Hydrologic control of litter decomposition in seasonally flooded prairie marshes

The effect of seasonal inundation on the decomposition of emergent macrophyte litter (Scolochloa festucacea) was examined under experimental flooding regimes in a northern prairie marsh. Stem and leaf litter was subjected to six aboveground inundation treatments (ranging from never flooded to flooded April through October) and two belowground treatments (nonflooded and flooded April to August). Flooding increased the rate of mass loss from litter aboveground but retarded decay belowground. Aboveground, N concentration decreased and subsequently increased earlier in the longer flooded treatments, indicating that flooding decreased the time that litter remained in the leaching and immobilization phases of decay. Belowground, both flooded and nonflooded litter showed an initial rapid loss of N, but concentration and percent of original N remaining were greater in the nonflooded marsh throughout the first year. This suggested that more N was immobilized on litter under the nonflooded, more oxidizing soil conditions. Both N concentration and percent N remaining of belowground litter were greater in the flooded than the nonflooded marsh the second year, suggesting that N immobilization was enhanced after water-level drawdown. These results suggest different mechanisms by which flooding affects decomposition in different wetland environments. On the soil surface where oxygen is readily available, flooding accelerates decomposition by increasing moisture. Belowground, flooding creates anoxic conditions that slow decay. The typical hydrologic pattern in seasonally flooded prairie marshes of spring flooding followed by water-level drawdown in summer may maximize system decomposition rates by allowing rapid decomposition aboveground in standing water and by annually alleviating soil anoxia.     

Changes in the characteristics of several carbohydrate metabolism enzymes during differentiation of loach skeletal muscle]

The gradual change of enzymes of glycogen metabolism proceeds during the skeletal muscle differentiation in the loach. The portion of the muscle type phosphorylase in the skeletal muscles of the embryo at the stage of the beginning of movement amounts to 30% and that at the stage of hatching to slightly over 50%. At the stage of yolk resorption, the skeletal muscles contain the muscle type phosphorylase only. At the same time the value of KM(UDPG) for glycogen synthetase gradually increases from 0,1 X 10(-3) up to 0,57 X 10(-3) M. The activity of alpha-glycerophosphate dehydrogenase increases more than 70 times.     

Reproductive variations of cladocerans in grasslands periodically flooded for irrigation in Mantecal,Venezuela

The present work is a study of the cladoceran fauna and its reproduction during drought, in grasslands modified by embankment for irrigation be periodical flooding at Mantecal, Venezuela. Due to the importance of changing reproductive mechanisms of cladocerans in response to changing conditions, we present the daily variation of certain species that have both sexual and parthenogenetic females, thus contributing a first report on the reproductive cycles of cladocerans in this country. During February and March of 1980, corresponding to the final period of the dry season, samples were collected in the whole water column (5–38 cm) every two days with a Van Dorn sampler of 1-liter capacity. Environmental conditions were recorded at the same time. The cladoceran community consisted of 13 species. Study of six of these species revealed that sexual females were most abundant in March when the water level was lowest, while parthenogenetic females were at their peaks in February. However, all species showed variation at the beginning and end of their reproductive periods.     

Changes during aerobic exposure of wheat silages

Aerobic stability is an important characteristic of silages because they are exposed to air during storage and feedout. The objective of the current study was to investigate changes that occur in wheat silages during aerobic exposure. Silages of whole crop wheat harvested at the flowering, milk and dough stages of maturity were prepared in 1.5 L anaerobic glass jars. Three months after ensiling, silages were subjected to a 7-day aerobic stability test. The silages of wheat harvested at the flowering stage were the most stable upon aerobic exposure, but had the largest fermentation losses. Silages of milk-stage wheat were unstable upon aerobic exposure, and had large amounts of CO₂ and heating, large yeast populations, decreased amounts of fermentation products and decreased dry matter (DM) and neutral detergent fiber (NDF) digestibility (from 667 to 572 g/kg DM and from 597 to 558 g/kg DM, following 7-day aerobic exposure, respectively). Silages of dough-stage wheat had relatively low fermentation losses and were quite stable for at least 4 days of aerobic exposure. Silage samples from the center of commercial bunker silos, and from areas adjacent to the walls of the silos, were judged to be of good quality. Samples from the shoulders of bunker silos were spoiled with higher pH (P<0.05), higher ash content and lower DM and NDF digestibility compared with samples from the center of the silos and areas near the walls (6.8 vs. 4.0, 19.0 vs. 7.8, 477 g/kg DM vs. 634 g/kg DM and 230 g/kg DM vs. 487 g/kg DM, respectively).     

Changes in photosynthetic characteristics during leaf development in apple

A comprehensive developmental survey of leaf area, chlorophyll, photosynthetic rate, leaf resistance, transpiration ratio, CO₂ compensation point and photorespiration was conducted in apple. The largest changes in each of the photosynthetic characteristics studied took place during the earliest stages of leaf development, coinciding with the period of greatest leaf expansion and chlorophyll synthesis. During early development, photosynthesis increased 5-fold, reaching a maximum rate of 40 mg CO₂ dm^-2 hr^-1 at a leaf plastochron index (LPI) of 10. During this same period, leaf resistance, transpiration ratio, CO₂ compensation point and mesophyll resistance decreased, while carboxylation efficiency increased. Two especially interesting aspects of the data discussed are simultaneous changes that occur at a LPI of 10 and 12 in all of the photosynthetic characteristics examined and an apparent decrease in photorespiration as leaves age. From our results it is clear that stage of leaf development is an important factor affecting the rate of photosynthesis and photorespiration.Scientific Paper No. 5687, College of Agriculture, Washington State University, Pullman. This work is supported by the National Science Foundation Grant 80-10958 and the Columbia River Orchards Foundation.     

Greenhouse gas emissions and extracellular enzyme activity variability during decomposition of native versus invasive riparian tree litter

Plant Ecology - Invasive plants alter riparian vegetation communities and shift biogeochemical processes by changing decomposition rates and the soil chemical environment created by leaf litter. It...     

三江平原小叶章湿地枯落物分解及主要元素变化动态

应用分解袋法研究了三江平原小叶章湿地枯落物的分解失重及其主要营养元素的变化动态。结果表明,小叶章枯落物的年分解速率为0.257,二次指数模型:Wt/W0=0.0399e-0.545t+0.9601e0.018t(R2=0.945)能更好地描述其分解失重动态。分解过程中,C、N、P、Ca的积累系数(NAI)<100%(P<0.05),元素发生了净释放;K、Na的NAI>100%(P<0.05),元素发生了净积累;Mg、Mn、Fe的NAI值与100%无显著差异(P>0.05),元素既有释放又有积累。分解16个月后,小叶章枯落物各元素总体释放率的大小顺序为:Fe>P>Ca>N>C>Mg>Mn>K>Na,而相应元素的释放量分别为:0.106、0.147、0.971、0.568、65.37、-0.017、-0.114、-0.209和-0.125 g.m-2。     

Changes in the content of glycogen and its metabolites during acute exposure ofAnabas testudineus (Bloch) to furadan

Significant differences were observed in glycogen metabolism ofAnabas testudineus exposed to an acute lethal (1.56 mg/litre) and a sublethal (0.56 mg/litre) concentration of furadan. At sublethal concentration, the muscle glycogen which was utilized during the early periods of exposure, was replenished in the later period of exposure and at 120 h, the muscle glycogen levels were higher than the control. At higher concentration, the liver glycogen levels showed an increase presumably at the expense of fuel reserves of the muscle.     

Changes in several characteristics of the erythrocyte membrane and erythrocyte structure in severe burns in animal experiments

It is determined in experiments on rats that the IIIB degree thermal injuries of 20% of the total body surface significantly reduce the erythrocytic membrane's resistance and cause the production of peroxides in 15 minutes after trauma. Simultaneously the electrical properties begin to change. The structure of erythrocytes is also altered. In 30 minutes post injury these alterations are in progress, but in 60 minutes they are less expressed. The structure of the erythrocytes is significantly altered. The authors consider that the influence of membranotoxic factors--the products of free radicals' reactions and phospholipases--is accounted for all noticed alterations.     

Changes in the respiratory muscles and their microcirculatory bed during exposure of the body to chronic hypoxia and its aftereffects

Changes of the respiratory muscles have been studied under the effect of a rarefied atmosphere when the pressure is 560 mm Hg (2,500 m), 405 mm Hg (5,000 m), 286 mm Hg (7,500 m) and during the period of their aftereffect. The experimental group consists of 260 and the control group--of 130 white rats. Adaptation of the respiratory muscles to the effect of the rarefied atmosphere at the pressure of 560 mm Hg takes place mainly at the expense of certain functional changes of the microcirculatory bed and hypertrophy of the muscle fibers. The period of aftereffect is characterized with normalization of these phenomena. Adaptation of the respiratory muscles at the pressure of 405 mm Hg takes place at the expense of hypertrophy of the muscle fibers, small destructive changes and a complex rearrangement of the microcirulatory bed. During the period of aftereffect, by the 40th day no destructive changes are noted in the muscle tissue. The capillary bed undergoes some rearrangements by the 42d -56th day with increasing quantitative indices per area unit. This results in improvement of the muscles nutrition. In the respiratory muscles at the pressure 286 mm Hg, atrophic changes in the muscle fibers take place at certain stages of the experiment. Essential destructive changes are observed, rearrangement of the microcirculatory bed with decreasing convolution of the longitudinal capillaries and a decreasing number of the transversal capillaries are noted by the end of the experiment. During the period of aftereffect, by the 56th day, the external and internal intercostal muscles completely restore their structure, and in the diaphragm the destructive changes remain. By the same time, the microcirculatory bed becomes more rare at the expense of decreasing capillarization of the muscle fibers and a decreasing number of the transversal capillaries.     

Changes in the photosynthetic characteristics of cotton leaves infested by invasive mealybugs tended by native ant species

Herbivore injury has a direct effect on the growth and performance of host plants through photosynthetic suppression. However, changes in plant photosynthesis affected by ant tending of hemipteran sap feeders remain poorly understood. We investigated the effects of an invasive mealybug (Phenacoccus solenopsis) tended by native ants (Paratrechina longicornis) on the chlorophyll content and chlorophyll fluorescence characteristics of cotton (Gossypium hirsutum) leaves under greenhouse conditions. The results showed that the relative chlorophyll content of the infested cotton leaves significantly decreased after 10 days, and the chlorophyll contents were reduced by 26.4 and 34.9 % after 20 days in the without and with ant treatments compared to the control, respectively. In addition, the light utilization efficiency and maximum relative electron transport rate were reduced by 53.0 and 51.3 % compared to the control, respectively. However, no significant differences in these factors were found between the without and with ant treatments. The light saturation coefficient, describing the capacity of a sample to resist glare, exhibited no significant difference among treatments. The number of tending P. longicornis ants increased with P. solenopsis numbers, and the P. solenopsis numbers decreased after 20 days compared to the without ant treatment. We suggest that the tending ants may enhance the feeding ability of individual mealybugs in spite of the decreased number of mealybugs in this situation. Additionally, P. longicornis decrease the relative chlorophyll content of infested cotton leaves and may accelerate the damage caused by P. solenopsis to plants over time.     

Effect of aboveground litter on belowground plant interactions in a native Rough Fescue grassland

Chemical compounds from plants may exhibit stimulatory and/or inhibitory effects on surrounding organisms. However, research on belowground biochemical interactions among plants has focused more effort on elucidating negative effects. Moreover, the effect of shoot litter on belowground plant–plant interactions has remained relatively unexplored. In a field experiment with four target plant species (Artemisia frigida Willd., Solidago missouriensis Nutt.), Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths and Poa pratensis L.) interacting with intact grassland neighbours, we manipulated root competition using PVC tubes and shoot litter, and belowground chemical interaction by adding activated carbon (AC) to the soil. In A. frigida, shoot litter significantly interacted with root competition and root chemicals. Plants grown plus AC were larger than those minus AC when shoot litter was left intact suggesting inhibitory effects from neighbours and/or decomposing products. However, when shoot litter was removed, plants grown minus AC were larger suggesting stimulatory effects of root exudates. B. gracilis showed a similar trend but results were non-significant. Results demonstrate that the effects of neighbours can be inhibitory or facilitative depending on the presence or absence of shoot litter and mediation through AC.     

Changes in temperature tolerance ofBalanus balanoides during its life-cycle

Summary 1. The barnacleBalanus balanoides exhibits little seasonal variation in upper lethal temperatures in North Wales.2. There are marked seasonal changes in resistance to sub-zero temperatures, the lower lethal varying from –6.0° C in June to –17.6° C in January.3. Exceptional tolerance to cold is acquired between December and January and is lost between February and April. Although these dates coincide with oviposition and naupliar liberation respectively, it was found that cold tolerance did not necessarily depend upon, or accompany, the normal breeding cycle.4. Cold tolerance was not acquired by animals kept cold in the laboratory during winter, nor was it lost in animals kept in the laboratory during spring. There was no evidence that changes in nutrition or in the light régime led to loss of cold tolerance.5. The cyprids were considerably less resistant to both high and low temperatures than the overwintering adults and the late-stage embryos. There was a marked increase in resistance at metamorphosis.6. The appearance of cold tolerance in the adult coincides with a period of physiological hibernation, involving loss of certain tissues, diminished feeding activity, respiration and biosynthesis. The metabolic inactivity of the animal may be a factor promoting the greatly increased tolerance to cold that we have observed, while the composition of the body fluids may also be modified during the winter in such a way as to protect the tissues.

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Veränderungen der Temperaturtoleranz vonBalanus balanoides während seines Lebenszyklus

Kurzfassung In Nordwales weisen die oberen Letaltemperaturen des CirripediersB. balanoides nur geringe jahreszeitliche Variationen auf. Jedoch treten je nach der Jahreszeit merkbare Resistenzveränderungen bei Temperaturen unter Null auf, wobei die untere Letaltemperatur von –6,0° C im Juni bis zu –17,6° C im Januar schwankt. Eine außergewöhnlich starke Kältetoleranz wird in der Zeit von Dezember und Januar erworben und zwischen Februar und April wieder verloren. Obwohl diese Zeitspanne mit der Oviposition beziehungsweise dem Schlüpfen der Nauplien zusammenfallen, konnte festgestellt werden, daß die Kältetoleranz nicht notwendigerweise vom Brutzyklus abhing oder diesen begleitete. Unter Laboratoriumsbedingungen wurde von kalt gehaltenen Tieren eine Kälteresistenz nicht erworben, auch ging diese bei Tieren, die während des Frühlings im Labor verblieben, nicht verloren. Es ließ sich nicht beweisen, daß Veränderungen in der Ernährung oder Änderungen in der Tageslänge zu einem Verlust der Kälteresistenz führen. Die Cypriden waren wesentlich weniger widerstandsfähig, sowohl gegenüber hohen wie niedrigen Temperaturen, als überwinternde Adulte und die ältesten Embryostadien. Während der Metamorphose zeigte sich eine merkliche Erhöhung der Temperaturresistenz. Das Auftreten der Kälteresistenz beim Adultus fiel mit einer Periode physiologischen Winterschlafs zusammen, wobei gewisse Gewebe reduziert wurden und Nahrungsaufnahme, Atmung und biosynthetische Aktivität nachließen. Dieser stoffwechselphysiologische Aktivitätsrückgang könnte ein Faktor sein, der die beobachtete erhöhte Kältetoleranz fördert. Außerdem wird möglicherweise auch die Zusammensetzung der Körperflüssigkeiten während des Winters so verändert, daß die Gewebe geschützt werden.

     

Volume and activity of micro-organisms in litter from native and sown temperate pasture species

A serial extraction method was developed to estimate microbial volume in pasture plant litter. Litter from six species was evaluated over four seasons and a five fold range in microbial volume per unit mass was established in the descending order of: Trifolium repens, Lolium perenne, Festuca arundinacea, Phalaris aquatica, Poa sieberana and Themeda australis. The ranking among litter sources was the same for both fungi (F) and bacteria (B) and the ratio F/B ranged from 4 to 10. Accompanying respiration measurements (O₂) were made over a range of litter moisture and at temperatures which represented field conditions. Maximum responses of respiration to moisture were estimated for each source and season, along with the Q10 temperature effects between 5, 15 and 25°C. Potential microbial production and generation times were calculated for the six litters. Differences between litters were associated with microbial standing crops rather than turnover times. However, moisture and temperature appeared to be the major determinants of seasonal responses, for example, Q₁₀ effects. Microbial parameters calculated for Phalaris aquatica. in the field environment, were in substantial agreement with those from Eriophorum sp. in a tundra site (Flanagan & Bunnell 1976). Residues quality, as reflected by the amount and activity of microbial colonizers, is discussed in relation to the potential of management to enhance biological mineralization of pasture residues.     

Changes in energy metabolism in several brain regions and vegetative responses of white rats during neurotization

Changes of vegetative reactions and cytochrome oxidase (CChO) activity in various brain structures were studied in rats during neurotization. One week neurotization led to an increase of arterial blood pressure, respiration rate, cardiac stroke volume and heart rate. In three weeks of neurotization there was a decrease of stroke volume accompanied by an increase of heart rate and some decrease or respiration rate leading to a reduction of oxygen consumption. Neurotization during one and especially three weeks elicited an enhancement of CChO activity in various brain areas, more pronounced in the cerebral cortex. A four week "rest" after neurotization during three weeks normalized the CChO activity. CChO activation during neurotization is supposed to be one of the mechanisms of adaptation to hypoxia accompanying neurosis.     

Changes of reliability and efficiency of micronucleus bioassay in Vicia faba after exposure to metal contamination for several generations

Mitotic root micronucleus (MCN) frequency in Vicia faba as a bioassay, is primarily based on the extent of the sentinel Vicia response in terms of cytogenetic damage quantitatively or qualitatively to indicate the presence of mutagenic contaminants. This paper describes an investigation designed to assess changes in MCN frequencies of Vicia faba from three generation plants obtained, respectively from a reference site (RS) and a metal-contaminated experimental field (EF) in the bioassay of mutagenic Cd(2+) and NaN(3). The background value, dose-response to Cd(2+) and to NaN(3) in three generation (F(1), F(2) and F(3)) plants of the EF and the initial (F(0)) plants were determined in terms of MCN frequencies. With more generations of growing Vicia plants in the EF, a higher background value of MCN frequency, a lower slope value in the regression equation, a smaller ratio of MCN frequency between the control and treatment in the same generation and larger perturbation values were observed. This denotes that the decreased reliability and efficiency are represented in Vicia plants from the EF if the plants are used as sentinels in the bioassay of mutagenic Cd(2+) and NaN(3). It was concluded that the Vicia MCN bioassay should be used as an endpoint biomarker acceptable in biomonitoring environmental mutagens when the sentinel plants were collected from clean areas. Because no place is absolutely without pollutants, it is suggested that several seed stock centers should be established for providing sentinel Vicia if Vicia MCN bioassay is used as a biomarker to identify the global environmental status.