Growth, Carbon Isotope Discrimination and Nitrogen Uptake in Silicon and/or Potassium Fed barley Grown under Two Watering Regimes

The present pot experiment was an attempt to monitor the beneficial effects of silicon (Si) and/or potassium (K) applications on growth and nitrogen uptake in barley plants grown under water (FC1) and non water (FC2) stress conditions using 15N and 13C isotopes. Three fertilizer rates of Si (Si50, Si100 and Si200) and one fertilizer rate of K were used. Dry matter (DM) and N yield (NY) in different plant parts of barley plants was affected by Si and/ or K fertilization as well as by the watering regime level under which the plants have been grown. Solely added K or in combination with adequate rate of Si (Si 100) were more effective in alleviating water stress and producing higher yield in barley plants than solely added Si. However, the latter nutrient was found to be more effective than the former in producing higher spike's N yield. Solely added Si or in combination with K significantly reduced leaves ∆13 C reflecting their bifacial effects on water use efficiency (WUE), particularly in plants grown under well watering regime. This result indicated that Si might be involved in saving water loss through reducing transpiration rate and facilitating water uptake; consequently, increasing WUE. Although the rising of soil humidity generally increased fertilizer nitrogen uptake (Ndff) and its use efficiency (%NUE) in barley plants, applications of K or Si fertilizers to water stressed plants resulted in significant increments of these parameters as compared with the control. Our results highlight that Si or K is not only involved in amelioration of growth of barley plants, but can also improve nitrogen uptake and fertilizer nitrogen use efficiency particularly under water deficit conditions

Growth, Nitrogen Uptake and Carbon Isotope Discrimination in Barley Genotypes Grown under Saline Conditions

The effect of different salinity levels of irrigation water (ECw range 1-12 dS/m) on dry matter yield, nitrogen uptake, fertilizer nitrogen use efficiency (%NUE), stomatal conductance and carbon isotope discrimination (Δ13C‰) in three barley genotypes originating from different geographic areas (Arabi.Abiad, Syria; Pk-30-136, Pakistan and WI-2291, Australia) was investigated in a pot experiment. An increase in salinity resulted in a decrease in Δ13C in all the genotypes. Increasing salinity reduced leaf stomatal conductance which was less pronounced in WI-2291 comparing to other genotypes. At high salinity level, the reduction in Δ13C corresponded to a considerable decrease in the ratio (Ci/Ca) of intercellular (Ci) and atmospheric (Ca) partial pressures of CO2 in all the genotypes indicating that such a decrease was mainly due to the stomatal closure. Moreover, since the reduction in dry matter yield in all the genotypes grown at 12 dS/m did not exceed 50% in comparison with their controls, the photosynthetic apparatus of all studied genotypes seemed to be quit tolerant to salinity. At the moderate salinity level (8 dS/m), the enhancement of leaf dry matter yield in the WI2291 genotype might have been due to positive nutritional effects of the salt as indicated by a significant increase in nitrogen uptake and NUE. Thus, the lower Ci/Ca ratio could result mainly from higher rates of photosynthetic capacity rather than stomatal closure. On the other hand, relationships between dry matter yield or NUE and Δ13C seemed to be depending on plant genotype, plant organ and salinity level. Based on growth, nutritional and Δ13C data, selection of barley genotypes for saline environments was affected by salinity level. Therefore, such a selection must be achieved for each salinity level under which the plants have been grown

Evaluation of Water Stress Tolerance in Advanced Breeding Lines of Durum and Bread Wheat Using 13C

Dry matter (DM), nitrogen uptake (TN) along with water (WUE) and nitrogen (15NUE) use efficiencies in twelve advanced breeding lines (ACSAD) and two varieties (Cham1&6) of durum (DW) and bread (BW) wheat grown under well water (I1) and water stress conditions (I2) were evaluated using 15N and Δ13C. Water stress decreased Δ13C in all studied genotypes. The extent of the decrease in Δ by stress was relatively higher in BW (-1.08‰) than DW (-0.8‰). Cham1 (DW) exhibited the highest DM, TN, NUE, WUE and Δ13C values under I1, indicating its suitability to be grown under irrigated conditions. However, ACSAD1261 (DW) seemed to be a promising line to be grown in semi arid areas due to higher values in the aforementioned criteria under I2. For BW, the highest DM of ACSAD59 under I1 may suggest its suitability to be grown under well irrigated conditions. However, DM of ACSAD883 and 1115 were not affected by watering regime. Additionally, due to the high DM of Cham6 and ACSAD1135 in both watering regimes, and because of the decrease in Δ13C values under stress, it can be suggested that they could be suitable for both irrigated and water stress conditions. Since Δ13C values were affected by wheat genotype and watering regime as a result of the effects on the balance between stomatal conductance and carboxilation, it cannot be relied, completely, upon this technique to select drought tolerant genotypes. Therefore, we suggest that using Δ13C along with agro-physiological parameters are better selection criteria for water stress tolerance in breeding programs than when used separately

Growth and Nitrogen Fixation in Silicon and/or Potassium Fed Chickpeas Grown under Drought and Well Watered Conditions

A pot experiment was conducted to study the effects of silicon (Si) and/or potassium (K) on plant growth, nitrogen uptake and N2-fixation in water stressed (FC1) and well watered (FC2) chickpea plants using 15N and 13C isotopes. Three fertilizer rates of Si (Si50, Si100 and Si200) and one fertilizer rate of K were used. For most of the growth parameters, it was found that Si either alone or in combination with K was more effective to alleviate water stress than K alone. Increasing soil water level from FC1 to FC2 often had a positive impact on values of almost all studied parameters. The Si100K+ (FC1) and Si50K+ (FC2) treatments gave high enough amounts of N2-fixation, higher dry matter production and greater nitrogen yield. The percent increments of total N2-fixed in the above mentioned treatments were 51 and 47% over their controls, respectively. On the other hand, increasing leave’s dry matter in response to the solely added Si (Si50K- and Si100K-) is associated with lower Δ13C under both watering regimes. This may indicate that Si fertilization had a beneficial effect on water use efficiency (WUE). Hence, Δ13C could be an adequate indicator of WUE in response to the exogenous supply of silicon to chickpea plants. Our results highlight that Si is not only involved in amelioration of growth and in maintaining of water status but it can be also considered an important element for the symbiotic performance of chickpea plants. It can be concluded that the synergistic effect of silicon and potassium fertilization with adequate irrigation improves growth and nitrogen fixation in chickpea plants