Fine Root Lifespan Research Articles

Linking fine root lifespan to root chemical and morphological traits—A global analysis

Fine root lifespan is a critical trait associated with contrasting root strategies of resource acquisition and protection. Yet, its position within the multidimensional "root economics space" synthesizing global root economics strategies is largely uncertain, and it is rarely represented in frameworks integrating plant trait variations. Here, we compiled the most comprehensive dataset of absorptive median root lifespan (MRL) data including 98 observations from 79 woody species using (mini-)rhizotrons across 40 sites and linked MRL to other plant traits to address questions of the regulators of MRL at large spatial scales. We demonstrate that MRL not only decreases with plant investment in root nitrogen (associated with more metabolically active tissues) but also increases with construction of larger diameter roots which is often associated with greater plant reliance on mycorrhizal symbionts. Although theories linking organ structure and function suggest that root traits should play a role in modulating MRL, we found no correlation between root traits associated with structural defense (root tissue density and specific root length) and MRL. Moreover, fine root and leaf lifespan were globally unrelated, except among evergreen species, suggesting contrasting evolutionary selection between leaves and roots facing contrasting environmental influences above vs. belowground. At large geographic scales, MRL was typically longer at sites with lower mean annual temperature and higher mean annual precipitation. Overall, this synthesis uncovered several key ecophysiological covariates and environmental drivers of MRL, highlighting broad avenues for accurate parametrization of global biogeochemical models and the understanding of ecosystem response to global climate change.

Evolution history dominantly regulates fine root lifespan in tree species across the world

Understanding the drivers of variations in fine root lifespan is key to informing nutrient cycling and productivity in terrestrial ecosystems. However, the general patterns and determinants of forest fine root lifespan at the global scale are still limited. We compiled a dataset of 421 fine root lifespan observations from 76 tree species globally to assess phylogenetic signals among species, explored relationships between fine root lifespan and biotic and abiotic factors, and quantified the relative importance of phylogeny, root system structure and functions, climatic and edaphic factors in driving global fine root lifespan variations. Overall, fine root lifespan showed a clear phylogenetic signal, with gymnosperms having a longer fine root lifespan than angiosperms. Fine root lifespan was longer for evergreens than deciduous trees. Ectomycorrhizal (ECM) plants had an extended fine root lifespan than arbuscular mycorrhizal (AM) plants. Among different climatic zones, fine root lifespan was the longest in the boreal zone, while it did not vary between the temperate and tropical zone. Fine root lifespan increased with soil depth and root order. Furthermore, the analysis of relative importance indicated that phylogeny was the strongest driver influencing the variation in forest fine root lifespan, followed by soil clay content, root order, mean annual temperature, and soil depth, while other environmental factors and root traits exerted weaker effects. Our results suggest that the global pattern of fine root lifespan in forests is shaped by the interplay of phylogeny, root traits and environmental factors. These findings necessitate accurate representations of tree evolutionary history in earth system models to predict fine root longevity and its responses to global changes.

Soil warming alters fine root lifespan, phenology, and architecture in a Cunninghamia lanceolata plantation

The mechanisms by which warming affects fine root lifespan remain unclear. In a large-scale soil warming experiment in a Chinese fir plantation, fine root dynamics were monitored for four years using minirhizotrons, and the effects of increasing temperature and co-varying factors on fine root lifespan, such as soil moisture, fine root phenology and architecture, were analysed. Fine root non-structural carbohydrate concentrations and respiration rates were measured to test if fine root lifespan is affected by carbon (C) supply. Warming shortened the overall fine root lifespan by 27.6% (warming vs. control: 197.0 ± 3.5 d vs. 272.0 ± 4.5 d). Cox regression models suggest that increased soil temperature directly and negatively affects root lifespan, whereas decreased soil moisture prolongs root lifespan. Fine roots grew thinner and deeper in warm soil and showed higher emergence in winter but lower emergence in summer; all factors affected the fine root lifespan in an integrated manner. Glucose addition stimulated fine root respiration only in warm soil, indicating a depletion of readily available carbohydrates under warming. Overall, our findings suggest that warming could accelerate the input of C by roots into soil due to shortened fine root lifespans, highlighting the important consideration of simultaneously increasing temperature and its co-varying factors to predict root lifespan under climate change.

On the Below- and Aboveground Phenology in Deciduous Trees: Observing the Fine-Root Lifespan, Turnover Rate, and Phenology of Fagus sylvatica L., Quercus robur L., and Betula pendula Roth for Two Growing Seasons

We tested the relation between the below- and aboveground tree phenology, determining if beech and oak have a greater fine-root lifespan and a smaller turnover rate than birch and if thinner fine-roots or fine-roots born in spring have a shorter lifespan and greater turnover rate than thicker fine-roots or fine-roots born in another season. The fine-root phenology, bud burst, and leaf senescence in Belgian stands were monitored using minirhizotrons, visual observations, and chlorophyll measurements, respectively. The fine-root phenology and the lifespan and turnover rate were estimated using generalized additive models and Kaplan–Meier analyses, respectively. Unlike the aboveground phenology, the belowground phenology did not show a clear and repeating yearly pattern. The cumulative root surface remained stable for birch but peaked for beech and oak around summer to autumn in 2019 and spring in 2020. The new root count was larger in 2019 than in 2020. The mean lifespan of fine-roots with a diameter below 0.5 mm (308 to 399 days) was shorter than those with a diameter between 0.5 to 1 mm (438 to 502 days), 1 to 2 mm (409 to 446 days), or above 2 mm (418 to 471 days). Fine-roots born in different seasons showed a species-specific lifespan and turnover rate.

Topographical shifts in fine root lifespan in a mixed, mesic temperate forest.

Root lifespan, often is estimated in landscape- and ecosystem-level carbon models using linear approximations. In water manipulation experiments, fine root lifespan can vary with soil water content. Soil water content is generally structured by complex topography, which is largely unaccounted for in landscape- and ecosystem-scale carbon models. Topography governs the range of soil water content experienced by roots which may impact their lifespan. We hypothesized that root lifespan varied nonlinearly across a temperate, mesic, forested catchment due to differences in soil water content associated with topographic position. We expected regions of the landscape that were too wet or too dry would have soils that were not optimal for roots and thus result in shorter root lifespans. Specifically, we hypothesized that root lifespan would be longest in areas that consistently had soil water content in the middle of the soil water content spectrum, while in soils at either very low or very high soil water content, root lifespan would be relatively short. We tested this hypothesis by collecting and analyzing two years of minirhizotron and soil moisture data in plots widely distributed in the Shale Hills catchment of the Susquehanna-Shale Hills Critical Zone Observatory in Pennsylvania. We found that fine root lifespans were longer in traditionally wetter topographic regions, but detected no short term (biweekly) effect of soil moisture on root lifespan. Additionally, depth in soil, soil series, slope face orientation, and season of birth strongly affected root lifespans across the catchment. In contrast, lifespan was unaffected by root diameter or mycorrhizal association. Failure to account for these variables could result in erroneous estimates of fine root lifespan and, consequentially, carbon flux in temperate forested regions.

Belowground consequences of converting broadleaf to conifer forest: Comparing the fine root systems of European beech and Scots pine

Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world’s largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species’ fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees’ susceptibility to climate-warming and drought.

Fine Roots Dynamics in Two Forest Strata of a Semi-Deciduous Forest in Northern Republic of Congo

The belowground biomass is represented by coarse and fine roots. Concentrated in the superficial horizons of the soil, the fine roots play a crucial role in the functioning of a forest ecosystem. However, studies on their dynamics in natural forests are almost non-existent in the Republic of Congo. Here, we estimated the biomass, production, turnover and fine root lifespan of two forest strata of a semi-deciduous forest: the Gilbertiodendron dewevrei (De Wild.) J. Léonard forest (GF) and the mixed forest (MF) of land. The ingrowth cores method was used to estimate the biomass, production, turnover and lifespan of fine roots. The results of this study revealed that the biomass, production and fine root turnover of the two forest strata studied significantly decreased with increasing soil depth, with an increase in lifespan. The annual fine root biomass of GF (2284.50 ± 37.62 and 1034.61 ± 14.52 ) was slightly lower than that of MF (2430.07 ± 40.68 and 1043.10 ± 11.75 ) in the 0-15 cm and 15-30 cm horizons, respectively. The annual production of fine roots from these latter horizons was respectively 1300.19 ± 32.17 and 539.18 ± 11.55 in GF and 1362.24 ± 39.59 and 492.95 ± 14.38 in the MF. Root turnover was higher in the GF (1.68 ± 0.05 and 1.35 ± 0.03 ) than in the MF (1.57 ± 0.05 and 1.13 ± 0.02 ). The lifespan of fine roots increased with the depth of the soil. The difference in fine root dynamics observed between the forest strata studied was influenced by the Evenness index and the above-ground biomass.

Lifespan and morphological traits of absorptive fine roots across six typical tree species in subtropical China

Lifespan and morphological traits of absorptive fine roots across six typical tree species in subtropical China

Biomass, Morphology, and Dynamics of the Fine Root System Across a 3,000-M Elevation Gradient on Mt. Kilimanjaro.

Fine roots (≤2 mm) consume a large proportion of photosynthates and thus play a key role in the global carbon cycle, but our knowledge about fine root biomass, production, and turnover across environmental gradients is insufficient, especially in tropical ecosystems. Root system studies along elevation transects can produce valuable insights into root trait-environment relationships and may help to explore the evidence for a root economics spectrum (RES) that should represent a trait syndrome with a trade-off between resource acquisitive and conservative root traits. We studied fine root biomass, necromass, production, and mean fine root lifespan (the inverse of fine root turnover) of woody plants in six natural tropical ecosystems (savanna, four tropical mountain forest types, tropical alpine heathland) on the southern slope of Mt. Kilimanjaro (Tanzania) between 900 and 4,500 m a.s.l. Fine root biomass and necromass showed a unimodal pattern along the slope with a peak in the moist upper montane forest (~2,800 m), while fine root production varied little between savanna and upper montane forest to decrease toward the alpine zone. Root:shoot ratio (fine root biomass and production related to aboveground biomass) in the tropical montane forest increased exponentially with elevation, while it decreased with precipitation and soil nitrogen availability (decreasing soil C:N ratio). Mean fine root lifespan was lowest in the ecosystems with pronounced resource limitation (savanna at low elevation, alpine heathland at high elevation) and higher in the moist and cool forest belt (~1,800–3,700 m). The variation in root traits across the elevation gradient fits better with the concept of a multi-dimensional RES, as root tissue density and specific root length showed variable relations to each other, which does not agree with a simple trade-off between acquisitive and conservative root traits. In conclusion, despite large variation in fine root biomass, production, and morphology among the different plant species and ecosystems, a general belowground shift in carbohydrate partitioning is evident from 900 to 4,500 m a.s.l., suggesting that plant growth is increasingly limited by nutrient (probably N) shortage toward higher elevations.

四种不同生活型树种细根寿命及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 四种不同生活型树种细根寿命及影响因素 DOI: 10.5846/stxb201904020641 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（30800137，31270489） Fine root lifespan and influencing factors of four tree species with different life forms Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以4种不同生活型树种（常绿阔叶和针叶树种、落叶阔叶和针叶树种）为研究对象，通过微根管法现地观测细根的生长动态，比较不同生活型树种细根寿命在种内和种间的差异，探讨影响细根寿命的主要因子，研究结果对理解和预测森林生态系统碳及养分循环过程具有重要的理论意义。结果表明：（1）细根形态特征（分枝结构和直径）显著影响种内细根寿命，分枝等级越低、直径越小，细根的寿命越短；（2）4个树种的细根寿命表现出明显的土层效应和季节效应，即随土壤深度增加，细根的累积存活率逐渐增加，寿命延长；而不同季节出生的细根其寿命长短模式在树种间不一致，春季或夏季出生的细根寿命要长于秋冬季；（3）常绿树种（柳杉、石栎）的细根寿命要长于落叶树种（池杉、麻栎），同时，针叶树种（池杉、柳杉）的细根寿命要长于阔叶树种（麻栎、石栎）。在同一树种内，细根寿命受细根直径、根系分枝结构、土壤环境因子（土层）等因素显著影响，但在不同树种间，细根寿命可能更依赖于树木生长速率、碳分配模式等树木整体的功能性状差异。 Abstract:In this study, four tree species with different life forms (evergreen broad-leaved, coniferous species, deciduous broad-leaved, and coniferous species) were used as the experimental materials. The growth dynamics of fine roots were observed by minirhizotron method. We compared differences in the root lifespan for tree species with different life forms within and between species, and also explored the main factors affecting the lifespan of fine roots. The study would help us to understand carbon and nutrient cycling processes in forest ecosystems. The results showed that: (1) fine root morphological characteristics (branched structure and root diameter) significantly affected the lifespan of fine roots within the species. The fine root lifespan with the lower branching order and the smaller diameter was shorter than that of the higher-order roots and the coarser roots. (2) The root lifespan showed obvious soil layer effect and the seasonal effect, that is, with the increase of soil depth, the cumulative survival rate of fine roots gradually increased and the root lifespan was prolonged; while the lifespan pattern of fine roots born in different seasons was inconsistent among tree species. The lifespan of the fine roots born in spring or summer was longer than that born in autumn and winter. (3) The fine roots lifespan of evergreen trees (Lithocarpus glaber and Cryptomeria fortunei) was longer than that of deciduous trees (Quercus acutissima and Taxodium ascendens). The fine root lifespan of conifers trees was longer than that of broadleaf species. Generally, within the tree species, the fine root lifespan is significantly affected by factors such as fine root diameter, root branching structure, and soil environmental factors (soil layer). However, between tree species, fine root lifespan may be more dependent on the differences in functional traits of trees as a whole, such as tree growth rate, carbohydrate distribution patterns. 参考文献 相似文献 引证文献

The effect of drought and season on root life span in temperate arbuscular mycorrhizal and ectomycorrhizal tree species

AbstractFine roots play a key role in carbon (C) and nutrient cycling, since fine root life span drives soil organic C input and, thus, nitrogen (N) availability. The two main fungal symbioses found in temperate forest trees, ectomycorrhizae (ECM) and arbuscular mycorrhizae (AM), induce different root morphological changes upon infection, but the consequences for root life span are not clear.We explored differences in fine root life span between four AM and four ECM tree species using mini‐rhizotrons in a factorial drought experiment in large mesocosms.Median root life span of young AM and ECM trees differed fundamentally in its response to soil moisture and season of root birth; ECM root life span was reduced from 176 to 81 days in dry soil compared to moist soil, independent of season. By contrast, AM root life span was less responsive to drought, but decreased from 185 to 127 days when comparing roots produced early in the growing season versus mid‐season. In both mycorrhizal types, root life span was positively related to root diameter and negatively to the portion of lower order roots.Synthesis. While our results indicate morphological and architectural traits that predict root life span across tree species, they also indicate fundamental differences in the environmental response of root life span in young AM and ECM trees. This knowledge helps to improve global predictions of root life span.

Productivity and morphological traits of fine roots in forest ecosystems along an elevation gradient of Yakushima Island

ABSTRACTWe measured the productivity and morphological traits of fine roots in seven forests between 170 and 1550 m along an elevation gradient on Yakushima Island, Japan. Yakushima Island is continuously covered by forests ranging from the lowland evergreen broad-leaved forests below 1000 m to the upland evergreen coniferous forests above. Mean annual temperature decreases linearly and soil nutrient availabilities (both N and P) also decrease with increasing elevation. We employed an in-growth core method to determine fine-root productivity. Mean fine-root biomass ranged from 0.123 to 0.297 kg m−2 in the lowland broad-leaved forests and from 0.092 to 0.097 kg m−2 in the upland coniferous forests. Mean fine-root productivity ranged from 0.063 to 0.173 kg m−2 yr−1 in the lowland broad-leaved forests and from 0.033 to 0.044 kg m−2 yr−1 in the upland coniferous forests. Both mean fine-root biomass and mean fine-root productivity were significantly greater in middle-elevation broad-leaved forests than in the lower broad-leaved or the higher coniferous forests. Fine-root turnover rate tended to be lower and mean specific root length (SRL) tended to be higher in the coniferous forests. In the upland coniferous forests, trees may adapt to nutrient limitation and/or cooler climate by increasing the life span and SRL of fine roots instead of increasing carbon allocation to fine roots, thereby decreasing fine-root productivity. Fine-root dynamics along the elevational gradient on Yakushima reflected the species shift from broad-leaved to coniferous trees rather than the monotonous reduction of temperature and nutrient availability.

连作杨树人工林细根寿命的代际差异及其影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 连作杨树人工林细根寿命的代际差异及其影响因素 DOI: 10.5846/stxb201612202624 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31570618）；中国博士后科学基金项目（2015M572070）；山东省双一流奖补资金（SYL2017XTTD03）；山东省博士后创新基金项目 The difference in fine root lifespan between successive rotations of poplar plantation and the dominant causal factors Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:细根寿命是调控森林生产力形成的关键。通过在连作Ⅰ、Ⅱ代杨树人工林固定样地内埋设微根管，对杨树不同根序细根年度生长动态开展连续观测并进行生存分析。结果表明，杨树不同根序细根累积生存率存在显著差异，高级根（3-5级）寿命较长，其累积生存率显著高于1级和2级细根。杨树细根寿命存在显著的代际差异，连作Ⅱ代人工林活根量、死根量和细根总量均高于Ⅰ代林。连作Ⅱ代人工林细根中位值寿命为（90±16）d，显著低于Ⅰ代人工林（（102±22）d）。连作Ⅱ代林各根序细根数量、分布比例均高于Ⅰ代林，低级细根累积生存率低于Ⅰ代林而高级细根累积生存率显著高于Ⅰ代林。连作杨树人工林细根寿命显著受制于土壤环境，1级细根寿命与土壤速效氮相关性极显著（r=-0.861），2级细根寿命与土壤物理性状相关性较强且与土壤酚酸含量呈现极显著相关（r=0.870），高级根序细根寿命与土壤物理性质和养分状况等也具有一定相关性。连作杨树人工林土壤酚酸累积和养分有效性下降影响了细根寿命和周转，并进而造成净初级生产力损耗，相关结论为连作杨树人工林生产力衰退机理模型的建立提供了科学依据。 Abstract:The lifespan of fine roots plays an important role in forest productivity. On the basis of minirhizotron technology, this study focused on the annual dynamics of different order fine roots in successive rotation poplar plantations and analyzed their survival. The results showed that the cumulative survival rates of poplar fine roots were significantly different among root orders. The lifespan of higher order roots (3rd-5th order) was longer than that of lower order roots (1st-2nd order), and their cumulative survival rate was also higher. Furthermore, there was a significant difference in the lifespan of poplar fine roots between two plantations (the first and second generations). There were more live roots, dead roots, and total roots in the second rotation forest than in the first. The median lifespan of fine roots was 90±16 d in the second rotation poplar plantation, whereas it was 102±22 d in the first rotation plantation. The root number and the proportion of roots of each order in the second rotation poplar plantation were significantly higher than those in the first rotation plantation. However, the cumulative survival rate of lower order roots was significantly higher, whereas that of higher order roots was significantly lower, in the first rotation poplar plantation. The lifespan of poplar fine roots was responsive to soil environments, with the lifespan of the first order roots being significantly correlated with soil available nitrogen (r=-0.861) and that of the second order roots being significantly correlated with phenolic acid content (r=0.870). The lifespan of the higher order roots also showed some correlation with soil physical properties and nutrient conditions. The findings of this study indicate that the accumulation of phenolic acids and a decreased soil nutrient availability might influence fine root lifespan and turnover of poplar trees and lead to a loss of net primary productivity in poplar plantations, thereby providing an important insight into the mechanism of declining poplar plantation productivity. 参考文献 相似文献 引证文献

Effects of root diameter, branch order, soil depth and season of birth on fine root life span in five temperate tree species

Fine root life span is a key variable influencing the belowground dynamics of forest ecosystems and is known to be associated with a complex suite of endogenous and environmental factors. We investigated how root life span is influenced by root diameter, branch order, season of birth and soil depth of birth for five temperate tree species growing in monoculture plantations at a common site in northeastern China. The minirhizotron approach was used to estimate root life span from April 2008 to October 2009. Cox proportional hazards regression analysis was employed to determine the impact of those four factors on root life span of each species. There was no consistent difference in fine root life span between evergreen conifers and deciduous hardwoods. A bimodal frequency distribution of root life span was observed for all the species; the majority of roots born in summer and autumn survived to the following year, while roots born in spring mostly died in the current growing season. Root life span tended to increase with root diameter across all species, except Juglans mandshurica. The first two root branch orders within each species generally shared similar life span, with the exception of Picea koraiensis. Root life span tended to be longer at greater depths in the soil profile across all five species. Our results suggest that root life span generally depends on complex interrelations among root anatomy, soil environment and seasonal climatic conditions.

Understory fine roots are more ephemeral than those of trees in subtropical Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) stands

We tested the life span of fine roots of Chinese fir trees and understory plants in two stands in subtropical China. Fine roots from understory plants were much more ephemeral than those from trees. The life span of fine roots of understory plants and Chinese fir was shorter in the younger than in the older stand, although most of the factors affecting fine-root life spans were similar between trees and understory plants. Understory fine root can contribute significantly to total fine root biomass and belowground carbon. The contribution of understory vegetation to belowground carbon and nutrient cycling is often neglected in forest stands. Potential differences in fine-root life span between understory and trees remain poorly known. This study aimed to document fine-root life spans in trees and understory plants in two Chinese fir plantations with different ages. We measured fine-root (≤2 mm in diameter) life span for trees and understory vegetation in 16- and 88-year-old Chinese fir plantations in southern China during 4 years with minirhizotron. Factors controlling fine-root life spans were identified with Cox proportional hazards regression. Fine roots were more ephemeral in understory plants than in trees in the two plantations. Fine-root life spans for both trees and understory plants were longer in the older than in the younger plantation. Root diameter at appearance, rooting depth, and season of emergence had a significant effect on fine-root life span. These results highlight the importance of taking into account understory fine-root life span estimates when assessing the dynamics of fine-root recycling in Chinese fir forests.

Unexpected phenology and lifespan of shallow and deep fine roots of walnut trees grown in a silvoarable Mediterranean agroforestry system

Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of root dynamics have principally been observed in shallow soil horizons ( 2.5 m) root growth occurred at two distinct periods, at bud break in spring and throughout the winter i.e., after leaf fall. In contrast, shallow roots grew mainly during the spring-summer period. Maximum root elongation rates ranged from 1 to 2 cm day−1 depending on soil depth. Most root mortality occurred in upper soil layers whereas only 10 % of fine roots below 4 m died over the study period. Fine root lifespan was longer in thicker and in deeper roots with the lifespan of the thinnest roots (0.0–0.5 mm) increasing from 129 days in the topsoil to 190 at depths > 2.5 m. The unexpected growth of very deep fine roots during the winter months, which is unusual for a deciduous tree species, suggests that deep and shallow roots share different physiological strategies and that current estimates based on the shortest root growth periods (i.e., during spring and summer) may be underestimating root production. Although high fine root turnover rates might partially result from the minirhizotron approach used, our results help gain insight into some of the factors driving soil organic carbon content.

Root-zone management practices impact above and belowground growth in Cabernet Franc grapevines

Background and Aims The objective of this study was to assess the effect of root pruning (RP) and annual under-trellis cover crops (UTCC) on vegetative growth and physiological processes in Cabernet Franc (Vitis vinifera L.) grapevines grafted on 3309C rootstock. Methods and Results Five root-zone management treatments, namely under-trellis vegetation-free strip control (C), RP and three distinct annual UTCC [annual ryegrass (AR), buckwheat, (BW) and turnip (TP)] were evaluated and compared over three seasons in a vigorous vineyard in the Northeastern USA. Root pruning had the greatest impact in reducing grapevine size; AR reduced the duration of shoot growth 2 out of 3 years. Competition between grapevine and AR and BW fine roots resulted in a lower grapevine fine root production in shallow soil layers and in a decrease in fine root lifespan. Conclusions Root pruning was effective in reducing grapevine size for 3 years; RP effectiveness, however, may vary greatly depending on site conditions. Annual UTCC hold potential for reducing grapevine size in vigorous plantings in regions with ample precipitation. Appropriate choice of cover crop species, however, remains unclear. Significance of the Study This work demonstrates that root-zone management practices impact grapevine vegetative growth and induce changes in root morphological traits.

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.

Acclimation of fine root respiration to soil warming involves starch deposition in very fine and fine roots: a case study in Fagus sylvatica saplings.

Root activities in terms of respiration and non-structural carbohydrates (NSC) storage and mobilization have been suggested as major physiological roles in fine root lifespan. As more frequent heat waves and drought periods within the next decades are expected, to what extent does thermal acclimation in fine roots represent a mechanism to cope with such upcoming climatic conditions? In this study, the possible changes in very fine (diameter < 0.5 mm) and fine (0.5-1 mm) root morphology and physiology in terms of respiration rate and NSC [soluble sugars (SS) and starch] concentrations, were investigated on 2-year-old Fagus sylvatica saplings subjected to a simulated long-lasting heat wave event and to co-occurring soil drying. For both very fine and fine roots, soil temperature (ST) resulted inversely correlated with specific root length, respiration rates and SSs concentration, but directly correlated with root mass, root tissue density and starch concentration. In particular, starch concentration increased under 28 °C for successively decreasing under 21 °C ST. These findings showed that thermal acclimation in very fine and fine roots due to 24 days exposure to high ST (∼ 28 °C), induced starch accumulation. Such 'carbon-savings strategy' should bear the maintenance costs associated to the recovery process in case of restored favorable environmental conditions, such as those occurring at the end of a heat wave event. Drought condition seems to affect the fine root vitality much more under moderate than high temperature condition, making the temporary exposure to high ST less threatening to root vitality than expected.

Old carbon in young fine roots in boreal forests

A large proportion of the soil carbon (C) in boreal forests originates from roots and ectomycorrhizal fungi, and accurate quantification of fine-root litter production is needed. Methods for determination of root turnover have been under debate in recent years. Two recently used methods—radiocarbon (14C) dating and use of minirhizotrons (MR)—have yielded different results. This has been attributed to analysis of different roots by use of these methods. At Flakaliden, northern Sweden, in a long-term soil warming and irrigation experiment, we compared MR lifespan with the 14C-derived age of fine roots from soil cores of the same root diameter class. We also determined the 14C-derived age of ingrowth core roots of Norway spruce. The median lifespan of fine roots around MR tubes installed 15 years previously was shorter than 2.5 years whereas the 14C-derived age of the fine roots from soil cores varied from recently grown to 14 years. Correspondingly, the age of 14C in fine roots harvested from ingrowth cores installed in soil 3 months previously was between 1 and 20 years. Thus, cellulose in these roots contained older 14C than is possible from photosynthesis during the time of cellulose formation. By investigating whether the age of Norway spruce and Scots pine seedlings was less than their root 14C-derived age, we tested the possibility of root C originating from soil uptake. This was found to be unlikely, because fine roots of four and eight-year-old seedlings had 14C that was dated to be as old as or younger than the seedlings. We propose that further effort is required to identify the ecological conditions leading to root growth utilization of stored or recycled C.