Effect of aboveground intervention on fine root mass, production, and turnover rate in a Chinese cork oak (Quercus variabilis Blume) forest

Aims

Fine root is an important part of the forest carbon cycle. The growth of fine roots is usually affected by forest intervention. This study aims to investigate the fine root mass, production, and turnover in the disturbed forest.

Methods

The seasonal and vertical distributions of fine root (diameter ≤2 mm) were measured in a Chinese cork oak (Quercus variabilis Blume) forest. The biomass and necromass of roots with diameters ≤1 mm and 1-2 mm in 0-40 cm soil profiles were sampled by using a sequential soil coring method in the stands after clear cutting for 3 years, with the stands of the remaining intact trees as the control.

Results

The fine root biomass (FRB) and fine root necromass (FRN) varied during the growing season and reached their peak in August. Lower FRB and higher FRN were found in the clear cutting stands. The ratio between FRN and FRB increased after forest clear cutting compared with the control and was the highest in June. The root mass with diameter ≤1 mm was affected proportionately more than that of diameter 1-2 mm root. Clear cutting reduced FRB and increased FRN of roots both ≤1 mm and 1-2 mm in diameter along the soil depths. Compared with the control, the annual fine root production and the average turnover rate decreased by 30.7 % and 20.7 %, respectively, after clear cutting for 3 years. The decline of canopy cover contributed to the dramatic fluctuation of soil temperature and moisture from April to October. With redundancy discriminate analysis (RDA) analysis, the first axis was explained by soil temperature (positive) and moisture (negative) in the control stands. Aboveground stand structure, including canopy cover, sprout height, and basal area, influenced FRB and FRN primarily after forest clear cutting.

Conclusions

This study suggested that the reduction of fine root biomass, production, and turnover rate can be attributed to the complex changes that occur after forest intervention, including canopy damage, increased soil temperature, and degressive soil moisture.     

Effects of long-term temperature and nutrient manipulation on Norway spruce fine roots and mycelia production

Aims and methods

The effects of changing climate on ectomycorrhizal (EcM) fine roots were studied in northern Sweden by manipulating soil temperature for 14 years and/or by fertilizing for 22 years. Fine root biomass, necromass, EcM root tip biomass, morphology and number as well as mycelia production were determined from soil cores and mesh bags.

Results and conclusions

The fine root biomass and necromass were highest in the fertilized plots, following similar trends in the above-ground biomass, whereas the EcM root tip biomass per basal area decreased by 22 % in the fertilized plots compared to the control. Warming increased the fine root biomass, live/dead-ratio and the number of EcM root tips in the mineral soil and tended to increase the production of EcM mycelia. Greater fine root biomass meant more EcM root tips, although the tip frequency was not affected by fertilization or warming. Significantly higher specific root length of EcM root tips indicated an increased need for nutrients in warmed and in unfertilized plots. Better nutrient supply and warmer soil temperature provide a potential to increase the flow of carbon into the soil via increased fine root biomass, but the carbon balance also depends on root turnover.     

Variety specific relationships between effects of rhizobacteria on root exudation,growth and nutrient uptake of soybean

Aims

It has been increasingly recognized that only distal lower order roots turn over actively within the <2 mm fine root system of trees. This study aimed to estimate fine root production and turnover rate based on lower order fine roots and their relations to soil variables in mangroves.

Methods

We conducted sequential coring in five natural mangrove forests at Dongzhai Bay, China. Annual fine root production and turnover rate were calculated based on the seasonal variations of the biomass and necromass of lower order roots or the whole fine root system.

Results

Annual fine root production and turnover rate ranged between 571 and 2838 g m^?2 and 1.46–5.96 yr^?1, respectively, estimated with lower order roots, and they were increased by 0–30 % and reduced by 13–48 %, respectively, estimated with the whole fine root system. Annual fine root production was 1–3.5 times higher than aboveground litter production and was positively related to soil carbon, nitrogen and phosphorus concentrations. Fine root turnover rate was negatively related to soil salinity.

Conclusions

Mangrove fine root turnover plays a more important role than aboveground litter production in soil C accumulation. Sites with higher soil nutrients and lower salinity favor fine root production and turnover, and thus favor soil C accumulation.

     

Fine root and litterfall dynamics of three Korean pine (Pinus koraiensis) forests along an altitudinal gradient

Background and aims

Fine root and aboveground litterfall, two large fluxes of nutrients and carbon in the forest ecosystems, are key processes to be considered in efforts of measuring, modeling and predicting soil carbon sequestration.

Methods

We used sequential coring and litter trap to measure seasonal dynamics of fine root and litterfall in three Korean pine dominated forests along an altitudinal gradient in the Changbai Mountain during the 2012 growing season.

Results

Fine root biomass decreased significantly while necromass increased remarkably with altitude. Patterns and amounts of fine root production and mortality varied among forest types. Litterfall decreased significantly with altitude, whereas forest floor mass increased. Carbon inputs through fine root mortality and litterfall decreased significantly with altitude while carbon storage of fine root mass did not differ among forest types and carbon storage of forest floor mass was significantly larger in higher altitudinal forests due to lower turnover rates.

Conclusions

This study provided an insight into the variations of fine root and litterfall dynamics among three Korean pine forests which were associated with different vegetation traits and environmental conditions, and also the quantification of carbon fluxes through fine root mortality and litterfall for estimating carbon budget of temperate forest.     

Fine root biomass and turnover of two fast-growing poplar genotypes in a short-rotation coppice culture

Background and aims

The quantification of root dynamics remains a major challenge in ecological research because root sampling is laborious and prone to error due to unavoidable disturbance of the delicate soil-root interface. The objective of the present study was to quantify the distribution of the biomass and turnover of roots of poplars (Populus) and associated understory vegetation during the second growing season of a high-density short rotation coppice culture.

Methods

Roots were manually picked from soil samples collected with a soil core from narrow (75 cm apart) and wide rows (150 cm apart) of the double-row planting system from two genetically contrasting poplar genotypes. Several methods of estimating root production and turnover were compared.

Results

Poplar fine root biomass was higher in the narrow rows than in the wide rows. In spite of genetic differences in above-ground biomass, annual fine root productivity was similar for both genotypes (ca. 44 g DM m^?2 year^?1). Weed root biomass was equally distributed over the ground surface, and root productivity was more than two times higher compared to poplar fine roots (ca. 109 g DM m^?2 year^?1).

Conclusions

Early in SRC plantation development, weeds result in significant root competition to the crop tree poplars, but may confer certain ecosystem services such as carbon input to soil and retention of available soil N until the trees fully occupy the site.     

Biomass of extramatrical ectomycorrhizal mycelium and fine roots in a young Norway spruce stand — a study using ingrowth bags with different substrates

Background and aims

The partitioning of below ground carbon inputs into roots and extramatrical ectomycorrhizal mycelium (ECM) is crucial for the C cycle in forest soils. Here we studied simultaneously the newly grown biomass of ECM and fine roots in a young Norway spruce stand.

Methods

Ingrowth mesh bags of 16 cm diameter and 12 cm height were placed in the upper soil and left for 12 to 16 months. The 2 mm mesh size allowed the ingrowth of fungal hyphae and roots whereas a 45 μm mesh size allowed only the ingrowth of hyphae. The mesh bags were filled with either EA horizon soil, pure quartz sand or crushed granite. Controls without any ingrowth were established for each substrate by solid tubes (2010) and by 1 μm mesh bags (2011). The fungal biomass in the substrates was estimated by the PLFA 18:2ω6,9 and ECM biomass was calculated as difference between fungal biomass in mesh bags and controls.

Results

The maximum ECM biomass was 438 kg ha^?1 in October 2010 in 2 mm mesh bags with EA substrate, and the minimum was close to zero in 2011 in 45 μm mesh bags with quartz sand. The high P content of the crushed granite did not influence the ECM biomass. Fine root biomass reached a maximum of 2,343 kg ha^?1 in October 2010 in mesh bags with quartz sand after 16 months exposure. In quartz sand and crushed granite, ECM biomass correlated positively with fine root biomass and the number of root tips, and negatively with specific root length.

Conclusion

The ratio of ECM biomass/fine root biomass in October ranged from 0.1 to 0.3 in quartz sand and crushed granite, but from 0.7 to 1.8 in the EA substrate. The results for the EA substrate suggest a large C flux to ECM under field conditions.     

Factors controlling decomposition rates of fine root litter in temperate forests and grasslands

Background and aims

Fine root decomposition contributes significantly to element cycling in terrestrial ecosystems. However, studies on root decomposition rates and on the factors that potentially influence them are fewer than those on leaf litter decomposition. To study the effects of region and land use intensity on fine root decomposition, we established a large scale study in three German regions with different climate regimes and soil properties. Methods In 150 forest and 150 grassland sites we deployed litterbags (100 μm mesh size) with standardized litter consisting of fine roots from European beech in forests and from a lowland mesophilous hay meadow in grasslands. In the central study region, we compared decomposition rates of this standardized litter with root litter collected on-site to separate the effect of litter quality from environmental factors.

Results

Standardized herbaceous roots in grassland soils decomposed on average significantly faster (24?±?6 % mass loss after 12 months, mean ± SD) than beech roots in forest soils (12?±?4 %; p?Conclusions Grasslands, which have higher fine root biomass and root turnover compared to forests, also have higher rates of root decomposition. Our results further show that at the regional scale fine root decomposition is influenced by environmental variables such as soil moisture, soil temperature and soil nutrient content. Additional variation is explained by root litter quality.     

Fine root production in three zones of secondary mangrove forest in eastern Thailand

Key message

High root productions, especially in the fine roots, estimated by ingrowth cores were confirmed in mangrove forests. The zonal variation in root production was caused by inundation regime and soil temperature.

Abstract

Mangrove forests have high net primary productivity (NPP), and it is well known that these trees allocate high amounts of biomass to their root systems. In particular, fine root production (FRP) comprises a large component of the NPP. However, information on root production remains scarce. We studied FRP in three zones (Avicennia, Rhizophora, and Xylocarpus) of a mangrove forest in eastern Thailand using ingrowth cores (0–30 cm of soil depth). The root biomass and necromass were periodically harvested from the cores and weighed during the one-year study. The FRP was determined by summation of the fine root biomass (FRB) and root necromass. The results showed that the FRB clearly increased in the wet and cool dry seasons. Magnitude of FRB in the Rhizophora and Xylocarpus zones was 1171.07 and 764.23 g/m²/30 cm, respectively. The lowest FRB (292.74 g/m²/30 cm) was recorded in the Avicennia zone locating on the river edge where there is a greater frequency of inundation than the other zones. Root necromass was high in the Rhizophora and Xylocarpus zones, and accumulated noticeably when soil temperatures rapidly declined during the middle of the wet season to cool dry season. However, root necromass in the Avicennia zone varied within a small range. We attributed the small accumulation of root necromass in the Avicennia zone to the relative high soil temperature that likely caused a high root decomposition rate. The average FRP (3.403–4.079 ton/ha/year) accounted for 74.4, 81.5, and 92.4 % of the total root production in the Avicennia, Rhizophora, and Xylocarpus zone, respectively. The root production and causative factors (i.e., soil temperature and inundation regime) are discussed in relation to the carbon cycle of a mangrove forest.

     

Effects of irrigation on the soil CO2 efflux from different poplar clone plantations in arid northwest China

Aims

Soil respiration in forest plantations can be greatly affected by management practices such as irrigation. In northwest China, soil water is usually a limiting factor for the development of forest plantations. This study aims to examine the effects of irrigation intensity on soil respiration from three poplar clone plantations in this arid area.

Methods

The experiment included three poplar clones subjected to three irrigation intensities (without, low and high). Soil respiration was measured using a Li-6400-09 chamber during the growing season in 2007.

Results

Mean soil respiration rates were 2.92, 4.74 and 3.49 μmol m^?2 s^?1 for control, low and high irrigation treatments, respectively. Soil respiration decreased once soil water content was below a lower (14.8 %) or above an upper (26.2 %) threshold. When soil water content ranged from 14.8 % to 26.2 %, soil respiration increased and correlated with soil temperature. Fine root also played a role in the significant differences in soil CO₂ efflux among the three treatments. Furthermore, the three poplar hybrid clones responded differently to irrigation regarding fine root production and soil CO₂ efflux.

Conclusions

Irrigation intensity had a strong impact on soil respiration of the three poplar clone plantations, which was mainly because fine root biomass and microbial activities were greatly influenced by soil water conditions. Our results suggest that irrigation management is a main factor controlling soil carbon dynamics in forest plantation in arid regions.     

Fine-root turnover rates of European forests revisited: an analysis of data from sequential coring and ingrowth cores

Background and Aims

Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values.

Methods

We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature.

Results

Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0.86 yr^?1 for Fagus sylvatica and 0.88 yr^?1 for Picea abies when maximum biomass data were used for the calculation, and 1.11 yr^?1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula.

Conclusions

We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting.     

Root traits and soil properties in harvested perennial grassland,annual wheat,and never-tilled annual wheat

Background and aims

Root functional traits are determinants of soil carbon storage; plant productivity; and ecosystem properties. However, few studies look at both annual and perennial roots, soil properties, and productivity in the context of field scale agricultural systems.

Methods

In Long Term and Conversion studies in North Central Kansas, USA; root biomass and length, soil carbon and nitrogen, microbial biomass, nematode and micro-arthropod communities were measured to a depth of one meter in paired perennial grassland and cropland wheat sites as well as a grassland site that had been converted to cropland using no tillage five years prior.

Results

In the Long Term Study root biomass was three to seven times greater (9.4 Mg ha^?1 and 2.5 Mg ha^?1 in May), and root length two times greater (52.5 km m^?2 and 24.0 km m^?2 in May) in perennial grassland than in cropland. Soil organic carbon and microbial biomass carbon were larger, numbers of Orbatid mites greater (2084 vs 730 mites m^?2), and nematode communities more structured (Structure Index 67 vs 59) in perennial grassland versus annual cropland. Improved soil physical and biological properties in perennial grasslands were significantly correlated with larger, deeper root systems. In the Conversion Study root length and biomass, microbial biomass carbon, mite abundance and nematode community structure differed at some but not all dates and depths. Isotope analysis showed that five years after no-till conversion old perennial roots remained in soils of annual wheat fields and that all soil fractions except coarse particulate organic matter were derived from C₄ plants.

Conclusions

Significant correlation between larger, longer roots in grasslands compared to annual croplands and improved soil biological, physical and chemical properties suggest that perennial roots are an important factor allowing perennial grasslands to maintain productivity and soil quality with few inputs. Perennial roots may persist and continue to influence soil properties long after conversion to annual systems.     

Root dynamics of Carex stricta-dominated tussock meadows

Background and aims

The roots of tussock-forming plants contribute to the formation of microtopographic features in many ecosystems, but the dynamics of such roots are poorly understood. We examined the spatial heterogeneity of tussock fine root dynamics to investigate allocation patterns and the role of root productivity in the persistence of tussock structures.

Methods

We compared the spatial variability of fine root (<1 mm, 1–2 mm) density, biomass, % live, allocation, turnover rate (using bomb 14C), and productivity of four Carex stricta Lam.-dominated tussock meadows in the upper Midwest, USA (3 reference, 1 restored site).

Results

Relative to underlying microsites, tussocks were warm, dry, and high in root density, productivity, % live biomass, and turnover. Root productivity averaged 649 g?m^?2 yr^?1 (±208) in reference sites, comprised 57 % (±10) of total net production, and was concentrated in tussocks (70 %?±?4). Root turnover rate averaged 0.63 yr^?1 (±0.08), but tussocks had ~50 % faster root turnover than the underlying soil, and <1 mm roots turned over ~40 % faster than 1–2 mm roots.

Conclusions

Our detailed analysis of the spatial heterogeneity of tussock root dynamics suggests that high allocation and elevated turnover of tussock roots facilitates organic matter accumulation and tussock persistence over time.     

An optimized fine root sampling methodology balancing accuracy and time investment

Aims

Tree roots are spatially highly heterogeneous and it thus requires large numbers of samples to detect statistically significant changes in root biomass. The objectives of this study were to understand and quantify the sources of error in the assessment of fine root biomass (<2 mm) during the second year of a high-density Populus plantation.

Methods

Soil cores were collected in winter (n?=?35) and in summer (n?=?20), and fine roots were picked by hand for varying lengths of time: 1, 2, 5, 20, 40, and 60 min. The root biomass data were used to identify the best combination of the time spent for root picking and the number of samples collected, that minimizes the overall uncertainty (i.e. the combination of the spatial error due to the incomplete sampling and the temporal error due to the incomplete core processing).

Results

On average, 25 min was enough time to pick 90 % of the fine root biomass in winter, while in summer only 10 min were needed. In winter fewer samples were needed, but more time for picking was necessary as compared to summer when root biomass was higher.

Conclusions

Fine root sampling can be optimized by minimizing the uncertainty of the biomass estimates and simultaneously decreasing root sampling time investment.     

Fine root turnover and litter production of Norway spruce in a long-term temperature and nutrient manipulation experiment

Background and aims

Increased soil temperature and nutrient availability enhance soil biological activity. We studied how these affect fine root growth and survival, i.e. below-ground litter production, in relation to above-ground foliage litter production of Norway spruce (Picea abies (L.) Karst.).

Methods

The treatments, irrigation (I), soil warming + irrigation (WI), fertilization + irrigation (FI) and soil warming + fertilization + irrigation (WFI) were started in 1987 (F, I) and in 1995 (W). The annual production of fine root litter was estimated from minirhizotrons (survival) and soil-cores (biomass) and the annual above-ground litter production from litter traps.

Results and conclusions

The number and elongation of fine roots tended to be higher in WI and I compared to the other treatments, which may indicate nutrient shortage. Fine roots in the WFI treatment had the lowest median longevity and from three to fourfold higher below-ground litter production compared to WI, FI or I - higher soil temperature increased the litter input particularly into the mineral soil. Only fertilization increased the above-ground litter production. As warmer and more nutrient-rich soil significantly shortened the fine root lifespan and increased the litter input, the storage of carbon in boreal forest soil may increase in the future.     

Standing fine root mass and production in four Chinese subtropical forests along a succession and species diversity gradient

Background and aims

The influences of succession and species diversity on fine root production are not well known in forests. This study aimed to investigate: (i) whether fine root biomass and production increased with successional stage and increasing tree species diversity; (ii) how forest type affected seasonal variation and regrowth of fine roots.

Methods

Sequential coring and ingrowth core methods were used to measure fine root production in four Chinese subtropical forests differing in successional stages and species diversity.

Results

Fine root biomass increased from 262 g·m^?2 to 626 g·m^?2 with increasing successional stage and species diversity. A similar trend was also found for fine root production, which increased from 86 to 114 g·m^?2 yr ^?1 for Cunninghamia lanceolata plantation to 211–240 g·m^?2 yr ^?1 for Choerospondias axillaries forest when estimated with sequential coring data. Fine root production calculated using the ingrowth core data ranged from 186 g·m^?2 yr ^?1 for C. lanceolata plantation to 513 g·m^?2 yr ^?1 for Lithocarpus glaber – Cyclobalanopsis glauca forest.

Conclusions

Fine root biomass and production increased along a successional gradient and increasing tree species diversity in subtropical forests. Fine roots in forests with higher species diversity exhibited higher seasonal variation and regrowth rate.     

Relation of fine root distribution to soil C in a Cunninghamia lanceolata plantation in subtropical China

Background and aims

Growth and distribution of fine roots closely depend on soil resource availability and affect soil C distribution in return. Understanding of relationships between fine root distribution and soil C can help to predict the contribution of fine root turnover to soil C accumulation.

Methods

A study was conducted in a subtropical Cunninghamia lanceolata plantation to assess the fine root mass density (FRMD), fine root C density (FRCD) of different fine root groups as well as their relations with soil C.

Results

The FRMD and FRCD of short-lived roots, dead roots and herb roots peaked in the 0–10 cm soil layer and decreased with soil depth, while FRMD, FRCD of long-lived roots peaked in the 10–20 cm soil layer. Soil C was positively related to FRMD and FRCD of total fine roots (across all three soil layers), dead roots (0–10 cm) and herb roots (10–20 cm) as well as FRCD of short-lived roots (20–40 cm) (P <0.05).

Conclusions

Soil C was mainly affected by herb roots in upper soil layers and by woody plant roots in deeper soil layers.     

Variation of carbon age of fine roots in boreal forests determined from 14C measurements

Background and aims

The main objectives of this study were to determine how the carbon age of fine root cellulose varies between stands, tree species, root diameter and soil depth. In addition, we also compared the carbon age of fine roots from soil cores of this study with reported values from the roots of the same diameter classes of ingrowth cores on the same sites.

Methods

We used natural abundance of ¹⁴C to estimate root carbon age in four boreal Norway spruce and Scots pine stands in Finland and Estonia.

Results

Age of fine root carbon was older in 1.5–2 mm diameter fine roots than in fine roots with <0.5 mm diameter, and tended to be older in mineral soil than in organic soil. Fine root carbon was older in the less fertile Finnish spruce stands (11–12 years) than in the more fertile Estonian stand (3 and 8 years), implying that roots may live longer in less fertile soil. We further observed that on one of our sites carbon in live fine roots with the 1.5–2 mm diameter was of similar C age (7–12 years) than in the ingrowth core roots despite the reported root age in the ingrowth cores – being not older than 2 years.

Conclusions

From this result, we conclude that new live roots may in some cases use old carbon reserves for their cellulose formation. Future research should be oriented towards improving our understanding of possible internal redistribution and uptake of C in trees.     

Effects of drip irrigation on deep root distribution, rooting depth, and soil water profile of jujube in a semiarid region

Aims

Aimed to understand how soil water was depleted by deep roots, the effects of drip irrigation and stand age on the deep root distribution, rooting depth, and soil water profile dynamics were investigated in a jujube (Ziziphus jujube Mill. CV. Lizao) plantation.

Methods

A soil coring method with a LuoYang shovel was used for sampling until no more roots were found.

Results

It showed that the maximum fine rooting depth (<2 mm in diameter) increased with stand age and it extended deep into the soil rapidly during the first 4 years, but more slowly in the subsequent 4 years. The maximum rooting depth reached 5 m in a 9-year-old jujube plantation, but it stabilized and did not increase thereafter. However, it was 10 m in a 12-year-old jujube plantation that lacked irrigation.

Conclusions

We found that the application of 33.3 mm of irrigation water (equivalent to 7 % of the local annual precipitation) could halve the maximum rooting depth, thereby reducing deep soil water depletion. Our results showed that a low-volume water supply reduced the maximum rooting depth in jujube and prevented the depletion of the deep soil water. Appropriate drip irrigation is an effective water management strategy for sustainable artificial forest development in semiarid regions.     

Fine root turnover of Japanese white birch (<Emphasis Type="Italic">Betula platyphylla</Emphasis> var. <Emphasis Type="Italic">japonica</Emphasis>) grown under elevated CO<Subscript>2</Subscript> in northern Japan

Key message

Elevated CO ₂ reduced fine root dynamics (production and turnover) of white birch seedlings, especially grown in volcanic ash soil compared with brown forest soil.

Abstract

Increased atmospheric CO₂ usually enhances photosynthetic ability and growth of trees. To understand how increased CO₂ affects below-ground part of trees under varied soil condition, we investigated the responses of the fine root (diameter <2 mm) dynamics of Japanese white birch (Betula platyphylla var. japonica) which was planted in 2010. The three-year-old birch seedlings were grown in four experimental treatments comprising two levels of CO₂, i.e., ambient: 380–390 and elevated: 500 μmol mol^?1, in combination with two kinds of soil: brown forest (BF) soil and volcanic ash (VA) soil which has few nutrients. The growth and turnover of fine roots were measured for 3 years (2011–2013) using the Mini-rhizotron. In the first observation year, live fine root length (standing crop) in BF soil was not affected by CO₂ treatment, but it was reduced by the elevated CO₂ from the second observation year. In VA soil, live fine root length was reduced by elevated CO₂ for all 3 years. Fine root turnover tended to decrease under elevated CO₂ compared with ambient in both soil types during the first and second observation years. Turnover of fine root production and mortality was also affected by the two factors, elevated CO₂ and different soil types. Median longevity of fine root increased under elevated CO₂, especially in VA soil at the beginning, and a shorter fine root lifespan appeared after 2 years of observation (2011–2012). These results suggest that elevated CO₂ does not consistently stimulate fine root turnover, particularly during the plant seedlings stage, as it may depend on the costs and benefits of constructing and retaining roots. Therefore, despite the other uncontrollable environment factors, carbon sequestration to the root system may be varied by CO₂ treatment period, soil type and plant age.

     

帽儿山温带落叶阔叶林细根生物量、生产力和周转率

细根在森林生态系统能量流动与物质循环中占有重要地位,但其生物量、生产和周转测定尚存在很大的不确定性,而且局域尺度空间变异机制尚不清楚。本研究分析了帽儿山温带天然次生林活细根生物量和死细根生物量在0～100 cm剖面的垂直分布与0～20 cm细根的季节动态、生产力和周转率,对比了采用连续根钻法(包括决策矩阵法和极差法)和内生长袋(直径3和5 cm)估测细根生产力和细根周转率,并探讨了可能影响细根的林分因子。结果表明: 76.8%的活细根生物量和62.9%的死细根生物量均集中在0～20 cm土层,随着深度增加,二者均呈指数形式减少。活细根生物量和死细根生物量的季节变化不显著,可能与冬季几乎无降雪而夏季降雨异常多有关。2种直径内生长袋估计的细根生产力无显著差异;对数转换后决策矩阵、极差法和内生长法估计的细根生产力和细根周转率差异显著。随着土壤养分增加,活细根生物量和死细根生物量比值显著增加,死细根生物量显著减少,但活细根生物量、细根生产力和细根周转率均无显著变化;细根周转率与前一年地上木质生物量增长量呈显著正相关,但与当年地上木质生物量增长量无显著相关关系。