Contrasting physiological responses to excess heat and irradiance in two tropical savanna sedges.

Tropical hyperseasonal savannas provide a rare example of a tropical climax community dominated by graminoid species. Species living in such savannas are frequently exposed to excess heat and light, in addition to drought and waterlogging, and must possess traits to avoid or tolerate these stress factors. Here we examine the contrasting heat and light stress adaptations of two dominant savanna sedges: Lagenocarpus guianensis, which is restricted to the sheltered forest edge, and Lagenocarpus rigidus, which extends from the forest edge to the open savanna. An ecotone extending from the forest edge to the open savanna was used to assess differences in a range of physiological traits (efficiency of photosystem II, cell membrane thermostability, stomatal conductance, leaf surface reflectance and canopy temperature depression) and a range of leaf functional traits (length : width ratio, specific leaf area and degree of folding). Lagenocarpus guianensis showed significantly less canopy temperature depression than L. rigidus, which may explain why this species was restricted to the forest edge. The range of leaf temperatures measured was within the thermal tolerance of L. guianensis and allowed photosystem II to function normally, at least within the cool forest edge. The ability of L. rigidus to extend into the open savanna was associated with an ability to decouple leaf temperature from ambient temperature combined with enhanced cell membrane thermostability. The high degree of canopy temperature depression seen in L. rigidus was not explained by enhanced stomatal conductance or leaf reflectance, but was consistent with a capacity to increase specific leaf area and reduce leaf length: width ratio in the open savanna. Plasticity in leaf functional traits and in cell membrane thermostability are key factors in the ability of this savanna sedge to survive abiotic stress.

Respiratory symptoms in West Sussex firemen.

There are few reports of long term follow up of symptoms in firemen. In a four year study of symptoms in a group of 96 firemen (31 non-smokers, 40 smokers, and 25 ex-smokers) of which 89 remained in the study for its full duration a volunteer control group of 69 male non-smokers from a variety of occupations was also followed up. A history of symptoms and of smoking habits was obtained on entry to the study, then every six months for two years, and annually for a further two years. All those remaining in the study after four years were interviewed and a history of their use of breathing apparatus and of being affected by smoke and fumes was obtained. Symptom frequency was least in control subjects, intermediate in non-smokers and ex-smokers, and most in smokers. Before the study period (history obtained at the first session) smoking increased symptoms 3.9 times and being affected by smoke in the past increased symptoms 2.3 times, compared with non-smokers who had not been affected by smoke. In smokers who had also been affected by smoke symptoms increased by 9.1 times, suggesting a multiplicative effect. During the study period symptom frequency was increased about 4.4 times in smokers and 5.7 times in those who had been affected by smoke at work in the past compared with non-smokers who had not been affected by smoke. In smokers who had also been affected by smoke symptom frequency increased by 7.4 times, the combined effects of the two types of smoker being less than additive. These results suggest that being affected by smoke and fumes at work may be a cause of long term symptoms in firemen. In firemen who are non-smokers and who had not been affected by smoke symptom frequency was similar to that observed in the control subjects. Thus the current routine use of breathing apparatus appears to be effective in preventing long term symptoms.

Lung function in West Sussex firemen: a four year study.

Although firefighting is a hazardous occupation, published evidence of long-term lung damage in firemen is inconsistent. A group of 96 men from the West Sussex Fire Brigade, which covers a simi-rural, semi-urban area, were followed up for between one and four years. They included 31 non-smokers, 40 smokers, and 25 ex-smokers. After four years 12 firemen had been lost to the study. A control group of 69 volunteers, consisting of non-smoking men from various other occupations, were followed up in parallel. Lung function tests, covering a wider range than has been previously used in similar studies, were repeated six monthly for two years and annually for a further two years. The results were expressed in terms of the rate of change with time of the lung function variables. Many of the variables deteriorated in both firemen and controls, but the rate of deterioration was greater in the controls than the firemen for vital capacity, ratio of residual volume to total lung capacity, FEV1, FVC, peak expiratory flow (PEF), flow at 50% and 25% remaining vital capacity (V50 and V25 respectively), and airways resistance (Raw). With respect to PEF, V50, V25, and Raw the control subjects deteriorated more rapidly even than the smokers and ex-smokers among the firemen. Alveolar mixing efficiency (AME), a measure of small airways function, did not change significantly over the study period in any group. Non-smoking firemen had the highest mean value of AME, decreasing through ex-smokers, controls, and smokers. We conclude that these results show no evidence of chronic lung damage in West Sussex firemen; indeed, the firemen as a group show a lower rate of deterioration of lung function with age than do the control subjects. This is attributed to the selection of fit men for the service, continued physical training, and the regular use of breathing apparatus.