Litter Addition Research Articles

Effects of different loads of Pinus pinaster Ait. litter and ash on the germination and growth of Cistus ladanifer L

Key messageCistus ladanifer L. shows an extraordinary plasticity of germination and growth. Fire promotes the regeneration of C. ladanifer by triggering its germination through thermal shock as well as by enhancing its seedling growth through the addition of ashes. On the contrary, stacking of Pinus pinaster Ait. leaf litter may hinder seedling establishment, at least in the first months after germination.ContextPinus pinaster Ait. is affected by forest fires in the Mediterranean basin. Its extreme flammability is due to the high spatial continuity together with the massive accumulation of leaf litter. Cistus ladanifer L. is a species which is widely distributed in the west Mediterranean region where it can form vast shrublands and flourish under these pinewoods. Although high temperatures associated with the occurrence of fire trigger germination of C. ladanifer, knowledge on how other factors, such as the presence of litter on the forest floor or the ash left after the fire, influence germination and seedling growth is essential to improve land management plans.AimsThe main objective of this study was to determine the effects of different loads of litter from P. pinaster and ash from their combustion on the germination and growth of seedlings of C. ladanifer.MethodsTwo experiments were carried out to assess the effect of heat shock (100 °C for 10 min) and two loads of litter and ash from P. pinaster (control, high and low loads of litter, high and low loads of ash) on the germination and growth after 2 and 4 months of C. ladanifer.ResultsHeat shock significantly increased the germination of C. ladanifer. In contrast, the addition of litter and ash had no effect on total germination but affected the growth of the seedlings coming from seeds exposed to heat shock. Litter treatments reduced biomass of 2 months seedlings and ash increased biomass of 4 months seedlings.ConclusionC. ladanifer is a species favoured by fire in different ways depending on the stage of regeneration. Germination is promoted by heat shock while seedling growth is favoured by ash nutrients. In contrast, pine leaf litter hinders seedling growth, although this effect disappears 4 months after germination. Alternative forest management practices to prescribed fires are recommended if preventing the spread of Cistus is a priority.

Miscanthus litter additions induce a successional change in the soil micro-food web with apparent decreases in soil nitrogen

The rapid loss of soil carbon (C) from cultivated peatland soils is leading to the use of high lignin, C-rich litter amendments as a potential solution to slow C losses. These chemically recalcitrant litter inputs are expected to cause microbial nitrogen (N) immobilization as a result of changes in the soil micro-food web, but whether bioavailable N is altered by litter as it is decomposed by the micro-food web remains unclear. We monitored changes in the soil nematode, fungal, and bacterial communities over time and across space (the rhizosphere and bulk soil) after field-applying different types of ligneous litter from miscanthus, ash, willow, or larch to a cultivated peatland soil. We found that miscanthus grass (C:N = 118) induced succession from fast-growing nematodes (cp-1) to slower-growing, cp-3 and cp-4 nematodes and this corresponded to reduced N availability. This lower soil N was likely due to relatively higher microbial biomass we observed with miscanthus, combined with a decrease in fast-growing bacterivores, limiting N mineralization from nematode grazing. We did not observe strong effects on the soil micro-food web or microbial biomass N for the other woody litters that had much higher C:N. This indicates that the changes in nematode community composition following ligneous litter inputs and subsequent impacts on soil N depend on litter type but are independent of litter C:N. Miscanthus amendments also corresponded to the lowest lettuce yield of all the amendments and thus caution is raised when using miscanthus straw as a widely-applied litter. Our results provide a useful reference to predict the effect of litter amendments on cultivated peatland soils through soil micro-food web dynamics, and bioavailable N for the crop.

Response of submerged macrophytes of different growth forms to multiple sediment remediation measures for hardened sediment.

Climate change and intensified human activities have disrupted the natural hydrological regime and rhythm of river-connected lakes, extending the dry season, increasing water loss, and exposing previously submerged lake floors. This exposure has led to significant sediment hardening, which directly impacts submerged macrophytes. However, strategies to mitigate the negative effects of hardened sediments and promote the growth and development of submerged macrophytes remain largely unexplored. In this study, we selected typical hardened sediment from Dongting Lake to investigate the response of different growth forms of submerged macrophytes to multiple sediment remediation measures (loosening and litter addition) using a mesocosm experiment. The results indicated that loosening alone uniformly benefited all submerged macrophytes by increasing total biomass, relative growth rate (RGR), and the root/shoot ratio. Additionally, loosening altered the root traits of submerged macrophytes, promoting maximum root length (MRL) while reducing average root diameter (ARD). Moreover, different submerged macrophytes exhibited species-specific responses to the combination of loosening and litter addition. Notably, the combination of loosening and adding Miscanthus lutarioriparius litter had an antagonistic effect on the growth of Potamogeton wrightii and Myriophyllum spicatum. The response of functional traits of submerged macrophytes with similar growth forms to the same treatment was consistent. Our findings suggest that future sediment remediation efforts should consider matching specific treatments with the growth forms of submerged macrophytes to achieve optimal outcomes.

Plant litter as a heavy metal migration strategy following application of sewage sludge to subtropical forest soils

The environmental risks of migration of heavy metals (HMs) following applications of sewage sludge (SS) to forest soils are garnering increased attention. Plant litter at the forest floor may modify HM migration pathways through impacts on soil aggregates and water/soil erosion; however, HM migration responses to plant litter are poorly understood. The aim of this study was to determine the effects of plant litter cover on HMs migration, and water and soil erosion following the application of SS to subtropical forest soils. Effects of addition of SS along and SS plus plant litter at 0.75 or 1.5 kg m−2 on the migration of cadmium, chromium, copper, nickel, lead, and zinc in surface runoff, soil interflow, and sediments were quantified across nine simulated rainfall events in a laboratory experiment and following natural intense rain events in a field experiment. Addition of SS elevated HM concentrations in surface runoff by 38.7 to 98.5 %, in soil interflow by 48.3 to 312.5 %, and in sediment by 28.5 to 149.4 %, and increased the production of sediment aggregates <0.05 mm that led to greater cumulative migrations of HMs in surface runoff and sediment; sediment accounted for 89.5 % of HM migrations. Addition of plant litter reduced cumulative migration of HMs by 87.1–97.27 %; however, the higher rate of plant litter led to a decrease in surface runoff and sediment yield, and an increase in soil interflow. Addition of plant litter shifted the main pathway of HM migration from sediment to surface runoff and soil interflow. The potential ecological HM risk index was “low” for each treatment. We found consistency in HM concentrations and migrations via surface runoff between the field and laboratory experiments. Overall, the addition of plant litter with SS mitigated soil erosion and reduced total migration of HMs, resulting in a 88.7–97.3 % decrease in the ecological risk index of the six HMs. We conclude that the addition of plant litter may provide a management strategy for the mitigation of HM risks to environmental safety for the disposal of SS in subtropical forest systems.

Different regulatory mechanisms on carbon-degrading enzyme activities under short-term litter input manipulations in subalpine coniferous and broad-leaved forest soils

Soil carbon (C)-degrading extracellular enzyme activities (EEAs) are important regulators in targeting litter and soil organic carbon (SOC) decomposition in territorial ecosystems. However, the responses of enzymes involved in C-cycling to short-term litter input manipulations in different forest ecosystems remain unclear. Here, we examined oxidative C-degrading EEAs (Ox-EEAs), hydrolytic C-degrading EEAs (Hy-EEAs) and their ratios (Ox-to-Hy C EEA ratios) at topsoil (0–10 cm) and subsoil (10–30 cm) after two years of litter manipulations (i.e., Detritus Input and Removal Treatments-DIRT: control, CK; double litter, DL; no roots and double litter, NRDL; no litter, NL; no roots, NR; no roots and no litter, NRNL) in a coniferous forest (Pinus yunnanensis) and a broad-leaved forest (Quercus pannosa) in subalpine area of Southwest China. The litter addition did not significantly affect Ox-EEAs, Hy-EEAs, and their ratios in two forest soils. In contrast, the litter removal significantly decreased Hy-EEAs and slightly affected Ox-EEAs in coniferous forest soil, whereas they increased Ox-EEAs and slightly affected Hy-EEAs in broad-leaved forest soil. Consequently, the Ox-to-Hy C EEA ratios were significantly enhanced by litter removal in both two forest soils. This different variation in Ox-EEAs and Hy-EEAs under litter removal in two forest soils could be attributed to initial soil properties, where soil properties (e.g., pH, total nitrogen [TN], NO3−-N, SOC) with lower C: N ratios in coniferous forest were more likely to promote Hy-EEAs. Whereas microbial parameters (e.g., microbial biomass C) and soil properties (e.g., dissolved organic C) mainly regulated Ox-to-Hy C EEA ratios at topsoil and subsoil in broad-leaved forest, respectively. Overall, our findings revealed different mechanisms and associated drivers on enzymes involved in C-cycling under short-term litter input manipulation of the subalpine coniferous forest and broad-leaved forest soils, which further strengthened our understanding of C-cycling in forest soils.

Wildfire Effects on the Soil Respiration and Bacterial Microbiota Composition in Mediterranean-Type Ecosystems

This work provides insights into the effect of fire on soil processes in Mediterranean-type ecosystems in Cyprus. Soil samples from mountainous sites that were subjected to a summer wildfire and adjacent control samples were collected. Incubations were used to estimate basal respiration and isolate soil CO2 release of heterotrophic microorganisms from autotrophic root respiration and heterotrophic respiration from litter decomposition. Physicochemical property changes, bacteria community changes using DNA extraction and 16S rRNA gene analysis, and the effects of ash and fresh litter addition were studied to reveal the microbial composition and the post-fire soil function. Laboratory incubation showed that burned soils constantly showed higher microbial respiration rates compared with control unburned areas, even six months after a fire. Adding ash to unburned samples increased microbial respiration, suggesting that increased nutrient availability positively corelates with the increased release of CO2 from fire-affected soil. Elevated temperatures due to the wildfire exerted significant effects on the composition of soil bacterial microbiota. Nevertheless, the wildfire did not affect the alpha-diversity of soil bacteria. New communities of microorganisms are still able to decompose fresh plant material after a fire, but at a slower rate than natural pre-fire populations.

Impact of earthworms on soil Si availability and wheat Si concentration in low- and high-Si soils

Silicon (Si) is a beneficial element known to increase growth and the stress resistance of plants, including resistance against drought. However, as with many other elements, only a small fraction of Si in soils is available for plant uptake. Plant-available Si originates either from the weathering of soil minerals or from the dissolution of phytoliths in plant litter. It is known that soil fauna plays a role in both processes that contribute to the availability of Si in the soil. However, very little is known about the interactions between the weathering of soil minerals and the dissolution of Si by earthworms from phytoliths and subsequent Si uptake by plants. In greenhouse pot experiments, this study investigated the effect of an epigeic earthworm species (Dendrobaena veneta) on Si availability and uptake by wheat (Triticum aestivum) grown in soils with high or low Si availability. In addition, Si-rich plant litter (wheat straw) was added to the topsoil in some treatments. The addition of plant litter significantly increased the available Si in the soil. Plant litter addition was positively correlated with the Si concentration in wheat in low-Si soil, but not in high-Si soil. Earthworms increased Si availability in soil and casts of the low-Si soil and partly of the high-Si soil, but not Si uptake by wheat. These results suggest that earthworms play an important role in regulating the Si status of soils and may influence Si uptake by plants, especially in soils with initially low Si content and when earthworm population densities are high.

Changes in litter and nitrogen deposition differentially alter forest soil organic matter biogeochemistry

Global climate change has altered forest productivity across the globe. Although extreme drought and temperature have lowered forest productivity in some regions, increased productivity has been observed in many forests over the last few decades due to increases in atmospheric carbon dioxide, temperature, and nitrogen (N) deposition. These factors can lead to changes in both the quantity and quality of litterfall and root inputs to soil. Additionally, few studies have investigated multifactorial treatments (e.g., detrital changes and N deposition), on soil carbon (C) sequestration. To investigate the long-term compositional changes to soil organic matter (SOM) in response to litter and N inputs, soil samples were collected from the University of Michigan Biological Station (UMBS) Detrital Input and Removal Treatment (DIRT) site after 15 years of experimental treatments. The samples were characterized using elemental analysis, targeted SOM compound analyses, nuclear magnetic resonance spectroscopy and microbial biomass and community composition measurements. The exclusions of C inputs (litter and/or roots) resulted in molecular-level biogeochemical changes, however, the soils at UMBS are seemingly more resistant to losses in soil C compared to other DIRT studies. Although the addition treatments (Double Litter, Double Wood, Double Litter + N, and N) led to increased soil C concentrations at UMBS, we found evidence for enhanced SOM decomposition occurring with litter additions. Notably, the observations made from the concurrent treatment of Double Litter + N demonstrated that the responses of individual treatments are not representative of simultaneous applications. Collectively, these results demonstrate that soil C biogeochemistry is sensitive to fluctuations in C and N deposition and overall, these processes are dictated by site-specific ecological properties.

Performance and economic efficiency of laying hens in response to adding zeolite to feed and litter

This study investigated the effect of different levels of zeolite in laying hen (Silver Montazah) diet and litter on productive performance, egg quality criteria, and economics during the second stage of production (40-56 wk of age). An experiment with a 3 × 4 factorial design was performed to study the effects of four levels of zeolite (0, 10, 15, and 20 g/kg feed) in the diet and three levels of zeolite (0, 1.5, and 2 kg/m2) in the litter. Adding zeolite to diet and litter significantly improved final BW and BW change, egg number, egg weight, egg mass, laying rate, feed consumption (FC), and feed conversion ratio (FCR), as well as egg quality criteria when compared to the unsupplemented group. Additionally, adding zeolite at a level of 2 kg /m2 litter and 20 g/kg diet achieved the greatest enhancement in productive performance features. Therefore, it can be suggested that the greatest results were obtained in laying farms when zeolite was added as a litter addition and as a supplement to feed.

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.

Soil phosphorus availability is enhanced by nitrogen and litter addition during the growing season

Soil phosphorus availability is enhanced by nitrogen and litter addition during the growing season

Interaction of reed litter and biochar presences on performances of constructed wetlands

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions.

SAMM version 1.0: a numerical model for microbial- mediated soil aggregate formation

Abstract. Maintaining soil organic matter (SOM) is crucial for healthy and productive agricultural soils and requires understanding at the process level, including the role of SOM protection by soil aggregates and the connection between microbial growth and aggregate formation. We developed the Soil Aggregation through Microbial Mediation (SAMM) model, to represent this important connection. The pools of SAMM are fully measurable, and we calibrated and evaluated it against data from a long-term bare fallow experiment in a tropical sandy soil. This experiment received additions of plant litter of different compositions, which resulted in twice the soil carbon stocks in the best treatment compared to the control (about 8 vs. 4 t C ha−1 in 0–15 cm soil depth) after 25 years. As hypothesized, the SAMM model effectively represented the microbial growth response after the addition of litter and the subsequent formation and later destabilization of aggregates. The low correlations between different calibrated model parameters (r&lt;0.5 for all parameters; r&gt;0.4 for only 4 of 22) showed that SAMM is parsimonious. SAMM was able to capture differences between treatments in soil organic carbon (Nash–Sutcliffe modeling efficiency (EF) of 0.68), microbial nitrogen (EF of 0.24), and litter carbon (EF of 0.80). The amount of carbon within the aggregates (EF of 0.60) and in the free silt and clay fraction (EF of 0.24) was also simulated very well to satisfactorily. Our model results suggested that in spite of the sandy soil, up to 50 % of carbon stocks were stabilized through aggregate protection mechanisms; and that microbial and physical aggregate formation coexists. A version of the SAMM model without aggregate protection (SAMMnoAgg) initially failed to stabilize soil organic carbon (EF decreased to −3.68) and the simulation of microbial nitrogen worsened (EF of 0.13). By recalibrating SAMMnoAgg, it was possible to partially correct for the lack of aggregate protection by reducing the rate of mineral-attached carbon decomposition by about 85 % (EF of 0.68, 0.75, and 0.18 for SOC, litter carbon, and microbial nitrogen, respectively). However, the slightly better evaluation statistics of SAMM (e.g., Akaike information criterion of 5351 vs. 5554) suggest that representing aggregate dynamics in SOM models can be beneficial and necessary to understand the mechanism behind SOM dynamics. Our results indicate that current models without aggregate formation partly compensate for the absence of aggregate protection by lowering the turnover rates of other pools. Thus, they remain suitable options where data on aggregate associated carbon are not available.

Habitat selection and refuge-use by a color polymorphic salamander reveal behavioral niche differences.

Color polymorphic species provide an excellent opportunity to investigate the ecology and evolution of intraspecific niche differences. The red-backed salamander, Plethodon cinereus, is a fully terrestrial lungless salamander with two common color forms, striped and unstriped. Previous research suggests the morphs may be differentially adapted to surface and subsurface microhabitats, with the unstriped morph being more fossorial. This hypothesis predicts that the unstriped morph should be more sensitive to the risks of surface activity (e.g., thermal stress, dehydration, predation), and therefore be more selective than striped morphs when choosing soil surface microhabitats. To test this hypothesis, we experimentally manipulated leaf litter mass in small forest patches (~0.45 m2). Leaf litter addition reduced soil temperatures, buffered against changes in air temperature, and likely provided physical protection from predators. Over 3 years, we found that unstriped adults responded positively to leaf litter addition, but striped adults did not. In addition, unstriped morphs spent significantly more time in protective refuges (opaque, moistened tubes) than striped morphs in laboratory assays. Taken together, the field and laboratory results support the hypothesis that the unstriped morph is more sensitive to the risks of surface activity, and therefore is more likely to be fossorial. This difference in microhabitat use, combined with spatiotemporal variation in leaf litter accumulation on the forest floor, may play an important role in the maintenance of the polymorphism.

Tropical forest above‐ground productivity is maintained by nutrients cycled in litter

Abstract Tropical forest productivity represents an important global carbon sink, but many tropical forests grow on infertile soils. Efficient nutrient cycling by litterfall has long been assumed to maintain tropical tree growth, but there is no direct evidence that the nutrients cycled in litterfall are essential for tropical forest productivity. To test whether nutrient cycling by litterfall maintains tropical forest above‐ground productivity, we established large‐scale long‐term litter removal (L−) and litter addition (L+) treatments in a mature lowland tropical forest. We hypothesised that the removal of nutrients in litter would reduce tree growth, survival and litter production in L− plots. By contrast, the addition of nutrients in litter would enhance tree growth, survival and litter production in L+ plots. To test our hypotheses, we recorded tree growth and survival every 2 years, and measured litterfall monthly during 17 years of treatments. Tree growth and litterfall declined over time in L− plots, with consistently lower growth rates compared to controls after 8 years, and lower litter production after 4 years of treatments. By contrast, although litterfall was higher in the L+ plots relative to the controls, there was only a minor transient increase in tree growth immediately after the start of treatments. Tree survival declined over time in all treatments but was not affected by litter manipulation. The long‐term decline in tree growth and litterfall in the L− plots provides the first empirical evidence that nutrient cycling by litterfall plays a key role in maintaining above‐ground productivity in this tropical forest. By contrast, the transient increase in growth in the L+ plots can be attributed to the large inputs of nutrients with the addition of the entire litter standing crop at the start of treatments. The addition of nutrients in litter over the long term was nonetheless sufficient to enhance litter production, possibly by accelerating leaf turnover. Synthesis: Efficient nutrient cycling by litterfall makes an important contribution to the annual nutrient requirements of mature tropical forest trees, compensating for infertile soils. Disturbances that disrupt this finely balanced cycle could therefore reduce biomass carbon sequestration in tropical forests.

Evaluating long‐term introduction success of the Florida scrub endemic Crotalaria avonensis (Fabaceae) using a decade of demographic data

Introductions are a critical tool in the recovery of many imperiled species, yet adequate evaluation and development of best practices has lagged. Importantly, long‐term post‐introduction data are typically lacking, as well as suitable comparisons to wild populations to provide a baseline against which to assess performance. Here, we report on three experimental introductions of Crotalaria avonensis (Fabaceae), a federally endangered perennial herb that is narrowly endemic to scrub of the Lake Wales Ridge in peninsular Florida, U.S.A. We synthesize 10 years of post‐introduction monitoring at both the introduced and a nearby, protected wild population to (1) develop best practices for conservation, and (2) evaluate the success of the introduction. First, our study identified best practices that included using transplants propagated from stem cuttings, as well as several factors that may increase seed germination such as habitat choice, seed burial, and litter addition. Second, during the 10 years following the introduction, population density in the introduced population was higher than in a nearby protected, wild population, and a comparison of vital rates revealed that this result was due to relatively high clonal and seedling recruitment rates in the introduced population. Furthermore, the source population, which occurred on unprotected lands, precipitously declined during this time period, further highlighting the importance of safeguarding plants from that population. We report that a new, growing population of C. avonensis has been established to date, with important implications for the species' conservation as well as how introductions are evaluated.

Response of soil microbial necromass carbon to litter and root carbon inputs in a mid-subtropical Castanopsis carlesii plantation

Microbial necromass carbon (MNC) is a crucial source for stable soil carbon pool, and understanding its response to carbon inputs from both aboveground (litter) and belowground (roots) in subtropical forest soils is essential for assessing soil carbon stocks in global ecosystems. In a Castanopsis carlesii plantation at the Sanming Forest Ecosystem National Observation and Research Station in Fujian Province, we conducted an experiment with five treatments, including root removal (NR), aboveground litter removal (NL), no litter input (removals of both aboveground litter and roots, NI), double aboveground litter addition (DL), and control (CK). After seven years, we collected soil samples in the 0-10 cm soil layer to examine changes in MNC content and its contribution to soil organic carbon (SOC). Results showed that NR treatment reduced MNC, bacterial necromass carbon (BNC), and fungal necromass carbon (FNC) by 15.9%, 20.2%, and 14.5%, respectively, while other treatments did not induce significant changes. The NR, NL, NI, and DL treatments did not affect the contributions of BNC, FNC, and MNC to SOC. Correlation and path analyses revealed that litter and root carbon input treatments could alter the MNC content directly or indirectly through changing soil available substrates and microbial community structure. Our results suggested that roots exert a stronger influence on the maintenance of MNC than aboveground carbon source in the mid-subtropical plantations.

Jointly soil properties affect N and P uptakes and utilizations in Pinus tabuliformis Carr. and Quercus liaotungensis Koidz. subjected to growing media with decomposed litter

Monocultured pine plantation is suffering ecological degradation that is highly associated with low regeneration. Decomposed litter is an important soil amendment for enhancing regeneration through promoting nitrogen (N) and phosphorus (P) uptakes and utilizations. It is necessary to detect key soil attributes that contributed to this positive effect for regenerations in pine plantations. In this study, in-situ soils and litter were collected from local Chinese pine (Pinus tabuliformis Carr.) plantations (objective) and secondary forests dominated by Liaodong oak (Quercus liaotungensis Koidz.) (control). Soils were used for culturing one-year-old Chinese pine and Liaodong oak seedlings with a prolonged photoperiod in a greenhouse. Litter was composted with effective microorganisms and mixed to soils at ratios of 0% (control), 25%, and 50% (v/v). Compared to the control, the 25% ratio decreased shoot height and root-collar diameter, and the 50% ratio decreased the comprehensive seedling quality. Decomposed litter addition reduced shoot biomass and P content in pine seedlings and utilizations for N and P in both species. Multivariate linear regression indicated that high pH in growing media impaired root P content and biomass increments in shoot and root parts, and high organic matter content inhibited N content and concentration in shoots. Overall, the addition of decomposed litter resulted in overdoses of nutrient supply for both species. Our results contradict the argument that N and P released from decomposed litter are both beneficial for regenerations in plantations, neither did in secondary forests.

Limiting resources for soil microbial growth in climate change simulation treatments in the subarctic.

The microbial use of resources to sustain life and reproduce influences for example, decomposition and plant nutrient provisioning. The study of "limiting factors" has shed light on the interaction between plants and their environment. Here, we investigated whether carbon (C), nitrogen (N), or phosphorus (P) was limiting for soil microorganisms in a subarctic tundra heath, and how changes in resource availability associated with climate change affected this. We studied samples in which changes in resource availability due to climate warming were simulated by the addition of birch litter and/or inorganic N. To these soils, we supplied factorial C (as glucose), N (as NH4 NO3 ), and P (as KH2 PO4 /K2 HPO4 ) additions ("limiting factor assays," LFA), to determine the limiting factors. The combination of C and P induced large growth responses in all soils and, combined with a systematic tendency for growth increases by C, this suggested that total microbial growth was primarily limited by C and secondarily by P. The C limitation was alleviated by the field litter treatment and strengthened by N fertilization. The microbial growth response to the LFA-C and LFA-P addition was strongest in the field-treatment that combined litter and N addition. We also found that bacteria were closer to P limitation than fungi. Our results suggest that, under a climate change scenario, increased C availability resulting from Arctic greening, treeline advance, and shrubification will reduce the microbial C limitation, while increased N availability resulting from warming will intensify the microbial C limitation. Our results also suggest that the synchronous increase of both C and N availability might lead to a progressive P limitation of microbial growth, primarily driven by bacteria being closer to P limitation. These shifts in microbial resource limitation might lead to a microbial targeting of the limiting element from organic matter, and also trigger competition for nutrients between plants and microorganisms, thus modulating the productivity of the ecosystem.

Do earthworm and litter inputs promote decomposition or stabilization of cryoturnated organic matter from melted permafrost?

As global climate change progresses, Artic permafrost melts. Deeper layers of permafrost contain organic matter which can migrate into deeper soil by a process called cryoturbation. While this organic matter does not decompose in frozen soils, it decomposes rapidly in melting permafrost. Warming soils may experience increased litter input and earthworm colonization. The effects of litter addition and earthworm colonization on the decomposition and condition of permafrost remain unclear. This study used laboratory experiments to compare effects of willow litter (Salix caprea) addition and earthworm activity (Aporectodea caliginosa) on cryogenic organic matterfrom permafrost soils mixed in mineral soil and mineral soil itself. Respiration and stability of organic matter was monitored over two years with new litter added three times once litter in the soil with earthworms had disappeared from the soil surface. After a two-year period, treatments with litter addition and with earthworms alone showed increased system respiration, but effects were non-cumulative. The soil samples receiving earthworms showed higher proportions of organic matter stabilized in the mineral fraction by the end of the experiment. These preliminary lab results suggest that litter supply and earthworm colonization may both stabilize and speed up mineralization of organic matter released from melting permafrost.