1993. influence of food type on the growth of a riverine amphipod, Garnmarus frasciatus. Can. J. Fish. Aquat. Sci. 50: 1891-1 896.A laboratory experiment and natural-diet study were conducted to examine the feeding ecology and importance of food type for growth of Grammarus fasciatus from the Ohio River. Po determine effects on growth, amphipods were fed four diets: (1) filamentous algae (Cladophora) and diatoms, (2) dead animal matter (chironomids), (3) coarse particulate organic matter (CPOM), and (4) fine particulate organic matter (FPOM). Organic matter was obtained by shredding preconditioned sycamore leaves (Platanus occideniealis), Growth was evaluated from weekly measurements of head length. There were no significant differences in growth among food types before week 3 of the experiment, but from week 4 to week 6, amphipods fed algae and dead animal matter were significantly larger than those maintained on CPOM and FPOM. Gut analysis of natural populations showed that G. fascbatus consumed all food types used in the laboratory study. The weighted proportions of filamentous algae and animal matter in riverine populations increased consistently from smallest to largest size-class. The availability of, and ability to use, algae and animal matter by G. fasciatus benefits natural populations in large rivers by enabling then1 to exploit seasonal changes in the relative abundance of different food sources.Nous avons effectuk une expkrienee de laboratoire et une etude sur ['alimentation naturelle pour examiner I'kcoIogie alimentaire et I'importance des types de nourriture dans la croissance de Gammasus dasciratus du fleuve Ohio. Pour dkterminer les effets de I'alimentation sur la croissance, nous avons administre aux amphipodes quatre types d'aliments : I ) des algues filamenteuses (Cladophora) et des diatomees, 2) de la matiere animale morte (chironsmid6s, 3) de la matikre organique particulaire grossi6re (MOPC) et 4) de la rnati68-e organique pat-ticulaire Ci ne (MOW). La matiitre organique a 6t6 obtenue par dkchiquetage de feuilles pr6conditionnkes de sycomore (Platanus occidentalis). Nous avons 6valu6 la eroissance par des rnesures hebdomadaires de la longueur de la tete. Nous n'avons pas observe de differences significatives dans la croissance entre les types de nourriture avant la troisi6me semaine de 11exp6rience mais, de la q u a t r i h e 2 [a sixiitme semaine, les amphipodes nout-ris d'algues et de matigre animale morte etaient significativement plus gros que ceux qui 6taient nourris de MBPG et MOPF. L'analyse des intestins des populations naturelles a montr6 que G. dasciatus consommait taus [es types d'aliments utilis6s dans l'ktude de laboratoire. Les proportions pond6rees des algues filamenteuses et de la matikre aslimale shez les populations lotiques augrnentaient reguli6rement de la plus petite i la plus grande classe de taille. La disponibilitk des algues et de la rnatigre animale pour G. fasciatus, et I'aptitude A les utiliser, avantagent les populations naturelles des gros eours d'eau qui snt ai...

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Experimental research involving Arabidopsis thaliana often involves the quantification of phenotypic traits during cultivation on compost or other growing media. Many commercially-available growing media contain peat, but peat extraction is not sustainable due to its very slow rate of formation. Moreover, peat extraction reduces peatland biodiversity and releases stored carbon and methane into the atmosphere. Here, we compared the experimental performance of Arabidopsis on peat-based and several types of commercially-available peat-free growing media (variously formed from coir, composted bark, wood-fibre, and domestic compost), to provide guidance for reducing peat use in plant sciences research with Arabidopsis. Arabidopsis biomass accumulation and seed yield were reduced by cultivation on several types of peat-free growing media. Arabidopsis performed extremely poorly on coir alone, presumably because this medium was completely nitrate-free. Some peat-free growing media were more susceptible to fungal contamination. We found that autoclaving of control (peat-based) growing media had no effect upon any physiological parameters that we examined, compared with non-autoclaved control growing media, under our experimental conditions. Overall, we conclude that Arabidopsis performs best when cultivated on peat-based growing media because seed yield was almost always reduced when peat-free media were used. This may be because standard laboratory protocols and growth conditions for Arabidopsis are optimized for peat-based media. However, during the vegetative growth phase several phenotypic traits were comparable between plants cultivated on peat-based and some peat-free media, suggesting that under certain circumstances peat-free media can be suitable for phenotypic analysis of Arabidopsis.

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