Comparative Morphological Studies of Microspore Derived and F2 Plants Obtained from an Interspecific Rice Hybrid Oryza sativa Linn. ×O. rufipogon Griff.)*

Anther culture of an interspecific rice hybrid from a cross of Oryza sativa× O. rufipogon was attempted. Of the 117 regenerated pollen clones, 56 could survive to maturity. A majority of these were either haploids or doubled haploids and very few turned out to be chromosomal variants. Comparative study of doubled haploids and the seed derived F₂ plants indicate the distinct advantages of anther culture techniques. (1) Androgenic plants, though few in number, showed greater ariation for all the traits with the exception of ear bearing tillers. (2) Predominance of recombinants with wild traits was observed in F₂ segregation. (3) It was possible to recover indica type recombinants among the anther-derived plants with one or two traits introgressed from O. rufipogon. These results suggest the feasibility and utility of anther culture in distant hybridization for incorporation of alien variation into cultivated rice.     

Competition between 2x and x pollen in styles of Solanum tuberosum determined by a quick in vivo method

Summary Pollen competition in vivo was studied by placing two pollen samples on one stigma and comparing the length of the tubes under a U.V. microscope. Comparisons involving pollen of Solanum tuberosum and S. phureja showed that 2x pollen grew faster than x pollen, both in 2x and x styles. Consequences for induction of dihaploids in S. tuberosum are discussed.     

细胞水平高赖氨酸小麦选择的研究

Soil carbon dioxide (CO₂) flux is an integrative measure of ecosystem functioning representing both biotic and physical controls over carbon (C) balance. In the McMurdo Dry Valleys of Antarctica, soil CO₂ fluxes (approximately −0.1-0.15 μmol m⁻² s⁻¹) are generally low, and negative fluxes (uptake of CO₂) are sometimes observed. A combination of biological respiration and physical mechanisms, driven by temperature and mediated by soil moisture and mineralogy, determine CO₂ flux and, therefore, soil organic C balance. The physical factors important to CO₂ flux are being altered with climate variability in many ecosystems including arid forms such as the Antarctic terrestrial ecosystems, making it critical to understand how climate factors interact with biotic drivers to control soil CO₂ fluxes and C balances. We measured soil CO₂ flux in experimental field manipulations, microcosm incubations and across natural environmental gradients of soil moisture to estimate biotic soil respiration and abiotic sources of CO₂ flux in soils over a range of physical and biotic conditions. We determined that temperature fluctuations were the most important factor influencing diel variation in CO₂ flux. Variation within these diel CO₂ cycles was explained by differences in soil moisture. Increased temperature (as opposed to temperature fluctuations) had little or no effect on CO₂ flux if moisture was not also increased. We conclude that CO₂ flux in dry valley soils is driven primarily by physical factors such as soil temperature and moisture, indicating that future climate change may alter the dry valley soil C cycle. Negative CO₂ fluxes in arid soils have recently been identified as potential net C sinks. We demonstrate the potential for arid polar soils to take up CO₂, driven largely by abiotic factors associated with climate change. The low levels of CO₂ absorption into soils we observed may not constitute a significant sink of atmospheric CO₂, but will influence the interpretation of CO₂ flux for the dry valley soil C cycle and possibly other arid environments where biotic controls over C cycling are secondary to physical drivers.     

The magnitude and variability of soil-surface CO2 efflux increase with mean annual temperature in Hawaiian tropical montane wet forests

Soil-surface CO₂ efflux (F_S; ‘soil respiration’) accounts for ≥50% of the CO₂ released annually by the terrestrial biosphere to the atmosphere, and the magnitude and variability of this flux are likely to be sensitive to climate change. We measured F_S in nine permanent plots along a 5.2 °C mean annual temperature (MAT) gradient (13-18.2 °C) in Hawaiian tropical montane wet forests where substrate type and age, soil type, soil water balance, disturbance history, and canopy vegetation are constant. The objectives of this study were to quantify how the (i) magnitude, (ii) plot-level spatial variability, and (iii) plot-level diel variability of F_S vary with MAT. To address the first objective, annual F_S budgets were constructed by measuring instantaneous F_S monthly in all plots for one year. For the second objective, we compared plot-level mean instantaneous F_S in six plots derived from 8 versus 16 measurements, and conducted a power analysis to determine adequate sample sizes. For the third objective, we measured instantaneous F_S hourly for 24 h in three plots (cool, intermediate and warm MATs). The magnitude of annual F_S and the spatial variability of plot-level instantaneous F_S increased linearly with MAT, likely due to concomitant increases in stand productivity. Mean plot-level instantaneous F_S from 8 versus 16 measurements per plot yielded statistically similar patterns. The number of samples required to estimate plot-level instantaneous F_S within 10% and 20% of the actual mean increased with MAT. In two of three plots examined, diel variability in instantaneous F_S was significantly correlated with soil temperature but minimal diel fluctuations in soil temperature (<0.6 °C) resulted in minimal diel variability in F_S. Our results suggest that as MAT increases in tropical montane wet forests, F_S will increase and become more spatially variable if ecosystem characteristics and functioning undergo concurrent changes as measured along this gradient. However, diel variation in F_S will remain a minor component of overall plot-level variation.     

Short‐term response of the Ca cycle of a montane forest in Ecuador to low experimental CaCl2 additions

The tropical montane forests of the E Andean cordillera in Ecuador receive episodic Sahara‐dust inputs particularly increasing Ca deposition. We added CaCl₂ to isolate the effect of Ca deposition by Sahara dust to tropical montane forest from the simultaneously occurring pH effect. We examined components of the Ca cycle at four control plots and four plots with added Ca (2 × 5 kg ha^–1 Ca annually as CaCl₂) in a random arrangement. Between August 2007 and December 2009 (four applications of Ca), we determined Ca concentrations and fluxes in litter leachate, mineral soil solution (0.15 and 0.30 m depths), throughfall, and fine litterfall and Al concentrations and speciation in soil solutions. After 1 y of Ca addition, we assessed fine‐root biomass, leaf area, and tree growth. Only < 3% of the applied Ca leached below the acid organic layer (pH 3.5–4.8). The added CaCl₂ did not change electrical conductivity in the root zone after 2 y. In the second year of fertilization, Ca retention in the canopy of the Ca treatment tended to decrease relative to the control. After 2 y, 21% of the applied Ca was recycled to soil with throughfall and litterfall. One year after the first Ca addition, fine‐root biomass had decreased significantly. Decreasing fine‐root biomass might be attributed to a direct or an indirect beneficial effect of Ca on the soil decomposer community. Because of almost complete association of Al with dissolved organic matter and high free Ca²⁺ : Al³⁺ activity ratios in solution of all plots, Al toxicity was unlikely. We conclude that the added Ca was retained in the system and had beneficial effects on some plants.     

Influence of temperature on nutrient concentration and tetany potential of hardinggrass and tall fescue

Grass tetany (Hypomagnesemia) potential of TAM Wintergreen Hardinggrass and 16 tall fescue lines and varieties was estimated by determining the K, Ca and Mg concentrations in the herbage and the ratio of K/(Ca + Mg) (milliequivalent basis). Data were obtained at four dates during a two‐year period to determine the environmental conditions under which selections should be made to achieve the greatest progress in decreasing the tetany potential of tall fescue and to determine if either of the grasses have high tetany potential in the North Texas area. Hardinggrass had a greater potential to produce grass tetany than tall fescue when grown on the Northern Blackland Prairie of Texas. There were significant differences in K, Ca and Mg concentrations and K/(Ca + Mg) ratio among dates and tall fescue lines. The average temperature for the 30 days before harvest was related to the mineral content and to the K/(Ca + Mg) ratio in all varieties. The K(Ca + Mg) ratio was highest at approximately 18°C but the Mg content fell below the 0.18% required for lactating beef cows when the average temperature for the 30 days before harvest was 22.4°C. Progress could be made in breeding for low grass tetany proneness but selections should be made over a wide range of temperatures considering both the Mg content and ratio of K/(Ca + Mg).     

Influence of thigmic stress or chlormequat chloride on tomato morphology and elemental uptake

Root dry weight and leaf number were not affected by thigmic stress or chlormequat chloride. Shoot dry weight, shoot:root dry weight ratio, shoot height, leaf area, and root surface area were decreased by both thigmic stress and chlormequat chloride. However, root length was decreased and root radius increased only by chlormequat chloride. Total element uptake was decreased by both thigmic stress and chlormequat chloride. In the shoot and root, N was not affected, P was increased in the shoots, K decreased in the shoots but increased in the roots, and Mg decreased in the roots as a result of thigmic stress and chlormequat chloride. Whereas, Ca was decreased in the roots and Mg increased in the shoots by chlormequat chloride. The uptake of N, P, Ca, or Mg was not affected by thigmic stress or chlormequat chloride, however, K uptake per root surface area decreased. Thigmic stress decreased K in both the upper and lower stem but did not affect leaf concentration of K. However, chlormequat chloride decreased K in both the stem and leaves. Thigmic stress because of the role of K in cell elongation. Chemical name used: (2‐chloroethyl)trimethyl‐ammonium chloride (chlormequat chloride).