Increase In Non-structural Carbohydrates Research Articles

Stability in the leaf functional traits of understory herbaceous species after 12-yr of nitrogen addition in temperate larch plantations.

Leaf functional traits play critical roles in plant functioning. Although the functional traits of overstory trees have been extensively studied, minimal research has been conducted regarding understory species, despite the understory layer is an important component of temperate forests. Such insufficiency limit the broader understanding of processes and functions in forest ecosystems, particularly when under the increasing atmospheric nitrogen (N) deposition. Here, we investigated the responses of 18 leaf functional traits in six understory herbaceous species within young and mature stands (three species per stand) in larch (Larix principis-rupprechtii) plantations that subjected to 12 years of anthropogenic N addition. We found that N addition did not significantly impact the photosynthetic traits of understory herbaceous species in either stand; it only led to increased chlorophyll content in Geum aleppicum Jacq. Similarly, with the exception of decreases in the predawn leaf water potential of Sanguisorba officinalis L., N addition did not significantly affect leaf hydraulic traits. With the exception of changes to adaxial epidermis thickness in Potentilla chinensis Ser. (decreased) and G. aleppicum (increased), N addition had negligible effects on leaf anatomical traits and specific leaf area, however, interspecific variations in the plasticity of leaf anatomical traits were observed. Stable responses to N addition were also observed for nonstructural carbohydrates (NSC) and their components (soluble sugars and starch), with the exception of Polygonum divaricatum L., which exhibited increases in NSC. Overall, our results suggest that the functional traits of understory herbaceous species exhibit stability under conditions of long-term N enrichment in temperate plantations.

Whole plant water status and non‐structural carbohydrates under progressive drought in a Caatinga deciduous woody species

Progressive drought induced a gradual increase in non-structural carbohydrates in roots and leaves, slowing the drop in water status. The roots had an increase of 95 % compared to well-watered plants, while the leaves only increased by 21 %. Since Cenostigma pyramidale is a deciduous species, the non-structural carbohydrates are mainly found in the roots, which helps the plant survive the intense drought period. The ability to produce and control the distribution of non-structural carbohydrates (NSC) may be critical to the success of deciduous woody plants from seasonally dry tropical forests. Thus, our aim was to investigate how carbohydrate allocation occurs and the dynamics of water status during the pre-senescence leaf period. We performed a controlled experiment on progressive drought stress using Cenostigma pyramidale, and found that leaf relative water content decreased only under severe drought conditions (SVD), when soil water content was approximately 5%, three times less than well-hydrated plants, and foliar relative water content (RWC) was close to 35%. Gas exchange was maintained at a high level until the moderate drought stage (MD), with soil water content and RWC of 8% and 75%, respectively. Prior to leaf senescence, C. pyramidale maintained the net CO2 assimilation and intense production of NSC, which were stored mainly in the leaves (45%), and roots (44%), with only 11% in the stems. This increase in root NSC content during progressive drought levels suggests that this tissue may be the main storage site for NSC, which could allow the plant to survive the dry season, and also have reserves for leaf sprouting at the beginning of the next rainy season. The results suggest that studies involving carbon metabolism in woody species under stress should consider root tissue, as this is an important source of NSC during drought.

Beneficial effects of nitrogen deposition on carbon and nitrogen accumulation in grasses over other species in Inner Mongolian grasslands

Globally, chronic nitrogen (N) deposition into terrestrial ecosystems has resulted in changes in community composition, depending on the responses of co-existing species to increasing soil N availability. The levels of plant non-structural carbohydrates (NSCs) produced by photosynthesis are associated with leaf N content, and together they represent the capital of a plant for its life including competitive ability. However, the specific ways that concentrations of plant NSCs, and also N, influence the growth of plants, and thus their productivity, are still abscue. Here, we explored the effect of variations in plant leaf NSCs (starch and soluble sugars) and N concentrations on the growth of plants with different soil N uptake capacities, i.e. two grasses (Leymus chinensis and Stipa baicalensis), two forbs (Potentilla tanacetifolia and Galium verum), and one legume (Thermopsis lanceolate) in Inner Mongolian grasslands subjected to three N addition rates (i.e., 0, 10, or 20 g N m−2 yr−1) and three N forms [i.e., NH4NO3, (NH4)2SO4, or CO(NH2)2] for four years. Irrespective of N addition rate and N form, N addition significantly increased aboveground biomass of the grasses, but not that of the forbs or the legume. The grasses had higher increase in N concentrations than the forbs and the legume. N addition increased the starch concentrations of grasses, but decreased that of forbs and the legume. Changes in the aboveground biomass of all tested plant species were significantly positively correlated with changes in concentrations of both NSCs and N. Our results indicate that, irrespective of the N addition rates and N forms, greater increase in NSCs and N concentrations contributed to higher aboveground productivity in grasses, but not in forbs and legumes. These results imply that future nitrogen deposition will benefit grasses over other plant forms, and thus the former may become more dominant in grasslands in northern China.

Carbon allocation to growth and storage depends on elevation provenance in an herbaceous alpine plant of Mediterranean climate.

It is unclear whether the frequently observed increase in non-structural carbohydrates (NSC) in plants exposed to low temperatures ordrought reflects a higher sensitivity of growth than photosynthesis in such conditions (i.e. sink limitation), or a prioritization of carbon (C) allocation to storage. Alpine areas in Mediterranean-type climate regions are characterized by precipitation increases and temperature decreases with elevation. Thus, alpine plants with wide elevational ranges in Mediterranean regions may be good models to examine these alternative hypotheses. We evaluated storage and growth during experimental darkness and re-illumination in individuals of the alpine plant Phacelia secunda from three elevations in the Andes of central Chile. We hypothesized that storage is prioritized regarding growth in plants of both low- and high elevations where drought and cold stress are greatest, respectively. We expected that decreases in NSC concentrations during darkness should be minimal and, more importantly, increases in NSC after re-illumination should be higher than increases in biomass. We found that darkness caused a significant decrease in NSC concentrations of both low- and high-elevation plants, but the magnitude of the decrease was lower in the latter. Re-illumination caused higher increase in NSC concentration than in biomass in both low- and high-elevation plants (1.5- and 1.9-fold, respectively). Our study shows that C allocation in Phacelia secunda reflects ecotypic differences among elevation provenances and suggests that low temperature, but not drought, favours C allocation to storage over growth after severe C limitation.

Exogenous Calcium Alleviates Nocturnal Chilling-Induced Feedback Inhibition of Photosynthesis by Improving Sink Demand in Peanut (Arachis hypogaea).

Arachis hypogaea (peanut) is a globally important oilseed crop with high nutritional value. However, upon exposure to overnight chilling stress, it shows poor growth and seedling necrosis in many cultivation areas worldwide. Calcium (Ca2+) enhances chilling resistance in various plant species. We undertook a pot experiment to investigate the effects of exogenous Ca2+ and a calmodulin (CaM) inhibitor on growth and photosynthetic characteristics of peanut exposed to low night temperature (LNT) stress following warm sunny days. The LNT stress reduced growth, leaf extension, biomass accumulation, gas exchange rates, and photosynthetic electron transport rates. Following LNT stress, we observed larger starch grains and a concomitant increase in nonstructural carbohydrates and hydrogen peroxide (H2O2) concentrations. The LNT stress further induced photoinhibition and caused structural damage to the chloroplast grana. Exogenous Ca2+ enhanced plant growth following LNT stress, possibly by allowing continued export of carbohydrates from leaves. Foliar Ca2+ likely alleviated the nocturnal chilling-dependent feedback limitation on photosynthesis in the daytime by increasing sink demand. The foliar Ca2+ pretreatment protected the photosystems from photoinhibition by facilitating cyclic electron flow (CEF) and decreasing the proton gradient (ΔpH) across thylakoid membranes during LNT stress. Foliar application of a CaM inhibitor increased the negative impact of LNT stress on photosynthetic processes, confirming that Ca2+–CaM played an important role in alleviating photosynthetic inhibition due to the overnight chilling-dependent feedback.

13-year nitrogen addition increases nonstructural carbon pools in subtropical forest trees in southern China

Nonstructural carbohydrates (NSC) are important for plant growth and defense, and represent an important carbon pool that contributes to carbon (C) cycling and balance, but we know little about the variation of NSC in trees under global change scenarios, particularly nitrogen (N) deposition. Here, we investigated the responses of NSC (sugar and starch) pools of two dominant tree species (Castanopsis chinensis (broadleaf) and Pinus massoniana (coniferous)) to 13-year N treatments in different seasons in southern Chinese forests. Nitrogen addition increased NSC pools of the two tree species at the whole-tree and organ levels. We observed the larger starch pool (only in the wet season) and the highest increased NSC in the branches (3.8-fold) of C. chinensis following N addition. We also found the larger sugar pools (both in the dry and wet season) and the highest increased NSC in the roots (2.2-fold) of P. massoniana after N addition. Despite the increases in NSC of trees, we found no changes in chloroplast and photosynthetic capacity in response to N addition; however, the increased NSC may support prime defense of trees, as evidenced by significant correlations between NSC pools with volatile organic compounds (VOCs) emission (P < 0.05, R2 in the range of 0.5–0.8). Our findings indicate that long-term N deposition induced carbon distribution and adaptation strategies of different subtropical trees, with increased NSC storage at the whole-tree and organ levels and more NSC being allocated to the branches of broadleaf tree species and to the roots of coniferous tree species, respectively. This study provides a new insight into understanding the mechanisms of subtropical forest trees adapting and surviving under long-term N deposition, and is also important for exploring the ecosystem C-N coupling relationships under global environment changes.

High Soil Available Phosphorus Favors Carbon Metabolism in Cotton Leaves in Pot Trials

Phosphorus (P) is an essential macronutrient for plant growth and its metabolism. Because reproductive growth could be influenced by carbon metabolism of the functional leaf (MSL), we hypothesized that soil available phosphorus (AP) deficiency would limit boll dry mass distributions of the whole cotton plant by decreasing photosynthesis of MSL and inhibiting carbon metabolism in the MSL. This study aimed to determine the correlations between carbon metabolism and cotton boll dry mass in relation to soil AP deficiency, and key carbon-metabolism enzymes responsive to P for different low-P-sensitive cultivars. A three-year (2015–2017) pot experiment was conducted with three available phosphorus (AP) levels [3 (P0, AP deficiency), 8 (P1), and 12 (P2, as a control) mg P2O5 kg−1] with two cotton cultivars (CCRI 79 and LMY 28). Low soil AP had significant decreases on leaf P content, net photosynthetic rate (Pn) in the functional leaf (MSL), as well as boll dry mass. The P0 and P1 caused a significant increase in nonstructural carbohydrates (soluble sugar, sucrose, hexose, starch), in especial sucrose (↑8–17% for CCRI 79 and ↑20–32% for LMY 28). Similarly, the lower P levels (P0 and P1) prominently down-regulated the activities of Rubisco, sucrose phosphate synthase (SPS), and amylase, but up-regulated cytosolic fructose-1,6-bisphosphatases and soluble acid invertase (SAI). Moreover, only the absolute value of slope in SAI for LMY 28 was higher than that for CCRI 79 in 2015 and 2016. Our results indicated that the response of carbon-metabolizing enzymes to low AP content was mediated by SAI for CCRI 79 and LMY 28. In our results, Pn, Rubisco, and SAI were the dominant factors affecting the boll dry mass under low soil AP.

Effects of ocean acidification and hydrodynamic conditions on carbon metabolism and dissolved organic carbon (DOC) fluxes in seagrass populations

Global change has been acknowledged as one of the main threats to the biosphere and its provision of ecosystem services, especially in marine ecosystems. Seagrasses play a critical ecological role in coastal ecosystems, but their responses to ocean acidification (OA) and climate change are not well understood. There have been previous studies focused on the effects of OA, but the outcome of interactions with co-factors predicted to alter during climate change still needs to be addressed. For example, the impact of higher CO2 and different hydrodynamic regimes on seagrass performance remains unknown. We studied the effects of OA under different current velocities on productivity of the seagrass Zostera noltei, using changes in dissolved oxygen as a proxy for the seagrass carbon metabolism, and release of dissolved organic carbon (DOC) in a four-week experiment using an open-water outdoor mesocosm. Under current pH conditions, increasing current velocity had a positive effect on productivity, but this depended on shoot density. However, this positive effect of current velocity disappeared under OA conditions. OA conditions led to a significant increase in gross production rate and respiration, suggesting that Z. noltei is carbon-limited under the current inorganic carbon concentration of seawater. In addition, an increase in non-structural carbohydrates was found, which may lead to better growing conditions and higher resilience in seagrasses subjected to environmental stress. Regarding DOC flux, a direct and positive relationship was found between current velocity and DOC release, both under current pH and OA conditions. We conclude that OA and high current velocity may lead to favourable growth scenarios for Z. noltei populations, increasing their productivity, non-structural carbohydrate concentrations and DOC release. Our results add new dimensions to predictions on how seagrass ecosystems will respond to climate change, with important implications for the resilience and conservation of these threatened ecosystems.

Carbon allocation and partitioning in Populus tremuloides are modulated by ectomycorrhizal fungi under phosphorus limitation.

The fate of carbon (C) captured by forest trees during photosynthesis is influenced by the supply of other resources. Fixed C may be partitioned among biomolecules within the leaf and/or allocated throughout the tree to growth, storage and maintenance activities. Phosphorus (P) availability often limits tree productivity due to its high biological demand and strong interactions with soil minerals. As ectomycorrhizal (ECM) fungi play critical roles in enhancing phosphate (Pi) acquisition by their hosts, these symbioses will influence the fate of C within trees and forested ecosystems. Using Populus tremuloides Michx. (trembling aspen) in symbiosis with Laccaria bicolor (Marie) P.D. Orton or Paxillus involutus (Batsch) Fr., we assessed C acquisition, allocation and partitioning under Pi limitation, specifically focusing on primary and secondary C compounds. Both ECM fungi moderated the effects of low P on photosynthesis and C partitioning among carbohydrates and secondary metabolites by sustaining Pi uptake and translocation in P. tremuloides under Pi limitation. As leaf P declined, reductions in photosynthesis were accompanied by significant shifts in C partitioning from nonstructural carbohydrates (NSCs) to phenolic glycosides and tannins. Carbon partitioning in roots exhibited more complex patterns, with distinct increases in NSCs in nonmycorrhizal (NM) plants under Pi limitation that were not evident in plants colonized by either ECM symbiont. In general, aspen colonized by L. bicolor exhibited C partitioning patterns intermediate between those of NM and P. involutus aspen. The C cost of symbiosis was pronounced for plants supporting P. involutus, where ECM plants exhibited maintenance of photosynthesis yet reduced biomass in comparison with NM and L. bicolor aspen under Pi replete conditions. Our results indicate that the ECM symbiosis affects the disposition of C in forest trees in part by altering the acquisition of other limiting resources from soils, but also through ECM species-specific influences on host physiology. This modulation of C partitioning will have broad implications for forest ecosystem C capture, storage and cycling where nutrient resources may be limited.

Similar variation in carbon storage between deciduous and evergreen treeline species across elevational gradients

The most plausible explanation for treeline formation so far is provided by the growth limitation hypothesis (GLH), which proposes that carbon sinks are more restricted by low temperatures than by carbon sources. Evidence supporting the GLH has been strong in evergreen, but less and weaker in deciduous treeline species. Here a test is made of the GLH in deciduous-evergreen mixed species forests across elevational gradients, with the hypothesis that deciduous treeline species show a different carbon storage trend from that shown by evergreen species across elevations. Tree growth and concentrations of non-structural carbohydrates (NSCs) in foliage, branch sapwood and stem sapwood tissues were measured at four elevations in six deciduous-evergreen treeline ecotones (including treeline) in the southern Andes of Chile (40°S, Nothofagus pumilio and Nothofagus betuloides; 46°S, Nothofagus pumilio and Pinus sylvestris) and in the Swiss Alps (46°N, Larix decidua and Pinus cembra). Tree growth (basal area increment) decreased with elevation for all species. Regardless of foliar habit, NSCs did not deplete across elevations, indicating no shortage of carbon storage in any of the investigated tissues. Rather, NSCs increased significantly with elevation in leaves (P < 0·001) and branch sapwood (P = 0·012) tissues. Deciduous species showed significantly higher NSCs than evergreens for all tissues; on average, the former had 11 % (leaves), 158 % (branch) and 103 % (sapwood) significantly (P < 0·001) higher NSCs than the latter. Finally, deciduous species had higher NSC (particularly starch) increases with elevation than evergreens for stem sapwood, but the opposite was true for leaves and branch sapwood. Considering the observed decrease in tree growth and increase in NSCs with elevation, it is concluded that both deciduous and evergreen treeline species are sink limited when faced with decreasing temperatures. Despite the overall higher requirements of deciduous tree species for carbon storage, no indication was found of carbon limitation in deciduous species in the alpine treeline ecotone.

The temporal and species dynamics of photosynthetic acclimation in flag leaves of rice (Oryza sativa) and wheat (Triticum aestivum) under elevated carbon dioxide

In this study, we tested for the temporal occurrence of photosynthetic acclimation to elevated [CO₂] in the flag leaf of two important cereal crops, rice and wheat. In order to characterize the temporal onset of acclimation and the basis for any observed decline in photosynthetic rate, we characterized net photosynthesis, g(s) , g(m) , C(i) /C(a) , C(i) /C(c) , V(cmax) , J(max) , cell wall thickness, content of Rubisco, cytochrome (Cyt) f, N, chlorophyll and carbohydrate, mRNA expression for rbcL and petA, activity for Rubisco, sucrose phosphate synthase (SPS) and sucrose synthase (SS) at full flag expansion, mid-anthesis and the late grain-filling stage. No acclimation was observed for either crop at full flag leaf expansion. However, at the mid-anthesis stage, photosynthetic acclimation in rice was associated with RuBP carboxylation and regeneration limitations, while wheat only had the carboxylation limitation. By grain maturation, the decline of Rubisco content and activity had contributed to RuBP carboxylation limitation of photosynthesis in both crops at elevated [CO₂]; however, the sharp decrease of Rubisco enzyme activity played a more important role in wheat. Although an increase in non-structural carbohydrates did occur during these later stages, it was not consistently associated with changes in SPS and SS or photosynthetic acclimation. Rather, over time elevated [CO₂] appeared to enhance the rate of N degradation and senescence so that by late-grain fill, photosynthetic acclimation to elevated [CO₂] in the flag leaf of either species was complete. These data suggest that the basis for photosynthetic acclimation with elevated [CO₂] may be more closely associated with enhanced rates of senescence, and, as a consequence, may be temporally dynamic, with significant species variation.

Acclimation of photosynthesis and respiration is asynchronous in response to changes in temperature regardless of plant functional group

Gas exchange, fluorescence, western blot and chemical composition analyses were combined to assess if three functional groups (forbs, grasses and evergreen trees/shrubs) differed in acclimation of leaf respiration (R) and photosynthesis (A) to a range of growth temperatures (7, 14, 21 and 28 degrees C). When measured at a common temperature, acclimation was greater for R than for A and differed between leaves experiencing a 10-d change in growth temperature (PE) and leaves newly developed at each temperature (ND). As a result, the R : A ratio was temperature dependent, increasing in cold-acclimated plants. The balance was largely restored in ND leaves. Acclimation responses were similar among functional groups. Across the functional groups, cold acclimation was associated with increases in nonstructural carbohydrates and nitrogen. Cold acclimation of R was associated with an increase in abundance of alternative and/or cytochrome oxidases in a species-dependent manner. Cold acclimation of A was consistent with an initial decrease and subsequent recovery of thylakoid membrane proteins and increased abundance of proteins involved in the Calvin cycle. Overall, the results point to striking similarities in the extent and the biochemical underpinning of acclimation of R and A among contrasting functional groups differing in overall rates of metabolism, chemical composition and leaf structure.

Estimation of Canopy Photosynthesis in Rice by Means of Daily Increases in Leaf Carbohydrate Concentrations

Procedures for rapid measurement of canopy photosynthesis are needed because current methods are time consuming and labor intensive. Our objective was to demonstrate that daily increases in nonstructural carbohydrates of shoots provide a good estimate of daily canopy photosynthesis for rice (Oryza sativa L.). Four cultivars— ‘IR72’, ‘IR64’, ‘IR50’, and ‘YRL39’— were grown in the field on a verlic tropaquept clay soil. Canopy photosynthesis was measured in the field every 2 h from sunrise (0600 h) to sunset (1800 h) and plotted over time to determine daily photosynthesis. Increases in shoot nonstructural carbohydrates per day were calculated by subtracting sunrise concentrations from those at sunset. Highly significant positive relationships between daily canopy photosynthesis and irradiance (r2 = 0.999) and leaf soluble sugars and irradiance (r2 = 0.981) were observed. Coefficients of determination for relationships between daily canopy photosynthesis and daily increases in leaf soluble sugars were high (r2 = 0.987). Growth stage comparisons showed the highest coefficients of determination at panicle initiation because non‐structural carbohydrates in the shoot were dependent on canopy light interception and photosynthesis. Relationships during flowering were intermediate because the spikelet was the main carbon sink. Removal of panicles at flowering increased coefficients of determination to r2 = 0.8. Relationships among cultivars for daily irradiance versus daily canopy photosynthesis or daily increases in leaf soluble sugars had r2 values of 0.7 to 1.0. We conclude that measuring daily increases in leaf carbohydrates can provide a simple, rapid screening procedure for evaluating canopy photosynthesis in rice.

Isotope discrimination and photosynthesis of vegetation growing in the Bossoleto CO 2 spring

The Bossoleto CO 2 spring emits CO 2 which has a stable carbon isotopic ration ( δ 13 C = −8‰ ). We determined δ 13C on leaves of several individual species growing in Bossoleto and in a nearby control site at ambient CO 2. δ 13C was 6% more negative in leaves of species collected from the grassland community of Bossoleto, indicating discrimination (Δ) against the heavy carbon isotope. No such changes were found in ruderal species growing in teh same spring, suggesting that photosynthetic capacity was much less affected. Δ was substantially increased under elevated CO 2 in leaves of Quercus pubescens but not in Quercus ilex, which also did not show any increase in non-structural carbohydrates. Gas-exchange measurements made on Plantago lanceolata, supported the view that photosynthetic capacity is decreased in plants grown under elevated CO 2 and on poor soils.

Effects of short- and long-term elevated CO2 on the expression of ribulose-1,5-bisphosphate carboxylase/oxygenase genes and carbohydrate accumulation in leaves of Arabidopsis thaliana (L.) Heynh.

To investigate the proposed molecular characteristics of sugar-mediated repression of photosynthetic genes during plant acclimation to elevated CO2, we examined the relationship between the accumulation and metabolism of nonstructural carbohydrates and changes in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) gene expression in leaves of Arabidopsis thaliana exposed to elevated CO2. Long-term growth of Arabidopsis at high CO2 (1000 microL L-1) resulted in a 2-fold increase in nonstructural carbohydrates, a large decrease in the expression of Rubisco protein and in the transcript of rbcL, the gene encoding the large subunit of Rubisco (approximately 35-40%), and an even greater decline in mRNA of rbcS, the gene encoding the small subunit (approximately 60%). This differential response of protein and mRNAs suggests that transcriptional/posttranscriptional processes and protein turnover may determine the final amount of leaf Rubisco protein at high CO2. Analysis of mRNA levels of individual rbcS genes indicated that reduction in total rbcS transcripts was caused by decreased expression of all four rbcS genes. Short-term transfer of Arabidopsis plants grown at ambient CO2 to high CO2 resulted in a decrease in total rbcS mRNA by d 6, whereas Rubisco content and rbcL mRNA decreased by d 9. Transfer to high CO2 reduced the maximum expression level of the primary rbcS genes (1A and, particularly, 3B) by limiting their normal pattern of accumulation through the night period. The decreased nighttime levels of rbcS mRNA were associated with a nocturnal increase in leaf hexoses. We suggest that prolonged nighttime hexose metabolism resulting from exposure to elevated CO2 affects rbcS transcript accumulation and, ultimately, the level of Rubisco protein.