The Dependence of Net Assimilation Rate on Leaf-area Index

The leaf-area index (leaf area per unit area of land, L) offield crops of kale and sugar-beet was varied experimentallyby removing different fractions of the plant population distributeduniformly through the crop. The net assimilation rate (E) wasdetermined in subsequent periods of 10–14 days. For kale, E decreased nearly linearly with increase of L throughoutthe range from I to 5. E of sugar-beet was less affected bychange in L and was apparently not decreased until L rose aboveabout 3. Because of this dependence of E on L, the rate of dry-matterproduction per unit area of land, or crop growth-rate (C=EL),showed a curved relation to L; for kale it increased to a maximumwhen L was between 3 and 4 and fell again at higher values ofL. Maximal C for sugar-beet occurred beyond the range of L tested,probably between L=6 and L=9. This optimal L for dry-matterproduction by sugar-beet crops probably lies near the upperlimit of the current agricultural range, so there is little,if any, scope for increasing the dry-matter yield by furtherincrease in L. For heavy kale crops L is already far in excessof the optimum, and it may be possible to increase the totaldry-matter yield of kale by repeated thinning or defoliationto hold L near the optimum.     

Dependence of Root Growth Rate on Holoploid DNA Content

Russian Journal of Developmental Biology - Analysis of root growth rate’s dependence on the holoploid DNA content was carried out on different plant species. Such dependence was found weakly...     

Effect of Temperature on Net Assimilation Rate

Net assimilation rates and other growth attributes were comparedfor rape, sunflower, and maize plants growing widely spacedat temperatures of 10°, 16°, 22°, 28°, and 34°C, in light of 3, 000 f.c. intensity. The optimum temperature for net assimilation rate lay between20° and 30° C, and was lowest for rape and highest formaize. The temperature coefficient of the net assimilation ratewas lower than that of the relative growth-rate, especiallyin rape and sunflower, corresponding to an increase in leaf-arearatio with in temperature. This arose to an increase in leaf-arearatio with rise in temperature. This mcrease arose through changeinleafarea/leaf weight; temperature had little effect on leafweight/plant weight. In moderate to warm conditions the net assimilation rate variedlittle with temperature: by only± 10 per cent between12° and 30° C for rape, and 23° and 36° C formaize. This agrees with observations in natural climates whichsuggest that temperature is generally less important than lightin controlling net assimilation rates, except in cool climates.In natural climates, as in these controlled climates, relativegrowth-rate is more temperature-dependent.     

Net Assimilation Rate Determines the Growth Rates of 14 Species of Subtropical Forest Trees

Growth rates are of fundamental importance for plants, as individual size affects myriad ecological processes. We determined the factors that generate variation in RGR among 14 species of trees and shrubs that are abundant in subtropical Chinese forests. We grew seedlings for two years at four light levels in a shade-house experiment. We monitored the growth of every juvenile plant every two weeks. After one and two years, we destructively harvested individuals and measured their functional traits and gas-exchange rates. After calculating individual biomass trajectories, we estimated relative growth rates using nonlinear growth functions. We decomposed the variance in log(RGR) to evaluate the relationships of RGR with its components: specific leaf area (SLA), net assimilation rate (NAR) and leaf mass ratio (LMR). We found that variation in NAR was the primary determinant of variation in RGR at all light levels, whereas SLA and LMR made smaller contributions. Furthermore, NAR was strongly and positively associated with area-based photosynthetic rate and leaf nitrogen content. Photosynthetic rate and leaf nitrogen concentration can, therefore, be good predictors of growth in woody species.     

Net CO(2) Assimilation Rate of Grapevine Leaves in Response to Trunk Girdling and Gibberellic Acid Application

Net CO₂ assimilation rate (A), stomatal conductance (g_s), and weight per unit leaf area (W) were determined on Thompson Seedless grapevines grown in the field. Treatments included fruit set applications of gibberellic acid (40 milligrams gibberellic acid (GA₃) per liter) to vines, shoots and clusters, alone and in combination with trunk girdling. Leaf A and g_s were measured prior to and 3, 6, and 13 days after fruit set. Weight per unit leaf area was determined on leaves collected subsequent to gas exchange measurements. Leaf A of girdled vines was reduced approximately 30% when compared to the control 13 days after treatment. The reduction in A due to girdling was not as great when vines were sprayed with GA₃. GA₃ sprays alone had no significant effect on A. Stomatal conductance was reduced by girdling 13 days after treatment. Weight per unit leaf area was 17% greater for trunk girdled vines when compared to the controls. Results indicate GA₃ affected net CO₂ assimilation rate only on girdled vines, a treatment which increased weight per unit leaf area.     

Dependence of Root Growth on Photosynthesis in Populus tremula

Hoot elongation of rooted cuttings of aspen, Populus tremula L., was followed on moist filter paper. The time course of root growth during treatments which decrease or interrupt the supply of carbohydrates to the roots was studied. At light intensities below 4000 lux the rate of root elongation was found to berelated to the light intensity over the leaves. In the dark, root growth decreased within 24 hours and the roots stopped growing completely during the second or third day. Excision of the leaves or steam-killing of the tissue in a stem section below the leaves was followed by root growth stoppage within 24 hours. These results imply that the rate of root growth under certain conditions is determined by the supply of carbohydrates from the leaves.     

The Influence of Removing Tubers on Dry-matter Production and Net Assimilation Rate of Potato Plants

To study the effect of removing tubers on growth and net assimilationrate (E) of potato, plants were grown in pots partly filledwith soil with the shoot growing through a polythene cover.Tubers developed in the space between the cover and the soilsurface. Removing tubers immediately they began to form had little effecton E at the beginning of the experiment but later greatly reducedit. Shading reduced E more at the beginning of the experimentthan later. Removing tubers decreased total dry weight, butmuch of the material that would have moved to tubers accumulatedin leaves and stems. In intact plants the loss of weight byshading was mainly from the tubers; in plants without tubersit was mainly from stems and leaves. Removing tubers increasedleaves on lateral stems. Increasing the amount of nitrogen supplieddiminished the effect on E of removing tubers, presumably becausethe extra allowed other sinks for carbohydrate to develop. Thegrowth of some buds of the potato plant is so strongly inhibitedthat they cannot grow and act as sinks for excess carbohydratewhen tubers are removed. Such internal inhibition of growthmay sometimes suffice to influence the magnitude of E of normalplants. Removing tubers usually increased sugar and starch contentand protein N content of stems and leaves.     

Influence of Flooding on Net CO2Assimilation, Growth and Stem Anatomy of Annona Species

A series of experiments was conducted to assess net CO₂assimilationand growth responses to waterlogging of grafted and seedlingtrees in the genus Annona. Seedlings of A. glabra, A. muricataandA. squamosa L., and scions of ‘Gefner’ atemoya(A. squamosaxA. cherimola Mill.), ‘49-11’ (‘Gefner’atemoyaxA. reticulata L.), ‘4-5’ (‘Priestley’atemoyaxA. reticulata), A. reticulata grafted onto either A.glabra, A. reticulata orA. squamosa rootstocks were floodedfor up to 60 d. Soil anaerobiosis occurred on the third dayof flooding. Seedlings ofA. glabra and A. muricata, and thescions ‘49-11’, ‘Gefner’ atemoya, andA. reticulata grafted onto A. glabra rootstock were consideredflood tolerant based on their ability to survive and grow inflooded conditions. Scions of the normally flood-sensitive A.reticulata, ‘Gefner’ atemoya, and ‘49-11’tolerated root waterlogging when grafted onto the flood-tolerantspecies, A. glabra. In contrast, flooding of A. squamosa seedlingsand rootstocks, and A. reticulata rootstocks greatly reducedgrowth and net CO₂assimilation rates, and resulted in 20–80%tree mortality. Stem anatomical responses to long-term flooding(12 continuous months) were assessed in seedlings of A. glabraand A. muricata, and trees of ‘49-11’ grafted ontoA. glabra. Flooded trees developed hypertrophied stem lenticels,particularly in A. glabra, and enlarged xylem cells resultingin thicker stems with reduced xylem density. Flooding did notincrease air spaces in pre-existing xylem near the pith or inxylem tissue that was formed during flooding. Thus, flood tolerancedid not involve aerenchyma formation in the stem. Copyright1999 Annals of Botany Company Flood tolerance, net CO₂assimilation, photosynthesis, stem anatomy, shoot growth, anaerobiosis, Annonaceae.     

Influence of Tops and Roots on Net Assimilation Rate of Sugar-beet and Spinach Beet and Grafts between them

Sugar-beet has a larger storage root and greater net assimilationrate (E) than spinach beet. To determine whether the greaterroot was a result or cause of the greater E, grafts were madebetween tops and roots of sugar-beet and spinach-beet in allfour possible combinations. Grafted plants with sugar-beet roots had greater E and rootdry weight, less leaf area and top dry weight and lower concentrationof sugar in the leaf lamina, than those with spinach-beet roots,irrespective of the type of top. Grafted plants with sugar-beettops had greater E, total and root dry weight, but less leafarea, than those with spinach-beet tops, irrespective of thetype of root. The difference in E between grafted plants withsugar-beet tops and spinach-beet tops was similar to that betweengrafted plants with sugar-beet roots and spinach-beet roots.It increased with time to 60 per cent. Increases in E probably represent increases in rate of photosynthesis.Sugar-beet roots probably increased photosynthesis by providinga better sink for assimilates than spinach-beet roots.     

Effect of Moisture Supply, Root Temperature, and Growth Regulators on Photosynthesis of Isolated Rooted Leaves of Sweet Potato (Ipomoea batatas)

Isolated rooted sweet potato leaves were used to study the effectof carbohydrate use and storage on photosynthesis. Tuberingof the roots was controlled (1) by varying the moisture aroundthe roots, (2) by varying the root temperature, or (3) by treatingthe leaves with growth regulators. When tubering was greatestthe total dry matter formed per unit area of leaf was also greatest.Benzyl adenine applied to the lamina increased the proportionof total dry matter in the tubers. The experiments show that increasing tuber growth increasesnet assimilation rate, supporting the view that rate of photosynthesisdepends on the capacity of sinks to accept photosynthate.     

Dependence of the Rate of Synthesis of Phosphatidylethanolamine and Phosphatidylglycerol on the Rate of Growth of Escherichia coli

The rates of synthesis of phosphatidylethanolamine and phosphatidylglycerol vary inversely with the rate of growth of Escherichia coli.     

The Effect of Rapid Temperature Increase on the Growth Rate of Wheat Leaves

The growth rate of the first leaf of eight-day-old wheat plants was measured using a DLT-2 highly sensitive linear displacement transducer. Leaf extensibility was evaluated from the growth rate under the increase in the pulling force by 2 g. An increase in the air temperature resulted in the doubling of the transpiration rate and immediate slowing of the leaf growth followed by the leaf shrinkage. However, growth was later resumed almost completely. Heat treatment did not induce any changes in the leaf extensibility, indicating that cell-wall mechanical properties were not changed. Growth retardation was supposed to result from a decrease in the water content in the leaf tissues because the balance between water influx from roots and its loss through transpiration was shifted toward the water loss. An initial drop in the relative water content (RWC) indicates such a misbalance. Subsequent growth resumption coincided with a decreased water deficiency. Since the rate of transpiration was not reduced, RWC and growth rate restoring evidently occurred due to the activated water uptake by roots, which can be explained by the increased hydraulic permeability detected in our experiments.     

Effects of Seasonal Variation in Radiation and Temperature on Net Assimilation and Growth Rates in an Arid Climate

The net assimilation rate (E_A), relative growth-rate (R_w), andleaf-area ratio (F_A) were measured for rape (Brassica napus),sunflower (Hetianthus annuus), and maize (Zea mays) at varioustimes of year in an arid climate, using young plants grown widelyspaced on nutrient culture. Multiple regression analysis accountedfor 90–95 per cent of the variation in E_A and R_W in termsof two climatic variables: mean temperature and radiation receipt. E_A rose linearly with radiation in all three species; increasein E_A with temperature was greatest in maize and least (notsignificant) in rape. R_Wrose with radiation and temperature,the latter being the more important variable especially in coolweather; a temperature optimum was shown at 24° C in rape.F_A rose with increase in temperature or decrease in radiation;its variation was due to change in leaf area/leaf weight ratherthan in leaf weight/plant weight. Multiple regression analyses can lead to faulty interpretationif the independent variables are correlated (as are climaticvariables in nature), but conclusions can be checked by controlled-environmentstudies in which climatic factors are not correlated. The presentconclusions are supported by such studies. The regression equations, coupled with average weather records,indicate seasonal cycles of growth parameters. E_A is maximalnear midsummer and minimal near midwinter, following the radiationcycle. Maxima and minima in R_W are about a month later, becauseR_W is affected by the temperature cycle and this lags behindthe radiation cycle. F_A is maximal in autumn and minimal inspring. E_A is highest where radiation receipts near 750 cal cm^–2day^–1 coincide with high temperatures. This combinationoccurs only in clear midsummer weather at low latitudes, andis maintained over long periods only in arid regions. The fact that E_A rose linearly with radiation suggests thatleaf water deficits arising under high radiation had littleeffect on E_A and that saturating levels of light were very high.     

Changes in Net Assimilation Rate and Leaf-area Ratio with Time in Dactyl is glomerata L.

Two natural populations of Dactylis glomerata, one from Norwayand the other from Portugal, were grown at four temperaturesin a 16-h photoperiod. Seedlings were harvested at six equalintervals of 7 days at 5 and 10 °C, and 3.5 days at 20 and30 °C. Time curves of net assimilation rate (NAR), leaf-arearatio (LAR) and other growth attributes were derived from curvesfitted to loge leaf area and loge plant weight as functionsof time. Three types of curves were found for both NAR and LARand these conformed to theoretical expectations. There was ageneral decline in NAR and LAR with time, but in certain treatmentsNAR increased during the later harvests, and the possible reasonsfor this are discussed. A similar rise in NAR was also obtainedin an experiment with 12 harvest times.     

Assimilation Rate and Growth of Lolium Populations in the Glasshouse in Contrasting Light Intensities

Using growth-analysis techniques, the variation in relativegrowth-rate (RGR) and its components, net assimilation rate(NAR), and leaf-area ratio (LAR), was examined in 18 populationsof L. perenne, six of L. multiflorum, and two hybrid cultivarsfrom contrasting climatic and agronomic origins, grown at lowand high light intensities in the glasshouse. Significant differences between populations were found for RGR,NAR, and LAR at both light intensities. At both intensitiesthe annual or biennial multiflorum group had a greater LAR anda lower specific leaf weight and chlorophyll content than theperennial perenne group. At the low intensity this was compensatedby a greater NAR in the perenne group, with no resultant differencein RGR. At the high intensity there was no difference betweenthe groups in NAR, and hence a greater RGR in the multiflorumgroup. Within the perenne and multiflorum groups, at both light intensities,the variation between populations in RGR was based on differencesin NAR rather than in LAR. There was no regular correlationof NAR with either specific leaf weight, or chlorophyll contentat either light intensity, though at low light intensity itwas significantly correlated with shoot-root ratio.     

Physiological Basis of the Difference in Net Photosynthetic Rate of Leaves between Two Maize Strains

Significant differences in net photosynthetic rate (P _N) of leaves between two maize (Zea mays L.) strains (Shuang 105 and 40×44) grown in the field were observed. At several growth stages, P _N of 40×44 was higher than that of Shuang 105 (from 10.3 to 32.5 %). Moreover, the strain 40×44 had a higher plant height, larger leaf area, lower chlorophyll content, and higher photochemical efficiency of photosystem 2 (PS2) (F_v/F_m and F/F_m) than strain Shuang 105. Shuang 105, which showed lower P _N, had lower stomatal conductances (g _s) but slightly higher intercellular CO₂ concentrations (C _i) than those of 40×44. Hence the differences in P _N between the two strains did not result from the difference in g _s, but probably from that in light reaction system.     

光慈姑叶片光合速率日变化规律的研究

以野生和栽培光慈姑植株为材料,研究了光慈姑叶片光合速率日变化规律和环境因子对其的影响,比较了不同生育期光合速率的大小。结果表明:3月份结果的光慈姑叶片净光合速率日变化呈单峰曲线,4月结果的光慈姑叶片净光合速率日变化呈双峰曲线,光合“午睡”现象明显;开花期与结果期的净光合速率日变化差异显著,开花期的净光合速率大于结果期的净光合速率。栽培条件下,叶片净光合速率大于野生状态下的光合速率。     

Light-dependent Assimilation of Nitrite by Isolated Pea Chloroplasts

Chloroplasts were prepared from peas (Pisum sativum) in glucose-phosphate medium. In the presence of dl-glyceraldehyde, they catalyzed nitrite-dependent O₂ evolution (mean of 13 preparations, 17.5 μmole per mg chlorophyll per hour, sd 3.64). The optimum concentration of nitrite was 0.5 mm; 0.12 mm nitrite supported V_max/2. The reaction was accompanied by the consumption of nitrite; 55 to 80% of the nitrite-N consumed was recovered as ammonia. In short experiments (less than 10 minutes) the O₂ to nitrite ratio approached 1.5, but thereafter decreased. There was no nitrite-dependent O₂ evolution with chloroplasts from plants grown without added nitrate but such chloroplasts could assimilate ammonia at about the usual rate. The results are consistent with the reduction of nitrite to ammonia involving nitrate-induced nitrite reductase and a reductant generated by the chloroplast electron transport chain.     

局部供磷对玉米根系生长、磷吸收速率的影响

玉米幼苗种子根局部供磷可明显改变根系的形态。供磷区侧根生长增加,无磷区侧极生长减少。供磷区1次、2次侧根长度与2次侧根数量明显增加;而1次侧根数量则不增加。供磷区缩小时,根系生长加快,单位根区磷吸收速率增加,但单位根重磷吸收速率的增加不很明显。磷局部供应植株主要通过供磷区根系的生长来增加磷的吸收,以满足植株对磷的需求。局部供磷植株中转运到供磷根区的光合产物明显多于无磷根区。