Belowground Litter Research Articles

Climate Effects on Belowground Tea Litter Decomposition Depend on Ecosystem and Organic Matter Types in Global Wetlands.

Patchy global data on belowground litter decomposition dynamics limit our capacity to discern the drivers of carbon preservation and storage across inland and coastal wetlands. We performed a global, multiyear study in over 180 wetlands across 28 countries and 8 macroclimates using standardized litter as measures of "recalcitrant" (rooibos tea) and "labile" (green tea) organic matter (OM) decomposition. Freshwater wetlands and tidal marshes had the highest tea mass remaining, indicating a greater potential for carbon preservation in these ecosystems. Recalcitrant OM decomposition increased with elevated temperatures throughout the decay period, e.g., increase from 10 to 20 °C corresponded to a 1.46-fold increase in the recalcitrant OM decay rate constant. The effect of elevated temperature on labile OM breakdown was ecosystem-dependent, with tidally influenced wetlands showing limited effects of temperature compared with freshwater wetlands. Based on climatic projections, by 2050 wetland decay constants will increase by 1.8% for labile and 3.1% for recalcitrant OM. Our study highlights the potential for reduction in belowground OM in coastal and inland wetlands under increased warming, but the extent and direction of this effect at a large scale is dependent on ecosystem and OM characteristics. Understanding local versus global drivers is necessary to resolve ecosystem influences on carbon preservation in wetlands.

Season-Dependent Effect of Fire-Derived Charcoal on Above- and Belowground Litter Decomposition in Boreal Forests

Fire-derived charcoal (charcoal) is a stable byproduct of forest fires that accumulates in the litter layer and soils of boreal forests. Therefore, decomposition of litter and roots, as one of the key processes in the carbon cycle, in the soils of northern forests almost everywhere go in the presence of charcoal. To date, there are extremely scarce data on the influence of charcoal on decomposition in boreal forests, and most of them do not consider the cold period, which lasts on average half a year in this zone. The purpose of this work was to determine the seasonal influence of charcoal on the decomposition of plant litter of different quality (larch needles, birch leaves, grasses, and mixtures of these species of litter) on the surface of the soil and the roots of these same species in the soil. In “litterbag” experiment it was found that charcoal accelerated decomposition of litter and that its effect was species-specific. The acceleration of mass loss in the presence of charcoal occurred for recalcitrant litter (needles) and all types of roots during the cold period. In the warm period, acceleration of decomposition in the presence of charcoal was observed only for needles and was not observed for roots. Thus, our study shows a greater influence of charcoal on intra-soil decomposition especially in the cold period. Seasonal influence of charcoal was established for the first time and should be taken into account as an important factor of humus formation and carbon dynamics in soils of boreal forests.

Regulation of soil organic carbon dynamics by microbial communities during reforestation of Chinese fir plantations after clear‐cutting

AbstractReforestation after forest clear‐cutting is an effective measure to increase soil organic carbon (SOC) sequestration; still, the soil C balance under reforestation and the role of microbial communities in that process remain to be determined. Samples of organic (0–2 cm) and mineral (2–10 cm) horizons were collected from the 7‐, 15‐, 20‐, 29‐, and 36‐year‐old forest stands of Chinese fir (Cunninghamia lanceolata) after plantation clear‐cutting in subtropical zone under the condition of phosphorus limitation. Particulate organic carbon (POC), mineral‐associated organic carbon (MAOC), microbial phospholipid fatty acids (PLFAs), and enzymatic activities for C, nitrogen (N), and phosphorus (P) acquisition were analyzed. The lowest contents of POC (10%) and MAOC (13%) in the organic horizon were found in 7‐year‐old stands due to the slow tree regrowth and extensive decomposition of SOC in the first years of forest regrowth. POC (2.0×) and MAOC (0.8×) increases in the organic horizon with forest age were attributed to the stand development and accumulation of above‐ and belowground litter. The organic horizon had a higher POC:MAOC ratio than the mineral (0.7–1.1 vs. 0.2–0.5), indicating lower SOC stability in the first one. The ratio of POC:MAOC increased with the Gram‐positive to Gram‐negative bacteria (G+:G‐) ratio, pointing out that microbial communities developed a specific community structure and substrate utilization strategies of organic matter under plantation restoration. The increase of total PLFAs and the G+:G‐ ratio was closely linked with the microbial C and P limitations, indicating that microorganisms shifted community structure to slow‐growing species and increased their content to cope with the C and P restrictions. In the soils of young plantations, microorganisms were limited by C and P; however, the C limitation was alleviated in the 36‐year‐old plots in the organic horizon due to increased litter input, whereas the P limitation was not. This discrepancy between C and P limitation suppressed the decomposition of litter entering the soil, which was seen in decreased specific activity of C degrading enzymes and led to the accumulation of POC in the organic horizon. Thus, soil C sequestration under reforestation of Chinese fir can be controlled by the amount of litter entering the soil and by metabolic C, N, and P limitations that force microorganisms to shift community structure and change their activity.

Season-Dependent Effect of Fire-Derived Charcoal on the Above- and Belowground Litter Decomposition in Boreal Forests

Season-Dependent Effect of Fire-Derived Charcoal on the Above- and Belowground Litter Decomposition in Boreal Forests

Ecological Stoichiometry of N and P across a Chronosequence of Chinese Fir Plantation Forests

Ecological stoichiometry is crucial in understanding nutrient dynamics and its impact on plant growth and development at various ecological scales. Among the different nutrients, nitrogen (N) and phosphorus (P) have been widely recognized as key elements regulating substance transport, energy utilization, and ecosystem conversion. The N:P ratio in plants serves as a sensitive indicator of ecological processes, reflecting the availability and balance of these nutrients. Therefore, studying the ecological stoichiometry of N and P is essential for accurately assessing soil fertility and site productivity, particularly in forest ecosystems with low-fertility soils. In this study conducted in Huitong, Hunan province, southern China, the contents of N and P, as well as the N:P ratios, were investigated in plant-soil systems across four different aged stands of Chinese fir forests (3-, 8-, 18-, and 26-year-old stands). The results revealed varying concentrations of N and P in soils and foliage across the different plantations. Soil N concentrations increased by approximately 4%, 30%, and 22% in 8-, 18-, and 26-year-old plantations compared to the 3-year-old plantation. Soil P concentration was significantly higher in 8-, 18-, and 26-year-old plantations compared to the 3-year-old plantation. The average soil N:P ratio followed the order of 3-year-old plantation > 18-year-old plantation > 26-year-old plantation > 8-year-old plantation. Regarding foliage, both N and P contents exhibited a similar pattern across the different aged leaves, with current-year-old leaves having higher concentrations than 1-year-old, 2-year-old, and 3-year-old leaves in all four Chinese fir plantations. The study further established relationships between soil and foliage nutrient ratios. Soil N:P ratio was positively correlated with soil N content but negatively associated with soil P content. The foliage N:P ratio also showed a significant negative correlation between leaf N and foliage P content. These findings suggest that soil nutrient conditions improved with the aging of Chinese fir plantations, mainly due to increased inputs of above- and below-ground litter. Overall, this study provides valuable insights into the ecological stoichiometry of N and P in Chinese fir plantations, offering a scientific basis for sustainable forest management practices in southern China.

How do harvesting methods applied in continuous-cover forestry and rotation forest management impact soil carbon storage and degradability in boreal Scots pine forests?

Forest management affects soil carbon (C) storage through forest composition, microclimate and litter inputs. How two major forest management systems, continuous-cover forestry (CCF) and clear-cut-based rotation forest management (RFM), differ in their impact on soil C in boreal forests is still poorly understood, however. We compared their effects on soil organic carbon (SOC) storage and quality in boreal Scots pine (Pinus sylvestris L.) dominated forests in eastern Finland. We tested the hypotheses that (1) colder microclimates and continuous litter inputs will lead to higher SOC stocks in CCF plots than in clear-cuts and (2) the more labile litter in clear-cuts with varying ground vegetation will enhance SOC decomposition rates. We sampled uncut mature forests, clear-cuts, retention-cuts and gap-cuts, in which we analysed SOC concentrations and calculated the stocks. We measured stand characteristics such as diameter-at-breast height, basal area, dominant tree height, and understorey species coverage of the various treatments and modelled the above- and belowground litter inputs based on these parameters. We used laboratory incubation and sequential fractionation of SOC to assess its degradability under standardized conditions. To estimate the decomposition rate in the various environments we incubated cellulose bags in situ. We assessed the impact of microclimate on SOC decomposition, using data from soil-temperature and soil-moisture field measurements. We quantified the microbial biomass C pool, using chloroform fumigation extraction to gain insight on the impact of forest management practice on soil microbes. The SOC concentrations and SOC stocks did not differ significantly between the treatments, despite the presence of a warmer microclimate and lower litter inputs in the clear-cut plots. However, we found differences in the quality of the SOC. Soils in clear-cut sites showed lower proportions of labile SOC compounds than did the other treatments. As hypothesized, the decomposition rates were elevated in clear-cuts, but were equally as high within the canopy gaps on gap-cut stands. Our work highlights that forest management affects the quality, degradability, long-term accumulation and storage of SOC. We conclude that the accumulation of labile compounds in uncut forests and retention-cuts, combined with the decreased decomposition rates, indicate a higher potential for future C accumulation in the soil than in clear-cuts.

Above and belowground litter decomposition of cover crops grazed at different intensities

AbstractGrazing cover crops may increase land‐use efficiency while promoting sustainability. We investigated how grazing intensity affects cover crop litter quantity, quality, decomposition, and cotton (Gossypium hirsutum L.) N uptake. Cover crops were a mixture of rye (Secale cereale L.) and oat (Avena sativa L.) managed as follows: no grazing +34 kg N ha−1 (NG34), no grazing +90 kg N ha−1 (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG). Grazed treatments received 90 kg N ha−1. After cover crop termination, above‐ and belowground litter was collected and incubated in situ for 0, 4, 8, 16, 32, 64, and 128 days, with cotton plants sampled on the same days to estimate N recovery and synchrony between N release from litter and uptake by cotton. By Day 128, only 13% of initial NG34 aboveground biomass had disappeared, whereas 42% of HG disappeared. Nitrogen retained in aboveground litter of HG was less than NG90 (27 vs. 60 kg N ha−1), and aboveground final N stock (at Day 128) of HG was less than NG90 and LG (16, 47, and 41 kg N ha−1, respectively). Belowground litter contributed 98 kg N ha−1 versus 46 for aboveground. Belowground N disappearance from litter bags was greater from NG90 than NG34 (39 vs. 21 kg N ha−1). Cotton N uptake by Day 128 was similar across treatments (191 kg N ha−1). Grazing cover crops impact aboveground litter quantity, quality, and decomposition rates, and belowground litter plays an important role on the N cycling.

Warming accelerates belowground litter turnover in salt marshes – insights from a Tea Bag Index study

Abstract. Salt marshes play an important role in the global carbon cycle due to the large amount of organic carbon stored in their soils. Soil organic carbon formation in these coastal wetland ecosystems is strongly controlled by the plant primary production and initial decomposition rates of plant belowground biomass and litter. This study used a field warming experiment to investigate the response of belowground litter breakdown to rising temperature (+1.5 and +3.0 ∘C) across whole-soil profiles (0–60 cm soil depth) and the entire intertidal flooding gradient ranging from the pioneer zone via the low marsh to high marsh. We used standardized plant materials, following the Tea Bag Index approach, to assess the initial decomposition rate (k) and the stabilization factor (S) of labile organic matter inputs to the soil system. While k describes the initial pace at which labile (= hydrolyzable) organic matter decomposes, S describes the part of the labile fraction that does not decompose during deployment in the soil system and stabilizes due to biochemical transformation. We show that warming strongly increased k consistently throughout the entire soil profile and across the entire flooding gradient, suggesting that warming effects on the initial decomposition rate of labile plant materials are independent of the soil aeration (i.e., redox) status. By contrast, negative effects on litter stabilization were less consistent. Specifically, warming effects on S were restricted to the aerated topsoil in the frequently flooded pioneer zone, while the soil depth to which stabilization responded increased across the marsh elevation gradient via the low to high marsh. These findings suggest that reducing soil conditions can suppress the response of belowground litter stabilization to rising temperature. In conclusion, our study demonstrates marked differences in the response of initial decomposition rate vs. stabilization of labile plant litter to rising temperature in salt marshes. We argue that these differences are strongly mediated by the soil redox status along flooding and soil-depth gradients.

Contribution of tree and crop roots to soil carbon stocks in a Sub-Sahelian agroforestry parkland in Senegal

In the Sub-Sahelian region (Senegal), Faidherbia albida trees have been maintained for years in agroforestry parklands for their numerous services offered to people and to crops. The aerial crop biomass and yield are notably greater under the tree crown, but most of this biomass is exported and does not contribute to soil carbon (C) inputs. Belowground litter inputs are crucial, but little is known about the root system distribution, productivity and contribution to soil C inputs. This study aims to assess the field heterogeneity of F. albida and crop root systems along the soil profile based on the distance to the tree to evaluate the root contribution to soil C stocks.During two successive rotations of pearl millet in 2020 and groundnut in 2021, soils and roots were sampled from two locations (Under and Far from the tree), in 5 soil layers to a depth of 150 cm and with three tree replicates. The aerial biomass was also sampled. The annual relative contribution of roots to soil C stocks was estimated as the ratio between root litter-derived C inputs (considering hypothetical root turnover only for trees and the whole root biomass for crops) and soil C stocks.We found a similar crop root biomass density Under and Far from the tree, but the higher root:shoot ratio Far from than Under the tree confirmed the beneficial effect of trees on the aerial crop biomass. Unexpectedly, the tree root biomass density was higher at + 30 m from the trunk than Under the tree in the 30–100 cm soil layer, suggesting a long-distance soil exploration by the trees. Down to 150 cm of depth, the tree root litter contribution to soil C stocks represented 6.1 % and 7.1 % of the total root litter-derived C inputs (Under and Far from the tree, respectively). In this type of Sub-Sahelian parklands with low soil C stocks, increasing the tree density or selecting deep and highly rooted crop varieties should be favoured.

Belowground plant traits and their ecosystem functions along aridity gradients in grasslands

Ecosystem responses to environmental change are usually studied solely using aboveground (usually leaf) traits. However, belowground plant traits, such as fine roots and coarse belowground organs, likely play a crucial role in ecosystem response, especially under aridifcation. We conducted a literature survey on belowground plant traits along aridity gradients in temperate grasslands to propose which effect traits might be connected with abrupt vegetation changes that would occur with aridification due to environmental change. With increasing aridity, seasonal regeneration decreasingly relies on recruitment from the belowground bud bank and increasingly relies on regeneration from seeds. This leads to greater inter-annual variability in biomass production. Other belowground traits, such as bud bearing organs and fine root distribution in the soil, also shifts along the aridity gradient. As aridifcation begins, we propose that plants would become more conservative in their belowground traits producing lower amounts of belowground litter. Increasing aridifcation would lead to the loss of rhizomatous plants from the community and a prevalence of deep rooting plants leading to changes in soil resource utilization and increasing susceptibility to soil erosion. Under extreme aridification, perennial plants, except those with bulbs, would be lost from the community and replaced by annuals which produce low amounts of litter and use only ephemeral water resources in the upper soil layers. Belowground plant traits, such as belowground clonal growth organs, bud banks, and fine root distributions, may provide a more mechanistic understanding behind shifts in ecosystem functioning due to environmental change.

Additional N Input May Alter the Species-Specific Blue Carbon Cycling Differently in Mangroves

Aquaculture is one of the fastest-growing economic activities in the world that results in a high amount of nitrogen-rich wastewater discharge into mangroves and affects the plant tissue’s decomposition. However, a comprehensive analysis of above- and belowground litter affected by the nitrogen (N) input is rare. This study investigated the responses of above- and belowground litter decomposition to the different levels of N input in decomposition rates, chemical components, and the release of chemical compounds. Exogenous N input had stimulating, retarding, or even no effect on plants’ litter decomposition and nutrient release in mangroves. The above- and belowground litter decompositions had different responses to anthropogenic N addition and varied among different mangrove species. The mechanism of the impacts of anthropogenic nitrogen input varies depending on species identity, litter composition, and additional N level. These results show that N enrichment in mangroves can be beneficial and detrimental to ecosystem function. For the native mangrove species, Kandelia obovata and Avicennia marina , the belowground tissues that had a direct correlation with carbon accumulation were significantly influenced by the additional N input. The worldwide problem of offshore aquaculture effluent discharge is a potential risk to the ecological function of mangroves in carbon storage.

Carbon and Nutrient Transfer via Above- and Below-Ground Litter in Forests

Plants periodically shed more than 90% of their biomass production as above- and below-ground litter, including leaves, twigs, flowers, logs, roots and other tissues [...]

Plant litter traits control microbial decomposition and drive soil carbon stabilization

A bstract Efforts to manage soils for carbon (C) sequestration remain limited by our understanding of how differences in plant traits and microbial traits mechanistically drive soil organic C (SOC) storage. Addressing this uncertainty is particularly critical in bioenergy agriculture, due to its potential to enhance soil C and provide a C neutral fuel. As such, we examined differences between two contrasting feedstocks, Zea mays (corn) and Miscanthus x giganteus (miscanthus), in the ability of their litter to form new chemically resistant particulate SOC vs. physically protected mineral associated SOC and used this data to improve the parameterization of a microbial SOC model. We tested a hypothesized conceptual model whereby easy to decompose corn litters drive greater microbial carbon use efficiency (CUE) and the formation of more mineral associated SOC over particulate SOC than more complex miscanthus litters. To do this, we performed a soil microcosm experiment where we added 13 C enriched aboveground and belowground litters to soils and traced the fate of the 13 C into microbial respiration and SOC pools. We found that corn litters promoted higher microbial CUE (0.37) than miscanthus litters (0.24). In turn, corn litter formed approximately 50% more mineral associated SOC than miscanthus litters. Similarly, structurally complex root litters promoted a lower CUE and formed less mineral associated SOC than leaf and shoot litters for both crops. When we used our data to parameterize the SOC model, we found that modelling microbial trait differences uniquely allowed the model to capture the fate of litter C in SOC. Collectively, we found a robust link between litter quality, microbial efficiency, and the formation of SOC. This link bridges the empirical uncertainty in how different crops can form new soil C and provides an empirical basis for modelling SOC transformations. • Corn forms more mineral-associated and less particulate soil carbon than miscanthus. • Complex litter chemistry reduces microbial carbon use efficiency. • Greater microbial carbon use efficiency leads to more mineral-associated soil carbon. • Empirically based microbial parameters improve modeled soil carbon stabilization.

Soil organic matter molecular composition with long-term detrital alterations is controlled by site-specific forest properties.

Forest ecosystems are important global soil carbon (C) reservoirs, but their capacity to sequester C is susceptible to climate change factors that alter the quantity and quality of C inputs. To better understand forest soil C responses to altered C inputs, we integrated three molecular composition published data sets of soil organic matter (SOM) and soil microbial communities for mineral soils after 20 years of detrital input and removal treatments in two deciduous forests: Bousson Forest (BF), Harvard Forest (HF), and a coniferous forest: H.J. Andrews Forest (HJA). Soil C turnover times were estimated from radiocarbon measurements and compared with the molecular-level data (based on nuclear magnetic resonance and specific analysis of plant- and microbial-derived compounds) to better understand how ecosystem properties control soil C biogeochemistry and dynamics. Doubled aboveground litter additions did not increase soil C for any of the forests studied likely due to long-term soil priming. The degree of SOM decomposition was higher for bacteria-dominated sites with higher nitrogen (N) availability while lower for the N-poor coniferous forest. Litter exclusions significantly decreased soil C, increased SOM decomposition state, and led to the adaptation of the microbial communities to changes in available substrates. Finally, although aboveground litter determined soil C dynamics and its molecular composition in the coniferous forest (HJA), belowground litter appeared to be more influential in broadleaf deciduous forests (BH and HF). This synthesis demonstrates that inherent ecosystem properties regulate how soil C dynamics change with litter manipulations at the molecular-level. Across the forests studied, 20 years of litter additions did not enhance soil C content, whereas litter reductions negatively impacted soil C concentrations. These results indicate that soil C biogeochemistry at these temperate forests is highly sensitive to changes in litter deposition, which are a product of environmental change drivers.

Responses of aboveground litterfall respiration to unexpected snowfall events in Ailao subtropical forests in Southwest China

Soil respiration, the second largest CO2 flux in terrestrial ecosystems, involves the microbial respiration of litter from aboveground sources, belowground litter and root respiration, from rhizodeposition. In the subtropical forests of the Ailao Mountain, a chamber with automated CO2 efflux was set up with two treatments: a control treatment with litterfall to measure the total soil respiration (RT) and a litter removal treatment to measure aboveground litterfall respiration (RL). This study aimed to examine the responses of RL to unexpected heavy snowfall events and soil temperature (ST), soil moisture (SM), rainfall (RF), total litterfall (TL), litter water content (LWC), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N). The period of the study was divided into two: before the heavy snowfall event (BS) and during and after the heavy snowfall event (AS). The rate of RL was slightly decreased in AS (1.18 ± 0.03 μmol CO2 m−2 s−1) compared with that in BS (1.19 ± 0.02 μmol CO2 m−2 s−1). The relationships between RL and ST, SM, RF, and LWC, respectively, were all statistically significant (p < 0.05) in both periods. However, the relationships between RL and TL and NH4+-N, respectively, were not statistically significant for either period. The relationship between RL and NO3−-N was statistically significant for AS but not for BS. The relationship between RL and RF was statistically significant from 2011 to 2018. The temperature dependence of soil respiration was higher in BS than in AS, and the effect of litter removal was 2.55 % and 2.32 % for AS and BS respectively. The results indicate that current global terrestrial models underestimate RL trends for the feedback of global climate change in subtropical forests.

Role of hydrological parameters in the uncertainty in modeled soil organic carbon using a coupled water-carbon cycle model

Soil organic carbon is the largest carbon pool in the terrestrial biosphere. Large uncertainties exist in the numerical simulations of soil organic carbon due to inaccuracies in their mathematical descriptions of hydrological processes. In this study, the upper limit of uncertainty in modeled soil organic carbon that is induced by hydrological parameter errors, which may stem from measurement or experiential errors, is estimated in China under four different arid and humid conditions. The study was conducted using a conditional nonlinear optimal perturbation related to parameters (CNOP-P) approach and a model of the coupled water-carbon cycle (the Lund-Potsdam-Jena Wetland Hydrology and Methane Dynamic Global Vegetation Model, LPJ-WHyMe). Uncertainties in hydrological processes resulted in the largest error (2.73 kg C m−2 yr−1, 20.2%) in the modeled soil organic carbon in the arid and semiarid regions of northern China, with errors of 1.20 kg C m−2 yr−1 (6.1%) in northeastern China, 0.45 kg C m−2 yr−1 (3.3%) in southern China, and -1.71 kg C m−2 yr−1 (13.7%) in the semihumid region of northern China. By analyzing the three components of soil organic carbon, the fast soil carbon pool was found to be the main cause of the uncertainties in modeled soil organic carbon in the four regions of China. Moreover, belowground litter was another cause of the uncertainties in the modeled soil organic carbon in northeastern China and in the semihumid region of northern China. Additional results indicated that the simulation and prediction abilities of soil organic carbon could be improved by reducing parameter errors in hydrological processes through observations or targeted observations. The parameter sensitivity test showed that the benefits to modeling soil organic carbon were similar when reducing the errors in the sensitive hydrological parameter subset, compared to the benefits of reducing the errors in all the hydrological parameters.

IMPACT OF LITTER TURNOVER ON CARBON CYCLING IN FORESTS WITH DRAINED AND NATURALLY WET NUTRIENT-RICH ORGANIC SOILS IN LATVIA

Litter production is a key parameter for estimation of forest soil carbon (C) stock. The aim of the study was to evaluate carbon stock in above and below-ground litter in forests with drained and naturally wet nutrient-rich organic soils in Latvia to improve National GHG inventory and to integrate data into AGM and EPIM models. To estimate C input with tree above-ground litter, sampling of litter was done in 46 research sites in Latvia. A modelling approach based on a literature review was used to estimate C input with tree below-ground litter and litter of ground vegetation. Our study highlights a connection between C input to soil with litter and stand characteristics – stand basal area, stand age and dominant tree species. There is a trend for C input from above- and below- ground litter to increase along with increasing stand basal area. In conifer stands the C input with ground vegetation increased with stand basal area, whereas for broadleaves the trend is reverse. There is still uncertainty regarding C input with below-ground litter and ground vegetation. In order to improve the modeling approach additional data and country-specific models are required.

Estimation of litter input in hemi-boreal forests with drained organic soils for improvement of GHG inventories

Assessments of net greenhouse gas (GHG) emissions in forest land with drained organic soils conducted within the scope of National GHG inventories requires reliable data on litter production and carbon (C) input to soil information. To estimate C input through tree above-ground litter, sampling of above-ground litter was done in 36 research sites in Latvia representing typical forests with drained organic soils in hemiboreal region. To estimate C input through tree below-ground litter and litter from ground vegetation, modelling approach based on literature review and data on characteristics of forest stands with drained organic soils in Latvia provided by National Forest Inventory (NFI) was used. The study highlighted dependence of C input to soil through litter production from the stand characteristics and thus significant differences in the C input with litter between young and middle age stands. The study also proves that drained organic soils in middle age forests dominated by Silver birch, Scots pine and Norway spruce may not be the source of net GHG emissions due to offset by C input through litter production. However, there is still high uncertainty of C input with tree below-ground litter and ground vegetation, particularly, mosses, herbs and grasses which may have crucial role in C balance in forests with drained organic soils. Key words: forests, drained organic soils, litter production, carbon input, National GHG inventory

Mycorrhizal roots slow the decay of belowground litters in a temperate hardwood forest.

There is increasing evidence that plant roots and mycorrhizal fungi, whether living or dead, play a central role in soil carbon (C) cycling. Root-mycorrhizal-microbial interactions can both suppress and enhance litter decay, with the net result dependent upon belowground nutrient acquisition strategies and soil nutrient availability. We measured the net effect of living roots and mycorrhizal fungi on the decay of dead roots and fungal hyphae in a hardwood forest dominated by either sugar maple (Acer saccharum) or white oak (Quercus alba) trees. Root and fungal litter were allowed to decompose within root-ingrowth bags and root-exclusion cores. In conjunction with root effects on decay, we assessed foraging responses and root induced changes in soil moisture, nitrogen (N) availability and enzyme activity. After 1 year, maple root production increased, and mycorrhizal fungal colonization decreased in the presence of decaying litter. In addition, we found that actively foraging roots suppressed the decay of root litter (-14%) more than fungal litter (-3%), and suppression of root decay was stronger for oak (-20%) than maple roots (-8%). Suppressive effects of oak roots on decay were greatest when roots also reduced soil N availability, which corresponded with reductions in hydrolytic enzyme activity and enhanced oxidative enzyme activities. These findings further our understanding of context-dependent drivers of root-mycorrhizal-microbial interactions and demonstrate that such interactions can play an underappreciated role in soil organic matter accumulation and turnover in temperate forests.

Effects of hydrological environment on litter carbon input into the surface soil organic carbon pool in the Dongting Lake floodplain

Litter carbon is the main source of the surface soil organic carbon pool (S-SOCP). However, the impact of changes in the hydrological environment of natural wetlands on litter input to S-SOCP remains unclear. In the present study, the effects of hydrological changes (soil water content [SWC] and days of flooding [DF]) on the litter decomposition process and S-SOCP were investigated from January 2018 to November 2019 in the Dongting Lake floodplain of China. Furthermore, the contribution of litter to the S-SOCP in Carex meadow and Reed wetland were calculated. The results showed that a large part of litter (approximately 50%–70%) decomposed annually, especially during the flooding season. Litter contributed 283.68 g C m−2 a–1 to the S-SOCP in the Carex meadow and 275.24 g C m−2 a–1 to the Reed wetland. In the Carex meadow and Reed wetland, the belowground litter contribution was higher than the aboveground litter during the non-flooding season. In contrast, during the flooding season, the aboveground litter contribution in the Carex meadow is higher, whereas the belowground litter dominates in the Reed wetland. The SWC indicated a positive correlation with soil organic carbon (SOC) and a negative correlation with the microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in the Carex meadow. However, SWC shows a negative correlation with SOC and a positive correlation with MBC in the Reed wetland during the non-flooding season. During the flooding season, the variation of DOC during the flooding season (ΔDOC) is positively correlated with DF in the Carex meadow and Reed wetland. SWC and DF are the main drivers of litter decomposition into the S-SOCP in non-flooding and flooding seasons, respectively. Therefore, the construction of microhabitat with prolonged flooding and relatively higher soil water content are essential ways to improve the carbon sequestration potential in floodplains.