Ecological assessment of an intermittent Mediterranean river using community structure and function: evaluating the role of different organism groups

1. Reliable lotic ecological monitoring requires knowledge of river typology, environmental factors, the effect of stressors known here as ‘pressures’ and appropriate indicators of anthropogenically induced change. We sampled benthic macroinvertebrate, fish, bird and macrophyte communities along an intermittent Mediterranean river and analysed community structure (relative abundance) and function (metrics) relative to environmental and pressure gradients in order to identify suitable indicator group(s) for future monitoring and mitigation programmes. 2. Principal components analysis revealed that scale‐dependent longitudinal differences in valley form separated narrower higher lying sites and tributaries with good quality habitats from more open degraded sites lower down the river continuum on a small floodplain and large scale pressures describing changes in land use related to agriculture with associated physical bankside and channel impacts. 3. Forward selection of variables in redundancy analysis (RDA) showed that reach scale environmental variables were selected more frequently than pressure variables for each organism group. Altitude and pH were highly redundant within and between groups, indicating essentially longitudinal structural and functional distribution patterns. Redundancy was far lower between selected pressure variables, but single or no pressure variables were retained for some organism groups indicating poor association of functional data, in particular, with the identified pressures. All RDA results indicated a longitudinal pH gradient, highlighting the combined effect of multiple environmental and pressure based mechanisms on organism groups. 4. Large, mobile organisms such as fish and birds provided a reliable link between organism structure and function, environmental factors and physical disturbance of the channel, bankside and wider river corridor. Benthic macroinvertebrate and macrophyte structural data revealed distribution patterns in relation to water velocity, a key parameter for developing appropriate compensation measures. 5. Results clearly show the importance of assessing patterns of both functional and structural change across multiple organism groups in order to identify typologically appropriate links with complex environmental and pressure gradients and develop and implement appropriate monitoring systems.     

A Comparison of the Effects of Diurnal Variation in Light Intensity with Constant Light Intensity on Growth of Chrysanthemum morifolium cv. Bright Golden Anne

Rooted cuttings were grown in controlled environment cabinetsat two daily light totals (63 and 125 J cm^–2 day^–1)with the light intensity constant throughout the day or in stepsgiving the same daily light total Plants were sampled frequentlyover a period of 83 days by which time they were in full flower.A comparison of the various growth measures derived from theprimary data on leaf area, fresh and dry weight of the plantand its parts, and morphological and floral characteristics,revealed only negligibly small differences between results forconstant and stepped regimes The results for the constant regimeswere compared with other experiments earned out simultaneouslyin order to indicate the reproducibility of growth in independentcabinets having nominally the same conditions     

Transmission properties of an oak canopy in relation to photoperception

Abstract The spectra of incoming daylight and shadelight in a mature oak woodland were measured at intervals during the canopy cycle, and mean transmittance spectra were derived. Transmittance was spectrally neutral at ca. 0.55 during the light phase but, following leaf emergence, transmittance of PAR (400–700 nm) fell to ca. 0.1. Simultaneously, the red : far-red transmittance ratio fell to circa 0.6. Both showed little change during the summer and autumn until senescence, indicating that the optical properties of the canopy were surprisingly stable. There was no evidence that cloud cover influenced mean canopy transmittance, although transient sunflecks introduced great variability which, in combination with sampling bias, might explain previous contradictory reports. The red : far-red fluence rate ratio in the woodland showed a temporary increase in late summer, a result of a small increase in the red : far-red ratio of incoming daylight during this period. Reflectance and transmittance spectra and pigment content of sun and shade leaves were measured. Leaf transmittance spectra showed changes correlated with those of the canopy, and were related to changes in pigment content.     

Interrelations of Flowering and Vegetative Growth in Callistephus chinensis (var. Queen of the Market)

In a study of the effect of photoperiod upon the growth andflowering of Calistephus chinensis (var. Queen of the Market)it has been shown that a one-hour night break of low intensityred light given to plants growing in eight hours daylight canhave a number of morphogenetic effects. In the young plant, such a treatment increased the total areaof the leaf surface and the area per unit weight of leaf material,i.e. the specific leaf area. This effect enabled the treatedplants to make greater use of the incident light, for afternine weeks they were at least 25 per cent heavier than comparableplants which had not had the benefit of the night-break treatment.This treatment also caused flower induction and concomitantstem extension, but transfer back into eight-hour days afteran inductive period accelerated further flower development andrestricted stem extension of both the main axis and the laterals.If flower development was delayed by continuing night breaksor by delaying the onset of induction then more flowers wereeventually formed, but in the very prolific treatments flowersize was reduced. The experiment also indicated that the partition of availabledry weight between leaves, stems, and roots followed a definitepattern dependent only upon total plant dry weight. The diversionof dry weight into flowers was strongly accelerated by transferinto eight-hour days after induction but the remaining dry matterstill appeared to be distributed between the vegetative partsalong the general pattern determined by total vegetative weight. Finally the experiment showed that a wide range of plant formsbearing varying amounts of flowers could be obtained by appropriatetransfers between treatments.     

Isolation and characterization of eight polymorphic microsatellite loci in the rainforest canopy tree,Syzygium sayeri (Myrtaceae)

Eight polymorphic microsatellite loci were isolated from the rainforest canopy tree, Syzygium sayeri, in order to study parentage and subsequently pollen dispersal among individuals in wild populations. Screening of one natural population (n = 64) mapped in a 500 × 500 m area at Cape Tribulation, north Queensland, Australia, yielded two to 11 alleles per locus with observed levels of heterozygosity ranging from 0.07 to 0.70. One locus was significantly out of Hardy–Weinberg equilibrium after Bonferroni correction for multiple tests. These loci should provide a useful tool in further understanding the dispersal patterns of this species.     

Effects of soil incorporation on the efficacy of the rhabditid nematode, Phasmarhabditis hermaphrodita, as a biological control agent for slugs

The effects of soil cultivation immediately after application of the rhabditid nematode, Phasmarhabditis hermaphrodita , to the soil surface were investigated in two field experiments. The first experiment was done in mini-plots separated by barriers, with an artificially introduced population of slugs ( Deroceras reticulatum ). Nematodes were applied as a drench at a rate of 3 times 10⁹ ha^-1 in one of two application volumes and then left undisturbed or incorporated into the soil by cultivation to 2 cm or 10 cm depth. Moist soil conditions were maintained by irrigation throughout the experiment. Nematode application significantly reduced slug damage to Chinese cabbage seedlings throughout the 7 wk duration of the experiment and the population of D. reticulatum in soil 7 wk after treatment. However, soil cultivation had no effect and did not interact with the effect of nematodes. In the second experiment, in a crop of winter wheat, nematodes were applied to soil by hand-lance at a rate of 3 times 10⁹ ha^-1 and left undisturbed on the soil surface or incorporated by spring-tine cultivation to a depth of 2, 5 or 10 cm. In this experiment, nematodes were applied to dry soil. Cultivation alone had no effect. Nematode application reduced slug damage to wheat plants in plots where nematodes were incorporated into the soil, but not where they were left on the surface. There was no detectable impact of nematodes on slug populations in the wheat experiment.