Trophic stability in an Irish mesotrophic lake: Lough Melvin

• 1. Mesotrophic lakes are a threatened habitat in the United Kingdom (UK), and are specified within the UK Biodiversity Action Plan (UKBAP) as requiring protection. Lough Melvin is a large mesotrophic lake that is of particular interest owing to the genetic diversity of its brown trout, but it is currently showing signs of nutrient enrichment.
• 2. In 1990, average lake total phosphorus (TP) was less than 19 µg P L^?1 but increased to 29.5 µg P L^?1 by July 2001. Inflow TP also increased from 34 µg P L^?1 to 41 µg P L^?1 over the same period. Neither phosphorus nor nitrogen appeared to be limiting.
• 3. Despite higher lake TP, annual chlorophyll a did not increase, remaining less than 5 µg L^?1. The phytoplankton was dominated by cyanobacteria and seems to have remained unchanged since the 1950s. Rotifer numbers increased significantly after 2001 but the macro‐zooplankton did not. The absence of a phytoplankton response to P enrichment is attributed to light limitation caused by peat staining and thorough mixing.
• 4. In the catchment, an accelerated programme of clear‐felling began in 1999. Recent changes in the lake are consistent with the known impacts of clear‐felling conifers on peat soils, namely larger P and dissolved organic carbon (DOC) losses. The latter was reflected in a lower Secchi depth and an enhanced microbial food‐web supporting a larger rotifer population.
• 5. It is suggested that, for the purposes of the Water Framework Directive (WFD), Lough Melvin and other large, alkaline but peat‐stained lakes may be treated as a distinct lake type as they do not fit easily into the conventional classifications of dystrophic or mesotrophic lakes.

Copyright © 2006 John Wiley & Sons, Ltd.     

模拟氮沉降对低磷胁迫下3个种源木荷幼苗生长及叶片氮磷含量的影响

【目的】讨论不同产区木荷种源在 NH4+-N或 NO3－-N沉降下的生长表现和响应差异,揭示不同形态氮素对木荷生长发育的影响,为在大气氮沉降环境背景下,选育营养高效利用的木荷速生优质新品种提供理论依据。【方法】以木荷北缘种源区－浙江杭州种源、中部种源区－福建建瓯种源和中部靠南边缘种源区－江西信丰种源3个有代表性的木荷种源作为试验材料,模拟不同形态氮沉降( NH4+和NO3－)增加对不同土壤磷素处理下木荷幼苗生长和叶片氮、磷元素含量的影响。盆栽试验设置土壤低磷(1.1 mg·kg －1)处理和高磷(25 mg·kg －1)对照,以人为喷施 NH4 Cl和 NaNO3溶液进行氮沉降模拟,分别设置3个氮沉降量水平：0,80和200 kg·N·hm －2·a －1,试验按完全随机区组设计,每种源每处理重复12株苗。2013年11月收获,测定苗高、地径等生长指标,并分别测定根、茎、叶各部分干物质量和磷、氮含量。【结果】不同形态氮沉降对木荷苗木生长影响差异显著,磷素可提高种源间对氮素的响应差异。在低磷环境下,不同氮处理下木荷植株生物量和根冠比变异系数较大,这为氮沉降下木荷耐受型植株的选择提供了可能。低磷环境下,NO3－-N 对木荷苗木生长促进作用显著,苗高、地径和生物量分别较 NH4+-N处理高4．5%,17．8%和75．2%,叶片氮、磷含量提高,叶片 N：P 比下降。NH4+-N 对木荷植株的生长抑制作用较强,导致叶片磷含量下降,N：P升高,植株受到磷胁迫增强。而在高磷环境下,NH4+-N的促进作用增强,苗高、地径和生物量分别较 NO3－-N处理高13.5%,10.4%和25.4%。无论土壤在高磷还是低磷环境下,NO3－-N 降低叶片N/P比,而 NH4+-N增加叶片 N/P比。木荷种源间对不同形态氮沉降响应差异显著,在土壤低磷环境下,NH4+-N处理抑制了福建建瓯种源和江西信丰种源生长,生物量下降,而杭州种源却在 NH4+-N80处理下,苗高和地径生长较对照分别增加19%和20%。【结论】在低磷环境下,NO3－-N对木荷不同种源幼苗生长促进作用更强,而当土壤磷含量提高时,NH4+-N的促进作用增强,同时苗木生长差异增大。浙江杭州种源对 NH4+-N 的适应性更强,而福建建瓯和江西信丰种源则对 NO3－-N适应性更强。     

The role of gape‐limitation in intraguild predation between endangered Mohave tui chub and non‐native western mosquitofish

Intraguild predation (IGP) is a mechanism that may facilitate the co‐existence of native species with non‐native invasive species. We conducted laboratory predation trials to assess the role of predator gape‐limitation in the context of IGP between the endangered Mohave tui chub (Siphateles bicolor mohavensis) and invasive western mosquitofish (Gambusia affinis). Larval tui chubs had significantly lower (χ² = 74.74; P < 0.001) survival in the presence of female mosquitofish (10.0%) than in the presence of male mosquitofish (73.3%). Reciprocally, adult tui chubs preyed upon adult mosquitofish, causing a significantly lower (χ² = 11.33; P < 0.001) survival for male mosquitofish (60%) compared to female mosquitofish survival (96.7%). Vulnerability modelling revealed that mosquitofish with a body depth < 4.6 mm and a larval tui chub with a body depth < 1.2 mm were completely vulnerable to predation by adult Mohave tui chub and adult mosquitofish, respectively. IGP in this study system is size‐structured based on gape‐size limitation and may have some conservation implications for the recovery of endangered Mohave tui chub. Our findings also provide an important caveat to the dogmatic view of mosquitofish as a threat whenever they invade. It is important to note that many previous studies that reported negative impacts of mosquitofish involved native species with relatively small body sizes, often the same size as mosquitofish.     

Responses of legumes to rhizobia and arbuscular mycorrhizal fungi: A meta-analysis of potential photosynthate limitation of symbioses

Legumes are prized for their seed protein and lipid mass fractions. Since legumes spend up to 4-16% of photosynthesis on each of the rhizobial and arbuscular mycorrhizal (AM) fungal symbioses, it might be expected that positive responses in yield due to rhizobial and AM symbioses are accompanied by decreases in seed protein and lipid mass fractions due to a photosynthate (C) limitation. We performed a meta-analysis of 348 data points from published studies with 12 legume species to test whether yield, harvest index, and seed protein and lipid mass fractions are affected by symbioses. There was a significant increase in yield due to rhizobial inoculation (16% in the field; 59% in pot experiments). There were no responses of yield to AM fungi and rhizobial + AM fungi inoculations in the field (presumably because an AM fungi-free control cannot be ensured), but significant responses in pots (45% with AM fungi; 44% with rhizobial + AM fungi). Rhizobial inoculation improved seed protein mass fraction by 7% in the field; AM fungi increased this parameter by 14% in pots. There were no discernable effects of symbioses on seed lipid mass fraction. Rhizobial symbioses in the field increased harvest index (+5%), but AM fungi did not affect harvest index. In conclusion, increases in yield due to symbioses also resulted in increases in seed protein and constant lipid mass fractions, indicating that legumes are not C-limited under symbiotic conditions.     

Reproductive biology and conservation implications of three endangered snapdragon species (Antirrhinum, Plantaginaceae)

About 32% of Antirrhinum species are considered to be endangered; however, no field studies have focused on their reproductive biology. In this work, several aspects of the reproductive biology (flowering phenology, floral biology, breeding system) and potential limits on seed quantity and quality (pollen limitation, inbreeding depression) were studied in natural populations of three endangered species of the genus (Antirrhinum charidemi, Antirrhinum subbaeticum, Antirrhinum valentinum). Results disclose that all three species need insect visitors for seed production since fruit set after autonomous self-pollination was lower than under hand cross-pollination. A. charidemi and A. valentinum were mainly self-incompatible, whereas A. subbaeticum was self-compatible but herkogamous. Supplementary pollination in open-pollinated flowers only increased fruit set and seed set relative to controls in a given population of A. valentinum. Preliminary data on inbreeding depression at early life-cycle stages of the self-compatible A. subbaeticum revealed that the cumulative level was low. Despite the three species being closely related and sharing many ecological characteristics, they show different mating systems, and different factors limit seed quantity and quality. Thus, caution should be taken when making a common conservation plan for a group of closely related taxa.     

台风"达维"对海南农垦橡胶产业的损害及所引发的对今后产业发展的思考

海南岛地处热带北缘,是全国遭遇热带气旋次数最多的省份。介绍了2005年18号台风“达维”的登陆地点、影响范围、强度等基本情况;并调查了它对海南垦区橡胶的破坏程度及造成的经济损失。调查发现,已开割树受害率(3级损害以上)50.9%,未开割树受害率33.9%,橡胶种植业经济总损失达24亿元;针对台风“达维”所造成的危害暴露出的一些问题,如产业布局的不合理、科技投入的不足、胶园管理水平低等,提出了灾后重建和产业可持续发展的建议。     

Multiple-nutrient limitation of upland rainfed rice in ferralsols: a greenhouse nutrient-omission trial

Abstract

To optimize the nutrient management of upland rice production on tropical ferralsols, a greenhouse experiment was established using the multi-nutrient omission approach. A reciprocal soil origin-rice cultivar transplant experiment was also conducted to better understand the relative contributions of the soil origin and the rice cultivar in rice nutrient limitation. We tested the deficiency of seven major and secondary nutrients [nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), and silicon (Si)] and a solution of six micronutrients (B, Mn, Cu, Co, Na, Mo) likely to limit the growth of two upland rice cultivars, Chhomrong Dan and Nerica 4, on two Ferralsols from the highlands of Madagascar. We found severe multiple nutrient deficiencies. For both cultivars, P, Ca, N, Mg omission significantly depressed the shoot and root dry biomass and their amounts in plant tissues. However, the main limiting nutrients were not the same in both soils. We conclude that the multinutrient deficiencies observed for rice growth in the Ferralsols are site-specific, even though P limitation appears to be in common, and requires a holistic consideration of the mineral fertility, including micronutrients.     

Physiological responses of Eucalyptus nitens × nitens under experimentally imposed water stress

This study reports on how a cold- and frost-tolerant clone of Eucalyptus nitens × nitens responds to drought stress. The aim was to identify physiological traits that contribute to drought acclimation. Macropropagated saplings were grown in a climate-controlled greenhouse in pots filled with coarse river sand supplied with a slow-release fertiliser. One group of plants was kept regularly watered (control), and another group was subjected to four cycles of water stress (drought) whereby water was withheld for periods lasting 6, 10, 10 and 14 d, with 4 d of regular watering (recovery) inbetween. A drought cycle was terminated once saplings showed signs of wilting. Daily responses in stomatal conductance (g _s) were similar between control and drought treatments, except on the day of termination of the cycle, when g _s was significantly depressed in droughted plants. During the fourth and most severe drought cycle, there was a physiological adaptation to water stress because g _s was similar between control and droughted plants. Stomatal conductance was significantly positively correlated with volumetric soil moisture content in the drought treatment, but not in the control treatment. Electron transport capacity (J _max) increased during each drought cycle, and the increase was significant during the fourth cycle. Other parameters derived from A/c _i response curves were similar between the treatments. Under experimentally imposed water stress, E. nitens × nitens reduced leaf area, increased assimilate rate per unit leaf area, and maintained high stomatal conductance until leaves wilted. After 46 d droughted plants had accumulated half the biomass of control plants. Therefore, a cold- and frost-tolerant clone of E. nitens × nitens may be tolerant to drought stress but at a reduced growth rate because of reduced leaf area.     

竹在现代园林中的应用与发展

本文分析了中国古典园林中竹子的造景手法、审美价值和功能利用方面的特点及其局限性,结合世界现代园林的实践与理论,阐述了为满足尺度更广阔、内容更丰富、功能更齐全、技术更发达、审美更多样的现代园林的需要,现代竹子造景在表达方式、文化内涵和生态功能方面进行拓展的必要性,并对于新的竹子造景手法进行了归纳和探索。     

The effects of epibenthic communities on reef fishes in the northern Gulf of Mexico

Abstract  Reef fishes were compared between artificial reefs with ( n  =   20) and without ( n  =   20) epibenthic communities in the northern Gulf of Mexico. Artificial reefs were built in June 2003; half were coated with copper-based paint to prevent epibenthic community development. Reefs were surveyed by SCUBA divers to estimate fish abundance in the autumn and winter 2003 and spring 2004. Total fish abundance and abundance of red snapper, Lutjanus campechanus (Poey), and gray triggerfish, Balistes capriscus Gmelin, were significantly ( P  ≤   0.05) higher on reefs with epibenthic communities. In the spring 2004, the abundance of belted sandfish, Serranus subligarius (Cope), the size of red snapper and community measures of diversity and evenness were significantly ( P  ≤   0.05) greater on unpainted reefs. These significant differences provide evidence that reef fishes were positively affected by the presence of epibenthic organisms that probably provided increased food resources.