We studied the dominant environmental factors that affect the
gas-exchange characteristics and water potential (ψ) of broad-ovate leaves of Populus euphratica Oliv. in extreme arid area of Tarim River, China, and their correlation to water status of P. euphratica by analyzing on-field monitored meteorological data, soil moisture and salinity, P. euphratica leaf gas exchange and ψ, and revealed the indicative threshold of environmental factors for P. euphratica leaf water changes and growth. The results indicated that meteorological factors such as air relative humidity (RH), air temperature (T air), etc. are the dominant factors. The threshold value of RH is (48.19 ± 1.06)% for P. euphratica growth, i.e. RH from 10.69% to 48.19% is suitable for P. euphratica growth in extremely arid region of Tarim River. This study provides a theoretical basis for reducing drought damage to P. euphratica and maintaining normal growth of P. euphratica by in-time watering. and A. H. Fu ... [et al.].
Net rates of photosynthesis (PN) saturated by irradiance of >500 μmol m-2 s-1 (PAR) significantly decreased in water-stressed potato (Solanum tuberosum L. cv. Kufri Sindhuri) plants. The quantum yield of photochemical energy conversion (Fv/Fm), relative electron transport rate (ETR), and photochemical quenching (Qp) exhibited a parallel decline at high irradiance. A slight decrease in relative water content (RWC) was accompanied by a drastic decline in leaf water potential (Ψw) from -0.2 to -1.0 MPa. Dehydrated leaves showed an increase in the amount of total soluble sugars per unit leaf area which inhibited the photosynthesis in a feedback manner. After rewatering, PN and Fv/Fm were restored to the values of control plants within 24 h, and the restoration was accompanied by a proportionate lowering of content of total soluble sugars in the leaves. and P. S. Basu, Ashoo Sharma, N. P. Sukumaran.
Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D. and M. T. Grzesiak ... [et al.].
Chlorophyll a fluorescence, water potential (Ψs), and root system of Juniperus oxycedrus ssp. macrocarpa, Juniperus phoenicea ssp. turbinata, and Pinus pinea were studied in Mediterranean coastal dunes of SW Spain during summer drought and after fall rains in 1999, the driest year in the 90's. A strong and reversible depression in the photochemical efficiency of photosystem 2 of the three species was recorded, which happened concomitantly with the diurnal increase and decrease in radiation. J. phoenicea, with superficial root system, was the most affected species by summer drought. It showed high rates of down-regulation of photosynthesis by photoinhibition and positive correlation between Ψs and Fv/Fp, with Ψs lower than -7 MPa. However, it tolerated this high stress, showing a fast recovery of its physiological state after fall rains. On the other hand, J. oxycedrus and P. pinea, both with deep root systems, kept their Ψs values up to -3 MPa, showing lower stress during summer drought. On the other hand, J. oxycedrus and J. phoenicea were more sensible to changes in edaphic water content than P. pinea. These specific responses to summer drought would be determined by their root distributions and stomatal control of transpiration, conditioning the efficiency in getting and using the available water resources. Ecophysiological responses indicate that these species are well-adapted to long periods of drought in Mediterranean climate areas, developing different strategies: J. phoenicea tolerates high stress with a fast recovery after fall rains, while J. oxycedrus and P. pinea are less affected by summer drought since their deep root systems would allow them to reach deep water resources. and J. M. Castillo ... [et al.].
The effect of drought stress (DS) on photosynthesis and photosynthesis-related enzyme activities was investigated in F. pringlei (C3), F. floridana (C3-C4), F. brownii (C4-like), and F. trinervia (C4) species. Stomatal closure was observed in all species, probably being the main cause for the decline in photosynthesis in the C3 species under ambient conditions. In vitro ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and stromal fructose 1,6-bisphosphatase (sFBP) activities were sufficient to interpret the net photosynthetic rates (PN), but, from the decreases in PN values under high CO2 (C a = 700 µmol mol- 1) it is concluded that a decrease in the in vivo rate of the RuBPCO reaction may be an additional limiting factor under DS in the C3 species. The observed decline in the photosynthesis capacity of the C3-C4 species is suggested to be associated both to in vivo decreases of RuBPCO activity and of the RuBP regeneration rate. The decline of the maximum PN observed in the C4-like species under DS was probably attributed to a decrease in maximum RuBPCO activity and/or to decrease of enzyme substrate (RuBP or PEP) regeneration rates. In the C4 species, the decline of both in vivo photosynthesis and photosynthetic capacity could be due to in vivo inhibition of the phosphoenolpyruvate carboxylase (PEPC) by a twofold increase of the malate concentration observed in mesophyll cell extracts from DS plants. and M. C. Dias, W. Brüggemann.
The rate of photosynthesis (PN) in leaves and pods as well as carbon isotope content in leaves, pod walls, and seeds was measured in well-watered (WW) and water-stressed (WS) chickpea plants. The PN, on an area basis, was negligible in pods compared to leaves and was reduced by water stress (by 26%) only in leaves. WS pod walls and seeds discriminated less against 13CO2 than did the controls. This response was not observed for leaves as is usually the case. Pod walls and seeds discriminated less against 13CO2 than did leaves in both WW and WS plants. Measurement of carbon isotope composition in pods may be a more sensitive tool for assessing the impact of water stress on long-term assimilation than is the instantaneous measurement of gas exchange rates. and M. H. Behboudian ... [et al.].
We investigated the strategies of four co-occurring evergreen woody species Quercus ilex, Quercus coccifera, Pinus halepensis, and Juniperus phoenicea to cope with Mediterranean field conditions. For that purpose, stem water potential, gas exchange, chlorophyll (Chl) fluorescence, and Chl and carotenoid (Car) contents were examined. We recognized two stress periods along the year, winter with low precipitation and low temperatures that led to chronic photoinhibition, and summer, when drought coincided with high radiation, leading to an increase of dynamic photoinhibition and a decrease of pigment content. Summer photoprotection was related to non-photochemical energy dissipation, electron flow to alternative sinks other than photosynthesis, decrease of Chl content, and proportional increase of Car content. Water potential of trees with deep vertical roots (Q. coccifera, Q. ilex, and P. halepensis) mainly depended on precipitation, whereas water potential of trees with shallow roots (J. phoenicea) depended not only on precipitation but also on ambient temperature. and F. J. Baquedano, F. J. Castillo.
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.
The interactive effect of elevated CO2 (EC) and moisture stress (MS) on Brassica juncea cv. Pusa Bold was studied using open-top chambers. The EC markedly increased net photosynthetic rate and internal CO2 concentration and reduced variable and maximal chlorophyll fluorescence. Under MS, EC increased water potential and relative water content, and reduced transpiration rate. The greater allocation of biomass to the roots, which serve as a strong sink for assimilated carbon under EC, helped in better root growth. and B. K. Rabha, D. C. Uprety.
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.