Degradation-driven changes in fine root carbon stocks, productivity, mortality, and decomposition rates in a palm swamp peat forest of the Peruvian Amazon

Abstract Background Amazon palm swamp peatlands are major carbon (C) sinks and reservoirs. In Peru, this ecosystem is widely threatened owing to the recurrent practice of cutting Mauritia flexuosa palms for fruit harvesting. Such degradation could significantly damage peat deposits by altering C fluxes through fine root productivity, mortality, and decomposition rates which contribute to and regulate peat accumulation. Along a same peat formation, we studied an undegraded site (Intact), a moderately degraded site (mDeg) and a heavily degraded site (hDeg) over 11 months. Fine root C stocks and fluxes were monthly sampled by sequential coring. Concomitantly, fine root decomposition was investigated using litter bags. In the experimental design, fine root stocks and dynamics were assessed separately according to vegetation type (M. flexuosa palm and other tree species) and M. flexuosa age class. Furthermore, results obtained from individual palms and trees were site-scaled by using forest composition and structure. Results At the scale of individuals, fine root C biomass in M. flexuosa adults was higher at the mDeg site than at the Intact and hDeg sites, while in trees it was lowest at the hDeg site. Site-scale fine root biomass (Mg C ha−1) was higher at the mDeg site (0.58 ± 0.05) than at the Intact (0.48 ± 0.05) and hDeg sites (0.32 ± 0.03). Site-scale annual fine root mortality rate was not significantly different between sites (3.4 ± 1.3, 2.0 ± 0.8, 1.5 ± 0.7 Mg C ha−1 yr−1 at the Intact, mDeg, and hDeg sites) while productivity (same unit) was lower at the hDeg site (1.5 ± 0.8) than at the Intact site (3.7 ± 1.2), the mDeg site being intermediate (2.3 ± 0.9). Decomposition was slow with 63.5−74.4% of mass remaining after 300 days and it was similar among sites and vegetation types. Conclusions The significant lower fine root C stock and annual productivity rate at the hDeg site than at the Intact site suggests a potential for strong degradation to disrupt peat accretion. These results stress the need for a sustainable management of these forests to maintain their C sink function.

Download Full-text

Heterogeneity in Decomposition Rates and Nutrient Release in Fine-Root Architecture of Pinus massoniana in the Three Gorges Reservoir Area

Forests ◽

10.3390/f11010014 ◽

2019 ◽

Vol 11 (1) ◽

pp. 14

Author(s):

Shao Yang ◽

Ruimei Cheng ◽

Wenfa Xiao ◽

Yafei Shen ◽

Lijun Wang ◽

...

Keyword(s):

Lower Order ◽

Fine Root ◽

C:N Ratio ◽

Pinus Massoniana ◽

Higher Order ◽

Root Decomposition ◽

Decomposition Rates ◽

N Release ◽

Residual N ◽

Fine Root Decomposition

Fine-root decomposition contributes a substantial amount of nitrogen that sustains both plant productivity and soil metabolism, given the high turnover rates and short root life spans of fine roots. Fine-root decomposition and soil carbon and nitrogen cycling were investigated in a 1-year field litterbag study on lower-order roots (1–2 and 3–4) of Pinus massoniana to understand the mechanisms of heterogeneity in decomposition rates and further provide a scientific basis for short-time research on fine-root decomposition and nutrient cycling. Lower-order roots had slower decay rates compared with higher-order roots (5–6). A significantly negative correlation was observed between the decay constant mass remaining and initial N concentrations as well as acid unhydrolyzable residues. Results also showed that in lower-order roots (orders 1–2 and 3–4) with a lower C:N ratio, root residual N was released and then immobilized, whereas in higher-order roots (order 5–6) with a higher C:N ratio, root residual N was immobilized and then released in the initial stage. In the later stage, N immobilization occurred in lower-order roots and N release in higher-order roots, with the C:N ratio gradually decreasing to about 40 in three branching-order classes and then increasing. Our results suggest that lower-order roots decompose more slowly than higher-order roots, which may result from the combined effects of high initial N concentration and poor C quality in lower-order roots. During the decomposition of P. massoniana, N release or N immobilization occurred at the critical C:N ratio.

Download Full-text

An improved method for quantifying total fine root decomposition in plantation forests combining measurements of soil coring and minirhizotrons with a mass balance model

Tree Physiology ◽

10.1093/treephys/tpaa074 ◽

2020 ◽

Vol 40 (10) ◽

pp. 1466-1473

Author(s):

Xuefeng Li ◽

Kevan J Minick ◽

Tonghua Li ◽

James C Williamson ◽

Michael Gavazzi ◽

...

Keyword(s):

Fine Roots ◽

Root Biomass ◽

Turnover Rate ◽

Fine Root ◽

Fine Root Biomass ◽

Balance Model ◽

Root Decomposition ◽

Mass Balance Model ◽

Monthly Total ◽

Fine Root Decomposition

Abstract Accurate measurement of total fine root decomposition (the amount of dead fine roots decomposed per unit soil volume) is essential for constructing a soil carbon budget. However, the ingrowth/soil core-based models are dependent on the assumptions that fine roots in litterbags/intact cores have the same relative decomposition rate as those in intact soils and that fine root growth and death rates remain constant over time, while minirhizotrons cannot quantify the total fine root decomposition. To improve the accuracy of estimates for total fine root decomposition, we propose a new method (balanced hybrid) with two models that integrate measurements of soil coring and minirhizotrons into a mass balance model. Model input parameters were fine root biomass, necromass and turnover rate for Model 1, and fine root biomass, necromass and death rate for Model 2. We tested the balanced hybrid method in a loblolly pine plantation forest in coastal North Carolina, USA. The total decomposition rate of absorptive fine roots (ARs) (a combination of first- and second-order fine roots) using Models 1 and 2 was 107 ± 13 g m−2 year−1 and 129 ± 12 g m−2 year−1, respectively. Monthly total AR decomposition was highest from August to November, which corresponded with the highest monthly total ARs mortality. The ARs imaged by minirhizotrons well represent those growing in intact soils, evident by a significant and positive relationship between the standing biomass and the standing length. The total decomposition estimate in both models was sensitive to changes in fine root biomass, turnover rate and death rate but not to change in necromass. Compared with Model 2, Model 1 can avoid the technical difficulty of deciding dead time of individual fine roots but requires greater time and effort to accurately measure fine root biomass dynamics. The balanced hybrid method is an improved technique for measuring total fine root decomposition in plantation forests in which the estimates are based on empirical data from soil coring and minirhizotrons, moving beyond assumptions of traditional approaches.

Download Full-text

Fine root decomposition rates do not mirror those of leaf litter among temperate tree species

Oecologia ◽

10.1007/s00442-009-1479-6 ◽

2009 ◽

Vol 162 (2) ◽

pp. 505-513 ◽

Cited By ~ 179

Author(s):

Sarah E. Hobbie ◽

Jacek Oleksyn ◽

David M. Eissenstat ◽

Peter B. Reich

Keyword(s):

Leaf Litter ◽

Tree Species ◽

Fine Root ◽

Root Decomposition ◽

Decomposition Rates ◽

Fine Root Decomposition

Download Full-text

Stable isotopic constraints on global soil organic carbon turnover

Biogeosciences ◽

10.5194/bg-15-987-2018 ◽

2018 ◽

Vol 15 (4) ◽

pp. 987-995 ◽

Cited By ~ 17

Author(s):

Chao Wang ◽

Benjamin Z. Houlton ◽

Dongwei Liu ◽

Jianfeng Hou ◽

Weixin Cheng ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Linear Relationship ◽

Root Decomposition ◽

Mean Annual Precipitation ◽

Mean Annual Temperature ◽

Turnover Rates ◽

Decomposition Rates ◽

Soil C ◽

C Stocks

Abstract. Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2 concentrations and global climate change. However, reliably measuring SOC turnover rates on large spatial and temporal scales remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ13C of vegetation and soil reported in the literature (176 separate soil profiles), to examine large-scale controls of climate, soil physical properties and nutrients over patterns of SOC turnover across terrestrial biomes worldwide. We report a significant relationship between β and calculated soil C turnover rates (k), which were estimated by dividing soil heterotrophic respiration rates by SOC pools. ln( − β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with mean annual precipitation, implying strong-feedbacks of SOC turnover to climate changes. Soil nitrogen (N) and clay content correlate strongly and positively with ln( − β), revealing the additional influence of nutrients and physical soil properties on SOC decomposition rates. Furthermore, a strong (R2 = 0.76; p < 0.001) linear relationship between ln( − β) and estimates of litter and root decomposition rates suggests similar controls over rates of organic matter decay among the generalized soil C stocks. Overall, these findings demonstrate the utility of soil δ13C for independently benchmarking global models of soil C turnover and thereby improving predictions of multiple global change influences over terrestrial C-climate feedback.

Download Full-text

Fine-root decomposition and N dynamics in coniferous forests of the Pacific Northwest, U.S.A.

Canadian Journal of Forest Research ◽

10.1139/x01-202 ◽

2002 ◽

Vol 32 (2) ◽

pp. 320-331 ◽

Cited By ~ 75

Author(s):

Hua Chen ◽

Mark E Harmon ◽

Jay Sexton ◽

Becky Fasth

Keyword(s):

Pacific Northwest ◽

Fine Roots ◽

Fine Root ◽

Root Decomposition ◽

N Availability ◽

Soil N ◽

Decomposition Rates ◽

N Dynamics ◽

The Pacific ◽

Fine Root Decomposition

We examined the effects of species, initial substrate quality, and site differences (including temperature, precipitation, and soil N availability) on fine-root (<2 mm diameter) decomposition in litter bags and its N dynamics in Sitka spruce (Picea sitchensis (Bong) Carrière), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) forests in Oregon, U.S.A. Species significantly influenced fine-root mass loss during the first 2 years of decomposition. Over the same period, site differences had little impact on decomposition of fine roots. The percentage of initial mass remaining of decomposing fine roots fitted a single-exponential model. The decomposition rate constant (k) for all 15 species examined ranged from 0.172 year1 for Engelmann spruce (Picea engelmanni Parry ex Engelm.) to 0.386 year1 for Oregon ash (Fraxinus latifolia Benth.). Initial C quality indices (e.g., cellulose concentration, lignin concentration) of fine roots were correlated with fine-root decomposition rates. In contrast, initial N concentration and soil N availability were not correlated with fine-root decomposition rates. The rate of N released from decomposing roots was positively correlated with the initial N concentration of the fine roots. The data suggest that decomposing fine roots could release at least 20 kg N/ha annually in mature Douglas-fir forests of the Pacific Northwest.

Download Full-text

Fine root biomass and root length density in a lowland and a montane tropical rain forest, SP, Brazil

Biota Neotropica ◽

10.1590/s1676-06032011000300018 ◽

2011 ◽

Vol 11 (3) ◽

pp. 203-209 ◽

Cited By ~ 14

Author(s):

Bruno Henrique Pimentel Rosado ◽

Amanda Cristina Martins ◽

Talita Cristina Colomeu ◽

Rafael Silva Oliveira ◽

Carlos Alfredo Joly ◽

...

Keyword(s):

Resource Use ◽

Rain Forest ◽

Fine Root ◽

Root Length Density ◽

Fine Root Biomass ◽

Montane Forest ◽

Atlantic Rain Forest ◽

Wet Season ◽

Decomposition Rates ◽

Ecosystem Level

Fine roots, <2 mm in diameter, are responsible for water and nutrient uptake and therefore have a central role in carbon, nutrient and water cycling at the plant and ecosystem level. The root length density (RLD), fine root biomass (FRB) and vertical fine root distribution (VRD) in the soil profile have been used as good descriptors of resource-use efficiency and carbon storage in the soil. Along altitudinal gradients, decreases in temperature and radiation inputs (depending on the frequency of fog events) may reduce decomposition rates and nutrient availability what might stimulate plants to invest in fine roots, increasing acquisition of resources. We evaluated the seasonal variation of fine root parameters in a Lowland and Montane forest at the Atlantic Rain Forest. We hypothesized that, due to lower decomposition rates at the Montane site, the FRB and RLD at soil surface will be higher in this altitude, which can maximize the efficiency of resource absorption. FRB and RLD were higher in the Montane forest in both seasons, especially at the 0-5 layer. At the 0-5 soil layer in both sites, RLD increased from dry to wet season independently of variations in FRB. Total FRB in the top 30 cm of the soil at the Lowland site was significantly lower (334 g.m-2 in the dry season and 219 g.m-2 in the wet season) than at the Montane forest (875 and 451 g.m-2 in the dry and wet season, respectively). In conclusion, despite the relevance of FRB to describe processes related to carbon dynamics, the variation of RLD between seasons, independently of variations in FRB, indicates that RLD is a better descriptor for studies characterizing the potential of water and nutrient uptake at the Atlantic Rain Forest. The differences in RLD between altitudes within the context of resource use should be considered in studies about plant establishment, seedling growth and population dynamics at the Atlantic Rain Forest. At the ecosystem level, RLD and it seasonal variations may improve our understanding of the Atlantic rain forest functioning in terms of the biogeochemical fluxes in a possible scenario of climate change and environmental changes.

Download Full-text