Variation In Fine Root Biomass Research Articles

Soil warming duration and magnitude affect the dynamics of fine roots and rhizomes and associated C and N pools in subarctic grasslands.

The response of subarctic grassland's below-ground to soil warming is key to understanding this ecosystem's adaptation to future climate. Functionally different below-ground plant organs can respond differently to changes in soil temperature (Ts). We aimed to understand the below-ground adaptation mechanisms by analysing the dynamics and chemistry of fine roots and rhizomes in relation to plant community composition and soil chemistry, along with the duration and magnitude of soil warming. We investigated the effects of the duration [medium-term warming (MTW; 11 years) and long-term warming (LTW; > 60 years)] and magnitude (0-8.4 °C) of soil warming on below-ground plant biomass (BPB), fine root biomass (FRB) and rhizome biomass (RHB) in geothermally warmed subarctic grasslands. We evaluated the changes in BPB, FRB and RHB and the corresponding carbon (C) and nitrogen (N) pools in the context of ambient, Ts < +2 °C and Ts > +2 °C scenarios. BPB decreased exponentially in response to an increase in Ts under MTW, whereas FRB declined under both MTW and LTW. The proportion of rhizomes increased and the C-N ratio in rhizomes decreased under LTW. The C and N pools in BPB in highly warmed plots under MTW were 50 % less than in the ambient plots, whereas under LTW, C and N pools in warmed plots were similar to those in non-warmed plots. Approximately 78 % of the variation in FRB, RHB, and C and N concentration and pools in fine roots and rhizomes was explained by the duration and magnitude of soil warming, soil chemistry, plant community functional composition, and above-ground biomass. Plant's below-ground biomass, chemistry and pools were related to a shift in the grassland's plant community composition - the abundance of ferns increased and BPB decreased towards higher Ts under MTW, while the recovery of below-ground C and N pools under LTW was related to a higher plant diversity. Our results indicate that plant community-level adaptation of below ground to soil warming occurs over long periods. We provide insight into the potential adaptation phases of subarctic grasslands.

Seasonal Variations of Fine Root Dynamics in Rubber-Flemingia macrophylla Intercropping System in Southwestern China.

Intercropping cover crops with trees enhance land productivity and improves the soil’s physio-chemical properties while reducing the negative environmental impact. However, there is a lack of quantitative information on the relationships between fine root biomass and available soil nutrients, e.g., nitrogen (N), phosphorus (P), and potassium (K), especially in the rubber-Flemingia macrophylla intercropping system. Therefore, this study was initiated to explore the seasonal variation in fine root biomass and available soil nutrients at different stand ages (12, 15, and 24 years) and management systems, i.e., rubber monoculture (mono) and rubber-Flemingia macrophylla intercropping. In this study, we sampled 900 soil cores over five seasonal intervals, representing one year of biomass. The results showed that the total fine root biomass was greater in 12-year-old rubber monoculture; the same trend was observed in soil nutrients P and K. Furthermore, total fine root biomass had a significant positive correlation with available N (p < 0.001) in rubber monoculture and intercropping systems. Thus, it suggests that fine root growth and accumulation is a function of available soil nutrients. Our results indicate that fine root biomass and soil nutrients (P and K) may be determined by the functional characteristics of dominant tree species rather than collective mixed-species intercropping and are closely linked to forest stand type, topographic and edaphic factors. However, further investigations are needed to understand interspecific and complementary interactions between intercrop species under the rubber-Flemingia macrophylla intercropping system.

Temporal variation in fine-root biomass, production, and mortality in a cool-temperate forest covered with understory &lt;i&gt;Sasa senenensis&lt;/i&gt;

Temporal variation in fine-root biomass, production, and mortality in a cool-temperate forest covered with understory &lt;i&gt;Sasa senenensis&lt;/i&gt;

Changes in Biomass and Diversity of Soil Macrofauna along a Climatic Gradient in European Boreal Forests.

Simple SummaryWe used a 1000 km long latitudinal gradient in north-western Russia to study the potential impacts of a changing climate on soil invertebrates visible by a naked eye (insects, spiders, earthworms etc.). We extracted these animals from soil, weighed them and identified them to the species level. We found that the diversity of soil invertebrates decreased towards the north, whereas the latitudinal pattern in biomass depended on the animal’s feeding habit. The biomass of species feeding on live plant roots and fungal mycelia decreased towards the north, whereas the biomass of species feeding on dead plant tissues and live invertebrates showed no significant latitudinal changes. The discovery of this variation in latitudinal biomass patterns suggests that soil invertebrates from different feeding guilds may respond differently to climate change. As a result, the biomass ratio between consumers and their food resources (e.g., herbivores and plants, predators and prey) may change. We poorly understood how this change will affect the future structure and functions of boreal forest ecosystems.Latitudinal gradients allow insights into the factors that shape ecosystem structure and delimit ecosystem processes, particularly climate. We asked whether the biomass and diversity of soil macrofauna in boreal forests change systematically along a latitudinal gradient spanning from 60° N to 69° N. Invertebrates (3697 individuals) were extracted from 400 soil samples (20 × 20 cm, 30 cm depth) collected at ten sites in 2015–2016 and then weighed and identified. We discovered 265 species living in soil and on the soil surface; their average density was 0.486 g d·w·m−2. The species-level diversity decreased from low to high latitudes. The biomass of soil macrofauna showed no latitudinal changes in early summer but decreased towards the north in late summer. This variation among study sites was associated with the decrease in mean annual temperature by ca 5 °C and with variation in fine root biomass. The biomass of herbivores and fungivores decreased towards the north, whereas the biomass of detritivores and predators showed no significant latitudinal changes. This variation in latitudinal biomass patterns among the soil macrofauna feeding guilds suggests that these guilds may respond differently to climate change, with poorly understood consequences for ecosystem structure and functions.

Effects of stand age and inter-annual precipitation variability on fine root biomass in poplar plantations in the eastern coastal China

Although we know that fine roots play an important role in carbon and nutrient cycling in forest ecosystems, knowledge on how fine root biomass (FRB) and its vertical distribution change with stand age and inter-annual precipitation variability is limited. In this study, we conducted a field experiment to explore the effects of stand age and inter-annual precipitation variability on FRB and its vertical distribution along the soil profile (0–100 cm) in poplar plantations on the eastern coast of China. We found that both poplar and understory vegetation FRB increased with increasing stand age. While the vertical distribution of fine roots in understory vegetation was not significantly affected by stand age, the distribution of FRB of poplar trees in deep soil layers was highest at the intermediate stand age (9-year-old). Poplar and understory vegetation FRB varied among sampling years and importantly, variation differed among stand ages. Compared with normal years, FRB of young poplar trees increased in the drought year (2019), while that in old stands decreased. In the subsequent drought recovery year, poplar FRB decreased in all stand ages; especially old stands. We found that poplar trees also optimize water absorption by changing the vertical distribution pattern of fine roots in the drought year. Moreover, unlike poplar trees, FRB of understory vegetation in all stand ages increased significantly in the drought year, but with little difference between the drought recovery and normal years. Structural equation models showed that variation in FRB of both poplar trees and understory vegetation were predominantly determined by soil total nitrogen while the vertical distribution of fine roots was regulated by soil water content. Our findings not only provide a scientific basis for sustainable management of poplar plantations, but also improve the ability to predict carbon dynamics of plantation ecosystems in confronting global climate change.

Spatial and Seasonal Pattern of Fine Root Biomass and Turnover Rate in Different Land Use Systems in Central Himalaya, India

Variation in fine root biomass (FRB) and turnover rate (TOR) were examined in four land use systems at two altitudes by using ingrowth core method. The aim of the study was to analyse the effect of altitude, depth and distance from tree stem on FRB and TOR. Significant variations (p < 0.05) were observed among land use systems, over seasons, depth and distances from the tree stem. The FRB varied between 47.09 and 528.59 kg ha–1. It was maximum in agri-horticulture (AH) system in bhabhar region and in homegarden (HG) system in hill region. In each land use system at both the altitudes FRB was maximum at uppermost layer (0‒20 cm) during rainy season at 50 cm distance from tree stem while, TOR did not showed any particular trend with soil depth and distance from the tree bole. FRB and turnover rate showed significance correlation with distance from tree bole at both the altitudes i.e. (r2 = 0.898 for low and r2 = 0.899 for high altitude).

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.

Influence of tree functional diversity and stand environment on fine root biomass and necromass in four types of evergreen broad-leaved forests

Positive effects of tree diversity on above-ground biomass have been well documented, whereas the relationships between tree functional diversity and fine root biomass and necromass remain unclear. This study explored the variation in fine root biomass and necromass among different evergreen broad-leaved forest types, the relative importance of the niche complementarity and the mass ratio hypotheses in driving biodiversity effects, as well as forest stand attributes and environmental factors causing variation in fine root biomass and necromass. We detected no significant differences between most forest types, and the prominently lower amount of fine root biomass and necromass in monsoon evergreen broad-leaved forests may be ascribed to the accelerated turnover rate caused by the elevated temperature. Conversely, the functional divergence showed marginally positive effects on fine root necromass, hence the effects of functional diversity may be negligible; however, community-weighted mean trait values, i.e. specific leaf area and leaf phosphorus concentration, demonstrated significantly negative effects on them. Basal area and stem density showed significant influence in regulating fine root biomass. The optimal GAM models explained 79.5% and 54.4% of the variation of fine root biomass and necromass, respectively. Our results suggest that fine root biomass and necromass may be determined by the functional characteristics of dominant tree species rather than collective functional diversity and closely linked to forest stand, topographic and edaphic factors.

Variation in fine root biomass along a 1000 km long latitudinal climatic gradient in mixed boreal forests of North-East Europe

The geographical patterns in the distribution of fine root biomass (FRB) and in the contribution of fine roots to below-ground nitrogen and carbon stocks are poorly documented. Here, we examined FRB and the ecological factors that govern it, along a 1000 km long latitudinal gradient in unmanaged mixed boreal forests in North-East Europe. We sampled fine roots (diameter ≤2 mm; trees and field layer vegetation combined) twice per growing season in 2015 and 2016 from ten sites spaced one degree of latitude between 60°N (near St. Petersburg) and 69°N (near Murmansk, Russia). We separated living fine roots. The roots were dried and weighed; tissue carbon and nitrogen concentrations were measured. The obtained values were correlated with climatic, plant community and soil characteristics. Among-site variation in the total FRB and carbon and nitrogen concentrations were not explained by latitude or by climatic, plant community or soil characteristics. However, fine root density in the organic layer increased towards the north. The more superficial root system in the north than in the south may indicate a poleward increase in the vulnerability of boreal forests to abiotic risks (forest fires, drought). Our results suggest that the future climate may shift fine roots as well as carbon and nitrogen cycling from the organic layer to mineral soils, thereby increasing the volume of soil utilized by fine roots for water and nutrient uptake.

Conifer proportion explains fine root biomass more than tree species diversity and site factors in major European forest types

Abstract Fine roots (diameter ≤ 2 mm) contribute significantly to the forest carbon cycle and are essential for resource acquisition from the soil. We conducted a study to assess the relationships between tree and ground vegetation fine root biomass and tree species diversity (monocultures compared to 2–5 species mixtures), conifer proportion and other site factors (stand basal area, soil carbon stocks and C:N ratio) in the six major European forest types, boreal forest in Finland, temperate forests in Poland, Germany and Romania, thermophilous deciduous forests in Italy, and Mediterranean forests in Spain. We sampled the fine roots of trees and ground vegetation to the depth of 20 cm in the mineral soil and allocated the fine root biomass to individual tree species using near-infrared reflectance spectroscopy (NIRS). We did not find any general positive effects of tree species diversity on the fine root biomass of trees or ground vegetation across the forest types and tree species combinations. However, our results suggest that tree fine root biomass increases with tree species diversity in pure broadleaf forests, but not in pure conifer forests. Species diversity explained 7% of the variation in tree fine root biomass in the broadleaf stands. The narrow tree species diversity gradient (1–2 species) in the conifer forests compared to the broadleaf forests (1−4) may have decreased the probability of conifer species combinations with below-ground functional traits conducive to over-yielding. Some evidence of diversity-mediated changes in the vertical rooting patterns of broadleaf trees and ground vegetation were found within the entire organic and 0–20 cm mineral soil layer although the weighted mean depth of fine root biomass was not affected. Negative diversity effects were found in the organic layer and positive diversity effects in the 0–10 cm mineral soil layer for broadleaf tree fine root biomass. Diversity effects were negative for ground vegetation fine root biomass in the 0–10 cm mineral soil layer. There was a general positive effect of conifer proportion on total fine root biomass in the organic layer, but not in the mineral soil layers. In general conifer proportion and site factors explained more of the variation in tree fine root biomass than tree species diversity. More research covering the annual variation in fine root biomass and deeper soil layers is needed before recommending managing species-rich forest for increasing below-ground biomass and carbon pools.

Modelling fine root biomass of boreal tree stands using site and stand variables

Quantification of fine root biomass is needed for estimating the role of roots as carbon (C) stores and sources of C input into the soil, as well as for modelling of forest nutrient cycling. Due to the laborious nature of root biomass determinations, there is a need to develop indirect methods that would allow fine root biomass to be estimated using data on easily measurable stand and site variables. We developed models for estimating tree fine root (diameter⩽2mm) biomass of boreal forests by compiling data from 95 Finnish forest stands (55 on upland soils and 40 on drained peatlands). Stand basal area predicted fine root biomass (R2-adj.=0.35, p<0.001) better than any other stand variable alone. A model that included stand basal area, dominant tree species group [birch/other], soil type [upland soil/drained peatland], temperature sum and the interaction of soil type and temperature sum accounted for 46% of the variation in fine root biomass. Stand basal area, the C:N ratio of the organic layer or upper 0–20cm peat layer and the dominant tree species group together explained 45% of the variation in fine root biomass. Temperature sum correlated with fine root biomass in opposite ways in upland soils and in drained peatlands: fine root biomass increased with decreasing temperature sum in upland soil sites, whereas in peatlands fine root biomass decreased as the temperature sum decreased. Although the models were based on a large dataset representing well the variation in stand age, basal area, site fertility and climatic conditions in northern European boreal forests, half of the variation in fine root biomass remained unexplained. More comprehensive fine root biomass sampling in relation to spatial and temporal variation in the forthcoming studies, for example in connection with monitoring campaigns, and additional predictors such as soil texture, successional stage and the fine root biomass of ground vegetation might improve the predictive power of fine root biomass models.

Variation in the aboveground stand structure and fine-root biomass of Bornean heath (kerangas) forests in relation to altitude and soil nitrogen availability

Borneo’s tropical heath (kerangas) forest has limited soil nutrient availability, and high variation in aboveground structure and fine-root biomass. This variation depends on altitude and soil nitrogen availability. To elucidate the biotic and abiotic factors affecting the variation in fine-root biomass (FRB, <2 mm diameter) of trees growing under nutrient-poor environments in Sabah, North Borneo, we investigated FRB in different forests with varying soil nitrogen (N) availability. We selected two study sites at different altitudes: the Maliau Basin (ca. 1000 m asl) and Nabawan (ca. 500 m asl). Both sites included tropical heath (kerangas) forest, on infertile soils (podzols) with a surface organic horizon overlying a bleached (eluviated) mineral horizon, and taller forests on more fertile non-podzolic soils. FRB was obtained from each plot by soil coring (to a depth of 15 cm). FRB increased with decreasing soil inorganic N content (NH4–N and NO3–N), tree height, and aboveground biomass. Thus, higher proportions of carbon resources were allocated to fine-roots in stands with lower N availability. FRB was significantly greater at the Maliau Basin than at Nabawan, reflecting lower soil N availability at higher altitude. Our results demonstrate high variation in FRB among the heath forests, and suggest that fine-root development is more prominent under a cooler climate where N availability limits tree growth owing to slower decomposition. The variation in N availability under the same climate (i.e., at the same altitude) appears to be related to the extent of soil podzolization.

Aggregated and complementary: symmetric proliferation, overyielding, and mass effects explain fine-root biomass in soil patches in a diverse temperate deciduous forest landscape.

Few studies describe root distributions at the species level in diverse forests, although belowground species interactions and traits are often assumed to affect fine-root biomass (FRB). We used molecular barcoding to study how FRB of trees relates to soil characteristics, species identity, root diversity, and root traits, and how these relationships are affected by proximity to ecotones in a temperate forest landscape. We found that soil patch root biomass increased in response to soil resources across all species, and there was little belowground vertical or horizontal spatial segregation among species. Root traits and species relative abundance did not explain significant variation in FRB after correcting for soil fertility. A positive relationship between phylogenetic diversity and FRB indicated significant belowground overyielding attributable to local root diversity. Finally, variation in FRB explained by soil fertility and diversity was reduced near ecotones, but only because of a reduction in biomass in periodically anoxic areas. These results suggest that symmetric responses to soil properties are coupled with complementary species traits and interactions to explain variation in FRB among soil patches. In addition, landscape-level dispersal among habitats and across ecotones helps explain variation in the strength of these relationships in complex landscapes.

Temporal variation in fine-root biomass, production and mortality in a cool temperate forest covered with dense understory vegetation in northern Japan

To understand the temporal pattern of fine-root dynamics and the factors that affect it, we investigated the seasonal and interannual variation in fine-root production (FRP) and fine-root mortality (FRM) rates, as well as fine-root biomass (FRB) and necromass in a cool temperate forest in northern Japan that was covered with dense understory vegetation of Sasa senanensis. We measured the root length density (RLD) and the rate of root production and mortality over 3yr using minirhizotrons, and compared these rates with temperature, precipitation, soil moisture, and plant area indices (PAI). We also measured the FRB and the necromass of fine roots four times per year for 2yr using soil cores and calculated dry weight-based FRP and FRM. FRB in the uppermost 15cm of the surface-soil layer accounted for 41–61% of the biomass up to 60cm soil depth, and decreased with increasing soil depth. The biomass of fine roots with root diameters <0.5mm was almost equivalent to that of roots measuring 0.5–2mm in diameter. Sasa roots accounted for 59–88% of the total FRB. FRB did not fluctuate seasonally, whereas RLD did. The FRP rate was high in mid- to late summer and correlated significantly with air and soil temperatures, indicating that temperature affects FRP. However, the relationship between FRP and soil moisture was weak. FRP was significantly correlated with the PAI of oak trees and the increment in the PAI of Sasa, suggesting that endogenous factors also affect FRP. Depending on the method used to calculate turnover, mean FRP for the 3-year study period was 589 or 726g m−2 yr−1, accounting for 36% or 41% of forest net primary production, respectively. The results of this study illustrate the substantial seasonal and interannual fluctuations in FRP, and indicate that a significant proportion of assimilated carbon was allocated to below-ground root systems in an oak-Sasa stand.

Factors causing variation in fine root biomass in forest ecosystems

Fine roots form one of the most significant components contributing to carbon cycling in forest ecosystems. We study here the effect of variation in root diameter classes, sampling depth and the inclusion of understorey vegetation root biomass in fine root biomass (FRB) estimates. The FRB estimates for different forest biomes are updated using a database of 512 forest stands compiled from the literature. We also investigate the relationships between environmental or forest stand variables and fine root biomass (≤2 mm in diameter) at the stand (g m −2) and tree level (g tree −1). The FRB estimates extrapolated for the whole rooting depth were 526 ± 321 g m −2, 775 ± 474 g m −2 and 776 ± 518 g m −2 for boreal, temperate and tropical forests, respectively, and were 26–67% higher than those based on the original sampling depths used. We found significant positive correlations between ≤1 and ≤2 mm diameter roots and between ≤2 and ≤5 mm roots. The FRB estimates, standardized to the ≤2 mm diameter class, were 34–60% higher and 25–29% smaller than those standardized to the ≤1 mm and ≤5 mm diameter classes, respectively. The FRB of the understorey vegetation accounted for 31% of the total FRB in boreal forests and 20% in temperate forests. The results indicate that environmental factors (latitude, mean annual precipitation, elevation, temperature) or forest stand factors (life form, age, basal area, density) can not explain a significant amount of the variation in the total FRB and a maximum of 30% that in the FRB of trees at the stand level, whereas the mean basal area of the forest stand can explain 49% of the total FRB and 79% of the FRB of trees at the tree level.

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m−2, and that of spruce and pine 297 g m−2 and 277 g m−2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length (SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter 60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates) at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live and dead) was 189.1 g·m−2·a−1, 50% (95.4 g·m−2·a−1) in the surface soil layer (0–10 cm), 33% (61.5 g·m−2·a−1), 17% (32.2 g·m−2·a−1) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased during the growing season. Mean RLD (7,411.56 m·m−3·a−1) and SRL (10.83 m·g−1·a−1) in the surface layer were higher than RLD (1 474.68 m·m−3·a−1) and SRL (8.56 m·g−1·a−1) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m−3 and 14.83m·g−1) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m−3) and SRL in October (3.77 m·g−1). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature, and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability.

Fine Root Biomass and Soil N and P in North Queensland Rain Forests1

[Extract] The development of an extensive surface root mat is one of the major mechanisms that enhances nutrient conservation in tropical rain forest, particularly in ecosystems growing on nutrient-poor, heavily leached soils (Jordan & Herrera 1981, Cuevas & Medina 1988). In these root mats, it is the fine unsuberized roots that are primarily responsible for the retention of nutrients (Edwards & Grubb 1982, Gower 1987, Berish & Ewe1 1988). The level of development of these fine root mats has been found to be very variable within the tropics, with the biomass of roots <5-mm diameter in the top 40 cm of soil ranging from 1.1 t/ha to 123.4 t/ha (Sanford 1985, Gower 1987, Cavelier 1992). According to the source-sink theory of resource allocation, based on theorem three of Bloom et al. (1985), trees growing on infertile sites should allocate a greater proportion of their resources into fine root production than those growing on fertile sites, as this “investment” in nutrient acquisition should increase growth and/or reproduction. Vitousek and Sanford (1 986) found that the available data suggested that the biomass of functionally active roots was substantially greater on infertile sites. Soil nitrogen has been suggested as the major factor governing belowground carbon allocation in temperate forest ecosystems (Grier et al. 1981, Aber et al. 1985, Nadelhoffer et al. 1985); however, there is conflicting evidence of the role nitrogen plays in influencing fine root biomass in tropical rain forest. A nutrient amendment study in a tropical rain forest in Hawaii found that nitrogen addition resulted in a significant reduction in fine root biomass (Gower & Vitousek 1989). In contrast, the availability of nitrogen was not a significant factor influencing fine root biomass at two sites in Costa Rica (Gower 1987). At these sites, the availabilities of phosphorus and calcium were suggested to be the major factors influencing fine root biomass (Gower 1987). The aims of this study were to document the variation in fine root biomass in soils of differing fertility and to investigate the relationship between fine root biomass and soil nitrogen and available phosphorus in north Queensland tropical rain forests.

Assessing fine-root biomass and production in a Scots pine stand: Comparison of soil core and root ingrowth core methods

Soil core and root ingrowth core methods for assessing fine-root (< 2 mm) biomass and production were compared in a 38-year-old Scots pine (Pinus sylvestris L) stand in eastern Finland. 140 soil cores and 114 ingrowth cores were taken from two mineral soil layers (0–10 cm and 10–30 cm) during 1985–1988. Seasonal changes in root biomass (including both Scots pine and understorey roots) and necromass were used for calculating fine-root production. The Scots pine fine-root biomass averaged annually 143 g/m2 and 217 g/m2 in the upper mineral soil layer, and 118 g/m2 and 66 g/m2 in the lower layer of soil cores and ingrowth cores, respectively. The fine-root necromass averaged annually 601 g/m2 and 311 g/m2 in the upper mineral soil layer, and 196 g/m2 and 159 g/m2 in the lower layer of soil cores and ingrowth cores, respectively. The annual fine-root production in a Scots pine stand in the 30 cm thick mineral soil layer, varied between 370–1630 g/m2 in soil cores and between 210 – 490 g/m2 in ingrowth cores during three years. The annual production calculated for Scots pine fine roots, varied between 330–950 g/m2 in soil cores and between 110 – 610 g/m2 in ingrowth cores. The horizontal and vertical variation in fine-root biomass was smaller in soil cores than in ingrowth cores. Roots in soil cores were in the natural dynamic state, while the roots in the ingrowth cores were still expanding both horizontally and vertically. The annual production of fine-root biomass in the Scots pine stand was less in root ingrowth cores than in soil cores. During the third year, the fine-root biomass production of Scots pine, when calculated by the ingrowth core method, was similar to that calculated by the soil core method. Both techniques have sources of error. In this research the sampling interval in the soil core method was 6–8 weeks, and thus root growth and death between sampling dates could not be accurately estimated. In the ingrowth core method, fine roots were still growing into the mesh bags. In Finnish conditions, after more than three growing seasons, roots in the ingrowth cores can be compared with those in the surrounding soil. The soil core method can be used for studying both the annual and seasonal biomass variations. For estimation of production, sampling should be done at short intervals. The ingrowth core method is more suitable for estimating the potential of annual fine-root production between different site types.

Contribution of forest fine roots in reclamation of semiarid sodic soils

Fine root biomass (<2 mm diameter) was estimated to a depth of 0.3 m in a 40‐year‐old rehabilitated forest on sodic wasteland at Lucknow, India (26°45'N, 80°53'E). The mass of live fine roots was estimated to be 166 g m‐ 2 (75% of total) on an ash‐free dry weight basis. Spatial and temporal variation in fine root biomass (11% and 17%) was not significant. Classification of fine roots into three diameter classes revealed that the proportion of very fine live roots <0.5 mm increased with soil depth. A significant negative correlation of fine roots (0.5–2.0 mm) with time was observed during 20 months of regular sampling (r2 = 0.71, P < 0.01). Fine root production was measured as 194 g m−2 a−1 by an in‐growth core technique including the decomposition loss during this period. Production differs significantly under different species (P < 0.05) and time (P < 0.01). Fine root mortality was 86 g m−2 a−1. Fine root decomposition rate declined through time and accounted for approximately 77% mass loss per year. Nutrient concentrations (N, P, K, Ca, Na) of live and dead roots were almost similar except for C, indicating almost no resorption. Nutrient inputs to the soil from fine roots were less than that of litter, corresponding to their lower turnover rate. However, the contribution of fine roots was apparently greater in the reclamation of soil structure, pH, and water permeability. The net change in soil nutrient pool on afforestation increased the soil C pool to 13 times and total N twice through the regular inputs from fine roots and litter fluxes. In forested soil, Na content was decreased by 74% and Ca elevated by 33% from the surrounding barren soil, whereas, P and K were not significantly different between sites.