Mediterranean shrublands carbon sequestration: environmental and economic benefits

To date, only a few attempts have been done to estimate the contribution of Mediterranean ecosystems to the global carbon cycle. Within this context, shrub species, composition and structure of the Mediterranean shrublands developing along the Latium coast (Italy) were analyzed in order to evaluate their contribution to carbon (C) sequestration, also taking into consideration the economic benefits at a national level. The considered shrublands had a shrub density of 1,200?±?500 shrubs ha^?1. Shrubs were classified into small (S), medium (M) and large (L), according to their volume (V) and leaf area index (LAI). The total yearly carbon dioxide (CO₂) sequestration per species (SC_y) was calculated multiplying the total photosynthetic leaf surface area (spt) of each species by the mean yearly photosynthetic rate and the total yearly photosynthetic activity time (in hours). Q. ilex and A. unedo had the highest SC_y (46.2?±?15.8 kg CO₂ year^?1, mean value), followed by P. latifolia (17.5?±?6.2 kg CO₂ year^?1), E. arborea, E. multiflora, C. incanus, P. lentiscus, R. officinalis, and S. aspera (6.8?±?4.2 kg CO₂ year^?1, mean value). The total yearly CO₂ sequestration per shrub (SC_shy) was 149?±?5 kg CO₂ year^?1 in L, decreasing 30 % in M and 80 % in S shrubs. Taking into account the frequency of S, M and L and their SC_shy, the total CO₂ sequestration of the Mediterranean maquis was quantified in 80 Mg CO₂ ha^?1?year^?1, corresponding to 22 Mg C ha^?1?year^?1. From a monetary viewpoint, this quantity could be valued to more than 500 US$ ha^?1?year^?1. Extending this benefit to the Mediterranean shrublands throughout the whole country, we obtained a nationwide estimated annual benefit in the order of $500 million.     

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.     

Greenhouse gas emission factors for land use and land-use change in Southeast Asian peatlands

Tropical peat swamp forests, which are predominantly located in Southeast Asia (SEA) and play a prominent role as a global carbon store, are being intensively degraded and converted to agricultural lands and tree plantations. For national inventories, updated estimates of peat emissions of greenhouse gases (GHG) from land use (LU) and land-use change in the tropics are required. In this context, we reviewed the scientific literature and calculated emission factors of peat net emissions of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in seven representative LU categories for SEA i.e. intact peat swamp forest, degraded forest (logged, drained and affected by fire), mixed croplands and shrublands, rice fields, oil palm, Acacia crassicarpa and sago palm plantations. Peat net CO₂ uptake from or emissions to the atmosphere were assessed using a mass balance approach. The balance included main peat C inputs through litterfall and root mortality and outputs via organic matter mineralization and dissolved organic carbon. Peat net CO₂ loss rate from degraded forest, croplands and shrublands, rice fields, oil palm, A. crassicarpa and sago palm plantations amounted to 19.4?±?9.4, 41.0?±?6.7, 25.6?±?11.5, 29.9?±?10.6, 71.8?±?12.7 and 5.2?±?5.1 Mg CO₂ ha^?1 y^?1, respectively. Total peat GHG losses amounted to 20.9?±?9.4, 43.8?±?6.8, 36.1?±?12.9, 30.4?±?10.6, 72?±?12.8 and 8.6?±?5.3 Mg CO₂-equivalent ha^?1 y^?1 in the same LU categories, respectively. A single land-clearing fire would result in additional emissions of 493.6?±?156.0 Mg CO₂-equivalent ha^?1.     

CO2 emissions from tropical drained peat in Sumatra,Indonesia

With the increasing use of tropical peatland for agricultural development, documentation of the rate of carbon dioxide (CO₂) emissions is becoming important for national greenhouse gas inventories. The objective of this study was to evaluate soil-surface CO₂ fluxes from drained peat under different land-use systems in Riau and Jambi Provinces, Sumatra, Indonesia. Increase of CO₂ concentration was tracked in measurement chambers using an Infrared Gas Analyzer (IRGA, LI-COR 820 model). The results showed that CO₂ flux under oil palm (Elaeis guineensis) plantations ranged from 34?±?16 and 45?±?25 Mg CO₂ ha^–1 year^–1 in two locations in Jambi province to 66?±?25 Mg CO₂ ha^–1 year^–1 for a site in Riau. For adjacent plots within 3.2 km in the Kampar Peninsula, Riau, CO₂ fluxes from an oil palm plantation, an Acacia plantation, a secondary forest and a rubber plantation were 66?±?25, 59?±?19, 61?±?25, 52?±?17 Mg ha^–1 year^–1, respectively, while on bare land sites it was between 56?±?30 and 67?±?24 Mg CO₂ ha^–1 year^–1, indicating no significant differences among the different land-use systems in the same landscape. Unexplained site variation seems to dominate over land use in influencing CO₂ flux. CO₂ fluxes varied with time of day (p?<?0.001) with the noon flux as the highest, suggesting an overestimate of the mean flux values with the absence of night-time measurements. In general, CO₂ flux increased with the depth of water table, suggesting the importance of keeping the peat as wet as possible.     

Root- and peat-based CO2 emissions from oil palm plantations

Measured carbon dioxide (CO₂) flux from peat soils using the closed chamber technique combines root-related (autotrophic + heterotrophic where rhizosphere organisms are involved) and peat-based (heterotrophic) respiration. The latter contributes to peat loss while the former is linked to recent CO₂ removal through photosynthesis. The objective of this study was to separate root- from peat-based respiration. The study was conducted on peatland under 6 and 15 year old oil palm (Elaeis guineensis Jacq.) plantations in Jambi Province, Indonesia in 2011 to 2012. CO₂ emissions were measured in the field from 25 cm diameter and 25 cm tall closed chambers using an infrared gas analyser. Root sampling and CO₂ emissions measurements were at distances of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 m from the centre of the base of the palm tree. The emission rate for the six and 15 year old oil palm plantations at ≥3.0 m from the centre of the tree were 38.2?±?9.5 and 34.1?±?15.9 Mg CO₂ ha^?1 yr^?1, respectively. At distances <2.5 m, total respiration linearly decreased with distances from the trees. Heterotrophic respirations were 86 % of the 44.7?±?11.2 and 71 % of 47.8?±?21.3 Mg CO₂ ha^?1 yr^?1 of weighted surface flux, respectively for the 6 and 15 year old plantations. We propose that CO₂ flux measurements in oil palm plantations made at a distance of ≥3 m from the tree centre be used to represent the heterotrophic respiration that is relevant for the environmental impact assessment.     

Carbon stocks in Swiss agricultural soils predicted by land-use,soil characteristics,and altitude

Effects of agricultural land-use and land-use change on soil organic carbon (SOC) pools play an important role in the mitigation of the global greenhouse effect. To estimate these effects, baseline SOC data for individual regions or countries are needed. The aim of this study was to quantify current SOC stocks in Swiss agricultural soils, to identify meaningful predictors for SOC, and to estimate historical SOC losses. SOC stocks in mineral soils were estimated from combined georeferenced data for land-use, topography, and profile data (n=544) from soil surveys. Mean SOC density in the layer 0–20 cm ranged between 40.6±8.9 t ha⁻¹ (±95% confidence interval (CI)) for arable land and 50.7±12.2 t ha⁻¹ for favourable permanent grassland, and in the layer 0–100 cm from 62.9±15.2 t ha⁻¹ for unfavourable grassland to 117.4±29.8 t ha⁻¹ for temporary grasslands (leys). SOC stocks in organic soils were quantified separately for intact and cultivated peatlands using data from peatland inventories and current SOC densities calculated from average peat decay rates. Organic soils account for less than 3% of the total area but store about 28% (47.2±7.3 Mt) of the total SOC stock of 170±17 Mt. Land-use type, clay content, and altitude (serving as a climate proxy for grassland soils at higher altitudes) were identified as main SOC predictors in mineral soils. Clay content explained up to 44% of the variability in SOC concentrations in the fine earth of arable soils, but was not significantly related to SOC in grassland soils at higher altitudes. SOC concentration under permanent grassland increases linearly with altitude, but because soil depth and stone content limit carbon storage in alpine grassland soils, no relationship was found between altitude and SOC stock. A preliminary estimate suggested that about 16% of the national SOC stock has been lost historically due to peatland cultivation, urbanisation, and deforestation. It seems unlikely that future changes in agricultural practices could compensate for this historical SOC loss in Swiss agricultural soils.     

Carbon storage and sequestration potential of selected tree species in India

A dynamic growth model (CO2FIX) was used for estimating the carbon sequestration potential of sal (Shorea Robusta Gaertn. f.), Eucalyptus (Eucalyptus Tereticornis Sm.), poplar (Populus Deltoides Marsh), and teak (Tectona Grandis Linn. f.) forests in India. The results indicate that long-term total carbon storage ranges from 101 to 156 Mg C?ha^?1, with the largest carbon stock in the living biomass of long rotation sal forests (82 Mg C?ha^?1). The net annual carbon sequestration rates were achieved for fast growing short rotation poplar (8 Mg C?ha^?1?yr^?1) and Eucalyptus (6 Mg C?ha^?1?yr^?1) plantations followed by moderate growing teak forests (2 Mg C?ha^?1?yr^?1) and slow growing long rotation sal forests (1 Mg C?ha^?1?yr^?1). Due to fast growth rate and adaptability to a range of environments, short rotation plantations, in addition to carbon storage rapidly produce biomass for energy and contribute to reduced greenhouse gas emissions. We also used the model to evaluate the effect of changing rotation length and thinning regime on carbon stocks of forest ecosystem (trees?+?soil) and wood products, respectively for sal and teak forests. The carbon stock in soil and products was less sensitive than carbon stock of trees to the change in rotation length. Extending rotation length from the recommended 120 to 150 years increased the average carbon stock of forest ecosystem (trees?+?soil) by 12%. The net primary productivity was highest (3.7 Mg ha^?1?yr^?1) when a 60-year rotation length was applied but decreased with increasing rotation length (e.g., 1.7 Mg ha^?1?yr^?1) at 150 years. Goal of maximum carbon storage and production of more valuable saw logs can be achieved from longer rotation lengths. ‘No thinning’ has the largest biomass, but from an economical perspective, there will be no wood available from thinning operations to replace fossil fuel for bioenergy and to the pulp industry and such patches have high risks of forest fires, insects etc. Extended rotation lengths and reduced thinning intensity could enhance the long-term capacity of forest ecosystems to sequester carbon. While accounting for effects of climate change, a combination of bioenergy and carbon sequestration will be best to mitigation of CO₂ emission in the long term.     

Soil-profile organic carbon and total nitrogen during 12 years of pasture management in the Southern Piedmont USA

Soil organic C (SOC) and total soil N (TSN) sequestration estimates are needed to improve our understanding of management influences on soil fertility and terrestrial C cycling related to greenhouse gas emission. We evaluated the factorial combination of nutrient source (inorganic, mixed inorganic and organic, and organic as broiler litter) and forage utilization (unharvested, low and high cattle grazing pressure, and hayed monthly) on soil-profile distribution (0–150 cm) of SOC and TSN during 12 years of pasture management on a Typic Kanhapludult (Acrisol) in Georgia, USA. Nutrient source rarely affected SOC and TSN in the soil profile, despite addition of 73.6 Mg ha^?1 (dry weight) of broiler litter during 12 years of treatment. At the end of 12 years, contents of SOC and TSN at a depth of 0–90 cm under haying were only 82 ± 5% (mean ± S.D. among treatments) of those under grazed management. Within grazed pastures, contents of SOC and TSN at a depth of 0–90 cm were greatest within 5 m of shade and water sources and only 83 ± 7% of maximum at a distance of 30 m and 92 ± 14% of maximum at a distance of 80 m, suggesting a zone of enrichment within pastures due to animal behavior. During 12 years, the annual rate of change in SOC (0–90 cm) followed the order: low grazing pressure (1.17 Mg C ha^?1 year^?1) > unharvested (0.64 Mg C ha^?1 year^?1) = high grazing pressure (0.51 Mg C ha^?1 year^?1) > hayed (?0.22 Mg C ha^?1 year^?1). This study demonstrated that surface accumulation of SOC and TSN occurred, but that increased variability and loss of SOC with depth reduced the significance of surface effects.     

Greenhouse gas emissions in restored secondary tropical peat swamp forests

Restoration of deforested and drained tropical peat swamp forests is globally relevant in the context of reducing emissions from deforestation and forest degradation. The seasonal flux of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) in a restoration concession in Central Kalimantan, Indonesia, was measured in the two contrasting land covers: shrubs and secondary forests growing on peatlands. We found that land covers had high, but insignificantly different, soil carbon stocks of 949?+?56 and 1126?+?147 Mg ha^?1, respectively. The mean annual CO₂ flux from the soil of shrub areas was 52.4?±?4.1 Mg ha^?1 year^?1, and from secondary peat swamp forests was 42.9?±?3.6 Mg ha^?1 year^?1. The significant difference in mean soil temperature in the shrubs (31.2 °C) and secondary peat swamp forests (26.3 °C) was responsible for the difference in total CO₂ fluxes of these sites. We also found the mean annual total soil respiration was almost equally partitioned between heterotrophic respiration (20.8?+?1.3 Mg ha^?1 year^?1) and autotrophic respiration (22.6?+?1.5 Mg ha^?1 year^?1). Lowered ground water level up to ??40 cm in both land covers caused the increase of CO₂ fluxes to 40–75%. These numbers contribute to the provision of emission factors for rewetted organic soils required in the national reporting using the 2013 Supplement of the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for wetlands as part of the obligation under the United Nations Framework Convention on Climate Change (UNFCCC).

     

Classification and ordination of understory vegetation using multivariate techniques in the <Emphasis Type="Italic">Pinus wallichiana</Emphasis> forests of Swat Valley,northern Pakistan

An understory vegetation survey of the Pinus wallichiana-dominated temperate forests of Swat District was carried out to inspect the structure, composition and ecological associations of the forest vegetation. A quadrat method of sampling was used to record the floristic and phytosociological data necessary for the analysis using 300 quadrats of 10 × 10 m each. Some vegetation parameters viz. frequency and density for trees (overstory vegetation) as well as for the understory vegetation were recorded. The results revealed that in total, 92 species belonging to 77 different genera and 45 families existed in the area. The largest families were Asteraceae, Rosaceae and Lamiaceae with 12, ten and nine species, respectively. Ward’s agglomerative cluster analysis for tree species resulted in three floristically and ecologically distinct community types along different topographic and soil variables. Importance value indices (IVI) were also calculated for understory vegetation and were subjected to ordination techniques, i.e. canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA). DCA bi-plots for stands show that most of the stands were scattered around the centre of the DCA bi-plot, identified by two slightly scattered clusters. DCA for species bi-plot clearly identified three clusters of species revealing three types of understory communities in the study area. Results of the CCA were somewhat different from the DCA showing the impact of environmental variables on the understory species. CCA results reveal that three environmental variables, i.e. altitude, slope and P (mg/kg), have a strong influence on distribution of stands and species. Impact of tree species on the understory vegetation was also tested by CCA which showed that four tree species, i.e. P. wallichiana A.B. Jackson, Juglans regia Linn., Quercus dilatata Lindl. ex Royle and Cedrus deodara (Roxb. ex Lamb.) G. Don, have strong influences on associated understory vegetation. It is therefore concluded that Swat District has various microclimatic zones with suitable environmental variables to support distinct flora.     

Beetle adhesive hairs differ in stiffness and stickiness: in vivo adhesion measurements on individual setae

Leaf beetles are able to climb on smooth and rough surfaces using arrays of micron-sized adhesive hairs (setae) of varying morphology. We report the first in vivo adhesive force measurements of individual setae in the beetle Gastrophysa viridula, using a smooth polystyrene substrate attached to a glass capillary micro-cantilever. The beetles possess three distinct adhesive pads on each leg which differ in function and setal morphology. Visualisation of pull-offs allowed forces to be measured for each tarsal hair type. Male discoidal hairs adhered with the highest forces (919?±?104?nN, mean?±?SE), followed by spatulate (582?±?59?nN) and pointed (127?±?19?nN) hairs. Discoidal hairs were stiffer in the normal direction (0.693?±?0.111?N?m^?1) than spatulate (0.364?±?0.039?N?m^?1) or pointed (0.192?±?0.044?N?m^?1) hairs. The greater adhesion on smooth surfaces and the higher stability of discoidal hairs help male beetles to achieve strong adhesion on the elytra of females during copulation. A comparison of pull-off forces measured for single setae and whole pads (arrays) revealed comparable levels of adhesive stress. This suggests that beetles are able to achieve equal load sharing across their adhesive pads so that detachment through peeling is prevented.     

Ecological consistency across space: a synthesis of the ecological aspects of Dromiciops gliroides in Argentina and Chile

Dromiciops gliroides is an arboreal marsupial found in the temperate forests of South America (36–43 °S). This species is the sole extant representative of the order Microbiotheria, and is a key seed disperser of many native plant species, including the keystone mistletoe Tristerix corymbosus. Here, we synthesized the current knowledge on the ecological aspects of this species, and compared the available information from Argentina and Chile. Population density (23?±?2 (mean ± SE) individual/ha) and home range (1.6?±?0.6?ha) appear to be relatively similar across a marked ecological gradient in the mainland, but lower densities (7?±?2 individual/ha) and smaller home ranges (0.26?±?0.04?ha) were detected at island sites. We detected regional variation in body condition in Chile, but there were no significant differences across a wider E-W gradient. Movement patterns fit a random walk model; such behavior might have important consequences in shaping plant’s spatial patterns. Although our data suggest that D. gliroides is more tolerant to habitat disturbance than previously thought, its incapability to disperse across non-forested areas suggests that the rapid rate of habitat loss and fragmentation that characterizes southern temperate forests likely poses a serious threat to this species. These ecological similarities are surprising given that forests studied receive dramatically different rainfall and correspond to distinct forest types. The evidence synthetized here dispels some of the myths about this species but also stresses the need for more comprehensive ecological studies across its distribution range.     

Assessment of trophic change and its probable impact on tropical estuarine environment (the Kodungallur-Azhikode estuary, India)

The cumulative effects of global change, including climate change, increased population density and domestic waste disposal, effluent discharges from industrial processes, agriculture and aquaculture will likely continue and increases the process of eutrophication in estuarine environments. Eutrophication is one of the leading causes of degraded water quality, water column hypoxia/anoxia, harmful algal bloom (HAB) and loss of habitat and species diversity in the estuarine environment. The present study attempts to characterize the trophic condition of coastal estuary using a simple tool; trophic index (TRIX) based on a linear combination of the log of four state variables with supplementary index Efficiency Coefficient (Eff. Coeff.) as a discriminating tool. Numerically, the index TRIX is scaled from 0 to10, covering a wide range of trophic conditions from oligotrophic to eutrophic. Study area Kodungallur-Azhikode Estuary (KAE) was comparatively shallow in nature with average depth of 3.6?±?0.2?m. Dissolve oxygen regime in the water column was ranged from 4.7?±?1.3?mgL^?1 in Station I to 5.9?±?1.4?mgL^?1 in Station IV. The average nitrate-nitrogen (NO₃-N) of KAE water was 470?mg?m^?3; values ranged from Av. 364.4?mg?m^?3 at Station II to Av. 626.6?mg?m^?3at Station VII. The mean ammonium-nitrogen (NH ₄ ⁺ -N) varied from 54.1?mg?m^?3 at Station VII to 101?mg?m^?3 at Station III. The average Chl-a for the seven stations of KAE was 6.42?±?3.91?mg?m^?3. Comparisons over different spatial and temporal scales in the KAE and study observed that, estuary experiencing high productivity by the influence of high degree of eutrophication; an annual average of 6.91 TRIX was noticed in the KAE and seasonal highest was observed during pre monsoon period (7.15) and lowest during post monsoon period (6.51). In the spatial scale station V showed high value 7.37 and comparatively low values in the station VI (6.93) and station VII (6.96) and which indicates eutrophication was predominant in land cover area with comparatively high water residence time. Eff. Coeff. values in the KAE ranges from ?2.74 during monsoon period to the lowest of ?1.98 in pre monsoon period. Present study revealed that trophic state of the estuary under severe stress and the restriction of autochthonous and allochthonous nutrient loading should be keystone in mitigate from eutrophication process.     

Prediction of enteric methane emission from cattle using linear and non-linear statistical models in tropical production systems

The objective of this study was to develop linear and nonlinear statistical models to predict enteric methane emission (EME) from cattle (Bos) in the tropics based on dietary and animal characteristic variables. A database from 35 publications, which included 142 mean observations of EME measured on 830 cattle, was constructed to develop EME prediction models. Several extant equations of EME developed for North American and European cattle were also evaluated for suitability of those equations in this dataset. The average feed intake and methane production were 7.7?±?0.34 kg/day and 7.99?±?0.39 MJ/day, respectively. The simple linear equation that predicted EME with high precision and accuracy was: methane (MJ/day)?=?1.29_(±0.906)?+?0.878_(±0.125)?×?dry matter intake (DMI, kg/day), [root mean square prediction error (RMSPE)?=?31.0 % with 92 % of RMSPE being random error; R ²?=?0.70]. Multiple regression equation that predicted methane production slightly better than simple prediction equations was: methane (MJ/day)?=?0.910_(±0.746)?+?1.472_(±0.154)?×?DMI (kg/day) – 1.388_(±0.451)?×?feeding level as a multiple of maintenace energy intake – 0.669_(±0.338)?×?acid detergent fiber intake (kg/day), [RMSPE?=?22.2 %, with 99.6 % of MSPE from random error; R ²?=?0.84]. Among the nonlinear equations developed, Mitscherlich model, i.e., methane (MJ/day)?=?71.47_(±22.14.6)?×?(1 - exp{?0.0156_(±0.0051)?×?DMI (kg/day), [RMSPE?=?30.3 %, with 97.6 % of RMSPE from random error; R ²?=?0.83] performed better than simple linear and other nonlinear models, but the predictability and goodness of fits of the equation did not improve compared with the multiple regression models. Extant equations overestimated EME, and many extant models had low accuracy and precision. The equations developed in this study will be useful for improved estimates of national methane inventory preparation and for a better understanding of dietary factors influencing EME for tropical cattle feeding systems.     

秦岭太白红杉林土壤有机碳密度研究

土壤有机碳(Soil Organic Carbon,SOC)库是陆地生态系统中最大的碳库,确定土壤有机碳储量及影响因子对碳循环和气候变化的研究具有重要意义.在秦岭太白山南、北坡分别沿不同海拔梯度共调查了太白红杉(Larix chinensis Beissn)林的18个样点,共计54个土壤剖面,分南、北坡对太白红杉林土壤有机碳密度进行了估算,并分析了土壤有机碳的主要影响因子.结果表明:太白红杉林北坡土壤有机碳平均密度在枯落物层为(0.31±0.18)kg/m2,在0～100 cm土层为(15.84±9.08)kg/m2;南坡土壤有机碳平均密度在枯落物层为(0.27±0.07)kg/m2,在0～100 cm土层为(14.51±7.85)kg/m2;太白红杉林南、北坡0～100 cm土层土壤有机碳平均密度为(15.18±8.51)kg/m2.秦岭太白红杉林北坡0～100 cm土层土壤有机碳密度随海拔的增加呈显著减小趋势(P0.05),此外,该层土壤有机碳密度随年降水量的增加呈下降趋势.土壤容重与w(有机碳)呈显著负相关(P0.05).     

Interactive effects of water and controlled release urea on nitrogen metabolism,accumulation, translocation,and yield in summer maize

To investigate the interactive effects of water and N from controlled release urea (CRU) on N metabolism, accumulation, translocation, and yield in Zhengdan958 (a summer maize cultivar planted widely in China), three water levels (adequate water W3, mild water stress W2, severe water stress W1) and four amounts of CRU (N) (N0, N1, N2, and N3 were 0, 105, 210, and 315 kg N ha^?1, respectively) were carried out under the waterproof shed and soil column conditions. The results showed that yield, N metabolism, accumulation, and translocation were significantly affected by water, CRU, and their interactions after tasseling. Yields showed an increasing trend in response to N rates from 100.2 to 128.8 g plant^?1 under severe water stress (W1), from 124.7 to 174.6 g plant^?1 under mild water stress (W2), and from 143.7 to 177.0 g plant^?1 under adequate water conditions (W3). There was an associated optimum amount of N for each water level. Under W1 and W2, N3 treatments showed significant advantages in three N metabolism enzymes’ activities and the N accumulations, and yield and its components were highest. But the nitrogen harvest index (NHI) of N3 had no significant difference with other nitrogen treatments. Under W3, the N translocation efficiency (NTE) and N translocation conversion rate (NTCR) of N2 in stem and leaf were higher than those of N3, but the N metabolism enzymes’ activities and yields of N2 and N3 had no significant difference, which indicated that N2 was superior to N3. The N3 treatment under W2 and N2 under W3 increased the N accumulation capacity in maize grain as well as the N translocation to grain that contributed to the increase of 1000-gain weight and grains per ear after tasseling. Under this experimental condition, a CRU rate of 225 kg ha^?1 was the best treatment when the soil moisture content was 75 ± 5% of field capacity, but an N rate of 300 kg ha^?1 was superior when soil moisture content was maintained at 55 ± 5% of field capacity during the entire growing season.     

Is CO2 flux from oil palm plantations on peatland controlled by soil moisture and/or soil and air temperatures?

Measurements of carbon dioxide (CO₂) flux at the soil surface of oil palm (Elaeis guineensis Jacq.) plantations on peatlands typically exhibit considerable temporal and spatial variation, which challenges the derivation of emission factors required in land use discussions. We tested 20 cm surface soil moisture content, and the diurnal patterns in soil and air temperatures as CO₂ flux controls during an annual measurement schedule in a 15-year-old oil palm plantation in Jambi Province, Sumatra, Indonesia. A total of 480 CO₂ flux measurements were obtained using an Infrared Gas Analyser (IRGA) at six different time intervals each day. Samples were recorded at 20 observation points distributed along four transects located 15, 42, 50, 70, and 84 m from the edge of the drainage canal. Results showed CO₂ flux exhibited no relationship to soil and air temperature, however values tended to increase with volumetric soil moisture content; the highest annual flux of 55 Mg ha^?1 yr^?1 was observed at mid-day, when air temperature was highest, and lowest at dawn when soil and air temperatures were lowest. CO₂ flux decreased consistent with distance from the drainage canal, suggesting a higher flux with a deeper water table. This result indicates a shallow water table must be maintained. The annual mean CO₂ flux of 46?±?30 Mg CO₂ ha^?1 yr^?1 was comparable to other studies, and can be set as a baseline emissions factor for areas with similar land use and peat characteristics.     

Linking spatio-temporal variation of crop response with sediment deposition along paddy rice terraces

In tropical mountainous regions of South East Asia, intensive cultivation of annual crops on steep slopes makes the area prone to erosion resulting in decreasing soil fertility. Sediment deposition in the valleys, however, can enhance soil fertility, depending on the quality of the sediments, and influence crop productivity. The aim of the study was to assess (i) the spatio-temporal variation in grain yield along two rice terrace cascades in the uplands of northern Viet Nam, (ii) possible linkage of sediment deposition with the observed variation in grain yield, and (iii) whether spatial variation in soil water or nitrogen availability influenced the obtained yields masking the effect of inherent soil fertility using carbon isotope (¹³C) discrimination and ¹⁵N natural abundance techniques. In order to evaluate the impact of seasonal conditions, fertilizer use and sediment quality on rice performance, ¹⁵N and ¹³C stable isotope compositions of rice leaves and grains taken after harvest were examined and combined with soil fertility information and rice performance using multivariate statistics. The observed grain yields for the non-fertilized fields, averaged over both cascades, accounted for 4.0 ± 1.4 Mg ha^?1 and 6.6 ± 2.5 Mg ha^?1 in the spring and summer crop, respectively, while for the fertilized fields, grain yields of 6.5 ± 2.1 Mg ha^?1 and 6.9 ± 2.1 Mg ha^?1 were obtained. In general, the spatial variation of rice grain yield was strongly and significantly linked to sediment induced soil fertility and textural changes, such as soil organic carbon (r 0.34/0.77 for Cascades 1 and 2, respectively) and sand fraction (r ?0.88/?0.34). However, the observed seasonal alteration in topsoil quality, due to sediment deposition over two cropping cycles, was not sufficient to fully account for spatial variability in rice productivity. Spatial variability in soil water availability, assessed through ¹³C discrimination, was mainly present in the spring crop and was linearly related to the distance from the irrigation channel, and overshadowed in Cascade 2 the expected yield trends based on sediment deposition. Although δ¹⁵N signatures in plants indicated sufficient N uptake, grain yields were not found to be always significantly influenced by fertilizer application. These results showed the importance of integrating sediment enrichment in paddy fields within soil fertility analysis. Furthermore, where the effect of inherent soil fertility on rice productivity is masked by soil water or nitrogen availability, the use of ¹³C and ¹⁵N stable isotopes and its integration with conventional techniques showed potential to enhance the understanding of the influence of erosion – sedimentation and nutrient fluxes on crop productivity, at toposequence level.     

Are soils of Iowa USA currently a carbon sink or source? Simulated changes in SOC stock from 1972 to 2007

Upscaling the spatial and temporal changes in carbon (C) stocks and fluxes from sites to regions is a critical and challenging step toward improving our understanding of the dynamics of C sources and sinks over large areas. This study simulated soil organic C (SOC) dynamics within 0–100 cm depth of soils across the state of Iowa in the USA from 1972 to 2007 using the General Ensemble biogeochemical Modeling System (GEMS). The model outputs with variation coefficient were analyzed and assembled from simulation unit to the state scale based upon major land use types at annual step. Results from this study indicate that soils (within a depth of 0–100 cm) in Iowa had been a SOC source at a rate of 190 ± 380 kg C ha^?1 yr^?1. This was likely caused by the installation of a massive drainage system which led to the release of SOC from deep soil layers previously protected under poor drainage conditions. The annual crop rotation was another major force driving SOC variation and resulted in spatial variability of annual budgets in all croplands. Annual rate of change of SOC stocks in all land types depended significantly on the baseline SOC levels; soils with higher SOC levels tended to be C sources, and those with lower levels tended to be C sinks. Management practices (e.g., conservation tillage and residue management practices) slowed down the C emissions from Iowa soils, but could not reverse the general trend of net SOC loss in view of the entire state due mainly to a high level of baseline SOC stocks.     

Optimising yield and resource utilisation of summer maize under the conditions of increasing density and reducing nitrogen fertilization

The inefficient use of resources always poses risks of maize (Zea mays L.) yield reduction in China. We performed this research to monitor the effects of increasing plant density and reducing nitrogen (N) rate on radiation-use efficiency (RUE), N efficiency traits, grain yield (GY) and their inter-relationships. Besides, whether GY and resource-use efficiency can both be maximized was examined. Hence, a 2-year field experiment was conducted using a widely grown variety “Denghai 618” in Shandong, China. Treatments contained two different plant densities [67,500 (D₁) and 97,500 (D₂) plant ha^?1] and three N levels [0 (N_?2), 180 (N_?1), 360 (N_ck) kg ha^?1], set D₁N_ck as control. Significant increases in grain yield, biomass, RUE, above-ground N uptake (AGN) and N efficiency were observed when density increased from D₁ to D₂. Declining N application was accompanied by reductions in yield, RUE and AGN especially under high density, yet an obvious improvement in N recovery efficiency (NRE), agronomic N efficiency and N partial factor productivity. The increased GY was positive related with population biomass (r = 0.895**), RUE (r = 0.769**) and AGN (r = 0.923**), whereas it has no significant correlation with N efficiency. In this study, D₂N_ck obtained 18.8, 17.9, 24.8 and 29.7% higher grain yield, RUE, AGN and NRE respectively, compared to control, optimizing both yield and the efficiencies of radiation and N use. Furthermore, higher yield and RUE with more desirable N efficiency may be possible via optimizing density and N rate combination.