Nonstructural carbon in woody plants Dietze, Michael C; Sala, Anna; Carbone, Mariah S ...
Annual review of plant biology,
01/2014, Letnik:
65
Journal Article
Recenzirano
Odprti dostop
Nonstructural carbon (NSC) provides the carbon and energy for plant growth and survival. In woody plants, fundamental questions about NSC remain unresolved: Is NSC storage an active or passive ...process? Do older NSC reserves remain accessible to the plant? How is NSC depletion related to mortality risk? Herein we review conceptual and mathematical models of NSC dynamics, recent observations and experiments at the organismal scale, and advances in plant physiology that have provided a better understanding of the dynamics of woody plant NSC. Plants preferentially use new carbon but can access decade-old carbon when the plant is stressed or physically damaged. In addition to serving as a carbon and energy source, NSC plays important roles in phloem transport, osmoregulation, and cold tolerance, but how plants regulate these competing roles and NSC depletion remains elusive. Moving forward requires greater synthesis of models and data and integration across scales from -omics to ecology.
Nonstructural carbohydrate reserves support tree metabolism and growth when current photosynthates are insufficient, offering resilience in times of stress.
We monitored stemwood nonstructural ...carbohydrate (starch and sugars) concentrations of the dominant tree species at three sites in the northeastern United States. We estimated the mean age of the starch and sugars in a subset of trees using the radiocarbon (14C) bomb spike. With these data, we then tested different carbon (C) allocation schemes in a process-based model of forest C cycling.
We found that the nonstructural carbohydrates are both highly dynamic and about a decade old. Seasonal dynamics in starch (two to four times higher in the growing season, lower in the dormant season) mirrored those of sugars. Radiocarbon-based estimates indicated that the mean age of the starch and sugars in red maple (Acer rubrum) was 7–14 yr.
A two-pool (fast and slow cycling reserves) model structure gave reasonable estimates of the size and mean residence time of the total NSC pool, and greatly improved model predictions of interannual variability in woody biomass increment, compared with zero- or one-pool structures used in the majority of existing models. This highlights the importance of nonstructural carbohydrates in the context of forest ecosystem carbon cycling.
Fire‐derived black carbon (BC: charcoal and soot) has been thought to be a passive player in soils, contributing to the refractory soil organic carbon (SOC) pool, but playing no role in pedogenesis ...and regional short‐term carbon cycling. This model, however, is at odds with recent results on the role of charcoal in soil fertility and its detection in the dissolved organic carbon (DOC) pool. For example, if BC simply accumulated passively in soils, its pattern of accumulation should match a simple model correlating fire frequency to BC storage. Instead, soil type, climate, biota, and land use practices all appear to play roles in controlling whether BC accumulates or is lost from soils. We summarize current knowledge of BC‐soil interactions and construct a new paradigm describing the controls on BC storage in soils. We reconcile the refractory‐labile BC paradox by proposing a model where BC storage is controlled by (1) fire frequency, (2) ecosystem presence or absence of aromatic precursor carbon and appropriate combustion conditions, (3) biological or physical mixing to remove BC from the soil surface, where it is vulnerable to combustion in future fires, (4) the presence or absence of soil mineral fractions able to sorb BC into the long‐term stable carbon pool, and (5) the presence of microbial communities capable of degrading aromatic carbon. We also recognize that soil BC/SOC ratios are strongly influenced by land‐use practices and add (6) human activities as a final control.
Measuring isotopic ratios in aerosol particles is a powerful tool for identifying major sources, particularly in separating fossil from non-fossil sources and investigating aerosol formation ...processes. We measured the radiocarbon, stable carbon, and stable nitrogen isotopic composition of PM2.5 in Beijing (BJ) and Changdao (CD) in the North China Plain (NCP) from May to mid-June 2016. The mean PM2.5 concentrations were 48.6 ± 28.2 μg m−3 and 71.2 ± 29.0 μg m−3 in BJ and CD, respectively, with a high contribution (∼66%) from secondary inorganic aerosol (SIA; NO3−, NH4+, and SO42−).
The mean δ13C of total carbon (TC) and δ15N of total nitrogen (TN) values differed significantly between the two sites (p-value of <0.001): −25.1 ± 0.3‰ in BJ and −24.5 ± 0.4‰ in CD and 10.6 ± 1.8‰ in BJ and 5.0 ± 3.1‰ in CD, respectively. In BJ, the average δ15N (NH4+) and δ15N (NO3−) values were 12.9 ± 2.3‰ and 5.2 ± 3.5‰, respectively. The ionic molar ratios and isotopic ratios suggest that NO3− in BJ was formed through the phase-equilibrium reaction of NH4NO3 under sufficient NH3 (g) conditions, promoted by fossil-derived NH3 (g) transported with southerly winds. In BJ, fossil fuel sources comprised 52 ± 7% of TC and 45 ± 28% of NH4+ on average, estimated from radiocarbon (14C) analysis and the δ15N and isotope mixing model, respectively. These multiple-isotopic composition results emphasize that PM2.5 enhancement is derived from fossil sources, in which vehicle emissions are a key contributor. The impact of the coal source was sporadically noticeable. Under regional influences, the fossil fuel-driven SIA led to the PM2.5 enhancements. Our findings demonstrate that the multiple-isotope approach is highly advantageous to elucidate the key sources and limiting factors of secondary inorganic PM2.5 aerosols.
Display omitted
•In Beijing, the contribution of fossil-fuel sources to PM2.5 TC was 52 ± 7%.•For NH4+, the contribution of fossil-fuel sources was 45 ± 28%.•Vehicle emissions are main fossil sources responsible for PM2.5 enhancement.•High PM2.5 was due to collocated NH3 and NOx emissions in North China Plain.
The allocation of nonstructural carbon (NSC) to growth, metabolism and storage remains poorly understood, but is critical for the prediction of stress tolerance and mortality.
We used the radiocarbon ...(14C) ‘bomb spike’ as a tracer of substrate and age of carbon in stemwood NSC, CO2 emitted by stems, tree ring cellulose and stump sprouts regenerated following harvesting in mature red maple trees. We addressed the following questions: which factors influence the age of stemwood NSC?; to what extent is stored vs new NSC used for metabolism and growth?; and, is older, stored NSC available for use?
The mean age of extracted stemwood NSC was 10 yr. More vigorous trees had both larger and younger stemwood NSC pools. NSC used to support metabolism (stem CO2) was 1–2 yr old in spring before leaves emerged, but reflected current-year photosynthetic products in late summer. The tree ring cellulose 14C age was 0.9 yr older than direct ring counts. Stump sprouts were formed from NSC up to 17 yr old.
Thus, younger NSC is preferentially used for growth and day-to-day metabolic demands. More recently stored NSC contributes to annual ring growth and metabolism in the dormant season, yet decade-old and older NSC is accessible for regrowth.
Carbon- and nitrogen-containing aerosols are ubiquitous in urban atmospheres and play important roles in air quality and climate change. We determined the
C fraction modern (
) and δ
C of total ...carbon (TC) and δ
N of NH
in the PM
collected in Seoul megacity during April 2018 to December 2019. The seasonal mean δ
C values were similar to -25.1‰ ± 2.0‰ in warm and -24.2‰ ± 0.82‰ in cold seasons. Mean δ
N values were higher in warm (16.4‰ ± 2.8‰) than in cold seasons (4.0‰ ± 6.1‰), highlighting the temperature effects on atmospheric NH
levels and phase-equilibrium isotopic exchange during the conversion of NH
to NH
. While 37% ± 10% of TC was apportioned to fossil-fuel sources on the basis of
values, δ
N indicated a higher contribution of emissions from vehicle exhausts and electricity generating units (power-plant NH
slip) to NH
: 60% ± 26% in warm season and 66% ± 22% in cold season, based on a Bayesian isotope-mixing model. The collective evidence of multiple isotope analysis reasonably supports the major contribution of fossil-fuel-combustion sources to NH
, in conjunction with TC, and an increased contribution from vehicle emissions during the severe PM
pollution episodes. These findings demonstrate the efficacy of a multiple-isotope approach in providing better insight into the major sources of PM
in the urban atmosphere.
Carbonaceous aerosols are major components in PM2.5 of both polluted and clean atmosphere. Accurate source apportionment of carbonaceous aerosols may support effective PM2.5 control. Dual-carbon ...isotope method (14C and 13C) was adopted to identify the contribution of three main air pollution sources biogenic and biomass (fbb), liquid fossil (fliq.fossil) and coal (fcoal). The aerosol samples were collected at three types of sites with distinctly different degree of air pollution: urban, rural and regional background. The seasonal variation of source apportionment of the carbonaceous aerosols in urban Beijing was discussed. Modern biogenic and biomass made an absolute dominance of 92.9 ± 0.5% contribution to the carbonaceous aerosols at the background site Mt. Yulong due to long-range transport from Southeast Asia. The three main sources contributed jointly to the atmospheric carbonaceous aerosols at the rural site Wangdu and the urban site Beijing. The biogenic and biomass source was the major contribution in summer (47.0 ± 0.3%) and autumn (49.3 ± 0.3%) of Beijing, while coal source increased from summer (26.8 ± 13.8%) to autumn (34.7 ± 11.5%). Heating significantly increased the coal source to the dominant contribution (47.0 ± 16.9%) in winter of Beijing. Separate day and night time coal contributions were used to evaluate the two origins of coal combustion: industrial use vs. residential use. The results of source apportionment for carbonaceous aerosols provide scientific support for the prevention and control of air pollution.
Display omitted
•C source contributions to the carbonaceous aerosols in different regions were demonstrated with dual-carbon isotope method.•Biomass burning took over 90% to the carbonaceous aerosols at Mt. Yulong due to the long-range transport from Southeast Asia.•Anthropogenic impact varied by season in urban Beijing. The coal combustion contribution increased in heating seasons.
We know surprisingly little about whole‐tree nonstructural carbon (NSC; primarily sugars and starch) budgets. Even less well understood is the mixing between recent photosynthetic assimilates (new ...NSC) and previously stored reserves. And, NSC turnover times are poorly constrained. We characterized the distribution of NSC in the stemwood, branches, and roots of two temperate trees, and we used the continuous label offered by the radiocarbon (carbon‐14,¹⁴C) bomb spike to estimate the mean age of NSC in different tissues. NSC in branches and the outermost stemwood growth rings had the¹⁴C signature of the current growing season. However, NSC in older aboveground and belowground tissues was enriched in¹⁴C, indicating that it was produced from older assimilates. Radial patterns of¹⁴C in stemwood NSC showed strong mixing of NSC across the youngest growth rings, with limited ‘mixing in’ of younger NSC to older rings. Sugars in the outermost five growth rings, accounting for two‐thirds of the stemwood pool, had a mean age < 1 yr, whereas sugars in older growth rings had a mean age > 5 yr. Our results are thus consistent with a previously‐hypothesized two‐pool (‘fast’ and ‘slow’ cycling NSC) model structure. These pools appear to be physically distinct.
Climate warming could increase rates of soil organic matter turnover and nutrient mineralization, particularly in northern high-latitude ecosystems. However, the effects of increasing nutrient ...availability on microbial processes in these ecosystems are poorly understood. To determine how soil microbes respond to nutrient enrichment, we measured microbial biomass, extracellular enzyme activities, soil respiration, and the community composition of active fungi in nitrogen (N) fertilized soils of a boreal forest in central Alaska. We predicted that N addition would suppress fungal activity relative to bacteria, but stimulate carbon (C)-degrading enzyme activities and soil respiration. Instead, we found no evidence for a suppression of fungal activity, although fungal sporocarp production declined significantly, and the relative abundance of two fungal taxa changed dramatically with N fertilization. Microbial biomass as measured by chloroform fumigation did not respond to fertilization, nor did the ratio of fungi : bacteria as measured by quantitative polymerase chain reaction. However, microbial biomass C : N ratios narrowed significantly from 16.0 ± 1.4 to 5.2 ± 0.3 with fertilization. N fertilization significantly increased the activity of a cellulose-degrading enzyme and suppressed the activities of protein- and chitin-degrading enzymes but had no effect on soil respiration rates or ¹⁴C signatures. These results indicate that N fertilization alters microbial community composition and allocation to extracellular enzyme production without affecting soil respiration. Thus, our results do not provide evidence for strong microbial feedbacks to the boreal C cycle under climate warming or N addition. However, organic N cycling may decline due to a reduction in the activity of enzymes that target nitrogenous compounds.
Undisturbed grasslands can sequester significant quantities of organic carbon (OC) in soils. Irrigation and fertilization enhance CO2 sequestration in managed turfgrass ecosystems but can also ...increase emissions of CO2 and other greenhouse gases (GHGs). To better understand the GHG balance of urban turf, we measured OC sequestration rates and emission of N2O (a GHG ∼ 300 times more effective than CO2) in Southern California, USA. We also estimated CO2 emissions generated by fuel combustion, fertilizer production, and irrigation. We show that turf emits significant quantities of N2O (0.1–0.3 g N m−2 yr−1) associated with frequent fertilization. In ornamental lawns this is offset by OC sequestration (140 g C m−2 yr−1), while in athletic fields, there is no OC sequestration because of frequent surface restoration. Large indirect emissions of CO2 associated with turfgrass management make it clear that OC sequestration by turfgrass cannot mitigate GHG emissions in cities.
PDF
