F.J. Adamsen

Leaf nitrogen concentration of wheat subjected to elevated [CO2] and either water or N deficits

Leaf N concentration is important because it is associated with the CO2 assimilatory capacity of crops, and in grasslands, it is an important determinant of forage nutritive value. Consequently, the productivity of both domestic and native animals in future global environments may be closely linked to possible changes in leaf N concentration of grasses. Since grasslands are frequently subjected to water-deficit or N-deficit conditions, it is important to investigate the interactive responses between elevated [CO2] and these stress conditions. Therefore, this 4-year research program was undertaken with wheat (Triticum aestivum L.) as a model system for forage grasses, to document the potential changes in leaf N concentration in response to global environment changes. Wheat crops grown under field conditions near Phoenix, AZ, USA, were subjected to elevated [CO2] and either water-deficit or N-deficit treatments using large Free Air Carbon dioxide Enrichment (FACE) arrays. Surprisingly, the elevated [CO2] treatment under optimum conditions resulted in little change in leaf N concentration. Therefore, no change in the nutritive value of forage from highly managed pastures would be expected. Further, water-deficit treatment had little influence on leaf N concentration. To some extent, the lack of response to the water-deficit treatment resulted because severe deficits did not develop until late in the growing seasons. Only on one date late in the season was the water-deficit treatment found to result in decreased leaf N concentration. The low N treatment in combination with elevated [CO2], however, had a large influence on leaf N concentration. Low levels of applied N resulted in decreased leaf N concentration under both [CO2] treatments, but the lowest levels of leaf N concentration were obtained under elevated [CO2] through much of the growing season. These results point to a potential problem with grasslands in that the nutritive value of the forage consumed by animals will be decreased under future global environment changes.

CO2 enrichment and soil nitrogen effects on wheat evapotranspiration and water use efficiency

Evapotranspiration (ET) and water use efficiency (WUE) were evaluated for two spring wheat crops, grown in a well-watered, subsurface drip-irrigated field under ambient (about 370 mmol mol 1 during daytime) and enriched (200mmol mol 1 above ambient) CO2 concentrations during 1995‐1996 and 1996‐1997 in Free-Air CO2 Enrichment (FACE) experiments in central Arizona. The enriched (FACE) and ambient (Control) CO2 treatments were replicated in four, circular plots, each 25 m in diameter. Two soil nitrogen (N) treatments, ample (High N) and limited (Low N), were imposed on one-half of each circular plot. Wheat ET, determined using soil water balance procedures, was significantly greater in High N than Low N treatments starting in late-March (anthesis) during both years. Differences in ET between CO2 treatments during the seasons were generally small and not statistically significant, however, there was a tendency for the ET to be lower for FACE than Control under the High N treatment. The reduction in the cumulative seasonal ET due to FACE averaged 3.7 and 4.0% under High N and 0.7 and 1.2% under Low N in the first and second years, respectively. However, WUE (grain yield per unit seasonal ET) was significantly increased for the FACE treatment under both soil N treatments. For the High N treatment, the WUE was 19 and 23% greater for FACE than Control and for the Low N treatment the WUE was 12 and 7% greater for FACE than Control in the 2 years, respectively. Published by Elsevier Science B.V.

Elevated CO2 stimulates soil respiration in a FACE wheat field

Summary Understanding the response of soil carbon (C) dynamics to higher atmospheric CO 2 concentrations is critical for evaluating the potential for soil C sequestration on time scales of decades to centuries. Here, we report on changes in soil respiration under Free-Air CO 2 Enrichment (FACE) where spring wheat was grown in an open field at two CO 2 concentrations (ambient and ambient+200 μmol mol −1 ), under natural meteorological conditions. FACE increased soil respiration rates by 40—70% during the peak of wheat growth. On the FACE plots, stable C isotopic composition of soil CO 2 was used to partition the soil CO 2 flux into C from rhizosphere respiration and decomposition of pre-existing C. Decomposition contributed 100% of the soil CO 2 flux before crop growth commenced, and only 35—45% of the flux at the peak of the growing season. Decomposition rates were not correlated with soil temperature, but rhizosphere respiration rates were strongly correlated with green leaf area index. Ein Verstandnis der Antwort der Kohlenstoff-Dynamik (C) im Boden auf hohere CO 2 -Konzentrationen in der Atmosphare ist bedeutsam fur die Bewertung des Potentials fur die C-Sequestration in Zeitraumen von Jahrzehnten bis Jahrhunderten. Hier berichten wir uber Veranderungen in der Bodenatmung unter Free-Air CO 2 Enrichment (FACE), bei dem Sommerweizen in einem offenen Feld unter zwei CO 2 -Konzentrationen (Umgebung und Umgebung + 200 (mol mol −1 ) und unter naturlichen meteorologischen Bedingungen angebaut wurde. FACE erhohte die Bodenatmungsraten um 40—70% wahrend des Maximums des Weizenwachstums. Auf den FACE Plots wurde die Zusammensetzung an stabilen C Isotopen des Boden-CO 2 genutzt, um den Boden CO 2 -Fluss zu C durch Rhizospharen-Atmung von der Zersetzung von zuvor existierendem C zu trennen. Die Zersetzung trug 100% des Boden-CO 2 -Flusses vor dem Beginn des Weizenwachstums bei, und nur 35—45% des Flusses wahrend des Maximums des Wachstums. Die Zersetzungsraten waren nicht mit der Bodentemperatur korreliert, aber die Rhizospharen-Atmungsraten waren eng korreliert mit dem grunen Blattflachen-Index.

Flowering and seed yield of lesquerella as affected by nitrogen fertilization and seeding rate

The lesquerolic acid in lesquerella seed can be used in industrial applications such as greases, cosmetics, polishes, inks, and coatings. Successful commercialization of lesquerella will depend on the development of improved cultural practices. Lesquerella flowers are bright yellow and are prominently displayed. As a result, many cultural practices could be tied to flowering in a qualitative way. A new method of estimating flowers such as those of lesquerella using digital images has been developed that is rapid, not labor intensive, and can be automated. The purpose of this study was to determine the effects of nitrogen fertilizer and plant density on flowering of lesquerella and to develop relationships between seed yield and flowering. The lesquerella crop was planted on 15 October 1997, at the Maricopa Agricultural Center, approximately 40 km south of Phoenix, Arizona on a variable Mohall sandy loam (fine-loamy, mixed hyperthermic, Typic Haplargid). The experimental design was a complete factorial of three fertilizer rates and four seeding rates. Ammonium sulfate at rates of 0, 60 and 120 kg of N ha−1 was applied at flowering on 18 March 1998. Digital images of the plots were taken periodically from 19 March 1998 to 4 June 1998 using a color digital camera. Images were acquired between 1030 and 1300 h MST. In this experiment, the crop did not respond to seeding rate. Flowers present at initial bloom could be used to estimate stand establishment. The early flowers did not contribute much to final yield, but flowers present in the first 3 weeks of May were a good predictor of yield. Flowering increased with N additions and noticeable peaks in flowering occurred after irrigations. The new method was verified as a viable method for estimating flower number. The method of flower estimation should also be useful for plant breeders for selection of earlier maturing lines, which would increase the potential for use of lesquerella in rotational systems.