旱生和湿生生境对蒲公英体内抗氧化物质的影响

选择旱生和湿生生境中生长的蒲公英(Taraxacum mongolicum Hand.-Mazz)分根、叶、花序分别测定抗氧化成分及总抗氧化能力,并比较了SOD同工酶谱的变化情况。结果表明不同生境选取的蒲公英叶片中抗氧化物质以SOD、POD、CAT等抗氧化酶和Vc等小分子为主,花序中可溶性糖、类黄酮和绿原酸含量最高;湿生蒲公英各器官尤其是根中的SOD、CAT、POD活性高于旱生蒲公英对应器官中的酶活性,旱生蒲公英各器官尤其是花序中的可溶性糖、类黄酮和绿原酸含量高于湿生蒲公英对应器官中的含量;旱生和湿生生境未诱导出新的SOD同工酶带;旱生和湿生蒲公英对应器官的总抗氧化能力接近。     

Woody-tissue respiration for Simarouba amara and Minquartia guianensis,two tropical wet forest trees with different growth habits

We measured CO₂ efflux from stems of two tropical wet forest trees, both found in the canopy, but with very different growth habits. The species were Simarouba amara, a fast-growing species associated with gaps in old-growth forest and abundant in secondary forest, and Minquartia guianensis, a slow-growing species tolerant of low-light conditions in old-growth forest. Per unit of bole surface, CO₂ efflux averaged 1.24 mol m^–2 s^–1 for Simarouba and 0.83 mol m^–2s^–1 for Minquartia. CO₂ efflux was highly correlated with annual wood production (r ²=0.65), but only weakly correlated with stem diameter (r ²=0.22). We also partitioned the CO₂ efflux into the functional components of construction and maintenance respiration. Construction respiration was estimated from annual stem dry matter production and maintenance respiration by subtracting construction respiration from the instantaneous CO₂ flux. Estimated maintenance respiration was linearly related to sapwood volume (39.6 mol m^–3s^–1 at 24.6° C, r ²=0.58), with no difference in the rate for the two species. Maintenance respiration per unit of sapwood volume for these tropical wet forest trees was roughly twice that of temperate conifers. A model combining construction and maintenance respiration estimated CO₂ very well for these species (r ²=0.85). For our sample, maintenance respiration was 54% of the total CO₂ efflux for Simarouba and 82% for Minquartia. For our sample, sapwood volume averaged 23% of stem volume when weighted by tree size, or 40% with no size weighting. Using these fractions, and a published estimate of aboveground dry-matter production, we estimate the annual cost of woody tissue respiration for primary forest at La Selva to be 220 or 350 g C m^–2 year^–1, depending on the assumed sapwood volume. These costs are estimated to be less than 13% of the gross production for the forest.     

APNP对白念珠菌杀菌效果研究

目的 研究常压低温等离子体(APNP)喷流对白念珠菌的杀灭作用,并初步探讨其杀菌机制.方法 观察白念珠菌标准株经不同放电气体流量、作用时间及作用距离的APNP喷流处理后的菌落生长情况,并利用扫描电镜与透射电镜观察处理后念珠菌细胞内外超微结构的变化.结果 经APNP处理后的菌株生长明显被抑制,通入的放电气体He/O2以2/0.06 L/min的抑制作用比2/0.02 L/min明显,处理时间10 min明显优于2 min,作用距离1 cm优于2 cm.扫描电镜观察APNP处理后的菌体细胞壁有不同程度的破裂,菌体干瘪,透射电镜下可见菌体细胞壁、细胞膜破裂,胞内物质外漏,细胞内物质稀疏.结论 APNP喷流对白念珠菌有明显的杀灭效果,且放电气体中氧气含量相对越大,处理时间越长,作用距离越短,杀菌效果也越明显.其主要杀菌机制可能与APNP中活性粒子导致微生物细胞壁、细胞膜的破裂有关.     

Diversity of insect‐induced galls along a temperature– rainfall gradient in the tropical savannah region of the Northern Territory,Australia

Evidence regarding the effect of temperature and rainfall on gall‐inducing insects is contradictory: some studies indicate that species richness of gall‐inducing insects increases as environments become hotter and drier, while others suggest that these factors have no effect. The role of plant species richness in determining species richness of gall‐inducing insects is also controversial. These apparent inconsistencies may prove to be due to the influence of soil fertility and the uneven distribution of gall‐inducing insect species among plant taxa. The current study tested hypotheses about determinants of gall‐inducing insect species richness in a way different to previous studies. The number of gall‐inducing insect species, and the proportion of species with completely enclosed galls (more likely to give protection against heat stress and desiccation), were measured in replicate plots at five locations along a 500‐km N‐S transect in the seasonal tropics of the Northern Territory, Australia. There is a strong temperature–rainfall gradient along this transect during the wet season. Plant species lists had already been compiled for each collection plot. All plots were at low elevation in eucalypt savannah growing on infertile soils. There was no evidence to suggest that hot, dry environments in Australia have more gall‐inducing insect species than cooler, wetter environments, or that degree of enclosure of galls is related to protecting insects from heat stress and desiccation. The variable number of gall‐inducing insect species on galled plant species meant that plant species richness did not influence gall species richness. Confirmation is still required that low soil fertility does not mask temperature–rainfall effects and that galls in the study region are occupied predominantly in the wet season, when the temperature–rainfall gradient is most marked.     

施氮量和土壤灭菌对根结线虫侵染番茄根系的影响

设施蔬菜生产中,根结线虫病害频繁发生,严重威胁了设施蔬菜生产的安全性和可持续性.为了探究氮肥施用量和土壤灭菌对根结线虫侵染番茄根系的影响,采用二因素(施氮量和土壤是否灭菌)二水平完全随机区组设计,进行盆栽试验.施氮量分别为100和300 mg·kg-1,采用γ射线对土壤灭菌或不灭菌.结果表明:未灭菌条件下,与高氮处理相比,低氮处理单位根长和单位根干重的根结数分别减少了42.5%和30.4%,地上部干重和根干重分别增加了43.9%和31.4%,氮素农学利用效率提高4.3倍;对土壤进行γ射线灭菌,有效地消除了根结线虫对番茄根系的侵染,地上部干重增加了31.8%;适当减少氮肥施用量能显著降低根结线虫对设施番茄根系的侵染,促进番茄生长,提高氮素农学利用效率.     

丹江口水库淅川库区大气氮湿沉降特征

大气氮沉降是除河流输入外水库水体重要的外源氮输入途径。以丹江口水库淅川库区为研究区,于2018年11月至2019年10月在库区周边设置了6个采样点,采集并分析了库区大气氮湿沉降样品,探讨氮湿沉降的时空分布特征以及对水库水体外源氮输入的贡献。研究结果表明,研究区大气氮湿沉降量为24.21 kg hm^-2 a^-1,其中氨氮占比（47.45％）为最大,有机氮占比（36.34％）次之,硝氮占比（16.21％）最小。硝氮湿沉降量在空间上表现出显著差异性。氨氮、有机氮湿沉降量的季节差异显著,氨氮是以夏季最高,秋季次之,冬季最低,而有机氮是以秋季最高,夏季次之,冬季最低。氨氮、硝氮、有机氮湿沉降量之间存在显著相关性,氨氮、有机氮湿沉降量与降水量之间存在显著相关性。总氮、氨氮湿沉降量分别为1321.98 t/a和627.34 t/a,分别占河流总氮、氨氮入库量的10.82％、34.85％。研究结果可为探索有针对性的库区水体氮污染控制途径提供重要理论基础。     

土壤呼吸对降雨响应的研究进展

土壤呼吸是当前区域碳收支及全球变化研究中的一个热点问题。降雨作为一个重要的扰动因子, 对准确估算土壤呼吸具有重要影响, 这在干旱和半干旱地区尤为明显。尽管关于土壤呼吸对降雨响应过程与规律的研究已取得了较大进展, 但是对于其机制的解释仍然存在较大的争议, 集中体现在对“Birch效应” (降雨强烈激发土壤呼吸的现象)的解释上, 即到底是“底物供应改变机制”还是“微生物胁迫机制”在调控该过程。该文综述了土壤呼吸对降雨事件、降雨量及降雨格局的响应过程与规律; 阐述了土壤呼吸各组分对降雨响应的差异, 分析了雨后物理替代与阻滞、底物供应、根系和微生物活性、微生物群落结构与功能等一系列过程引起土壤呼吸改变的机制; 重点阐述了微生物对土壤水分波动的响应与适应机制。在此基础上提出了今后需重点关注的4个方面：1) “底物供应改变机制”与“微生物胁迫机制”的区分; 2)土壤呼吸各组分对降雨响应的差异; 3)不同时空尺度上土壤呼吸对降雨响应的模拟与估算; 4)降雨带来的外援N和H⁺的作用。     

What is a suitable management for Typha latifolia control in wet meadows?

Aim

Typha latifolia causes serious problems in wet meadows by overgrowing and suppressing other native plants. To determine suitable management for T. latifolia control, we addressed the following question: What are the effects of long-term cutting at different frequencies (once or twice per year and no management) and biomass removal on cover and other characteristics of T. latifolia, and on sward productivity and plant species composition?

Location

Malá Strana nature reserve, Jizerské hory Mountains, Czechia.

Methods

A long-term experiment arranged in a randomised block design with three blocks was established in 2005. Data were collected from five treatments: unmanaged control; cutting once a year in June without biomass removal and with biomass removal; cutting twice per year in June and August without biomass removal and with biomass removal. Percentage cover of T. latifolia and other vascular plant species was visually estimated and T. latifolia characteristics (tiller density, height, dry-matter biomass [DMB] yield and litter), sward height and DMB yield were measured during 2005–2018 at the end of June.

Results and Discussion

Regular cutting once or twice per year regardless of cut biomass removal led to reductions in tiller density, height, litter and DMB yield of T. latifolia. Biomass removal had only a slight tendency to affect T. latifolia characteristics. The higher frequency of cutting significantly decreased the mean T. latifolia cover, litter and DMB yield. Cutting once or twice per year regardless of biomass removal led to successive changes in plant species composition but had no effect on the species richness and evenness.

Conclusions

Cutting at least once per year without biomass removal seems to be sufficient to achieve a decrease in DMB yield and litter of T. latifolia plants, and thereby maintain the wet-meadow vegetation without loss of species richness and also preventing the overgrowth of shrubs and trees.     

Hydraulic variability of tropical forests is largely independent of water availability

Tropical rainforest woody plants have been thought to have uniformly low resistance to hydraulic failure and to function near the edge of their hydraulic safety margin (HSM), making these ecosystems vulnerable to drought; however, this may not be the case. Using data collected at 30 tropical forest sites for three key traits associated with drought tolerance, we show that site-level hydraulic diversity of leaf turgor loss point, resistance to embolism (P₅₀), and HSMs is high across tropical forests and largely independent of water availability. Species with high HSMs (>1 MPa) and low P₅₀ values (< −2 MPa) are common across the wet and dry tropics. This high site-level hydraulic diversity, largely decoupled from water stress, could influence which species are favoured and become dominant under a drying climate. High hydraulic diversity could also make these ecosystems more resilient to variable rainfall regimes.     

Interim Responses of Floodplain Wetland Vegetation to Phase I of the Kissimmee River Restoration Project: Comparisons of Vegetation Maps from Five Periods in the River's History

Phase I of the Kissimmee River Restoration Project (KRRP) reestablished intermittent inundation of the river's floodplain by backfilling 12 km of the C‐38 flood control canal in 2001. We compared floodplain vegetation maps based on 2003 and 2008 aerial imagery (2 and 7 years following completion of Phase I, respectively) to vegetation maps from 1954 (pre‐channelization), 1974 (3 years after channelization), and 1996 (25 years after channelization) to evaluate broad‐scale vegetation responses to Phase I restoration. Results indicate that the extent of wetland plant communities expanded rapidly, more than doubling in area within 2 years after completion of Phase I, and that by 2008 wetlands had nearly recovered to pre‐channelization levels. However, full reestablishment of the pre‐channelization wetland mosaic has not yet occurred. Prior to channelization, much of the floodplain was dominated by a broadleaf marsh (BLM) community associated with extended, deep annual flooding, while shorter‐hydroperiod communities dominated the floodplain in 2003 and 2008. Prior to restoration construction, the reestablishment of BLM was predicted to be slow because suitable hydrology is dependent on project components that will not be in place until all restoration components are completed (projected for 2019). Hydrologic data indicate that the duration and variability of floodplain inundation have not yet achieved restoration targets over the entire Phase I study area. Other factors affecting vegetation responses are likely involved, including the age and viability of soil seed banks, the rarity of relict propagule sources following the channelized period, and competition from an invasive wetland shrub species.