Soil respiration and soil CO<Subscript>2</Subscript> concentration in a tropical forest,Thailand

Soil respiration and soil carbon dioxide (CO₂) concentration were investigated in a tropical monsoon forest in northern Thailand, from 1998 to 2000. Soil respiration was relatively high during the rainy season and low during the dry season, although interannual fluctuations were large. Soil moisture was widely different between the dry and wet seasons, while soil temperature changed little throughout the year. As a result, the rate of soil respiration is determined predominantly by soil moisture, not by soil temperature. The roughly estimated annual soil respiration rate was 2560gCm^–2year^–1. The soil CO₂ concentration also increased in the rainy season and decreased in the dry season, and showed clearer seasonality than soil respiration did.     

Temperature controls temporal variation in soil CO2 efflux in a secondary beech forest in Appi Highlands, Japan

Forest soil is a huge reserve of carbon in the biosphere. Therefore to understand the carbon cycle in forest ecosystems, it is important to determine the dynamics of soil CO₂ efflux. This study was conducted to describe temporal variations in soil CO₂ efflux and identify the environmental factors that affect it. We measured soil CO₂ efflux continuously in a beech secondary forest in the Appi Highlands in Iwate Prefecture for two years (except when there was snow cover) using four dynamic closed chambers that automatically open after taking measurements. Temporal changes in soil temperature and volumetric soil water content were also measured at a depth of 5 cm. The soil CO₂ efflux ranged from 14 mg CO₂ m⁻² h⁻¹ to 2,329 mg CO₂ m⁻² h⁻¹, the peak occurring at the beginning of August. The relationship between soil temperature and soil CO₂ efflux was well represented by an exponential function. Most of temporal variation in soil CO₂ efflux was explained by soil temperature rather than volumetric soil water content. The Q ₁₀ values were 3.7 ± 0.8 and estimated annual carbon emissions were 837 ± 210 g C m⁻² year⁻¹. These results provide a foundation for further development of models for prediction of soil CO₂ efflux driven by environmental factors.     

Q10 values of soil respiration in Japanese forests

Q₁₀ is the most important index of soil respiration, and is essential for accurate prediction of soil carbon response to global warming. The response of soil carbon storage is an issue on global and regional scales. In this study, published Q₁₀ values of soil respiration in Japanese forests were examined (n = 44). The Q₁₀ values ranged from 1.30 to 3.45, and the mean value was 2.18 (SD = 0.61, median = 2.02). These results were slightly lower than those of global compilations. The number of studies of Q₁₀ values is still lacking, especially with regard to those in managed forests, those in northeast Japan, and those using modern measurement techniques such as infrared gas analysis. For accurate prediction of soil carbon dynamics and storage in Japanese forests, more such studies are required.     

Seasonality of vertically partitioned soil CO<Subscript>2</Subscript> production in temperate and tropical forest

Soil CO₂ production seasonality at a number of depths was investigated in a temperate forest in Japan and in a tropical montane forest in Thailand. The CO₂ production rates were evaluated by examining differences in the estimated soil CO₂ flux at adjacent depths. The temperate forest had clear temperature seasonality and only slight rainfall seasonality, whereas the tropical montane forest showed clear rainfall seasonality and only slight temperature seasonality. In the temperate forest, the pattern of seasonal variation in soil respiration was similar at all depths, except the deepest (0.65 m–), and respiration was greater in summer and less in winter. The contribution of the shallowest depth (around 0.1 m) was more than 50% of total soil-surface CO₂ flux all year round, and the annual mean contribution was about 75%. CO₂ production mostly appeared to increase with temperature in shallower layers. In contrast, in the tropical forest, soil CO₂ production seasonality appeared to differ with depth. The CO₂ production rate in the shallowest layer was high during the rainy season and low during the dry season. Soil CO₂ production at greater depths (0.4 and 0.5 m–) showed the opposite seasonality to that in the shallower layer (around 0.1 m). As a result, the contribution from the shallow depth was greatest in the tropical forest during the rainy season (more than 90%), whereas it decreased during the dry season (about 50%). CO₂ production appeared to be controlled by soil water at all depths, and the different ranges of water saturation seemed to cause the difference in seasonality at each depth. Our results suggest the importance of considering the vertical distribution of soil processes, particularly in areas where soil water is a dominant controller of soil respiration.     

Relationships between soil CO2 concentration and CO2 production, temperature, water content, and gas diffusivity: implications for field studies through sensitivity analyses

Soil CO₂ levels reflect CO₂ production and transport in soil and provide valuable information about soil CO₂ dynamics. However, extracting information from soil CO₂ profiles is often difficult because of the complexity of these profiles. In this study, we constructed a simple numerical model that simulated soil CO₂ dynamics and performed sensitivity analyses for CO₂ production rates, soil water content and temperature, and gas diffusivity at the soil surface to clarify the relationships among these parameters. Increased soil surface CO₂ flux did not always coincide with higher soil CO₂ concentrations; increased CO₂ production at shallow depths had little effect on soil CO₂ concentrations, while the opposite may be true for high levels of soil water content. Higher soil CO₂ concentration did not always coincide with greater soil surface CO₂ flux; under high soil water conditions, soil surface CO₂ flux sometimes decreased despite increased soil CO₂ concentration. Increases in soil water content did not always enhance both soil surface CO₂ flux and soil CO₂ concentration. Under high soil water conditions, increases in soil water content could lower soil surface CO₂ flux and increase soil CO₂ concentration. Increases in soil temperature resulted in greater soil surface CO₂ flux and higher soil CO₂ concentration in our simulation (extremely high temperatures were not assumed in this study). Gas diffusivity in very shallow layers did affect, albeit weakly, soil CO₂ concentration. The findings of this study may help direct future observations and aid in the interpretation of their results.     

Climate and historical stand dynamics in the tropical pine forests of northern Thailand

Forest recruitment is the outcome of local- and regional-scale factors such as disturbances and climate. The relative importance of local- and regional-scale factors will determine the spatial scale at which temporal pulses of recruitment occur. In seasonal tropical forests, where the annual dry-season is a critical bottleneck to seedling survival, multi-year periods of relatively cool, wet dry seasons may be required for successful tree recruitment. Consequently, when such conditions are present, region-wide synchronisation of recruitment may occur. To examine the case for regional synchronisation of forest dynamics in the seasonal tropical pine forests of northern Thailand, we investigated forest age structures at three spatial scales: stand, site and region. We compared forest age structures with instrumental climatic records beginning in 1902. We found significant statistical evidence of synchronous recruitment at the stand- and site-scales, but not at the regional-scale. While correlations between recruitment and climate were not statistically significant, recruitment success was often linked to favourable climatic conditions. For example, recruitment at all sites was associated with multi-year periods of cool-wet dry seasons. The lack of significant correlations between recruitment and climate appears to reflect complex interactions among local disturbance history, regional climate variability and pine recruitment.     

Effects of winter selective tree harvest on soil microclimate and surface CO2 flux of a northern hardwood forest

Soil surface CO₂ flux (S_flux) is the second largest terrestrial ecosystem carbon flux, and may be affected by forest harvest. The effects of clearcutting on S_flux have been studied, but little is known about the effect of alternative harvesting methods such as selective tree harvest on S_flux. We measured S_flux before and after (i) the creation of forest canopy gaps (simulating group tree selection harvests) and (ii) mechanized winter harvest but no tree removal (simulating ground disturbance associated with logging). The experiment was carried out in a sugar maple dominated forest in the Flambeau River State Forest, Wisconsin. Pre-treatment measurements of soil moisture, temperature and S_flux were measured throughout the growing season of 2006. In January–February 2007, a harvester created the canopy gaps (200–380 m²). The mechanization treatment consisted of the harvester traveling through the plots for a similar amount of time as the gap plots, but no trees were cut. Soil moisture and temperature and S_flux were measured throughout the growing season for 1 year prior to harvest and for 2 years after harvest. Soil moisture and temperature were significantly greater in the gap than mechanized and control treatments. Instantaneous S_flux was positively correlated to soil moisture and soil temperature at 2 and 10 cm, but temperature at 10 cm was the single best predictor. Annual S_flux was not significantly different among treatments prior to winter 2007 harvest, and was not significantly different among treatments after harvest. Annual (+1 std. err.) S_flux averaged 967 + 72, 1011 + 72, and 1012 + 72 g C m⁻² year⁻¹ in the control, mechanized and gap treatments, respectively, for the 2-year post-treatment period. The results from this study suggest selective group tree harvest significantly increases soil moisture and temperature but does not significantly influence S_flux.     

Impacts of understory species removal and/or addition on soil respiration in a mixed forest plantation with native species in southern China

Although the removal or addition of understory vegetation has been an important forest management practice in forest plantations, the effects of this management practice on soil respiration are unclear. The overall objective of this study was to measure and model soil respiration and its components in a mixed forest plantation with native species in south China and to assess the effects of understory species management on soil respiration and on the contribution of root respiration (R_r) to total soil respiration (R_s). An experiment was conducted in a plantation containing a mixture of 30 native tree species and in which understory plants had been removed or replaced by Cassia alata Linn. The four treatments were the control (Control), C. alata addition (CA), understory removal (UR) and understory removal with C. alata addition (UR + CA). Trenched subplots were used to quantify R_r by comparing R_s outside the 1-m² trenched subplots (plants and roots present) and inside the trenched subplots (plants and roots absent) in each treatment. Annual soil respiration were modeled using the values measured for R_s, soil temperature and soil moisture. Our results indicate that understory removal reduced R_s rate and soil moisture but increased soil temperature. Regression models revealed that soil temperature was the main factor and soil moisture was secondary. Understory manipulations and trenching increased the temperature sensitivity of R_s. Annual R_s for the Control, CA, UR and UR + CA treatments averaged 594, 718, 557 and 608 g C m⁻² yr⁻¹, respectively. UR decreased annual R_s by 6%, but CA increased R_s by about 21%. Our results also indicate that management of understory species increased the contribution of R_r to R_s.     

Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Variability of soil CO₂ efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO₂ efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO₂ flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO₂ efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO₂ efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.     

Characteristics of the temperature coefficient, Q 10, for the respiration of non-photosynthetic organs and soils of forest ecosystems

The temperature coefficient, Q ₁₀ (fractional change in rate with a 10°C increase in temperature) describes the temperature sensitivity of soils, roots, and stems, as well as their possible performance in global warming processes. It is also a necessary parameter for the estimation of total CO₂ efflux from each element. A number of studies have focused on Q ₁₀ values to date; however, their conclusions are not universal and do not always agree. A review of these reported Q ₁₀ values therefore becomes necessary and important for a global understanding of the temperature sensitivity of different forest types and elements. The aims of our present paper are, first, to find the frequency distribution pattern of soils, roots, and stems (branches) and compare their temperature sensitivity; then, to find the Q ₁₀ differences between conifer and deciduous tree species and the effect of methodology on Q ₁₀ values; finally we want to give a perspective on future Q ₁₀-related studies. We found that most Q ₁₀ values of each element were concentrated in a relatively narrow range despite a total data distribution over quite a wide range. For soil respiration, the median Q ₁₀ value was 2.74 and the center of the frequency distribution was between 2.0 and 2.5 with a percentage of 23%. Most of the data (>80%) were within the range from 1.0 to 4.0. The median Q ₁₀ value for root respiration was 2.40 and the center of the frequency distribution was from 2.5 to 3.0 with a percentage of 33%. Most of the results (>80%) ranged from 1.0 to 3.0. For stem respiration, the median Q ₁₀ value was 1.91 and the frequency distribution was concentrated between 1.5 and 2.0. Over 90% of the data ranged from 1.0 to 3.0. Obvious differences in Q ₁₀ value were found between different elements, stem < root < soil including root < soil excluding root. The differences between woody organisms of stems, roots, and soils excluding roots were statistically significant (p<0.05), indicating that heterotrophic respiration from microorganism activity may be more sensitive to global warming. The duration of the period with leaves slightly affects the temperature sensitivity of woody organisms since the Q ₁₀ values for root and stem of coniferous evergreen trees did not differ significantly from deciduous trees (p>0.10). CO₂ analytical methods (soda lime absorption method, IRGA (Infra-read gas analysis), and chromatograph analysis) and root separation methods (excised root and trenched box) slightly affected the Q ₁₀ values of soil and root respiration (p>0.10), but an in vitro measurement of stem respiration yielded a significantly higher Q ₁₀ value than an in vivo method (p<0.05). In general, although the Q ₁₀ values of non-photosynthetic organisms stayed within a relatively conservative range, considerable variation between and within elements were still detectable. Accordingly, attention should be paid to the quantitative estimation of total CO₂ efflux by Q ₁₀-related models. In future studies, the biochemical factors and the environmental and biological factors controlling respiration should be emphasized for precise estimation of total CO₂ efflux. The difficulty is how to clarify the underlying mechanism for fluctuations of Q ₁₀ values for one specific habitat and element (e.g. temperature acclimation or adaptation of Q ₁₀ values) and then allow the Q ₁₀ values to be more conservative for representation of temperature sensitivity in global warming processes. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(4) [译自:植物生态学报, 2005, 29 (4)]     

Effect of collar insertion on soil respiration in a larch forest measured with a LI-6400 soil CO2 flux system

Little information is available on the effect of root cutting by the collar pre-insertion technique on soil respiration. In this study, we found that soil respiration rates decreased with increasing depth of collar insertion in both the with live roots intact and with live roots severed treatments, but the rate of decrease was substantially higher in the former. The cutting of roots, especially fine roots, may be responsible for this result.     

Development of a CO2 gas analyzer for monitoring soil CO2 concentrations

Measurement of soil CO₂ concentrations is important for investigating the dynamics and diffusion of CO₂ in soil. In this study, we developed a small CO₂ analyzer for measuring in situ-soil CO₂ concentrations. The CO₂ analyzer consists of a module containing an infrared CO₂ gas sensor, a temperature sensor, and a relative humidity sensor. These sensors are installed in a protective box with an air vent, which is suitable for burying in the soil. The output response time of the CO₂ analyzer was 349 s, as evaluated from the phase lag after input of known CO₂ concentrations. This response time is short enough to measure soil CO₂ concentrations, because variations in concentration are slower than the response time of the analyzer. In a field test, we used the CO₂ analyzer to measure soil CO₂ concentrations at five depths (0–50 cm) over 2.5 months. While the CO₂ concentration generally increased with depth, the amplitude of the variation in CO₂ concentration decreased with depth. The phase lag of the variations in soil CO₂ concentration also increased with depth, as did soil temperature. The tests confirm that the CO₂ analyzer is applicable to continuous monitoring of soil CO₂ concentrations.     

Effects of fertilisation on phosphorus pools in the volcanic soil of a managed tropical forest

Acacia koa forests benefit from phosphorus fertilisation, but it is unknown if fertilisation is a short or long term effect on P availability. Past research suggests that P cycling in soils with high P sorption capacity, such as Andisols, was through organic pathways. We studied leaf P and soil P fractions in a tropical forest Andisol for 3 years after fertilisation with triple super phosphate. Leaf P concentration and labile P remained high after fertilisation. Fertilisation had increased all the inorganic P fractions over the length of the study, while organic P fractions had not. The results suggested that the organic P fractions had a reduced role as a source of labile P after fertilisation. The size and dynamics of the sodium hydroxide- and hydrochloric acid-extractable P pools would suggest that either pool could be major sources of labile P. Because of the high level of poorly crystalline minerals in Andisols (allophone and imogolite), it would be expected that applied P would quickly lead to strong P sorption onto mineral surfaces and thus a rapid decline in P availability. We propose that the high organic matter present in these soils had masked some of the Al and Fe sorption sites, which allowed the sorption and desorption when large amounts of addition P were applied.     

Soil CO2 evolution from Korean pine virgin forest at Changbai Mountain

The soil CO₂ evolution rate was measured in a virgin Korean pine forest. The results in June showed that the lowest value of evolution rate was 220 mg/(m²·h) and appeared at 6:00 a.m. The highest value was 460 mg/(m²·h) at 18:00. The rates of CO₂ evolution were related with soil temperature. On the basis of the constructed regression equation and the monthly average values of temperature, the magnitude of CO₂ evolution from Korean pine forest soil was 10.4 t/hm² during a growing season. This project was funded by the Opened Research Station of Changbai Mountain Forest Ecosystem, Chinese Academy of Sciences. Responsible editor: Zhu Hong     

Short- and long-term responses of total soil organic carbon to harvesting in a northern hardwood forest

The long-term response of total soil organic carbon pools (‘total SOC’, i.e. soil and dead wood) to different harvesting scenarios in even-aged northern hardwood forest stands was evaluated using two soil carbon models, CENTURY and YASSO, that were calibrated with forest plot empirical data in the Green Mountains of Vermont. Overall, 13 different harvesting scenarios that included four levels of aboveground biomass removal (20%, 40%, 60% and 90%) and four different rotation lengths (60 year, 90 year, 120 year, and No Rotation (NR)) were simulated for a 360 year period. Simulations indicate that following an initial post-harvest increase, total SOC decreases for several decades until carbon inputs into the soil pool from the re-growth are greater than losses due to decomposition. At this point total SOC begins to gradually increase until the next harvest. One consequence of this recovery pattern is that between harvests, the size of the SOC pool in a stand may change from −7 to 18% of the pre-harvest pool, depending on the soil pool considered. Over 360 years, the average annual decrease in total SOC depends on the amount of biomass removed, the rotation length, and the soil pool considered. After 360 years a stand undergoing the 90yr-40% scenario will have 15% less total SOC than a non-harvested stand. Long-term declines in total SOC greater than 10% were observed in the 60yr-60%, 60yr-90%, and 90yr-90% scenarios. Long-term declines less than 5% were observed in scenarios with 120 year rotations that remove 60% or less of the aboveground biomass. The long-term decreases simulated here for common management scenarios in this region would require intensive sampling procedures to be detectable.     

Seasonal and spatial variation of nitrogen dynamics in the litter and surface soil layers on a tropical dry evergreen forest slope

Seasonal and spatial variability of litterfall and NO₃⁻ and NH₄⁺ leaching from the litter layer and 5-cm soil depth were investigated along a slope in a tropical dry evergreen forest in northeastern Thailand. Using ion exchange resin and buried bag methods, the vertical flux and transformation of inorganic nitrogen (N) were observed during four periods (dry, early wet, middle wet, and late wet seasons) at 15 subplots in a 180-m × 40-m rectangular plot on the slope. Annual N input via litterfall and inorganic N leached from the litter layer and from 5-cm depth soil were 12.5, 6.9, and 3.7 g N m⁻² year⁻¹, respectively, whereas net mineralization and the inorganic N pool in 0–5-cm soil were 7.1 g N m⁻² year⁻¹ and 1.4 g N m⁻², respectively. During the early wet season (90 days), we observed 82% and 74% of annual NO₃⁻ leaching from the litter layer and 5-cm soil depth, respectively. Higher N input via leaf litterfall in the dry season and via precipitation in the early wet season may have led to higher NO₃⁻ leaching rate from litter and surface soil layers during the early wet season. Large spatial variability in both NO₃⁻ vertical flux and litterfall was also observed within stands. Small-scale spatial patterns of total N input via litterfall were significantly correlated with NO₃⁻ leaching rate from the surface soil layer. In tropical dry evergreen forests, litterfall variability may be crucial to the remarkable seasonal changes and spatial variation in annual NO₃⁻ vertical flux in surface soil layers.     

Effects of elevated CO2 concentrations on soil microbial respiration and root/rhizosphere respiration in forest soils

The two main components of soil respiration, i.e., root/rhizosphere and microbial respiration, respond differently to elevated atmospheric CO₂ concentrations both in mechanism and sensitivity because they have different substrates derived from plant and soil organic matter, respectively. To model the carbon cycle and predict the carbon source/sink of forest ecosystems, we must first understand the relative contributions of root/rhizosphere and microbial respiration to total soil respiration under elevated CO₂ concentrations. Root/rhizosphere and soil microbial respiration have been shown to increase, decrease and remain unchanged under elevated CO₂ concentrations. A significantly positive relationship between root biomass and root/rhizosphere respiration has been found. Fine roots respond more strongly to elevated CO₂ concentrations than coarse roots. Evidence suggests that soil microbial respiration is highly variable and uncertain under elevated CO₂ concentrations. Microbial biomass and activity are related or unrelated to rates of microbial respiration. Because substrate availability drives microbial metabolism in soils, it is likely that much of the variability in microbial respiration results from differences in the response of root growth to elevated CO₂ concentrations and subsequent changes in substrate production. Biotic and abiotic factors affecting soil respiration were found to affect both root/rhizosphere and microbial respiration. __________ Translated from Journal of Plant Ecology, 2007, 31(3): 386–393 [译自: 植物生态学报]     

Impact of soil drought on sap flow and water status of evergreen trees in a tropical monsoon forest in northern Thailand

Hill evergreen forest is the dominant vegetation type in northern Thailand. In this region, there is higher atmospheric evaporative demand and lower soil moisture during the 5- to 7-month dry season than in the rainy season under influences from Asian monsoons. In an earlier study we revealed that canopy-scale transpiration is actively maintained even during the latter part of the dry season in hill evergreen forest. However, the impact of soil drought on tree water use was not investigated. To clarify the ecohydrological processes at this site, we used individual tree-scale measurements during a 2-year period to base our examination of whether limited water use in individual trees is caused by soil drought in the latter part of the dry season. Sap flow and water potential measurements were conducted in four evergreen trees, two large emergent trees 29.8 and 25.4 m high, and two smaller understory trees 4.8 and 1.4 m high.The amount of rainfall preceding the late dry season of 2004 was significantly less than that preceding the late dry season of 2003. Although a distinct decrease in sap-flow velocities in individual trees due to soil water stress was not found in the late dry season of 2003, it did become comparatively apparent in the late dry season of 2004; ranging from 10 to 40% for a given atmospheric evaporative demand. Furthermore, the reductions in sap-flow velocities and predawn stem-water potential were most significant in the smallest tree. The recovery of sap-flow velocities and water potential in the smallest tree after irrigation confirmed that the reductions in sap-flow velocity and predawn stem-water potential in the smallest tree were caused by soil drought. These results suggest that shallower roots could be reason for the significant decrease in water use in the smallest trees. The deeper roots of larger trees could be the reason for the reduced impact of soil drought on water use in larger trees, and canopy-scale transpiration might be maintained by larger trees, even in an unusually severe drought. These possibilities provide a new insight for management of evergreen forests under Asian monsoon influences.     

模拟氮沉降对云冷杉红松林土壤呼吸的影响

2011年5月至2011年10月在黑龙江省小兴安岭云冷杉红松林内进行模拟氮沉降试验,使用便携式土壤CO2通量观测仪LI-8100测定不同氮沉降浓度CK(0)、TL(50 kg.hm-2.a-1)、TM(100 kg.hm-2.a-1)和TH(150 kg.hm-2.a-1)对土壤呼吸的影响。结果表明,氮沉降未显著改变土壤呼吸的日变化和季节性变化规律;对比CK,TL、TM和TH处理,分别使土壤日呼吸速率提高了13.72%、23.22%和5.12%,年呼吸速率提高了13.98%、18.26%和1.12%;土壤呼吸与温度呈极显著的指数相关(P<0.001),与土壤湿度无显著相关;CK,TL、TM和TH处理下,土壤呼吸温度敏感系数Q10分别为4.77、5.71、6.62和5.49,氮沉降处理提高了小兴安岭云冷杉红松林的土壤呼吸速率和温度敏感性。     

Stem respiration is influenced by pruning and girdling in Pinus sylvestris

Abstract

Stem respiration was measured in the growing season (June to July) and in the dormant season (October) to detect cambial activity induced by pruning live branches or girdling stems in Scots pine trees (Pinus sylvestris L.) growing in northern Sweden. Immediately after the treatments, the treatment:control ratio of stem respiration increased to between 1.38 and 1.44 in the pruning treatment and between 1.17 and 1.20 in the girdling treatment. The treatment:control ratio of stem respiration then decreased by the end of July, to 0.65 in the pruning treatment and 0.55 in the girdling treatment. In October, the treatment:control ratios were higher: between 0.87 and 0.97 in the pruning treatment and between 0.85 and 0.97 in the girdling treatment. In both pruning and girdling treatments, the time trends of stem respiration rates largely followed those of stem temperatures: the stem respiration rate increased exponentially with an increase in stem temperature. The Q ₁₀ values were 2.83–4.05 and 2.57–2.89 in the pruning treatment and control, and 2.10–2.60 and 1.99–3.19 in the girdling treatment and control, respectively. In most cases, the values of Q ₁₀ in both treatments did not differ significantly from those in the controls.