中国热带天然林变迁对大气CO2的影响及经济损益评估

我国目前保存较好的热带天然林（包括热带原始林、结构良好的天然更新林,而不包括疏林、残次林、灌木林等）面积约１１８７万ｈｍ２,其中云南南部约有６０万ｈｍ２,海南中南部山区约有５８７万ｈｍ２。在过去的４５年中,我国的热带原始林面积减少了５０％（约１１０ｈｍ２）。在海南岛尖峰岭的实例结果表明,热带原始林的生态系统的Ｃ素库为３４２ｔ／ｈｍ２（其中,森林群落Ｃ素库为２３４ｔ／ｈｍ２,土壤为１０５ｔ／ｈｍ２,凋落物层为３ｔ／ｈｍ２）,系统每年净固定ＣＯ２量为１３３６ｔ／ｈｍ２,折合Ｃ量为０３７３ｔ／ｈｍ２;热带天然更新林生态系统每年净固定ＣＯ２量为７２１３ｔ／ｈｍ２,折合成Ｃ量为１９７ｔ／ｈｍ２。在我国现有的热带天然林生态系统中,森林植被层的Ｃ素库为１４４８亿ｔ,土壤中的Ｃ素库为１４２２亿ｔ,与植被层Ｃ库相当。在减少的热带森林中,Ｃ素库减少了约２２３１亿ｔ、ＣＯ２净同化量减少了０１８３亿ｔ,其经济损益高达２２００亿元。最后从森林与ＣＯ２的关系方面探讨了热带林可持续经营的问题。     

Impact of Atmospheric Nitrogen Deposition on Carbon Dynamics in Two Scots Pine Forest Soils of Northern Germany

The impact of atmospheric N deposition on the dynamics of various carbon fractions was investigated in two Scots pine forest soils (cambisol, podzol) of Northern Germany in microcosm experiments. Total organic carbon (TOC), CO₂ emission, microbial carbon (C_mic) as well as organic hot- and coldwater extractable carbon fractions (C_hwe, C_cwe) were analyzed before, during, and after soil incubation in microcosms, run in three treatments: 0, +45, and +90 kg N ha⁻¹a⁻¹. On both sites, the N treatment showed no response to total organic carbon (TOC) contents in most of the investigated soil layers. Microbial carbon (C_mic) was significantly increased in the organic layer of both soil types by the N application. Subsequent to the N application, the CO₂ emission increased in all mineral soil layers of the cambisol but remained almost unaffected in the podzol. After the N application, a remarkable increase of hotwater extractable C (C_hwe) was detected for the organic layer of the cambisol but not for the podzol, whereas coldwater extractable C (C_cwe) concentrations decreased at both sites. The N application did not have a significant impact on the leachate concentrations of total organic carbon (TOC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in the podzol, whereas the concentrations of these C fractions were decreased in the organic layer and the 35–70~cm mineral soil layer of the cambisol. The N treatment changed the contents of most of the investigated C fractions in both soil types and resulted in a considerable C~mobilization. But the processes of the C~mobilization between the cambisol and the podzol were completely different. According to the presented data, the cambisol obtaining moderate atmospheric N loads is much more sensitive to additional N inputs than the podzol that already received high amounts of atmospheric N.     

Leaf photosynthesis and carbohydrate dynamics of soybeans grown throughout their life-cycle under Free-Air Carbon dioxide Enrichment

A lower than theoretically expected increase in leaf photosynthesis with long‐term elevation of carbon dioxide concentration ([CO₂]) is often attributed to limitations in the capacity of the plant to utilize the additional photosynthate, possibly resulting from restrictions in rooting volume, nitrogen supply or genetic constraints. Field‐grown, nitrogen‐fixing soybean with indeterminate flowering might therefore be expected to escape these limitations. Soybean was grown from emergence to grain maturity in ambient air (372 µmol mol^?1[CO₂]) and in air enriched with CO₂ (552 µmol mol^?1[CO₂]) using Free‐Air CO₂ Enrichment (FACE) technology. The diurnal courses of leaf CO₂ uptake (A) and stomatal conductance (g_s) for upper canopy leaves were followed throughout development from the appearance of the first true leaf to the completion of seed filling. Across the growing season the daily integrals of leaf photosynthetic CO₂ uptake (A′) increased by 24.6% in elevated [CO₂] and the average mid‐day g_s decreased by 21.9%. The increase in A′ was about half the 44.5% theoretical maximum increase calculated from Rubisco kinetics. There was no evidence that the stimulation of A was affected by time of day, as expected if elevated [CO₂] led to a large accumulation of leaf carbohydrates towards the end of the photoperiod. In general, the proportion of assimilated carbon that accumulated in the leaf as non‐structural carbohydrate over the photoperiod was small (< 10%) and independent of [CO₂] treatment. By contrast to A′, daily integrals of PSII electron transport measured by modulated chlorophyll fluorescence were not significantly increased by elevated [CO₂]. This indicates that A at elevated [CO₂] in these field conditions was predominantly ribulose‐1,5‐bisphosphate (RubP) limited rather than Rubisco limited. There was no evidence of any loss of stimulation toward the end of the growing season; the largest stimulation of A′ occurred during late seed filling. The stimulation of photosynthesis was, however, transiently lost for a brief period just before seed fill. At this point, daytime accumulation of foliar carbohydrates was maximal, and the hexose:sucrose ratio in plants grown at elevated [CO₂] was significantly larger than that in plants grown at current [CO₂]. The results show that even for a crop lacking the constraints that have been considered to limit the responses of C₃ plants to rising [CO₂] in the long term, the actual increase in A over the growing season is considerably less than the increase predicted from theory.     

Alteration of Soil Carbon Pools and Communities of Mycorrhizal Fungi in Chaparral Exposed to Elevated Carbon Dioxide

We examined the effects of atmospheric carbon dioxide (CO₂) enrichment on belowground carbon (C) pools and arbuscular mycorrhizal (AM) fungi in a chaparral community in southern California. Chambers enclosing intact mesocosms dominated by Adenostoma fasciculatum were exposed for 3.5 years to CO₂ levels ranging from 250 to 750 ppm. Pools of total C in bulk soil and in water-stable aggregates (WSA) increased 1.5- and threefold, respectively, between the 250- and 650-ppm treatments. In addition, the abundance of live AM hyphae and spores rose markedly over the same range of CO₂, and the community composition shifted toward dominance by the AM genera Scutellospora and Acaulospora. Net ecosystem exchange of C with the atmosphere declined with CO₂ treatment. It appears that under CO₂ enrichment, extra C was added to the soil via AM fungi. Moreover, AM fungi were predominant in WSA and may shunt C into these aggregates versus bulk soil. Alternatively, C may be retained longer within WSA than within bulk soil. We note that differences between the soil fractions may act as a potential feedback on C cycling between the soil and atmosphere.     

Carbon Dioxide and Methane Production in Small Reservoirs Flooding Upland Boreal Forest

The FLooded Uplands Dynamics EXperiment (FLUDEX) was designed to assess the impact of reservoir creation on carbon cycling in boreal forests by (a) determining whether production of the greenhouse gases (GHG) carbon dioxide (CO₂) and methane (CH₄) in reservoirs is related to the amount of organic carbon (OC) stored in the flooded landscape, (b) examining temporal trends in GHG production during initial stages of flooding, and (c) considering the net difference between GHG fluxes before and after flooding to estimate the true effect of reservoir creation on atmospheric GHG levels. Three forested sites that varied in the amount of OC stored in soils and vegetation (30,870–45,860 kg C ha^–1) were experimentally flooded from June to September in 1999–2001. Throughout the study, net CO₂ and CH₄ production in all three reservoirs was not related to overall site OC storage. During the 1st flooding season, net CO₂ production in the three reservoirs was 703–797 kg C ha^–1, but it decreased during the 2nd and 3rd flooding seasons to between 408 and 479 kg C ha^–1. However, CH₄ production increased in all reservoirs with each flooding season, from about 3.2–4.6 kg C ha^–1 in 1999 to 12.8–24.9 kg C ha^–1 in 2000 and 29.7–35.2 kg C ha^–1 in 2001. Over the long term, effects of boreal reservoir creation on atmospheric GHG levels may be largely due to net changes in CH₄ cycling between the undisturbed and flooded ecosystems.     

Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 1. Leaf position and phenology determine acclimation response

We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO₂ concentration, and ample and limiting N supplies, within a field experiment using free-air CO₂ enrichment (FACE). To understand how leaf age and developmental stage affected any acclimation response, measurements were made on a vertical profile of leaves every week from tillering until maturity. The response of assimilation (A) to internal CO₂ concentration (C_i) was used to estimate the in vivo carboxylation capacity (Vc_max) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (A _sat). The total activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and leaf content of Rubisco and the Light Harvesting Chlorophyll a/b protein associated with Photosystem II (LHC II), were determined. Elevated CO₂ did not alter Vc_max in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vc_max and A _sat was observed, and was found to correlate with reduced Rubisco activity and content. The dependency of acclimation on N supply was different at each developmental stage. With adequate N supply, acclimation to elevated CO₂ was also accompanied by an increased LHC II/Rubisco ratio. At low N supply, contents of Rubisco and LHC II were reduced in all leaves, although an increased LHC II/Rubisco ratio under elevated CO₂ was still observed. These results underscore the importance of leaf position, leaf age and crop developmental stage in understanding the acclimation of photosynthesis to elevated CO₂ and nutrient stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbon Dioxide Variation in a Hardwood Forest Stream: An Integrative Measure of Whole Catchment Soil Respiration

The concentration of CO₂ in stream water is a product of not only instream metabolism but also upland, riparian, and groundwater processes and as such can provide an integrative measure of whole catchment soil respiration. Using a 5-year dataset of pH, alkalinity, Ca²⁺, and Mg²⁺ in surface water of the West Fork of Walker Branch in eastern Tennessee in conjunction with a hydrological flowpath chemistry model, we investigated how CO₂ concentrations and respiration rates in stream, bedrock, and soil environments vary seasonally and interannually. Dissolved inorganic carbon concentration was highest in summer and autumn (P < 0.05) although the proportion as free CO₂ (pCO₂) did not vary seasonally (P > 0.05). Over the 5 years, pCO₂ was always supersaturated with respect to the atmosphere ranging from 374 to 3626 ppmv (1.0- to 10.1-fold greater than atmospheric equilibrium), and CO₂ evasion from the stream to the atmosphere ranged from 146 to 353 mmol m⁻² d⁻¹. Whereas pCO₂ in surface water exhibited little intra-annual or interannual variation, distinct seasonal patterns in soil and bedrock pCO₂ were revealed by the catchment CO₂ model. Seasonally, soil pCO₂ increased from a winter low of 8167 ppmv to a summer high of 27,068 ppmv. Driven by the seasonal variation in gas levels, evasion of CO₂ from soils to the atmosphere ranged from 83 mmol m⁻² d⁻¹ in winter to 287 mmol m⁻² d⁻¹ in summer. The seasonal variation in soil CO₂ tracked soil temperature (r ²= 0.46, P < 0.001) and model-derived estimates of CO₂ evasion rate from soils agreed with previously reported fluxes measured using chambers (Pearson correlation coefficient = 0.62, P < 0.05) supporting the model assumptions. Although rates of CO₂ evasion were similar between the stream and soils, the overall rate of evasion from the channel was only 0.4% of the 70,752 mol/d that evaded from soils due to the vastly different areas of the two subsystems. Our model provides a means to assess whole catchment CO₂ dynamics from easily collected and measured stream-water samples and an approach to study catchment scale variation in soil ecosystem respiration. Received 24 July 1997; accepted 14 November 1997.     

罗浮栲林土壤微生物碳利用效率对短期氮添加的响应

作为调节土壤碳矿化过程的重要参数,微生物碳利用效率(CUE)对理解陆地生态系统中的碳循环至关重要。本研究在戴云山罗浮栲林设置对照(0 kg N·hm^-2·a^-1)、低氮(40 kg N·hm^-2·a^-1)和高氮(80 kg N·hm^-2·a^-1) 3个氮添加水平以模拟氮沉降,测定了表层(0～10 cm)土壤基本理化性质、有机碳组分、微生物生物量和酶活性;并利用¹⁸O标记水方法测定土壤微生物CUE,以更好地理解氮沉降加剧对微生物CUE的影响及其影响因素。结果表明: 短期氮添加显著降低了土壤微生物的呼吸速率、碳和氮获取酶活性,但显著增加了土壤微生物CUE。β-N-乙酰氨基酸葡糖苷酶(NAG)/微生物生物量碳(MBC)、微生物呼吸速率、β-葡萄糖苷酶(BG)/MBC、纤维素水解酶(CBH)/MBC和土壤有机碳含量是影响CUE的主要因素,且CUE与NAG/MBC、微生物呼吸速率、BG/MBC和CBH/MBC呈显著负相关,与土壤有机碳呈显著正相关。综上,短期氮添加导致土壤微生物获取碳和氮的成本降低,减少微生物呼吸,从而提高了土壤微生物CUE,这将有助于提高罗浮栲林土壤碳固存潜力。     

Interactive Effects of Fire, Elevated Carbon Dioxide, Nitrogen Deposition, and precipitation on a California Annual Grassland

Although it is widely accepted that elevated atmospheric carbon dioxide (CO₂), nitrogen (N) deposition, and climate change will alter ecosystem productivity and function in the coming decades, the combined effects of these environmental changes may be nonadditive, and their interactions may be altered by disturbances, such as fire. We examined the influence of a summer wildfire on the interactive effects of elevated CO₂, N deposition, and increased precipitation in a full-factorial experiment conducted in a California annual grassland. In unburned plots, primary production was suppressed under elevated CO₂. Burning alone did not significantly affect production, but it increased total production in combination with nitrate additions and removed the suppressive effect of elevated CO₂. Increased production in response to nitrate in burned plots occurred as a result of the enhanced aboveground production of annual grasses and forbs, whereas the removal of the suppressive effect of elevated CO₂ occurred as a result of increased aboveground forb production in burned, CO₂-treated plots and decreased root production in burned plots under ambient CO₂.The tissue nitrogen–phosphorus ratio, which was assessed for annual grass shoots, decreased with burning and increased with nitrate addition. Burning removed surface litter from plots, resulting in an increase in maximum daily soil temperatures and a decrease in soil moisture both early and late in the growing season. Measures of vegetation greenness, based on canopy spectral reflectance, showed that plants in burned plots grew rapidly early in the season but senesced early. Overall, these results indicate that fire can alter the effects of elevated CO₂ and N addition on productivity in the short term, possibly by promoting increased phosphorus availability.     

Detecting Tropical Forests' Responses to Global Climatic and Atmospheric Change: Current Challenges and a Way Forward

Because of tropical forests' disproportionate importance for world biodiversity and for the global carbon cycle, we urgently need to understand any effects on these ecosystems from the ongoing changes in climate and atmosphere. This review, intended to complement existing data reviews on this topic, focuses on three major classes of challenges that we currently face when trying to detect and interpret directional changes in tropical forests. One is the very limited existing information on the historical context of study sites. Lasting effects from past climate, natural disturbances, and/or human activities could be significantly affecting current-day processes in tropical forests and need to be investigated for all active field sites. Second, while progress has been made in recent years on standardizing and refining research approaches, a number of methods- and data-limitations continue to affect efforts both to detect within-forest changes and to relate them to ongoing environmental change. Important outstanding needs are improved sampling designs, longer time-series of observations, filling key data gaps, and data access. Finally, forest responses to ongoing environmental change are complex. The effects of many simultaneously changing environmental factors are integrated by the plants, and their responses can involve significant lags, carryovers, and non-linearities. Specifying effects of individual environmental changes, however, is required for accurate ecosystem-process models and thus for projecting future impacts on these forests. After discussing these several types of challenges and ways to address them, I conclude with a priority agenda for this critical area of research.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp .     

The Effect of Atmospheric Carbon Dioxide Elevation on Plant Growth in Freshwater Ecosystems

We developed a dynamic model to investigate the effect of atmospheric carbon dioxide (CO₂) increase on plant growth in freshwater ecosystems. Steady-state simulations were performed to analyze the response of phytoplankton and submerged macrophytes to atmospheric CO₂ elevation from 350 to 700 ppm. We studied various conditions that may affect this response, such as alkalinity, the air–water exchange rate of CO₂, the community respiration rate, and the phosphorus (P) supply rate. The increase in atmospheric CO₂ could affect submerged plant growth only under relatively eutrophic conditions and at a low community respiration rate. Alkalinity had little effect on the response of the different species. When the air–water exchange was low, the proportional effect of the CO₂ increase on plant growth was higher. Under eutrophic conditions, algae and macrophytes using CO₂ and HCO₃^– may double their growth rate due to atmospheric CO₂ elevation, while the growth of macrophytes restricted to CO₂ assimilation may be threefold. The differences in response of the species under various conditions indicate that the elevation of atmospheric CO₂ may induce drastic changes in the productivity and species dominance in freshwater systems.     

Impacts of Elevated Carbon Dioxide and Temperature on a Boreal Forest Ecosystem (CLIMEX Project)

To evaluate the effects of climate change on boreal forest ecosystems, both atmospheric CO₂ (to 560 ppmv) and air temperature (by 3°–5°C above ambient) were increased at a forested headwater catchment in southern Norway. The entire catchment (860 m²) is enclosed within a transparent greenhouse, and the upper 20% of the catchment area is partitioned such that it receives no climate treatment and serves as an untreated control. Both the control and treatment areas inside the greenhouse receive deacidified rain. Within 3 years, soil nitrogen (N) mineralization has increased and the growing season has been prolonged relative to the control area. This has helped to sustain an increase in plant growth relative to the control and has also promoted increased N export in stream water. Photosynthetic capacity and carbon–nitrogen ratio of new leaves of most plant species did not change. While the ecosystem now loses N, the long-term fate of soil N is a key uncertainty in predicting the future response of boreal ecosystems to climate change. Received 18 November 1997; accepted 13 April 1998.     

Effects of short- and long-term water-level drawdown on the populations and activity of aerobic decomposers in a boreal peatland

We analysed the response of microbial communities, characterized by phospholipid fatty acids (PLFAs), to changing hydrological conditions at sites with different nutrient levels in a southern boreal peatland. Although PLFAs of Gram‐negative bacteria were characteristic of the peatland complex, microbial communities differed among sites (ombrotrophic bog, oligotrophic fen, mesotrophic fen) and sampling depths (0–5, 5–10, 10–20, 20–30 cm). The microbial communities in each site changed significantly following water‐level drawdown. The patterns of change varied among sites and sampling depths. The relative proportion of Gram‐negative bacteria decreased in the upper 10 cm but increased in deeper layers of the fen sites. Fungi benefited from water‐level drawdown in the upper 5 cm of the mesotrophic fen, but suffered in the drier surfaces of the ombrotrophic bog, especially in the 5–10 cm layer. In contrast, actinobacteria suffered from water‐level drawdown in the mesotrophic fen, but benefited in the drier surfaces of the ombrotrophic bog. Basal respiration rate correlated positively with pH and fungal PLFA, and negatively with depth. We suggest that the changes in microbial community structure after persistent water‐level drawdown follow not only the hydrological conditions but also the patterns of vegetation change. Our results imply that changes in structure and activity of the microbial community in response to climate change will be strongly dependent on the type of peatland.     

Production of Dissolved Organic Carbon in Canadian Forest Soils

To identify the controls on dissolved organic carbon (DOC) production, we incubated soils from 18 sites, a mixture of 52 forest floor and peats and 41 upper mineral soil samples, at three temperatures (3, 10, and 22°C) for over a year and measured DOC concentration in the leachate and carbon dioxide (CO₂) production from the samples. Concentrations of DOC in the leachate were in the range encountered in field soils (<2 to >50 mg l⁻¹). There was a decline in DOC production during the incubation, with initial rates averaging 0.03–0.06 mg DOC g⁻¹ soil C day⁻¹, falling to averages of 0.01 mg g⁻¹ soil C day⁻¹; the rate of decline was not strongly related to temperature. Cumulative DOC production rates over the 395 days ranged from less than 0.01 to 0.12 mg g⁻¹ soil C day⁻¹ (0.5–47.6 mg g⁻¹ soil C), with an average of 0.021 mg g⁻¹ soil C day⁻¹ (8.2 mg g⁻¹ soil C). DOC production rate was weakly related to temperature, equivalent to Q₁₀ values of 0.9 to 1.2 for mineral samples and 1.2 to 1.9 for organic samples. Rates of DOC production in the organic samples were correlated with cellulose (positively) and lignin (negatively) proportion in the organic matter, whereas in the mineral samples C and nitrogen (N) provided positive correlations. The partitioning of C released into CO₂–C and DOC showed a quotient (CO₂–C:DOC) that varied widely among the samples, from 1 to 146. The regression coefficient of CO₂–C:DOC production (log₁₀ transformed) ranged from 0.3 to 0.7, all significantly less than 1. At high rates of DOC production, a smaller proportion of CO₂ is produced. The CO₂–C:DOC quotient was dependent on incubation temperature: in the organic soil samples, the CO₂–C:DOC quotient rose from an average of 6 at 3 to 16 at 22°C and in the mineral samples the rise was from 7 to 27. The CO₂–C:DOC quotient was related to soil pH in the organic samples and C and N forms in the mineral samples.     

Nutrient Input and Carbon and Microbial Dynamics in an Ombrotrophic Bog

Slow rates of plant production and decomposition in ombrotrophic bogs are believed to be partially the result of low nutrient availability. To test the effect of nutrient availability on decomposition, carbon dioxide (CO₂) flux dynamics, microbial biomass, and nutrients, we added nitrogen (N) with phosphorus (P) and potassium (K), to prevent limitation of the latter 2 nutrients, over 2 growing seasons to plots at Mer Bleue peatland, Ontario, Canada. After the first growing season, increasing N fertilization (with constant P and K) decreased in vitro CO₂ production potential and increased microbial biomass measured with a chloroform fumigation-extraction technique in the upper peat profile, while by the end of the second season, CO₂ production potential was increased in response to N plus PK treatment, presumably due to more easily decomposable newly formed plant material. In situ CO₂ fluxes measured using chamber-techniques over the second year corroborated this presumption, with greater photosynthetic CO₂ uptake and ecosystem respiration (ER) during high N plus PK treatments. The more efficient microbial community, with slower CO₂ production potential and larger biomass, after the first year was characterized by larger fungal biomass measured with signature phospholipid fatty acids. The majority of N was likely quickly sequestered by the vegetation and transferred to dissolved organic forms and microbial biomass in the upper parts of the peat profile, while additional P relative to controls was distributed throughout the profile, implying that the vegetation at the site was N limited. However, in situ CO₂ flux data suggested the possibility of P or NPK limitation. We hypothesize that nutrient deposition may lead to enhanced C uptake by altering the microbial community and decomposition, however this pattern disappears through subsequent changes in the vegetation and production of more readily decomposable plant tissues.     

Responses of respiration to increasing atmospheric carbon dioxide concentrations

It has been recently recognized that increases in carbon dioxide concentration such as are anticipated for the earth's atmosphere in the next century often reduce plant respiration. There can be both a short-term reversible effect of unknown cause, and long-term acclimation, which may reflect the synthesis and maintenance of less metabolically expensive materials in plants grown at elevated carbon dioxide concentrations. Because respiration provides energy and carbon intermediates for growth and maintenance, reductions in respiration by increasing carbon dioxide concentrations may have effects on physiology beyond an improvement in plant carbon balance. As atmospheric carbon dioxide concentration increases, reduced respiration could be as important as increased photosynthesis in improving the ability of terrestrial vegetation to act as a sink for carbon, but it could also have other consequences.     

中国森林生态系统中植物固定大气碳的潜力

1　前　言在引起全球温室效应的痕量气体中 ,尤以含Ｃ气体的作用最为显著。ＣＯ2 和ＣＨ4两种含碳气体的贡献将达到 75 %[1] 。而且 ,在大气中这两种气体的浓度正在不断增加[2 ] 。为了弄清大气中这些含碳痕量气体的来源和归宿 ,首先应该搞清楚全球主要碳库的现有贮量及其潜力。森林是全球陆地生态系统中的最大有机碳库 ,它贮有1 1 4 6ＰｇＣ ,占整个陆地碳库的 5 6%[3] 。而且更重要的是森林生态系统具有较高的碳贮存密度(ｃａｒｂｏｎｄｅｎｓｉｔｙ ,即与别的土地利用方式相比 ,单位面积内可以贮存更多量的有机碳 )。据研究 ,森林生态系…     

Free Atmospheric CO2 Enrichment (FACE) Increased Labile and Total Carbon in the Mineral Soil of a Short Rotation Poplar Plantation

The global net terrestrial carbon sink was estimated to range between 0.5 and 0.7 Pg C y⁻¹ for the early 1990s. FACE (free atmospheric CO₂ enrichment) studies conducted at the whole-tree and community scale indicate that there is a marked increase of primary production, mainly allocated into below-ground biomass. The enhanced carbon transfer to the root system may result in enhanced rhizodeposition and subsequent transfer to soil C pools. During the first rotation of the POP/EuroFACE experiment in a short-rotation Poplar plantation, total soil C content increased more under ambient CO₂ treatment than under FACE, while under FACE more new C was incorporated than under ambient CO₂. These unexpected and opposite effects may have been caused by a priming effect, where priming effect is defined as the stimulation of SOM decomposition caused by the addition of labile substrates. In order to gain insight into these processes affecting SOM decomposition, we obtained the labile, refractory and stable pools of soil C and N by chemical fractionation (acid hydrolysis) and measured rates of N-mineralization. Results of the first 2 years of the second rotation show a larger increase of total soil C% under FACE than under ambient CO₂. In contrast to the first rotation, total C% is now increasing faster under FACE than under ambient CO₂. Based on these observations we infer that the priming effect ceased during the second rotation. FACE treatment increased the labile C fraction at 0–10 cm depth, which is in agreement with the larger input of plant litter and root exudates under FACE. N-mineralization rates were not affected by FACE. We infer that the system switched from a state where extra labile C and sufficient N-availability (due to the former agricultural use of the soil) caused a priming effect (first rotation), to a state where extra C input is accumulating due to limited N-availability (second rotation). Our results on N-mineralization (second rotation) are in agreement with observations made at three forest FACE sites (Duke Forest, Oak Ridge, and Rhinelander), but our finding of increasing mineral soil C content contrasted with results at the Duke Forest where no significant increase in C content of the mineral soil occurred. However, the FACE induced increase in total C content occurred within the fraction with the shortest turnover time, i.e. the labile fraction. The refractory and stable fractions were not affected. The question remains whether the currently observed larger increase of total soil C and the increase of labile C under FACE will eventually result in long-term C storage in refractory and stable organic matter fractions.     

复合群落土壤微生物和酶活性对大气CO2浓度和温度升高的响应

应用自控、封闭、独立的生长室系统,研究川西亚高山林线复合群落根际、非根际土壤微生物数量以及根际、非根际土壤酶活性对大气CO2浓度升高(环境CO2浓度+350(±25)μmol.mol-1,EC)和温度升高(环境温度+2.0(±0.5)℃,ET)及其两者同时升高(ECT)的响应。结果表明:(1)与对照(CK)相比,EC、ET和ECT处理能够增加土壤根际微生物数量,但不同微生物种类对EC、ET和ECT的反应有所差异。(2)不同种类的根际土壤酶对EC、ET和ECT的响应不同。(3)与CK相比,EC、ET和ECT的非根际土壤微生物数量以及非根际土壤酶活性均无显著提高。(4)EC、ET和ECT处理对复合群落土壤微生物总数的根际效应明显;除ET处理的转化酶为负根际效应,其余处理的过氧化氢酶,脲酶及转化酶均表现为正根际效应。