relative abundance and diversity dominant bacteria exceeded that of the 0-10 cm soil. A significant positive correlation was found between the soil properties and the alpha diversity indices during the first 30 d after smoke deposition; the correlation then decreased gradually. Redundancy analysis revealed that Proteobacteria, Firmicutes, and Actinobacteria were generally positively correlated with TC, TN, and SWC. As a whole, the study reveals that the effects of smoke deposition on soil physico-chemical properties and bacterial community depends on smoke concentration where relatively low concentration appears to be beneficial to soil bacterial community.

Soil nitrogen isotopic composition (δ15Nsoil) is an invaluable tool as it integrates nitrogen (N) transformations in soils. In addition to serving as a baseline to understand the N cycle, spatial representations of δ15Nsoil across landscapes (or isoscapes) is a multi-purpose tool useful to investigate, for example, plant-microbe interactions, animal migration and forensics. We investigate the climatic and edaphic controls of δ15Nsoil utilising data from 29 geographical locations sampled across the semiarid Brazilian Caatinga biome. The sampling covered a mean annual precipitation (PA) gradient ranging from 0.51 to 1.36 m a-1 and eight soil types originating from three different geological origins. Our data show that the combination of higher aridity and lower seasonality (ψ) leads to higher values of δ15Nsoil. Moreover, soil total carbon had a positive relationship with δ15Nsoil, appearing within the best-supported models according to the information-theoretic approach undertaken here. The contribution to the plant communities by the Fabaceae trees expressed as their basal area was not related to δ15Nsoil values, suggesting that the magnitude of biological N fixation in the Caatinga is not large enough to be reflected in the soil. In addition, considering PA in a categorical fashion, i.e., \'high\' (> 0.8 m a-1) and \'low\' PA (< 0.8 m a-1), we found that, within the wetter category, δ15Nsoil was positively related to several soil properties (i.e., clay content, effective cation exchange capacity, exchangeable calcium, silt content, pHH2O, total phosphorus and sum of bases) and negatively related to sand content. Our study provides new insights into the functioning of semiarid ecosystems from a pedo-isotopic perspective and contributes to the overall understanding of the N cycle in the Caatinga region, with the potential to support the development of new conceptualisation of biogeochemical process and testing of global models that simulate N and C cycles.

OBJECTIVE: Plant roots modulate microbial nitrogen (N) cycling by regulating the supply of root-derived carbon and nitrogen uptake. These differences in resource availability cause distinct micro-habitats to develop: soil near living roots, decaying roots, near both, or outside the direct influence of roots. While many environmental factors and genes control the microbial processes involved in the nitrogen cycle, most research has focused on single genes and pathways, neglecting the interactive effects these pathways have on each other. The processes controlled by these pathways determine consumption and production of N by soil microorganisms. We followed the expression of N-cycling genes in four soil microhabitats over a period of active root growth for an annual grass. We found that the presence of root litter and living roots significantly altered gene expression involved in multiple nitrogen pathways, as well as tradeoffs between pathways, which ultimately regulate N availability to plants.

Tree-ring δ15N may depict site-specific, long-term patterns in nitrogen (N) dynamics under N2-fixing species, but field trials with N2-fixing tree species are lacking and the relationship of temporal patterns in tree-ring δ15N to soil N dynamics is controversial. We examined whether the tree-ring δ15N of N2-fixing red alder (Alnus rubra Bong.) would mirror N accretion rates and δ15N of soils and whether the influence of alder-fixed N could be observed in the wood of a neighboring conifer. We sampled a 27-year-old replacement series trial on south-eastern Vancouver Island, with red alder and coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) planted in five proportions (0/100, 11/89, 25/75, 50/50 and 100/0) at a uniform stem density. An escalation in forest floor N content was evident with an increasing proportion of red alder, equivalent to a difference of ~750 kg N ha-1 between 100% Douglas-fir versus 100% alder. The forest floor horizon also had high δ15N values in treatments with more red alder. Red alder had a consistent quadratic fit in tree-ring δ15N over time, with a net increase of $\\sim$1.5‰, on average, from initial values, followed by a plateau or slight decline. Douglas-fir tree-ring δ15N, in contrast, was largely unchanged over time (in three of four plots) but was significantly higher in the 50/50 mix. The minor differences in current leaf litter N content and δ15N between alder and Douglas-fir, coupled with declining growth in red alder, suggests the plateau or declining trend in alder tree-ring δ15N could coincide with lower N2-fixation rates, potentially by loss in alder vigor at canopy closure, or down-regulation via nitrate availability.