Fine Root Biomass Research Articles

Invasion alters plant and mycorrhizal communities in an alpine tussock grassland.

Plant invasions are impacting alpine zones, altering key mutualisms that affect ecosystem functions. Plant-mycorrhizal associations are sensitive to invasion, but previous studies have been limited in the types of mycorrhizas examined. Consequently, little is known about how invaders that host rarer types of mycorrhizas may affect community and ecosystem properties. We studied invasion by an ericoid mycorrhizal host plant (Calluna vulgaris L., heather) in alpine tussock grasslands in New Zealand. We investigate the effects of increasing C. vulgaris density on the plant and soil microbial community and on mycorrhization in the dominant native species (Chionochloa rubra Z., red tussock), an arbuscular mycorrhizal host. We show that variation in plant community composition was primarily driven by invader density. High invader densities were associated with reductions in C. rubra diameter and in the cover, richness and diversity of the subordinate plant community. Belowground, we show that higher invader densities were associated with lower rates of mycorrhization in C. rubra and higher proportional abundance of the fungal lipid biomarker 18:2ω6 but had little effect on total microbial biomass, which may suggest increased ericoid mycorrhizal and fine root biomass in high C. vulgaris density stands. Our data suggest that disruption of native plant-arbuscular mycorrhizal networks may contribute to the competitive success of C. vulgaris, and that the dramatic decline of C. rubra with invasion reflects its relatively high mycorrhizal dependence. By exploring invasion of a plant with a less common mycorrhizal type, our study expands knowledge of the ecosystem consequences of biological invasions.

Spatial Distribution of Fine Roots in Pinus tabuliformis and Populus tomentosa and Their Competition in Soils Response to Nutrient Availability and Proximity

Developing high-efficiency mixed forests or converting low-efficiency pure forests into near-natural mixed forests with optimal structure and function is a crucial aspect of forest management. In the initial stages of afforestation or stand improvement, fertilization and planting distance significantly influence the formation and development of mixed forests. This study investigated how nutrients and planting distance affect root competition between five-year-old Chinese pine (Pinus tabuliformis) and one-year-old Chinese white poplar (Populus tomentosa) and identified the factors influencing the competitive ability of these two species. Field planting experiments used three fertilization gradients (63 g·m−2, 125 g·m−2, and 250 g·m−2) of Stanley compound fertilizer with an N:P:K ratio of 2:1:1 and two planting distances (25 cm and 50 cm). Each experimental group was planted in circular plots with a radius of 0.5 m, yielding a total of nine plots. The effects of different fertilization concentrations and planting distances on root distribution were analyzed both horizontally and vertically. Pearson correlation analysis was used to assess the relationship between roots and soil nutrients, while Levins’ niche overlap formula evaluated the differences in root competition between the species. Furthermore, principal component analysis quantified the relationships between impact factors and the root competitiveness of the two species. Results indicated that both species primarily allocated their fine root biomass to the shallow 0–10 cm layer. Pinus tabuliformis primarily extended to the southwest, while Populus tomentosa predominantly grew to the north. Both species exhibited enhanced root growth at moderate nutrient concentrations of 125 g·m−2. At a planting distance of 50 cm from Pinus tabuliformis, Populus tomentosa seedlings demonstrated superior root growth compared to those planted 25 cm apart. Pinus tabuliformis demonstrated greater competitive ability in the deeper 10–30 cm soil layers compared to Populus tomentosa, which showed the opposite pattern in the shallow 0–10 cm layers. Furthermore, available phosphorus (contribution rate of one impact factor on the competitiveness indexes, CR: −0.998), organic matter (CR: −0.978), total nitrogen (CR: −0.947), and alkali-hydrolysable nitrogen (CR: −0.937) significantly negatively impacted the competitiveness indexes of Pinus tabuliformis. The fine root surface area, volume, and length of Populus tomentosa also significantly negatively affected its competitiveness indexes, with all contribution rates exceeding an absolute value of 0.847. Results indicated that the root distributions of Pinus tabuliformis and Populus tomentosa overlapped spatially, with each species exhibiting advantages in different regions. Therefore, in future plantation reconstruction and forest management, it is essential to thoroughly evaluate root, soil, and fertilizer factors, adjusting planting distances accordingly, to effectively mitigate competition between the two species and successfully establish a mixed forest.

Thinning-induced decrease in fine root biomass, but not other fine root traits in global forests

In forest ecosystems, changes in the expression of tree absorptive root traits following management interventions are expected to influence post-thinning forest structure and function. Fine root traits are expected to be especially responsive to forest thinning—one of the most common forest management interventions and the focus of our research here—influencing tree-level responses to environmental change, and thereby contributing to post-thinning stand-level dynamics and ecosystem processes. However, there remains limited understanding surrounding whether or not forest thinning influences the expression of root morphological, chemical, and physiological traits associated with belowground resource acquisition. We conducted a global meta-analysis to evaluate the response of 13 fine root traits to forest thinning. Our study included analysis of 769 paired observations of root traits values pre- and post-thinning, derived from 89 peer-reviewed publications. Our meta-analysis found that forest thinning leads to a decrease in fine root biomass by 11.7% on average, while other root traits including fine root length, root C and N concentrations, root lifespan, and root respiration rates, are largely unresponsive to thinning treatments. Thinning tended to reduce fine root biomass at early stand recovery stages, with increases in fine root biomass being detected at later seral stages, especially in heavy thinning experiments. The effect of thinning on fine root biomass was most pronounced in deeper soil horizons. The influence of thinning on fine root trait expression was not affected by ecosystem or stand type, with the exception of biomass which decreased in temperate and coniferous forests. Our results demonstrate variations of fine root traits to forest management, as well as the importance of stand recovery time and thinning intensity in regulating fine root trait expression in retention trees. These patterns may have strong implications for governing soil carbon stocks in managed forests associated with decreased root inputs into deeper soils. Overall, our findings can enhance our comprehension of how forest management affects fine root trait expression, and relationship between managed forests and belowground ecosystem structure and function.

Vegetation restoration changed the soil aggregate stability and aggregate carbon stabilization pathway according to δ13C signatures

Vegetation restoration can increase soil organic carbon (SOC) sequestration through the physical protection of soil aggregates. However, the soil aggregate stability and C flow pathway associated with long-term plantation restoration have not yet been fully characterized. Here, we conducted a study on Robinia pseudoacacia plantations at different recovery stages, studied the distribution and stability of aggregates, analysed the aggregate-associated organic carbon (OC) content and δ13C value, and quantified the aggregate C flow pathway. The results revealed that vegetation restoration increased the proportion of large macroaggregates (LMAs) and decreased the proportion of small macroaggregates (SMAs), with no changes observed in the proportion of microaggregates (MIAs) or silt + clay (SC) at 0–20 cm. The indices of aggregate stability, namely, the mean weight diameter (MWD), geometric mean diameter (GMD) and structural stability index (SSI), increased under vegetation restoration at 0–20 cm, with maximum values of 3.83 mm, 2.88 mm, and 2.00 %, respectively, at 35 years of age (35Y). The OC content of the LMAs increased from 10.96 to 21.64 g kg−1 and from 7.27 to 10.05 g kg−1 in the 0–20 cm and 20–40 cm layers, respectively. LMAs and SMAs had the greatest contributions to SOC accumulation in the 0–20 cm and 20–40 cm layers, respectively. The δ13C value increased with decreasing aggregate size. The C flow pathway was from macroaggregates to MIAs or SC. Compared with abandoned farmland, vegetation restoration decreased the aggregate C flow intensity in the 0–20 cm layer. The soil aggregate stability and aggregate-associated OC content decreased with increasing soil depth, but the soil δ13C value exhibited the opposite trend. Vegetation restoration regulated soil aggregate stability by influencing the fine root biomass (FRB) and SOC content. In summary, our analysis offers a valuable reference for the controlling effect of aggregation on C stability influenced by vegetation restoration.

Soil water regime and nutrient availability modulate fine root distribution and biomass allocation in amazon forests with shallow water tables

Soil water regime and nutrient availability modulate fine root distribution and biomass allocation in amazon forests with shallow water tables

Species mixtures enhance fine root biomass but inhibit root decay under throughfall manipulation in young natural boreal forests

Fine roots play crucial roles in terrestrial biogeochemical cycles. Although biodiversity loss and changes in precipitation are two major drivers of global change, our understanding of their effects on fine root biomass (FRB), root functional traits, and fine root decay (FRD) remains incomplete. We manipulated precipitation in young boreal forests dominated by Populus tremuloides, Pinus banksiana, and their relatively even mixtures using 25 % addition, ambient, and 25 % reduction in throughfall during the growing season. We collected root samples using soil core and trunk-traced methods to quantify FRB and root traits, and we simulated fine root decay using an in-situ experiment over 531 days. We found that compared to the average of single-species-dominated stands, species mixtures increased FRB by 41 % under ambient throughfall, by 89 % under throughfall reduction and by 71 % under throughfall addition. Root surface area, fine root volume, and root length density responded to species mixtures similarly to FRB. Meanwhile, species mixtures reduced FRD across all water treatments. There was a positive relationship between the effect of species mixtures on the FRD of absorptive roots and those on the FRB. Our results highlight that species mixtures could modify carbon cycling by enhancing fine root biomass accumulation and reducing its decomposition of young boreal forests under changing precipitation.

Decline of beech trees in a Mediterranean forest is associated with high rhizosphere oomycete diversity

In the last decades, tree decline in European beech forests has been related to extreme climatic events and with the activity of parasitic oomycetes such as Phytophthora species. In Spain, little is known about the association of beech decline and soil oomycete composition. We hypothesized that the weakening of beech trees is associated with the activity and proliferation of parasitic oomycetes. We studied the rhizosphere oomycete community of large beech trees located in one of the southernmost beech forests in Europe. From soil samples collected in the rhizosphere, we used a metabarcoding approach to explore the oomycete community associated to asymptomatic and declining trees. We also studied fine root parameters in both groups of trees. A total of 99 oomycete amplicon sequence variants (ASVs) were detected. Higher diversity and richness of oomycetes were observed in declining than in asymptomatic trees. The oomycete composition also differed between the two groups of trees. Declining trees showed lower fine root biomass and root density than asymptomatic trees, and root density was negatively correlated with the abundance of Pythium ASV counts. The genus Phytophthora, associated with beech decline in central Europe, was underrepresented in the oomycete community. The results suggest that decline-associated processes in beech trees are related with fine root weakening and loss which probably facilitates the entrance and colonization of opportunistic oomycete microbes. Although members in the genus Pythium do not seem to be a primary factor on beech decline, they probably contribute to the chronic decline of Fagus sylvatica trees.

Differential Responses of Soil Nitrogen Forms to Climate Warming in Castanopsis hystrix and Quercus aliena Forests of China

Climate warming impacts soil nitrogen cycling in forest ecosystems, thus influencing their productivity, but this has not yet been sufficiently studied. Experiments commenced in January 2012 in a subtropical Castanopsis hystrix Hook. f. and Thomson ex A. DC. plantation and in May 2011 in a temperate Quercus aliena Blume forest, China. Four treatments were established comprising trenching, artificial warming (up to 2 °C), artificial warming + trenching, and untreated control plots. The plots were 2 × 3 m in size. In 2021 and 2022, soil nitrogen mineralization, soil nutrient availability, fine root biomass and microbial biomass were measured at 0–20 cm soil depth in 6 replicate plots per treatment. Warming significantly increased soil temperature in both forests. In the C. hystrix plantation, warming significantly increased available phosphorus (AP) and fine root biomass (FRB), but it did not affect soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) and their ratios. Warming depressed the net mineralization rate (NMR) and net ammonification rate (NAR) of the C. hystrix plantation, probably because the competition for nitrogen uptake by fine roots and microorganisms increased, thus decreasing substrates for nitrogen mineralization and ammonification processes. Trenching and warming + trenching increased the net nitrification rate (NNR), which might be related to decreased NH4+-N absorption of trees in the trenched plots and the increased microbial activity involved in soil nitrification. In the Q. aliena forest, warming significantly increased NH4+-N, MBC/MBN, Root C/N, Root N/P, and decreased pH, MBN, MBN/MBP and Root P; and there was no effect of trenching. Notably, the NAR, NNR and NMR were largely unaffected by long-term warming. We attributed this to the negative effect of increasing NH4+-N and decreasing MBN/MBP offsetting the positive effect of soil warming. This study highlights the vulnerability of subtropical forest stands to long-term warming due to decreased soil N mineralization and increased NO3−-N leaching. In contrast, the soil N cycle in the temperate forest was more resilient to a decade of continuous warming.

Optimization of soil hydrological properties in degraded grasslands by soil amendments

Soil amendments facilitate the restoration of degraded soil fertility and vegetation productivity. Soil hydrological functions are crucial for assessing soil degradation and restoration in grassland ecosystems. However, the manner in which soil amendments drive changes in the hydrological properties of grassland ecosystems at different soil depths remains unclear. In this study, we conducted a five-year soil amendment experiment in a semi-arid grassland of the Loess Plateau to evaluate the impact of aluminum sulfate (AS) and biochar (BC), both individually and in combination, on the hydrological properties of soil profiles. The results showed that AS significantly increased saturated water-holding capacity (SWHC) by 19.04 %, field capacity (FC) by 27.39 %, soil water storage (SWS) by 1.57 %, and saturated hydraulic conductivity (Ks) by 19.03 % in the upper soil layer (0–40 cm). BC application increased SWHC by 20.09 %, FC by 17.56 %, SWS by 12.94 %, and Ks by 16.66 % in the 0–40 cm soil layers. The combined effects of AS and BC optimized the soil hydrological properties by increasing SWHC, FC, SWS, and Ks by 25.74 %, 35.45 %, 18.47 %, and 25.80 %, respectively. These improvements were driven by significant changes in the soil organic matter, fine root biomass, total porosity, clay content, and soil bulk density. Notably, the soil amendments did not significantly affect the hydrological properties of the deep soil layer (40–80 cm). Our study demonstrated that the strategic use of AS and BC, particularly in combination, effectively enhanced soil fertility and hydrological functions, thereby increasing grassland ecosystem productivity. These findings offer critical insights for sustainable grassland management and highlight the potential of tailored soil amendments to restore and improve soil fertility and plant productivity in degraded grassland ecosystems.

Extramatrical mycelial biomass is mediated by fine root mass and ectomycorrhizal fungal community composition across tree species

In many ecosystems, a large fraction of gross primary production is invested in mycorrhiza. Ectomycorrhizal (ECM) mycelium is involved in regulating soil carbon and nutrient cycling. However, little is known about how mycelial biomass, production and turnover differ depending on ECM fungal community composition and associated tree species. We quantified fine root biomass and length using soil cores, and mycelial traits (biomass, production, and turnover) using mesh-bags and ergosterol analysis, and identified ECM exploration types by Illumina MiSeq sequencing of four ECM-dominated tree species (Picea asperata, Larix gmelinii, Quercus aquifolioides and Betula albosinensis) in subalpine forest. The ECM fungal community composition separated between needle-leaved and broadleaved species, and between evergreen and deciduous species. The ratio of mycelial to fine root biomass was similar across the species regardless of genus-scale community composition and the relative abundance of exploration types. Compared to the other species, Q. aquifolioides displayed higher fine root biomass and mycelial biomass and production, dominated by contact-short exploration type. Mycelial turnover rate tended to be lowest in P. asperata, dominated by medium-long exploration type. Much higher production of mycelium and only slightly higher turnover rate in Q. aquifolioides suggests that its steady-state mycelial biomass would be higher than of the other species. Moreover, compared to the two deciduous species, with similar production but somewhat lower turnover rate, the standing crop of mycelium in P. asperata may stabilize at a higher value. Our findings, that exploration type may affect production and turnover, highlight the importance of characterizing ECM fungal communities by exploration types when estimating the contribution of mycelium biomass to forest carbon sink and storage.

Environmental aridity driving latitudinal pattern of biomass allocation fractions in root systems of 63 shrub species in dry valleys.

Fine roots and absorptive roots play key roles in acquiring resources throughout soil profiles and determining plant functions along environmental gradients. Yet, the geographical pattern of carbon allocation in fine roots, particularly in absorptive roots, and their relations with plant sizes and evironment are less understood. We sampled 243 xerophytic shrubs from 63 species distributed along the latitudinal gradient (23°N to 32°N) in dry valleys of southwest China and synthetically measured biomass fractions of plant organs, especially fine roots and absorptive roots (1st to 3rd root order). We identified latitudinal patterns of biomass allocation fractions of organs and their relationships with plant sizes and environmental factors. The latitudinal patterns of both absorptive root and fine-root fractions followed weak unimodal distributions; stem biomass fraction increased with the latitude, while the leaf biomass fraction decreased. The fraction of fine-root biomass had negative relationships with plant height and root depth. The fractions of root, fine root, and absorptive root biomass were largely explained by soil moisture. Furthermore, fraction of fine-root biomass increased in a relatively humid environment. Overall, soil moisture was the most important factor in driving latitudinal patterns of biomass fraction. Our study highlighted that functional redistribution of root system biomass was the critical adaptive strategy along a latitudinal gradient.

Frass deposition from pest outbreaks affects soil organic carbon and its relationship with environmental factors in a deciduous broad-leaved forest

Forest defoliators are one of the major biological disturbances to forest ecosystems. As one of the abnormal nutrient input paths into forest ecosystems, frass deposition from the pest outbreak plays a critical role in regulating soil organic carbon (SOC) in forest ecosystems. However, how frass deposition affects SOC and its fractions in forests remains unclear. Based on a severe outbreak of defoliator in an oak-sweetgum mixed forest in Jigong Mountain in 2014, we compared the difference in SOC between plots with and without frass deposition for 4 consecutive years. The results showed that frass deposition led to a significant increase of 25.1 % in soil microbial biomass C (MBC) and 32.0 % in dissolved organic C (DOC) in 2014, which further escalated to 50.4 % and 50.6 % in the subsequent year (2015), respectively. The response of SOC to frass deposition lagged behind MBC and DOC. Specifically, there was no change in SOC in 2014, but a significant increase (50.9 %) was observed in the subsequent 2–3 years. The positive dependences of MBC and DOC upon fine root biomass were negated under frass deposition, while the relationship between SOC and fine root biomass remained unaffected. Soil organic carbon and DOC showed non-linear responses to frass amount and the changed soil nitrogen content. Our finding that the response of SOC to frass deposition lagged behind soil labile C indicates that SOC exhibits a certain resilience towards forest disturbance. The findings also imply that investigating the long-term impacts of frass deposition on SOC in forests would contribute to the scientific assessment of forest C cycling under disturbance.

Root foraging strategies and niche segregation of three mediterranean shrub species

Shrubs are usually adapted to stressful environments in which soil resources are limited, and thus, roots are fundamental for their biological success. However, root measures are challenging to collect, especially in field conditions and at the individual level. For this study, we collected data on the three‐dimensional distribution of fine root biomass of twenty‐three individuals belonging to three shrub species in a mediterranean shrubland in central Spain: gum rockrose Cistus ladanifer, rosemary Salvia rosmarinus, and hairy‐fruited broom Cytisus striatus. Our goal was to determine the soil‐foraging strategies adopted by the plants. We hypothesized that plants would show stabilizing niche differences explaining the high plant biodiversity characteristic of mediterranean shrublands and that they would follow the game theory model's prediction of exploitative segregation of roots behaving territorially but also over‐proliferating roots close to their stem and engaging in a root tragedy of the commons. We found that two‐thirds to three‐fourths of the biomass was belowground, and the system's productivity was roughly 500–600 g C m−2 year−1. Only rosemary plants competed with neighbors following the exploitative segregation predictions. Broom plants had the shallowest and most widespread root systems but significantly reduced their root range toward competing neighbors. Gum rockrose presented deep, narrow root systems avoiding extensive overlap with neighbors but did not appear to respond to competitive pressure levels. Shrubs appeared to stratify their roots at different soil depths, supporting the niche segregation hypothesis.

Non-Linear Relationships between Fine Root Functional Traits and Biomass in Different Semi-Arid Ecosystems on the Loess Plateau of China

As a key soil carbon process, changes in plant root growth may have a dramatic impact on the global ecosystem’s carbon cycle. Fine root functional traits and fine root biomass can be used as important indexes of plant root growth. Compared with the much better understood relationships between aboveground plant functional traits and aboveground biomass, knowledge on the relationships between fine root functional traits and belowground biomass still remains limited. In this study, plant fine roots in 30 abandoned lands, 9 woodlands, 29 alfalfa grasslands, 30 Caragana shrublands and 29 croplands were sampled at 0–20 and 20–40 cm soil depths in Zhonglianchuan, Yuzhong County, Gansu Province, China (36°02′ N, 104°24′ E), to clarify the characteristics of the relationships between fine root functional traits (e.g., diameter, specific root area (SRA) and specific root length (SRL)) and fine root biomass at 0–20 and 20–40 cm soil depths. The results showed that the relationships between the fine root functional traits and fine root biomass in these ecosystems were robust, allowing for the use of an allometric growth model at both 0–20 and 20–40 cm soil depths (p < 0.05). Specifically, the relationship between root diameter and fine root biomass was consistent with highly significant positive power, while highly significant negative power relationships of SRA and SRL with fine root biomass were observed (p < 0.01, except the root diameter–biomass models in the woodlands in the 0–20 cm soil layer (p = 0.017) and 20–40 cm soil layer (p = 0.025)). The results can provide some parameters for these terrestrial ecosystem process models. From this perspective, our study is beneficial in the construction of suitable strategies to increase plant biomass, which will help with the restoration of the semi-arid region of the Loess Plateau of China.

Conversion of pure Chinese fir plantation to multi-layered mixed plantation increases organic phosphorus accumulation and transformation within soil aggregates

Evaluation of the impacts of environmental factors and microbial communities on soil organic phosphorus (Po) availability is needed to clarify P cycling and regulate plantations productivity. However, the effects on Po accumulation and transformation of converting pure Chinese fir plantation to multi-layered mixed plantation and their regulatory mechanisms remain unclear. The aim of this study was to examine the impacts of the transformation of pure stand of Chinese fir (Cunninghamia lanceolata; PP) to mixed plantation with multiple tree species (C. lanceolata, Castanopsis hystrix, and Michelia hedyosperma; MP) on Po accumulation and transformation within topsoil (0–10 cm) aggregates in subtropical China. Our results showed that the soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH4+-N), and available phosphorus (AP), as well as the carbon‑nitrogen ratio of soil (C/Nsoil) and carbon‑phosphorus ratio of soil (C/Psoil) were significantly higher (P < 0.05) of all aggregates in MP than those in PP. The quantities of soil microbial biomass C, N, P (MBC, MBN, and MBP) in all different aggregates were significantly greater (P < 0.05) in MP than in PP. The phospholipid fatty acid contents related to bacteria, fungi, arbuscular mycorrhizal fungi (AMF), and actinomycetes were significantly greater in all aggregate classes (P < 0.05) in MP relative to PP. The activities of all tested C, N, and P hydrolytic enzymes, as well as labile organic P, moderately labile organic P, moderately resistant organic P, and highly resistant organic P contents, were significantly higher of most aggregate size classes in MP. Finally, redundancy analysis (RDA) suggested that Po fractions were primarily affected by the NH4+-N, litterfall biomass (LF), carbon‑nitrogen ratio of litter (C/Nlitter), SOC and fine root biomass (FR). Our findings suggest that converting pure Chinese fir plantations into multi-layered mixed plantations may represent an effective management strategy for promoting organic P accumulation and transformation by regulating soil and microbial properties in degraded soils of Chinese fir plantations.

Edaphic factors mediate the responses of forest soil respiration and its components to nitrogen deposition along an urban-rural gradient

Exploring the influences of nitrogen deposition on soil carbon (C) flux is necessary for predicting C cycling processes; however, few studies have investigated the effects of nitrogen deposition on soil respiration (Rs), autotrophic respiration (Ra) and heterotrophic respiration (Rh) across urban-rural forests. In this study, a 4-year simulated nitrogen deposition experiment was conducted by treating the experimental plots with 0, 50, or 100 kg·ha−1·year−1 of nitrogen to check out the mechanisms of nitrogen deposition on Rs, Ra, and Rh in urban-rural forests. Our finding indicated a positive association between soil temperature and Rs. Soil temperature sensitivity was significantly suppressed in the experimental plots treated with 100 kg·ha−1·year−1 of nitrogen only in terms of the urban forest Rs and Ra and the rural forest Ra. Nitrogen treatment did not significantly increase Rs and had different influencing mechanisms. In urban forests, nitrogen addition contributed to Rh by increasing soil microbial biomass nitrogen and inhibited Ra by increasing soil ammonium‑nitrogen concentration. In suburban forests, the lack of response of Rh under nitrogen addition was due to the combined effects of soil ammonium‑nitrogen and microbial biomass nitrogen; the indirect effects from nitrate‑nitrogen also contributed to a divergent effect on Ra. In rural forests, the soil pH, dissolved organic C, fine root biomass, and microbial biomass C concentration were the main factors mediating Rs and its components. In summary, the current rate of nitrogen deposition is unlikely to result in significant increases in soil C release in urban-rural forests, high nitrogen deposition is beneficial for reducing the temperature sensitivity of Rs in urban forests. The findings grant a groundwork for predicting responses of forest soil C cycling to global change in the context of urban expansion.

Study on Associations between Root and Aboveground Growth of Mixed-Planting Seedlings of Populus tomentosa and Pinus tabuliformis under Soil Nutrient Heterogeneity

Near-natural transformation can convert artificial monoculture forests into mixed forests with diverse ages, multi-layered structures, and enhanced ecological functions. This transformation optimizes stand structure, improves soil physical and chemical properties, and enhances stand productivity and species diversity. This study aimed to explore the relationship between the underground roots and aboveground growth of Pinus tabuliformis and Populus tomentosa under conditions of nutrient heterogeneity, with the goal of advancing plantation transformation. This research focused on 1-year-old Populus tomentosa and 5-year-old Pinus tabuliformis, employing two planting densities (25 cm and 50 cm) and three fertilization levels, low (50 g·m−2), medium (100 g·m−2), and high (200 g·m−2), using Stanley Potassium sulfate complex fertilizer (N:P:K = 15:15:15). Each treatment had three replicates, resulting in a total of nine experimental groups, all planted in circular plots with a radius of 1 m. Standard major axis (SMA) regression was used to analyze the allometric relationship between underground fine root biomass and aboveground organ biomass. This study further explored correlations between fine root length, root surface area, volume, biomass, and aboveground biomass, culminating in a mixed-effects model. The mixed-effects model quantified the relationships between underground roots and aboveground growth in varying soil nutrient environments. The results indicated optimal root growth in Populus tomentosa and Pinus tabuliformis, characterized by maximum root length, surface area, and volume, under conditions of 200 g·m−2 soil nutrient concentration and 50 cm planting distance; Populus tomentosa fine roots had a vertical center at a depth of 8.5 cm, whereas Pinus tabuliformis roots were centered at depths of 5–7.5 cm, indicating differing competitive strategies. Pinus tabuliformis exhibited competitive superiority in the soil’s surface layer, in contrast to Populus tomentosa, which thrived in deeper layers. The study of the allometric growth model revealed that under conditions where the nutrient gradient was 200 g·m−2 and the planting distance was 25 cm, Populus tomentosa demonstrated its highest allometric growth index (2.801), indicative of positive allometric growth. Furthermore, there was a notable inclination of resource allocation towards the aboveground, which enhances the accumulation of aboveground biomass. The mixed-effects model equation showed a clear linear relationship between underground roots and aboveground biomass. The final fitting coefficient of the model was high, providing a robust theoretical basis for future management practices. The mixed-effects model revealed the following hierarchy of fixed-effect coefficients for root system characteristics affecting aboveground biomass: fine root volume (132.11) &gt; fine root biomass (6.462) &gt; root surface area (−4.053) &gt; fine root length (0.201). In subsequent plantation reconstruction and forest management, increasing soil fertility and planting distance can promote the growth of underground roots and biomass accumulation. Appropriately increasing soil fertility and reducing planting distance can effectively promote aboveground biomass accumulation, achieving sustainable forest development.

Estimating the global root exudate carbon flux

Root exudation, the export of low-molecular weight organic carbon (C) from living plant roots to soil, influences microbial activity, nutrient availability, and ecosystem feedbacks to climate change, but the magnitude of this C flux at ecosystem and global scales is largely unknown. Here, we synthesize in situ measurements of root exudation rates and couple those to estimates of fine root biomass to estimate global and biome-level root exudate C fluxes. We estimate a global root exudate flux of 13.4 (10.1–20.2) Pg C y−1, or about 9% (7–14%) of global annual gross primary productivity. We did not find differences in root mass-specific exudation rates among biomes, though total exudate fluxes are estimated to be greatest in grasslands owing to their high density of absorptive root biomass. Our synthesis highlights the global importance of root exudates in the terrestrial C cycle and identifies regions where more in situ measurements are needed to improve future estimates of root exudate C fluxes.

Relationship Between Fine Root Biomass and Soil Physico-chemical Properties of Grassland Ecosystem in Bhadrapur Municipality of Jhapa district, Eastern Nepal

This study investigated the distribution of fine root biomass and various soil properties in a grassland ecosystem within Bhadrapur Municipality, Nepal. Soil samples were systematically collected from randomly selected blocks in undisturbed, disturbed, and roadside areas during the late rainy season. Analyses included soil texture, moisture content, temperature, pH, and quantification of fine root biomass (FRB; &lt;5 mm diameter) within the top 15 cm soil depth. Results showed the mean FRB was significantly higher in undisturbed areas (7.77 t/ha) compared to disturbed (7.053 t/ha) and roadside (1.76 t/ha) areas. Across all sites, FRB exhibited a positive correlation with soil moisture content. Soil pH was slightly more acidic in undisturbed versus disturbed and roadside areas. Soil temperature demonstrated a positive correlation with FRB in undisturbed and roadside areas but a negative correlation in disturbed areas. Additionally, FRB negatively correlated with sand content in disturbed and roadside areas. The findings highlight how soil moisture is a key driver of fine root proliferation in this grassland ecosystem. Variations in soil texture, pH, and temperature between sites reveal their influence on root growth dynamics. Understanding these root-soil interactions has implications for sustainable grassland management, biodiversity conservation, and ecosystem resilience under changing environmental conditions.

Nitrogen and potassium limit fine root growth in a humid Afrotropical forest

Nutrient limitations play a key regulatory role in plant growth, thereby affecting ecosystem productivity and carbon uptake. Experimental observations identifying the most limiting nutrients are lacking, particularly in Afrotropical forests. We conducted an ecosystem-scale, full factorial nitrogen (N)-phosphorus (P)-potassium (K) addition experiment consisting 32 40 × 40 m plots (eight treatments × four replicates) in Uganda to investigate which (if any) nutrient limits fine root growth. After two years of observations, added N rapidly decreased fine root biomass by up to 36% in the first and second years of the experiment. Added K decreased fine root biomass by 27% and fine root production by 30% in the second year. These rapid reductions in fine root growth highlight a scaled-back carbon investment in the costly maintenance of large fine root network as N and K limitations become alleviated. No fine root growth response to P addition was observed. Fine root turnover rate was not significantly affected by nutrient additions but tended to be higher in N added than non-N added treatments. These results suggest that N and K availability may restrict the ecosystem’s capacity for CO2 assimilation, with implications for ecosystem productivity and resilience to climate change.