Belowground Root Research Articles

Evaluating Burn Severity and Post-Fire Woody Vegetation Regrowth in the Kalahari Using UAV Imagery and Random Forest Algorithms

Accurate burn severity mapping is essential for understanding the impacts of wildfires on vegetation dynamics in arid savannas. The frequent wildfires in these biomes often cause topkill, where the vegetation experiences above-ground combustion but the below-ground root structures survive, allowing for subsequent regrowth post-burn. Investigating post-fire regrowth is crucial for maintaining ecological balance, elucidating fire regimes, and enhancing the knowledge base of land managers regarding vegetation response. This study examined the relationship between bush burn severity and woody vegetation post-burn coppicing/regeneration events in the Kalahari Desert of Botswana. Utilizing UAV-derived RGB imagery combined with a Random Forest (RF) classification algorithm, we aimed to enhance the precision of burn severity mapping at a fine spatial resolution. Our research focused on a 1 km2 plot within the Modisa Wildlife Reserve, extensively burnt by the Kgalagadi Transfrontier Fire of 2021. The UAV imagery, captured at various intervals post-burn, provided detailed orthomosaics and canopy height models, facilitating precise land cover classification and burn severity assessment. The RF model achieved an overall accuracy of 79.71% and effectively identified key burn severity indicators, including green vegetation, charred grass, and ash deposits. Our analysis revealed a >50% probability of woody vegetation regrowth in high-severity burn areas six months post-burn, highlighting the resilience of these ecosystems. This study demonstrates the efficacy of low-cost UAV photogrammetry for fine-scale burn severity assessment and provides valuable insights into post-fire vegetation recovery, thereby aiding land management and conservation efforts in savannas.

Rice Under Dry Cultivation–Maize Intercropping Improves Soil Environment and Increases Total Yield by Regulating Belowground Root Growth

Under the one-season-a-year cropping pattern in Northeast China, continuous cropping is one of the main factors contributing to the degradation of black soil. Previous studies (on maize–soybean, maize–peanut, and maize–wheat intercropping) have shown that intercropping can alleviate this problem. However, it is not known whether intercropping is feasible for maize and rice under dry cultivation, and its effects on yield and soil fertility are unknown. A three-year field-orientation experiment was conducted at Jilin Agricultural University in Changchun city, Jilin Province, China, consisting of three cropping regimes, namely rice under dry cultivation–maize intercropping (IRM), sole rice under dry cultivation (SR), and sole maize (SM). All straw was fully returned to the field after mechanical harvesting. Rice under dry cultivation–maize intercropping with a land-equivalent ratio of 1.05 (the average of three years values) increased the total yield by 8.63% compared to the monoculture system. The aggressivity (A), relative crowding coefficient (K), time–area-equivalent ratio (ATER), and competition ratio (CR) value were positive or ≥1, also indicating that the rice under dry cultivation–maize intercropping had a yield advantage of the overall intercropping system. This is because the intercropped maize root length density (RLD) increased by 33.94–102.84% in the 0–40 cm soil layer, which contributed to an increase in the soil porosity (SP) of 5.58–10.10% in the 0–30 cm soil layer, an increase in the mean weight diameter of soil aggregates (MWD) of 3.00–15.69%, an increase in the geometric mean diameter of soil aggregates (GMD) of 8.16–26.42%, a decrease in the soil bulk density (SBD) of 4.02–7.35%, and an increase in the soil organic matter content (SOM) of 0.60–4.35%. This increased the water permeability and aeration of the soil and facilitated the absorption of nutrients and water by the root system and their transportation above ground, and the plant nitrogen, phosphorus, and potassium accumulation in the intercropping system were significantly higher than that in monoculture treatment, further promoting the total yield of intercropping. This suggests that rice under a dry cultivation–maize intercropping system is feasible in Northeast China, mainly because it promotes belowground root growth, improves the soil environment, and increases the total yield of intercropping.

Effects of Grazing on Plant Diversity and Their Carbon Stocks in Different Types of Grasslands

With the drying and warming of the climate and irrational grazing, various types of grasslands in Inner Mongolia have been degraded to different degrees, and different management modes will inevitably affect the plant diversity and vegetation carbon stock of soil grasslands. To clarify the changes and influencing factors of plant diversity and carbon stock in different types of grasslands under different management modes, plant species composition, aboveground biomass, and vegetation carbon were analyzed based on 18 sentinel monitoring stations across three different types of grasslands in Inner Mongolia. The results showed that grazing increased the dominance of typical grassland and desert grassland, whereas meadow grassland decreased, and the evenness index and Shannon Wiener diversity index increased less in meadow grassland and desert grassland. Grazing decreased graminaceous biomass in meadow grassland and typical grassland, whereas it increased in desert grassland. Above-ground vegetation and below-ground root carbon stocks were much higher than those in grazing areas, 1.5 and 1.2 higher, respectively, but vegetation carbon stocks in long-term grazing sites were significantly lower than those in short-term grazing. Further, the structural equations showed that the effects of geographic location, climatic factors, and soil factors on the biomass and vegetation carbon stocks of the three grassland types differed significantly. The results can provide a reference for the ecologically sustainable development of grassland and the optimization of management mode.

Phenotyping Alfalfa (Medicago sativa L.) Root Structure Architecture via Integrating Confident Machine Learning with ResNet-18.

Background: Root system architecture (RSA) is of growing interest in implementing plant improvements with belowground root traits. Modern computing technology applied to images offers new pathways forward to plant trait improvements and selection through RSA analysis (using images to discern/classify root types and traits). However, a major stumbling block to image-based RSA phenotyping is image label noise, which reduces the accuracies of models that take images as direct inputs. To address the label noise problem, this study utilized an artificial intelligence model capable of classifying the RSA of alfalfa (Medicago sativa L.) directly from images and coupled it with downstream label improvement methods. Images were compared with different model outputs with manual root classifications, and confident machine learning (CL) and reactive machine learning (RL) methods were tested to minimize the effects of subjective labeling to improve labeling and prediction accuracies. Results: The CL algorithm modestly improved the Random Forest model's overall prediction accuracy of the Minnesota dataset (1%) while larger gains in accuracy were observed with the ResNet-18 model results. The ResNet-18 cross-population prediction accuracy was improved (~8% to 13%) with CL compared to the original/preprocessed datasets. Training and testing data combinations with the highest accuracies (86%) resulted from the CL- and/or RL-corrected datasets for predicting taproot RSAs. Similarly, the highest accuracies achieved for the intermediate RSA class resulted from corrected data combinations. The highest overall accuracy (~75%) using the ResNet-18 model involved CL on a pooled dataset containing images from both sample locations. Conclusions: ResNet-18 DNN prediction accuracies of alfalfa RSA image labels are increased when CL and RL are employed. By increasing the dataset to reduce overfitting while concurrently finding and correcting image label errors, it is demonstrated here that accuracy increases by as much as ~11% to 13% can be achieved with semi-automated, computer-assisted preprocessing and data cleaning (CL/RL).

Light Intensity: A Key Ecological Factor in Determining the Growth of Pseudolarix amabilis Seedlings

The notable absence of juvenile Pseudolarix amabilis trees in forest understories suggests their vulnerability to ecological niche competition, leading to limited survival prospects. This study examines the key factors limiting the growth of P. amabilis seedlings by investigating the effects of five ecological factors: light intensity, rainfall, groundwater level, soil type, and type of fertilization, on the growth of one-year-old P. amabilis seedlings. Our results demonstrate that increasing the light intensity promotes plant growth by augmenting the leaf count, leaf biomass, plant height, stem biomass, root biomass, and total biomass. Further analysis reveals that increased light intensity influences biomass allocation, reducing the specific leaf area and leaf–stem biomass ratio, and favoring root and stem growth over leaf investment. Rainfall, groundwater level, fertilization type, and rhizosphere soil type primarily influence root growth by impacting the soil’s physicochemical properties. Specifically, rising groundwater levels lower the soil temperature and increase the soil moisture, total potassium content, and soil pH, leading to reductions in root biomass, plant height, net height increment, leaf number, and total biomass. When groundwater levels reach 21 cm and 28 cm, submerging the surface soil layer, root biomass decreases by 1.6 g/plant (−51.6%) and 2.3 g/plant (−74.2%), respectively. Further analysis reveals a gradual decrease in the root–shoot ratio above the 14 cm groundwater level, while the specific leaf area and leaf–stem biomass ratio remains unaffected, indicating stronger belowground root stress compared to aboveground stem and leaf components. The results highlight light intensity as the key ecological factor determining the growth of P. amabilis seedlings. These findings underscore the importance of considering light intensity in the management of natural stands, the cultivation of artificial forests, and the nursery cultivation of endangered P. amabilis.

Imaging tree root systems using ground penetrating radar (GPR) data in Brazil

Trees sequester carbon dioxide from the atmosphere through photosynthesis, storing it in branches, stems, and roots, where the belowground carbon fraction, approximately ¼ of the total amount, exhibits significant interspecies root biomass variability. Estimating the amount of carbon stored in tree roots of different species is key to understanding an important aspect of climate change and exploring how natural forests, urban tree planting policies, and reforestation projects might help to address it. In this context, one of the most prominent Non-Destructive Testing methods capable of estimating the diameter and length of roots at different depths is ground penetrating radar (GPR). It has been widely used for geological, archaeological, and geotechnical studies due to its accuracy in locating buried material in different contexts, although standards for the correct management of datasets related to belowground root systems are still been developed. This paper reports a GPR signal processing flow to estimate the root diameter of three species of tropical forest trees, and to demonstrate the method’s viability, a dataset was collected in a study area with a 900 MHz shielded antenna. A multi-stage data processing flow is then presented, including raw data, file format conversion, zero-time adjustment, background removal, signal gain, Stolt FK migration, and time-to-depth conversion with hyperbolic adjustment velocity. The resulting data were converted from true amplitude data to a trace envelope. High amplitudes on the envelope section, with lateral continuity in parallel sections, were interpreted as roots. However, the interpretation of outcomes encounters notable complexities, primarily attributable to the intricate nature of subsurface root architectures, the soil matrix characterized by significant clay content, and the co-occurrence of buried materials proximate to the arboreal subjects. Consequently, amplitudes discerned within ground penetrating radar (GPR) 2D sections necessitate cautious interpretation, as they are not immediately indicative of subsurface roots. To overcome this difficulty, this study used direct measurements of the roots in the field, to confirm the GPR data. Despite these complexities, the study demonstrates GPR’s efficacy, particularly in the uppermost soil layer-a pivotal carbon reservoir with a 96% correlation (R2) between GPR-derived coarse-root diameter estimates and field measurements.

Insect root feeders incur negative density-dependent damage across plant species in an alpine meadow.

Although herbivores are well known to incur positive density-dependent damage and mortality, thereby likely shaping plant community assembly, the response of belowground root feeders to changes in plant density has seldom been addressed. Locally rare plant species (with lower plant biomass per area) are often smaller with shallower roots than common species (with higher plant biomass per area) in competition-intensive grasslands. Likewise, root feeders are often distributed in the upper soil layers. We hypothesized, therefore, that root feeders would incur negative density (biomass)-dependent damage across plant species. To test this hypothesis, we investigated the diversity and abundance of plant and root feeder species in an alpine meadow and determined the diet of the root feeders using metabarcoding. Across all species, root feeder load decreased with increasing aboveground plant biomass, root biomass, and total plant biomass per area, indicating a negative density dependence of damage across plant species. Aboveground plant biomass per area increased with increasing individual plant biomass and root depth per area across species, suggesting that rare plant species were smaller in size and had shallower root systems compared to common plant species. Both root biomass per area and root feeder biomass per area decreased with soil depth, but the root feeder biomass decreased disproportionately faster compared to root biomass with increasing root depth. Root feeder load decreased with increasing root depth but was not correlated with the feeding preference of root feeder species. Moreover, the prediction derived from a random process incorporating vertical distributions of root biomass and root feeder biomass significantly accounted for interspecific variation in root feeder load. In conclusion, the data indicate that root feeders incur negative density-dependent damage across plant species. On this basis, we suggest that manipulative experiments should be conducted to determine the effect of the negative density-dependent damage on plant community structure and that different types of plant-animal interactions should be concurrently examined to fully understand the effect of plant density on overall herbivore damage across plant species.

Land-use legacies affect the composition and distribution of tree species and their belowground functions in a succession from old-field to mature temperate forest

Forests undergoing ecological succession following abandonment from agricultural use (i.e., old fields) are ubiquitous in temperate regions of the U.S. and Europe. Ecological succession in old fields involves changes in vegetation composition influenced by factors such as land-use history, soil conditions, and dispersal limitations. Species’ behavioral, morphological, physiological and life-history attributes influence the outcomes of environmental and biotic filters on distribution and abundance. However, many studies have focused on aboveground attributes, while less attention has been placed on belowground species characteristics that influence community assembly and function. In this study, we used a trait-based approach to examine how aboveground plant composition and distribution vary with plant root functional traits (e.g., mycorrhizal association) that mediate access for nutrients such as nitrogen (N) and phosphorous (P). We inventoried every tree stem (n ​= ​11,551) in a 10-ha forested area containing old-field and historical forests and matched every species with root functional traits (n ​= ​33) from established databases. We found that land-use history influences community composition and distribution in old-field forests, which also varied with belowground root functional traits. Community composition in old-field forests, which were dominated by Acer saccharum and non-native species, were largely associated with arbuscular mycorrhizae (AM) and higher root nutrient concentrations. On the other hand, community composition in historical forests – largely dominated by Tsuga canadensis – were associated with ectomycorrhiza (EcM) and more variation of root length and depth. These results suggest that changes in aboveground communities have implications for belowground ecosystem services (e.g., nutrient cycling) which are important to forest ecosystem development. Trait-based approaches can elucidate mechanisms of community assembly, and understanding how traits influence species coexistence and interactions can inform management decisions related to biodiversity conservation and restoration efforts in disturbed or altered forests.

Quantification of maize brace root formation after vertical stalk displacement.

Maize brace roots develop from aboveground stem nodes in both upright and vertically displaced stalks. The cues that trigger brace root development after displacement are unknown. Possibilities include disturbance of the belowground roots, gravity, moisture, physical interaction, or node anatomical changes. We show that brace root formation occurs at all growth stages, with more nodes producing brace roots when plants are displaced at later growth stages. This occurs with the underground roots intact, without moisture accumulation and without physical interaction. We propose that the formation of brace roots after vertical stalk displacement is most likely due to gravity or anatomical changes at the node.

What drives carbon stocks in a mangrove forest? The role of stand structure, species diversity and functional traits

Mangrove forests provide a variety of ecosystem services, and among them, the ability to sequester large quantities of below-ground carbon reservoirs is considered the most critical service for mitigating climate change. Therefore, most mangrove studies are highly concerned with estimating ecosystem carbon stocks, while only a few studies have focused on the factors driving these carbon stocks. Thus, we examined the role of stand structure, species diversity, and functional traits on above-ground, below-ground, and total carbon stocks using data from 28 sample plots from the low salinity zone of the Sundarbans mangrove forest of Bangladesh. We also aimed to understand the distribution patterns of carbon stocks among different components of the ecosystem, such as above-ground, below-ground soil, and roots. The study results revealed that tree height, diameter at breast height (DBH), and basal area were highly correlated with both above-ground (AGC) and below-ground carbon (BGC, incuding soil carbon at 0–50 cm depth) stocks. Multiple regression models indicated that tree height and basal area were two significant positive predictors for AGC, BGC and total carbon stocks (TCS) (p < 0.05). Species richness and community-weighted mean wood density were significant positive predictors for BGC and TCS. In contrast, Simpson diversity and community-weighted mean specific leaf area negatively influenced BGC. Furthermore, we observed that the above-ground tree carbon (AGTC = 80.4 ± 32.0 Mg ha−1) was significantly higher than below-ground soil carbon to 50 cm depth (BGSC-50 cm = 41.0 ± 5.4 Mg ha−1), followed by below-ground root carbon (BGRC = 37.1 ± 10.1 Mg ha−1), pneumatophore (Pneu_C = 28.8 ± 18.8 Mg ha-1), and downed wood (DW = 0.03 ± 0.02 Mg ha−1) (p < 0.05). In terms of specific species contribution, Heritiera fomes contributed the most to AGTC and BGRC, followed by other species such as Avicennia officinalis > Excoecaria agallocha > Sonneratia apetala > Xylocarpus mekongensis > Bruguiera sexangula. Our findings indicate that maintaining dominant trees (H. fomes) and a diverse stand can be an effective way to enhance carbon stocks in a mangrove ecosystem.

Impacts of aboveground litter and belowground roots on soil greenhouse gas emissions: Evidence from a DIRT experiment in a pine plantation

Plant detritus alteration may influence soil greenhouse gas emissions, but the direction, extent and mechanisms remain uncertain. Here we conducted a DIRT (Detritus Input and Removal Treatment) experiment in a Pinus sylvestris var. mongolica plantation in Saihanba (Hebei Province, China), manipulating aboveground litter (L-: litter removal, L: normal litter, L+: litter doubling) and belowground roots (R-: root removal, R: with root) resulting in six treatments. We measured CO2, N2O, and CH4 fluxes during 2019 and 2020 growing seasons, along with soil physicochemical, enzymatic and microbial variables. Our findings revealed that soil CO2 and N2O emissions increased with litter input, while CH4 uptake decreased. The absence of roots decreased soil CO2 emission and CH4 uptake but increased N2O emission. Aboveground litter enhanced the carbon cycling variables, such as extractable organic carbon (EOC), the ratio of soil extractable organic carbon to extractable total nitrogen (EOC:ETN), soil carbon mineralization rate (Cmin), and peroxidase activity (PER), resulting in increased CO2 emission. In contrast, the absence of roots increased the nitrogen cycling variables, such as soil extractable total nitrogen (ETN), nitrate nitrogen content (NO3−-N), the ratio of soil extractable organic carbon to extractable total nitrogen (EOC:ETN), soil net nitrogen mineralization rate (Nmin), and the abundance of ammonia-oxidizing bacteria (AOB), leading to increased N2O emission. Moreover, soil CH4 uptake was mainly influenced by soil microclimate: aboveground litter input reduced CH4 uptake by lowering soil temperature, while belowground roots benefited CH4 uptake via reducing soil moisture by water uptake. Taken together, our study suggests that soil CO2, N2O, and CH4 emissions (or uptake) are influenced by both aboveground and belowground plant inputs through various pathways. While aboveground litter input promotes the emissions of greenhouse gasses, the mitigating effect of belowground roots on N2O and CH4 partially offsets the increment of CO2 emission in this plantation.

High temperature can improve the performance of invasive plants by facilitating root growth.

The ever-increasing temperatures of the Anthropocene may facilitate plant invasions. To date, studies of temperature effects on alien plants have mainly focused on plant aboveground traits but ignored belowground roots, which may hinder our predictions of plant invasion risks under climate change. The temperature effects on the root growth dynamics of two alien shrubs, invasive Mimosa sepiaria and naturalized Corchorus capsulari, were studied through a 3D transparent growth system under five temperature treatments (18/13°C - 34/29°C), which cover the present and future warming scenario temperature distributions in China. We measured the dynamics of both root depth and width growth in response to temperature treatments across time (84 days). We also investigated the intraspecies and interspecies competitions of the two alien species along the temperature gradient by planting two individuals together. Both M. sepiaria and C. capsularis showed optimum shoot growth in the middle-temperature treatment, whereas M. sepiaria exhibited the fastest root growth under the highest temperature treatment (34/29°C), and the root growth of C. capsularis persistently decreased as temperature increased. Root depth growth was more susceptible than root width to neighbor competition pressure in both species. Compared to C. capsularis, M. sepiaria had relatively stronger intraspecies and interspecies competition advantages with increasing temperature, possibly because high temperature improved root growth. These results suggest that temperature increases can improve the performance of alien plants by facilitating the groth of their underground root widths and depths, which deserves serious concern in future invasion risk management. This article is protected by copyright. All rights reserved.

Nitrogen addition and mowing had only weak interactive effects on macronutrients in plant-soil systems of a typical steppe in Inner Mongolia

Effective management of macronutrients is pivotal in the optimization and provisioning of ecosystem services in grassland areas, particularly in degraded grasslands. In such instances where mowing and nitrogen (N) fertilization have emerged as predominant management strategies, nutrient management is especially important. However, the precise effects of these concurrent practices on the distribution of macronutrients in plant-soil systems remain unclear. Here we evaluated the effects of 12 years of N addition (2, 10, and 50 g N m−2 year−1) and mowing on the concentrations and pools of six macronutrients (i.e., N; phosphorus P; sulfur S, calcium Ca, magnesium Mg, and potassium K) in three plant components (aboveground plants, litter, and belowground roots) at the community level and in the soil in a typical steppe in Inner Mongolia. Our results revealed that N addition generally raised the N concentration in the entire plant-soil system, regardless of whether plots were mowed. Higher N addition (10 and 50 g N m−2 year−1) also led to higher concentrations of P (+22%, averaging two N addition rates), S (+16%), K (+22%), Ca (+22%), and Mg (+24%) in plants but lower concentrations of these nutrients in the litter. Similar decreases in K (−9%), Ca (−46%), and Mg (−8%) were observed in the roots. In light of the observed increases in vegetation biomass and the lack of pronounced changes in soil bulk density, we found that the ecosystem N enrichment resulted in increased pools of all measured macronutrients in plants, litter, and roots (with the exception of Ca in the roots) while concurrently decreased the pools of P (−20%, averaging two higher N addition rates), S (−12%), K (−10%), Ca (−37%), and Mg (−19%) in the soil, with no obvious effect of the mowing practice. Overall, mowing exhibited a very limited capacity to alleviate the effects of long-term N addition on macronutrients in the plant-soil system. These findings highlight the importance of considering the distribution of macronutrients across distinct plant organs and the dynamic nutrient interplay between plants and soil, particularly in the context of long-term fertilization and mowing practices, when formulating effective grassland management strategies.

Relationships between root exudation and root morphological and architectural traits vary with growing season.

Plants allocate a substantial amount of C belowground for root exudates and for the construction and adjustment of root morphological and architectural traits. What relationships exist between root exudates and other root traits and these relationships change with growing season, however, remain unclear. We quantified the root exudation rate and root morphological traits, including total root length (RL), total root surface area (RS), root diameter (RD), specific root length (SRL), specific root area (SRA) and root tissue density (RTD), and architectural traits, such as branching intensity (BI), and investigated their associations during the rapidly growing season (April and August) and the slowly growing season (December) of three common native tree species, Liquidambar formosana, Michelia maudiae and Schima superba, in subtropical China. We found that the linkages of RD, SRL, SRA, RTD and BI did not change with the growing season, reflecting their highly conservative relationships. The root exudation rate varied significantly with growing season (P<0.05) and produced various associations with other root traits at different growing seasons. During the rapidly growing season (i.e., April), the exudation rate was the highest and was positively correlated with RL. The exudation rate was the lowest during the slowly growing season (i.e., December) and was negatively associated with RL, RS and RTD. Our findings demonstrate the seasonality of the linkages of root exudation rate with other root traits, which highlights the highly plastic and complex associations of belowground root traits. These findings help to deepen our understanding of plant nutrient acquisition strategies.

Enhancing maize yield through understanding the novel shoot-root interaction in morphology among hybrids with dense planting

ContextUnderstanding the shoot-root characteristics and their interaction of maize is essential to break the constraints of the densification process and improve grain yield. ObjectiveThe objective of the work was to study the interaction between the above-ground canopy and below-ground root system in morphology and its relationship to grain yield in dense planting with different hybrids. MethodsThis study conducted a 2-yr field experiment with three modern hybrids (JNK728, ZD958 and XY335) at the Wuqiao Experimental Station in Northern China. ResultsAmong hybrids, XY335 attained the highest grain yield of 14,886.9 kg hm−2 in 2019 and 10,078.8 kg hm−2 in 2020 with a density of 7.5 × 104 plants hm−2. For the shoot at the silking stage (R1), the lowest leaf orientation value for both middle and upper leaves and ear-to-height ratio among three hybrids were found in XY335 with the compact plant phenotype. Meanwhile, the highest photosynthesis rate of ear leaves (33.0 umol m2˙s−1) at R1 was also observed in XY335. At physiological maturity (R6), the above-ground dry matter (AGDM) was 4.6%− 10.4% higher in XY335 than the other two hybrids. For the root system at both R1 and R6 with the density of 7.5 × 104 plants hm−2, the highest value for root system indicators in morphology such as root total length (RL), root surface area (RSA), root volume (RV) was observed in XY335. From R1 to R6, RL, RSA and RV in XY335 averaged 24,749.6 cm, 3486.8 cm2, 51.5 cm3, 1.3–14.6% higher than JNK728, and 10.2–23.9% higher than ZD958, respectively. Furthermore, the lower senescence of the root system was also observed in XY335, with a 22.0–32.1% lower decrease from R1 to R6 in RL, RSA, and RV compared with the other two hybrids. ConclusionsFor the shoot-root interaction, per unit decrease in morphology indicator in the root per plant with density increase of XY335 accompanied with more AGDM accumulation and thus higher grain yield. ImplicationsThe observations on shoot-root characteristics and their interaction from this study are essential to selecting a hybrid that allows a better adaptation to planting at high density, developing an effective management strategy, and breeding high-density tolerant hybrids.

Root Architecture of Forage Species Varies with Intercropping Combinations

Belowground root systems under pasture intercropping exhibit complex interactions, and the root interactions of different intercropping combinations are still poorly understood. Therefore, in this work, two perennial and annual herbages were intercropped in pairs and evaluated at a ratio of 1:1. The root morphology and topological structure differed significantly with intercropping combinations. (1) Compared with other cropping patterns, the mean root diameter (RD) of intercropped alfalfa (Medicago sativa L.) and common vetch (Vicia sativa L.) increased notably. The root surface area (RSA), root volume (RV), and mean RD increased significantly when oat (Avena sativa L.) was intercropped with alfalfa. Similarly, the RSA and RV increased in intercropped oat, intercropping relative to monocropping. (2) The forage topological index of the intercropping system was close to one, which was close to that of the herringbone branching. Additionally, the intercropping system had a lower intensity of underground root competition. The root system of the different forage intercropping combinations tended to transition to dichotomous branching. (3) The correlations between root parameters differed according to forage species. Therefore, different intercropping combinations had different belowground root levels of competitiveness and interactions, thereby changing the resource competition environment.

Analysis on the transpiration response of Japanese cedar (Crytomeria fortunei) and influencing factors after expansion of moso bamboo (Phyllostachys edulis)

Moso bamboo (Phyllostachys edulis) expansion into adjacent forests has been reported to alter the local water cycle. Transpiration is the most important component of the water budget. However, the changes in transpiration within Japanese cedar forests following moso bamboo expansion, as well as the primary factors driving these changes, remain unclear. In this study, we conducted an investigation in a mixed plantation of Japanese cedar and moso bamboo, a pure Japanese cedar forest, and a Japanese cedar forest after the removal of moso bamboo, from July 2017 to June 2018. We measured leaf area index (LAI), root biomass (Root), and sap flow density (Js). The annual transpiration of Japanese cedar significantly decreased from 521.48 mm in the pure Japanese cedar forest to 293.34 mm in the mixed plantation of Japanese cedar and moso bamboo. Likewise, the leaf area index decreased from 5.26 to 3.96, and the root biomass decreased from 252.78 g/m2 to 160.24 g/m2. In Japanese cedar forest, the transpiration in summer (189.47 mm) is greater than the sum of transpiration in autumn and winter (143.36 mm). The partial least squares path modeling (PLS-PM) analysis demonstrated that the decrease in root biomass was the direct cause of the reduced transpiration, while the decrease in leaf area index primarily led to the decline in root biomass. The results imply that the expansion of moso bamboo changed the above-ground canopy structure of Japanese cedar through the competition of above-ground mechanical damage, which reduced the leaf area and photosynthetic capacity of Japanese cedar, and then affected the below-ground root biomass, finally leading to the reduction of transpiration and the variation of ecohydrological process.

Tree roots exert greater impacts on phosphorus fractions than aboveground litter in mineral soils under a Pinus sylvestris var. mongolica plantation

Detritus inputs from aboveground litter and belowground roots, as well as roots exudates sustain soil phosphorus (P) supply in forests, but how the aboveground litter and roots differentially and interactively drive soil P transformations and availability is poorly understood. We experimentally removed aboveground litter, and then excluded roots in litter intact/removed plots in a nutrient-poor Mongolian pine (Pinus sylvestris var. mongolica) plantation in northern China. Phosphorus fractions with different bioavailability (labile P, moderately labile P, stable P, and occluded P), P adsorption characteristics and related biochemical properties in mineral soils were examined five years after the establishment of the experiment. Root exclusion significantly reduced labile organic P by 56%, and did not affect other recalcitrant organic P fractions and total organic P in both the litter intact and removed plots. Root exclusion significantly elevated all inorganic P fractions by 21%–26% in the litter removed plots, but not in the litter intact plots. Litter removal alone did not change soil P fractions except that it slightly increased labile organic and stable inorganic P concentrations. Maximum P adsorption capacity was improved by litter removal, but maximum P buffer capacity was neither affected by litter removal nor by root exclusion. Soil organic P fractions were correlated closely with soil microbial biomass, acid phosphatase activities and soil organic carbon, while inorganic P fractions were correlated significantly with exchangeable Ca2+ concentration and pH. The results revealed the predominant role of roots in driving the mobilization of inorganic, as well as mineralization-immobilization of organic P in this Mongolian pine plantation, and highlighted the facilitation of aboveground litter on root driving mobilization of soil inorganic P.

The effect of soil microplastics on Oryza sativa L. root growth traits under alien plant invasion

Invasive alien plants pose severe threats to agroecosystems. Microplastic (MP) contamination in farmland soil is also concerning, as it causes crop stress and reduces productivity. However, the effects of the interactions between invasive alien plants and MP in the soil impact crops remain unclear. Herein, belowground plant characteristics associated with stress responses were examined in a pot experiment using root scan analyzes of rice plants exposed to Solidago canadensis L. invasion, polyethylene MP contamination, and a combined treatment. The observed changes in root growth traits under Canada goldenrod (Solidago canadensis L.) invasion were the least adverse, whereas S. canadensis invasion combined with soil MP contamination had the most adverse effects on root growth. Solidago canadensis L. invasion increased all belowground indices except root height and mean root diameter, which was upregulated in the soil MP contamination treatment. The combined treatment (S. canadensis invasion and soil MP contamination) reduced the belowground root growth traits more than the other treatments. The root growth traits may have been affected by changes in the antioxidant enzyme activity of the roots caused by the treatments. The combined effects of S. canadensis invasion and MP toxicity on rice root growth traits raise concerns regarding potential yields, financial damage, and consequences related to a potential move into the food web.

Biochar enhances multifunctionality by increasing the uniformity of energy flow through a soil nematode food web

Soil multifunctionality is the consequence of biotic interactions that drive decomposition, nutrient cycling and net primary production. Energy flux describes the energy consumed and transferred among multitrophic groups in the soil food web, which are logically linked to multifunctionality. In a subtropical agroecosystem with an annual sweet potato-oilseed rape rotation, we explored how biochar and synthetic fertilizer jointly affected agroecosystem multifunctionality (e.g., crop production, soil carbon storage and nutrient cycling) and the energetic structure of the nematode food web during two consecutive years. Results showed that biochar increased soil multifunctionality by 37–110% mainly by promoting a uniform energy flow through the soil nematode food web, which was largely due to increased energy fluxes of fungivores and omnivores-carnivores at the expense of decreased energy flux through herbivores. Applying a lower rate of synthetic fertilizer led to non-uniform energy flow in the soil nematode food web, suggesting that nitrogen limitation could offset the stimulatory effect of biochar on soil multifunctionality. This was because biochar induced oligotrophic conditions (a stoichiometry-induced nitrogen limitation), effectively warranting that continuous biochar application would aggravate nutrient limitations to crops, especially when low rates of synthetic fertilizer are applied. Notably, soil nutrient impoverishment could lead to resource reallocation from aboveground shoot to belowground root production, thereby fueling the energy flow through the herbivore channel. Our findings highlight the importance of balancing biochar and synthetic fertilizer applications to sustain a stable energetic structure in soil nematode food webs, which are associated with greater crop production and soil health in subtropical region.