The effect of shading on photosynthesis,growth, and regrowth following defoliation for Bromus tectorum

Summary The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects.     

Photosynthetic acclimation of Tradescantia albiflora to growth irradiance: morphological, ultrastructural and growth responses

Tradescantia albiflora (Kunth), a trailing ground species naturally occurring in deep shade in rainforests, has an unusual photosynthetic acclimation profile for growth irradiance. Although capable of increasing its capacity for electron transport, photophosphorylation and carbon fixation when grown in full sunlight, Tradescantia has constant chlorophyll alb ratios, photosystem reaction centre stoichiometry and pigment-protein composition at all growth irradiances (Chow et al. 1991. Physiol. Plant. 81: 175–182). To gain an insight into the compensatory strategies which allow Tradescantia to grow in both high and low lights, plants were grown under shade cloth (100 to 1.4% relative growth irradiance) and leaf and chloroplast attributes were compared. While shade Tradescantia chloroplasts had three times more chlorophyll per chloroplast and twice the length of thylakoid membranes compared to plants grown in full sunlight, the ratios of appressed to nonappressed thylakoid membranes were constant. The average net surface charge density of destacked thylakoids was the same for plants grown at moderate and low-irradiance, consistent with their similar stacking profiles. Tradescantia plants grown in direct sunlight had 10-times more fresh and dry weight per plant compared to plants grown in shade, despite a lower photosynthetic capacity on a leaf area basis with partial photoinhibition. We conclude that having a light-harvesting apparatus permanently locked into the "shade-plant mode " does not necessarily prevent a plant from thriving in high light. Analyses of leaf growth at different irradiances provide a partial explanation of the manner in which Tradescantia compensates for very low photosynthetic capacity per unit leaf in sunlight.     

Functional analysis of the relative growth rate, chemical composition, construction and maintenance costs, and the payback time of Coffea arabica L. leaves in response to light and water availability

In this study, the combined effects of light and water availability on the functional relationships of the relative growth rate (RGR), leaf chemical composition, construction and maintenance costs, and benefits in terms of payback time for Coffea arabica are presented. Coffee plants were grown for 8 months in 100% or 15% full sunlight and then a four-month water shortage was implemented. Plants grown under full sunlight were also transferred to shade and vice versa. Overall, most of the traits assessed were much more responsive to the availability of light than to the water supply. Larger construction costs (12%), primarily associated with elevated phenol and alkaloid pools, were found under full sunlight. There was a positive correlation between these compounds and the RGR, the mass-based net carbon assimilation rate and the carbon isotope composition ratio, which, in turn, correlated negatively with the specific leaf area. The payback time was remarkably lower in the sun than in shade leaves and increased greatly in water-deprived plants. The differences in maintenance costs among the treatments were narrow, with no significant impact on the RGR, and there was no apparent trade-off in resource allocation between growth and defence. The current irradiance during leaf bud formation affected both the specific leaf area and leaf physiology upon transferring the plants from low to high light and vice versa. In summary, sun-grown plants fixed more carbon for growth and secondary metabolism, with the net effect of an increased RGR.     

光强对四种亚热带树苗生长特征影响的比较

鼎湖山亚热带森林优势树种藜蒴、荷木、黄果厚壳桂和马尾松2－3年生树苗,盆栽于16％、40％和100％的自然光下生长16个月．3种阔叶树无论在全自然光还是在弱光下均能较好地存活,遮光下的马尾松则出现不同程度的死亡．全光下的马尾松、黄果厚壳桂树苗的基径和树高生长大于遮光下的树苗．4个树种的侧枝数均随光照的减弱而下降．在不考虑新老叶更新的情况下,全光下的藜蒴、黄果厚壳桂单株叶片数大于弱光下的树苗,而荷木则相反．如果以全光下单株树苗干物质量为100％,那么在相对光照为40％和16％下生长的马尾松、黄果厚壳桂、荷木和藜蒴单株树苗的干物质量分别为57．4％和32．7％、73．8％和62．1％、78．0％和78．6％、93．9％和76．2％．不同光强下的藜蒴、荷木地上部分干物质量的变化不大,地下部分则随光照的减弱而下降,马尾松、黄果厚壳桂无论地上还是地下部分干物质量均随光强的减弱而明显减少．遮光下生长的3个阔叶树种树苗的冠根比（CRR）、叶重比（LWR）、叶面积比（LAR）和比叶面积（SLA）均高于全光下的树苗．马尾松为喜光树种,对阴生环境的适应能力极为有限;黄果厚壳桂为耐阴树种,在全光下仍然比遮光条件下生长较快．     

全日光强下5种植物叶片的UV-B防护

通过测定马尾松(Pinus massoniana)和荷木(Schima superba),及黄果厚壳桂(Cryptocarw concinna)、藜蒴(Castanopsis fissa)和锥树(Castartopsis chinensis)叶片中甲醇提取物和细胞壁碱性酚类提取物中UV-B吸收物质的含量,以及叶片叶绿素含量和比叶面积,研究全日光强下植物对UV-B的防护策略。结果表明,在全日光强下植物叶片甲醇提取物的UV-B吸收能力较遮阴下的高,如藜蒴和锥树分别高出42．6％和32．6％,而马尾松仅高出4．2％。全日光强下的黄果厚壳桂和荷木叶片细胞壁碱性酚类提取物的UV-B吸收能力亦分别比遮阴下的高3596和11．7％,而马尾松、锥树和藜蒴则较遮阴下的低,可能这些树种在全日光下细胞壁UV-B吸收物质有部分转移到细胞质,以增强栅栏组织细胞的保护。全目光强下这几种植物叶片的叶绿素含量较遮阴下的低,但有较高的比叶面积,这可能有利于减少对光的吸收和对深层组织细胞器的保护。可见不同植物是采取不同的策略来适应增高的UV-B辐射。     

Plasticity in seedling morphology,biomass allocation and physiology among ten temperate tree species in response to shade is related to shade tolerance and not leaf habit

• Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle‐leaved) and observed tolerance to shade, when growing in two contrasting light treatments – open (about 20% of full sunlight) and shade (about 5% of full sunlight).
• We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments.
• Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) – leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area‐based rates of light‐saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade.
• We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle‐leaved conifers in response to shade. However, an expectation of higher plasticity in shade‐intolerant species than in shade‐tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.

     

Leaf area and photosynthesis of newly emerged trifoliolate leaves are regulated by mature leaves in soybean

Leaf anatomy and the stomatal development of developing leaves of plants have been shown to be regulated by the same light environment as that of mature leaves, but no report has yet been written on whether such a long-distance signal from mature leaves regulates the total leaf area of newly emerged leaves. To explore this question, we created an investigation in which we collected data on the leaf area, leaf mass per area (LMA), leaf anatomy, cell size, cell number, gas exchange and soluble sugar content of leaves from three soybean varieties grown under full sunlight (NS), shaded mature leaves (MS) or whole plants grown in shade (WS). Our results show that MS or WS cause a marked decline both in leaf area and LMA in newly developing leaves. Leaf anatomy also showed characteristics of shade leaves with decreased leaf thickness, palisade tissue thickness, sponge tissue thickness, cell size and cell numbers. In addition, in the MS and WS treatments, newly developed leaves exhibited lower net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E), but higher carbon dioxide (CO ₂ ) concentration in the intercellular space (Ci) than plants grown in full sunlight. Moreover, soluble sugar content was significantly decreased in newly developed leaves in MS and WS treatments. These results clearly indicate that (1) leaf area, leaf anatomical structure, and photosynthetic function of newly developing leaves are regulated by a systemic irradiance signal from mature leaves; (2) decreased cell size and cell number are the major cause of smaller and thinner leaves in shade; and (3) sugars could possibly act as candidate signal substances to regulate leaf area systemically.     

Carbohydrate storage,survival, and growth of two evergreen <Emphasis Type="Italic">Nothofagus</Emphasis> species in two contrasting light environments

A number of traits have been attributed important roles in tolerance of shade by plants. Some explanations emphasize traits enhancing net carbon gain; others emphasize energy conservation traits such as storage of non-structural carbohydrates (NSC). To date, cross-species studies have provided mixed support for the role of NSC storage in low-light survival. We examined NSC status, survival, biomass, and growth of large seedlings of two evergreen species of differing shade tolerance (Nothofagus nitida and N. dombeyi) grown in deep shade and 50% light for two growing seasons. We expected to find higher NSC concentration in the more shade-tolerant N. nitida and since allocation to storage involves sacrificing growth, higher growth rate in the shade-intolerant N. dombeyi. NSC concentration of both species was >twofold higher in 50% light than in deep shade, and in roots and stems did not differ significantly between species in either environment. NSC contents per plant were also similar between dead and living plants in deep shade. N. dombeyi outgrew N. nitida in 50% light, while this pattern was reversed in deep shade. Survival in deep shade was not correlated with NSC concentration. Leaf mass fraction was similar between species in 50% light, but lower in N. dombeyi in deep shade. Results provide little evidence of a link between carbohydrate storage and low-light survival in Nothofagus species, and support the view that understorey survival is primarily a function of net carbon gain. Patterns of variation in NSC concentration of the temperate species we studied are likely dominated by more important influences than adaptation to shade, such as limitation of growth or adaptation to cold stress.     

Photosynthetic responses of <Emphasis Type="Italic">Chrysanthemum morifolium</Emphasis> to growth irradiance: morphology,anatomy and chloroplast ultrastructure

Seedlings of Chrysanthemum, cultivar ‘Puma Sunny’, were grown under a range of shading regimes (natural full sunlight, 55, 25, and 15% of full sunlight) for 18 days. Here, we characterized effects of varying light regimes on plant morphology, photosynthesis, chlorophyll fluorescence, anatomical traits, and chloroplast ultrastructure. We showed that leaf color was yellowish-green under full sunlight. Leaf area, internode length, and petiole length of plants were the largest under 15% irradiance. Net photosynthetic rate, water-use efficiency, PSII quantum efficiency, and starch grain were reduced with decreasing irradiance from 100 to 15%. Heavy shading resulted in the partial closure of PSII reaction centers and the CO₂ assimilation was restricted. The results showed the leaves of plants were thinner under 25 and 15% irradiance with loose palisade tissue and irregularly arranged spongy mesophyll cells, while the plants grown under full sunlight showed the most compact leaf palisade parenchyma. Irradiance lesser than 25% of full sunlight reduced carbon assimilation and led to limited plant growth. Approximately 55% irradiance was suggested to be the optimal for Chrysanthemum morifolium.     

Effects of light availability on host plant chemistry and the consequences for behavior and growth of an insect herbivore

We examined how light availability influenced the defensive chemistry of tomato (Lycopersicon esculentum: Solanaceae). Tomato plants were grown either in full sunlight or under shade cloth rated at 73%. Leaves from plants grown in full sunlight were tougher, had higher concentrations of allelochemicals (chlorogenic acid, rutin and tomatine), and had less protein than leaves from plants grown in shade. We determined how these differences in host plant quality due to light availability affected the behavior and growth of a Solanaceae specialist, Manduca sexta. Both in the greenhouse and in the field, caterpillars on shade-grown plants grew heavier in a shorter amount of time than those on plants that had previously been grown in full sunlight. In contrast, the effects of previous light availability to plants on caterpillar behavior appeared to be minor.To further investigate how light availability to plants influenced herbivore growth, we examined the effects of leaf-powder diets made from tomato leaves of different ages (new, intermediate, or mature) grown in full sunlight or shade on caterpillar performance. Caterpillars fed diets made from plants grown in shade consumed less but grew faster than larvae fed diets made from tomato plants grown in full sunlight. Caterpillars fed diets made from new leaves grew larger in less time than caterpillars fed diets made from intermediate aged leaves. Caterpillars did not survive on the mature leaf powder diets. There were plant-light treatment by larval thermal regime interactions. For example, at 26:15 °C , plant-light treatment had no effect on stadium duration, but at 21:10 °C, stadium duration was prolonged with the full sunlight-new leaf diet compared with the shaded-new leaf diet. In a second diet experiment, we examined the interactive effects of protein and some tomato allelochemicals (rutin, chlorogenic acid and tomatine) on the performance of caterpillars. There were food quality by thermal regime interactions. For instance, at 26:15 °C , neither protein nor allelochemical concentration influenced stadium duration, whereas at 21:10 °C, stadium duration was prolonged with the low protein-high allelochemical diet, which simulated full sunlight leaves. In sum, light availability to plants affected defensive chemistry and protein concentration. The difference in food quality was great enough to influence the growth of a specialist insect herbivore, but the effects were temperature-dependent.     

The effect of altered sink-source relations on photosynthetic traits and matter transport during the phase of reproductive growth in the annual herb <Emphasis Type="Italic">Chenopodium album</Emphasis>

Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO₂ concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20^th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20^th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant’s ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.     

Acclimation of Myrtus communis to contrasting Mediterranean light environments - effects on structure and chemical composition of foliage and plant water relations

Leaf anatomical and chemical characteristics, water relations and stomatal regulation were studied in the shrub Myrtus communis growing under two contrasting Mediterranean light environments (full light versus 30% of full light) during the spring-summer period. These studies aimed to assess plant response to the combined effects of light and water availability. Foliar morphology, anatomy and chemistry composition acclimated positively to light conditions. Leaves of sun-exposed plants were thicker (38.7%) than those of shaded plants, mainly due to increased palisade parenchyma thickness, had a higher nitrogen concentration and stomatal density than the shade ones, which maximized foliar area (>SLA) and Chl/N molar ratio to improve light interception. Chlorophyll concentration per leaf area (Chl(a)) was always higher in sun leaves while, as expressed on dry mass (Chl(m)), significant differences were only apparent in September, shade leaves presenting higher values. During the summer period Chl(a) and Chl(m) markedly declined in sun leaves and remained unchanged in shade ones. The ratio of chlorophyll a/b was not affected either by the light intensity or by the season. Shade leaves presented generally a higher concentration of soluble carbohydrates per dry mass. No significant differences in starch concentration were apparent between sun and shade leaves and a gradual depletion occurred during the water stress period. Maximum stomatal conductances correlated positively with predawn water potential. Throughout the season, sun plants always presented higher leaf conductance to water vapour and lower minimum leaf water potentials, indicating an interaction of light-environment on these water relation parameters. Stomatal closure constitutes a mechanism to cope with diurnal and seasonal water deficits, sun plants presenting a more efficient control of water losses during water deficiency period. In addition, both sun and shade plants evidenced leaf osmotic adjustment ability in response to water stress, which was greater in sun ones.     

Interactive effects of lateral shade and wind on stem allometry, biomass allocation, and mechanical stability in Abutilon theophrasti (Malvaceae)

The effects of lateral shade and wind on stem allometry, whole-plant biomass allocation, and mechanical stability were examined for Abutilon theophrasti in a fully factorial glasshouse experiment. Lateral shade from neighboring plants increased stem height by 33% relative to control plants grown individually, despite a decrease in plant dry mass. Intermittent wind decreased stem height by 18% in unshaded plants, but by only 3% in shaded plants. Surprisingly, both lateral shade and wind caused decreases in stem diameter, even with diameter controlled for height, resulting in low diameter?:?height ratios in wind-treated plants relative to untreated plants. Under shade, wind-treated plants had higher root allocation than untreated plants, which allowed wind-treated shade plants to compensate for a low diameter?:?height ratio. This did not occur in the absence of shade, where stem tissue density and root allocation of wind-treated plants did not exceed that of untreated plants. Nevertheless, wind-treated plants experienced low drag relative to untreated plants due to a lower leaf area. Consequently, stem deflections of wind-treated plants did not exceed those of untreated plants at any given windspeed. Our results document a complex interaction between shade and wind on plant morphology and suggest that the nature of this interaction is generally that lateral shade acts to reduce or eliminate thigmomorphogenic responses.     

Use of a SPAD meter to estimate chlorophyll content in Eugenia uniflora L. leaves as affected by contrasting light environments and soil flooding

In three separate experiments, the effectiveness of a SPAD-502 portable chlorophyll (Chl) meter was evaluated for estimating Chl content in leaves of Eugenia uniflora seedlings in different light environments and subjected to soil flooding. In the first experiment, plants were grown in partial or full sunlight. In the second experiment plants were grown in full sunlight for six months and then transferred to partial sunlight or kept in full sunlight. In the third experiment plants were grown in a shade house (40% of full sunlight) for six months and then transferred to partial shade (25–30% of full sunlight) or full sunlight. In each experiment, plants in each light environment were either flooded or not flooded. Non-linear regression models were used to relate SPAD values to leaf Chl content using a combination of the data obtained from all three experiments. There were no significant effects of flooding treatments or interactions between light and flooding treatments on any variable analyzed. Light environment significantly affected SPAD values, chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll [Chl (a+b)] contents in Experiment I (p≤0.01) and Experiment III (p≤0.05). The relationships between SPAD values and Chl contents were very similar among the three experiments and did not appear to be influenced by light or flooding treatments. There were high positive exponential relationships between SPAD values and Chl (a+b), Chl a, and Chl b contents.     

Elevated atmospheric partial pressure of CO2 and plant growth

Cotton plants were grown in late spring under full sunlight in glasshouses containing normal ambient partial pressure of CO₂ (32±2Pa) and enriched partial pressure of CO₂ (64±1.5Pa) and at four levels of nitrogen nutrition. Thirty-five days after planting, the total dry weights of high CO₂-grown plants were 2- to 3.5-fold greater than plants grown in normal ambient CO₂ partial pressure. Depending on nitrogen nutrition level, non-structural carbohydrate content (mainly starch) in the leaves of plants grown in normal CO₂ was between 4 and 37% of the total leaf dry weight compared to 39 to 52% in the leaves of high CO₂-grown plants. Specific leaf weight calculated using total dry weight was 1.6- to 2-fold greater than that based on structural dry weight. In high CO₂-grown plants the amount of non-structural carbohydrate translocated from the leaves at night was between 10 and 20% of the level at the end of the photoperiod. This suggests that the plant was unable to utilize all the carbohydrate it assimilated in elevated CO₂ atmosphere. While there was a 1.5-fold enhancement in the rate of CO₂ assimilation in plants grown in 64 Pa CO₂, there was, however, some evidence to suggest that the activities of other metabolic pathways in the plants were not stimulated to the same extent by the enriched CO₂ atmosphere. This resulted in massive accumulation of non-structural carbohydrate, particularly at low level of nitrogen nutrition.Abbreviations A rate of CO₂ assimilation - PPFD photosynthetic photo flux density - NAR net assimilation rate - pCO₂ partial pressure of CO₂ - RGR relative growth rate     

光强对杉木幼苗形态特征和叶片非结构性碳含量的影响

选取南方重要的造林树种杉木(Cunninghamia lanceolata(Lamb.)Hook)幼苗为研究对象,通过搭建遮荫棚设置5个光照强度(分别为自然光照的100%、60%、40%、15%和5%),研究了幼苗在不同光照强度下的生长形态、生物量积累及分配、叶片的非结构性碳含量(NSC)特征。结果显示:(1)叶长、叶宽和叶面积在40%光照强度下最大,而比叶面积和叶片相对含水量随着光照强度的降低呈递增趋势;(2)随着光照强度的降低,杉木幼苗各器官生物量下降,根生物量比和根冠比降低,茎和叶生物量比增加;(3)杉木幼苗在60%光照强度下叶片非结构性碳含量最高,5%光照强度下含量最低;(4)杉木幼苗比叶面积与叶生物量以及与非结构性碳含量之间存在极显著的负相关关系(P0.01),叶生物量与非结构性碳含量之间存在极显著的正相关关系(P0.01)。杉木幼苗能够通过形态学上的可塑性来适应不同的光强环境,提高光竞争能力和生存适合度,但在5%光照强度下,由于较难维持碳收支平衡而不利于其生长和存活。     

Evergreen Foliage Contributions to the Spring Growth of Taxus

Taxus media cv. Hicksii plants were grown one season under a low and high level of nitrogen fertilization. Before growth in the spring the plants were divided into two groups, one of which was defoliated and the other left intact. The growth and spring utilization of the nitrogen and carbohydrate reserves of defoliated plants were compared to the intact plants 0, 2, 4 and 6 weeks after growth started in the spring. The plants were separated into buds (all new growth), roots and stems and analyzed for changes in total nitrogen, basic and non-basic amino acids, hemicelluloses, soluble sugars, organic acids and chlorophyll. The older evergreen needles from plants grown under low nitrogen levels contain 20 % of the carbohydrate and 24% of the nitrogen used in spring growth. The needles from plants grown under high nitrogen levels contained 56% of the carbohydrate and 49% of the nitrogen used in spring growth. Removal of the old needles before spring growth removed this nitrogen and carbohydrate reserve and reduced the total plant chlorophyll content after 6 weeks of growth to 50% of that found in intact plants, with the result that defoliated plants did not show a growth response to nitrogen. Amino acids accumulated in the stems and buds of defoliated plants as carbohydrates became limiting. The defoliated plants removed 25% more available carbohydrates from the roots and stems than intact plants and their buds contained 50% less available carbohydrates. Plants without old needles showed similar growth rates under low and high nitrogen regimes and produced 33% of the dry weight of intact plants grown under high nitrogen levels and 66% of the dry weight of intact plants grown under low nitrogen levels. The old needles of taxus plants contain substantial amounts of reserve nitrogen and carbohydrate and these needles greatly influence the extent and rapidness of growth in the spring. When the needles are removed, the other tissues can supply an adequate amount of nitrogen but the carbohydrate supply becomes limiting for spring growth.     

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.     

Changes in chemical composition of hydrophyte leaves during adaptation to aquatic environment

Leaf chemical composition of 19 hydrophytes was studied. The content of carbon, nitrogen, nonstructural carbohydrates, organic acids, minerals, and water was determined. Hydrophytes were shown to contain less carbon (below 410 mg/g dry wt in 60% species) than terrestrial plants. Hydrophytes and terrestrial plants did not differ in the nitrogen concentration in the leaves (33 and 29 mg/g dry wt, respectively). Hydrophytes were characterized by a low content of organic acids (40–90 mg/g dry wt in 60% species) and high content of mineral compounds (90–170 mg/g dry wt in 50% species). Total amount of nonstructural carbohydrates was similar in the leaves of hydrophytes and terrestrial plants (from 120 to 190 mg/g dry wt), but the proportions of various carbohydrate fractions differed substantially. In the hydrophyte leaves, the content of soluble carbohydrates was 2.4-fold lower, whereas the content of nonstructural polysaccharides 1.2-fold higher than in terrestrial plant leaves. Two groups of correlations between parameters of leaf chemical composition were distinguished: the contents of carbon, nitrogen, and soluble sugars were positively correlated, and the negative correlation was observed between these parameters and the amounts of mineral compounds, organic acids, water, and nonstructural polysaccharides. We concluded that hydrophyte leaf chemical composition reflects a specificity of plant adaptation to aquatic environment.     

Photosynthetic performance of <Emphasis Type="Italic">Lycoris radiata</Emphasis> var. <Emphasis Type="Italic">radiata</Emphasis> to shade treatments

The effects of shade on the growth, leaf photosynthetic characteristics, and chlorophyll (Chl) fluorescence parameters of Lycoris radiata var. radiata were determined under differing irradiances (15, 65, and 100% of full irradiance) within pots. The HI plants exhibited a typical decline in net photosynthetic rate (P _N) during midday, which was not observed in MI- and LI plants. This indicated a possible photoinhibition in HI plants as the ratio of variable to maximum fluorescence (F_v/F_m) value was higher and the minimal fluorescence (F₀) was lower in the, and LI plants. Diurnal patterns of stomatal conductance (g _s) and transpiration rate (E) were remarkably similar to those of P _N at each shade treatments, and the intercellular CO₂ concentration (C _i) had the opposite change trend. Under both shading conditions, the light saturation point, light compensation point and photon-saturated photosynthetic rate (P _max) became lower than those under full sunlight, and it was the opposite for the apparent quantum yield (AQY). The higher the level of shade, the lower the integrated daytime carbon gain, stomatal and epidermis cell densities, specific leaf mass (SLM), bulb mass ratio (BMR), leaf thickness, and Chl a/b ratio. In contrast, contents of Chls per dry mass (DM), leaf area ratio (LAR), leaf mass ratio (LMR), leaf length, leaf area and total leaf area per plant increased under the same shade levels to promote photon absorption and to compensate for the lower radiant energy. Therefore, when the integrated daytime carbon gain, leaf area and total leaf area per plant, which are the main factors determining the productivity of L. radiata var. radiata plant, were taken into account together, this species may be cultivated at about 60∼70% of ambient irradiance to promote its growth.