Carbon Allocation Patterns Research Articles

Environmental aridity driving latitudinal pattern of biomass allocation fractions in root systems of 63 shrub species in dry valleys.

Fine roots and absorptive roots play key roles in acquiring resources throughout soil profiles and determining plant functions along environmental gradients. Yet, the geographical pattern of carbon allocation in fine roots, particularly in absorptive roots, and their relations with plant sizes and evironment are less understood. We sampled 243 xerophytic shrubs from 63 species distributed along the latitudinal gradient (23°N to 32°N) in dry valleys of southwest China and synthetically measured biomass fractions of plant organs, especially fine roots and absorptive roots (1st to 3rd root order). We identified latitudinal patterns of biomass allocation fractions of organs and their relationships with plant sizes and environmental factors. The latitudinal patterns of both absorptive root and fine-root fractions followed weak unimodal distributions; stem biomass fraction increased with the latitude, while the leaf biomass fraction decreased. The fraction of fine-root biomass had negative relationships with plant height and root depth. The fractions of root, fine root, and absorptive root biomass were largely explained by soil moisture. Furthermore, fraction of fine-root biomass increased in a relatively humid environment. Overall, soil moisture was the most important factor in driving latitudinal patterns of biomass fraction. Our study highlighted that functional redistribution of root system biomass was the critical adaptive strategy along a latitudinal gradient.

Floral deception in dioecious Actinidia polygama (Actinidiaceae) revealed by differential nitrogen investment in male organs

AbstractAnimal‐pollinated plants have evolved rewards and advertisements to attract pollinators, which learn to associate advertisements with rewards. Pollen‐collecting insects, such as bees, associate stamens with pollen (a reward) essential for brood rearing. In some dioecious plants, female flowers have stamens with sterile pollen grains to mimic male flowers. It is not yet fully understood whether females offer less nutritious pollen to pollinators in order to conserve nutrition. Here, we tested this hypothesis in a perennial vine, Actinidia polygama, which bears nectarless flowers. We quantified flower production and measured the dry mass of floral parts as well as carbon and nitrogen concentrations in floral parts and pollen in both sexes. Males produced more flowers per inflorescence and more inflorescences per shoot than females, while the dry mass of each flower was greater in females. The carbon allocation pattern was similar to that of biomass, but nitrogen allocation exhibited a remarkable reduction in sterile stamens and pollen of female flowers. In addition, as sterile pollen of females was sparse, when compared at the same volume, it was lighter than the pollen of males. Sterile pollen produced in female flowers appears to be as voluminous as that of male flowers but extremely poor in nutrients, especially in nitrogen, which clearly suggests that A. polygama females deceive pollen‐collecting pollinators for brood rearing.

Photosynthetic carbon allocation in native and invasive salt marshes undergoing hydrological change

Biogeochemical processes mediated by plants and soil in coastal marshes are vulnerable to environmental changes and biological invasion. In particular, tidal inundation and salinity stress will intensify under future rising sea level scenarios. In this study, the interactive effects of flooding regimes (non-waterlogging vs. waterlogging) and salinity (0, 5, 15, and 30 parts per thousand (ppt)) on photosynthetic carbon allocation in plant, rhizodeposition, and microbial communities in native (Phragmites australis) and invasive (Spartina alterniflora) marshes were investigated using mesocosm experiments and 13CO2 pulse-labeling techniques. The results showed that waterlogging and elevated salinity treatments decreased specific root allocation (SRA) of 13C, rhizodeposition allocation (RA) 13C, soil 13C content, grouped microbial PLFAs, and the fungal 13C proportion relative to total PLFAs-13C. The lowest SRA, RA, and fungal 13C proportion occurred under the combined waterlogging and high (30 ppt) salinity treatments. Relative to S. alterniflora, P. australis displayed greater sensitivity to hydrological changes, with a greater reduction in rhizodeposition, soil 13C content, and fungal PLFAs. S. alterniflora showed an earlier peak SRA but a lower root/shoot 13C ratio than P. australis. This suggests that S. alterniflora may transfer more photosynthetic carbon to the shoot and rhizosphere to facilitate invasion under stress. Waterlogging and high salinity treatments shifted C allocation towards bacteria over fungi for both plant species, with a higher allocation shift in S. alterniflora soil, revealing the species-specific microbial response to hydrological stresses. Potential shifts towards less efficient bacterial pathways might result in accelerated carbon loss. Over the study period, salinity was the primary driver for both species, explaining 33.2–50.8 % of 13C allocation in the plant-soil-microbe system. We propose that future carbon dynamics in coastal salt marshes under sea-level rise conditions depend on species-specific adaptive strategies and carbon allocation patterns of native and invasive plant-soil systems.

Trade-off in the partitioning of recent photosynthate carbon under global change.

There may be trade-offs in the allocation patterns of recent photosynthetic carbon (RPC) allocation in response to environmental changes, with a greater proportion of RPC being directed towards compartments experiencing limited resource availability. Alternatively, the allocation of RPC could shift from sources to sinks as plants processing excess photosynthates. It prompts the question: Does the pattern of RPC allocation vary under global changes? If so, is this variation driven by optimal or by residual C allocation strategies? We conducted a meta-analysis by complicating 273 pairwise observations from 55 articles with 13 C or 14 C pulse or continuous labeling to assess the partitioning of RPC in biomass (leaf, stem, shoot, and root), soil pools (soil organic C, rhizosphere, and microbial biomass C) and CO2 fluxes under elevated CO2 (eCO2 ), warming, drought and nitrogen (N) addition. We propose that the increased allocation of RPC to belowground under sufficient CO2 results from the excretion of excess photosynthates. Warming led to a significant reduction in the percentage of RPC allocated to shoots, alongside an increase in roots allocation, although this was not statistically significant. This pattern is due to the reduced water availability resulting from warming. In conditions of drought, there was a notable increase in the partitioning of RPC to stems (+7.25%) and roots (+36.38%), indicative of a greater investment of RPC in roots for accessing water from deeper soil. Additionally, N addition led to a heightened allocation of RPC in leaves (+10.18%) and shoots (+5.78%), while reducing its partitioning in soil organic C (-8.92%). Contrary to the residual C partitioning observed under eCO2 , the alterations in RPC partitioning in response to warming, drought, and N supplementation are more comprehensively explained through the lens of optimal partitioning theory, showing a trade-off in the partitioning of RPC under global change.

A neutral theory of plant carbon allocation.

How plants use the carbon they gain from photosynthesis remains a key area of study among plant ecologists. Although numerous theories have been presented throughout the years, the field lacks a clear null model. To fill this gap, I have developed the first null model, or neutral theory, of plant carbon allocation using probability theory, plant biochemistry and graph theory at the level of a leaf. Neutral theories have been used to establish a null hypothesis in molecular evolution and community assembly to describe how much of an ecological phenomenon can be described by chance alone. Here, the aim of a neutral theory of plant carbon allocation is to ask: how is carbon partitioned between sinks if one assumes plants do not prioritize certain sinks over others? Using the biochemical network of plant carbon metabolism, I show that, if allocation was strictly random, carbon is more likely to be allocated to storage, defense, respiration and finally growth. This 'neutral hierarchy' suggests that a sink's biochemical distance from photosynthesis plays an important role in carbon allocation patterns, highlighting the potentially adaptive role of this biochemical network for plant survival in variable environments. A brief simulation underscores that our ability to measure the carbon allocation from photosynthesis to a given sink is unreliable due to simple probabilistic rules. While neutral theory may not explain all patterns of carbon allocation, its utility is in the minimal assumptions and role as a null model against which future data should be tested.

Physiological transition of Chlorella vulgaris from planktonic to immobilized conditions

Biofilm-based technologies present many advantages (e.g., higher productivity, lower water demand and harvesting costs) compared with the conventional planktonic approaches for microalgae cultivation. A better understanding of photosynthetic biofilm formation is though still needed in order to develop and run biofilm-based systems at large-scale. In this study, for the first time the physiological transition of C. vulgaris cells from planktonic to immobilized state was tracked (cell number, morphology, photosynthetic performance, and cellular composition) during the first 24 h of immobilization. The results clearly confirmed that microalgae rapidly respond to immobilization via physiological adjustments. Over very short time-scales (3 h), cells used photosynthesis to grow (increase in size, 140 %), at expense of cell division, and adjusted their carbon allocation patterns (increase in the relative carbohydrates pool, 135 %). The experiments confirmed that this behavior is specific to cells in the immobilized state. Triggering factors such as water and/or nutrient availability may be responsible for this fast acclimation process. Additionally, lipid content doubled by the end of cultivation, possibly due to imbalanced carbon and nitrogen metabolisms. These results offer new insights for understanding the mechanisms involved in microalgae biofilm formation and development, further helping the operators to optimize the biofilm-based systems.

Study on the relationship between ecological spatial network structure and regional carbon use Efficiency: A case study of the Wuding river basin

Plant carbon use efficiency (CUE) reflects the carbon assimilation ability and carbon sequestration potential of organisms, and is an important quantitative index in ecology. Therefore, investigating CUE can better understand and explore ecosystem carbon flux and carbon allocation patterns. In this paper, the Wuding River Basin is taken as the research area. MODIS were used to calculate CUE and explore its spatiotemporal variations. Using remote sensing environmental indicators (RSEI) extract ecological sources, and the MCR model were used to construct an ecological spatial network. By analogy with complex network theory, calculate topological indicators, and combine its ecological significance to investigate the relationship between CUE and these indicators, considering their ecological significance. The results are as follows: (1) The average CUE value slightly increased, with an overall increase in the southeastern part of the study area, minor changes in the southern parts, and an overall decrease in the western and northern parts of the basin. (2) CUE showed a strong positive correlation with closeness centrality, betweenness centrality, harmonic closeness centrality, and a negative correlation with eccentricity, while no significant correlation was found with component number.

Topography shapes the carbon allocation patterns of alpine forests

Topography plays a crucial role in determining the structure of alpine forests, as it restricts the availability of nutrients and water necessary for plant growth. Nevertheless, our information on how variations in forest carbon allocation patterns driven by fine-scale topography are influenced by broader-scale environmental contexts is limited. In the northern Tibetan Plateau, we combined field data from 89 forest plots with a high-resolution (1 m2) digital elevation model (DEM) and utilized a linear mixed-effects model to investigate how microtopography (characterized by slope, aspect, and topographic wetness index (TWI)) and broader-scale environmental context (characterized by elevation) and their interactions affect the carbon allocation patterns of alpine forest. Our results revealed that at low and high elevations with pronounced subsurface resource limitations, plants tend to allocate a higher proportion of carbon to the root system and have lower aboveground carbon stocks (ACS). Microtopographic heterogeneity significantly influenced the carbon allocation patterns of forest, with the intensity and direction of these effects varying across the environmental gradient. At low elevations, topographically wetter and northerly microhabitats had higher ACS and lower ratios of below- and aboveground carbon stocks (RBA); however, at high elevations, topographically drier and southerly microhabitats had higher ACS and lower RBA. TWI and aspect had the weakest effect on ACS and RBA in the mid-elevations. The relationship between slope and ACS and RBA was significantly positive but not evidently related to the broader-scale environmental gradient.

Above-ground biomass allocation and potential carbon sink of black pine – a case study from southern Poland

Biomass allocation is a key factor for understanding the forest carbon balance and reflects plants’ ecological strategies in different environmental conditions. Allocation patterns and biomass models outside of the native range of black pine have not been analyzed in the context of the observed climate changes. The study's goals were to develop biomass equations for mature black pine from southern Poland and assess biomass and carbon allocation patterns and the potential of trees of different social statuses for carbon sequestration. A total of 129 felled black pine trees were measured, among which 14 were destructively sampled to determine biomass and carbon content in tree components. The developed set of biomass equations provided allocation patterns and accumulation of trees of different social statuses. Biomass and carbon allocation patterns were different but related to tree social status. The introduction of diameter at crown base significantly improved the accuracy of the developed models. The analyzed trees allocated relatively more in stem than in crown in comparison with that observed in other studies. Biomass and carbon allocation patterns of the analyzed black pines differ from those of the native range. They should be considered in biomass modeling with factors influencing social status structure.

Comparing carbon and nutrient allocations among the different organs of plants Suaeda salsa between two typically coastal wetlands, China

The allocations of nutrients and biomass are important in understanding the growth processes of plants affected by different environmental conditions. In this study, two coastal wetlands were chosen to study the same species how to adapt to soil environments if plant biomass C allocation existed. The results showed that plants Suaeda salsa from the different coastal wetlands had similar carbon allocation patterns that C contents of plants Suaeda salsa’ leaves were lower than their stems and roots, while N contents were contrary. By analysis, C, N, P contents of plants Suaeda salsa’s leaves, stems and roots in the Yellow River Delta coastal wetlands were almost higher than in the Yancheng coastal wetlands. For soil total N, no differences existed between the two coastal wetlands while soil total P was higher in the Yancheng coastal wetlands than in the Yellow River Delta wetlands. When N:P of soil was lower than 2, the N:P variations of plants Suaeda salsa were described by line correlation significantly, and this phenomenon also existed in their corresponding soil nutrients. Plants Suaeda salsa, the growth of which at different sites was limited by soil nutrition, would allocate their biomass C to their stems and roots more than leaves to adapt to coastal environments such as strong wind and inundation of tide.

Photosynthetic recovery in drought-rehydrated grapevines is associated with high demand from the sinks, maximizing the fruit-oriented performance.

To understand how grapevine sinks compete with each other during water stress and subsequent rehydration, carbon (C) allocation patterns in drought-rehydrated vines (REC) at the beginning of fruit ripening were compared with control vines maintained under drought (WS) or fully irrigated (WW). In the 30 days following rehydration, the quantity and distribution of newly fixed C between leaves, roots and fruits was evaluated through 13 CO2 pulse-labeling and stable isotope ratio mass spectrometry. REC plants diverted the same percentage of fixed C towards the berries as the WS plants, although the percentage was higher than that of WW plants. Net photosynthesis (measured simultaneously with root respiration in a multichamber system for analysis of gas exchange above- and below-ground) was approximately two-fold greater in REC compared to WS treatment, and comparable or even higher than in WW plants. Maximizing C assimilation and delivery in REC plants led to a significantly higher amount of newly fixed C compared to both control treatments, already 2 days after rehydration in root, and 2 days later in the berries, in line with the expression of genes responsible for sugar metabolism. In REC plants, the increase in C assimilation was able to support the requests of the sinks during fruit ripening, without affecting the reserves, as was the case in WS. These mechanisms clarify what is experienced in fruit crops, when occasional rain or irrigation events are more effective in determining sugar delivery towards fruits, rather than constant and satisfactory water availabilities.

Biomass Estimation and Carbon Storage of Taxodium Hybrid Zhongshanshan Plantations in the Yangtze River Basin

As a pivotal wetland tree, Taxodium hybrid Zhongshanshan has been widely planted in the region of Yangtze River for multipurpose of ecological restoration, field shelter, landscape aesthetics as well as carbon sequestration. However, the carbon allocation patterns across distinct stages of stand development of T. Zhongshanshan are poorly documented. Using a sample of 30 trees which were destructively harvested, this study compared 3 models for assessing aboveground biomass. Furthermore, a linear seemingly unrelated regression (SUR) approach was introduced to fit the system of the best selected model that ensured the additivity property. On this basis, biomass and carbon storage of T. Zhongshanshan stands in the Yangtze River Basin (YRB) were fairly estimated. Specifically, the study developed height-diameter at breast (H-DBH) function. The results showed that the selected 3-parameter polynomial model performed better, and the SUR approach provided more accurate estimates of leaf and stem fractions. The total tree biomass was 53.43, 84.87, 140.67, 192.71 and 156.65 t ha−1 in the 9-, 11-, 13-, 15-, and 22-year-old T. Zhongshanshan stands, and contributed averagely 94.40% of the ecosystem biomass accumulation. The current T. Zhongshanshan stands in the YRB area can store 124.76 to 217.64 t ha−1 carbon, of which total tree ranges from 25.32 to 90.89 t ha−1, with 55.19% to 77.66% storing in the soil. The T. Zhongshanshan had continuous potential for carbon storage during its growth, particularly in the incipient stages. The findings of this research are firsthand information for forest managers for the sustainable management of T. Zhongshanshan in the YRB and similar subtropical areas.

Long-term compost amendment modulates wheat genotype differences in belowground carbon allocation, microbial rhizosphere recruitment and nitrogen acquisition

The implementation of soil health-promoting practices, such as cover cropping and compost application, has important implications for nutrient cycling and management in agroecosystems. At the same time, plant belowground carbon (C) allocation patterns can influence nutrient cycling and availability in soil through changes to the microbial community, but the effects may depend on the crop genotype and management practices in place. We evaluated belowground C allocation patterns using 13C labeling and root architecture in two genotypes of winter wheat (Triticum aestivum) with different levels of exudation and belowground allocation strategies in soils with contrasting compost amendment legacy (108.7 Mg ha−1 every 2 years over 10 years vs. no compost). We also measured microbial community structure and function in the rhizosphere and quantified uptake of residue-derived N from 15N-labelled cover crop residues. We found an interactive effect between soil management and genotype, where in the no-compost soil, the high-exudation genotype (Snowmass) increased exudation by over 4-fold, while the low-exudate genotype (Byrd) increased only 2-fold. While we did not observe genotype differences in rhizosphere enzyme activity or dissolved N pools, residue N uptake was 1.8 times greater for Snowmass in the compost-amended soil. There were more rhizosphere microbial taxa associated with the high-exudate genotype (Snowmass); nine bacterial and seven fungal families were indicative of Snowmass, versus one bacterial and four fungal families for Byrd. Our results suggest that the high-exudation strategy can influence the rhizosphere microbial community, and lead to greater short-term residue N uptake in high SOM soil. By directly linking root architecture, exudation, microbial communities, and N mineralization and uptake dynamics, this work demonstrates that plasticity in root C allocation is genotype-specific and influences microbial communities and nutrient cycling depending on the soil health context.

Drought and warming alter gross primary production allocation and reduce productivity in a widespread pasture grass

Carbon allocation determines plant growth, fitness and reproductive success. However, climate warming and drought impacts on carbon allocation patterns in grasses are not well known, particularly following grazing or clipping. A widespread C3 pasture grass, Festuca arundinacea, was grown at 26 and 30°C in controlled environment chambers and subjected to drought (65% reduction relative to well-watered controls). Leaf, root and whole-plant carbon fluxes were measured and linked to growth before and after clipping. Both drought and warming reduced gross primary production and plant biomass. Drought reduced net leaf photosynthesis but increased the leaf respiratory fraction of assimilated carbon. Warming increased root respiration but did not affect either net leaf photosynthesis or leaf respiration. There was no evidence of thermal acclimation. Moreover, root respiratory carbon loss was amplified in the combined drought and warming treatment and, in addition to a negative carbon balance aboveground, explained an enhanced reduction in plant biomass. Plant regrowth following clipping was strongly suppressed by drought, reflecting increased tiller mortality and exacerbated respiratory carbon loss. These findings emphasize the importance of considering carbon allocation patterns in response to grazing or clipping and interactions with climatic factors for sustainable pasture production in a future climate.

Carbon allocation patterns in forbs and grasses differ in responses to mowing and nitrogen fertilization in a temperate grassland

Mowing has been a routine grassland management with consequences of removing nutrients from the nitrogen (N)-limited grassland ecosystems. Carbon (C) allocation plays important roles in plant growth and responses to changing environments. Despite studies on interactions between N fertilization and mowing, no studies have specifically focused on responses of C allocation priorities to N fertilization and mowing at plant functional groups and individual species levels. In the present study, 13C isotope labelling was used to trace the effects of 3-year of N fertilization and mowing on the fate of newly-assimilated C (accumulation and allocation priorities) at community, functional group and species levels in a temperate grassland of northern China. We applied the allometric allocation theory to explain the differential C allocation patterns among the organs of different species. Mowing and N fertilization for three consecutive years had no impacts on accumulation of newly-assimilated C at community level. However, C allocation in forbs and grasses differed markedly in their responses to mowing and N fertilization, such that mowing enhanced C accumulation in forbs and N fertilization enhanced C accumulation in grasses. In addition, mowing increased 13C allocation to stolon of forb species, thus facilitating their propagation. Moreover, N fertilization increased 13C allocation to rhizomes of grass species, ensuring clonal grasses to occupy a new niche. We demonstrated that grasses and forbs in a temperate grassland evolved different strategies of C allocation in response to mowing and N fertilization. The contrasting responses may account for the observation that N fertilization and mowing had no impacts on C accumulation at the community level. Our results highlight the necessity to monitor C allocation at functional group and dominant plant species levels, rather than at community level of grasslands exclusively for mechanistically understanding how grasslands respond to mowing and N fertilization.

Divergent belowground carbon allocation patterns of winter wheat shape rhizosphere microbial communities and nitrogen cycling activities

Plant roots add carbon (C) -rich rhizodeposits to the soil, which can alter microbial activity and nitrogen (N) cycling with implications for N availability and uptake by plants. We evaluated root architecture, rhizodeposit C, and microbial community structure and function across a breeding gradient of twelve winter wheat genotypes and examined how these rhizosphere traits were related to the availability and uptake of N from fresh cover crop residues in the soil. We traced wheat-derived C into soil and microbial pools using continuous isotopic labelling (13C–CO2) and applied 15N labelled plant residues to quantify plant and microbial uptake of residue-derived N. Wheat genotypes differed in root C allocation patterns, influencing N cycling. Thicker roots released more C into soil, which enhanced N mineralization through stimulation of the microbial biomass. Microbial biomass increased N-cycling enzyme activity and residue N-uptake by wheat. Microbial communities did not differ between wheat genotypes but were strongly related to patterns in root C allocation, and several genera showed strong relationships with root C deposition and N uptake. The microbial community associated with extractable root-derived C was structurally different from the community associated with residue N uptake, indicating that N-cycling and mineralization was not necessarily carried out by the same microbial community members as those stimulated by rhizosphere C inputs. Our results indicate that differential patterns of rhizodeposition and associated belowground C allocation strategies in winter wheat can alter microbial communities and influence cycling and plant availability of residue N. Ecologically-based nutrient management in agricultural systems should consider the role of crop root traits and associated microbiomes to optimize soil nutrient dynamics.

Grass(stage)root movement to ensure future resilience of longleaf pine ecosystems

Recent interest in restoring longleaf pine ecosystems highlights the need for an improved understanding, appreciation, and consideration of longleaf pine’s unique life history compared to other southern pines. Longleaf pine ecosystems are considered more resilient than other southern pine ecosystems and the attributes that confer this resilience may be related to belowground carbon allocation patterns that occur during the seedling stage of its life history where it exists for years in a grass stage. The long residence time spent in the grass stage has impeded adoption of longleaf pine by landowners for decades, which has resulted in efforts to expedite emergence from the grass stage through silviculture, nursery production, and selection breeding techniques; however, expedited emergence may come at the expense of root and belowground carbohydrate storage reserve development—traits that purportedly enhance longleaf pine tree and ecosystem resilience relative to other southern pine species. Here, I caution that efforts to expedite longleaf pine emergence from the grass stage also consider the potential implications on belowground carbon allocation and identify research priorities to help facilitate the improvement of longleaf pine seedling silviculture, nursery production, and breeding in a way that ensures the maintenance of attributes linked to resilience.

Variations of carbon allocation and turnover time across tropical forests

AbstractAimThe carbon sink in tropical forests is a highly uncertain component of the global carbon budget. An understanding of the processes controlling this sink requires better quantification of carbon allocation, stocks and turnover times.LocationTropical forests.Time period2010–2017.Major taxa studiedTropical forest ecosystem.MethodsWe develop a novel data assimilation system using satellite‐based annual above‐ground biomass derived from L‐band vegetation optical depth with 25 km × 25 km grid spacing, together with leaf area, to constrain the 25 km × 25 km carbon allocation patterns of net primary productivity (NPP) into the wood, leaf and root pools, and their turnover times. Our average data‐driven estimates of these variables are broadly consistent with independent ground‐based estimates of NPP allocation and wood turnover from forest inventory plots.ResultsIn tropical forest, on average, the NPP allocation into wood (0.30 ± 0.04) is significantly higher than that into leaves (0.24 ± 0.07). From the wet to dry tropics, forest NPP allocation into both wood and leaves declines slightly. The turnover times of forest leaf pools exhibit little spatial variation, whereas the turnover times of wood pools in Africa (median and interquartile range: years) are slightly longer than those in South America ( years) and Southeast Asia ( years). Our datasets reveal emergent trade‐offs across climatic and vegetation gradients between growth and life span/turnover for both wood and leaves. The spatial gradients of NPP allocation to wood/leaves are associated with canopy height, adjusted by climate condition and nutrient acquisition. The spatial gradients of wood and leaf turnover times are influenced mainly by climate and leaf characteristics.Main conclusionsOur data‐driven estimates of carbon allocation and turnover times provide a basis for more detailed exploration of these mechanisms in field studies. This highlights that improved model representation of carbon allocation and turnover is necessary for more accurate prediction of future carbon dynamics.

Canopy status modulates formation of wood rays in scots pine under hemiboreal conditions

Non-structural carbohydrates (NSC) reserves are crucial for trees to cope with weather extremes, thus to ensure their survival and ecological plasticity. The NSC reserves can depend on social status, suggesting uneven plasticity of trees at the stand level. In stemwood of Scots pine (Pinus sylvestris L.), which is a widespread and important species, NSC reserves are stored in parenchyma in wood rays (WR). The quantity of WRs is adjusted intra-annually, allowing retrospective analysis of factors affecting their formation. Accordingly, the differences in WR quantity in stemwood of dominant and intermediate (canopy trees with reduced and narrow crowns) maturing Scots pine were assessed by quantitative wood anatomy. Tangential cuts from the outermost 30 tree-rings were analysed. The relative ray area was intermediate, i.e. covering about 5% of the tangential cut, yet expressed high individuality among the trees. The size and amount of WR mainly differed between the earlywood and latewood; WRs in latewood were higher although narrower in comparison to earlywood, yet their total amount was higher in earlywood. Canopy status had only a slight effect, as quantity and height of WR tended to be higher for the intermediate trees, particularly in earlywood. The size and quantity of WR expressed inter-annual variation, which was mainly related to the meteorological conditions prior to the formation of the tree-ring (previous summer and autumn) indicating legacy effects of climatic factors on NSC and susceptibility of trees to cumulative effects of weather extremes. However, the climatic signals in the inter-annual variation of WR were weaker than observed before, likely due to location of the studied stand in the mid-part of the species range. Nevertheless, the observed differences in mean values and inter-annual variation of WR suggested a within-species diversity of carbon allocation patterns, supporting adaptability of the species.

Climate implications on forest above- and belowground carbon allocation patterns along a tropical elevation gradient on Mt. Kilimanjaro (Tanzania)

Tropical forests represent the largest store of terrestrial biomass carbon (C) on earth and contribute over-proportionally to global terrestrial net primary productivity (NPP). How climate change is affecting NPP and C allocation to tree components in forests is not well understood. This is true for tropical forests, but particularly for African tropical forests. Studying forest ecosystems along elevation and related temperature and moisture gradients is one possible approach to address this question. However, the inclusion of belowground productivity data in such studies is scarce. On Mt. Kilimanjaro (Tanzania), we studied aboveground (wood increment, litter fall) and belowground (fine and coarse root) NPP along three elevation transects (c. 1800–3900 m a.s.l.) across four tropical montane forest types to derive C allocation to the major tree components. Total NPP declined continuously with elevation from 8.5 to 2.8 Mg C ha−1 year−1 due to significant decline in aboveground NPP, while fine root productivity (sequential coring approach) remained unvaried with around 2 Mg C ha−1 year−1, indicating a marked shift in C allocation to belowground components with elevation. The C and N fluxes to the soil via root litter were far more important than leaf litter inputs in the subalpine Erica forest. Thus, the shift of C allocation to belowground organs with elevation at Mt. Kilimanjaro and other tropical forests suggests increasing nitrogen limitation of aboveground tree growth at higher elevations. Our results show that studying fine root productivity is crucial to understand climate effects on the carbon cycle in tropical forests.