The effect of different rates of potassium (K+) on shoot water potential, photosynthesis and carbon movement (using 14C) at the V3/4 growth stages was studied in mungbean (Vigna radiata L. Wilczek), ...a drought‐susceptible legume, and cowpea (Vigna unguiculata L. Walp), a drought‐tolerant legume, grown under low‐ and high‐irrigation regimes under controlled conditions. Soil moisture and K+ affected all measured parameters in the two species. The rate of photosynthesis was higher at reduced water stress when K+ was applied. The impact was greater in cowpea, which had an inherently high rate of carbon assimilation. Mungbean and to a lesser extent cowpea allocated greater quantities of carbon to roots under dry conditions, especially with added K+. The distribution of 14C into other plant parts was also increased at higher rates of K+ application under both soil moisture regimes. Thus, application of K+ seems to have a beneficial effect in overcoming soil moisture stress and increasing physiological parameters and carbon partitioning in these two important tropical food legumes.
Zusammenfassung
Der Einfluss unterschiedlicher Mengen Kalium (K+) auf Sprosswasserpotenzial, Fotosynthese und Kohlenstoffverteilung wurde (unter Verwendung von 14C) in den V3/4 Wachstumsstadien bei Mungbohne (Vigna radiata L. Wilczek), einer trockenheitsempfindlichen Leguminose und Kuhbohne (Vigna unguiculata L. Walp), einer dürreresistenten Leguminose, unter der Einwirkung geringer und hoher Wasserversorgung bei kontrollierten Bedingungen untersucht. Bodenfeuchtigkeit und K+ beeinflussten unterschiedlich alle untersuchten Parameter bei beiden Arten. Die Fotosyntheseraten nahmen mit geringer werdendem Wasserstress in Reaktion zu K+ zu. Die Auswirkungen waren bei der Kuhbohne, die anlagebedingt eine hohe Rate der Kohlenstoff‐Assimilation aufweist größier. Mungbohne und, in einem geringeren Umfang, Kuhbohne verlagerten unter Trockenbedingungen größiere Anteile des Kohlenstoffs zu den Wurzeln.; K+ förderte dieses Phänomen. Die Verteilung von 14C in andere Pflanzenteile wurde bei hohen Raten von K+ in beiden Bodenfeuchtigkeitsverhältnissen erhöht. Der günstige Einfluss von K+ bei stärker werdendem Bodenfeuchtigkeitsstress im Hinblick auf eine Förderung der physiologischen Parameter und der Kohlenstoff‐Aufteilung bei diesen beiden bedeutenden tropischen Futterleguminosen wird besprochen.
Symbiotic N2 fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously ...increasing atmospheric CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole
To test inter- and intraspecific variability in the responsiveness to elevated CO₂, 9-14 different genotypes of each of 12 perennial species from fertile permanent grassland were grown in Lolium ...perenne swards under ambient (35 Pa) and elevated (60 Pa) atmospheric partial pressure of CO₂ (pCO₂) for 3 years in a free air carbon dioxide enrichment (FACE) experiment. The plant species were grouped according to their functional types: grasses (L. perenne, L. multiflorum, Arrhenatherum elatius, Dactylis glomerata, Festuca pratensis, Holcus lanatus, Trisetum flavescens), non-legume dicots (Rumex obtusifolius, R. acetosa, Ranunculus friesianus), and legumes (Trifolium repens, T. pratense). Yield (above a cutting height of 4.5 cm) was measured three times per year. The results were as follow. (1) There were highly significant differences in the responsiveness to elevated pCO₂ between the three functional types; legumes showed the strongest and grasses the weakest yield increase at elevated pCO₂. (2) There were differences in the temporal development of responsiveness to elevated pCO₂ among the functional types. The responsiveness of the legumes declined from the first to the second year, while the responsiveness of the non-legume dicots increased over the 3 years. During the growing season, the grasses and the non-legume dicots showed the strongest response to elevated pCO₂ during reproductive growth in the spring. (3) There were no significant genotypic differences in responsiveness to elevated pCO₂. Our results suggest that, due to interspecific differences in the responsiveness to elevated pCO₂, the species proportion within fertile temperate grassland may change if the increase in pCO₂ continues. Due to the temporal differences in the responsiveness to elevated pCO₂ among species, complex effects of elevated pCO₂ on competitive interactions in mixed swards must be expected. The existence of genotypic variability in the responsiveness to elevated pCO₂, on which selection could act, was not found under our experimental conditions.
Summary
•
Plant response to elevated atmospheric CO2 may depend on the carbon sink strength, determined by the availability of resources other than CO2, and the developmental stage.
•
In a 2‐yr ...field experiment with model swards of Lolium perenne, the effect of CO2 enrichment (FACE) on yield and allocation of dry mass (DM) and N were examined under three N fertilization treatments during vegetative and reproductive growth.
•
During vegetative growth, in the highest N treatment, the greatest increase in DM yield occurred at elevated CO2; there was no change in DM allocation. By contrast, at low N, residual biomass, but not yield, increased under CO2 enrichment, and the tillers were shorter. During reproductive growth, under CO2 enrichment DM yield increased similarly across all N treatments; there was no change in DM and N partitioning. The mean weight and height of the reproductive tillers increased.
•
At high N availability, or during reproductive growth, L. perenne swards overcome carbon‐sink limitation and show a strong yield response to elevated CO2. Biomass allocation and the height of the plants, in response to elevated CO2, clearly depend on N fertilization and developmental stage.
Managed Ecosystems and CO2 Nösberger, Josef; Long, S. P; Norby, R. J ...
2006, 2006-06-22, Volume:
187
eBook
This book provides an up-to-date review of the effects of increasing atmospheric carbon dioxide on agroecosystems, forests, and grasslands. It summarizes the main findings from 13 experiments with ...annual crops, permanent pastures and plantation forests at 11 sites throughout the world during the past ten years. The results significantly alter our perception of how rising CO2 will directly affect these managed ecosystems.
The mechanisms responsible for fluctuations in species composition of semi-natural grassland are not well understood. To identify plant traits that determine the poor competitive ability of Festuca ...pratensis compared to Dactylis glomerata especially during summer, the growth of both grasses was monitored over time and at different temperatures and photoperiods. Plants of both grasses were grown from seed with non-limiting nutrient supply at three day/night temperatures (11/6, 18/13 and 25/20°C) and two photoperiods (16 and 12 h). F. pratensis had a significantly lower relative growth rate than D. glomerata, mainly due to its lower specific leaf area and reduced nitrogen productivity. At high temperature, F. pratensis had a considerably lower root weight ratio than D. glomerata leading to substantially slower root growth. F. pratensis responded to a shorter photoperiod with an increase in the net assimilation rate, whereas D. glomerata responded with an increase in specific leaf area. The low competitive ability of F. pratensis compared to D. glomerata was mainly associated with its lower specific leaf area and nitrogen productivity. The stronger decline of its competitive ability during summer was probably related to the decreased allocation of dry matter to the roots at higher temperatures which leads to slower root growth compared to D. glomerata.
The fructan-β-fructosidase activity (1-FEH; EC 3.2.1.80) that
degrades inulin in tubers of Helianthus tuberosus
L. appears to be developmentally regulated; it was low in growing tubers
but
increased ...during dormancy and
sprouting. In spite of relatively high 1-FEH activity in vitro,
fructose concentration was very low in developing
and dormant tubers and increased markedly only during sprouting. A
fructan-β-fructosidase from such sprouting
tubers was purified 41-fold to a single protein band on one-dimensional
sodium dodecylsulphate–polyacrylamide
gels. The purification procedure included ammonium sulphate precipitation,
lectin-affinity chromatography on
concanavalin A, anion-exchange and cation-exchange chromatography. The
enzyme
had an apparent molecular
mass of 75000 measured by size-exclusion chromatography, and 79000 measured
by
one-dimensional sodium
dodecylsulphate-polyacrylamide gel electrophoresis. It exhibited a high
substrate specificity, hydrolysing terminal
β-(2-1)-fructosyl-fructose-linkages in linear and branched fructan
oligomers; β-(2-6)-linkages were hardly
hydrolysed. Hydrolysis of inulin oligomers followed normal saturation kinetics:
Km values for 1,1-kestotetraose
and 1,1,1-kestopentaose were 8·3 mM and 12 mM,
respectively. Fructosyl residues were hydrolysed from inulin
oligomers by a multi-chain mechanism. The fructan-β-fructosidase showed
optimal enzyme activity at pH 5·2,
and it retained its full activity after pre-incubation for 1 h at up to
40 °C.
The release of fructose from 5 mM 1,1-kestotetraose was reduced
by
25% when 1-FEH was assayed in the presence of 10 mM sucrose. It
is
proposed that the inhibition of 1-FEH activity by sucrose is a mechanism
for
controlling fructan degradation in planta.
Festuca pratensis Huds. is a forage grass with the ability to withstand harsh climatic conditions. However, its potential agronomic use is limited by its poor competitive ability, which can be traced ...to limitations in leaf growth. In order to characterize this process and to identify genes which might function as markers for leaf growth, three XET‐related genes in the leaf elongation zone (LEZ) of F. pratensis are reported. A detailed expression analysis is presented of the three genes in two F. pratensis genotypes with contrasting leaf growth characteristics grown under two nitrogen levels. By means of a detailed spatial analysis of growth and XET encoding transcript pattern along the LEZ, a specific correlation is shown between FpXET1 expression and tissue elongation that is maintained under the different growth conditions, while the two other XETs expressed in the LEZ show different transcript dynamics. Tissue localization of FpXET1 and FpXET2 transcripts indicate an accumulation throughout young tissue, which is consistent with the encoded proteins playing roles in cell wall modification processes during growth. It is proposed that FpXET1 is a potential marker for tissue elongation and leaf growth in F. pratensis.
Grasses contain a number of genes encoding both alpha- and beta-expansins. These cell wall proteins are predicted to play a role in cell wall modifications, particularly during tissue elongation. We ...report here on the characterisation of five alpha- and three vegetative beta-expansins expressed in the leaf elongation zone (LEZ) of the forage grass, Festuca pratensis Huds. The expression of the predominant alpha-expansin (FpExp2) was localised to the vascular tissue, as was the beta-expansin FpExpB3. Expression of another beta-expansin (FpExpB2) was not localised to vascular tissue but was highly expressed in roots and initiating tillers. This is the first description of vegetative beta-expansin gene expression at the organ and tissue level and also the first evidence of differential expression between members of this gene family. In addition, an analysis of both alpha- and beta-expansin expression along the LEZ revealed no correlation with growth rate distribution, whereas we were able to identify a novel xyloglucan endotransglycosylase (FpXET1) whose expression profile closely mimicked leaf growth rate. These data suggest that alpha- and beta-expansin activities in the grass leaf are associated with tissue differentiation, that expansins involved in leaf growth may represent more minor components of the spectrum of expansin genes expressed in this tissue, and that XETs may be useful markers for the analysis of grass leaf growth.
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