Effects of Nitrogen Application on Photosynthetic Characteristics and Nitrogen Use Efficiency in Wheat after Rice

In the present study, appropriate nitrogen(N) application mode in Jianghan Plain was explored by investigating the effects of different N applications on the photosynthetic characteristics of flag leaves and nitrogen use efficiency(NUE) in a wheat cultivar Zhengmai 9023. Nitrogen was top-dressed before sowing, before winter, and during the jointing stage, at different ratios:1:1:0(N1), 1:0:1(N2), 2:1:1(N3), 1:1:1(N4), and 0:0:1(N5), under the same amount of total N(180 kg/hm^2) during the growing season. No nitrogen fertilizer was used in the control(N0). Results showed that the SPAD values and photosynthetic rate(Pn) of different treatments in flag leaves increased initially and then decreased around the anthesis stage. The two indices in N1 and N5 treatments decreased rapidly after flowering, whereas those in N2, N3, and N4 treatments maintained at high levels for a long period after anthesis. Thus, reasonable nitrogen application could retard the decline of SPAD and Pn after anthesis.N4 and N1 treatments showed large dry matter accumulation. In decreasing order of crop yield, the treatments were: N4 >N1 >N3 >N5 >N2 >N0. The effective panicle number and grain number per spike of N2 were significantly lower than those of other treatments, and there was no significant difference among other treatments. No significant correlation was found between nitrogen application and 1 000-grain weight in this experiment. The nitrogen accumulation, agronomic efficiency of nitrogen fertilizer,nitrogen uptake and use efficiency of above-ground parts, nitrogen uptake and use efficiency of grain of N4 treatment were higher than those of other treatments, but the nitrogen harvest index of N4 was at a low level. In summary, N4 treatment is the most suitable nitrogen application mode in wheat after rice.

Adjusting Nitrogen Application in Accordance with Soil Water Availability Enhances Yield and Water Use by Regulating Physiological Traits of Maize under Drip Fertigation

Knowledge of the interactive effects of water and nitrogen(N)on physio-chemical traits of maize(Zea mays L.)helps to optimize water and N management and improve productivity.A split-plot experiment was conducted with three soil water conditions(severe drought,moderate drought,and fully water supply referring to 45%-55%,65%-75%,and 85%-95%field capacity,respectively)and four N application rates(N0,N150,N240,and N330 referring to 0,150,240,330 kg N ha^(-1)respectively)under drip fertigation in 2014 and 2015 in the Huang-Huai-Hai Plain of China.The results indicated that drought stress inhibited physiological activity of plants(leaf relative water content,root bleeding sap,and net photosynthetic rate),resulting in low dry matter accumulation after silking,yield,and N uptake,whereas increased WUE and NUE.N application rates over than 150 kg ha^(-1)aggravated the inhibition of physiological activity under severe drought condition,while it was offset under moderate drought condition.High N application rates(N330)still revealed negative effects under moderate drought condition,as it did not consistently enhance plant physiological activity and significantly reduced N uptake as compared to the N240 treatment.With fully water supply,increasing N application rates synergistically enhanced physiological activity,promoted dry matter accumulation after silking,and increased yield,WUE,and N uptake.Although the N240 treatment reduced yield by 5.4%in average,it saved 27.3%N under full water supply condition as compared with N330 treatment.The results indicated that N regulated growth of maize in aspects of physiological traits,dry matter accumulation,and yield as well as water and N use was depended on soil water status.The appropriate N application rates for maize production was 150 kg ha^(-1)under moderate drought or 240 kg ha^(-1)under fully water supply under drip fertigation,and high N supply(>150 kg ha^(-1))should be avoided under severe drought condition.

Growth traits and nitrogen assimilation-associated physiological parameters of wheat(Triticum aestivum L.) under low and high N conditions

In this study, 14 wheat cultivars with contrasting yield and N use efficiency （NUE） were used to investigate the agronomic and NUE-related traits, and the N assimilation-associated enzyme activities under low and high N conditions. Under deficient-N, the cultivars with high N uptake efficiency （UpE） and high N utilization efficiency （UtE） exhibited higher plant biomass, yields, and N contents than those with medium and low NUEs. The high UpE cultivars accumulated more N than other NUE type cultivars. Under sufficient-N, the tested cultivars showed similar patterns in biomass, yield, and N content to those under deficient-N, but the varietal variations in above traits were smaller. In addition, the high UpE cultivars displayed much more of root biomass and larger of root length, surface area, and volume than other NUE type cultivars, indicating that the root morphological traits under N deprivation are closely associated with the plant biomass through its improvement of the N acquisition. The high UtE cultivars showed higher activities of nitrate reductase （NR）, nitrite reductase （NIR）, and gluta- mine synthetase （GS） at stages of seediling, heading and filling than other NUE type cultivars under both low and high N conditions. Moreover, the high UpE and UtE cultivars also displayed higher photosynthetic rate under deficient-N than the medium and low NUE cultivars. Together, our results indicated that the tested wheat cultivars possess dramatically genetic variations in biomass, yield, and NUE. The root morphological traits and the N assimilation enzymatic acitivities play critical roles in regulating N accumulation and internal N translocation under the N-starvation stress, respectively. They can be used as morphological and biochemical references for evaluation of UpE and UtE in wheat.

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.

热带水稻光合特性及氮素光合效率的差异研究

在国际水稻研究所(IRRI)农场试验条件下,选用6个不同的热带水稻材料,其中包括2个常规籼稻、2个杂交籼稻和2个新株型稻(NPT),研究氮肥农学利用率(AE)和氮素光合效率(PNUE)及其相关叶片参数的基因型差异,并探讨了它们之间的关系。结果表明,新株型稻的净光合速率(Pn)大于常规籼稻,杂交籼稻居中。各基因型间的气孔导度(Gs)、胞间CO2浓度(Ci)、蒸腾速率(Tr)和Ci/Gs的差异趋势不同。不同基因型叶片的氮浓度(N%)和比叶重(SLW)存在一定的差异。常规籼稻的单位叶绿素的净光合速率(Pn/Chl)较NPT低,杂交籼稻为中间类型;叶片净光合速率和单位面积含氮量(Na)之间存在显著的正相关;本研究所选用的热带杂交籼稻的PFP(氮肥偏生产力)和AE比新株型稻和常规籼稻高,两者最低的均为常规籼稻。氮素光合效率与AE间存在显著正相关,表明后期的氮素光合效率对氮肥利用率具有一定的指示和预测作用,这对于判断水稻品种氮肥利用率将具有重要的应用价值。

Exploration of rice yield potential: Decoding agronomic and physiological traits

Rice grain yield is determined by three major"visible"morphological traits:grain weight,grain number per panicle,and effective tiller number,which are affected by a series of"invisible"physiological factors including nutrient use efficiency and photosynthetic efficiency.In the past few decades,substantial progress has been made on elucidating the molecular mechanisms underlying grain yield formation,laying a solid foundation for improving rice yield by molecular breeding.This review outlines our current understanding of the three morphological yield-determining components and summarizes major progress in decoding physiological traits such as nutrient use efficiency and photosynthetic efficiency.It also discusses the integration of current knowledge about yield formation and crop improvement strategies including genome editing with conventional and molecular breeding.

Effects of drip irrigation modes on growth and physiological characteristics of Arabica coffee under different N levels

The objective of this study was to obtain the water-saving and efficient production mode of Arabica coffee. The effects of three drip irrigation modes,conventional drip irrigation( CDI),alternate drip irrigation( ADI) and fixed drip irrigation( FDI) on growth,photosynthetic characteristics,biomass accumulation and irrigation water use efficiency of Arabica coffee were investigated under three nitrogen levels,high nitrogen( NH),middle nitrogen( NM) and low nitrogen( NL). The results show that there was a significant Logistic curve between the plant height,the stem diameter of Arabica coffee and growth days. Compared with CDI,ADI had no significant effects on leaf net photosynthetic rate,stomatal conductance,instantaneous water use efficiency and biomass accumulation above ground of Arabica coffee,while FDI decreased significantly,ADI and FDI increased irrigation water use efficiency by 50. 59% and 32. 85%,respectively. Compared with NH,with the reduction of N application rate,net photosynthetic rate,stomatal conductance,biomass accumulation above ground and irrigation water use efficiency decreased by 6. 81%-12. 30%,13. 70%-22. 69%,9. 61%-16. 67% and 9. 78%-15. 64%,respectively. Compared with CDINH,ADINHdecreased net photosynthesis rate and the stomatal conductance not significantly,other treatments decreased by 9. 16%-19. 22%,14. 49%-32. 91%,and decreased biomass accumulation above ground by 8. 26%-27. 34% except ADINH,and increased irrigation water use efficiency by 16. 46%-60. 95% except CDINMand CDINL. Therefore,alternate drip irrigation under high N level( ADINH) is the best water and nitrogen coupling mode of young Arabica coffee tree for water efficiency.

Effects of nitrogen and salt on growth and physiological characteristics of processing tomato under drip irrigation

Xinjiang of China is one of the three largest planting bases of processing tomato in the world,but soil salinization has restricted the production of tomato processing.In order to study the effects of soil nitrogen,salt and their interaction on growth and physiological characteristics of processing tomato under drip irrigation,different amount of nitrogen fertilizer were added to reconcile different salt stress to explore the response mechanisms of growth and yield of processing tomato to soil nitrogen and salt contents with a two-year experiments.The results showed that the effects of soil salinity on the growth and physiological characteristics of processing tomato were significantly greater than that of input of nitrogen fertilizers.The higher soil salt content(≥5.0 g/kg)significantly inhibited the growth of processing tomato.The increase in addition of nitrogen fertilizer could alleviate the salt inhibition and promote the growth of processed tomato with the increase of soil salt content,and the maximum nitrogen application rate was 300 kg/hm2.The linear plus platform was selected to determine the nitrogen effect models of non-saline-alkali soil and weak saline-alkali soil,but the square root nitrogen effect model of moderate saline-alkali soil was selected to accurately predict the yield of processing tomato.It was suggested that the processing tomatoes should be planted in moderate saline-alkali soil to achieve higher yields due to lower input of nitrogen fertilizer,potentially reducing fertilizer costs and maximizing profits from high processing tomato yields.The results have a strong guiding significance for planting of processing tomato on saline-alkali land and appropriate fertilization to increase the yield of processing tomato.

A global meta-analysis of woody plant responses to elevated CO_(2):implications on biomass,growth,leaf N content,photosynthesis and water relations

Background:Atmospheric CO_(2)may double by the year 2100,thereby altering plant growth,photosynthesis,leaf nutrient contents and water relations.Specifically,atmospheric CO_(2)is currently 50%higher than pre-industrial levels and is projected to rise as high as 936μmol mol^(−1)under worst-case scenario in 2100.The objective of the study was to investigate the effects of elevated CO_(2)on woody plant growth,production,photosynthetic characteristics,leaf N and water relations.Methods:A meta-analysis of 611 observations from 100 peer-reviewed articles published from 1985 to 2021 was conducted.We selected articles in which elevated CO_(2)and ambient CO_(2)range from 600–1000 and 300–400μmol mol^(−1),respectively.Elevated CO_(2)was categorized into<700,700 and>700μmol mol^(−1)concentrations.Results:Total biomass increased similarly across the three elevated CO_(2)concentrations,with leguminous trees(LTs)investing more biomass to shoot,whereas non-leguminous trees(NLTs)invested to root production.Leaf area index,shoot height,and light-saturated photosynthesis(A_(max))were unresponsive at<700μmol mol^(−1),but increased significantly at 700 and>700μmol mol^(−1).However,shoot biomass and A_(max)acclimatized as the duration of woody plants exposure to elevated CO_(2)increased.Maximum rate of photosynthetic Rubisco carboxylation(V_(cmax))and apparent maximum rate of photosynthetic electron transport(J_(max))were downregulated.Elevated CO_(2)reduced stomatal conductance(g_(s))by 32%on average and increased water use efficiency by 34,43 and 63%for<700,700 and>700μmol mol^(−1),respectively.Leaf N content decreased two times more in NLTs than LTs growing at elevated CO_(2)than ambient CO_(2).Conclusions:Our results suggest that woody plants will benefit from elevated CO_(2)through increased photosyn-thetic rate,productivity and improved water status,but the responses will vary by woody plant traits and length of exposure to elevated CO_(2).