Fast growth involves high dependence on stored resources in seedlings of Mediterranean evergreen trees.
ABSTRACT: BACKGROUND AND AIMS:The carbon (C) and nitrogen (N) needed for plant growth can come either from soil N and current photosynthesis or through remobilization of stored resources. The contribution of remobilization to new organ growth on a whole-plant basis is quite well known in deciduous woody plants and evergreen conifers, but this information is very limited in broadleaf evergreen trees. This study compares the contribution of remobilized C and N to the construction of new organs in spring, and assesses the importance of different organs as C and N sources in 1-year-old potted seedlings of four ecologically distinct evergreen Mediterranean trees, namely Quercus ilex, Q. coccifera, Olea europaea and Pinus hapelensis. METHODS:Dual (13)C and (15)N isotope labelling was used to unravel the contribution of currently taken up and stored C and N to new growth. Stored C was labelled under simulated winter conditions. Soil N was labelled with the fertilization during the spring growth. KEY RESULTS:Oaks allocated most C assimilated under simulated winter conditions to coarse roots, while O. europaea and P. halepensis allocated it to the leaves. Remobilization was the main N source (>74 %) for new fine-root growth in early spring, but by mid-spring soil supplied most of the N required for new growth (>64 %). Current photosynthesis supplied >60 % of the C in new fine roots by mid-spring in most species. Across species, the proportion of remobilized C and N in new shoots increased with the relative growth rate. Quercus species, the slowest growing trees, primarily used currently acquired resources, while P. halepensis, the fastest growing species, mainly used reserves. Increases in the amount of stored N increased N remobilization, which fostered absolute growth both within and across species. Old leaves were major sources of remobilized C and N, but stems and roots also supplied considerable amounts of both in all species except in P. halepensis, which mainly relied on foliage formed in the previous growing season to supply stored resources. CONCLUSIONS:Seedlings of Mediterranean evergreen trees have distinct C and N storage physiologies, with relative growth rate driving the contribution of remobilized resources to new growth. These differences may reduce competition and facilitate species coexistence.
Project description:Seasonal nitrogen (N) storage and reuse is important to the N-use efficiency of temperate deciduous trees. In poplar, bark storage proteins (BSPs) accumulate in protein storage vacuoles of the bark parenchyma and xylem ray cells in the fall. During spring growth, N from stored BSPs is remobilized and utilized by growing shoots. The goal of this study is to investigate global gene expression changes in the bark during BSP remobilization and shoot regrowth under long-day conditions. Long-day (LD) grown poplar (Populus trichocarpa, Nisqually-1) plants were transferred to short-day (SD) for 8 weeks at 20°C followed by an addition 12 weeks of SD at 10°C (day) and 4°C (night). Following this treatment plants were then moved to LD and 20°C for 3 weeks for regrowth. Bark samples were collected from plants released from dormancy just prior to transfer to LD and at weekly intervals for 3 weeks after exposure to LD at 20°C.
Project description:Nitrogen (N) is, after water, the most limiting resource in semiarid ecosystems. However, knowledge on the N cycling ability of semiarid woody plants is still very rudimentary. This study analyzed the seasonal change in the N concentrations and pools of the leaves and woody organs of two species of semiarid sub-shrubs with contrasting leaf habit. The ability of both species to uptake, remobilize and recycle N, plus the main storage organ for N during summer drought were evaluated. We combined an observational approach in the field with experimental (15)N labelling of adult individuals grown in sand culture. Seasonal patterns of N concentrations were different between species and organs and foliar N concentrations of the summer deciduous Lepidium subulatum were almost double those of the evergreen Linum suffruticosum. L. subulatum up took ca. 60% more external N than the evergreen and it also had a higher N resorption efficiency and proficiency. Contrastingly, L. suffruticosum relied more on internal N remobilization for shoot growth. Differently to temperate species, the evergreen stored N preferentially in the main stem and old trunks, while the summer deciduous stored it in the foliage and young stems. The higher ability of L. subulatum to uptake external N can be related to its ability to perform opportunistic growth and exploit the sporadic pulses of N typical of semiarid ecosystems. Such ability may also explain its high foliar N concentrations and its preferential storage of N in leaves and young stems. Finally, L. suffruticosum had a lower ability to recycle N during leaf senescence. These strategies contrast with those of evergreen and deciduous species from temperate and boreal areas, highlighting the need of further studies on semiarid and arid plants.
Project description:Higher plants have to cope with fluctuating mineral resource availability. However, strategies such as stimulation of root growth, increased transporter activities, and nutrient storage and remobilization have been mostly studied for only a few macronutrients. Leaves of cultivated crops (Zea mays, Brassica napus, Pisum sativum, Triticum aestivum, Hordeum vulgare) and tree species (Quercus robur, Populus nigra, Alnus glutinosa) grown under field conditions were harvested regularly during their life span and analyzed to evaluate the net mobilization of 13 nutrients during leaf senescence. While N was remobilized in all plant species with different efficiencies ranging from 40% (maize) to 90% (wheat), other macronutrients (K-P-S-Mg) were mobilized in most species. Ca and Mn, usually considered as having low phloem mobility were remobilized from leaves in wheat and barley. Leaf content of Cu-Mo-Ni-B-Fe-Zn decreased in some species, as a result of remobilization. Overall, wheat, barley and oak appeared to be the most efficient at remobilization while poplar and maize were the least efficient. Further experiments were performed with rapeseed plants subjected to individual nutrient deficiencies. Compared to field conditions, remobilization from leaves was similar (N-S-Cu) or increased by nutrient deficiency (K-P-Mg) while nutrient deficiency had no effect on Mo-Zn-B-Ca-Mn, which seemed to be non-mobile during leaf senescence under field conditions. However, Ca and Mn were largely mobilized from roots (-97 and -86% of their initial root contents, respectively) to shoots. Differences in remobilization between species and between nutrients are then discussed in relation to a range of putative mechanisms.
Project description:Invasive herbivores can dramatically impact the nitrogen (N) economy of native hosts. In deciduous species, most N is stored in stem tissues, while in evergreen conifer species N is stored in needles, making them potentially more vulnerable to herbivory. In eastern forests of the USA, the long-lived, foundational conifer eastern hemlock (Tsuga canadensis) is under the threat of extirpation by the invasive hemlock woolly adelgid (HWA: Adelges tsugae). We assessed the impact of HWA infestation on the patterns of seasonal foliar N availability in hemlock planted in a deciduous forest understory. Over the course of a year, we sampled needles and twigs and measured N, carbon (C), C:N ratio, and total protein concentrations. Tissue sampling events were timed to coincide with key life-history transitions for HWA to determine the association between HWA development and feeding with these foliar nutrients. In uninfested trees, needle and twig N concentrations fluctuated across seasons, indicating the potential importance of N storage and remobilization for the N economy of eastern hemlock. Although N levels in HWA-infested trees also cycled annually, the degree to which N concentrations fluctuated seasonally in tissues was significantly affected by HWA feeding. These fluctuations exceeded N levels observed in control trees and coincided with HWA feeding. HWA feeding generally increased N concentrations but did not affect protein levels, suggesting that changes in N do not occur via adelgid-induced protein breakdown. Herbivore-induced mobilization of N to feeding sites and its rapid depletion may be a significant contributor to eastern hemlock mortality in US forests.
Project description:Knowledge of the function of the ear as a key organ in the uptake, remobilization and partitioning of nitrogen is essential for understanding its contribution to grain filling and thus guiding future breeding strategies. In this work, four Chinese winter wheat genotypes were grown on a 15N-enriched nutrient solution. N absorption and further remobilization to the flag leaf, the ear and the mature grains were calculated via the 15N atom % excess. The results indicated that the high yields of the Chinese wheat genotype were determined by higher grain numbers per ear, with greater plant height and a larger ear size, while the thousand-grain weight did not affect grain yield. In the mature grains, 66.7% of total N was remobilized from the pre-anthesis accumulation in the biomass, while the remaining 33.3% was derived from the N taken up during post-anthesis. From anthesis to 2 weeks after the anthesis stage, the flag leaf remobilized 3.67 mg of N outwards and the ear remobilized 3.87 mg of N inwards from the pre-anthesis accumulation in each plant. The positive correlation between ear Nrem and grain Nrem indicated that the ear was an important organ for providing N to the grain, whereas the remobilized N stream from the leaves was not correlated with grain Nrem, thus indicating that flag leaf N was not translocated directly to the grain. The grain Nrem was negatively correlated with the ear N concentration throughout grain filling, which suggested that higher-yielding genotypes had better sink activity in the ear, while Rubisco played a critical role in N deposition. Therefore, to improve yield potential in wheat, the N accumulation in the ear and the subsequent remobilization of that stored N to the grains should be considered. N accumulation and remobilization in the ear may at least be valuable for Chinese breeding programs that aim at optimizing the sink/source balance to improve grain filling.
Project description:Several grain legumes are staple food crops that are important sources of minerals for humans; unfortunately, our knowledge is incomplete with respect to the mechanisms of translocation of these minerals to the vegetative tissues and loading into seeds. Understanding the mechanism and partitioning of minerals in pea could help in developing cultivars with high mineral density. A mineral partitioning study was conducted in pea to assess whole-plant growth and mineral content and the potential source-sink remobilization of different minerals, especially during seed development. Shoot and root mineral content increased for all the minerals, although tissue-specific partitioning differed between the minerals. Net remobilization was observed for P, S, Cu, and Fe from both the vegetative tissues and pod wall, but the amounts remobilized were much below the total accumulation in the seeds. Within the mature pod, more minerals were partitioned to the seed fraction (>75%) at maturity than to the pod wall for all the minerals except Ca, where only 21% was partitioned to the seed fraction. Although there was evidence for net remobilization of some minerals from different tissues into seeds, continued uptake and translocation of minerals to source tissues during seed fill is as important, if not more important, than remobilization of previously stored minerals.
Project description:A clear-cutting of canopy trees during winter often causes severe foliar damage during the following spring in forest floor seedlings of Abies sachalinensis, a typical shade-tolerant evergreen coniferous species. The maximum photochemical efficiency of photosystem II after an overnight dark adaptation showed a temporary decrease immediately before budbreak in 1-year-old shoots of A. sachalinensis seedlings grown under full sunlight in a nursery, suggesting "springtime photoinhibition" related to the phenology of evergreen coniferous species. In the field, a greater rate of canopy tree cutting during winter was associated with more severe photoinhibition in the following spring, immediately before budbreak, which subsequently resulted in a reduction in carbon gain in 1-year-old shoots, and consequently suppressed the growth of current-year shoots. Although photoinhibition under low temperature is a well-known factor to determine the survival rate of tree seedlings during winter in cool regions, the present study additionally proposes that the temporary increase in the susceptibility to photoinhibition in springtime i.e. "springtime photoinhibition" would be a constraint for the regeneration of coniferous seedlings especially when the canopy trees are removed during winter.
Project description:The need to repeat peripheral blood (PB) stem cell mobilization and collection in healthy donors arises infrequently but may be required due to insufficient initial collection, graft failure, or relapse of the recipient's disease. Little data exist on the efficacy of remobilization. Therefore, we retrospectively reviewed 18 years of remobilization records from healthy stem cell donors at our institution.We identified 62 healthy donors who underwent remobilization, a cohort of 30 mobilized and remobilized with cytokines and a cohort of 32 mobilized with a CXCR4 antagonist and remobilized with cytokines. For each cohort we compared the PB CD34+/L level, the number of CD34+ cells collected/kg (recipient weight), and the number of CD34+ cells/L collected on the first day of leukapheresis during initial mobilization and remobilization.Initial mobilization with cytokines was associated with reduced remobilization. The mean PB CD34/L level at initial mobilization was 69 × 10(6) compared to 37 × 10(6) at remobilization (p?=?0.029). In contrast, initial mobilization with a CXCR4 antagonist was not associated with reduced remobilization. The mean PB CD34/L level at initial mobilization was 15 × 10(6) compared to 68 × 10(6) at remobilization (p?<?0.001). In both cohorts, initial mobilization results were positively correlated with remobilization results but the interval between was not.This study suggests that poor remobilization yields may be due to decreased efficacy of cytokines after repeat exposure. The underlying mechanism of these findings remains unclear and further studies are needed.
Project description:Phosphorus (P) in durum wheat grains after anthesis originates from either the external P source or the internal remobilization of P from different plant organs. The supply of P and its use by the plant are important factors that can affect the contribution of each source to grain P nutrition. Thus, this experiment aimed to quantify the origin of P in grains of durum wheat plants with different P nutritional status. Wheat plants were grown from juvenile stages to maturity in complete nutrient solutions with either high (0.125 mM) or low (0.025 mM) P concentrations in greenhouse conditions. Phosphorus in nutrient solutions was spiked by introducing 32P after anthesis to quantify the external P uptake and its partitioning within plant organs (spikelets, leaves, stems, roots, and post-anthesis tillers) and grains. Phosphorus use efficiency in durum wheat plants was also determined. The low and high P supply resulted in two highly different plant nutritional P status. Plants with low P status remobilized most of their stored P in all organs and allocated more than 72% of post-anthesis P uptake to grain P nutrition, whereas in the high P plants this was only 56%. Enhanced remobilization of P and the efficient allocation of newly acquired P to grains were crucial for durum wheat grain P nutrition grown under low P supply. The remobilization of P represented 81% of grain P in low P plants while it represented 65% for high P plants. Organs that contributed the most to P remobilization in low P plants were spikelets (43%) and leaves (35%). The post-anthesis tiller development was reduced in low P plants suggesting a preferential allocation of P to grains under this treatment. We concluded that P loading into grains in durum wheat is mainly derived from the remobilization of internal P sources stored before anthesis, even at high external P supply during grain filling.
Project description:Successful growth of a tree is the result of combined effects of biotic and abiotic factors. It is important to understand how biotic and abiotic factors affect changes in forest structure and dynamics under environmental fluctuations. In this study, we explored the effects of initial size [diameter at breast height (DBH)], neighborhood competition, and site condition on tree growth, based on a 3-year monitoring of tree growth rate in a permanent plot (120 × 80 m) of montane Fagus engleriana-Cyclobalanopsis multiervis mixed forest on Mt. Shennongjia, China. We measured DBH increments every 6 months from October 2011 to October 2014 by field-made dendrometers and calculated the mean annual growth rate over the 3 years for each individual tree. We also measured and calculated twelve soil properties and five topographic variables for 384 grids of 5 × 5 m. We defined two distance-dependent neighborhood competition indices with and without considerations of phylogenetic relatedness between trees and tested for significant differences in growth rates among functional groups. On average, trees in this mixed montane forest grew 0.07 cm year-1 in DBH. Deciduous, canopy, and early-successional species grew faster than evergreen, small-statured, and late-successional species, respectively. Growth rates increased with initial DBH, but were not significantly related to neighborhood competition and site condition for overall trees. Phylogenetic relatedness between trees did not influence the neighborhood competition. Different factors were found to influence tree growth rates of different functional groups: Initial DBH was the dominant factor for all tree groups; neighborhood competition within 5 m radius decreased growth rates of evergreen trees; and site condition tended to be more related to growth rates of fast-growing trees (deciduous, canopy, pioneer, and early-successional species) than the slow-growing trees (evergreen, understory, and late-successional species).