Effects of solar radiation and fine roots on suction of Amorpha fruticose-vegetated soil

The thickness of shallow landslides is generally less than 2 m,which is of the same order of magnitude as the growth range of vegetation roots.Vegetation roots can improve the stability of shallow soil through mechanical and hydraulic effects.Therefore,the landslide process is closely related to the plant roots growing on the slope surface.Plant roots play a dominant role in the regulation of soil suction through solar radiation induced transpiration.However,little is known about the correlation between cumulative solar radiation and soil suction.Moreover,the specific effects of fine roots on the suction distribution are not clear in most previous studies.In this study,a vegetated soil of a drought-tolerant and water-tolerant shrub,namely Amorpha fruticose,was adopted.The suction and volumetric water content of bare and vegetated soils were monitored under natural conditions for 4 months.The results demonstrate that there is a nearly linear relationship between cumulative solar radiation and suction ranging from zero to 100 kPa.Regarding the modeling of the soil-plant-atmosphere interactions,this relationship could serve a significant role in calculating the root water uptake under given solar radiation conditions.In addition,higher suctions were observed at the lower layer of the vegetated soil than those at the middle layer,which is different from the results of vegetated soil from previous investigations.This is due to the fact that the root area index(RAI)of fine roots at the lower layer is twice that of the middle layer.Importantly,the higher concentration of fine roots at the lower layer of vegetated soil sample resembles the root distribution of shrub near the soil-bedrock interface on shallow bedrock landslides.The fine roots would increase soil suction through transpiration,and hence reduce the permeability and increase shear strength of landslides.Eventually,these new findings serve as a preliminary step on the evaluation of the stability of this common type of landslides.

Nutrient retranslocation from the fine roots of Fraxinus mandshurica and Larix olgensis in northeastern China

Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash （Fraxinus mandshurica） and a Larch （Larix olgensis） plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements （Ca/other elements ratio） and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.

Dynamics of nitrogen and phosphorus concentrations of fine roots in a mixed forest of Cunninghamia lanceolata and Tsoongiodendron odorum

From September 1999 to July 2000, N and P concentrations of fine roots were measured with the method of sequential soil core at bimonthly intervals in a mixed forest of Tsoong's tree (Tsoongiodendron odorum Chun) and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in Sanming, Fujian. The results showed that N, P concentration of Chinese fir and Tsoong's tree in fine roots were negatively related to root diameter size. The concentrations of N and P in living roots and dead roots were compared. The order of N concentration in fine roots in different samples was Tsoong's tree>undergrowth>Chinese fir, while that of P was undergrowth>Tsoong's tree>Chinese fir. For Chinese fir, the seasonal change of N, P concentrations in fine roots with various diameter classes showed a single-apex curve with a maximum in September. For Tsoong's tree, maximized concentration of N in fine roots appeared in July or September and maximized P concentration in May.

Spatial distribution of fine roots of larch and ash in the mixed plantation stand

The spatial distribution of standing fine roots in tree rows of different species in a 12-year-old mixed stand of ash (Fraxinus mandshurica Rupr.) and larch (Larix olgensis Henry) was studied by soil core sampling in early spring, 2001. It is found that ash and larch differ greatly in their belowground biomass distribution. Ash has much higher fine root biomass density in the soil than larch at stand level (with the max value of 4442.3 vs. 2234.9 gm-3). Both tree species deployed more fine roots in their neighboring zone, suggesting a less intensive competition between roots of the two species. Both fine root biomass density and root length density of ash in the zone between larch tree rows are greater than that of larch in zone between ash tree rows, indicating that ash is more powerful than larch in belowground competition. The spatial distribution feature of roots favors the growth of ash in the mixed stand.

Estimating the production and mortality of fine roots using minirhizotrons in a Pinus densiflora forest in Gwangneung,Korea

The aim of this study was to estimate fine root production （FP） and fine root mortality （FM） at 0-10, 10-20, and 20-30 cm soil depths using minirhizotrons in a 75-year-old Pinus densiflora Sieb. et Zucc. forest located in Gwangneung, Korea. We developed the conversion factors （frame cm-2） of three soil depths （0.158 for 0-10 cm, 0.120 for 10-20 cm, and 0.131 for 20-30 cm） based on soil coring and minirhizotron data. FP and FM were estimated using conversion factors from March 26, 2013 to March 2, 2014. The annual FP and FM values at the 0-30 cm soil depth were 3200.2 and 2271.5 kg ha-1 yr -1, respectively. The FP estimate accounted for approximately 17 % of the total net primary production at the study site. FP was highest in summer （July 31-September 26）, and FM was highest in autumn （September 27-November 29）. FP was positively correlated with seasonal change in soil temperature, while FM was not related to that change. The sea- sonality of FP and FM might be linked to above-ground photosynthetic activity. Both FP and FM at the 0-10 cm depth were significantly higher than at 10-20 and 20-30 cm depths, and this resulted from the decrease in nutrient availability with increasing soil depth. The minirhizotron approach and conversion factors developed in this study will enable fast and accurate estimation of the fine root dynamics in P. densiflora forest ecosystems.

Definition of fine roots on the basis of the root anatomy, diameter,and branch orders of one-year old Fraxinus mandshurica seedlings

Fine roots are important in root absorption of nutrient and water,and in root turnover.Accurate definition of fine roots is a prerequisite to improved estimation of the physiological and ecological functions of forest ecosystems.Root development and physiological functions are reflections of root anatomical structure.In this study,the anatomical structures of different root orders were analyzed by examining paraffin sections of one-year old Fraxinus mandshurica seedlings.One-year-old F.mandshurica seedlings had over five root orders.The root anatomical structures of all orders showed more differences.First and second order roots consisted of four sections： the epidermis,cortex,pericycle,and vascular bundles.Fourth and fifth order roots were mainly composed of the skin and peripheral vascular bundles（including the xylem and phloem）.Third order roots had root epidermal and cortical structures,but the quantity and integrity of the cortical cells were inferior to those of the first and second order roots,and superior to those of the fourth and fifth order roots.All the first and second order roots and some third order roots with discontinuous cork layer（〈0.4 mm in diameter）,but not the fourth and fifth order roots,were the fine roots of one-year old F.mandshurica seedlings.Although they had similar diameters,different portions of root systems had different anatomical structures and therefore,vary in capacity to absorb water and nutrients.Fine roots were accurately defined by root diameter,branch orders,and anatomical structural features of one-year old F.mandshurica seedlings.

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.

Morphological Characteristics and Nutrient Content of Fine Roots of 2-Year-Old and 3-Year-Old Eucalyptus grandis Plantation

[ Objective] This study aimed to explore the morphological characteristics and nutrient content of f＇me roots of 2-year-old and 3-year-old Euca/yptus grand/s plantation and investigate the correlation. [ Method] Fine roots of 2-year-old and 3-year-old Eucalyptus grandis plantation were collected as experimental materials, to determine the root diameter （D）, root length （L）, specific root length （SRL） and contents of major nutrient elements N, P, K, Ca, Mg and C of fine roots （level 1 -5）, study the morphological characteristics and major nutrient element content and investigate the correlation. [ Result] The results showed that morphological differences of fine roots （ level 1 - 5 ） of Eucalyptus grandis plantation were great with the increase of root order, to be specific, D and L increased and SRL decreased with the increasing root order; SRL, L and D of 3-year-old Eucalyptus grauclis plantation were greater than those of 2-year-old Euca/yptus grand/s plantation. Contents of N, Ca, Mg and C of fine roots of 2-year-old and 3-year-old Eucalyptus grandis plantation showed consistent orders with the increase of root order： N and Mg contents were reduced, while Ca and C contents were enhanced; P and K contents varied with different forest ages; both 2-year-old and 3-year- old Eucalyptus grandis showed an order of C 〉 K 〉 Ca （Mg） 〉 N. Major nutrient element content and morphological characteristics of Eucalyptus grand/s fine roots （level 1 -5 ） were extremely significantly correlated （P 〈0.01 ）, SRL, L and D could be adopted as reference indices to evaluate nutrient status of Eucalyptus grand/s. Required nutrients and fine root morphology of Eucalyptus grandis plantation changed with the increase of forest age, and the nutrient cycling and energy flow patterns also changed; major nutrient dements in fine roots of 2-year-old and 3-year-old Eucalyptus grandis plantation transferred in a different order from the growth order, therefore N fertilizer could be applied to improve the growth of fine roots. [ Condusion] This study laid the foundation for understanding the fine root morphology and nutrient variation pattern of Eucalyptus grandis plantation and enriching the response and adaptation mechanism theory of roots to environment, pos- sessing important reference significance for the sustainable development of Eucalyptus grand/s plantation.

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.

Functional traits of poplar leaves and fine roots responses to ozone pollution under soil nitrogen addition

Concurrent ground-level ozone(O_(3))pollution and anthropogenic nitrogen(N)deposition can markedly influence dynamics and productivity in forests.Most studies evaluating the functional traits responses of rapid-turnover organs to O_(3) have specifically examined leaves,despite fine roots are another major source of soil carbon and nutrient input in forest ecosystems.How elevated O_(3) levels impact fine root biomass and biochemistry remains to be resolved.This study was to assess poplar leaf and fine root biomass and biochemistry responses to five different levels of O_(3) pollution,while additionally examining whether four levels of soil N supplementation were sufficient to alter the impact of O_(3) on these two organs.Elevated O_(3) resulted in a more substantial reduction in fine root biomass than leafbiomass;relative to leaves,more biochemically-resistant components were present within fine root litter,which contained high concentrations of lignin,condensed tannins,and elevated C:N and lignin:N ratios that were associated with slower rates of litter decomposition.In contrast,leaves contained more labile components,including nonstructural carbohydrates and N,as well as a higher N:P ratio.Elevated O_(3) significantly reduced labile components and increased biochemically-resistant components in leaves,whereas they had minimal impact on fine root biochemistry.This suggests that O_(3) pollution has the potential to delay leaf litter decomposition and associated nutrient cycling.N addition largely failed to affect the impact of elevated O_(3) levels on leaves or fine root chemistry,suggesting that soil N supplementation is not a suitable approach to combating the impact of O_(3) pollution on key functional traits of poplars.These results indicate that the significant differences in the responses of leaves and fine roots to O_(3) pollution will result in marked changes in the relative belowground roles of these two litter sources within forest ecosystems,and such changes will independently of nitrogen load.

Intraspecific variations in fine root N and P and factors affecting their concentrations in Masson pine plantations across subtropical China

Fine roots(<2 mm)play vital roles in water and nutrient uptake.However,intraspecific variations in their chemical traits and their controlling mechanisms remain poorly understood at a regional scale.This study examined these intraspecific variations in fine roots in Masson pine(Pinus massoniana Lamb.)plantations across subtropical China and their responses to environmental factors.Root nitrogen(N)and phosphorus(P)concentrations and their mass ratios(N:P)ranged from 3.5 to 11.7 g kg^(-1),0.2 to0.9 g kg^(-1),and 7.8 to 51.6 g kg^(-1),respectively.These three chemical traits were significantly different between sites and in longitudinal patterns across subtropical China.Mean annual temperature was positively related to root N concentration but negatively related to root P concentration.There were significant,negative relationships between clay content and root P concentration and between pH and root N concentration.Available N had no significant relationship with root N concentration,while available P was a significantly positive relationship with root P concentration.The combined effects of altitude,climate(temperature and precipitation)and soil properties(pH,clay content,available N and P)explained 26%and 36%of the root N and P concentrations variations,respectively.These environmental variables had direct and indirect effects and exhibited disproportionate levels of total effects on root N and P concentrations.Root N and P concentrations explained 35%and 65%variations in their mass ratios,respectively.The results highlight different spatial patterns of chemical traits and various environmental controls on root N and P concentrations in these ecosystems.More cause-effect relationships of root chemical traits with abiotic and biotic factors are needed to understand nutrient uptake strategies and the mechanisms controlling intraspecific variations in plant traits.

Fine Root Distribution Characteristics of Populus cathayana Plantations at Different Ages in Alpine Sandy Land

[Objectives]The paper was to study the fine root distribution characteristics of Populus cathayana plantations at different ages in alpine sandy land.[Methods]With 5,10,15,20,and 25 years old P.cathayana plantation in the eastern margin of Gonghe Basin,Qinghai Province as the research objects,fine roots were collected by root core drilling method,and the differences of fine root biomass,root length density,average diameter and root tip number at the soil depths of 0-20,20-40,40-60,60-80 and 80-100 cm were analyzed.[Results]The total biomass density of P.cathayana plantation was mainly distributed in the soil layer of 0-60 cm,accounting for 76%of the entire soil layer,and its value increased with the increase in forest age.With the increase in different forest ages,the root length density,average diameter and root tip number of living fine roots in the soil layer of 0-60 cm accounted for 74%-81%of the entire soil layer,and the proportions in the soil layers of 60-80 and 80-100 cm were 9%-11%.The biomass density,root length density,average diameter and root tip number of living and dead fine roots of P.cathayana plantation increased with the increase of forest age.The root length density,average diameter and root tip number of P.cathayana fine roots showed a linear function change trend with the growth of forest age,which could be described by the linear function equation y=ax+b(a>0).The analysis results showed that the root length density,average diameter and root tip number of P.cathayana were significantly correlated with the total biomass density of fine roots,and the root length density and average diameter had an extremely positive correlation with the total biomass density.[Conclusions]In the future,P.cathayana plantation should be properly tended to promote the development of fine roots and maximize its ecological benefits.

Effects of Thinning and Litter Fall Removal on Fine Root Production and Soil Organic Carbon Content in Masson Pine Plantations

Soils play a critical role in the global carbon cycle, and can be major source or sink of CO2 depending upon land use, vegetation type and soil management practices. Fine roots are important component of a forest ecosystem in terms of water and nutrient uptake. In this study the effects of thinning and litter fall removal on fine root production and soil organic carbon content were examined in 20-year-old Masson pine （Pinus resinosa） plantations in Huitong, Hunan Province of China in the growing seasons of 2004 and 2005. The results showed that fine root production was significantly lower in the thinning plots than in the control plots, with a decrease of 58% and 14% in 2004 and 2005 growing seasons, respectively. Litter fall removal significantly increased fine root production by 14% in 2004. Soil temperature （Tsoil） and soil moisture （Msoil） were higher in the thinning plots than those in the controls. Litter fall removal had significant effects on Tsoil and Msoil. Soil organic carbon content was higher in the thinning plots but was lower in the plots with litter fall removal compared with that in the controls. Our results also indicated that annual production of fine roots resulted in small carbon accumulation in the upper layers of the soil, and removal of tree by thinning resulted in a significant increase of carbon storage in Masson pine plantations.

Response of density-related fine root production to soil and leaf traits in coniferous and broad-leaved plantations in the semiarid loess hilly region of China

Fine roots are the most active and functional component of root systems and play a significant role in the acquisition of soil resources. Density is an important structural factor in forest plantations but information on changes in fine roots along a density gradient is limited. In this study, plantations of black locust (Robinia pseudoacacia L.) and Chinese pine (Pinus tabuliformis Carr.) with four density classes were analyzed for the influence of soil and leaf traits on fine root growth. Fine root biomass increased with stand density. High fine root biomass was achieved through increases in the fine root production and turnover rate in the high-density black locust plantations and through an increase in fine root production in the pine plantations. In the high-density Chinese pine stand, there was a high fine root turnover which, coupled with high fine root production, contributed to a high fine root biomass. Overall, fine root production and turnover rate were closely related to soil volumetric water content in both kinds of plantations, while fine root biomass, especially the component of necromass, was related to soil nutrient status, which refers to phosphorous content in black locust plantations and nitrogen content in Chinese pine plantations. There was a close linkage between leaf area index and fine root dynamics in the black locust plantations but not in the pine plantations.

Root overlap and allocation of above- and belowground growth of European beech in pure and mixed stands of Douglas fir and Norway spruce

Site conditions and species identity have a combined effect on fine root growth of trees in pure and mixed stands.However,mechanisms that may contribute to this effect are rarely studied,even though they are essential to assess the potential of species to cope with climate change.This study examined fine root overlap and the linkage between fine root and stem growth of European beech(Fagus sylvatica)growing in pure and mixed stands with Douglas fir(Pseudotsuga menziesii)or Norway spruce(Picea abies)at two different study sites in northwestern Germany.The study sites represented substantially different soil and climate conditions.At each site,three stands,and at each stand,three pairs of trees were studied.In the pure beech stand,the pairs consisted of two beech trees,while in the mixed stands each pair was composed of a beech tree and a conifer.Between each pair,three evenly spaced soil cores were taken monthly throughout the growing season.In the pure beech stands,microsatellite markers were used to assign the fine roots to individual trees.Changes in stem diameter of beech were quantified and then upscaled to aboveground wood productivity with automatic high-resolution circumference dendrometers.We found that fine root overlap between neighboring trees varied independently of the distance between the paired trees or the stand types(pure versus mixed stands),indicating that there was no territorial competition.Aboveground wood productivity(wood NPP)and fine root productivity(root NPP)showed similar unimodal seasonal patterns,peaking in June.However,this pattern was more distinct for root NPP,and root NPP started earlier and lasted longer than wood NPP.The influence of site conditions on the variation in wood and root NPP of beech was stronger than that of stand type.Wood NPP was,as expected,higher at the richer site than at the poorer site.In contrast,root NPP was higher at the poorer than at the richer site.We concluded that beech can respond to limited resources not only above-but also belowground and that the negative relationship between above-and belowground growth across the study sites suggests an‘optimal partitioning’of growth under stress.

Variation patterns of fine root biomass, production and turnover in Chinese forests

China's forests cover 208.3 million ha and span a wide range of climates and a large variety of forest types, including tropical, temperate, and boreal forests. However, the variation patterns of fine root (< 2 mm in diameter) biomass, production, and turnover from the south to the north are unclear. This study summarizes fine root biomass (FRB), production (FRP) and turnover rate (FRT) in China's forests as reported by 140 case studies published from 1983 to 2014. The results showed that the mean values of FRB, FRP and FRT in China's forests were 278 g m(-2), 366 g m(-2) a(-1), and 1.19 a(-1), respectively. Compared with other studies at the regional or global scales, FRB in China's forests was lower, FRP was similar to estimates at the global scale, but FRT was much higher. FRB, FRP, and FRT in China's forests increased with increasing mean annual precipitation (MAP), indicating that fine root variables were likely related to MAP, rather than mean annual temperature or latitude. This is possibly due to the small variation in temperature but greater variation in precipitation during the growing season. These findings suggest that spatiotemporal variation in precipitation has a more profound impact on fine root dynamics in China's forests, and this will impact carbon and nutrient cycles driven by root turnover in the future.

Vertical Distribution and Seasonal Dynamics of Fine Root Parameters for Apple Trees of Different Ages on the Loess Plateau of China

The vertical distribution pattern and seasonal dynamics of fine root parameters for the apple trees of different ages （3, 10, 15, and 20 years old） on the Loess Plateau of China were studied. Soil coring method was used to determine the vertical distribution and seasonal dynamics of fine roots at different root radial distances （1.0, 1.5, and 2.0 m from the main tree trunk）. The fine root biomass density （FRD）, fine root length density （RLD）, and specific root length （SRL）, as well as soil water content and soil temperature were also measured. The FRD and RLD for the 10, 15, and 20 years old trees reached peak values in the 20-30 cm soil layer. For the 3 years old tree, the highest FRD and RLD were observed in the 10-20 cm soil layer. The FRD and RLD decreased with increased soil depth from the 10-20 or 20-30 cm soil layer for all age apple trees. The SRL declined with the increase of tree age. The FRD at the 1.0 m radial distance from the main tree trunk was higher than that at other radial distances in the 3 and 10 years old orchard. However, in the 15 and 20 years old orchards, especially the 20 years old orchard, the FRD at the 2.0 m radial distance was nearly equal to or higher than that at the 1.0 and 1.5 m radial distances. For all the root radiuses or the tree ages, the FRD, RLD, and SRL were the highest in spring and the lowest in autumn. The age of an apple tree does not affect the vertical distribution pattern but the biomass of fine roots and the SRL. Radial distance affects the root horizontal distribution of 3 and 10 years old trees but the 15 and 20 years old trees. Additionally, effects of soil temperature and soil moisture on fine root distribution or seasonal dynamics are not significant.

Thinning effects on biomass and element concentrations of roots in adjacent hornbeam and oak stands in Istanbul,Turkey

Background:Thinning is a commonly used treatment in forest management which affects the tree root systems.The effects of thinning on element concentrations and seasonal change of roots were evaluated in adjacent oak(Quercus frainetto Ten.)and hornbeam(Carpinus betulus L.)stands according to the different root diameter classes.Method:Two replicated control and thinning plots(50m×50 m)were set for each species(hornbeam and oak).Thinning treatments(November 2010)reduced 50%of the basal area in both oak and hornbeam stands.Roots were assessed by seasonal collection over 2 years(from October 2010 to October 2012).The roots were then sorted into diameter classes of 0–2mm(fine roots),2–5mm(small roots)and>5mm(coarse roots).C,N,P,K,Ca,Na,Mg,S,Mn,Fe,Al,Zn,Pb,Ni,Cu and Cd were analyzed.Results:Except coarse roots,the highest root biomasses were determined in April-2011 in all plots.Fine-root biomass in oak was found significantly higher in control plots.In contrast to the oak,the fine-root biomass in the thinned hornbeam plots was higher than in the controls.The small-root biomass did not significantly differ between the thinned and the control plots in both oak and hornbeam stands.However,the coarse-root biomass showed significant differences between the control(1989 g∙m^(−2))and thinned plots(1060 g∙m^(−2))in oak,while no difference was detected in hornbeam.The concentrations of C,Al,Pb,Cd,Ni,Zn,Mn,Na,K,Mg and P in the fine roots of oak were significantly higher in the thinned plots.However,the concentration of Pb,Cd and Fe in the fine roots was significantly higher in the thinned plots of hornbeam.Significant differences were observed between the species for all elements in the fine roots except for C,N and P.In particular,elements in the fine roots tended to increase in July in the oak.In the hornbeam,all element concentrations in the fine roots(except C,N,and S)in the thinned plots showed a tendency to increase in April.The concentrations of Pb,Ni,Al,Fe,Cu,Ca,Na,K,Mg and P in the hornbeam control plots increased during the April 2011 period.Conclusion:The results indicated that thinning effects on temporal changes and concentrations of elements in the roots could be attributed to species-specific characteristics.

Spatial heterogeneity of fine root biomass of Pinus massoniana forests in the Three Gorges Reservoir Area, China

Environmental heterogeneity is a constant presence in the natural world that significantly affects plant behavior at a variety of levels of complexity. In order to estimate the spatial pattern of fine root biomass in the Three Gorges Reservoir Area, the spatial heterogeneity of fine root biomass in the upper layer of soils （0-10 cm） in three Mas- son pine （Pinus massoniana） stands in the Three Gorges Reservoir Area, China, was studied in 30 m x 30 m plots with geostatistical analysis. The results indicate that 1） both the live and dead fine root biomass of stand 2 were less than those of other stands, 2） the spatial variation of fine roots in the three stands was caused together by structural and ran- dom factors with moderate spatial dependence and 3） the magnitude of spatial heterogeneity of live fine roots ranked as： stand 3 〉 stand 1 〉 stand 2, while that of dead fine roots was similar in the three stands. These findings suggested that the range of spatial autocorrelation for fine root biomass varied considerably in the Three Gorges Reservoir Area, while soil properties, such as soil bulk density, organic matter and total nitrogen, may exhibit great effect on the spatial distribution of fine roots. Finally, we express our hope to be able to carry out further research on the quantitative relation- ship between the spatial heterogeneous patterns of plant and soil properties.

Comparing growth and fine root distribution in monocultures and mixed plantations of hybrid poplar and spruce

Disease prevention, biodiversity, productivity improvement and ecological considerations are all factors that contribute to increasing interest in mixed plantations. The objective of this study was to evaluate early growth and productivity of two hybrid poplar clones, P. balsamifera x trichocarpa （PBT） and P. maximowiczii x balsamifera （PMB）, one improved family of Norway spruce （Picea glauca （PA）） and one improved family of white spruce （Picea abies （PG）） growing under different spacings in monocultures and mixed plots. The plantations were established in 2003 in Abitibi-Témiscamingue, Quebec, Canada, in a split plot design with spacing as the whole plot factor （1 × 1 m, 3 × 3 m and 5 × 5 m） and mixture treatments as subplot factor （pure： PBT, PMB, PA and PG, and 1：1 mixture PBT：PA, PBT：PG, PMB：PA and PMB：PG）. Results showed a beneficial effect of the hybrid poplar-spruce mixture on diameter growth for hybrid poplar clones, but not for the 5 × 5 m spacing because of the relatively young age of the plantations. Diameter growth of the spruces decreased in mixed plantings in the 1 × 1 m, while their height growth increased, resulting in similar aboveground biomass per tree across treatments. Because of the large size differences between spruces and poplars, aboveground biomass in the mixed plantings was generally less than that in pure poplar plots. Leaf nitrogen concentration for the two spruce families and hybrid poplar clone PMB was greater in mixed plots than in monocultures, while leaf nitrogen concentration of clone PBT was similar among mixture treatments. Because of its faster growth rate and greater soil resources demands, clone PMB was the only one showing an increase in leaf N with increased spacing between trees. Fine roots density was greater for both hybrid poplars than spruces. The vertical distribution of fine roots was insensitive to mixture treatment.