Root Exclusion Research Articles

Temporal dynamics, drivers, and components of soil respiration in urban forest ecosystems

The objective of the study was to estimate the seasonal dynamics, the contribution of roots, litter, and soil microorganisms, as well as the primary drivers (soil moisture and temperature) of soil respiration (Rs) in urban forest ecosystems. Trenching and litter exclusion methods were used to distinguish root-derived (Rr) and litter-derived respiration (Rl) in soils of the Lomonosov Moscow State University (LMSU) Botanical Garden Arboretum, planted with Picea obovata (spruce) and Carpinus betulus (hornbeam). Measurements were taken every 1–2 weeks year round, as well as moisture (Θ10) and temperature (T10) of upper soil horizons (top 10 cm). The major factors affecting Rs were T10 throughout the year and Θ10 in summer. The results indicate that the contribution of Rr to Rs during the growing season on average for the spruce plantation was 34%, and for the hornbeam plantation was 38%. Our results indicated that trenching might significantly increase soil moisture, which could confound the results. The contribution of Rl to Rs on average during a year for the spruce plantation was 27%, and for the hornbeam plantation was 18%. Our data indicated a decrease in basal respiration due to litter and root exclusion in the hornbeam plantation. Year-round experiments have revealed that Rs, its temporal dynamics and drivers, as well as the contribution of individual components (roots, litter) are similar to the data obtained for natural forests. Thus, any climatic changes associated with urban development will affect the values of soil respiration similarly to natural forests. Also, the value of Rs will be influenced by manipulations carried out in urban environments, such as litter removal, the replacement of trees with lawns, and watering. Additionally, our data suggest the possibility of using such urban ecosystems as objects for research related to the carbon cycle.

Rapid root assimilation of added phosphorus in a lowland tropical rainforest of French Guiana

Tree growth on weathered soils in lowland tropical forests is limited by low phosphorous (P) availability. However, nutrient manupulation experiments do not always increase the P content in these trees, which raises the question whether trees are taking up added P. In French Guianese lowland rainforest, we measured changes in nitrogen (N) and P availability before and up to two months after N and P fertilizer addition, in soils with intact root systems and in soils where roots and mycorrhizal fungi were excluded by root exclusion cylinders. When the root system was excluded, P addition increased P availability to a much greater extent and for a longer time than in soils with an intact root system. Soil N dynamics were unaffected by root presence/absence. These results indicate rapid P uptake, but not N uptake, by tree roots, suggesting a very effective P acquisition process in these lowland rainforests.

Autotrophic and Heterotrophic Soil Respiration in Cryolithozone: Quantifying the Contributions and Methodological Approaches (The Case of Soils of the North of Western Siberia)

In the course of research performed in the continuous and discontinuous permafrost zone of the north of Western Siberia, the values of autotrophic (root) and heterotrophic (microbial) soil respiration and their ratio were estimated for typical ecosystems of the area. The data were obtained on the basis of a complex of field, laboratory, and calculation methods: shading, the root exclusion technique (comparison of emissions at similar sites with and without vegetation), the method of component integration or separate incubation, and the regression method. For soils of plateau palsa, the root contribution to total soil respiration was 16–30% with the use of the shading method and 14 ± 6% under the application of the component integration method. The contribution of root respiration was 60% for soils of shrub–green-moss pine forests and 30% for lichen pine forests. It may be assumed that, in forest ecosystems of the studied area, the contribution of root-derived respiration is even higher, which is related to the undercounting of respiration of tree roots and/or of rhizomicrobial microorganisms and priming effect by some methods. The contribution of root respiration in soils of mound palsa averaged 40%. For tundra with frost-boil ecosystems, the variation in the contribution of root respiration was 15–70%, depending on the location on microelements of cryogenic topography (boils and interboils). All the methods are characterized by disadvantages and some assumptions. These require additional studies to check or correct the data. The interpretation of the results is not always obvious. When using different techniques, similar results were obtained at a large number of replications of experiments during several seasons. The work also presents data on the absolute values of the specific root respiration for different species and size fractions, the value of the root biomass, and the microbial respiration of soils of different permafrost landscapes.

Contrasting Nitrogen Fertilisation Rates Alter Mycorrhizal Contribution to Barley Nutrition in a Field Trial.

Controlled environment studies show that arbuscular mycorrhizal fungi (AMF) may contribute to plant nitrogen (N) uptake, but the role of these near-ubiquitous symbionts in crop plant N nutrition under natural field conditions remains largely unknown. In a field trial, we tested the effects of N fertilisation and barley (Hordeum vulgare L.) cultivar identity on the contribution of AMF to barley N uptake using 15N tracers added to rhizosphere soil compartments. AMF were shown capable of significantly increasing plant 15N acquisition from root exclusion zones, and this was influenced by nitrogen addition type, N fertiliser application rate and barley cultivar identity. Our data demonstrate a previously overlooked potential route of crop plant N uptake which may be influenced substantially and rapidly in response to shifting agricultural management practices.

Root litter inputs exert greater influence over soil C than does aboveground litter in a subtropical natural forest

Changes in plant net primary production due to climate change can influence aboveground and belowground litter inputs to forest soils. We aim to examine the effects of such changes on soil carbon in subtropical forest ecosystems where these effects have not been thoroughly investigated. We manipulated aboveground litter inputs and excluded roots in a factorial design, and measured the effects of each treatment and their interactions on soil carbon (C) and soil microbial community structure. After only 3 years of treatment, aboveground litter addition and root exclusion respectively caused 9% and 21% reductions in soil C concentration in the 0–10 cm soil, likely through different mechanisms. The reduction of soil C with aboveground litter addition was attributed to a priming effect, while reduced root-derived C inputs were likely the cause of the C reduction associated with root exclusion. PLFA analysis showed that both aboveground and belowground litter manipulations reduced Gram-positive bacteria biomass (by 30%–58%) compare to the control, but only root exclusion significantly reduced the actinobacteria biomarkers (by 46%–58%). Fungi, arbuscular mycorrhizal fungi, and ratios of Gram-negative to Gram-positive bacteria and bacteria to fungi did not differ among treatments. Our results show that root-derived C inputs exert a stronger control on soil C concentrations and microbial community structures than aboveground litter does in subtropical natural forest soils. Our study also highlights that that both increases in aboveground litter and decreases in belowground C input to soil can lead to reduced soil C.

Plant roots increase both decomposition and stable organic matter formation in boreal forest soil

Boreal forests are ecosystems with low nitrogen (N) availability that store globally significant amounts of carbon (C), mainly in plant biomass and soil organic matter (SOM). Although crucial for future climate change predictions, the mechanisms controlling boreal C and N pools are not well understood. Here, using a three-year field experiment, we compare SOM decomposition and stabilization in the presence of roots, with exclusion of roots but presence of fungal hyphae and with exclusion of both roots and fungal hyphae. Roots accelerate SOM decomposition compared to the root exclusion treatments, but also promote a different soil N economy with higher concentrations of organic soil N compared to inorganic soil N accompanied with the build-up of stable SOM-N. In contrast, root exclusion leads to an inorganic soil N economy (i.e., high level of inorganic N) with reduced stable SOM-N build-up. Based on our findings, we provide a framework on how plant roots affect SOM decomposition and stabilization.

Sodium interception by xylem parenchyma and chloride recirculation in phloem may augment exclusion in the salt tolerant Pistacia genus: context for salinity studies on tree crops.

Working in tandem with root exclusion, stems may provide salt-tolerant woody perennials with some additional capacity to restrict sodium (Na) and chloride (Cl) accumulation in leaves. The Pistacia genus, falling at the nexus of salt tolerance and human intervention, provided an ideal set of organisms for studying the influences of both variable root exclusion and potentially variable discontinuities at the bud union on stem processes. In three experiments covering a wide range of salt concentrations (0 to 150mM NaCl) and tree ages (1, 2 and 10years) as well as nine rootstock-scion combinations we show that proportional exclusion of both Na and Cl reached up to ~85% efficacy, but efficacy varied by both rootstock and budding treatment. Effective Na exclusion was augmented by significant retrieval of Na from the xylem sap, as evidenced by declines in the Na concentrations of both sap and wood tissue along the transpiration stream. However, while we observed little to no differences between the concentrations of the two ions in leaves, analogous declines in sap concentrations of Cl were not observed. We conclude that some parallel but separate mechanism must be acting on Cl to provide leaf protection from toxicity specific to this ion and suggest that this mechanism is recirculation of Cl in the phloem. The presented findings underline the importance of holistic assessments of salt tolerance in woody perennials. In particular, greater emphasis might be placed on the dynamics of salt sequestration in the significant storage volumes offered by the stems of woody perennials and on the potential for phloem discontinuity introduced with a bud/graft union.

Interactive effects of soil warming, throughfall reduction, and root exclusion on soil microbial community and residues in warm-temperate oak forests

Soil microbes are both drivers and contributors of soil organic C (SOC) dynamics. However, information on how the multiple co-occurring environmental changes affecting microbial community and residues is unclear. Here, we measured phospholipid fatty acids and amino sugars (ASs) to explore how soil microbial community and residues changed under soil warming, throughfall reduction, root exclusion and their interactions in a natural deciduous broad-leaved oak forest. Soil warming significantly increased the Gram-positive to Gram-negative bacteria (G+/G−) ratio, and its interaction with root exclusion significantly reduced fungi-to-bacteria (F/B) ratio but stimulated the contributions of ASs to SOC (AS/SOC). Throughfall reduction also marginally increased G+/G− and AS/SOC, and suppressed F/B ratio. However, no interactive effects of soil warming and throughfall reduction on soil microbial community and residues were observed. Light fraction organic C and inorganic nitrogen were the key drivers in regulating the variation in the microbial community structure, and SOC was the controlling factor of microbial residue accumulations. Hence, soil C quality instead of water dominates the responses of microbial community structure and residues contribution to SOC to soil warming. Our results highlight the importance of soil substrate quality when predicting the terrestrial climate-C feedback.

Roots Mediate the Effects of Snowpack Decline on Soil Bacteria, Fungi, and Nitrogen Cycling in a Northern Hardwood Forest.

Rising winter air temperature will reduce snow depth and duration over the next century in northern hardwood forests. Reductions in snow depth may affect soil bacteria and fungi directly, but also affect soil microbes indirectly through effects of snowpack loss on plant roots. We incubated root exclusion and root ingrowth cores across a winter climate-elevation gradient in a northern hardwood forest for 29 months to identify direct (i.e., winter snow-mediated) and indirect (i.e., root-mediated) effects of winter snowpack decline on soil bacterial and fungal communities, as well as on potential nitrification and net N mineralization rates. Both winter snowpack decline and root exclusion increased bacterial richness and phylogenetic diversity. Variation in bacterial community composition was best explained by differences in winter snow depth or soil frost across elevation. Root ingrowth had a positive effect on the relative abundance of several bacterial taxonomic orders (e.g., Acidobacterales and Actinomycetales). Nominally saprotrophic (e.g., Saccharomycetales and Mucorales) or mycorrhizal (e.g., Helotiales, Russalales, Thelephorales) fungal taxonomic orders were also affected by both root ingrowth and snow depth variation. However, when grouped together, the relative abundance of saprotrophic fungi, arbuscular mycorrhizal fungi, and ectomycorrhizal fungi were not affected by root ingrowth or snow depth, suggesting that traits in addition to trophic mode will mediate fungal community responses to snowpack decline in northern hardwood forests. Potential soil nitrification rates were positively related to ammonia-oxidizing bacteria and archaea abundance (e.g., Nitrospirales, Nitrosomondales, Nitrosphaerales). Rates of N mineralization were positively and negatively correlated with ectomycorrhizal and saprotrophic fungi, respectively, and these relationships were mediated by root exclusion. The results from this study suggest that a declining winter snowpack and its effect on plant roots each have direct effects on the diversity and abundance of soil bacteria and fungal communities that interact to determine rates of soil N cycling in northern hardwood forests.

Soil net methane uptake rates in response to short-term litter input change in a coniferous forest ecosystem of central China

The uptake of CH4 by well-drained soil plays a vital role in mitigating the atmospheric CH4, but the impacts of shift in plant litter input on uptake of CH4 and the underlying mechanism are not fully understood. Here, we conducted in situ measurements of soil CH4 flux rates monthly throughout the year after the short-term litter input manipulations (i.e. Detritus Input and Removal Treatment-DIRT: control, CK; double litter, DL; no litter, NL; no roots, NR; and no aboveground litter and no roots, NRNL) in a coniferous forest (Platycladus orientalis (Linn.) Franco) ecosystem in subtropical China. The associated microclimates, soil properties and microbial PLFAs were also measured. Our results showed that soils acted as CH4 sink in all litter manipulation treatments, and the CH4 sink capacity significantly differed under litter manipulation treatments. Based on annual average values, net CH4 uptake rates decreased by 37.7 ± 4.9% and 41.7 ± 5.8% in the NL and NRNL treatments (i.e. litter layer removal), respectively, compared to the CK treatment. Thus, the net CH4 uptake induced by litter layer approximately accounted for 37.7 ± 4.9% of the total net CH4 uptake rate. The net CH4 uptake rate was not significantly influenced by the root exclusion (NR) treatment. In contrast, the effect of litter addition on net CH4 uptake rate was strongly depended on soil water content. During the dry season, litter addition did not significantly affect net CH4 uptake rate. In contrast, during the wet season, the net CH4 uptake rate decreased by 47.1 ± 4.9% in the DL treatment compared to the CK treatment. There was no significant difference in net CH4 uptake rate between dry and wet season under other litter input manipulation treatments. The net CH4 uptake rate was positively correlated with the abundance of methanotrophic bacteria across all litter input manipulation treatments, whereas the significant negative relationship between net CH4 uptake rate and water filled pore space (WFPS) was only found in the DL treatment. Overall, our results suggest that aboveground organic layer (i.e. litter) is more important in regulating the soils acting as atmospheric CH4 sink than roots, while the regulating function primarily depends on soil dry/wet conditions and the abundance of methanotrophic bacteria.

Bioaccumulation and Effects of Aluminium on Plant Growth in Three Culture Plants Species

Aluminium toxicity is one of the major factors that limit plant growth and development in many acid soils, by multiple, and still poorly understood mechanisms. In this paper, the aluminium content determinations were done through atomic absorption spectrometry method, on seedlings of three culture plants, Helianthus annuus L. (sunflower), Sinapis alba L. (white mustard) and Triticum aestivum L. (wheat), grown in hydroponic conditions with different aluminium concentrations (50, 100 and 250 mg/kg) expose. AAS data were correlated with biometrical determinations (shoot length and dry biomass) and leaf pigments concentration assessment. Results emphasize that none of the selected species accumulates aluminium in aboveground organs such as shoots and leaves, indicating that root exclusion and/or sequestration are the strategies employed by all three species for limiting aluminium toxicity. In all three studied species, both average shoot length and dry biomass tended to be lower at higher aluminium concentration. Due to high variations among seedlings grown at the same aluminium concentration expose, these differences are not statistically significant. In sunflower seedlings, chlorophyll a and carotenoids had maximum values at the highest aluminium concentration (250 mg/kg), while chlorophyll b was more abundant at 100 mg/kg. In mustard, all pigments had their maximum concentrations at 100 mg/kg, while in wheat, an aluminium concentration increase progressively lead to a drop in pigments concentration.

Effect of organic matter manipulation on the seasonal variations in microbial composition and enzyme activities in a subtropical forest of China

Purpose The aim of this study was to determine the impacts of reduced aboveground and belowground C inputs on the community composition of soil microbes and enzyme activities in a seasonal context. Materials and methods Litterfall removal, root exclusion, and stem girdling treatments under a subtropical conifer plantation growing on a coarse texture of sandy soil in southeast China were employed. One year after the initiation of the treatments, we measured the soil microbial biomass, community composition, and enzyme activities, including hydrolytic and oxidative extracellular enzymes on a seasonal basis. Soil inorganic N, dissolved organic C and N, and available P were also determined. Results and discussion Seasonal variations of soil microbial composition and enzyme activities were attributed to soil temperature and moisture and soil nutrient availability. Girdling treatments significantly increased the abundances of gram-negative bacteria and actinomycetes in winter when soil temperature, moisture, and available nutrients were at the lowest level among the four seasons. Girdling alone and girdling combined with litter removal and root trenching significantly decreased the cellobiohydrolase, β-glucosidase, β-1,4-N-acetylglucosaminidase, and acid phosphatase activities in autumn. These hydrolytic enzyme activities were significantly correlated with soil moisture, NH4+, DOC, and available P. We also found a significant relationship between hydrolytic enzyme activities and the ratio of gram-positive to gram-negative bacteria. Conclusions Plant belowground C allocation, soil temperature, and moisture drove the seasonal patterns of soil microbial composition and enzyme activities. Labile C input by root exudates is a key determinant of ecosystem functions mediated by soil microbes such as microbial decomposition processes.

Roots, mycorrhizal fungi and altitude as determinants of litter decomposition and soil animal communities in tropical montane rainforests

This study assesses the importance of root- and mycorrhiza-derived resources for decomposition processes and as food resources for microarthropod communities along an altitudinal gradient of tropical montane rainforests in southern Ecuador. At 1000, 2000 and 3000 m microcosms with openings of different mesh sizes (4 mm, 45 μm) or closed were exposed in the field, manipulating accessibility by roots and mycorrhizal fungi. The microcosms contained undisturbed soil with a mixture of leaf litter from three abundant plant species from the site at which the microcosms were exposed. After 12 months water content, microbial biomass, remaining litter mass, C-to-N ratio and the soil microarthropod community structure were analysed. Water content and C-to-N ratio were lower and microbial biomass was highest at the lowest altitude, while litter decomposition and microarthropod abundance were at a maximum at the intermediate altitude. Exclusion of roots and mycorrhizal fungi did not affect litter decomposition, but decreased the abundance and diversity of Oribatida, while the abundance of Collembola increased in closed microcosms. The effect of root and mycorrhizal exclusion on all investigated parameters did not differ between the three altitudes. The results indicate that in nutrient limited tropical montane rainforests mycorrhizal fungi suppress the activity of other microorganisms, potentially competing for litter-derived resources, at each of the investigated altitudes. Collembola benefitted from this reduced competition while Oribatida strongly depended on root-derived resources.

Soil Respiration Components and their Temperature Sensitivity Under Chemical Fertilizer and Compost Application: The Role of Nitrogen Supply and Compost Substrate Quality

AbstractUnderstanding autotrophic (Ra) and heterotrophic (Rh) components of soil respiration (Rs) and their temperature sensitivity (Q10) is critical for predictingsoil carbon (C) cycle and its feedback to climate change. In agricultural systems, these processes can be considerably altered by chemical fertilizer and compost application due to changes in nitrogen (N) supply and substrate quality (decomposability). We conducted a field experiment including control, urea, and four compost treatments. Ra and Rh were separated using the root exclusion method. Composts were characterized by chemical analyses, 13C solid‐state nuclear magnetic resonance, and lignin monomers. Annual cumulative Ra, along with root biomass, increased with soil mineral N, while Rh was suppressed by excessive N supply. Thus, Ra was stimulated but Rh was decreased by urea alone application. Annual Rh was increased by application of compost, especially that containing most lignin vanillyl and syringyl units, O‐alkyl C, di‐O‐alkyl C, and manganese. However, during the initial period, Rh was most effectively stimulated by the compost containing most carbohydrates, lignin cinnamyl units, phenolic C, and calcium. Ra was mediated by N release from compost decomposition and thus exhibited similar responses to compost quality as Rh. The Rh Q10 was reduced, while Ra Q10was increased by chemical fertilizer and compost application. Moreover, the Rh Q10 negatively related to soil mineral N supply and compost indicators referring to high substrate quality. Overall, our results suggest that N supply and substrate quality played an important role in regulating soil C flux and its response to climate warming.

Soil respiration from winter wheat-based cropping systems in the US Southern Great Plains as influenced by tillage managements

ABSTRACTThis study compared soil respiration (SR) fluxes from winter wheat-based cropping systems in the US Southern Great Plains (SGP) under reduced and conventional tillage. The study consisted of four sets of paired paddocks assigned to conventional or reduced tillage with a four-year crop rotation applied over time. During the 2016–2017 study year, four sets of paired paddocks were planted to: winter wheat managed for grazing, dual-purpose (grazing and grain production), and grain-only systems of production, and winter canola. Heterotrophic SR fluxes were measured using a plant and root exclusion method on eight permanently deployed PVC cores per paddock. Fluxes from the cores were measured manually using a closed chamber connected to an infrared gas analyser on 12–13 dates during the winter wheat growing season (October through May). There were strong seasonal patterns of SR flux, with lower rates during dry and cold periods, and higher rates during warm and wet periods. Large rainfall induced pulses of SR flux were observed for both tillage systems. There was no consistent large-scale difference in SR flux between tillage treatments applied to paired paddocks. Results from this study indicate SR fluxes from winter wheat-based cropping systems are controlled more by soil environmental conditions than form of tillage.

Environmental and Vegetative Controls on Soil CO2 Efflux in Three Semiarid Ecosystems

Soil CO2 efflux (Fsoil) is a major component of the ecosystem carbon balance. Globally expansive semiarid ecosystems have been shown to influence the trend and interannual variability of the terrestrial carbon sink. Modeling Fsoil in water-limited ecosystems remains relatively difficult due to high spatial and temporal variability associated with dynamics in moisture availability and biological activity. Measurements of the processes underlying variability in Fsoil can help evaluate Fsoil models for water-limited ecosystems. Here we combine automated soil chamber and flux tower data with models to investigate how soil temperature (Ts), soil moisture (θ), and gross ecosystem photosynthesis (GEP) control Fsoil in semiarid ecosystems with similar climates and different vegetation types. Across grassland, shrubland, and savanna sites, θ regulated the relationship between Fsoil and Ts, and GEP influenced Fsoil magnitude. Thus, the combination of Ts, θ, and GEP controlled rates and patterns of Fsoil. In a root exclusion experiment at the grassland, we found that growing season autotrophic respiration accounted for 45% of Fsoil. Our modeling results indicate that a combination of Ts, θ, and GEP terms is required to model spatial and temporal dynamics in Fsoil, particularly in deeper-rooted shrublands and savannas where coupling between GEP and shallow θ is weaker than in grasslands. Together, these results highlight that including θ and GEP in Fsoil models can help reduce uncertainty in semiarid ecosystem carbon dynamics.

Molecular-level changes in soil organic matter composition after 10 years of litter, root and nitrogen manipulation in a temperate forest

With climate change, forests are expected to receive increased inputs of carbon (C) and nitrogen (N) but it is unclear how this will modify forest C cycling and storage at the molecular-level. To investigate the response of forest soil organic matter (SOM) to changes in soil inputs, a study area was established in a Michigan hardwood forest as part of the Detrital Input and Removal Treatments (DIRT) network. Experimental treatments were comprised of both exclusions of detrital inputs (No Litter, No Roots, No Inputs) and additions of C and N (Double Litter, N-Addition, Double Litter + N, Wood). After 10 years of treatment, the soils were characterized using elemental analysis, molecular biomarker techniques, nuclear magnetic resonance spectroscopy, and microbial biomass C measurements. Although manipulation of detrital inputs did not significantly change the soil C and N content after 10 years, alterations in the cycling and distribution of SOM components were observed. Root exclusion enhanced SOM degradation, while doubling litter favoured the degradation of more labile forms of soil C such as unsaturated n-alkanoic acids and simple sugars. N-Addition and Double Litter + N increased the concentrations of extractable biomarkers, including aliphatic and cyclic lipids and compounds derived from cutin, suberin, and lignin. Microbial biomass C also varied with experimental litter input manipulations and N addition, and these data were consistent with the observed changes in SOM composition. Overall, the observed shifts in SOM chemistry after 10 years of manipulating ecosystem inputs highlight the sensitivity of natural systems to changes in amounts of C and N inputs from roots and litter, and N inputs from external sources.

Shifts in soil organic carbon dynamics under detritus input manipulations in a coniferous forest ecosystem in subtropical China

The underlying mechanism of how shifts in plant detritus input impact soil organic carbon (SOC) dynamics is not fully understood. Here we investigated the soil C content in different fractions (aggregates, labile and recalcitrant pool) after two years of detritus input manipulations (i.e. detritus input and removal treatment–DIRT: control, CK; double litter, DL; no litter, NL; no roots, NR; no aboveground litter and no roots, NRNL) in a coniferous forest (Platycladus orientalis (Linn.) Franco) ecosystem in subtropical China. The root exclusion treatments (NR and NRNL) significantly decreased the macro-aggregate (>2000 μm) fraction by 23.4%–27.7% compared to CK after two-year detritus input manipulation, and accordingly decreased the C content in macroaggregates. In contrast, the aboveground litter removal and addition (DL and NL) did not significantly impact those properties. Labile SOC significantly declined in the detritus removal treatments, while recalcitrant SOC remained relatively stable. In addition, root exclusion significantly reduced total microbial biomass and most of the taxonomic biomarkers compared to the CK. Fungal biomass were positively correlated with the proportion of macroaggregates across treatments. Principal component analysis revealed the separation of root exclusion treatments from the other detritus input manipulations was based on lower soil C content and proportion of macroaggregates. Overall, our results suggest that future shifts in plant detritus input, especially decreases in belowground litter inputs, can strongly and rapidly reduce SOC pools by reducing the proportion of macroaggregates and the C content in macroaggregates, highlighting the importance of root in regulating soil C sequestration in response to future climatic scenarios.

Partitioning soil respiration: quantifying the artifacts of the trenching method

Total soil respiration (Rt) is a combination of autotrophic (Ra) and heterotrophic respiration (Rh). Root exclusion methods, such as soil trenching, are often utilized to separate these components. This method involves severing the rooting system surrounding a plot to remove the Ra component. However, soil trenching has potential limitations including (1) reduced water uptake in trenched plots that increases soil water content, which is one of the environmental controllers of Rt in many ecosystems, and (2) increased available carbon substrate for Rh caused by recently severed dead roots. We present a methodology that utilizes a bayesian modeling framework to quantify the magnitude of artifacts from a large trenching manipulation experiment. Thus methodology corrects Rh and Ra observations at daily to seasonal time scales. This study finds that the artifacts, due to recently severed roots, persist over a 2 years study period and the artifacts due to altered soil moisture had the greatest impact during drought conditions.

Local root status: a neglected bio-factor that regulates the home-field advantage of leaf litter decomposition

The ‘home-field advantage (HFA) hypothesis’ predicts a litter-field affinity effect on litter decomposition. In terrestrial ecosystems, plant roots have comprehensive roles in regulating litter-decomposer interactions, yet their potential influences on HFA remain unsolved. To fill this gap, we conducted a litter transplant experiment in a subtropical forest, and tested whether roots affect litter-field affinity via interactions with soil microbial functions. Leaf litters of Quercus variabilis and Pinus massoniana were incubated at their conspecific-dominated and heterospecific-dominated forests. Root-specific incubation microcosms were manipulated by using a series of root ingrowth cores to control the access of living fine roots. Entire exclusion of roots led to a significant suppression of HFA, and the affinity effect was amplified under a medium root constraint treatment (by 0.5 mm mesh). Incubation field (‘home’ vs. ‘away’) generally had a positive effect on litter mineralization when roots were present, and roots became more influential after 9 months than 3 months of incubation. Although microbial enzymatic functions and their impact on litter N loss depended on root status, they were not associated with incubation field. Our findings advocate that a moderate amount of local roots is essential for HFA in leaf litter decomposition, and taking account of root-mediated species-specific bio-interactions will advance our understanding of native litter- home field affinity.