Lower Carbon Gain Research Articles

Increases in CO2 from past low to future high levels result in “slower” strategies on the leaf economic spectrum

Depending on resource availability plants exhibit a specific suite of traits. At the interspecific level these traits follow the leaf economic spectrum (LES), traits related to slow turnover when resources are poor and fast turnover when resources are plentiful. Limited data shows that within species, CO2 availability, low in the recent geologic past, high in the near future, has led to plants shifting their trait levels on the LES towards faster traits. We asked whether adjustments of physiological traits could underpin faster growth from low to high CO2 and how these responses varied among plant functional types. We analysed the trait response of seedlings of up to 28 C3 plant species grown at low (160ppm), near-ambient (450ppm), and high (750ppm) CO2. We measured growth, specific leaf area (SLA), leaf gas exchange, chemical composition and stomatal traits. On average photosynthesis was reduced by 59% at low CO2 and increased by 14% at high CO2 compared to ambient CO2. Respiration decreased by 21% at low CO2 and increased by 39% at high CO2. Nitrogen content (N) per mass increased by 50% at low CO2 and decreased by 9% at high CO2. Plants drastically increased SLA at low CO2 so that despite lower carbon gain per area, carbon gain per unit mass was not reduced as much. Contrary to the responses to other resources, plant traits along the LES are adjusted towards the “fast” end of the spectrum (higher SLA, higher N) at low CO2 and towards the “slow” end (lower SLA, lower N) with increasing CO2. For a limited number of species photosynthesis per unit mass showed the same, increase at low CO2. From a resource economics perspective plants thus adjust the cost for growth towards the availability of carbon and the rate of assimilation: at lower CO2 the carbon costs decrease due to decreased respiration and lower leaf mass per area (higher SLA thinner leaves). At higher CO2 the carbon costs increase due to increased respiration and higher leaf mass per area (lower SLA thicker leaves). This suggests that CO2 increases from the past to the future are allowing plant species globally to combine faster growth with more robust, resource conservative leaves.

Photosynthetic and Photoinhibition Behavior of Two Field-Grown Grapevine Cultivars under Multiple Summer Stresses

The identification of drought-resistant genotypes of <i>Vitis vinifera</i> that can optimize their water use is attracting increasing interest, especially in areas where it is difficult to extend irrigation and that are undergoing a progressive shift toward subtropicalization. This study was carried out in 2003 (a year characterized by severe drought conditions) and 2004 (characterized by absence of drought conditions) to evaluate the changes in morphostructural characteristics and physiological behavior of two red grapevine cultivars widely cultivated in Italy: Sangiovese and Montepulciano. Unlike 2004, data recorded during 2003 showed that, contrary to Montepulciano vines, the vertical shoot-positioned canopy of Sangiovese vines was divided into two different zones. The basal zone was close to the fruiting zone, featured low carbon gain, and was characterized by 57% of leaves affected by chlorosis and necrosis, while the remaining leaves were affected by chronic photoinhibition (Fv/Fm &lt;0.50). The upper zone was characterized by high photosynthetic activity and water-use efficiency. The changes in leaf inclination and lower leaf absorption and the greater leaf transmittance in Sangiovese leaves appeared to help in the avoidance of excessive light and heat absorption. Irrespective of their positions, the leaves of Montepulciano promptly closed their stomata and saved water, while reducing their physiological activity. Results indicate that grapevine strategies in response to multiple and severe summer stress conditions are a function of genotype, leaf age, and leaf position along the shoot. Unlike Montepulciano, under drought conditions, Sangiovese can be considered to be well adapted, since it can optimize the whole-vine carbon gain.

Environmental constraints on the invasion of Triadica sebifera in the eastern United States: an experimental field assessment

Identifying the environmental constraints that affect the distribution of an invasive species is fundamental to its effective control. Triadica sebifera (Chinese tallow tree) has invaded the southeastern United States, but its potential for further range and habitat extension has been unresolved. We explored experimentally environmental factors in macro- and microhabitats that affect its persistence at five widely separated sites along the Atlantic seaboard of the United States and at two sites inland; three sites occur well beyond the tree's current range. At each site, seeds and young vegetative plants (0.5-0.65 m tall) of T. sebifera were placed in four microhabitats (closed-canopy upland, closed-canopy lowland, open-canopy upland, and open-canopy lowland). Plant growth, leaf CO(2) assimilation rates, leaf N concentrations and delta(13)C ratios, and stem water potential were measured for two growing seasons. Percent seed germination was consistently higher in open-canopy microhabitats and lowest at northern and inland sites. T. sebifera grew in all open-canopy microhabitats, even 300-500 km beyond its current distribution. Plant growth in closed-canopy habitats was lower, attributable to lower carbon gain per unit leaf area in shaded compared with open-canopy environments, especially at northern and inland sites. Neither competition, other than canopy shade, nor grazing was a key constraint on distribution at any scale. Our results demonstrate that T. sebifera is dispersal limited at landscape scales but limited locally by dispersal and overstory shade; it has yet to occupy the full extent of its new range in North America. Quantifying environmental factors both within and well beyond a species' current range can effectively highlight the limits on its distribution.

Effect of Ammonium and Nitrate Nutrition On Some Physiological Processes in Higher Plants ‐ Growth, Photosynthesis, Photorespiration, and Water Relations

Ammonium and nitrate as different forms of nitrogen nutrients impact differently on some physiological and biochemical processes in higher plants. Compared to nitrate, ammonium results in small root and small leaf area, which may contribute to a low carbon gain, and an inhibition on growth. On the other hand, due to (photo)energy saving, a higher CO (2) assimilation rate per leaf area was observed frequently in plants supplied with ammonium than in those supplied with nitrate. These results were dependent not only on higher Rubisco content and/or activity, but also on RuBP regeneration rate. The difference in morphology such as chloroplast volume and specific leaf weight might be the reason why the CO (2) concentration in the carboxylation site and hence the photorespiration rate differs in plants supplied with the two nitrogen forms. The effect of nitrogen form on water uptake and transportation in plants is dependent both on leaf area or shoot parameter, and on the root activity (i.e., root hydraulic conductivity, aquaporin activity).

Performance of two Picea abies (L.) Karst. stands at different stages of decline : I. Carbon relations and stand growth.

This is the first in a series of papers on the growth, photosynthetic rate, water and nutrient relations, root distribution and mycorrhizal frequency of two Norway spruce forests at different stages of decline. One of the stands was composed of green trees only while the other included trees ranging in appearance from full green crowns to thin crowns with yellow needles. In this paper we compare the growth and carbohydrate relations of the two stands and examine relationships among growth variables in ten plots. The declining stand produced 65 percent of the wood per ground area compared with the stand in which all trees were green because its foliage produced less wood at any level of leaf area index. The difference in foliage efficiency between the sites could not be explained by differeneces in climate, competition or stand structure. The declining stand appeared to have lower carbon gain as indicated by a smaller increase in reserve carbohydrates before bud break, and weaker sinks for carbohydrates as indicated by less use of the stored carbohydrates than the healthy stand. Thus, growth reduction was probably related to factors which affect both photosynthesis and, even more, the sinks for carbohydrate.

CO2 Assimilation and Activities of Photosynthetic Enzymes in High Chlorophyll Fluorescence Mutants of Maize Having Low Levels of Ribulose 1,5-Bisphosphate Carboxylase

Photosynthetic properties were examined in several hcf (high chlorophyll fluorescence 11, 21, 42 and 45) nuclear recessive mutants of maize which were previously found to have normal photochemistry and low CO(2) fixation. Mutants usually either died after depletion of seed reserves (about 18 days after planting), or survived with slow growth up to 7 or 8 weeks. Both the activity and quantity of ribulose 1,5-bisphosphate carboxylase (Rubisco) were low in the mutants (5-25% of the normal siblings on a leaf area basis) and the loss of Rubisco tended to parallel the reduction in photosynthetic capacity. The Rubisco content in the mutants was often marginal for photosynthetic carbon gain, with some leaves and positions along a leaf having no net photosynthesis, while other leaves had a low carbon gain. Conversely, the activities of C(4) cycle enzymes, phosphoenolpyruvate carboxylase, pyruvate, Pi dikinase, NADP-malate dehydrogenase, and NADP-malic enzyme, were the same or only slightly reduced compared to the normal siblings. The mutants had about half as much chlorophyll content per leaf area as the normal green plants. However, the Rubisco activity in the mutants was low on both a leaf area and chlorophyll basis. Low Rubisco activity and lower chlorophyll content may both contribute to the low rates of photosynthesis in the mutants on a leaf area basis.