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Key message Short-term nitrogen (N) deposition stimulates phosphorus (P) demand owing to the growth improvment of Phyllostachys edulis seedlings. Increased N loads led to the acquisition and utilization of sufficient P, while the limitation of P starvation could be alleviated by the higher activity of soil acid phosphatase and P use efficiency rather than P resorption from senescent organs. Context Plants in most terrestrial ecosystems are usually subjected to natural phosphorus (P) deficiency or surplus by overfertilization associated with increasing global nitrogen (N) deposition. As the widely distributed gramineous plant in Southern China, moso bamboo (Phyllostachys edulis (Carrière) J. Houz) grows fast and it also shows a relatively good growth performance under the variable N and P conditions. However, few studies focus on the special mechanism of P mobilization and utilization of moso bamboo, especially with the N loads. Aims The objective of this study was to figure out the mechanisms of P mobilization and utilization in P. edulis seedlings under varying levels of soil P and N deposition conditions in the subtropical region of China. Methods We grew P. edulis seedlings under 3 experimental N deposition rates (0 (N −), 30 (N +), and 60 (N + +) kg N ha−1·a−1) and 3 levels of soil P (2.99 mg·kg−1, soil available P content under natural conditions, denoted as P1; 20 mg·kg−1, P2; and 40 mg·kg−1, P3). We measured growth traits and analyzed the related P use indices. Results Dry weight and P accumulation of new leaves and stems increased with increasing N loads under the 3 P treatments, with the positive effects of N deposition being stronger in the P2 and P3 treatments. Compared with N − , N + , and N + + significantly increased P use efficiency (PUE) (+ 15.54% and + 12.47%, respectively) regardless of soil P conditions. The P resorption efficiency showed a decreasing tendency under variable P conditions with increasing N, whereas PUE was further increased. Acid phosphatase (APase) activity and soil available P content were significantly improved by N loads in P1. Conclusion Phyllostachys edulis seedlings showed high growth plasticity and P mobilization mechanisms under different soil P availability with N loads. In general, N addition stimulated P demand of P. edulis seedlings owing to the growth promotion in the short period of experiment. A special P use mechanism in P deficiency conditions was that the limitation of P starvation was alleviated by the higher soil APase activity and PUE instead of P resorption from senescent organs. The long-term effect of N deposition on P mobilization and utilization in P. edulis forests requires further monitoring.

Drought stress is an important limiting factor of plant performance, and how it interacts with increasing nitrogen (N) deposition to affect seedling development requires further investigation. This study addresses the combined effects of N deposition and drought on growth and physiological attributes of Phyllostachys edulis (Carr.) seedlings. Seedling growth attributes and nitrogen metabolism indicators were evaluated after the fast-growing period in the presence of four simulated N deposition rates (control, 0 kg·ha−1·yr−1; low N, 30; medium N, 60; high N, 90) and two watering conditions (normal, 75 ± 5% of field capacity; or drought, 35 ± 5%). Drought stress significantly inhibited P. edulis seedling growth and N metabolism. Under normal watering conditions, greater simulated N deposition was associated with higher seedling component mass, free amino acid and soluble protein content in leaves, and enzyme activity related to N metabolism. Under drought conditions, medium N deposition maximized seedling component mass and enzyme activity related to N metabolism. Overall, low and medium N deposition improved seedling performance under drought conditions, but high N deposition did not. Moderate N deposition can partially offset the negative effects of drought stress on P. edulis seedling development.

Camptotheac acuminata Decne is a unique tree species in China with an important secondary metabolite, camptothecin (CPT), used in the treatment of cancer. Nitrogen (N) is an important element that affects plant growth and the accumulation of CPT. Reports on the effect of N on CPT synthesis from a genetic perspective are scarce. To explore the effects of different N sources and levels on CPT synthesis in C. acuminata, two-year-old seedlings were fertilized with different concentrations of pure ammonium sulphate, source of ammonium N (NH4+–N), and potassium nitrate for nitrate N (NO3−–N). Concentrations of 2.5, 5, 7.5, and 10 g pot−1 NH4+–N and NO3−–N were used. The results showed that 7.5 g NH4+–N and NO3−–N treatments were best for growth and fresh weight of leaves. Compared with the other treatments, the CPT content, tryptophan synthase and tryptophan decarboxylase activities, and expression of the CaTSB and CaTDC1 genes under the 2.5 g NH4+–N and NO3−–N treatments peaked significantly at 30 days. However, the expression of CaTDC2 surpassed that of the other two genes at 60 days. Therefore, compared with NH4+–N source, the NO3−–N source was more beneficial for growth, and NO3−–N was better for CPT yield. Consequently, leaves of C. acuminata treated with 2.5 g NO3−–N could be harvested after 30 days to obtain maximum CPT content. CaTDC1 is more closely linked to CPT synthesis. The results of this study improved the production of CPT in C. acuminata via fertilization.

The effects of nitrogen (N) deposition and management practices on leaf litterfall and N and P return in Moso bamboo forest are not yet known. In this study, we investigated the effects of four levels of simulated N deposition, including low-N (N30, 30 kg ha−1 year−1), medium-N (N60, 60 kg ha−1 year−1), and high-N (N90, 90 kg ha−1 year−1), and a control with no N (N-free addition). The experiment was performed in a Moso bamboo forest under conventional management (CM) and intensive management (IM). The results showed that leaf litterfall and N and P return occurred mainly from March to June and accounted for 78.2–82.2, 78.5–82.1, and 85.6–94.6% of annual leaf litterfall, N return, and P return, respectively. Unlike CM, IM significantly increased leaf litterfall and N and P return. The positive effects were further amplified by low- and medium-N deposition, but not high-N deposition. The combination of low- and medium-N deposition and IM significantly increased N and P return, but not litterfall. Our results indicated that the interaction of anthropogenic management practices and N deposition need to be considered when estimating the effects of N deposition on the biogeochemical cycle of a forest ecosystem.

Light quality is an important environmental factor for plant growth and development. In this study, the effects of light quality (white, blue, yellow, and red light) on plant growth, photosynthesis, and radical oxygen species production and scavenging were investigated, in Camptotheca acuminata (C. acuminata) seedlings, by means of measuring growth parameters, photosynthetic pigments, gas exchange, and chlorophyll fluorescence, as well as stomatal structure and density, chloroplast ultrastructure, and ROS contents and antioxidant activities. Compared with white light, red light significantly increased seedling height, shoot, and total plant biomass, and promoted the highest photosynthetic capacity, electron transport, and photochemical efficiency. Red light also helped facilitate leaf development, indicated by higher total and specific leaf area, as well as decreased malondialdehyde content and relative electrolyte conductivity and contents of superoxide anion production rate and peroxide. In contrast, blue and yellow light significantly reduced plant growth, and increased activities of superoxidase dismutase, peroxidase, and catalase. Furthermore, red light promoted chloroplast development, which enhanced photosynthetic efficiency. These results suggest that red light could improve plant growth in C. acuminata seedlings through activating photosynthetic processes, reducing ROS accumulation, and maintaining chloroplast structure.

The elite indica rice variety Hua-jing-xian 74 and its 12 single segment substitution lines (SSSLs), all of which have been shown to have quantitative trait loci (QTL) for panicle number (PN), were used as crossing parents to construct a half-diallel crossing population with the aim of analyzing the expression of these QTL under different cropping densities. A total of 91 half-diallel crossing combinations were grown in two planting seasons at three cropping densities. PN was measured at the mature stage. The additive, dominant and epistatic effects of the 12 QTL as well as their interaction effects with the seasons and with the densities were estimated based on genetic effect components. Our analysis revealed that PN generally decreased with increasing cropping density. In the six single environments, eight additive QTL, nine dominant QTL and 49 pairs of epistatic QTL were detected, which were mostly associated with estimated positive, positive and negative effects, respectively. Expression of these QTL differed across planting seasons and cropping densities, implying an existing of QTL-by-environment interaction. Further analysis of the QTL effect components revealed that seven, eight and 28 pairs of QTL were present with significant additive, dominance, epistasis and/or interaction effects with densities. QTL additive and dominant effects were mostly positive, while epistatic effects were all negative. No significant QTL-by-season effects were detected. QTL Pn3-1, without any significant additive-by-density interaction effect, showed stable additive expression across densities. QTL Pn3-1, Pn3-2 and Pn6-1 showed stable dominance expression, and QTL pairs Pn2-1/Pn9, Pn2-2/Pn3-1, Pn2-2/Pn6-2, Pn3-1/Pn6-1, Pn3-1/Pn7 and Pn6-1/Pn6-3 had stable epistasis expression. The remaining significant QTL had different effects across densities. We determined that a density of 10 × 16.7 cm2 had little influence on QTL expression, that a density of 16.7 × 16.7 cm2 mostly increased QTL additive and dominant effects and decreased QTL epistatic effects and that a density of 23.3 × 16.7 cm2 had the opposite impact on QTL effects compared with 16.7 × 16.7 cm2. Additionally, the influence of density on QTL epistatic effect was generally larger than that on QTL additive or dominant effect. These results provide the information on cropping density and how it influences PN QTL expression, which may be useful information to improve rice PN via heterosis and/or QTL pyramiding.

Chronic exposure to arsenic (As) in rice has raised many health and environmental problems. As reported, great variation exists among different rice genotypes in As uptake, translocation, and accumulation. Under hydroponic culture, we find that the Chinese wild rice (Oryza rufipogon; acc. 104624) takes up the most arsenic among tested genotypes. Of the cultivated rice, the indica cv. 93-11 has the lowest arsenic translocation factor value but accumulates the maximum concentration of arsenic followed by Nipponbare, Minghui 86, and Zhonghua 11. Higher level of arsenite concentration (50 μM) can induce extensive photosynthesis and root growth inhibition, and cause severe oxidative stress. Interestingly, external silicate (Si) supplementation has significantly increased the net photosynthetic rate, and promoted root elongation, as well as strongly ameliorated the oxidative stress by increasing the activities of antioxidant enzymes superoxide dismutase, ascorbate peroxidase, and peroxidase in roots and/or leaves of 93-11 seedlings. Notably, 1.873 mM concentration of Si considerably decreases the total As uptake and As content in roots, but significantly increases the As translocation from roots to shoots. In contrast, Si supplementation with 1.0 mM concentration significantly increases the total As uptake and As concentrations in roots and shoots of 93-11 seedlings after 50 μM arsenite treatment for 6 days.

Water stress is one of the main environmental stresses that affect plant growth and development. Salicylic acid (SA) induces water stress tolerance in plants. In this study, the effect of exogenous SA on physiological and biochemical process in Red bayberry (Myric rubra) seedlings, of three different genotypes, that were grown under water stress (soil ranging from 20 to 50 % of field capacity) was evaluated. Results showed that water stress severely affected the relative water content (RWC), photosynthesis, stomatal conductance and enzymes activities. Genotypes differed in RWC, Chlorophyll content, gas exchange parameter, antioxidant enzymes activities and proline, and the genotype Biqi had the RWC, photosynthesis, stomatal conductance and enzymes activities greater than the other two genotypes Wangdao and Shenhong. SA treated plants showed, in general, a higher RWC, chlorophyll content, photosynthetic rate, stomatal conductance, superoxide dismutase activity and proline content, and a lower relative electrolyte conductivity, methane dicarboxylic aldehyde content and catalase activity compared to those of untreated seedlings. These results signified the role of SA in diminishing the negative effects of drought on Red bayberry plants and suggest that SA could be used as a potential growth regulator, for improving plant growth under water stress.

Camptotheca acuminata (C. acuminata) is utilized in preparation of drugs and as constituent in functional foods of China due to high camptothecin (CPT) content in different plant parts. Light intensity is one of the most critical factors which affect plant growth and secondary metabolites. Pot experiment was conducted to study the effect of light intensity (i.e., 100 % irradiance (control), 75 % irradiance, 50 % irradiance and 25 % irradiance) on contents of CPT, activity of enzymes and genes expression related to CPT biosynthesis of C. acuminata seedlings. The study examined total leaf biomass, CPT content, activities of tryptophan synthase (TSB) and tryptophan decarboxylase (TDC), and relative expression of TSB, TDC1, and TDC2 genes. Plants grown in 75 % irradiance possessed the greatest leaf biomass compared with 100 % light irradiance. Highest values of CPT contents were found after 60 days in plants grown in 50 % irradiance, followed by 25, 75 % and full sunlight. Furthermore, activities of TSB, TDC and relative expression of genes of TSB, TDC1, and TDC2, were significantly increased after 60 days of 50 % irradiance compared with full sunlight. Irradiance of 50 % up-regulated the expression of CPT biosynthesis-related genes and induced CPT biosynthesis. In addition to that lower or higher irradiance inhibited the expression of CPT biosynthesis-related genes and CPT biosynthesis. It is concluded that manipulating light intensity can be an effective means to achieve highest CPT yield in medicinal plants.

KEY MESSAGE : We develop a set of universal genetic markers based on single-copy orthologous (COSII) genes in Poaceae. Being evolutionary conserved, single-copy orthologous (COSII) genes are particularly useful in comparative mapping and phylogenetic investigation among species. In this study, we identified 2,684 COSII genes based on five sequenced Poaceae genomes including rice, maize, sorghum, foxtail millet, and brachypodium, and then developed 1,072 COSII markers whose transferability and polymorphism among five bamboo species were further evaluated with 46 pairs of randomly selected primers. 91.3 % of the 46 primers obtained clear amplification in at least one bamboo species, and 65.2 % of them produced polymorphism in more than one species. We also used 42 of them to construct the phylogeny for the five bamboo species, and it might reflect more precise evolutionary relationship than the one based on the vegetative morphology. The results indicated a promising prospect of applying these markers to the investigation of genetic diversity and the classification of Poaceae. To ease and facilitate access of the information of common interest to readers, a web-based database of the COSII markers is provided ( http://www.sicau.edu.cn/web/yms/PCOSWeb/PCOS.html ).