Intensity and Importance of Competition for a Grass (Festuca rubra) and a Legume (Trifolium pratense) Vary with Environmental Changes

How plant competition varies across environmental gradients has been a long debate among ecologists. We conducted a growth chamber experiment to determine the intensity and importance of competition for plants grown in changed environmental conditions. Festuca rubra and Trifolium pratense were grown in monoculturs and in two- and/or three-species mixtures under three environmental treatments. The measured competitive variations in terms of growth (height and biomass) were species-dependent. Competition intensity for Festuca increased with decreased productivity, whilst competition importance displayed a humpback response. However, significant response was detected in neither competition intensity nor importance for Trifolium. Intensity and importance of competition followed different response patterns, suggesting that they may not be correlated along an environmental gradient. The biological and physiological variables of plants play an important role to determine the interspecific competition associated with competition intensity and importance. However, the competitive feature can be modified by multiple environmental changes which may increase or hinder how competitive a plant is.     

Is it possible to modify serotonin receptor sensitivity?

It is possible to induce sub- and super-sensitivity of β-adrenergic receptors by long-term treatment with drugs acting on catecholamine systems. In contrast, analogous treatment with drugs acting on serotoninergic systems does not modify serotonin receptor sensitivity as measured by serotonin binding. Firstly, chronic 1-5HTP, the precursor amino acid, increases serotonin turnover but does not decrease serotonin binding. Secondly, chronic clomipramine, a predominantly serotonin uptake inhibitor also has no effect on serotonin binding. Thirdly, chronic metergoline, a selective serotonin antagonist in the cortex, does not induce supersensitivity.This apparent intractability of the serotonin receptor to changes after long-term treatment indicates a different post-synaptic regulatory mechanism than that found in catecholaminergic neurones. Furthermore, modification of serotonin receptor sensitivity is probably not relevant to the mode of action of antidepressant drugs. Rather, the response of pineal melatonin stimulation found after chronic clomipramine in these experiments implicates induction of β-receptor subsensitivity.     

A relationship between heat loss and sleepiness: effects of postural change and melatonin administration

Kräuchi, Kurt, Christian Cajochen, and AnnaWirz-Justice. A relationship between heat loss and sleepiness:effects of postural change and melatonin administration.J. Appl. Physiol. 83(1): 134-139, 1997.Both the pineal hormone melatonin (Mel) and postural changeshave thermoregulatory sequelae. The purpose of the study was toevaluate their relationship to subjective sleepiness. Eight healthyyoung men were investigated under the unmasking conditions of aconstant routine protocol. Heart rate, rectal temperature(T_re), skin temperatures (foot,T_fo; and stomach), and subjectivesleepiness ratings were continuously recorded from 1000 to 1700. Mel (5 mg po) was administered at 1300, a time when Mel should not phaseshift the circadian system. Both the postural change at1000 from upright to a supine position (lying down in bed) and Meladministration at 1300 reduced T_reand increased T_fo in parallel withincreased sleepiness. These findings suggest that under comfortableambient temperature conditions, heat loss via the distal skin regions(e.g., feet) is a key mechanism for induction of sleepiness as corebody temperature declines.