Plant Carbon Research Articles

MeSWEET15a/b genes play a role in the resistance of cassava (Manihot esculenta Crantz) to water and salt stress by modulating sugar distribution

The sugar transporter SWEET plays a role in plant growth, carbon allocation, and abiotic stress resistance. We examined the function of SWEET in cassava (Manihot esculenta Crantz) under water and salt stress. Bioinformatics, subcellular localization, yeast deficient complementation, and virus-induced gene silencing (VIGS) were used to examine the function of SWEET in cassava. Twenty-eight MeSWEETs genes were found based on the conserved domain MtN3/saliva of SWEET transporters, two MeSWEET15a/b of them were identified by phylogenetic analysis, which were located on the cell membrane. They transfer sucrose, fructose, glucose, and mannitol from culture media to yeast cells, predominately transferring sucrose via bleeding fluid saps in plant. Leaf sucrose content was increased in MeSWEET15a/b-silenced cassava plants, resulting in changes in carbon distribution, with an increase in starch accumulation in the leaves and a decrease in starch accumulation in the roots. The silencing of MeSWEET15a/b genes led to tolerance to water and salt stress, consistent with a high accumulation of osmolytes, and low lipid membrane peroxidation. Changes in sugar distribution increased the expression of MeTOR and MeE2Fa in pTRV2-MeSWEET15a and pTRV2-MeSWEET15b cassava leaves. MeSWEET15a/b acts as pivotal modulators of sugar distribution and tolerance to water and high salt stress in cassava.

Evaluation of the carbon capacity of single breed wood stands – elements of the green infrastructure of Kharkiv

The value of the carbon capacity of the elements of the green infrastructure makes it possible to find out the amount of accumulated carbon in plants throughout their life, and, as a result, to establish the provision of the city with green spaces. Purpose. To investigate the carbon capacity of the green infrastructure of the Kharkiv city. Methods. Statistical, modeling methods, methods of measurement and comparison. Results. Six objects of single-breed tree stands of the green infrastructure of the city of Kharkiv were studied: linear protective plantings, green boulevards, where the main species is maple (Acer platanoides) and on the territory of the objects of the nature reserve fund - a regional landscape park and a forest reserve, where the main the species is pedunculated oak (Quercus robur). It was determined that about 60-80% of the total amount of carbon accumulates in the living phytomass of plants, litter deposits from 1 to 7% of carbon, and the rest accumulates in the soil. In living phytomass, the largest share of carbon is accumulated in the trunk of the plant, and the smallest amount is in the leaves. There is a direct dependence of the amount of deposited carbon on the area of green spaces, which increases along with the increase in the area of the facility. The total mass of deposited carbon on six researched objects, with a total area of 252.1 ha, is 48357.47 t, or 191.84 t/ha. Conclusions. A direct relationship between the area of green infrastructure objects and the amount of organic carbon deposited in them has been established. The most carbon accumulates in the living phytomass of plants, namely in the trunk of plants, and the least in the leaves of plants. Oak plantations store more carbon than maple plantations.

STRUKTUR DAN KOMPOSISI HUTAN BEKAS PERLADANGAN DI DESA HILIFALAGO KECAMATAN ONOLALU KABUPATEN NIAS SELATAN

Forests can experience a decline as a result of various activities carried out by humans, one of which is shifting cultivation. Decreasing forest quality reduces plant carbon absorption and storage, thereby affecting plant biological activity and impacting biodiversity. This study aims (1) to understand the structure and of ex-swidden forest in Hilifalago village, Onolalu district, South Nias Regency, (2) to understand the composition of ex-swidden forest. This study uses a descriptive quantitative approach. This study used the plot method with a size of 40 x 40 m, the sampling technique was purposive sampling. Based on the results of the study, it was found that the structure of ex-swidden forest in Hilifalago Village, Onolalu District consisted of upper and lower canopy layers, namely stratum A, B, C, and D and the most commonly found was the canopy layer in stratum C, while the composition of ex-swidden forest in the district Onolalu consists of 8 families and 10 species with 44 individuals. The highest important value index was found in Hevea brasiliensis Muell. Arg. (110.68%) and the family that was classified as the dominant family was the Euphorbiaceae

Comparative transcriptomic analysis provides insights into the molecular basis underlying pre-harvest sprouting in rice

BackgroundPre-harvest sprouting (PHS) is one of the most serious rice production constraints in areas where prolonged rainfall occurs during harvest. However, the molecular mechanisms of transcriptional regulation underlying PHS remain largely unknown.ResultsIn the current study, comparative transcriptome analyses were performed to characterize the similarities and differences between two rice varieties: PHS-sensitive Jiuxiangzhan (JXZ) and PHS-resistant Meixiangxinzhan (MXXZ). The physiological experimental results indicated that PHS causes a significant decrease in starch content and, in contrast, a significant increase in soluble sugar content and amylase activity. The extent of change in these physiological parameters in the sensitive variety JXZ was greater than that in the resistant variety MXXZ. A total of 9,602 DEGs were obtained from the transcriptome sequencing data, and 5,581 and 4,021 DEGs were identified in JXZ and MXXZ under high humidity conditions, respectively. The KEGG pathway enrichment analysis indicated that many DEGs under high humidity treatment were mainly linked to plant hormone signal transduction, carbon metabolism, starch and sucrose metabolism, and phenylpropanoid biosynthesis. Furthermore, the number of upregulated genes involved in these pathways was much higher in JXZ than in MXXZ, while the number of downregulated genes was higher in MXXZ than in JXZ. These results suggest that the physiological and biochemical processes of these pathways are more active in the PHS-sensitive JXZ than in the PHS-resistant MXXZ.ConclusionBased on these results, we inferred that PHS in rice results from altered phytohormone regulation, more active carbon metabolism and energy production, and enhanced phenylpropanoid biosynthesis. Our study provides a theoretical foundation for further elucidation of the complex regulatory mechanism of PHS in rice and the molecular breeding of PHS-resistant rice varieties.

Shifts in plant and soil C, N, and P concentrations and C:N:P stoichiometry associated with environmental factors in alpine marshy wetlands in West China

Ecological stoichiometry, a novel method for predicting nutrient cycling rates in different habitats, represents the demands of an organism for natural resources and links different levels of biogeochemical cycling. In this study, plant and soil carbon (C), nitrogen (N), and phosphorus (P) concentrations, their stoichiometric characteristics (C:N, C:P, and N:P ratios), and other physicochemical properties of soil were characterized using 243 soil and 81 plant samples collected from three habitats—hummocks, depressions, and meadows—in the marshy wetlands of West China. The results showed that leaf N and P concentrations, soil C, N, and P storage and concentrations, and C:N, C:P, and N:P ratios differed significantly among the three habitats (p < 0.05). Kobresia humilis leaves had the highest N and P content, followed by the leaves of Kobresia tibetica, while Carex mullis leaves had the lowest N and P content. The surface soil of depressions exhibited the highest C, N, C:P, and N:P ratios, hummocks exhibited the highest C:N ratio, whereas meadows exhibited the lowest C and N contents and C:N, and C:P ratios. A structural equation model (SEM) verified that leaf C, N, and P contents and C:P and N:P ratios were positively correlated with soil moisture (SM) and soil organic C contents, whereas the leaf C:N ratio was significantly and negatively correlated with SM content and bulk density. Our findings highlight the ability of alpine marshy wetlands to maintain and even increase the current C, N, and P storage capacities of the ecosystem under increased flooding in the study area.

The Effects of Elevated Tropospheric Ozone on Carbon Fixation and Stable Isotopic Signatures of Durum Wheat Cultivars with Different Biomass and Yield Stability.

Tropospheric ozone (O3) enrichment caused by human activities can reduce important crop yields with huge economic loss and affect the global carbon cycle and climate change in the coming decades. In this study, two Italian cultivars of durum wheat (Claudio and Mongibello) were exposed to O3 (80 ppb, 5 h day-1 for 70 consecutive days), with the aim to investigate the changes in yield and biomass, ecophysiological traits, and stable carbon and nitrogen isotope values in plants, and to compare the stable isotope responses under environmental stressors. Both cultivars showed a relative O3 tolerance in terms of photosynthetic performance, but in cultivar Mongibello, O3 was detrimental to the grain yield and plant biomass. The δ13C values in the leaves of plants identified that the impact of O3 on CO2 fixation by RuBisCO was dominant. The δ15N value showed significant differences between treatments in both cultivars at seven days from the beginning of the exposure, which could be considered an early indicator of ozone pollution. Under increasingly frequent extreme climates globally, the relationships among stable isotope data, ecophysiological traits, and agronomic parameters could help breed future cultivars.

Intensive grassland management disrupts below-ground multi-trophic resource transfer in response to drought

Modification of soil food webs by land management may alter the response of ecosystem processes to climate extremes, but empirical support is limited and the mechanisms involved remain unclear. Here we quantify how grassland management modifies the transfer of recent photosynthates and soil nitrogen through plants and soil food webs during a post-drought period in a controlled field experiment, using in situ 13C and 15N pulse-labelling in intensively and extensively managed fields. We show that intensive management decrease plant carbon (C) capture and its transfer through components of food webs and soil respiration compared to extensive management. We observe a legacy effect of drought on C transfer pathways mainly in intensively managed grasslands, by increasing plant C assimilation and 13C released as soil CO2 efflux but decreasing its transfer to roots, bacteria and Collembola. Our work provides insight into the interactive effects of grassland management and drought on C transfer pathways, and highlights that capture and rapid transfer of photosynthates through multi-trophic networks are key for maintaining grassland resistance to drought.

Responses of carbon dynamics to grazing exclusion in natural alpine grassland ecosystems on the QingZang Plateau.

In the context of "Carbon Emissions Peak" and "Carbon Neutrality", grazing exclusion (GE) has been applied widely to rehabilitate degraded grasslands and increase carbon sequestration. However, on the QingZang Plateau (QZP), the impacts of GE on the carbon dynamics of alpine grasslands are poorly understood, particularly at a regional scale. To fill this knowledge gap, we evaluated the responses of carbon sequestration to GE in different alpine grasslands across QZP by using meta-analysis. The effects of GE on ecosystem carbon fractions were dependent on GE duration, grassland types and climate factors. Specifically, our results indicated that GE had more obviously positive effects on carbon stock across the alpine meadow than the alpine steppe. However, when considering different GE duration, the longer duration of GE was more effective for increasing ecosystem carbon sequestration (R 2 = 0.52, P<0.0001) in the alpine steppe. Our results further demonstrated that annual mean precipitation (AMP) and temperature (AMT) began to dominate ecosystem carbon sequestration after three years of GE duration across the alpine meadow; and AMP was an important climate factor limiting ecosystem carbon sequestration (R 2 = 0.34, P<0.01) in the alpine steppe. In terms of plant carbon fraction, GE generated continuous positive effect (P<0.05) on aboveground biomass with the increased GE duration in the alpine meadow, while this positive effect disappeared after the 8th year of GE duration. And no positive effects were found on belowground biomass in the 11th year in alpine steppe. For soil organic carbon (SOC), there existed periodic fluctuations (increased and then decreased) on SOC in response to GE. For microbial biomass carbon, there were no obvious trends in response to GE duration. In general, we highlighted that the responses of different carbon fractions (plant-soil-microbe) to GE were non-uniform at spatial and temporal scales, thereby we should adopt different carbon management practices for sustainable development of different grasslands.

Study of spatialtemporal changes in Chinese forest eco-space and optimization strategies for enhancing carbon sequestration capacity through ecological spatial network theory

The conservation of forest ecosystems and the enhancement of carbon sequestration capacity play a crucial role in maintaining ecological balance and human development. However, with excessive deforestation, the flow of energy and information within the ecosystem has changed, which in turn has led to changes in the topological properties and carbon sequestration capacity of forest ecosystems. In order to better investigate the nature and carbon sequestration capacity of forest ecological space in mainland China during 2000–2018, we constructed a time-series Chinese forest ecological spatial network based on complex network theory and graph theory, combined with the modified minimal cumulative resistance model (MCR). By combining the net primary productivity (NPP) values obtained from the Boreal Ecosystem Productivity Simulator (BEPS) model of existing scholars, we further explored the relationship between topology and carbon sequestration capacity within forest ecosystems, and proposed strategies and suggestions for optimization. The results show that forest ecological sources and ecological corridors showed an increasing trend and resistance values decreased year by year during 2000–2018, especially in the western region, indicating that ecological restoration projects in western China have achieved certain effects. However, the stability of forest ecosystems has been decreasing year by year, and the forest carbon sequestration capacity in western China is also decreasing. Through correlation analysis, we found that carbon sequestration capacity showed highly significant positive correlation with closeness centrality, harmonic closeness centrality, clustering, and eigen centrality, and carbon sequestration capacity showed highly significant negative correlation with betweeness centrality. Through Principal Components Analysis (PCA), we suggest that consolidating small patches in the northeast, reducing the number of redundant ecological corridors, adding stepping stone patches to shorten the length of ecological corridors, and increasing ecological corridors in non-northeast areas are conducive to enhancing plant carbon sequestration capacity. This study provides theoretical support and ecological engineering recommendations for China to achieve its strategic goals of carbon neutrality and carbon peaking.

Species Diversity, Aboveground Biomass, and Carbon Storage of Watershed Forest in Phayao Province, Thailand

Restoration of watershed forest ecosystems can perform different disturbance regimes over remnant forests, which can ultimately affect plant diversity, soil formation, and carbon storage. To address an issue, this study assessed tree species diversity, aboveground biomass (AGB), and aboveground carbon (AGC) storage of the watershed forest in Phayao Province, Thailand. Data collection was conducted in 18 plots along nine watersheds along the topographic gradients. Tree height and diameter at breast height (DBH) were collected. AGB of vegetation was estimated by using the allometric equation. Likewise, AGC storage was evaluated from half of AGB. A total of 133 species belonging to 105 genera and 39 families were recorded from the watershed forests (1.8 ha). Mixed deciduous forest (MDF) and dry evergreen forest (DEF) exhibited high density and high diversity index, respectively. The highest value of total AGC storage was found in the MDF with 91.2 ton C/ha, following by DEF (78.3 ton C/ha) and dry dipterocarp forest (DDF) (60.5 ton C/ha). Detrended correspondence analysis (DCA) revealed that the occurrences of Albizia saman, Hopea odorata, Lagerstroemia calyculata, and Acrocarpus fraxinifolius related to AGB, AGC, slope, and tree canopy in the DEF. Intensity of slope influenced tree species occurrence in the watershed forest of Phayao.

Precipitation increase counteracts warming effects on plant and soil C:N:P stoichiometry in an alpine meadow

Temperature and precipitation are expected to increase in the forthcoming decades in the northeastern Qinghai-Tibetan Plateau, with uncertain effects of their interaction on plant and soil carbon:nitrogen:phosphorus (C:N:P) stoichiometry in alpine ecosystems. A two-year field experiment was conducted to examine the effects of warming, precipitation increase, and their interaction on soil and plant C:N:P stoichiometry at functional groups and community level in an alpine meadow. Warming increased aboveground biomass of legumes and N:P ratios of grasses and community, but did not affect soil C:N:P stoichiometry. The piecewise structural equation model (SEM) indicated that the positive effect of warming on community N:P ratio was mainly resulted from its positive influence on the aboveground biomass of functional groups. Precipitation increase reduced C:N ratios of soil, grasses, and community, indicating the alleviation in soil N-limitation and the reduction in N use efficiency of plant. SEM also demonstrated the decisive role of grasses C:N:P stoichiometry on the response of community C:N:P stoichiometry to precipitation increase. The interaction of warming and precipitation increase did not alter plant community and soil, N:P and C:P ratios, which was resulting from their antagonistic effects. The stable soil and plant community C:N:P stoichiometry raised important implications that the effect of warming was offset by precipitation increase. Our study highlights the importance of considering the interaction between warming and precipitation increase when predicting the impacts of climate change on biogeochemical cycles in alpine meadow ecosystems.

Can seasonal fire management reduce the risk of carbon loss from wildfires in a protected Guinea savanna?

AbstractFire is fundamental to the functioning of tropical savannas and routinely used as a management tool. Shifting prescribed burning from later to earlier in the growing season has the potential to reduce greenhouse gas emissions. However, large uncertainties surround the impact of seasonal burning on longer term plant and soil carbon sequestration. In this study, we quantify ecosystem carbon storage across burn seasons and histories in a wet‐to‐mesic Guinea tropical savanna in Mole National Park, Ghana. Aboveground (plant and litter) and belowground (soil plus roots) carbon storage was quantified across four burning seasons and histories: recent (&lt;3 years) early‐season burns, recent late‐season burns, old (&gt;4 years) late‐season burns, and long‐unburned (&gt;15 years) sites. We found that recent late‐season burns significantly lowered belowground carbon storage to a depth of 17 cm compared with all other burn seasons and histories. Belowground carbon was 1.2 kg C m−2, or 27% lower, for recent late‐season burns compared with prescribed early‐season burns. However, in older late‐season burns sites, belowground carbon “recovered” after 4–13 burn years to comparable storage as long‐unburned and early‐season burn sites. For most aboveground carbon pools, there was no significant difference in carbon storage across burn seasons and histories, except higher aboveground tree carbon in long‐unburned sites. We suggest that observed changes in belowground carbon are likely due to the turnover and production of root carbon. Prescribed early‐season burning is promoted to reduce greenhouse gas emissions and our findings affirm that early‐season burning has limited impact on plant and soil carbon stocks compared with long‐unburned sites. While early‐season burning regimes will have some patches that become late‐season wildfires, our results suggest on balance early‐season burning regimes are a low‐risk land management practice in reducing plant and soil carbon storage losses and sustaining a patch‐mosaicked landscape with multiple other ecosystem service benefits for savannas.

Anisohydric characteristics of a rice genotype 'ARC 11094' contribute to increased photosynthetic carbon fixation in response to high light.

Photosynthetic induction, which is the response of the CO2 assimilation rate to a stepwise increase in light intensity, potentially affects plant carbon gain and crop productivity in field environments. Although natural variations in photosynthetic induction are determined by CO2 supply and its fixation, detailed factors, especially CO2 supply, are unclear. This study investigated photosynthesis at steady and non-steady states in three rice (Oryza sativa L.) genotypes: ARC 11094, Takanari and Koshihikari. Stomatal traits and water relations in the plants were evaluated to characterise CO2 supply. Photosynthetic induction in ARC 11094 and Takanari was superior to that in Koshihikari owing to an efficient CO2 supply. The CO2 supply in Takanari is attributed to its high stomatal density, small guard cell length and extensive root mass, whereas that in ARC 11094 is attributed to its high stomatal conductance per stoma and stomatal opening in leaves with insufficient water (i.e., anisohydric stomatal behaviour). Our results suggest that there are various mechanisms for realising an efficient CO2 supply during the induction response. These characteristics can be useful for improving photosynthetic induction and, thus, crop productivity in field environments in future breeding programmes.

Carbon sequestration potential of rubber plantation in East Kalimantan

Forestry and Other Land Use (FOLU) sector has significant contributions to greenhouse gas emissions in Indonesia. Besides reducing deforestation and forest degradation, plantation development also plays an important role in climate change mitigation, particularly for carbon stock enhancement. This study aims to estimate the carbon sequestration potential of rubber plantations in East Kalimantan. Rubber plantation carbon stock was measured by establishing 24 sample plots with the size of 20x20 m in two locations, Kutai Timur and Penajam Paser Utara regencies. Above-ground biomass of rubber was estimated using the allometric equation AGB = 0.144 x D2.40. While the carbon stock was further calculated using the lifetime average approach. The result shows that the carbon stock of rubber plantations in East Kalimantan is 75.71 tons C ha-1. With a total plantation area of 123,460 ha, the potential carbon sequestration of rubber plantations in East Kalimantan is about 9.05 Mt, equivalent to 33.19 Mt CO2e. Given the high carbon sequestration potential, rubber plantation development needs to be considered as an important strategy to achieve FOLU net sink by 2030. This is part of the enhancement of carbon stock through land rehabilitation, which is prioritized to be implemented in degraded lands to avoid deforestation and forest degradation in forested areas.

High aerosol loading decreases the transpiration of poplars both in the day- and night-time

Aerosols alter plant photosynthesis and ecosystem carbon uptake through radiative effects. These effects inevitably change plant transpiration and ecosystem water use as CO2 and water exchange couple through leaf stomatal conductance. However, because of lacking field observations, we know poorly about how elevated aerosols could affect plant transpiration, which greatly hinders our confidence in projecting aerosol's climate impacts. In this study, taking the advantage of aerosol loading in northern China fluctuated periodically over a wide range, we conducted five year-site observations of the stem sap flow of poplar saplings (Populus euramericana Neva.), and simultaneously monitored environmental factors such as PM2.5 concentration, total and diffuse radiation, air temperature, humidity, and soil water content. These observations enabled us to comprehensively explore how aerosols affect the daily dynamics of plant canopy transpiration in the field. We found that high aerosol loading significantly decreased the sap flow density of poplars both in the day- and night-time, indicating that aerosols decreased canopy transpiration. Furthermore, during the day-time, a reduction in total solar radiation and moisture demand (vapor pressure deficit, VPD) dominated the decrease of sap flow density, but an increase in diffuse radiation had an insignificant impact. In the night-time, VPD significantly decreased under high aerosol loading conditions, thereby reducing nocturnal sap flow density. Our in-situ observations revealed that different from the positive response of canopy photosynthesis associated with the diffuse fertilization effect, aerosols inhibit canopy transpiration mainly because of the declined VPD. Our findings highlighted that plant carbon and water fluxes are governed by different meteorological factors under elevated aerosol.

Quantification of excess Carbon-14 specific activity in terrestrial biota in the off-site locations of the PHWR nuclear power plant at Kaiga, India

This is the first detailed study on 14C activity in the environment surrounding a nuclear facility in India. Samples of food matrices and wild plants from the off-site locations of the PHWR nuclear power plant (NPP) at Kaiga were analysed by liquid scintillation spectrometry, results were validated by accelerator mass spectrometry, and an extensive database (N = 142) was established. The stable isotope ratio of carbon (δ13C) in terrestrial plants varied from −33.5 to −23.3 ‰. The maximum excess 14C activity recorded in terrestrial biota was 44 Bq kg−1C (19 pMC). About 75 % of the samples exhibited specific activity in the range 228–249 Bq kg−1C (101–110 pMC). Statistical tests on the 14C specific activity dataset for 2.3–5, 5–10, and 10–20 km radial zones confirmed that the impact of the operation of the NPP on the environment beyond 5 km is minimal. The study suggests that the 14C activity released through gaseous effluents from Kaiga NPP is transported to greater distances along the axis of the valley than that predicted by the Gaussian plume model and those reported for other NPP sites worldwide. This is due to the unique topography of the Kaiga valley in which wind flow channelling, strong winds in the valley mouth, and calm wind within the valley due to the blocking effect by hills for the south-westerly wind regime play dominant roles in the transport of gaseous effluents. The 14C specific activity values at upwind monitoring stations located at >5 km distance from the NPP during the south-westerly wind regime were higher than those observed during the north-easterly wind regime when the same monitoring stations were located on the downwind side. The ingestion dose to the population in the 2.3–5 km radius zone, attributable to the release of 14C from the NPP, was 0.75 μSv y−1. This is a negligibly small fraction of the ICRP recommended dose limit of 1000 μSv y−1 for the public from other than natural sources. The dose due to the natural 14C activity in the Kaiga region was 12 µSv y-1, corresponding to the ambient natural activity of 230 Bq kg-1 C.

Lowland tundra plant stoichiometry is somewhat resilient decades following fire despite substantial and sustained shifts in community structure

ABSTRACT The Arctic is experiencing the greatest increase in average surface temperature globally, which is projected to amplify wildfire frequency and severity. Wildfire alters the biogeochemical characteristics of arctic ecosystems. However, the extent of these changes over time—particularly with regard to plant stoichiometries relative to community structure—is not well documented. Four years after the Yukon-Kuskokwim Delta, Alaska, experienced its largest fire season, aboveground plant and lichen biomass was harvested across a gradient of burn history: unburned (“reference”), 2015 burn (“recent burn”), and 1972 burn (“historic burn”) to assess the resilience of tundra plant communities to fire disturbance. Fire reduced aboveground biomass in the recent burn; early recovery was characterized by evergreen shrub and graminoid dominance. In the historic burn, aboveground biomass approached reference conditions despite a sustained reduction of lichen biomass. Although total plant and lichen carbon (C) and nitrogen (N) were reduced immediately following fire, N stocks recovered to a greater degree—reducing community-level C:N. Notably, at the species level, N enrichment was observed only in the recent burn. Yet, community restructuring persisted for decades following fire, reflecting a sustained reduction in N-poor lichens relative to more N-rich vascular plant species.

Species-Specific and Altitude-Induced Variation in Karst Plants’ Use of Soil Dissolved Inorganic Carbon

Root-derived carbon sources supporting photosynthesis have been demonstrated to contribute to plant carbon gain in many laboratory experiments. However, it remains largely unknown whether and to what extent soil dissolved inorganic carbon (DIC) influences leaf photosynthesis in karst habitats characterized by alkaline soils with low water content. We explored this relationship by measuring the concentrations and carbon isotope signals (δ13C) of soil DIC, as well as the δ13C of water-soluble organic matter (δWSOM) in leaves of nine woody species across an altitudinal gradient in karst habitats. The δWSOM varied among species by 7.23‰ and deviated from the δ13C of photosynthates solely assimilated from atmospheric CO2 (δA) by 0.44–5.26‰, with a mean value of 2.20‰. This systematical discrepancy (δA − δWSOM) could only be explained by the contribution of soil DIC to leaf total photosynthesis (fDIC_soil). The average values of fDIC_soil considerably varied among the nine species, ranging from 2.48% to 9.99%, and were comparable with or slightly lower than those of previous laboratory experiments. Furthermore, the fDIC_soil of two species significantly increased with altitude, whereas another species exhibited an opposite pattern, suggesting a highly spatial heterogeneity of DIC utilization. The present study improved our understanding of how plants adapt to the alkaline–drought soil conditions of karst habitats and thus acquire additional carbon for growth.

Litter accumulation retards the positive effects of nitrogen inputs on plant carbon sequestration in grassland

Litter accumulation retards the positive effects of nitrogen inputs on plant carbon sequestration in grassland

Exogenous sucrose promotes the growth of apple rootstocks under high nitrate supply by modulating carbon and nitrogen metabolism

Excessive nitrogen (N) supply often leads to an imbalance of carbon (C) and N metabolism and inhibits plant growth. Sucrose, an important source and signaling substance of C in plants, is closely linked to N metabolism. However, it is not clear whether exogenous sucrose can mitigate the inhibitory effect of high N on plant growth by regulating C and N metabolism. In this study, we investigated the effects of exogenous sucrose on the growth, N metabolism, and C assimilation in the apple rootstock M26 seedlings under normal (5 mM NO3－, NN) and high (30 mM NO3－, HN) NO3－ concentrations. Our results showed that high NO3－ supply reduced plant growth, photosynthesis, and chlorophyll fluorescence, but spraying with 1% sucrose (HN + 1% Sucrose) significantly alleviated this inhibition. Application of 1% sucrose increased sucrose and sorbitol contents as well as sucrose-phosphate synthase and sucrose synthase activities in the plants under HN treatment and promoted the distribution of 13C photoassimilation products to the root. In addition, spraying with 1% sucrose alleviated the inhibition of N metabolizing enzyme activities by high NO3－ supply, reduced NO3－ accumulation and N content, increased free amino acid content, and promoted 15N distribution to the aboveground parts. However, spraying with 1% sucrose under the NN treatment negatively affected plant photosynthesis and carbon assimilation. In conclusion, exogenous sucrose increased the C level in plants in the presence of excess N, promoted the balance of C and N metabolism, and alleviated the inhibitory effect of high N on the apple plant growth.