摘要:

SummaryThe preceding account has attempted to examine the interactions between light absorption and photosynthesis, with reference to both unicellular and multicellular terrestrial and aquatic plants. There are, however, some notable plant groups to which no direct reference has been made, e.g. mosses, liverworts and lichens. Although many have similar optical properties to terrestrial vascular plants (Gates, 1980) and apparently similar photosynthetic responses (see Green&Snelgar, 1982; Kershaw, 1984) they may possess subtle, as yet unknown differences. For instance, the lichen thallus has a high surface reflectance although the transmittance is virtually zero (Gates, 1980; Osborne, unpublished results). It is envisaged, however, that differences in optical properties between species will reflect differences in degree not kind.Although not all variation in photosynthesis is due to differences in light absorption a number of accounts suggest that this is a contributing factor. Variations in leaf absorptance have been found to account for most of the variation in leaf photosynthesis at low Jis (see Ehleringer&Björkman, 1978a; Osborne&Garrett, 1983). There is, however, little direct experimental evidence on light absorption and photosynthesis in either microalgal species or aquatic macrophytes. We also do not know over what range of incident photon flux densities photosynthesis is determined largely by changes in light absorption. Plants growing under natural conditions also experience large diurnal and seasonal fluctuations in Ji, unlike species grown under laboratory conditions. The occurrence of transitory peaks in Jitends to overshadow the fact that the average Jiis often lower than the J1required to saturate photosynthesis, i.e. 1500–2000 μmol m‐2s‐1, depending on the growth treatment. Using the data of Monteith (1977) and I W m2= 5 μmol m‐2s‐1, and with photosynthetically active radiation 50% of total solar radiation, the daily mean value for Britain is approximately 450 μmol m‐2s‐1, with a maximum in June of 1000μmol m‐2s‐1and a minimum during the winter of 75 μmol m‐2s‐1. Such values could be even lower on shaded understory leaves and considerably lower for aquatic species. Based on average values of net photosynthesis for a terrestrial plant leaf, light saturation would only be expected in June while for most of the year theaveragevalues would lie largely on the light‐limited portion of the photosynthesis light response curve. Although the daily average values in tropical climates may be higher during the winter months, they are remarkably similar throughout the world for the respective summers in the northern and southern hemispheres, because the increased daylength at high latitudes compensates for the lower Jis. The expected lower dark respiration rates during the winter may also partially offset the effects of a lower light level. There is therefore a trade‐off between high Jis for a short period of time against a lower Jifor a longer period of time. We might expect different photosynthetic responses to these two very different conditions. Importantly, a low Jiwith a long daylength may enable a plant to photosynthesize at or near its maximum photon efficiency for most of the day. Although the response of the plant to fluctuations in Jiis complicated because it is affected by the previous environmental conditions, this may indicate that light absorption has a much greater significance under natural conditions, particularly for perennial species.The bias in many laboratories towards research on terrestrial vascular plants also tends to ignore the fact that a number of multicellular and unicellular aquatic species survive in very low light environments. Furthermore, the direct extrapolation of photosynthetic responses from measurements on single leaves to those of whole plants is clearly erroneous. Although this is obvious, many physiological ecologists have attributed all manner of things to the photosynthetic responses of ‘primary’ leaves.Most researchers have ignored problems associated with composite plant tissues and internal light gradients. Clearly caution is required in interpreting the photosynthesis light‐response curve of multicellular tissues based on biochemical features alone. Also, the importance of cell structure on light absorption and photosynthesis has generally been ignored and attributed solely to the effects of structural features on CO2diffusion. In doing so the work of two or three generations of plant physiologists has been ignored. Haberlandt (1914) at the turn of the century probably first implicated the role of cell structure in leaf optics, and Heath (1970) stressed that in order to completely understand the role of light in photosynthesis we need to know the flux incident on the chloroplast itself. Even this suggestion may need modification because of the capacity of the internal chloroplast membranes for scattering light.It is worth emphasizing the importance of light gradients within tissues and their role in regulating photosynthesis, particularly at light saturation. Measurements of light gradients are fraught with problems because of experimental difficulties and the majority (few) are based on reflectance and transmittance measurements. Seyfried&Fukshansky (1983) have shown that light incident on the lower surface of aCucurbitacotyledon produced a larger light gradient than light incident from above, indicating the importance of the spatial arrangement of the tissues with respect to the light source. Also, light incident on the lower surface of leaves ofPicea sitchensiswas less ‘effective’ in photosynthesis than light from above (Leverenz&Jarvis, 1979). Clearly, two tissues could have the same gross absorptance but different photosynthetic rates because of differences in the internal light environment. Fisher&Fisher (1983) have recently found asymmetries in the light distribution within leaves, which they related to asymmetries in photosynthetic products due to differences in solar elevation. Such modifications in light distribution could be important for a number of solar‐tracking species.Changes in light absorption are brought about by a whole gamut of physiological, morphological and behavioural responses which serve to optimize the amount of light absorbed. Perhaps the simplest way of regulating the amount of light absorbed is by restricting growth either to particular times of the year or to conditions when the light climate is favourable. We are still largely ignorant of many details of these modifications. In particular, differences in tissue structure such as the size and number of vacuoles or the effects of organelles on the scattering component of the internal light environment of photosynthetic tissues are not understood. A better understanding of the interaction of light with plants in aquatic systems is also required.It is unfortunate that light‐absorptance measurements are not routinely made in photosynthetic studies, and this is quite clearly a neglected area of study. That these measurements are not made is even more surprising, since techniques have been available for over sixty years (Ulbricht, 1920). Absorptance measurements are of particular importance in the photosynthetic adaptation of microalgae, where only a small proportion of the incident photon flux density is absorbed. For multicellular species more detailed information is required on internal light gradients and their variability. Light‐absorptance measurements are also important in any study relating kinetic data on CO2fixation to in vivo photosynthesis, especially when there are large variations in the morph

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00425.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00426.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

General Summary1. The aim of this paper has been to review the theory behind kin recognition to examine the benefits individuals obtain by recognizing their kin and to review the mechanisms used by individuals in their recognition of kin.2. The ability to discriminate between kin and non‐kin, and between different classes of kin gives individuals advantages in fitness greater than individuals unable to recognize their kin. Four specific areas of benefit were considered: altruistic behaviour, co‐operative behaviour, parental care and mate choice. Finally the possibility that kin recognition has arisen as a byproduct from some other ability was discussed.3. Mechanisms of kin recognition were considered with respect to three essential components of kin recognition. The cue used to discriminate kin, how individuals classify conspecifics as kin, etc. and how the ability to recognize kin develops.4. Individuals can use a number of cues to discriminate kin from non‐kin. These were divided into cues presented by conspecifics (conspecific cues), of which three types were considered: individual, genetic and group/colony cues, and non‐conspecific cues, environmental, state and no cues. Kin recognition could be achieved by use of all these cues.5. How individuals classify their conspecifics as kin, etc. can be achieved in a number of ways; dishabituation or self‐matching, which require no learning of kinship cues, or by phenotype matching or familiarity, both of which require the learning of kinship information.6. It may be necessary for individuals to acquire information concerning kinship. This may be learned, and can be achieved in a number of ways; physiological imprinting, exposure learning or associative learning. Acquisition by these means is non‐selective, in that the cues which are most salient in the individual's environment will be learned. Selectivity can be introduced into this process to increase the probability of acquiring kinship information by a number of means; learning from parents, sensitive periods for learning and prenatal learning. Finally, kinship information could be supplied by recognition genes.7. A distinction is drawn between cues which are used by an individual in the discrimination of kin, discriminators, and cues which are used by individuals in the acquisition of information about kinship, acquisitors.8. Experiments used to support previous categories of mechanisms of kin recognition were examined in the light of this discussion and it was found that the results were open to a number of different interpretations and yielded little specific information about the mechanisms of kin recognition.9. It was concluded that there was much evidence, both theoretical and experimental to support the proposed benefits individuals gain from recognizing kin, but much more research is required before the mechanisms of kin recognition are fully

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00427.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00428.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY