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1.
Elevated CO 2 may increase nutrient availability in the rhizosphere by stimulating N release from recalcitrant soil organic matter (SOM) pools through enhanced rhizodeposition. We aimed to elucidate how CO 2-induced increases in rhizodeposition affect N release from recalcitrant SOM, and how wild versus cultivated genotypes of wheat mediated differential responses in soil N cycling under elevated CO 2. To quantify root-derived soil carbon (C) input and release of N from stable SOM pools, plants were grown for 1 month in microcosms, exposed to 13C labeling at ambient (392 μmol mol −1) and elevated (792 μmol mol −1) CO 2 concentrations, in soil containing 15N predominantly incorporated into recalcitrant SOM pools. Decomposition of stable soil C increased by 43%, root-derived soil C increased by 59%, and microbial- 13C was enhanced by 50% under elevated compared to ambient CO 2. Concurrently, plant 15N uptake increased (+7%) under elevated CO 2 while 15N contents in the microbial biomass and mineral N pool decreased. Wild genotypes allocated more C to their roots, while cultivated genotypes allocated more C to their shoots under ambient and elevated CO 2. This led to increased stable C decomposition, but not to increased N acquisition for the wild genotypes. Data suggest that increased rhizodeposition under elevated CO 2 can stimulate mineralization of N from recalcitrant SOM pools and that contrasting C allocation patterns cannot fully explain plant mediated differential responses in soil N cycling to elevated CO 2. 相似文献
2.
The effects of enriched CO 2 atmosphere on partitioning of recently assimilated carbon were investigated in a plant-soil-microorganism system in which Lolium perenne seedlings were planted into cores inserted into the resident soil within a sward that had been treated with elevated CO 2 for 9 consecutive years, under two N fertilisation levels (Swiss FACE experiment). The planted cores were excavated from the ambient (35 Pa pCO 2) and enriched (60 Pa pCO 2) rings at two dates, in spring and autumn, during the growing season. The cores were brought back to the laboratory for 14C labelling of shoots in order to trace the transfer of recently assimilated C both within the plant and to the soil and microbial biomass. At the spring sampling, high N supply stimulated shoot and total dry matter production. Consistently, high N enhanced the allocation of recently fixed C to shoots, and reduced it to belowground compartments. Elevated CO 2 had no consequences for DM or the pattern of C allocation. At the autumn sampling, at high N plot, yield of L. perenne was stimulated by elevated CO 2. Consistently, 14C was preferentially allocated aboveground and, consequently belowground recent C allocation was depressed and rhizodeposition reduced. At both experimental periods, total soil C content was similar in all treatments, providing no evidence for soil carbon sequestration in the Swiss Free Air CO 2 Enrichment experiment (FACE) after 9 years of enrichment. Recently assimilated C and soil C were mineralised faster in soils from enriched rings, suggesting a CO 2-induced shift in the microbial biomass characteristics (structure, diversity, activity) and/or in the quality of the root-released organic compounds. 相似文献
3.
Although extreme climatic events such as drought have important consequences for belowground carbon (C) cycling, their impact on the plant-soil system of mixed plant communities is poorly understood. Our objective was to study the effect of drought on C allocation and rhizosphere-mediated CO 2 fluxes under three plant species: Lolium perenne, Festuca arundinacea and Medicago sativa grown in monocultures or mixture. The conceptual approach included 14CO 2 pulse labeling of plants grown under drought and optimum water conditions in order to be able to follow above- and belowground C allocation. After 14C pulse labeling, we traced 14C allocation to shoots and roots, soil and rhizospheric CO 2, dissolved organic carbon (DOC) and microbial biomass.Drought and plant community composition significantly affected assimilate allocation in the plant-soil system. Drought conditions changed the source sink relationship of monocultures, which transferred a relatively larger portion of assimilates to their roots compared to water sufficient plants. In contrast, plant mixture showed an increase in 14C allocation to shoots when exposed to drought.Under drought stress, root respiration was reduced for all monocultures except under the legume species. Microbial respiration remained similar in all cases showing that microbial activity was less affected by drought than root activity. This may be explained by strongly increased assimilate allocation to easily available exudates or rhizodeposits under drought. In conclusion, plant community composition may modify the impact of climatic changes on carbon allocation and belowground carbon fluxes. The presence of legume species attenuates drought effects on rhizosphere processes. 相似文献
4.
Several recent studies have indicated that an enriched atmosphere of carbon dioxide (CO 2) could exacerbate the intensity of plant invasions within natural ecosystems, but little is known of how rising CO 2 impacts the belowground characteristics of these invaded systems. In this study, we examined the effects of elevated CO 2 and nitrogen (N) inputs on plant and soil microbial community characteristics of plant communities invaded by reed canary grass, Phalaris arundinacea L. We grew the invasive grass under two levels of invasion: the invader was either dominant (high invasion) at >90% plant cover or sub-dominant (low invasion) at <50% plant cover. Experimental wetland communities were grown for four months in greenhouses that received either 600 or 365 μl l −1 (ambient) CO 2. Within each of three replicate rooms per CO 2 treatment, the plant communities were grown under high (30 mg l −1) or low (5 mg l −1) N. In contrast to what is often predicted under N limitation, we found that elevated CO 2 increased native graminoid biomass at low N, but not at high N. The aboveground biomass of reed canary grass did not respond to elevated CO 2, despite it being a fast-growing C3 species. Although elevated CO 2 had no impact on the plant biomass of heavily invaded communities, the relative abundance of several soil microbial indicators increased. In contrast, the moderately invaded plant communities displayed increased total root biomass under elevated CO 2, while little impact occurred on the relative abundance of soil microbial indicators. Principal components analysis indicated that overall soil microbial community structure was distinct by CO 2 level for the varying N and invasion treatments. This study demonstrates that even when elevated CO 2 does not have visible effects on aboveground plant biomass, it can have large impacts belowground. 相似文献
5.
Global climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO2.Thus,climate change regarding elevated ambient CO2 and drought may consequently affect the growth of crops.In this study,plant physiology,soil carbon,and soil enzyme activities were measured to investigate the impacts of elevated CO2 and drought stress on a Stagnic Anthrosol planted with soybean (Glycine max).Treatments of two CO2 levels,three soil moisture levels,and two soil cover types were established.The results indicated that elevated CO2 and drought stress significantly affected plant physiology.The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO2 conditions.Elevated CO2 resulted in a longer retention time of dissolved organic carbon (DOC) in soil,probably by improving the soil water effectiveness for organic decomposition and mineralization.Drought stress significantly decreased C:N ratio and microbial biomass carbon (MBC),but the interactive effects of drought stress and CO2 on them were not significant.Elevated CO2 induced an increase in invertase and catalase activities through stimulated plant root exudation.These results suggested that drought stress had significant negative impacts on plant physiology,soil carbon,and soil enzyme activities,whereas elevated CO2 and plant physiological feedbacks indirectly ameliorated these impacts. 相似文献
6.
The impact of rising atmospheric carbon dioxide (CO 2) may be mitigated, in part, by enhanced rates of net primary production and greater C storage in plant biomass and soil organic matter (SOM). However, C sequestration in forest soils may be offset by other environmental changes such as increasing tropospheric ozone (O 3) or vary based on species-specific growth responses to elevated CO 2. To understand how projected increases in atmospheric CO 2 and O 3 alter SOM formation, we used physical fractionation to characterize soil C and N at the Rhinelander Free Air CO 2-O 3 Enrichment (FACE) experiment. Tracer amounts of 15NH 4+ were applied to the forest floor of Populus tremuloides, P. tremuloides-Betula papyrifera and P. tremuloides-Acer saccharum communities exposed to factorial CO 2 and O 3 treatments. The 15N tracer and strongly depleted 13C-CO 2 were traced into SOM fractions over four years. Over time, C and N increased in coarse particulate organic matter (cPOM) and decreased in mineral-associated organic matter (MAOM) under elevated CO 2 relative to ambient CO 2. As main effects, neither CO 2 nor O 3 significantly altered 15N recovery in SOM. Elevated CO 2 significantly increased new C in all SOM fractions, and significantly decreased old C in fine POM (fPOM) and MAOM over the duration of our study. Overall, our observations indicate that elevated CO 2 has altered SOM cycling at this site to favor C and N accumulation in less stable pools, with more rapid turnover. Elevated O 3 had the opposite effect, significantly reducing cPOM N by 15% and significantly increasing the C:N ratio by 7%. Our results demonstrate that CO 2 can enhance SOM turnover, potentially limiting long-term C sequestration in terrestrial ecosystems; plant community composition is an important determinant of the magnitude of this response. 相似文献
7.
Elevated CO 2 and defoliation effects on nitrogen (N) cycling in rangeland soils remain poorly understood. Here we tested whether effects of elevated CO 2 (720 μl L −1) and defoliation (clipping to 2.5 cm height) on N cycling depended on soil N availability (addition of 1 vs. 11 g N m −2) in intact mesocosms extracted from a semiarid grassland. Mesocosms were kept inside growth chambers for one growing season, and the experiment was repeated the next year. We added 15N (1 g m −2) to all mesocosms at the start of the growing season. We measured total N and 15N in plant, soil inorganic, microbial and soil organic pools at different times of the growing season. We combined the plant, soil inorganic, and microbial N pools into one pool (PIM-N pool) to separate biotic + inorganic from abiotic N residing in soil organic matter (SOM). With the 15N measurements we were then able to calculate transfer rates of N from the active PIM-N pool into SOM (soil N immobilization) and vice versa (soil N mobilization) throughout the growing season. We observed significant interactive effects of elevated CO 2 with N addition and defoliation with N addition on soil N mobilization and immobilization. However, no interactive effects were observed for net transfer rates. Net N transfer from the PIM-N pool into SOM increased under elevated CO 2, but was unaffected by defoliation. Elevated CO 2 and defoliation effects on the net transfer of N into SOM may not depend on soil N availability in semiarid grasslands, but may depend on the balance of root litter production affecting soil N immobilization and root exudation affecting soil N mobilization. We observed no interactive effects of elevated CO 2 with defoliation. We conclude that elevated CO 2, but not defoliation, may limit plant productivity in the long-term through increased soil N immobilization. 相似文献
8.
The response of terrestrial ecosystems to elevated atmospheric CO 2 is related to the availability of other nutrients and in particular to nitrogen (N). Here we present results on soil N transformation dynamics from a N-limited temperate grassland that had been under Free Air CO 2 Enrichment (FACE) for six years. A 15N labelling laboratory study (i.e. in absence of plant N uptake) was carried out to identify the effect of elevated CO 2 on gross soil N transformations. The simultaneous gross N transformation rates in the soil were analyzed with a 15N tracing model which considered mineralization of two soil organic matter (SOM) pools, included nitrification from NH 4+ and from organic-N to NO 3− and analysed the rate of dissimilatory NO 3− reduction to NH 4+ (DNRA). Results indicate that the mineralization of labile organic-N became more important under elevated CO 2. At the same time the gross rate of NH 4+ immobilization increased by 20%, while NH 4+ oxidation to NO 3− was reduced by 25% under elevated CO 2. The NO 3− dynamics under elevated CO 2 were characterized by a 52% increase in NO 3− immobilization and a 141% increase in the DNRA rate, while NO 3− production via heterotrophic nitrification was reduced to almost zero. The increased turnover of the NH 4+ pool, combined with the increased DNRA rate provided an indication that the available N in the grassland soil may gradually shift towards NH 4+ under elevated CO 2. The advantage of such a shift is that NH 4+ is less prone to N losses, which may increase the N retention and N use efficiency in the grassland ecosystem under elevated CO 2. 相似文献
9.
The aim of the present study was to test and improve the reliability of the 15N cotton-wick method for measuring soil N derived from plant rhizodeposition, a critical value for assessing belowground nitrogen input in field-grown legumes. The effects of the concentration of the 15N labelling solution and the feeding frequency on assessment of nitrogen rhizodeposition were studied in two greenhouse experiments using the field pea ( Pisum sativum L.). Neither the method nor the feeding frequency altered plant biomass and N partitioning, and the method appeared well adapted for assessing the belowground contribution of field-grown legumes to the soil N pool. However, nitrogen rhizodeposition assessment was strongly influenced by the feeding frequency and the concentration of labelling solution. At pod-filling and maturity, despite similar root 15N enrichment, the fraction of plants' belowground nitrogen allocated to rhizodeposition in both Frisson pea and the non-nodulating isoline P2 was 20 to more than 50% higher when plants were labelled continuously than when they were labelled using fortnightly pulses. Our results suggest that when 15N root enrichment was high, nitrogen rhizodeposition was overestimated only for plants that were 15N-fed by fortnightly pulses, and not in plants 15N-fed continuously. This phenomenon was especially observed for plants that rely on symbiotic N 2 fixation for N acquisition, and it may be linked to the concentration of the labelling solution. In conclusion, the assessment of nitrogen rhizodeposition was more reliable when plants were labelled continuously with a dilute solution of 15N urea. 相似文献
10.
A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO 2 may be an important factor limiting nitrification. Soil samples amended with wheat straw (0%, 0.1% and 0.2%) and ( 15NH 4) 2SO 4 (200 mg N kg –1 soil, 2.213 atom% 15N excess) were incubated at 30±2°C for 20 days with or without the arrangement for trapping CO 2 resulting from the decomposition of organic matter. Nitrification (as determined by the disappearance of NH 4+ and accumulation of NO 3–) was found to be highly sensitive to available CO 2 decreasing significantly when CO 2 was trapped in alkali solution and increasing substantially when the amount of CO 2 in the soil atmosphere increased due to the decomposition of added wheat straw. The co-efficient of correlation between NH 4+-N and NO 3–-N content of soil was highly significant ( r =0.99). During incubation, 0.1–78% of the applied NH 4+ was recovered as NO 3– at different incubation intervals. Amendment of soil with wheat straw significantly increased NH 4+ immobilization. From 1.6% to 4.5% of the applied N was unaccounted for and was due to N losses. The results of the study suggest that decreased availability of CO 2 will limit the process of nitrification during soil incubations involving trapping of CO 2 (in closed vessels) or its removal from the stream of air passing over the incubated soil (in open-ended systems). 相似文献
11.
Soil respiration represents the integrated response of plant roots and soil organisms to environmental conditions and the availability of C in the soil. A multi-year study was conducted in outdoor sun-lit controlled-environment chambers containing a reconstructed ponderosa pine/soil-litter system. The study used a 2×2 factorial design with two levels of CO 2 and two levels of O 3 and three replicates of each treatment. The objectives of our study were to assess the effects of long-term exposure to elevated CO 2 and O 3, singly and in combination, on soil respiration, fine root growth and soil organisms. Fine root growth and soil organisms were included in the study as indicators of the autotrophic and heterotrophic components of soil respiration. The study evaluated three hypotheses: (1) elevated CO 2 will increase C assimilation and allocation belowground increasing soil respiration; (2) elevated O 3 will decrease C assimilation and allocation belowground decreasing soil respiration and (3) as elevated CO 2 and O 3 have opposing effects on C assimilation and allocation, elevated CO 2 will eliminate or reduce the negative effects of elevated O 3 on soil respiration. A mixed-model covariance analysis was used to remove the influences of soil temperature, soil moisture and days from planting when testing for the effects of CO 2 and O 3 on soil respiration. The covariance analysis showed that elevated CO 2 significantly reduced the soil respiration while elevated O 3 had no significant effect. Despite the lack of a direct CO 2 stimulation of soil respiration, there were significant interactions between CO 2 and soil temperature, soil moisture and days from planting indicating that elevated CO 2 altered soil respiration indirectly. In elevated CO 2, soil respiration was more sensitive to soil temperature changes and less sensitive to soil moisture changes than in ambient CO 2. Soil respiration increased more with days from planting in elevated than in ambient CO 2. Elevated CO 2 had no effect on fine root biomass but increased abundance of culturable bacteria and fungi suggesting that these increases were associated with increased C allocation belowground. Elevated CO 2 had no significant effect on microarthropod and nematode abundance. Elevated O 3 had no significant effects on any parameter except it reduced the sensitivity of soil respiration to changes in temperature. 相似文献
12.
Emissions of N 2O and N 2 were measured from Lolium perenne L. swards under ambient (36 Pa) and elevated (60 Pa) atmospheric CO 2 at the Swiss free air carbon dioxide enrichment experiment following application of 11.2 g N m −2 as 15NH 415NO 3 or 14NH 415NO 3 (1 at.% excess 15N). Total denitrification (N 2O+N 2) was increased under elevated pCO 2 with emissions of 6.2 and 19.5 mg 15N m −2 measured over 22 d from ambient and elevated pCO 2 swards, respectively, supporting the hypothesis that increased belowground C allocation under elevated pCO 2 provides the energy for denitrification. Nitrification was the predominant N 2O producing process under ambient pCO 2 whereas denitrification was predominant under elevated pCO 2. The N 2-to-N 2O ratio was often higher under elevated pCO 2 suggesting that previous estimates of gaseous N losses based only on N 2O emissions have greatly underestimated the loss of N by denitrification. 相似文献
13.
Plant response to increasing atmospheric CO 2 partial pressure ( pCO 2) depends on several factors, one of which is mineral nitrogen availability facilitated by the mineralisation of organic N. Gross rates of N mineralisation were examined in grassland soils exposed to ambient (36 Pa) and elevated (60 Pa) atmospheric pCO 2 for 7 years in the Swiss Free Air Carbon dioxide Enrichment experiment. It was hypothesized that increased below-ground translocation of photoassimilates at elevated pCO 2 would lead to an increase in immobilisation of N due to an excess supply of energy to the roots and rhizosphere. Intact soil cores were sampled from Lolium perenne and Trifolium repens swards in May and September, 2000. The rates of gross N mineralisation ( m) and NH 4+ consumption ( c) were determined using 15N isotopic dilution during a 51-h period of incubation. The rates of N immobilisation were estimated either as the difference between m and the net N mineralisation rate or as the amount of 15N released from the microbial biomass after chloroform fumigation. Soil samples from both swards showed that the rates of gross N mineralisation and NH 4+ consumption did not change significantly under elevated pCO 2. The lack of a significant effect of elevated pCO 2 on organic N turnover was consistent with the similar size of the microbial biomass and similar immobilisation of applied 15N in the microbial N pool under ambient and elevated pCO 2. Rates of m and c, and microbial 15N did not differ significantly between the two sward types although a weak ( p<0.1) pCO 2 by sward interaction occurred. A significantly larger amount of NO 3− was recovered at the end of the incubation in soil taken from T. repens swards compared to that from L. perenne swards. Eleven percent of the added 15N were recovered in the roots in the cores sampled under L. perenne, while only 5% were recovered in roots of T. repens. These results demonstrate that roots remained a considerable sink despite the shoots being cut at ground level prior to incubation and suggest that the calculation of N immobilisation from gross and net rates of mineralisation in soils with a high root biomass does not reflect the actual immobilisation of N in the microbial biomass. The results of this study did not support the initial hypothesis and indicate that below-ground turnover of N, as well as N availability, measured in short-term experiments are not strongly affected by long-term exposure to elevated pCO 2. It is suggested that differences in plant N demand, rather than major changes in soil N mineralisation/immobilisation, are the long-term driving factors for N dynamics in these grassland systems. 相似文献
14.
PurposeElevated CO2 and nitrogen (N) addition both affect soil microbial communities, which significantly influence soil processes and plant growth. Here, we evaluated the combined effects of elevated CO2 and N addition on the soil–microbe–plant system of the Chinese Loess Plateau. Materials and methodsA pot cultivation experiment with two CO2 treatment levels (400 and 800 μmol mol?1) and three N addition levels (0, 2.5, and 5 g N m?2 year?1) was conducted in climate-controlled chambers to evaluate the effects of elevated CO2 and N addition on microbial community structure in the rhizosphere of Bothriochloa ischaemum using phospholipid fatty acid (PLFA) profiles and associated soil and plant properties. Structural equation modeling (SEM) was used to identify the direct and indirect effects of the experimental treatments on the structure of microbial communities. Results and discussionElevated CO2 and N addition both increased total and fungal PLFAs. N addition alone increased bacterial, Gram-positive, and Gram-negative PLFAs. However, elevated CO2 interacting with N addition had no significant effects on the microbial community. The SEM indicated that N addition directly affected the soil microbial community structure. Elevated CO2 and N addition both indirectly affected the microbial communities by affecting plant and soil variables. N addition exerted a stronger total effect than elevated CO2. ConclusionsThe results highlighted the importance of comprehensively studying soil–microbe–plant systems to deeply reveal how characteristics of terrestrial ecosystems may respond under global change. 相似文献
15.
A greenhouse rhizobox experiment was carried out to investigate the fate and turnover of 13C‐ and 15N‐labeled rhizodeposits within a rhizosphere gradient from 0–8 mm distance to the roots of wheat. Rhizosphere soil layers from 0–1, 1–2, 2–3, 3–4, 4–6, and 6–8 mm distance to separated roots were investigated in an incubation experiment (42 d, 15°C) for changes in total C and N and that derived from rhizodeposition in total soil, in soil microbial biomass, and in the 0.05 M K 2SO 4–extractable soil fraction. CO 2‐C respiration in total and that derived from rhizodeposition were measured from the incubated rhizosphere soil samples. Rhizodeposition C was detected in rhizosphere soil up to 4–6 mm distance from the separated roots. Rhizodeposition N was only detected in the rhizosphere soils up to 3–4 mm distance from the roots. Microbial biomass C and N was increased with increasing proximity to the separated roots. Beside 13C and 15N derived from rhizodeposits, unlabeled soil C and N (native SOM) were incorporated into the growing microbial biomass towards the roots, indicating a distinct acceleration of soil organic matter (SOM) decomposition and N immobilization into the growing microbial biomass, even under the competition of plant growth. During the soil incubation, microbial biomass C and N decreased in all samples. Any decrease in microbial biomass C and N in the incubated rhizosphere soil layers is attributed mainly to a decrease of unlabeled (native) C and N, whereas the main portion of previously incorporated rhizodeposition C and N during the plant growth period remained immobilized in the microbial biomass during the incubation. Mineralization of native SOM C and N was enhanced within the entire investigated rhizosphere gradient. The results indicate complex interactions between substrate input derived from rhizodeposition, microbial growth, and accelerated C and N turnover, including the decomposition of native SOM ( i.e., rhizosphere priming effects) at a high spatial resolution from the roots. 相似文献
16.
Increasing atmospheric CO2 concentration impacts the terrestrial carbon(C) cycle by affecting plant photosynthesis, the flow of photosynthetically fixed C belowground, and soil C pool turnover. For managed agroecosystems, how and to what extent the interactions between elevated CO2 and N fertilization levels influence the accumulation of photosynthesized C in crops and the incorporation of photosynthesized C into arable soil are in urgent need of exploration.We conducted an experiment simulating elevated CO2 with spring wheat(Triticum aestivum L.) planted in growth chambers.13C-enriched CO2 with an identical 13C abundance was continuously supplied at ambient and elevated CO2 concentrations(350 and 600 μmol mol-1, respectively) until wheat harvest.Three levels of N fertilizer application(equivalent to 80, 120, and 180 kg N ha-1 soil) were supplied for wheat growth at both CO2 concentrations. During the continuous 62-d 13CO2 labeling period, elevated CO2 and increased N fertilizer application increased photosynthesized C accumulation in wheat by 14%–24% and 11%–20%, respectively, as indicated by increased biomass production, whereas the C/N ratio in the roots increased under elevated CO2 but declined with increasing N fertilizer application levels. Wheat root deposition induced 1%–2.5% renewal of soil C after 62 d of 13CO2 labeling. Compared to ambient CO2, elevated CO2 increased the amount of photosynthesized C incorporated into soil by 20%–44%. However, higher application rates of N fertilizer reduced the net input of root-derived C in soil by approximately 8% under elevated CO2. For the wheat-soil system, elevated CO2 and increased N fertilizer application levels synergistically increased the amount of photosynthesized C. The pivotal role of plants in photosynthesized C accumulation under elevated CO2 was thereby enhanced in the short term by the increased N application. Therefore, robust N management could mediate C cycling and sequestration by influencing the interactions between plants and soil in agroecosystems under elevated CO2. 相似文献
17.
Potassium (K) deficiency reduces photosynthesis and biomass production of crop plants and also renders them vulnerable to drought stress, whereas elevated carbon dioxide (CO 2) has a positive effect on photosynthesis and yield and ameliorates the adverse effects of drought stress. This study aimed to characterize the physiological responses of wheat ( Triticum aestivum L.) stressed with K deficiency under elevated CO 2 and drought conditions. Increased biomass production caused by elevated CO 2 as a consequence of increased photosynthesis and water use efficiency was absent in young K‐deficient wheat plants. Shoot K concentration was negatively affected by elevated CO 2 particularly under K‐deficient conditions, whereas K content per plant was greatest in plants supplied with adequate K and adequate water. Specific leaf weight was increased as a consequence of carbohydrate accumulation in the source leaves of K‐deficient plants particularly under elevated CO 2 and drought stress. Potassium deficiency clearly impeded the impact of elevated CO 2 in both well watered as well as drought‐stressed plants. Adequate K fertilization is a prerequisite for efficient harvesting of atmospheric CO 2 through increased photosynthesis, decreased transpiration, and increased biomass production under changing atmospheric CO 2 and soil moisture conditions. 相似文献
18.
Plants link atmospheric and soil carbon pools through CO 2 fixation, carbon translocation, respiration and rhizodeposition. Within soil, microbial communities both mediate carbon-sequestration and return to the atmosphere through respiration. The balance of microbial use of plant-derived and soil organic matter (SOM) carbon sources and the influence of plant-derived inputs on microbial activity are key determinants of soil carbon-balance, but are difficult to quantify. In this study we applied continuous 13C-labelling to soil-grown Lolium perenne, imposing atmospheric CO 2 concentrations and nutrient additions as experimental treatments. The relative use of plant- and SOM-carbon by microbial communities was quantified by compound-specific 13C-analysis of phospholipid fatty acids (PLFAs). An isotopic mass-balance approach was applied to partition the substrate sources to soil respiration (i.e. plant- and SOM-derived), allowing direct quantification of SOM-mineralisation. Increased CO 2 concentration and nutrient amendment each increased plant growth and rhizodeposition, but did not greatly alter microbial substrate use in soil. However, the increased root growth and rhizosphere volume with elevated CO 2 and nutrient amendment resulted in increased rates of SOM-mineralisation per experimental unit. As rhizosphere microbial communities utilise both plant- and SOM C-sources, the results demonstrate that plant-induced priming of SOM-mineralisation can be driven by factors increasing plant growth. That the balance of microbial C-use was not affected on a specific basis may suggest that the treatments did not affect soil C-balance in this study. 相似文献
19.
Understanding rhizodeposited carbon (C) dynamics of winter wheat ( Triticum aestivum L.) is important for improving soil fertility and increasing soil C stocks. However, the effects of nitrogen (N) fertilization on photosynthate C allocation to rhizodeposition of wheat grown in an intensively farmed alkaline soil remain elusive. In this study, pot‐grown winter wheat under N fertilization of 250 kg N ha ?1 was pulse‐labeled with 13CO 2 at tillering, elongation, anthesis, and grain‐filling stages. The 13C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO 2 was measured 28 d after each 13C labeling. The proportion of net‐photosynthesized 13C recovered (shoots + roots + soil + soil respired CO 2) in the shoots increased from 58–64% at the tillering to 86–91% at the grain‐filling stage. Likewise, the proportion in the roots decreased from 21–28% to 2–3%, and that in the SOC pool increased from 1–2% to 6–7%. However, the 13C respired CO 2 allocated to soil peaked (17–18%) at the elongation stage and decreased to 6–8% at the grain‐filling stage. Over the entire growth season of wheat, N fertilization decreased the proportion of net photosynthate C translocated to the below‐ground pool by about 20%, but increased the total amount of fixed photosynthate C, and therefore increased the below‐ground photosynthate C input. We found that the chase period of about 4 weeks is sufficient to accurately monitor the recovery of 13C after pulse labeling in a wheat–soil system. We conclude that N fertilization increased the deposition of photoassimilate C into SOC pools over the entire growth season of wheat compared to the control treatment. 相似文献
20.
After 8-y of elevated CO 2, we previously detected greater amounts of total soil nitrogen, suggesting that rates of ecosystem N flux into or out of tallgrass prairie had been altered. Denitrification and associative N fixation rates are the two primary biological processes that are known to control N loss and accumulation in tallgrass prairie soil. Therefore, our objective was to assess the natural abundance of plant and soil 15N isotopes as a cumulative index of potential change in efflux or influx of N into and out of the tallgrass prairie after 8-y of exposure to elevated CO 2. Aboveground plant delta 15N values of Andropogon gerardii were close to zero and more positive as a result of elevated CO 2, but whole-soil values at the 5-30 cm depth were significantly reduced (6.8 vs 7.3; P<0.05) under elevated CO 2-chamber (EC) relative to ambient CO 2- chamber (AC). Total, aboveground plant biomass, root-in-growth, extractable N, microbial biomass N, and soil pools collectively exhibited a range of delta 15N values from −2.8 to 7.3. Measurements of surface soil 15N indicate that a change in N inputs and outputs has occurred as a result of elevated atmospheric CO 2. In addition to possible changes in denitrification and N 2 fixation, other sources of N such as the re-translocation of N to the surface from deeper soil layers are needed to explain how soil N accrues in surface soils as a consequence of elevated CO 2. Our results support the notion that C accrual may promote N accrual, possibly driven by high plant and microbial N demand amplified by soil N limitation. 相似文献
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