Low-quality Litter Research Articles

Litter quality modulates changes in bacterial and fungal communities during the gut transit of earthworm species of different ecological groups.

Earthworms are keystone animals stimulating litter decomposition and nutrient cycling. However, earthworms comprise diverse species which live in different soil layers and consume different types of food. Microorganisms in the gut of earthworms are likely to contribute significantly to their ability to digest organic matter, but this may vary among earthworm species. Here, we analyse the effect of food (litter) quality on gut microbiota and their changes during the gut passage (from foregut to hindgut) of earthworms of different ecological groups. The endogeic (soil living) species Aporrectodea caliginosa and the anecic (litter feeding) species Lumbricus terrestris were fed with high- (rape leaves) and low-quality litter (wheat straw) in a microcosm experiment for 18weeks. Irrespective of earthworm species, alpha diversity of bacterial and fungal communities changed little during the gut passage, with the composition and diversity of microbial communities in the gut generally resembling those in soil more than in litter. In addition, the low-quality litter supported higher alpha diversity and more complex communities than high-quality litter. Further, gut microbial communities of the anecic L. terrestris changed less during gut passage than those of the endogeic A. caliginosa, especially when fed low-quality litter. Our findings indicate that earthworm gut microbial communities are predominantly shaped by the soil they ingest, but are modulated by the quality of litter they feed on and earthworm ecological group. Overall, the results suggest that earthworms primarily influence soil microbiota by mixing and spreading microorganisms from different microhabitats through bioturbation rather than by digesting microorganisms.

Microbial and mineral interactions decouple litter quality from soil organic matter formation

Current understanding of soil carbon dynamics suggests that plant litter quality and soil mineralogy control the formation of mineral-associated soil organic carbon (SOC). Due to more efficient microbial anabolism, high-quality litter may produce more microbial residues for stabilisation on mineral surfaces. To test these fundamental concepts, we manipulate soil mineralogy using pristine minerals, characterise microbial communities and use stable isotopes to measure decomposition of low- and high-quality litter and mineral stabilisation of litter-C. We find that high-quality litter leads to less (not more) efficient formation of mineral-associated SOC due to soil microbial community shifts which lower carbon use efficiency. Low-quality litter enhances loss of pre-existing SOC resulting in no effect of litter quality on total mineral-associated SOC. However, mineral-associated SOC formation is primarily controlled by soil mineralogy. These findings refute the hypothesis that high-quality plant litters form mineral-associated SOC most efficiently and advance our understanding of how mineralogy and litter-microbial interactions regulate SOC formation.

High-quality litter exerts a greater effect on soil carbon gain in unrestored than restored pine plantations

Vegetation restoration of degraded land affects litter quality by changing the composition of tree species, providing direct effects on regulating the dynamic of soil organic C (SOC) through the priming effect (PE). However, it is unclear how the combined effects caused by vegetation restoration and input of different quality litters on PE-related C loss and gain. Here, we collected soils from an unrestored site and a site restored for 20 years, adding 13C-labeled low-quality (with high C/nitrogen [N] and lignin/N) and high-quality (with low C/N and lignin/N) litters to the soil, respectively. Our results revealed that adding high- and low-quality litter in two sites produced positive PEs after 150-day laboratory-based incubation. The PE induced by high-quality litter was lower than that of low-quality in two sites, which can be interpreted as low-quality litter has higher C/N that aggravates the nutrient imbalance of microorganisms and enhances their demand for N, prompting microorganisms to accelerate the mineralization of SOC through the “N mining”. High-quality litter inputs can boost microbial C use efficiency and alleviate soil C loss due to PE in unrestored and restored pine forests. Moreover, high-quality litter input has a greater positive effect on SOC gain in unrestored lands than in restored lands, suggesting that litter with higher nutrient availability or fertilization is especially needed for the restoration of degraded soil fertility and C formation. Taken together, this study highlights the importance of tree species producing high-quality litter in mediating SOC decomposition and formation during degraded lands restoration, which is beneficial for the restoration of degraded lands and the enhancement of soil C sequestration.

Enlarging interface reverses the dominance of fungi over bacteria in litter decomposition

Soil microorganisms are primary decomposers driving carbon and nutrient cycling in terrestrial ecosystems. One prevailing view is that fungi, rather than bacteria, play a predominant role in litter decomposition. However, the roles of bacteria and factors that restrict their activity during decomposition remain unclear. We hypothesized that the limiting activity of bacterial decomposers is associated with litter size beyond chemical quality. To address this gap, we conducted a 180-d decomposition microcosm experiment to investigate the effect of fragment size (large, 1–2 mm; middle, 0.18–0.28 mm; small, <0.07 mm) of oak and pine litters on bacterial or fungal decomposition. Bacterial and fungal decomposition were accelerated with fragment size decrease, suggesting that an interface effect existed between microbial decomposers and litter. Generally, the decomposition ability of bacteria was more sensitive to changes in fragment size compared to fungi. Fungi resulted in faster decomposition of large fragments than bacteria. For small oak litter fragments, bacteria showed faster decomposition than fungi, whereas the opposite was true for small pine litter. Therefore, the decomposition dominance of bacteria and fungi was regulated by fragment size and influenced by the chemical quality of litter, especially the lignin:N ratio. The contrasting decomposition dominances of bacteria versus fungi were likely attributed to filamentous fungi penetrating litter interiors and forming mycelial bridges between scattered litters. Bacteria resided on litter surfaces and even formed biofilms. Consistent with the findings of the microcosm experiment, the proportion of small fragments was greater in the fresh litter layer than in the decomposed layer in the field, and greater in the pine forest than in the oak forest, suggesting the fresh, large, and low-quality litter was preferentially fragmented by fungi. Consequently, the dominance of fungi and bacteria during litter decomposition in the conventional view should be revisited considering the litter size.

Input of high-quality litter reduces soil carbon losses due to priming in a subtropical pine forest

To date, it is unclear how differences in litter quality affect soil organic matter (SOM) decomposition through a phenomenon called 'priming effects' (PEs), especially for low-fertility forest soils under field conditions. Here, the effects of low- and high-quality leaf litter on PE and microbial metabolism of litter-derived carbon (C) were explored in a low-fertility pine (Pinus massoniana) plantation. A 185-day in situ incubation experiment was carried out by adding two 13C-labeled leaf litters to the pine soil—a low-quality (high lignin: nitrogen ratio) litter sourced from pine and a broadleaved species Schima superba produced high-quality (low lignin: nitrogen ratio) litter. To determine the key microbial groups contributing to PEs, the abundance of 13C-labeled litter enrichment in soil phospholipid fatty acids (13C-PLFAs) was quantified. We found that high-quality litter decomposed more rapidly than low-quality litter, with both litter-derived CO2 efflux reaching a plateaued level during the experimental period. Low-quality litter induced net positive PEs, while high-quality litter induced net negative PEs during the litter decomposition processes. The 13C-PLFAs results showed that bacterial groups governed the negative PEs induced by high-quality litter, whereas fungal communities targeted the positive PEs induced by low-quality litter. Random forest model and variation partitioning analysis demonstrated that the direction and magnitude of PEs were driven by litter-induced changes in key microbial groups rather than the structure of the microbial community. Our results demonstrate that microorganisms preferentially utilized litter-derived C in high-quality litter treatment and SOM in low-quality litter treatment, respectively. In contrast to low-quality litter, adding high-quality litter promoted the microbial metabolism of litter-derived C, reducing SOM decomposition (strong negative PEs). Taken together, this study provides isotope-based suggestions for the improvement of degraded pine forests—introducing tree species that produce high-quality litter may benefit soil C sequestration by reducing soil C losses due to PE in nutrient-poor pine forests.

Effects of microbial groups on soil organic carbon accrual and mineralization during high- and low-quality litter decomposition

Litter input regulates the mineralization and accrual of soil organic carbon (SOC), depending on microbial groups and litter quality. Stable isotope probing was used after the addition of 13C-labeled litter of different recalcitrance, including Populus davidiana (characterized by low quality, high C:N, and lignin content) and Quercus wutaishanica (characterized by high quality, low C:N, and lignin content). The flow of litter C to microbial biomass and necromass was followed by quantification of 13C incorporation into phospholipid fatty acids (13C-PLFAs) and amino sugars (13C-AS), and their respiration. The CO2 efflux and positive priming effects (PE) were higher, but the 13C-necromass was lower (8.5% vs. 10%) in the soil with P. davidiana than with Q. wutaishanica. The 13C-necromass continuously increased with P. davidiana litter decomposition, but reached a peak at day 14 after Q. wutaishanica litter addition. These results indicated that the decomposition of resistance compounds mainly resulted in necromass formation after low-quality litter addition. The P. davidiana-derived 13C in fungal PLFAs increased with decomposition, suggesting the importance of these microorganisms in decomposing resistance compounds in low-quality litter despite the bacterial-dominated decomposition process of both litters. Bacteria frequently exhibit versatility in utilizing C from different sources, whereas a larger proportion of fungi display specialization. SOC mineralization increased with the remaining litter but decreased with 13C-G- bacterial PLFAs and 13C-actinobacterial PLFAs after both types of litter addition because starving microbes need to invest more soil C in maintenance respiration vs. biomass formation. 13C-necromass increased with 13C-PLFA because microbial biomass is the primary precursor of necromass. Altogether, low-quality compounds are more readily respired, whereas C from high-quality biopolymers is relatively more assimilated into the necromass. This study further explains the effect of soil microbial groups on SOC under different qualities of litter decomposition and deepens our understanding of the mechanism of SOC sequestration.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including β-1,4-glucosidase, β-D-cellobiosidase, β-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Macrofauna amplify plant litter decomposition and stabilization in arctic soils in a warming climate

The soil organic carbon (SOC) pool of the Arctic region is currently protected by low temperatures, but is likely to decrease due to greater organic matter (OM) decomposition under a warmer climate. Negative feedback for climate warming can, however, be reversed by SOC accrual as climate warming leads to shifts in arctic vegetation (from grass to shrub) and soil faunal (introduction of macrofauna) communities affecting plant-soil C allocation. To decipher these contrasting effects, we performed a laboratory experiment with soils from dry tundra to test the interacting effects of plant litter quality (high-quality grass litter vs. the intermediate- and low-quality litter of shrubs) and soil fauna functional grouping (micro-, meso- and macrofauna [millipede]) on the processes of litter decomposition and OM stabilization.Our findings showed that macrofauna largely promoted decomposition of shrub litter, while soil micro- and mesofauna were mainly responsible for the decomposition of grass litter. Our study thus confirmed that, when introduced and established in a warmer Arctic, macrofauna may become an important agent in shrub litter decomposition. Our data also showed that with shrub litter, higher C content was stabilized as particulate OM (POM) in aggregates, whereas in grass litter and low-quality shrub litter, higher C content was stabilized as mineral-associated OM (MAOM). Both these effects were larger in the presence of macrofauna and with a higher abundance of fungi. This suggests that consequent shrub OM stabilization in occluded POM and MAOM fractions will be carried out jointly by macrofauna and fungi, which will probably lead to more efficient OM stabilization in Arctic soils than in the case of grass litter OM stabilization by micro- and mesofauna and bacteria. In conclusion, our study suggests that vegetation changes and the introduction of macrofauna in a warming climate will most probably lead to higher OM stabilization in Arctic soils.

Species and Structural Diversity of Coniferous-Broadleaved Mixed Forests of the Pshekha River, North-Western Caucasus

The article presents the species and structural diversity of coniferous-broadleaved forests of the Pshekha river – the largest tributary of the Kuban river. All in all, 7 main types of forest were identified and described: fir-beech fern-forb forest, fir-hornbeam blackberry-forb forest, aspen-hornbeam honeysuckle-small-herb forest, hornbeam-black alder nitrophilic-tall-herb forest, hornbeam-oak rhododendron-blackberry forest, hornbeam-beech blackberry-forb forest and hornbeam honeysuckle-blackberry forest. The composition of the forest flora of the Pshekha river includes 270 species, including 221 species of vascular plants and 49 species of mosses. Floristic diversity of coniferous-broadleaved forests of the Pshekha river is inversely related to the crown density of the stand and the proportion of oriental beech (Fagus orientalis). The highest species saturation was noted in the hornbeam-black alder nitrophilic-high-grass forest type, the lowest – in the fir-beech fern-forb type. Ecological and coenotic structure of coniferous-broadleaved forest types of the Pshekha river depends on the height above sea level, which determines the indicators of the average annual precipitation and average annual temperature – with a decrease in altitude above sea level. m. the proportion of boreal species in the composition of the flora decreases, while the proportion of nemoral and meadow-edge species increases. In the coniferous-broadleaved forests of the river. Pshekha, 11 species of earthworms were identified, belonging to four morpho-ecological groups: epigeic, epi-endogeic and endogeic, as well as anecic. In forests with a high quality of litter (hornbeam-dominated), the greatest contribution to the biomass is made by epigeic (up to 41%) and endogeic (up to 45%) groups of earthworms. In forests with low quality litter (fir- and beech-dominated), the share of endogeic earthworms is high (up to 66%). Anecic worms are mostly confined to forests on moist soils. In all types of forests, Crimean-Caucasian endemics make a large contribution to biomass and abundance: polymorphic species D. schmidti, anecic D. mariupolienis, as well as Mediterranean species: litter D. attemsi (often inhabiting oak and hornbeam deadwood) and proper soil A. jassyensis. Cosmopolitan species (D. r. tenuis, D. octaedra) are numerous among the epigeic worms and often inhabit deadwood of coniferous tree species.

Contrasting Effects of Leaf Litter Quality and Diversity on Oviposition of Mosquitoes.

The quality and diversity of leaf litter are important variables in determining the availability of energy in detritus-based food webs. These factors can be represented by the stoichiometric proportion between carbon and multiple nutrients, and the mixture of litter from different taxonomic and/or functional origins. In aquatic ecosystems, factors that accelerate litter decomposition can influence the secondary productivity of planktonic microbiota, which act as a link between litter and higher trophic levels. This study aimed to analyze the influence of litter quality and diversity on the oviposition behavior of medically important mosquitoes. We hypothesized that both factors would have a positive effect on the attraction of female mosquitoes and would stimulate a greater amount of oviposition. To test this hypothesis, microcosms containing isolated leaf litter leachates from four plant species were used to manipulate gradients of litter quality, and microcosms with all leachates combined were used to test the effects of litter diversity. The results showed a positive effect of litter quality (p < 0.05) on mosquito oviposition rate, with lower C:P ratio litter species (high-quality litter) presenting higher oviposition rates than litter species with high C:P ratios (low-quality litter). However, contrary to our expectations, litter diversity had a negative effect (p = 0.002) on the magnitude of egg-laying by mosquitoes. Our results highlight the importance of litter quality and diversity for insect reproductive behavior. Our data shows that litter quality can serve as a crucial indicator of a suitable environment utilized by female mosquitoes for oviposition. This finding can enhance our ability to understand and develop effective methods for mitigating the reproduction of medically significant mosquitoes, whether by allowing us to predict, based on the composition of vegetation species, areas more prone to mosquito infestation, or by using high-quality litter in oviposition traps. Furthermore, maintaining vegetation diversity can help control mosquito reproduction.

Biochar effects on early decomposition of standard litter in a European beech forest (northern Italy)

The release of biochar (BC) on forest soil is a strategy aimed at increasing carbon reserves and forest productivity. The effect of BC amendments on the decomposition of different quality litter is, however, poorly understood. With this study we investigate the effects of wood-derived BC applications on early decomposition in a European beech (Fagus sylvatica L.) forest through the burial of standard material, i.e. green tea and rooibos tea (high- and low-quality litter surrogates, respectively). Two main questions were addressed: 1) Do BC applications influence the decomposition of high- and low-quality standard litter and, if so, in what way? and 2) Does this effect (if measurable) depend on where the sample is placed with respect to the BC application layer? To test BC amendment effects, four application percentages were employed (0, 10, 20 and 100 %), after which standard litter mass loss was recorded. To investigate the effects of sample position, only three BC application percentages were used (0, 10 and 20 %), with teabags buried at three different depths – within the BC amended layer, between this layer and the unamended soil, and below the latter. Results show that early decomposition of high-quality standard litter was not influenced by BC applications, while a significant reduction in mass loss of low-quality standard litter was observed when the percentage of BC application was higher, specifically of litter within the 20 % and 100 % BC amended layers. Decomposition was also affected by sample position relative to the BC layer, exhibiting higher levels of mass loss when samples were placed within the BC amended layer. Overall, BC applications on beech forest soils not only seem to produce negligible effects on the early decomposition rate of high-quality standard litter, but such applications also seem to have the ability to reduce carbon loss following plant material degradation.

Effects of litter quality on foraging behaviour and demographic parameters in Folsomia candida (Collembola).

Litter quality has long been associated with demographic parameters of Collembola populations. However, little is known about the capacity of Collembola to perceive and seek better litter quality. To address this gap, three complementary laboratory experiments were carried out with the Collembola Folsomia candida. First, populations were fed on three different types of leaf litters (Quercus pubescens, Acer opalus and Prunus avium) and a control (agar-agar-brewer's yeast mixture) for 6 weeks to assess their impacts on demography (reproduction rate and population size). Second, the body length of individuals differentially fed with the same four types of resources was measured to assess a functional trait that can potentially affect movement parameters such as prospected area or foraging speed. Third, F. candida single individuals were exposed to the same litter quality gradient and placed at an increasing distance from the litter (from 1 to 5 cm). For 10 min, their foraging behaviour was recorded which included prospected area, foraging speed, perception distance and success in reaching the litter (foraging success). As expected, low-quality litter (i.e. Q. pubescens) contributed to low population growth compared to the control treatment and the high-quality litters (P. avium and A. opalus). In the third experiment, the probability of finding the resource was negatively correlated to the distance, but was unrelated to the litter quality and the Collembola body length. When resource was perceived, F. candida was able to switch from non-directional to directional movements, with a large variability in the perception distance from a few millimetres to several centimetres. Taken together, our results indicate that litter quality plays a relevant role in Collembola demographic parameters once the population settles on litter patch, but not on foraging behaviour to select high-quality resources.

Fine root litter quality regulates soil carbon storage efficiency in subtropical forest soils

Decomposing root litter is a major contributor to soil carbon (C) storage in forest soils. During decomposition, the quality of root litter could play a critical role in soil C storage. However, it is unclear whether root litter quality influences soil C storage efficiency. We conducted a two-year greenhouse decomposition experiment using 13C-labeled fine root litter of two tree species to investigate how root litter quality, represented by C to nitrogen (C/N) ratios, regulates decomposition and C storage efficiency in subtropical forest soils in China. ‘High-quality’ root litter (C/N ratio = 26) decayed faster during the first year (0–410 days), whereas ‘low-quality’ root litter (C/N ratio = 46) decomposed faster toward the end of the two-year period (598–767 days). However, over the two years of the study, mass loss from high-quality root litter (29.14 ± 1.42%) was lower than ‘low-quality’ root litter (33.01 ± 0.54%). Nonetheless, root litter C storage efficiency (i.e., the ratio of new root litter-derived soil C to total mineralized root litter C) was significantly greater for high-quality root litter, with twice as much litter-derived C stored in soils compared to low-quality root litter at the end of the experiment. Root litter quality likely influenced soil C storage via changes in microbial diversity, as the decomposition of high-quality litter declined with increasing bacterial diversity, whereas the amount of litter-derived soil C from low-quality litter increased with fungal diversity. Our results thus reveal that root litter quality mediates decomposition and C storage in subtropical forest soils in China and future work should consider the links between root litter quality and soil microbial diversity.

Home-field advantage effects in litter decomposition is largely linked to litter quality

Climate change and associated environmental alterations affect plant communities, potentially decoupling links between plants and their associated soil microbial communities. This may in turn affect processes like litter decomposition, an important function that controls nutrient and carbon cycling as well as many other ecosystem processes. Microbial decomposers have been proposed to specialize, being able to easier decompose litter from its ‘home’ community than litter from other communities, in what is termed the home field advantage (HFA) hypothesis. We report a litter decomposition experiment including four alpine meadow communities spread along a geographical gradient that ranged from the Atlas in Morocco to the Iberian Peninsula to the Swiss Alps. We tested whether litter decomposition rate would differ depending on litter and soil origin, expecting interactions between litter and soil microbial communities to be at the core of responses. We expected to find HFA in all four alpine communities. HFA ranged from very negative to neutral to positive along our geographical gradient, in a variation that could be attributed to the interaction of microbial communities with soil and plant traits, and linked to the relative abundance of microbial groups performing specific functions. Litter decomposition depended on litter quality and on the fungal community, which seemed adapted to deal with poor-quality, recalcitrant litter, leading to HFA. Climate plays a role as well, indirectly through plant community composition. Phyllosphere communities competed with soil communities when in interaction, a fact that may have blurred results of some previous HFA experiments. In summary, there is a clear HFA in systems with low-quality litter that requires a specialised fungal community to maximize decomposition. By contrast, high-quality, easy to decompose litter would be dealt with by any decomposer community, not showing evidence of HFA.

Variations in litter-soil properties between planted and naturally restored forests drive microbial community structure and function

How forest restoration can affect soil microbial composition and functionality remains unclear, limiting our ability to evaluate restoration approaches. Here, we used metagenomes, 16S rRNA, and ITS gene sequencing to distinguish the composition and functional attributes of soil microbial communities between plantation forest of Pinus massoniana (PF) and naturally restored secondary forest (SF) in their organic horizon and mineral soil from a typical karst region in Southwest China. Our results showed that fungal communities differed more than bacterial communities between PF and SF, while the differences in archaeal communities were not significant. The most abundant fungal phylum in both mineral soil and organic horizon was Ascomycota at SF and Basidiomycota at PF, respectively. The PF soil had lower nitrogen (N) cycling gene abundance and lower inorganic N availability compared to SF soil probably because of the poor soil and lower litter quality. The SF soil had higher abundances of genes associated with labile carbon (C) (i.e., starch, hemicellulose, cellulose, pectin, and chitin) degradation compared with PF soil, but lower abundances of genes responsible for recalcitrant C (i.e., lignin and aromatics) degradation, which was strongly correlated with the litter properties. Simultaneous effects of soil and litter variables explained >50 % of the variation in microbial community structure and functional gene composition; soil nitrate-N had the strongest effect on the soil bacterial and fungal community structure. Our results highlight the superiority of naturally restored secondary forests for improving both soil fertility and soil microbial-mediated C and N cycling functions, which can support forest managers in selecting forest restoration approaches that optimize C and N storage in forest stands.

Nitrogen addition mediates monospecific and mixed litter decomposition in a boreal peatland

Litter decomposition is a key determinant of soil organic matter accumulation in boreal peatlands. Climate warming and atmospheric nitrogen (N) deposition have recently increased N availability in boreal peatlands. However, how increased N availability alters decomposition dynamics of plant litter is uncertain in these ecosystems, especially for litter mixtures. Here, we collected fresh litter of four common species (Betula fruticosa, Ledum palustre, Eriophorum vaginatum, and Sphagnum palustre) in a poor fen of northeast China, and established an N addition (6 g N m−2 year−1) experiment to assess the effect of increased N availability on monospecific and mixed litter decomposition in the hummocks and hollows after one and three years of decomposition. In both hummocks and hollows, N addition increased mass loss of four monospecific litter after one year of decomposition but only accelerated litter decomposition of E. vaginatum and S. palustre with low litter quality after three years of decomposition. Moreover, N addition effects on monospecific litter decomposition were negatively related to monospecific litter decomposition in the absence of N addition. Irrespective of decomposition position, additive effects were more frequent than synergistic effects during decomposition of litter mixtures. In addition, N addition generally changed synergistic effects to additive effects after one and three years of decomposition, and such changing trends were stronger in hummocks than in hollows. These observations suggest that litter quality mediates N addition effects on monospecific litter decomposition, and highlight that increased N availability will alter mixed litter decomposition by reducing synergistic effects in boreal peatlands.

Multidimensional stoichiometric mismatch explains differences in detritivore biomass across three forest types.

The ecological stoichiometry theory provides a framework to understand organism fitness and population dynamics based on stoichiometric mismatch between organisms and their resources. Recent studies have revealed that different soil animals occupy distinct multidimensional stoichiometric niches (MSNs), which likely determine their specific stoichiometric mismatches and population responses facing resource changes. The goals of the present study are to examine how long-term forest plantations affect multidimensional elemental contents of litter and detritivores and the population size of detritivores that occupy distinct MSNs. We evaluated the contents of 10 elements of two detritivore taxa (lumbricid earthworms and julid millipedes) and their litter resources, quantified their MSNs and the multidimensional stoichiometric mismatches, and examined how such mismatch patterns influence the density and total biomass of detritivores across three forest types spanning from natural forests (oak forest) to plantations (pine and larch forests). Sixty-year pine plantations changed the multidimensional elemental contents of litter, but did not influence the elemental contents of the two detritivore taxa. Earthworms and millipedes exhibited distinct patterns of MSNs and stoichiometric mismatches, but they both experienced severer stoichiometric mismatches in pine plantations than in oak forests and larch plantations. Such stoichiometric mismatches led to lower density and biomass of both earthworms and millipedes in pine plantations. In other words, under conditions of low litter quality and severe stoichiometric mismatches in pine plantations, detritivores maintained their body elemental contents but decreased their population biomass. Our study illustrates the success in using the multidimensional stoichiometric framework to understand the impact of forest plantations on animal population dynamics, which may serve as a useful tool in addressing ecosystem responses to global environmental changes.

Cross-species coprophagy in small stream detritivores counteracts low-quality litter: native versus invasive plant litter

Cross-species coprophagy in small stream detritivores counteracts low-quality litter: native versus invasive plant litter

Differences in leaf and root litter decomposition in tropical montane rainforests are mediated by soil microorganisms not by decomposer microarthropods.

Plant litter decomposition is a key process in carbon and nutrient cycling. Among the factors determining litter decomposition rates, the role of soil biota in the decomposition of different plant litter types and its modification by variations in climatic conditions is not well understood. In this study, we used litterbags with different mesh sizes (45 µm, 1 mm and 4 mm) to investigate the effect of microorganisms and decomposer microarthropods on leaf and root litter decomposition along an altitudinal gradient of tropical montane rainforests in Ecuador. We examined decomposition rates, litter C and N concentrations, microbial biomass and activity, as well as decomposer microarthropod abundance over one year of exposure at three different altitudes (1,000, 2,000 and 3,000 m). Leaf litter mass loss did not differ between the 1,000 and 2,000 m sites, while root litter mass loss decreased with increasing altitude. Changes in microbial biomass and activity paralleled the changes in litter decomposition rates. Access of microarthropods to litterbags only increased root litter mass loss significantly at 3,000 m. The results suggest that the impacts of climatic conditions differentially affect the decomposition of leaf and root litter, and these modifications are modulated by the quality of the local litter material. The findings also highlight litter quality as the dominant force structuring detritivore communities. Overall, the results support the view that microorganisms mostly drive decomposition processes in tropical montane rainforests with soil microarthropods playing a more important role in decomposing low-quality litter material.

Effects of establishing cultivated grassland on soil organic carbon fractions in a degraded alpine meadow on the Tibetan Plateau.

BackgroundThe degradation of alpine meadows has induced substantial losses of soil organic carbon (SOC) on the Tibetan Plateau. A commonly-used method for rehabilitating degraded alpine meadows in this region is establishing cultivated grasslands through sowing seed mixtures, but its impact on the biochemical stability of SOC has remained inadequately explored.MethodsIn this study, a total of 20 composited 0-20 cm soil samples were collected from a heavily degraded alpine meadow (DM) and three adjacent cultivated grasslands established for 3 years (CG3), 12 years (CG12), and 17 years (CG17) on the eastern Tibetan Plateau, and the SOC pool was separated into labile C pool I (LOC I), labile C pool II (LOC II), and recalcitrant C pool (ROC) in order to investigate changes in contents of SOC fractions that have different biochemical stabilities after the establishment of cultivated grassland.ResultsAlthough the establishment of cultivated grasslands led to increases in soil total organic C content, the increase was only significant in samples with 17 years of cultivation. We found that the contents of the three SOC fractions were higher at CG3 and CG12 compared with those in the DM, and the differences were only significant for soil LOC II. By comparison, 17 years of cultivation led to significant increases in all of the SOC fraction contents. The results implied that different cultivation years had distinct impacts on SOC fractions in cultivated grasslands, and longer cultivation years contributed to accumulated soil ROC. The recalcitrance index of SOC in the DM was higher than that at CG3 and CG12, but lower than that at CG17. This was possibly due to the generally low litter quality of cultivated grasslands, which led to a slow release of complex compounds to soils. Moreover, it was observed that soil C:N ratio was a potential indicator of SOC biochemical stability because of their close correlation.ConclusionsOur findings suggest that the long-term establishment of cultivated grasslands on DM is a promising solution to recovering both the quantity and stability of SOC on the Tibetan Plateau.