The potential importance of CO2 derived from host tree respiration at night as a substrate for night time CO2 uptake during CAM was investigated in the subtropical and tropical epiphytic vine Hoya carnosa in a subtropical rainforest in north-eastern Taiwan. Individuals were examined within the canopies of host trees in open, exposed situations, as well as in dense forests. Although night time CO2 concentrations were higher near the epiphytic vines at night, relative to those measured during the day, presumably the result of CO2 added to the canopy air by the host tree, no evidence for substantial use of this CO2 was found. In particular, stable carbon isotope ratios of H. carnosa were not substantially lower than those of many other CAM plants, as would be expected if host-respired CO2 were an important source of CO2 for these CAM epiphytes. Furthermore, laboratory measurements of diel CO2 exchange revealed a substantial contribution of daytime CO2 uptake in these vines, which should also result in lower carbon isotope values than those characteristic of a CAM plant lacking daytime CO2 uptake. Overall, we found that host-respired CO2 does not contribute substantially to the carbon budget of this epiphytic CAM plant. This finding does not support the hypothesis that CAM may have evolved in tropical epiphytes in response to diel changes in the CO2 concentrations within the host tree canopy. and C.-C. Hsu ... [et al.].
An ecophysiological approach was used to determine if competition can be detected among plants in a recently abandoned old-field and in a native tallgrass prairie in northeastern Kansas. In situ photosynthetic parameters and water potentials (Ψ) of target plants were measured 1-2 d after neighbor (intra- and interspecific) removal as well as 1-4 weeks later, and compared with values for plants with neighbors. Only two of the six study species (four old-field and two prairie species) responded to removal of neighboring plants, and only after several weeks had elapsed. Net photosynthetic rates (PN) and stomatal conductances (gs) of Ambrosia trifida in an old-field increased after removal of both intra- and interspecific neighbors. For Apocynum cannabinum, another old-field species, PN of target plants without neighbors was significantly higher than that of target plants with neighbors. For both these species, values of Ψ were not different between target plants with and without neighbors, suggesting that increased availability of nutrients may have been responsible for the observed ecophysiological responses. Though numerous past studies indicate that competition is a major factor influencing plants in old-field and in prairie communities, the experimental approach used in this study revealed that neighbor removal had only limited effects on ecophysiology of the target plants in either community. and F. Norman, C. E. Martin.
Tomato seeds exposed to space conditions for nearly six years on board the Long Duration Exposure Facility (LDEF) satellite were subsequently germinated and the resultant seedlings grown on earth under controlled conditions for analysis. Photosynthesis, biomass, and water relations were compared between mature plants grown from earth-based control seeds and space-exposed seeds under both well-watered and drought-stressed conditions. No consistent significant differences in photosynthesis and water relations were observed in the two sets of plants at any level of drought stress. Fruit production, however, though limited and variable, was significantly greater in plants grown from space-exposed seeds than in plants grown from earth-based seeds. Overall, exposure of seeds to space had only minor effects on the physiology and growth of plants grown from such seed. and M. S. Marmor, C. E. Martin.
The ecophysiological function(s) and consequences of guttation, a phenomenon by which water is exuded by and accumulated as droplets along the leaf margins under high humidity in many plants that grow in wet soil, has been poorly studied and remains largely unknown. Thus, leaf gas exchange and chlorophyll fluorescence were examined, using two experimental approaches, in Alchemilla mollis plants under conditions that promoted guttation and those that prevented this phenomenon. Although results were variable, depending on the experimental approach, prevention of guttation effected reductions in photosynthesis and transpiration, as well as photochemical activity measured with fluorescence techniques. These findings lend partial support for a previously hypothesized function of guttation: prevention of excess water in leaves, yet they contradict those of several other studies. More work is required in order to adequately understand the function of guttation., Y.-C. Chen, T.-C. Lin, C. E. Martin., and Obsahuje bibliografii
In the terrestrial bromeliad, Puya floccosa, a value of carbon isotopic composition (δ13C) of -22‰ has been previously reported, suggesting the operation of weak and/or intermediate (C3-CAM) crassulacean acid metabolism (CAM). In order to characterize the operation of CAM in P. floccosa and its possible induction by drought, plants were grown in Caracas and subjected to four independent drought cycles. Additionally, since plants of this species grow in Venezuela in a large range of elevations, leaf samples were collected at elevations ranging from 725 to 2,100 m a.s.l. in the Venezuelan Andes and the Coastal Range, in order to evaluate the effect of elevation on CAM performance. Even though nocturnal acid accumulation occurred in both watered and droughted plants, mean ΔH+ was higher in droughted than watered plants [ΔH+ = 60.17.5 and 22.9 ± 5.2 μmol g-1(FM), respectively]. The majority of plants from all the natural populations sampled had low values of δ13C not differing significantly from those of C3 plants collected as standards and δ13C did not change with elevation. We conclude that P. floccosa is capable of a weak CAM activity, with a large variability among populations and drought experiments probably due to local and temporal differences in microclimatic variables and drought stress; elevation bears no influence on values of δ13C in this species. and A. Herrera ... [et al.].
Recently, Werner and Stelzer reported C3 gas exchange simultaneous with CAM acid fluctuatíons, i.e., CAM-cycling, in seedlings of the mangrove species Rhizophora mangle L. The potential for CAM-cycling was investigated in mature individuals of R. mangle and of Laguncularia racemosa (L.) Gaertn. f in šitu in southwestem Florida and in seedlings of R. mangle grown in a growth chamber. Only C3 CO2 exchange was observed, while diumal fluctuatíons of tissue acid content were absent. Thus, no evidence for CAM-cycling was found in the field or in the growth chamber for R. mangle, nor in the field for L. racemosa.
Net CO2 exchange rate (PN) of shoots and diel fluctuations in titratable acidity of leaves of Senecio rowleyanus were measured to determine whether penetration of radiant energy through leaf "windows" (narrow, translucent strips on the leaf epidermis) resulted in increased CAM. Nocturnal PN and nighttime increases in acidity were compared among plants with windows covered with reflective adhesive tape, transparent adhesive tape (to control for potential effects of the adhesive), and no tape. The windows did not significantly enhance the degree of CAM in S. rowleyanus. and K. J. Egbert, C. E. Martin.
Four fluorescence parameters [Fv/Fm = the intrinsic efficiency of energy conversion via photosystem 2 (PS2); Fv'/Fm'= the efficiency of energy conversion via PS2 in the light; P = fraction of absorbed radiant energy utilized for photosynthesis; and D = fraction of absorbed radiant energy dissipated as heat] were measured on leaves of seven species of succulents having epidermal windows. While the function of leaf windows has reportedly been to increase absorption of radiant energy and, hence, the rate of photosynthesis in these species, recent evidence indicates that this translucent portion of epidermal tissue, lacking chlorophyll, may also result in photoinhibition in these species, especially for those with growth habits aboveground. Species with aboveground and belowground growth habits were compared with their leaf windows covered with reflective tape and with windows unobstructed. Results showed no increase in photoinhibition for these species resulting from the radiant energy penetrating the window tissue. Although the efficiency of the photosynthetic mechanism was not significantly influenced by the additional radiant energy provided by the window for individual species, there were significant differences in the efficiencies of radiant energy capture (Fv'/Fm') and utilization (P) between the two growth habits. Species with an aboveground growth habit were less efficient in radiant energy utilization compared with the species having a belowground growth habit. and K. J. Egbert, C. E. Martin.
The photosynthetic pathway of the roots (both the white velamentous main portions and the green, nonvelamentous tips) was investigated in twelve taxa (natural species and intergeneric hybrid cultivars) of epiphytic orchids having CAM leaves. All organs contained chlorophyll, and the a/b ratios indicate that the organs, especially the roots, are likely shade-adapted. Stable carbon isotope ratios of the tissues were near -15‰ for all organs, a value typical of obligate (constitutive) CAM plants. Values for root tissues were slightly lower (more negative) than those of the leaves. The presence of CAM in the leaves of these orchids did not ensure that their roots performed CAM photosynthesis. Further work is needed to address the questions raised in this study and to determine if the photosynthetic roots of these taxa are capable of assimilating atmospheric CO2. and C. E. Martin ... [et al.].
Past reports of correlations between Crassulacean acid metabolism (CAM) and leaf succulence are based on multi-species comparisons. When different individuals of the same species were compared in two epiphytic CAM vines growing in a subtropical rainforest in northeastern Taiwan, the degree of CAM was not correlated with leaf thickness, a measure of succulence. Leaf chlorophyll (Chl) a and b concentrations and ratios correlated well with leaf succulence, indicating that differences in leaf succulence were likely a result of sun/shade adaptations, not photosynthetic pathway. These findings challenge the assumption that CAM-succulence correlations are causal. and C. E. Martin, R. C.-C. Hsu, T.-C. Lin