Annual Fine Root Production Research Articles

Fine root dynamics and associated nutrient flux in Sal dominated forest ecosystems of Central Himalaya, India

The belowground systems of trees have a major role in forest functioning through absorption of water and nutrient cycling. This study deals with the fine root dynamics including fine root biomass, necromass, production, turnover, and nutrient return in transitional Sal (Shorea robusta Gaertn. f.) dominated sub-tropical forest ecosystems of Central Himalaya, India. Four sites namely, Site-1 (Kaladhungi), Site-2 (Fatehpur), Site-3 (Ranibagh), Site-4 (Amritpur) were selected in Sal forest within an elevational range between 405 and 580 m above sea level. The dominant and associated co-dominant species were selected from each site for the estimation of fine root dynamics by using sequential core and ingrowth core methods. The results revealed that the fine root biomass, necromass, and production were significantly (p < 0.05) affected by location, seasons, and soil properties. The fine root biomass and production decreased with increasing soil depth and also influenced by stand characteristics including tree density and basal area. The rainy season was most productive with maximum fine root biomass (507.37 kg ha–1) as well as fine root production (600.26 kg ha–1 season–1) in the dominant tree species S. robusta. Among the associated co-dominant tree species highest fine root biomass (330.48 kg ha–1) and fine root production (410.04 kg ha–1 season–1) was reported for Tectona grandis L. during the rainy season, while lowest fine root biomass (126.72 kg ha–1) and fine root production (195.59 kg ha–1 season–1) in the Glochidion velutinum Wight tree species during the winter season. Annual fine root production ranged from 460.26 to 1583.55 kg ha–1 yr –1, while turnover rate varied from 1.37 to 4.45 yr–1 across all the studied sites. The fine roots added carbon input of 154.38 to 564.20 kg ha–1 yr–1 and nitrogen input of 6.58 to 24.34 kg ha–1 yr–1 to the soil through annual flux. The study improves our understanding on fine root parameters under the influence of sites, soils and seasonal and spatial variation. The return of nutrients to the soil through fluxes from the roots illustrates the role of fine roots in carbon and nitrogen cycling of the forests and this potential can be harnessed to assess the long-term carbon and nitrogen pool estimations in forests and to plan and manage the forest ecosystems.

Readily available resources across sites and genotypes result in greater aboveground growth and reduced fine root production in Pinus taeda

Fine roots serve as the primary interface between trees and the soil, and they are dynamic in their response to environmental conditions. Among many functions, they are principle in gathering nutrients and water, and they constitute a major component of the tree. Their overall contribution to soil carbon flux is not well understood, nor is the effect of site and genotype on their dynamics, and these factors are crucial to understanding nutrient cycles and tree growth under variable conditions. This study evaluated how the fine root dynamics of loblolly pine (Pinus taeda L.) might be different between genotypes and on different sites. Three loblolly pine plantations were established, two in 2009 in North Carolina (NC) and Virginia (VA), and one in 2011 in Brazil (BR). Root biomass was estimated with soil cores across the three sites and between two genotypes in 2020. Seasonal and annual fine root production was measured at the NC and VA sites over the 12th growing season using ingrowth cores. The trees in BR that were two years younger were much larger than those in NC and VA and had more fine root biomass at initial sampling than those in NC, despite similar levels of fertility. Meanwhile, fine root production rates decreased with higher rates of aboveground productivity across all measured plots in NC and VA. These results indicate that (1) standing fine root biomass may be related to environmental conditions that are not easily manipulated, which could inform modeling of carbon cycles, and (2) in these intensively managed plots, sufficient resources were available to allow for increased aboveground growth despite lower rates of fine root production, which supports the employment of these intensive silvicultural practices.

Promotion effect of AM fungi and rhizobia co-inoculations on alfalfa (Medicago Sativa L.) growth

Arbuscular mycorrhizal fungi (AMF) and rhizobia have been widely used in agriculture in recent years to increase production, reduce fertilizer consumption and control plant diseases. However, it is unclear whether there are differences in the effects of AMF and rhizobia inoculation alone and in combination. In this study, alfalfa seedlings were inoculated with AMF Glomus mosseae (G.m), Glomus intraradices (G.i) and co-inoculated with AMF and rhizobia Sinorhizobium meliloti (S.m) before being transplanted outdoors. The growth characteristics, fine root yield and fine root death of alfalfa were measured throughout the experiment, and the results showed that co-inoculation with AMF and rhizobia promoted alfalfa growth, while increasing plant height, branch number and total biomass. However, the growth promoting effects of AMF and rhizobia differed; AMF inoculation displayed no advantage over S.m inoculation in increasing aboveground biomass (P > 0.05) but did lead to an increase in underground biomass (P < 0.05). Compared with that observed following the single inoculations with G.m or S.m, the annual fine root production following co-inoculation with G.m and S.m increased by 15.38% and 47.06%, respectively, although there was less effect following co-inoculation with G. i and S.m. These results indicated that there was mutual selectivity and interaction between AMF and rhizobia. G.m and S.m inoculation treatment has a positive effect on alfalfa growth, on the one hand, it is because that AMF-Rhizobia synergically promoted alfalfa root system to absorb nutrients (N), then improve the plant growth, on the other hand, their vaccination can reduce the death of alfalfa fine roots, significantly improve the alfalfa biomass of underground part.

Estimation of total fine root production using continuous inflow methods in tropical mangrove forest on Pohnpei Island, Micronesia: Fine root necromass accumulation is a substantial contributor to blue carbon stocks

AbstractFine root decomposition, mortality, and production are fundamental components of belowground carbon dynamics in mangrove ecosystems. Mangroves are highly productive ecosystems with huge carbon stocks; however, information on the dynamics of submerged fine roots in mangrove soils is limited. To estimate fine root production in several sites of mangrove communities on Pohnpei Island, Micronesia, we estimated continuous inflows using a simple mass balance model to combine ingrowth core and litterbag experimental results. According to our findings, previously reported mangrove fine root production values were severely underestimated because the fine root decomposition process was disregarded during the experimental period. We estimated that annual fine root production up to 0.3 m in depth ranged from 13.8 (Bruguiera gymnorrhiza in a landward plot) to 56.3 Mg ha−1 year−1 (B. gymnorrhiza in a seaward plot). However, comparing the fine root production with respect to the unit of stem cross‐section area increase in the sample tree, the fine root production of Rhizophora spp. was greater than that of other species. The annual fine root mortality and decomposition to annual fine root production was 70%–105% and 11%–52% of annual production, respectively. The annual fine root production estimated here was much higher than that previously reported. These findings begin to quantify the contribution and importance of highly productive mangrove fine roots for carbon sequestration in blue carbon ecosystems. Moreover, this study provides new insights into the organic carbon dynamics in mangrove soils with mangrove vegetation succession.

Estimation of fine root production, mortality, and decomposition by using two core methods and litterbag experiments in a mangrove forest

AbstractMangrove forests are characterized by high rates of carbon sequestration, with much of this carbon being derived from fine roots. In this study, we sought to estimate the dynamics of the fine (&lt;2 mm) and small (≥2 mm) roots of Kandelia obovata, one of the mangrove forest species found on Okinawa Island, southern Japan, and to evaluate annual root production considering root decomposition estimated using root litterbags. To estimate root production and mortality, we applied two approaches, sequential soil core sampling and ingrowth core methods. We found that annual root production determined by sequential soil core sampling was 3.2 times higher than that estimated by ingrowth core methods. The annual production of fine roots (545 and 294 g m−2 year−1 for sequential soil core sampling and ingrowth core methods, respectively) was higher than that of small roots (536 and 44 g m−2 year−1 for sequential soil core sampling and ingrowth core methods, respectively). The results obtained using sequential soil core sampling indicated a high proportion of fine root necromass to total fine root mass (81%), most of which comprised very fine roots (&lt;0.5 mm). We also established that the decomposition ratio of fine roots was lower than that of small roots. Collectively, our observations indicate that the slow rate of decomposition and high rate of production of fine roots contribute significantly to the accumulation of fine root necromass, particularly that of very fine roots, in the mangrove forest.

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

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

Multifunctions of fine root phenology in vegetative and reproductive growth in mature beech forest ecosystems

AbstractMasting, a large interannual variation of reproductive investment spatially synchronized within perennial plants, is an important factor for understanding the use and storage of carbon and nutrient resources in various forest ecosystems. Fine roots play essential roles in water and nutrient uptake but also consume a large amount of net primary production (NPP) during growth. Understanding masting mechanisms requires knowledge of how masting trees succeed in abundant fructification by adjusting resource acquisition via fine roots and how mast seeding influences fine root dynamics. The aims of the present study were to estimate interannual variations in NPP, including belowground production, over several years while evaluating fine root phenology and to suggest possible relationships between fine root growth and the production of nuts, leaves, and woody biomass in mature forest ecosystems. Nut and leaf production was quantified using litter traps in two beech forests located at different altitudes of 550 and 1500 m, and woody biomass increment was estimated using allometric equations. Seasonal and mass‐based annual fine root production was determined using minirhizotrons and soil cores. Correlations between seasonal fine root and aboveground production were analyzed using the state‐space model, which can verify masting effects on fine root production between flower bud formation and mast seeding. NPP estimates exhibited almost biennial or irregular masting behavior. Nut production was positively correlated with fine root production in autumn of the previous year in the lower site but showed negative correlations with that in the early growing season of the same year in the upper site. The former indicated enhanced fine root production to absorb nutrients prior to mast seeding, and the latter suggested the suppression of fine root production due to resource depletion during masting. Fine root production increased with increasing leaf production in the early growing season in both sites, indicating the corresponding water transport between them. Thus, fine root phenology has distinct multiple functions to ensure water and nutrient resources in supporting aboveground vegetative and reproductive growth, resulting in variable seasonal patterns of fine root production.

Density manipulation and pruning on fine root production and decomposition dynamics in a mature Acacia mangium Willd. stand in Kerala, India

Fine roots play a major role in water and mineral uptake and nutrient cycling in woody perennial-based ecosystems. Just as other biomass components, stand density manipulation and tree pruning may influence fine root production (FRP) and its decomposition dynamics. However, quantitative information on FRP and its turnover under different density and pruning regimes are meagre for most tropical trees. A field study was conducted to characterize FRP and associated nutrient release under varying stand density and pruning regimes in a 12-year-old Acacia mangium stand in Kerala, India. Soil ingrowth core method was employed for quantifying FRP and sequential core method for estimating standing fine root biomass. Annual FRP estimates were 5.78, 5.39, 3.74, and 3.38 Mg ha–1 for the 5000, 2500, 1250 and 625 trees ha−1 treatments, respectively. Allometric models based on tree diameter and basal area gave a good fit for annual FRP. Fine root turnover rates ranged from 2.81 to 3.16 yr−1, which however, was not influenced by stand density. Carbon stocks ranged from 1.36 to 2.39 Mg ha−1 with highest FRP during rainy season and lowest during the dry period. The litterbag study using nylon mesh bags indicated that annual fine root mass loss ranged from 76.2 (5000 trees ha−1) to 96.8% (625 trees ha−1). Tree pruning had only modest effects on tree growth, FRP, and carbon and nutrient release patterns. The study highlights the importance of stand density manipulation in altering A. mangium FRP, soil carbon and mineral nutrient dynamics.

Remarkable Similarity in Timing of Absorptive Fine-Root Production Across 11 Diverse Temperate Tree Species in a Common Garden.

Long-term minirhizotron observations of absorptive fine roots provide insights into seasonal patterns of belowground root production and carbon dynamics. Our objective was to compare root dynamics over time across mature individuals of 11 temperate trees species: five evergreen and six deciduous. We analyzed the timing and growth on 1st-and 2nd-order roots in minirhizotron images down to a vertical depth of 35 cm, as well as monthly and total annual length production. Production patterns were related to total annual precipitation of the actual and previous year of root production over 6 years. The main or largest peak of annual fine-root production occurred between June and September for almost all species and years. In most years, when peaks occurred, the timing of peak root production was synchronized across all species. A linear mixed model revealed significant differences in monthly fine-root length production across species in certain years (species x year, P < 0.0001), which was strongly influenced by three tree species. Total annual root production was much higher in 2000–2002, when there was above-average rainfall in the previous year, compared with production in 2005–2007, which followed years of lower-than-average rainfall (2003–2006). Compared to the wetter period all species experienced a decline of at least 75% in annual production in the drier years. Total annual root length production was more strongly associated with previous year’s (P < 0.001) compared with the actual year’s precipitation (P = 0.003). Remarkably similar timing of monthly absorptive fine-root growth can occur across multiple species of diverse phylogeny and leaf habit in a given year, suggesting a strong influence of extrinsic factors on absorptive fine-root growth. The influence of previous year precipitation on annual absorptive fine-root growth underscores the importance of legacy effects in biological responses and suggests that a growth response of temperate trees to extreme precipitation or drought events can be exacerbated across years.

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.

Seasonal patterns of fine root dynamics and their contribution to net primary production in hinoki cypress (Chamaecyparis obtusa) and konara oak (Quercus serrata) forests

Key messageFine root and litterfall are major contributor of NPP and fine root production may reflect forest productivity in a warm-temperate forest in Japan.Forest ecosystems play an important role as the major carbon sink on land, with fine root dynamics and litterfall representing major carbon fluxes. The objectives of this research were to estimate NPP including annual fine root production values, to investigate fine root dynamics and the relationships between above– and belowground organs in konara oak (Quercus serrata) and hinoki cypress (Chamaecyparis obtusa) forests. Litterfall was collected seasonally for 1 year from June 2013. The ingrowth core method and the sequential soil core method were applied with a root litterbag experiment to estimate fine root (< 2 mm) production (FRP), mortality (FRM), and decomposition (FRD) for 1 year (from 2013 to 2014), using the continuous inflow estimate method and the simplified decision matrix. The total NPP ranged from 8.2 to 13.9 (t ha− 1 yr− 1), and the sum of aboveground litterfall and FRP accounted for 60% of the total NPP on average, confirming the significance of above- and belowground litter for the forest NPP as a source of detritus for the decomposer system. In hinoki cypress stand, fine root biomass peaked in the end of winter while fine root necromass showed the highest peak in late summer. In konara oak stand, only very fine root (< 0.05 mm) biomass and necromass demonstrated significant seasonal patterns. The seasonal patterns of fine root production did not differ between forest types and root diameter classes. We found a possible relationship between above- and belowground production and fine root production tended to be high in productive forests. This study improves our understanding of different patterns of carbon dynamics between temperate broadleaved and coniferous forest ecosystems.

Biomass Allocation to Resource Acquisition Compartments Is Affected by Tree Density Manipulation in European Beech after Three Decades

This study reports on an investigation of fine root and foliage productivity in forest stands dominated by European beech (Fagus sylvatica L.) and exposed to contrasting intensities of mature forest harvesting. The main aim of this study was to consider the long-term effects of canopy manipulation on resource acquisition biomass compartments in beech. We made use of an experiment established in 1989, when five different light availability treatments were started in plots within a uniform forest stand, ranging from no reduction in tree density to full mature forest removal. We measured fine root standing stock in the 0–30 cm soil layer by coring in 2013 and then followed annual fine root production (in-growth cores) and foliage production (litter baskets) in 2013–2015. We found that the plot where the tree density was reduced by 30% had the lowest foliage and the highest fine root production. In 2013, this plot had the highest fine root turnover rate (0.8 year−1), while this indicator of fine root dynamics was much lower in the other four treatments (around 0.3 year−1). We also found that the annual fine root production represented around two thirds of annual foliage growth on the mass basis in all treatments. While our findings support the maintenance of source and sink balance in woody plants, we also found a long-lasting effect of tree density manipulation on investment into resource acquisition compartments in beech forests.

Patterns and controls on fine-root dynamics along a rainfall gradient in Ghana

Fine-root biomass relates to environmental variables differently along a rainfall gradient in Ghana. Understanding changes in root dynamics in response to environmental factors is crucial for projections of climate change, yet information on controls of root dynamics is limited in the tropics. This study quantified fine-root dynamics along a rainfall gradient in Ghana, ranging from dry to wet evergreen forests. Fine-root biomass and necromass were estimated by the sequential coring method for a year and analyzed in relation to measured environmental factors (rainfall, soil moisture content, air temperature and soil temperature). Overall, fine-root biomass increased along the gradient with the highest estimate found in the wet forest site. Mean annual fine root production ranged from 276.60 to 348.95 gm−2 year−1 across the different forest types. Fine-root turnover rates ranged from 2.3 to 3.1 year−1, and roots tended to turn over faster in the dry than in the moist and wet forest sites. There was a non-linear but significant relationship between fine-root biomass and soil moisture content in the wet forest. None of the environmental factors related to fine-root biomass in the moist forest. However, there was a significant non-linear relationship between rainfall and fine-root biomass in the dry forest site. These results suggest that environmental factors influence fine-root biomass differently across the three forest types. Therefore, future studies should focus on a comprehensive measurement of environmental controls to deepen our understanding of fine root dynamics.

FINE ROOT BIOMASS OF ERICA TRIMERA (ENGL.) ALONG AN ALTITUDINAL GRADIENT ON BALE MOUNTAINS, ETHIOPIA

Fine roots biomass of Erica trimera was investigated at three altitudinal levels, i.e. 3000, 3300, and 3500 masl across three depth classes (0-10, 10-20, and 20-40 cm) for each of the four seasons of Bale Mountains by using sequential soil coring. Soil chemical characteristics and moisture were analyzed for all of the three altitudinal levels and depth classes. The annual fine root production of the species was calculated based on min-max method. Fine root production increased markedly from 3270 kg. ha-1. yr-1 at 3000 masl and 2850 kg. ha-1. yr-1 at 3300 masl to 9987 kg. ha-1. yr-1 at 3500 masl. Total nitrogen, available phosphorous, organic carbon, moisture content and PH of the soil increased significantly as altitude increased. In the two lower altitudinal levels, 3000 and 3300masl, fine root mass and biomass decreased as depth increased, but at the higher altitude (3500 masl) fine root tended to more concentrated at the deeper depths while the availability of soil nutrient and soil acidity showed a tendency to decreased as depth increased at all of the three sites. The highest fine root mass and biomass was recorded at the major rainy season followed by the transition period, the small rainy and dry period, in that order. The highest fine root mass during the major rainy season and lowest fine root mass in the dry season indicated that soil moisture was critical factor in governing the pattern of root growth in this ecosystem.

Role of Fine Tree Roots in the Nitrogen Cycle of Boreal Forests

Despite the insignificant contribution to the total forest phytomass, fine roots form 30% of the production of forest ecosystems, playing a crucial role in biogeochemical cycles. However, estimates of the biomass, annual production, dieback, and age of fine roots remain understudied, especially in Russian forests, due to technical difficulties. There are only a few estimates of nitrogen consumption for the annual production of fine roots. It is believed that they comprise up to 75 kg N ha–1 in mature forests. This is up to 60% of the total consumption of nitrogen for annual yield and is comparable with mineralized soil nitrogen. However, these values are approximate because the methods of measuring fine roots production are debatable.

Interactive effects of warming and nitrogen addition on fine root dynamics of a young subtropical plantation

Forest aboveground production and soil carbon (C) pools are closely linked to fine root dynamics. Uncertainty about the effects of warming and nitrogen (N) deposition on fine root dynamics limits our ability to predict how C will transfer between biological and atmospheric pools in tropical and subtropical forests. In order to examine the effects of warming and N deposition on fine roots in subtropical plantations, we used a randomized complete block design with factorial soil warming (ambient, ambient + 5 °C) and N deposition (ambient, ambient + 80 kg N ha−1 yr−1) manipulation. Minirhizotrons were used to monitor fine root production, mortality and turnover rate of Chinese fir (Cunninghamia lanceolata) seedlings for two years, and seedling growth was measured. We found warming had positive effects on annual fine root production, mortality and turnover rate both under ambient and increased N addition. N addition had positive effects on annual fine root production, mortality and turnover rate in the warmed plots, but had no influence on annual fine root production, mortality and turnover rate in the unwarmed plots. Warming and N addition had an additive (not interactive) effect on fine root production, mortality and turnover rate. There was an interaction between warming and N addition on living fine root biomass in the second year. These changes can be largely attributed to belowground/aboveground C allocation. There was no evidence of root respiration acclimation to warming. In addition, increased fine root turnover rate after warming implies accelerated root C inputs to soils, which may affect soil C and nutrient dynamics. Nitrogen addition may exacerbate this. There was no acclimation of root respiration to warming, which may alter C balance and cause more CO2 release to the atmosphere through autotrophic respiration.

Positive species mixture effects on fine root turnover and mortality in natural boreal forests

The positive species mixture effects on both above- and below-ground productivity have been well documented in diverse ecosystem types. However, whether the results obtained on productivity can be generalized to other ecosystem processes remains unclear. We investigated the effects of tree species mixtures on fine root biomass turnover and biomass loss from mortality by sampling 18 stands dominated by Populus tremuloides and Pinus banksiana, respectively, and their relatively even mixtures in post-fire boreal forests of two stand ages (8 and 34 years following stand-replacing fire). Fine root biomass turnover and mortality were higher in mixtures than expected from those of single species-dominated stands in both stand ages, with a higher magnitude of mixture effects in the 34-year-old than in the 8-year-old stands. Mixture effects on turnover and mortality did not differ with soil depth in 8-year-old stands, but turnover increased while mortality decreased from the forest floor to the mineral layers in 34-year-old stands. Both turnover and mortality significantly increased with tree species evenness in 34-year-old stands, but not in 8-year-old stands. Root turnover and biomass loss from mortality were positively associated with annual fine root production across all stand types and ages. Our results provide the first evidence for positive mixture effects on fine root biomass turnover and biomass loss from mortality in natural forests. Moreover, our results suggest that the positive mixture effects resulted from increased competition induced by the increase of fine root biomass production in tree species mixtures.

Relative contributions of leaf litter and fine roots to soil organic matter accumulation in mangrove forests

Mangrove above- and belowground litter contributes greatly to soil carbon (C) especially in systems with limited allochthonous input. This study aims to estimate the relative contributions of mangrove leaf litter vs. fine roots to the annually accumulated plant debris in the soil. Annual production of leaf litter and fine roots in four mono-specific mangrove forests was combined with their mass remaining after one year of decomposition to make the estimation. Annual fine root production was 2.2–5.1 times greater than leaf litter production, which ranged between 266 and 814 g m−2. After 391 days of decomposition, 0–41% and 75–88% of leaf litter and fine root initial mass respectively remained. Only 5.9–69 months were expected for leaf litter to reach an approximately complete decomposition, in contrast to 111–655 months expected for fine roots. Annual plant detritus accumulation in the soil amounted to 405–2812 g m−2, with leaf litter and fine roots contributing 2.5–7.6% and 92.4–97.5%, respectively. Fine roots are the dominant contributor to soil organic matter accumulation in mangroves due to high production and low decomposition rates. Management practices that foster fine root production are expected to accelerate soil C accumulation.

Litterfall production and fine root dynamics in cool-temperate forests.

Current understanding of litterfall and fine root dynamics in temperate forests is limited, even though these are the major contributors to carbon and nutrient cycling in the ecosystems. In this study, we investigated litterfall and fine root biomass and production in five deciduous and four coniferous forests at the Gwangneung Experimental Forest in Korea. We used ingrowth cores to measure fine root production and root turnover rate. The litterfall was separated into leaves, twigs, and others, and then leaves were further separated according to species. Annual litterfall mass was not significantly different between the years, 360 to 651 g m-2 in 2011 and 300 to 656 g m-2 in 2012. Annual fine root (<5 mm) production was significantly higher in 2012 (421 to 1342 g m-2) than in 2011 (99 to 872 g m-2). Annual litterfall mass was significantly different among the stands, while fine root production did not statistically differ among the stands. The average fine root turnover rate, calculated by dividing the annual fine root production by the maximum standing fine root biomass, was 1.65 for deciduous forests and 1.97 for coniferous forests. Fine root production constituted 18–44% of NPP, where NPP was the sum of woody biomass production, litterfall production, and fine root production. Belowground production was a greater fraction of NPP in more productive forests suggesting their greater carbon allocation belowground.

Effects of species diversity on fine root productivity increase with stand development and associated mechanisms in a boreal forest

Summary There is a growing interest in understanding the relationship between diversity and below‐ground productivity due to the critical contribution of below‐ground systems to overall terrestrial productivity. Yet, the temporal (seasonal and developmental) changes in diversity effects on below‐ground productivity and their underlying mechanisms remain unclear. We hypothesized that (i) diversity effects on fine root productivity increase with stand development, and (ii) increased diversity effects associated with stand development result from augmented horizontal soil space utilization, increased forest floor depth for rooting, enhanced effects in nutrient‐poor soil layers and/or foraging towards high nutrient availability. We investigated the effects of tree species diversity on fine root productivity by sampling 18 stands dominated by single species and their mixtures in post‐fire boreal forests of two stand ages (8 and 34 years following stand‐replacing fire). Species evenness was significantly higher in species mixtures than in single‐species‐dominated stands at both age classes, while species richness did not differ across stand types and age classes. We found that the annual fine root production was higher in mixtures than the mean of single‐species‐dominated stands in both stand ages, with a significantly higher magnitude of effects in the 34‐year‐old than 8‐year‐old stands. Mixtures had higher horizontal soil volume filling than single‐species‐dominated stands with a more pronounced increase in the 34‐year‐old than 8‐year‐old stands. Compared with the 8‐year‐old stands, the 34‐year‐old stands had increased forest floor depth and greater overyielding with soil depth, and their fine root productivity was more responsive to the vertical variation in soil phosphorus concentrations among soil layers. Synthesis. Our results provide evidence for increasing positive diversity effects on fine root productivity with stand development in heterogeneous natural forests. Moreover, our results indicate that the increased positive diversity effects with stand development was the result of multiple mechanisms, including higher horizontal soil volume filling, a thicker forest floor layer for rooting, a higher magnitude of complementarity in nutrient‐poor deep soil layers and stronger nutrient foraging towards soil layers with high nutrient concentrations in older than younger stands.