Increasing atmospheric nitrogen (N) deposition could profoundly impact community structure and ecosystem functions in forests. However, conventional experiments with understory addition of N (UAN) largely neglect canopy-associated biota and processes and therefore may not realistically simulate atmospheric N deposition to generate reliable impacts on forest ecosystems. Here we, for the first time, designed a novel experiment with canopy addition of N (CAN) vs. UAN and reviewed the merits and pitfalls of the two approaches. The following hypotheses will be tested: i) UAN overestimates the N addition effects on understory and soil processes but underestimates those on canopy-associated biota and processes, ii) with low-level N addition, CAN favors canopy tree species and canopy-dwelling biota and promotes the detritus food web, and iii) with high-level N addition, CAN suppresses canopy tree species and other biota and favors rhizosphere food web. As a long-term comprehensive program, this experiment will provide opportunities for multidisciplinary collaborations, including biogeochemistry, microbiology, zoology, and plant science to examine forest ecosystem responses to atmospheric N deposition.
Summary1. Soil micro-organisms play important roles in ecosystems and respond quickly to environmental changes. We examined how understory removal and tree girdling influence the composition of soil microbial community and the litter decomposition in two subtropical plantations. 2. Phospholipid fatty acids (PLFAs) analysis was used to characterize soil microbial community. Redundancy analysis and principal response curves (PRC) were used to investigate the relationships between soil microbial community and environmental factors. 3. Understory removal significantly reduced the amount of fungal PLFAs, the ratio of fungal to bacterial PLFAs, and the litter decomposition but did not affect bacterial PLFAs and total PLFAs. In contrast, tree girdling did not affect the soil microbial characteristics. The changes in soil microbial community caused by understory removal were mainly attributed to the indirect effects such as increased soil temperature and soil NO 3 ) -N availability. In addition, PRC analysis showed that the relative abundance of most PLFAs increased in response to understory removal in the 2-year-old plantation but decreased in the 24-year-old plantation. 4. We propose that understory plants are important components in subtropical forest ecosystems, and play different roles in maintaining soil microbial community and driving litter decomposition processes in young vs. old plantations. The functions of understory plants should be considered in forest management and restoration. The negligible effect of tree girdling on the soil micro-organisms can be attributed to the resprouting trait and mycorrhizal interactions of Eucalyptus.
Due to their ultrathin layered structure and rich elemental variety, MXenes are emerging as a promising electrode candidate in energy generation and storage. MXenes are generally synthesized via hazardous fluoride‐containing reagents from robust MAX materials, unfortunately resulting in plenty of inert fluoride functional groups on the surface that noticeably decline their performance. Density functional theory calculations are used to show the etching feasibility of hydrochloric acid (HCl) on various MAX phases. Based on this theoretical guidance, fluoride‐free Mo2C MXenes with high efficiency about 98% are experimentally demonstrated. The Mo2C electrodes produced by this process exhibit high electrochemical performance in supercapacitors and sodium‐ion batteries owing to the chosen surface functional groups created via the HCl etch process. This strategy enables the development of fluoride‐free MXenes and opens a new window to explore their potential in energy‐storage applications.
Plant and microbial responses to nitrogen and phosphorus addition across an elevational gradient in subarctic tundra.Ecology, 95 (7): [1819][1820][1821][1822][1823][1824][1825][1826][1827][1828][1829][1830][1831][1832][1833][1834][1835] Access to the published version may require subscription. N.B. When citing this work, cite the original published paper. Abstract. Temperature and nutrients are major limiting factors in subarctic tundra. Experimental manipulation of nutrient availability along elevational gradients (and thus temperature) can improve our understanding of ecological responses to climate change. However, no study to date has explored impacts of nutrient addition along a tundra elevational gradient, or across contrasting vegetation types along any elevational gradient. We set up a full factorial nitrogen (N) and phosphorus (P) fertilization experiment in each of two vegetation types (heath and meadow) at 500 m, 800 m, and 1000 m elevation in northern Swedish tundra. We predicted that plant and microbial communities in heath or at lower elevations would be more responsive to N addition while communities in meadow or at higher elevations would be more responsive to P addition, and that fertilizer effects would vary more with elevation for the heath than for the meadow. Although our results provided little support for these predictions, the relationship between nutrient limitation and elevation differed between vegetation types. Most plant and microbial properties were responsive to N and/or P fertilization, but responses often varied with elevation and/or vegetation type. For instance, vegetation density significantly increased with N þ P fertilization relative to the other fertilizer treatments, and this increase was greatest at the lowest elevation for the heath but at the highest elevation for the meadow. Arbuscular mycorrhizae decreased with P fertilization at 500 m for the meadow, but with all fertilizer treatments in both vegetation types at 800 m. Fungal to bacterial ratios were enhanced by N þ P fertilization for the two highest elevations in the meadow only. Additionally, microbial responses to fertilization were primarily direct rather than indirect via plant responses, pointing to a decoupled response of plant and microbial communities to nutrient addition and elevation. Because our study shows how two community types differ in their responses to fertilization and elevation, and because the temperature range across this gradient is ;38C, our study is informative about how nutrient limitation in tundra may be influenced by temperature shifts that are comparable to those expected under climate change during this century.
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