Photosynthetic N-use Efficiency Research Articles

The Physiological Adjustments of Two Xerophytic Shrubs to Long-Term Summer Drought

Adaptive characteristics of plants, such as those associated with photosynthesis and resource use efficiency, are usually affected by synthesis costs and resource availability. The impact of extreme climate events such as long-term drought on plant physiological functions needs to be examined, particularly as it concerns the internal management of water and nitrogen (N) resources. In this study, we evaluated the resource management strategies for water and N by xerophytic shrubs, Artemisia ordosica and Salix psammophila, under extreme summer drought. This was carried out by comparing the plants’ physiological status during periods of wet and dry summer conditions in 2019 and 2021. Compared with the wet period, A. ordosica and S. psammophila both decreased their light-saturated net carbon (C) assimilation rate (Asat), stomatal conductance (gs), transpiration rate (E), leaf N content per leaf area (Narea), and photosynthetic N use efficiency (PNUE) during the summer drought. Whether in wet or dry summers, the gas-exchange parameters and PNUE of A. ordosica were generally greater than those associated with S. psammophila. The instantaneous water use efficiency (IWUE) response to drought varied with species. As a drought-tolerant species, the A. ordosica shrubs increased their IWUE during drought, whereas the S. psammophila shrubs (less drought-tolerant) decreased theirs. The divergent responses to drought by the two species were largely related to differences in the sensitivity of gs, and as a result, E. Compared with A. ordosica, S. psammophila’s inferior plasticity regarding gs response affected its ability to conserve water during drought. Our research illustrates the need for assessing plasticity in gs when addressing plant adaptation to long-term drought. A high dry-season IWUE in xerophytic shrubs can benefit the plants by augmenting their C gain.

Genetic improvement of photosynthetic nitrogen use efficiency of winter wheat in the Yangtze River Basin of China

ContextImproving the photosynthetic capacity of crops is key to achieving synergism between high crop yield and nitrogen (N) efficiency, and it is also an important target for future cultivar breeding and cultivation management. Although photosynthetic N use efficiency (PNUE) is commonly used to determine the N economy of leaves, it is unclear whether the PNUE of wheat has improved through genetic engineering of wheat cultivars. ObjectivesThe objectives of this study were to investigate the development of net photosynthetic rate (Pn) and PNUE, and to identify the key factors that limited Pn and PNUE in the tested cultivars. MethodsA 2-year field experiment with three different N fertilizer application rates using five wheat cultivars developed between 1950 s and 2010 s was conducted to examine the evolution and physiological processes of wheat Pn and PNUE. ResultsGrain yield, N recovery efficiency (NRE), leaf Pn, leaf area, the content of N in leaves (LNC), and the content of N per unit area in leaves (NA) increased through genetic engineering of wheat cultivars. However, the increase in Pn was lower than that in NA, resulting in a decrease in PNUE. Modern cultivars had a higher Pn, which was attributed to the improvement of NA, which likely enhanced the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), maximum electron transport rate (Jmax), electron transport rate from photosystem II (JF), and electron transport rate from the cytochrome b6f complex (Jc). The Rubisco content and activity of modern cultivars were higher than those of early cultivars, but the activation state decreased, which was related to the downregulation expression of TaRca1α and TaRca2β-A and the decrease of the adenosine diphosphate/adenosine triphosphate (ADP/ATP) ratio in modern cultivars, resulting in decreased Rubisco activase (Rca) content and activity. Increasing N application increased NA and Pn but decreased the PNUE. N fertilizer had a greater effect on Rubisco content and PNUE than genetic engineering, while it had a smaller effect on NA, leaf mass per area (LMA), Rubisco activity, and Rca content and activity than genetic engineering. ConclusionsOur results suggest that lower Rubisco activation is a major reason for the lower PNUE of modern wheat cultivars, and improving Rca content and activity in the future could enhance Pn and PNUE while improving the N utilization of leaves to enhance crop yield and N efficiency of wheat under current or lower leaf N conditions.

Comparative physiological and transcriptome analysis of leaf nitrogen fluxes in stay-green maize during the vegetative stage

In maize, nitrogen (N) stored in leaves is an important internal source for supporting subsequent growth and development. However, the regulation of N fluxes and photosynthesis and the molecular and genotypic regulations that modify them are less clear in source leaves during the vegetative stage. This knowledge is crucial for improving N use efficiency (NUE). By using 15N labeling and transcriptome methods, an analysis of the physiological and molecular basis of leaf N import and export processes and photosynthetic N use efficiency (PNUE) was conducted in two maize hybrids (XY335 and XY696) with different stay-green characteristics during the vegetative stage. Leaf N import and export in XY696 were 45% and 33% greater than those in XY335. However, the PNUE in XY335 was 17% greater than that in XY696 due to the higher net photosynthetic rate (A) and lower SLN. Correspondingly, the chlorophyll content and photosynthesis-related enzyme (PEPc, PEPck, PPDK) activities increased by 18∼30% in XY335. Transcriptome analysis indicated that the expression levels of several N and carbon metabolism-related genes encoding Rubisco, PEPc, Nir, GS and AS were significantly increased or decreased in XY696 in parallel with enzyme activities. Moreover, there was a large difference in the expression abundance of genes encoding nitrate/nitrite transporters and transmembrane proteins. Our results suggest that two hybrids modulate leaf N fluxes and photosynthesis differently by altering gene expression and enzyme activities. Our study contributes to understanding leaf N fluxes and PNUE regulation and serves as a crucial reference for NUE improvement in maize breeding research.

Late nitrogen fertilization increases biomass of cotton bolls by reinforcing source[sbnd]sink performance

The decrease in reproductive organ biomass is a principal constraint for cotton yield under conditions of limited nitrogen (N). We aimed to alleviate this challenge by reasoning N applications in order to exploit the photosynthetic potential and improve the distribution of photosynthates. Cotton crops were grown in a two-year field experiment (2019–2020) under N-reduced cultivation (23.9 ×104 plants ha−1, 76 cm row spacing, and applied 240 kg N ha−1), N fertigated with five ratios at squaring (SQ): flowering to peak boll (FPB): late peak boll (LPB), i.e., 4:6:0 (N460), 3:6:1 (N361), 2:6:2 (N262, Control), 1:6:3 (N163) and 0:6:4 (N064). Impacts of N treatment (ratio) were investigated for leaf area, chlorophyll content, photosynthetic characteristics, photosynthetic N use efficiency (PNUE), sink capacity characteristics, and biomass accumulation. Correlations between traits were also analyzed. Compared with conventional N262, N064 increased reproduction organs biomass by 10.1–10.3%. Furthermore, during the LPB to boll opening stage, N064 increased fruit branch leaf area by 1.4–26.8%, chlorophyll content by 6.4–27.6%, net photosynthetic rate by 15.1–35.9%, actual photosynthetic efficiency by 14.4–41.6%, photochemical quenching by 18.0–57.7%, PNUE by 15.7–41.0%, and sink capacity by 6.7–10.5%; while it decreased foliage branch leaf area by 13.1–22.4% and chlorophyll a/b by 6.1–10.2%. Overall, late N fertilization was an effective strategy to (1) retain post-flowering photosynthetic capacity by developing more fruit branch leaf area with higher chlorophyll content and lower chlorophyll a/b, (2) optimize sourcesink relationship by increasing boll capacity, and (3) increase biomass in reproductive organs, thus enhancing sustainable and efficient production of cotton under N-reduced cultivation in arid regions.

Leaf trait responses to global change factors in terrestrial ecosystems

Global change influences plant growth by affecting plant morphology and physiology. However, the effects of global change factors vary based on the climate gradient. Here, we established a global database of leaf traits from 192 experiments on elevated CO2 concentrations (eCO2), drought, N deposition, and warming. The results showed that the leaf mass per area (LMA) significantly increased under eCO2 and drought conditions but decreased with N deposition, whereas eCO2 levels and drought conditions reduced stomatal conductance and increased and decreased photosynthetic rates, respectively. Leaf dark respiration (Rd) increased in response to global change, excluding N deposition. Leaf N concentrations declined with eCO2 but increased with N deposition. Leaf area increased with eCO2, N deposition, and warming but decreased with drought. Leaf thickness increased with eCO2 but decreased with warming. eCO2 and N deposition enhanced plant water-use efficiency (WUE), eCO2 and warming increased photosynthetic N-use efficiency (PNUE), while N fertilization reduced PNUE significantly. eCO2 produced a positive relationship between WUE and PNUE, which were limited under drought but increased in areas with high humidity and high temperature. Trade-offs were observed between WUE and PNUE under drought, N deposition, and warming. These findings suggest that the effects of global change factors on plants can be altered by complex environmental changes; moreover, diverse plant water and nutrient strategy responses can be interpreted against the background of their functional traits.

Within leaf nitrogen allocation regulates the photosynthetic behavior of xerophytes in response to increased soil rock fragment content

There is limited information on how plant functional traits vary with soil rock fragment content (RFC), especially for xerophytes growing in stony soils. We examined leaf functional traits of three xerophytes (Sophora davidii; Cotinus szechuanensi; and Artemisia vestita) grown under an RFC gradient in a heavy loamy soil. Our results show that photosynthetic capacity increased linearly with RFC in S. davidii, whereas unimodal patterns were observed for the other two species. The RFC that maximized photosynthetic capacity (Asat) and photosynthetic N use efficiency (PNUE) were achieved by allocating more N to photosynthetic apparatus at the expense of cell walls. For C. szechuanensis, the increased fraction of photosynthetic N allocated to carboxylation (PC) bioenergetics (PB), and thylakoid light-harvesting components (PL) together contributed to the higher Asat and PNUE values. As for S. davidii, both PC and PB mainly contributed to higher Asat and PNUE, whereas for A. vestita only PB was the main contributor. Our results suggest that increased non-capillary porosity of high RFC soil conditions through promoting the root growth of S. davidii and C. szechuanensis ensures sufficient water and N supply for photosynthetic capacity. In shallow-rooted species A. vestita, low RFC soil maintained higher nitrate N in the topsoil, enhancing leaf photosynthetic capacity. We conclude that rock fragments promoted leaf photosynthetic capacity in the studied loamy soil system, but the promoting effect was species-specific. The results highlight the relevance of consideration of soil rock fraction in evaluation of photosynthetic behavior of xerophytes in heterogeneous rocky soils.

Understanding the Physiological Mechanisms of Canopy Light Interception and Nitrogen Distribution Characteristics of Different Maize Varieties at Varying Nitrogen Application Levels

Reasonable canopy structure and leaf physiological characteristics are considered as important factors for improving canopy nitrogen (N) distribution by matching the available light resources and thus increasing the grain yield of maize (Zea mays L.). However, the determinants of different maize varieties in light–N matching and grain yields with specific canopy structures and leaf physiological characteristics, as well as the response to the N application rate, remain poorly understood. In this study, we analyzed the relationships between different canopy structures and the enzyme activity and light utilization of spring maize in the field. Two maize varieties (XY335 and ZD958) with different canopy structures were used as the experimental material in a 2-year field experiment from 2014 to 2015, grown under different N inputs of 0, 100, 200, and 300 kg N ha−1 (N0, N1, N2, and N3) at a planting density of 90,000 plants ha−1 in Jilin Province on the Northeast China Plain. The results show that XY335 combined with N3 had a greater leaf angle, upper internode length and number, and upper leaf area index of the upper layer compared with ZD958. Higher N assimilatory enzyme (glutamine synthase (GS), glutamate synthase (GOGAT), and nitrate reductase (NR)) activities in the upper and middle leaves were observed in XY335 compared to ZD958. Furthermore, the light interception and light utilization efficiency of the upper leaves of XY335 increased, especially at higher N application rates, which significantly affected the N translocation post-silking and its distribution in different populations. As a result, the photosynthetic N use efficiency (PNUE) values of the upper leaves (10.4%) and middle leaves (5.2%) of XY335 were higher than those of ZD958, coordinating the canopy light and N distributions and being positively correlated with the maize grain yield. This suggested that the superior canopy structure of the upper layer and N assimilatory enzymes of the upper and middle leaves of this maize variety significantly increased the light interception of the canopy, while the synchronization of light and the N of the upper and middle leaves increased the light and N utilization efficiency of maize, which ultimately increased the grain yield at a high plant density.

Within-branch photosynthetic gradients are more related to the coordinated investments of nitrogen and water than leaf mass per area

Nitrogen (N) and water are key resources for leaf photosynthesis and the growth of whole plants. Within-branch leaves need different amounts of N and water to support their differing photosynthetic capacities according to light exposure. To test this scheme, we measured the within-branch investments of N and water and their effects on photosynthetic traits in two deciduous tree species Paulownia tomentosa and Broussonetia papyrifera. We found that leaf photosynthetic capacity gradually increased from branch bottom to top (i.e. from shade to sun leaves). Concomitantly, stomatal conductance (gs) and leaf N content gradually increased, owing to the symport of water and inorganic mineral from root to leaf. Variation of leaf N content led to large gradients of mesophyll conductance, maximum velocity of Rubisco for carboxylation, maximum electron transport rate and leaf mass per area (LMA). Correlation analysis indicated that the within-branch difference in photosynthetic capacity was mainly related to gs and leaf N content, with a relatively minor contribution of LMA. Furthermore, the simultaneous increases of gs and leaf N content enhanced photosynthetic N use efficiency (PNUE) but hardly affected water use efficiency. Therefore, within-branch adjustment of N and water investments is an important strategy used by plants to optimize the overall photosynthetic carbon gain and PNUE.

Within-leaf chloroplasts and nitrogen allocation to thylakoids in relation to photosynthesis during grain filling in maize

Nitrogen (N) is an important contributor to photosynthetic rate (Pn). However, during grain-filling stage in maize, some leaf N is remobilized to meet demands for grain protein accumulation rather than photosynthetic demands. Therefore, plants that can maintain a relatively high Pn during the N remobilization process would have the key to achieving both high grain yields (HGY) and high grain protein concentrations (HGPC). In this study, we investigated two high-yielding maize hybrids in photosynthetic apparatus and N allocation in a two-year field experiment. During grain filling, XY335 had a higher Pn and photosynthetic N-use efficiency than ZD958 had in the upper leaf, but not in the middle or lower leaves. In the upper leaf, the diameter and area of the bundle sheath (BS) were larger and the distance between bundle sheaths was greater in XY335 than in ZD958. XY335 had more bundle sheath cells (BSCs) and a larger BSC area, as well as a larger chloroplast area in the BSC, resulting in a higher total number and total area of chloroplasts in the BS. XY335 also had higher stomatal conductance (gs), intercellular CO2 concentration, and N allocation to the thylakoids. No genotypic differences were found in mesophyll cell ultrastructure, N content and starch content in the three types of leaves. Therefore, a trifecta of higher gs, greater N allocation to thylakoids for photo-phosphorylation and electron transport, and more and larger chloroplasts promoting CO2 assimilation in the BS confers a high Pn to simultaneously achieve HGY and high HGPC in maize.

High nitrogen inhibits biomass and saponins accumulation in a medicinal plant Panax notoginseng.

Nitrogen (N) is an important macronutrient and is comprehensively involved in the synthesis of secondary metabolites. However, the interaction between N supply and crop yield and the accumulation of effective constituents in an N-sensitive medicinal plant Panax notoginseng (Burkill) F. H. Chen is not completely known. Morphological traits, N use and allocation, photosynthetic capacity and saponins accumulation were evaluated in two- and three-year-old P. notoginseng grown under different N regimes. The number and length of fibrous root, total root length and root volume were reduced with the increase of N supply. The accumulation of leaf and stem biomass (above-ground) were enhanced with increasing N supply, and LN-grown plants had the lowest root biomass. Above-ground biomass was closely correlated with N content, and the relationship between root biomass and N content was negatives in P. notoginseng (r = -0.92). N use efficiency-related parameters, NUE (N use efficiency, etc.), NC (N content in carboxylation system component) and P n (the net photosynthetic rate) were reduced in HN-grown P. notoginseng. SLN (specific leaf N), Chl (chlorophyll), NL (N content in light capture component) increased with an increase in N application. Interestingly, root biomass was positively correlated with NUE, yield and P n. Above-ground biomass was close negatively correlated with photosynthetic N use efficiency (PNUE). Saponins content was positively correlated with NUE and P n. Additionally, HN improved the root yield of per plant compared with LN, but reduced the accumulation of saponins, and the lowest yield of saponins per unit area (35.71 kg·hm-2) was recorded in HN-grown plants. HN-grown medicinal plants could inhibit the accumulation of root biomass by reducing N use and photosynthetic capacity, and HN-induced decrease in the accumulation of saponins (C-containing metabolites) might be closely related to the decline in N efficiency and photosynthetic capacity. Overall, N excess reduces the yield of root and C-containing secondary metabolites (active ingredient) in N-sensitive medicinal species such as P. notoginseng.

苗圃氮加载及水分胁迫对栓皮栎苗木叶片光合氮分配及生物量积累的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 苗圃氮加载及水分胁迫对栓皮栎苗木叶片光合氮分配及生物量积累的影响 DOI: 10.5846/stxb202203080563 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(32101503,32171764,31670638) The combined effects of nitrogen loading and spring drought on photosynthetic machinery nitrogen distribution and accumulation of biomass of Quercus variabilis seedlings Author: Affiliation: Fund Project: The National Natural Science Foundation of China (32101503、32171764、31670638) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:苗圃科学施氮(N)作为提高苗木N贮存水平与质量的核心手段,能否提高干旱立地苗木造林效果仍存在争议;N贮存水平与干旱如何协同作用影响叶片光合N分配及苗木生物量积累尚不明确。阐明上述问题,能够为干旱立地下的森林植被恢复以及造林苗木科学精准施N提供科学依据。选择栓皮栎(Quercus variabilis Blume)为研究对象,对一年生苗木设置2个苗圃木质化期N加载水平(0、24 mg N/株),翌年春苗木移栽后设置2个灌溉水平(85%、40%田间持水量),取样测定苗木生物量、叶片N、叶绿素与脯氨酸水平、以及气体交换参数,计算光合N分配及光合N利用效率(PNUE)。结果表明,叶片发育完成后,干旱抑制N向光合系统分配,但N加载处理提高了干旱下的光合N含量,从而在一定程度上抵消干旱对生物量积累的抑制;无N加载苗木则向光合系统投入更少的N,而提高脯氨酸水平,生物量积累受抑制更为显著。无N加载苗木在遭受干旱后将N向羧化组分分配,而N加载苗木遭遇干旱后则显著抑制叶片将N向羧化系统以及电子传递系统分配,捕光组分N的分配则不受植物体内N贮存或外部水分状况的影响,栓皮栎苗木通过调整不同功能组分光合N含量和分配以维持干旱下较高的PNUE。 Abstract:As one of the most important ways to improve seedling stored nitrogen (N) levels and quality, whether manipulating N fertilization could improve the field performance in dry areas was still under discussion. It was also not clear that the combined effects of stored N levels and drought on the partitioning of total leaf N among the different pools of the photosynthetic machinery and the accumulation of biomass. Clarifying above problems could provide a scientific basis for forest vegetation restoration and nursery N fertilization regimes for seedlings in dry areas, as well as the improvement of seedling quality under the difficult sites. During the first growing season, we produced Quercus variabilis Blume seedlings with distinct N content by applying two hardening phase N fertilization rates (0, 24 mg N per seedling). At the beginning of the second growing season, the seedlings were transplanted into larger pots and subjected to two watering levels (85%, 40% of field capacity). The seedling biomass, leaf N, chlorophyll, proline, and gas exchange parameters were measured. N distribution of functional components of leaf photosynthetic system and photosynthetic N-use efficiency (PNUE) were calculated. The results showed that water stress during spring reduced N allocation of leaf photosynthetic system. Nevertheless, high N storage could partially counteract the effect of drought on the accumulation of seedlings biomass due to increased N allocation to photosynthetic machinery. However, low N storage allocated less N to photosynthetic machinery, but increased the proline level, and the biomass inhibition of low N storage seedlings was more significant. The proportion of N allocated leaf Rubisco enzyme in low N storage seedlings increased under drought, while the proportion of N allocated leaf Rubisco enzyme and electron transport component in high N storage seedlings decreased under drought. Light-harvesting component was not affected by N storage levels or drought. Q. variabilis seedlings maintained higher PNUE under drought by adjusting photosynthetic N allocation content and distribution of different functional components. 参考文献 相似文献 引证文献

Suppression of leaf growth and photosynthetic capacity as an acclimation strategy to nitrogen deficiency in a nitrogen-sensitive and shade-tolerant plant Panax notoginseng

ABSTRACT Photosynthesis is susceptible in response to nitrogen (N) deficiency. However, the acclimation of shade-tolerant and high-N sensitive species to N deficiency is unclear. Leaf morpho-physiological traits, photosynthetic performance related parameters were examined in a shade-tolerant and high-N sensitive species P. notoginseng grown under different N levels. Lower N content and Chl content were recorded in the N0-grown P. notoginseng. The maximum values of leaf morpho-physiological traits, photosynthetic rate, and photosynthetic N use efficiency (PNUE) were obtained in the N15-grown P. notoginseng. Coefficients for leaf N allocation into the carboxylation and light-harvesting system components in the N0-grown plants were significantly higher than others. N0 and N7.5 plants showed higher K phase. N addition decreased the absorption and capture of the light energy per unit area (ABS/RC and TRO/RC) and non-photochemical quenching (NPQ). Photochemical quenching (qP), electron transport rate (ETR), and effective quantum yield of photosystem II (ϕPSII) were reduced in the N0-grown plants. The reduction of light-harvesting and utilization capacity not only leads to a decrease in PNUE, but also induces the damage of PSII reaction center. Overall, the inhibition of leaf growth and photosynthetic capacity is an essential strategy for high-N sensitive and shade-tolerant plants in response to N deficiency.

Nitrogen Allocation Tradeoffs Within-Leaf between Photosynthesis and High-Temperature Adaptation among Different Varieties of Pecan (Carya illinoinensis [Wangenh.] K. Koch).

Interpreting leaf nitrogen (N) allocation is essential to understanding leaf N cycling and the economy of plant adaptation to environmental fluctuations, yet the way these mechanisms shift in various varieties under high temperatures remains unclear. Here, eight varieties of pecan (Carya illinoinensis [Wangenh.] K. Koch), Mahan, YLC10, YLC12, YLC13, YLC29, YLC35, YLJ042, and YLJ5, were compared to investigate the effects of high temperatures on leaf N, photosynthesis, N allocation, osmolytes, and lipid peroxidation and their interrelations. Results showed that YLC35 had a higher maximum net photosynthetic rate (Pmax) and photosynthetic N-use efficiency (PNUE), while YLC29 had higher N content per area (Na) and lower PNUE. YLC35, with lower malondialdehyde (MDA), had the highest proportions of N allocation in rubisco (Pr), bioenergetics (Pb), and photosynthetic apparatus (Pp), while YLC29, with the highest MDA, had the lowest Pr, Pb, and Pp, implying more leaf N allocated to the photosynthetic apparatus for boosting PNUE or to non-photosynthetic apparatus for alleviating damage. Structural equation modeling (SEM) demonstrated that N allocation was affected negatively by leaf N and positively by photosynthesis, and their combination indirectly affected lipid peroxidation through the reverse regulation of N allocation. Our results indicate that different varieties of pecan employ different resource-utilization strategies and growth-defense tradeoffs for homeostatic balance under high temperatures.

Divergent leaf nutrient-use strategies of coexistent evergreen and deciduous trees in a subtropical forest

Abstract Evergreen and deciduous species coexist in the subtropical forests in southeastern China. It has been suggested that phosphorus (P) is the main limiting nutrient in subtropical forests, and that evergreen and deciduous species adopt different carbon capture strategies to deal with this limitation. However, these hypotheses have not been examined empirically to a sufficient degree. In order to fill this knowledge gap, we measured leaf photosynthetic and respiration rates, and nutrient traits related to P-, nitrogen (N)- and carbon (C)-use efficiencies and resorption using 75 woody species (44 evergreen and 31 deciduous species) sampled in a subtropical forest. The photosynthetic N-use efficiency (PNUE), respiration rate per unit N and P (Rd,N and Rd,P, respectively) of the deciduous species were all significantly higher than those of evergreen species, but not in the case of photosynthetic P-use efficiency. These results indicate that, for any given leaf P, evergreen species manifest higher carbon-use efficiency (CUE) than deciduous species, a speculation that is empirically confirmed. In addition, no significant differences were observed between deciduous and evergreen species for nitrogen resorption efficiency, phosphorus resorption efficiency or N:P ratios. These results indicate that evergreen species coexist with deciduous species and maintain dominance in P-limited subtropical forests by maintaining CUE. Our results also indicate that it is important to compare the PNUE of deciduous species with evergreen species in other biomes. These observations provide insights into modeling community dynamics in subtropical forests, particularly in light of future climate change.

Declined photosynthetic nitrogen use efficiency under ammonium nutrition is related to photosynthetic electron transport chain disruption in citrus plants

Nitrogen (N) is an essential nutrient for citrus growth and development. Previously, we identified citrus as an ammonium (as NH4+-N or AN) sensitive plant; however, the mechanism underlying the changes in photosynthetic physiology in response to AN stress remain unclear. ‘Lugan’ (Citrus reticulata Blanco cv. Ponkan) citrus seedlings were sand cultivated in the presence of two forms of N (AN and nitrate as NO3−-N or NN), and three N levels (1, 4 and 8 mmol L−1, as N1, N4 and N8). Biomass, leaf N concentration per unit leaf area (LNC), gas exchange, relative chlorophyll value (SPAD), photosynthetic N use efficiency (PNUE), chlorophyll a fluorescence, reactive oxygen metabolism, and non-structural carbohydrates (NSC) were determined. Compared with NN, AN significantly inhibited the growth of citrus seedlings, accompanied by a reduced net photosynthetic rate at N4 and N8, as well as LNC at N4, with a concomitant decline in PNUE. Leaf NSC, SPAD, light energy absorption and trapping were remarkably elevated by AN, which damaged the oxygen-evolving complex and increased the heat dissipation, resulting in disruption of the photosynthetic electron transport chain. Moreover, increased superoxide anion, H2O2, and malonaldehyde content, and downregulated superoxide dismutase, peroxidase, and catalase activities were also observed in citrus leaves under AN. However, the severity of these adverse effects of AN in citrus plants increased with N levels. Overall, these results indicate that AN supply reduces PNUE by disrupting the photosynthetic electron transport chain, which inhibits the growth of citrus seedlings.

Variation in Leaf Type, Canopy Architecture, and Light and Nitrogen Distribution Characteristics of Two Winter Wheat (Triticum aestivum L.) Varieties with High Nitrogen-Use Efficiency

Studies of traits related to nitrogen (N)-use efficiency (NUE) in wheat cultivars are important for breeding N-efficient cultivars. Canopy structure has a major effect on NUE, as it determines the distribution of light and N. However, the mechanism by which canopy structure affects the distribution of light and N within the canopy remains unclear. The N-efficient winter wheat varieties YM49 and ZM27 and N-inefficient winter wheat varieties XN509 and AK58 were grown in the field under two N levels. Light transmittance was enhanced, and the leaf area index and photosynthetically active radiation were lower in the N-efficient cultivar population, which was characterized by moderately sized flag leaves, a low frequency of canopy leaf curling, a low light attenuation coefficient (KL), and high plant compactness. Reductions in the amount of shade increased the distribution of light and N resources to the middle and lower layers. The photosynthetic rate, transpiration rate, instant water-use efficiency, and canopy photosynthetic NUE were higher, N remobilization of the upper and middle canopy leaves was reduced, and the leaf N content was high in the N-efficient cultivars. A higher ratio of the N extinction coefficient (KN) to KL reflects the assimilation ability of the N-efficient winter wheat cultivars, resulting in improved canopy structure and distribution of light and N, higher 1000-grain weight and grain yield, and significantly increased light and NUE. An improved match between gradients of light and N in the leaf canopy promotes balanced C and N metabolism and reduces energy and nutrient losses. This should be a goal when breeding N-efficient wheat cultivars and implementing tillage regimes.

Arbuscular Mycorrhizal Fungi Alleviate Salt Stress Damage by Coordinating Nitrogen Utilization in Leaves of Different Species

With the intensification of coastal erosion, damage to coastal shelterbelts has gradually increased. Arbuscular mycorrhizal fungi (AMF) can improve the salinity tolerance and productivity of plants in saline–alkali soils using various strategies including nutrient uptake, osmotic regulation, soil shaping, etc. Thus, the application of AMF to alleviate the impacts of salinization for these shelterbelts has become a research hotspot. For this study, we investigated the effects of inoculation with different AMF strains on the growth and nitrogen (N) utilization of Gleditsia sinensis Lam. and Zelkova serrata (Thunb.) Makino leaves under different salt concentrations. As the salt concentration increased, the growth rates and leaf areas of the autoclaved AMF inoculant (CK) treatment exhibited a decreasing trend for both G. sinensis and Z. serrata, while Funneliformis mosseae (FM) and Corymbiglomus tortuosum (CT) treatments weakened this trend. Between them, on average, FM increased the G. sinensis height growth rate by 396.9%, ground diameter growth rate by 99.0%, and Z. serrata leaf area by 29.1%. At a salt concentration of 150 mM, the chlorophyll content and nitrate reductase activities of leaves under the FM treatment for both tree species were significantly higher than for CK, with an average increase in chlorophyll content of 106.1% and nitrate reductase activities by 74.6%. Moreover, the AMF inoculation significantly reduced the leaf N content and photosynthetic N-use efficiency of G. sinensis in contrast to Z. serrata. Further, in contrast to G. sinensis, the photosynthetic N-use efficiency was significantly positively correlated with the growth rate and leaf area of Z. serrata. Meanwhile, the nitrate reductase activity contributed most to the growth rate and leaf area of Z. serrata. Our results suggest that the issues with coastal shelterbelts might be effectively alleviated through appropriate AMF–plant combinations, which is of great significance for the optimization of forestry production.

Improvement in the photoprotective capability benefits the productivity of a yellow-green wheat mutant in N-deficient conditions

Wheat yellow-green mutant Jimai5265yg has a more efficient photosynthetic system and higher productivity than its wild type under N-deficient conditions. To understand the relationship between photosynthetic properties and the grain yield, we conducted a field experiment under different N application levels. Compared to wild type, the Jimai5265yg flag leaves had higher mesophyll conductance, photosynthetic N-use efficiency, and photorespiration in the field without N application. Chlorophyll a fluorescence analysis showed that PSII was more sensitive to photoinhibition due to lower nonphotochemical quenching (NPQ) and higher nonregulated heat dissipation. In N-deficient condition, the PSI acceptor side of Jimai5265yg was less reduced. We proposed that the photoinhibited PSII protected PSI from over-reduction through downregulation of electron transport. PCA analysis also indicated that PSI photoprotection and electron transport regulation were closely associated with grain yield. Our results suggested that the photoprotection mechanism of PSI independent of NPQ was critical for crop productivity.

Improved Utilization of Nitrate Nitrogen Through Within-Leaf Nitrogen Allocation Trade-Offs in Leymus chinensis.

The Sharply increasing atmospheric nitrogen (N) deposition may substantially impact the N availability and photosynthetic capacity of terrestrial plants. Determining the trade-off relationship between within-leaf N sources and allocation is therefore critical for understanding the photosynthetic response to nitrogen deposition in grassland ecosystems. We conducted field experiments to examine the effects of inorganic nitrogen addition (sole NH4+, sole NO3– and mixed NH4+/NO3–: 50%/50%) on N assimilation and allocation by Leymus chinensis. The leaf N allocated to the photosynthetic apparatus (NPSN) and chlorophyll content per unit area (Chlarea) were significantly positively correlated with the photosynthetic N-use efficiency (PNUE). The sole NO3– treatment significantly increased the plant leaf PNUE and biomass by increasing the photosynthetic N allocation and Chlarea. Under the NO3 treatment, L. chinensis plants devoted more N to their bioenergetics and light-harvesting systems to increase electron transfer. Plants reduced the cell wall N allocation or increased their soluble protein concentrations to balance growth and defense under the NO3 treatment. In the sole NH4+ treatment, however, plants decreased their N allocation to photosynthetic components, but increased their N allocation to the cell wall and elsewhere. Our findings demonstrated that within-leaf N allocation optimization is a key adaptive mechanism by which plants maximize their PNUE and biomass under predicted future global changes.

Sex-specific nitrogen allocation tradeoffs in the leaves of Populus cathayana cuttings under salt and drought stress

Nitrogen (N) partitioning within a leaf affects leaf photosynthesis and adaptation to environmental fluctuations. However, how plant sex influences leaf N allocation and its tradeoffs in acclimation to drought, excess salt and their combination remains unknown. Here, leaf N allocation between the photosynthetic and non-photosynthetic apparatus and among the components of the photosynthesis in Populus cathayana Rehder females and males were investigated under drought, salt and their combination to clarify the underlying mechanism. We found that males with a lower leaf N allocation (NL) into non-protein N (Nnp), showed a greater leaf N allocation into photosynthetic apparatus, especially into the carboxylation component under all treatments, and a greater leaf N allocation into cell wall under drought and salt stress alone, consequently causing higher photosynthetic N use efficiency (PNUE) and tolerance to stresses. Conversely, females had a greater leaf N allocation into Nnp under all treatments than males and a lower leaf photosynthetic N (NP) allocation. There was a tradeoff in leaf N allocation among photosynthetic apparatus (NP/NL), cell wall (NCW/NL) and Nnp, which explained plant responses to drought, salt and their combination. Moreover, the leaf N allocation into the carboxylation component could explain the intersexual difference in responses to all treatments, while leaf cell wall N (NCW) and Nnp reflected intrasexual differences among treatments in both sexes. These findings indicate sex-specific strategies in coping with drought, salt and their combination that relate to leaf N allocation, which may contribute to sex-specific photosynthesis and niche segregation.