Effects of elevated CO\u3csub\u3e2\u3c/sub\u3e, increased nitrogen deposition, and plant diversity on aboveground litter and root decomposition

Global change-induced litter decomposition strongly affects the carbon (C) and nitrogen (N) dynamics in grassland ecosystems. However, few studies show the interactive effects of global change factors on litter and root decomposition. We conducted a four-year grassland field experiment to examine the quality and decomposition of litter and root in a three-factorial experiment with elevated CO2, increased N deposition, and plant species richness. We found that elevated CO2 decreased the litter N content and root lignin content. N addition increased the root N content and decreased the litter lignin content. Increasing plant richness decreased the N and lignin contents in litter and root. In contrast to the quality changes, elevated CO2 had no effect on decomposition of litter and root. N addition increased the C loss of the litter by 4.8%, but did not affect C and N loss in root. Increasing plant richness affected the C and N loss in litter and root. ANCOVAs showed that tissue quality and root biomass affected the C and N loss in litter and root, and soil C and N affected the N loss of litter and root. However, changes in tissue quality, biomass, and soil as covariates did not significantly change the effects of CO2, N, and plant richness on decomposition. The structural equation model showed that elevated CO2 indirectly decreased litter N loss and increased root N loss, while N addition indirectly increased the C and N loss in litter and root, via their effects on tissue quality. Increasing plant richness increased litter C and N loss, but indirectly decreased root C and N loss. N deposition can accelerate litter and root decomposition, thus modifying the limitation of elevated CO2 on soil N availability. Biodiversity loss greatly alters litter and root decomposition, potentially driving any changes in C and N cycling. Our study clearly demonstrates a relative certainty of a predicted increase in the C loss and N release in litter and root decomposition with increased N deposition, whereas the effects of elevated CO2 and plant diversity changes on decomposition strongly differ between litter and root in grassland ecosystems

Effects of extreme drought on plant nutrient uptake and resorption in rhizomatous vs bunch grass dominated grasslands

Both the dominance and the mass ratio hypotheses predict that plant internal nutrient cycling in ecosystems is determined by the dominant species within plant communities. We tested this hypothesis under conditions of extreme drought by assessing plant nutrient (N, P and K) uptake and resorption in response to experimentally imposed precipitation reductions in two semiarid grasslands of northern China. These two communities shared similar environmental conditions, but had different dominant species-one was dominated by a rhizomatous grass (Leymus chinensis) and the other by a bunchgrass (Stipa grandis). Results showed that responses of N to drought differed between the two communities with drought decreasing green leaf N concentration and resorption in the community dominated by the rhizomatous grass, but not in the bunchgrass-dominated community. In contrast, negative effects of drought on green leaf P and K concentrations and their resorption efficiencies were consistent across the two communities. Additionally, in each community, the effects of extreme drought on soil N, P and K supply did not change synchronously with that on green leaf N, P and K concentrations, and senesced leaf N, P and K concentrations showed no response to extreme drought. Consistent with the dominance/mass ratio hypothesis, our findings suggest that differences in dominant species and their growth form (i.e., rhizomatous vs bunch grass) play an important nutrient-specific role in mediating plant internal nutrient cycling across communities within a single region

Bench to Bed Evidences for Pharmacokinetic and Pharmacodynamic Interactions Involving Oseltamivir and Chinese Medicine

Oseltamivir (OA), an ethyl ester prodrug of oseltamivir carboxylate (OC), is clinically used as a potent and selective inhibitor of neuraminidase. Chinese medicines have been advocated to combine with conventional drug for avian influenza. The current study aims to investigate the potential pharmacokinetic and pharmacodynamic interactions of a Chinese medicine formula, namely, Yin Qiao San and Sang Ju Yin (CMF1), commonly used for anti-influenza in combination with OA in both rat and human, and to reveal the underlined mechanisms. It was found that although Cmax, AUC and urinary recovery of OC, as well as metabolic ratio (AUCOC/AUCOA), were significantly decreased in a dose-dependent manner following combination use of CMF1 and OA in rat studies (P<0.01), such coadministration in 14 healthy volunteers only resulted in a trend of minor decrease in the related parameters. Further mechanistic studies found that although CMF1 could reduce absorption and metabolism of OA, it appears to enhance viral inhibition of OA (P<0.01). In summary, although there was potential interaction between OA and CMF1 found in rat studies, its clinical impact was expected to be minimal. The coadministration of OA and CMF1 at the clinical recommended dosages is, therefore, considered to be safe

Drought intensity and post-drought precipitation determine vegetation recovery in a desert steppe in Inner Mongolia, China

Extreme drought events are expected to increase in frequency and severity, posing significant threats to ecosystems worldwide. While considerable research has been concentrated on the effects of climate extremes on the stability of grasslands, the process by which grassland productivity may recover after extreme drought events are still not well understood. Here, we conducted a four-year (2019–2022) recovery investigation after four-year's (2015–2018) extreme drought treatments of different intensities (control, press and pulse) to explore the vegetation recovery of desert-grassland ecosystems Inner Mongolia, China. Press drought involved a 66 % reduction in natural precipitation from May to August, while pulse drought reduced it by 100 % during June and July. We found that both press and pulse droughts led to a sharp decrease in aboveground net primary productivity (ANPP) after four years, primarily due to reduced growth, density, and productivity of annual and perennial plants. However, ANPP under pulse drought could recover fully after four years of stopping of drought treatment, and it could not under press drought. Additionally, community structure (i.e., species richness, plant density, and height) fully recovered within 1 year after the end of the two extreme drought treatments. Both plant density and height contributed to the ANPP recovery after press and pulse droughts. Structural equation modeling (SEM) results further revealed that the reduction in ANPP during the extreme drought was primarily due to a decrease in plant density caused by reduced soil water content. The recovery of ANPP in pulse drought was directly caused by increased soil water content in the post-extreme drought. These results suggest that drought intensity and precipitation determine ANPP recovery in a degraded desert steppe. Our findings are crucial for deepening understanding of the processes and mechanisms of ecosystem recovery after extreme drought, as well as for the successful management and protection of grassland ecosystems

Effects of elevated CO\u3csub\u3e2\u3c/sub\u3e, increased nitrogen deposition, and plant diversity on aboveground litter and root decomposition

Global change-induced litter decomposition strongly affects the carbon (C) and nitrogen (N) dynamics in grassland ecosystems. However, few studies show the interactive effects of global change factors on litter and root decomposition. We conducted a four-year grassland field experiment to examine the quality and decomposition of litter and root in a three-factorial experiment with elevated CO2, increased N deposition, and plant species richness. We found that elevated CO2 decreased the litter N content and root lignin content. N addition increased the root N content and decreased the litter lignin content. Increasing plant richness decreased the N and lignin contents in litter and root. In contrast to the quality changes, elevated CO2 had no effect on decomposition of litter and root. N addition increased the C loss of the litter by 4.8%, but did not affect C and N loss in root. Increasing plant richness affected the C and N loss in litter and root. ANCOVAs showed that tissue quality and root biomass affected the C and N loss in litter and root, and soil C and N affected the N loss of litter and root. However, changes in tissue quality, biomass, and soil as covariates did not significantly change the effects of CO2, N, and plant richness on decomposition. The structural equation model showed that elevated CO2 indirectly decreased litter N loss and increased root N loss, while N addition indirectly increased the C and N loss in litter and root, via their effects on tissue quality. Increasing plant richness increased litter C and N loss, but indirectly decreased root C and N loss. N deposition can accelerate litter and root decomposition, thus modifying the limitation of elevated CO2 on soil N availability. Biodiversity loss greatly alters litter and root decomposition, potentially driving any changes in C and N cycling. Our study clearly demonstrates a relative certainty of a predicted increase in the C loss and N release in litter and root decomposition with increased N deposition, whereas the effects of elevated CO2 and plant diversity changes on decomposition strongly differ between litter and root in grassland ecosystems

Effects of Grazing, Extreme Drought, Extreme Rainfall and Nitrogen Addition on Vegetation Characteristics and Productivity of Semiarid Grassland

Grassland use patterns, water and nutrients are the main determinants of ecosystem structure and function in semiarid grasslands. However, few studies have reported how the interactive effects of rainfall changes and nitrogen deposition influence the recovery of semiarid grasslands degraded by grazing. In this study, a simulated grazing, increasing and decreasing rainfall, nitrogen deposition test platform was constructed, and the regulation mechanism of vegetation characteristics and productivity were studied. We found that grazing decreased plant community height (CWMheight) and litter and increased plant density. Increasing rainfall by 60% from May to August (+60%) increased CWMheight; decreasing rainfall by 60% from May to August (–60%) and by 100% from May to June (−60 d) decreased CWMheight and coverage; −60 d, +60% and increasing rainfall by 100% from May to June (+60 d) increased plant density; −60% increased the Simpson dominance index (D index) but decreased the Shannon–Wiener diversity index (H index); −60 d decreased the aboveground biomass (ABG), and −60% increased the underground biomass (BGB) in the 10–60 cm layer. Nitrogen addition decreased species richness and the D index and increased the H index and AGB. Rainfall and soil nitrogen directly affect AGB; grazing and rainfall can also indirectly affect AGB by inducing changes in CWMheight; grazing indirectly affects BGB by affecting plant density and soil nitrogen. The results of this study showed that in the semiarid grassland of Inner Mongolia, grazing in the nongrowing season and grazing prohibition in the growing season can promote grassland recovery, continuous drought in the early growing season will have dramatic impacts on productivity, nitrogen addition has a certain impact on the species composition of vegetation, and the impact on productivity will not appear in the short term

Different Fire Frequency Impacts Over 27 Years on Vegetation Succession in an Infertile Old-Field Grassland

We examined the effect of fire on vegetation composition with the use of an experiment with four different fire frequencies (annual, 2-yr interval, 4-yr interval, and an intended control with no burning) over a 27-yr period in an infertile, old-field grassland at the Cedar Creek Ecosystem Science Reserve, located in Minnesota, United States. We measured the plant species’ aboveground biomass in permanent plots in 1983, 1987, 1991, 2000, and 2010. None of these fire frequencies, even after 27 yr, had a large impact on the vegetation composition. The plant functional groups’ responses to fire frequency were consistent with their respective dominant species. The most abundant C4 grass, little bluestem (Schizachyrium scoparium Michx.), did not change in biomass with fire frequency over time. The biomass of the introduced, invasive grass, Kentucky bluegrass (Poa pratensis L.) decreased significantly with increasing fire frequency, but this decrease did not result in change to the rate and trajectory of vegetation change. Bush clover (Lespedeza capitata Michx.), the only legume in the community, strongly increased with more frequent fire, but only after 20 yr. Species richness and litter mass decreased significantly with increasing fire frequency. These small fire-induced vegetation changes contrast with large fire-induced vegetation changes in fertile grasslands. Management strategies using fire in infertile grasslands can lower Poa abundance; however, increased fire also decreased overall plant diversity.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202