共查询到20条相似文献,搜索用时 0 毫秒
1.
Succession-driven changes in soil respiration following fire in black spruce stands of interior Alaska 总被引:1,自引:0,他引:1
Boreal forests are highly susceptible to wildfire, and post-fire changes in soil temperature and moisture have the potential
to transform large areas of the landscape from a net sink to a net source of carbon (C). Understanding the ecological controls
that regulate these disturbance effects is critical to developing models of ecosystem response to changes in fire frequency
and severity. This paper combines laboratory and field measurements along a chronosequence of burned black spruce stands into
regression analyses and models that assess relationships between moss succession, soil microclimate, decomposition, and C
source-sink dynamics. Results indicate that post-fire changes in temperature and substrate quality increased decomposition
in humic materials by a factor of 3.0 to 4.0 in the first 7 years after fire. Bryophyte species exhibited a distinct successional
pattern in the first five decades after fire that corresponded to decreased soil temperature and increased C accumulation
in organic soils. Potential rates of C exchange in mosses were greatest in early successional species and declined as the
stand matured. Residual sources of CO2 (those not attributed to moss respiration or humic decomposition) increased as a function of stand age, reflecting increased
contributions from roots as the stand recovered from disturbance. Together, the field measurements, laboratory experiments,
and models provide strong evidence that interactions between moss and plant succession, soil temperature, and soil moisture
largely regulate C source-sink dynamics from black spruce systems in the first century following fire disturbance. 相似文献
2.
《Plant Ecology & Diversity》2013,6(2-3):227-241
Background: Although forest floor forms a large biomass pool in forested peatlands, little is known about its role in ecosystem carbon (C) dynamics. Aim: We aimed to quantify forest floor photosynthesis (P FF) and respiration (R FF) as a part of overall C dynamics in a drained peatland forest in southern Finland. Methods: We measured net forest floor CO2 exchange with closed chambers and reconstructed seasonal CO2 exchange in the prevailing plant communities. Results: The vegetation was a mosaic of plant communities that differed in CO2 exchange dynamics. The reconstructed growing season P FF was highest in the Sphagnum community and lowest in the feather moss communities. On the contrary, R FF was highest in the feather moss communities and lowest in the Sphagnum community. CO2 assimilated by the forest floor was 20–30% of the total CO2 assimilated by the forest. The forest floor was a net CO2 source to the atmosphere, because respiration from ground vegetation, tree roots and decomposition of soil organic matter exceeded the photosynthesis of ground vegetation. Conclusions: Tree stand dominates C fluxes in drained peatland forests. However, forest floor vegetation can have a noticeable role in the C cycle of peatlands drained for forestry. Similarly to natural mires, Sphagnum moss-dominated communities were the most efficient assimilators of C. 相似文献
3.
Partitioning sources of soil respiration in boreal black spruce forest using radiocarbon 总被引:5,自引:0,他引:5
Separating ecosystem and soil respiration into autotrophic and heterotrophic component sources is necessary for understanding how the net ecosystem exchange of carbon (C) will respond to current and future changes in climate and vegetation. Here, we use an isotope mass balance method based on radiocarbon to partition respiration sources in three mature black spruce forest stands in Alaska. Radiocarbon (Δ14C) signatures of respired C reflect the age of substrate C and can be used to differentiate source pools within ecosystems. Recently‐fixed C that fuels plant or microbial metabolism has Δ14C values close to that of current atmospheric CO2, while C respired from litter and soil organic matter decomposition will reflect the longer residence time of C in plant and soil C pools. Contrary to our expectations, the Δ14C of C respired by recently excised black spruce roots averaged 14‰ greater than expected for recently fixed photosynthetic products, indicating that some portion of the C fueling root metabolism was derived from C storage pools with turnover times of at least several years. The Δ14C values of C respired by heterotrophs in laboratory incubations of soil organic matter averaged 60‰ higher than the contemporary atmosphere Δ14CO2, indicating that the major contributors to decomposition are derived from a combination of sources consistent with a mean residence time of up to a decade. Comparing autotrophic and heterotrophic Δ14C end members with measurements of the Δ14C of total soil respiration, we calculated that 47–63% of soil CO2 emissions were derived from heterotrophic respiration across all three sites. Our limited temporal sampling also observed no significant differences in the partitioning of soil respiration in the early season compared with the late season. Future work is needed to address the reasons for high Δ14C values in root respiration and issues of whether this method fully captures the contribution of rhizosphere respiration. 相似文献
4.
During the 1975 and 1976 seasons the net primary production of five common bryophytes in different stands of mature vegetation near Fairbanks, Alaska was investigated. Overall annual moss production at the intensive black spruce site was about 120 g m?1 yr?1 or about twice as high as the corresponding annual spruce production. Maximum rates of net photosynthesis varied from 2.7 mg CO2 g?1 h?1 in Polytrichum commune Hedw. to 0.6 mg CO2 g?1 h?1 in Sphagnum nemoreum Scop. The photosynthesis of overwintered leaves early in the season was low and as a result of new growth a steady increase in net photosynthesis occurred throughout the season. Leaf water content was found to be the most important limiting factor for growth under natural conditions. There was a strong increase in growth and photosynthesis of Sphagnum nemoreum after application of N and P, indicating nutrient deficiency. 相似文献
5.
Dendroclimatological research is often based on the assumption that the relationship between tree growth and climate is not variable over time. Here we test this assumption by exploring if climate sensitivity of Picea mariana (Mill.) trees growing in open-stand lowland forest and on top of a neighboring peatland in Interior Alaska is stable or changing over time. Climate–growth correlations at the study sites are strongly dependent on microtopography and vary substantially over time. Trees growing in the open forest site generally display stronger climate–growth correlations, especially significantly negative correlations with late summer temperatures (July, August) starting in the period 1920–1970. Trees growing on the peatland site are less climate sensitive, but display positive correlations between annual growth and temperature of October and December in the early 20th century, while in the late 20th century, significant negative correlations exist with January and February temperatures. This study, thus, demonstrates a transient climate–growth response for P. mariana (Mill.) on two sites typical for lowland Interior Alaska. However, due to multiple possible explanations (e.g. changing climate, coupled with aging trees and a growing peatland surface) it is not possible at this time to pinpoint the exact cause for these changes in the climate–growth relationships. 相似文献
6.
Nine years (2003–2011) of carbon dioxide (CO2) flux were measured at a black spruce forest in interior Alaska using the eddy covariance method. Seasonal and interannual variations in the gross primary productivity (GPP) and ecosystem respiration (RE) were associated primarily with air temperature: warmer conditions enhanced GPP and RE. Meanwhile, interannual variation in annual CO2 balance was controlled predominantly by RE, and not GPP. During these 9 years of measurement, the annual CO2 balance shifted from a CO2 sink to a CO2 source, with a 9‐year average near zero. The increase in autumn RE was associated with autumn warming and was mostly attributed to a shift in the annual CO2 balance. The increase in autumn air temperature (0.22 °C yr?1) during the 9 years of study was 15 times greater than the long‐term warming trend between 1905 and 2011 (0.015 °C yr?1) due to decadal climate oscillation. This result indicates that most of the shifts in observed CO2 fluxes were associated with decadal climate variability. Because the natural climate varies in a cycle of 10–30 years, a long‐term study covering at least one full cycle of decadal climate oscillation is important to quantify the CO2 balance and its interaction with the climate. 相似文献
7.
Soil acidification and N saturation are considered to affect the decomposition of soil organic matter as well as growth and mortality of fine roots in many forest soils. Here we report from a field experiment where ‘clean rain’ has been applied to the soil for about 10 years under a roofed plot of a 71‐year‐old Norway spruce plantation at Solling, Central Germany. Reduced amounts of protons (?78%), sulphate (?53%), ammonium (?86%), and nitrate (?49%) were sprayed on the soil surface of the clean rain plot between 1992 and 2001. In an adjacent roofed control plot, throughfall was collected and immediately re‐sprinkled below the roof construction without any chemical manipulation. One year before the clean rain treatment started, live and dead fine root masses (≤2 mm) were determined from undisturbed soil cores down to 40 cm mineral soil depth. Total live fine root mass was significantly lower in the clean rain plot than in the control plot. After the first sampling, the soil holes were refilled with quartz sand and repeatedly sampled in June 1992, June 1996, and October 2001. There were no differences in live and dead fine root masses between the plots in 1992 and 1996. In 2001, both live and dead fine root masses of the clean rain plot were about twice as high as in the control plot, indicating that fine root growth recovered in the mineral soil following 10 years of clean rain treatment. Moreover, the clean rain treatment significantly reduced the total N concentrations of live fine roots and 1‐year‐old needles. Our results suggest that the reduced N input promoted fine root growth to compensate N deficiency. Reduced Al concentration in soil solution may have contributed to the recovery of fine root growth, however, the toxicity of Al species is largely unknown. Mean annual soil respiration rate was 24% higher in the period from 2000 to 2001, indicating that the clean rain treatment increased respiration of roots and heterotrophic microorganisms within the rhizosphere. Laboratory incubation of samples from the organic horizon and the top mineral soil revealed no differences between the plots in the decay rate of soil organic matter. Our results suggest that strong reductions in atmospheric N deposition from about 30 to 10 kg N ha?1 yr?1 and decreasing acid stress can have beneficial effects on growth of fine roots in the mineral soil within a decade. We conclude that biological recovery under reduced atmospheric loads can affect the nutrient and carbon budget of spruce soils in the long run. 相似文献
8.
Foliar respiration is a major component of ecosystem respiration, yet extrapolations are often uncertain in tropical forests because of indirect estimates of leaf area index (LAI). A portable tower was used to directly measure LAI and night-time foliar respiration from 52 vertical transects throughout an old-growth tropical rain forest in Costa Rica. In this study, we (1) explored the effects of structural, functional and environmental variables on foliar respiration; (2) extrapolated foliar respiration to the ecosystem; and (3) estimated ecosystem respiration. Foliar respiration temperature response was constant within plant functional group, and foliar morphology drove much of the within-canopy variability in respiration and foliar nutrients. Foliar respiration per unit ground area was 3.5 ± 0.2 µ mol CO2 m−2 s−1 , and ecosystem respiration was 9.4 ± 0.5 µ mol CO2 m−2 s−1 [soil = 41%; foliage = 37%; woody = 14%; coarse woody debris (CWD) = 7%]. When modelled with El Niño Southern Oscillation (ENSO) year temperatures, foliar respiration was 9% greater than when modelled with temperatures from a normal year, which is in the range of carbon sink versus source behaviour for this forest. Our ecosystem respiration estimate from component fluxes was 33% greater than night-time net ecosystem exchange for the same forest, suggesting that studies reporting a large carbon sink for tropical rain forests based solely on eddy flux measurements may be in error. 相似文献
9.
寒温针叶林土壤呼吸作用的时空特征 总被引:2,自引:0,他引:2
利用Li-6400便携式CO2分析系统对寒温针叶林土壤呼吸作用观测数据分析表明,土壤呼吸作用日、季动态均呈单峰型变化,日最大值出现在16:00左右,与5 cm土壤温度日动态相似,滞后于气温日动态变化;月最大值出现在8月份,2006年和2007年分别为8.19 和6.89 μmol CO2 m-2 s-1。日、季土壤呼吸作用与土壤温度的相关性均好于气温。土壤呼吸作用存在较大的空间变异性,一天内3:00 am、7:00 am和11:00 am的土壤呼吸作用变异系数分别为35.5%、27.6%和23.0%,根系和凋落物与土壤呼吸作用表现出相似的空间变异性,其中细根与土壤呼吸作用的相关性最好。 相似文献
10.
K. Kreutzer K. Butterbach-Bahl H. Rennenberg & H. Papen 《Plant biology (Stuttgart, Germany)》2009,11(5):643-649
Long-term nitrogen deposition into forest ecosystems has turned many forests in Central Europe and North America from N-limited to N-saturated systems, with consequences for climate as well as air and groundwater quality. However, complete quantification of processes that convert the N deposited and contributed to ecosystem N cycling is scarce. In this study, we provide the first complete quantification of external and internal N fluxes in an old-growth spruce forest, the Höglwald, Bavaria, Germany, exposed to high chronic N deposition. In this forest, N cycling is dominated by high rates of mineralisation of soil organic matter, nitrification and immobilisation of ammonium and nitrate into microbial biomass. The amount of ammonium available is sufficient to cover the entire N demand of the spruce trees. The data demonstrate the existence of a highly dynamic internal N cycle within the soil, driven by growth and death of the microbial biomass, which turns over approximately seven times each year. Although input and output fluxes are of high environmental significance, they are low compared to the internal fluxes mediated by microbial activity. 相似文献
11.
Tianshan Zha Seppo Kellomäki Kai-Yun Wang† Ismo Rouvinen 《Global Change Biology》2004,10(9):1492-1503
The net exchange of CO2 (NEE) between a Scots pine (Pinus sylvestris L.) forest ecosystem in eastern Finland and the atmosphere was measured continuously by the eddy covariance (EC) technique over 4 years (1999–2002). The annual temperature coefficient (Q10) of ecosystem respiration (R) for these years, respectively, was 2.32, 2.66, 2.73 and 2.69. The light‐saturated rate of photosynthesis (Amax) was highest in July or August, with an annual average Amax of 10.9, 14.6, 15.3 and 17.1 μmol m?2 s?1 in the 4 years, respectively. There was obvious seasonality in NEE, R and gross primary production (GPP), exhibiting a similar pattern to photosynthetically active radiation (PAR) and air temperature. The integrated daily NEE ranged from 2.59 to ?4.97 g C m?2 day?1 in 1999, from 2.70 to ?4.72 in 2000, from 2.61 to ?4.71 in 2001 and from 5.27 to ?4.88 in 2002. The maximum net C uptake occurred in July, with the exception of 2000, when it was in June. The interannual variation in ecosystem C flux was pronounced. The length of the growing season, based on net C uptake, was 179, 170, 175 and 176 days in 1999–2002, respectively, and annual net C sequestration was 152, 101, 172 and 205 g C m?2 yr?1. It is estimated that ecosystem respiration contributed 615, 591, 752 and 879 g C m?2 yr?1 to the NEE in these years, leading to an annual GPP of ?768, ?692, ?924 and ?1084 g C m?2 yr?1. It is concluded that temperature and PAR were the main determinants of the ecosystem CO2 flux. Interannual variations in net C sequestration are predominantly controlled by average air temperature and integrated radiation in spring and summer. Four years of EC data indicate that boreal Scots pine forest ecosystem in eastern Finland acts as a relatively powerful carbon sink. Carbon sequestration may benefit from warmer climatic conditions. 相似文献
12.
Starch and carboxymethyl starch were added to forest floor samples collected from a sitka spruce stand near Aberdeen, Scotland. Samples were incubated for one month and were periodically analyzed for respiration, biomass-C, net and gross N-mineralization/immobilization. Gross mineralization/immobilization was measured by using a 15N-isotope pool dilution technique. Starch additions did not significantly affect respiration rates or biomass-C but caused net immobilization. The mechanism of this appeared to be inhibition of the decomposition of N-containing soil organic matter by the available starch-C, which resulted in decreased gross mineralization. Carboxymethyl starch acted as a biocide, probably as a result of an osmotic effect. 相似文献
13.
A distinct seasonal pattern of the ratio of soil respiration to total ecosystem respiration in a spruce-dominated forest 总被引:5,自引:0,他引:5
E. A. Davidson A. D. Richardson† K. E. Savage D. Y. Hollinger‡ 《Global Change Biology》2006,12(2):230-239
Annual budgets and fitted temperature response curves for soil respiration and ecosystem respiration provide useful information for partitioning annual carbon budgets of ecosystems, but they may not adequately reveal seasonal variation in the ratios of these two fluxes. Soil respiration (Rs) typically contributes 30–80% of annual total ecosystem respiration (Reco) in forests, but the temporal variation of these ratios across seasons has not been investigated. The objective of this study was to investigate seasonal variation in the Rs/Reco ratio in a mature forest dominated by conifers at Howland, ME, USA. We used chamber measurements of Rs and tower‐based eddy covariance measurements of Reco. The Rs/Reco ratio reached a minimum of about 0.45 in the early spring, gradually increased through the late spring and early summer, leveled off at about 0.65 for the summer, and then increased again to about 0.8 in the autumn. A spring pulse of aboveground respiration presumably causes the springtime minimum in this ratio. Soil respiration ‘catches up’ as the soils warm and as root growth presumably accelerates in the late spring, causing the Rs/Reco ratios to increase. The summertime plateau of Rs/Reco ratios is consistent with summer drought suppressing Rs that would otherwise be increasing, based on increasing soil temperature alone, thus causing the Rs/Reco ratios to not increase as soils continue to warm. Declining air temperatures and litter fall apparently contribute to increased Rs/Reco ratios in the autumn. Differences in phenology of growth of aboveground and belowground plant tissues, mobilization and use of stored substrates within woody plants, seasonal variation in photosynthate and litter substrates, and lags between temperature changes of air and soil contribute to a distinct seasonal pattern of Rs/Reco ratios. 相似文献
14.
Net primary production and net ecosystem production of a boreal black spruce wildfire chronosequence 总被引:11,自引:0,他引:11
Net primary production (NPP) was measured in seven black spruce (Picea mariana (Mill.) BSP)‐dominated sites comprising a boreal forest chronosequence near Thompson, Man., Canada. The sites burned between 1998 and 1850, and each contained separate well‐ and poorly drained stands. All components of NPP were measured, most for 3 consecutive years. Total NPP was low (50–100 g C m?2 yr?1) immediately after fire, highest 12–20 years after fire (332 and 521 g C m?2 yr?1 in the dry and wet stands, respectively) but 50% lower than this in the oldest stands. Tree NPP was highest 37 years after fire but 16–39% lower in older stands, and was dominated by deciduous seedlings in the young stands and by black spruce trees (>85%) in the older stands. The chronosequence was unreplicated but these results were consistent with 14 secondary sites sampled across the landscape. Bryophytes comprised a large percentage of aboveground NPP in the poorly drained stands, while belowground NPP was 0–40% of total NPP. Interannual NPP variability was greater in the youngest stands, the poorly drained stands, and for understory and detritus production. Net ecosystem production (NEP), calculated using heterotrophic soil and woody debris respiration data from previous studies in this chronosequence, implied that the youngest stands were moderate C sources (roughly, 100 g C m?2 yr?1), the middle‐aged stands relatively strong sinks (100–300 g C m?2 yr?1), and the oldest stands about neutral with respect to the atmosphere. The ecosystem approach employed in this study provided realistic estimates of chronosequence NPP and NEP, demonstrated the profound impact of wildfire on forest–atmosphere C exchange, and emphasized the need to account for soil drainage, bryophyte production, and species succession when modeling boreal forest C fluxes. 相似文献
15.
Samuel Olajuyigbe Brian Tobin Michael Hawkins Maarten Nieuwenhuis 《Plant and Soil》2012,360(1-2):77-91
Background and aims
The decomposition of roots is an important process in the loss of carbon (C) and the mineralization of nitrogen (N) in forest ecosystems. The early stage decomposition rate of Sitka spruce (Picea sitchensis (Bong.) Carr.) roots was determined using trenched plots and decomposition bags.Methods
Stumps of known age were trenched and quadrants (50?cm by 50?cm) excavated from randomly selected stumps every 6?months over 4?years, while the mass loss from buried roots in decomposition bags, divided among four diameter categories (ranging from fine roots <2?mm to large roots >50?mm), was monitored for 27?months. The C and N concentrations of excavated samples at different time points were analysed.Results
The change in total root necromass per quadrant showed a higher decomposition rate-constant (k) of 0.24?±?0.068?year?1 than the k-value of roots in decomposition bags (0.07?±?0.005?year?1). The C concentration (47.24?±?0.609?%) did not significantly change with decomposition. There was a significant increase in the C:N ratio of roots in all diameter categories (fine: 48.92?%, small: 38.53?%, medium 11.71?%, large: 76.25?%) after 4?years of decomposition, driven by N loss. Root diameter accounted for 78?% of the variation in the N concentration of roots as decomposition progressed.Conclusion
Though the trenched plot approach offered an alternative to the more common decomposition bag method for estimating root decomposition, high spatial variation and sampling difficulties may lead to an overestimation of the mass loss from trenched roots, thus, the decomposition bag method gives a more reliable decomposition rate-constant. 相似文献16.
长白山阔叶红松林退化生态系统的土壤呼吸作用 总被引:3,自引:1,他引:3
选择处于全球变化中国东北样带东部典型生态系统的长白山阔叶红松林作为研究区,采用动态气室-CO2红外分析法测定了森林生态系统不同退化阶段的土壤呼吸作用.结果表明:在生长季,长白山阔叶红松林不同退化阶段的土壤呼吸动态变化呈单峰型曲线,在7-8月达到最大值;不同退化阶段林地土壤呼吸大小顺序为:杨桦林>蒙古栎林>阔叶红松林>硬阔叶林>裸地.其中,杨桦林和蒙古栎林样地的碳释放量分别为对照阔叶红松林的1.4和1.3倍,硬阔叶林和裸地的碳释放量分别为对照阔叶红松林的88%和78%. 相似文献
17.
Summary Carbon dioxide exchange rates in excised 2-year-old shoot sections of five common moss species were measured by infrared gas analysis in mosses collected from different stands of mature vegetation near Fairbanks, Alaska. The maximum rates of net photosynthesis ranged from 2.65 mg CO2 g-1h-1 in Polytrichum commune Hedw. to 0.25 in Spagnum nemoreum Scop. Intermediate values were found in Sphagnum subsecundum Nees., Hylocomium splendens (Hedw.) B.S.G., and Pleurozium schreberi (Brid.) Mitt. Dark respiration rates at 15°C ranged from 0.24 mg CO2 g-1h-1 in S. subsecundum to 0.57 mg CO2 g-1h-1 in H. splendens. The dark respiration rates were found to increase in periods of growth or restoration of tissue (i.e., after desiccation). There was a strong decrease in the rates of net photosynthesis during the winter and after long periods of desiccation.Due to increasing amounts of young, photosynthetically active tissue there was a gradual increase in the rates of net photosynthesis during the season to maximum values in late August. As an apparent result of constant respiration rates and increasing gross photosynthetic rates, the optimum temperature for photosynthesis at light saturation and field capacity increased during the season in all species except Polytrichum, with a corresponding drop in the compensation light intensities. Sphagnum subsecundum seemed to be the most light-dependent species.Leaf water content was found to be an important limiting factor for photosynthesis in the field. A comparison between sites showed that the maximum rates of net photosynthesis increased with increasing nutrient content in the soil but at the permafrostfree sites photosynthesis was inhibited by frequent moisture stress. 相似文献
18.
19.
Alexander Knohl Astrid R. B. Søe Werner L. Kutsch Mathias Göckede Nina Buchmann 《Plant and Soil》2008,302(1-2):189-202
Respiration has been proposed to be the main determinant of the carbon balance in European forests and is thus essential for
our understanding of the carbon cycle. However, the choice of experimental design strongly affects estimates of annual respiration
and of the contribution of soil respiration to total ecosystem respiration. In a detailed study of ecosystem and soil respiration
fluxes in an old unmanaged deciduous forest in Central Germany over 3 years (2000–2002), we combined soil chamber and eddy
covariance measurements to obtain a comprehensive picture of respiration in this forest. The closed portable chambers offered
to investigate spatial variability of soil respiration and its controls while the eddy covariance system offered continuous
measurements of ecosystem respiration. Over the year, both fluxes were mainly correlated with temperature. However, when soil
moisture sank below 23 vol.% in the upper 6 cm, water limitations also became apparent. The temporal resolution of the eddy
covariance system revealed that relatively high respiration rates occurred during budbreak due to increased metabolic activity
and after leaf fall because of increased decomposition. Spatial variability in soil respiration rates was large and correlated
with fine root biomass (r
2 = 0.56) resulting in estimates of annual efflux varying across plots from 730 to 1,258 (mean 898) g C m−2 year−1. Power function calculations showed that achieving a precision in the soil respiration estimate of 20% of the full population
mean at a confidence level of 95%, requires about eight sampling locations. Our results can be used as guidelines to improve
the representativeness of soil respiration measurements by nested sampling designs, being applied in long-term and large-scale
carbon sequestration projects such as FLUXNET and CarboEurope. 相似文献
20.
Dynamics of carbon dioxide exchange in the Common Spruce (Picea abies L.) in relation to environmental factors was monitored during several seasons. Direct linear dependence of photosynthesis rate from the levels of air temperature and illumination was found, and correlation coefficients were 0.860 (p < 0.001) and 0.704 (p < 0.001). It was found that seasonal maximum of net photosynthesis production was attained at temperatures of 23–25°C. A decrease in temperature optimum was associated with reduction of the CO2 assimilation intensity level. The impact of environmental factors on photosynthesis intensity is discussed in terms of the developed model. Using this model, we demonstrated that temperature and illumination dynamics in toto accounts for 82% of changes in photosynthesis rate. It is the air temperature that exerts the strongest influence on the process of photosynthesis. According to our calculations, the net photosynthesis level was three times higher than the level of respiration. This is indicative of a positive carbon dioxide balance in the needles of the Common Spruce. 相似文献