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981.
Maria Loreto Contador Louise H. Comas Samuel G. Metcalf William L. Stewart Ignacio Porris Gomez Claudia Negron Bruce D. Lampinen 《Annals of botany》2015,116(1):49-60
Background and Aims Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature.Methods Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia ‘Chandler’) using minirhizotron techniques.Key Results Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production.Conclusions The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs. 相似文献
982.
The functional and numerical responses of grazers are key pieces of information in predicting and modeling predator–prey interactions. It has been demonstrated that exposure to toxic algae can lead to evolved resistance in grazer populations. However, the influence of resistance on the functional and numerical response of grazers has not been studied to date. Here, we compared the functional and numerical responses of populations of the copepod Acartia hudsonica that vary in their degree of resistance to the toxic dinoflagellate Alexandrium tamarense. In common environment experiments carried out after populations had been grown under identical conditions for several generations, female copepods were offered solutions containing different concentrations of either toxic A. tamarense or the non-toxic green flagellate Tetraselmis sp. ranging from 25 to 500 μgC L−1, and ingestion and egg production rates were measured. Throughout most of the range of concentrations of the toxic diet, copepod populations that had been historically exposed to toxic blooms of Alexandrium exhibited significantly higher ingestion and egg production rates than populations that had little or no exposure to these blooms. In contrast, there were no significant differences between populations in ingestion or egg production for the non-toxic diet. Hence, the between population differences in functional and numerical response to A. tamarense were indeed related to resistance. We suggest that the effect of grazer toxin resistance should be incorporated in models of predator and toxic prey interactions. The potential effects of grazer toxin resistance in the development and control of Alexandrium blooms are illustrated here with a simple simulation exercise. 相似文献
983.
The effects of implementing Directive 91/271/EEC of 21 May 1991 (Waste Water Treatment Plan Directive) and Directive 91/676/EEC
of 12 December (Nitrates Directive) are analysed in 7 Portuguese estuaries (Minho, Lima, Douro, Mondego, Tagus, Sado and Guadiana)
and two coastal lagoons (Ria de Aveiro and Ria Formosa), with a modelling approach. MOHID Water Modelling System was used
to perform simulations with three nitrogen load scenarios for each system: a reference scenario, a 50% nitrate removal by
agriculture scenario and another with a 100% nutrients removal by waste water treatment plants (WWTP). It is shown that the
interaction between hydrodynamic and ecological processes is an important feature to study trophic problems in estuaries.
Ecological processes such as primary production only occur inside the system if the residence time of water is high enough
to enable organismal activity and if the adequate conditions are found (e.g. light, nutrients, temperature). From the model
results it is possible to conclude: (i) in systems with short residence time a reduction in nutrient load will only produce
a decrease in nutrient transit and will not affect the system’s global ecological status (e.g. Douro Estuary); (ii) in systems
with long residence time the effects will range from significant, when primary production is mostly limited by nutrients (e.g.
Ria de Aveiro), to non-significant, when primary production in the system is light-limited (e.g. Tagus Estuary). 相似文献
984.
Facultative joint colony founding by social insects (pleometrosis) provides an outstanding opportunity to analyze the costs
and benefits of sociality. Pleometrosis has been documented for a range of social insects, but most studies on the adaptive
benefits of this behavior are restricted to the Hymenoptera. In this study, we provide the first analysis of costs and benefits
associated with pleometrosis for Australian Dunatothrips, which form domiciles by glueing together phyllodes (leaves) of their Acacia host plant. In Dunatothrips aneurae, the distribution of foundress numbers per nest indicated that females formed associations non-randomly. Furthermore, average
group size was independent of both the number of foundresses on the host plant and the number of mature colonies, suggesting
that this behavior was not simply a response to limited availability of nesting sites. Although per capita reproduction declined
with increasing group size, we also identified two benefits of pleometrosis: (1) individual foundresses in groups had higher
survival than solitary foundresses during the brood development period, and (2) larger colony sizes resulting from pleometrosis
provided a benefit later in colony development, because a higher proportion of D. aneurae adults survived invasions by the kleptoparasite Xaniothrips mulga when colony size was larger. These results demonstrate that the reproductive costs of pleometrosis are at least partially
counterbalanced by survival benefits.
Received 4 April 2006; revised 9 September 2006; accepted 20 September 2006. 相似文献
985.
986.
987.
The effects of irrigation and fertiliser regimes on N leaching from the production of couch grass (Cynodon dactylon L.) sod, on a free-draining sandy soil, were evaluated in a 22-month field study. The experimental design used a randomised-block,
split-plot design with three replicates. Main plots consisted of two irrigation treatments: 70 and 140% daily replacement
of pan evaporation; four subplot fertiliser types (water-soluble (predominately NH4NO3), control-release, pelletised poultry manure and pelletised biosolids); and three N application rates (100, 200 and 300 kg
N ha−1 per crop). Nitrogen leaching was assessed by measuring the leachate volumes and concentrations of N species leached from
soil lysimeters (250 mm in diameter by 950 mm in length) installed in 10 m2 turfgrass plots. Nitrogen leaching ranged from 33 to 167 kg N ha−1 over 22 months, depending upon the irrigation and fertiliser treatment. Irrigation treatment affected N leaching more than
fertiliser treatment, and increasing the irrigation from 70 to 140% replacement of daily pan evaporation increased N leaching
for all fertiliser types, and by up to four times. Forty six to 76% of losses occurred from the high irrigation treatments
during the first 16 weeks after the turfgrass was planted as rhizomes. By contrast, N leaching did not appear to increase
following harvest of sod. At the high irrigation treatment, N leaching was greater for the pelletised biosolids than the control-release;
while at the low irrigation treatment, N leaching did not vary between fertiliser types. A significant proportion of the N
leached was in the organic form. Therefore, we recommend total N and mineral N be measured when assessing N leaching from
turfgrass. Nitrogen leaching from turfgrass production is low from all fertiliser types when the irrigation matches turfgrass
water use and N is applied at a rate and frequency that approximates turfgrass requirements.
Section Editor: P. J. Randall 相似文献
988.
The fermentation of carbohydrates and hemicellulose hydrolysate by Mucor and Fusarium species has been investigated, with the following results. Both Mucor and Fusarium species are able to ferment various sugars and alditols, including d-glucose, pentoses and xylitol, to ethanol. Mucor is able to ferment sugar-cane bagasse hemicellulose hydrolysate to ethanol. Fusarium F5 is not able to ferment sugar-cane bagasse hemicellulose hydrolysate to ethanol. During fermentation of hemicellulose hydrolysates, d-glucose was utilized first, followed by d-xylose and l-arabinose. Small amounts of xylitol were produced by Mucor from d-xylose through oxidoreduction reactions, presumably mediated by the enzyme aldose reductase1 (alditol: NADP+ 1-oxidoreductase, EC 1.1.1.21). For pentose fermentation, d-xylose was the preferred substrate. Only small amounts of ethanol were produced from l-arabinose and d-arabitol. No ethanol was produced from l-xylose, d-arabinose or l-arabitol. 相似文献
989.
990.
Starch is a natural energy storage compound and is hypothesized to be a high-energy density chemical compound or solar fuel. In contrast to industrial hydrolysis of starch to glucose, an alternative ATP-free phosphorylation of starch was designed to generate cost-effective glucose 6-phosphate by using five thermophilic enzymes (i.e., isoamylase, alpha-glucan phosphorylase, 4-α-glucanotransferase, phosphoglucomutase, and polyphosphate glucokinase). This enzymatic phosphorolysis is energetically advantageous because the energy of α-1,4-glycosidic bonds among anhydroglucose units is conserved in the form of phosphorylated glucose. Furthermore, we demonstrated an in vitro 17-thermophilic enzyme pathway that can convert all glucose units of starch, regardless of branched and linear contents, with water to hydrogen at a theoretic yield (i.e., 12 H2 per glucose), three times of the theoretical yield from dark microbial fermentation. The use of a biomimetic electron transport chain enabled to achieve a maximum volumetric productivity of 90.2 mmol of H2/L/h at 20 g/L starch. The complete oxidation of starch to hydrogen by this in vitro synthetic (enzymatic) biosystem suggests that starch as a natural solar fuel becomes a high-density hydrogen storage compound with a gravimetric density of more than 14% H2-based mass and an electricity density of more than 3000 W h/kg of starch. 相似文献