Effects of Short-Term Nitrogen Addition on Soil Fungal Community Increase with Nitrogen Addition Rate in an Alpine Steppe at the Source of Brahmaputra.

The soil fungal community plays a crucial role in terrestrial decomposition and biogeochemical cycles. However, the responses of the soil fungal community to short-term nitrogen addition and its related dominant drivers still remain unclear. To address this gap, we conducted an experiment to explore how different levels of nitrogen addition (five levels: 0, 2.5, 5, 10, and 20 g N m-2 y-1) affected the soil fungal community in an alpine steppe at the source of Brahmaputra. Results showed that the reduced magnitudes of soil fungal species and phylogenetic α-diversity increased with the increasing nitrogen addition rate. Nitrogen addition significantly changed the community composition of species, and the dissimilarity of the soil fungal community increased with the increasing nitrogen addition rate, with a greater dissimilarity observed in the superficial soil (0-10 cm) compared to the subsurface soil (10-20 cm). Increases in the soil nitrogen availability were found to be the predominant factor in controlling the changes in the soil fungal community with the nitrogen addition gradient. Therefore, short-term nitrogen addition can still cause obvious changes in the soil fungal community in the alpine grassland at the source of Brahmaputra. We should not underestimate the potential influence of future nitrogen deposition on the soil fungal community in the high-altitude grassland of the Qinghai-Tibet Plateau. Adverse effects on the soil fungal community should be carefully considered when nitrogen fertilizer is used for ecosystem restoration of the alpine grassland of the Qinghai-Tibet Plateau.

Non-growing/growing season non-uniform-warming increases precipitation use efficiency but reduces its temporal stability in an alpine meadow.

There are still uncertainties on the impacts of season-non-uniform-warming on plant precipitation use efficiency (PUE) and its temporal stability (PUEstability) in alpine areas. Here, we examined the changes of PUE and PUEstability under two scenes of non-growing/growing season non-uniform-warming (i.e., GLNG: growing-season-warming lower than non-growing-season-warming; GHNG: growing-season-warming higher than non-growing-season-warming) based on a five-year non-uniform-warming of non-growing/growing season experiment. The GLNG treatment increased PUE by 38.70% and reduced PUEstability by 50.47%, but the GHNG treatment did not change PUE and PUEstability. This finding was mainly due to the fact that the GLNG treatment had stronger influences on aboveground biomass (AGB), non-growing-season soil moisture (SMNG), temporal stability of AGB (AGBstability), temporal stability of non-growing-season air temperature (T a_NG_stability), temporal stability of growing-season vapor pressure deficit (VPDG_stability) and temporal stability of start of growing-season (SGSstability). Therefore, the warming scene with a higher non-growing-season-warming can have greater influences on PUE and PUEstability than the warming scene with a higher growing-season-warming, and there were possibly trade-offs between plant PUE and PUEstability under season-non-uniform-warming scenes in the alpine meadow.

Increasing connections among temporal invariability, resistance and resilience of alpine grasslands on the Tibetan Plateau.

Ecological stability contains multiple components, such as temporal invariability, resistance and resilience. Understanding the response of stability components to perturbations is beneficial for optimizing the management of biodiversity and ecosystem functioning. Although previous studies have investigated the effects of multiple perturbations on each stability component, few studies simultaneously measure the multiple stability components and their relationships. Alpine grasslands on the Tibetan Plateau are exposed to co-occurring perturbations, including climate change and human activities. Here, we quantified three stability components (temporal invariability, resistance, and resilience) of alpine grasslands on the Tibetan Plateau during periods of high (2000-2008) and low (2009-2017) human activity intensity, respectively. We focused on the effects of climate variables (temperature, precipitation, radiation) and human activities (grazing intensity) on covariation among stability components. The results show that (1) for periods of high and low human activity, temporal invariability was positively correlated with resistance and resilience, while resistance was independent of resilience; (2) the dimensionality of alpine grasslands decreased by almost 10%, from 0.61 in the first period to 0.55 in the second period, suggesting the increasing connections among temporal invariability, resistance and resilience of alpine grasslands; and (3) temperature but not grazing intensity dominated the changes in the dimensionality of stability. These findings improve our understanding of multi-dimensional stability and highlight the importance of climate variability on alpine grassland stability on the Tibetan Plateau.

Effects of 7 years experimental warming on soil bacterial and fungal community structure in the Northern Tibet alpine meadow at three elevations.

A warming experiment was established along an altitudinal gradient (low elevation: 4313 m, mid-elevation: 4513 m and high elevation: 4693 m) in alpine meadows of the Northern Tibet to investigate the effects of warming on soil bacterial and fungal community structure. Elevation had significant effects on vegetation community coverage (CC), soil temperature (Ts) and pH, but not soil fungal diversity. Soil bacterial diversity at the high elevation was significantly lower than that at the low and mid-elevations, whereas there was no significant difference of soil bacterial diversity between the low and mid-elevations. After seven years of warming, soil fungal diversity was significantly increased at the mid-elevation but not the low and high elevations, and soil bacterial diversity was not significantly altered at the low, mid- and high elevations. Soil bacterial community structure was significantly altered at the low and mid-elevations but not the high elevation. Soil fungal community structure was significantly altered at all the three elevations. CC, Ts and pH significantly explained 20.55%, 5.30% and 12.61% of the variation of bacterial community structure, respectively. CC and Ts significantly explained 17.40% and 5.86% of the variation of fungal community structure, respectively. Therefore, responses of soil microbial community structure to warming may vary with elevation, which was mainly attributed to different vegetation coverage, soil temperature and/or pH conditions among the three elevations in this study alpine meadows.

Natural plant colonization improves the physical condition of bauxite residue over time.

Freshly stacked bauxite residue in Central China has little vegetative growth probably as a result of its poor physical condition and chemical properties which deter plant establishment. Over the last 20 years, spontaneous plant colonization on the deposits has revealed that natural weathering processes may improve bauxite residue to the extent that it can support vegetation. Bauxite residue samples were collected from a chronosequence and analyzed to determine the effect of natural processes over time. The freshly stacked residue showed considerable physical degradation, having a high bulk density, low porosity, and poor aggregate stability. Through natural processes over a 20-year period, the texture changed from a silty loam to a sandy loam, porosity was enhanced (43.88 to 58.24 %), while improvements in both aggregate stability (43.32 to 93.20 %) and structural stability (1.33 to 5.46 %) of the stacked residue were observed. Plant growth had a positive effect on pH, exchangeable sodium percentage, soil organic carbon, water-stable aggregation, and structural stability, probably due to the presence of plant roots and associated microbial activity. It was concluded that natural processes of regeneration, stabilization, and attenuation have improved the hostile physical environment of bauxite residue allowing plant establishment to take place.

The extracellular matrix protein mindin as a novel adjuvant elicits stronger immune responses for rBAG1, rSRS4 and rSRS9 antigens of Toxoplasma gondii in BALB/c mice.

BACKGROUND: Vaccines are the most effective agents to control infections. However, recombinant vaccines often do not elicit strong immune responses. Protein antigens combined with proper adjuvants have been widely used to induce immune responses, especially the humoral immune responses, against various pathogens, including parasites. The extracellular matrix protein mindin has been recognised as an immune facilitator for initiating innate immune responses. It has therefore been expected to be a potentially potent adjuvant in the development of novel vaccines. The aim of this study was to investigate whether mindin could facilitate the induction of antigen-specific immune responses to recombinant antigens (rBAG1, rSRS4 and rSRS9) of Toxoplasma gondii in BALB/c mice. METHODS: In this study, we explored the adjuvant effect of the recombinant mindin in the generation of specific Th1 and Th2 responses to each of three T. gondii antigens, BAG1, SRS4 and SRS9. All mice in the experimental groups received either antigen alone or in combination with Freund's adjuvant or with the recombinant mindin. The immune responses after immunisation were measured by ELISA and lymphoproliferative assays. The immunised mice were challenged with live T. gondii tachyzoites, and the protection efficiency was compared between the groups. RESULTS: Our results revealed that mindin as an adjuvant could facilitate the recombinant proteins to efficiently stimulate humoral and cellular responses, including antigen-specific IgG1 and IgG2a, as well as lymphocyte proliferation. Furthermore, significantly improved protection against T. gondii infection was observed in the mindin group compared with that of Freund's adjuvant and no-adjuvant groups. CONCLUSIONS: The extracellular matrix protein mindin can effectively induce antigen-specific humoral and cell-mediated immune responses. Our study provides a valuable basis for the development of an efficient, safe, non-toxic vaccine adjuvant for future use in humans and animals.