Non-structural Carbohydrate Reserves Research Articles

Metabolic and enzymatic changes associated with carbon mobilization, utilization and replenishment triggered in grain amaranth (Amaranthus cruentus) in response to partial defoliation by mechanical injury or insect herbivory.

BackgroundAmaranthus cruentus and A. hypochondriacus are crop plants grown for grain production in subtropical countries. Recently, the generation of large-scale transcriptomic data opened the possibility to study representative genes of primary metabolism to gain a better understanding of the biochemical mechanisms underlying tolerance to defoliation in these species. A multi-level approach was followed involving gene expression analysis, enzyme activity and metabolite measurements.ResultsDefoliation by insect herbivory (HD) or mechanical damage (MD) led to a rapid and transient reduction of non-structural carbohydrates (NSC) in all tissues examined. This correlated with a short-term induction of foliar sucrolytic activity, differential gene expression of a vacuolar invertase and its inhibitor, and induction of a sucrose transporter gene. Leaf starch in defoliated plants correlated negatively with amylolytic activity and expression of a β-amylase-1 gene and positively with a soluble starch synthase gene. Fatty-acid accumulation in roots coincided with a high expression of a phosphoenolpyruvate/phosphate transporter gene. In all tissues there was a long-term replenishment of most metabolite pools, which allowed damaged plants to maintain unaltered growth and grain yield. Promoter analysis of ADP-glucose pyrophosphorylase and vacuolar invertase genes indicated the presence of cis-regulatory elements that supported their responsiveness to defoliation. HD and MD had differential effects on transcripts, enzyme activities and metabolites. However, the correlation between transcript abundance and enzymatic activities was very limited. A better correlation was found between enzymes, metabolite levels and growth and reproductive parameters.ConclusionsIt is concluded that a rapid reduction of NSC reserves in leaves, stems and roots followed by their long-term recovery underlies tolerance to defoliation in grain amaranth. This requires the coordinate action of genes/enzymes that are differentially affected by the way leaf damage is performed. Defoliation tolerance in grain is a complex process that can’t be fully explained at the transcriptomic level only.

Resprouting ability and mobile carbohydrate reserves in an oak shrubland decline with increasing elevation on the eastern edge of the Qinghai–Tibet Plateau

Resprouting is the main regeneration mechanism of most Quercus species after severe disturbance such as fire or coppicing. Yet little is known about the relationships between the amounts of resources stored in the roots and resprouting ability when the total aboveground part of plants/trees was fully removed or destroyed, and about the resprouting ability in relation to increasing elevation associated with decreasing site productivity. The present study investigated the non-structural carbohydrate (NSC) concentrations and its pool size in roots of Quercus aquifolioides clumps grown at 3000m, 3500m, and 3950m a.s.l. on Zheduo Mt., southwestern China, to test two competing hypotheses that (1) decreases in net primary productivity and growing season length with increasing elevation result in less allocation to storage of belowground NSC reserves, so that after coppicing, shrubs at higher elevations produce fewer resprouts and less total biomass than those at lower elevations, vs. (2) the shrubs growing at high-elevation sites with low-productivity produce more resprouts and biomass than those at low-elevation sites after coppicing, as it is expected that resprouting is favored in low-productivity environments. Our results indicated that early resprouting of Q. aquifolioides shrubs after coppicing is largely determined by the initial carbohydrate pool but not by the carbohydrate concentrations in roots. The large resprouting vigor of this species may be mainly ascribed to its large ratios of root to shoot biomass or root NSC pool to shoot NSC pool. The resprouting vigor of clumps decreased significantly with increasing elevation, which corresponds to significant decreases in the root biomass or root NSC pool size per clump with increasing elevation. Resprouts self-thinned more early and rapidly in clumps at lower elevations than at higher elevations, which may be mainly resulted from competition occurred more early in the more productive sites at lower elevations compared to higher elevations. Our results support the 1st but not the 2nd hypothesis. The present study has important implications for resources storage dealing with ecophysiology-based management strategy of coppicing woodland across scales.

Infestation and Hydraulic Consequences of Induced Carbon Starvation

Drought impacts on forests, including widespread die-off, are likely to increase with future climate change, although the physiological responses of trees to lethal drought are poorly understood. In particular, in situ examinations of carbon starvation and its interactions with and effects on infestation and hydraulic vulnerability are largely lacking. In this study, we conducted a controlled, in situ, repeated defoliation experiment to induce carbon stress in isolated trembling aspen (Populus tremuloides) ramets. We monitored leaf morphology, leaves per branch, and multitissue carbohydrate concentrations during canopy defoliation. We examined the subsequent effects of defoliation and defoliation-induced carbon stress on vulnerability to insect/fungus infestation and hydraulic vulnerability the following year. Defoliated ramets flushed multiple canopies, which coincided with moderate drawdown of nonstructural carbohydrate reserves. Infestation frequency greatly increased and hydraulic conductivity decreased 1 year after defoliation. Despite incomplete carbohydrate drawdown from defoliation and relatively rapid carbohydrate recovery, suggesting considerable carbohydrate reserves in aspen, defoliation-induced carbon stress held significant consequences for vulnerability to mortality agents and hydraulic performance. Our results indicate that multiyear consequences of drought via feedbacks are likely important for understanding forests' responses to drought and climate change over the coming decades.

Effect of stock type characteristics and time of planting on field performance of aspen (Populus tremuloides Michx.) seedlings on boreal reclamation sites

Aspen (Populus tremuloides Michx) has great potential as a reclamation species for mining sites in the boreal forest, but planting stock has shown poor field performance after outplanting. In this study we tested how different aspen seedling characteristics and planting times affect field outplanting performance on reclamation sites. We produced three different types of aspen planting stock, which varied significantly in seedling size, root-to-shoot ratio (RSR), and total non-structural carbohydrate (TNC) reserves in roots, by artificially manipulating shoot growth during seedling production. All three stock types were then field-planted either in late summer, late fall, or early spring after frozen storage. Seedlings were outplanted onto two reclaimed open-pit mining areas in the boreal forest region of central and east-central Alberta, Canada, which varied significantly in latitude, reclamation history, and soil conditions. Overall, height growth was better in aspen stock types with high RSR and TNC reserves. Differences in field performance among aspen stock types appeared to be more strongly expressed when seedlings were exposed to more stressful environmental site conditions, such as low soil nutrients and moisture. Generally, aspen seedlings planted with leaves in the summer showed the poorest performance, and summer- or fall-planted seedlings with no shoot growth manipulation had much greater stem dieback after the first winter. This indicates that the dormancy and hardening of the stem, as a result of premature bud set treatments, could improve the outplanting performance of aspen seedlings, particularly those planted during summer and fall.

Partitioning of carbon allocation to reserves or growth determines future performance of aspen seedlings

Increasingly, trembling aspen (Populus tremuloides Michx.) is being planted in stressful situations such as forest land reclamation, afforestation and forest restoration in North America. This is due to its fast potential for growth and high resiliency, but its indeterminate growth strategy provides a special challenge in creating suitable planting stock for these sites. Clues from naturally established aspen seedlings suggest that root total non-structural carbohydrate (TNC) reserves and root:shoot ratio could be strongly related to subsequent seedling establishment and growth. Carbon allocation in plants is generally partitioned between reserve accumulation and growth and development. Under conditions in controlled nurseries, the allocation of carbohydrates to reserves could be manipulated in order to produce seedlings designed for specific environmental conditions. To manipulate seedling characteristics we attempted to induce premature bud set during nursery culture while allowing continued photosynthesis. Treatments included applying different fertilizer regimes, light intensities, reducing photoperiod and use of a shoot growth inhibitor. The shoot growth inhibitor was the most reliable treatment and resulted in complete bud set, while blackout was successful only when seedlings were grown outside. Low nutrient treatments also resulted in early bud set; however, leaves were abscised much earlier. There was a distinct trade-off between growth and reserve accumulation with the late bud set. A longer period of height growth reduced root and total TNC reserves, while early bud set allowed for continued photosynthesis and produced the highest levels of root and total TNC reserves in seedlings. Increased TNC reserves of aspen planting stock was positively related to height growth after outplanting, with root TNC reserves as high as 33% of dry weight and root:shoot ratios greater than 2 associated with the best growth.

Delayed response to ring nematode (Mesocriconema xenoplax) feeding on grape roots linked to vine carbohydrate reserves and nematode feeding pressure

The chronic impact of ring nematode (Mesocriconema xenoplax) feeding on grapevine (Vitis vinifera) was studied under controlled conditions. ‘Pinot noir’ grapevines were exposed to ring nematode or kept nematode-free for three growing seasons and vines were either grown in full sunlight, 15% of full sun, or partially defoliated to manipulate vine carbohydrate status. Whole plants were destructively sampled to assess the impact of ring nematode on whole plant biomass, carbohydrate, and mineral nutrient accumulation. Vine shoot growth and total biomass was unaffected by ring nematode in the first growing season, although reserves of nonstructural carbohydrates (NSC), P, K, and Ca in the roots and wood were reduced in all canopy management treatments. Vine shoot growth and total biomass were reduced by ring nematode in Year 2, and greater declines in reserve NSC and most mineral nutrients had occurred. Reserves of NSC were affected more than biomass or nutrients during the second year. During the third year of exposure to ring nematode, vines in the 15% sun treatment were dying (prompting an earlier destructive harvest), even though these vines had similar biomass and NSC reserves as the partially defoliated vines at the end of the second year. The demise of the 15% sun vines was associated with higher ring nematodes per unit of root mass, as compared to either full sun or defoliated vines. Therefore, predicting plant response to this nematode requires an understanding of nematode density per quantity of roots, not nematodes per unit of soil which is how plant parasitic nematodes are currently enumerated.

Defoliation increases risk of carbon starvation in root systems of mature aspen

Large trees are noted to decline and die over several years after defoliation or extended periods of drought. The underlying mechanisms of this decline are thought to be driven by moisture limitations to photosynthesis, but alternative considerations also suggest carbon storage limitations as a driver. This research assesses the non-structural carbohydrate reserves in crowns and roots tissues during and after defoliation by insects in trembling aspen. We monitored the non-structural carbon reserves of nine tall mature aspen forest stands over 8 years, including two defoliation events. We report on the carbohydrate dynamics in root and crown tissues during and after defoliation. Following defoliation, branch reserves recovered to levels of undefoliated control trees within the same season, while roots took up to 2 years to recover. We argue that in large trees, tissues closest to the foliage are the first sinks to access C in the phloem stream, while roots, which are more distal and separated by a long bole, will only receive adequate supplies of C when the other more proximate sinks are sated. These results support the hypothesis that in times of limited carbon assimilation, root tissues in mature trees experience the longest reduction in carbon reserves, which likely plays a critical role in tree decline and mortality.

Pre-anthesis non-structural carbohydrate reserve in the stem enhances the sink strength of inferior spikelets during grain filling of rice

Sink strength plays an important role in grain filling of cereals but how it is related to the pre-anthesis non-structural carbohydrate (NSC) reserves is not clear. This study investigated if and how an increase in NSC reserves could enhance sink strength, and consequently improve grain filling of later-flowering inferior spikelets (in contrast to the earlier flowering superior spikelets) for rice varieties with large panicles. Two “super” rice varieties (the recently bred high-yielding rice) and two New Plant Type (NPT, named in IRRI for the extra-large panicle) rice lines were compared with two elite inbred varieties under field-grown conditions. Three nitrogen (N) treatments, applied at the stages of panicle initiation, spikelet differentiation or both, were adopted with no N application during the mid-season as control. Both super rice and NPT rice showed a greater yield capacity as a result of a larger panicle than the elite inbred rice. However, a lower percentage of filled grains limited the realization of higher yield potential in super rice and especially in NPT rice, due to their lower grain filling rate and the smaller grain weight of their inferior spikelets. The low grain filling rate and small grain weight of inferior spikelets are mainly attributed to a poor sink strength as a result of small sink size (small number of endosperm cells) and low sink activity, e.g. low activities of sucrose synthase (SuSase) and adenosine diphosphoglucose pyrophosphorylase (AGPase). The amounts of NSC in the stem and NSC per spikelet at the heading time are significantly and positively correlated with sink strength (number of endosperm cells and activities of SuSase and AGPase), grain filling rate, and grain weight of inferior spikelets. Nitrogen application at the spikelet differentiation stage significantly increased, whereas N application at the panicle initiation or at both panicle initiation and spikelet differentiation stages, significantly reduced, NSC per spikelet at the heading time, sink strength, grain filling rate, and grain weight of inferior spikelets in super rice. The results suggest that pre-anthesis NSC reserves in the stem are closely associated with the sink strength during grain filling of rice, and N application at the spikelet differentiation stage would be a good practice to increase pre-anthesis NSC reserves, and consequently to enhance sink strength for rice varieties with large panicles, such as super rice varieties.

Phenology, growth and physiological adjustments of oil palm (Elaeis guineensis) to sink limitation induced by fruit pruning.

Despite its simple architecture and small phenotypic plasticity, oil palm has complex phenology and source-sink interactions. Phytomers appear in regular succession but their development takes years, involving long lag periods between environmental influences and their effects on sinks. Plant adjustments to resulting source-sink imbalances are poorly understood. This study investigated oil palm adjustments to imbalances caused by severe fruit pruning. An experiment with two treatments (control and complete fruit pruning) during 22 months in 2006-2008) and six replications per treatment was conducted in Indonesia. Phenology, growth of above-ground vegetative and reproductive organs, leaf morphology, inflorescence sex differentiation, dynamics of non-structural carbohydrate reserves and light-saturated net photosynthesis (A(max)) were monitored. Artificial sink limitation by complete fruit pruning accelerated development rate, resulting in higher phytomer, leaf and inflorescence numbers. Leaf size and morphology remained unchanged. Complete fruit pruning also suppressed the abortion of male inflorescences, estimated to be triggered at about 16 months before bunch maturity. The number of female inflorescences increased after an estimated lag of 24-26 months, corresponding to time from sex differentiation to bunch maturity. The most important adjustment process was increased assimilate storage in the stem, attaining nearly 50 % of dry weight in the stem top, mainly as starch, whereas glucose, which in controls was the most abundant non-structural carbohydrate stored in oil palm, decreased. The development rate of oil palm is in part controlled by source-sink relationships. Although increased rate of development and proportion of female inflorescences constituted observed adjustments to sink limitation, the low plasticity of plant architecture (constant leaf size, absence of branching) limited compensatory growth. Non-structural carbohydrate storage was thus the main adjustment process.

Role of transitory carbon reserves during adjustment to climate variability and source-sink imbalances in oil palm (Elaeis guineensis)

Oil palm (Elaeis guineensis Jacq.) is a perennial, tropical, monocotyledonous plant characterized by simple architecture and low phenotypic plasticity, but marked by long development cycles of individual phytomers (a pair of one leaf and one inflorescence at its axil). Environmental effects on vegetative or reproductive sinks occur with various time lags depending on the process affected, causing source-sink imbalances. This study investigated how the two instantaneous sources of carbon assimilates, CO(2) assimilation and mobilization of transitory non-structural carbohydrate (NSC) reserves, may buffer such imbalances. An experiment was conducted in Indonesia during a 22-month period (from July 2006 to May 2008) at two contrasting locations (Kandista and Batu Mulia) using two treatments (control and complete fruit pruning treatment) in Kandista. Measurements included leaf gas exchange, dynamics of NSC reserves and dynamics of structural aboveground vegetative growth (SVG) and reproductive growth. Drought was estimated from a simulated fraction of transpirable soil water. The main sources of variation in source-sink relationships were (i) short-term reductions in light-saturated leaf CO(2) assimilation rate (A(max)) during seasonal drought periods, particularly in Batu Mulia; (ii) rapid responses of SVG rate to drought; and (iii) marked lag periods between 16 and 29 months of environmental effects on the development of reproductive sinks. The resulting source-sink imbalances were buffered by fluctuations in NSC reserves in the stem, which mainly consisted of glucose and starch. Starch was the main buffer for sink variations, whereas glucose dynamics remained unexplained. Even under strong sink limitation, no negative feedback on A(max) was observed. In conclusion, the different lag periods for environmental effects on assimilate sources and sinks in oil palm are mainly buffered by NSC accumulation in the stem, which can attain 50% (dw:dw) in stem tops. The resulting dynamics of growth and production are complex because several dozen phytomers of different phenological ages develop at any given time and interact with a common pool of reserves.

Responses of the Mediterranean seagrass Posidonia oceanica to in situ simulated salinity increase

Abstract The dominant Mediterranean seagrass Posidonia oceanica inhabits sublittoral environments with very stable salinity regimes; the species is considered highly sensitive to even moderate increases in salinity caused by hypersaline effluents (brine) from desalination plants. We analysed the effect of salinity increase on seagrass vitality and survival by means of an in situ mesocosm experiment. To this end, we used the brine (70–75 psu) produced by a pilot desalination plant, which was diluted with seawater to obtain brine solutions of 1 psu (high salinity increase, HS) and 2.5 psu (very high salinity increase, VS) over the mean natural salinity (37.5±0.16 psu) and then interspersed a set of experimental units in a nearby P. oceanica meadow. At the end of the experimental period (3 months), these treatments had produced differential effects on all seagrass descriptors, i.e., intense and significant in the VS experimental units and more modest (or even negligible) in the HS ones. Seagrass meadow declined through a significant decrease in shoot density in both HS (12.4±3.4%, mean±SE) and VS (18.5±3.05%, mean±SE) in comparison to control experimental units (<5%). Surviving shoots had reduced size and lower leaf growth rate than control plants, but more generally a reduction in the photosynthetic leaf surface caused by the increase in the proportion of necrotic leaf area (up to 60% in VS treatments). Non-structural carbohydrate (soluble and reserve) concentrations decreased in rhizomes, probably in relation to physiological osmoregulation processes. All these responses support the hypothesis that the threshold salinity tolerance of P. oceanica is very close to the upper limit of its natural salinity range (ca. 38 psu).

Short-term effect of beach replenishment on a shallow Posidonia oceanica meadow

Putative perturbations on a Posidonia oceanica meadow produced by recent artificial beach nourishment were evaluated in relation to four undisturbed meadows. Temporal variations of putative impacted location vs. control locations of environmental (light availability and sediment features), plant (associated epiphytes, silt–clay fraction attached to epiphytes, herbivore attack, non-structural carbohydrate reserves) and structural parameters (cover and density) of meadows were tested by asymmetrical analysis of variance beyond BACI (Before/After, Control/Impact). Additionally, two asymmetrical analyses of variance were used to test for differences in vegetative growth of horizontal rhizomes (leaf production, horizontal rhizome growth, biomass production and net secondary rhizome recruitment) before and after beach replenishment. Environmental effects induced by dumping works were only detected in connection with a higher silt–clay deposition rate. This increase was consistent with the increase of silt–clay cover attached to epiphytes. As a consequence of silt–clay smothering, a decrease of filter feeding epiphytes, starch reserves, shoot surface and shoot biomass was observed. The sensitivity of plants to sediment inputs, leads us to recommend avoidance of dumping or sediment movement in the vicinity of P. oceanica meadows.

Seasonal Changes in Carbohydrate and Nitrogen Concentrations in Oregon and California Populations of Brazilian Egeria (Egeria densa)

AbstractTotal nonstructural carbohydrate (TNC) reserves support growth, formation of reproductive structures, and sprouting of plant tissues, and nitrogen (N) is essential for amino acid synthesis and photosynthetic enzyme production. Timing of weed management to periods when these critical resources are most limiting might improve efficacy. We examined seasonal changes in carbohydrate and nitrogen concentrations in Brazilian egeria (Egeria densa), a common submersed aquatic weed, from two locations in the United States. Plants were collected from a coastal Oregon reservoir and from California's Central Valley in the Sacramento–San Joaquin Delta. Starch comprised between 35 to 51% of the TNC in lower stems and root crowns. Seasonal changes in resource concentrations were not consistent between years within a population or for the same plant part between different populations. Lowest TNC concentrations were observed earlier in the growing season (March) in Disappointment Slough than in Big Creek (May to June). Conversely, highest concentrations were observed in October in Disappointment Sough and from August to March in Big Creek. Nitrogen concentrations were highest in stem tips in both populations, with more distinct seasonal changes in the California population. These data suggest western populations of E. densa might exhibit less-discernible low points in root crown and lower stem energy storage for targeting management activities to vulnerable phenological stages. Brazilian egeria has high phenological plasticity despite its low genetic diversity and lack of specialized reproductive and perennating structures, which allows the plant to invade and dominate submersed plant communities in areas with mild winters.

Whole-plant adjustments in coconut (Cocos nucifera) in response to sink-source imbalance

Coconut (Cocos nucifera L.) is a perennial tropical monocotyledon that produces fruit continuously. The physiological function of the large amounts of sucrose stored in coconut stems is unknown. To test the hypothesis that reserve storage and mobilization enable the crop to adjust to variable sink-source relationships at the scale of the whole plant, we investigated the dynamics of dry matter production, yield and yield components, and concentrations of nonstructural carbohydrate reserves in a coconut plantation on Vanuatu Island in the South Pacific. Two treatments were implemented continuously over 29 months (April 2002 to August 2004): 50% leaf pruning (to reduce the source) and 100% fruit and inflorescence pruning (to reduce the sink). The pruning treatments had little effect on carbohydrate reserves because they affected only petioles, not the main reserve pool in the stem. Both pruning treatments greatly reduced dry matter production of the reproductive compartment, but vegetative growth and development were negligibly affected by treatment and season. Leaf pruning increased radiation-use efficiency (RUE) initially, and fruit pruning greatly reduced RUE throughout the experiment. Changes in RUE were negatively correlated with leaflet soluble sugar concentration, indicating feedback inhibition of photosynthesis. We conclude that vegetative development and growth of coconut show little phenotypic plasticity, assimilate demand for growth being largely independent of a fluctuating assimilate supply. The resulting sink-source imbalances were partly compensated for by transitory reserves and, more importantly, by variable RUE in the short term, and by adjustment of fruit load in the long term. Possible physiological mechanisms are discussed, as well as modeling concepts that may be applied to coconut and similar tree crops.

Responses of nonstructural carbohydrates to shoot removal and soil moisture treatments in Salix nigra

Aboveground disturbances are common in dynamic riparian environments, and Salix nigra is well adapted with a vigorous resprouting response. Soil moisture stresses are also common, and S. nigra is flood tolerant and drought sensitive. The objective of this study was to quantify nonstructural carbohydrate (NSC) reserves in S. nigra following shoot removal and soil moisture treatments. NSC reserves provide energy for regeneration of shoot tissue until new functional leaves are developed. Three soil moisture treatments: well-watered (W), periodic flooding (F) and drought (D); and three shoot removal treatments: no shoots removed (R0), partial shoot removal (R1), and complete shoot removal (R2) were applied. Plants were harvested when new shoot development was observed (day 13). Statistical significance in the 3 × 3-factorial design was determined in two-factor ANOVA at P < 0.05. Both roots and cuttings were important reservoirs for NSC during resprouting response, with decreases in root (31%) and cutting (14%) biomass in R2 compared to R0. Rapid recovery of photosynthetic surface area (from 15 to 37% of R0) was found in R1. A clear pattern of starch mobilization was found in roots in R0, R1 and R2, with lowest root starch concentration in W, F higher than W, and D higher than F. Shoot starch concentration was lower in F and D compared to W in R0, however, in R1 shoot starch was reduced in W compared to F and D, possibly indicating reduced rates of translocation during soil moisture stress. Evidence of osmotic adjustment was found in roots and shoots with higher total ethanol-soluble carbohydrates (TESC) during soil moisture stress in F and D treatments. Total plant NSC pool was greater in F and D treatments compared to W, and progressively reduced from R0 to R1 to R2. Results indicated negative effects of drought, and to a lesser extent periodic flooding on resprouting response in S. nigra, with implications for reduced survival when exposed to combined stresses of aboveground disturbance and soil moisture.

Spatial and temporal changes in non-structural carbohydrate reserves in eelgrass (Zostera marina L.) in Danish coastal waters

Abstract The spatial and seasonal changes of total non-structural carbohydrate (TNC) reserves in above- and belowground tissues in eelgrass (Zostera marina) were assessed at four different sampling sites in Danish waters. The study consisted of annual field sampling, where sites differed in water depth and nutrient content in sediments. The TNC concentrations varied considerably in all tissues, and rhizomes generally represented the major storage organ. Sucrose was the main sugar contributing to TNC whilst starch represented the minor (&lt;15%) reserves. Trehalose, which is reported in Z. marina here for the first time, due to the use of a recently developed HPLC method, was found in low concentrations (up to ∼2%) and showed a reverse seasonal variation compared to other sugars, with maximum concentrations in winter. Plants growing near depth limits (5.5 m) had significantly higher reserves, whereas no significant effect of sediment nutrient contents on the TNC concentrations was observed, reflecting the ability of Z. marina to tolerate a range of different growth conditions.

Dynamics of non-structural carbohydrate reserves in pruned Erythrina poeppigiana and Gliricidia sepium trees

In alley cropping systems, fast growing leguminous trees are pruned to reduce competition with crops for light and to provide organic inputs for crop nutrition. Tree regrowth depends on non-structural carbohydrate reserves in the remaining tree parts. In this study, the dynamics of starch and soluble carbohydrates in roots and stems of completely pruned (all shoots removed), partially pruned (one branch retained on the pruned stump) and unpruned Erythrina poeppigiana (Walp.) O.F. Cook and Gliricidia sepium (Jacq.) Kunth ex Walp. trees were studied under humid tropical conditions in Turrialba, Costa Rica. Measurements on starch and soluble carbohydrates in roots and stems were made at 0, 2, 6 and 12 weeks after pruning during both a “rainy” and a “dry” season. In general, the dynamics of non-structural carbohydrates in roots and stems of pruned E. poeppigiana and G. sepium trees were similar. Starch concentration was highest in unpruned trees and higher in roots than in stems of pruned trees. The effect of pruning intensity was first observed in stems, and starch reserves were more depleted in stems than in roots, an effect more evident during the “dry” season. The critical tree regrowth stage for starch mobilisation was that of vigorous sprout development at six or four weeks after pruning particularly in completely pruned trees. At this time, fine root biomass and length and nodule biomass in pruned trees decreased. Survival of fine roots and nodules was greater in partially pruned than in completely pruned trees. Starch accumulation in roots recommenced at 12 weeks after pruning in G. sepium, and later than 12 weeks after pruning in E. poeppigiana roots. This study showed that E. poeppigiana responded better to pruning regimes than G. sepium. Recovery of trees after pruning is better when trees are partially pruned than when completely pruned.

Ecophysiological Traits and Genetic Analysis of Yield and Ripening in High-Yielding Semi-Dwarf Indica Rice Varieties

Experiments were conducted to examine the ecophysiological traits of yield and ripening and the genetic backgrounds of these traits in high-yielding semi-dwarf indica rice. Field experiments were performed over four years to examine the yield and growth characteristics of these traits. A large sink size with large numbers of spikelets per panicle and a high ripening ability in the background of a large sink size were found to be two of the major ecophysiological traits that enhance the yield of semi-dwarf indica. High dry matter productivity after heading was suggested to be linked to a high ripening ability. To determine the genetic backgrounds that control these traits, quantitative trait locus (QTL) analysis was conducted using two different semi-dwarf indica/japonica inbred lines: recombinant inbred lines of Milyang23 (semi-dwarf indica)/Akihikari (japonica), and back-crossed inbred lines of Sasanishiki (japonica)/Habataki (semi-dwarf indica)//Sasanishiki///Sasanishiki. QTLs for larger sink size, higher ripening ability, higher dry matter production, and larger nonstructural carbohydrate (NSC) reserves in leaf sheaths and culms at heading within semi-dwarf indica alleles were detected. The effects of these QTLs probably combine to express the large sink size and high ripening ability traits, resulting in the high yields of the semi-dwarf indica rice varieties.

Treelines of the Japanese Alps – altitudinal distribution and species composition under contrasting winter climates

Summary In Japan, contrasting winter climate conditions between the Sea of Japan and the Pacific Ocean side have created conspicuous differences in species composition and altitudinal distribution of subalpine forests and treeline ecotones. In the Japanese Alps the altitudinal distribution of principal subalpine and treeline tree species was investigated along the slopes of four mountain ranges, two located in snowy regions facing the Sea of Japan (Mt. Hakusan, Mt. Naeba), and two with little snow cover located near the Pacific Ocean (Mt. Akaishi, Mt. Fuji). On Mt. Fuji many years of temperature records at different altitudes up to the treeline and at the summit provided the database for calculation of monthly lapse rates of air temperature, particularly the decrease of absolute and mean minima. High and prolonged snow cover causes the descent of the upper distribution limit of the subalpine coniferous forest by 800 to 1000 m altitude towards the Sea of Japan. A subalpine deciduous broad-leaved woodland of 500 m of vertical spread is formed only on snowy mountains, and does not exist on the Pacific Ocean side. With reference to Betula ermanii, the thermal upperdistribution limit of treelines in the Japanese Alps unimpaired by snow is determined by two periods of minimum temperature: (1) periods of subzero temperature which determine the occurrence of spring frost injury and affect the onset of the growing season, (2) minimum temperatures during the growing season which affect the thermal-time requirement (TTR) for fully differentiated tissues in overwintering plant organs. It is suggested to quantify TTR as thermal sum [(t–5.5), given in day-degrees], where t is the daily minimum air temperature above 5.5°C during the growing season. For B. ermanii the TTR is 210 day-degrees, which corresponds to 82 d of growing season length at the species’ upper distribution limit at 2800 m altitude. The descent of deciduous treelines on snowy mountains in humid northeastern Asia below the general thermal forest line of the Northern Hemisphere is discussed in terms of a hypoxia-induced carbohydrate limitation hypothesis. Tree survival will be im-paired by high and prolonged snow cover if oxygen deprivation causes hypoxia in wood parenchymas, which in turn will accelerate the depletion of nonstructural carbohydrate reserves. The impact of oxygen deprivation will increase towards spring, when most of the nonstructural reserve carbohydrates have been consumed so that enhanced ATP demand of live tissues at that time cannot be further compensated.

Uncertainties in interpretation of isotope signals for estimation of fine root longevity: theoretical considerations

AbstractThis paper examines uncertainties in the interpretation of isotope signals when estimating fine root longevity, particularly in forests. The isotope signals are depleted δ13C values from elevated CO2 experiments and enriched Δ14C values from bomb 14C in atmospheric CO2. For the CO2 experiments, I explored the effects of six root mortality patterns (on–off, proportional, constant, normal, left skew, and right skew distributions), five levels of nonstructural carbohydrate (NSC) reserves, and increased root growth on root δ13C values after CO2 fumigation. My analysis indicates that fitting a linear equation to δ13C data provides unbiased estimates of longevity only if root mortality follows an on–off model, without dilution of isotope signals by pretreatment NSC reserves, and under a steady state between growth and death. If root mortality follows the other patterns, the linear extrapolation considerably overestimates root longevity. In contrast, fitting an exponential equation to δ13C data underestimates longevity with all the mortality patterns except the proportional one. With either linear or exponential extrapolation, dilution of isotope signals by pretreatment NSC reserves could result in overestimation of root longevity by several‐fold. Root longevity is underestimated if elevated CO2 stimulates fine root growth. For the bomb 14C approach, I examined the effects of four mortality patterns (on–off, proportional, constant, and normal distribution) on root Δ14C values. For a given Δ14C value, the proportional pattern usually provides a shorter estimate of root longevity than the other patterns. Overall, we have to improve our understanding of root growth and mortality patterns and to measure NSC reserves in order to reduce uncertainties in estimated fine root longevity from isotope data.