Low-quality Litter Research Articles

Global pattern of soil priming effect intensity and its environmental drivers.

The microbial priming effect-the decomposition of soil organic carbon (SOC) induced by plant inputs-has long been considered an important driver of SOC dynamics, yet we have limited understanding about the direction, intensity, and drivers of priming across ecosystem types and biomes. This gap hinders our ability to predict how shifts in litter inputs under global change can affect climate feedbacks. Here, we synthesized 18,919 observations of CO2 effluxes in 802 soils across the globe to test the relative effects (i.e., log response ratio [RR]) of litter additions on native SOC decomposition and identified the dominant environmental drivers in natural ecosystems and agricultural lands. Globally, litter additions enhanced native SOC decomposition (RR = 0.35, 95% CI: 0.32-0.38), with greater priming effects occurring with decreasing latitude and more in agricultural soils (RR = 0.43) than in uncultivated soils (RR = 0.28). In natural ecosystems, soil pH and microbial community composition (e.g., bacteria: fungi ratio) were the best predictors of priming, with greater effects occurring in acidic, bacteria-dominated sandy soils. In contrast, the substrate properties of plant litter and soils were the most important drivers of priming in agricultural systems since soils with high C:N ratios and those receiving large inputs of low-quality litter had the highest priming effects. Collectively, our results suggest that, though different factors may control priming effects, the ubiquitous nature of priming means that alterations of litter quality and quantity owing to global changes will likely have consequences for global C cycling and climate forcing.

Cover crop functional types differentially alter the content and composition of soil organic carbon in particulate and mineral-associated fractions.

Cover crops (CCs) can increase soil organic carbon (SOC) sequestration by providing additional OC residues, recruiting beneficial soil microbiota, and improving soil aggregation and structure. The various CC species that belong to distinct plant functional types (PFTs) may differentially impact SOC formation and stabilization. Biogeochemical theory suggests that selection of PFTs with distinct litter quality (C:N ratio) should influence the pathways and magnitude of SOC sequestration. Yet, we lack knowledge on the effect of CCs from different PFTs on the quantity and composition of physiochemical pools of SOC. We sampled soils under monocultures of three CC PFTs (legume [crimson clover]; grass [triticale]; and brassica [canola]) and a mixture of these three species, from a long‐term CC experiment in Pennsylvania, USA. We measured C content in bulk soil and C content and composition in contrasting physical fractions: particulate organic matter, POM; and mineral‐associated organic matter, MAOM. The bulk SOC content was higher in all CC treatments compared to the fallow. Compared to the legume, monocultures of grass and brassica with lower litter quality (wider C:N) had higher proportion of plant‐derived C in POM, indicating selective preservation of complex structural plant compounds. In contrast, soils under legumes had greater accumulation of microbial‐derived C in MAOM. Our results for the first time, revealed that the mixture contributed to a higher concentration of plant‐derived compounds in POM relative to the legume, and a greater accumulation of microbial‐derived C in MAOM compared to monocultures of grass and brassica. Mixtures with all three PFTs can thus increase the short‐ and long‐term SOC persistence balancing the contrasting effects on the chemistries in POM and MAOM imposed by monoculture CC PFTs. Thus, despite different cumulative C inputs in CC treatments from different PFTs, the total SOC stocks did not vary between CC PFTs, rather PFTs impacted whether C accumulated in POM or MAOM fractions. This highlights that CCs of different PFTs may shift the dominant SOC formation pathways (POM vs. MAOM), subsequently impacting short‐ and long‐term SOC stabilization and stocks. Our work provides a strong applied field test of biogeochemical theory linking litter quality to pathways of C accrual in soil.

Severe drought rather than cropping system determines litter decomposition in arable systems

Litter decomposition is a fundamental process in soil carbon dynamics and nutrient turnover. However, litter decomposition in arable systems remains poorly explored, and it is unclear whether different management practices, such as organic farming, conservation agriculture can mitigate drought effects on litter decomposition.Thus, we examined the effects of a severe experimental drought on litter decomposition in four cropping systems, i.e., organic vs. conventional farming, each with two levels of tillage (intensive vs. conservation tillage) in Switzerland. We incubated two types of standard litter (tea bags), i.e., high-quality green tea with a low C:N ratio and low-quality rooibos tea with a high C:N ratio. We assessed litter decomposition during the simulated drought and in the post-drought period during three years in three different crops, i.e., pea-barley, maize, and winter wheat. Subsequently, we assessed whether decomposition in the four cropping systems differed in its resistance and resilience to drought.Drought had a major impact on litter decomposition and suppressed decomposition to a similar extent in all cropping systems. Both drought resistance and resilience of decomposition were largely independent of cropping systems. Drought more strongly reduced decomposition of the high-quality litter compared to the low-quality litter during drought conditions regarding the absolute change in mass remaining (12.3% vs. 6.5 %, respectively). However, the decomposition of high-quality litter showed a higher resilience, i.e., high-quality approached undisturbed decomposition levels faster than low-quality litter after drought. Soil nitrate availability was also strongly reduced by drought (by 32–86 %), indicating the strong reduction in nutrient availability and, most likely, microbial activity due to water shortage. In summary, our study suggests that severe drought has a much stronger impact on decomposition than cropping system indicating that it might not be possible to maintain decomposition under drought by the cropping system approaches we studied. Nevertheless, management options that improve litter quality, such as the use of legume crops with high N concentrations, may help to enhance the resilience of litter decomposition in drought-stressed crop fields.

Balancing litterfall and decomposition in cacao agroforestry systems

Backgrounds and aimsLitter protects the underlying soil, depending on litterfall and decomposition, but dynamics of the standing litter stock in agroforestry systems remain poorly understood. We aimed to unravel effects of litter quality, temporal patterns, microclimate, and a possible home-field advantage (HFA) on standing litter dynamics across a land-use gradient.MethodsWe quantified litterfall, the standing litter stock, and microclimate during a year in (remnant) forest, cacao-based simple and complex agroforestry, cacao monocultures, and annual crops in a cacao producing area in Indonesia. We conducted a reciprocal litter transfer experiment, and tested decomposition rates of pruning residues. Standing litter stocks during the year were estimated from monthly litterfall and decomposition rates.ResultsVariation in litter quality influenced decomposition rates more strongly than variation in microclimate or HFA. Lower litter quality in complex agroforestry and in the cacao monoculture decreased the decay rate compared to simple agroforestry systems; mean litter residence time was over a year. Mixing high- and low-quality material in pruning residues modified the decomposition rate, soil C and N changes, offering options for targeted management of soil protection and nutrient release.ConclusionsThe seasonal patterns of litterfall and relatively slow decomposition rates supported permanence of the litter layer in all cacao production systems, protecting the underlying soil.

Impact of litter quality on the stability and storage of soil carbon in flooded wetlands

Context High inputs of plant litters and slow decomposition of soil organic carbon (SOC) influence the biogeochemical cycling of soil carbon in flooded wetlands. Aims To investigate the effects of different quality litter inputs on SOC stability and storage in flooded wetlands. Methods A 180-day microcosmic experiment to investigated the decomposition of litters of two dominant plants (Carex cinerascens Kukenth., CC; Cyperaceae family) and Triarrhena lutarioriparia L. Liu, TL; Poaceae family), in Poyang Lake Wetlands. Key results CC litters (high-quality, low lignin/N mass ratio) reduced gross content of SOC, but increased labile carbon and labile index (LI) of soils. In contrast, inputs of TL litters (low-quality, high lignin/N mass ratio) increased SOC gross content and recalcitrant carbon fractions of soils, but reduced soil labile carbons and LI. Significant effects of litters on SOC were not observed until ∼30 days indicating that the effects of litter inputs on soil carbon pools in flooded wetlands need time to be activated. CC and TL litters both increased the soil microbial biomass carbon (MBC) content. Soil MBC in CC treatments was significantly affected by the litter ash-free dry mass, while that in TL treatments was significantly affected by mass loss. Conclusions Litter quality may regulate the growth of soil MBC via different microbial growth strategies. Implications Our results suggest that inputs of high-quality litters can yield a high amount of labile carbon through stimulated microbial decomposition, leading to an overall loss of carbon. In contrast, inputs of low-quality litters can promote the microbial production of more recalcitrant carbons and increase soil carbon stability and carbon sequestration.

Soil fauna communities and microbial activities response to litter and soil properties under degraded and restored forests of Hyrcania

Reforestation has long been the best practice to restore degraded forests due to human interventions. In this paper we investigated the effect of forest degradation (DNF) along with reforestation using 4 endemic species (Alnus subcordata, ASP; Acer velutinum, AVP; Cupressus sempervirens, CSP; Quercus castaneifolia Mey, QCP) on forest’s soil chemical and biological indicators compared to a close-to-virgin natural forest (VNF). For this study, a total of 24 physico-chemical and 25 biological and microbial indicators were measured in soils of all 6 forest stands along with the litter properties. Results showed that the lowest soil quality was observed under DNF, CSP, and QCP which was the result of forest cover degradation in DNF and low litter quality, especially low pH and high C:N, in CSP and QCP. Soil fauna communities were significantly affected by tree species. We found two times higher density of earthworms in VNF compared to ASP, but in DNF the density was 5 times lower than VNF. We found no epigeic earthworms in QCP, CSP and DNF and no endogeic earthworms in DNF. Acarina and Collembola density was high in VNF and ASP, but they showed significant differences (VNF>ASP), and their density sharply decreased in other stands, especially in CSP (3 times lower than VNF) and DNF (8 to 10 times lower than VNF). Nematode density was statistically equal in VNF, ASP, and AVP, but significantly lower in other stands. Protozoa, bacteria and fungi densities were significantly higher in VNF and ASP (VNF>ASP) compared to each other and other forest stands. Basal respiration, substrate induced respiration, microbial biomass N and P, and carbon availability index was also higher in VNF and ASP compared to other stands. Although VNF has the best condition because of old forest cover and high diversity, ASP soil showed significant improvements, demonstrating the importance of litter quality in soil restoration. Restoration effectiveness ranking of the four tested species on soil improvement are therefore ASP>AVP>QCP>CSP. The significant improvement of soil quality under ASP compared to other reforestated stands, only after 3 decades, emphasizes the importance of tree species selection and litter quality on soil chemical and biological restoration.

Decreased Soil Organic Carbon under Litter Input in Three Subalpine Forests

Soil organic carbon (SOC) is the largest terrestrial organic carbon pool. Plant litter is an important source of SOC, but the knowledge gap between SOC fractions and plant litter input remains inconsistent. Here, a litter input control experiment was conducted at three subalpine forest types (coniferous forest, mixed forest, and broadleaved forest). We assessed the variations of total organic C, active organic C (easily oxidizable C, labile organic C), recalcitrant organic C, and microbial biomass C under litter input or removal. The results showed that soil total organic C decreased greatly under litter input. It was mainly caused by the change of easily oxidizable C and labile C, while the influence of recalcitrant C was small. At the same time, this effect varied among different forest types. Among them, the effect of litter input on SOC was weak and slow in the coniferous forest with low-quality litter input, while a quick effect was observed in the mixed and broadleaved forests with high-quality litter input. Microbial biomass C declined under litter input in most cases, and its variation was strongly controlled by soil temperature and freeze-thaw events. Overall, our results provide new evidence that forest type would strongly control SOC dynamics, in concert with litter quality shifts, with potential consequences for long-term C sequestration. We highlighted that litter input could reduce microbial biomass carbon which might limit the native SOC decomposition, but the loss of active C ultimately changed the SOC in the subalpine forests. It suggested that the interaction of multiple mechanisms should be considered in the study of SOC in this region.

Substrate quality effects on stabilized soil carbon reverse with depth

High-quality plant inputs to the soil with low lignin to nitrogen ratios have been conceptualized to foster the formation of soil organic matter (SOM) and carbon (C) in stabilized soil compartments, such as aggregates and organo-mineral associations (MAOM), in dependence of the soil’s capacity to store additional C (i.e., C saturation deficit). Yet, evidence for these conceptualizations from field experiments is scarce and it is unclear whether factors commonly not included in laboratory experiments (such as soil depth) may modulate the influence of substrate quality on SOM formation. We, thus, tested the effect of substrates with different qualities (from European alder and Scots pine) on C stocks in bulk soil, free particulate and aggregate-occluded organic matter, and MAOM in soils at various ages after reclamation and at different soil depths in a common-garden field experiment.Our results revealed that substrate quality generally acted in the predicted way in the upper investigated soil layer (0–5 cm depth), i.e., high-quality substrates increased C stocks in MAOM. Surprisingly, the effect of substrate quality reversed with depth (5–15 cm; i.e., low-quality litters were associated with higher C stocks in MAOM), potentially due to a higher sensitivity (or “priming”) of native SOM in response to high-quality substrates at depth or a lower probability of such substrates reaching deeper soil layers. These patterns appeared to be largely independent of the soils’ theoretical capacity to stabilize additional C, which was exceeded in all investigated soils. Based on the results of our field experiment, we highlight the need to refine recent conceptualizations by focusing on environmental factors that are commonly not accounted for in laboratory-scale experiments and that may alter the direction in which substrate quality acts to influence the formation of SOM.

Microbial succession and changes in carbon and nitrogen during decomposition of leaf litters of Tephrosia candida (Roxb.) DC. and Oryza sativa L. under shifting cultivation in Mizoram, northeast India

The present study aims to understand microbial succession and dynamics of dry matter, carbon and nitrogen during the decomposition of leaf litters of Tephrosia candida (Roxb.) DC. and Oryza sativa L. in two fallow lands (FL) of 3 years (FL-3) and 8 years (FL-8) following shifting cultivation in Mizoram. A total of 64 microorganisms were isolated from two leaf litters by serial dilution method, out of which 13 microbes were identified as decomposers as they exhibited a positive response towards the enzyme activity. Among these 13 microorganisms, 4 (SKT 02, SKT 05, SKT 09 and SKT 020) were bacteria (Streptobacillus sp. and Bacillus sp.), 5 (SKT 033, SKT 034, SKT 035, SKT 040 and SKT045) were fungi (Microsporum sp., Rhizopus sp. and Aspergillus sp.) and 4 (SKT 030, SKT 052, SKT 053 and SKT 060) were actinomycetes (Streptomycetes sp.). T. candida leaf litter possessed low initial Carbon/Nitrogen (8.77) and Lignin/Nitrogen ratio (2.29) and considered a high-quality resource exhibiting higher decomposition rate. Mass loss of carbon and nitrogen (~ 40-80%) was maximum during the initial two months, which slowed down in the later period of decomposition. It was concluded that the number of bacteria, fungi and actinomycetes regulate organic matter and nutrient dynamics in the soil through various enzymatic actions on high- and low-quality litters. The combination of O. sativa and T. candida litter is recommended to manage soil fertility in shifting cultivation of Mizoram,Northeast India.

Linking Vegetation, Soil Carbon Stocks, and Earthworms in Upland Coniferous–Broadleaf Forests

Linking vegetation, soil biota, and soil carbon stocks in forests has a high predictive value. The specific aim of this study was to identify the relationships between vegetation, earthworms, and soil carbon stocks in nine types of forests dominating autonomous landscape positions in a coniferous–broadleaf forest zone of the European part of Russia. Mountain forests were selected in the Northwest Caucasus, while plain forests were selected in Bryansk Polesie and on the Moskva-Oka plain. One-way analysis of variance (ANOVA) and v-tests were used to assess the impact of different factors on soil C stocks. To assess the contribution of vegetation, litter quality, and earthworms to variation of carbon stocks in organic (FH-layer) and mineral layer (0–50 cm), the method of hierarchical partitioning was performed. The highest C stocks in the organic horizons were associated with the low-quality litter, i.e., with a low base saturation, high acidity, and wide C/N ratio. The highest soil C stocks in the mineral layers were found in mixed forests with the highest richness of plant species, producing litterfall of different quality. The C stock in the organic horizon was negatively related to the biomass of worms that process the litter, while the carbon stock in the mineral layers was positively related to the biomass of worms whose life activity is related to the mineral layers. These findings demonstrated the substantial influence of plants producing a litter of different quality, and of earthworms, belonging to different functional groups, on soil C stocks in coniferous–broadleaf forests.

Effects of Climate and Atmospheric Nitrogen Deposition on Early to Mid-Term Stage Litter Decomposition Across Biomes

Litter decomposition is a key process for carbon and nutrient cycling in terrestrial ecosystems and is mainly controlled by environmental conditions, substrate quantity and quality as well as microbial community abundance and composition. In particular, the effects of climate and atmospheric nitrogen (N) deposition on litter decomposition and its temporal dynamics are of significant importance, since their effects might change over the course of the decomposition process. Within the TeaComposition initiative, we incubated Green and Rooibos teas at 524 sites across nine biomes. We assessed how macroclimate and atmospheric inorganic N deposition under current and predicted scenarios (RCP 2.6, RCP 8.5) might affect litter mass loss measured after 3 and 12 months. Our study shows that the early to mid-term mass loss at the global scale was affected predominantly by litter quality (explaining 73% and 62% of the total variance after 3 and 12 months, respectively) followed by climate and N deposition. The effects of climate were not litter-specific and became increasingly significant as decomposition progressed, with MAP explaining 2% and MAT 4% of the variation after 12 months of incubation. The effect of N deposition was litter-specific, and significant only for 12-month decomposition of Rooibos tea at the global scale. However, in the temperate biome where atmospheric N deposition rates are relatively high, the 12-month mass loss of Green and Rooibos teas decreased significantly with increasing N deposition, explaining 9.5% and 1.1% of the variance, respectively. The expected changes in macroclimate and N deposition at the global scale by the end of this century are estimated to increase the 12-month mass loss of easily decomposable litter by 1.1–3.5% and of the more stable substrates by 3.8–10.6%, relative to current mass loss. In contrast, expected changes in atmospheric N deposition will decrease the mid-term mass loss of high-quality litter by 1.4–2.2% and that of low-quality litter by 0.9–1.5% in the temperate biome. Our results suggest that projected increases in N deposition may have the capacity to dampen the climate-driven increases in litter decomposition depending on the biome and decomposition stage of substrate.

Low‐quality carbon and lack of nutrients result in a stronger fungal than bacterial home‐field advantage during the decomposition of leaf litter

Abstract Decomposition of litter is a key biochemical process that regulates the rate and magnitude of CO2 fluxes from biosphere to atmosphere and determines soil nutrient availability. Although several studies have shown that plant litter decomposition accelerated in their native compared to a foreign environment, that is, a home‐field advantage (HFA) for litter degradation, to date HFA has only been considered in terms of respiration or litter mass loss. The competitive success of the decomposer micro‐organism will be determined by its ability to transform used OM into population growth. Therefore, we hypothesized that HFA for microbial growth would be more pronounced than that for decomposition. We also expected that HFA effect for decomposition and microbial growth would increase with lower quality litter, which the fungal role in litter decomposition would be more dominant than that of bacteria, and that HFA effects would strengthen with more pronounced differences between ‘home’ and ‘away’ environments. We designed a 2‐month microcosm reciprocal transplant experiment with litter from two sites with contrasting climates (Atlantic and Sub‐Mediterranean climates) and including three tree species (Quercus robur, Pinus sylvestris and Fagus sylvatica). We found a stronger HFA for microbial growth than for decomposition, that the nutrient content and C‐quality of litter influenced the microbial HFA and that interactions between bacterial and fungal communities during litter decomposition modulated the HFA for litter degradation. Low litter nutrient content, strong nutrient limitations and low C‐qualities all favoured fungal over bacterial decomposers, and our results suggest a dominant functional role of the fungal community and gave rise to HFA effect for fungal growth but that this translated to only marginal implications for overall decomposition of litter. A free Plain Language Summary can be found within the Supporting Information of this article.

半干旱草地不同植物枯落物分解对放牧和封育的响应

为探究放牧和封育对半干旱草地植物枯落物分解的影响，选取赖草、牛枝子及其混合物为研究对象，调查了不同网孔分解袋中宁夏半干旱草地植物枯落物分解特征及对放牧和封育的响应规律。结果表明：（1）放牧样地250目网孔中，枯落物质量残留率表现为牛枝子显著高于赖草和混合物（P<0.05），而在放牧样地30目网孔、封育样地2种网孔中，枯落物质量残留率均表现为3种枯落物间无显著差异。（2）250目网孔中，放牧和封育样地枯落物分解衰减常数均表现为混合物显著高于牛枝子，而赖草居中；并且，牛枝子枯落物分解衰减常数表现为封育样地显著高于放牧样地。30目网孔中，放牧和封育样地枯落物分解衰减常数均表现为赖草、混合物显著高于牛枝子（P<0.05）；并且，牛枝子枯落物分解衰减常数表现为封育样地显著高于放牧样地（P<0.05）。（3）在放牧样地，仅牛枝子枯落物R_m表现为30目显著低于250目网孔（P<0.05），k表现为30目显著高于250目网孔（P<0.05）；土壤动物对枯落物分解的贡献率表现为混合物显著低于牛枝子，赖草居中（P<0.05）。而在封育样地，仅牛枝子枯落物k表现为30目显著高于250目网孔（P<0.05）；土壤动物对枯落物分解的贡献率表现为混合物和牛枝子均显著高于赖草，且混合枯落物的土壤动物贡献率表现为封育样地显著高于放牧样地（P<0.05）。（4）枯落物残留率与其初始N、P、木质素/N、C/P呈显著相关性（P<0.05）；枯落物分解衰减常数与其初始N、P、木质素、N/P、C/P和木质素/P间均呈显著相关性（P<0.05）。研究表明，植物种类组成显著影响枯落物的残留率和分解衰减常数。放牧与封育管理通过影响网孔中土壤动物分布来调控半干旱区草地植物枯落物的分解，而且封育管理更有利于促进土壤动物对低质量枯落物（牛枝子）的分解。;This present study was to explored litter decomposition of different plant species under grazing and enclosure management in semi-arid grassland ecosystems. The remaining mass and decay constant (k) of Leymus secalinus, Lespedeza potaninii litter, and their mixture were investigated within 30-and 250-mesh litterbags in semiarid grasslands under grazing and enclosure management in Ningxia. In addition, the contribution of litter arthropods to decomposition was analyzed in order to discuss the effects of grazing management on decomposition process. The results showed that:(1) there was a significant higher final litter mass remaining rate (R_m) in L. potaninii than in L. secalinus and mixture from 250-mesh litterbags in grazing grasslands, whereas there were no significant differences in R_m of plant litter either from 30-mesh litterbags in grazing grasslands, or from both size-mesh treatments in enclosure grasslands. (2) In 250-mesh litterbags, the k was significantly higher in the mixture than in L. potaninii in both grasslands under grazing and enclosure managements, with the intermediate values in L. secalinus litter (P<0.05). But the k of L. potaninii was significantly higher in enclosure than in grazing grasslands (P<0.05). In 30-mesh litterbags, the litter decay constant (k) was significantly higher in L. secalinus and mixture than in L. potaninii in both grasslands under grazing and enclosure managements; the k of L. potaninii litter was significantly higher in enclosure than in grazing grasslands (P<0.05). (3) In grazing grassland, the R_m of L. potaninii was significantly higher in 250-mesh than 30-mesh (P<0.05), while k was significantly higher in 30-mesh than in 250-mesh. There were significantly lower values in the mixture than in L. potaninii, with the intermediate values in L. secalinus (P<0.05). In enclosure grassland, the k of L. potaninii was significantly higher in 30-mesh than 250-mesh (P<0.05), while the contribution rate of litter arthropods to litter decomposition was significant higher in the mixture and L. potaninii than in L. secalinus. The contribution rate of litter arthropods to mixture litter decomposition was significantly higher in enclosure than in grazing grasslands (P<0.05). (4) The R_m indicated a positive correlation with litter lignin/N and litter C/P, but it indicated a negatively correlation with litter initial N and P content. And the k indicated a positive correlation with litter initial N and P, while it indicated a negatively correlation with litter lignin, N/P, C/P and lignin/P. It was suggested that plant species composition presented a significant effect on the litter final mass remaining and decay constant. The effect of grazing management on litter arthropod distribution between different mesh-size litterbags induced the decomposition differences between various species of plant litter. In conclusion, the enclosure management was conducive to promoting the contribution of litter arthropods to low-quality litter (i.e., L. potaninii) decomposition in semi-arid grasslands.

Extreme temperature events alter stream ecosystem functioning

Extreme temperature events have increased in intensity, duration and frequency in the last century, with potential consequences on organisms and ecosystems. In many streams, leaf litter of terrestrial origin is a key resource for microorganisms and some detritivores, and its decomposition has a main role on ecosystem functioning and is often used as an indicator of ecological integrity. As litter is often exposed to atmospheric conditions before entering the stream, extreme warming and freezing events may alter its physicochemical structure and affect decomposition and associated detritivores. We tested this prediction in a microcosm experiment by exposing litter of three tree species (in single-species treatments and the 3-species mixture) to different temperature pre-treatments: heating (40 °C), freezing (−20 °C) and both (heating followed by freezing). We then examined changes in litter traits due to leaching (72 h), litter decomposition in the absence and presence of detritivores, and detritivore growth (28 d), with focus on mass and nutrient (nitrogen and phosphorus) changes. Nutrient leaching was promoted mostly by the heating pre-treatment, which apparently produced lower-quality litter. However, microbial activity mostly resulted in litter mass and nutrient gain, which were reinforced by the heating pre-treatment, while freezing had the opposite effect. When detritivores were present, decomposition showed high variation among litter types but, again, the heating and freezing pre-treatments tended to reduce and enhance nutrient loss, respectively. The greatest and more consistent effects occurred for detritivore growth, which was reduced by temperature pre-treatments, particularly in the highest-quality litter type. In general, the sequential application of heating and freezing pre-treatments showed no synergistic effect, and the litter mixture showed similar responses to single-species treatments. Our results demonstrate that short-term extreme temperatures can modify litter quality in riparian soils and have subsequent effects on its decomposition within the stream and associated fauna, potentially altering stream food webs, ecosystem functioning and biogeochemical cycles.

Five-year study on the effects of warming and plant litter quality on litter decomposition rate in a Tibetan alpine grassland

The decomposition of plant litter is a key link in global C budgets and provides strong feedback to changes in climate and biogeochemical cycles. However, the combined effects of global warming and plant litter quality on the rate of plant litter decomposition and nutrient dynamics in alpine ecosystems are still poorly understood. We conducted a warming experiment to investigate the effects of litter quality and temperature on decomposition rates and variations in nutrients of four common herbaceous plants (low-quality litter species Stipa purpurea and Carex moorcroftii and high-quality litter species Astragalus confertus and Leontopodium nanum) during 2011–2016. During the initial stages of decomposition, warming had no significant effect on the mass loss of plant litter for low-quality litter species, but in the later stages of decomposition, it had a negative effect on the mass loss across all species (P < 0.05). Litter quality was the best predictor of N and P release/immobilisation during the decomposition of aboveground plant litter. Low-quality litter had the highest immobilisation of N at about 80% of the initial remaining mass; nutrients were then released in the following stages of decomposition. However, the fraction of initial P decreased with the mass remaining during the initial and later phases of decomposition, but a short period of P immobilisation occurred in the middle phase of decomposition. For high-quality litter, the fraction of initial N and P decreased with the mass remaining during the whole decomposition process. Warming had a marginal influence on the N and P dynamics throughout the decomposition process. Our study showed that the decay of plant litter was strongly suppressed by warming climate and that the N and P dynamics on the investigated Tibetan grassland were mainly regulated by litter quality, providing valuable insights into the biogeochemical cycles of nutrients in alpine ecosystems.

Trading tree growth for soil degradation: Effects at 10 years of black plastic mulch on fine roots, earthworms, organic matter and nitrate in a multi-species riparian buffer

This study assessed the effects of two vegetation management treatments (black polyethylene mulch and a control treatment) on tree growth, fine root biomass of trees and of competing vegetation, earthworms, and physiochemical soil properties in a 10 year-old agricultural riparian buffer planted in southern Québec (Canada) with five trees species: Populus × canadensis Moench (hybrid poplar), Fraxinus pennsylvanica Marsh. (red or green ash), Quercus macrocarpa Michx. (bur oak), Quercus rubra L. (red oak), and Pinus strobus L. (eastern white pine). Vegetation management treatments had a significant effect on tree growth, fine root biomass, earthworms and on many soil properties. Overall, the use of plastic mulch increased tree growth in all species (not to the same extent), but locally decreased soil organic matter, total soil carbon, total soil nitrogen, earthworm biomass and abundance, competing vegetation fine root biomass and the biomass of the total pool of fine roots. Also, more than three times more soil nitrate was measured under mulch despite the higher tree growth. Lower soil phosphorus availability (in some species), base cation saturation and moisture content under the mulch suggested higher uptake of these soil resources to sustain high tree growth. Across treatments and species, significant and strong correlations were observed between total fine root biomass and soil carbon, between competing vegetation fine root biomass and earthworm biomass, and between total soil carbon and earthworm biomass. These highlight the central role of the total pool of fine roots in maintaining or enhancing soil carbon, the importance of understory herbaceous vegetation for earthworm populations and the importance of organic matter as a factor limiting earthworm activity. Species × Treatment interactions were observed on tree growth, fine roots, and earthworms. Pine growth was little enhanced by the mulch and its fine root biomass peaked in the control treatment, suggesting plasticity in allocation to fine roots in response to resource limitations. Pine had similar earthworm biomass across both vegetation management treatments, with two to three times less earthworm biomass than other tree species observed in control plots, reflecting its low needle litter quality. Only poplar and ash had higher tree fine root biomass under the mulch. Red oak was the species the most negatively affected by herbaceous competition. In practice, plastic mulch is rarely removed from tree plantation sites. This should change in a context where plastic mulch is increasingly used as an alternative to herbicide, and where riparian agroforestry projects need to meet both timber and non-timber objectives (carbon sequestration in the soil and in tree biomass, N and P storage in woody biomass, soil quality restoration), while minimizing their impacts in terms of nitrate leaching. Identifying alternative mulching materials and strategies that would provide high growth benefits without degrading the soil or water quality is a priority to optimize ecosystem services provision in tree plantations and riparian buffers.

Chemical Compounds and Decomposition Process from Four Species Leaf Litter As a Source of Organic Matter Soil in Anggori Education Forest, Manokwari

Decomposition is a simple change of physical and chemical processes by soil microorganisms—the rate of decomposition process influenced by climate and litter quality factors. Litter content of chemical compounds is essential to determine the litter's quality so that it can be estimated the decomposition process. Leaves litter of Magnolia tsiampacca, Intsia bijuga, Cinnamomum cullilawan, and Aglaia sp., were collected and analyzed for their chemical compounds. Based on lignin and nitrogen content (L/N) value, Cinnamomum cullilawan have the fastest decomposition process. On the contrary, Intsia bijuga has low litter quality, so that has the slowest decomposition process. However, it has the lowest lignin content and high polyphenol content. Our research found that four observed species were able to be used as sources of soil organic matter, although the litter quality is relatively low.

Temporal dynamics of litter quality, soil properties and microbial strategies as main drivers of the priming effect

The priming effect describes the change in the rate of soil organic matter (SOM) mineralisation due to the addition of fresh organic matter (FOM), and is thus central to the evaluation of carbon fluxes in terrestrial ecosystems. However, little is known about how litter quality interact with soil properties and microbial communities to explain the priming effect. Here, we provide new empirical evidence showing how litter, soil and microbial parameters control FOM and SOM decomposition. We monitored the kinetics of carbon fluxes over 202 days and at 23 dates after additions of two 13C-labelled plant litters of contrasted quality (nutrient-rich and labile litter [i.e., high quality] vs nutrient-poor and recalcitrant litter [i.e., low quality]) using four soil types originating from different ecosystems (forest, grassland, cropland and plantation). We found that the priming effect varied over time with: (i) an ‘immediate’ priming effect after the addition of high quality litter, which rapidly decreases when nitrogen is available; and (ii) a ‘delayed’ priming effect after the addition of low quality litter, which increases continuously when nitrogen is depleted. The ‘immediate’ priming was mainly related to the decomposition of accessible carbon compounds, whereas the ‘delayed priming’ was mainly related to the decomposition of recalcitrant carbon compounds. These results were linked to changes in microbial resource acquisition strategies as indicated by shifts in enzyme activities from hydrolytic to oxidative and nitrogen-related enzymes, therefore suggesting that two series of mechanisms act in succession at different time scales in relation to litter quality and nitrogen availability. Furthermore, our data demonstrate that incorporating carbon in the soil via the increase in soil microbial biomass can counterbalance carbon losses via priming effect. This highlights the importance to assess the balance between the carbon outputs and inputs to determine whether terrestrial ecosystems act as a sink or a source of carbon. We conclude that shifts in litter quality, nutrient availability and microbial resource acquisition strategies need to be taken into consideration for accurate assessment of the variability of the priming effect from the short to the long term.

Invasive red oak (Quercus rubra L.) modifies soil physicochemical properties and forest understory vegetation

This study assessed the effects of invasive Quercus rubra on soil physicochemical properties and understory vegetation in native plant communities. Chemical properties of senesced tree leaves were also analysed. The study was performed at paired invaded-native plots in managed forests in southern Poland. Freshly fallen senesced leaves were characterized in terms of C, Ca, K, Mg, N, P, total phenolics and condensed tannins concentrations. Soil physicochemical parameters, namely bulk soil density, moisture, water holding capacity (WHC), pH, organic C, total Ca, K, Mg, N, P, exchangeable Ca, K, Mg, N-NH4, N-NO3, P-PO4, and total phenolics were analysed in organic and mineral soil horizons, and condensed tannins were analysed in organic soil horizon. The diversity, cover and composition of understory vegetation were assessed. Although, senesced leaves of Q. rubra and native trees, Quercus robur, Fagus sylvatica, Carpinus betulus and Acer pseudoplatanus among others, differed only in total K, N and C/N ratio, we observed considerable differences in soil physicochemical parameters between the plot types. Soil beneath Q. rubra was characterised by significantly lower WHC, organic C, total Mg, N, P, exchangeable Ca, Mg, N-NH4, N-NO3, total phenolics and higher moisture in organic and mineral soil horizons as well as lower content of P-PO4 and condensed tannins in organic soil horizon relative to native plant communities. Q. rubra negatively influenced species richness and cover of understory vegetation. The changes in soil physicochemical parameters and understory vegetation under Q. rubra may be associated with low quality (low N, high C/N) litter that decomposes slowly and generates a physical barrier, limiting seed germination and seedling growth. The changes in soil properties and vegetation under invasive Q. rubra indicate that this species may alter the structure and function of forest ecosystems and should be avoided in forest management practices.

The roles of initial litter traits in regulating litter decomposition: a “common plot” experiment in a subtropical evergreen broadleaf forest

Leaf litter decomposition constitutes a valuable ecosystem service by recycling nutrients, transferring energy, and sequestrating carbon (C) in terrestrial ecosystems. However, variations in microclimate and decomposers among studies have impeded a mechanistic understanding of what controls litter decomposition. We conducted a “common plot” experiment leveling-off impacts of environmental and biotic factors to explore roles of the initial leaf litter traits in decomposition. The experiment was carried out in an evergreen broadleaf forest in the Wuyi Mountains from May 2017 to August 2018. Leaf litter was collected from Populus deltoids in a nitrogen (N) addition experiment at Dongtai Forest Farm, Liriodendron chinense × tulipifera and Platanus acerifolia on campus Nanjing Forestry University, and Quercus variabilis and Pinus taeda at Xiashu Forest Farm. Our results showed that N addition significantly increased leaf litter decomposition of P. deltoids. This may result from N induced increases in litter quality, indicated by a high N content and a low C:N ratio of leaf litter. Across the five tree species (with no litter from P. deltoids under N addition treatment), we found litter decomposition of the coniferous tree (P. taeda) was much lower than that of the other four broadleaf trees due to its lower litter quality. Multiple regression analyses indicated that the initial C:N ratio and sodium (Na) content that was critical for decomposers dominated decomposition. Our results confirmed the importance of the initial litter quality, such as C:N ratio, in regulating leaf litter decomposition. In addition, our results suggest the Na control of the decomposition of leaf litter in subtropical ecosystems through Na limiting the activity and abundance of decomposers in brown food webs.