The photosynthetic capacity of stubble leaves and their contribution to growth of the lucerne plant after low level cutting

1972 ◽  
Vol 23 (2) ◽  
pp. 225 ◽  
Author(s):  
KC Hodgkinson ◽  
NG Smith ◽  
GE Miles
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rate ◽  
Photosynthetic Capacity ◽  
Dry Weight ◽  
Carbon Dioxide Exchange ◽  
Weight Changes ◽  
Plant Parts ◽  
Tap Root ◽  
Leaf Resistance ◽  
Mesophyll Resistance

The net carbon dioxide exchange rate (NCE) of lucerne (Medicago sativa cv. Hunter River) stubble leaves was found to be low (c. 55 ng CO2 cm-2 sec-1) immediately after removing shoots 15 cm above the stem base. However, within several days the NCE rose to a maximum of 130 ng CO2 cm-2 sec-1 on day 8. This peak rate was similar to that of recently expanded new leaves and held for about 3 days before declining. Leaves of similar age and position on uncut plants showed a steady decline in NCE. Leaf resistance, r'l, was low (c. 0.8 sec cm-1) and did not change as the NCE increased during the first 8 days. Mesophyll resistance, r'm, to carbon dioxide diffusion was initially high and declined from c. 9 to 2 sec cm-1 during this period. Comparison of dry weight changes of plant parts after stubble leaves were either retained or removed suggested that the tap-root benefited most by stubble leaf retention. The contribution to new shoots from stubble leaves appeared to be slight. However, when stubble leaves were exposed to 14CO2 on day 11, photosynthate was mainly exported into the shoot arising from the axil of the exposed leaf. This suggests that stubble leaves substitute, in part or completely, for the supply of carbohydrate to stubble shoots normally derived from reserves mobilized in the tap-root. The likely causes of rejuvenation in NCE of stubble leaves after partial shoot removal are discussed along with the significance of this photosynthetic contribution to regrowth of the lucerne plant.

Characteristics of the canopy, root system and grain yield of a crop of Lupinus angustifolius cv. Unicrop

1975 ◽  
Vol 26 (3) ◽  
pp. 497 ◽  
Author(s):  
EAN Greenwood ◽  
P Farrington ◽  
JD Beresford
Keyword(s):  
Carbon Dioxide ◽  
Grain Yield ◽  
Leaf Area ◽  
Time Course ◽  
Dry Weight ◽  
Grain Filling ◽  
Main Axis ◽  
Carbon Dioxide Exchange ◽  
Area Index ◽  
Plant Parts

The time course of development of a lupin crop was studied at Bakers Hill, Western Australia. The aim was to gain insight into the crop factors influencing yield. Weekly measurements were made of numbers and weights of plant parts, and profiles of roots, leaf area and light interception. A profile of carbon dioxide in the crop atmosphere was taken at the time of maximum leaf area, and the net carbon dioxide exchange (NCE) of pods was estimated for three successive weeks. The crop took 10 weeks to attain a leaf area index (LAI) of 1 and a further 9 weeks to reach a maximum LAI of 3.75, at which time only 33% of daylight reached the pods on the main axis. Once the maximum LAI was attained at week 19, leaf fall accelerated and rapid grain filling commenced almost simultaneously on all of the three orders of axes which had formed pods. Measurements of NCE between pods on the main axis and the air suggest that the assimilation of external carbon dioxide by the pods contributed little to grain filling. Grain dry weight was 2100 kg ha-1 of which 30%, 60% and 10% came from the main axis, first and second order apical axes respectively. Only 23% of the flowers set pods and this constitutes an important physiological limitation to grain yield.

COMPARISON OF PHOTOSYNTHESIS IN NORMAL AND TRIAZINE-RESISTANT Brassica

1987 ◽  
Vol 67 (2) ◽  
pp. 457-466 ◽  
Author(s):  
S. L. A. HOBBS
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rate ◽  
Chlorophyll A ◽  
Dry Weight ◽  
Stomatal Resistance ◽  
Carbon Dioxide Exchange ◽  
Shoot Dry Weight ◽  
Significant Difference ◽  
The Difference ◽  
Net Assimilation

In spaced field plantings, triazine-resistant types of Brassica campestris L. and B. napus L. had a carbon dioxide exchange rate (CER) 28% lower in 1983 and 25% lower in 1984 than normal (triazine-susceptible) types. In plots simulating agronomic spacings in 1984, the difference between CER in normal and resistant types was 17% for B. campestris, 14% for B. napus and 13% for B. juncea L. Differences were apparent throughout the season and were not associated with any particular stage of growth. Resistant progeny from reciprocal crosses between resistant and susceptible plants of B. napus exhibited reduced CER at all levels of photosynthetically active radiation and at all temperatures. There was no significant difference between plant types for chlorophyll a + b content or chlorophyll a/b ratio. Shoot dry weight, stomatal resistance and specific leaf weight were higher in the normal types, but there was no difference between types in either relative growth rate or net assimilation rate. The reduced biomass was not therefore linked to reduced CER.Key words: Carbon dioxide exchange rate, herbicide, oilseed, rapeseed

RELATIONSHIPS BETWEEN CARBON DIOXIDE EXCHANGE RATE, PHOTOSYNTHETIC AREA AND BIOMASS IN PEA

1986 ◽  
Vol 66 (3) ◽  
pp. 465-472 ◽  
Author(s):  
S. L. A. HOBBS
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rate ◽  
Pisum Sativum ◽  
Chlorophyll Content ◽  
Substantial Reduction ◽  
Dry Weight ◽  
Stomatal Resistance ◽  
Carbon Dioxide Exchange ◽  
Shoot Dry Weight ◽  
Pisum Sativum L

Compensation between carbon dioxide exchange rate per unit photosynthetic area (CER) and total photosynthetic area (TPA) of a plant was examined in field-grown pea (Pisum sativum L.). Eight near-isogenic lines of cv. Alaska, representing all possible phenotypes of the genes af (leaflets transformed to tendrils), st (reduced stipule area) and tl (tendrils transformed to leaflets), were examined. The CER was measured on the leaflets (AfAf), tendrils (afafTlTl) or minute leaflets (afaftltl). The TPA was significantly reduced by the st gene in AfAf types (normal leaflets) with an apparently associated increase in CER. The st gene also significantly reduced the TPA in afaf types but there was no associated increase in CER. Tendrils had a lower CER than normal leaflets and comprised 22% of the TPA of the semi-leafless (afafStStTlTl) type. Crosses were made between a semi-leafless pea and four normal-leafed types previously selected for high or low CER. The CER means (normal leaflets) of the F1 progeny showed variability which was related to parental values. This was also true for the CER means (tendrils) of the populations of semi-leafless F2 segregants showing that genetic variability for CER can exist in tendrils. In the F2, tendril CER was correlated negatively to stomatal resistance and positively to chlorophyll content and final shoot dry weight (biomass). Genetic improvement in CER may be important when a plant ideotype requires substantial reduction in TPA.Key words: Photosynthesis, pea, chlorophyll content, stomatal resistance, Pisum sativum

Herbicidal Effects on Crownvetch Rhizobia and Nodule Activity

Weed Science ◽  
1986 ◽  
Vol 34 (3) ◽  
pp. 338-343 ◽  
Author(s):  
John Cardina ◽  
Nathan L. Hartwig ◽  
Felix L. Lukezic
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rate ◽  
Bacterial Growth ◽  
Indirect Effects ◽  
Carbon Dioxide Exchange ◽  
N Fixation ◽  
Intact Plants ◽  
Coronilla Varia ◽  
Direct Toxicity

Two strains of crownvetch (Coronilla variaL. # CZRVA) rhizobia were cultured in vitro with various rates of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate]. Growth, measured turbidimetrically over 48 h, was similar for both strains. Atrazine and bifenox significantly reduced bacterial growth after 14 and 36 h, respectively, only at the highest concentrations tested (463 μM atrazine and 292 μM bifenox). Since growth of crownvetch rhizobia was apparently not affected by rates of atrazine or bifenox above reasonable soil solution concentrations, it is likely that herbicidal effects on nodulation were due to toxicity to the host plant rather than toxicity to these bacteria. In a growth chamber experiment, total nodule activity (TNA) and carbon dioxide exchange rate (CER) were measured simultaneously in an effort to distinguish direct atrazine effects on nodule function from indirect effects due to inhibition of photosynthesis and a resulting decrease in photosynthate supply to nodules. When 5 and 50 mg atrazine per kg soil were applied to intact plants, CER was severely reduced within 24 h, but similar reductions in TNA were not observed until 48 h after treatment. Total nodule activity was reduced similarly by atrazine and defoliation; the application of atrazine to defoliated plants did not inhibit TNA more than did defoliation alone. The data indicate that reductions in crownvetch nodule activity by atrazine are due to inhibition of photosynthesis or other processes rather than direct toxicity to N fixation.

Effects of temperature on the morphology and photosynthetic activity of newly matured leaves of alfalfa

1973 ◽  
Vol 51 (10) ◽  
pp. 1907-1916 ◽  
Author(s):  
S. B. Ku ◽  
L. A. Hunt
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rate ◽  
Water Content ◽  
Intercellular Space ◽  
Leaf Water Content ◽  
Carbon Dioxide Exchange ◽  
Specific Leaf Weight ◽  
Leaf Density ◽  
Effects Of Temperature ◽  
Space Volume

Effects of temperature on (1) physical characteristics of newly matured leaves throughout regrowth, and (2) net carbon dioxide exchange–irradiance response curves throughout regrowth and throughout the day are described for two alfalfa (Medicago saliva L.) genotypes (AT171 and CC120) grown at 20/15C and 30/25C day/night temperatures and 53 nE cm−2 s−1 irradiance (400–700 nm).Area per leaf increased linearly with increasing leaf number up to the fourth or fifth leaf, and thereafter remained constant. Both specific leaf weight and leaf density were constant for the first four leaves, and increased sharply thereafter, particularly at day/night temperatures of 20/15C. Percentage of leaf water content did not change throughout regrowth at 30/25C, but decreased after leaf 4 at 20/15C. Intercellular space volume fluctuated with leaf number. Leaf area was larger, specific leaf weight, and leaf density were greater, intercellular space volume was higher, and percentage of leaf water content was lower, with plants grown at 20/15C than at 30/25C.The net carbon dioxide exchange rate at 116 nE cm−2 s−1 increased with leaves produced progressively until a peak was reached at leaf 4 or 5 and then decreased. At any given leaf position, net carbon dioxide exchange rate at 116 nE cm−2 s−1 was greater at 20/15C than at 30/25C for AT171, but was the same at both temperatures for CC120. In contrast, net carbon dioxide exchange rate at 76 nE cm−2 s−1 was greater at 20/15C than 30/25C for both genotypes. Net carbon dioxide exchange rates measured in the morning were always lower than those measured in the afternoon regardless of irradiance, genotype, and growth temperature.

Carbon dioxide exchange rates and leaf nitrogen contents during ageing of the flag and penultimate leaves of five spring-wheat cultivars

1985 ◽  
Vol 63 (9) ◽  
pp. 1605-1609 ◽  
Author(s):  
L. A. Hunt ◽  
G. van der Poorten
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rate ◽  
Spring Wheat ◽  
Transpiration Rate ◽  
Flag Leaf ◽  
Leaf Nitrogen ◽  
Carbon Dioxide Exchange ◽  
Leaf Nitrogen Content ◽  
Flag Leaves ◽  
Nitrogen Contents

Postanthesis carbon dioxide exchange and transpiration rates of flag and penultimate leaves of five spring-wheat (Triticum aestivum L. emend. Thell.) cultivars were measured from complete flag-leaf expansion to senescence. Leaf nitrogen contents were determined from anthesis to maturity. Both the absolute level of and the time-related decline of the carbon dioxide exchange rate varied among the cultivars. The flag-leaf carbon dioxide exchange rate decreased steadily throughout for one cultivar and slowly for a varying period and then rapidly for most others. The penultimate-leaf carbon dioxide exchange rate decreased throughout with one cultivar but did not decline in the period from 1 to 3 weeks postanthesis in others. The transpiration rate peaked at or near anthesis for the flag leaves and then either declined or fluctuated around the peak value for 3 weeks. The penultimate-leaf transpiration rate increased to a second peak late in ontogeny for most genotypes. In general, the time course of the transpiration rate matched that of the carbon dioxide exchange rate, but the transpiration rate at a specific carbon dioxide exchange rate was lower for penultimate than for flag leaves. The carbon dioxide exchange rate was linearly related to leaf nitrogen content, with the same regression applying for both flag and penultimate leaves; regressions were similar for all genotypes. There were no marked deviations from the overall carbon dioxide exchange rate – nitrogen regression that could be indicative of a "sink" influence on the activity of photosynthetic enzymes.

The response of defoliated swards of subterranean clover to temperature

1976 ◽  
Vol 27 (5) ◽  
pp. 593 ◽  
Author(s):  
EAN Greenwood ◽  
BA Carbon ◽  
RC Rossiter ◽  
JD Beresford
Keyword(s):  
Subterranean Clover ◽  
Trifolium Subterraneum ◽  
Dry Weight ◽  
Carbon Dioxide Exchange ◽  
Short Term ◽  
Plant Parts ◽  
Pre Treatment ◽  
Reproductive Phases ◽  
Whole Life Cycle

The objective was to characterize the response of Trifolium subterraneum L. (cv. Daliak) swards to short-term and to long-term changes in temperature at several stages of plant growth. Short-term responses were studied with microswards growing in boxes in the open and defoliated every week to simulate heavy grazing. At seven stages, one subsample of boxes was harvested and three other subsamples were moved to controlled-temperature glasshouses and grown for 14 days at 10/5° (day/night), 17.5/12.5° and 25/20°C respectively, and then harvested. Dry weights and numbers of plant parts, and areas of leaves, height, light penetration and net carbon dioxide exchange of swards were measured. For long-term responses, young, defoliated microswards were transferred to the above temperatures for 9 weeks and cut weekly. On days 32 (pre-treatment harvest), 53, 74 and 95, tops and roots were harvested. The results support three generalizations. Firstly, severely defoliated subterranean clover pastures respond to temperature between 10/5° and 25/20° in a variety of ways over the whole life cycle. However, temperature is of greater importance as a determinant of dry weight of tops during the post-emergence and reproductive phases than it is during the preflowering phase. Secondly, total growth rate (TGR) after the first 8–10 weeks of growth does not increase at temperatures above 10/5°. And thirdly, even with moderately low LAI values of 1–4, temperatures of 25/20° can inhibit TGR after about 8 weeks of growth. The biological and agricultural implications are discussed.

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