Shoot Respiration Research Articles

Alleviating the Injuries of NaCl Exposure on Respiratory Activities, Leaf Stomatal and Antioxidant Defense of Silybum marianum L. Seedlings by Exogenous Nitric Oxide

Nitric oxide (NO) is recognized as an endogenous signaling molecule that plays an important role in the defence responses of medicinal plants to NaCl stress. In this study, we investigated the effects of sodium nitroprusside (SNP) as an NO donor at three concentrations (0, 100, and 200 µmol l−1) to alleviate the deleterious effects of salt stress (100 mM NaCl) on leaf gas exchange and biochemical characteristics of Silybum marianum L. seedlings. This study showed that salt stress significantly decreased relative water content (RWC), chlorophyll b content, endogenous NO concentration, maximum quantum yield (Fv/Fm), leaf gas exchange, stomatal size, K+/Na+ ratio, and plant dry weight, and increased malondialdehyde (MDA) content, hydrogen peroxide (H2O2) content, proline content, stomatal density, and enzyme activities. SNP treatment increased Fv/Fm, photosynthetic pigments, K+/Na+ ratio, and dry weights of the shoots and roots of NaCl-exposed plants. The exogenous application of NO increased the proline content under salinity stress more than under stress conditions without SNP application, so that the proline content increased from 32 to 47 µmol g−1. Application of 100 µM SNP also increased endogenous NO concentration (up to 43%) and consequently protected plants against salt stress-induced damage by improving enzyme activity and reducing the H2O2 generation rate (up to 14%) and MDA content (up to 50%) compared to plants treated with NaCl alone. Foliar application of NO to salt-stressed plants increased root and shoot respiration rates from 20 and 12%, respectively, under salinity stress to 57% under the application of SNP and stress conditions, and decreased stomatal conductance by up to 70%, resulting in improved RWC. Increased internal NO generation in plants induced by 100 µM SNP application has the potential to mitigate salinity injury in Silybum marianum L. plants.

The “Oxygen Sink” of Bamboo Shoots Regulates and Guarantees the Oxygen Supply for Aerobic Respiration

The amazingly rapid growth of bamboo shoots requires strong respiration and provides a large amount of energy and intermediate metabolites. Strong aerobic respiration requires a large amount of O2. This raises the following question: What is the source and mechanism of O2 supply to meet aerobic respiration? However, currently, this remains unknown. The underground buds (US), the 2-m-high overground buds (AS), and the 8-m-high growth arrest buds (HS) of bamboo (Phyllostachys prominens) were collected to represent their different stages of growth and development. The fifth bamboo shoot node at each stage was sealed by two membranes, and treated in a polyethylene zip-lock bag filled with air (21% O2 + 79% N2) and nitrogen (100% N2) for 1.5 h. The concentrations of free O2 and CO2 in the shoot cavities in polyethylene zip-lock bags, and the ethanol content in the shoot body before and after treatment were determined. In addition, the photosynthetic rates of the fifth bamboo internodes of 1 y/o, 2 y/o and 3 y/o bamboo in the field were measured. The results indicated that: (1) When treated with air and nitrogen, US, AS and HS mainly exhibited aerobic respiration, and there was almost no anaerobic respiration; (2) When treated with air, 59.66%, 54.47% and 45.84% of the O2 in the aerobic respiration of US, AS and HS came from the polyethylene zip-lock bag, 0.06%, 0.57% and 0.650% came from the shoot cavity, but 40.28%, 44.96% and 53.51% of the O2 was of an unknown source; (3) Treated by nitrogen, 0.19%, 4.71% and 4.79% of O2 in aerobic respiration of US, AS and HS came from shoot cavity, while the other 99.808%, 95.290% and 95.21% of O2 came from unknown sources; and (4) The photosynthesis of the fifth internodes of 1 y/o, 2 y/o and 3 y/o bamboo generated little oxygen that could not absolutely meet the huge O2 supply for aerobic respiration. It was concluded that the respiration of P. prominens shoots in its different growth and development stages was dominated by aerobic respiration. O2 supply pathways were mainly via the sheath stomata; however, there was little absorption from dissolved O2 in the soil water and little supply produced by shoot/stem photosynthesis. It was found that the large supply of oxygen in the aerobic respiration of bamboo shoots and young bamboo was of an unknown source under air treatment and nitrogen treatment, i.e., 40.28%–53.51% and 95.21%–99.81% of oxygen in the aerobic respiration of bamboo shoots and young bamboo was of unknown origin, respectively. Therefore, we proposed that bamboo shoots may exhibit the phenomenon of acting as an “oxygen sink”, which can provide a large amount of O2 from unknown sources to ensure the rapid growth of bamboo shoots and young bamboo.

Ontogenetic changes in root and shoot respiration, fresh mass and surface area of Fagus crenata.

To date, studies on terrestrial plant ecology and evolution have focused primarily on the trade-off patterns in the allocation of metabolic production to roots and shoots in individual plants and the scaling of whole-plant respiration. However, few empirical studies have investigated the root : shoot ratio by considering scaling whole-plant respiration at various sizes throughout ontogeny. Here, using a whole-plant chamber system, we measured the respiration rates, fresh mass and surface area of entire roots and shoots from 377 Fagus crenata individuals, from germinating seeds to mature trees, collected from five different Japanese provenances. Non-linear regression analysis was performed for scaling of root and shoot respiration, fresh mass and surface area with body size. Whole-plant respiration increased rapidly in germinating seeds. In the seedling to mature tree size range, the scaling of whole-plant respiration to whole-plant fresh mass was expressed as a linear trend on the log-log coordinates (exponent slightly greater than 0.75). In the same body size range, root and shoot respiration vs. whole-plant fresh mass were modelled by upward-convex (exponent decreased from 2.35 to 0.638) and downward-convex trends (exponent increased from -0.918 to 0.864), respectively. The root fraction in whole-plant respiration, fresh mass and surface area shifted continuously throughout ontogeny, increasing in smaller seedlings during early growth stages and decreasing in larger trees. Our results suggest a gradual shift in allocation priorities of metabolic energy from roots in seedlings to shoots in mature trees, providing insights into how roots contribute to shoot and whole-plant growth during ontogeny. The models of root : shoot ratio in relation to whole-plant physiology could be applied in tree growth modelling, and in linking the different levels of ecological phenomena, from individuals to ecosystems.

Physiological Changes of Bamboo (Fargesia yunnanensis) Shoots During Storage and the Related Cold Storage Mechanisms.

The mechanisms for physiological senescence in bamboo shoots after harvest remain unclear. This study investigated physiological changes in Fargesia yunnanensis shoots during storage at different temperatures. The relationship between morphological and physiological changes in bamboo shoots during storage was also analyzed. The results show that cold storage can reduce weight loss, browning, respiration rates, and sugar degradation in bamboo shoots; decrease related enzymatic activities; and inhibit the increase in lignin and cellulose content. The quality of bamboo shoots declines more during the first 3d after harvesting than it does during subsequent periods. The increase in the degree of lignification and fibrosis is the main reason for senescence and for the decline in quality of bamboo shoots after harvest. The bamboo shoots under RT conditions began browning during the third 3d of storage, with a browning rate of 688gkg−1 even in the upper parts; the increase in shoot browning degrees significantly decreased the quality. Low temperatures had better inhibitory effects on browning than they did on lignification and fibrosis. Nonstructural carbohydrates in bamboo shoots are degraded and flow into sheath and shoot respiration, phenols, and shoot fibrosis and lignification at room temperature, but only flow into sheath respiration, shoot fibrosis, and lignification at cold temperature. Soluble protein and free amino acids are primarily distributed into shoot and sheath respiration and into phenols at room temperature, but that process is well inhibited at cold temperature. Bamboo shoots, once removed from cold storage, should be consumed rapidly because enzyme activity recovers quickly. This research provides new theoretical information on the preservation of bamboo shoots.

Consistent scaling of whole-shoot respiration between Moso bamboo (Phyllostachys pubescens) and trees

Both Moso bamboo (Phyllostachys pubescens) and tree forests have a large biomass; they are considered to play an important role in ecosystem carbon budgets. The scaling relationship between individual whole-shoot (i.e., aboveground parts) respiration and whole-shoot mass provides a clue for comparing the carbon budgets of Moso bamboo and tree forests. However, nobody has empirically demonstrated whether there is a difference between these forest types in the whole-shoot scaling relationship. We developed whole-shoot chambers and measured the shoot respiration of 58 individual mature bamboo shoots from the smallest to the largest in a Moso bamboo forest, and then compared them with that of 254 tree shoots previously measured. For 30 bamboo shoots, we measured the respiration rate of leaves, branches, and culms. We found that the scaling exponent of whole-shoot respiration of bamboo fitted by a simple power function on a log–log scale was 0.843 (95 % CI 0.797–0.885), which was consistent with that of trees, 0.826 (95 % CI 0.799–0.851), but higher than 3/4, the value typifying the Kleiber’s rule. The respiration rates of leaves, branches, and culms at the whole-shoot level were proportional to their mass, revealing a constant mean mass-specific respiration of 1.19, 0.224, and 0.0978 µmol CO2 kg− 1 s− 1, respectively. These constant values suggest common traits of organs among physiologically integrated ramets within a genet. Additionally, the larger the shoots, the smaller the allocation of organ mass to the metabolically active leaves, and the larger the allocation to the metabolically inactive culms. Therefore, these shifts in shoot-mass partitioning to leaves and culms caused a negative metabolic scaling of Moso bamboo shoots. The observed convergent metabolic scaling of Moso bamboo and trees may facilitate comparisons of the ecosystem carbon budgets of Moso bamboo and tree forests.

Effects of rotational and continuous overgrazing on newly assimilated C allocation

In situ 13CO2 pulse labeling was conducted in temperate grasslands, managed by no grazing, rotational, or continuous overgrazing, to trace the allocation pattern and the dynamics of newly assimilated C into the plant-soil system. Forty-eight days after the labeling, the belowground 13C allocations under overgrazing were substantially lower than those under no grazing (55% for no grazing, 29% for rotational grazing, 36% for continuous grazing). Overgrazing reduced the relative amount of C incorporation into soil organic C (SOC). Overgrazing led to more C losses through shoot respiration (23%, 54%, 46% by no, rotational, and continuous grazing, respectively), but fewer losses via soil respiration (33%, 12%, 13% by no, rotational, and continuous grazing, respectively). Continuous grazing produced more C allocation to roots than rotational grazing (12% vs 4%), indicating that plants had stronger root C storage capacity under continuous than rotational grazing. The mean C residence time of the belowground rhizodeposits and C used for root respiration under rotational grazing (2.08 days) was longer than that under no grazing (1.47 days) or continuous grazing (1.37 days). Overgrazing decreased the C stocks in shoots but remained stable in roots. Meanwhile, overgrazing decreased the newly assimilated C allocation to belowground, creating a negative effect on C sequestration. Under overgrazing regimes, continuous grazing is more preferable in the investigated temperate grasslands than rotational grazing for C allocation and sequestration in soil.

Sea-level rise will reduce net CO2 uptake in subtropical coastal marshes

Coastal marshes have a significant capacity to sequester carbon; however, sea-level rise (SLR) is expected to result in prolonged flooding and saltwater intrusion in coastal regions. To explore the effects of SLR projections on net CO2 uptake in coastal marshes, we conducted a “double-check” investigation, including the eddy covariance (EC) measurements of the CO2 fluxes in subtropical coastal marshes along inundation and salinity gradients, in combination with a mesocosm experiment for analyzing CO2 flux components under waterlogging and increased salinity conditions. During the same measurement periods, the net ecosystem CO2 exchange (NEEEC based on the EC dataset) in an oligohaline marsh was higher than that in a low-elevation mesohaline marsh, whereas the NEEEC was lower than that in a high-elevation freshwater marsh. The declines in NEEEC between the marshes could be attributed to a greater decrease in gross primary production relative to ecosystem respiration. Waterlogging slightly increased the NEEms (NEE based on the mesocosms) because of inhibited soil respiration and slight changes in plant photosynthesis and shoot respiration. However, the NEEms measured during the drainage period decreased significantly due to the stimulated soil respiration. The NEEms decreased with increasing salinity (except under mild salinity), and waterlogging exacerbated the adverse impacts of salinity. The amplificatory effect of decreases in both leaf photosynthesis and growth under hydrological stresses contributed more to reduce the NEEms than to respiratory effluxes. Both waterlogging and increased salinity reduced the root biomass, soil microbial biomass, and activities of assayed soil enzymes (except for cellulase under waterlogging conditions), leading to limited soil respiration. The declines in plant growth, photosynthesis, and soil respiration could also be attributed to the decrease in soil nutrients under waterlogging and increased salinity conditions. We propose that the coupling of SLR-driven hydrological effects lowers the capacity of CO2 uptake in subtropical coastal marshes.

Corrigendum

Functional EcologyVolume 34, Issue 2 p. 545-545 CorrigendumFree Access Corrigendum This article corrects the following: Does plant biomass partitioning reflect energetic investments in carbon and nutrient foraging? Deliang Kong, Jason D. Fridley, Julia Cooke, Volume 33Issue 9Functional Ecology pages: 1627-1637 First Published online: July 12, 2019 First published: 24 January 2020 https://doi.org/10.1111/1365-2435.13518AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Kong, D, Fridley, JD. Does plant biomass partitioning reflect energetic investments in carbon, nutrient foraging? Functional Ecology, 2019, 33, 1627–1637. https://doi.org/10.1111/1365-2435.13392 In the paper by Kong and Fridley (2019), the authors have determined that three of the 311 values of root mass fraction (RMF) are erroneous. Upon further examination, it was determined that the shoot mass values of the rows in question were summed incorrectly in Excel, leading to three spuriously low RMF values. The authors regret this error. Subsequently, the authors re-ran all analyses with the three revised RMF values. Because they are a small proportion of the dataset, no statistical tests or study interpretations are affected by the error. In one regression analysis conducted on a subset of the data (Figure 2a, N = 131), the slope coefficient decreases from 0.61 to 0.54, due to the high leverage of the three points in question, lowering the R2 from 0.22 to 0.20. An updated figure is provided. Figure 2Open in figure viewerPowerPoint Relationships between total below-ground energy allocation and root mass fraction in carbon allocation studies of individual plants. Whole-plant energy budgets in studies shown in (a) include night-time shoot respiration (N = 131); those in (b) ignore above-ground respiratory costs (N = 270; note some studies are used in both figures). Observations are distinguished by whether plants were inoculated with fungal (AMF, ECM) or bacterial (Rhizobium spp.) mutualist microbes (purple), and triangles represent grasses. Dashed lines are ordinary least squares regressions, and solid lines are 1:1 In the first paragraph of the Results section, it currently reads: We found a positive correlation of RMF and TBCA across studies, regardless of whether TBCA was calculated in reference to plant GPP (R2 = 0.22, p < .001, Figure 2a) or GPP-Rshoot (R2 = 0.32, p < .001, Figure 2b). Because Rshoot was often the smallest component of plant energy budgets, our statistical tests did not depend on which metric of TBCA was used. Slopes of the simple linear relationships of TBCA and RMF (0.61, 0.74) were both significantly lower than 1 (p < .01 in Wald tests), and the intercepts (0.18, 0.19) were both higher than zero (all p < .01), indicating greater underestimation of TBCA at low RMF values (Figure 2). It should read: We found a positive correlation of RMF and TBCA across studies, regardless of whether TBCA was calculated in reference to plant GPP (R2 = 0.20, p < .001, Figure 2a) or GPP-Rshoot (R2 = 0.33, p < .001, Figure 2b). Because Rshoot was often the smallest component of plant energy budgets, our statistical tests did not depend on which metric of TBCA was used. Slopes of the simple linear relationships of TBCA and RMF (0.54, 0.73) were both significantly lower than 1 (p < .01 in Wald tests), and the intercepts (0.19, 0.18) were both higher than zero (all p < .01), indicating greater underestimation of TBCA at low RMF values (Figure 2). REFERENCE Kong, D., & Fridley, J. D. (2019). Does plant biomass partitioning reflect energetic investments in carbon and nutrient foraging? Functional Ecology, 33, 1627– 1637. https://doi.org/10.1111/1365-2435.13392Wiley Online LibraryWeb of Science®Google Scholar Volume34, Issue2Special Features: Sensory ecology and cognition in social decisions Guest Editors: Karin Schneeberger and Michael Taborsky & Epigenetics in ecology and evolution Guest Editors: Anthony Herrel, Dominique Joly and Etienne DanchinFebruary 2020Pages 545-545 FiguresReferencesRelatedInformation

When the Mediterranean becomes harsh: Heat pulses strongly affect C allocation in plant-soil-atmosphere continuum in Eucalyptus camaldulensis

Mediterranean vegetation is frequently subjected to the heat waves with temperature peaks exceeding 45 °C. While the effects of drought on assimilates allocation are deeply studied, little information is available regarding the effects of the acute heat stress on this aspect of the plant physiology. We evaluated the effects of acute heat pulses on plant C internal allocation in Eucalyptus camaldulensis saplings and its transfer into the soil. Shoots of Eucalyptus were subjected to an increase of the air temperatures up to 45 °C. Allocation of C was inferred after pulse labelling of heated and non-heated shoots with 13CO2. Heat pulse lowered the photosynthesis and almost tripled the C losses from shoots through respiration. Assimilated 13C was preferentially allocated to leaf soluble sugar fractions rather than to starch. Heat pulse interrupted 13C allocation to the trunk, roots and soil. 13C allocation to new non labelled leaves was detected in some replicate plants, independently of treatment, suggesting that this process is sink-driven. Although, shoots subjected to the heat pulse modified allocation strategy, “saving” assimilated 13C at a leaf level, the rate of 13C involvement in shoot respiration was restricted by photosynthetic rates measured during the labelling. The results suggest that photosynthetic and non-photosynthetic organs may be constrained to rely on C reserves under elevated temperatures with further negative consequences for C balance in case the duration and frequency of the heat waves will increase as projected by climate change.

Effects of rain shortage on carbon allocation, pools and fluxes in a Mediterranean shrub ecosystem – a 13C labelling field study

Hydrological cycle is expected to become the primary cause of ecosystem's degradation in near future under changing climate. Rain manipulation experiments under field conditions provide accurate picture on the responses of biotic processes to changed water availability for plants. A field experiment, mimicking expected changes in rain patterns, was established in a Mediterranean shrub community at Porto Conte, Italy, in 2001. In November 2011 Cistus monspeliensis, one of the dominating shrub species in the Mediterranean basin, was 13C labelled on plots subjected to extended rain shortage period and on control non manipulated plots. Carbon (C) allocation was traced by 13C dynamics in shoots, shoot-respired CO2, roots, microbial biomass, K2SO4-extractable C and CO2 respired from soil.Most of the recovered 13C (60%) was respired by shoots within 2weeks in control plots. In rain shortage treatment, 13C remained incorporated in aboveground plant parts. Residence time of 13C in leaves was longer under the rain shortage because less 13C was lost by shoot respiration and because 13C was re-allocated to leaves from woody tissues. The belowground C sink was weak (3–4% of recovered 13C) and independent on rain manipulation. Extended rain shortage promoted C exudation into rhizosphere soil in expense of roots. Together with lowered photosynthesis, this “save” economy of new C metabolites reduces the growing season under rain shortage resulting in decrease of shrub cover and C losses from the system on the long-term.

Physiological acclimation dampens initial effects of elevated temperature and atmospheric CO2 concentration in mature boreal Norway spruce.

Physiological processes of terrestrial plants regulate the land-atmosphere exchange of carbon, water, and energy, yet few studies have explored the acclimation responses of mature boreal conifer trees to climate change. Here we explored the acclimation responses of photosynthesis, respiration, and stomatal conductance to elevated temperature and/or CO2 concentration ([CO2 ]) in a 3-year field experiment with mature boreal Norway spruce. We found that elevated [CO2 ] decreased photosynthetic carboxylation capacity (-23% at 25°C) and increased shoot respiration (+64% at 15°C), while warming had no significant effects. Shoot respiration, but not photosynthetic capacity, exhibited seasonal acclimation. Stomatal conductance at light saturation and a vapour pressure deficit of 1kPa was unaffected by elevated [CO2 ] but significantly decreased (-27%) by warming, and the ratio of intercellular to ambient [CO2 ] was enhanced (+17%) by elevated [CO2 ] and decreased (-12%) by warming. Many of these responses differ from those typically observed in temperate tree species. Our results show that long-term physiological acclimation dampens the initial stimulation of plant net carbon assimilation to elevated [CO2 ], and of plant water use to warming. Models that do not account for these responses may thus overestimate the impacts of climate change on future boreal vegetation-atmosphere interactions.

Carbon input by roots into the soil: Quantification of rhizodeposition from root to ecosystem scale.

Despite its fundamental role for carbon (C) and nutrient cycling, rhizodeposition remains 'the hidden half of the hidden half': it is highly dynamic and rhizodeposits are rapidly incorporated into microorganisms, soil organic matter, and decomposed to CO2 . Therefore, rhizodeposition is rarely quantified and remains the most uncertain part of the soil C cycle and of C fluxes in terrestrial ecosystems. This review synthesizes and generalizes the literature on C inputs by rhizodeposition under crops and grasslands (281 data sets). The allocation dynamics of assimilated C (after 13 C-CO2 or 14 C-CO2 labeling of plants) were quantified within shoots, shoot respiration, roots, net rhizodeposition (i.e., C remaining in soil for longer periods), root-derived CO2 , and microorganisms. Partitioning of C pools and fluxes were used to extrapolate belowground C inputs via rhizodeposition to ecosystem level. Allocation from shoots to roots reaches a maximum within the first day after C assimilation. Annual crops retained more C (45% of assimilated 13 C or 14 C) in shoots than grasses (34%), mainly perennials, and allocated 1.5 times less C belowground. For crops, belowground C allocation was maximal during the first 1-2months of growth and decreased very fast thereafter. For grasses, it peaked after 2-4months and remained very high within the second year causing much longer allocation periods. Despite higher belowground C allocation by grasses (33%) than crops (21%), its distribution between various belowground pools remains very similar. Hence, the total C allocated belowground depends on the plant species, but its further fate is species independent. This review demonstrates that C partitioning can be used in various approaches, e.g., root sampling, CO2 flux measurements, to assess rhizodeposits' pools and fluxes at pot, plot, field and ecosystem scale and so, to close the most uncertain gap of the terrestrial C cycle.

Determining the timepoint when 14C tracer accurately reflect photosynthate use in the plant-soil system

Only the carbon (C) isotope pulse labeling approach can provide time-resolved data concerning the input and turnover of plant-derived C in the soil, which are urgently needed to improve the performance of terrestrial C cycle models. However, there is currently very limited information about the point in time after pulse labeling at which the distribution of tracer C accurately represents the usage of photosynthates in different components of the plant-soil system. This should be the case as soon as the tracer has disappeared from the mobile C pool due to respiration, incorporation into the structural C pool of shoot and root tissue and exudation into the soil (rhizodeposition). Following $^{14} {CO}_{2}$ pulse labeling in laboratory and outdoor experiments with spring rye, the 14C dilution rates of soluble fractions and different substances from the structural C pool of the shoot (molecular level), the release of labeled CO2 by belowground respiration (component level), and the 14C kinetics of shoot respiration and 14C remaining in the plant-soil-soil gas continuum (system level) were analyzed during different stages of plant development. At all three levels investigated, 14C kinetics indicated that the C tracer levels changed very little between 15 and 21 days after labeling. Results also showed increasing tracer depletion in the mobile C pool. Consequently, only 0.42 % and 0.06 % of all 14C was still available for shoot respiration 15 and 21 days after labeling, respectively. The similarities between 14C tracer kinetics at the three investigated levels indicate that tracer disappearance from the mobile pool and distribution throughout the plant-soil system was nearly complete between 15 and 21 days after labeling. Therefore, this appears to be the point at which the pulse labeling approach provides sufficiently precise data concerning the use of C (assimilated during labeling) for root growth, rhizodeposition, root respiration and the microbial turnover of rhizodeposits.

Influence of arbuscular mycorrhizal colonization on whole-plant respiration and thermal acclimation of tropical tree seedlings.

Symbiotic arbuscular mycorrhizal fungi (AMF) are ubiquitous in tropical forests. AMF play a role in the forest carbon cycle because they can increase nutrient acquisition and biomass of host plants, but also incur a carbon cost to the plant. Through their interactions with their host plants they have the potential to affect how plants respond to environmental perturbation such as global warming. Our objective was to experimentally determine how plant respiration rates and responses to warmer environment are affected by AMF colonization in seedlings of five tropical tree species at the whole plant level. We evaluated the interaction between AMF colonization and temperature on plant respiration against four possible outcomes; acclimation does or does not occur regardless of AMF, or AMF can increase or decrease respiratory acclimation. Seedlings were inoculated with AMF spores or sterilized inoculum and grown at ambient or elevated nighttime temperature. We measured whole plant and belowground respiration rates, as well as plant growth and biomass allocation. There was an overall increase in whole plant, root, and shoot respiration rate with AMF colonization, whereas temperature acclimation varied among species, showing support for three of the four possible responses. The influence of AMF colonization on growth and allocation also varied among plant species. This study shows that the effect of AMF colonization on acclimation differs among plant species. Given the cosmopolitan nature of AMF and the importance of plant acclimation for predicting climate feedbacks a better understanding of the patterns and mechanisms of acclimation is essential for improving predictions of how climate warming may influence vegetation feedbacks.

Responses of carbon transfer, partitioning, and residence time to land use in the plant–soil system of an alpine meadow on the Qinghai-Tibetan Plateau

We conducted an in situ C-13 pulse-labeling experiment from July to September 2011, involving three land use types: native alpine meadow with winter grazing (native meadow), cultivated perennial Elymus nutans (perennial grass), and annual Avena sativa (annual grass) pastures in the Qinghai-Tibetan Plateau. Thirty-two days after labeling, 32, 23, and 43 % of recovered C-13 of native meadow, perennial grass, and annual grass, respectively, were released by shoot respiration, and 43, 34, and 22 % were allocated to belowground C pools. About half of C-13 allocated to belowground C pools was released by soil respiration. Mean residence time of net assimilate C in this ecosystem was 67, 118, and 43 days for native meadow, perennial grass, and annual grass, respectively. Our results imply that species abundance and root/shoot ratio are the major controlling factors of soil C stocks in high-altitude grassland ecosystems, explaining 35 and 73 %, respectively. We suggest that conversion to monoculture for food production on the Qinghai-Tibetan Plateau may deteriorate soil health through rapid loss of soil organic C. The main cause of C transfer reduction after conversion to monoculture is the change in species richness and root/shoot ratio. Together with previous research studies, our results also support the finding that moderate grazing benefits grassland C transfer and stock, owing to higher species richness and root/shoot ratio.

Peach Water Relations, Gas Exchange, Growth and Shoot Mortality under Water Deficit in Semi-Arid Weather Conditions

In this study the sensitivity of peach tree (Prunus persica L.) to three water stress levels from mid-pit hardening until harvest was assessed. Seasonal patterns of shoot and fruit growth, gas exchange (leaf photosynthesis, stomatal conductance and transpiration) as well as carbon (C) storage/mobilization were evaluated in relation to plant water status. A simple C balance model was also developed to investigate sink-source relationship in relation to plant water status at the tree level. The C source was estimated through the leaf area dynamics and leaf photosynthesis rate along the season. The C sink was estimated for maintenance respiration and growth of shoots and fruits. Water stress significantly reduced gas exchange, and fruit, and shoot growth, but increased fruit dry matter concentration. Growth was more affected by water deficit than photosynthesis, and shoot growth was more sensitive to water deficit than fruit growth. Reduction of shoot growth was associated with a decrease of shoot elongation, emergence, and high shoot mortality. Water scarcity affected tree C assimilation due to two interacting factors: (i) reduction in leaf photosynthesis (-23% and -50% under moderate (MS) and severe (SS) water stress compared to low (LS) stress during growth season) and (ii) reduction in total leaf area (-57% and -79% under MS and SS compared to LS at harvest). Our field data analysis suggested a Ψstem threshold of -1.5 MPa below which daily net C gain became negative, i.e. C assimilation became lower than C needed for respiration and growth. Negative C balance under MS and SS associated with decline of trunk carbohydrate reserves – may have led to drought-induced vegetative mortality.

Effects of waterlogging on carbon assimilate partitioning in the Zoigê alpine wetlands revealed by 13CO2 pulse labeling.

Waterlogging has been suggested to affect carbon (C) turnover in wetlands, but how it affects C allocation and stocks remains unclear in alpine wetlands. Using in situ 13CO2 pulse labelling, we investigated C allocation in both waterlogged and non-waterlogged sites in the Zoigê wetlands on the Tibetan Plateau in August 2011. More than 50% of total 13C fixed by photosynthesis was lost via shoot respiration. Shoots recovered about 19% of total 13C fixed by photosynthesis at both sites. Only about 26% of total fixed 13C was translocated into the belowground pools. Soil organic C pool accounted for 19% and roots recovered about 5–7% of total fixed 13C at both sites. Waterlogging significantly reduced soil respiration and very little 13C was lost via soil respiration in the alpine wetlands compared to that in grasslands. We conclude that waterlogging did not significantly alter C allocations among the C pools except the 13CO2 efflux derived from soil respiration and that shoots made similar contributions to C sequestration as the belowground parts in the Zoigê alpine wetlands. Therefore, changes in waterlogging due to climate change will not affect C assimilate partitioning but soil C efflux.

Ecosystem respiration and its components from a Carex meadow of Poyang Lake during the drawdown period

Little is known about the components of ecosystem respiration from a subtropical littoral wetland with dramatic annual inundation dynamics. In this study, we investigated ecosystem respiration and its components in a Poyang lake Carex meadow during the drawdown periods from May 2009 to June 2011. Both ecosystem respiration and its components showed clear temporal variation pattern, with temperature being the dominant control. Ecosystem respiration ranged from 98.01 to 1359.25 mg CO2 m−2 h−1. Shoot and root respiration contributed approximately 36% and 26% to the ecosystem respiration, respectively, whereas microbial respiration accounted for 38% of the ecosystem respiration. The ratio of total soil respiration to ecosystem respiration varied from 0.45 to 0.90, depending on growing season stages. Their Q10 values ranged from 1.72 to 2.51, with the maximum for shoot respiration and the minimum for microbial respiration. In addition, the Q10 values varied with time and among ecosystem respiratory components and hence could not be treated as a constant. None of the respiration measurements was significantly related to soil moisture, suggesting that soil moisture was not a limiting environmental factor for respiratory activity during the drawdown periods in this meadow. The Carex meadow acted as strong carbon sink during the drawdown periods due to double growing seasons, but the previous summer flood duration could substantially alter carbon sink intensity in the following drawdown period. The total carbon sink of the littoral zone of Poyang Lake during drawdown periods was estimated to be 0.17–0.59 Tg C yr−1.

Thermal acclimation of shoot respiration in an Arctic woody plant species subjected to 22 years of warming and altered nutrient supply

Despite concern about the status of carbon (C) in the Arctic tundra, there is currently little information on how plant respiration varies in response to environmental change in this region. We quantified the impact of long-term nitrogen (N) and phosphorus (P) treatments and greenhouse warming on the short-term temperature (T) response and sensitivity of leaf respiration (R), the high-T threshold of R, and associated traits in shoots of the Arctic shrub Betula nana in experimental plots at Toolik Lake, Alaska. Respiration only acclimated to greenhouse warming in plots provided with both N and P (resulting in a ~30% reduction in carbon efflux in shoots measured at 10 and 20 °C), suggesting a nutrient dependence of metabolic adjustment. Neither greenhouse nor N+P treatments impacted on the respiratory sensitivity to T (Q10 ); overall, Q10 values decreased with increasing measuring T, from ~3.0 at 5 °C to ~1.5 at 35 °C. New high-resolution measurements of R across a range of measuring Ts (25-70 °C) yielded insights into the T at which maximal rates of R occurred (Tmax ). Although growth temperature did not affect Tmax , N+P fertilization increased Tmax values ~5 °C, from 53 to 58 °C. N+P fertilized shoots exhibited greater rates of R than nonfertilized shoots, with this effect diminishing under greenhouse warming. Collectively, our results highlight the nutrient dependence of thermal acclimation of leaf R in B. nana, suggesting that the metabolic efficiency allowed via thermal acclimation may be impaired at current levels of soil nutrient availability. This finding has important implications for predicting carbon fluxes in Arctic ecosystems, particularly if soil N and P become more abundant in the future as the tundra warms.

Changes in microbial biomass C, extractable C and available N during the early stages of decomposition of residue mixtures

Decomposition of mixed residues is common in many ecosystems, with residues from different species or above- and below-ground residues from the same species. Although decomposition of litter mixtures has been extensively studied, little is known about the changes in microbial biomass carbon (C) and available nitrogen (N) in the early stages of decomposition of mixtures of shoots and roots. An incubation experiment was carried out in a sandy clay loam with shoot and root residues of two grasses, annual barley (Hordeum vulgare L.), and perennial Stipa sp., added separately or as mixtures. Soil respiration was measured continuously, and soil microbial biomass C, extractable C and available N were measured by destructive sampling on days 0, 3, 6, 9, 12 and 18. Cumulative respiration and microbial biomass C concentration were higher with barley shoots alone or in mixtures than with Stipa residues alone. In the mixture of Stipa shoots and roots, which had similar decomposition rates when incubated individually, the measured cumulative respiration was greater than the expected value (average of the cumulative respiration of the individual residues), but this did not result in greater microbial biomass or changes in available N concentration compared with the individual residues. Cumulative respiration of barley shoots alone was higher than of barley root and Stipa shoot incubated individually. In the mixtures of barley shoots with barley roots or Stipa shoots, the measured cumulative respiration was either lower than the expected value or similar. Compared with barley shoots alone, microbial biomass C concentrations in the mixtures were generally lower in the first 3 days. It is concluded that mixing of residues with similar decomposition rates can stimulate microbial activity (respiration) but has little effect on microbial growth or concentrations of available N. Further, our findings provide information about extractable C and N dynamics during the early stages of decomposition of individual residue and residue mixtures.