A sensitive,simultaneous analysis of ribulose 1,5-bisphosphate carboxylase/oxygenase efficiencies: Graphical determination of the CO2/O2 specificity factor

A simple approach to determine CO₂/O₂ specificity factor () of ribulose 1,5-bisphosphate carboxylase/oxygenase is described. The assay measures the amount of CO₂ fixation at varying [CO₂]/[O₂] ratios after complete consumption of ribulose 1,5-bisphosphate (RuBP). Carbon dioxide fixation catalyzed by the carboxylase was monitored by directly measuring the moles of ¹⁴CO₂ incorporated into 3-phosphoglycerate (PGA). This measurement at different [CO₂]/[O₂] ratios is used to determine graphically by several different linear plots the total RuBP consumed by the two activities and the CO₂/O₂ specificity factor. The assay can be used to measure the amounts of products of the carboxylase and oxygenase reactions and to determine the concentration of the substrate RuBP converted to an endpoint amount of PGA and phosphoglycolate. The assay was found to be suitable for all [CO₂]/[O₂] ratios examined, ranging from 14 to 215 micromolar CO₂ (provided as 1–16 mM NaHCO₃) and 614 micromolar O₂ provided as 50% O₂. The procedure described is extremely rapid and sensitive. Specificity factors for enzymes of highly divergent values are in good agreement with previously published data.Abbreviations HEPPS N-(2-hydroxyethyl)piperazine-N-(3-propanesulfonic acid) - L large subunit of rubisco - PGA 3-phosphoglyceric acid - rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP d-ribulose 1,5-bisphosphate - S small subunit of rubisco - XuBP d-xylulose 1,5-bisphosphate     

Feedback inhibition of photosynthesis in rice measured by O2 dependent transients

The kinetic properties of photosynthesis (both transient and steady-state) were monitored using three non-invasive techniques to evaluate limitations on triose-phosphate (triose-P) conversion to carbohydrate in rice. These included analyzing the O₂ sensitivity of CO₂ fixation and the assimilatory charge (AC) using gas exchange (estimate of the ribulose 1,5- bisphosphate pool) and measuring Photosystem II activity by chlorophyll fluorescence analysis under varying light, temperature and CO₂ partial pressures. Photosynthesis was inhibited transiently upon switching from 20 to 2 kPa O₂ (reversed O₂ sensitivity), the degree of which was correlated with a terminal, steady-state suppression of low O₂ enhancement of photosynthesis. Under current ambient levels of CO₂ and moderate to high light, the transient pattern was more obvious at 18 °C than at 26 °C while at 34 °C no tra nsient response was observed. The transient inhibition at 18 °C ranged from 15% to 31% depending on the pre-measurement temperature. This pattern, symptomatic of feedback, was observed with increasing light and CO₂ partial pressures with the degree of feedback decreasing from moderate (18 °C) up to high temperature (34 °C). Under feedback conditions, the rate of assimilation is shifted from being photorespiration limited to being triose-P utilization limited. Transitory changes in CO₂ assimilation rates (A) under low O₂ indicative of feedback coincided with a transitory drop in assimilatory charge (AC) and inhibition of electron transport. In contrast to previous studies with many C₃ species, our studies indicate that rice shows susceptibility to feedback inhibition under moderate temperatures and current atmospheric levels of CO₂.     

Dependency of the O2 consumption/O2 transport relationship on amino acid supply in sepsis

Summary In sepsis tissue O₂ uptake may be abnormally limited because of a depressed O₂ consumption/O₂ transport relationship. This study has been performed to assess patterns of O₂ consumption, CO₂ production and O₂ transport in septic patients undergoing total parenteral nutrition; more in particular, this study has investigated the interdependence between the patterns of blood O₂ uptake and simultaneous CO₂ release, and the availability of substrates (amino acids, glucose and fat). It has been shown that the O₂ consumption/O₂ transport relationship is significantly influenced by the exogenous amino acid load, which tends to increase O₂ uptake and O₂ consumption at any given O₂ transport, thus suggesting a favourable effect of amino acid administration on energy metabolism. The data on CO₂ production and CO₂ release, in addition to reconfirming the results of previous studies, have shown that the changes in O₂ uptake and in CO₂ production mediated by substrate doses have a quantifiable impact on blood O₂-CO₂ exchange interactions.     

Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply

We investigated the effect of CO₂ concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO₂ altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO₂ had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO₂ decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO₂ on N loss fromlitter also differed among species, with Vulpia litter from high-CO₂ plants releasing N more slowly than ambient-CO₂litter, whereas growth under elevated CO₂ caused increased Nloss from Avena litter. CO₂ effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO₂ on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO₂ effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO₂.     

Nitrogen supply effects on productivity and potential leaf litter decay of Carex species from peatlands differing in nutrient limitation

We investigated the effect of increased N-supply on productivity and potential litter decay rates of Carex species, which are the dominant vascular plant species in peatlands in the Netherlands. We hypothesized that: (1) under conditions of N-limited plant growth, increased N-supply will lead to increased productivity but will not affect C:N ratios of plant litter and potential decay rates of that litter; and (2) under conditions of P-limited plant growth, increased N-supply will not affect productivity but it will lead to lower C:N ratios in plant litter and thereby to a higher potential decay rate of that litter. These hypotheses were tested by fertilization experiments (addition of 10 g N m^-2 year^-1) in peatlands in which plant growth was N-limited and P-limited, respectively. We investigated the effects of fertilization on net C-fixation by plant biomass, N uptake, leaf litter chemistry and potential leaf litter decay. In a P-limited peatland, dominated by Carex lasiocarpa, there was no significant increase of net C-fixation by plant biomass upon enhanced N-supply, although N-uptake had increased significantly compared with the unfertilized control. Due to the N-fertilization the C:N ratio in the plant biomass decreased significantly. Similarly, the C:N ratio of leaf litter produced at the end of the experiment showed a significant decrease upon enhanced N-supply. The potential decay rate of that litter, measured as CO₂-evolution from the litter under aerobic conditions, was significantly increase upon enhanced N-supply. In a N-limited peatland, dominated by C. acutiformis, the net C-fixation by plant biomass increased with increasing N-supply, whereas the increase in N-uptake was not significant. The C:N ratio of both living plant material and of dead leaves did not change in response to N-fertilization. The potential decay rate of the leaf litter was not affected by N-supply. The results agree with our hypotheses. This implies that atmospheric N-deposition may affect the CO₂-sink function of peatlands, but the effect is dependent on the nature of nutrient limitation. In peatlands where plant growth is N-limited, increased N-supply leads to an increase in the net accumulation of C. Under conditions of P-limited plant growth, however, the net C-accumulation will decrease, because productivity is not further increased, whereas the amount of C lost through decomposition of dead organic matter is increased. As plant growth in most terrestrial ecosystems is N-limited, increased N-supply will in most peatlands lead to an increase of net C-accumulation.     

Mutations in a sequence near the N-terminus of the small subunit alter the CO2/O2specificity factor for ribulose bisphosphate carboxylase/oxygenase

Seven unique substitutions have been introduced by site-directed mutagenesis into the first conserved region of the small subunit of ribulose bisphosphate carboxylase/oxygenase from Anacystis nidulans 6301. After expression of each large, altered-small subunit gene tandem in Escherichia coli, two substitutions in the small subunit tyr17asp17 (Y17D) and arg10gly10 (R10G) result in little or no carboxylase activity. For the latter substitution, no L₈S₈enzyme complex could be detected suggesting that this mutation prevents assembly. Mutant enzymes containing the following substitutions R11G, T14A, S16A, Y17D and P19A have CO₂/O₂specificity factors ( values) of 40, 35, 18, 39 and 44, respectively, compared with that of 44 for wild-type recombinant enzyme whereas P20A has full carboxylase activity and a value of 55.     

铜镉污染土壤上CO2浓度升高对籼稻稻米品质的影响

采用盆栽试验,利用开顶式气室(Open Top Chamber,OTC)研究了5个籼稻品种在高、低铜镉复合污染土壤上,CO2浓度升高对水稻生长及吸收Cu、Cd和矿质元素Fe、Zn、Ca、Mn的影响,并对稻米中Cd的安全性进行了评价,了解Cd污染对人类健康的潜在风险。结果表明:CO2浓度升高,显著降低了低复合污染土壤上稻米的生物量,而显著增加了高复合污染土壤上的稻米生物量。CO2浓度升高降低了低污染土壤上稻米Cu含量,降低幅度为4.75%—24.49%,增加了高污染土壤上稻米Cu含量,增加幅度为6.60%—40.37%;而稻米Cu的总吸收量在低、高复合污染土壤上均是降低的。低、高复合污染土壤上,CO2浓度升高显著降低了三香优974稻米的Cd含量和吸收量;增加了其他4个品种稻米Cd含量和吸收量。CO2浓度升高对不同品种稻米中Fe、Zn、Ca、Mn含量影响存在显著差异。CO2浓度正常、升高条件下,两种污染土壤上金优463稻米中Cd含量超过食品卫生标准(Cd≤0.2mg/kg),三香优974在正常CO2浓度条件下其稻米Cd含量超过食品卫生标准。在低、高复合污染土壤上,金优463和三香优974稻米中Cd的THQ值均大于1,说明对人体暴露接触的潜在风险比较严重。CO2浓度升高显著降低了三香优974稻米中Cd对人体暴露接触的潜在风险,而对其他4个水稻品种稻米Cd的THQ值影响不明显。     

Growth and shoot: root ratio of seedlings in relation to nutrient availability

The influence of mineral nutrient availability, light intensity and CO₂ on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experiments with small Betula pendula plants, in which the concept of steady-state nutrition has been applied.Three distinctly different dry matter allocation patterns were observed when growth was limited by the availability of mineral nutrients: 1, Root growth was favoured when N, P or S were the major growth constraints. 2, The opposite pattern obtained when K, Mg and Mn restricted growth. 3, Shortage of Ca, Fe and Zn had almost no effect on the shoot:root ratio. The light regime had no effect on dry matter allocation except at very low photon flux densities (< 6.5 mol m^-2 day^-1), in which a small decrease in the root fraction was observed. Shortage of CO₂, on the other hand, strongly decreased root development, while an increase of the atmospheric CO₂ concentration had no influence on dry matter partitioning. An increased allocation of dry matter to below-ground parts was associated with an increased amount of starch in the tissues. Depletion of the carbohydrate stores occurred under all conditions in which root development was inhibited. It is concluded that the internal balance between labile nitrogen and carbon in the root and the shoot system determines how dry matter is being partitioned in the plant. The consistency of this statement with literature data and existing models for shoot:root regulation is examined.     

A study on the relationship between leaf conductance,CO2 concentration and carboxylation rate in various species

Leaf conductance g_L is strongly influenced by environmental factors like CO₂, irradiance and air humidity. According to Ball et al. (1987), g_L is correlated with an index calculated as the product of net CO₂ exchange rate A and ambient water vapour concentration W_a, divided by ambient CO₂ concentration c_a. However, this empirical model does not apply to high values of g_L observed at c_a below CO₂ compensation concentration . Therefore, we applied modified indices in which A is replaced by estimates for the rate of carboxylation. Such estimates, P₁ and P₂, were determined by adding to A the quotient of and the sum of gas phase resistance r_g and intracellular resistance for CO₂ exchange r_i, P₁ = A+/(r_g + r_i), or the quotient of and r_i, P₂ = A + /r_i. If P₂ is chosen, c_a in the Ball index has to be replaced by the intercellular CO₂ concentration c_i. By using the modified indices P₁·W_a/c_a and P₂·W_a/c_i, we analysed data from the C₃ species Nicotiana tabacum and Nicotiana plumbaginifolia, the C₃–C₄ intermediate species Diplotaxis tenuifolia, and the C₄ species Zea mays. The data were collected at widely varying levels of irradiance and CO₂ concentration. For all species uniform relationships between g_L and the new indices were found for the whole range of CO₂ concentrations below and above . Correlations between g_L and P₁·W_a/c_a were closer than those between g_L and P₂·W_a/c_i because P₁/c_a implicitly contains g_L. Highly significant correlations were also obtained for the relationships between g_L and the ratios P₁/c_a and P₂/c_i.     

Differential responses of rice to inoculation with wild-type and non-pathogenic mutants of Magnaporthe oryzae

We analyzed the response of rice to Magnaporthe oryzae infection using two mutant strains deficient in Mgb1 and Mst12, which are essential for the development of appresoria and penetration pegs. Both mutants induced the much lower levels of accumulation of phytoalexins than wild-type, suggesting that the massive production of phytoalexins requires the fungal invasion of rice cells. Intense accumulation of H₂O₂ in a single whole cell also required fungal penetration. Microarray analysis of rice gene expression revealed mutant-specific gene expression, indicating that signal exchange between rice and M. oryzae commence before fungal penetration of the rice cell. In situ detection of mRNAs for peroxidase and β-1,3-glucanase showed that expression of these genes also occurs after penetration as observed for phytoalexin production. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Tomoaki Kato, Shigeru Tanabe, and Marie Nishimura contributed equally to this work. Accession number of the original microarray data in NCBI is GSE9450.     

Photosynthesis in rice under a salt stress

In four cultivars of Oryza sativa L., a gradual decrease in the activity of photosystems 1 and 2 as well as in chlorophyll (Chl) fluorescence transients and emission at 688 nm was observed with an increase in NaCl concentration. This decrease was more pronounced in salt-sensitive cultivars as compared to the tolerant ones. A drastic decrease in net photosynthetic rate was found in both cultivar types. This revised version was published online in June 2006 with corrections to the Cover Date.     

高CO2浓度对杂交水稻光合作用日变化的影响——FACE研究

大气二氧化碳(CO_2)浓度增高导致全球变暖,但作为光合作用底物促进绿色作物的光合作用。为了明确高CO_2浓度对杂交水稻结实期光合日变化的影响,2014年利用稻田FACE(Free Air CO_2Enrichment)平台,以生产上曾创高产纪录的两个杂交稻新组合甬优2640和Y两优2号为供试材料,设置环境CO_2和高CO_2浓度(增200μmol/mol)两个水平,测定杂交稻抽穗期和灌浆中期光合作用日变化和成熟期生物量。结果表明,高CO_2浓度环境下两组合抽穗期叶片净光合速率均大幅增加(全天平均52%),但灌浆中期的平均增幅减半,其中Y两优2号这种光合下调表现更为明显。大气CO_2浓度升高使两杂交稻组合抽穗和灌浆中期叶片气孔导度均大幅下降,导致蒸腾速率下降而水分利用效率大幅增加,Y两优2号气孔导度和蒸腾速率对CO_2的响应上午大于下午,而甬优2640表现相反。尽管大气CO_2浓度升高使杂交稻结实期不同时刻胞间CO_2浓度均大幅增加,但对气孔限制值特别是胞间CO_2与空气CO_2浓度之比多无显著影响,两品种趋势一致。大气CO_2浓度升高对甬优2640地上部生物量及其组分的影响明显大于Y两优2号,CO_2与品种间多存在互作效应。以上结果表明,与甬优2640相比,Y两优2号最终生产力从高CO_2浓度环境中获益较少可能与该品种生长后期存在明显的光合适应有关,但这种光合适应似乎不是由气孔限制造成的。     

Individual vs. population plastic responses to elevated CO2, nutrient availability, and heterogeneity: a microcosm experiment with co-occurring species

We conducted an experiment to evaluate the plastic phenotypic responses of individuals, growing under intra-specific competition, and populations of three co-occurring grassland species (Lolium perenne, Plantago lanceolata, and Holcus lanatus) to joint variations in atmospheric CO₂ partial pressure (P _CO2; 37.5 vs. 70 Pa), nutrient availability (NA; 40 vs. 120 mg N added as organic material), and the spatial pattern of nutrient supply (SH; homogeneous vs. heterogeneous nutrient supply). At both the population and individual levels, the aboveground biomass of the three species significantly increased when the nutrients were heterogeneously supplied. Significant two- (SH × NA) and three-term (P _CO2 × NA × SH) interactions determined the response of traits measured on populations (aboveground biomass and below: aboveground biomass ratio, BAR) and individuals (aboveground biomass and specific leaf area). The combination of a high SH and NA elicited the highest plasticity of aboveground biomass in populations and individuals of the three species evaluated, and of BAR in Holcus. Soil heterogeneity and elevated P _CO2 elicited the highest plasticity in the SLA of Plantago and Lolium individuals. Our results show that populations, and not only individuals, respond to soil heterogeneity in a plastic way, and that plastic responses to elevated P _CO2 are complex since they vary across traits and species, and are influenced by the availability of nutrients and by their spatial distribution. They also emphasize the importance of soil heterogeneity as a modulator of plant responses to global change drivers. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Responsible Editor: Angela Hodge     

The inductive responses of the antioxidant enzymes by salt stress in the rice (Oryza sativa L.)

To access contributions of inductive responses of the antioxidant enzymes in the resistance to salt stress, activities of the enzymes were determined in the rice (Oryza sativaL. cv. Dongjin) plant. In the leaves of the rice plant, salt stress preferentially enhanced the content of H₂O₂ as well as the activities of the superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase specific to guaiacol, whereas it induced the decrease of catalase activity. On the other hand, salt stress had little effect on the activity levels of glutathione reductase (GR). In order to analyze the changes of antioxidant enzyme isoforms against salt stress, plant extracts were subjected to native PAGE. Leaves of the rice plant had two isoforms of Mn-SOD and five isoforms of Cu/Zn-SOD. Fe-SOD isoform was not observed in the activity gels. Expression of Cu/Zn-1, -2, and Mn-SOD-2 isoforms was preferentially enhanced by salt stress. Seven APX isoforms were presented in the leaves of the rice plants. The intensities of APX-4 to -7 were enhanced by salt stress, whereas those of APX-1 to -3 were minimally in changed response to salt stress. There were seven GR isoforms in the leaves of rice plants. Levels of activity for most GR isoforms did not change in the stressed plants compared to the control plants. On the other hand, the levels of activity for most antioxidant enzymes changed little in the roots of stressed plants compared to the control plants. These results collectively suggest that SOD leads to the overproduction of hydrogen peroxide in the leaves of rice plants subjected to salt stress: The overproduction of hydrogen peroxide functions as the signal of salt stress, which induces the induction of specific APX isoforms but not specific GR isoforms under catalase deactivation.     

Combined effects of CO2 concentration and nutrient status on the biomass production and nutrient uptake of birch seedlings (Betula pendula)

Birch seedlings (Betula pendula) were grown for four months in a greenhouse at three nutrient levels (fertilization of 0, 100 and 500 kg ha^-1 monthy) and at four CO₂ concentrations (350, 700, 1050 and 1400 ppm). The effect of CO₂ concentration on the biomass production depended on the nutrient status. When mineralization of the soil material was the only source of nutrients (0 kg ha^-1), CO₂ enhancement reduced the biomass production slightly, whereas the highest production increase occurred at a fertilization of 100 kg ha^-1, being over 100% between 350 and 700 ppm CO₂. At 500 kg ha^-1 the production increase was smaller, and the production decreased beyond a CO₂ concentration of 700 ppm. The CO₂ concentration had a slight effect on the biomass distribution, the leaves accounting for the highest proportion at the lowest CO₂ concentration (350 ppm). An increase in nutrient status led to a longer growth period and increased the nutrient concentrations in the plants, but the CO₂ concentration had no effect on the growth rhythm and higher CO₂ reduced the nutrient concentrations.     

二氧化碳储存通量对森林生态系统碳收支的影响

涡度相关系统观测高度以下的CO₂储存通量对准确评价森林生态系统与大气间净CO₂交换量（NEE）有着重要的影响.本研究以长白山阔叶红松林为研究对象,利用2003年的涡度相关观测数据以及CO₂浓度廓线数据,分析了CO₂储存通量的变化规律及其对碳收支过程的影响.结果表明：涡度相关观测高度以下的CO₂储存通量具有典型的日变化特征,其最大变化量出现在大气稳定与不稳定层结转换期.利用涡度相关系统观测的单点CO₂浓度变化方法与利用CO₂浓度廓线方法计算的CO₂储存通量差异不显著.忽略CO₂储存通量,在半小时尺度上会造成对夜间和白天的NEE分别低估25%和19%,在日和年尺度上,会对NEE低估10%和25%;忽略CO₂储存通量,会低估Michaelis-Menten光响应方程及Lloyd-Taylor呼吸方程的参数,并且对表观初始量子效率α和参考呼吸R_ref的低估最大;忽略CO₂储存通量,在半小时、日及年尺度上,均会对总光合作用（GPP）和生态系统呼吸（R_e）低估约20%.     

Physiological responses of carbon-sequestering microalgae to elevated carbon regimes

In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO₂ concentrations of 0.03–15% and NaHCO₃ of 0.05–2 g CO₂ l^–1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (μ_max) and the biomass carrying capacity (B_max). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The B_max of I-3 significantly increased from 214 to 828 mg l^–1 when CO₂ concentration was increased from 0.03 to 15% (r = 0.955, P = 0.012). Additionally, the B_max of I-3 increased with increasing NaHCO₃ (r = 0.885, P = 0.046) and was recorded at 153 mg l^–1 (at 0.05 g CO₂ l^–1) and 774 mg l^–1 at (2 g CO₂ l^–1). Relative electron transport rate (rETR) and maximum quantum yield (F_v/F_m) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in F_v/F_m with increasing carbon was similar for strains I-3 and the reference strain. Based on partial 28s ribosomal RNA gene sequencing, strain I-3 was homologous to the ribosomal genes of Chlorella sp.     

Effects of elevated CO2 on plant growth and nutrient partitioning of rice (Oryza sativa L.) at rapid tillering and physiological maturity

Abstract

This work investigates the relationship between plant growth, grain yield, nutrient acquisition and partitioning in rice (Oryza sativa L.) under elevated CO₂. Plants were grown hydroponically in growth chambers with a 12-h photoperiod at either 370 or 700 µmol CO₂ mol^?1 concentration. Plant dry mass (DM), grain yield and macro- and micronutrient concentrations of vegetative organs and grains were determined. Elevated CO₂ increased biomass at tillering, and this was largely due to an increase in root mass by 160%. Elevated CO₂ had no effect on total nutrient uptake (N, P, K, Mg and Ca). However, nutrient partitioning among organs was significantly altered. N partitioning to leaf blades was significantly decreased, whereas the N partitioning into the leaf sheaths and roots was increased. Nutrient use efficiency of N, P, K, and Mg in all organs was significantly increased at elevated CO₂. At harvest maturity, grain yield was increased by 27% at elevated CO₂ while grain (protein) concentration was decreased by a similar magnitude (28%), suggesting that critical nutrient requirements for rice might need to be reassessed with global climate change.     

Effects of enhanced atmospheric CO2 and nutrient supply on the quality and subsequent decomposition of fine roots of Betula pendula Roth. and Picea sitchensis (Bong.) Carr.

Fine root litter derived from birch (Betula pendula Roth.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) plants grown under two CO₂ atmospheric concentrations (350 ppm and 600 ppm) and two nutrient regimes was used for decomposition studies in laboratory microcosms. Although there were interactions between litter type, CO₂/fertiliser treatments and decomposition rates, in general, an increase in the C/N ratio of the root tissue was observed for roots of both species grown under elevated CO₂ in unfertilized soil. Both weight loss and respiration of decomposing birch roots were significantly reduced in materials derived from enriched CO₂, whilst the decomposition of spruce roots showed no such effect. A parallel experiment was performed using Betula pendula root litter grown under different N regimes, in order to test the relationship between C/N ratio of litter and root decomposition rate. A highly significant (p<0.001) negative correlation between C/N ratio and root litter respiration was found, with an r²=0.97. The results suggest that the increased C/N ratio of plant tissues induced by elevated CO₂ can result in a reduction of decomposition rate, with a resulting increase in forest soil C stores.