Acclimation of rice to changing atmospheric carbon dioxide concentration

Abstract. The effects were studied of season-long (75 and 88d) exposure of rice (Oryza sativa L. cv. IR-30) to a range of atmospheric CO₂ concentrations in outdoor, computer-controlled, environment chambers under natural solar radiation. The CO₂ concentrations were maintained at 160, 250, 330, 500, 660 and 900μmol mol^-1 air. Photosynthesis increased with increasing growth CO₂ concentrations up to 500u.mol moP1, but levelled off at higher CO₂ values. Specific leaf area also increased significantly with increasing CO₂. Although leaf dry weight and leaf area index increased, the overall response was not statistically significant. Leaf nitrogen content dropped slightly with elevated CO₂, but the response was not statistically significant. The specific activity of ribulose bisphosphate carboxylase/oxygenase (rubisco) declined significantly over the CO₂ concentration range 160 to 900μmol mol^-1. When expressed on a leaf area basis, rubisco activity decreased by 66%. This was accompanied by a 32% decrease in the amount of rubisco protein as a fraction of the total soluble leaf protein, and by 60% on a leaf area basis. For leaves in the dark, the total rubisco activity (CO₂/Mg²⁺-activated) was reduced by more than 60%. This indicates that rice accumulated an inhibitor in the dark, probably 2-car-boxyarabinitol 1-phosphate (CA-1-P). However, the inhibitor did not seem to be involved in the acclimation response. The degree of carbamylation of the rubisco enzyme was unchanged by the CO2 growth regime, except at 900 [μmol mol^-1 where it was reduced by 24%. The acclimation of rice to different atmospheric CO₂ conditions involved the modulation of both the activity and amount of rubisco protein in the leaf.     

Long term water stress inactivates Rubisco in subterranean clover

In long-term field experiments, during consecutive years, microswards of subterranean clover were irrigated to minimise water deficits or subjected to progressively increasing drought over 30 days. Both leaf water potential and relative water content steadily decreased during the experiments. Plants affected by drought grew more slowly and photosynthesis was decreased. Photosynthetic rate (A) and Rubisco were analysed in relation to midday water potentials and relative water contents. The difference in A between draughted and irrigated plants increased progressively, in part as a result of decreased stomatal conductance and CO₂ concentration within leaf (Ci). However, A-Ci curves suggest that the photosynthetic capacity in plants experiencing long-term stress was reduced by 50% when compared with irrigated plants. Drought decreased both the initial and the total Rubisco activity per unit area in a similar way but did not reduce the amount of Rubisco protein per unit leaf area. Thus, the specific activity of Rubisco, rather than its activation state, decreased suggesting that under water stress the active sites were blocked by inhibitors.     

No overall stimulation of soil respiration under mature deciduous forest trees after 7 years of CO2 enrichment

The anthropogenic rise in atmospheric CO₂ is expected to impact carbon (C) fluxes not only at ecosystem level but also at the global scale by altering C cycle processes in soils. At the Swiss Canopy Crane (SCC), we examined how 7 years of free air CO₂ enrichment (FACE) affected soil CO₂ dynamics in a ca. 100‐year‐old mixed deciduous forest. The use of ¹³C‐depleted CO₂ for canopy enrichment allowed us to trace the flow of recently fixed C. In the 7th year of growth at ～550 ppm CO₂, soil respiratory CO₂ consisted of 39% labelled C. During the growing season, soil air CO₂ concentration was significantly enhanced under CO₂‐exposed trees. However, elevated CO₂ failed to stimulate cumulative soil respiration (R_s) over the growing season. We found periodic reductions as well as increases in instantaneous rates of R_s in response to elevated CO₂, depending on soil temperature and soil volumetric water content (VWC; significant three‐way interaction). During wet periods, soil water savings under CO₂‐enriched trees led to excessive VWC (>45%) that suppressed R_s. Elevated CO₂ stimulated R_s only when VWC was ≤40% and concurrent soil temperature was high (>15 °C). Seasonal Q₁₀ estimates of R_s were significantly lower under elevated (Q₁₀=3.30) compared with ambient CO₂ (Q₁₀=3.97). However, this effect disappeared when three consecutive sampling dates of extremely high VWC were disregarded. This suggests that elevated CO₂ affected Q₁₀ mainly indirectly through changes in VWC. Fine root respiration did not differ significantly between treatments but soil microbial biomass (C_mic) increased by 14% under elevated CO₂ (marginally significant). Our findings do not indicate enhanced soil C emissions in such stands under future atmospheric CO₂. It remains to be shown whether C losses via leaching of dissolved organic or inorganic C (DOC, DIC) help to balance the C budget in this forest.     

Photosynthetic responses of Populus przewalski subjected to drought stress

Cuttings of P. przewalski were exposed to two different watering regimes which were watered to 100 and 25 % of field capacity (WW and WS, respectively). Drought stress not only significantly decreased net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), efficiency of photosystem 2 (PS2) (F_v/F_m and yield), and increased intrinsic water use efficiency (WUE_i) under controlled optimal conditions, but also altered the diurnal changes of gas exchange, chlorophyll fluorescence, and WUE_i. On the other hand, WS also affected the P _N-photosynthetically active radiation (PAR) response curve. Under drought stress, P _N peak appeared earlier (at about 10:30 of local time) than under WW condition (at about 12:30). At midday, there was a depression in P _N for WS plants, but not for WW plants, and it could be caused by the whole microclimate, especially high temperature, low relative humidity, and high PAR. There were stomatal and non-stomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, and low P _N at midday was caused by both stomatal and non-stomatal limitations, whereas non-stomatal limitation dominated in the afternoon. In addition, drought stress also increased compensation irradiance and dark respiration rate, and decreased saturation irradiance and maximum net photosynthetic rate. Thus drought stress decreased plant assimilation and increased dissimilation through affected gas exchange, the diurnal pattern of gas exchange, and photosynthesis-PAR response curve, thereby reducing plant growth and productivity.     

The relationship between the Rubisco reaction mechanism and models of photosynthesis*

Abstract. A new model of photosynthesis published recently in this journal (H. Farazdaghi & G. E. Edwards, Plant, Cell and Environment (1988) 11 , 789–798; 799–809) clams to have a more complete mechanistic basis than currently used models based on the paper of G. D. Farquhar, S. von Caemmerer & J. A. Berry (Planta (1980) 149 , 78–90). In this paper, we examine the validity of the new kinetic expression for the rate of CO₂ fixation by Rubisco, and the derivation of an equation for photosynthetic CO₂ assimilation as a function of light intensity and CO₂ concentration presented in the new model. In addition, we compare measured response curve of photosynthesis to CO₂ and light with simulated curves using alternative models. We conclude that the new model is mechanistically misleading and, empirically, overestimates the extent to which light and CO₂ co-limit the rate of photosynthesis under most physiological conditions.     

Responses of Plant Dark Respiration to Doubled CO2 Concentration

Ten species of plants were grown at ambient (350μmol CO2·mol-1 air) and doubled (700 μmol CO2·mol-1 air) CO2 concentrations at ambient temperature and illumination in order to examine changes of dark respiration of whole seedlings or detached leaves. Effects of CO2 on dark respiration were determined by brief exposure ( ≤ 5 min) to corresponding CO2 concentration and temperatures ( 15,20,25,30 and 35 ℃ ) with infrared CO2 analyzer. The reductions in dark respiration on a weight base for leaves of East-Liaoning oak (Quercus liaotungensis Koidz. ) at 15,20 and 25 ℃ and of soybean ( Glycine max L. ) at 20,25,30 and 35 ℃ and for whole seedlings of three- tcoloured amaranth (Amaranthus tricolor L. ) at 15 and 20 ℃ and cucumber ( Cucumis sativus L. ) at 15 cE measured at elevated concentration relative to the ambient CO2 concentration were observed. No significant difference in respiration responded was observed to elevated or ambient CO2 concentrations at 15 ℃ in maize (Zea mays L. ) seedlings and alfalfa (Medicago sativa L. ) leaves, at 35 ℃ in East-Liaoning oak leaves and at 20,25 and 30 ℃ in three-coloured amaranth seedlings. However CO2 efflux in leaves of weeping willow (Salix babylonica L. ), simon poplar (Populus simonii Carr. ) and eucommia (Eucommia ulmoides Oliv. ) at 15,20,25,30 and 35 ℃, alfalfa at 20,25,30 and 35 ℃, East-Liaoning oak at 30 ℃, maize at 15 ℃, seedlings of common buckwheat (Fagotrytum esculentum Moench) at 15,20,25,30 and 35 ℃, cucumber and maize at 20,25,30 and 35 ℃ and three-coloured amaranth at 35 ℃ showed an increase at elevated in contrast to ambient CO2 concentration. In general, at lower temperatures (i. e. 15, 20 ℃ ) there was no significant difference between elevated and ambient CO2 concentration for dark respiration, while at higher temperatures (i. e. 30,35 ℃ ) elevated CO2 concentration positively stimulate clark respiretion. It has not yet been described that double CO2 concentration could enhance plant dark respiration at 30 and 35 ℃. Impacts of the characteristics in dark respiration on the future changes of vegetation and its mechanism were discussed.     

CO_2增长对杉木中龄林针叶光合生理生态的影响

通过对 1 7a生杉木人工林小枝的活体测定 ,研究了大气 CO2 增长对杉木中龄林净光合、呼吸、气孔导度和水分利用效率等生理生态特性的影响。结果表明 ,在 CO2 浓度为 4 5μmol/ L左右时 ,杉木针叶净光合速率比正常大气 CO2 下提高 1倍以上 ,气孔导度和蒸腾速率有不同程度的降低 ,水分利用效率提高约 1～ 2倍 ;同时使光补偿点降低 ,饱和点和光抑制点提高 ,光量子效率提高 4 0 %～ 2 95%且阳枝大于阴枝 ,针叶暗呼吸降低 2 0 %～ 72 %。随着 CO2 浓度的增加 ,针叶净光合速率和水分利用效率呈线性上升 ,约到 4 5μmol/ L以后 ,增加速率减慢 ,但 CO2 饱和点可达 1 1 6μmol/ L以上。杉木针叶对CO2 增长的这种反应 ,对大气 CO2 不断增长的条件下杉木生长是有利的 ,但对其长期反应还有待进一步研究。     

Physiological responses of forest trees to heat and drought

The heat wave of summer 2003 was the largest and the most persistent ever experienced in Central Europe and has fuelled concern about the effects of climate change on European ecosystems. Since forests constitute the most important European ecosystems, in this review article we assess current knowledge on the effects of heat and drought on key metabolic processes for growth and productivity of forest trees. In particular, the general consequences of heat and drought on (1) photosynthesis and respiration at the cellular and community level, and (2) on nutrient uptake, partitioning and competition for nutrients are summarized. The latter are a major sink for photosynthetic energy and, therefore, are indirectly but strongly connected to the performance of photosynthesis. In addition, the interaction of heat and drought with stress compensation mechanisms and emission of biogenic volatile organic compounds (BVOC) are discussed, since these processes are directly connected to carbon metabolism. Effects on the emission of BVOC are also included because they constitute an important feedback mechanism on ozone formation and, thus, on atmospheric pollution. As far as available, data collected during the 2003 heat wave are included and discussed.     

Sensitivity of chickpea and faba bean to root‐zone hypoxia,elevated ethylene,and carbon dioxide

During soil waterlogging, plants experience O₂ deficits, elevated ethylene, and high CO₂ in the root‐zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 μL L^?1), CO₂ (2–20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO₂ reduced root growth of both species, but O₂ deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO₂ inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas‐filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O₂ movement was more prominent in faba bean when in an O₂‐free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O₂, such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO₂ partially inhibited root extension in both species, but low O₂ in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O₂ condition than faba bean.     

Photosynthetic responses of Eucalyptus nitens (Deane and Maiden) Maiden to green pruning

 Three-year-old Eucalyptus nitens (Deane and Maiden) Maiden trees and 1-year-old ramets of a single clone of E. nitens were pruned to remove 0, 50% or 70% of the green crown length. This was equivalent to removal of 0, 55% or 88% of foliage area of trees, and 0, 77% or 94% of foliage area of ramets. CO₂ assimilation (A) and stomatal conductance (g_s) were measured at constant illumination in five height zones and three foliage-age classes of trees over a 16-month period following pruning. Foliar nitrogen (N) and phosphorus (P) concentrations were determined for each measurement time during the first 12 months of the experiment. In ramets A and g_s were measured in four height zones and two foliage-age classes over a six-week period, and N and P concentrations were measured only once, at the end of the experiment. Rates of A increased by up to 175% following pruning. This response occurred throughout the canopy irrespective of position in the crown or foliage age. The magnitude of the response was generally greater in ramets than in trees, and increased with increasing severity of pruning. The initiation of the response was later, and the duration of the response was longer, in trees than ramets. In the lower crown of trees there was evidence of delayed senescence following pruning. Photosynthetic enhancement was not related to changes in foliar N concentrations. The ratio of A/N increased in many zones following pruning, especially after more severe defoliation. There was no evidence that changes in P concentrations were responsible for the result. The increases in A may have been related to changes in g_s, as maximum values of g_s were greater, and the ratio of A/g_s was generally lower, in pruned than unpruned plants. Received: 31 December 1996 / Accepted: 19 August 1997     

CO2增长对杉木中龄林针叶光合生理生态的影响

通过对１７ａ生杉木人工林小枝的活体测定,研究了大气ＣＯ２增长对杉木中龄林净光合、呼吸、气孔导度和水分利用效率等生理生态特性的影响。结果表明,在ＣＯ２浓度为４５μｍｏｌ／Ｌ左右时,杉木针叶净光合速率比正常大气ＣＯ２下提高１倍以卢,气孔导度和蒸速率有不同程度的降低,水分利用效率提高约１￣２倍;同时使光补偿点降低,饱和点和光抑制点提高,光量子效率提高４０％￣２９５％且阳酝 大于阴枝,针叶暗呼吸降低２０％     

Effects of phosphorus nutrition on the response of photosynthesis to CO2 and O2, activation of ribulose bisphosphate carboxylase and amounts of ribulose bisphosphate and 3-phosphoglycerate in spinach leaves

Phosphorus-deficient spinach plants were grown by transferring them to nutrient solutions without PO₄. Photosynthetic rates were measured at a range of intercellular CO₂ partial pressures from 50–500 bar and then the leaves were freeze-clamped in situ to measure ribulose bisphosphate carboxylase (Rubisco) activity and metabolite concentrations. Compared with control leaves, deficient leaves had significantly lower photosynthetic rates, percentage activation of Rubisco, and amounts of ribulose bisphosphate and 3-phosphoglycerate at all CO₂ partial pressures. After feeding 10 mM PO₄ to the petioles of detached deficient leaves, all these measurements increased within 2 hours. At atmospheric CO₂ partial pressure the photosynthetic rate was stimulated in 19 mbar O₂ compared with 200 mbar. At higher CO₂ partial pressures this stimulation was less but the percentage stimulation in deficient leaves was no different from controls in either CO₂ partial pressure. It was concluded that phosphorus deficiency affects both Rubisco activity and the capacity for ribulose bisphosphate regeneration, and possible causes are discussed.Abbreviations A CO₂ assimilation rate - C_i intercellular CO₂ partial pressure - PGA 3-phosphoglycerate - RuP₂ ribulose 1,5-bisphosphate - Rubisco RuP₂ carboxylase/oxygenase     

Foliar maintenance respiration of subalpine and boreal trees and shrubs in relation to nitrogen content

A nitrogen-based model of maintenance respiration (R_m) would link R_m with nitrogen-based photosynthesis models and enable simpler estimation of dark respiration flux from forest canopies. To test whether an N-based model of R_m would apply generally to foliage of boreal and subalpine woody plants, I measured R_m (CO₂ efflux at night from fully expanded foliage) for foliage of seven species of trees and shrubs in the northern boreal forest (near Thompson, Manitoba, Canada) and seven species in the subalpine montane forest (near Fraser, Colorado, USA). At 10°C, average R_m for boreal foliage ranged from 0.94 to 6.8μmol kg^?1 s^?1 (0.18–0.58 μmol m^?2 s^?1) and for subalpine foliage it ranged from 0.99 to 7.6 μmol kg^?1 s^?1 (0.28–0.64μmol m^?2 s^?1). CO₂ efflux at 10°C for the samples was only weakly correlated with sample weight (r = 0.11) and leaf area (r = 0.58). However, CO₂ efflux per unit foliage weight was highly correlated with foliage N concentration [r = 0.83, CO₂ flux at 10°C (mol kg^?1 s^?1) = 2.62 × foliage N (mol kg^?1)J, and slopes were statistically similar for the boreal and subalpine sites (P=0.28). CO₂ efflux per unit of foliar N was 1.8 times that reported for a variety of crop and wildland species growing in warmer climates.     

厚壁毛竹光合作用对CO2浓度倍增的短期响应

采用Li-6400P光合测定仪对比测定了大气CO2浓度和短期CO2浓度倍增下不同季节厚壁毛竹的光合特性,结果表明:CO2浓度加倍促使最大净光合速率、净光合速率、水分利用率、光合量子效率和光饱和点升高,年平均增幅分别为62.79%、48.74%、94.41%、8.70%和16.67%;CO2浓度加倍促使蒸腾速率、暗呼吸速率和光补偿点下降,年平均降幅分别为17.60%、37.25%和40.50%。不同季节厚壁毛竹光合生理特性参数在CO2浓度加倍后的增加幅度或降低幅度与叶片生理活性和气候变化密切相关。CO2浓度的倍增并未明显改变厚壁毛竹光合特性的季节变化规律,除光补偿点外,其它光合参数的季节大小顺序仍与大气CO2浓度下的相同。厚壁毛竹光合作用对短期CO2浓度升高的响应特征与C3植物光合作用对短期CO2浓度升高响应的普遍规律相符。     

Winter photosynthesis by saplings of evergreen broad-leaved trees in a deciduous temperate forest

* Here we investigated photosynthetic traits of evergreen species under a deciduous canopy in a temperate forest and revealed the importance of CO2 assimilation during winter for annual CO2 assimilation. * Saplings were shaded by the canopy trees from spring through to autumn, but were less shaded during the winter months. Photosynthetic rates at light saturation (Aarea) were lower during winter than during the growing season. Aarea was higher in Camellia, Ilex and Photinia than in Castanopsis, Cleyera and Quercus during the winter, but differed little during summer and autumn. * Estimated daily CO2 assimilation (Aday) was higher during the winter than during the growing season in Camellia, Ilex and Photinia but was higher than that during the growing season only at the beginning and end of winter in Castanopsis, Cleyera and Quercus. Aday was higher in Camellia, Ilex and Photinia than in Castanopsis, Cleyera and Quercus but differed little among them during the growing season. * These results reveal the importance of winter CO2 assimilation for the growth of Camellia, Ilex and Photinia. Furthermore, differences in annual CO2 assimilation among species are strongly modified by species-specific photosynthetic traits during the winter under deciduous canopy trees.     

Extreme rainfall and snowfall alter responses of soil respiration to nitrogen fertilization: a 3‐year field experiment

Extreme precipitation is predicted to be more frequent and intense accompanying global warming and may have profound impacts on soil respiration (Rs) and its components, that is, autotrophic (Ra) and heterotrophic (Rh) respiration. However, how natural extreme rainfall or snowfall events affect these fluxes are still lacking, especially under nitrogen (N) fertilization. In this study, extreme rainfall and snowfall events occurred during a 3‐year field experiment, allowing us to examine their effects on the response of Rs, Rh, and Ra to N supply. In normal rainfall years of 2011/2012 and 2012/2013, N fertilization significantly stimulated Rs by 23.9% and 10.9%, respectively. This stimulation was mainly due to the increase of Ra because of N‐induced increase in plant biomass. In the record wet year of 2013/2014, however, Rs was independent on N supply because of the inhibition effect of the extreme rainfall event. Compared with those in other years, Rh and Ra were reduced by 36.8% and 59.1%, respectively, which were likely related to the anoxic stress on soil microbes and decreased photosynthates supply. Although N supply did not affect annual Rh, the response ratio (RR) of Rh flux to N fertilization decreased firstly during growing season, increased in nongrowing season and peaked during spring thaw in each year. Nongrowing season Rs and Rh contributed 5.5–16.4% to their annual fluxes and were higher in 2012/2013 than other years due to the extreme snowfall inducing higher soil moisture during spring thaw. The RR of nongrowing season Rs and Rh decreased in years with extreme snowfall or rainfall compared to those in normal years. Overall, our results highlight the significant effects of extreme precipitation on responses of Rs and its components to N fertilization, which should be incorporated into models to improve the prediction of carbon‐climate feedbacks.     

CO2浓度升高对红松和长白松土壤呼吸作用的影响

以开顶箱法研究了CO₂浓度升高对红松和长白松土壤呼吸作用的影响.结果表明,500 μmol CO₂·mol^-1使红松和长白松土壤呼吸速率明显降低,土壤表面CO₂浓度升高导致CO₂扩散受阻可能是土壤呼吸受到抑制的主要原因.500 μmol CO₂·mol^-1下两树种土壤表面CO₂浓度明显高于对照箱和裸地条件下的CO₂浓度,增加幅度在40～150 μmol·mol^-1之间;对照箱内长白松土壤表面CO₂浓度略高于裸地,差异不显著,红松差异显著500 μmol CO₂·mol^-1下的长白松土壤全氮及总有机碳含量略高于对照组,差异不显著,红松裸地的碳氮含量明显低于500 μmol CO₂·mol^-1 及对照箱内土壤碳氮含量;500 μmol CO₂·mol^-1 及开顶箱的微环境对地下3 cm处土壤温度没有明显影响.     

草地土壤呼吸研究进展

土壤呼吸是生态系统物质循环和能量流动的重要过程,具有多方面的生态意义。在综合比较了土壤呼吸的各种测定方法,概括了草地土壤呼吸的速率和年排放量,并就影响草地土壤呼吸的一些重要因素进行了阐述,文章最后讨论了草地土壤呼吸今后的研究方向。