The influence of nitrogen, phosphate and microbial associations on photosynthesis, respiration and growth in Vicia faba L.

This project represents the development of a comprehensive description of growth in Vicia faba L. Particular attention has been paid to the impact in the tripartite legume-Rhizobium-AMF on the growth. The development of the description was divided into two parts. The first one was made up of (i) different N supply (0, 10, 25, 50, 100, 250 and 500ppm soil N) with normal P supply and (ii) different N supply (0, 10, 25, 50, 100, 250 and 500ppm soil N) with two phosphorus (0.05 and 1.6 mmol P) concentration applied and the Vicia faba seeds were planted pots filled with autoclaved river sand in order to non-producing the nodules just like normal cereal crops. As leaf nitrogen concentration (NL) increased, the quantum yield efficiency (α)，carboxylation efficiency (Ce), photon saturated net photosynthetic rats (PNmax) were converged onto a maximum asymptotic value，the Ci value fell to an asymptotic minimum. A monotonic decline in the steady-state value of Rf occurred with increasing N supply. Specific leaf area (δL) increased with increasing N supply or with increasing NL. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency in terms of Pmax and α. An increase in P was also associated with an increase in Ce and a decrease in Ci.. Under variable daily meteorological conditions, the values for NL, specific leaf phosphorus content (PL), specific leaf phosphorus content (PL), specific leaf area (δL), root mass fraction (Rf), PNmax and α remained constant for a given N supply during the stage of steady-state exponential growth. This study tests the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for Pmax, Ce, and the lower limit for Ci in response to increasing N. The short-term photosynthetic responses to the increasing concentrations of CO2 were observed to be co-limited by both N and P supply. These findings support the proposal that the N:P supply ratio controls the plant photosynthetic capacity in response to elevated CO2 concentrations. Also, the short-term photosynthetic responses to the increasing concentrations of CO2 were observed to be co-limited by both N and P supply. The second part is tripartite symbiosis experiment with the concentration of nitrate-N for (a) the low N (LN, 10ppm N) and the high N treatments (HN, 250ppm N) without any microbial symbiotic associations;; (b) two different N supply rates plus AMF association, LNM and HNM; (c) two different N supply rates plus Rhizobium association, LNR and HNR; and (d) two different N supply rates plus both AMF and Rhizobium symbiotic associations: LNMR and HNMR. All treatments received a low level of phosphorus supply with 0.05mg P L-1 (1.61 mM NaH2PO4 ). AMF promoted biomass production and photosynthetic rates by increasing the ratio of P to N accumulation. An increase in P was consistently associated with an increase in N accumulation and N productivity, expressed in terms of biomass and leaf area. Photosynthetic N use efficiency, irrespective of the inorganic source of N (e.g. NO3‾ or N2 ), was enhanced by increased P supply due to AMF. The presence of Rhizobium resulted in a significant decline in AMF colonization levels irrespective of N supply. Without Rhizobium, AMF colonization levels were higher in low N treatments. Presence or absence of AMF did not have a significant effect on nodule mass but high N with or without AMF led to a significant decline in nodule biomass. Plants with the Rhizobium and AMF symbiotic associations had higher photosynthetic rates per unit leaf area and increased plant productivity. The plants colonized with both microbial symbionts had significantly higher total biomasses, leaf areas, the whole plant photosynthesis and respiration rates than plants with only one or no microbial symbionts. Similarly, plants with both microbial symbionts also had significantly higher growth yield (Yg ) values than all the other treatments. Maintenance respiration rates were also highest in plants with two microbial symbionts. In low N plants colonized by both microbial symbionts there was evidence of compensatory increases in the photosynthetic rates in response to the carbon sink demands of the microbial symbionts. It was shown that the plant potential photosynthetic capacity exceeds the carbon demand of the Rhizobium–AMF symbiotic associations

Short-term physiological responses to drought stress in seedling of tropical and temperate maize (Zea mays L.) cultivars

Understanding of the response of tropical and temperate maize (Zea mays L.) to drought is the first step for tolerant temperate maize improvement. Eight maize hybrids were used to investigate physiology responses under drought stress, four of them were tropical maize and the others were temperate maize. Results showed that there were different drought tolerances but similar trends in both tropical maize and temperate maize. Gas exchange parameters revealed different strategies of maize under the stress. In our study, most of the temperate hybrids maintained open stomata to keep a higher photosynthesis rate at the beginning of stress, while the other hybrids decreased stomatal conductance. Compared to temperate maize, the tropical maize had higher antioxidase activity and greater physiological parameter variation among hybrids. KS5731 and ZD309 had stronger drought resistance among tropical and temperate maize hybrids separately. Tolerant hybrids maintained active photosynthesis, have higher osmotic adjustment ability and antioxidase activities but lower malonaldehyde content than the sensitive ones. Our results led to a better understanding of the physiological responses of tropical and temperate maize plants to drought stress and may provide an insight of breeding for drought resistance in maize

Salt-tolerance identification and quality evaluation of Abelmoschus manihot (L.) Medik

Abelmoschus manihot (L.) Medik. is a medicinal and edible plant. To evaluate its suitability for cultivation on the coastal saline-alkali land in northern China for high quality functional products, salt-tolerance identification and flavonoid contents were evaluated under saline treatments. Results showed that the salt-tolerance threshold of A. manihot ranged from 4.1 to 6.9 g L−1; however, low soil salt content (<3 g L−1) had the best growth and accumulation of total flavonoids. Sixteen kinds of common functional components such as hyperoside, rutoside, and quercetin were found. Of these components, the four (myricetin-3-0-glucoside, rutoside, quercetin-3′-0-glucoside, and gossypetin-8-0-β-d-glucuronic acid) with the highest content were chosen as the quality evaluation indexes. High levels of quality and yield occurred at a soil salt content of 3 g L−1. Our results suggested that soil salt content should not exceed 3 g L−1 in field cultivation for high quality and high yield of A. manihot.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author