Effects of climate change on labile and structural carbon in Douglas-fir needles as estimated by δ13C and Carea measurements

Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO₂ but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar C_area (C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (δ¹³C) caused by inputs of ¹³C‐depleted CO₂ to estimate labile and structural C in needles of different ages in a four‐year, closed‐chamber mesocosm experiment in which Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO₂ (ambient + 179 ppm). Declines in δ ¹³C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. The δ ¹³C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second‐ and third‐year needles, respectively, with higher proportions of new C in elevated than ambient CO₂ chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second‐year needles). Relative to ambient CO₂, elevated CO₂ increased labile C in both first‐ and second‐year needles. Relative to ambient temperature, elevated temperature diminished labile C in second‐year needles but not in first‐year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant‐soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations suggested that labile C was primarily determined by carbohydrates. Labile C was negatively correlated with concentrations of cellulose and protein. Elevated temperature increased foliar %C, possibly due to a shift of labile constituents from low %C carbohydrates to relatively high %C protein. Decreased sugar concentrations and increased nitrogen concentrations with elevated temperature were consistent with this explanation. Because foliar constituents that vary in isotopic signature also vary in concentrations with leaf age or environmental conditions, inferences of c_i/c_a values from δ ¹³C of bulk leaf tissue should be done cautiously. Tracing of ¹³C through foliar carbon pools may provide new insight into foliar C constituents and turnover.     

A METHODOLOGICAL COMPARISON OF PHOTOSYNTHETIC OXYGEN EVOLUTION AND ESTIMATED ELECTRON TRANSPORT RATE IN TROPICAL ULVA (CHLOROPHYCEAE) SPECIES UNDER DIFFERENT LIGHT AND INORGANIC CARBON CONDITIONS1

Gross oxygen evolution was compared with the electron transport rate (ETR), estimated from chl a fluorescence parameters on the common tropical green macro alga Ulva fasciata Delile with confirmatory carbon saturation curves from U. reticulata Forskål. Theoretically, the relationship between estimated ETR and gross oxygen evolution should be 4:1, that is, four electrons are transported through PSII for each molecule of oxygen evolved. However, deviations of the 4:1 relationship have previously been reported. Measurements were conducted with two commercially available and portable pulse amplitude modulated (PAM) chl fluorometers. We sought experimental approaches that minimize discrepancies between the two different measuring techniques of photosynthetic rates, both for in situ and laboratory conditions. Using fresh algal tissue for each of the different irradiances gave the best fit of gross oxygen evolution and ETR even at irradiances above light saturation, where large discrepancies between oxygen evolution and ETR are common. With increasing dissolved inorganic carbon (DIC) concentrations, there was a curvilinear response of gross oxygen evolution in relation to ETR. We therefore suggest to establish DIC saturation curves in the laboratory, oxygen evolution is probably the most relevant choice. Photorespiration could not readily explain a curvilinear response of O₂ evolution and proportionally higher ETR at high irradiances. ETRs measured with the rapid light curve function of the PAM were compared with steady‐state rates of gross and net oxygen evolution, and the ETR was found to decrease at higher irradiances whereas oxygen evolution was constant.     

High-Resolution Chlorophyll Fluorescence Imaging Serves as a Non-Invasive Indicator to Monitor the Spatio-Temporal Variations of Metabolism during the Day-Night Cycle and during the Endogenous Rhythm in Continuous Light in the CAM Plant Kalanchoë daigremontiana

Abstract: Chlorophyll fluorescence imaging is a powerful tool to monitor temporal and spatial dynamics of photosynthesis and photosynthesis-related metabolism. In this communication, we use high resolution chlorophyll fluorescence imaging techniques under strictly controlled conditions to quantify day courses of relative effective quantum yield (φ_PSII) of an entire leaf of the crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana at different light intensities. Careful interpretation of the combined gas exchange and fluorescence data, in combination with micro malate samples, allow the interpretation of underlying metabolic properties, such as leaf internal CO₂ concentration (ci_CO2) and energy demand of the cells. Spatial variations of φ_PSII, which occur as running wave fronts at the transition from phase III to phase IV of CAM, may reflect spatial differences of ci_CO2, which are preserved in the tightly packed mesophyll cells of K. daigremontiana. An endogenous rhythm is driven by a master switch which mediates between malate storage and malate release to and from the vacuole, however, using fluorescence techniques, four different metabolic states can be distinguished which also account for the activity of phosphoenolpyruvate carboxylase.     

PHYSIOLOGICAL INDICATORS OF NUTRIENT DEFICIENCY IN CLADOPHORA (CHLOROPHYTA) IN THE CLARK FORK OF THE COLUMBIA RIVER,MONTANA1

Cellular nutrient concentrations and nutrient uptake rates of Cladophora glomerata (L.) Kuetzing were determined during summer and fall in 1989–1990 at a site on the upper Clark Fork of the Columbia River, Montana. Both physiological tests indicated that Cladophora growth is likely to be limited by nitrogen during late summer-early fall. Maximum uptake rates of ammonia-N and nitrate-N were 5935–6991 and 507–984 μg · g DW^?1· h^?1, respectively, during July–October when dissolved inorganic nitrogen (DIN) concentrations in the river were less than 10 μg · L^?1. During November-December, when DIN was 72–376 μg · L^?1, maximum ammonia-N uptake was 1137–1633 μg · g DW^?1· h^?1 and maximum nitrate-N uptake was 0–196 μg · g DW^?1· h^?1. Cellular nitrogen during summer–early fall was 0.78–1.80% of Cladophora dry weight, frequently at or below 1.1%, a level suggested as a critical minimum N concentration for maximum growth. In contrast, cellular P was 0.18–0.36% of dry weight, 3–6 times the suggested critical P concentration of 0.06%. Molar ratios of cellular N:P (< 16:1) and DIN: SRP (< 4:1) during late summer-early fall also indicated potential N limitation. Cellular N and P from Cladophora collected from a second site influenced by a municipal wastewater discharge in 1990 displayed similar seasonal trends. At both sites, seasonal fluctuations in DIN were closely tracked by changes in cellular N, Cellular P, however, increased through the growing season despite declining levels of SRP in the river.     

Elevated CO2 reduces the nitrogen concentration of plant tissues

We summarize the impacts of elevated CO₂ on the N concentration of plant tissues and present data to support the hypothesis that reductions in the quality of plant tissue commonly occur when plants are grown under elevated CO₂. Synthesis of existing data showed an average 14% reduction of N concentrations in plant tissue generated under elevated CO₂ regimes. However, elevated CO₂ appeared to have different effects on the N concentrations of different plant types, as the reported reductions in N have been larger in C3 plants than in C4 plants and N₂-fixers. Under elevated CO₂ plants changed their allocation of N between above- and below-ground components: root N concentrations were reduced by an average of 9% compared to a 14% average reduction for above-ground tissues. Although the concentration of CO₂ treatments represented a significant source of variance for plant N concentration, no consistent trends were observed between them.     

Effects of carbon concentration and carbon-to-nitrogen ratio on growth, conidiation, spore germination and efficacy of the potential bioherbicide Colletotrichum coccodes

The effect of carbon concentration and carbon-to-nitrogen ratio (C:N) as well as their interaction on Colletotrichum coccodes growth and sporulation in submerged flask culture were evaluated. When C:N ratios were held constant, both mycelial dry biomass and spore yield increased with increasing carbon concentration. The specific spore yields (spore yield g⁻¹ carbon), however, were not significantly different for the same C:N ratio in most cases. The highest spore yields (1.3 × 10⁸ spores per ml) were obtained from media containing 20 g per liter carbon with C:N ratios ranging from 5:1 to 10:1. When the C:N ratio was greater than 15:1, spore yields were significantly decreased with increasing C:N ratios. High carbon concentration (20 g L⁻¹) combined with high C:N ratios (above 15:1) reduced both mycelial growth and sporulation, and increased spore matrix production. Spores produced in medium containing 10 g L⁻¹ carbon with C:N ratios from 10:1 to 15:1 had 90% germination on potato dextrose agar after 12 h and caused extensive shoot dry weight reduction on the target weed, velvetleaf. These results suggest that C:N ratios from 10:1 to 15:1 are optimal for C. coccodes spore production. Received 9 December 1997/ Accepted in revised form 22 May 1998     

rhlL-6影响巨噬细胞内钙离子浓度和空间分布

使用重组人白细胞介素６（ｒｈＩＬ－６）刺激小鼠腹腔巨噬细胞,应用荧光分光光度计和激光扫描共焦显微镜检测胞浆内游离钙离子的时空分布。静息状态巨噬细胞Ｃａ２＋浓度１０－８｀～１０－７ｍｏｏ／Ｌ,加入１００ｕ／ｍｌｒｈＩＬ－６后,未见作用。从２００ｕ／ｍｌ至４００ｕ／ｍｌ不同浓度的ｒｈＩＬ－６则使细胞内游离Ｃａ２＋浓度呈尖峰状迅速升高３００％左右,然后急剧下降至静息值。且各个浓度对Ｃａ２＋的升高幅度及峰形基本一致,但随浓度的升高,Ｃａ２＋浓度达到高峰所需的时间逐渐缩短。这说明,胞外ＩＬ－６浓度存在着一阈值,只有达到或超过这一阈值,才能通过一定机制造成细胞内Ｃａ２＋的升高