Comparative <Emphasis Type="Italic">in vitro</Emphasis> germination ecology of <Emphasis Type="Italic">Calopogon tuberosus</Emphasis> var. <Emphasis Type="Italic">tuberosus</Emphasis> (Orchidaceae) across its geographic range

Seed responses to temperature are often essential to the study of germination ecology, but the ecological role of temperature in orchid seed germination remains uncertain. The response of orchid seeds to cold stratification have been studied, but the exact physiological role remains unclear. No studies exist that compare the effects of either cold stratification or temperature on germination among distant populations of the same species. In two separate experiments, the role of temperature (25, 22/11, 27/15, 29/19, 33/24°C) and chilling at 10°C on in vitro seed germination were investigated using distant populations of Calopogon tuberosus var. tuberosus. Cooler temperatures promoted germination of Michigan seeds; warmer temperatures promoted germination of South Carolina and north central Florida seeds. South Florida seed germination was highest under both warm and cool temperatures. More advanced seedling development generally occurred at higher temperatures with the exception of south Florida seedlings, in which the warmest temperature suppressed development. Fluctuating diurnal temperatures were more beneficial for germination compared to constant temperatures. Cold stratification had a positive effect on germination among all populations, but South Carolina seeds required the longest chilling treatments to obtain maximum germination. Results from the cold stratification experiment indicate that a physiological dormancy is present, but the degree of dormancy varies across the species range. The variable responses among populations may indicate ecotypic differentiation.     

Long-term temperature evolution in a deep sub-alpine lake,Lake Bourget,France: how a one-dimensional model improves its trend assessment

Water temperature and the alternation of stratification and mixing count amongst key drivers of lake ecology. Reliable long time-series of water temperature are rare. Here, we investigated how a numerical model can fill the gaps in heterogeneous time-series and make it possible to identify a significant trend in the lake thermal regime. We computed the mean water temperature and the Schmidt stability, an indicator of the stratification strength, in a deep and well-stratified lake (Lake Bourget, France), between 1976 and 2008. We first used temperature measurements and then a one-dimensional vertical model, which we describe here. The model performs as well as the best existing models. During the 1976–2008 periods, whereas no statistically significant trend came out of the measurements, we found in the simulation results an increase of 0.12 °C per decade in the water temperature and of 5.9 days per decade in the stratification duration. This shows that the temperature history of a lake can be reconstructed and a reliable long-term trend computed when weather data and a calibrated temperature model are available. Our results also suggest that different local climatic influences cause a slower warming in this lake of the south-western Alps than in other sub-alpine lakes.     

Thermal regimes of Florida lakes

Water column temperatures were determined monthly for 24 lakes and bimonthly for 5 lakes in peninsular Florida during 1979. Three geographical groups (north, central, south) were delineated from mean monthly water column temperatures for individual lakes. On a monthly basis, northern lakes were least similar to southern lakes, while central Florida lakes displayed greater affinity to the southern than to the northern lake group. Temperature differences between lake groups broke down during late summer. Subtropical lakes have been defined tentatively as those Florida lakes south of 28° latitude which possess warm monomictic circulation and a mean annual temperature of 24.2 ± 4.8 °C with minimum water column temperature rarely less than 14 °C and summer maxima rarely exceeding 31 °C. While all lakes in Florida are clearly warm monomictic annual nutrient cycling and productivity patterns may be influenced by inter-group differences in the timing and duration of water column circulation.     

A spatially explicit computer model for immature distributions of Glyptotendipes paripes (Diptera: Chironomidae) in central Florida lakes

Density and spatial distribution data of immature Glyptotendipes paripes Edwards (Diptera: Chironomidae), in relation to selected water and sediment characteristics prevailing in three central Florida lakes, were used to develop and calibrate a qualitative model of G. paripes distributions with the purpose of developing more efficient sampling plans for research or population management. For the model, each lake habitat was defined by a two-dimensional matrix, while a three-dimensional matrix was used to simulate the life stage-structured population. A Lefkovitch population matrix was used to project survival and development of the population in each spatial unit. The model incorporated lake bathymetry, sediment dry weight, water level, food availability (as a function of Secchi disk transparency) and strength of density dependence as influences on immature survival and adult fecundity. Temperature-dependent development data for G. paripes were incorporated to estimate development time. A simple redistribution function was used to simulate the dispersal of adults over the simulated habitat for oviposition. Immatures and relevant environmental data taken for eight dates, at each of two other central Florida lakes were used to validate the model. The mean correct prediction rate of the model for field density distributions within 0.5 log(n+1) immatures/m² density in spatial habitat cells was 0.64 and 0.66 for the validation lakes. Presence/absence correct prediction rates were 0.61 and 0.76, while matching to a proposed sampling stratification based on a treatment threshold was 0.85 and 0.88. These values indicate that the model is efficient for preparing stratified immature G. paripes sampling plans for central Florida lakes.     

Application of a numerical model to predict impacts of climate change on water temperatures in two deep, oligotrophic lakes in New Zealand

We applied a numerical hydrodynamic model (DYRESM) to two large, deep New Zealand lakes that are characterised by deep thermoclines and high wind forcing, to assess their sensitivity to changes in climate. Modifications to standard model parameters were necessary for the successful application of DYRESM. Predictions from downscaled global circulation models suggest an increase in mean air temperature, rainfall, and wind speeds. Modelling the hydrodynamics of the lakes suggests that increasing air temperatures would offset the cooling influences of increased rainfall and river flows, resulting in warmer overall lake temperatures, and an earlier, longer, and shallower thermal stratification. These physical changes could affect phytoplankton production as their light limitation would decrease in duration and intensity. However, deeper mixing caused by increases in wind speed would negate this reduction of thermocline depth. While warmer air temperatures appear to be the dominant driver of changes in thermal structure, changes in other meteorological factors, especially wind speed, are important in predicting future hydrodynamics. Compared to large, deep lakes in the Northern Hemisphere, the predicted warming rates in Lakes Wanaka and Wakatipu are slower, due partly to a lower predicted rate of atmospheric warming and the absence of winter ice cover in these lakes.     

A dynamic-bioenergetics model to assess depth selection and reproductive growth by lake trout (Salvelinus namaycush)

We coupled dynamic optimization and bioenergetics models to assess the assumption that lake trout (Salvelinus namaycush) depth distribution is structured by temperature, food availability, and predation risk to maximize reproductive mass by autumn spawning. Because the model uses empirical daily thermal-depth profiles recorded in a small boreal shield lake (lake 373 at the Experimental Lakes Area, northwestern Ontario) during 2 years of contrasting thermal stratification patterns, we also assessed how climate-mediated changes in lakes may affect the vertical distribution, growth, and fitness of lake trout, a cold-water top predator. The depths of acoustic-tagged lake trout were recorded concurrently with thermal-depth profiles and were compared to model output, enabling an assessment of model performance in relation to the observed fish behavior and contrasting thermal conditions. The depths and temperatures occupied by simulated fish most closely resembled those of the tagged fish when risk of predation was included in the model, indicating the model may incorporate the most important underlying mechanisms that determine lake trout depth. Annual differences suggest less use of shallow (warm), productive habitats, resulting in markedly less reproductive mass, during the year with the warm stratification pattern. Mass for reproduction may be lower in warmer conditions because of reduced reproductive investment, yet survival may be inadvertently higher because risky surface waters may be avoided more often in warmer, shallower, and metabolically costly conditions. At a minimum our study suggests that lake trout reproductive mass and fitness may be expected to change under the anticipated longer and warmer stratification patterns.     

The role of gibberellic acid (GA3) in the removal of dormancy inFraxinus excelsior L. seeds

The seeds ofFraxinus excelsior L. were stratified at 17-20 °C (warm stratification), at 4-6 °C (cold stratification) and at alternating temperature (warm — cold stratification). The seeds subjected to warm stratification only, remained dormant. The seeds stratified only at 4-6 °C germinated gradually during a long period of time. The seeds subjected to warm — cold stratification, however, germinated with great intensity within a relatively short period of time. GA₃ was shown to stimulate the growth of embryos markedly, and its effect on the germination of seeds depended on the temperature of stratification. GA₃ applied during the cold stratification accelerated the removal of dormancy by shortening the period of stratification and by influencing the germination of seeds. The results obtained indicate a similarity between the effect of temperature 17-20 °C during the warm stratification and that of gibberellic acid. Both those factors applied separately affect favourably after-ripening of the embryos and accelerate the germination of seeds.     

Climate-related differences in the dominance of submerged macrophytes in shallow lakes

It has been suggested that shallow lakes in warm climates have a higher probability of being turbid, rather than macrophyte dominated, compared with lakes in cooler climates, but little field evidence exists to evaluate this hypothesis. We analyzed data from 782 lake years in different climate zones in North America, South America, and Europe. We tested if systematic differences exist in the relationship between the abundance of submerged macrophytes and environmental factors such as lake depth and nutrient levels. In the pooled dataset the proportion of lakes with substantial submerged macrophyte coverage (> 30% of the lake area) decreased in a sigmoidal way with increasing total phosphorus (TP) concentration, falling most steeply between 0.05 and 0.2 mg L⁻¹. Substantial submerged macrophyte coverage was also rare in lakes with total nitrogen (TN) concentrations above 1–2 mg L⁻¹, except for lakes with very low TP concentrations where macrophytes remain abundant until higher TN concentrations. The deviance reduction of logistic regression models predicting macrophyte coverage from nutrients and water depth was generally low, and notably lowest in tropical and subtropical regions (Brazil, Uruguay, and Florida), suggesting that macrophyte coverage was strongly influenced by other factors. The maximum TP concentration allowing substantial submerged macrophyte coverage was clearly higher in cold regions with more frost days. This is in agreement with other studies which found a large influence of ice cover duration on shallow lakes' ecology through partial fish kills that may improve light conditions for submerged macrophytes by cascading effects on periphyton and phytoplankton. Our findings suggest that, in regions where climatic warming is projected to lead to fewer frost days, macrophyte cover will decrease unless the nutrient levels are lowered.     

Water temperature and stratification depth independently shift cardinal events during plankton spring succession

In deep temperate lakes, the beginning of the growing season is triggered by thermal stratification, which alleviates light limitation of planktonic producers in the surface layer and prevents heat loss to deeper strata. The sequence of subsequent phenological events (phytoplankton spring bloom, grazer peak, clearwater phase) results in part from coupled phytoplankton–grazer interactions. Disentangling the separate, direct effects of correlated climatic drivers (stratification‐dependent underwater light climate vs. water temperature) from their indirect effects mediated through trophic feedbacks is impossible using observational field data, which challenges our understanding of global warming effects on seasonal plankton dynamics. We therefore manipulated water temperature and stratification depth independently in experimental field mesocosms containing ambient microplankton and inocula of the resident grazer Daphnia hyalina. Higher light availability in shallower surface layers accelerated primary production, warming accelerated consumption and growth of Daphnia, and both factors speeded up successional dynamics driven by trophic feedbacks. Specifically, phytoplankton peaked and decreased earlier and Daphnia populations increased and peaked earlier at both shallower stratification and higher temperature. The timing of ciliate dynamics was unrelated to both factors. Volumetric peak densities of phytoplankton, ciliates and Daphnia in the surface layer were also unaffected by temperature but declined with stratification depth in parallel with light availability. The latter relationship vanished, however, when population sizes were integrated over the entire water column. Overall our results suggest that, integrated over the entire water column of a deep lake, surface warming and shallower stratification independently speed up spring successional events, whereas the magnitudes of phytoplankton and zooplankton spring peaks are less sensitive to these factors. Therefore, accelerated dynamics under warming need not lead to a trophic mismatch (given similar grazer inocula at the time of stratification). We emphasize that entire water column dynamics must be studied to estimate global warming effects on lake ecosystems.     

Drought-induced changes in nutrient concentrations and retention in two shallow Mediterranean lakes subjected to different degrees of management

While extensive knowledge exists on the relationship between nutrient loading and nutrient concentrations in lakes in the cold temperate region, few studies have been conducted in warm lakes, not least in warm arid lakes. This is unfortunate as a larger proportion of the world’s lakes will be situated in arid climates in the future due to climate change and a larger proportion will suffer from a higher frequency of intensive drought. We conducted a comprehensive 11–13 year mass balance study in two interconnected shallow Mediterranean lakes in Turkey, covering a period with substantial changes in climate conditions. The upstream lake was only affected by natural changes in nutrient loading, while the downstream lake was additionally influenced by sewage diversion and restoration by fish removal. Contrasting to experience from north temperate lakes we found an increase in in-lake concentrations of total phosphorus and inorganic nitrogen (ammonia as well as nitrate) in dry years despite lower external nutrient loading, and submerged macrophytes did not increase the nitrogen retention capacity of the lakes. In contrast, fish removal modulated the nitrogen concentration as in north temperate lakes, but the effect was not long-lasting. Our results suggest that climate warming reduces the nutrient retention capacity of shallow lakes in the Mediterranean and exacerbates eutrophication. Lower thresholds of nutrient loading for shifting turbid shallow lakes to a clear water state are therefore to be expected in arid zones in a future warmer climate, with important management implications.     

Seasonal Distribution of Thermotolerant Free-Living Amoebae. II. Lake Issaqueena1

A quantitative study of the seasonal distribution of thermotolerant (37°C and 45°C), small free-living amoebae (FLA) was conducted in Lake Issaqueena, a warm, monomictic lake with steep, sloping banks and a maximum basin depth of 10 m in the Piedmont region of South Carolina. Naegleria and Vahlkampfia were the most frequently encountered FLA in littoral sediment and surface water samples whereas Acanthamoeba was most commonly isolated from profundal sediment, especially during late summer. In the water column, FLA populations were highest in a persistent detrital layer; however, few amoebae were isolated from a massive (～1.5 m thick) layer of Oscillatoria. The only N. fowleri isolated in this study was from the detrital layer. Discussion of the influence of differences in watershed and basin morphology on variations in the size and generic composition of FLA populations for the aquatic ecosystems of Lake Issaqueena and Willard's Pond is included.     

Limnological and ecological sensitivity of Rwenzori mountain lakes to climate warming

An increasing number of studies forecast that anthropogenic climate change poses serious consequences for the biodiversity and ecosystem functioning of high-elevation mountain lakes, through a series of both direct and indirect effects. The impacts of future climate warming on alpine ecosystems are of particular concern, given that warming is expected to be most pronounced at high elevations around the globe. Here, we evaluate the limnological and ecological sensitivity of high-elevation lakes in the Rwenzori Mountains (Uganda-D. R. Congo) to climate change. This is done by comparing the species assemblages of larval chironomid remains deposited recently in lake sediments with those deposited at the base of short cores (dated to within or shortly after the Little Ice Age) in 16 lakes. Chironomid-based reconstructions of mean annual air temperature (MATemp) are made using a variety of inference models (with transfer functions based on weighted averaging, weighted-averaging partial least squares, and a weighted modern analogue technique), and two different calibration data sets, one covering the full regional temperature gradient and one comprising only high-elevation Rwenzori lakes and ponds. The reconstructed historical temperature change ranges between a cooling of −2.03°C and a warming of +3.22°C (with n = 16 lakes × 3 models × 2 calibration data sets). However, excluding the atypical mid-elevation lake Mahoma (2,990 m altitude), we find a three-to-one ratio of cases of inferred warming against inferred cooling, and of the 24 Δ MATemp values exceeding 0.60°C, 23 are positive and only one is negative. Chironomid-inferred temperature changes mostly fall within the error range of the regional temperature inference models. A generalized linear mixed model analysis of the combined result from all lakes (except Mahoma) nevertheless indicates significantly warmer MATemp (on average +0.38 ± 0.11°C) at present compared to between ~85 and ~645 years ago. Inferred temperature changes are independent of whether lakes are located in glaciated or non-glaciated catchments, and of the age of the core base, suggesting that at least part of the signal is due to relatively recent, anthropogenic warming. The direction of faunal change at the lakes in relation to established species–environment relationships suggests that part of the observed shifts in species composition reflect lake-specific evolution in habitat features other than temperature, such as nutrients, pH or oxygen regime, which in our present calibration data set co-vary with temperature to a greater or lesser extent. The fairly uniform and marked historical warming trend in Rwenzori lakes documented by this study highlights their ecological vulnerability and their value as early warning systems for detecting the limnological and ecological effects of global warming.     

Effects of temperature, salinity and fish in structuring the macroinvertebrate community in shallow lakes: implications for effects of climate change

Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lakes.     

Response of endemic Clarias species’ life-history biometrics to land use around the papyrus-dominated Mpologoma riverine wetland,Uganda

Climate change may threaten the fisheries of Lake Victoria by increasing density differentials in the water column, thereby strengthening stratification and increasing the intensity and duration of deoxygenation in the deeper waters. Between 1927 and 2008 the lake's temperature increased by 0.99 °C at the surface and by 1.34 °C at depths >50 m, with the rate of warming increasing most rapidly between 2000 and 2008. In February 2000 there were marked thermal discontinuities in the water column at a number of deep stations, with marked oxyclines at depths ranging from 30–50 m, and with all stations being anoxic from 50 m downwards. In contrast, in February 2007 the lake's temperature had risen, especially at the bottom, and both the thermal discontinuities and oxyclines were much reduced, only one station recording a dissolved oxygen concentration of <2.0 mg l^–1 at 50 m. This may reflect the fact that deeper waters were warming faster, and the reasons for this are discussed. These data suggest that the impacts of warming on the thermal regime of African lakes may be highly variable and unpredictable and, in this case, may have reduced its threat to the fisheries.     

Temperature acclimation alters cardiac performance in the lobster Homarus americanus

The American lobster is a poikilotherm that inhabits a marine environment where temperature varies over a 25°C range and depends on the winds, the tides and the seasons. To determine how cardiac performance depends on the water temperature to which the lobsters are acclimated we measured lobster heart rates in vivo. The upper limit for cardiac function in lobsters acclimated to 20°C is approximately 29°C, 5°C warmer than that measured in lobsters acclimated to 4°C. Warm acclimation also slows the lobster heart rate within the temperature range from 4 to 12°C. Both effects are apparent after relatively short periods of warm acclimation (3–14 days). However, warm acclimation impairs cardiac function at cold temperatures: following several hours exposure to frigid (<5°C) temperatures heart rates become slow and arrhythmic in warm acclimated, but not cold acclimated, lobsters. Thus, acclimation temperature determines the thermal limits for cardiac function at both extremes of the 25°C temperature range lobsters inhabit in the wild. These observations suggest that regulation of cardiac thermal tolerance by the prevailing environmental temperature protects against the possibility of cardiac failure due to thermal stress.     

Effects of a half a millennium winter on a deep lake – a shape of things to come?

Analyses of the effects of extreme climate periods have been used as a tool to predict ecosystem functioning and processes in a warmer world. The winter half‐year 2006/2007 (w06/07) has been extremely warm and was estimated to be a half‐a‐millennium event in central Europe. Here we analyse the consequences of w06/07 for the temperatures, mixing dynamics, phenologies and population developments of algae and daphnids (thereafter w06/07 limnology) in a deep central European lake and investigate to what extent analysis of w06/07 limnology can really be used as a predictive tool regarding future warming. Different approaches were used to put the observations during w06/07 into context: (1) a comparison of w06/07 limnology with long‐term data, (2) a comparison of w06/07 limnology with that of the preceding year, and (3) modelling of temperature and mixing dynamics using numerical experiments. These analyses revealed that w06/07 limnology in Lake Constance was indeed very special as the lake did not mix below 60 m depth throughout winter. Because of this, anomalies of variables associated strongly with mixing behaviour, e.g., Schmidt stability and a measure for phosphorus upward mixing during winter exceeded several standard deviations the long‐term mean of these variables. However, our modelling results suggest that this extreme hydrodynamical behaviour was only partially due to w06/07 meteorology per se, but depended also strongly on the large difference in air temperature to the previous cold winter which resulted in complete mixing and considerable cooling of the water column. Furthermore, modelling results demonstrated that with respect to absolute water temperatures, the model ‘w06/07’ most likely underestimates the increase in water temperature in a warmer world as one warm winter is not sufficient to rise water temperatures in a deep lake up to those expected under a future climate.     

Impacts of climate warming on the long-term dynamics of key fish species in 24 European lakes

Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10–100 years) fish data series from 24 European lakes (area: 0.04–5,648 km²; mean depth: 1–177 m; a north–south gradient from Sweden to Spain). Along with an annual temperature increase of about 0.15–0.3°C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species. These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal brown trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike–perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems.     

Ecosystem response to earlier ice break‐up date: Climate‐driven changes to water temperature,lake‐habitat‐specific production,and trout habitat and resource use

Climate warming has yielded earlier ice break‐up dates in recent decades for lakes leading to water temperature increases, altered habitat, and both increases and decreases to ecosystem productivity. Within lakes, the effect of climate warming on secondary production in littoral and pelagic habitats remains unclear. The intersection of changing habitat productivity and warming water temperatures on salmonids is important for understanding how climate warming will impact mountain ecosystems. We develop and test a conceptual model that expresses how earlier ice break‐up dates influence within lake habitat production, water temperatures and the habitat utilized by, resources obtained and behavior of salmonids in a mountain lake. We measured zoobenthic and zooplankton production from the littoral and pelagic habitats, thermal conditions, and the habitat use, resource use, and fitness of Brook Trout (Salvelinus fontinalis). We show that earlier ice break‐up conditions created a "resource‐rich" littoral–benthic habitat with increases in zoobenthic production compared to the pelagic habitat which decreased in zooplankton production. Despite the increases in littoral–benthic food resources, trout did not utilize littoral habitat or zoobenthic resources due to longer durations of warm water temperatures in the littoral zone. In addition, 87% of their resources were supported by the pelagic habitat during periods with earlier ice break‐up when pelagic resources were least abundant. The decreased reliance on littoral–benthic resources during earlier ice break‐up caused reduced fitness (mean reduction of 12 g) to trout. Our data show that changes to ice break‐up drive multi‐directional results for resource production within lake habitats and increase the duration of warmer water temperatures in food‐rich littoral habitats. The increased duration of warmer littoral water temperatures reduces the use of energetically efficient habitats culminating in decreased trout fitness.     

Deep and intermediate complex morphophysiological dormancy in seeds of Ferula gummosa (Apiaceae)

We tested the hypothesis that seeds of the monocarpic perennial Ferula gummosa from the Mediterranean area and central Asia have deep complex morphophysiological dormancy. We determined the water permeability of seeds, embryo morphology, temperature requirements for embryo growth and seed germination and responses of seeds to warm and cold stratification and to different concentrations of GA₃. The embryo has differentiated organs, but it is small (underdeveloped) and must grow inside the seed, reaching a critical embryo length, seed length ratio of 0.65–0.7, before the seed can germinate. Seeds required 9 weeks of cold stratification at <10°C for embryo growth, dormancy break and germination to occur. Thus, seeds have morphophysiological dormancy (MPD). Furthermore, GA₃ improved the germination percentage and rate at 5°C and promoted 20 and 5% germination of seeds incubated at 15 and 20°C, respectively. Thus, about 20% of the seeds had intermediate complex MPD. For the other seeds in the seed lot, cold stratification (5°C) was the only requirement for dormancy break and germination and GA₃ could not substitute for cold stratification. Thus, about 80% of the seeds had deep complex MPD.     

Twentieth century human and climate impacts on a large mountain lake in southwest China

Subfossil chironomid and sediment geochemistry data from Lugu Lake, a large high-elevation lake in southwest China, were used to assess the influences of climate warming and direct human impacts on the lake through time. A 95-year-long sediment record was recovered from the lake. Principal components analysis (PCA) and redundancy analysis of fossil chironomid data were performed to determine the controlling factors on the chironomid community. The four prominent environmental controls were summer air temperature, organic matter C:N ratio (C_org:N), dry mass accumulation rate (DMAR), and total nitrogen. C_org:N proved to be the most important controlling factor through time. However, C_org:N and summer air temperature were highly co-linear, possibly due to temperature directly impacting lake productivity (and thus C:N ratios) through increased stratification and a longer growing season. PCA Axis 1 scores were a strong predictor of summer temperatures even after DMAR was factored out to account for direct human influences. The strong temperature–chironomid relationship over the last 50 years could be due to the lake becoming more responsive to climate warming after cultural eutrophication of the 1950s, as lakes with higher nutrient loads are shown to be more responsive to the effects of climate warming.