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1.
Photosynthetic light and temperature response curves were measured seasonally in seedlings of white spruce (Picea glauca (Moench.) Voss) grown for two years in the understory of aspen (Populus tremuloides Michx.) or in the open in central Alberta. Light-saturated rate of net photosynthesis, the optimum temperature for net photosynthesis, transpiration rate, photochemical efficiency, and stomatal and mesophyll conductances increased from spring to summer and declined thereafter, whereas dark respiration rate and compensation and saturation points were highest in spring. Depression of photosynthetic parameters was greater in open-grown seedlings than in understory seedlings during the periods in spring and autumn when night frosts were common. Net photosynthetic rates were similar in understory and open-grown seedlings in summer, but they were significantly lower in open-grown seedlings in spring and autumn. Significantly lower transpiration rates and stomatal conductances in open-grown seedlings than in understory seedlings were also observed at 15 and 25 degrees C in the autumn. Shoot and needle growth were less in open-grown seedlings than in understory seedlings. In summer, when irradiances were low in the aspen understory, understory white spruce seedlings maintained a positive carbon balance by decreasing their compensation and saturation points and increasing their photochemical efficiency compared to spring and autumn. 相似文献
2.
Carbon exchange of an old-growth eastern hemlock (Tsuga canadensis) forest in central New England 总被引：1，自引：0，他引：1
Carbon (C) exchange of an approximately 200-year-old eastern hemlock (Tsuga canadensis L.) forest in central Massachusetts, USA, was estimated from mid-October 2000 through October 2001 based on eddy covariance measurements and statistical modeling from microclimatic data. Measurements were made in 68% of the hours during the year of study, with > 50% coverage in all months except December and August. Data were filtered by wind direction and atmospheric turbulence to remove invalid measurements. Analysis of filtered data showed that photosynthetically active radiation (PAR) was significant in predicting C exchange, except during the winter. Daily minimum air temperature affected C exchange in autumn and winter, whereas time of day, water vapor pressure deficit and air temperature had significant effects on C storage in spring, summer and fall. Most C storage in the stand occurred in April through July and in October 2001, with maximum rates in April and May. Persistent cold weather prevented C storage in December through March. In early spring 2001, C uptake was sensitive to nocturnal frost: daily minimum air temperatures below 0 degrees C reduced C fixation, and minima below -5 degrees C caused its virtual cessation. Soil temperature was a poor predictor of C balance during this period. In August, high soil and air temperatures (averaging 16.7 and 21.1 degrees C, respectively) drove high ecosystem respiration, which approximately balanced C uptake. These patterns show potential for stimulated C storage in hemlock forests in a warmer climate with fewer spring and autumn frosts, but reduced C storage during warmer summers. Estimated annual C storage was 3.0 Mg ha(-1), which is higher than for younger coniferous and deciduous forests during earlier years in the northeastern USA. Long-term data are needed to determine if the estimated high C storage in this hemlock forest is a result of interannual climate variation or an effect of forest composition. 相似文献
3.
Net photosynthesis and stomatal conductance were measured in ten red spruce (Picea rubens Sarg.) saplings, growing near Ithaca, New York, throughout the early spring and late-fall growing periods. Gas exchange and daily minimum and maximum soil and air temperatures were also measured. Linear regression analysis showed that rates of net photosynthesis were positively correlated with both minimum daily soil and air temperatures but that minimum soil temperature was a better predictor of net photosynthesis. Moreover, net photosynthesis was more sensitive to changes in soil temperature than to changes in air temperature, and photosynthesis was approximately twice as sensitive to temperature changes during the fall than during the spring. 相似文献
4.
An increased risk of frost is expected during the growing season, as climate warming increases spring temperatures in the Arctic. Because deciduous species have a growth season limited in length and also have generally larger conduit volumes, they are more likely than evergreens to be injured by freeze-thaw-induced cavitation during the growing season. To test whether growth at elevated temperature increases susceptibility to freeze-thaw damage, we grew a deciduous arctic shrub species (Salix pulchra Cham.) in simulated Alaskan summer temperatures and at 5 degrees C above the ambient simulation (+5 degrees C plants) in controlled environments. Stem specific hydraulic conductivity (k(s)) and leaf stomatal conductance (g(s)) were measured in plants grown at both temperatures before and after a freeze treatment simulating a mid-season frost. Before the freeze treatment, specific xylem conductivity was 2.5 times higher and stomatal conductances were 1.3 times higher in +5 degrees C plants than in ambient-grown plants. Reductions in hydraulic conductivity and stomatal conductance as a result of the freeze were 3.5 and 1.8 times greater respectively in +5 degrees C plants than in ambient-grown plants. Many of the +5 degrees C plants showed extensive leaf damage. Plants grown in the two treatments also differed in comparative xylem anatomy; +5 degrees C plants had larger vessel diameters (25.4 versus 22.6 micro m) and higher vessel densities (71 versus 67.4 vessels mm(-2)) than ambient-grown plants. Our results suggest that higher growing season temperatures will increase the susceptibility of arctic deciduous shrubs to frost damage, which may offset their competitive growth advantage. 相似文献
5.
Climatic factors controlling the productivity of Norway spruce: A model-based analysis 总被引：8，自引：0，他引：8
The process-based growth model, BIOMASS, was modified to incorporate low-temperature effects on photosynthetic production in Norway spruce (Picea abies) stands growing in northern Sweden. The low-temperature features incorporated in BIOMASS made it possible to simulate and estimate the reduction in photosynthetic rates caused by boreal conditions. The following four simulation-scenarios were used: (i) ‘potential' photosynthesis without boreal restrictions; (ii) reduction caused by a frozen soil; (iii) reduction caused by incomplete recovery of photosynthetic capacity during spring as a result of damage caused by low winter temperatures; and (iv) reduction as an effect of frost-induced autumn decline. Annual photosynthetic production (or gross primary production (GPP)) was simulated for three calendar years, 1990–1992, for stands with low (control) and high (irrigated and fertilized) nutrient availability. The reduction of ‘potential' GPP, caused by the low-temperature effects, ranged from 35–44% for control (C) and from 34–42% for irrigated-fertilised (IL) stands, respectively. The most pronounced loss of ‘potential' GPP originated from reduced photosynthetic capacity, in spring and early summer, which led to losses of 21–28% for C and 19–26% for IL stands. The variation between years differed mainly as an effect of differences in spring temperatures, which resulted in different rates of recovery of photosynthetic capacity. Reductions caused by frozen soil and low photosynthetic capacity during winter were similar in C and IL stands (12–13%), as were the losses resulting from severe autumn frosts (3–4%). It is concluded that, unless the effects of frozen soils and reduced photosynthetic capacity during spring and early summer are considered, large errors (ca. 40%) will be introduced into estimates of the annual photosynthetic production of boreal conifer forests. 相似文献
6.
Photosynthesis in balsam fir (Abies balsamea (L.) Mill.) was measured in the field at two locations in New Brunswick, Canada from late winter to late spring in 2004 and 2005. No photosynthesis was detectable while the soil remained below 0 degrees C throughout the rooting zone. In both years, photosynthesis began once soil temperature rose to 0 degrees C. In potted seedlings in growth chambers, there was no photosynthesis at an air temperature of 10 degrees C if the pots were frozen. These findings suggest that, once air temperatures permit photosynthesis, it is the availability of unfrozen soil water that triggers the onset of photosynthesis. In the field, full recovery of photosynthetic capacity following the onset of soil thaw was dependent on air temperature and took 5 weeks in 2005, but 10 weeks in 2004. There were two substantial frost events during the recovery period in 2004 that may explain the extended recovery period. In 2005, recovery was complete after the accumulation of 200 growing degree days above 0 degrees C after the start of soil thaw. 相似文献
7.
Effects of artificial frosts on light-saturated photosynthesis (A(max)) and ground, maximal and variable fluorescence variables (F(o), F(m), and F(v) and F(v)/F(m)) were monitored on 1-year-old foliage of black spruce seedlings (Picea mariana (Mill.) BSP) grown at high (25 degrees C), moderate (15 degrees C) and low (5 degrees C) temperatures and moderate (240 &mgr;mol m(-2) s(-1)) and low (80 &mgr;mol m(-2) s(-1)) irradiances. Photoinhibition of 1-year-old foliage was greater in seedlings grown in moderate light than in seedlings grown in low light. Photoinhibition increased with decreasing growth chamber temperature at both irradiances. Most changes in F(v)/F(m) were caused by changes in F(v). Exposure to -4 degrees C decreased both F(v)/F(m) and A(max) compared with control values. The effect of the -4 degrees C frost treatment was greater in seedlings grown in low light than in seedlings grown in moderate light, probably because seedlings grown in moderate light were already partially photoinhibited before the frost treatment. Following -4 degrees C treatment, neither F(v)/F(m) nor A(max) recovered in seedlings grown in low light. Light-saturated photosynthesis decreased with decreasing growth chamber temperature. Light-saturated photosynthesis was more sensitive to the -3 and -4 degrees C frost treatments in seedlings grown at 25 degrees C than in seedlings grown at 15 and 5 degrees C. The A(max) of seedlings grown at 15 degrees C was sensitive only to the -4 degrees C frost treatment, whereas A(max) of seedlings grown at 5 degrees C was not sensitive to any of the frost treatments. Recovery of A(max) following frost took longer in seedlings grown at high temperatures than in seedlings grown at low temperatures. For seedlings grown at the same temperature but under different irradiances, both A(max) and F(v)/F(m) reflected damage to the photosynthetic system following a moderate frost. However, for seedlings grown at the same irradiance but different temperatures, A(max) provided a more sensitive indicator of frost damage to the photosynthetic system than F(v)/F(m) ratio. 相似文献
8.
《Scandinavian Journal of Forest Research》2012,27(1-4):73-78
Effects of soil temperature on gas exchange of Scots pine seedlings were studied to evaluate the significance of reduced gas exchange in seedlings planted in cold soils. The patterns of net photosynthesis during the 3‐week period at the two constant soil temperatures (8°C and 12°C) were quite similar but at 12°C the photosynthetic rate was higher. After U days differences were no more significant. Photosynthesis at the increasing soil temperature, from 5.5°C to 13°C, decreased for the first 18 days and then recovered up to the level of other treatments. The same patterns were found for transpiration, stomatal conductance, and photosynthetic efficiency. Xylem pressure potentials and relative resistance to water flow after 3 weeks did not differ among soil temperatures. Initiation and development of current‐year needles affected all the results of gas exchange parameters. 相似文献
9.
J. Peters Á. M. González-Rodríguez M. S. Jiménez D. Morales G. Wieser 《European Journal of Forest Research》2008,127(4):293-299
We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade
crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age
classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and
needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher
during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the
cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to
the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards
lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics
indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability. 相似文献
10.
We compared the effects of short-term (hours) and long-term (days) exposure to chilling temperatures on the photosynthetic gas exchange, leaf characteristics and chlorophyll a fluorescence of seedlings of the mangrove species Kandelia candel Druce and Avicennia marina (Forsk.) Vierh. Both species occur along the west coast of Taiwan, but K. candel occurs further north than A. marina. We hypothesized that temperature was one of the major environmental factors limiting the northern distribution of A. marina. Avicennia marina was more sensitive to chilling temperatures than K. candel. Leaves of both species showed reductions in light-saturated photosynthetic rates (Amax), stomatal conductance (gs) and quantum yield of photosystem II after a 1-h exposure to 15 degrees C, with A. marina showing significantly greater reductions in Amax and gs than K. candel. No significant differences in Amax, gs and electron transport rate (ETR) were found between leaves of K. candel grown at 15 and 30 degrees C for 10 days. However, leaves of A. marina grown for 10 days at 15 degrees C had significantly lower Amax, gs and ETR than plants grown at 30 degrees C. After 20 days at 15 degrees C, leaf mass per area of both species was increased significantly, whereas area-based chlorophyll concentrations were reduced, with significantly greater changes in A. marina than in K. candel. We concluded that sensitivity to low winter temperatures is a primary limiting factor in the distribution of A. marina along the western coast of Taiwan. 相似文献
11.
Juniperus thurifera L. is an endemic conifer of the western Mediterranean Basin where it is subjected to a severe climatic stress characterized by low winter temperatures and summer drought. Given the trend of increased warming-induced drought stress in this area and the climatic sensitivity of this species, we expect a negative impact of climate change on growth and ecophysiological performance of J. thurifera in the harsh environments where it dominates. To evaluate this, we measured long- and short-term radial growth using dendrochronology, photosynthesis and water-use efficiency in males, females and juveniles in three sites in Central Spain. Climate was monitored and completed with historical records. Mean annual temperature has increased +0.2?°C per decade in the study area, and the main warming trends corresponded to spring (+0.2?°C per decade) and summer (+0.3?°C per decade). Radial growth and maximum photosynthesis peaked in spring and autumn. Positive photosynthetic rates were maintained all year long, albeit at reduced rates in winter and summer. Radial growth was enhanced by wet conditions in the previous autumn and by warm springs and high precipitation in summer of the year of tree-ring formation. Cloud cover during the summer increased growth, while cloudy winters led to impaired carbon gain and reduced growth in the long term. We argue that maintenance of carbon gain under harsh conditions (low winter temperatures and dry summer months) and plastic xylogenesis underlie J. thurifera's ability to profit from changing climatic conditions such as earlier spring onset and erratic summer rainfall. Our results highlight that not only the magnitude but also the sign of the impact of climate change on growth and persistence of Mediterranean trees is species specific. 相似文献
12.
J Riikonen S Kontunen-Soppela V Ossipov A Tervahauta M Tuomainen E Oksanen E Vapaavuori J Heinonen M Kivimäenpää 《Tree physiology》2012,32(9):1102-1112
Northern forests are currently experiencing increasing mean temperatures, especially during autumn and spring. Consequently, alterations in carbon sequestration, leaf biochemical quality and freezing tolerance (FT) are likely to occur. The interactive effects of elevated temperature and ozone (O(3)), the most harmful phytotoxic air pollutant, on Norway spruce (Picea abies (L.) Karst.) seedlings were studied by analysing phenology, metabolite concentrations in the needles, FT and gas exchange. Sampling was performed in September and May. The seedlings were exposed to a year-round elevated temperature (+1.3 °C), and to 1.4× ambient O(3) concentration during the growing season in the field. Elevated temperature increased the concentrations of amino acids, organic acids of the citric acid cycle and some carbohydrates, and reduced the concentrations of phenolic compounds, some organic acids of the shikimic acid pathway, sucrose, cyclitols and steroids, depending on the timing of the sampling. Although growth onset occurred earlier at elevated temperature, the temperature of 50% lethality (LT(50)) was similar in the treatments. Photosynthesis and the ratio of photosynthesis to dark respiration were reduced by elevated temperature. Elevated concentrations of O(3) reduced the total concentration of soluble sugars, and tended to reduce LT(50) of the needles in September. These results show that alterations in needle chemical quality can be expected at elevated temperatures, but the seedlings' sensitivity to autumn and spring frosts is not altered. Elevated O(3) has the potential to disturb cold hardening of Norway spruce seedlings in autumn, and to alter the water balance of the seedling through changes in stomatal conductance (g(s)), while elevated temperature is likely to reduce g(s) and consequently reduce the O(3)-flux inside the leaves. 相似文献
13.
We studied the effects of high temperature and drought on the survival, growth and water relations of seedlings of Pinus ponderosa (Dougl.) Lawson, one of few coniferous tree species that can successfully colonize drought-prone sites with high soil surface temperatures. Temperature profiles were measured with 0.07-mm thermocouples in a sparse ponderosa pine forest in northern Idaho. The soil surface and the adjacent 5 mm of air reached maximum temperatures exceeding 75 degrees C, well above the lethal temperature threshold for most plants. Air temperatures 50 mm above the soil surface (seedling needle height) rarely exceeded 45 degrees C. Pinus ponderosa seedlings that survived maintained basal stem temperatures as much as 15 degrees C lower than the surrounding air. The apparent threshold temperature at the seedling stem surface resulting in death was approximately 63 degrees C for less than 1 min. No correlation between seedling mortality and needle temperature was found, although some needles reached temperatures as high as 60 degrees C for periods of 相似文献
14.
We explored environmental and genetic factors affecting seasonal dynamics of starch and soluble nonstructural carbohydrates in needle and twig cohorts and roots of Scots pine (Pinus sylvestris L.) trees of six populations originating between 49 degrees and 60 degrees N, and grown under common garden conditions in western Poland. Trees of each population were sampled once or twice per month over a 3-year period from age 15 to 17 years. Based on similarity in starch concentration patterns in needles, two distinct groups of populations were identified; one comprised northern populations from Sweden and Russia (59-60 degrees N), and another comprised central European populations from Latvia, Poland, Germany and France (49-56 degrees N). Needle starch concentrations of northern populations started to decline in late spring and reached minimum values earlier than those of central populations. For all populations, starch accumulation in spring started when minimum air temperature permanently exceeded 0 degrees C. Starch accumulation peaked before bud break and was highest in 1-year-old needles, averaging 9-13% of dry mass. Soluble carbohydrate concentrations were lowest in spring and summer and highest in autumn and winter. There were no differences among populations in seasonal pattern of soluble carbohydrate concentrations. Averaged across all populations, needle soluble carbohydrate concentrations increased from about 4% of needle dry mass in developing current-year needles, to about 9% in 1- and 2-year-old needles. Root carbohydrate concentration exhibited a bimodal pattern with peaks in spring and autumn. Northern populations had higher concentrations of fine-root starch in spring and autumn than central populations. Late-summer carbohydrate accumulation in roots started only after depletion of starch in needles and woody shoots. We conclude that Scots pine carbohydrate dynamics depend partially on inherited properties that are probably related to phenology of root and shoot growth. 相似文献
15.
The hydraulic limitation hypothesis (Ryan and Yoder 1997) proposes that leaf-specific hydraulic conductance (kl) and stomatal conductance (gs) decline as trees grow taller, resulting in decreased carbon assimilation. We tested the hydraulic limitation hypothesis by comparison of canopy-dominant Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) trees in stands that were approximately 15 m (20 years old), 32 m (40 years old) and 60 m (> 450 years old) tall in Wind River, Washington, USA. Carbon isotope discrimination (Delta) declined with tree height (18.6, 17.6 and 15.9 per thousand for stands 15, 32 and 60 m tall, respectively) indicating that gs may have declined proportionally with tree height in the spring months, when carbon used in the construction of new foliage is assimilated. Hydraulic conductance decreased by 44% as tree height increased from 15 to > 32 m, and showed a further decline of 6% with increasing height. The general nonlinear pattern of kl versus height was predicted by a model based on Darcy's Law. Stemwood growth efficiency also declined nonlinearly with height (60, 35 and 28 g C m-2 leaf area for the 15-, 32- and 60-m stands, respectively). Unlike kl and growth efficiency, gs and photosynthesis (A) during summer drought did not decrease with height. The lack of decline in cuvette-based A indicates that reduced A, at least during summer months, is not responsible for the decline in growth efficiency. The difference between the trend in gs and A and that in kl and D may indicate temporal changes (spring versus summer) in the response of gas exchange to height-related changes in kl or it may be a result of measurement inadequacies. The formal hydraulic limitation hypothesis was not supported by our mid-summer gs and A data. Future tests of the hydraulic limitation hypothesis in this forest should be conducted in the spring months, when carbon uptake is greatest. We used a model based on Darcy's Law to quantify the extent to which compensating mechanisms buffer hydraulic limitations to gas exchange. Sensitivity analyses indicated that without the observed increases in the soil-to-leaf water potential differential (DeltaPsi) and decreases in the leaf area/sapwood area ratio, kl would have been reduced by more than 70% in the 60-m trees compared with the 15-m trees, instead of the observed decrease of 44%. However, compensation may have a cost; for example, the greater DeltaPsi of the largest trees was associated with smaller tracheid diameters and increased sapwood cavitation, which may have a negative feedback on kl and gs. 相似文献
16.
辽西地区引种野杏的光合生理生态特性研究 总被引：1，自引：0，他引：1
利用LI-6400光合仪测定引种野杏家系苗木在辽西地区6、7、9月的光合生理参数,研究各参数的日变化和季节变化规律,以了解引种野杏的适应能力,为辽西地区品种选育和栽培利用提供理论基础。结果表明:野杏家系净光合速率(Pn)在夏季具有明显的"光合午休"现象,夏、秋季的日均Pn达10.0μmol·m-2·s-1,春季6.9μmol·m-2·s-1;蒸腾速率夏季(6.39 mmol·m-2·s-1)秋季(4.84 mmol·m-2·s-1)春季(2.33 mmol·m-2·s-1);水分利用效率春、秋高,夏季低;光能利用效率春季高、夏秋季较低;不同季节的生态因子影响野杏苗木的光合生理特性。引种野杏优良品种的选育要注重其对当地环境的适应能力,在了解其光合生理特性的基础上做出最佳选种策略。 相似文献
17.
筇竹光合日变化特征研究 总被引：2，自引：1，他引：1
对筇竹春季、夏季和秋季的光合日变化特征进行了研究。结果表明:筇竹春季净光合速率日变化为单峰曲线,没有光合"午休"现象;夏季和秋季净光合速率日变化为双峰曲线,有明显的光合"午休"现象;筇竹光合"午休"现象的主要原因是非气孔因素所致;夏季的净光合速率最高,光合能力最强,是筇竹枝叶生长旺季。影响筇竹不同季节净光合速率的最稳定环境因子为光合有效辐射和大气温度。筇竹夏季和秋季蒸腾速率变化趋势均表现为双峰曲线,春季为单峰曲线;夏季和秋季均有蒸腾"午休"现象,春季则没有。光合有效辐射、大气温度和气孔导度是影响筇竹不同季节蒸腾速率的最稳定因子。 相似文献
18.
Net photosynthesis was measured under field conditions in 23-year-old slash pine (Pinus elliottii Engelm. var. elliottii) trees to determine how it was affected by fertilization and climate. There was only a small decrease in rates of net photosynthesis from late summer through winter demonstrating that appreciable carbon gain occurs throughout the year in slash pine. Although fertilization substantially increased leaf area and aboveground biomass, it only slightly increased the rate of net photosynthesis. Simultaneous measurements of gas exchange in fertilized and unfertilized (control) plots allowed the detection of a small, but statistically significant difference in average net photosynthesis of 0.14 micro mol m(-2) s(-1). Irradiance, and to a lesser extent air temperature, were the environmental factors that exerted the most control on net photosynthesis. The highest rates of net photosynthesis occurred between air temperatures of 25 and 35 degrees C. Because air temperatures were within this range for 46% of all daylight hours during the year, air temperature was not often a significant limitation. Soil and atmospheric water deficits had less effect on photosynthesis than irradiance or air temperature. Although the depth to the water table changed during the year from 10 to 160 cm, predawn and midday xylem pressure potentials only changed slightly throughout the year. Predawn values ranged from -0.63 to -0.88 MPa in the control plot and from -0.51 to -0.87 MPa in the fertilized plot and were not correlated with water table depth. There was no correlation between xylem pressure potentials and net photosynthesis, presumably because water uptake was adequate. Although vapor pressure deficits reached 3.5 kPa during the summer, they had little effect on net photosynthesis. Over a vapor pressure deficit range from 1.0 to 3.0 kPa, net photosynthesis only decreased 21%. No differences in responses to these environmental factors could be attributed to fertilization. 相似文献
19.
Photosynthetic activity in winter needles of the evergreen tree Taxus cuspidata at low temperatures 总被引：2，自引：0，他引：2
Tanaka A 《Tree physiology》2007,27(5):641-648
Photosystems harvest light energy, yet this energy cannot be efficiently employed for CO(2) assimilation at the below-freezing temperatures to which plants are typically exposed during winter in the temperate and boreal zones. To elucidate the mechanisms whereby this energy is dissipated, I evaluated performance of photosystems in winter needles of the evergreen tree Taxus cuspidata Sieb. et Zucc. Chloroplasts were localized adjacent to plasma membranes in needle cells in summer, whereas they congregated together in the centers of the cells during winter. When winter needles were acclimated to a temperature of 20 degrees C, their chloroplasts gradually dispersed to the edges of the cells, as in the summer. Acclimation-dependent relocalization coincided with changes in CO(2) uptake. Examination of photosystem II fluorescence kinetics in winter needles indicated that the quinone electron acceptor (Q(A)) reduction rate exceeded the Q(A) oxidation rate at low temperatures. The majority of Q(A) remained reduced even when winter needles were subjected to a temperature of -5 degrees C at low irradiance. 相似文献
20.
笔者分析了川西米亚罗林区典型低效林经不同强度的抚育间伐后,对5种处理的2个土层(0 cm~15 cm,15 cm~30 cm)的土壤总有机碳、微生物量碳含量的变化进行了动态监测,并分析了土壤总有机碳和微生物量碳含量的季节变化。结果表明,5种处理的土壤总有机碳和微生物量碳含量均是上层高于下层;在观测的4个季节内,上层、下层土壤总有机碳均是夏季春季冬季秋季,土壤总有机碳含量的上、下层均值是F3F2F1F4CK;土壤微生物量碳含量均是秋季冬季春季夏季;土壤微生物量碳含量的上、下层均值表现为F3F2F1CKF4,而且30%的间伐强度样地土壤总有机碳含量和微生物量碳含量均最高。 相似文献