Xunzhong Zhang

Response of photosynthesis and superoxide dismutase to silica applied to creeping bentgrass grown under two fertility levels

Abstract Responses of photosynthesis, Superoxide dismutase activity, and disease tolerance of creeping bentgrass (Agrostis palustris Huds. A.) to soluble potassium silicate (20.8% SiO2) treatments was investigated under two fertilization regimes during 1997 and 1998. Potassium silicate was applied twice a month at 603 and 1205 mL 100 m−2 under high or low fertilization regimes in the field, sampled from which were subjected to low soil moisture in a greenhouse environment. Foliar application of silicate stimulated antioxidant superoxide dismutase (SOD) activity in the bentgarss, especially under the high fertilization regime. Silicate increased photosynthetic capacity (PC) and chlorophyll content when applied at 603 mL 100 m−2. Dollarspot disease incidence was significantly reduced with silicate treatment regardless of fertilization regime. Silicate did not significantly impact clipping weight. Under low soil moisture (‐0.05 MPa), silicate also enhanced SOD activity, PC, and chlorophyll content as well as...

Enzymatic antioxidant responses to biostimulants in maize and soybean subjected to drought

Water stress is one of the most important environmental factors inducing physiological changes in plants, such as decrease in the water potential of the cells, the stomatal closure; and the development of oxidative processes mediated by reactive oxygen species (ROS). Antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) are efficient scavengers of ROS. The aim of this research was to examine how the application of biostimulant based on humic substances and aminoacids may affect activity levels of SOD, CAT, and APX of maize and soybean plants under well-watered or drought stress conditions. Pots (4.5 L) were filled with a Typic Hapludult soil where the biostimulants doses were applied. It was taken leaf samples in order to analyze SOD, CAT, and APX activities in plants. SOD and APX activity levels were increased by application of biostimulant 1 in maize subjected to stress. Catalase activity was not enhanced in plants by using the biostimulants. The composition of the biostimulants was not able to enhance stress tolerance in maize and soybean plants subjected to water stress.

Assessment of drought tolerance of 49 switchgrass (Panicum virgatum) genotypes using physiological and morphological parameters.

BackgroundSwitchgrass (Panicum virgatum L.) is a warm-season C4 grass that is a target lignocellulosic biofuel species. In many regions, drought stress is one of the major limiting factors for switchgrass growth. The objective of this study was to evaluate the drought tolerance of 49 switchgrass genotypes. The relative drought stress tolerance was determined based on a set of parameters including plant height, leaf length, leaf width, leaf sheath length, leaf relative water content (RWC), electrolyte leakage (EL), photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), and water use efficiency (WUE).ResultsSRAP marker analysis determined that the selected 49 switchgrass genotypes represent a diverse genetic pool of switchgrass germplasm. Principal component analysis (PCA) and drought stress indexes (DSI) of each physiological parameter showed significant differences in the drought stress tolerance among the 49 genotypes. Heatmap and PCA data revealed that physiological parameters are more sensitive than morphological parameters in distinguishing the control and drought treatments. Metabolite profiling data found that under drought stress, the five best drought-tolerant genotypes tended to have higher levels of abscisic acid (ABA), spermine, trehalose, and fructose in comparison to the five most drought-sensitive genotypes.ConclusionBased on PCA ranking value, the genotypes TEM-SEC, TEM-LoDorm, BN-13645-64, Alamo, BN-10860-61, BN-12323-69, TEM-SLC, T-2086, T-2100, T-2101, Caddo, and Blackwell-1 had relatively higher ranking values, indicating that they are more tolerant to drought. In contrast, the genotypes Grif Nebraska 28, Grenville-2, Central Iowa Germplasm, Cave-in-Rock, Dacotah, and Nebraska 28 were found to be relatively sensitive to drought stress. By analyzing physiological response parameters and different metabolic profiles, the methods utilized in this study identified drought-tolerant and drought-sensitive switchgrass genotypes. These results provide a foundation for future research directed at understanding the molecular mechanisms underlying switchgrass tolerance to drought.

Analysis of salt-induced physiological and proline changes in 46 switchgrass (Panicum virgatum) lines indicates multiple response modes

Switchgrass (Panicum virgatum) is targeted as a biofuel feedstock species that may be grown on marginal lands including those with saline soils. Our study investigated salt stress responses in 46 switchgrass lines from the lowland and upland ecotypes by assessing physiological phenotypes and proline concentrations. Lowland switchgrass lines demonstrated less severe responses to salt stress than most upland switchgrass lines, but a number of upland lines performed as well as lowland individuals. Photosynthetic rate (Pn), the most important physiological trait measured, was reduced by salt treatment in all lines. Tolerant lines showed ∼50% reduction in Pn under salt stress, and sensitive lines exhibited ∼90% reduction in Pn after salt stress. Proline analysis showed the largest amount of variation under salt stress with some lines exhibiting minor increases in proline, but some salt-sensitive lines demonstrated more than 5000-fold increase in proline concentration in response to salt treatment. Clustering of salt-stress phenotypic responses revealed five groups of switchgrass. Lowland lines were present in two of the phenotypic clusters, but upland lines were found in all five of the phenotypic clusters. These results suggest that there are multiple modes of salt response in switchgrass including two distinct modes of salt tolerance.

Soil carbon and physiological responses of corn and soybean to organic amendments.

Field research was conducted to assess the effects of organic and inorganic soil amendments on soil humified carbon content and plant physiological properties. Long term applications of various types and rates of compost, poultry litter and inorganic fertilizer were assessed for their effects on corn [Zea mays (L.) Pioneer 31G20] and soybean [Glycine max (l.) Delta Pine 4933RR] grown in a Virginia (United States) Piedmont soil in 2004 and 2005. Treatment differences in leaf antioxidant activity were only observed in the corn plots. Corn fertilized with amendments supplying the crops nitrogen needs, regardless of the source, had greater leaf nitrogen (+29%), chlorophyll (+33%), and protein contents (+37%), lower superoxide dismutase (−29%) and ascorbate peroxidase (−17%) activities, and lower malondialdehyde (−33%) contents than the control and low nitrogen treatments. Yield was strongly related to midseason leaf nitrogen contents (R2=0.87, p<0.0001) and not with soil humified carbon (R =0.02, p=0.0543). Soybean grown in the organically amended soil had higher yields (9-21% increase), protein contents (4-9% increase) and seed weights (5-14% increase) than the inorganically fertilized and unfertilized treatments. Improvements in soybean yield and seed quality were due to organic amendment benefits other than plant available water or nutrient supply.

EFFECTS OF NITRATE AND CYTOKININ ON CREEPING BENTGRASS UNDER SUPRAOPTIMAL TEMPERATURES

Heat stress reduces creeping bentgrass performance in temperate to sub-tropical climates. The research objective was to characterize effects of nitrogen (N) and cytokinin (CK) on creeping bentgrass under heat stress. In a 38°C/28°C chamber, grasses were treated with two nitrogen (2.5 and 7.5 kg N ha−1) and three CK rates (0, 10 and 100 μM) biweekly. Grass grown at high N had better turf quality, higher photochemical efficiency (Fv/Fm), normalized difference vegetation index (NDVI), and chlorophyll concentration at d15 and 28 than low N. CK increased NDVI at d15, with Fv/Fm of the CK100 treatment being 18% higher than that of CK0 at d28. Under high N with 100 μM CK, root trans-zeatin riboside (tZR) and isopentenyl adenosine (iPA) were 160% and 97% higher than under low N without CK, respectively. These results demonstrate positive impacts of N and CK on creeping bentgrass under heat, with N playing a dominant role.

Determination of Fatty Acid Composition of Turfgrass by High‐Performance Liquid Chromatography

Abstract The fatty acid composition of warm‐season turfgrasses is physiologically regulated by environmental changes, particularly temperature. Species or cultivars, which have increased degree of unsaturation, usually have a greater freeze resistance. Quantifying fatty acid composition not only can help understand the freeze‐resistant mechanism of warm‐season turfgrasses but also in practice develop a management strategy for better turf. A high‐performance liquid chromatography (HPLC) method was developed for this purpose. The method is based on the bromophenacyl reaction of fatty acids and separation on a C8 column with gradient elution. Information on limit of identification, linearity of quantification, response factor, and derivatization conditions is presented and discussed. The method presented is simple to apply and provides an alternative to the traditional gas chromatography (GC) method. The results of fatty acid composition from a field freezing‐resistance experiment are discussed.

Application of the End-Of-Season Stalk Nitrate Test for High-Yield Maize Production System in Northwestern China

ABSTRACT Excessive nitrogen application has caused serious environmental pollution under high-yield maize system in China. Our objective was to evaluate critical stalk nitrate (NO3−) levels that support high yield (>13 Mgha−1), but are not in excess. Optimal stalk NO3− concentration was determined by conducting seven nitrogen levels experiments in two high yield maize regions: Dongyang County (DY) and Wenshui County (WS). Optimal stalk NO3− concentration category range to obtain maximum yield in DY (sandy loam, higher accumulated temperature and solar radiation compared with WS) was 0.44–1.19, which similar to the criteria of US (0.70–2.0 g kg−1). While for WS (loam soil, lower accumulated temperature and solar radiation compared with DY), optimal stalk NO3− concentration category range to obtain maximum yield was 1.95–4.15, greatly higher than the US criteria. These results suggested thatit is necessary to establish matching optimal stalk NO3− category ranges for different ecological regions in China.