光质对菠菜草酸、单宁及硝酸盐积累效应的影响

用彩色荧光灯得到红光、蓝光和黄光,以白光为对照,研究不同光质对菠菜产量,草酸、单宁及硝酸盐积累的影响。结果表明,处理间的菠菜叶柄和叶片硝酸盐和草酸含量的变化不同,但地上部生长量的变化趋势相同。叶片占植株地上部鲜质量的比例高于叶柄。不同处理叶片和叶柄鲜质量依次为白光(对照)>黄光>红光>蓝光。红光处理有利于干物质和碳水化合物的形成与积累。菠菜叶柄的硝酸盐含量显著高于叶片,是积累硝酸盐的主要场所,并且各处理间叶片硝酸盐和单宁含量的差异远大于叶柄。白光和黄光处理下,菠菜叶片草酸含量大于叶柄,而红光和蓝光处理则相反,其中红光处理草酸含量最低。菠菜在红光处理下生物量虽不高,但可极大地降低硝酸盐和草酸含量,提高菠菜品质。     

Calcium nutrition of white rose potato in relation to growth and leaf minerals

Abstract

White Rose potato plants were grown in nutrient solutions containing Ca from 0 to 20 meq/l. After 32 days of growth, 16 plant parts were taken for analysis. The critical level for the immature to the recently matured leaf was determined to be about 0.15% Ca for the petiole and the blade tissues at the breaking point of the transition zone. Ca concentrations of petioles and blades (dry basis) increased with leaf age with the greatest increase in the blade tissues. The petioles of recently matured leaves under severe Ca deficiency were higher in Na, Mg, and PO₄‐P, lower in N0₃‐N and about the same in K concentration in comparison with non‐deficient petioles while the corresponding blades did not differ appreciably. Calcium deficiency has no major effect on the uptake of these minerals since all values were in the adequate range.     

Effect of restricted supply of nitrate on fruit growth and nutrient concentrations in the petiole sap of tomato cultured hydroponically

Tomato plants (Lycopersicon esculentum Mill. cv. Momotaro) were cultured in nutrient solution supplying 35 meq or 50 meq of nitrate (NO₃) per plant weekly from the flowering stage of the first truss in two cropping seasons. The effects of NO₃ supply levels and cropping season on fruit growth of tomato were investigated. Furthermore, the relationship between the results of the plant sap analysis and fruit growth of tomato was analyzed. In the spring to summer cropping, NO₃ supplied was almost all absorbed and high productivity of tomato fruits was obtained in each treatment. In the fall to winter cropping, however, high NO₃ supply did not increase the uptake of NO₃, but tended to decrease the rate of fruit set and marketable yield. Accumulation of NO₃ in the petiole sap was found with high NO₃ supply in the fall to winter cropping. Cropping season greatly influenced not only fruit growth but also the concentration of NO₃ in the petiole sap in relation to the ability of tomato plants to use available nitrogen (N). Furthermore, reduction in the rate of fruit set and weight of tomato fruit were found to relate to the low concentration of NO₃ in the petiole sap of the leaf just below this fruit truss. High NO₃ supply tended to increase potassium (K) concentration and electrical conductivity (EC) value, and to decrease phosphate (P), calcium (Ca), and magnesium (Mg) concentrations in the petiole sap. On the whole, concentrations of these elements in the petiole sap consistently reflected their uptake rates in two cropping seasons.     

不同品种菠菜叶柄和叶片的硝态氮含量及其与植株生长的关系

温室盆栽试验研究了我国北方不同菠菜品种叶柄和叶片的硝态氮含量及其与植株生长的关系。结果表明,30个菠菜品种地上部分的生长量和硝态氮含量存在显著差异。叶柄和叶片在反映品种间生长量和硝态氮含量变异方面的作用并不相同。叶片占植株地上部鲜重的比例高于叶柄,品种间叶片生长量的差异亦大于叶柄,叶片与植株生长量的正相关关系更为显著。但与生长量的情况不同,叶柄的硝态氮含量、累积总量均显著高于叶片,是菠菜累积硝态氮的主要器官。叶柄硝态氮含量的品种间差异远大于叶片,与植株地上部硝态氮含量的正相关性更为显著。菠菜不同品种之间,叶柄硝态氮含量与地上部鲜重、干重及水分均表现出显著的正相关关系,而叶片硝态氮含量与植株生物量及其各组分之间却无这种关系。     

Seasonal variation of macro and micronutrients in blades and petioles of Vitis vinifera L. cv. Mencía and Sousón

In the case of grapevine (Vitis vinifera L.), leaf blade and petioles at different sampling times are used for nutritional diagnosis and planning fertilization practices. However, reference values for each nutrient depend on the scion‐rootstock combination. In this sense, the current study aimed at determining the reliability of leaf blade and petiole for diagnosis at different phenological stages and, also, of the period of validity, around flowering and veraison, in which the nutrient concentrations obtained could be compared with reference values. The study was carried out in three vineyards (two planted with cv. Mencía and one with cv. Sousón) within the Ribeira Sacra Designation of Origin (NW Spain). Blades and petioles were collected throughout a growth season (2014) and total concentrations of ten essential elements were determined in both tissues. In general, petioles showed greater variability between replicates for P, K, Ca, Mg, and Zn, while N, Fe, Mn, Cu, and B presented greater variability in blades. Differences between consecutive sampling dates suggest that references for flowering were valid until fruit‐set. Furthermore, blade and petiole references at the beginning of veraison were valid until the advanced ripening stage for most nutrients, with the exception of N, P, and Zn. The seasonal variation of the concentrations in both tissues confirmed the need for reference values for each phenological stage and tissue.     

Physiological changes associated with potassium deficiency in cotton

Potassium (K) fertility recommendations based on cotton petiole diagnostic analysis results have been inconsistent in the past, partly because the lowest acceptable petiole K concentration is unknown. Therefore, cotton was grown in sand filled 8‐L pots under two K treatments in a growth chamber at the Altheimer Laboratory in Fayetteville, AR to determine the petiole K concentration that will impact leaf physiology. Chamber‐grown plants were watered every second day with nutrient solution and with deionized water on alternate days. At 14 days after planting two treatments were established consisting of (1) continued complete nutrient solution, and (2) nutrient solution containing no K. Measurements were taken 13, 19, and 26 days after treatment establishment (DATE). Organ K concentrations, leaf chlorophyll, photosynthesis, adenosine triphosphate (ATP), and nonstructural carbohydrate concentrations were monitored as plant K deficiencies developed. All organ K concentrations were much lower in the no‐K treatment on each analysis date. Visual K deficiencies were first observed at 19 DATE along with reductions reductions in leaf chlorophyll concentration. Leaf photosynthesis was greatly reduced in the no‐K treatment beginning at 19 DATE. However, leaf ATP and nonstructural carbohydrate concentrations were higher at 19 and 26 DATE in the no‐K treatment, which may have been the result of reduced utilization and translocation of these metabolites. Our studies show that reductions in leaf physiological processes and plant growth did not occur until the petiole K concentration fell below 0.88% on a dry weight basis. Therefore, reductions in lint yield and quality should not develop until this critical petiole level is attained.     

Impact of time of day and time since irrigation on cotton leaf blade and petiole nutrient concentrations

Abstract

Petioles are used in weekly nutrient monitoring programs because they are more responsive to short‐term changes than leaf blades. However, this responsiveness may allow other factors, such as sampling time, to mask genuine changes in nutrient status. The objectives of this study were to measure the influence of time of day and time since irrigation on petiole and blade phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and to compare petiole and blade samples in their stability and usefulness in evaluation of cotton nutrient status. Cotton was grown on a sandy soil in the Coastal Plain region of Georgia. Treatments were K application rates of 0, 55, and 110 kg K₂O/ha. In early bloom, leaf blades and petioles were sampled from the first fully expanded leaf immediately following irrigation at 13: 00 Monday through Friday and on Tuesday at 7: 00, 9: 00, 11: 00, 15: 00, 17: 00, and 19: 00. Blades were separated from petioles, and P, K, Ca, and Mg were measured. Petiole and blade nutrient levels were positively correlated for P, K, Ca, and Mg. The difference in K rates was not as well reflected in the blade K levels as in the petiole K levels. As time since irrigation increased and the soil dried out, the petiole K levels of the 55 and 110 kg K₂O/ha treatments became significantly different. Petiole and blade P and K levels declined earlier in the day than Ca and Mg levels as the moisture content of the leaves declined. Blade moisture content dropped earlier than petiole moisture content which led to increased nutrient concentrations. The large daily variation in petiole nutrient levels could result in altered fertilizer recommendations. Therefore, it is of critical importance to sample cotton petioles consistently at the same time of day and the same time in relation to irrigation scheduling in order to differentiate between these timing effects and the timing effect due to crop growth stage.     

玉米不同生育阶段养分效应评价方法研究

了解作物养分效应机制是提高作物养分利用效率的重要基础。本文以玉米品种"农华101"为试验材料, 进行不同播期、密度、肥料试验, 记录了生育时期的日均温, 并对玉米不同生育时期叶片及其他器官中氮、磷、钾元素含量进行了测定, 然后基于改进后的BLUP方法, 在考虑植株干物质日均积累量与自身效应、环境效应关系的基础上, 引入群体效应和温度效应, 探讨并建立了玉米不同生育阶段养分效应评价方法。在此基础上, 进一步对养分效应评价效果进行分析。结果表明: 干物质日均积累量理论值与实际值的相关性r值为0.72~0.99; 各生育阶段配对t检验的α值均大于0.05, 各生育阶段的干物质日均积累量的理论值和实测值差异均不显著(P>0.05)。研究结果表明, 用建立的玉米不同生育阶段的养分效应评价方法得到的各养分特征效应值存在较大差异, 其中: 三叶期到拔节期各养分效应值为0~0.58, 拔节期到大口期为 0.43~2.57, 大口期到吐丝期为 0.45~4.58, 吐丝期到成熟期为 0.86~4.71。综上, 利用改进后的BLUP法提出的养分效应评价方法对玉米各阶段养分效应的评价结果具有一定的指导意义, 该方法可作为玉米养分效应评价的参考手段。     

Nutritional changes in petiole sap over space and time in a tomato crop greenhouse

The aims of this trial were to determine the spatial and temporal variability of the nutrients in petiole sap in a tomato crop under greenhouse and to determine the number of sub-samples for a representative sample. The experiment consisted of the selection of 20 sampling points. Petiole of fully expanded leaf was collected weekly in order to determine Cl, NO₃-N, H₂PO₄-P, SO₄-S, Na, K, Ca and Mg concentrations. Our results showed that variations of NO₃-N, Na, Ca and K concentrations in sap were affected by the spatial distribution, whereas SO₄-S and Mg concentrations in sap were affected by their temporal distribution. The spatial variability of our experiment could be related to radiation, yield and antagonism between nutrients, whereas the time variability could be related to the phenological stage of the plant and the antagonism between nutrients. The suggested number of petiole sub-sample ranging from 25 to 113 depending on nutrient.     

Blade or petiole analysis as a guide for grape nutrition

Abstract

The leaf opposite the first fruit cluster was used for the investigation of grape nutrition at bloomtime and ripening. The data show that blade analysis and petiole analysis are both suitable for the assessment of the nutrient status in the case of P, K, Mg and Ca. However, the data obtained for nitrogen differ markedly, depending on the organ considered.

For phosphorus and potassium, the differences in nutrient content between vineyards as well as the seasonal variations are better reflected by petiole analysis. This effect, which should be favourable to the diagnosis, is paralleled by a wider scattering of the nutrient levels; as a result, the differences observed in the petiole are not statistically more significant than those in the blade.

Under relatively homogeneous conditions (same variety, same climate), the differences induced by variable parameters (soil type, sampling times, years) appear to be fluctuating, so that nutrient reference levels cannot be recommended, whether for the blade or the petiole. Both sampling modes (blade or petiole) are complementary to each other and could therefore be used advantageously for a better control of grape nutrition and fertilization.     

Effects of different magnesium levels on some morphophysiological characteristics and nutrient elements uptake in Khatouni melons (cucumis melo var. inodorus)

A nutrient solution experiment was carried out to evaluate effects of different magnesium (Mg) concentrations (0, 25, 50, 75 and 100 percent of magnesium concentration of Hoagland solution) on growth and physiological characteristics of Iranian melons (Cucumis melo var. inodorus subvar. Khatouni). The experiment was done based on completely randomized design using plastic pots and sand culture. The results showed that SPAD value of leaves, plant leaf number, stem diameter, shoot fresh and dry weight, root fresh weight, chlorophyll b, carotenoids, protein, catalase and peroxidase activities were constantly increased by increasing Mg levels of nutrient solution until 75 or 100% Mg levels, while leaf area, petiole length, internodes length were highest in lower levels of Mg compared to full Mg of nutrient solution. Moreover, the leaf concentrations of nitrogen (N), phosphorus (P), potassium (K), magnesium, and iron (Fe), but not calcium (Ca), were increased by increasing magnesium concentration to full Hoagland nutrient solution Mg level.     

Phosphorus nutrition of white rose potato in relation to growth and minerals of leaf and root tissues

Abstract

White Rose potato plants (Solanum tuberosum, L.) were grown outdoors, without tuber formation, in a modified Hoagland's nutrient solution with 9 treatments of KH₂PO₄ ranging from 0 to 4.0 mmoles per liter. Deficiency symptoms ranged from very severe to none at harvest after 27 days of growth. Growth of the potato plants increased with increased P supply and was associated with an increased P content of the plant tissues. The critical H₂PO₄‐P concentration at a 10% reduction of top growth, based on a second leaf analysis, was about 1,000 ppm for the petiole and terminal bladelet and about 1,200 ppm for the lateral bladelet, dry weight basis.

Phosphorus nutrition had only a slight effect on the K, Na, Mg and NO₃‐N concentrations of the root tissues but Ca increased as phosphate increased which suggests a calcium phosphate precipitation. Phosphorus stress lowered the K, Na, Ca, Mg and NO₃‐N concentrations of the petiole tissues of the recently matured leaf which suggests that P increases salt accumulation. Phosphorus nutrition had only a slight effect on the concentrations of K, Na, Mg and Ca of the blade tissues of the recently matured leaf but NO₃‐N increased greatly with P supply.     

Evaluation of a rapid method for plant sap nitrate analysis

Abstract

A rapid method of analysis of nitrate in plant sap using Merck test strips was evaluated. Accuracy and precision of the strips was found to be acceptable in a test in which aqueous samples were tested by four operators. Nitrate N was measured in five vegetable crops at two stages of growth by two methods: squeezing sap from fresh petiole or stem tissue with NO3‐N determination by Merck test strip; and acetic acid extraction from dried petiole or stem tissue with NO3‐N determination by autoanalyser. The relationship between the two methods was found to be highly significant with coefficient of determination exceeding 0.82 in eight out of 10 cases (crops x sampling dates). When the strip results were corrected for moisture content the relationship with the laboratory method improved in most cases.     

A petiole sap nitrate test for broccoli

Nitrogen (N) status of vegetable crops is often monitored by analysis of dried plant tissues. However, dry tissue analysis often causes a significant delay between sampling and analysis. This study was conducted to examine the accuracy of a portable nitrate meter for determining petiole sap nitrate (NO₃) contents, and the relationship between NO₃‐N concentration in fresh petiole sap and in dried petiole tissue of broccoli grown in southern Arizona during the 1993–94 and 1994–95 winter growing seasons. Experiments were factorial combinations of three irrigation rates and four N rates, both ranging from deficient to excessive. Petioles were sampled throughout each season, and split for sap and dry tissue analysis. A linear correlation was obtained between the two measurements in both seasons, with no consistent effect due to irrigation treatment or crop maturity. The regression coefficients did not differ among seasons. Therefore, a combined regression equation: Y=343+0.047X (r² = 0.799) was derived, in which Y=NO₃‐N (mg/L) in fresh petiole sap, and X=NO₃‐N (mg/kg) in dried petioles. These results suggest that the sap test can be a valuable and rapid technique to predict N needs of broccoli. Differences between the two methods are likely due to interferences in fresh petiole sap and slight differences in pools of extracted NO₃.     

Seasonal dynamics of mineral nutrients and carbohydrates by walnut tree leaves

The dry weight accumulation per leaf as well as the concentration per gram of dry weight and the accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined in walnut tree leaves (Juglans regia L.) during a complete life cycle. Additionally, the dynamics of plant nutrient concentration in leaf petiole sap and carbohydrate accumulation in leaves were studied in relation to the main life cycle events of the walnut tree. Total N, P, K, Cu, and Zn concentrations decreased, whereas that of Ca, Mg, and Mn increased during the season. Iron concentration fluctuated around a mean value. Total N, P, K, Mg, and Cu concentrations detected in younger mature leaves were at the sufficient level, whereas Ca, Fe, Mn, and Zn concentrations were at higher levels as compared to those previously reported. All the detected nutrient accumulations increased abruptly during leaf ontogeny and leaf maturation until a maximum level was attained in the younger mature leaves. Similarly, sucrose, glucose, and fructose accumulation were observed at the same period. The rates of total N, P, Cu, and Zn accumulation were lower than the rates of the observed dry matter accumulation and nutrient concentration dilution. Potassium and Mn accumulation rates were almost equal, whereas those for Ca and Mg were higher as compared to the dry matter accumulation rate. The fast embryo growing phase resulted in a considerable decrease in dry weight, total N, P, K, Cu, Zn, and carbohydrate accumulation, and to a lesser degree in Ca, Mg, and Mn accumulation. Nutrient accumulation reduction in leaves by the influence of the growing fruits were estimated to be: total N 52%, K 48%, P 29.5%, Mg 16.3%, Ca 15%, Fe 51.2%, Cu 55.2%, Zn 37.3%, and Mn 5.4% of the maximum nutrient value of the younger mature leaves. Old leaves preserved nutrients before leaf fall as follows: total N 25.4%, P 45%, K 31%, Ca 74.8%, Mg 76.5%, Mn 89.2%, Fe and Zn 50%, and Cu 37%. Nutrient remobilization from the senescing old leaves before leaf fall were: total N 22.6%, P 25.5%, K 21%, Ca 10.2%, Mg 7%, Fe 3.2%, Mn 5.4%, Cu 8%, and Zn 13.3% of the maximum value in the younger mature leaves. In early spring, the absorption rates of N, P, and Ca were low while those of Mg, Fe, Mn, Cu, and Zn were high. During the fast growing pollen phase, the N, P, Fe, Mn, Cu, and Zn concentrations were reduced. Calcium concentration is supposed to be more affected by the rate of transpiration rather than during the growing of embryo. Calcium and Mg concentrations in the sap were negatively correlated. The detected K concentration level in the sap was as high as 33 to 50 times that of soluble N, 12 to 21 times to that of P, 5 times to that of Ca, and 10 to 20 times to that of Mg. The first maximum of starch accumulation in mature leaves was observed during the slow growing embryo phase and a second one after fruit ripening. Old senescing leaves showed an extensive carbohydrate depletion before leaf fall.     

Influence of shade on mineral nutrient status of field‐grown cotton

Photosynthetic irradiance has variable effects on cotton (Gossypium hirsutum L.) growth, development, lint yield and fiber quality. However, little is known about the effect of shade on the mineral nutrient status of cotton plants. A two‐year study was conducted to determine the effects of shade (63% light reduction) at different growth stages on mineral nutrient concentrations in plant components of field‐grown cotton. Averaged over the three growth stages of first flower, peak flower, and boll development, an 8‐day period of shade increased petiole NO₃‐N, phosphorus (P), potassium (K), and sulfur (S) concentrations by 145, 17, 20, and 18%, respectively. Total nitrogen (N), P, K, S, calcium (Ca), and magnesium (Mg) concentrations in the leaf blades of the sampled petioles increased 19, 29, 22, 22, 13, and 16%, respectively, compared with those of unshaded control plants. However, bracts and floral buds of 20‐day‐old squares of shaded cotton plants showed a slight decrease (6%) in total N concentration, and increases in the other mineral nutrient concentrations. The increased mineral nutrients of shaded plants were closely associated with decreased carbohydrate accumulation. Shade during plant reproductive growth significantly affected nutrient status and TNC/N ratio of cotton. This study indicated that light intensity at the time of sampling can cause non‐representative nutrient analysis and erroneous diagnostic recommendations. Therefore, the time of day and light conditions must be considered when sampling cotton petioles and other tissues for nutrient diagnoses.     

油菜叶片扩展的功能性需硫量及其作为缺硫诊断的探讨

利用人工气候室进行了双低冬油菜Canola（Brassicanapus L.）苗期的控流试验，以探讨供硫不足条件下对植株不同生长参数动态变化的影响效应。结果表明，单位重量叶面积（即A／W）的变化是反映植株硫营养状况的最敏感指示参数。根据其相对增产率的变化求得了对油菜叶片扩展的功能性需硫（S）量为0.32％。这一数值较传统方法，即采用全株或某一器官的干物重（DM）变化所求得的临界值，能更有效地反映植株（器官）的硫素丰缺状况。当再利用能力较弱的硫元素供应不足时，最先受到影响的是幼叶的扩展速率，而植株（或叶片）的干物量往往因净同化率（EA）和相对生长率（RW）在缺硫后的一定时间内相对增加而产生累积效应。因此，油菜叶片扩展的功能性需硫量可以作为油菜缺硫的诊断指标。     

NITRATE IN LEAF PETIOLE AND BLADE OF SPINACH CULTIVARS AND ITS RELATION TO BIOMASS AND WATER IN PLANTS

A pot experiment was carried out, with 30 spinach cultivars to determine nitrate accumulation in leaf blade and petiole, and its relationship to biomass and water in plants. Results showed that the fresh weight proportion of blade to shoot was higher than that of petiole. Furthermore, a higher positive correlation was found between fresh weights of blades and shoots than that of petioles and shoots. Unlike biomass, nitrate-nitrogen (N) concentration and total amount of nitrate-N accumulated in petiole were significantly higher than those in blade, and petiole was obviously the main organ for nitrate accumulation. Differences of nitrate-N concentration in petiole and the observed positive correlation between nitrate-N concentrations in petioles and shoots were more significant than that in blades and shoots. Nitrate-N concentration in petiole was also significantly correlated with fresh and dry shoot weight and total amount of water in shoots. However, this relationship was not found for blade.     

Positional difference in potassium concentration as diagnostic index relating to plant K status and yield level in rice (Oryza sativa L.)

Plant tissue testing is used as a guide for rice (Oryza sativa L.) fertilization and has been extensively used in the diagnosis of potassium (K) deficiency. However, little attention has been paid to the variation in the diagnostic index of K status in different parts of the rice plant. Here, we assessed the feasibility by testing K concentrations of whole plants, leaf blades and leaf sheaths to develop a suitable diagnostic index of plant K status and yield level in rice under different K application rates. The results showed that this research could satisfy the requirements of K status diagnosis, based on the quadratic-plus-plateau relationship between K application rates and grain yield. The K concentrations of the leaf blades and leaf sheaths on the main stem showed differences based on position. Leaf blade K concentrations significantly decreased from the top of the plant to the bottom in the effective tillering and jointing stages. Conversely, K concentrations in the lower leaf blades exceeded those in the upper leaf blades in the booting and full heading stages. K concentrations in the leaf sheath were significantly reduced with declining leaf position except during the jointing stage under high K treatments. Leaf sheath/leaf blade K concentration ratios increased significantly more in lower tissues than in upper plant tissues. Correlation analysis showed that the K concentrations of all sampled plant tissues were positively correlated to plant K uptake and grain yield. However, K concentrations of the whole plant were more useful as a diagnostic index at the effective tillering stage than at other growth stages. Leaf sheaths in lower positions were preferable to upper leaf sheaths and all leaf blades for evaluating plant K status, although their K concentrations were greatly influenced by plant growth stage. Furthermore, this study demonstrated that the ratio between the K concentrations of the first and fourth leaf blades (LBKR_1/4) was grouped into significantly exponential curves (P < 0.01) to describe the relationship between plant K uptake and relative grain yield. Thus, LBKR_1/4 could be an ideal indicator of rice plant K status and yield level, as it eliminated the effects of plant growth stage.     

Leaf nitrate partitioning and growth response in pumpkin as influenced by nitrogen rate

Abstract

Pumpkin species Cucurbita moschata ‘Dickenson Field’ and C. pepo ‘Connecticut Field’ were grown in the greenhouse in a Plain‐field sand at 8 rates of N applied as Ca(NO₃)_2. Petiole NO₃ concentrations in recently mature and mature leaves were highly responsive to N rate. Wien plants were stressed for N, translocation of petiole NO₃ was primarily to the corresponding blade. The levels as well as the range of NO₃ concentration in the leaf blade were lower than those in the petiole. The NO₃ content in the leaf blade was slower to react to N stress than that in the petiole. Variability in NO₃ concentration among leaf parts was lowest in the petiole and highest in the blade. For each leaf part, variability in NO₃ concentration decreased with leaf age. Critical NO₃‐N concentrations in C. moschata were estimated at 18950 and 3500 ppm in mature petioles and 14700 and 3050 ppm in recently mature petioles at early vegetative and full flower growth stages, respectively.