Root Mass Loss Research Articles

Root-order-associated variations in fine-root decomposition and their effects on soil in a subtropical evergreen forest

BackgroundDespite the importance of root decomposition in predicting ecosystem responses to future climate change, the effects of branch order on root decomposition and the feedback to soil still remains poorly understood. Here we separated root samples taken from two tree species (Castanopsis fargesii and Schima superba in subtropical forests along the coastal area in eastern China) into four-order classes (1st–2nd order, 3rd order, 4th order, and 5th order) and conducted a 540-day litterbag incubation experiment in laboratory to examine root mass loss, nutrient release, and the influence on soil during decomposition.ResultsC. fargesii roots of 1st–2nd and 3rd order decayed more slowly than those of 4th and 5th order, but this pattern was not significant for S. superba. Of all the measured root traits, the decomposition rates correlated best with root C/N ratio, diameter and specific root length (SRL) based on the structural equation modeling. Both tree species and root order exhibited significantly effects on root initial traits. Overall, C. fargesii roots decay faster than S. superba, and this appears to be associated with root initial C quality and N concentration. In addition, root order positively affected root decomposition rates mainly through root diameter and SRL. However, no significant difference was found in C and N content between soils below the litterbag with different-order roots.ConclusionsOur findings suggest the effects of branch order on root decomposition are dependent on tree species. Moreover, root morphological properties might also be the controlling factor in root decay besides root chemistry fractions. Overall, the integrative effects should be considered to improve our understanding of the fate of fine-root litter and their contribution to soil C and N pool.

Mowing Facilitated Shoot and Root Litter Decomposition Compared with Grazing

Shoot and root litter are two major sources of soil organic carbon, and their decomposition is a crucial nutrient cycling process in the ecosystem. Altitude and land use could affect litter decomposition by changing the environment in mountain grassland ecosystems. However, few studies have investigated the effects of land use on litter decomposition in different altitudes. We examined how land-use type (mowing vs. grazing) affected shoot and root litter decomposition of a dominant grass (Bromus inermis) in mountain grasslands with two different altitudes in northwest China. Litterbags with 6 g of shoot or root were fixed in the plots to decompose for one year. The mass loss rate of the litter, and the environmental attributes related to decomposition, were measured. Litter decomposed faster in mowing than grazing plots, resulting from the higher plant cover and soil moisture but lower bulk density, which might promote soil microbial activities. Increased altitude promoted litter decomposition, and was positively correlated with soil moisture, soil organic carbon (SOC), and β-xylosidase activity. Our results highlight the diverse influences of land-use type on litter decomposition in different altitudes. The positive effects of mowing on shoot decomposition were stronger in lower than higher altitude compared to grazing due to the stronger responses of the plant (e.g., litter and aboveground biomass) and soil (e.g., soil moisture, soil bulk density, and SOC). Soil nutrients (e.g., SOC and soil total nitrogen) seemed to play essential roles in root decomposition, which was increased in mowing plots at lower altitude and vice versa at higher altitude. Therefore, grazing significantly decreased root mass loss at higher altitude, but slightly increased at lower altitude compared to mowing. Our results indicated that the land use might variously regulate the innate differences of the plant and edaphic conditions along an altitude gradient, exerting complex impacts in litter decomposition and further influencing carbon and nutrient cycling in mountain grasslands.

Additive effects of warming and grazing on fine-root decomposition and loss of nutrients in an alpine meadow

AbstractFine-root decomposition is a critical process regulating ecosystem carbon cycles and affecting nutrient cycling and soil fertility. However, whether interaction between warming and grazing affects fine-root decomposition is still under-researched in natural grasslands. A two-factorial experiment with asymmetric warming (i.e. daytime vs. nighttime and growing season vs. nongrowing season) and moderate grazing (i.e. about average 50% forage utilization rate) was conducted to explore whether warming and grazing affect fine-root decomposition and loss of nutrients during a 2-year decomposition period in an alpine meadow on the Tibetan Plateau. Both warming and grazing facilitated carbon cycling through increase in fine-root decomposition, and influenced element cycling which varies among elements. The effects of warming and grazing on fine-root decomposition and loss of nutrients were additive. Both warming and grazing significantly increased cumulative percentage mass loss and total organic carbon loss of fine roots during the 2-year experiment. Only warming with grazing treatment reduced percentage nitrogen loss, whereas warming, regardless of grazing, decreased percentage phosphorus loss. Warming and grazing alone increased percentage loss of potassium, sodium, calcium and magnesium compared with control. There were no interactions between warming and grazing on fine-root decomposition and loss of nutrients. There was greater temperature sensitivity of decreased phosphorus loss than that of decreased nitrogen loss. Different temperature sensitivities of percentage loss of nutrients from fine-root decomposition would alter ratios of the available nutrients in soils, and may further affect ecosystem structure and functions in future warming.

Ethylene and its inhibitors affect the quality of processed sweet potatoes

Sweet potato fried chips have great acceptance and high market value. Sprouting and fresh mass loss of tuberous roots during storage compromise the quality of the processed products. The objective of this work was to evaluate the effect of 1-Methylcyclopropene (1-MCP), amino-oxyacetic acid (AOA), and ethylene on the physico-chemical quality of fresh sweet potato and its relationship with fried color score in processed chips of cv. BRS Rubissol stored at room temperature. During storage, the weight loss, sprouts number, dry matter content, non-enzymatic browning, protein content, soluble phenols fraction, reducing sugars, total amino acids, pH, soluble solids (SS), titratable acidity (TA) and SS/TA ratio were evaluated. The sweet potato roots cv. BRS Rubissol present good potential for processing as fried chips. 1-MCP and AOA treatments reduced the root sprouting, physico-chemical quality was maintained in all treatments and the fried chips showed less browning in all treatments with storage. Since the sprouting process compromises the storage of roots, AOA and 1-MCP treatments may be applied to extend the shelf-life of roots and improve the processing potential.

The Dynamics of Mass Loss and Nutrient Release of Decomposing Fine Roots, Needle Litter and Standard Substrates in Hemiboreal Coniferous Forests

Litter decomposition is a key process that drives carbon and nutrient cycles in forest soils. The decomposition of five different substrate types was analyzed in hemiboreal coniferous forests, focusing on the mass loss and nutrient (N, P, and K) release of fine roots (FR) and needle litter in relation to the initial substrate and soil chemistry. A litterbag incubation experiment with site-specific FR and needle litter and three standard substrates (green and rooibos tea, α-cellulose) was carried out in four Norway spruce and four Scots pine-dominated stands in Estonia. Substrate type was the primary driver of mass loss and the decay rate of different substrates did not depend on the dominant tree species of the studied stands. Alpha-cellulose lost 98 ± 1% of the mass in 2-years, while the FR mass loss was on average 23 ± 2% after 3-years of decomposition. The FR decomposition rate could be predicted using a corresponding model of green tea, although the rate of FR decomposition is approximately five times lower than the rate of green tea in the first 3-years. The annual decomposition rate of the needle litter is rather constant in hemiboreal coniferous forests in the first 3 years. The initial substrate of fine roots or needle litter and soil chemistry jointly had a significant effect on mass loss in the later stage of decomposition. The critical N concentration for N release was lower for pine FR and needle litter (0.9–1.3% and 0.7–1.1%) compared to spruce (1.2–1.6% and 1.5–1.9%, respectively). The release rate of K depended on the initial K of substrate, while the release of N and P was significantly related to the initial C:N and N:P ratios, respectively. The results show the central role of soil and substrate initial chemistry in the decomposition of fine roots and needle litter across hemiboreal forests, especially at later stage (after 2 years) of decomposition. The slower decomposition and higher retention of N in the fine roots relative to needle litter suggests that fine roots have a substantial role in the carbon and nitrogen accumulation in boreal and hemiboreal forest ecosystems.

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.

Effects of nutrient fertilization on root decomposition and carbon accumulation in intensively managed grassland soils

AbstractOur knowledge of root mass decomposition processes has greatly benefited from studies carried out in natural and semi‐natural ecosystems. It is less known, however, how root mass loss might occur in intensively managed ecosystems, such as agricultural grasslands, which receive chronic additions of nitrogen (N) fertilizers. Key questions remain about (1) how repeated N applications either in organic or inorganic forms might influence fine root mass decomposition, and (2) what implications root mass loss might have for soil carbon (C) storage. Here, we use a long‐term grassland experiment established in 1970 at Hillsborough, Northern Ireland (UK), to address how repeated additions of organic (i.e., liquid manures) and inorganic (i.e., NPK) fertilizers over >45 yr might influence fine root mass decomposition and how. We found that after a 10‐month incubation period under field conditions, highest root mass loss (~43%) was associated with highest additions of organic slurries, whereas lowest root mass loss (~29%) occurred in inorganically N‐fertilized and unfertilized soils. Root decomposition was significantly and negatively related to root C:N ratios and fungal‐to‐bacterial (F:B) ratios. Root decomposition, however, was not related to changes in soil C stocks or rates of soil C accumulation. N applications either maintained or increased (up to three times) soil C accumulation compared to unfertilized soils after five decades of intensive management. Our findings suggest that in the short‐term organic fertilization can enhance root detritus decomposition (thus promoting N release in soils for plant uptake) while contributing in the long‐term to soil C accumulation either through extra C inputs from manures or through N‐induced effects on microbial activity or both. Further studies need to address how this dual effect of organic fertilization could contribute making grassland intensification more sustainable by reducing the use of artificial NPK fertilizers.

Effects of Microtopography on Absorptive and Transport Fine Root Biomass, Necromass, Production, Mortality and Decomposition in a Coastal Freshwater Forested Wetland, Southeastern USA

Forested wetlands are an important carbon (C) sink. Fine roots (diameter < 2 mm) dominate belowground C cycling and can be functionally defined into absorptive roots (order 1–2) and transport roots (order ≥ 3). However, effects of microtopography on the function-based fine root dynamics in forested wetlands are poorly understood. We studied fine root biomass allocation and biomass, necromass, mass loss rate, production, mortality and decomposition of absorptive and transport roots in hummocks and hollows in a coastal plain freshwater forested wetland (FFW) in the southeastern USA using dynamic-flow method. Biomass ratios of first- to second-order roots and absorptive to transport roots and the biomass and necromass of absorptive and transport roots were significantly higher in top 0–10 cm organic peat layer than in 10–20 cm muck and mineral layer, and were significantly higher in hummocks than in hollows. The mass loss rate, production, mortality and decomposition were significantly higher in hummocks than in hollows. Absorptive roots did not have a lower mass loss rate than transport roots. Microtopography significantly affected the contributions of absorptive and transport roots to the total production, mortality and decomposition. Production, mortality and decomposition of absorptive roots were higher than those of transport roots in hummocks but lower than those of transport roots in hollows. Total (hummocks plus hollows) fine root production, mortality and decomposition were 455 ± 106 g m−2 y−1, 475 ± 79 g m−2 y−1 and 392 ± 60 g m−2 y−1, respectively. Greater mortality than decomposition resulted in net fine root C input to soil. The observed microtopographic controls on fine root dynamics have great implications for soil C cycling. As sea level rises, the relative area of hollows in coastal plain FFWs will increase, causing a decrease in fine root mass loss rate, biomass, production, mortality and decomposition and it is the balance of these processes that will determine future soil C storage and cycling.

Levels and times of artificial defoliation on performance of second cycle cassava

The information on behavior of crop linked to defoliation is essential to determine the management of herbivore pests. The aim of this study was to evaluate the performance of cassava as a function of the time and level of defoliation applied in the second cycle of cultivation, that is, after the first year of cultivation in which the crop was naturally submitted to the physiological rest period, caused by low temperatures and pluviometric precipitation typical of the southern Brazilian region. We used a randomized block design in factorial 5 x 5.in which 5 levels of defoliation (0, 25, 50, 75 or 100% of defoliation) were applied at 5 different times of 45, 90, 135, 180, or 225 days after sprouting (DAS) of the stems. The following variables were measured: plant height, stem diameter, number of roots per plant, root mass and amount of starch in the roots. The means were submitted to the F test at 5% of probability and analyzed by the regression test using the Sisvar software. Plant height and diameter were inversely proportional to the degree of defoliation when subjected to treatments, especially when subjected to 100% defoliation at 90 DAS. For the root mass, the more drastic defoliation treatments (100 %), when applied at 132 DAS, led to a low production, whereas only the defoliation levels induced a meaningful reduction in the deposition of starch in roots, showing a linear effect and decreasing according to the increase in defoliation. It can be concluded that defoliation between 90 and 135 DAS at the more drastic levels resulted in a greater root mass loss, regardless of the time of defoliation, caused the greatest losses in the amount of starch, therefore, it is recommended to the producer to control this pest before the 90 days of sprouting of the stems at the beginning of the defoliation.

Root diameter controls the accumulation of humic substances in decomposing root litter

The humification of plant litter is a crucial step for the buildup of soil organic matter in terrestrial ecosystems. Yet, how environmental change and substrate quality affect root humification still remains poorly understood. A two-year litterbag experiment was conducted to assess the root mass remaining and accumulation of humic substances in roots of three diameter classes (0–2, 2–5 and 5–10 mm) of two common subalpine tree species (Picea asperata and Abies faxoniana) at two elevations (3037 m and 3580 m) on the eastern Tibetan Plateau. No significant differences were found between elevation treatments in the concentration of humic substances. Both root mass loss and concentrations of humic substance, humic acid and fulvic acid decreased with increasing root diameter. Both fulvic acid concentration and humification degree declined as root decomposition progressed but humic acid concentration exhibited an opposite trend. Our results reveal that the diameter-associated variations in accumulation of humic substances were substantially stronger than altitudinal and interspecific differences in decomposing root litters. These findings have important implications for carbon sequestration via root humification in the subalpine forests experiencing snow-covered winter.

Increased soil temperature stimulates changes in carbon, nitrogen, and mass loss in the fine roots of Pinus koraiensis under experimental warming and drought

The effects of warming (+3 °C) and drought (-30% precipitation) on the fine root decomposition of Pinus koraiensis seedlings were examined using a litter bag method. The study site included a full factorial design with two temperature and two precipitation levels, with three replicates. Litter bags containing fine root litter of 2-year-old P. koraiensis seedlings were retrieved after 3, 6, and 12 months of decomposition. After 12 months, the mass loss of fine roots was significantly increased in response to warming (control = 31.1%, warming = 35.9%, drought = 29.2%, and warming plus drought = 35.5%); no change was observed until 6 months. Mass loss was not influenced by drought or by the interaction between warming and drought. Warming increased the nitrogen concentration of fine root litter but decreased the carbon concentration and carbon/nitrogen ratio after 6 and 12 months. This may be because warming stimulated nitrogen immobilization, which reduced the carbon/nitrogen ratio. Therefore, the carbon/nitrogen ratio may be affected by warming prior to changes in the mass loss of fine roots because roots with a low carbon/nitrogen ratio are generally characterized by high available nitrogen for decomposers. These results suggest that climate change (especially warming) may cause rapid decomposition of organic matter.

Root chemistry and soil fauna, but not soil abiotic conditions explain the effects of plant diversity on root decomposition.

Plant diversity influences many ecosystem functions including root decomposition. However, due to the presence of multiple pathways via which plant diversity may affect root decomposition, our mechanistic understanding of their relationships is limited. In a grassland biodiversity experiment, we simultaneously assessed the effects of three pathways-root litter quality, soil biota, and soil abiotic conditions-on the relationships between plant diversity (in terms of species richness and the presence/absence of grasses and legumes) and root decomposition using structural equation modeling. Our final structural equation model explained 70% of the variation in root mass loss. However, different measures of plant diversity included in our model operated via different pathways to alter root mass loss. Plant species richness had a negative effect on root mass loss. This was partially due to increased Oribatida abundance, but was weakened by enhanced root potassium (K) concentration in more diverse mixtures. Equally, grass presence negatively affected root mass loss. This effect of grasses was mostly mediated via increased root lignin concentration and supported via increased Oribatida abundance and decreased root K concentration. In contrast, legume presence showed a net positive effect on root mass loss via decreased root lignin concentration and increased root magnesium concentration, both of which led to enhanced root mass loss. Overall, the different measures of plant diversity had contrasting effects on root decomposition. Furthermore, we found that root chemistry and soil biota but not root morphology or soil abiotic conditions mediated these effects of plant diversity on root decomposition.

Short-term root and leaf decomposition of two dominant plant species in a Siberian tundra

In tundra ecosystems, global warming is expected to accelerate litter decomposition and to lead to shifts in vegetation composition. To understand these shifts, it is important to understand the interactions between global warming, vegetation composition, litter quality and decomposition in the tundra. In addition, it is important to consider root litter since roots are the major part of plant biomass in the tundra. In order to increase our understanding of decomposition, and root decomposition in particular, we performed a litter transplant experiment in northeastern Siberia, in which we measured mass loss for leaf and root litter (live and dead material) of the two dominant plant species, graminoid Eriophorum vaginatum and shrub Betula nana, in three vegetation types (E. vaginatum or B. nana dominated and mixed vegetation) during the growing season.Our results show that although leaf decomposition did not differ between the two species, root decomposition showed significant differences. Mass loss of live roots was higher for E. vaginatum than for B. nana, but mass loss of E. vaginatum dead roots was lowest. In addition, we found evidence for home-field advantage in litter decomposition: litter of a plant decomposed faster in vegetation where it was dominant. Mass loss rates of the litter types were significantly correlated with phosphorus content, rather than nitrogen content. This indicates that phosphorus limits decomposition in this tundra site.The low decomposition rate of B. nana live roots compared to E. vaginatum live roots suggests that the acceleration of decomposition in the Arctic may be partly counteracted by the expected expansion of shrubs. However, more information on litter input rates and direct effects of climate change on decomposition rates are needed to accurately predict the effects of climate change on carbon dynamics in tundra ecosystems.

The Mass Loss and Humification of Stumps and Roots in Masson Pine Plantations Based on Log File Records.

Stumps account for a large proportion of coarse woody debris in managed forests, but their decay dynamics are poorly understood. The loss of mass and the degree of humification of the above-ground woody debris, below-ground woody debris, bark and root system (R1, 10 mm ≥ diameter > 0 mm; R2, 25 mm ≥ diameter >10 mm; 100 mm ≥ R3 > 25 mm; R4 > 100 mm) of Masson pine (Pinus massoniana) stump systems were evaluated in southwestern China in a chronosequence of plantations cut 1–15 years prior to the study. The results indicated that above-ground woody debris decomposed more quickly than below-ground woody debris and bark, whereas the degree of humification followed the opposite trend. Compared with one-year stumps, the mass losses of 15-year stump systems were 60.4% for above-ground woody debris, 42.1% for below-ground woody debris, 47.3% for bark, 69.9% for R1, 47.3% for R2, 51.0% for R3, and 83.2% for R4. In contrast, below-ground woody debris showed a greater degree of humification compared with other components in the stump system. Among the root system, fine roots (R1, diameter ≤ 10 mm) had the largest k value (0.09), whereas the decay rate of coarser roots (R2, R3, R4; diameter > 10 mm) increased with increasing root diameter. However, coarse roots showed a larger degree of humification (0.2–0.6) than fine roots (0.3–0.4). These results suggest that below-ground woody debris and coarse roots may display a higher degree of humification, showing greater short-term contributions to overall humification when compared with the other components in the stump system.

Effects of Increased Summer Precipitation and Nitrogen Addition on Root Decomposition in a Temperate Desert.

BackgroundClimate change scenarios that include precipitation shifts and nitrogen (N) deposition are impacting carbon (C) budgets in arid ecosystems. Roots constitute an important part of the C cycle, but it is still unclear which factors control root mass loss and nutrient release in arid lands.Methodology/Principal FindingsLitterbags were used to investigate the decomposition rate and nutrient dynamics in root litter with water and N-addition treatments in the Gurbantunggut Desert in China. Water and N addition had no significant effect on root mass loss and the N and phosphorus content of litter residue. The loss of root litter and nutrient releases were strongly controlled by the initial lignin content and the lignin:N ratio, as evidenced by the negative correlations between decomposition rate and litter lignin content and the lignin:N ratio. Fine roots of Seriphidium santolinum (with higher initial lignin content) had a slower decomposition rate in comparison to coarse roots.Conclusion/SignificanceResults from this study indicate that small and temporary changes in rainfall and N deposition do not affect root decomposition patterns in the Gurbantunggut Desert. Root decomposition rates were significantly different between species, and also between fine and coarse roots, and were determined by carbon components, especially lignin content, suggesting that root litter quality may be the primary driver of belowground carbon turnover.

Factors controlling decomposition rates of fine root litter in temperate forests and grasslands

Background and aims Fine root decomposition contributes significantly to element cycling in terrestrial ecosystems. However, studies on root decomposition rates and on the factors that potentially influence them are fewer than those on leaf litter decomposition. To study the effects of region and land use intensity on fine root decomposition, we established a large scale study in three German regions with different climate regimes and soil properties. Methods In 150 forest and 150 grassland sites we deployed litterbags (100 μm mesh size) with standardized litter consisting of fine roots from European beech in forests and from a lowland mesophilous hay meadow in grasslands. In the central study region, we compared decomposition rates of this standardized litter with root litter collected on-site to separate the effect of litter quality from environmental factors. Results Standardized herbaceous roots in grassland soils decomposed on average significantly faster (24± 6 % mass loss after 12 months, mean ± SD) than beech roots in forest soils (12±4 %; p<0.001). Fine root decomposition varied among the three study regions. Land use intensity, in particular N addition, decreased fine root decomposition in grasslands. The initial lignin:N ratio explained 15 % of the variance in grasslands and 11 % in forests. Soil moisture, soil temperature, and C:N ratios of soils together explained 34 % of the variance of the fine root mass loss in grasslands, and 24 % in forests. Conclusions Grasslands, which have higher fine root biomass and root turnover compared to forests, also have higher rates of root decomposition. Our results further show that at the regional scale fine root decomposition is influenced by environmental variables such as soil moisture, soil temperature and soil nutrient content. Additional variation is explained by root litter quality.

Entwicklung eines Systems für die schonende Ernte und Reinigung von Baldrianwurzeln

The state of the art equipment for harvesting valerian roots is not efficient enough. Therefore, the aim of this study is to create a method for careful lifting and successful cleaning of the roots. For that purpose, a new cleaning system “rotation” is developed and compared with two other existing systems in a field trial with regard to the parameters “root mass loss”, “ingredients loss” and “cleaning intensity”. No differences regarding the ingredients are found, but there are significant differences with respect to the root mass loss and the cleaning efficiency. However, taking all results into consideration, all three systems are suited for agricultural practice.

Fine root production, turnover, and decomposition in a fast-growth Eucalyptus urophylla plantation in southern China

A rapid increase of Eucalyptus plantation area in southern China has raised widespread attention in the field of ecology and forestry. It might be argued that fast-growth Eucalyptus would increase the consumption of resources and thus cause soil degradation. Fine root dynamics could provide insight into nutrient uptake or return. This study therefore focused on fine root production, turnover, and decomposition in a subtropical Eucalyptus urophylla plantation. Sequential coring method was used to estimate fine root production and turnover rate. Root decomposition rate and root nitrogen (N) and phosphorus (P) dynamics were determined using the litterbag method. In this study, roots were divided into three diameter classes: <1, 1–2, and 2–3 mm. We settled litterbags with all three different root diameter classes under the forest floor (0–10 cm) in winter, spring, and summer. The total production of fine roots at diameter <2 mm was 45.4 g m−2 year−1, and its turnover rate was 0.58 year−1. The roots at diameter <1 mm showed much greater production or turnover rate than those at diameter 1–2 mm. The root mass loss from litterbag across the three diameter classes (<1, 1–2, and 2–3 mm) was similar at the beginning period of 180 days, but significantly different later. The decomposition constant (k value) of roots estimated by exponential decay model decreased with increasing diameter class. In addition, the season of litterbag settlement also had effects on root mass loss. In root nutrient dynamics, the fractions of initial N immobilized increased with increasing diameter class. Root P at the three diameter classes showed a similar mineralization pattern. Our studies on fine root production, turnover, and decomposition give some important insights into nutrient cycling between plant and soil in Eucalyptus plantations. Our results which show that fine roots had relatively low production and turnover rate partly explain the potential soil degradation under the short rotation systems. The variation of root dynamics among different diameter classes suggests that to accurately assess fine root roles, one should consider the effects of root diameter size.

Tree species effects on fine root decomposition and nitrogen release in subtropical forests in southern China

Background: Root decomposition is an important process that contributes to forest ecosystem carbon (C) flux and nutrient cycling. Aims: To determine how tree species affected fine root (≤ 2 mm) decomposition rates and nitrogen (N) release. Methods: Fine root samples of the coniferous Pinus massoniana, the deciduous Choerospondias axillaris and the broadleaved evergreen Cyclobalanopsis glauca tree species were collected from three secondary successional subtropical forests (P. massoniana–Lithocarpus glaber mixed forest, C. axillaris forest and C. glauca–L. glaber mixed forest) in southern China. Samples were incubated in situ, using the litterbag method for a period of 500 days to measure mass loss and changes in fine root C and N concentrations. Results: C. axillaris exhibited the fastest decomposition rate (k) during the 500 day decomposition period, followed by P. massoniana and C. glauca. Fine root mass loss was positively correlated with initial N concentrations and negatively correlated with initial C:N ratios. Initial fine root C concentrations had a significant effect on N release, but the effect varied over time. Annual fine root production released ca. 16.2–44.2 kg N ha−1 through decomposition. Conclusions: Fine root mass loss during decomposition differed considerably among tree species. The chemical quality of fine roots was a key driver in the rates of decomposition. Soil properties partly accounted for the differences in decomposition rates.

Decomposition of the finest root branching orders: linking belowground dynamics to fine-root function and structure

Root turnover is fastest in the finest roots of the root system (first root order). Additionally, tissue chemistry varies among even the finest root orders and between white roots and older, pigmented roots. Yet the effects of pigmentation and order on root decomposition have rarely been examined. We separated the first four root orders (all <1 mm) of four temperate tree species into three classes: white first- and second-order roots; pigmented first- and second-order roots; and pigmented third- and fourth-order roots. Roots were enclosed in litterbags and buried under their own and under a common species canopy in a 34-year-old common garden in Poland. When comparing decomposition of different root orders over 36 months, pigmented third- and fourth-order roots with a higher C:N ratio decomposed more rapidly, losing 20–40% of their mass, than pigmented first- and second-order roots, which lost no more than 20%. When comparing decomposition of roots of different levels of pigmentation within the same root order over 14 months, pigmented (older) first- and second-order roots lost ∼10% of their mass, while white (younger) first- and second-order roots lost ∼30%. In contrast to root mass loss, root N content declined more rapidly in the first- and second-order roots than in third- and fourth-order roots. In higher-order roots, N increased in the first 10 months from ∼110% to nearly 150% of initial N content, depending on species; by the end of the study N content had returned to initial levels. These findings suggest that, in plant communities where root mortality is primarily of pigmented first- and second-order roots, microbial decomposition may be slower than estimates derived from bulk fine-root litterbag experiments, which typically contain at least four root orders. Thus, a more mechanistic understanding of root decomposition and its contribution to ecosystem carbon and nutrient dynamics requires a fundamental shift in experimental methods that stratifies root samples for decomposition along more functionally based criteria such as root order and pigmentation, which parallel the markedly different longevities of these different root classes.