Effects of droplet size and spray interval on root-to-shoot ratio,photosynthesis efficiency,and nutritional quality of aeroponically grown butter head lettuce

The proper selection of the atomizer(droplet size)and nutrient solution spray interval is one of the most important factors to be investigated in aeroponics system for sustainable agriculture.The aim of this study was to research the effects of four aeroponics atomizing nozzles(one air-assisted;A_(1),two air-less;A_(2) and A_(3),and one ultrasonic fogger;A_(4))with droplet sizes of 11.24μm,26.35μm,17.38μm,and 4.89μm,respectively,four spray intervals(15 min(I_(1)),30 min(I_(2)),45 min(I_(3))and 60 min(I_(4)))at a 5 min of constant spray time by atomizing the Hoagland’s nutrient solution on growth,root-to-shoot ratio,photosynthesis characteristics,pigments,and nutritional quality of the aeroponically grown lettuce.The experimental results demonstrated that in A_(1) atomizer and I_(2) interval,the growth,photosynthesis efficiency,chlorophyll,carotenoids,and nutritional values of the lettuce were significantly higher compared to that grown in A_(2) and A_(3) atomizers at all spray intervals.The shoot developments were more constrained than root,prominent to the alteration of root-to-shoot ratio(fresh and dry)in the influence of different droplet sizes and spray intervals.Moreover,the plants did not grow well in A_(4) atomizer associated with proposed spray intervals.The results disclosed that there was an obvious interaction between droplet sizes(atomizers)and spray intervals for growth,the ratio of root to shoot,photosynthesis efficiency,pigments,and nutritional quality of the aeroponically grown lettuce.This research study increases the awareness of the proper droplet size(atomizer)and the regulation of nutrient solution spray interval for leafy vegetables grown in an aeroponics system.

Varietal difference in the correlation between leaf nitrogen content and photosynthesis in rice(Oryza sativa L.) plants is related to specific leaf weight

Increasing leaf photosynthesis per area（A） is of great importance to achieve yield further improvement. The aim of this study was to exploit varietal difference in A and its correlation with specific leaf weight（SLW）. Twelve rice cultivars, including 6 indica and 6 japonica varieties, were pot-grown under two N treatments, low N（LN） and sufficient N（SN）. Leaf photosynthesis and related parameters were measured at tillering stage. Compared with LN treatment, A, stomatal conductance（g_s）, mesophyll conductance（g_m）, leaf N content（N_（area））, and chlorophyll content were significantly improved under SN treatment, while SLW and photosynthetic N use efficiency（PNUE） were generally decreased. Varietal difference in A was positively related to both g_s and g_m, but not related to N_（area）. This resulted in a low PNUE in high N_（area） leaves. Varietal difference in PNUE was generally negatively related to SLW. Response of PNUE to N supply varied among different rice cultivars, and interestingly, the decrease in PNUE under SN was negatively related to the decrease in SLW. With a higher N_（area）, japonica rice cultivars did not show a higher A than indica rice cultivars because of possession of high-SLW leaves. Therefore, varietal difference in A was not related to N_（area）, and SLW can substantially interfere with the correlation between A and N_（area）. These findings may provide useful information for rice breeders to maximize A and PNUE, rather than over reliance on N_（area） as an indicator of photosynthetic performance.

Effect of Nitrogen Fertilization on Growth and Photosynthetic Nitrogen use Efficiency in Tobacco （Nicotiana tabacum L.）

Soil pot experiments were conducted in a greenhouse to examine the effects of different nitrogen （N） supply （low, 0.15 g N/kg; middle, 0.3 g N/kg; and high, 0.6 g N/kg dry soil） on the growth, photosynthetic characteristics and photosynthetic nitrogen use efficiency （PNUE） of tobacco seedlings （Nicotiana tabacum L. Yunyan 87）. The results showed middle and high N significantly enhanced seedling growth including plant stem and leaf dry weight comparing with low N. High N supply could lead to a dramatic increase in the photosynthetic capacity of tobacco seedlings under low N conditions. There were significant differences in leaf N content between nitrogen treatments. About a 76% increase in leafN content in plants fed by high N resulted in about 43% increase in Rubisco content and 27% in net photosynthetic rate. The non-corresponding increases in photosynthetic rate in tobacco seedlings fed by high N relative to low N resulted from Rubisco activity and/or carboxylation efficiency （CE）. These results indicated that tobacco seedlings under high N application can maintain high net photosynthetic rate （Pn） but lower PNUE, will finally result in a decline in N use efficiency.

Effects of soil water and nitrogen availability on photosynthesis and water use efficiency of Robinia pseudoacacia seedlings

The efficient use of water and nitrogen （N） to promote growth and increase yield of fruit trees and crops is well studied.However,little is known about their effects on woody plants growing in arid and semiarid areas with limited water and N availability.To examine the effects of water and N supply on early growth and water use efficiency （WUE） of trees on dry soils,one-year-old seedlings of Robinia pseudoacacia were exposed to three soil water contents （non-limiting,medium drought,and severe drought） as well as to low and high N levels,for four months.Photosynthetic parameters,leaf instantaneous WUE （WUEi） and whole tree WUE （WUEb） were determined.Results showed that,independent of N levels,increasing soil water content enhanced the tree transpiration rate （Tr）,stomatal conductance （Gs）,intercellular CO2 concentration （Ci）,maximum net assimilation rate （Amax）,apparent quantum yield （AQY）,the range of photosynthetically active radiation （PAR） due to both reduced light compensation point and enhanced light saturation point,and dark respiration rate （Rd）,resulting in a higher net photosynthetic rate （Pn） and a significantly increased whole tree biomass.Consequently,WUEi and WUEb were reduced at low N,whereas WUE i was enhanced at high N levels.Irrespective of soil water availability,N supply enhanced Pn in association with an increase of Gs and Ci and a decrease of the stomatal limitation value （Ls）,while Tr remained unchanged.Biomass and WUEi increased under non-limiting water conditions and medium drought,as well as WUEb under all water conditions;but under severe drought,WUEi and biomass were not affected by N application.In conclusion,increasing soil water availability improves photosynthetic capacity and biomass accumulation under low and high N levels,but its effects on WUE vary with soil N levels.N supply increased Pn and WUE,but under severe drought,N supply did not enhance WUEi and biomass.

Iranian Grapevine Rootstocks and Hormonal Effects on Graft Union, Growth and Antioxidant Responses of Asgari Seedless Grape

This research investigated physiological and biochemical changes at rootstock–scion union of graft combinations between Iranian rootstocks and Asgari scion in response to NAA and BAP application.Grafting cuts of scion and rootstock were dipped into NAA(0,200 and 400 mg·L^(-1))and BAP(0,250 and 500 mg·L^(-1))solutions for 30 min,immediately after the cuttings were grafted using the wedge grafting technique.The highest successful grafting rate(82%)was recorded with Asgari–Asgari combination treated with 200 mg·L^(-1) NAA+500 mg·L^(-1) BAP.Treating the graft cut–surfaces with 200 mg·L^(-1) NAA+500 mg·L^(-1) BAP caused the lowest H 2 O 2 and MDA contents.Among all the graft combinations,the highest increase in chlorophyll content with a high photosynthesis efficiency occurred in Asgari–Shahani when treated with 200 mg·L^(-1)NAA+500 mg·L^(-1) BAP.The graft union formation in the presence of 200 mg·L^(-1) NAA+500 mg·L^(-1) BAP application enhanced CAT and POX activities.In conclusion,treatment of graft zone with 200 mg·L^(-1) NAA+500 mg·L^(-1) BAP enhanced antioxidant activities and reduced lipid peroxidation in scion leaves.However,several grapevine rootstocks tested in our research were also impacting the scion performance.

A Mathematical Model of the Photosynthetic Carbon Metabolism Has Multiple Steady States Under the Same Parameter Conditions

This paper analyzes a mathematical model of the photosynthetic carbon metabolism, which incorporates not only the Calvin-Benson cycle, but also another two important metabolic pathways： starch synthesis and photorespiratory pathway. Theoretically, the paper shows the existence of steady states, stability and instability of the steady states, the effects of CO2 concentration on steady states. Especially, a critical point is found, the system has only one steady state with C02 concentration in the left neighborhood of the critical point, but has two with C02 concentration in the right neighborhood. In addition, the paper also explores the influence of C02 concentration on the efficiency of photosynthesis. These theoretical results not only provide insight to the kinetic behaviors of the photosynthetic carbon metabolism, but also can be used to help improving the efficiency of photosynthesis in plants.