Yoana C. Newman

Photosynthetic acclimation of young sweet orange trees to elevated growth CO2 and temperature

Summary Two-year old trees of ‘Ambersweet’ orange, a hybrid of ‘Clementine’ tangerine (Citrus reticulata Blanco) and ‘Orlando’ tangelo (C. paradisi Macf. × C. reticulata), were grown for twenty-nine months under two daytime [CO2] of 360 (ambient) and 720 (elevated) μmol mol−1, and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize the physiology and biochemistry of citrus photosynthesis in response to both elevated [CO2] and temperature, and to test if the photosynthetic capacity of sweet orange, in terms of rubisco activity and protein concentration, was down-regulated under long-term elevated growth [CO2]. Both mature (old) and expanding (new) leaves of trees grown under elevated [CO2] had higher photosynthetic rates, lower transpiration and conductance, and higher water-use efficiency (WUE), compared to those grown under ambient [CO2]. Although leaf WUE was reduced by high temperature, elevated [CO2] compensated for adverse effect of high temperature on leaf WUE. Activity and protein concentration of rubisco were down-regulated in both new and old leaves at elevated [CO2]. In contrast, the amount of total leaf soluble protein was not affected by elevated [CO2] and high temperature. Down-regulation of photosynthetic capacity was greater for the old leaves, although activity and protein concentration of rubisco in the new leaves were higher. Contents of soluble sugars and starch in all leaves sampled, which were higher under elevated [CO2], were generally not affected by high temperature. Within each specific CO2-temperature treatment and leaf type, total soluble sugars remained relatively unchanged throughout the day, as did the starch content of early morning and midday samples, and only a moderate increase in starch for the old leaves at late afternoon sampling was observed. In contrast, starch content in the new leaves increased substantially at late afternoon. Activities of sucrose-P synthase and adenosine 5′-diphosphoglucose pyrophosphorylase were reduced at elevated [CO2] in the old leaves, but not in the new leaves. The photosynthetic acclimation of Ambersweet orange leaves at elevated [CO2] allowed an optimization of nitrogen use by reallocation/redistribution of the nitrogen resources away from rubisco. Thus, in the absence of other environmental stresses, citrus photosynthesis would perform well under rising atmospheric [CO2] and temperature as predicted for this century.

Managing harvest of 'Tifton 85' bermudagrass for production and nutritive value.

Abstract Harvest management is critical in hay or greenchop systems to sustain high yields of superior nutritive value. ‘Tifton 85’ bermudagrass [ Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] is a high-quality, high-yielding, warm-season perennial grass that dairy producers are using as hay, haylage, and/or pasture. Morphological features of this plant compared to other grasses used in the region suggest the adoption of a more conservative harvest stubble may be needed. During 2007 and 2008, different harvest intervals (21, 24, 27, and 35 days) and stubble heights (3 and 6 inches) were compared using established Tifton 85 bermudagrass fields. Results suggest that highest yields occur with larger interval between harvests (35 days) and when shorter stubble heights (3 inches) are used. Nevertheless, shorter stubble heights (3 inches) were associated with greater weed encroachment and are generally not recommended. Data show that greater nutritive value can be achieved with defoliation at 24- to 27-day intervals to a 6-inch stubble.

Fall and winter management affect spring growth and nutritive value of Tifton 85 bermudagrass.

Spring regrowth of ‘Tifton 85’ bermudagrass (Cynodon spp.) has been slow or stands have appeared weakened in some years in North Florida following overseeding with cool-season annuals. This 2-year experiment compared effects of (i) different bermudagrass sod management practices in fall and (ii) winter/spring grazing management of overseeded cool-season forages on subsequent spring and early-summer productivity of Tifton 85 bermudagrass. For overseeded pastures, postgraze stubble height of cool-season forages during winter/spring did not affect bermudagrass production in spring/early summer. Early-season bermudagrass yield generally was greater for pastures not overseeded the previous fall than those that were overseeded with cool-season forages; however, bermudagrass yields by July were as great or greater in plots that had been overseeded compared to unseeded controls. In plots that were not overseeded, leaving an 8-inch bermudagrass stubble entering winter resulted in greater early-season bermudagrass yields the following year than leaving a 2-inch stubble. The results of this study suggest that early-season growth of Tifton 85 bermudagrass may be reduced either by overseeding cool-season forages or by leaving insufficient bermudagrass residue in fall. There were, however, no longterm negative effects on bermudagrass stands of any of the management options tested.

Pest and Beneficial Arthropods in a ‘Tifton 85‘ Bermudagrass Field in North Central Florida

Summary Pest and beneficial arthropods were collected in a ‘Tifton 85’ bermudagrass pasture in north central Florida to assess their impact on forage production. The primary pests were Auchenorrhyncha (leafhoppers and spittlebugs), grasshoppers, grass loopers, plant bugs, fall armyworms, and stinkbugs. Major beneficial arthropods included spiders, damsel bugs, big-eyed bugs, and small possibly parasitoid wasps. The pest populations did not increase to obvious damaging levels during 35 d growing periods after the grass had been mowed to heights of 8 or 15 cm. Thus, pest arthropods probably can be managed by grazing or periodically mowing ‘Tifton 85’ bermudagrass.

Use of Rotational Stocking in Combination With Cultural Practices for Smutgrass Control—A Florida Case Study

On the Ground Smutgrass (Sporobolus indicus) is an invasive plant in Florida sandy soils, prevalent in central and south Florida where temperatures seldom drop below freezing and hard frost events are infrequent. Smutgrass becomes nonpalatable to cattle as it matures and cattle avoid grazing it after the emergence of seed stalks and when leaves become tough. However, young smutgrass growth is palatable to cattle. High stocking densities in combination with severe defoliation have proven deleterious for this grass. This study evaluated the use of increased stock density and rotational grazing management for 3 years following a one-time defoliation by mowing or burning smutgrass infested pastures.

Erratum to: Agro-ecological nitrogen management in soils vulnerable to nitrate leaching: a case study in the Lower Suwannee Watershed

In the original publication of the article, some sections were cited liberally from the previously published work. Authors regret for this error and would like to include the following sentence under the ‘‘Statistical Analysis’’ in the ‘‘Materials and Methods’’ section: ‘‘Analyses of the yield response model and economically optimum fertilizer rates, were carried out following the procedure described by Valkama et al. (2011)’’.