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Plants possess intricate defense mechanisms to resist cadmium (Cd) stress, including strategies like metal exclusion, chelation, osmoprotection, and the regulation of photosynthesis, with antioxidants playing a pivotal role. The application of nitrogen (N) and phosphorus (P) fertilizers are reported to bolster these defenses against Cd stress. Several studies investigated the effects of N or P on Cd stress in non-woody plants and crops. However, the relationship between N, P application, and Cd stress resistance in valuable timber trees remains largely unexplored. This study delves into the Cd tolerance mechanisms of Phoebe zhennan, a forest tree species, under various treatments: Cd exposure alone, combined Cd stress with either N or P and Cd stress with both N and P application. Our results revealed that the P application enhanced root biomass and facilitated the translocation of essential nutrients like K, Mn, and Zn. Conversely, N application, especially under Cd stress, significantly inhibited plant growth, with marked reductions in leaf and stem biomass. Additionally, while the application of P resulted in reduced antioxidant enzyme levels, the combined application of N and P markedly amplified the activities of peroxidase by 266.36%, superoxide dismutase by 168.44%, and ascorbate peroxidase by 26.58% under Cd stress. This indicates an amplified capacity of the plant to neutralize reactive oxygen species. The combined treatment also led to effective regulation of nutrient and Cd distribution in roots, shoots, and leaves, illustrating a synergistic effect in mitigating toxic impact of N. The study also highlights a significant alteration in photosynthetic activities under different treatments. The N addition generally reduced chlorophyll content by over 50%, while P and NP treatments enhanced transpiration rates by up to 58.02%. Our findings suggest P and NP fertilization can manage Cd toxicity by facilitating antioxidant production, osmoprotectant, and root development, thus enhancing Cd tolerance processes, and providing novel strategies for managing Cd contamination in the environment. [ABSTRACT FROM AUTHOR]

Increasing atmospheric nitrogen (N) deposition has a profound impact on the ecosystem functions and processes. Fine root decomposition is an important pathway for the reentry of nutrients into the soil. However, the effect of N addition on root decomposition and its potential mechanism is not well understood with respect to root branch orders. In this study, we conducted a 30-month decomposition experiment of fine roots under different concentrations of N addition treatments (0, 30, 60, and 90 kg N ha-1 year-1, respectively) in a typical Pinus massoniana plantation in the Three Gorges Reservoir Area of China. In the early stage of decomposition (0-18 months), N addition at all concentrations promoted the decomposition of fine roots, and the average decomposition rates of order 1-2, order 3-4, order 5-6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively. In the late stage of decomposition (18-30 months), high N addition inhibited the decomposition of fine root, and the average decomposition rates of order 1-2, order 3-4, order 5-6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively. At the same time, N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage, whereas high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage. The decomposition constant (k) was significantly correlated with the initial chemical quality of the fine roots and lignin-degrading enzyme activities. The higher-order (order 3-4 and order 5-6) fine roots decomposed faster than lower-order (order 1-2) fine roots due to higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrations. In addition, low N (30 kg N ha-1 year-1) treatments decreased soil organic matter content, whereas high N (90 kg N ha-1 year-1) treatment had the opposite effect. All the N treatments reduced soil pH and total P content, indicating that increased N deposition may led to soil acidification. Our findings indicated that the effect of N addition on decomposition varied with the decomposition stages. The decomposition difference between the lowerorder and higher-order fine roots were controlled strongly by the initial chemical quality of the fine roots. This study provides new insights into understanding and predicting possible changes in plant root decomposition and soil properties in the future atmospheric N deposition increase scenarios. [ABSTRACT FROM AUTHOR]

Construction economics of plant roots exhibit predictable relationships with root growth, death, and nutrient uptake strategies. Plant taxa with inexpensively constructed roots tend to more precisely explore nutrient hotspots than do those with costly constructed roots but at the price of more frequent tissue turnover. This trade-off underlies an acquisitive to conservative continuum in resource investment, described as the "root economics spectrum (RES)." Yet the adaptive role and genetic basis of RES remain largely unclear. Different ecotypes of switchgrass (Panicum virgatum) display root features exemplifying the RES, with costly constructed roots in southern lowland and inexpensively constructed roots in northern upland ecotypes. We used an outbred genetic mapping population derived from lowland and upland switchgrass ecotypes to examine the genetic architecture of the RES. We found that absorptive roots (distal first and second orders) were often "deciduous" in winter. The percentage of overwintering absorptive roots was decreased by northern upland alleles compared with southern lowland alleles, suggesting a locally-adapted conservative strategy in warmer and acquisitive strategy in colder regions. Relative turnover of absorptive roots was genetically negatively correlated with their biomass investment per unit root length, suggesting that the key trade-off in framing RES is genetically facilitated. We also detected strong genetic correlations among root morphology, root productivity, and shoot size. Overall, our results reveal the genetic architecture of multiple traits that likely impacts the evolution of RES and plant aboveground-belowground organization. In practice, we provide genetic evidence that increasing switchgrass yield for bioenergy does not directly conflict with enhancing its root-derived carbon sequestration. [ABSTRACT FROM AUTHOR]

The community species abundance and diversity declined with bamboo invasion had been widely reported worldwide. However, the physiological strategies used during root competition between native species and invasive bamboo are poorly understood. To clarify the mechanisms underlying such strategies, the stoichiometric dynamics and homeostasis of nitrogen, phosphorus, organic carbon in root orders of Phyllostachys edulis (I du [=I-Pe, years 1 and 2]; II du [=II-Pe, years 3 and 4]), Cunninghamia lanceolata in transition and pure forests were analyzed. With increasing intensity of bamboo invasion, N, P, and C content of C. lanceolata root orders declined, N and P content in P. edulis rhizome orders declined, while C increased, the stoichiometric ratios in mixed forest interface mainly increased, and the stoichiometric differences within native and invasive species root orders narrowed. Meanwhile, the stoichiometric homeostasis index (H) of elements in the same root order and even the same elements in different root orders were not consistent. H of most root orders (except some HP) was greater than 4, the H ranked order was I-Pe > Cl > II-Pe in mixed interfaces, and the N:P ratio of most species root orders was greater than 16, despite being affected by invasion. Our research concluded that the bamboo invasion narrows stoichiometric differences within root orders, and the juvenile bamboo rhizome has a stronger capacity for homeostatic regulation than in adult bamboo and C. lanceolata, which is a key determinant of bamboo invasion success. [ABSTRACT FROM AUTHOR]

Prunus genus species are widely spread in semi-arid regions due to their ability to adjust to the limited water supply. Former research described the effect of water deficit on their aboveground development. However, less is known about the effects of water stress on the development of the root system. In order to investigate the effects of the irrigation regime on the root system development, young plum (Prunus cerasifera) trees were grown under three irrigation regimes for a period of five months. The effects of the irrigation regime on different root order and total root system elongation, biomass growth and tip numbers were analyzed. The results indicate that the responses vary according to the stress level. Under moderate stress, the total root system biomass decreases relative to the full irrigation treatment. However, low-order root formation remains similar to that found under no stress conditions. Under severe stress, the formation of low-order roots is also inhibited. Our results suggest that plum trees' response to water deficit stress escalates according to the stress level. Namely, moderate stress affects the growth rate of the root system but does not alter the relative contribution of different orders, while severe stress both inhibits the total growth and changes the relative contribution of the different root orders. The combined measurements of the total root system and the different orders enable the identification of a stepwise response to water stress. [ABSTRACT FROM AUTHOR]

Decaying roots are the major source of carbon that is stabilized in soil, but our understanding of plant decomposition is primarily based on decay patterns observed in leaf tissues. Chemical traits that impact microbial activity are the primary intrinsic control over leaf decomposition, and it is usually assumed that similar mechanisms control root decay. We hypothesized that root morphological traits may be an alternative control over root decay because root tissue is embedded in soil and is similar in size to soil minerals and aggregates. We compared decomposition of roots from two coexisting tree species with contrasting traits: tulip poplar ( Liriodendron tulipifera ) and American elm ( Ulmus americana ). If morphological traits are a stronger control over decomposition than chemical traits, Ulmus roots should decompose faster due to their thinner structure and increased surface area. Alternatively, if chemical traits are more important, then Liriodendron roots should decompose faster because of greater nutrient and energy availability. Unlike previous studies, the experiment was conducted in the field using root litterbags that also included mineral soil to simulate realistic physical processes and root-soil mineral interactions. Our results indicate that controls over decomposition depend on root order. For 3–4th order roots, mass loss in Liriodendron roots was double that in Ulmus roots, reflecting chemical control, but the pattern was reversed for 1–2nd order roots, consistent with morphological control. In addition, tissue chemistry shifted dramatically during decomposition for all Liriodendron root orders, but not for Ulmus . In contrast, root morphology shifted for Ulmus , with large reductions in specific root length and tip abundance, but not for Liriodendron . These results indicate that Liriodendron decomposition occurs evenly across root orders through microbial activity, which is regulated by traditional chemical measures of recalcitrance. Ulmus roots are more chemically recalcitrant, but the finer 1–2nd order Ulmus roots still lost mass very rapidly through physical fragmentation. These differing mechanisms of decomposition have implications for how root carbon is deposited into differing pools of soil organic matter. Thick, labile roots may contribute more C to soil microbial biomass and clay-associated simple organic molecules, whereas thin, recalcitrant roots would be expected to contribute to particulate organic matter. [ABSTRACT FROM AUTHOR]

Ambient CO 2 concentration is currently 400 μmol mol −1 , and projections forecast an increase up to 970 μmol mol −1 by century’s end. Elevated CO 2 can stimulate C3 plant growth, whereas nitrogen is the main nutrient plants acquire from soils and often limits growth. Plants primarily obtain two nitrogen sources from the soil, ammonium (NH 4 + ) and nitrate (NO 3 − ). At elevated CO 2 levels, plant growth and nitrogen metabolism is affected by the nitrogen source. Most research has focused on shoot traits, while neglecting the plants’ hidden half, the root. We studied the effects of elevated CO 2 and nitrogen source on hydroponically grown tomato plants, a C3 model and crop plant. Our main objective was to determine how the nitrogen source and elevated CO 2 affect root development. Our results indicate they affect development in terms of the size and anatomy of different root orders. Specifically, root xylem development was found sensitive to the nitrogen source, whereas NO 3 − -supplied plants displayed greater xylem development compared to their NH 4 + counterparts, and also to a lesser extent, to elevated CO 2 , which we found inhibits this development. Additionally, elevated CO 2 decreased root respiration in different root orders exclusively in plants supplied with NH 4 + as the sole nitrogen source. [ABSTRACT FROM AUTHOR]

Background and Aims: Root branching leads to morphological and functional heterogeneity of fine roots. However, the structure of soil microbiota associated with root branching orders has never been investigated. Deep insights into rhizosphere microbial community could provide a better understanding of the plant-microbe relationship. Methods: Fine roots of poplar ( Populus × euramericana (Dode) Guinier.) were sampled and sorted into three groups according to their branching orders. Scanning electron microscopy (SEM) was used to observe the surface features of different orders of fine roots. Illumina MiSeq was employed to analyze the bacterial community structure of soil compartments from different root orders (i.e., R1, R2, and R3) and bulk soil compartment (NR). Results: SEM showed that the first-order root with smaller diameter had dense coverage of vigorous root hairs, whereas higher order roots with larger diameter had sloughed-off cortical tissues on the rhizoplane. The diversity of bacterial communities was higher in the R1 and R2 compartment than in R3 or NR. There were 80 genera with a relative abundance above 0.05% in soils. Ternary plot revealed that bacterial genera were significantly enriched in R1 than in R2 or R3. Redundant analysis (RDA) showed that 12 dominant bacterial genera with a relative abundance over 1% were significantly correlated with P and NH -N content of soils. Conclusions: Root orders could influence the inhabitation of bacterial communities. The core groups of bacterial communities inhabiting the rhizosphere were correlated with soil nutrients. The root order-dependent interactions of plant-microbe provided a new model about the association between roots and soils. [ABSTRACT FROM AUTHOR]

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Setting one-yearold potted Cnnmomum camphora seedlings as the research object, using exponential fertilization method, we detected the first to the fifth order fine roots C, N and P contents, in order to explore the effects of fertilization on C, camphora seedlings, and to provide a theoretical basis for C, camphor fatt growing and efficient use of resources in nurturing process. The results were as follows: (1) C concentrations of the differences orders' fine root were not significant, with the rise of the root order, while C content overall upward trend. Fertilization had no significant effect on the C concentration of fine root(P>0.05); (2) N and P concentrations of fist order roots were the maximum, while fifth order roots were the minimum, with the rise of root orders. N and P concentrations significantly decreased (P <0.05); (3) N significantly increased the N content level of the first to the second fine roots. P fertilizer significantly increased the P content of a root, mix of nitrogen and phosphorus fertilizer could improve the root uptake of P; (4) C : N : P had a significant difference in different root orders roots; (5) The firs order roots' mean C : N : P was 366 : 16 : 1. the fifth order root 807 : 12 : 1. with increased root order. C ratio of three kinds of elements increased significant ly. while the N : P changed little; (6) Fertilization did not change the proportion of C; however. N fertilizer or mix of nitrogen and phosphorus fertilizer significantly increased the N proportion of the fist to second order roots. In conclu-sion: The treatment 9 pairs of C. camphor on seedling stage indicators impatt mott significantly. A fertilizer with the nitrogen 4 g.plant-1 . the phosphorus 4 g.plant-1 and the potassium 2 g.plant-1 . would have significant promote growing for growing and development of fine roots in C. camphor seedlings. [ABSTRACT FROM AUTHOR]

The study on microbial community composition in rhizosphere soils surrounding different order roots is of great significance for understanding the interactions between roots and microbes. Using Illumina Miseq sequencing technology, this study analyzed the differences of fungal community structure in bulk soils and rhizosphere soils surrounding different root orders of poplar (Populus × euramericana 'Neva') tree. The microbial species annotation showed that 128, 124, 130 and 101 fungal genera were classified in the rhizosphere soils around 1-2 order roots (R1), 3 order roots (R2), 4-5 order roots (R3) and in the bulk soils (NR), respectively. The differences of present fungal genera indicated a selectivity mechanism driving fungal community assembly in poplar rhizosphere soils. There were seven fungal genera with more than 1% of relative abundance in rhizosphere soils. Trichoderma was the dominant fungal genus in R1. Trichosporon and Aspergillus were the dominant fungal genera in R2 and R3, respectively. Alpha (α) diversity indices showed that the fungal diversity was significantly different among root orders. Specifically, the diversity of soil fungal community in the rhizosphere soils around lower order roots was significantly higher than that of higher order roots (P＜0.05). Beta (β) diversity indices showed that the dissimilarity of fungal community composition increased along with the root orders. All these results implied the different composition and structure of fungal community are closely related with the function of fine root orders.