Mohamed A. Shahba

Exploring the importance of within-canopy spatial temperature variation on transpiration predictions

Models seldom consider the effect of leaf-level biochemical acclimation to temperature when scaling forest water use. Therefore, the dependence of transpiration on temperature acclimation was investigated at the within-crown scale in climatically contrasting genotypes of Acer rubrum L., cv. October Glory (OG) and Summer Red (SR). The effects of temperature acclimation on intracanopy gradients in transpiration over a range of realistic forest growth temperatures were also assessed by simulation. Physiological parameters were applied, with or without adjustment for temperature acclimation, to account for transpiration responses to growth temperature. Both types of parameterization were scaled up to stand transpiration (expressed per unit leaf area) with an individual tree model (MAESTRA) to assess how transpiration might be affected by spatial and temporal distributions of foliage properties. The MAESTRA model performed well, but its reproducibility was dependent on physiological parameters acclimated to daytime temperature. Concordance correlation coefficients between measured and predicted transpiration were higher (0.95 and 0.98 versus 0.87 and 0.96) when model parameters reflected acclimated growth temperature. In response to temperature increases, the southern genotype (SR) transpiration responded more than the northern (OG). Conditions of elevated long-term temperature acclimation further separate their transpiration differences. Results demonstrate the importance of accounting for leaf-level physiological adjustments that are sensitive to microclimate changes and the use of provenance-, ecotype-, and/or genotype-specific parameter sets, two components likely to improve the accuracy of site-level and ecosystem-level estimates of transpiration flux.

Growth temperature modulates the spatial variability of leaf morphology and chemical elements within crowns of climatically divergent Acer rubrum genotypes

Our understanding of leaf acclimation in relation to temperature of fully grown or juvenile tree crowns is mainly based on research involving spatially uncontrolled growth temperature. In this study, we test the hypothesis that leaf morphology and chemical elements are modulated by within-crown growth temperature differences. We ask whether within-species variation can influence acclimation to elevated temperatures. Within-crown temperature dependence of leaf morphology, carbon and nitrogen was examined in two genotypes of Acer rubrum L. (red maple) from different latitudes, where the mean annual temperature varies between 7.2 and 19.4 degrees C. Crown sections were grown in temperature-controlled chambers at three daytime growth temperatures (25, 33 and 38 degrees C). Leaf growth and resource acquisition were measured at regular intervals over long-term (50 days) controlled daytime growth temperatures. We found significant intraspecific variation in temperature dependence of leaf carbon and nitrogen accumulation between genotypes. Additionally, there was evidence that leaf morphology depended on inherited adaptation. Leaf dry matter and nitrogen content decreased as growth temperature was elevated above 25 degrees C in the genotype native to the cooler climate, whereas they remained fairly constant in response to temperature in the genotype native to the warmer climate. Specific leaf area (SLA) was correlated positively to leaf nitrogen content in both genotypes. The SLA and the relative leaf dry matter content (LM), on the other hand, were correlated negatively to leaf thickness. However, intraspecific variation in SLA and LM versus leaf thickness was highly significant. Intraspecific differences in leaf temperature response between climatically divergent genotypes yielded important implications for convergent evolution of leaf adaptation. Comparison of our results with those of previous studies showed that leaf carbon allocation along a vertical temperature gradient was modulated by growth temperature in the genotype native to the cooler climate. This indicates that within-crown temperature-induced variations in leaf morphology and chemical content should be accounted for in forest ecosystem models.

Erratum to: Comparative Responses of Bermudagrass and Seashore Paspalum Cultivars Commonly Used in Egypt to Combat Salinity Stress

In Egypt, salt-related problems have increased in the turfgrass industry during the last 30 years and the need for salt tolerant turfgrasses has increased. Two species of turfgrasses, bermudagrass (Cynodon dactylon L., ‘Tifway’, ‘Tifdwarf’ and ‘Tifgreen’) and seashore paspalum (Paspalum vaginatum Swartz, ‘Salam’, ‘Excalibur’, and ‘Adalayd’), were studied in a greenhouse to evaluate their performance under various electrical conductivity (EC) levels [2.2 (control); 8.0, 16.0, 32.0, 44.0 and 54.0 dS m -1 ] of equal weights of CaCl₂ and NaCl salinity in the culture medium. ‘Salam’ was found to have superior salt tolerance compared to the others. ‘Excalibur’ also exhibited high salinity tolerance, and both were better than ‘Tifgreen’, ‘Tifdwarf’, ‘Tifway’, and ‘Adalayd’. Under the highest salinity level (54.0 dS m -1 ), ‘Salam’ showed the lowest leaf firing percentage (80%) followed by ‘Excalibur’ (90.5%) while all others showed 100.0 % leaf firing. Only ‘Salam’ showed acceptable turf quality (6.0) at the salinity level of 32.0 dS m -1 . ‘Salam’, ‘Excalibur’ and ‘Tifgreen’ quality declined less severely with increasing salinity, while ‘Adalayd’ had the poorest quality among all cultivars. At the salinity level of 16.0 dS m -1 , all tested cultivars showed acceptable quality except ‘Tifway’ and ‘Adalayd’. ‘Salam’ and ‘Excalibur’ exhibited higher clipping yields than the others. ‘Adalayd’ had the lowest clipping yield at all salinity levels. Linear regression indicated a significant positive linear relationship between root mass and growth medium salinity levels in all tested turfgrass cultivars except ‘Adalayd’. ‘Adalayd’ exhibited a decrease in root mass as salinity increased from 16.0 to 32.0 dS m -1 . At the highest salinity level (54.0 dS m -1 ), ‘Salam’ exhibited the highest root activity among all cultivars and maintained an increasing linear trend. For 25% clipping yield reduction, salinity levels ranged from 10.5 dS m -1 for ‘Adalayd’ to 30.0 dS m -1 for ‘Salam’ and these levels were significantly different among the tested cultivars.

An Efficient In Vitro Propagation Protocol of Cocoyam [Xanthosoma sagittifolium (L) Schott]

Sprouted corm sections of “South Dade” white cocoyam were potted and maintained in a greenhouse for 8 weeks. Shoot tips of 3–5 mm comprising the apical meristem with 4–6 leaf primordial, and approximately 0.5 mm of corm tissue at the base. These explants were treated to be used into the culture medium. A modified Gamborgs B5 mineral salts supplemented with 0.05 μM 1-naphthaleneacetic acid (NAA) were used throughout the study. Thidiazuron (TDZ) solution containing 0.01% dimethyl sulfoxide (DMSO) was used. Erlenmeyer flasks and test tubes were used for growing cultures. The effect of different media substrate, thidiazuron, and the interaction between TDZ and Benzylaminopurine (BAP) on cocoyam culture were tested. Results indicated that cocoyam can be successfully micropropagated in vitro through various procedures. All concentrations tested (5–20 μM BAP and 1–4 μM TDZ) produced more axillary shoots per shoot tip than the control without cytokinins. Greater proliferation rates were obtained through the use of 20 μM BAP and 2 μM TDZ, respectively, 12 weeks from initiation. Shoots produced with BAP were larger and more normal in appearance than those produced with TDZ, which were small, compressed, and stunted. The use of stationary liquid media is recommended for economic reasons.

Comparative Growth Analysis and Acclimatization of Tissue Culture Derived Cocoyam (Xanthosoma sagittifolium L. Schott) Plantlets

The current study was carried out to compare the external leaf structure of tissue culture-derived and conventionally-propagated Cocoyam [ Xanthosoma sagittifolium (L) Schott] plantlets and to develop an efficient acclimatization protocol for these plantlets. Acclimatization studies were carried out during winter and summer to ascertain seasonal influence relative to plant survival upon transfer from in vitro to natural conditions. Results indicated that, cocoyam leaves have few stomates on both abaxial and adaxial surfaces with fewer on the adaxial surface. High levels of epicuticular wax (EW) found in vitro may have contributed to reduced transpiration rates. The reduced amounts of EW on acclimatized plants could be attributed to the rapid cell enlargement in expanding leaves, more rapid than the rate of wax formation. Acclimatization using humidity tent decreased leaf wilting