Biomass accumulation and partitioning, photosynthesis, and photosynthetic induction in field-grown maize (Zea mays L.) under low- and high-nitrogen conditions

The objectives of this comparative study were to investigate the responses of biomass accumulation and partitioning to nitrogen supply and to examine the effect of low-nitrogen supply on the photosynthetic responses of maize leaves to steady-state and dynamic light. While the difference in leaf number and stem diameter was not statistically significant, there was a significant difference in plant height between the low-nitrogen and high-nitrogen maize plants. During grain-filling period, the ear leaf of the low-nitrogen maize plants possessed lower values of maximum photosynthetic rate, maximum stomatal conductance, maximum transpiration rate, apparent quantum yield, light compensate point, and carboxylation efficiency than did that of the high-nitrogen maize plants. Contrarily, lower values of intercellular CO₂ concentration and dark respiration rate were observed in the high-nitrogen maize plants. In addition, a slower response to simulated sunflecks was found in the ear leaf of the low-nitrogen maize plants; however, stomatal limitations did not operate in the ear leaf of the high-nitrogen or low-nitrogen maize plants during the photosynthetic induction. As compared to the high-nitrogen maize plants, the low-nitrogen maize plants accumulated much less plant biomass but allocated a greater proportion of biomass to belowground parts. In conclusion, our results suggested that steady-state photosynthetic capacity is restricted by both biochemical and stomatal limitation and the photosynthetic induction is constrained by biochemical limitation alone in low-nitrogen maize plants, and that maize crops respond to low-nitrogen supply in a manner by which more biomass was allocated preferentially to root tissues.     

Carbohydrate Metabolism in Leaf Meristems of Tall Fescue : II. Relationship to Leaf Elongation Rates Modified by Nitrogen Fertilization

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arundinacea Schreb.). Dark respiration rates, concentrations of nonstructural carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kilograms per hectare) resulted in 140% higher leaf elongation rate when compared to plants receiving low nitrogen (22 kilograms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5.4 and 2.9 microliters O₂ consumed per milligram structural dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and takadiastase-soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-nitrogen plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.     

Interactions of Nitrogen, Phosphorus, and Potassium supplied in Leaf Sprays or in Fertilizer added to the Soil

When sugar-beet plants grown in pots were sprayed daily withnutrient solutions supplying nitrogen, phosphorus, and potassiumseparately or in all combinations, with precautions to preventspray falling on the soil in which the plants were grown, allthree nutrients were absorbed through the leaves. In one experimentnitrogen and potassium, and in another only nitrogen, causedincreases in plant dry weight and leaf area. Swedes absorbedphosphorus from leaf sprays and from fertilizer applied to thesoil, but only the fertilizer caused an increase in dry weight. Absorption of any of the nutrients tested from a spray containingmore than one nutrient was unaffected by the presence of othersin the spray, but spraying with nitrogen-containing solutionsincreased the absorption of phosphorus and potassium from thesoil, and potassium in sprays increased the uptake of phosphorusfrom the soil. Nitrogenous fertilizer applied to the soil increased the leafarea of sugar-beet plants, and hence it also increased the amountsof nitrogen, phosphorus, and potassium deposited on the leaveswhen they were sprayed with solutions of these nutrients, andthe amounts absorbed from the spray into the plants. Phosphaticfertilizer had no effect on uptake from leaf sprays. Potassicfertilizer did not affect leaf area or the estimated volumeof spray solution retained on the leaves, but it appeared toreduce uptake of potassium from the spray. Dry weight per plant was increased by all three nutrients infertilizer, and sugar yield of the roots was increased by nitrogenand potassium in fertilizer, and by nitrogen in spray. Applicationof a nutrient in leaf spray reduced the responses in dry weightand sugar yield to the same nutrient applied in fertilizer tothe soil. Less nitrogen, but more phosphorus, was taken up from the leafsprays than from fertilizer. Nutrients from sprays producedsmaller increases in total dry weight and in dry weight perunit of absorbed nutrient than the same nutrient from fertilizer. The apparent percentage recovery of nitrogen applied in spray,based on estimates of the volumes of solution retained on theleaves, was unaffected by fertilizer treatment, that of phosphoruswas increased by nitrogen fertilizer, and that of potassiumwas increased by nitrogen fertilizer and reduced by potassiumfertilizer. The volume of spray solution held on the leaveswas probably overestimated, so that the highest apparent recovery,about 60 per cent., may represent an almost complete true recovery,because only trivial amounts of the nutrients that had beenapplied in spray remained on the leaf surface to be removedby washing before harvest. Lower apparent recoveries may bedue to reduced uptake from the soil of the nutrient suppliedin spray.     

Effects of elevated [CO(2)] and nitrogen nutrition on cytokinins in the xylem sap and leaves of cotton

We measured the level of xylem-derived cytokinins (CKs) entering a cotton leaf, and the CK levels in the same leaf, thus enabling xylem sap and foliar CKs to be compared concurrently. Although zeatin was the dominant CK in xylem sap, zeatin, dihydrozeatin, and N(6)-(2-isopentenyl) adenine were present in approximately equimolar levels in leaves. Elevated [CO(2)] (EC) has an effect on the levels of cytokinins in sap and leaf tissues. This effect was modulated by the two levels of root nitrogen nutrition (2 and 12 mM nitrate). Growth enhancement (70%) in EC over plants in ambient [CO(2)] (AC) was observed for both nitrogen nutrition treatments. Low-nitrogen leaves growing in EC exhibited photosynthetic acclimation, whereas there was no sign of photosynthetic acclimation in high-nitrogen grown leaves. Under these prevailing conditions, xylem sap and leaf tissues were obtained for CK analysis. Higher nitrogen nutrition increased the delivery per unit leaf area of CKs to the leaf at AC. EC caused a greater increase in CK delivery to the leaf at low nitrogen conditions (106%) than at high nitrogen conditions (17%). EC induced a significant increase in CK content in low-nitrogen leaves, whereas CK content in leaf tissues was similar for high-nitrogen leaves growing in AC and EC.     

The effects of Cercospora leaf disease on the growth of groundnuts (Arachis hypogaea) in Nigeria

Three experiments with five alternately-branched and one sequentially-branched cultivar of groundnuts are described. Spraying to control Cercospora leaf spot disease doubled the leaf area duration and increased the total weight of a plant by about 65 %. Spraying increased the weight of kernels per plant but in the alternately-branched cultivars also increased the weight of stem and leaves. The proportion of the total dry weight in the kernels in the alternate cultivars was hardly changed by spraying. The sequentially-branched cultivar gave the same increase in total dry weight when sprayed but spraying resulted in a larger increase in the dry weight of kernels. The sequentially-branched cultivar, with few initials for vegetative growth, did not give the same increase in leaf growth.     

THE INFLUENCE OF GROWTH STAGE ON THE RESPONSE OF RED CLOVER (TRIFOLIUM PRATENSE L.) TO GIBBERELLIC ACID

The response of seedling and first harvest year plants of red clover ( Trifolium pratense L.) to treatment with gibberellic acid (GA) at various growth stages is described.
Seedlings sprayed before the seventh leaf stage developed into single-stemmed plants; treatment with GA at the third- or fourth-tiller stage resulted in final stem numbers similar to those of controls. Emergence was earliest, and the number of heads per plant greatest where sprayings were delayed until the third- or fourth-tiller stage.
In first harvest year plants significant increases in the number of heads per stem were obtained with certain treatments, especially those which had two applications of 0.5 mg. GA per plant during the elongation of the first four internodes. This was related in all treatment groups to modifications of the branching pattern, and also to the increased incidence of multiple heading. Earlier emergence resulted from treatment at all growth stages, the effect being maximal where three well-spaced sprayings were applied during active stem extension.     

Enhanced CO2 alters the relationship between photosynthesis and defence in cyanogenic Eucalyptus cladocalyx F. Muell.

The effect of elevated CO₂ and different levels of nitrogen on the partitioning of nitrogen between photosynthesis and a constitutive nitrogen-based secondary metabolite (the cyanogenic glycoside prunasin) was examined in Eucalyptus cladocalyx . Our hypothesis was that the expected increase in photosynthetic nitrogen-use efficiency of plants grown at elevated CO₂ concentrations would lead to an effective reallocation of available nitrogen from photosynthesis to prunasin. Seedlings were grown at two concentrations of CO₂ and nitrogen, and the proportion of leaf nitrogen allocated to photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), protein and prunasin compared. Up to 20% of leaf nitrogen was allocated to the cyanogenic glycoside, although this proportion varied with leaf age, position and growth conditions. Leaf prunasin concentration was strongly affected by nitrogen supply, but did not increase, on a dry weight basis, in the leaves from the elevated CO₂ treatments. However, the proportion of nitrogen allocated to prunasin increased significantly, in spite of a decreasing pool of leaf nitrogen, in the plants grown at elevated concentrations of CO₂. There was less protein in leaves of plants grown at elevated CO₂ in both nitrogen treatments, while the concentration of active sites of Rubisco only decreased in plants from the low-nitrogen treatment. These changes in leaf chemistry may have significant implications in terms of the palatability of foliage and defence against herbivores.     

EFFECTS OF GIBBERELLIN AND AMO-1618 ON GROWTH,DRY-MATTER ACCUMULATION,CHLOROPHYLL CONTENT AND PEROXIDASE ACTIVITY OF CITRUS SEEDLINGS

Monselise , S. P., and A. H. Halevy . (Hebrew U., Rehovot, Israel.) Effects of gibberellin and AMO–1618 on growth, dry-matter accumulation, chlorophyll content and peroxidase activity of citrus seedlings. Amer. Jour. Bot. 49(4): 405–412. Illus. 1962.—Sweet-lime seedlings, 6 months old, were sprayed with gibberellic acid (GA) and a growth retardant, AMO–1618, alone and in combination, at concentrations ranging between SO and 1600 ppm. Increasing concentrations of GA progressively increased shoot and internode length, did not influence number of leaves, and decreased leaf area. Dry weight of shoots was progressively increased up to 400 ppm, while dry weights of leaves and roots were decreased over all GA concentrations. Total dry weight of plants was increased by GA when related to leaf area or weight and to total chlorophyll content, which indicates a higher synthetic efficiency of leaves. This could not be detected by manometric determinations using leaf discs. It is suggested that a short determination period and/or work with detached leaves are responsible for failures to detect increased photosynthetic activity of GA-treated leaves. Chlorophyll content of leaves was decreased by increasing GA concentrations; it is shown that this is not due to “dilution” over a larger area of leaves. Peroxidase activity of leaves was only slightly reduced by GA, while it was increased by AMC–1618, acting as antagonist to GA. This is remarkable, since AMO–1618 did not clearly affect other procperties of citrus seedlings which are only slightly responsive to this chemical.     

THE DEVELOPMENTAL MORPHOLOGY OF NICOTIANA TABACUM ‘WHITE BURLEY’ AS INFLUENCED BY VIRUS INFECTION AND GIBBERELLIC ACID

Stein , Diana B. (U. Montana, Missoula.) The developmental morphology of Nicotiana tabacum ‘White Burley’ as influenced by virus infection and gibberellic acid. Amer. Jour. Bot. 49(5): 437–443. Illus. 1962.—‘White Burley’ tobacco with Severe Etch Virus (SEV) displayed a reduction of plant height which was overcome to a limited degree by spraying with gibberellic acid (GA). Spraying with GA, while hastening maturity in terms of earlier elongation and flowering, also prolonged the life of treated plants. Infection with SEV caused an increased rate of leaf production, and since flowering was also delayed, the greater number of leaves is produced by infected plants. Spraying with GA also increased the rate of leaf production but did not increase the final number of leaves produced. All groups except the unsprayed virus-infected plants showed a spurt in leaf production just prior to flowering. The pattern of internode elongation was obtained by the periodic measurement of individual internodes. In general, this pattern reflected the stunting properties of the virus and the growth-promoting properties of the GA. Internodes which were mature at time of spraying with GA were not affected. Infection with virus generally delayed elongation and shifted the internode pattern. Infection with SEV tended to reduce the size of leaves already present prior to inoculation, but some leaves produced after infection were actually 1arger than the same leaves on the controls. Spraying a healthy plant with GA made older leaves longer and wider, while less mature leaves at time of treatment tended to be longer and narrower. Spraying with GA reversed the reduction in size caused by the virus only if the leaf was a very young primordium or was formed during the course of treatment with GA.     

THE EFFECTS OF GIBBERELLIC ACID AND KINETIN ON THE GROWTH OF MAJESTIC POTATO

The effects of spraying potato plants (var. Majestic) with gibberellic acid and kinetin were investigated. Gibberellic acid increased both leaf area and dry-matter production over the short period of the experiment, but there were indications that this would not persist at maturity. Kinetin alone depressed leaf area and dry-matter production, but this did not occur in the presence of gibberellic acid. The mean net assimilation rate measured over a 2-week period was not significantly reduced by gibberellic acid.     

Using a biochemical C4 photosynthesis model and combined gas exchange and chlorophyll fluorescence measurements to estimate bundle-sheath conductance of maize leaves differing in age and nitrogen content

Bundle-sheath conductance (g(bs) ) affects CO(2) leakiness, and, therefore, the efficiency of the CO(2) -concentrating mechanism (CCM) in C(4) photosynthesis. Whether and how g(bs) varies with leaf age and nitrogen status is virtually unknown. We used a C(4) -photosynthesis model to estimate g(bs) , based on combined measurements of gas exchange and chlorophyll fluorescence on fully expanded leaves of three different ages of maize (Zea mays L.) plants grown under two contrasting nitrogen levels. Nitrogen was replenished weekly to maintain leaf nitrogen content (LNC) at a similar level across the three leaf ages. The estimated g(bs) values on leaf-area basis ranged from 1.4 to 10.3 mmol m(-2) s(-1) and were affected more by LNC than by leaf age, although g(bs) tended to decrease as leaves became older. When converted to resistance (r(bs) = 1/g(bs)), r(bs) decreased monotonically with LNC. The correlation was presumably associated with nitrogen effects on leaf anatomy such as on wall thickness of bundle-sheath cells. Despite higher g(bs), meaning less efficient CCM, the calculated loss due to photorespiration was still low for high-nitrogen leaves. Under the condition of ambient CO(2) and saturating irradiance, photorespiratory loss accounted for 3-5% of fixed carbon for the high-nitrogen, versus 1-2% for the low-nitrogen, leaves.     

The effects of different external nitrate concentrations on growth of Avena sativa cv. Amuri treated with diclofop-methyl

Avena sativa cv. Amuri fed either low or high nitrate was sprayed with diclofop-methyl (1 kg a.i. ha^-1) at the three leaf stage. The short term effects of the herbicide on chlorophyll concentration of leaves (laminae) and short and long term effects on d.wt of the component plant parts were determined by comparison with unsprayed plants. For unsprayed and sprayed plants, total leaf d.wt approximately doubled during the first twelve days after commencing treatments. Growth was substantially greater at high nitrate than low nitrate. For unsprayed plants, the increase in total leaf d.wt was due primarily to growth of leaf 3 but for sprayed plants it was due to growth of leaves 1 and 2. Twelve days after commencing treatments, d.wt of leaves 1 and 2 was substantially greater for sprayed plants than for unsprayed plants given similar nitrate, while chlorophyll concentration was substantially less. Leaf 3 d.wt and chlorophyll concentration were substantially greater in unsprayed plants than in sprayed plants given similar nitrate. For unsprayed plants, values were greater at high nitrate than low nitrate, for sprayed plants the converse was the case. Forty nine days after commencing treatments, unsprayed plants had a greater total plant d.wt than sprayed plants given similar nitrate. Total plant d.wt for unsprayed plants was greater at high nitrate than low nitrate, the opposite was the case for sprayed plants. Unsprayed plants at both nitrate levels and sprayed plants given low nitrate produced seed heads but sprayed plants given high nitrate did not. Diclofop-methyl at a rate of 0.3 kg a.i. ha^-' stopped seed head production at high nitrate. Retention and uptake of diclofop-methyl were not significantly different at low and high nitrate. At 1 kg a.i. ha-^l diclofop-methyl, plants switched from low to high nitrate at spraying showed damage similar to that shown by plants given high nitrate throughout. Addition of 200 μg GA into the leaf sheaths two days prior to spraying increased the efficacy of diclofop-methyl at low nitrate. It is proposed that increased efficiency of diclofop-methyl at high nitrate is due to increased leaf damage caused by a greater rate of leaf expansion.     

Absorption of Nitrogen, Phosphorus, and Potassium from Nutrient Sprays by Leaves

Barley, Brussels sprout, French bean, tomato, and sugar-beetplants grown in soil in pots and sprayed, usually daily, forseveral weeks, with nutrient solutions containing nitrogen,phosphorus, potassium, and a spreader, with precautions to preventthe spray solution falling on the soil, had higher nutrientcontents and dry weights than control plants sprayed with waterand spreader only. Increase in nutrient content occurred withhigh or low levels of nutrient supply to the roots and was approximatelyproportional to the concentration of spray and to the frequencyof spraying. The nitrogen content of sugar-beet plants was increased equallyby spraying with solutions supplying ammonium sulphate, calciumnitrate, or urea in equivalent concentrations. Nutrient uptake from solutions sprayed on leaves influenceduptake by the roots so that the additional amounts of nutrientcontained in sprayed plants may be greater or smaller than theamount absorbed from the spray by the leaves.     

峨眉冷杉幼苗叶片功能特征及其N、P化学计量比对模拟大气氮沉降的响应

通过人工施氮模拟大气氮沉降,研究了施氮对峨眉冷杉(Abies fabiri)幼苗叶片功能特征、氮和磷含量及其化学计量比的影响,以及幼苗对氮素的积累效应。结果表明:经过2个生长季节的施氮处理(2009年和2010年,N2)幼苗的总生物量、叶干重、叶重比、叶片氮和磷含量及其N:P分别高于对照处理11.29%、46.70%、41.40%、37.30%、22.33%和6.43%,而比叶面积则降低了6.61%,其中叶干重、叶重比和叶片氮含量与对照处理差异显著(P<0.05),N:P差异极显著(P<0.01),并且叶干重与叶片氮含量具有较强的线性相关;与经1个生长季节施氮处理(2009年,N1)的幼苗总生物量、叶干重、叶重比、比叶面积、叶片氮和磷含量及其N:P的比较分析表明,除叶重比和比叶面积外,其他指标N2均高于N1;人工施氮显著促进了幼苗叶片的生长,提高了叶片氮、磷含量及其N:P,但也反映幼苗生长仍受氮素限制,同时,峨眉冷杉幼苗具有氮素积累效应。     

Response of tomato plants infected with cucumber mosaic virus to foliar sprays of gibberellic acid

The effect of spraying tomato plants infected with cucumbermosaic virus (CMV) with gibberellic acid (GA) 1 and 5 ppm hasbeen studied in a glasshouse. Measurements showed that the differencein size between GA-treated healthy and infected plants eitherdisappeared or became insignificant and this was true at bothhigh and low planes of nutrition. Virus content was not reducedby GA. Virusinduced checks to leaf production and stem elongationtended to disappear in unsprayed plants but leaf area and shootweight did not show natural recovery. The stimulating effectof GA was primarily on leaf expansion and secondarily on shootweight.     

Growth Responses of Tomato Plants in Non-aerated Water Culture to Foliar Sprays of Gibberellic Acid and Benzyladenine

Tomato plants were grown to the five-six leaf stage in aeratedwater culture and aeration then discontinued. Foliar spraysof gibberellic acid (G), N⁶ benzyladenine (B), and ammoniumnitrate (N) were applied for periods up to 7 days and the plantsharvested on the eighth day. A mixture of 2·5 ppm G,5·0 ppm B, and 280 ppm N increased growth of the wholeplant and this was attributable almost entirely to G and B.In the leaf, both increased water content (B>G) and dry weight.G, but not B, increased leaf area; B, but not G, increased freshweight leaf/unit area. In the stem, G increased dry weight andheight; B reduced height but increased diameter and water content.Inclusion of O·I ppm indol-3yl-acetic acid in the mixturewas ineffective. The percentage increase in growth of non-aerated plants withG+B+N was greater with non-acrated than with aerated plantsfor weight of whole plant and leaf area, but not for stem height.Growth of non-aerated plants could not be increased by increasingthe volume of the nutrient solution, by ‘aerating’with nitrogen, or by applying minerals in foliar sprays.     

Field and laboratory studies of the effect of urea on ascospore production of Venturia inaequalis (Cke.) Wint

Applications of urea after harvest but before leaf-fall restricted perithecial production by Venturia inaequalis. Immersion of detached leaves in urea appeared to be the most effective method of preventing perithecial formation, although spraying attached leaves was equally effective when leaf abscission occurred within a week of treatment. A high nitrogen content within the leaf was one of the major factors contributing to suppression. Urea-treated leaves decomposed rapidly, thus destroying the overwintering substrate for the fungus. When apple plants (clone M. 111) were sprayed in autumn with 5 % urea, followed by a second (pre-bud-burst) application at 2 %, ascospore production in the spring was suppressed. The second treatment appeared to prevent the release of ascospores from mature perithecia.     

Growth Promoting Effect of a Transpiration Suppressant on Cotton

The transpiration suppressant Tag 16 (polyethylene emulsion), which is known to form thin films on leaves, was sprayed on cotton plants grown under varying weather and soil moisture conditions. In hot, dry weather and under restricted water supply 10 and 15% solution of the original Tag 16 promoted extension growth and increased fresh and dry weight of plants. In hot, humid weather three sprays at weekly intervals did not have any effect on plant height, fresh and dry weight, leaf number and flowering.     

ABA and GA3 affect the growth and pigment composition in Andrographis paniculata Wall.ex Nees., an important folk herb

In this study, 5 μmol·L-1 abscisic acid (ABA) and gibberellic acid (GA3) were used to study the effect of both growth regulators on the morphological parameters and pigment composition of Andrographispaniculata. The growth regulators were applied by means of foliar spray during morning hours. ABA treatment inhibited the growth of the stem and internodal length when compared with control, whereas GA3 treatment increased the plant height and internodal length. The total number of leaves per plant decreased in the ABA-treated plants, but GA3 treatment increased the total number of leaves when compared with the control. Both growth regulators (ABA and GA3) showed increased leaf area. ABA and GA3 treatments slightly decreased the total root growth at all the stages of growth. The growth regulator treatments increased the whole plant fresh and dry weight at all stages of growth. ABA enhanced the fresh and dry weight to a larger extent when compared with GA3. An increase in the total chlorophyll content was recorded in ABA and GA3 treatments. The chlorophyll-a, chlorophyll-b, and carote-noids were increased by ABA and GA3 treatments when compared with the control plants. The xanthophylls and anthocyanin content were increased with ABA and GA3 treatments in A. Paniculata plants.     

Leaf lifespan and lifetime carbon balance of individual leaves in a stand of an annual herb, Xanthium canadense

Leaf lifespan in response to resource availability has been documented in many studies, but it still remains uncertain what determines the timing of leaf shedding. Here, we evaluate the lifetime carbon (C) balance of a leaf in a canopy as influenced by nitrogen (N) availability. Stands of Xanthium canadense were established with high-nitrogen (HN) and low-nitrogen (LN) treatments and temporal changes of C gain of individual leaves were investigated with a canopy photosynthesis model. Daily C gain of a leaf was maximal early in its development and subsequently declined. Daily C gain at shedding was nearly zero in HN, while it was still positive in LN. Sensitivity analyses showed that the decline in the daily C gain resulted primarily from the reduction in light level in HN and by the reduction in leaf N in LN. Smaller leaf size in LN than in HN led to higher light levels in the canopy, which helped leaves of the LN stand maintain for a longer period. These results suggest that the mechanism by which leaf lifespan is determined changes depending on the availability of the resource that is most limiting to plant growth.