Root Carbon Research Articles

闽楠人工林细根寿命及其影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 闽楠人工林细根寿命及其影响因素 DOI: 10.5846/stxb201110231566 作者: 作者单位: 福建林业职业技术学院 南平 湿润亚热带山地生态省部共建国家重点实验室 福州,福建师范大学,福建师范大学地理科学学院 福州,福建师范大学地理科学学院 福州,福建师范大学地理科学学院 福州,福建师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(30972347) Fine root longevity and controlling factors in a Phoebe Bournei plantation Author: Affiliation: Fujian Forestry Vocational Technical College,,School of Geographical Sciences,Fujian Normal University,School of Geographical Sciences,Fujian Normal University,School of Geographical Sciences,Fujian Normal University,School of Geographical Sciences,Fujian Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用微根管技术对闽楠(Phoebe bournei (Hemsl.) Yang) 人工林细根生长动态进行了连续2a的观测,通过Kaplan-Meier方法估计细根寿命,使用对数秩检验(Log-rank test)比较单一因素(细根直径、序级、出生季节和土层)对细根寿命的影响;并分析细根化学性质对细根寿命的影响。结果表明:出生季节极显著影响闽楠细根寿命(P<0.01),细根主要在春季出生(82.36%),夏季出生的细根平均寿命和中值寿命皆最长,分别为(218±23)d和(175±65)d;土层对闽楠细根寿命的影响不显著(P>0.05),下层(20-40 cm)细根平均寿命为(126±4)d高于表层(0-20cm)的(116±5)d;细根平均寿命随直径增大而极显著增大(P<0.01),0-0.3 mm的细根平均寿命为(109±4)d,0.3-0.6 mm的为(123±5)d,0.6-1 mm的为(139±11)d,1-2 mm的为(185±25)d。随着径级增大,闽楠细根碳含量极显著增大(P<0.01),氮含量极显著减小(P<0.01),碳氮比极显著增大(P<0.01),磷含量极显著减小(P<0.01)。细根平均寿命随序级增大亦显著增大(P<0.05),其中一级根平均寿命和中值寿命分别为(120±4)d和(89±1)d,高级根的则为(137±7)d和(123±1)d。以上结果表明闽楠细根寿命受到细根形态结构(直径和序级)、出生季节以及细根化学性质的影响。 Abstract:Fine roots (<2mm), as the most dynamic component of root system, play an important role in energy flow and nutrient cycling in the forest ecosystems, which send enormous carbon belowground through root turnover. Fine root survivorship in a plantation of Phoebe bournei (Hemsl.) Yang in Xihou, Wangtai, Fujian province, was monitored by the minirhizotron method for two consecutive years. Fine root longevity was estimated by the Kaplan-Meier method and differences among single factors, including root diameter (<0.3mm, 0.3-0.6mm, 0.6-1mm, 1-2mm), root order (first order, higher order), season of birth (spring, summer, autumn and winter), and soil depth (<20cm, 20-40cm), were tested by the Log-rank test. The chemical properties of different root diameter (<0.3mm, 0.3-0.6mm, 0.6-1mm, 1-2mm) were also determined. The objective of this study was to understand whether the more rapidly the fine roots grow, the shorter their lifespans. The mean and median root lifespans of Phoebe bournei (Hemsl.) Yang were (121±3)d and (89±1)d, respectively. Root growth was highly dynamic during the year, with 82.36% of new roots born in spring. Fine root longevity was significantly affected by the season of birth (P<0.01); the mean and median lifespans were (218±23)d and (175±65)d for roots born in summer, (121±3)d and (89±1)d for those born in spring, and (93±3)d and (46±6)d for those born in autumn and winter, respectively. While soil depth had no significant effect on the median fine-root longevity ((89±3)d amd (89±2)d respectively in the lower and upper soil layer) (P>0.05), mean root lifespan in the lower layer ((126±4)d) was higher than that in the upper layer ((116±5)d). Mean root lifespan increased significantly with root diameter (P<0.01); the mean root lifespan was (109±4)d, (123±5)d, (139±11)d and (185±25)d, and the median root lifespan was (89±0)d, (89±1)d, (123±13)d and (130±13)d, respectively, for root diameter classes of <0.3mm, 0.3-0.6mm, 0.6-1mm and 1-2mm. Root lifespan was significantly affected by root order (P<0.05). Mean root lifespan and median root lifespan of the first root order were (120±4)d and (89±1)d, respectively, while those of the higher order were (137±7)d and (123±1)d, respectively. The root carbon content ranged from 455.2g/kg to 475.6g/kg and the root C/N ratio rangeed from 20.04 to 42.62, both increased significantly with root diameter (P<0.01). Whereas, both the nitrogen (from 11.16 g/kg to 22.71 g/kg) and phosphorus content (from 0.38 g/kg to 0.97g/kg) were decreased significantly with root diameter (P<0.01). It is evidenced from the above that the smaller the root diameter, the higher the root physiological activity, and the shorter the root lifespan. It's concluded that the fine-root longevity of the Phoebe bournei (Hemsl.) plantation was affected by the morphological (root diameter and root order) and chemical traits, and the season of birth. 参考文献 相似文献 引证文献

Aboveground and root carbon stocks for Chinese arborvitae plantation following different silvicultural thinning

We applied thinning prescription in arborvitae plantation in the northern Beijing to hasten secondary succession. We quantified the effect of thinning on the distribution of vegetation carbon stocks, and on the carbon accumulation rates between 2005 and 2009. The carbon stocks in the trees were highest in all control plots and lowest in total plots from high thinning, while total understory carbon stocks were different with trees across treatments. Plots from the control in shady slope with thick slope, the low thinning in sunny slope with thick soil and the sunny slope with thinned soil were highest in carbon accumulation rates. These results suggest that carbon recover following the treatments, it can be necessary to consider the compensatory responses of understory vegetation as such shifts in growth form can affect in the allocation of carbon in the vegetation ecosystem.

Fine Root Mercury Heterogeneity: Metabolism of Lower-Order Roots as an Effective Route for Mercury Removal

Fine roots are critical components for plant mercury (Hg) uptake and removal, but the patterns of Hg distribution and turnover within the heterogeneous fine root components and their potential limiting factors are poorly understood. Based on root branching structure, we studied the total Hg (THg) and its cellular partitioning in fine roots in 6 Chinese subtropical trees species and the impacts of root morphological and stoichiometric traits on Hg partitioning. The THg concentration generally decreased with increasing root order, and was higher in cortex than in stele. This concentration significantly correlated with root length, diameter, specific root length, specific root area, and nitrogen concentration, whereas its cytosolic fraction (accounting for <10% of THg) correlated with root carbon and sulfur concentrations. The estimated Hg return flux from dead fine roots outweighed that from leaf litter, and ephemeral first-order roots that constituted 7.2-22.3% of total fine root biomass may have contributed most to this flux (39-71%, depending on tree species and environmental substrate). Our results highlight the high capacity of Hg stabilization and Hg return by lower-order roots and demonstrate that turnover of lower-order roots may be an effective strategy of detoxification in perennial tree species.

Carbon Dynamics, Development and Stress Responses in Arabidopsis: Involvement of the APL4 Subunit of ADP-Glucose Pyrophosphorylase (Starch Synthesis)

An Arabidopsis thaliana T-DNA insertional mutant was identified and characterized for enhanced tolerance to the singlet-oxygen-generating herbicide atrazine in comparison to wild-type. This enhanced atrazine tolerance mutant was shown to be affected in the promoter structure and in the regulation of expression of the APL4 isoform of ADP-glucose pyrophosphorylase, a key enzyme of the starch biosynthesis pathway, thus resulting in decrease of APL4 mRNA levels. The impact of this regulatory mutation was confirmed by the analysis of an independent T-DNA insertional mutant also affected in the promoter of the APL4 gene. The resulting tissue-specific modifications of carbon partitioning in plantlets and the effects on plantlet growth and stress tolerance point out to specific and non-redundant roles of APL4 in root carbon dynamics, shoot-root relationships and sink regulations of photosynthesis. Given the effects of exogenous sugar treatments and of endogenous sugar levels on atrazine tolerance in wild-type Arabidopsis plantlets, atrazine tolerance of this apl4 mutant is discussed in terms of perception of carbon status and of investment of sugar allocation in xenobiotic and oxidative stress responses.

Assessing the C stocks in various land use practices: A case study from sub-humid tropics of Eastern India

Reducing emissions from deforestation and forest degradation in developing countries, the role of conservation, sustainable management of forests and enhancement of forest carbon stocks (REDD+) has arisen as a key issue in the international climate change negotiations. The efforts have already initiated in many developing countries including India as a global partner in mitigating the climate change through afforestation/reforestation programmes. Under Green India Mission and National Afforestation programme, India has targeted to increase the tree cover by 10 Mha in different land use systems between 2010 and 2020. There is huge knowledge gap on impact of land use practices on C sequestration potential. This paper compares C stocks in three land use systems viz. forest, plantation and agriculture under sub-humid tropics of eastern India. Results revealed that the amount of total carbon stock was comparatively higher in forest followed by plantation and Agroforestry system. The total C stock was lowest in the agriculture land. The difference in carbon stock across land use types are the primary consequences of variation in the vegetation biomass and the soil organic matter. Most of the soil organic C and the fine root carbon was concentrated in the upper 30 cm soil depth and decreased with soil depth. The study indicates that a relatively large amount of carbon lost due to conversion of forest in to agriculture land in the past. Therefore, conservation and sustainable management of forests are recommended to improve C stocks. Similarly, Agroforestry land management practises are suggested in degraded agricultural lands for enhancing the carbon sequestration.

Carbon storage by Atriplex lentiformis

Increasing level of carbon dioxide CO2 due to industrial activity is primarily cause of global warming. Planting Artoplex lentiformis can help to reduce atmospheric CO2 buildup partly replacing use of fuels and by carbon storage. The objective of this study was to determine the effects of row spacing on carbon storage. A split- plot design with three replications included three row spacing (2×2, 4×4, and 6×6m) was applied. Some laboratory samples were taken from aerial and root biomass of Artoplex, and soil for determination of carbon storage. Results showed the values of carbon storage of aerial and root biomass among row spacing was significant different (p=0/o5%). The highest carbon storage was related to 2×2 m row spacing, reached 74583.6 and 6862.5 kg/ha in aerial and root biomass respectively. The carbon amount of soil had no significant differences (p=0/o5%) between treatments. The ranking of the plantation carbon storage by row spacing was 2×2 m > 4×4 m > and 6×6m and by components was aerial carbon> root carbon > soil carbon

Contrasting nutrient stocks and litter decomposition in stands of native and invasive species in a sub-tropical estuarine marsh

We compared the influence of invasion by an alien invasive species ( Spartina alterniflora, smooth cordgrass) and a native aggressive species ( Phragmites australis, common reed) as they have expanded into the native Cyperus malaccensis (shichito matgrass)-dominated wetland ecosystem in the Min River estuary of southeast China. S. alterniflora is a perennial grass native to North America, which has spread rapidly along the southeast coast of China since its introduction in 1979. Our study compared the above and belowground biomass, net primary production, litter decomposition, plant nutrient stocks and soil organic carbon storage of the grasses in three ecosystems: (1) the native ecosystem dominated by C. malaccensis; (2) ecosystems previously dominated by C. malaccensis but presently replaced by P. australis; and (3) ecosystems previously dominated by C. malaccensis but presently replaced by S. alterniflora. Our results demonstrate that the recent invasion (3 years) of the exotic invasive species S. alterniflora has already significantly increased live aboveground biomass and aboveground plant nutrient stocks. However, there was no significant difference in these variables between native aggressive species P. australis and native C. malaccensis. The majority of belowground root Carbon (C), Nitrogen (N) and phosphorus (P) stocks of the three plant species were all distributed in the upper surface layer and there was a decrease with soil depth. There was little difference in litter decomposition rates among the three grass species; they were ranked in the following order: C. malaccensis>S. alterniflora> P. australis. Litter element concentration showed similar patterns for the three species. However, important differences were found between N and P; the litter N concentrations in each of the three species were greater at the end of the 280 days decomposition than at the start, but P concentrations followed a fluctuating pattern during the decomposition period. Soil organic carbon stocks (0–50 cm) under S. alterniflora, P. australis and C. malaccensis stands were statistically indistinguishable, which may be due to the invasion of S. alterniflora having been a relatively recent phenomenon. Thus, recent invasion of the exotic species S. alterniflora has already altered the nutrient cycle of C. malaccensis in the ecosystem in the Min River estuary.

Changes in CO2, 13C abundance, inorganic nitrogen, β-glucosidase, and oxidative enzyme activities of soil during the decomposition of switchgrass root carbon as affected by inorganic nitrogen additions

This study was conducted to investigate the effect of inorganic nitrogen (N) and root carbon (C) addition on decomposition of organic matter (OM). Soil was incubated for 200 days with nine treatments (three levels of N (no addition (N0) = 0, low N (NL) = 0.021, high N (NH) = 0.083 mg N g−1 soil) × three levels of C (no addition (C0) = 0, low C (CL) = 5, high C (CH) = 10 mg root g−1 soil)). The carbon dioxide (CO2) efflux rates, inorganic N concentration, pH, and potential activities of β-glucosidase and oxidative enzyme were measured during incubation. At the beginning and the end of incubation, the native soil organic carbon (SOC) and root-derived SOC were quantified by using a natural labeling technique based on the differences in δ13C between C3 and C4 plants. Overall, the interaction between C and N was not significant. The decomposition of OM in the NH treatment decreased. This could be attributed to the formation of recalcitrant OM by N because the potentially mineralizable C pool was significantly lower in the NH treatment (3.1 mg C g−1) than in the N0 treatment (3.6 mg C g−1). In root C addition treatments, the CO2 efflux rate was generally in order of CH > CL > C0 over the incubation period. Despite no differences in the total SOC concentration among C treatments, the native SOC in the CH treatment (18.29 mg C g−1) was significantly lower than that in the C0 treatment (19.16 mg C g−1).

The biogeochemistry of bioenergy landscapes: carbon, nitrogen, and water considerations

The biogeochemical liabilities of grain-based crop production for bioenergy are no different from those of grain-based food production: excessive nitrate leakage, soil carbon and phosphorus loss, nitrous oxide production, and attenuated methane uptake. Contingent problems are well known, increasingly well documented, and recalcitrant: freshwater and coastal marine eutrophication, groundwater pollution, soil organic matter loss, and a warming atmosphere. The conversion of marginal lands not now farmed to annual grain production, including the repatriation of Conservation Reserve Program (CRP) and other conservation set-aside lands, will further exacerbate the biogeochemical imbalance of these landscapes, as could pressure to further simplify crop rotations. The expected emergence of biorefinery and combustion facilities that accept cellulosic materials offers an alternative outcome: agricultural landscapes that accumulate soil carbon, that conserve nitrogen and phosphorus, and that emit relatively small amounts of nitrous oxide to the atmosphere. Fields in these landscapes are planted to perennial crops that require less fertilizer, that retain sediments and nutrients that could otherwise be transported to groundwater and streams, and that accumulate carbon in both soil organic matter and roots. If mixed-species assemblages, they additionally provide biodiversity services. Biogeochemical responses of these systems fall chiefly into two areas: carbon neutrality and water and nutrient conservation. Fluxes must be measured and understood in proposed cropping systems sufficient to inform models that will predict biogeochemical behavior at field, landscape, and regional scales. Because tradeoffs are inherent to these systems, a systems approach is imperative, and because potential biofuel cropping systems and their environmental contexts are complex and cannot be exhaustively tested, modeling will be instructive. Modeling alternative biofuel cropping systems converted from different starting points, for example, suggests that converting CRP to corn ethanol production under conventional tillage results in substantially increased net greenhouse gas (GHG) emissions that can be only partly mitigated with no-till management. Alternatively, conversion of existing cropland or prairie to switchgrass production results in a net GHG sink. Outcomes and policy must be informed by science that adequately quantifies the true biogeochemical costs and advantages of alternative systems.

Root carbon reserve dynamics in aspen seedlings: does simulated drought induce reserve limitation?

In a greenhouse study we quantified the gradual change of gas exchange, water relations and root reserves of aspen (Populus tremuloides Michx.) seedlings growing over a 3-month period of severe water stress. The aim of the study was to quantify the complex interrelationship between growth, water and gas exchange, and root carbon (C) dynamics. Various growth, gas exchange and water relations variables in combination with root reserves were measured periodically on seedlings that had been exposed to a continuous drought treatment over a 12-week period and compared with well-watered seedlings. Although gas exchange and water relations parameters significantly decreased over the drought period in aspen seedlings, root reserves did not mirror this trend. During the course of the experiment roots of aspen seedlings growing under severe water stress showed a two orders of magnitude increase in sugar and starch content, and roots of these seedlings contained more starch relative to sugar than those in non-droughted seedlings. Drought resulted in a switch from growth to root reserves storage which indicates a close interrelationship between growth and physiological variables and the accumulation of root carbohydrate reserves. Although a severe 3-month drought period created physiological symptoms of C limitation, there was no indication of a depletion of root C reserve in aspen seedlings.

Estimations of total ecosystem carbon pools distribution and carbon biomass current annual increment of a moist tropical forest

With increasing CO 2 in the atmosphere, there is an urgent need of reliable estimates of biomass and carbon pools in tropical forests, most especially in Africa where there is a serious lack of data. Information on current annual increment (CAI) of carbon biomass resulting from direct field measurements is crucial in this context, to know how forest ecosystems will affect the carbon cycle and also to validate eddy covariance flux measurements. Biomass data were collected from 25 plots of 13 ha spread over the different vegetation types and land uses of a moist evergreen forest of 772,066 ha in Cameroon. With site-specific allometric equations, we estimated biomass and aboveground and belowground carbon pools. We used GIS technology to develop a carbon biomass map of our study area. The CAI was estimated using the growth rates obtained from tree rings analysis. The carbon biomass was on average 264 ± 48 Mg ha −1. This estimate includes aboveground carbon, root carbon and soil organic carbon down to 30 cm depth. This value varied from 231 ± 45 Mg ha −1 of carbon in Agro-Forests to 283 ± 51 Mg ha −1 of carbon in Managed Forests and to 278 ± 56 Mg ha −1 of carbon in National Park. The carbon CAI varied from 2.54 ± 0.65 Mg ha −1 year −1 in Agro-Forests to 2.79 ± 0.72 Mg ha −1 year −1 in Managed Forests and to 2.85 ± 0.72 Mg ha −1 year −1 in National Park. This study provides estimates of biomass, carbon pools and CAI of carbon biomass from a forest landscape in Cameroon as well as an appropriate methodology to estimate these components and the related uncertainty.

Does mother know best? The preference-performance hypothesis and parent-offspring conflict in aboveground-belowground herbivore life cycles

1. A substantial amount of research on host-plant selection by insect herbivores is focused around the preference–performance hypothesis (PPH). To date, the majority of studies have primarily considered insects with aboveground life cycles, overlooking insect herbivores that have both aboveground and belowground life stages, for which the PPH could be equally applicable. 2. This study investigated the factors influencing the performance of the root-feeding vine weevil (Otiorhynchus sulcatus) larvae and whether this was linked to the oviposition behaviour of the maternal adult living aboveground. 3. Maternal insects feeding aboveground reduced root biomass by 34% and increased root carbon by 4%. Larvae feeding on plants subjected to aboveground herbivory had reduced mass. Irrespective of the presence of maternal herbivory, larval mass was positively correlated with root biomass. 4. Larval mass was also reduced by conspecific larvae, previously feeding on roots (19% reduction). However, the mechanism underpinning this effect remains unclear, as in contrast to maternal herbivory aboveground, prior larval feeding did not significantly affect root biomass or root carbon concentrations. 5. Maternal insects did not distinguish between plants infested with larvae and those that were free of larvae, in terms of their egg-laying behaviour. Conversely, maternal insects tended to lay eggs on plants with smaller root systems, a behaviour that is likely to negatively affect offspring performance. 6. The PPH is not supported by our findings for the polyphagous vine weevil feeding on the host plant raspberry (Rubus idaeus), and in fact our results suggest that there is the potential for strong parent–offspring conflict in this system.

The role of the Miombo Woodlands of the Southern Highlands of Tanzania as carbon sinks

-1 . Of the total carbon, 40 and 60% was contributed by stems and branches respectively. Different species contributed differently to carbon stocks in these ecosystems with Brachystegia spiciformis and Julbernardia globiflora contributing the most. The estimated carbon stocks in this ecosystem is within the range observed in dry forests elsewhere though they are in their early stages of regeneration after extensive exploitation pressure. Under proper management there is a tremendous capacity for carbon storage in these Miombo woodlands to mitigate carbon emissions. Since Miombo species tend to invest much in roots an assessment of below ground carbon in roots can add to the carbon storage potential of these ecosystems. Evaluation of the root and soil carbon in these ecosystems is important in determining the full potential of these ecosystems to act as carbon sink.

Estimating Net Primary Productivity and Nutrient Stock in Plant in Freshwater Marsh, Northeastern China

AbstractWe have investigated the contributions of three dominant macrophyte species, Deyeuxia angustifolia, Carex lasiocarpa, and Carex pseudocuraica (covering about 10 304 km2), to carbon (C), nitrogen (N), and phosphorus (P) stocks in the largest freshwater marsh (17 300 km2) in China for a 3‐year period (from 2002 to 2004). The monthly biomass, seasonal, and annual net primary productivity (NPP), and nutrient concentrations of three species were measured. All three plant species showed rapid growth in the rainy season. The maximum and minimum production rates in the freshwater marsh were ∼36.19 and ∼9.92 g m−2 day−1, respectively. The total NPP accounts 1900–2700 g m−2 year−1 in the studied area. Total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) concentrations in roots were higher than those in stem and leaf tissues. The vast beds of the three studied species comprise 80% of the grass covered marsh of Sanjiang plain, contributing annual nutrient stocks of ∼10.99 × 106, ∼788.36 × 103, and ∼18.10 × 103 t (tonnes) for TOC, TN, and TP, respectively. Our results suggest that the nutrient bioaccumulation capacity in freshwater marshes depend mainly on plant species, which are decided by hydrological conditions. The nutrient stocks in the Sanjiang plain marsh have been greatly reduced because some of the area occupied by C. lasiocarpa was replaced by D. angustifolia as a result of succession caused by the changes of water table.

ForCent model development and testing using the Enriched Background Isotope Study experiment

The ForCent forest ecosystem model was developed by making major revisions to the DayCent model including: (1) adding a humus organic pool, (2) incorporating a detailed root growth model, and (3) including plant phenological growth patterns. Observed plant production and soil respiration data from 1993 to 2000 were used to demonstrate that the ForCent model could accurately simulate ecosystem carbon dynamics for the Oak Ridge National Laboratory deciduous forest. A comparison of ForCent versus observed soil pool 14C signature (Δ 14C) data from the Enriched Background Isotope Study 14C experiment (1999–2006) shows that the model correctly simulates the temporal dynamics of the 14C label as it moved from the surface litter and roots into the mineral soil organic matter pools. ForCent model validation was performed by comparing the observed Enriched Background Isotope Study experimental data with simulated live and dead root biomass Δ 14C data, and with soil respiration Δ 14C (mineral soil, humus layer, leaf litter layer, and total soil respiration) data. Results show that the model correctly simulates the impact of the Enriched Background Isotope Study 14C experimental treatments on soil respiration Δ 14C values for the different soil organic matter pools. Model results suggest that a two‐pool root growth model correctly represents root carbon dynamics and inputs to the soil. The model fitting process and sensitivity analysis exposed uncertainty in our estimates of the fraction of mineral soil in the slow and passive pools, dissolved organic carbon flux out of the litter layer into the mineral soil, and mixing of the humus layer into the mineral soil layer.

Labile soil carbon inputs mediate the soil microbial community composition and plant residue decomposition rates

Root carbon (C) inputs may regulate decomposition rates in soil, and in this study we ask: how do labile C inputs regulate decomposition of plant residues, and soil microbial communities? In a 14 d laboratory incubation, we added C compounds often found in root exudates in seven different concentrations (0, 0.7, 1.4, 3.6, 7.2, 14.4 and 21.7 mg C g(-1) soil) to soils amended with and without (13) C-labeled plant residue. We measured CO(2) respiration and shifts in relative fungal and bacterial rRNA gene copy numbers using quantitative polymerase chain reaction (qPCR). Increased labile C input enhanced total C respiration, but only addition of C at low concentrations (0.7 mg C g(-1)) stimulated plant residue decomposition (+2%). Intermediate concentrations (1.4, 3.6 mg C g(-1)) had no impact on plant residue decomposition, while greater concentrations of C (>7.2 mg C g(-1)) reduced decomposition (-50%). Concurrently, high exudate concentrations (>3.6 mg C g(-1)) increased fungal and bacterial gene copy numbers, whereas low exudate concentrations (<3.6 mg C g(-1)) increased metabolic activity rather than gene copy numbers. These results underscore that labile soil C inputs can regulate decomposition of more recalcitrant soil C by controlling the activity and relative abundance of fungi and bacteria.

Nitrogen deposition limits photosynthetic response to elevated CO2 differentially in a dioecious species

Sexual dimorphisms of dioecious plants are important in controlling and maintaining sex ratios under changing climate environments. Yet, little is known about sex-specific responses to elevated CO(2) with soil nitrogen (N) deposition. To investigate sex-related physiological and biochemical responses to elevated CO(2) with N deposition, Populus cathayana Rehd. was employed as a model species. The cuttings were subjected to two CO(2) regimes (350 and 700 μmol mol(-1)) with two N levels (0 and 5 g N m(-2) year(-1)). Our results showed that elevated CO(2) and N deposition separately increased the total number of leaves, leaf area (LA), leaf mass, net photosynthetic rate (P(n)), light saturated photosynthetic rate (P(max)), chlorophyll a (Chl a), and chlorophyll a to chlorophyll b ratio (Chl a/b) in both males and females of P. cathayana. However, the effects on LA, leaf mass, P(n), P(max), Chl a and Chl a/b were weakened under the combined treatment of elevated CO(2) and N deposition. Males had higher leaf mass, P(n), P(max), apparent quantum yield (Φ), carboxylation efficiency (CE), Chl a, Chl a/b, leaf N, and root carbon to N ratio (C/N) than did females under elevated CO(2) with N deposition. In contrast to males, females had significantly higher levels of soluble sugars in leaves and greater starch accumulation in roots and stems under the same condition. The results of the present work imply that P. cathayana females are more responsive and suffer from greater negative effects on growth and photosynthetic capacity than do males when grown under elevated CO(2) with soil N deposition.

An assessment of carbon stock for various land use system in Aravally mountains, Western India

Reducing carbon emissions from deforestation and degradation in developing countries is of the central importance in efforts to combat climate change. A study was conducted to measure carbon stocks in various land-use systems including forms and reliably estimates the impact of land use on carbon (C) stocks in the forest of Rajasthan, western India (23°3′–30°12′N longitude and 69°30′–78°17′E). 22.8% of India is forested and 0.04% is the deforestation rate of India. In Indian forest sector of western India of Aravally mountain range covered large area of deciduous forest and it’s very helpful in carbon sequestration at global level. The carbon stocks of forest, plantation (reforestation) and agricultural land in aboveground, soil organic and fine root within forest were estimated through field data collection. Results revealed that the amount of total carbon stock of forests (533.64 ± 37.54 Mg·ha−1, simplified expression of Mg (carbon) ·ha−1) was significantly greater (P < 0.05) than the plantation (324.37 ± 15.0 Mg·ha−1) and the agricultural land (120.50 ± 2.17 Mg·ha−1). Soil organic carbon in the forests (172.84 ± 3.78 Mg·ha−1) was also significantly greater (P < 0.05) than the plantation (153.20 ± 7.48 Mg·ha−1) and the agricultural land (108.71 ± 1.68 Mg·ha−1). The differences in carbon stocks across land-use types are the primary consequence of variations in the vegetation biomass and the soil organic matter. Fine root carbon was a small fraction of carbon stocks in all land-use types. Most of the soil organic carbon and fine root carbon content was found in the upper 30-cm layer and decreased with soil depth. The aboveground carbon (ABGC): soil organic carbon (SOC): fine root carbon ratios (FRC), was 8:4:1, 4:5:1, and 3:37:1 for the forest, plantation and agricultural land, respectively. These results indicate that a relatively large proportion of the C loss is due to forest conversion to agricultural land.

Development and optimization of an Agro-BGC ecosystem model for C 4 perennial grasses

Extrapolating simulations of bioenergy crop agro-ecosystems beyond data-rich sites requires biophysically accurate ecosystem models and careful estimation of model parameters not available in the literature. To increase biophysical accuracy we added C 4 perennial grass functionality and agricultural practices to the Biome-BGC (BioGeochemical Cycles) ecosystem model. This new model, Agro-BGC, includes enzyme-driven C 4 photosynthesis, individual live and dead leaf, stem, and root carbon and nitrogen pools, separate senescence and litter fall processes, fruit growth, optional annual seeding, flood irrigation, a growing degree day phenology with a killing frost option, and a disturbance handler that simulates nitrogen fertilization, harvest, fire, and incremental irrigation. To obtain spatially generalizable vegetation parameters we used a numerical method to optimize five unavailable parameters for Panicum virgatum (switchgrass) using biomass yield data from three sites: Mead, Nebraska, Rockspring, Pennsylvania, and Mandan, North Dakota. We then verified simulated switchgrass yields at three independent sites in Illinois (IL). Agro-BGC is more accurate than Biome-BGC in representing the physiology and dynamics of C 4 grass and management practices associated with agro-ecosystems. The simulated two-year average mature yields with single-site Rockspring optimization have Root Mean Square Errors (RMSE) of 70, 152, and 162 and biases of 43, −87, 156 g carbon m −2 for Shabbona, Urbana, and Simpson IL, respectively. The simulated annual yields in June, August, October, December, and February have RMSEs of 114, 390, and 185 and biases of −19, −258, and 147 g carbon m −2 for Shabbona, Urbana, and Simpson IL, respectively. These RMSE and bias values are all within the largest 90% confidence interval around respective IL site measurements. Twenty-four of twenty-six simulated annual yields with Rockspring optimization are within 95% confidence intervals of Illinois site measurements during the mature fourth and fifth years of growth. Ten of eleven simulated two-year average mature yields with Rockspring optimization are within 65% confidence intervals of Illinois site measurements and the eleventh is within the 95% confidence interval. Rockspring optimized Agro-BGC achieves accuracies comparable to those of two previously published models: Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) and Integrated Farm System Model (IFSM). Agro-BGC suffers from static vegetation parameters that can change seasonally and as plants age. Using mature plant data for optimization mitigates this deficiency. Our results suggest that a multi-site optimization scheme using mature plant data from more sites would be adequate for generating spatially generalizable vegetation parameters for simulating mature bioenergy crop agro-ecosystems with Agro-BGC.

Does the age of fine root carbon indicate the age of fine roots in boreal forests?

To test the reliability of the radiocarbon method for determining root age, we analyzed fine roots (originating from the years 1985–1993) from ingrowth cores with known maximum root age (1–6 years old). For this purpose, three Scots pine (Pinus sylvestris L.) stands were selected from boreal forests in Finland. We analyzed root 14C age by the radiocarbon method and compared it with the above-mentioned known maximum fine root age. In general, ages determined by the two methods (root 14C age and ingrowth core root maximum age) were in agreement with each other for roots of small diameter (<0.5 mm). By contrast, in most of the samples of fine roots of larger diameter (1.5–2 mm), the 14C age of root samples of 1987–1989 exceeded the ingrowth core root maximum age by 1–10 years. This shows that these roots had received a large amount of older stored carbon from unknown sources in addition to atmospheric CO2 directly from photosynthesis. We conclude that the 14C signature of fine roots, especially those of larger diameter, may not always be indicative of root age, and that further studies are needed concerning the extent of possible root uptake of older carbon and its residence time in roots.