Fine Root Decomposition Research Articles

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.

Patterns of root decomposition in response to soil moisture best explain high soil organic carbon heterogeneity within a mesic, restored prairie

Spatially heterogeneous patterns of soil organic carbon (SOC) are related to topographically-defined soil moisture levels within Midwestern tallgrass prairies. While roots are regarded as the main contributor to SOC formation, relatively little is known about how fine root dynamics respond to landscape-level changes in soil moisture, and thus the mechanisms promoting spatial heterogeneity of SOC remain uncertain. We evaluated SOC, fine root (≤2mm) biomass, production, decomposition, and vertical rooting distributions among landscape positions varying in soil moisture within 25+ year old restored tallgrass prairies in Wisconsin, USA. We hypothesized that SOC, root biomass, and root production would increase, while root decomposition would decline with increasing soil moisture. Additionally, we hypothesized that relative root biomass and production distributions would become shallower as soils became wetter. We found no relationship between soil moisture and root biomass, production, or their vertical distributions, but decomposition decreased and SOC increased as expected with increasing soil moisture. However, we also observed a strong relationship between soil moisture and species assemblages, suggesting that community composition changed in response to soil moisture. Our findings indicate that SOC was highest in seasonally wet, lowland landscape positions due to greatly reduced root decomposition, not due to changes in root production or relative distributions. We suggest that species turnover may have reduced the effect of soil moisture on root biomass and production, thereby maintaining similar root production under notably disparate soil moisture conditions. Considering continued interest in monoculture biofuel plantings and their potential to sequester C in roots and soils, additional research is necessary at the landscape scale to elucidate the importance of species spatial heterogeneity on grassland belowground C dynamics.

三工河流域两种琵琶柴群落细根生物量、分解与周转

三工河流域两种琵琶柴群落细根生物量、分解与周转

Importancia de la caracterización de la biomasa de raíces en la simulación de ecosistemas forestales

Gárate, M., Blanco, J.A. 2013. Importance of root biomass characterization when simulating forest ecosystems. Ecosistemas 22(3):66-73. Doi.: 10.7818/ECOS.2013.22-3.10. Sensitivity analysis are an important tool to understand ecological models functioning, as well as to identify their most important parameters. In addition, sensitivity analysis can be used to design more effective field sampling regimes to calibrate ecological models. When studying forest ecosystems, quantitative analysis of the underground fraction is much more costly and complicated than studying the aboveground fraction, especially when studying the dynamics of production and decomposition of large and fine tree roots. In this work we show an example of sensitivity analysis of the forest ecosystem model FORECAST to parameters defining biomass, longevity and nitrogen concentration in tree roots. The model was calibrated to simulate two Scots pine (Pinus sylvestris L.) stands in the Pyrenees of Navarre. Results indicate that fine root turnover is the most influential parameter on model´s tree growth estimations, followed by fine root N concentration and the root biomass/total tree biomass ratio. Furthermore, the model is more sensitive to root-related parameters when calibrated to simulate poor sites with low productivity capacity and higher nutrient limitation.

The effect of limited availability of N or water on C allocation to fine roots and annual fine root turnover in Alnus incana and Salix viminalis

The effect of limited nitrogen (N) or water availability on fine root growth and turnover was examined in two deciduous species, Alnus incana L. and Salix viminalis L., grown under three different regimes: (i) supply of N and water in amounts which would not hamper growth, (ii) limited N supply and (iii) limited water supply. Plants were grown outdoors during three seasons in covered and buried lysimeters placed in a stand structure and filled with quartz sand. Computer-controlled irrigation and fertilization were supplied through drip tubes. Production and turnover of fine roots were estimated by combining minirhizotron observations and core sampling, or by sequential core sampling. Annual turnover rates of fine roots <1 mm (5-6 year(-1)) and 1-2 mm (0.9-2.8 year(-1)) were not affected by changes in N or water availability. Fine root production (<1 mm) differed between Alnus and Salix, and between treatments in Salix; i.e., absolute length and biomass production increased in the order: water limited < unlimited < N limited. Few treatment effects were detected for fine roots 1-2 mm. Proportionally more C was allocated to fine roots (≤2 mm) in N or water-limited Salix; 2.7 and 2.3 times the allocation to fine roots in the unlimited regime, respectively. Estimated input to soil organic carbon increased by ca. 20% at N limitation in Salix. However, future studies on fine root decomposition under various environmental conditions are required. Fine root growth responses to N or water limitation were less pronounced in Alnus, thus indicating species differences caused by N-fixing capacity and slower initial growth in Alnus, or higher fine root plasticity in Salix. A similar seasonal growth pattern across species and treatments suggested the influence of outer stimuli, such as temperature and light.

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.

CARBON AND NUTRIENT CYCLING THROUGH FINE ROOTS IN RUBBER (HEVEA BRASILIENSIS) PLANTATIONS IN INDIA

SUMMARYUnderstanding the growth dynamics of fine roots and their contribution to soil organic carbon and nutrient pools is crucial for estimating ecosystem carbon and nutrient cycling and how these are influenced by climate change. Rubber is cultivated in more than 10 million hectare globally and the area under rubber cultivation is fast expanding due to socio-economic reasons, apart from the importance given to this species for eco-restoration of degraded lands. An experiment was conducted to quantify fine root production, fine root turnover and carbon and nutrient cycling through fine roots in rubber plantations with different soil nutrient status and rainfall pattern. Fine root production was estimated by sequential coring and ingrowth core methods. Fine root decomposition was determined by the litter bag technique. Carbon and nutrient contents in fine roots were determined and their turnover was computed. Fine root biomass in the top 0–7.5-cm soil layer showed significant seasonal fluctuation and the fluctuations were particularly wide during the transition period from the dry season to the rainy season. Fine root production estimated by the different methods was significantly higher at the lower fertility site and during the higher soil moisture stress year. Fine root turnover ranged from 1.04 to 2.29 year−1. Root carbon and nutrient status showed seasonal variation and lower status was observed during the rainy season. The annual recycling of C, N, P, K, Ca and Mg through fine roots ranged from 590 to 1758, 30 to 85, 3 to 12, 13 to 31, 11 to 35 and 6 to 13 kg ha−1, respectively. Substantial quantities of carbon and nutrients were recycled annually in rubber plantations through fine roots. When soil moisture and nutrient stress were more severe, fine root production, turnover and carbon and nutrient recycling through fine roots were higher.

Dynamics and speciation of organic carbon during decomposition of leaf litter and fine roots in four subtropical plantations of China

Plant litter and fine roots turnover are important carbon (C) inputs to soil and a direct emission source of CO2 to the atmosphere. C dynamics during litter decomposition provide an insight into C flow in soils. To quantitatively assess how decomposition processes vary with litter types, the solid-state 13C nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (CPMAS-NMR) technique was applied to analyze the organic C dynamics of conifer (Pinus massoniana) and broadleaf (Castanopsis hystrix, Michelia macclurei and Mytilaria laosensis) leaf litter and fine roots which had degraded during one year litterbag experiment in four subtropical plantations of China. The results were used to estimate decomposition rates of different C types and compositional changes of leaf litter and fine roots during decomposition. The mass loss rates of different C fractions during decomposition varied significantly between litter types. Site environment and initial litter quality played more critical roles in regulating decomposition of fine roots than of leaf litter. The significant changes in the proportion of C forms and degree of humification occurred during leaf litter decomposition, but not during fine roots decomposition. The proportions of alkyl C and carbonyl C and alkyl/O-alkyl C ratio varied with leaf litter types, with an increase for the proportion of alkyl C and alkyl/O-alkyl C ratio in broadleaf leaf litters and an enhanced trend for the proportion of carbonyl C for P. massoniana. The results suggest that the patterns and main controlling factors of litter C compositional change during decomposition differed between above- and belowground, and the dynamics of leaf litter C fractions during decomposition differed between conifer and broadleaf species. The findings of litter C compositional decomposition of the main tree species in this study could contribute to the accurate estimation of soil C sequestration in subtropical plantation ecosystems.

Response of microbial respiration from fine root litter decomposition to root water content in a temperate broad-leaved forest

Microbial respiration from plant litter decomposition is sensitive to soil water status; however, its response to water status remains ambiguous, particularly in the litter of fine roots. We investigated the effect of fine-root water content on microbial respiration after 468 days of decomposition in forest soil for two diameter classes (0-0.5 and 0.5-2 mm) of Quercus serrata and Ilex pedunculosa in central Japan. Direct measurement of microbial respiration from root litter resulted in a range of 0.015-3.52 nmol CO2 g −1 s −1 . Microbial respiration in both diameter classes and species decreased linearly with decreasing root water content. These changing patterns of microbial respiration did not differ significantly between the diameter classes of either species, indicating that microbial respiration was regulated by the moisture of root litter, and not by characteristics associated with diameter class or species. In contrast, the carbon to nitrogen ratio and mass loss of the root litter differed significantly between diameter classes in both species. These findings suggest that along with chemical and morphological properties of fine root litter, the changes in root water content should also be considered as a viable factor in microbial activity variations. Drying-wetting cycles of fine roots could lead to sensitive responses of microorganisms during the short term, leading to variation in the decomposition rate of fine root litter over the long term. This study provided insight into the potential impact of microbial physiological performance on heterotrophic respiration and fine root decomposition under the varying root water content.

A modified ingrowth core method for measuring fine root production, mortality and decomposition in forests

The ingrowth core method is widely used to assess fine root (diameter < 2 mm) production but has many inherent deficiencies. In this study, we modified this method by adopting mini ingrowth cores (diameter 1.2 cm), extending sample intervals to a growing season, and developing new models to quantify the concurrent production, mortality and decomposition, and applied them to a secondary Mongolian oak (Quercus mongolica Fischer ex Ledebour) forest. Annual fine root production, mortality and decomposition estimated by our method were 2.10 ± 0.23, 1.78 ± 0.20 and 0.85 ± 0.13 t ha(-1), respectively, and 33.3% of the production was decomposed in the growing season. The production estimate using our method was significantly higher than those using two long-term ingrowth core (sample interval >2 months) methods. However, it was significantly lower than that using the short-term ingrowth core (sample interval <2 months) method, presumably due to the lower root competition and less decomposition occurring in the short-term cores. The fine root estimates using our method in the growing season were generally higher than those using the forward and continuous inflow methods but lower than those using the backward method. Our method reduces the disturbances in roots and soil, minimizes the sampling frequency and improves the quantification of fine root decomposition during the sample intervals. These modifications overcome the limitations associated with the previous ingrowth core methods. Our method provides an improved alternative for estimating fine root production, mortality and decomposition.

Litter-fall and decomposition in harvested and un-harvested boreal forests

Litter fall and litter decomposition were examined in harvested and unharvested western Newfoundland balsam fir (Abies balsamea) and black spruce (Picea mariana) forests. Rates of litterfall in mature 70-year-old forests were 2.4 to 3.5 Mg ha−1 year−1, which was reduced to 0.2 to 0.3 Mg ha−1 year−1 following harvesting. In contrast, rates of black spruce needle, balsam fir needle, fine (&lt;2 mm diameter) root, and moss (dominated by feather moss) litter decomposition were not affected by forest harvesting at either site during 24 to 54 months of field incubation in litterbags. Mass loss of balsam fir needle, black spruce needle, and moss (dominated by feather moss) were not significantly different indicating that moss forms a labile litter type in a forested setting.

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.

Linking litter production, quality and decomposition to vegetation succession following agricultural abandonment

Agricultural land abandonment has been increasing worldwide for environmental and socio-economic reasons, and knowledge of its key ecological processes (e.g., carbon (C) and nitrogen (N) input and accumulation) in relation to vegetation succession can provide important information for ecosystem management and greenhouse gas emissions mitigation. In order to better understand the above- and belowground litter dynamics following agricultural abandonment, we simultaneously studied the litter and fine root production, quality, decomposition, C and N input in ecosystems along a secondary successional gradient (i.e., grassland, shrub-grass land, young secondary forest, and mature secondary forest) following agricultural abandonment in China's Qinling Mountains. Results showed that the significant increase of aboveground woody plant litter and decrease of grass litter during vegetation succession led little changes in total litter production and annual total C and N input in different succession stages, while the fine root production, fine root biomass, C input from fine root production increased significantly with stand age. The initial litter C concentration and fine root carbon: phosphorous ratio (C:P) were the main factors in explaining the variations of decomposition rates of litter and fine root, respectively. The increasing C concentration in litter and the increasing C:P ratio in fine root during vegetation succession had potentially driven the decreases in litter and fine root decomposition rate respectively. The accumulation of litter standing crop during vegetation succession could be attributed to the decreases in litter decomposition rate partly caused by changes in litter quality, rather than the increases in litter production. Our results imply that the changes in vegetation type have a much smaller role in the annual total litter production and the total litter C and N input than previously assumed, while the changes in quality and decomposition rate may have largely influenced C accumulation in stand floor and soil during secondary succession following agricultural abandonment.

Fine Root Decomposition Dynamics in Moso Bamboo Forest of Southeast China

To provide an important basis for the biogeochemical cycle of bamboo forest ecosystem, particularly the cycling of carbon, we studied decomposition dynamics of fine root in moso bamboo forest. Our study area located in Miaoshanwu nature reserve, Fuyang, Zhejiang province. Based on our study, we concluded: (1) the process of bamboo fine root with diameter less than 2mm and within 2-5mm can be modeled with Olson Decomposition Exponential Model. It showed that decomposition for fine root with thinner diameter is faster than that with thicker diameter.(2) The mass loss for the fine root with less than 2mm diameter and within 2-5mm diameter is 41.30% and 37.64% after half-year decomposition respectively, 62.61% and 56.27% after one year decomposition respectively.(3) It takes 8.13 months and 9.75 months respectively for 50% mass loss and 38.77 months and 48.36 months for 95% mass loss respectively for the two diameter classes of fine root.

Decomposition of labelled roots and root-C and -N allocation between soil fractions in mountain grasslands

Given the high turnover of fine roots in mountain grasslands, knowledge of their decomposition rates and the capacity of mountain grassland soils to stabilize root-derived C are central to understand the role of these ecosystems as potential C sinks. Here we studied the decomposition of fine roots in mountain grasslands and estimated the rates at which root-C and -N incorporated into protected pools at two soil depths. For this purpose, we incubated standard 13C- and 15N-labelled wheat roots mixed with unlabelled soil at 5 and 20 cm depth in two mountain grassland sites. Particle size fractionation allowed the quantification of the labelled wheat root-C and -N allocated to each size fraction (coarse sand, fine sand and silt plus clay sized) as well as their incorporation rates into the finest fraction. Between 62% and 78% root-C remained in the soil after one year of field incubation, faster decomposition being registered at the warmest site. In the following two years, roots decomposed much more slowly. In contrast to reports in the literature, our results indicate that decay rates during the first year were highest in the deep layer. The incorporation of wheat root-derived organic matter into the silt plus clay size fraction was also much greater during the first year of decomposition than in the following two years and also slightly higher in the deep soil than in topsoil. The incorporation rates of root-13C and root-15N into this fraction also suggest that the wheat-derived organic matter associated with this fraction was N-enriched and less recalcitrant (i.e., less resistant to acid hydrolysis) than that recovered from the coarser fractions. Furthermore, recalcitrant organic matter incorporated much more slowly than labile organic matter did. We conclude that the conditions of the subalpine grassland subsoil are more favourable for root decomposition than the topsoil and that the organic matter that incorporates into the protected pool is characterised by a high N content and low biochemical recalcitrance.

A new approach to estimate fine root production, mortality, and decomposition using litter bag experiments and soil core techniques

A new approach is proposed to estimate fine root production, mortality, and decomposition that occur simultaneously in terrestrial ecosystems utilizing sequential soil core sampling or ingrowth core techniques. The calculation assumes knowledge of the decomposition rate of dead fine roots during a given time period from a litter bag experiment. A mass balance model of organic matter derived from live fine roots is applied with an assumption about fine root mortality and decomposition to estimate decomposed dead fine roots from variables that can be quantified. Comparison of the estimated fine root dynamics with the decision matrix method and three new methods (forward estimate, continuous inflow estimate, and backward estimate) in a ca. 80-year-old Chamaecyparis obtusa plantation in central Japan showed that the decision matrix nearly always underestimated production, mortality, and decomposition by underscoring the values of the forward estimate, which theoretically underestimates the true value. The fine root production and mortality obtained by the decision matrix were on average 14% and 38% lower than those calculated by the continuous inflow estimate method. In addition, the values by the continuous inflow estimate method were always between those calculated by the forward estimate and backward estimate methods. The latter is known to overestimate the true value. Therefore, we consider that the continuous inflow estimate method provides the best estimates of fine root production, mortality, and decomposition among the four approaches compared.

Relative contribution of foliar and fine root pine litter to the molecular composition of soil organic matter after in situ degradation

The influence of litter quality on soil organic matter (SOM) stabilization rate and pathways remains unclear. We used 13C/ 15N labeled litter addition and Curie-point pyrolysis gas chromatography–mass spectrometry combustion-isotope ratio mass spectrometry (Py–GC–MS–C–IRMS) to explore the transformation of litter with different composition and decay rate (ponderosa pine needle vs. fine root) to SOM during 18 months in a temperate conifer forest mineral (A horizon) soil. Based on 13C Py–GC–MS–C–IRMS the initial litter and bulk soil had ∼1/3 of the total pyrolysis products identified in common. The majority was related either to carbohydrates or was non-specific in origin. In bulk soil, carbohydrates had similar levels of enrichment after needle input and fine root input, while the non-specific products were more enriched after needle input. In the humin SOM fraction (260 yr C turnover time) we found only carbohydrate and alkyl C-derived compounds and greater 13C enrichment in the “carbohydrate” pool after fine root decomposition. 15N Py–GC–MS–C–IRMS of humic substances showed that root litter contributed more than needle litter to the enrichment of specific protein markers during initial decomposition. We found little evidence for the selective preservation of plant compounds considered to be recalcitrant. Our findings suggest an indirect role for decomposing plant material composition, where microbial alteration of fine root litter seems to favor greater initial stabilization of microbially derived C and N in SOM fractions with long mean turnover times, such as humin, compared to needles with a faster decay rate.

Incorporation and remobilization of 13C within the fine-root systems of individual Abies alba trees in a temperate coniferous stand

Forest ecosystems have a large carbon (C) storage capacity, which depends on their productivity and the residence time of C. Therefore, the time interval between C assimilation and its return to the atmosphere is an important parameter for determining C storage. Especially fine roots (≤2 mm in diameter) undergo constant replacement and provide a large biomass input to the soil. In this study, we aimed to determine the residence time of C in living fine roots and the decomposition rates of dead fine roots. Therefore, we pulse-labelled nine 20-year-old individual silver fir trees (Abies alba Miller; ∼70 cm tall) with ¹³CO₂ in situ to trace the assimilated C over time into the fine-root systems. Whole trees were harvested at different time points after labelling in autumn, biomass was determined and cellulose and starch of fine roots were extracted. Moreover, soil cores were taken and ingrowth cores installed, in which fine roots were genetically identified, to assess incorporation and remobilization of ¹³C in the fine roots of silver fir trees; litterbags were used to determine fine-root decomposition rates. The ¹³C label was incorporated in the fine-root system as cellulose within 3 days, with highest values after 30 days, before reaching background levels after 1 year. The highest δ¹³C values were found in starch throughout the experiment. ¹³C recovery and carbon mean residence times did not differ significantly among fine-root diameter classes, indicating size-independent C turnover times in fine roots of A. alba trees of ∼219 days. Furthermore, carbon was remobilized from starch into newly grown fine roots in the next spring after our autumn labelling. One year after installation, litterbags with fine roots revealed a decrease of biomass of ∼40% with relative ¹³C content in fine-root bulk biomass and cellulose of ∼50%, indicating a faster loss of ¹³C-labelled compounds compared with bulk biomass. Our results also suggest that genetic analysis of fine-root fragments found in soil and ingrowth cores is advisable when working in mixed forest stands with trees of similar fine-root morphology. Only then can one avoid dilution of the labelling signal by mistake, due to analysis of non-labelled non-target species roots.

Fine root decomposition of evergreen broadleaved and coniferous tree species in mid-subtropical China: dynamics of dry mass, nutrient and organic fractions

To gain insight into fine roots decomposition in subtropical China, the litter bag method was used to examine the decomposition dynamics of dry mass, N, P, K, and organic fractions in six natural forests and a Chinese fir plantation over a 2-year period in the Wanmulin Nature Reserve, Fujian. The seven tree species examined, representative of this area, differed significantly in their initial chemical quality and were used to determine the best substrate quality parameters to predict decomposition dynamics. Dry mass loss varied significantly among the different roots, which showed fast decomposition in the first year, with mass loss regulated by extractive and acid-soluble fraction, followed by a low rate in the second year, with mass loss dominated by acid-insoluble fraction. Net N release was constantly slower than the mass loss of acid-insoluble fractions, while K release was the other way around. Release of P seemed to be independent of disappearance of acid-insoluble fraction. Not all the very fine roots (0–1 mm) decomposed faster than the fine ones (1–2 mm), and decomposition rates of coniferous roots were not always lower than broadleaved species. Correlation analysis demonstrated that dry mass loss and net N and P release rates were not correlated with initial N concentration, but with acid-insoluble organic fraction and P related parameters at the end of a 2-year decomposition period. Our results suggest that N is a limiting factor of fine root decomposition. Additionally, P could also be an important driver of fine root decomposition and N and P dynamics in this low soil P availability area.

Correlation between leaf litter and fine root decomposition among subtropical tree species

Elucidating the processes of leaf litter and fine root decomposition has been a major research focus, while how the correlation between leaf litter and fine root decomposition is unclear. We studied the in situ decomposition and N dynamics of leaf litter and fine root of four subtropical tree species (Pinus massoniana, Castanopsis hystrix, Michelia macclurei and Mytilaria laosensis) to determine whether leaf litter and fine root decomposition is correlated across species as well as which factors influence decomposition above versus below ground. Decomposition rate of leaf litter was related to that of fine root across species. The strong correlation between leaf litter and fine root decomposition rates arose largely for several reasons. First, soil moisture had the similar influences on both leaf litter and fine root decomposition rates. Second, traits (i.e., initial Ca concentration) important to both leaf litter and fine root decomposition rates showed significant similarity among species. Third, initial P, N and aromatic C concentrations, and C/N ratio were uniquely important for fine root decomposition rate, while no unique traits for leaf litter decomposition rate. This also could account for the strong correlation between leaf litter and fine root decomposition rates. Our study suggests that among these subtropical trees, species effects on in situ decomposition rates of leaf litter and fine root are very similar. Thus, species differences in decomposition rates may be as large as they would be if faster decomposition of leaf litter was correlated with faster decomposition of fine root. N immobilization rate of leaf litter was unrelated to that of fine root across species. Our results help explain some important mechanisms by which tree species influence litter in situ decomposition.