渍水对冬小麦生长的危害及其生理效应

小麦受渍后叶片的光合和蒸腾速率迅速下降,而后则显微弱的回升趋势。渍害不仅削弱小麦光合产物的积累,并且改变光合产物在地上部分和根系中的分配比例;植株根／冠比下降,而黄叶的发展与根／冠比的变化呈显著负相关;渍害改变小麦的发育进程,尤其是后期渍害明显促使小麦早衰。认为清水使叶片光合速率降低、光合有效面积损失和衰老加速,从而危害小麦的生长。     

Pan-Arctic soil moisture control on tundra carbon sequestration and plant productivity

Long-term atmospheric CO₂ concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer.     

The ecosystem wilting point defines drought response and recovery of a Quercus-Carya forest

Soil and atmospheric droughts increasingly threaten plant survival and productivity around the world. Yet, conceptual gaps constrain our ability to predict ecosystem-scale drought impacts under climate change. Here, we introduce the ecosystem wilting point (Ψ_EWP), a property that integrates the drought response of an ecosystem's plant community across the soil–plant–atmosphere continuum. Specifically, Ψ_EWP defines a threshold below which the capacity of the root system to extract soil water and the ability of the leaves to maintain stomatal function are strongly diminished. We combined ecosystem flux and leaf water potential measurements to derive the Ψ_EWP of a Quercus-Carya forest from an “ecosystem pressure–volume (PV) curve,” which is analogous to the tissue-level technique. When community predawn leaf water potential (Ψ_pd) was above Ψ_EWP (=−2.0 MPa), the forest was highly responsive to environmental dynamics. When Ψ_pd fell below Ψ_EWP, the forest became insensitive to environmental variation and was a net source of carbon dioxide for nearly 2 months. Thus, Ψ_EWP is a threshold defining marked shifts in ecosystem functional state. Though there was rainfall-induced recovery of ecosystem gas exchange following soaking rains, a legacy of structural and physiological damage inhibited canopy photosynthetic capacity. Although over 16 growing seasons, only 10% of Ψ_pd observations fell below Ψ_EWP, the forest is commonly only 2–4 weeks of intense drought away from reaching Ψ_EWP, and thus highly reliant on frequent rainfall to replenish the soil water supply. We propose, based on a bottom-up analysis of root density profiles and soil moisture characteristic curves, that soil water acquisition capacity is the major determinant of Ψ_EWP, and species in an ecosystem require compatible leaf-level traits such as turgor loss point so that leaf wilting is coordinated with the inability to extract further water from the soil.     

Complete ammonia oxidization in agricultural soils: High ammonia fertilizer loss but low N2O production

The contribution of agriculture to the sustainable development goals requires climate-smart and profitable farm innovations. Increasing the ammonia fertilizer applications to meet the global food demands results in high agricultural costs, environmental quality deterioration, and global warming, without a significant increase in crop yield. Here, we reported that a third microbial ammonia oxidation process, complete ammonia oxidation (comammox), is contributing to a significant ammonia fertilizer loss (41.9 ± 4.8%) at the rate of 3.53 ± 0.55 mg N kg⁻¹ day⁻¹ in agricultural soils around the world. The contribution of comammox to ammonia fertilizer loss, occurring mainly in surface agricultural soil profiles (0–0.2 m), was equivalent to that of bacterial ammonia oxidation (48.6 ± 4.5%); both processes were significantly more important than archaeal ammonia oxidation (9.5 ± 3.6%). In contrast, comammox produced less N₂O (0.98 ± 0.44 μg N kg⁻¹ day⁻¹, 11.7 ± 3.1%), comparable to that produced by archaeal ammonia oxidation (16.4 ± 4.4%) but significantly lower than that of bacterial ammonia oxidation (72.0 ± 5.1%). The efficiency of ammonia conversion to N₂O by comammox (0.02 ± 0.01%) was evidently lower than that of bacterial (0.24 ± 0.06%) and archaeal (0.16 ± 0.04%) ammonia oxidation. The comammox rate increased with increasing soil pH values, which is the only physicochemical characteristic that significantly influenced both comammox bacterial abundance and rates. Ammonia fertilizer loss, dominated by comammox and bacterial ammonia oxidation, was more intense in soils with pH >6.5 than in soils with pH <6.5. Our results revealed that comammox plays a vital role in ammonia fertilizer loss and sustainable development in agroecosystems that have been previously overlooked for a long term.     

Upper thermal limits predict herpetofaunal responses to forest edge and cover

Amphibians and reptiles are sensitive to changes in the thermal environment, which varies considerably in human-modified landscapes. Although it is known that thermal traits of species influence their distribution in modified landscapes, how herpetofauna respond specifically to shifts in ambient temperature along forest edges remains unclear. This may be because most studies focus on local-scale metrics of edge exposure, which only account for a single edge or habitat patch. We predicted that accounting for the combined effect of multiple habitat edges in a landscape would best explain herpetofaunal response to thermally mediated edge effects. We (1) surveyed herpetofauna at two lowland, fragmented forest sites in central Colombia, (2) measured the critical thermal maximum (CT_max) of the species sampled, (3) measured their edge exposure at both local and landscape scales, and (4) created a thermal profile of the landscape itself. We found that species with low CT_max occurred both further from forest edges and in areas of denser vegetation, but were unaffected by the landscape-scale configuration of habitat edges. Variation in the thermal landscape was driven primarily by changes in vegetation density. Our results suggest that amphibians and reptiles with low CT_max are limited by both canopy gaps and proximity to edge, making them especially vulnerable to human modification of tropical forest. Abstract in Spanish is available with online material.     

Nupr1 deficiency downregulates HtrA1, enhances SMAD1 signaling,and suppresses age-related bone loss in male mice

Nuclear protein 1 (NUPR1) is a stress-induced protein activated by various stresses, such as inflammation and oxidative stress. We previously reported that Nupr1 deficiency increased bone volume by enhancing bone formation in 11-week-old mice. Analysis of differentially expressed genes between wild-type (WT) and Nupr1-knockout (Nupr1-KO) osteocytes revealed that high temperature requirement A 1 (HTRA1), a serine protease implicated in osteogenesis and transforming growth factor-β signaling was markedly downregulated in Nupr1-KO osteocytes. Nupr1 deficiency also markedly reduced HtrA1 expression, but enhanced SMAD1 signaling in in vitro-cultured primary osteoblasts. In contrast, Nupr1 overexpression enhanced HtrA1 expression in osteoblasts, suggesting that Nupr1 regulates HtrA1 expression, thereby suppressing osteoblastogenesis. Since HtrA1 is also involved in cellular senescence and age-related diseases, we analyzed aging-related bone loss in Nupr1-KO mice. Significant spine trabecular bone loss was noted in WT male and female mice during 6−19 months of age, whereas aging-related trabecular bone loss was attenuated, especially in Nupr1-KO male mice. Moreover, cellular senescence-related markers were upregulated in the osteocytes of 6−19-month-old WT male mice but markedly downregulated in the osteocytes of 19-month-old Nupr1-KO male mice. Oxidative stress-induced cellular senescence stimulated Nupr1 and HtrA1 expression in in vitro-cultured primary osteoblasts, and Nupr1 overexpression enhanced p16^ink4a expression in osteoblasts. Finally, NUPR1 expression in osteocytes isolated from the bones of patients with osteoarthritis was correlated with age. Collectively, these results indicate that Nupr1 regulates HtrA1-mediated osteoblast differentiation and senescence. Our findings unveil a novel Nupr1/HtrA1 axis, which may play pivotal roles in bone formation and age-related bone loss.     

Recovery of aSasa tsuboiana population after mass flowering and death

The recovery process of aSasa tsuboiana population after a mass flowering and death in 1977 was investigated by 15 years of observation in the Hira Mountains, Kinki district, western Japan. Seed production was high (6600–13 800 seeds m⁻² inSasa plots and 3900 seeds m⁻² in a forest plot) but emergent seedling density was low (14–21 seedlings m⁻²), probably because of seed predation byMicrotus montebelli occurring between seed shedding and the next spring. The seedling density had decreased further by the next year and theS. tsuboiana population recovered from only a limited number of seedlings. In spite of such a low initial density, theS. tsuboiana population was able to regenerate successfully and attained the previous full stand height in 7–16 years.Miscantbus sinensis invaded and delayed the recovery ofS. tsuboiana in one plot, butS. tsuboiana became dominant as it caught up with the height ofM. sinensis. Seedling growth patterns, such as frequent tillering, the onset of rhizome extension in the early stage of seedling growth and frequent culm production from rhizomes, played important roles in the successful regeneration ofS. tsuboiana.     

Elevated serum α-fetoprotein level of nude mice bearing hepatoma cells by treatment with monoclonal antibodies to α-fetoprotein

This study was carried out to clarify the reason for elevation of serum α-fetoprotein (AFP) level of nude mice bearing hepatoma cells after treatment with monoclonal antibodies (MoAbs) to AFP. MoAbs to AFP showed no effect on the cumulative amounts of AFP secreted from human hepatoma cell line, HuH-7, in vitro. However, the treatment of nude mice bearing HuH-7N cells (HuH-7 xenograft) with MoAbs to AFP led to elevation of the serum AFP level in spite of the fact that the growth curve of HuH-7N cells was similar to that for PBS treatment. This apparent elevation of the serum AFP level is thought to be due to the slow elimination of AFP-MoAb immune complexes with little lattice structure from circulation, but not the enhancement of AFP secretion of HuH-7N cells. Thus, when using a MoAb alone or MoAb-drug conjugate, the serum AFP level should only be cautiously used as a tumor marker for evaluating the targeting immunotherapy.