Qaiser Javed

Photosynthetic response of two okra cultivars under salt stress and re-watering

ABSTRACT Two cultivars of okra (Chinese green and Chinese red) were subjected to salt stress (0%, 6%, 12% and 18%) and equal proportions of NaCl and CaCl2 in Hoagland’s nutrient solution and re-watering. Salt stress significantly reduced growth parameters and photosynthetic attributes of both cultivars. Treatment subjected to 18% salt stress caused 90% redundancy in growth parameters of both cultivars compared to control. Re-watering gave a positive response for plant growth of both cultivars in different levels. Chinese green showed better recovery at 6–0% re-watering level and Chinese red showed 12–6% and 6–0%, due to its salt tolerance nature. Considering re-watering water use efficiency and net photosynthetic rate the optimum values of salt tolerance for Chinese green and Chinese red were 8.3% and 12.02%, respectively. The best re-watering degree found as salt stress level ranged from 12.02% to 6% for Chinese red and 8.3% to 2.3% for Chinese green. This study provided a new method for the determination of irrigation time and quantification in crops.

Estimating tomato water consumption by sap flow measurement in response to water stress under greenhouse conditions

ABSTRACT This research was conducted to determine the water consumption of tomato plants, the effects of water stress on stem sap flow (SF) and its response to climatic factors. SFs in 100% irrigation (T1), 75% (T2) and 50% (T3) of irrigation amount of T1 were monitored using Dynagage sensors. Compared to T1, the difference in SF was observed under deficit irrigation in the same climatic conditions on sunny days although there was no apparent difference between T1 and T2 on cloudy days. Under T1, the correlation and regression relationships between SF and climatic factors were analyzed at daytime (6:00–22:00), morning (6:00–14:00) and afternoon (14:00–22:00). Considering daytime, the order of sensitive indicators to SF was VPD > LI > Ta and LI > VPD > Ta for the Fall-Winter sunny days and Spring-Summer season, respectively. The water uptake over SFs measured for Fall-Winter and Spring-Summer periods were calculated as 168.65 and 229.18 mm, respectively.

Evaluation of irrigation effects using diluted salted water based on electrophysiological properties of plants

ABSTRACT Effect of salt stress and subsequent re-watering on growth and electrophysiological characteristics of Orychophragmus violaceus and Brassica napus was investigated, to construct a model for prediction of an appropriate regime for dilution of saline water. Different concentrations of NaCl, Na2SO4 and blend of both salts were applied with Hoagland solution. Growth and electrophysiology traits were highly restricted at high concentration levels. According to the results, the best dilution point was 5–2.5% for NaCl and Na2SO4 alternatively, whereas it was 10–0.0% for blend of salts. After re-watering, O. violaceus restore better leaf tensity under medium levels, because the effect of NaCl concentration on leaf tensity (XNC–LT) was 1.66%, which was lower in O. violaceus than the effect of XNC–LT (2.88%) in B. napus, followed by the same trend for all treatments. Therefore, the effect of salinity in O. violaceus and B. napus may also be reduced effectively by dilution of saline irrigation.

Re-watering: An effective measure to recover growth and photosynthetic characteristics in salt-stressed Brassica napus L.

CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 76(1) JANUARY-MARCH 2016 7 7 Salinity is one of major environmental problem which is limiting the agricultural production. This research was conducted to evaluate the effect of re-watering on Brassica napus L., and determination of an appropriate regime for dilution of salted water by studying photosynthetic and growth response of B. napus to salt stress and subsequent re-watering. Plants were treated with NaCl (Nc1: 2.5, Nc2: 5, Nc3: 10; g L-1); Na2SO4 (Ns1: 2.5, Ns2: 5, Ns3: 10; g L-1) and mixed salts treatments (M1: Nc1+ Ns3; M2: Nc3+ Ns1; M3: Nc2+ Ns2; g L-1) and 0 as control, followed by re-watering. In salt stress phase, maximum reduction in net photosynthetic rate (PN) was noted 79.54%, 80.72%, 84.54%, and 74.84% for Nc3, Ns3, M1 and M2, respectively, under high concentration levels. To maintain PN, carbonic anhydrase (CA) activity was stimulated and kept water status stable under low (Nc1 and Ns1) to medium concentration levels (Nc2, Ns2 and M3), and the decreases in PN under Nc2, Ns2 and M3 were 48.28%, 55.58% and 58.69%, respectively. However, during rewatering phase, growth and physiological parameters were recovered well due to regulation of CA activity under low to medium concentration levels. Relatively as compare to other stress levels more recovery in PN was found after rewatering under medium concentration levels, which were 44.94%, 53.45% and 63.04%, respectively. Though aimed at consideration of high production in B. napus, the best re-watering time was found to be when plants undergo medium concentration levels. Therefore, this study provides a new method for dilution of saline irrigation based on plant physiology.

Optimization of irrigation and nutrient concentration based on economic returns, substrate salt accumulation and water use efficiency for tomato in greenhouse

ABSTRACT To evaluate the effects of different irrigation and nutrient concentration strategy on growth, yield, water use efficiency (WUE), fruit quality and substrate salt accumulation, tomatoes were grown with five different levels of water (W: 50%, 75%, 100%, 125% and 150%) and nutrient concentrations (N: 0.5, 0.75, 1.0, 1.5 and 2.0 times of Hoagland strength(X)). Fruit quality index was determined by normalization of fruit quality parameters. Deficit irrigation at standard concentration of nutrients reduced yields by 17.43% and 15.52% for T7 (W75%-N1.0x) and 49.54%–51.99% for T8 (W50%-N1.0x) during spring-summer (SS) and fall-winter (FW) seasons, respectively. Contents of total soluble solids (TSS), titrable acidity (TA) and sugar acid ratio (SAR) were all increased in water-deficit treatments. T8 was found to be highest in TSS, TA and SAR except SAR in FW. Over-irrigation with excessive and standard Hoagland nutrient concentration caused non-significant reduction in yield except T6 (W125%-N1.0x) in SS. T2 (W100%-N2.0x) and T4 (W100%-N1.5x) caused more substrate salt accumulation which resulted in significant decrease in yield and WUE. Through economic analysis, over-watering along with excessive nutrients caused profit reductions. Considering water saving, yield and fruit quality through economic analysis, T7 found to be optimal strategy.

The influence of three mangrove species on the distribution of inorganic nitrogen and phosphorus in the Quanzhou Bay estuarine wetland soils

This study aims to investigate the effects of region and three regional dominated mangrove species (Avicennia marina, Aegiceras corniculatum and Kandelia candel) on the distribution of inorganic nitrogen and phosphorus. Measurement of the inorganic nitrogen and phosphorus and enzymatic activities was carried out in soils covered by three mangrove species in the Quanzhou Bay estuarine wetlands, a typical coastal wetland in China. Species with a higher biomass in upstream and midstream absorb more nitrogen from soils, and the retention of the available phosphorus in the soils of different regions causes the regional variation of phosphorus. In areas dominated by A. marina, nitrate nitrogen is lower while available phosphorus is higher. Meanwhile, nitrate nitrogen and available phosphorus are higher in the soils covered by K. candel. Moreover, all three species affect the elemental and enzymic stoichiometry. The mangrove species influences the diversity of the elemental and enzymic stoichiometric relationship through differential microenvironments, which induce the biodiversity of wetland ecosystems. Thus, this study may facilitate a better understanding of the transformation ability of mangroves to nitrogen and phosphorus and will therefore be beneficial for providing a basis for the ecological restoration of estuarine wetlands.