Mathematical modelling of runoff and material transport from drainage areas into recipient water bodies

This paper describes a set of mathematical models to calculate runoff, soil erosion and chemical substance yields for drainage areas. The models represent different degrees of complexity and details of describing hydrological and hydrochemical processes. The availability of initial information and the requirements of the task determine the choice of a model for each particular case. These models have been written as PC/AT programs, to enable their use by a wide range of specialists. The models have been tested in different physical and geographical conditions, e.g. in some small watersheds on the Karelian Isthmus, west of Lake Ladoga, and in experimental catchment areas located in the Valdai Hills area in the southern part of Lake Ladoga drainage area. In further applications the drainage area models have been combined with models of the recipient water body, to obtain a single model of a watershed-lake system. The results of tests have proved that the models can be used for evaluation, simulation and forecasting of the processes of rainfall and snowmelt runoff, infiltration, evaporation, water erosion and pollutant wash-off from drainage areas.     

Facultative mutualism between an herbivorous crab and a coralline alga: advantages of eating noxious seaweeds

Because encrusting coralline algae rely on herbivory or low light levels to prevent being overgrown by competitively superior fleshy algae, corallines are relatively rare in shallow areas with low rates of herbivory. In contrast to this general trend, the branching coralline alga Neogoniolithon strictum occurs primarily in shallow seagrass beds and along the margins of shallow reef flats where herbivory on macrophytes is low. This alga apparently persists in these habitats by providing refuge to the herbivorous crab Mithrax sculptus at mean densities of 1 crab per 75 g of algal wet mass. When crabs were removed from some host corallines, hosts without crabs supported 9 times the epiphytic growth of hosts with crabs after only 30 days. Crabs without access to a coralline alga were rapidly consumed by reef fishes, while most of those tethered near a host alga survived. These results suggest that the crabs clean their algal host of fouling seaweeds and associate with the host to minimize predation. However, to effectively clean the host, the crab must consume the wide array of macroalgae that commonly co-occur with coralline algae in these habitats, including chemically defended species in the genera Halimeda, Dictyota, and Laurencia. Crabs did readily consume these seaweeds, which were avoided by, and are chemically defended from, herbivorous fishes. Even though crabs readily consumed both Halimeda and Dictyota in whole-plant feeding assays, chemical extracts from these species significantly reduced crab feeding, suggesting that factors other than secondary chemistry (e.g., food value, protein, energy content), may determine whole-plant palatability. Having the ability to use a wide variety of foods, and choosing the most profitable rather than the least defended foods, would diminish foraging time, increase site fidelity, and allow the crab to function mutualistically with the host alga. Despite the obvious benefit of associating with N. strictum, M. sculptus did not prefer it over other habitats offering a structurally similar refuge, suggesting that these crabs are not N. strictum specialists, but rather occupy multiple habitats that provide protection from predators. Structurally complex organisms like N. strictum may commonly suppress competitors by harboring protective symbionts like M. sculptus. It is possible that diffuse coevolution has occurred between these two groups; however, this seems unlikely because both herbivore and host appear to respond most strongly to selective pressures from predators and competitors outside this association.     

Hydraulic control of stomatal conductance in Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and alder [Alnus rubra (Bong)] seedlings

Experiments were conducted on 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and 2- to 3-month-old alder [Alnus rubra (Bong)] seedlings growing in drying soils to determine the relative influence of root and leaf water status on stomatal conductance (g_c). The water status of shoots was manipulated independently of that of the roots using a pressure chamber that enclosed the root system. Pressurizing the chamber increases the turgor of cells in the shoot but not in the roots. Seedling shoots were enclosed in a whole-plant cuvette and transpiration and net photosynthesis rates measured continuously. In both species, stomatal closure in response to soil drying was progressively reversed with increasing pressurization. Responses occurred within minutes of pressurization and measurements almost immediately returned to pre-pressurization levels when the pressure was released. Even in wet soils there was a significant increase in g_c with pressurization. In Douglas fir, the stomatal response to pressurization was the same for seedlings grown in dry soils for up to 120 d as for those subjected to drought stress over 40 to 60 d. The stomatal conductance of both Douglas fir and alder seedlings was less sensitive to root chamber pressure at higher vapour pressure deficits (D), and stomatal closure in response to increasing D from 1.04 to 2.06 kPa was only partially reversed by pressurization. Our results are in contrast to those of other studies on herbaceous species, even though we followed the same experimental approach. They suggest that it is not always appropriate to invoke a ‘feedforward’ model of short-term stomatal response to soil drying, whereby chemical messengers from the roots bring about stomatal closure.     

Assays for the effects of volatile compounds from artificially damaged cotyledons of subterranean clover on the redlegged earth mite, Halotydeus destructor

The effects on the redlegged earth mite (Halotydeus destructor) (Acarina: Penthaleidae) of volatile compounds released from artificially damaged cotyledons of subterranean clover (Trifolium subterraneum L.), a host plant, were investigated with different assays. Mites were repelled by the volatile compounds in flask tube and in trimmed cotyledon disc tests. No differences could be shown between different tissue amounts and between resistant and susceptible varieties. When a membrane sachet was used containing either 2-(E)-hexenal, a compound produced by damaged subclover cotyledons, or the total volatile compounds collected from damaged cotyledons of Dalkeith (susceptible) admixed with 1% glucose, mites gathered to low but were deterred by high concentrations of the compounds. Volatile compounds collected from the resistant variety DGI007 were more deterrent than those from the susceptible Dalkeith. Membrane sachets containing 30 p.p.m. of 2-(E)-hexenal and 1% glucose were less preferred than cotyledons of Dalkeith (susceptible) but were not different from DGI007 (resistant). By increasing the glucose concentration to 5%, the membrane sachets with 30 p.p.m. of 2-(E)-hexenal were preferred to cotyledons of either variety. The results indicate that the membrane feeding technique provides a sensitive way of assaying volatile compounds from damaged subclover cotyledons against the mite.     

A telescopic method for photographing within 8×8 cm minirhizotrons

The volatile organic compounds produced during a sequence of soil incubations under controlled conditions, with either added NH₄ ⁺-N or NO₃ ^--N, were collected and identified. The nature and relative amounts of the volatile organic compounds produced by the microorganisms in the soils were remarkably reproducible and consistent.     

Introduction of sense and antisense cDNA for branching enzyme in the amylose-free potato mutant leads to physico-chemical changes in the starch

One isoform of the branching enzyme (BE; EC 2.4.1.18) of potato (Solarium tuberosum L.) is known and catalyses the formation of α-1,6 bonds in a glucan chain, resulting in the branched starch component amylopectin. Constructs containing the antisense or sense-orientated distal 1.5-kb part of a cDNA for potato BE were used to transform the amylose-free (amf) mutant of potato, the starch of which stains red with iodine. The expression of the endogenous BE gene was inhibited either largely or fully as judged by the decrease or absence of the BE mRNA and protein. This resulted in a low percentage of starch granules with a small blue core and large red outer layer. There was no effect on the amylose content, degree of branching or λ_max of the iodine-stained starch. However, when the physico-chemical properties of the different starch suspensions were assessed, differences were observed, which although small indicated that starch in the transformants was different from that of theamf mutant.     

Elicitation of volatile compounds in photomixotrophic cell culture of Petroselinum crispum

Photomixotrophic cells of Petroselinum crispum accumulated >500 mg chlorophyll per kg wet weight and grew well in a broad range of phytoeffector conditions. Autoclaved fungal cells were lethal for photoheterotrophic cells, but induced in photomixotrophic cells the formation of volatile n-alkanes, phthalides, coumarins, and elemicine. Most of the compounds elicited reached a concentration maximum between 20 and 30 h after addition of the mycelium, whereas the group of n-alkanes increased steadily during the 90 h monitored. Maximum concentrations were: 12 mg of graveolone, 1 mg of bergapten, 0.5 mg of sedanenolide, and 0.5 mg of n-tetradecane per 1 nutrient medium. A dose/effect relationship was found; 10 to 25 g of fungal wet weight per 1 culture medium resulted in maximum accumulation of volatiles. The formation of volatiles by photomixotrophic in vitro cells is discussed as an integral part of plant responses to ecological stress.     

植物资源与化学数据库系统（DPRC）的功能与应用

由中国科学院昆植物研究所和云南省机械研究设计院的植物资源化学数据库系统是一个将植物资源,植物化学成分及化学结构的多种信息、数据和图象融为一体的、开和式多功能软件系统、,包括植资源检索系统、植物化学成分检索系统及天然产物化学结构检索系统等三个子系统。     

Anaerobic acidogenesis of primary sludge: the role of solids retention time

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate. (c) 1994 John Wiley & Sons, Inc.