Specific Root Length Research Articles

Biochar can improve biological nitrogen fixation by altering the root growth strategy of soybean in Albic soil

Albic soil is a low-yielding soil that is widely distributed in Northeast China. The high viscosity and acidity and the lack of nutrients in the Albic layer limit the growth of crop. In our previous studies, we found that applying biochar as a soil amendment could improve the properties of Albic soil and promote soybean growth. Increases in the nitrogen contents of the soil and the soybeans were key aspects of these improvements. Soybean is a nitrogen-fixing crop, the increase in nitrogen in the Albic soil may have been due to an improvement in biological nitrogen fixation by the soybean with biochar amendment, but the function mechanism was still uncertain. We hypothesized that biochar could improve biological nitrogen fixation of soybean by affecting soybean root growth in the Albic soil. Therefore, we conducted pot experiments with five treatment levels (0, 10, 20, 30, and 40 g·kg−1 biochar) for two years to study how biochar affects the root growth strategy and biological nitrogen fixation of soybean based on its root structure and root nutrient acquisition ability at different stages. The soybean root structure and activity indexes, nodulation ability and nitrogen uptake were measured at different growth stages; in the second year, at the late seed-filling stage, the stable 15N isotope method was used to elucidate the biological nitrogen fixation process. Regarding root structure at the pod-setting stage, biochar resulted in increases in root length density, specific root length, root diameter and specific tip density but a decrease in root tissue mass density at the pod-setting stage. Biochar improved root nutrient acquisition by increasing root activity, root tip number and root-bleeding sap amount. The change in root growth strategy contributed to the promotion of biological nitrogen fixation by the rhizobia that live symbiotically with soybean, thereby increasing crop yield.

Plastic responses of fine root morphology and architecture traits to nitrogen addition in ectomycorrhizal and arbuscular mycorrhizal tree species in an evergreen broadleaved forest.

We measured the morphology traits (specific root length, specific root surface area, root tissue density, average root diameter) and architecture traits (root fork, root fork ratio, increase rate of root length, root tip density, root fork density) of fine roots in two mycorrhiza tree species, Castanopsis faberi (ectomycorrhizal) and Schima superba (arbuscular mycorrhizal), in an evergreen broadleaved forest in the middle subtropical zone. Root bags method was used in an in situ nitrogen deposition experiment. The aim of this study was to reveal the differences in the plastic responses of fine root morphology and architecture traits to nitrogen deposition between the different mycorrhizal trees. The plastic responses of specific root length, specific root surface area and root fork to nitrogen addition decreased from the first-order root to the fourth-order root, while root tissue density showed an opposite pattern. Such a result indicated a trade-off between nutrient acquisition and resource maintenance of different fine root orders. Different mycorrhizal tree species adopted diffe-rent adaptation strategies to the variations of soil nitrogen availability. C. faberi adopted an opportuni-stic strategy, which relied on fine root to improve nutrient absorption efficiency, enhanced the capacity of space expansion and in-situ nutrient absorption to focus on rapid nutrient absorption strategy. S. superba did not change fine root morphological traits through the trade-off between nutrient absorption efficiency and root construction cost, but relied more on the complementarity between mycorrhizal fungi and fine root architecture traits for nutrient acquisition. The differences in the cost of maintaining and constructing fine root C between different mycorrhizal trees led to fine root adopting the most suitable nutrient capture strategy.

Soil chemistry drives below ground traits in an alternate successional pathway from forest to heath.

To understand impacts of post-disturbance assembly mechanisms on the functional diversity (FD) of plant communities, it is necessary to determine how the environment drives their functional trait composition. In the boreal forest, post-fire abiotic filters may control community assembly by selecting plants with specific traits. Ericaceous heaths are characterized by low FD and are thought to be subject to such filters. We hypothesized that soil parameters select for a specific suite of traits and act as a secondary abiotic filter in post-fire ericaceous heath and contribute to the observed reduction of FD. We measured six soil parameters, five functional traits, and plant species abundances in eight post-fire heath and four regenerating forest sites in Eastern Canada. We conducted a combined analysis of RLQ (R-table Linked to Q-table) and fourth-corner methods to examine the links between plant traits and plot-level soil parameters, mediated by species abundances. Only below ground traits were significantly linked to soil variables. Specific root length and ericoid mycorrhizal associations were negatively linked to total soil nitrogen, available ammonium, and pH. Post-fire heath soils favour a specific suite of species traits. Only a portion of the regional species pool possesses the above-mentioned traits, and when they are favoured by habitat conditions, they assemble into a community with low FD. The novelty of our study is here we show how the relationship between traits and soil chemistry can act as a secondary filter and exert community-level trait changes responsible for the low functional diversity observed in heaths.

Soil biota suppress maize growth and influence root traits under continuous monoculture

This study investigated maize-soil biota interactions as well as the soil legacy effects of continuous monoculture (CM) on maize performance. We conducted a glasshouse experiment that compared the performance of maize inoculated with living or sterilized soil inocula collected from experimental field plots with cropping histories of 1 to 5 years of continuous maize monoculture, where the soil type is Nicollet clay loam with moderate fertility. We measured the biomass, yield, root traits and leaf nutrients of maize as well as eukaryotic soil organisms. Inoculation with living soil dramatically reduced maize biomass and yield compared to inoculation with sterilized soil, showing CM to have strong negative soil biotic legacy effects on maize. Nonetheless, the strength of soil biotic effects on most maize variables were relatively stable over time under CM. The response of maize total biomass to living soil inoculation correlated positively with arbuscular mycorrhizal (AM) fungal abundance but negatively with soil fauna abundance, whereas it did not relate with the abundance of plant pathogenetic fungi or herbivorous nematodes. The roots showed acquisitive syndromes (high specific root length but low root diameter) in sterilized soil but conservative syndromes (opposite traits) in living soil. The responses in root system structure were tightly related with AM fungal diversity and community composition. Our study shows strong and stable negative effects of soil biota on maize under CM. The complex effects of soil biota on maize performance highlight the need to explore the functions of different groups of soil organisms to better understand and control negative soil legacy effects in agroecosystems.

Inorganic nitrogen sources alter the root morphology of neotropical tree seedlings from different successional groups

Root morphological responses of neotropical tree seedlings to nitrate and ammonium nutrition vary according to the successional group, but may also depend on each species. Neotropical tree seedlings from contrasting successional groups have different nitrogen (N) use strategies, as well as they exhibit striking differences in root morphology. Here, we assessed the effects of hydroponic cultivation with nitrate or ammonium on the growth and root morphological traits of seedlings of pioneer (Cecropia pachystachya, Croton floribundus, Schinus terebinthifolius, Solanum mauritianum, and Trema micrantha) and non-pioneer (Cabralea canjerana, Campomanesia xanthocarpa, Cariniana estrellensis, Guarea kunthiana, and Poecilanthe parviflora) tree species native to Brazilian Atlantic Forest. Nitrate-grown seedlings of pioneer species showed higher shoot and root dry matters and total root length compared to those cultivated with ammonium, while non-pioneer trees showed smaller or no difference in these traits when comparing N sources. These results agree with the decrease of nitrate availability in the soil relative to that of ammonium over an Atlantic Forest succession. Regardless of the successional group, nitrate treatment resulted in longer main and lateral roots in most species. The effects of nitrate and ammonium on specific root length, lateral-root density, and fine-root diameter could be associated with successional groups and N source preference. However, root hair responses varied according to each species. Cecropia pachystachya and C. canjerana roots had morphological responses to N source intermediaries between the successional groups, which are coherent with their ecological niches. These results demonstrate that the effects of N source on the growth and root morphology of neotropical tree seedlings could be associated with their successional group, although species-specific responses were also observed.

Gap Size in Hyrcanian Forest Affects the Lignin and N Concentrations of the Oriental Beech (Fagus orientalis Lipsky) Fine Roots but Does Not Change Their Morphological Traits in the Medium Term

Research Highlights: Fine roots play an important role in plant growth as well as in carbon (C) and nutrient cycling in terrestrial ecosystems. Gaining a wider knowledge of their dynamics under forest gap opening would improve our understanding of soil carbon input and below-ground carbon stock accumulation. Single-tree selection is increasingly recognized as an alternative regime of selection cutting sustaining biodiversity and carbon stock, along with timber production, among ecosystem functions. However, the fine root response in terms of morphological and chemical composition to the resulting harvest-created gaps remains unclear. Background and Objectives: This paper investigates the effect in the medium term (i.e., 6 years after logging) of differently sized harvest-created gaps on fine root dynamics and chemical composition. Materials and Methods: A total of 15 differently sized gaps (86.05–350.7 m2) and the adjacent 20 m distant closed canopies (control) were selected in a temperate Fagus orientalis forest (Hyrcanian region, Iran). Eight soil cores were collected at the cardinal points of the gap edge, including four facing the gap area—the same at the adjacent intact forest. Results: For the selected edge trees, the different size of gaps, the core position, and the tree orientation did not affect the investigated morphological traits, except for the slightly higher specific root length (SRL) for the larger fine root fraction (1–2 mm) in the side facing the gap area. Differently, the investigated chemical traits such as N concentration and cellulose:lignin ratio significantly increased with increasing gap size, the opposite for C:N ratio and lignin. Moreover, N concentration and C:N significantly decreased and increased with the fine root diameter, respectively. Conclusions: This work highlighted that, in the medium term and within the adopted size range, artificial gap opening derived from single-tree selection practice affected the chemistry rather than the biomass and morphology of gap-facing fine roots of edge trees. The medium term of six years after gap creation might have been long enough for the recovery of the fine root standing biomass to the pre-harvest condition, particularly near the stem of edge trees. A clear size threshold did not come out; nevertheless, 300 m2 may be considered a possible cut-off determining a marked change in the responses of fine roots.

Species-Specific Responses of Root Morphology of Three Co-existing Tree Species to Nutrient Patches Reflect Their Root Foraging Strategies.

Root foraging strategies of plants may be critical to the competition for nutrient resources in the nutrient patches, but little is known about these of co-existing tree species in subtropical regions. This study aimed to elucidate root foraging strategies of three co-existing tree species in nutrient heterogeneous soils by exploring their root distribution, root morphology, photosynthates allocation and nutrient accumulation. Seedlings of the three tree species [moso bamboo (Phyllostachys edulis), Chinese fir (Cunninghamia lanceolata), and masson pine (Pinus massoniana)] were grown for 8months under one homogeneous soil [uniform nitrogen (N) plus phosphorus (P)] and three heterogeneous soils (localized N supply, localized P supply, or localized N plus P supply). The biomass, root morphological parameters (i.e., root length and root surface area), specific root length (SRL), non-structural carbohydrates (NSCs, i.e., mobile sugar and starch) in roots, total N and total P of plants were measured. The plasticity and distribution of root system were analyzed by calculating the root response ratio (RRR) and root foraging precision (FP), respectively. The results are as follows (i) Chinese fir tended to forage more N by promoting root proliferation in the N-rich patch, while root proliferation of bamboo and pine did not change. For P, bamboo absorbed more P by promoting root proliferation in the P-rich patch. The total P content of Pine and Chinese fir under localized P supply treatment remain the same despite the fact that the root length in the P-rich patch and the FP increased. (ii) Chinese fir foraged more N by increasing root length and decreasing SRL in the NP-rich patch; bamboo foraged more N and P by increasing root length and SRL in the NP-rich patch. The FP and foraging scale (FS) of both bamboo and Chinese fir were significantly improved under localized N plus P treatment. (iii) The concentrations of NSC were positively correlated with root morphological plasticity for moso bamboo and Chinese fir. Our results indicated that higher morphological plasticity is exhibited in moso bamboo and Chinese fir than masson pine in nutrient heterogeneous soils, allowing them to successfully forage for more nutrients.

Nutrient supply modulates species interactions belowground: dynamics and traits of fine roots in mixed plantations of Eucalyptus and Acacia mangium

Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized block design established in a nutrient depleted soil. Stands with NPK fertilization applied at planting (F+) were compared to unfertilized stands (F-). In the 0–15 cm soil layer, Eucalyptus root mass density (RMD) was higher than Acacia RMD by 50% in F+ and 10% in F-, considering both ages. At 34 months of age, Eucalyptus RMD was 94% higher near Acacia trees than near Eucalyptus trees in F-. In this layer, Eucalyptus specific root length (SRL) was 21% higher than Acacia SRL at 16 months of age and was 10% higher in F- than in F+ at 34 months of age. The cumulative Eucalyptus fine root length production between 16 and 34 months was 66% higher in F- than in F+ in the 0–1 m soil layer. Fertilization increased the competition between species and led to a partial exclusion of Acacia fine roots from the nutrient-rich topsoil. Soil exploration by Eucalyptus roots in the vicinity of Acacia trees was higher in F- than in F+, which suggests that unfertilized trees benefited from facilitation through higher soil N availability and direct N transfer from Acacia trees.

Bringing function to structure: Root-soil interactions shaping phosphatase activity throughout a soil profile in Puerto Rico.

Large areas of highly productive tropical forests occur on weathered soils with low concentrations of available phosphorus (P). In such forests, root and microbial production of acid phosphatase enzymes capable of mineralizing organic phosphorus is considered vital to increasing available P for plant uptake.We measured both root and soil phosphatase throughout depth and alongside a variety of root and soil factors to better understand the potential of roots and soil biota to increase P availability and to constrain estimates of the biochemical mineralization within ecosystem models.We measured soil phosphatase down to 1 m, root phosphatase to 30 cm, and collected data on fine‐root mass density, specific root length, soil P, bulk density, and soil texture using soil cores in four tropical forests within the Luquillo Experimental Forest in Puerto Rico.We found that soil phosphatase decreased with soil depth, but not root phosphatase. Furthermore, when both soil and root phosphatase were expressed per soil volume, soil phosphatase was 100‐fold higher that root phosphatase.Both root and soil factors influenced soil and root phosphatase. Soil phosphatase increased with fine‐root mass density and organic P, which together explained over 50% of the variation in soil phosphatase. Over 80% of the variation in root phosphatase per unit root mass was attributed to specific root length (positive correlation) and available (resin) P (negative correlation). Synthesis: Fine‐root traits and soil P data are necessary to understand and represent soil and root phosphatase activity throughout the soil column and across sites with different soil conditions and tree species. These findings can be used to parameterize or benchmark estimates of biochemical mineralization in ecosystem models that contain fine‐root biomass and soil P distributions throughout depth.

Functional Ecology of Forest, Heath, and Shrub Savannah Alternate States in Eastern Canada

In eastern Canada, alternation of wildfire regime due to fire suppression creates alternate vegetation states converting black spruce forest to heath and shrub savannah (SS). We compared the taxonomic diversity (TD) and functional diversity (FD) of post-fire forest, heath, and SS alternate states to determine if community FD can explain their persistence. We hypothesized that (i) species diversity (TD and FD) would be the highest in forest followed by SS and heath due to decreased interspecific competition and niche differentiation, (ii) differences between TD and FD indices would be greater in communities with high TD in forest due to high trait differentiation and richness, and (iii) changes in community trait values would indicate niche limitations and resource availability. We conducted this study in Terra Nova National Park, Newfoundland, Canada. We calculated functional dispersion (alpha FD), functional pairwise dissimilarity (beta FD), Shannon’s diversity (alpha TD), and Bray–Curtis dissimilarity (beta TD) from species cover. We used five functional traits (specific root length, specific leaf area, leaf dry matter content, height, and seed mass) related to nutrient acquisition, productivity, and growth. We found lower beta diversity in forest than heath and SS; forest also had higher species diversity and greater breadth in niche space utilization. SS was functionally similar to heath but lower than forest in functional dispersion and functional divergence. It had the highest functional richness and evenness. There was no difference in functional evenness between forest and heath. Functional beta diversity was the highest in forest, and did not differ between heath and SS. Resource acquisition and availability was the greatest in forest and the lowest in heath. We suspect that this might be due to forest having the highest functional trait turnover and niche utilization. We conclude that alternate vegetation states originating from alterations to the natural fire regime negatively impact ecosystem function.

Contribution of root traits to variations in soil microbial biomass and community composition

It is well known that plant root-microbe interactions are critical drivers of ecosystem processes such as soil carbon and nutrient cycling; however, considerable uncertainties exist about how root chemical and morphological traits influence soil microbial community composition. We used 13 tree species grown in field monocultures in subtropical China to explore the ecological linkages between leaves, leaf litter, and root chemical and morphological traits associated with plant growth and nutrient-acquisition strategies, as well as soil microbial biomass, the fungi to bacteria (F/B) ratio, and Gram-positive to Gram-negative bacteria (GP/GN) ratio. The combination of above- and belowground traits captured a greater proportion of variations in soil microbial biomass and community composition than did aboveground traits alone. Individually, root traits explained more variations of the F/B and GP/GN ratios than did the individual effects of aboveground leaf or leaf litter traits. All distinct microbial biomass groups and F/B ratios decreased with the specific root length, whereas the F/B ratio increased, and the GP/GN ratio decreased with root tissue density. Our study highlighted the importance of the functional traits of plant roots in determining the microbial biomass and community composition in forest ecosystems. The combination of leaf and root traits may improve our understanding of the mechanisms that underly plant-microbe interactions toward the sustainable management of forest ecosystems.

Shade affects fine-root morphology in range-encroaching eastern redcedars (Juniperus virginiana) more than competition, soil fertility and pH

Fine-root morphological variables are often directly correlated with soil nutrient availability and water absorption. Indirectly, these morphological variables could be related to nutrient depletion by other plants. The relationships of fine-root variables with shade, direct or indirect, are unknown. I tested the relationships between a number of soil quality variables (levels of nitrogen and lime), competition with a co-dominant tree, and shade for the range-encroaching eastern redcedar Juniperus virginiana. I measured seven fine-root parameters as indices of potential nutrient-uptake or competitive ability. I also assessed the relationships of these fine-root parameters with foraging return (i.e., tissue nitrogen, non-structural carbohydrates, relative growth rate and biomass). There were no significant (main) effects of soil amendments (added nitrogen and lime) or tree competition on any of the seven root parameters. There was a significant (indirect) effect of shade (affecting five out of seven fine-root morphological variables), and a significant interaction effect between fertilizer and lime amendments, although the last-mentioned interaction affected one fine-root variable only. There were two additional pieces of evidence that support the effect of shade: a significant difference between shaded and unshaded plants in the slope of the negative relationship between root diameter and specific root length, and a significant overall difference among all fine-root morphological variables in a principal components analysis between shaded and unshaded plants. I found that fractal dimension was the only variable for which there were positive correlations with foraging return, probably because a higher fractal dimension leads to more effective use of nutrients. I expected a negative correlation between foraging returns and fine-root characteristics that incurred substantial costs. I only found a significant cost for specific root length, which may be mediated by the unmeasured parameter of root lifespan.

Root positioning and trait shifts in Hibbertia racemosa as dependent on its neighbour's nutrient-acquisition strategy.

Nutrient-poor ecosystems globally exhibit high plant diversity. One mechanism enabling the co-existence of species in such ecosystems is facilitation among plants with contrasting nutrient-acquisition strategies. The ecophysiological processes underlying these interactions remain poorly understood. We hypothesized that root positioning plays a role between sympatric species in nutrient-poor vegetation. We investigated how the growth traits of the focal mycorrhizal non-cluster-rooted Hibbertia racemosa change when grown in proximity of non-mycorrhizal Banksia attenuata, which produces cluster roots that increase nutrient availability, compared with growth with conspecifics. Focal plants were placed in the centre of rhizoboxes, and biomass allocation, root system architecture, specific root length (SRL), and leaf nutrient concentration were assessed. When grown with B. attenuata, focal plants decreased root investment, increased root growth towards B. attenuata, and positioned their roots near B. attenuata cluster roots. SRL was greater, and the degree of localized root investment correlated positively with B. attenuata cluster-root biomass. Total nutrient contents in the focal individuals were greater when grown with B. attenuata. Focal plants directed their root growth towards the putatively facilitating neighbour's cluster roots, modifying root traits and investment. Preferential root positioning and root morphological traits play important roles in positive plant-plant interactions.

Mechanical fragmentation of leaf litter by fine root growth contributes greatly to the early decomposition of leaf litter

Understory plant root proliferation into the litter layer occurs in many forest ecosystems and dramatically accelerates litter decomposition and nutrient release in the early stages. Mechanical fragmentation of leaf litter by fine roots could be one main reason, but its mechanism is poorly understood. To quantitatively assess the influence of fine roots on the mechanical fragmentation of leaf litter in the early decomposition process, we examined the effects of fine root mass of Lolium multiflorum on morphological and physical characteristics of decomposing litters of Symplocos setchuensis, a dominant species in a mid-subtropical evergreen broad-leaved forest of China, via a litter bag simulation experiment. The results showed that there were various fine root growth forms in/on decomposing litters, including the penetration and tearing of leaf epidermis, and the “walking or inserting” between the mesophyll tissue and the leaf veins. Fine root mass had a significant positive effect on the mass loss during litter decomposition (F = 8.543, P < 0.01). In a duration of 170-day leaf litter incubation, the mass remaining ration was significantly higher in no roots treatments and fewer roots treatments than that in more roots treatments. In the case of more roots, the physical tensile strength of leaf litter fragments was 0.156 N/mm, which was significantly lower than that under the treatments with fewer roots and no roots (P < 0.05). More fine roots penetrating the litter layer could significantly promote the intensity of mechanical fragmentation by changing the morphology, structure, and physical properties of the leaf litter. The fine root biomass in the litter layer was positively correlated with the decomposition rate, and the specific root length and specific root tip density were two important indicators related to decomposition. In conclusion, fine roots growing into litter promoted the intensity of mechanical fragmentation by increasing root length and producing new root tips and by actively regulating litter traits, so as to improve the utilization efficiency of nutrient release in the early decomposition process.

Divergent root P uptake strategies of three temperate grassland forage species

Temperate grasslands are affected by nutrient deficiency and this deficiency is one of the main limiting factors for forage production, such as the grasslands of the Salado River Basin (Argentina), which exhibit low-P availability for plant growth. Alternatives to increase forage production include the selection of plant species adapted to grow under P deficiency, P fertilization, and arbuscular mycorrhizal (AM) fungi. In a pot experiment, we investigated the effect of low and high-P doses and AM fungi on the development of three forage species. The interaction of P addition and AM fungi increased L. tenuis (legume) biomass production and improve P nutrition, even with high-P dose, because of its higher P requirement to grow and lower ability for P uptake than grasses. High-P increased the biomass of S. arundinaceus (C3 grass) and P. coloratum (C4 grass), and AM fungi did not directly impact on plant growth of grasses, but did impact on P nutrition at either level of P fertilization. The specific P uptake of non-fertilized L. tenuis plants increased 97% due to AM inoculation and was the highest value among the three non-fertilized species. Furthermore, the specific P uptake of non-fertilized grasses was similar, despite the C metabolic pathway and AM fungi, but the specific root length was 70.88% lower for P. coloratum than for S. arundinaceus. Thus, the main strategy of L. tenuis was AM association, whereas that of S. arundinaceus was the highest ability of the root system to explore the soil. In P. coloratum, the strategy could not be explained by changes in specific root length or AM association. Our results would be an advantageous first step to promote better management of forage land sustainably while increasing forage production and preserve the beneficial effects of native AM communities in the Salado River Basin.

Linking root traits and soil moisture redistribution under Achnatherum splendens using electrical resistivity tomography and dye experiments

The rooting traits of deep-rooted alpine grasses strongly control the redistribution of soil moisture (i.e., the changes in the soil volumetric water content, ΔSVWC), which is the most important water resource supporting vegetation growth in cold semiarid regions. However, due to the difficulty of developing appropriate methods to characterize the hidden structures of root-soil systems, the linkages between root traits and ΔSVWC remain challenging to detect. This study aims to identify how the roots of Achnatherum splendens (A. splendens) affect soil water infiltration and spatiotemporal variations in the rhizosphere under different root densities and rainfall patterns using electrical resistivity tomography (ERT) and dye experiments, as well as to determine the relationship between root traits and soil water redistribution. Manipulative rainfall experiments 5, 10, 20 and 40 mm simulated rainfall were applied to sample plots with no plants (control), single and double A. splendens plantings (BAS, SAS, DAS, respectively). The results of ERT and the dyeing profiles showed that the roots of A. splendens greatly affected infiltration processes and the soil water distribution. The soil water was vertically and laterally funneled along the roots. In SAS, which had a lower root length density (RLD), the soil water accumulated mainly in the shallow layer (0–20 cm), while in DAS, which had a higher total root mass density (RMD), the soil water mainly infiltrated rapidly into the deep soil (>20 cm), especially during the extreme (40 mm) rainfall event. The temporal increases in soil moisture below 20 cm under DAS were higher than that those under BAS and SAS after rainfall for 2 and 24 h. The RMD, specific root length (SRL), specific root surface area (SSA) and RLD were all negatively and significantly correlated with the ΔSVWC at 0–20 cm. At 20–40 cm, the RMD and RLD were positively and significantly correlated with ΔSVWC, whereas the SRL and SSA showed the opposite trend. These findings provide direct evidence of the linkages between A. splendens root traits and ΔSVWC using ERT and the dye tracing method, and this evidence is important for the development of soil-plant-atmosphere continuum (SPAC) models.

金塔绿洲不同林龄多枝柽柳根系分叉数与分支角度的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 金塔绿洲不同林龄多枝柽柳根系分叉数与分支角度的关系 DOI: 10.5846/stxb201907261581 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41861009，41461013） Relationship between root forks and branch angle of Tamarix ramosissima at different stand ages in oasis of Jinta County Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:根系构型影响根系空间分布和营养吸收效率，反映了植物适应环境胁迫的生存策略。采用标准化主轴估计（Standardized major axis estimation，SMA）的方法，分析了甘肃金塔北海子国家湿地公园3年生和6年生多枝柽柳（Tamarix ramosissima）根系分叉数与分支角度的异速生长关系。结果表明：随着林龄的增长，湿地群落盖度、高度逐渐增加，多枝柽柳种群的盖度、密度、高度和地上生物量以及根系深度、分叉数、比根长、比表面积、各级根系直径随之增加，根系分支角度和根冠比逐渐减小；多枝柽柳根系分叉数与分支角度回归方程的标准主轴斜率逐渐增大（P<0.05），随着林龄的增长，多枝柽柳根系分叉数的增加速度逐渐大于根系分支角度的生长速度，二者在林龄间呈现出差异化的异速生长关系。随着林龄的增长，多枝柽柳根系构型模式由"扩散型"转变为"紧缩型"，体现了种群应对生境胁迫和竞争的生态适应机制。 Abstract:The root architecture influences root spatial distribution and resorptiton efficiency of nutrients, which may reflect the plant growth strategies to adapt to the environmental stresses. This paper studied the relationship between root forks and branch angle of Tamarix ramosissim at three-year and six-year. The study site was located in Jinta Beihaizi Wetland Park of Gansu Province with the method of standardized major axis estimation (SMA). The height, density and above-ground biomass of the wetland communities were recorded from 5 m×5 m grids at two plots with six replicates. Seventy-two plants of Tamarix ramosissim were selected; the above-ground parts of those plants were cut while the roots were collected by excavating the whole root system, and both were taken back to the lab. In the laboratory, the roots were scanned with Win-RHIZO to measure the root forks and root length. The individual roots was dissected according to the branching order, starting from the distal end of the root system that was numbered as the first order and then increasing sequentially with each branch from the first order to the third order roots. The biomasses of different plots were put in an oven and dried (at 80℃ for 12 h), and then measured. Similarly, the soil moisture content was also measured by oven-drying (at 105 ℃for 24 h). The results showed that with the increasing stand ages, the density, cover, height of the plant community increased, while the root-shoot ratio, root branch angle decreased, the specific cover, density, height, above biomass, root depth, root forks, specific root length and specific root surface area increased, and diameter of different root orders increased. In addition, with the increasing stand ages, the standardized major axis slope of regression equation in the scaling relationships between root forks and branch angle increased (P<0.05). Additionally, the increase speed of the root forks was greater than the growth speed of the root branch angle, and the allometric relationship between root forks and branch angle of Tamarix ramosissima was distinguished at different stand ages. With the increasing stand ages, the root architecture model of Tamarix ramosissima form diffusion to gathering, reflected the mechanism of ecological adaptation under conditions of environmental stresses and competition of the population. 参考文献 相似文献 引证文献

Plant communities, populations and individuals have distinct responses to short‐term warming and neighbour biomass removal in two montane grasslands

AbstractAimsClimate change will impact plant communities and populations but also individual plant performance. Most predictive models of community responses to climate change ignore individual‐level biotic interactions despite their known importance for community diversity and functioning. Here, we consider plant fitness and diversity responses to climate change associated factors at three organisational levels: communities, populations and individual plants, to increase our understanding of how plant communities respond to climate change.LocationMontane grassland, Tasmania, Australia.MethodsIn two plant communities, we manipulated temperature using open‐top chambers and removed random and dominant species biomass. Two years after experimental manipulations, we assessed the impact of treatments on species diversity, community‐ and population‐level functional traits and individual plant fitness.ResultsSpecies diversity was affected by warming in one of the two communities, while community‐level functional trait diversity metrics were unaffected by treatments. Mean community trait values were strongly impacted by dominant species biomass removal in both communities, notably increasing specific leaf area (SLA) and specific root length. SLA showed the strongest population‐level trait response, with higher values found in warmed plots and lower values found in dominant species biomass removal plots. Neighbours had a stronger competitive effect on individual plant fitness in warmed compared to unwarmed conditions at the higher‐elevation site and facilitation was common in both communities.ConclusionsWe demonstrated that over short time scales, plant communities respond to experimental warming and biomass removal across multiple organisational levels. Competitive and facilitative interactions played a significant role in determining fitness outcomes, but competitive interactions dominated under warmed conditions. We highlight the importance of local‐scale biotic interactions in mediating individual responses to warming and recommend their inclusion in future studies of how climate change will impact the long‐term structure and function of plant communities through short‐term impacts on individual plant fitness.

不同混交比例对杉木和大叶榉幼苗功能性状的影响

了解林木功能性状在不同培育模式下的变异和关联，对揭示林木生态适应性及其生态功能具有重要意义。选取了亚热带地区两种常见人工林树种杉木、大叶榉幼苗为研究对象，设置4种不同栽培模式的盆栽试验：单一杉木（4C），单一大叶榉（4Z）和杉木、大榉树3种混栽模式（1C3Z、2C2Z、3C1Z），研究不同混交比例对其叶、茎、根功能性状的影响。结果表明：（1）杉木总叶面积、叶干物质含量、净光合速率、蒸腾速率和气孔导度在混栽模式下显著减小，而比叶面积显著增大；根长和比根长在不同处理间无显著差异；叶、茎、根生物量和单株总生物量在混栽模式下显著低于4C处理，不同混栽模式之间差异不显著。（2）大叶榉单叶面积在3C1Z处理下最高，总叶面积随大叶榉在树种组成中所占比例的降低而逐渐增大，比叶面积在不同处理间无显著差异，叶干物质含量、净光合速率、蒸腾速率和气孔导度均在2C2Z处理下最大，而瞬时水分利用效率在2C2Z处理下最小；根长在3C1Z处理下显著增大，比根长在不同处理间无显著差异；叶、茎、根生物量和单株总生物量随大叶榉在树种组成中所占比例的降低而逐渐增大。综合来看，杉木和大叶榉混合处理中杉木种间竞争大于种内竞争，而大叶榉相反；随杉木在混栽处理中比例减少，其主要通过增加比叶面积，提高净光合速率，减少茎生物量积累来适应种间竞争关系；而大叶榉随其在混栽处理中比例的减少，显著增加叶面积和根长来提高资源利用率，减少地下资源分配，提高地上茎生物量积累。因此，树种混交比例将显著影响林木功能性状及其生物量积累，选择适宜混交比例对混交林可持续经营具有重要意义。;Understanding the variation and correlation of plant functional traits among different planting patterns is of great importance to reveal the ecological adaptability and function of different tree species. The variations of functional traits in two common tree species' seedlings (Cunninghamia lanceolata and Zelkova schneideriana) in subtropical area were studied among different mixing proportions based on pot experiment. These mixing proportions included a single-species C. lanceolata planting pattern (4C), a single-species Z. schneideriana planting pattern (4Z) and three mixed treatments (1C3Z, 2C2Z, and 3C1Z). The results showed that:(1) total leaf area, leaf dry matter content, net photosynthetic rate, transpiration rate and stomatal conductance of C. lanceolata decreased significantly in the mixed treatments compared to 4C treatment, while specific leaf area increased significantly. Root length and specific root length were no difference among different treatments. Leaf biomass, stem biomass, root biomass and total biomass per plant of C. lanceolata among different treatments were significantly lower than in the 4C treatment, and these variables were no significant difference among mixed treatments. (2) mean leaf area of Z. schneideriana was the highest in the 3C1Z treatment. Total leaf area increased gradually with the decrease of the proportion of Z. schneideriana in tree species composition, specific leaf area was no significant difference among treatments, leaf dry matter content was the highest in the 2C2Z treatment. Net photosynthetic rate, transpiration rate and stomatal conductance of Z. schneideriana were the highest in the 2C2Z treatment, while the instantaneous water use efficiency was the lowest in the 2C2Z treatment. Root length of Z. schneideriana increased significantly in the 3C1Z treatment, while specific root length showed less variation among different treatments. Leaf biomass, stem biomass, root biomass and total biomass per plant of Z. schneideriana increased gradually with the decrease of the proportion of Z. schneideriana in tree species composition. Overall, interspecific competition was greater than intraspecific competition for C. lanceolata in mixed C. lanceolata and Z.schneideriana treatments, while the pattern was opposite for Z. schneideriana. With the decrease of the proportion of C. lanceolata in mixed treatments, C. lanceolata enhanced interspecific competition by increasing specific leaf area and net photosynthetic rate and reducing stem biomass accumulation. While with the decrease of the proportion of Z. schneideriana in mixed treatments, Z. schneideriana significantly increased leaf area and root length to improve resource utilization, and reduced underground resource allocation and increased aboveground stem biomass accumulation. Therefore, mixing proportion of tree species will significantly affect functional traits and biomass accumulation. Determining appropriate mixing proportion is of great significance for sustainable management of mixed-plantation.

根系功能性状对干瘠立地适应的种间差异——以北京石质山地主要观赏树种为例

分析干瘠立地中不同树种根功能性状的变化及差异，研究不同树种对干瘠环境的适应对策。试验材料为林龄、林分密度相对一致的石质山区主要观赏树种（黄栌、山桃、栓皮栎），采用挖掘法获取树木细根，测定细根形态参数。根据田间持水量和石砾含量分别设置4个干瘠梯度（轻度、中度、重度、极度），对比分析北京干瘠地3种树种根功能性状，探讨干瘠立地中不同树种根系形态的差异及其对特殊生境的适应。结果表明：干旱、瘠薄均对树木的根功能性状产生影响，但对不同性状以及不同树种的影响程度具有差异，其中对山桃根系的影响最大；3种树种根功能性状在不同干瘠等级下存在显著变化，同一性状的变化因树种不同而异。从轻度到极度干旱，3种树种的RL均逐渐减小，但是黄栌变化不显著；黄栌、栓皮栎RTD随干瘠的加剧而减小，而山桃随干瘠的加剧而增加；黄栌和山桃SRL随干旱、瘠薄的加剧，表现出一致的规律，即从轻度到极度，其SRL随即减小，而栓皮栎SRL随干旱、瘠薄的加剧而增大；随干瘠的加剧，黄栌SRA显著减小，山桃、栓皮栎SRA随干瘠的加剧而增大。树木对干瘠环境的变化都有一定的响应能力及适应对策，能够通过自身的形态变化来适应不断变化的环境，但不同物种对干瘠环境变化的适应途径不同，通过权衡碳分配、碳消耗采取了相应的生态适应策略，不同树种间存在明显差异。本研究3种树种中，黄栌在干瘠环境下根系性状变化不显著，耐干瘠能力较强；干瘠胁迫对山桃根系性状影响显著，山桃通过主动调节根系形态变化来适应不断变化的环境，具有较强的抗干瘠能力；栓皮栎的细根数量多，吸收土壤水分、养分能力较强，能够在干瘠环境中快速生长。;The changes and differences of root functional traits of different tree species in dry-barren site were analyzed, and the adaptive strategies of different tree species to dry-barren environment were studied. The experimental materials were mainly ornamental tree species(C.coggygria, Amygdalus davidiana and Quercus variabilis) in the shallow mountain area with same age and stand density. Fine roots of trees were obtained by digging, and morphological parameters of fine roots were measured. According to the field water holding capacity and gravel content of the sample plots, four dry and barren gradients (light, moderate, heavy and extreme) were set. The root functional traits of three ornamental tree species were analyzed and compared, and then the difference of root morphology of different tree species in dry-barren site and their adaptability to special habitats were studied. The results showed that drought and barrenness had an impact on the root functional traits of trees, but the degree of influence on different traits and different tree species was different, and the impact on Amygdalus davidiana was the largest; The root functional traits of the three tree species varied significantly under different dry-barren grades, and the change of the same traits varied with tree species. From mild drought to extreme drought, the root link length (RL) of the three tree species decreased gradually, but the change of C.coggygria was not significant; The root tissue density (RTD) of C.coggygria and Quercus Variabilis variabilis decreased with the increase of dry and barren, but the Amygdalus davidiana increased with the increase of dry and barren; The specific root length (SRL) of C.coggygria and Amygdalus davidiana decreased from mild to extreme, and the SRL of Quercus variabilis increased with the increase of drought and barrenness; The specific root area (SRA) of C.coggygria increased with the increase of dry and barren soil, while the SRA of Amygdalus davidiana and Quercus variabilis decreased with the increase of dry and barren. Trees had a certain ability to respond and adapt to changes in dry-barren environments, which could adapt to the changing environment through their own morphological changes. Different species had different ways to adapt to the dry-barren environment, corresponding ecological adaptation strategies were adopted by balancing carbon allocation and carbon consumption. There were obvious differences between different tree species. Of the three tree species in this study, the root functional traits of C.coggygria did not change significantly in dry-barren environment, and the ability to tolerate dry and barren was strong; Dry and barren stress had a significant impact on the root traits of Amygdalus davidiana. By actively adjusting the morphological changes of the root system to adapt the changing environment, Amygdalus davidiana had a strong ability to resist dryness and barren; The fine roots of Quercus variabilis were abundant, so it could absorb soil moisture and nutrients, and could grow quickly in dry-barren environment.