Annual Litter Input Research Articles

Dynamics of soil organic carbon pools following conversion of savannah to cocoa agroforestry systems in the Centre region of Cameroon

Afforestation of gramineous-woody savannah with cocoa agroforestry systems (cAFS) is a common farmer practice in Cameroon considered as sustainable. Nevertheless, the effects of afforestation of savannah with cAFS on soil organic carbon (SOC) turnover and content, and the factors controlling SOC accumulation and stabilization are unknown. SOC content at 0–10 cm soil layer, and SOC distribution in soil particle size fractions (0–20 μm fraction considered as mineral-associated organic carbon, MAOC; 50–2000 μm considered as particulate organic carbon, POC; and 20–50 μm), were compared in different systems settled on degraded savannah (orthic ferralsols). These systems included annual cropland (≈ 5 years old), cocoa monoculture (≈10 years old), and cAFS (from 20 to 60 years old) including different shade tree species such as Albizia adianthifolia, Canarium schweinfurthii, Dacryodes edulis, Milicia excelsa and Ceiba pentandra. Savannah and nearby secondary forest patches were also included in the design as controls. Soil 13C was analysed to investigate the soil carbon turnover after afforestation (C3 plants) of gramineous savannah (C4 plants).SOC significantly increased in the 0–10 cm depth from 10.6 ± 3.1 g C kg−1 in degraded savannah to 17.9 ± 5.6 g C kg−1 in cAFS reaching similar levels as in nearby secondary forests (16.3 ± 5.8 g C kg−1), while annual cropland and cocoa monoculture presented a non-significant decrease in SOC content. These changes were due to rapid loss of SOC derived from savannah plants (C4) – about 76% within the first 15 years after conversion, and higher gain of SOC derived from C3 plants in cAFS than in the other land uses (e.g. from 3.4 ± 1.5 g C kg−1 in savannah to 17.8 ± 5.7 g C kg−1 in cAFS). This SOC enrichment in cAFS was distributed in POC (64%), MAOC (30%) and the intermediate 20–50 μm soil fraction (6%). The higher annual litter input accumulated on a longer period in cAFS (20 to 60 years) than in cocoa monoculture (10 years) concomitant with the lower litter recalcitrance of associated trees compared to cocoa could explain the higher enrichment of SOC in all fractions in cAFS. The soil pH and exch. Ca2+ differed under the different shade tree species, and were positively correlated to SOC content. The highest contents of soil exch. Ca2+ induced by Ceiba and Milicia in the top 10 cm soil layer could contribute to increase SOC enrichment under those species through soil aggregation and related C stabilization. We found no strong evidence of the effect of soil texture on additional soil carbon accumulation in cAFS, especially for the more stable C pool (MAOC). Our results evidenced that savannah afforestation with cAFS appears as a valuable option for top soil carbon enrichment and should consider tree species associated to cocoa to enhance soil C sequestration, soil quality and cocoa production sustainability.

A new method for estimating carbon dioxide emissions from drained peatland forest soils for the greenhouse gas inventory of Finland

Abstract. In peatlands drained for forestry, the soil carbon (C) or carbon dioxide (CO2) balance is affected by both (i) higher heterotrophic CO2-C release from faster decomposing soil organic matter (SOM) and (ii) higher plant litter C input from more vigorously growing forests. This balance and other greenhouse gas (GHG) sinks and sources in managed lands are annually reported by national GHG inventories to the United Nations Climate Change Convention. In this paper, we present a revised, fully dynamic method for reporting the CO2 balance of drained peatland forest soils in Finland. Our method can follow temporal changes in tree biomass growth, tree harvesting and climatic parameters, and it is built on empirical regression models of SOM decomposition and litter input in drained peatland forests. All major components of aboveground and belowground litter input from ground vegetation as well as live trees and trees that died naturally are included, supplemented by newly acquired turnover rates of woody plant fine roots. Annual litter input from harvesting residues is calculated using national statistics of logging and energy use of trees. Leaching, which also exports dissolved C from drained peatlands, is not included. The results are reported as time series from 1990–2021 following the practice in the GHG inventory. Our revised method produces an increasing trend of annual emissions from 0.2 to 2.1 t CO2 ha−1 yr−1 for the period 1990–2021 in Finland (equal to a trend from 1.4 to 7.9 Mt CO2 yr−1 for the entire 4.3 Mha of drained peatland forests), with a statistically significant difference between the years 1990 and 2021. Across the period 1990–2021, annual emissions are on average 1.5 t CO2 ha−1 yr−1 (3.4 Mt CO2 yr−1 for 2.2 Mha area) in warmer southern Finland and −0.14 t CO2 ha−1 yr−1 (−0.3 Mt CO2 yr−1 for 2.1 Mha area) in cooler northern Finland. When combined with data on the CO2 sink created by the growing tree stock, in 2021 the drained peatland forest ecosystems were a source of 1.0 t CO2 ha−1 yr−1 (2.3 Mt CO2 yr−1) in southern Finland and a sink of 1.2 t CO2 ha−1 yr−1 (2.5 Mt CO2 yr−1) in northern Finland. We compare these results to those produced by the semi-dynamic method used earlier in the Finnish GHG inventory and discuss the strengths and vulnerabilities of the new revised method in comparison to more static emission factors.

Global mass of buoyant marine plastics dominated by large long-lived debris

The fate of plastics that enter the ocean is a longstanding puzzle. Recent estimates of the oceanic input of plastic are one to two orders of magnitude larger than the amount measured floating at the surface. This discrepancy could be due to overestimation of input estimates, processes removing plastic from the surface ocean or fragmentation and degradation. Here we present a 3D global marine mass budget of buoyant plastics that resolves this discrepancy. We assimilate observational data from different marine reservoirs, including coastlines, the ocean surface, and the deep ocean, into a numerical model, considering particle sizes of 0.1–1,600.0 mm. We find that larger plastics (>25 mm) contribute to more than 95% of the initially buoyant marine plastic mass: 3,100 out of 3,200 kilotonnes for the year 2020. Our model estimates an ocean plastic input of about 500 kilotonnes per year, less than previous estimates. Together, our estimated total amount and annual input of buoyant marine plastic litter suggest there is no missing sink of marine plastic pollution. The results support higher residence times of plastics in the marine environment compared with previous model studies, in line with observational evidence. Long-lived plastic pollution in the world’s oceans, which our model suggests is continuing to increase, could negatively impact ecosystems without countermeasures and prevention strategies.

Estimating biomass and soil carbon change at the level of forest stands using repeated forest surveys assisted by airborne laser scanner data

BackgroundUnder the growing pressure to implement mitigation actions, the focus of forest management is shifting from a traditional resource centric view to incorporate more forest ecosystem services objectives such as carbon sequestration. Estimating the above-ground biomass in forests using airborne laser scanning (ALS) is now an operational practice in Northern Europe and is being adopted in many parts of the world. In the boreal forests, however, most of the carbon (85%) is stored in the soil organic (SO) matter. While this very important carbon pool is “invisible” to ALS, it is closely connected and feeds from the growing forest stocks. We propose an integrated methodology to estimate the changes in forest carbon pools at the level of forest stands by combining field measurements and ALS data.ResultsALS-based models of dominant height, mean diameter, and biomass were fitted using the field observations and were used to predict mean tree biophysical properties across the entire study area (50 km2) which was in turn used to estimate the biomass carbon stocks and the litter production that feeds into the soil. For the soil carbon pool estimation, we used the Yasso15 model. The methodology was based on (1) approximating the initial soil carbon stocks using simulations; (2) predicting the annual litter input based on the predicted growing stocks in each cell; (3) predicting the soil carbon dynamics of the annual litter using the Yasso15 soil carbon model. The estimated total carbon change (standard errors in parenthesis) for the entire area was 0.741 (0.14) Mg ha−1 yr−1. The biomass carbon change was 0.405 (0.13) Mg ha−1 yr−1, the litter carbon change (e.g., deadwood and leaves) was 0.346 (0.027) Mg ha−1 yr−1, and the change in SO carbon was − 0.01 (0.003) Mg ha−1 yr−1.ConclusionsOur results show that ALS data can be used indirectly through a chain of models to estimate soil carbon changes in addition to changes in biomass at the primary level of forest management, namely the forest stands. Having control of the errors contributed by each model, the stand-level uncertainty can be estimated under a model-based inferential approach.

Budget of Plant Litter and Litter Carbon in the Subalpine Forest Streams

Investigations on the budget of plant litter and litter carbon in forest streams can provide a key scientific basis for understanding the biogeochemical linkages of terrestrial–aquatic ecosystems and managing forest catchments. To understand the biogeochemical linkages among mountain forests, riparian vegetation, and aquatic ecosystems, the changes in litter input and output from the subalpine streams with stream characteristics and critical periods were investigated in an ecologically important subalpine coniferous forest catchment in the upper reaches of the Yangtze River. The annual litter input to the stream was 20.14 g m−2 and ranged from 2.47 to 103.13 g m−2 for 15 streams during the one-year investigation. Simultaneously, the litter carbon input to the stream was 8.61 mg m−2 and ranged from 0.11 to 40.57 mg m−2. Meanwhile, the annual litter output varied from 0.02 to 22.30 g m−2, and the average value was 0.56 g m−2. Correspondingly, the litter carbon output varied from 0.01 to 1.51 mg m−2, and the average value was 0.16 mg m−2. Furthermore, the average ratio of litter carbon input to output was 270.01. The maximum and minimum values were observed in the late growing season and the snowmelt season, respectively. Additionally, seasonal variations in temperature, together with the stream length, dominated the input of litter and litter carbon to the stream, while the precipitation, temperature, water level, and sediment depth largely determined their output. Briefly, the seasonal dynamics of litter and litter carbon were dominated by stream characteristics and precipitation as well as temperature patterns.

Distinct patterns of below- and aboveground growth phenology and litter carbon inputs along a boreal site type gradient

Forest ecosystem productivity is strongly linked to site nutrient availability, which is influenced by litter inputs and their decomposition rates. Fine roots and mycelia are key contributors in belowground soil carbon (C) accumulation, but studies have seldom reported how belowground litter C input is related to site types in boreal forests. In this study, three mature and one young Pinus sylvestris forests along a site type gradient in southern Finland were chosen for measurements of fine root biomass, fine root longevity, below- and aboveground growth phenology and annual litter input from tree and understorey vegetation. Site types were distinguished by understorey vegetation composition, which indicated the site fertility. Fine root biomass per tree stand basal area decreased significantly from nutrient-poor to nutrient-rich sites, the nutrient-poor sites with longer fine root longevity resulted in an equal belowground litter input with the nutrient-rich site. Above- and belowground annual litter inputs were 131–236 and 70–91 g m−2 year−1, respectively. Aboveground litter increased with site fertility, resulting into belowground litter having a decreasing trend from 37% to 23% of total litter inputs with increasing site fertility. Ectomycorrhizal mycelia and understory production contributed 8–13% and 18–41% of belowground production, respectively. Contribution of understorey vegetation to the belowground litter C input was lower than that of trees at xeric and sub-xeric sites but equaled to that of trees at the mesic site. Our study showed distinct dimensions of below- and aboveground litter inputs influenced by site types. Moreover, we emphasize that the belowground C inputs from ectomycorrhizal mycelia and the understorey in addition to those of trees should always be considered in C balances and C reporting in boreal conifers.

浙西南常绿阔叶林凋落物空间分布及其对土壤养分的影响

凋落物作为养分的有效载体对于森林养分循环具有重要作用。近年来学者们对凋落物开展了大量研究，但森林内部凋落物的空间分布及其对土壤养分空间异质性的作用一直没有得到充分重视。利用位于浙江西南部的百山祖亚热带中山常绿阔叶林5 hm²森林动态监测样地中50个凋落物收集器2009-2017年收集到的凋落物产量数据和相关的地形和土壤养分数据，运用同步自相关回归分析地形和群落结构因素对凋落物及其组分产量的影响，利用多元线性混合效应模型研究了地形和年均凋落物输入量与土壤养分含量的关系。结果表明（1）地形因子中仅凸度与总凋落物以及叶凋落物产量呈显著正相关；（2）邻域内的大树和中树（胸径≥ 5 cm）的平均胸径显著提高总凋落物、叶凋落物和小枝及树皮凋落物产量，而邻域物种数显著提高总凋落物、叶凋落物和繁殖器官凋落物产量；（3）地形凸度与表层（深0-10 cm）土壤有机质含量显著正相关，但与近表层（深10-20 cm）土壤总氮、有效磷和速效钾含量显著负相关；（4）凋落物输入量显著提高表层（深0-10 cm）土壤的碱解氮和有机质含量。总体来看，百山祖常绿阔叶林凋落物产量的空间变异受到地形和森林群落结构因素的制约，并影响林内土壤养分的空间异质性。;Litter, as an effective carrier of nutrients, plays an important role in forest nutrient cycles. In recent years, several studies have been carried out on litter; however, the spatial distribution of litter yield in a forest and its effects on the spatial heterogeneity of soil nutrients have not been thoroughly investigated. In August 2008, 50 litter traps with horizontal areas of 0.71 m×0.71 m along a path in the 5hm² forest dynamics plot in the Baishanzu midmountain subtropical evergreen broadleaf forest were set and all the litter falling into the traps was collected twice a month during a period from 2009 to 2017. The litter was dried in an oven at 80℃ at a constant weight and was weighed. In July 2014, soil samples were collected using an earth drill from three 1m×1m quadrats with an adjacent distance of 2 m for each of the 50 litter traps (50×3 samples). Each soil sample was divided into surface and near-surface layers (i.e., 0-10 cm and 10-20 cm, respectively). Total nitrogen, alkaline nitrogen, available phosphorus, available potassium, and organic matter contents of these soil samples were determined by common soil chemistry approaches. The elevation, convexity, and slope of each 10m×10m quadrat were assigned to the trap located in the quadrat. Simultaneous auto-regression was used to analyze effects of topography and community structure on the litter and its component yields. The community structure was described according to the total basal area, mean diameter at breast height (DBH), and species richness of trees with DBH ≥ 5 cm in the 5 or 10 m radius neighborhood of the traps. Further, the impact of the topography and annual litter input on the soil nutrient concentration was studied using a linear mixed effect model. The results showed that (1) only convexity was positively correlated with the total and leaf litter yields; (2) the mean DBH of the trees in the neighborhood significantly increased the total, leaf, twig and bark litter yields, while the number of species in the neighborhood significantly increased the total, leaf, and reproductive organ litter yields; (3) the terrain convexity significantly increased the soil organic matter content in the surface layer (0-10 cm deep) but significantly reduced the total nitrogen, available phosphorus, and available potassium contents in the near-surface layer (10-20 cm deep); and (4) the total litter input significantly increased the alkaline nitrogen and organic matter contents in the surface soil. Our results suggest that the spatial variation in the litter yield in the Baishanzu evergreen broadleaf forest is determined by the topography and forest structure and affects the spatial heterogeneity of soil nutrients in the forest.

Modeling soil organic carbon dynamics in temperate forests with Yasso07

Abstract. In a context of global changes, modeling and predicting the dynamics of soil carbon stocks (CSs) in forest ecosystems are vital but challenging. Yasso07 is considered to be one of the most promising models for such a purpose. We examine the accuracy of its prediction of soil carbon dynamics over the whole French metropolitan territory at a decennial timescale. We used data from 101 sites in the RENECOFOR network, which encompasses most of the French temperate forests. These data include (i) the quantity of above-ground litterfall from 1994 to 2008, measured yearly, and (ii) the soil CSs measured twice at an interval of approximately 15 years (once in the early 1990s and around 2010). We used Yasso07 to simulate the annual changes in carbon stocks (ACCs; in tC ha−1 yr−1) for each site and then compared the estimates with actual recorded data. We carried out meta-analyses to reveal the variability in litter biochemistry in different tree organs for conifers and broadleaves. We also performed sensitivity analyses to explore Yasso07's sensitivity to annual litter inputs and model initialization settings. At the national level, the simulated ACCs (+0.00±0.07 tC ha−1 yr−1, mean ± SE) were of the same order of magnitude as the observed ones (+0.34±0.06 tC ha−1 yr−1). However, the correlation between predicted and measured ACCs remained weak (R2<0.1). There was significant overestimation for broadleaved stands and underestimation for coniferous sites. Sensitivity analyses showed that the final estimated CS was strongly affected by settings in the model initialization, including litter and soil carbon quantity and quality and also by simulation length. Carbon quality set with the partial steady-state assumption gave a better fit than the model with the complete steady-state assumption. With Yasso07 as the support model, we showed that there is currently a bottleneck in soil carbon modeling and prediction due to a lack of knowledge or data on soil carbon quality and fine-root quantity in the litter.

Heterogeneity in decomposition rates and annual litter inputs within fine-root architecture of tree species: Implications for forest soil carbon accumulation

Fine roots (⩽2mm in diameter) of tree species, traditionally regarded as homogenous entities, are expected to be major contributors of forest soil organic carbon (C), but their contributions need to be reevaluated given the heterogeneity in many root characteristics within fine-root architecture. Here, literature data were synthesized to analyze whether there existed heterogeneity of decomposition rates within fine-root architecture of tree species and quantify the relative contributions of roots of each branching order to forest soil C storage by combining variations in annual litter inputs among fine-root branching hierarchies. Results showed the presence of heterogeneity in decomposition rates within fine-root architecture, and this pattern was influenced by classification methods (root order or diameter class). Specifically, the heterogeneity in decomposition rates was shown only when fine roots were classified by root order, but not when fine roots were classified by diameter class. The slower decomposition rates of lower-order roots (the first two orders) were related to their higher acid-unhydrolyzable residues. Furthermore, lower-order roots were found to account for 57–71% of annual root litter inputs of the first five orders. Given the slow decomposition rates and high annual litter inputs of lower-order roots of tree species, our findings suggest that lower-order roots should be important contributors to forest soil organic C.

Influências climáticas na produção de serapilheira em um cerradão em Prata – MG

http://dx.doi.org/10.5007/2175-7925.2016v29n2p7O estudo teve como objetivo principal analisar a influência climática na produção de serapilheira, em um pequeno fragmento de cerradão em Minas Gerais, Brasil, durante um ano. Foram utilizados 20 coletores (0,25 m2), dispostos em linha. A produção de serapilheira total foi de 7,5 t.ha-1.ano-1, composta pelas frações folhas, ramos e estruturas férteis. A fração foliar contribuiu com 67% do total acumulado em um ano. A correlação de Pearson (r) indicou a influência das variáveis climáticas precipitação e temperaturas médias e mínimas na produção da fração foliar. A análise de r resultou também em valor significativo entre ramos e velocidade média do vento, enquanto que estruturas férteis sofreram influência da precipitação, temperaturas médias máximas e mínimas. Características vegetacionais podem ter interferido nos resultados encontrados. Todavia, estudos complementares envolvendo análises fitossociológica e de ciclagem de nutrientes deverão ser desenvolvidos para a comprovação de hipóteses propostas.

Factors influencing litter delivery to streams

Leaves and needles are an important energy source for streams. However, relatively little is known about factors that determine width of the area contributing litter to streams. We assessed the relative effect of wind speed, wind direction, litter type, tree height and riparian topography on litter delivery to streams. Wind speed effect on litter travel distance was determined by releasing needles (Douglas-fir) and leaves (red alder) from mature and young tree canopies over a range of wind velocities. Short-term litter collections were conducted to determine the effect of wind speed on litter fall. Litter travel distance increased with increasing wind speed and increasing tree height. At low wind speeds leaves traveled further than needles. Litter fall increased with wind speed. These relationships were combined with literature values for seasonal rates of litter production and an annual wind speed and direction record from a riparian area in western Washington to evaluate the relative effect of various factors on litter delivery area width. We found that width of the contributing area for needles was about 35% greater in riparian stands supporting mature conifer trees than at sites with young trees. Increasing riparian area slope from 0° to 45° increased width of contributing area by 71–95%, depending on litter type and stand age. Doubling measured wind speed increased contribution zone width 67–82%. Estimated buffer width required to capture 95% of annual litter input ranged from about 14m to over 25m under the conditions which we evaluated. The variety of factors influencing litter delivery area width and the spatial and temporal variation in these factors indicates that the common practice of employing fixed-width buffers to protect stream–riparian interactions cannot be consistently effective.

Strong stoichiometric resilience after litter manipulation experiments; a case study in a Chinese grassland

Abstract. Global climate change has generally modified net primary production (NPP) which leads to increasing litter inputs in some ecosystems. Therefore, assessing the impacts of increasing litter inputs on soil nutrients, plant growth and ecological carbon (C) : nitrogen (N) : phosphorus (P) stoichiometry is critical for an understanding of C, N and P cycling and their feedback processes to climate change. In this study, we added plant above-ground litter, harvested near the experimental plots, to the 10–20 cm subsoil layer of a steppe community at rates equivalent to annual litter input of 0, 15, 30, 60 and 120%, respectively, covering the entire range of the expected NPP increases in this region due to climate change (10–60%). We measured the resulting C, N and P content of different pools (above- and below-ground plant biomass, litter, microbial biomass). Small litter additions, which are more plausible compared to the expected increase predicted by Earth system models, had no effect on the variables examined. Nevertheless, high litter addition (120% of the annual litter inputs) significantly increased soil inorganic N and available P, above-ground biomass, below-ground biomass and litter. Our results suggest that while very high litter addition can strongly affect C : N : P stoichiometry, the grassland studied here is resilient to more plausible inputs in terms of stoichiometric functioning.

Microbial enzyme activities, fungal biomass and quality of the litter and upper soil layer in a beech forest of south Italy

SummaryForest soils contain a large amount of organic matter (OM) and therefore represent a considerable carbon reserve. The amount of OM sequestered in the soil is dependent on annual input of litter and its quality. The aim of this study was to investigate the quantity and quality of OM, the microbial capacity to degrade it and its recalcitrance to further degradation, by considering some extracellular enzyme activities in a beech (Fagus sylvatica L.) forest in south Italy (Mediterranean area). Our attention was focused on the decomposition continuum of the litter horizon and upper soil layer. Because fungi are the major decomposers of plant material, fungal biomass was also measured and its relationship with enzyme activities was tested. The results showed that: (i) the litter horizon and the upper soil layer differed in chemical characteristics and biological activities; (ii) within the litter horizon, the three layers detected for their different degree of degradation (L, recently fallen, not decomposed and not compressed material; F, partially decomposed and fragmented but macroscopically recognizable material; H, compressed and strongly fragmented) differed more in chemical characteristics than in biological activities; (iii) the enzyme activities and fungal biomass changed during the study period but a clear relationship with succession of seasons was evident only for cellulase, laccase, peroxidase and fungal biomass; and (iv) the upper soil layer included 42% OM and less than 50% of that was susceptible to further decomposition. This percentage was 30% in the OM of L.

Role of Arthropods in Maintaining Soil Fertility

In terms of species richness, arthropods may represent as much as 85% of the soil fauna. They comprise a large proportion of the meso- and macrofauna of the soil. Within the litter/soil system, five groups are chiefly represented: Isopoda, Myriapoda, Insecta, Acari, and Collembola, the latter two being by far the most abundant and diverse. Arthropods function on two of the three broad levels of organization of the soil food web: they are plant litter transformers or ecosystem engineers. Litter transformers fragment, or comminute, and humidify ingested plant debris, which is deposited in feces for further decomposition by micro-organisms, and foster the growth and dispersal of microbial populations. Large quantities of annual litter input may be processed (e.g., up to 60% by termites). The comminuted plant matter in feces presents an increased surface area to attack by micro-organisms, which, through the process of mineralization, convert its organic nutrients into simpler, inorganic compounds available to plants. Ecosystem engineers alter soil structure, mineral and organic matter composition, and hydrology. The burrowing by arthropods, particularly the subterranean network of tunnels and galleries that comprise termite and ant nests, improves soil porosity to provide adequate aeration and water-holding capacity below ground, facilitate root penetration, and prevent surface crusting and erosion of topsoil. Also, the movement of particles from lower horizons to the surface by ants and termites aids in mixing the organic and mineral fractions of the soil. The feces of arthropods are the basis for the formation of soil aggregates and humus, which physically stabilize the soil and increase its capacity to store nutrients.

Linking litter decomposition of above‐ and below‐ground organs to plant–soil feedbacks worldwide

Summary Conceptual frameworks relating plant traits to ecosystem processes such as organic matter dynamics are progressively moving from a leaf‐centred to a whole‐plant perspective. Through the use of meta‐analysis and global literature data, we quantified the relative roles of litters from above‐ and below‐ground plant organs in ecosystem labile organic matter dynamics. We found that decomposition rates of leaves, fine roots and fine stems were coordinated across species worldwide although less strongly within ecosystems. We also show that fine roots and stems had lower decomposition rates relative to leaves, with large differences between woody and herbaceous species. Further, we estimated that on average below‐ground litter represents approximately 33 and 48% of annual litter inputs in grasslands and forests, respectively. These results suggest a major role for below‐ground litter as a driver of ecosystem organic matter dynamics. We also suggest that, given that fine stem and fine root litters decompose approximately 1.5 and 2.8 times slower, respectively, than leaf litter derived from the same species, cycling of labile organic matter is likely to be much slower than predicted by data from leaf litter decomposition only. Synthesis. Our results provide evidence that within ecosystems, the relative inputs of above‐ versus below‐ground litter strongly control the overall quality of the litter entering the decomposition system. This in turn determines soil labile organic matter dynamics and associated nutrient release in the ecosystem, which potentially feeds back to the mineral nutrition of plants and therefore plant trait values and plant community composition.

The effects of afforestation on soil organic and inorganic carbon: A case study of the Loess Plateau of China

The determination of the changes in soil organic carbon (SOC) and inorganic carbon (SIC) in the subsoil following afforestation is meaningful and necessary for assessing carbon sequestration, but such knowledge is limited. In this case study, a paired-site approach was used to determine the differences in the SOC and SIC stock in the topsoil and subsoil, respectively, between a black locust (Robinia pseudoacacia L.) forest site (converted from cropland 30 years ago) and a cropland site in the middle of the Loess Plateau of China. Compared with the cropland, the SOC stock was significantly greater under the forest in both the top 20 cm and the subsoil (30–60 cm layer). The annual litter input under the forest was more than twice that of the cropland, and the fine root biomass was significantly higher in the forest. We conclude that the higher litter input and fine root biomass may partly contribute to the greater SOC in the forest. In addition, the soil nitrogen (N) content changed in synchronicity with SOC during afforestation, which indicates that SOC accumulation in the top/subsoil may be determined by the increase in soil N in these layers. In contrast, the SIC stock in the top 20 cm of the forest was significantly lower than that of the cropland. However, this decrease in the SIC level in the topsoil of the forest was offset by an increase in SIC in the subsoil (60–100 cm). The change in SIC along the soil profile following afforestation could be explained by the dissolution and leaching of SIC from the topsoil and subsequent precipitation in the subsoil. The dissolution and leaching of SIC in the forest topsoil were due to the high biological activity associated with the high aboveground litter input, fine root biomass and SOC stock as well as the high soil water content, whereas the precipitation of the leached SIC in the subsoil was a result of the dramatic decrease in the soil water content and fine root biomass in the subsoil. These findings suggest that soil can accumulate organic carbon in the topsoil and subsoil following black locust plantation establishment on cropland (as in the Loess Plateau study area) and that this type of cropland to forest plantation conversion in this area can redistribute SIC along the soil profile without affecting the net SIC accumulation.

Input of litter in deforested and forested areas of a tropical headstream

Riparian vegetation is the main source of leaves and the main energy source for low order streams. Therefore, changes in its composition affect the structure and processes in streams. We studied the contribution of the riparian vegetation by analysing the annual input of litter in deforested and forested areas of a tropical stream. The lateral, vertical (aerial) and horizontal (drift) litter inputs were analysed separately. The lateral input differed significantly between the two areas and included mostly fallen dry leaves. The vertical input, represented mainly by fallen dry leaves, occurred only in the forested area. The drift transport of litter was not significantly different between the deforested and forested areas and the input was composed mostly by CPOM. The removal of the native forest was clearly reflected in the low contribution of leaf litter in the deforested area.

The dynamic response of soil respiration to land‐use changes in subtropical China

AbstractAssessing the impact of land‐use changes on soil respiration (RS) is of vital significance to understand the interactions between belowground metabolism and regional carbon budgets. In this study, the monthly in situ RS was examined between 09:00 and 12:00 hours over a 3‐year period within a representative land‐use sequence in the subtropical region of China. The land‐use sequence contained natural forest (control treatment), secondary forest, two plantations, citrus orchard and sloping tillage land. Results showed that the RS exhibited a distinct seasonal pattern, and it was dominantly controlled by the soil temperature. After the land‐use conversion, the apparent temperature sensitivity of RS (Q10) was increased from 2.10 in natural forest to 2.71 in sloping tillage land except for an abnormal decrease to 1.66 in citrus orchard. Contrarily, the annual RS was reduced by 32% following the conversion of natural forest to secondary forest, 46–48% to plantations, 63% to citrus orchard and 50% to sloping tillage land, with the average reduction of 48%. Such reduction of annual RS could be explained by the decrease of topsoil organic carbon and light‐fraction organic carbon storages, live biomass of fine root (<2 mm) and annual litter input, which indirectly/directly correlated with plant productivity. Our results suggest that substrate availability (e.g., soil organic carbon and nutrients) and soil carbon input (e.g., fine root turnover and litterfall) through plant productivity may drive the RS both in natural and managed ecosystems following strong disturbance events.

No short-term change in soil properties following four-fold litter addition in a Costa Rican rain forest

We experimentally manipulated forest floor litter to investigate the influence of litter quality and quantity on soil properties over the short-term (weeks to months) in a wet tropical forest in NE Costa Rica. The study included old growth forest on high fertility soils, old growth forest on low fertility soils, and secondary forest on intermediate fertility soils. Forest floor litter was removed from a 16 m 2 area and added to an adjacent 4 m 2 area in March 2003, resulting in a one to four-fold increase in the annual litter input to the forest floor. We created three addition, three removal and three control plots per forest type. We measured treatment effects on variation in soil moisture, temperature, pH, and Bray-1 P (plant available) over a 5-month period that captured the dry-wet season transition. Litter manipulation had no effect on any of the soil properties measured during the 5-month study period. Significant variability through time and a similar temporal pattern across the three forest stands suggest that climatic variability is driving short-term patterns in these soil properties rather than seasonal inputs of litter. In general, soils were warmer, drier and more basic with higher available P during dry season months. Even in wet tropical forests, small variability in climate can play an important role in soil dynamics over periods of weeks to months. Although litter manipulation did not influence soil properties over the 5-month study period, a longer lag may exist between the timing of litter inputs and the influence of that litter on soil properties, especially plant available P.

Litter layer residence time in forest and coffee agroforestry systems in Sumberjaya, West Lampung

Forest conversion to coffee-based agroforestry leads to sudden disappearance of the litter layer and a decrease in the rate of litter fall, reducing food for ecosystem engineers such as earthworms. With time, however, a new litter layer is created potentially returning to forest-like conditions at the soil surface. This research quantified litter thickness, earthworm populations and soil macroporosity in response to land use change in the Sumberjaya benchmark area (West Lampung, Indonesia) by comparing: (a) remnant forest (control); (b) multistrata shaded coffee with fruit and timber trees, as well as nitrogen-fixing shade trees; (c) shaded coffee (nitrogen-fixing shade trees, but less than five tree species per plot); and (d) sun coffee (‘monoculture’) with coffee forming more than 80% of total stem basal area. Plots were selected with tree ages of 7–10 years in three slope classes: (a) flat (0–10°); (b) medium (10–30°); and (c) steep (>30°). The mean standing necromass was 6.1, 4.5, 3.8 and 3.0 Mg ha −1 for forest, multistrata, shade coffee and sun coffee, respectively, without significant influences of slope. Fine, partly decomposed litter was 33–40% of total necromass, coarse leaf litter 14–16%, and twigs and branches comprised the remaining 43–52%. Soil organic carbon content (C org) was highest in the forest. The largest annual litter input was found in the remnant forest (14 Mg ha −1 year −1), followed by multistrata, shaded and monoculture coffee systems, i.e., 9.8, 6.6 and 4.0 Mg ha −1 year −1, respectively. The population density of earthworms in the forest was 50% lower than in multistrata coffee gardens (150 individuals m −2), but its biomass (31 g m −2) was twice that in the multistrata coffee gardens. The lowest population density of earthworms was found in the shade coffee system (150 individuals m −2) with a biomass of 7 g m −2. A simple model suggests that the standing litter in the various land use systems is consistent with measured litter inputs and decay rates, but that the soil organic matter (SOM) content and macroporosity of the shade and multistrata systems are less than predicted. The recovery of a surface litter layer in sun coffee systems can provide protection from erosion with time, but will not be sufficient to restore macroporosity at the level of forest soils, leading to hydrologic alterations that favor overland flow.