AimsGlobal change threatens ecosystem functions, including those driven by soil fauna. In temperate forests, soil nutrients, litter quality, and microarthropods are essential players during litter decomposition. However, the impact of nutrient enrichment on the functional role of soil fauna remains poorly understood.MethodsWe used a full factorial experiment to test the effects of nitrogen (N), phosphorus (P), and potassium (K) addition on litter decomposition through changes in soil conditions and litter quality. We incubated senesced leaves from fertilized and unfertilized control plots in litter bags with two different mesh sizes that included (2 mm) or excluded (45 mu m) microarthropods. We assessed the interactive effects of nutrient addition and litter quality on microarthropod-driven decomposition using linear mixed-effects models.ResultsNutrient addition was a stronger predictor than litter quality for organic matter remaining in litter bags over time. While N addition strongly influenced litter quality, it did not affect microarthropod activity in decomposition. P addition suppressed decomposition when microarthropods were present but enhanced it when microarthropods were absent. K strongly influenced litter quality and regulated the effects of phosphorus on decomposition.ConclusionsMicroarthropods may promote decomposition under conditions of limited nutrient availability in both litter and soil, potentially enhancing microbial activity. The responses of fungi and microbes to nutrient enrichment may explain the relatively modest effect of microarthropods on decomposition. Our study shows that nutrient enrichment in temperate forests may limit microarthropod participation in decomposition by possibly altering microsite conditions or affecting the availability of alternative food resources, thereby influencing carbon fluxes.

Summary Leaf decomposition varies widely across temperate forests, shaped by factors like litter quality, climate, soil properties, and decomposers, but forest heterogeneity may mask local tree influences on decomposition and litter‐associated microbiomes. We used a 24‐yr‐old common garden forest to quantify local soil conditioning impacts on decomposition and litter microbiology. We introduced leaf litter bags from 10 tree species (5 arbuscular mycorrhizal; 5 ectomycorrhizal) to soil plots conditioned by all 10 species in a full‐factorial design. After 6 months, we assessed litter mass loss, C/N content, and bacterial and fungal composition. We hypothesized that (1) decomposition and litter‐associated microbiome composition would be primarily shaped by the mycorrhizal type of litter‐producing trees, but (2) modified significantly by underlying soil, based on mycorrhizal type of the conditioning trees. Decomposition and, to a lesser extent, litter‐associated microbiome composition, were primarily influenced by the mycorrhizal type of litter‐producing trees. Interestingly, however, underlying soils had a significant secondary influence, driven mainly by tree species, not mycorrhizal type. This secondary influence was strongest under trees from the Pinaceae. Temperate trees can locally influence underlying soil to alter decomposition and litter‐associated microbiology. Understanding the strength of this effect will help predict biogeochemical responses to forest compositional change.

In grapevine, metabolic activity of absorptive roots changes rapidly as roots age but it is unclear whether nearby microbial assemblages shift as well. Here, we investigated whether first-order root age affects bacterial and fungal variation adjacent to the root surface, and whether root age should be integrated into future studies on root functional traits and associated microbes. We hypothesized that microbial diversity and composition would differ between young (≤11 days old) and old (11.5 to 40 days old) first-order roots due to expected differences in metabolism over the root lifespan (i.e., higher metabolism in young roots). Overall, we found that microbial composition was distinct between young and old absorptive roots, with stronger evidence at the phylum and amplicon sequence variant (ASV) taxonomic levels for fungi ( P = 0.003 and P = 0.038, respectively) than bacteria ( P = 0.082 and P = 0.129, respectively). Furthermore, we identified differentially abundant fungal and bacterial ASVs in young and old roots that related to expected differences in root function, including instances of microbes previously described as copiotrophs more abundant adjacent to young roots and microbes described as oligotrophs and saprotrophs more abundant adjacent to old roots. In contrast to the distinct shifts in microbial composition, there was little evidence of shifts in α diversity (i.e., observed ASVs and Shannon diversity) between young and old roots. Our study suggests that future work on the impacts of root functional traits on localized microbial composition may improve results interpretation and reduce some variation by accounting for root age at sampling.

Root-associated microbial communities are increasingly recognized as key contributors to plant function, but we still understand little about the factors driving interactions between microbes and individual roots. To have thorough understanding of this system, we must consider the immense functional and spatial heterogeneity of roots within complex root systems. In this Viewpoint, we describe a prototype study in which we map and analyze root-associated microbial communities throughout a woody root system. Our efforts demonstrate how spatially explicit sampling yields unique insights into the relative importance of factors structuring root-associated microbial communities.

While the invasive spotted lanternfly, Lycorma delicatula (White) [Hemiptera: Fulgoridae], continues to expand its range in the United States, there remains a knowledge gap regarding the economic threat that this pest presents to forest ecosystems and production nurseries. L. delicatula uses several common hardwood trees as hosts and a previous study found that short-term feeding can reduce growth of young maple saplings. Herein, long-term feeding over 4 consecutive seasons significantly reduced diameter growth and below-ground starch storage in roots of young silver maples (Acer saccharinum L.), weeping willows (Salix babylonica L.), river birches (Betula nigra L.), and trees of heaven (Ailanthus altissima [Mill.] Swingle) in response to L. delicatula feeding pressure in a density-dependent manner. In Year 3 when feeding pressure was the lowest, silver maple and willow recovered with greater diameter growth than in Year 2. Nutrients essential for photosynthesis and growth (iron, sulfur, and phosphorus) were reduced in leaves of all tree species compared to controls in the second year. This 4-yr study represents a worst-case scenario in which L. delicatula fed on the same trees for 4 consecutive growing seasons. In the wild, population numbers can vary greatly from year to year on individual trees and they move frequently among hosts (until autumn when they settle on A. altissima or other late-season hosts that have not yet senesced). Thus, we would not expect negative impacts of unconfined L. delicatula in natural settings on forest or ornamental trees to be as marked as reported here.

Soil microbial communities are key drivers of ecosystem processes and can be strongly affected by soil properties. While the effects of soil texture and aggregate have been well studied, the effect of rock fragment content (RFC) on soil microbial communities is still poorly understood, particularly in arid ecosystem. We examined the re-sponses of soil microbial biomass and communities to RFC gradients using a randomized block experiment with four RFCs (0 %, 25 %, 50 % and 75 %, V/V) and four planting treatments (Artemisia vestita, Bauhinia brachycarpa, Sophora davidii and no plants) in Minjiang arid valley. We explored soil community composition identified by total phospholipid fatty acids, and edaphic properties after two growth seasons. In most of current planting treatments, total phospholipid fatty acids, bacteria, saprotrophic fungi and arbuscular mycorrhizal fungi significantly decreased under 50-75 % RFCs versus 0-25 % RFCs. Compared to non-planted treatment, plants prominently increased soil microbial biomass and altered microbial communities only in 75% RFC. The ratio of gram-positive bacteria to gram-negative bacteria remarkably reduced in 75 % RFC of non-planted treatment, while significantly decreased in soil with 0 % RFC beneath A. vestita and S. davidii. These variations in soil microbial communities could be explained by the changes in soil water content, available nitrogen, total phosphorus and plant biomass allocation to fine root. These results indicated that both moderate and high RFC conditions inhibited soil microbial development, while plant can promote microbial biomass in high RFC by improving edaphic physiochemical properties and alleviating environmental stresses. Moreover, soil water content and nutrient levels explained much of the variation in soil microbial communities in these stony soils.

Plant species identity influences soil microbial communities directly by host specificity and root exudates, and indirectly by changing soil properties. As a native pioneer species common in early successional communities, Masson pine (Pinus massoniana) forests are widely distributed in subtropical China, and play a key role in improving ecosystem productivity. However, how pine forest composition, especially the dominance of plant functional groups, affects soil microbial diversity remains unclear. Here, we investigated linkages among woody plant composition, soil physicochemical properties, and microbial diversity in forests along a dominance gradient of Masson pine. Soil bacterial and fungal communities were mainly explained by woody plant community composition rather than by woody species alpha diversity, with the dominance of tree (without including shrub) species and ectomycorrhizal woody plant species accounting for more of the variation among microbial communities than pine dominance alone. Structural equation modeling revealed that bacterial diversity was associated with woody plant compositional variation via altered soil physicochemical properties, whereas fungal diversity was directly driven by woody plant composition. Bacterial functional groups involved in carbohydrate and amino acid metabolism were negatively correlated with the availability of soil nitrogen and phosphorus, whereas saprotrophic and pathogenic fungal groups showed negative correlations with the dominance of tree species. These findings indicate strong linkages between woody plant composition than soil microbial diversity; meanwhile, the high proportion of unexplained variability indicates great necessity of further definitive demonstration for better understanding of forest–microbe interactions and associated ecosystem processes.

Among the contributors to soil CO2 efflux, there remains uncertainty about the contribution of root activity to the overall soil efflux. Soil water and temperature frequently have been used to predict a large portion of the variation in soil CO2 efflux. We hypothesized that fine-root dynamics explain most of the remaining variability in soil CO2 efflux that cannot be explained by soil temperature and water content. We anticipated that seasonal increases in root production, mortality via decomposition, and standing crop would result in corresponding increases in soil CO2 efflux. We tested our hypotheses by collecting and analyzing two years of minirhizotron and soil chamber CO2 flux data from plots distributed throughout the Shale Hills Catchment of the Susquehanna-Shale Hills Critical Zone Observatory in Central Pennsylvania, USA. Here we showed that: (1) seasonal fluctuations in fine-root dynamics yielded only a very small increase in the predictability of soil CO2 efflux; (2) fine-root mortality effects on soil CO2 efflux were strongly tied to soil temperature; (3) fluctuations in fine-root presence or standing mass independent of temperature and moisture had little effect on soil CO2 efflux; and (4) new fine-root length and root length mortality had limited impacts on soil CO2 efflux rates. We conclude that, at least in temperate forests on rocky soils, characterizing fine-root dynamics may provide only limited improvement in the estimation of soil CO2 efflux.

Traditionally, fine roots were grouped using arbitrary size categories, rarely capturing the heterogeneity in physiology, morphology and functionality among different fine root orders. Fine roots with different functional roles are rarely separated in microbiome-focused studies and may result in confounding microbial signals and host-filtering across different root microbiome compartments. Using a 26-year-old common garden, we sampled fine roots from four temperate tree species that varied in root morphology and sorted them into absorptive and transportive fine roots. The rhizoplane and rhizosphere were characterized using 16S rRNA gene and internal transcribed spacer region amplicon sequencing and shotgun metagenomics for the rhizoplane to identify potential microbial functions. Fine roots were subject to metabolomics to spatially characterize resource availability. Both fungi and bacteria differed according to root functional type. We observed additional differences between the bacterial rhizoplane and rhizosphere compartments for absorptive but not transportive fine roots. Rhizoplane bacteria, as well as the root metabolome and potential microbial functions, differed between absorptive and transportive fine roots, but not the rhizosphere bacteria. Functional differences were driven by sugar transport, peptidases and urea transport. Our data highlights the importance of root function when examining root-microbial relationships, emphasizing different host selective pressures imparted on different root microbiome compartments.

Aims Complex topography, a common feature of forested areas, generates unique environmental gradients that may shape root dynamics in unexpected ways. Nevertheless, belowground studies rarely capture the environmental gradients imposed by complex topography, such as those found along hillslopes. This begs the question: how much information is lost when complex topography is ignored? Hillslope is a common aspect of complex topography with landscape features that impact water flow, sediment transfer, and water and nutrient storage. We hypothesized that soil water content would have a nonlinear impact on fine-root production, mortality, standing crop, and turnover. Specifically, we expected increased mortality and decreased production, root standing crop, and turnover at the driest and wettest regions of the hillslope. Methods Using minirhizotron observations from 150 tubes located at 50 sites strategically placed at different hillslope positions across a first-order catchment, we examined how position along a hillslope impacts fine root dynamics. Results Contrary to our hypotheses, we found no significant hillslope effects on fine root tip production or mortality. Root tip turnover, however, was higher at drier than wetter regions of the hillslope. Additionally, fine root standing crop length was higher in wetter topographic regions. Conclusions Considering fine root tip turnover and length standing crop in combination with previous research on fine root lifespan suggest two distinct strategies of trees in root deployment along a hillslope: temporal avoidance in drier regions of a landscape (midslope planar and ridgetops) and extended survival of roots in wetter, deeper-soil regions like valley floor and swales.

Spatiotemporal heterogeneity in soil CO2 efflux (FS) underlies one of our greatest gaps in understanding global carbon (C) cycles. Though scientists recognize this heterogeneity, FS sampling schemes often average across spatial heterogeneity or fail to capture fine temporal heterogeneity, and many ecosystem models assume flat terrain. Here, we test the idea that simple, remotely sensible terrain variables improve regression models of spatiotemporal variation in FS. We used automatic chambers that, for the first time, capture FS in complex temperate forest terrain at fine temporal resolution with 177,477 hourly FS measurements at 8 locations from ridgetop to valley along planar and swale hillslopes, across three years ranging from dry to record wet precipitation. In two of these years, we measured FS weekly at 50 additional locations distributed across the 8-ha catchment. Growing season Fs estimates were 1.25 times greater when sampling hourly versus weekly. At ridgetops, growing season FS increased by an average of 463 gC m−2 180 day−1 (75.9

The rhizosphere is a nexus for plant-microbe interactions and, as a host-structured environment, a location of high activity for distinct microbes and plant species. Although our insights into this habitat have exploded in recent years, we are still limited in our ability to answer key questions about the specificity of these root-microbial relationships. In particular, it can be difficult to confirm or reject microbiome heritability in many plant systems and to pinpoint which microbial taxa are key to plant functioning. Like other host-structured environments, the rhizosphere is structurally, chemically, and biologically complex, driven largely by differences in root anatomy, location, and function. In this Correspondence, we describe a review of 377 "rhizosphere microbiome" research papers and demonstrate how matching a sampling method to the biological question can advance our understanding of host-microbe interactions in a functionally heterogeneous environment. We found that the vast majority of studies (92%) pool all roots from a root system during sampling, ignoring variation in microbial composition between roots of different function and limiting insight into key root-microbial relationships. Furthermore, approaches for removing root-associated microbes are highly variable and non-standard, complicating multi-study analyses. Our understanding of the strength and nature of host-microbe relationships in heterogenous host-microbiome environments can be clarified by targeting sampling to locations of high interaction. While the high complexity of the rhizosphere creates logistical challenges, we suggest that unambiguous language and refined approaches will improve our ability to match methods to research questions and advance our understanding of the specificity of plant-microbial interactions.

In vineyards, cover crops typically grow concurrently with grapevines and can impart a multitude of agroecosystem services; yet concerns over potential disservices might limit adoption. Reductions in yield and vegetative growth are key disservices of concern, but at sites with high soil resources, reducing excessive vegetative growth is often considered beneficial, if the yield is not strongly penalized. To optimize agroecosystem services provided by cover crops, it is crucial to examine above- and belowground plant responses over multiple years. Documentation of the responses of fruit crop root systems to cover crops may clarify potential benefits for long-term agroecosystem services associated with aboveground growth and soil resources. In 2016, we established a perennial grass under young vines (full floor cover) to examine if agroecosystem services imparted by an under-vine cover crop change in the first five years of vineyard production and depend on rootstock vigor. Overall, cover crop reduced grapevine vegetative growth between 13% and 30% across all years and with a trend of more substantial reductions in the first two years. In contrast, yield was reduced in only three of the five years, between 9% and 25%, depending on the rootstock. Furthermore, neither cover crop nor differences in rootstock vigor resulted in relevant or consistent changes in fruit chemistry during the study. Overall, we found that in a relatively fertile, young vineyard, combining a lower vigor rootstock with a perennial, under-vine cover crop imparts substantial agroecosystem services in comparison to the more common practices of using a medium vigor rootstock and spraying herbicide under the vines. These services included improved crop load (ratio of fruit to vegetative mass), increased soil phosphorus availability, increased deep soil water content, and presumably lower labor and other costs associated with vineyard maintenance. Studies on a decadal timescale are needed to further clarify whether these services persist, accumulate with time, or if competition from the cover crop eventually leads to unacceptable decreases in vine nutrient status, growth, and production.

Belowground biodiversity loss from anthropogenic causes is far less addressed and quantified than aboveground biodiversity loss. Soil fauna supports soil productivity and biogeochemical cycles, and their decline needs further research. We tested the effects of a woodland harvest gradient (0, 30, 50, and 70% biomass removal) on litterfall, mesofauna density, and Oribatida diversity in three sites of northwestern Patagonia (Argentina). Sites contrasted in plant community structure and productivity. Acari from litter and soil were compared. Annual litter production showed a 58% decline at the highest harvest intensity level, which was constant across sites. Litter structural α- diversity decreased with the highest intensity harvest only at the high productivity site. The density of soil-inhabiting Acari did not change with increasing harvest intensity, while the density of Acari inhabiting the litter decreased by 65% at the highest harvest intensity. Within Acari, Oribatida inhabiting the litter had the most significant density decline with increasing harvest intensity. Oribatida richness and α- diversity only differed among sites, suggesting resistance to increasing biomass removal despite shifts in litter production and litter structural diversity. Prostigmata did not respond to increasing biomass removal either in soil or litter. Our study is the first to assess Acari response to an aboveground biomass removal gradient in southern woodlands. Applying high biomass removal to low productivity sites can compromise micro detritivore density and thus, impair its functional role. Site productivity should be considered in management plans entailing conservation of soil fauna in southern woodlands.

Woodlands are pivotal to carbon stocks, but the process of cycling C is slow and may be most effective in the biodiverse root zone. How the root zone impacts plants has been widely examined over the past few decades, but the role of the root zone in decomposition is understudied. Here, we examined how mycorrhizal association and macroinvertebrate activity influences wood decomposition across diverse tree species. Within the root zone of six predominantly arbuscular mycorrhizal (AM) (Acer negundo, Acer saccharum, Prunus serotina, Juglans nigra, Sassafras albidum, and Liriodendron tulipfera) and seven predominantly ectomycorrhizal (EM) tree species (Carya glabra, Quercus alba, Quercus rubra, Betula alleghaniensis, Picea rubens, Pinus virginiana, and Pinus strobus), woody litter was buried for 13 months. Macroinvertebrate access to woody substrate was either prevented or not using 0.22 mm mesh in a common garden site in central Pennsylvania. Decomposition was assessed as proportionate mass loss, as explained by root diameter, phylogenetic signal, mycorrhizal type, canopy tree trait, or macroinvertebrate exclusion. Macroinvertebrate exclusion significantly increased wood decomposition by 5.9%, while mycorrhizal type did not affect wood decomposition, nor did canopy traits (i.e., broad leaves versus pine needles). Interestingly, there was a phylogenetic signal for wood decomposition. Local indicators for phylogenetic associations (LIPA) determined high values of sensitivity value in Pinus and Picea genera, while Carya, Juglans, Betula, and Prunus yielded low values of sensitivity. Phylogenetic signals went undetected for tree root morphology. Despite this, roots greater than 0.35 mm significantly increased woody litter decomposition by 8%. In conclusion, the findings of this study suggest trees with larger root diameters can accelerate C cycling, as can trees associated with certain phylogenetic clades. In addition, root zone macroinvertebrates can potentially limit woody C cycling, while mycorrhizal type does not play a significant role.

Spotted lanternfly (SLF; Lycorma delicatula White; Hemiptera: Fulgoridae) invaded the US from Asia and was first detected in 2014; currently, populations have established in 14 states primarily in the Northeast and Mid-Atlantic. It feeds voraciously on phloem sap from a broad range of host plants, with a preference for tree of heaven (Ailanthus altissima [Sapindales: Simaroubaceae]), grapevines (Vitis spp. [Vitales: Vitaceae]), and several common hardwood tree species. We evaluated the impacts of fourth instars and adults confined to a single branch or whole trees on gas exchange attributes (carbon assimilation [photosynthetic rate], transpiration and stomatal conductance), selected nutrients, and diameter growth using young saplings of four host tree species planted in a common garden. In general, the effects of adults on trees were greater than nymphs, although there was variation depending on tree species, pest density, and time post-infestation. Nymphs on a single branch of red maple (Acer rubrum [Sapindales: Sapindaceae]), or silver maple (Acer saccharinum [Sapindales: Sapindaceae]) at three densities (0, 15, or 30) had no significant effects on gas exchange. In contrast, 40 adults confined to a single branch of red or silver maple rapidly suppressed gas exchange and reduced nitrogen concentration in leaves; soluble sugars in branch wood were reduced in the fall for silver maple and in the following spring for red maple. Fourth instars confined to whole silver maple trees reduced soluble sugars in leaves and branch wood, and reduced tree diameter growth by >50% during the next growing season. In contrast, fourth instars in whole tree enclosures had no effects on black walnut (Juglans nigra [Fagales: Juglandaceae]). SLF enclosed on tree of heaven at 80 adults per tree suppressed gas exchange after two weeks of feeding, but did not alter non-structural carbohydrates, nitrogen concentrations, or tree growth. Results suggest that moderate to heavy feeding by SLF on young maple saplings may impair tree growth, which could have implications for production nurseries and forest managers.

Additional file 1: Table of publications selected for review using “rhizosphere microbiome” search terms.

Vertical root segregation can be a key underpinning of species co-existence through below-ground niche partitioning but has rarely been tested in diverse forest communities. We randomly sampled > 4000 root samples from 625 0-30 cm soil profiles in a subtropical forest in China to determine the degree of vertical root segregation among 109 woody species and rooting plasticity in response to edaphic heterogeneity and root neighbours. Over 85% of species were predominantly distributed in the 0-10 cm soil zone, exhibiting low and inconsistent rooting plasticity in response to either edaphic heterogeneity or root neighbours. There was no evidence of vertical root segregation among co-occurring species. Contrastingly, the increase of one species’ root abundance tended to increase, but not reduce other species’ root abundance within soil zones. These findings suggest that interspecific differentiation of resource acquisition strategies might be more important than root segregation in mediating species co-existence in diverse forests.

Aims Root traits associated with resource foraging, including fine-root branching intensity, root hair and mycorrhiza, may change in soils with various physical structure indicated by rock fragment content (RFC), while how these traits covariate at the level of individual root branching order is largely unknown.Methods We subjected two xerophytic species, Artemisia vestita (subshrub) and Bauhinia brachycarpa (shrub), to increasing RFC gradients (0%, 25%, 50% and 75%, v v-1) in an arid environment and measured fine-root traits related to resource foraging.Results Root hair density and mycorrhizal colonization of both species decreased with increasing root order, but increased in 3rd- and 4th-order roots at high RFCs (50% or 75%). The two species tend to produce more root hairs than mycorrhizas under the high RFCs. For both species, root hair density and mycorrhizal colonization intensity were negatively correlated with root length and root diameter. Rockiness reduced root branching intensity in both species comparing with rock-free soil. At the same level of RFC, A. vestita had thicker roots and lower branching intensity than B. brachycarpa, and tended to produce more root hairs.Conclusion Our results suggest the high RFC soil conditions stimulated greater foraging functions in higher root orders. We found evidence for a greater investment in root hairs and mycorrhizal symbioses as opposed to building an extensive root system in rocky soils. The subshrub and shrub species took different approaches to foraging in the rocky soil through distinctive trait syndromes of fine-root components.

Root lifespan, often is estimated in landscape- and ecosystem-level carbon models using linear approximations. In water manipulation experiments, fine root lifespan can vary with soil water content. Soil water content is generally structured by complex topography, which is largely unaccounted for in landscape- and ecosystem-scale carbon models. Topography governs the range of soil water content experienced by roots which may impact their lifespan. We hypothesized that root lifespan varied nonlinearly across a temperate, mesic, forested catchment due to differences in soil water content associated with topographic position. We expected regions of the landscape that were too wet or too dry would have soils that were not optimal for roots and thus result in shorter root lifespans. Specifically, we hypothesized that root lifespan would be longest in areas that consistently had soil water content in the middle of the soil water content spectrum, while in soils at either very low or very high soil water content, root lifespan would be relatively short. We tested this hypothesis by collecting and analyzing two years of minirhizotron and soil moisture data in plots widely distributed in the Shale Hills catchment of the Susquehanna-Shale Hills Critical Zone Observatory in Pennsylvania. We found that fine root lifespans were longer in traditionally wetter topographic regions, but detected no short term (biweekly) effect of soil moisture on root lifespan. Additionally, depth in soil, soil series, slope face orientation, and season of birth strongly affected root lifespans across the catchment. In contrast, lifespan was unaffected by root diameter or mycorrhizal association. Failure to account for these variables could result in erroneous estimates of fine root lifespan and, consequentially, carbon flux in temperate forested regions.