Live Fine Roots Research Articles

Shifts in belowground processes along a temperate forest edge

ContextForests are increasingly fragmented, and as a result most forests in the United States are within one km of an edge. Edges change environmental conditions of the forest—especially radiation, roughness, temperature, and moisture—that can have consequences for plant productivity and ecosystem functions. However, edge effects on aboveground characteristics of plants and the environment are better understood relative to plant roots and soil in the belowground environment.ObjectivesOur main objectives were to determine if soil C pools and fluxes are higher at the edge relative to other landscape positions, and to understand how specific belowground processes contribute to bulk differences in pools and fluxes.MethodsWe measured environmental conditions, live and dead fine root traits, soil chemistry, and soil respiration along a 75 m transect from interior forest to meadow in Gaithersburg, MD.ResultsWe observed differences in the soil chemical, biological and hydrological environment between the forest interior, edge and adjacent meadow. In some cases, the forest edge represented a mid-point in environmental or belowground characteristics between the forest interior and meadow (e.g., pH, C-to-N ratio [C:N], live fine root biomass, heterotrophic respiration), likely reflecting the change in litter type and quality associated with the transition from grass to woody species. In other cases, neighboring landscape positions were different from the forest edge, which was drier and had higher dead fine root biomass. Although soil C contents were not significantly different across landscape positions, there was a tendency towards higher average soil C content at the edge relative to other landscape positions, suggesting that increased C loss related to root decay and greater soil respiration at the edge relative to the forest interior may have been offset by increased C gain from high plant productivity and subsequent inputs to soil.ConclusionsThis research provides insight into how forest edge environments may differ from the interior and how concurrent processes above- and belowground may contribute to those differences.

Effects of long-term nitrogen addition on fine root dynamics in a temperate natural secondary forest

ABSTRACT In order to study the response of fine root production (FRP), mortality (FRM) and turnover (FRT) to nitrogen (N) addition, we have conducted 12 years of continuous N addition experiments in the natural secondary forest in Northeast China. According to the local N deposition, three N treatments were set up. The response of FRP, FRM and FRT to N addition during the growing season was studied. The results showed that N addition would lead to phosphorus (P) limitation, and fine roots could increase the absorption of N and P by increasing their diameter. The increase in the diameter of fine roots led to a decrease in the FRT, and the soil layer also affected the FRT. Nitrogen addition increased the FRP and FRM in all soil layers. Nitrogen addition did not change the seasonal variation of FRP and FRM. The highest value of FRP occurred in May, and the lowest value of FRM occurred in August. Nitrogen addition increased the total number (TNLR) and surface area (TSALR) of live fine root in all soil layers. The TNLR and TSALR decreased with the deepening of soil layer. Collectively, fine roots may respond to environmental stress through self-regulation and changing growth strategies.

Dynamics of spatial and temporal growth of the root system of grapevine (Vitis vinifera L.) under nitrogen levels in sandy soil in subtropical climate

• N addition promotes the increase in the surface area of live fine roots. • Fine root production is higher in grapevine flowering stage. • N concentration in leaves is promoted by the increase in the fine roots. • Total number of dead and mortality of fine roots is increased by the addition of N. Nitrogen (N) supply to the soil via fertilization can influence important processes of the root system growth, which can increase N uptake and, consequently, the shoot growth. In this context, the study aimed to evaluate how the application of N levels can affect the dynamics of spatial and temporal growth of the root system of grapevines ( Vitis vinifera L.) in sandy soil and subtropical climate. ‘Alicante Bouschet’ grapevines, grafted on ‘Paulsen 1103’ rootstock, implanted in 2011. The N addition were: Low N: control (without the N addition; 0 kg N ha −1 year −1 ); Medium N (40 kg N ha −1 year −1 ); and High N (100 kg N ha −1 year −1 ). The study was carried out during 2016/17 and 2017/18 crop seasons. N concentration in the leaves and morphological parameters of fine roots were evaluated using the minirhizotron technique. The addition of Medium N and High N significantly increased the values ​​of the total surface area of ​​live fine roots and the total number of live and dead fine roots, at 0-20, 20-40 and 40-60 cm soil depth, in both crop seasons evaluated. The addition of Medium N and High N also directly influenced the production rates of live fine roots, with patterns of seasonal changes, especially increased in the flowering stage of the grapevines. This occurs due to the increase in the physiological demand of growing plant tissues, such as new roots, leaves and fruits.

Effects of Excess Nitrogen (N) on Fine Root Growth in Tropical Forests of Contrasting N Status

Elevated nitrogen (N) deposition may further acidify soils in tropical forests. Yet, we have limited evidence on this prediction and it remained unclear how this would affect fine root growth therein. Here, we report responses of fine root biomass, vitality, and chemistry, as well as related soil parameters to eight years of N additions in three tropical forests different in initial soil N status, with one primary forest being N-saturated, and another two younger forests (one secondary forest and one planted forest) less N-rich. Results showed that in the primary forest, fine root biomass decreased and fine root necromass increased following N addition, resulting in lower live fine root proportion (fine root vitality). Declining fine root vitality was associated with fine root Fe accumulation and soil acidification indicated by regression analysis. These alterations of fine root growth and chemistry co-occurred with soil pH decline, soil exchangeable Fe3+ mobilization, exchangeable Ca2+, and Mg2+ depletion after N treatments in the primary forest. In contrast, N addition only elevated fine root K, Al, and Fe content in the secondary forest. In the planted forest, moderate but significant decreases in soil pH, soil exchangeable K+, and Mg2+ were found after N treatment, with fine root biomass negatively correlated with soil exchangeable Al3+ and Al3+/(Ca2+ + Mg2+) ratio. Our results suggested that long-term N fertilization may negatively affect fine root growth, via severed soil acidification, Fe mobilization, and base cation depletion in highly acidified, N-saturated primary tropical forests. Initial forest N status, influenced by different land-use history, mediates N deposition effects on fine root growth.

Intensive plantations decouple fine root C:N:P in subtropical forests

Fine roots play key roles in carbon and nutrient cycling in terrestrial ecosystems. Despite the global conversion of natural forests to tree plantations, a quantitative evaluation of the dynamics of fine root nutrients and C:N:P stoichiometry in plantations and natural forests is lacking. This study examined the fine root elemental concentrations and C:N:P stoichiometry of Chinese fir plantations and natural secondary forests (5–41 years old), employing primary forests as a reference. Live fine root C, N, P and K concentrations did not differ with forest types, but live fine roots had lower Ca and Mg concentrations in plantations than natural secondary and primary forests. Dead roots contained higher N, P, and Mg in plantations than in natural forests. Live and dead fine root elemental concentrations and C:N:P stoichiometry did not change with stand age, except for a decrease in dead root Ca and Mg concentrations in 19–31-year-old stands. Live root C:N, C:P, and N:P ratios did not differ between forest types; however, dead root C:N, C:P, and N:P ratios were higher in natural forests than in plantations. Our findings suggest that intensively managed forest monoculture plantations have a negative impact on the resorption proficiency of fine root nutrients and decouple the C:N:P of fine roots in subtropical forests. We recommend reducing fertilization and increasing plant diversity in plantations to optimize the C:N:P of plants.

Monoculture or Mixed Culture? Relevance of Fine Root Dynamics to Carbon Sequestration Oriented Mangrove Afforestation and Restoration

Fine root dynamics have the potential to contribute to ecosystem biogeochemical cycling, especially for carbon. This is particularly true in mangroves which are the most productive and carbon-rich ecosystems of the world. However, few studies comprehensively evaluated the contribution of mangrove fine root dynamics to soil organic carbon accumulation. In southern China, while the introduced fast-growing Sonneratia apetala and native shrubby Kandelia obovata have been widely used in mangrove reforestation/afforestation programs since the mid-1980s, their implications and ecosystem services are still unclear. Here we show distinct differences in fine root dynamic among 12-year-old S. apetala, K. obovata monocultures, and their mixed stand using root coring, ingrowth core, and intact-core methods. Soil organic carbon storage was examined by soil coring method. One-year observation showed significant differences among the three mangrove plantations in fine root biomass, necromass, turnover rate, and decomposition decay rate constant. Soil organic carbon stock was 15.8 ± 0.8, 7.8 ± 0.5, and 11.9 ± 1.6 Mg C ha–1 for K. obovata, S. apetala monocultures and their mixed stand, respectively. Live fine root biomass, fine root necromass, annual fine root production and fine root mass decay rate constant are significantly correlated to soil organic carbon content across plantations. We suggest that mangrove fine root dynamics were mainly affected by soil nutrient conditions and species composition. Mixed stands may not have higher soil organic carbon storage than monocultures. The functional trait of different mangrove species is responsible to determine the carbon storage function of mixed stands. Fine roots play an important role in carbon storage, and fine root dynamics have a significant effect on carbon sequestration in mangrove ecosystems. The shrubby native K. obovata had a higher potential for belowground carbon sequestration and storage than the tall introduced S. apetala.

Fine root production and nutrient dynamics in relation to stand characteristics of chir pine mixed banj oak forests in central Himalaya

Stand density and basal area are considered to be an important indicator of aboveground as well as belowground dynamics in forests. To understand the relationship between stand characteristics and fine root dynamics of chir pine (Pinus roxburghii) mixed banj oak (Quercus leucotrichophora) forests in central Himalaya we studied fine root mass, productivity, turnover rate and nutrient dynamics. Four sites were selected on the basis of increasing density and basal area of trees. From each site, ten random fine root samples were collected for one year by sequential coring method, using root corer of 8.0 cm diameter from three depths (0–10, 10–20 and 20–30 cm) on a monthly basis. Total mean fine root mass varied from 2.15 to 3.12 Mg ha−1, with biomass and necromass varying from 1.48 to 1.93 Mg ha−1 and 0.67 to 1.18 Mg ha−1, respectively. In terms of vertical distribution, values of both biomass and necromass decreased with increasing soil depth. Productivity was estimated between 1.24 and 1.51 Mg ha−1 y−1 while turnover rate varied from 0.78 to 0.84 y−1 throughout the sites. Concentration of nitrogen was found higher in live fine roots whereas, phosphorus, potassium and calcium did not show any significant variation between live and dead fine roots. In the present study, higher fine root mass upon increase in density and basal area of trees suggests that stand characteristics positively correlate with fine root mass while nutrient dynamics remain unaffected by stand characteristics as well as seasonal changes.

In-situ measurement of the effect of canopy tree fine roots on nitrogen availability in forest soil

Plant fine roots affect the amount of soil inorganic nitrogen (N) via their N uptake and their effects on organic matter decomposition and N mineralization. However, the effects of the fine roots of canopy trees on N availability in forest soil remain largely unknown owing to the limitations of in-situ measurements. Therefore, to reveal the effects of the fine roots of canopy trees on forest soil N availability, we developed a novel in-situ method that combines a modified in-situ resin-core method, using live fine roots, with a tree N demand estimation, using the N-balance method. Furthermore, we measured soil extracellular enzyme activities in the rhizosphere and bulk soils to determine whether fine roots stimulate soil enzyme activities. The results showed that soil enzyme activities were stimulated by the fine roots of canopy trees, especially in the rhizosphere, and this indicates that fine roots stimulate organic matter decomposition and N mineralization. However, fine roots had no significant effect on either the pool size or leaching of inorganic N. The estimated amount of potential N uptake by fine roots was greater than the amount of inorganic N released via fine root-induced N mineralization. Overall, our results indicate that almost all of the fine root-induced increment of mineralized inorganic N is taken up by the fine roots; thus, the fine roots of canopy trees did not affect N availability in forest soil. This study was limited by the fact that the fine roots in the resin cores were less dense than natural roots, and the fact that the actual root N uptake can differ from the estimated N uptake; these limitations should be resolved in future studies. Nevertheless, the proposed method can be used to investigate the effects of fine roots on the N cycle in forest soil under field conditions considering N uptake and priming.

Variation in Fine Root Characteristics and Nutrient Dynamics Across Alaskan Ecosystems

Carbon cycle perturbations in high-latitude ecosystems associated with rapid warming can have implications for the global climate. Belowground biomass is an important component of the carbon cycle in these ecosystems, with, on average, significantly more vegetation biomass belowground than aboveground. Large quantities of dead root biomass are also in these ecosystems owing to slow decomposition rates. Current understanding of how live and dead root biomass carbon pools vary across high-latitude ecosystems and the environmental conditions associated with this variation is limited due to the labor- and time-intensive nature of data collection. To that end, we examined patterns and factors (abiotic and biotic) associated with the variation in live and dead fine root biomass (FRB) and FRB carbon (C), nitrogen (N) and phosphorus concentrations for 23 sites across a latitudinal gradient in Alaska, spanning both boreal forest and tundra biomes. We found no difference in the live or dead FRB variables between these biomes, despite large differences in predominant vegetation types, except for significantly higher live FRB C:N ratios in boreal sites. Soil C:N ratio, moisture, and temperature, along with moss cover, explained a substantial portion of the dead:live FRB ratio variability across sites. We find all these factors have negative relationships with dead FRB, while having positive or no relationship with live FRB. This work demonstrates that FRB does not necessarily correlate with aboveground vegetation characteristics, and it highlights the need for finer-scale measurements of abiotic and biotic factors to understand FRB landscape variability now and into the future.

Vertical distribution and production of fine roots in an old-growth forest, Japan

Fine roots (≤ 2 mm in diameter) account for up to 50% of total net primary production in forests, representing a major flow of both carbon and nutrients into the soil. We investigated the vertical distribution and production of fine roots in a warm temperate old-growth evergreen broadleaved forest in southwestern Japan. We used a continuous inflow method that considered different rates of diameter-dependent root mortality, decomposition, and thickening. Fine roots were classified into two classes (≤ 1 mm and 1–2 mm diameter). The experiment was conducted over a 1-year period to collect data on the mass of live fine roots and mass of dead fine roots in January, May, November and the following January. Decomposition ratios were assessed for three intervals (January to May, May to November, and November to January). More than 70% of fine roots occurred in the 0–20 cm soil layer, and less than 4% were found in the 50–80 cm soil layer. Decomposition ratios varied seasonally in both root size classes, peaking in summer and reaching a minimum in winter. The same pattern was found for production, mortality, and decomposition. The peak rate of production was 1.62 g·m–2·day–1 in ≤ 1 mm and 0.63 g·m-2·day–1 in 1–2 mm fine roots. The lowest production was 0.62 g·m–2·day–1 in ≤ 1 mm and 0.38 g·m–2·day–1 in 1–2 mm fine roots. Total fine root production over a 1-year period was 6.61 t·ha–1. A mass of 2.70 t·ha–1yr–1 of dead fine roots was decomposed to return nutrients to the soil. It is concluded that a warm temperate old-growth evergreen broadleaved forest in southwestern Japan plays an important role in carbon cycle and nutrient return through a high amount of production and decomposition.

The scaling of fine root nitrogen versus phosphorus in terrestrial plants: A global synthesis

AbstractLeaves and roots may differ in nitrogen (N), phosphorus (P) and N:P stoichiometry, which can influence plant growth and ecosystem functioning. As compared to leaves, however, relatively little is known about the N versus P scaling relationship and N:P stoichiometry in root systems, particularly in fine roots.We used a global dataset comprising 1,890 observations for a total of 763 terrestrial plant species in 123 families (spanning 433 sites world‐wide) to examine live fine root N and P concentrations and stoichiometry, and to determine the scaling of N versus P within and across different plant groups and ecosystems.The global geometric mean values of fine root N and P concentrations and N:P ratios were 10.84 mg/g, 0.94 mg/g and 11.55, respectively. Fine root N and P concentrations and N:P ratios varied both within and across plant groups and ecosystems. A 0.82‐power law described the scaling of fine root N with respect to P across the entire dataset and for major plant phylogenetic and functional groups; however, the numerical value of the N versus P scaling exponent declined from the tropics to higher latitudes and varied significantly at different local sites. Soil nutrient account for much of the variation observed in the scaling of fine root N versus P concentration at different local sites.This study advances our knowledge about limiting resource allocation strategies in below‐ground organs and has important implications for modelling plant growth at local, regional and global levels.A freePlain Language Summarycan be found within the Supporting Information of this article.

Abiotic and biotic factors controlling fine root biomass, carbon and nutrients in closed-canopy hybrid poplar stands on post-agricultural land

Fine roots (diameter <2 mm) have a pivotal role in resource acquisition, symbiosis development, and for elemental cycling in forests. Various abiotic and biotic factors affect their biomass and nutrient content. Understanding the effect of these factors on root traits could improve biogeochemical modelling, nutrient management and ecosystem services provision in planted forests. Data from 14-year old poplars planted along a fertility/climatic gradient in Southeastern Canada, show that live fine root biomass varied with genotype and environment, was negatively correlated to soil fertility, and uncorrelated to tree size. Dead fine root biomass varied with genotype and peaked during fall and in colder environments with slower element cycling. Root chemistry also varied with environment, genotype and season. The genotype producing recalcitrant leaf litter had the highest root biomass, suggesting a compensation strategy. Along the studied gradient, plasticity level observed for some root traits (biomass, element contents) was genotype-specific and high for some genotypes. Regionally, such plasticity patterns should be considered in elemental budgets, for nutrient management and ecosystem services provision in plantations (carbon storage, nutrient retention). The small inter-site aboveground productivity differences observed suggest that plasticity in fine root growth may contribute to overcome nutrient limitations on less fertile marginal lands.

Seasonal dynamics of fine root respiration in the degraded and successional primary Korean pine forests in the Lesser Khingan mountains of Northern China

The broad-leaved and Korean pine mixed forests in the Liangshui National Natural Reserve, China, are important components of boreal forests in areas that are sensitive to global climate change. Respiration rates of excised roots were measured using an oxygen electrode (Hansatech Oxy-Lab 2, UK) to examine the variation in and identify the controlling factors of fine root respiration (Rr) during the growing period (May–October) in 2016. The relationships between Rr and biotic/abiotic factors [e.g., soil temperature, live fine root biomass (LFRB), and the soil carbon index] were subsequently analyzed. The results showed that Rr was significantly higher in the secondary broad-leaved forest (SF) than that in the primary Korean pine forest (PK) (p < 0.001); whereas soil carbon sequestration showed the opposite trend (p < 0.05). Rr tended to exponentially increase with soil temperature (p < 0.001) in both forest types. The Q10 value of the PK was significantly higher than that of the SF (p < 0.01). Pearson correlation and regression analyses revealed that Rr was significantly linearly correlated with LFRB, total soil organic carbon, soil soluble organic carbon, and soil microbial biomass carbon (p < 0.01). Stepwise regression was used to further explain that LFRB and soil microbial biomass carbon were the major contributors to changes in Rr (F = 53.97, p < 0.001, R2 = 0.75). The findings of the present study offer insights into the variability of the soil carbon sink function in the degraded and successional primary Korean pine forests.

Improvements in the Root Morphology, Physiology, and Anatomy of Platycladus orientalis Seedlings from Air-root Pruning

Air-root pruning (AP) has been identified as an effective technique for enhancing root growth and development. However, little information is available regarding the temporal changes in the root system of Platycladus orientalis (L.) Franco under AP. We performed integrated morphological, physiological, and anatomical analyses of the roots in P. orientalis seedlings that had been air-root pruned for 120, 150, and 190 days. Our results found that the whole root length, number of root tips, and root surface area of AP seedlings at 120, 150, and 190 days were higher than those of the non–root-pruned (NP) seedlings (P &lt; 0.05), but the average root diameter did not differ significantly between the treatments. Compared with NP treatment, AP increased the root length, surface area, number of tips, and specific root length of the ≤0.5 mm diameter roots in P. orientalis during the experimental periods (P &lt; 0.05), but those of 0.5- to 1-mm-diameter roots were only increased on day 190 (P &lt; 0.05). The AP plants also exhibited higher root vitality and proportion of live fine roots than the NP plants (P &lt; 0.05). Our anatomical evaluation of the ≤0.5 mm roots and taproots revealed features that could account for the morphological differences found between the AP and NP plants. In conclusion, our results indicate that air-root pruning induced changes in the roots that promote the root system development in P. orientalis compared with the NP treatment during the experimental period. These results thus provide experimental evidence to support the use of AP in P. orientalis seedlings.

Spatial and temporal effects of nitrogen addition on root morphology and growth in a boreal forest

The production and turnover of fine roots play a critical role in regulating underground carbon (C) cycling of terrestrial ecosystems, which are a biological feature in regulating the capacity of plant to capture soil nutrients. Although the importance of fine root production (FRP) and turnover (FRT) to whole-plant and ecosystem C cycling is increasingly recognized, their response to nitrogen (N) deposition remains unclear. To understand how N addition affects the FRP and FRT of fine roots, a field experiment was conducted with four N treatment levels (0, 2.5, 5.0, and 7.5gNm−2yr−1) to quantify the effects of N deposition on fine root dynamics and vertical allocation in a boreal forest using the minirhizotron technique. Our results showed that N deposition significantly decreased total number of live and dead fine roots and total surface area of live fine roots in topsoil layers (0–20cm soil depth), while increased in subsoil layers (20–40cm soil depth) during 2015–2016. Average diameter of fine root was increased by N addition particularly in subsoil layers. The FRP rate was reduced by N addition in the topsoil, but increased in the subsoil layers, whereas patterns of their seasonal changes were not affected in both soil layers. The FRT rate tended to decrease under N addition compared with control in both soil layers during the observation years, potentially indicating a slower underground C cycle with N addition. Moreover, fine roots distributed more deeply in the soil due to N addition, indicating fine roots may through self-regulation and change of growth strategy to face environment stressor.

Ecosystem carbon density and allocation across a chronosequence of longleaf pine forests.

Forests can partially offset greenhouse gas emissions and contribute to climate change mitigation, mainly through increases in live biomass. We quantified carbon (C) density in 20 managed longleaf pine (Pinus palustris Mill.) forests ranging in age from 5 to 118years located across the southeastern United States and estimated above- and belowground C trajectories. Ecosystem C stock (all pools including soil C) and aboveground live tree C increased nonlinearly with stand age and the modeled asymptotic maxima were 168 Mg C/ha and 80 Mg C/ha, respectively. Accumulation of ecosystem C with stand age was driven mainly by increases in aboveground live tree C, which ranged from <1 Mg C/ha to 74 Mg C/ha and comprised <1% to 39% of ecosystem C. Live root C (sum of below-stump C, ground penetrating radar measurement of lateral root C, and live fine root C) increased with stand age and represented 4-22% of ecosystem C. Soil C was related to site index, but not to stand age, and made up 39-92% of ecosystem C. Live understory C, forest floor C, downed dead wood C, and standing dead wood C were small fractions of ecosystem C in these frequently burned stands. Stand age and site index accounted for 76% of the variation in ecosystem C among stands. The mean root-to-shoot ratio calculated as the average across all stands (excluding the grass-stage stand) was 0.54 (standard deviation of 0.19) and higher than reports for other conifers. Long-term accumulation of live tree C, combined with the larger role of belowground accumulation of lateral root C than in other forest types, indicates a role of longleaf pine forests in providing disturbance-resistant C storage that can balance the more rapid C accumulation and C removal associated with more intensively managed forests. Although other managed southern pine systems sequester more C over the short-term, we suggest that longleaf pine forests can play a meaningful role in regional forest C management.

Reduced Winter Snowpack and Greater Soil Frost Reduce Live Root Biomass and Stimulate Radial Growth and Stem Respiration of Red Maple (Acer rubrum) Trees in a Mixed-Hardwood Forest

Northeastern U.S. forests are currently net carbon (C) sinks, but rates of C loss from these ecosystems may be altered by the projected reduction in snowpack and increased soil freezing over the next century. Soil freezing damages fine roots, which may reduce radial tree growth and stem respiration. We conducted a snow removal experiment at Harvard Forest, MA to quantify effects of a reduced winter snowpack and increased soil freezing on root biomass, stem radial growth and respiration in a mixed-hardwood forest. The proportion of live fine root biomass during spring (late-April) declined with increasing soil frost severity (P = 0.05). Basal area increment index was positively correlated with soil frost severity for Acer rubrum, but not Quercus rubra. Rates of stem respiration in the growing season correlated positively with soil frost duration in the previous winter, ( $$ R^{2}_{{{\text{LMM}}({\text{m}})}} $$ = 0.15 and 0.24 for Q. rubra and A. rubrum, respectively). Losses of C from stem respiration were comparable to or greater than C storage from radial growth of Q. rubra and A. rubrum, respectively. Overall, our findings suggest that in mixed-hardwood forests (1) soil freezing has adverse effects on spring live root biomass, but at least in the short-term could stimulate aboveground processes such as stem respiration and radial growth for A. rubrum more than Q. rubra, (2) stem respiration is an important ecosystem C flux and (3) the increasing abundance of A. rubrum relative to Q. rubra may have important implications for C storage in tree stem biomass.

Fine root turnover of Japanese white birch (Betula platyphylla var. japonica) grown under elevated CO2 in northern Japan

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. 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.

DNA analysis of soil extracts can be used to investigate fine root depth distribution of trees.

Understanding the root distribution of trees by soil coring is time -: consuming as it requires the separation of roots from soil and classification of roots into particular size classes. This labour-intensive process can limit sample throughput and therefore sampling intensity. We investigated the use of quantitative polymerase chain reaction (qPCR) on soil DNA extractions to determine live fine root DNA density (RDD, mg DNA m(-2)) for mango (Mangifera indica) trees. The specificity of the qPCR was tested against DNA extracted from 10 mango cultivars and 14 weed species. All mango cultivars and no weeds were detected. Mango DNA was successfully quantified from control soil spiked with mango roots and weed species. The DNA yield of mango root sections stored in moist soil at 23-28 °C declined after 15 days to low concentrations as roots decayed, indicating that dead root materials in moist soil would not cause false-positive results. To separate large roots from samples, a root separation method for field samples was used to target the root fragments remaining in sieved (minimum 2 mm aperture) soil for RDD comparisons. Using this method we compared the seasonal RDD values of fine roots for five mango rootstock cultivars in a field trial. The mean cultivar DNA yields by depth from root fragments in the sieved soil samples had the strongest relationship (adjusted multiple R(2) = 0.9307, P < 0.001) with the dry matter (g m(-2)) of fine (diameter <0.64 mm) roots removed from the soil by sieving. This method provides a species-specific and rapid means of comparing the distribution and concentration of live fine roots of trees in orchards using soil samples up to 500 g.

Autotrophic and heterotrophic respiration of a poplar plantation chronosequence in northwest China

The partitioning of soil respiration is helpful for understanding the mechanism of soil CO2 production and for estimating net forest C budget. We investigated heterotrophic (Rh) and autotrophic (Ra) components of soil CO2 efflux (Rs) in a poplar chronosequence (3-, 8-, and 15-yr-old) using a trenching method in 2007 and 2008. Our results showed that Rh and Ra varied with stand age. Mean Rh increased from 1.85μmolm−2s−1 in the 3-yr-old stand to 2.59μmolm−2s−1 in the 15-yr-old stand, while Ra decreased from 3.41μmolm−2s−1 in the 3-yr-old stand to 1.89μmolm−2s−1 in the 15-yr-old stand. There was a significant stand-age effect on Ra. Autotrophic respiration in the three stands all peaked in June, while the maximum Rh and soil temperature occurred in July. The seasonal variations of Ra and Rh could be well explained by soil temperature (P<0.01). The contribution of Ra to Rs during the growing season was 57.1% averaged over the three stands. We found that Rh was positively correlated with dead fine root biomass (P<0.01) and with forest floor litter mass (P<0.05), and that Ra was significantly correlated with live fine root biomass. The root respiration significantly decreased with stand age, which was explained by a decrease in live fine root biomass over the age sequence, whereas the increase of heterotrophic respiration could be attributed predominantly to an increase in the labile C input with stand age. Our results highlight the importance of stand-age effects on different components of soil respiration and its significance to the estimation of forest C sink potential over a rotation.