Reconciling the optimal and empirical approaches to modelling stomatal conductance

Models of vegetation function are widely used to predict the effects of climate change on carbon, water and nutrient cycles of terrestrial ecosystems, and their feedbacks to climate. Stomatal conductance, the process that governs plant water use and carbon uptake, is fundamental to such models. In this paper, we reconcile two long‐standing theories of stomatal conductance. The empirical approach, which is most commonly used in vegetation models, is phenomenological, based on experimental observations of stomatal behaviour in response to environmental conditions. The optimal approach is based on the theoretical argument that stomata should act to minimize the amount of water used per unit carbon gained. We reconcile these two approaches by showing that the theory of optimal stomatal conductance can be used to derive a model of stomatal conductance that is closely analogous to the empirical models. Consequently, we obtain a unified stomatal model which has a similar form to existing empirical models, but which now provides a theoretical interpretation for model parameter values. The key model parameter, g₁, is predicted to increase with growth temperature and with the marginal water cost of carbon gain. The new model is fitted to a range of datasets ranging from tropical to boreal trees. The parameter g₁ is shown to vary with growth temperature, as predicted, and also with plant functional type. The model is shown to correctly capture responses of stomatal conductance to changing atmospheric CO₂, and thus can be used to test for stomatal acclimation to elevated CO₂. The reconciliation of the optimal and empirical approaches to modelling stomatal conductance is important for global change biology because it provides a simple theoretical framework for analyzing, and simulating, the coupling between carbon and water cycles under environmental change.     

clonality V.0.4: a randomization-based program to test for heterozygosity-genet size relationships in clonal organisms

clonality V.0.4 is a program for testing heterozygosity-genet size relationships in clonal organisms using a randomization procedure. The software has been developed under the Borland Delphi developing environment and a Windows-executable version is freely downloadable from http://gemi.mpl.ird.fr/SiteSGASS/Prugnolle/ClonalityPage.html. The program compares the observed F(IS) of the population with the F(IS) expected if genets (multilocus genotypes present in multiple copies within the population) were chosen randomly from the set of different multilocus genotypes. The randomization procedure is performed with the same number of genets and the same number of repetitions per genet as what is observed in the original data set.     

HYDROBIIDAE (GASTROPODA: HYDROBIOIDEA) FROM THE RIBEIRA VALLEY, S.E. BRAZIL, WITH DESCRIPTIONS OF TWO NEW CAVERNICOLOUS SPECIES

Potamolithus karsticus n. sp. and Potamolithus troglo-bius n.sp., two Brazilian aquatic cavesnails (Gastropoda: Hydrobiidae),are described. P. troglobius is blind and depigmented, and isthe first stygobiontic snail to be described from Brazil Additionally, specimens of Potamolithus ribeirensis Pilsbry,1911 were collected near the type locality for comparison withthe new cave species (Received 2 December 1993; accepted 20 June 1994)     

The reproductive biology, age and growth of the North American cyprinid, Notropis longirostris (Hay)

Notropis longirostris (Hay), the longnose shiner, in Catahoula Creek, Jourdan River drainage, Hancock County, Mississippi, was studied from May 1970 to May 1972. In 1971 reproduction occurred from late March into October, as indicated by gross examination of testes, breeding tubercles and breeding colour in males, and ovarian weights, measurements of ova, and gross examination of ovaries in females. Gross examination of ovaries in 1970 also indicated an extended reproductive season. Generally no significant differences from a 1 : 1 sex ratio or in the size of males and females in collections taken during the reproductive season were indicated. Males and females matured about the same size. Most females were sexually mature when 29–30 mm SL. The smallest female with mature ova was 28 mm; however, the majority of females did not have mature ova until 31–33 mm. The number of mature ova produced prior to spawning ranged from 15 to 129 for females 30.8–44 mm SL. There were significant differences in the number of mature ova with time, two peaks being indicated: the first in late March and April at the beginning of the reproductive period and the second in early July about the middle of the season. This conclusion is also supported by ovarian weight measurements and length frequency histograms. The mean diameters of mature ova ranged from 0.70–1.05 mm, averaging 0.90 mm, and were not significantly correlated with length. Most fish live about 1–1.5 years and do not live through two winters, indicating an annual turnover in the population. Maximum size was about 48 mm SL. Specific characteristics of the life history pattern of N. longirostris are discussed in relation to ecological conditions of the habitat.     

Thermal Sensitivity as a Specialization for Prey Capture and Feeding in Snakes

Behavior can be regarded as a result of various processes ofdecision based on the information provided by the sensory organs.In this review the role of the so-called additional heat sense,next to vision, smell and mechanoreception is discussed withrespect to the feeding behavior of snakes. The hierarchy ofthe sensory information in various phases of the feeding behaviordiffers between snakes possessing heat receptors (e.g., speciesof the Crotalinae and Pythoninae) and those without (e.g., speciesof the Viperinae and Colubrinae). Probably depending on theinfluence of ecological demands, visual or chemical cues arethe main information in the behavioral phases before the strikeHowever, in situations with little visual input, e.g., in darkness,rodents' burrows, etc., hunting behavior is guided in the firstplace by radiation of warm objects in Crotalus, Python and Trimeresurusflavoviridis, and by substrate vibrations in Vipera aspis, Pituophismelanoleucus and Boa constrictor. I suggest that in the sensoryhierarchy, heat information functionally replaces the mechanicalinformation which is utilized by snakes without pit organs.Poststrike behavior on the other hand is mainly guided by chemicalcues in all snakes.     

A Comparative Study on the Effects of H2S and SO2 Fumigation on the Growth and Accumulation of Sulphate and Sulphydryl Compounds in Trifolium pratense L., Glycine max Merr. and Phaseolus vulgaris L.

Maas, F. M., De Kok, L. J., Peters, J. L. and Kuiper, P. J.C. 1987. A comparative study on the effects of H₂S and SO₂ fumigationon the growth and accumulation of sulphate and sulphydryl compoundsin Trifolium pratense L., Glycine max Merr. and Phaseolus vulgarisL.—J. exp. Bot. 38: 1459-1469. The effects of 0—25 mm³ dm³ H₂S and SO₂ on growth andsulphur content of shoots of Trifolium pratense, Glycine maxand Phaseolus vulgaris were studied. After 2 weeks of fumigationthe yield of T. pralense was reduced by 32% by H₂S, but notaffected by SO₂. Yield of G. max was not affected by H₂S, butreduced by 20% by SO₂, whereas that of P. vulgaris was increasedby 11% by H₂S and not affected by SO₂. Increases in sulphydrylcontent were already observed after 24 h of exposure to H₂Sand SO₂ in all plants. The increase was greatest in T. pratenseand smallest in P. vulgaris and, except for T. pratense, alwaysgreater in the H₂S-exposed than the SO₂-exposed plants. Oneday of exposure resulted in an increase in sulphate contentonly in the SO₂-fumigated plants, with the highest accumulationin T. pratense and the lowest in P. vulgaris. After 2 weeksan increase in sulphate content was also observed in the H₂S-exposedplants. This increase was also highest in T. pratense and lowestin P. vulgaris. Transpiration rate was not affected by a 24 h exposure to H₂Sor SO₂ and was highest in T. pratense, intermediate in G. maxand lowest in P. vulgaris. The order of theoretical rates of deposition of H₂S and SO₂correlated with the observed increases in sulphydryl contentduring the first 24 h of exposure in both H₂S and SO₂-fumigatedplants and with the increase in sulphate content in the SO₂-exposedplants. The increases in sulphydryl content were only 8% ofthe theoretical H₂S and SO₂-deposition fluxes, whereas sulphateaccumulation accounted for at least 57% of the theoretical SO₂-depositionflux. Key words: Air pollution, clover, French bean, Glutathione, Soybean, sulphur metabolism.