Novel microbial community composition and carbon biogeochemistry emerge over time following saltwater intrusion in wetlands

Sea level rise and changes in precipitation can cause saltwater intrusion into historically freshwater wetlands, leading to shifts in microbial metabolism that alter greenhouse gas emissions and soil carbon sequestration. Saltwater intrusion modifies soil physicochemistry and can immediately affect microbial metabolism, but further alterations to biogeochemical processing can occur over time as microbial communities adapt to the changed environmental conditions. To assess temporal changes in microbial community composition and biogeochemical activity due to saltwater intrusion, soil cores were transplanted from a tidal freshwater marsh to a downstream mesohaline marsh and periodically sampled over 1 year. This experimental saltwater intrusion produced immediate changes in carbon mineralization rates, whereas shifts in the community composition developed more gradually. Salinity affected the composition of the prokaryotic community but did not exert a strong influence on the community composition of fungi. After only 1 week of saltwater exposure, carbon dioxide production doubled and methane production decreased by three orders of magnitude. By 1 month, carbon dioxide production in the transplant was comparable to the saltwater controls. Over time, we observed a partial recovery in methane production which strongly correlated with an increase in the relative abundance of three orders of hydrogenotrophic methanogens. Taken together, our results suggest that ecosystem responses to saltwater intrusion are dynamic over time as complex interactions develop between microbial communities and the soil organic carbon pool. The gradual changes in microbial community structure we observed suggest that previously freshwater wetlands may not experience an equilibration of ecosystem function until long after initial saltwater intrusion. Our results suggest that during this transitional period, likely lasting years to decades, these ecosystems may exhibit enhanced greenhouse gas production through greater soil respiration and continued methanogenesis.     

Immune changes in humans during cold exposure: effects of prior heating and exercise.

This study examined the immunological responses to cold exposure together with the effects of pretreatment with either passive heating or exercise (with and without a thermal clamp). On four separate occasions, seven healthy men [mean age 24.0 +/- 1.9 (SE) yr, peak oxygen consumption = 45.7 +/- 2.0 ml. kg(-1). min(-1)] sat for 2 h in a climatic chamber maintained at 5 degrees C. Before exposure, subjects participated in one of four pretreatment conditions. For the thermoneutral control condition, subjects remained seated for 1 h in a water bath at 35 degrees C. In another pretreatment, subjects were passively heated in a warm (38 degrees C) water bath for 1 h. In two other pretreatments, subjects exercised for 1 h at 55% peak oxygen consumption (once immersed in 18 degrees C water and once in 35 degrees C water). Core temperature rose by 1 degrees C during passive heating and during exercise in 35 degrees C water and remained stable during exercise in 18 degrees C water (thermal clamping). Subsequent cold exposure induced a leukocytosis and granulocytosis, an increase in natural killer cell count and activity, and a rise in circulating levels of interleukin-6. Pretreatment with exercise in 18 degrees C water augmented the leukocyte, granulocyte, and monocyte response. These results indicate that acute cold exposure has immunostimulating effects and that, with thermal clamping, pretreatment with physical exercise can enhance this response. Increases in levels of circulating norepinephrine may account for the changes observed during cold exposure and their modification by changes in initial status.     

Adaptive branchial mechanisms in the sturgeon Acipenser naccarii during acclimation to saltwater

Variations of Na(+)/K(+)-ATPase activity and fatty-acid composition in the gills of the sturgeon Acipenser naccarii subjected to progressive acclimation to full seawater (35 ppt) were determined in relation to the hypo-osmoregulatory capacity of this species in the hyperosmotic medium. Blood samples were taken and gills arches were removed at intermediate salinity levels between 0 and 35 ppt and after 20 days at constant salinity (35 ppt). Plasma osmolality and Na(+)/K(+)-ATPase activity increased significantly with growing environmental salinity. Total saturated fatty acids (SFAs) decreased, while total polyunsaturated fatty acids (PUFAs) increased significantly with increasing salinity due mainly to changes in n-3 PUFAs (20:5n-3 and 22:6n-3). The n-3/n-6 ratio increased significantly during the acclimation process. The results show a direct relationship between salinity, increased gill Na(+)/K(+)-ATPase activity and ultrastructural changes of the gill chloride cells. Changes in the fatty-acid composition in gills of A. naccarii during progressive acclimation to full seawater suggest that variations of gill fatty acids may also have a role in osmoregulatory mechanisms.     

Osmotic stress and mortality in adult American shad during transfer from saltwater to freshwater

Thirty-five adult American shad (Alosa sapidissima) were moved quickly (2.5 h) from saltwater to freshwater. Changes in the levels of osmotically active blood constituents and of mortality were observed during and after the transfer. These were compared with levels of corresponding constituents and of mortality in 20 shad maintained in saltwater under similar conditions and to 44 shad sampled immediately after capture in saltwater and in freshwater (40 km from the saltwater-freshwater interface). Sodium and chloride levels in theblood of the transferred group declined sharply during and after transfer. Calcium, glucose and lactic acid levels increased, and potassium and magnesium levels remained stable. Transferred shad experienced heavy mortality beginning 5 h after the initial reduction in salinity associated with movement into freshwater. No mortality was experienced in the group held in saltwater.
It was concluded that the extensive meandering exhibited by adult shad at the upper limit of the salt-freshwater interface during their spring migration in the Connecticut River is a behavioural response designed to slow the transition from the saltwater to the freshwater environment, thereby minimizing the physiological stress involved and/or allowing full recovery from this stress before proceeding upriver.     

Effects of aeration during cold storage of germinated vegetable seeds prior to fluid drilling on seedling viability

Germinated seeds of cabbage, carrot, lettuce and onion were stored for 15 days at 1 °C either in water or humid air before being fluid drilled. In aerated water and humid air, seedling viability was maintained for cabbage, carrot and lettuce, and only slightly reduced for onion. Storage in unaerated water reduced seedling viability by 48%-100%. Seeds continued to germinate in aerated storage, but radicle elongation occurred only with cabbage and lettuce.     

Follicular dynamics prior to and during superovulation in heifers

The present ultrasonographic study examined the relationship between certain follicular parameters and the superovulatory response in gonadotropin-stimulated heifers. Thirty heifers received a total of 35 mg FSH twice daily for 4 d and 0.75 mg cloprostenol were given to induce luteolysis and estrus at 72 h after the initial FSH injection. Transrectal ultrasonography was performed once daily from 1 or 2 d before the initial FSH injection and until the day of estrus. The number of small (2 to 4 mm), medium (5 to 9 mm), and large (>/=10 mm) size follicles as well as the diameter of the large follicles were recorded. Embryos were recovered non-surgically 6 or 7 d after estrus, and the number of corpora lutea was determined by palpation per rectum. Heifers with >2 or 0.05). The number of large follicles and the sum of medium and large follicles were positively correlated (r=0.43 and r=0.54, respectively; P<0.05) with the number of corpora lutea palpated on the day of embryo recovery (6 to 7 d after estrus). In conclusion, there was an effect of the day relative to initiation of FSH treatment on all follicular categories in heifers responding positively to superovulation, and there was no effect of side (left or right ovary) or of corpus luteum diameter (ipsilateral or contralateral).     

The role of genetic structure in the adaptive divergence of populations experiencing saltwater intrusion due to relative sea‐level rise

Saltwater intrusion into estuaries creates stressful conditions for nektonic species. Previous studies have shown that Gambusia affinis populations with exposure to saline environments develop genetic adaptations for increased survival during salinity stress. Here, we evaluate the genetic structure of G. affinis populations, previously shown to have adaptations for increased salinity tolerance, and determine the impact of selection and gene flow on structure of these populations. We found that gene flow was higher between populations experiencing different salinity regimes within an estuary than between similar marsh types in different estuaries, suggesting the development of saline‐tolerant phenotypes due to local adaptation. There was limited evidence of genetic structure along a salinity gradient, and only some of the genetic variation among sites was correlated with salinity. Our results suggest limited structure, combined with selection to saltwater intrusion, results in phenotypic divergence in spite of a lack of physical barriers to gene flow.     

Effect of IAA content Modulators on peroxidase activity and on endogenous IAA during cold pretreatment of maize anthers prior to androgenesis

A cold pretreatment is usually applied to induce maize androgenesis. Peroxidase activity, including indole-3-acetic acid (IAA) oxidase activity, and endogenous IAA concentrations were followed during a cold pretreatment (14 days, 7°C) in anthers of two maize genotypes, Seneca 60 and DH5×DH7, respectively with a low or high androgenetic response. The most prominent result was the absence of a detectable IAA oxidase activity in DH5×DH7. Adding effectors of IAA-oxidase activity or IAA transport did not affect significantly the crude peroxidase activity of DH5×DH7 anthers while inducing a clear inhibition of androgenesis at higher concentrations. No strict correlation was found between IAA level and physiological response, the low responding variety having as much IAA as DH5×DH7. However, for DH5×DH7, every treatment that lowered the IAA level after 14 days of cold resulted in a decrease in androgenetic response.     

The protein synthetic surge in response to mitogen triggers high glycolytic enzyme levels in human lymphocytes and occurs prior to DNA synthesis

A simultaneous increase is found in the level of protein synthesis and the major regulatory glycolytic enzyme, phosphofructokinase (PFK), in early phytohemagglutinin exposure of human lymphocytes. The induction of DNA synthesis is demonstrated to be a much later event. This indicates that the increase of glycolysis in mitogen-stimulated cells precedes cell proliferation, but occurs simultaneously with a general increase in protein synthesis. Chemical inhibitors are used to clarify the interrelationship of protein synthesis, glycolytic enzymes levels, and DNA synthesis. Inhibition of protein synthesis with cycloheximide in the mitogen-exposed lymphocytes prevents any increase in PFK levels, implicating protein synthesis as a cause for the increased glycolysis. Cycloheximide also prevents entry into S phase in mitogen-stimulated lymphocytes which may be due to inhibition of the synthesis of enzymes necessary for DNA synthesis, such as DNA polymerase. Aphidicolin, a specific DNA polymerase inhibitor, is found to have no effect on the increase in protein synthesis and PFK levels that precedes DNA synthesis. The increase in glycolysis in mitogen-stimulated lymphocytes occurs simultaneously with, and is dependent upon, increased protein synthesis, and precedes DNA synthesis and lymphocyte proliferation; thus, the high glycolytic rate of mitogen-stimulated cells is not merely a secondary manifestation of rapid cell proliferation as has been previously reported.     

Observations on the distribution of meroplankton during a downwelling event and associated intrusion of the Chesapeake Bay estuarine plume

We investigated the dispersal of larvae of benthic invertebratesand tested the hypothesis that larvae behaved as if they werepassive particles. Observations were made off Duck, North Carolina,USA during a period of wind driven downwelling at the coastand an intrusion of estuarine water from the Chesapeake Bay.The plume of estuarine water (salinity < 30 psu) was strongestat the shoreward stations in the more northern transects. Winddriven shoreward surface flow converged at the seaward edgeof the plume and downwelled. Offshore flow was present belowthe thermocline and caused the thermocline to bend downwardand contact the bottom at between 5 and 10 km offshore. In the zooplankton samples, we enumerated 33 taxa of larvae(17 taxa of bivalve veligers, 10 taxa of gastropod veligers,and 6 taxa of polychaete larvae). Using cluster analysis, larvaewere separated into groups with similar patterns of distribution.If larvae were acting as passive particles then we hypothesizedthat: 1) Their distribution should remain tied to a water massand 2) around a convergence or divergence, there should be nochange in larval concentration. The distributions of larvaein Clusters 1, 4, 5, and 6 were consistent with the hypothesisthat they were acting as passive particles. Larvae in Clusters2 and 3, however, did not appear to be acting as passive particles.Larvae in Cluster 2 did not remain tied to a water mass. Theyentered the study area in the estuarine plume waters, but within20 km they were nearly absent from the plume water and werefound seaward of the plume and at greater depth. Larvae in Cluster3 were most abundant in areas of converging currents where theshoreward flowing surface waters downwelled at the plume frontor against the shore. We hypothesized that larvae of organisms which as adults livein the intertidal or shallow subtidal zones would have morenearshore distributions than the larvae of adults that are broadlydistributed across the shelf. We compared the depth of the habitatof the adult bivalves from which the bivalve larvae in the differentclusters were derived. The results were consistent with thehypothesis; larvae with distributions closer to shore tendedto come from adults found at shallower depths or in the intertidalzone.     

Carbohydrate and lipid metabolism in rats during adaptation to cold

Cold adapted rats are shown to have glucose and fatty acids concentration in blood inchanged, lactate concentration increased and triglyceride concentration decreased against the control level. Glucose utilization rate in the tolerance test grows. Glycogen content falls, hexokinase and succinate dehydrogenase activity increases, glucose-6-phosphatase and NAD+-isocytratedehydrogenase activity decreases in the liver of experimental animals. The results indicate that utilization of carbohydrate and lipid substrates for thermogenesis is intensified in cold-adapted rats. The hypothesis is supported by the data of tests dealing with IPNA injection or with bringing the animals back under thermocomfortable conditions.     

不同风浪条件下太湖梅梁湾光合有效辐射的衰减

基于2003年7月12～17日在太湖梅梁湾进行的连续6d原位水下光场观测资料,分析了不同风浪条件下光合有效辐射(PAR)的衰减和真光层深度,探讨了影响水下光合有效辐射的主导因子.结果表明,整个观测期间向下PAR衰减系数为2.63～4.71·m^-1(均值为3.63±0.47·m^-1),对应的真光层深度为0.98～1.75m(均值为1.29±0.18m),显示1.5m以下深度浮游植物、沉水植物基本上无法获取足够的太阳光能进行光合作用.从小风浪到中风浪、大风浪向下PAR衰减系数分别是2.63、3.72和4.37·m^-1,衰减系数分别增加了41%、66%.透明度、PAR衰减系数、真光层深度与悬浮物浓度存在显著性线性相关,并且与悬浮物中无机颗粒物相关性最好,而与叶绿素a、脱镁叶绿素及溶解性有机碳相关性很低.多元逐步线性回归表明,叶绿素a和溶解性有机碳最先被剔除方程,说明在梅梁湾由于风浪扰动引起悬浮物浓度的改变是影响水下光场的主导因素.     

Effects of brassinosteroid infiltration prior to cold treatment on ion leakage and pigment contents in rape leaves

The effect of 24-epibrassinolide (BR₂₇) on cold resistance of rape seedlings was studied by ion leakage and photosynthetic pigment degradation measurements. Aqueous solutions of BR₂₇ were injected into cotyledons or primary leaves of rape plants and these plants were incubated at 2 °C or 20 °C. Cold treatment (2 °C) without BR₂₇ injection elevated the membrane permeability in both primary leaves and cotyledons significantly. Surprisingly, injection of leaves with water or 0.467 % aqueous ethanol solution led to a massive increase in membrane permeability after cold stress at 2 °C. The synergistic effect of leaf infiltration and cold on permeability was abolished by 0.05 and 1.00 μM of BR₂₇ in primary leaves and by 1.00 μM of BR₂₇ in cotyledons. On the other hand, BR₂₇ solutions strongly elevated the membrane permeability at 20 °C, while water and ethanol solutions brought about only negligible increases. Water or ethanol infiltrations strongly reduced the leaf contents of chlorophyll (Chl) a, Chl b and carotenoids at 2 °C but less markedly at 20 °C. However, in seedlings exposed to 2 °C pigments content was significantly higher in BR₂₇-treated leaves as compared to water/ethanol control. There were no differences between pigment contents of leaves injected with BR₂₇ solutions or only water/ethanol at 20 °C. The above data strongly support the stress protecting effect of BR₂₇.     

Extensive use of torpor in 13-lined ground squirrels in the fall prior to cold exposure

Mammalian hibernation is characterized by profound reductions in body temperature (T _b) and metabolic, heart and respiratory rates. These reductions are characteristic of torpor, which is temporally confined to winter. Hibernators including ground squirrels are heterothermic in winter, cycling between multiday periods of torpor with low T _b and brief periods of rewarming. In contrast, ground squirrels remain homeothermic during summer, like non-hibernating mammals. The transition between the homeothermic and heterothermic phases of the circannual rhythm of hibernation is often overlooked in hibernation studies. Here, we examined the use of torpor throughout the fall transition in laboratory-housed 13-lined ground squirrels by recording core body temperature with an implanted data logger. As is typical of laboratory-based hibernation studies, animals were kept in standard housing prior to being moved into a cold, dark room to simulate natural hibernation conditions. Significantly, the vast majority of both male and female ground squirrels expressed torpor in the fall while still housed conventionally and prior to cold exposure. The expression of torpor was not predicted by body weight or age, rather it appears to be preprogrammed in a time-dependent manner that is independent of, yet enhanced by, environmental cues. The timing and duration of these torpor bouts occurring prior to cold exposure were also remarkably sporadic. Thus, it is not possible to know with certainty which animals are torpor-naive before cold exposure in the absence of continuous measurement of body temperature. We conclude that fall animals encompass variable points in the transition between summer and winter phases of the circannual cycle of hibernation, thereby confounding studies in which they are used as non-hibernating controls. Conversely, these fall transition animals offer unique opportunities to define the molecular changes that accompany and enable hibernation.     

Body temperature regulation during acclimation to cold and hypoxia in rats

Extreme environmental conditions present challenges for thermoregulation in homoeothermic organisms such as mammals. Such challenges are exacerbated when two stressors are experienced simultaneously and each stimulus evokes opposing physiological responses. This is the case of cold, which induces an increase in thermogenesis, and hypoxia, which suppresses metabolism conserving oxygen and preventing hypoxaemia. As an initial approach to understanding the thermoregulatory responses to cold and hypoxia in a small mammal, we explored the effects of acclimation to these two stressors on the body temperature (T_b) and the daily and ultradian T_b variations of Sprague-Dawley rats. As T_b is influenced by sleep-wake cycles, these T_b variations reflect underlying adjustments in set-point and thermosensitivity. The T_b of rats decreased precipitously during initial hypoxic exposure which was more pronounced in cold (T_b=33.4±0.13) than in room temperature (T_b=35.74±0.17) conditions. This decline was followed by an increase in T_b stabilising at a new level ~0.5 °C and ~1.4 °C below normoxic values at room and cold temperatures, respectively. Daily T_b variations were blunted during hypoxia with a greater effect in the cold. Ultradian T_b variations exhibited daily rhythmicity that disappeared under hypoxia, independent of ambient temperature. The adjustments in T_b during hypoxia and/or cold are in agreement with the hypothesis that an initial decrease in the T_b set-point is followed by its partial re-establishment with chronic hypoxia. This rebound of the T_b set-point might reflect cellular adjustments that would allow animals to better deal with low oxygen conditions, diminishing the drive for a lower T_b set-point. Cold and hypoxia are characteristic of high altitude environments. Understanding how mammals cope with changes in oxygen and temperature will shed light into their ability to colonize new environments along altitudinal clines and increase our understanding of how T_b is regulated under stimuli that impose contrasting physiological constraints.