Developmental patterns of lamellae and stroma fractions of chloroplasts in rice plants

On examining the changes in lamellae and stroma nitrogen during leaf development, it is demonstrated that the lamellae and stroma fractions ofrice chloroplasts develop in quite different ways. In the case of stroma, the stroma materials existing in the leaf section which has just emerged from a leaf sheath are quite limited and the major part of this fraction is derived from the successive protein synthesis, i.e., the synthesis of this fraction was markedly increased during leaf expansion. This developmental pattern of the stroma coincided with the changes in the high-molecular-weight water soluble leaf protein, which seemed to be mainly composed of Fraction I protein. A rapid increase in stroma nitrogen was found to be a major cause for an increase in the leaf nitrogen content during leaf development.

On the other hand, the developmental pattern of the lamellae fraction was characterized by the fact that a considerable amount of this fraction had already been prepared when a leaf emerged from a leaf sheath and thereafter, no outstanding increase was seen compared to that of the stroma. This developmental pattern of the lamellae fraction resulted in a lowering of the proportion of lamellae nitrogen to the total leaf nitrogen during leaf development.

A great change in the lamellae-stroma composition of chloroplasts was observed. The proportion of stroma nitrogen to the total chloroplast nitrogen tended to increase as a leaf develops. Since the developmental stage varied according to the regions of a leaf, variation of the lamellaestroma composition was seen even within a leaf, i.e., the proportion of stroma nitrogen increased from base to tip.

In order to compare the synthetic rate of chlorophyll with those of the stroma and lamellae fractions, the changes in the ratios of stroma nitrogen/chlorophyll and lamellae nitrogen/chlorophyll were examined. The lamellae nitrogen/chlorophyll ratio decreased as a leaf developed, whereas the stroma nitrogen/chlorophyll ratio increased. Then the synthetic rates of these fractions during leaf development turned out to be of the same order as the stroma fraction, chlorophyll, lamellae fraction.     

Nitrogen rhizodeposition of young wheat plants under elevated CO<Subscript>2</Subscript> and drought stress

The objective of this study was to determine the effect of drought stress and elevated CO₂ concentrations around the shoots on N rhizodeposition of young wheat plants. In a pot experiment, the plant N pool was labeled through ¹⁵NH₃ application to shoots at nontoxic NH₃ concentrations, and the impact of low water supply (40% field capacity), elevated CO₂ (720 μmol mol⁻¹ CO₂), and the combination of both factors on the ¹⁵N distribution was studied. Total ¹⁵N rhizodeposition ranged from 5 to 11% of the total ¹⁵N recovered in the plant/soil system. Elevated CO₂ concentration as well as drought stress increased the belowground transport of N and increased the relative portion of N rhizodeposition on total ¹⁵N in the plant/soil system. However, while the increased N rhizodeposition with elevated CO₂ was the result of increased total belowground N transport, drought stress additionally increased the portion of ¹⁵N found in rhizodeposition vs roots. Elevated CO₂ intensified the effect of drought stress. The percentage of water soluble ¹⁵N in the ¹⁵N rhizodeposition was very low under all treatments, and it was significantly decreased by the drought-stressed treatments.     

Influence of Selenium on Cadmium Toxicity in Cucumber (Cucumis sativus cv. 4200) at an Early Growth Stage in a Hydroponic System

An experiment was established to assess the ability of selenium (Se) to reduce cadmium (Cd) toxicity when tomato was grown hydroponically. A factorial experiment was arranged in a completely randomized design with six replicates in cucumber (Cucumis sativus cv. 4200). The Se was applied at four levels [0 mg L^–1 (Se0), 2 mg L^–1 Se (Se1), 4 mg L^–1 Se (Se2), and 6 mg L^–1 Se (Se3)], whereas Cd was applied at three levels [0 µM Cd (Cd0), 5 µM Cd (Cd1), and 7 µM Cd (Cd2)]. The Se improved the dry weight of roots even when plants were exposed to Cd. Treatment Se1 improved the dry weight of shoots in Cd1 and Cd2. Treatments Se1 and Se2 improved photosynthesis in Cd1. Treatment Se1 significantly improved stomatal conductance in Cd2 at all levels of Se relative to Cd2. The greatest Cd concentration in leaves was observed in Cd2 × Se0 and while Se concentration in solution increased in response to Se1, Se2, and Se3. The greatest Se level reduced Cd uptake the most. Growth and photosynthetic attributes can be negatively affected by Cd, but Se has the ability to buffer, or improve, several attributes.     

Influence of temperature and drought on seasonal and interannual variations of soil, bole and ecosystem respiration in a boreal aspen stand

Continuous half-hourly measurements of soil (R_s) and bole respiration (R_b), as well as whole-ecosystem CO₂ exchange, were made with a non steady-state automated chamber system and with the eddy covariance (EC) technique, respectively, in a mature trembling aspen stand between January 2001 and December 2003. Our main objective was to investigate the influence of long-term variations of environmental and biological variables on component-specific and whole-ecosystem respiration (R_e) processes. During the study period, the stand was exposed to severe drought conditions that affected much of the western plains of North America. Over the 3 years, daily mean R_s varied from a minimum of 0.1 μmol m⁻² s⁻¹ during winter to a maximum of 9.2 μmol m⁻² s⁻¹ in mid-summer. Seasonal variations of R_s were highly correlated with variations of soil temperature (T_s) and water content (θ) in the surface soil layers. Both variables explained 96, 95 and 90% of the variance in daily mean R_s from 2001 to 2003. Aspen daily mean R_b varied from negligible during winter to a maximum of 2.5 μmol m⁻² bark s⁻¹ (2.2 μmol m⁻² ground s⁻¹) during the growing season. Maximum R_b occurred at the end of the aspen radial growth increment and leaf emergence period during each year. This was 2 months before the peak in bole temperature (T_b) in 2001 and 2003. Nonetheless, R_b was highly correlated with T_b and this variable explained 77, 87 and 62% of the variance in R_b in the respective years. Partitioning of R_b between its maintenance (R_bm) and growth (R_bg) components using the mature tissue method showed that daily mean R_bg occurred at the same time as aspen radial growth increment during each growing season. This method led, however, to systematic over- and underestimations of R_bm and R_bg, respectively, during each year. Annual totals of R_s, R_b and estimated foliage respiration (R_f) from hazelnut and aspen trees were, on average, 829, 159 and 202 g C m⁻² year⁻¹, respectively, over the 3 years. These totals corresponded to 70, 14 and 16%, respectively, of scaled-up respiration estimates of R_e from chamber measurements. Scaled R_e estimates were 25% higher (1190 g C m⁻² year⁻¹) than the annual totals of R_e obtained from EC (949 g C m⁻² year⁻¹). The independent effects of temperature and drought on annual totals of R_e and its components were difficult to separate because the two variables co-varied during the 3 years. However, recalculation of annual totals of R_s to remove the limitations imposed by low θ, suggests that drought played a more important role than temperature in explaining interannual variations of R_s and R_e.     

多重情景下半干旱地区人工杨树林光合生理特征

深刻剖析多重情景下主要防风固沙树种的光合生理特征,对半干旱地区生态系统的健康维持与恢复重建具有重要的指导意义。以半干旱典型区科尔沁沙地人工杨树为研究对象,采用Li-6400红外气体分析仪活体测量生长季不同月份、嫩叶与成熟叶、上午与下午以及不同CO2浓度和光强下杨树叶片的光响应和CO2响应曲线,进一步对比分析这些情景下净光合速率(Pn)、蒸腾速率(Tr)和水分利用率(WUE)的差异性。结果表明:在相同光强和CO2浓度下,生长旺盛期杨树叶片的Pn高于生长初期和生长末期;嫩叶与成熟叶的Pn、Tr、WUE差异明显,嫩叶的蒸腾作用相对较强,成熟叶的光合作用相对较强。研究结果对开展半干旱地区人工杨树光合生理相关研究具有一定的参考价值。     

Silicon modulates the activity of antioxidant enzymes and nitrogen compounds in sunflower plants under salt stress

Sunflower (Helianthus annuus L.) is an important oilseed crop with clear sensibility to salt stress. In this study, we evaluated silicon (Si) effect on the nitrogen metabolism and antioxidant enzyme activity in sunflower plants subjected to salinity. A 4 × 4 factorial arrangement of treatments in a completely randomized design with four replicates was used, consisting of four concentrations of Si (0.0; 1.0; 1.5; and 2.0 mM) and four concentrations of NaCl (0; 50; 100; and 150 mM) in the nutrient solution. The salinity reduced the nitrate content, but the increasing Si concentration in the medium improved the nitrate uptake, leading this ion to accumulate in salt-stressed plants, particularly in the roots. The nitrate reductase activity and the proline and soluble N-amino contents were also significantly increased by Si in salt conditions. The salinity increased electrolyte leakage and reduced the activity of enzymes superoxide dismutase, ascorbate peroxidase and catalase in sunflower plants, but these decreases were reversed by Si at 2 mM, thus alleviating the effects of salinity on these variables. We conclude that Si is able to positively modulate nitrogen metabolism and antioxidant enzyme activities in sunflower plants in order to alleviate the harmful effects of salinity.     

Modulation in growth,development, and yield of Camelina sativa by nitrogen application under water stress conditions

Camelina sativa has rejuvenated as a successful oilseed crop in the recent years. It is a low-input-requiring crop with an unusual fatty acid composition. A pot experiment was conducted in rain-out shelter to investigate the effect of different nitrogen levels (N₀ = 0, N₁ = 50, N₂ = 100, and N₃ = 150 kg ha^?1) on the growth and yield of two C. sativa genotypes (Australian and Canadian) under normal [100% field capacity (FC)] and water stressed (60% FC) conditions. The experiment was laid out in a completely randomized design with factorial arrangement having three replicates in the Department of Crop Physiology, University of Agriculture, Faisalabad. The results indicated that nitrogen doses and water stress levels significantly affected the growth and yield of C. sativa. Maximum values for growth indices like leaf area index (LAI), crop growth rate (CGR), leaf area duration (LAD), net assimilation rate (NAR), and yield attributes were observed under N₂ treatment (100 kg ha^?1) followed by the treatment in which nitrogen was applied at the rate of 50 kg ha^?1. However, growth and yield components significantly reduced under water stress conditions (60% FC). Of both the genotypes, Australian Camelina performed better as compared to Canadian Camelina under both non-stress and drought stress conditions.     

Elevated CO2 increases the effect of an arbuscular mycorrhizal fungus and a plant-growth-promoting rhizobacterium on structural stability of a semiarid agricultural soil under drought conditions

In arid and semiarid Mediterranean regions, an increase in the severity of drought events could be caused by rising atmospheric CO₂ concentrations. We studied the effects of the interaction of CO₂, water supply and inoculation with a plant-growth-promoting rhizobacterium (PGPR), Pseudomonas mendocina Palleroni, or inoculation with an arbuscular mycorrhizal (AM) fungus, Glomus intraradices (Schenk & Smith), on aggregate stabilisation of the rhizosphere soil of Lactuca sativa L. cv. Tafalla. The influence of such structural improvements on the growth of lettuce was evaluated. We hypothesised that elevated atmospheric CO₂ concentration would increase the beneficial effects of inoculation with a PGPR or an AM fungus on the aggregate stability of the rhizosphere soil of lettuce plants. Leaf hydration, shoot dry biomass and mycorrhizal colonisation were decreased significantly under water-stress conditions, but this decrease was more pronounced under ambient vs elevated CO₂. The root biomass decreased under elevated CO₂ but only in non-stressed plants. Under elevated CO₂, the microbial biomass C of the rhizosphere of the G. intraradices-colonised plants increased with water stress. Bacterial and mycorrhizal inoculation and CO₂ had no significant effect on the easily-extractable glomalin concentration. Plants grown under elevated CO₂ had a significantly higher percentage of stable aggregates under drought stress than under well-watered conditions, particularly the plants inoculated with either of the assayed microbial inocula (about 20% higher than the control soil). We conclude that the contribution of mycorrhizal fungi and PGPR to soil aggregate stability under elevated atmospheric CO₂ is largely enhanced by soil drying.     

Effects of co-overproduction of sedoheptulose-1,7-bisphosphatase and Rubisco on photosynthesis in rice

Overproduction of Rubisco did not proportionately increase the rate of CO₂ assimilation (A) in rice probably because the capacity of regeneration of the substrate of Rubisco, ribulose-1,5-bisphosphate (RuBP), could not afford the increased Rubisco capacity. Since sedoheptulose-1,7-bisphosphatase (SBPase) is thought to be one of the limiting factors of RuBP regeneration capacity, SBPase and Rubisco were co-overproduced in rice in order to improve photosynthesis. Although SBPase and Rubisco contents increased by 82–102% and 20–30%, respectively, A did not increase under the conditions of high irradiance and different [CO₂] partial pressures. Thus, co-overproduction of SBPase and Rubisco did not improve photosynthesis in rice. Overproduction and antisense suppression of SBPase did not greatly affect A at high [CO₂], although it is thought to be determined by RuBP regeneration capacity. These results strongly suggest that SBPase does not determine RuBP regeneration capacity in rice. This is likely to be the reason for the unimproved photosynthesis by co-overproduction of SBPase and Rubisco.     

Greenhouse gas emissions in response to straw incorporation,water management and their interaction in a paddy field in subtropical central China

A field experiment was conducted to study the effects of combination of straw incorporation and water management on fluxes of CH₄, N₂O and soil heterotrophic respiration (Rh) in a paddy field in subtropical central China by using a static opaque chamber/gas chromatography method. Four treatments were set up: two rice straw incorporation rates at 0 (S1) and 6 (S2) t ha^?1 combined with two water managements of intermittent irrigation (W1, with mid-season drainage) and continuous flooding (W2, without mid-season drainage). The cumulative seasonal CH₄ emissions for the treatments of S1W2, S2W1 and S2W2 increased significantly by 1.84, 5.47 and 6.63 times, respectively, while seasonal N₂O emissions decreased by 0.67, 0.29 and 1.21 times, respectively, as compared to S1W1 treatment. The significant increase in the cumulative Rh for the treatments S1W1, S2W1 and S2W2 were 0.54, 1.35 and 0.52 times, respectively, in comparison with S1W2. On a seasonal basis, both the CO₂-equivalents (CO₂e) and yield-scaled CO₂e (GHGI) of CH₄ and N₂O emissions increased with straw incorporation and continuous flooding, following the order: S2W2>S2W1>S1W2>S1W1. Thus, the practices of in season straw incorporation should be discouraged, while mid-season drainage is recommended in paddy rice production from a point view of reducing greenhouse gas emissions.     

Effects of plants on net mineralization of nitrogen in forest soil microcosms

Summary The effects of plant roots on net N mineralization were examined by comparing soil microcosms with and without plants. Additionally, inorganic N amendments were used to test for competition for N between plants and microorganisms. Daily watering and the application of suction to microcosms eliminated the effects of transpiration on soil moisture content. Monthly litter collections reduced the influence of the aboveground portions of plants. Plants decreased net N mineralization by 23% during days 0–114 and then increased net mineralization by the same amount during days 144–124. Root-free soil collected from with-plant microcosms on day 244 evolved 24% more CO₂ in laboratory incubations than soil from without-plant microcosms. This indicates that plants had increased substrate availability to soil microorganisms. Inorganic N amendments had no significant effects on the microcosms or on laboratory soil incubations. Evidence is most consistent with the hypothesis that plant roots increased microbial activity due to the increased substrate availability. Different net N mineralization rates probably resulted from changes in the substrate C : N ratio.     

Enchytraeids in a changing climate: A mini-review

The climate is undergoing rapid changes with rising atmospheric CO₂ concentration, increasing temperatures and changes in the hydrological regimes resulting in more frequent and intense drought periods. These three climate change factors will, separately and in combination, affect the biotic and abiotic components of soil communities. This paper reviews the impact of climate change on field communities of enchytraeids with special emphasis on Cognettia sphagnetorum because most relevant studies have involved this species. C. sphagnetorum prefers cold and wet environments and several studies suggest that reductions of soil moisture may have dramatic consequences for C. sphagnetorum and other enchytraeid species. Effects of changing temperatures are less clear partly because thermal conditions influence soil moisture, which complicate the predictions of the outcome from such changes. The predicted increasing annual mean temperature may be stimulating and expand the season for growth and reproduction of enchytraeids; on the other hand, an increased frequency of extreme weather events, with heat waves during summer and bare soil freezes during autumn and spring, may occasionally cause severe mortality. Stimulating effects of increased atmospheric CO₂ have been observed, perhaps due to increased food availability via root and litter production. However, effects of CO₂ are also influenced by moisture and temperature. Generally, there is a lack of research looking into the complicated interactions between various climate change factors, and little is known about the potential of enchytraeids to adapt to a changing climate. Existing data suggest that C. sphagnetorum is not capable of adapting to a drier climate, thus, a decline in abundance and distribution of this species is possible. Since enchytraeids are of ecological significance in some types of habitats, a reduction may result in serious disruption in the functioning of these decomposer communities.     

Nitrate accumulation,productivity and photosynthesis of Brassica alboglabra grown under low light with supplemental LED lighting in the tropical greenhouse

Abstract

Vegetables are a large source of nitrate (NO₃^?) in our diet. As NO₂^? is toxic to humans, it is undesirable to consume vegetables with high NO₃^? content. Therefore, this study aimed to investigate the effect of supplementing of red- and blue-LED lighting to B. alboglabra grown in the tropical greenhouse in terms of moderating NO₃^? accumulation, improving photosynthesis, and enhancing productivity. All plants were grown hydroponically in full nutrients under prevailing greenhouse conditions for 20?days (full sunlight). Thereafter, plants were subjected to three different light treatments for 12?days: full sunlight, shade, and shade supplemented with LEDs. The average midday photosynthetic photon flux density (PPFD) during the light treatment periods were 220?μmol m^?2 s^?1 (full sunlight), 55?μmol m^?2 s^?1 (shade), and 220?μmol m^?2 s^?1 (shade supplemented with LEDs). Shoot nitrate (NO₃^?) concentration increased significantly in plants grown in the shade. However, shoot NO₃^? concentration was reduced when plants were supplemented with red- and blue-LED lighting. Photosynthetic CO₂ assimilation, stomatal conductance, and productivity also improved in these plants. Our results suggest that supplemental red- and blue-LED lighting in a tropical greenhouse during periods of cloudy and hazy weather could improve productivity and nutrient quality of Chinese broccoli.     

Photosynthesis and Leaf Area of Brachiaria brizantha in Response to Phosphorus and Zinc Nutrition

Phosphorus (P) and zinc (Zn) are important determinants of plant productivity, particularly in the tropical grasslands of Brazil. Nutrient deficiency is one of the most important factors limiting plant productivity, decreasing photosynthesis efficiency and plant development. The present study investigates in Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. ‘Marandu’: 1) the gas exchange measurements; 2) the total leaf area development; and 3) the dry matter production due to P and Zn nutrition. Plants of B. brizantha cv. ‘Marandu’ were grown in nutrient solution under five rates of P (0.1, 0.6, 1.1, 1.6, and 2.1 mmol L^?1) and five rates of Zn (0.00, 0.75, 1.5, 2.25, and 3.00 μmol L^?1), in a fractioned factorial. Plants were harvested two times. Phosphorus supply increased carbon dioxide (CO₂) assimilation and stomatal conductance, and decreased intercellular CO₂. The interaction P rates x Zn rates were significant for the total leaf area variables and shoot dry matter in the second growth period. The nutrition of P and Zn interfered in the B. brizantha productivity by changing the grass photosynthesis and leaf area.     

CO2 fluxes and drivers as affected by soil type,tillage and fertilization

Abstract

Importance of agricultural practices for greenhouse gases mitigation is examined worldwide. However, there is no consensus on CO₂ emissions as affected by soil management practices. Deeper understanding of soil CO₂ fluxes and drivers under different management practices are needed. The investigation of net CO₂ exchange rate as dependent variable and drivers (soil water and temperature, air temperature) as affected by soil type (loam and sandy loam), tillage (conservation and no-tillage) and fertilization are presented.

Soil management practices and weather conditions affected the CO₂ flux through effects on soil water and temperature regime. Mean net CO₂ exchange rate on sandy loam was 8% higher than on loam. No-tillage, as a moisture-conserving tool, could be an appropriate tool for CO₂ emissions mitigation in any weather conditions on sandy loam; however, the advantage of no-tillage on loam was negligible. Mineral NPK fertilizers promoted significantly higher net CO₂ exchange rate in both soils, but suppressed it by 15% on sandy loam during a normal year. Effect of soil water content on net CO₂ exchange rate was direct in all tillage and fertilization treatments in both loam and sandy loam, whereas this effect was positive only in dry and normal weather conditions. In wet weather conditions, the direct effect of soil water content on net CO₂ exchange rate was negative. Soil and air temperature acted indirectly on net CO₂ exchange rate. The increase in temperature markedly suppressed the positive direct impact of soil water content on net CO₂ exchange rate in dry weather conditions, but did not reduce the direct effect of soil water content in normal weather conditions. In a wet year the negative indirect effect of increased temperature enhanced the negative direct impact of soil water surplus on net CO₂ exchange rate.     

Denitrification potential in a grassland subsoil: effect of carbon substrates

We examined the potential of a subsoil to denitrify nitrate under optimal anaerobic conditions in a laboratory-based incubation when supplied with a range of C substrates of increasing recalcitrance. Both topsoil and its associated subsoil were supplied with nitrate and either glucose, starch or cellulose. Microbial respiration and the evolution of N₂O and N₂ were measured. The subsoil supported low amounts of microbial activity and responded only to the glucose treatment; with less than one-fifth of the N₂O production measured in the top soil. Overall, our findings demonstrated that the denitrification potential of this particular subsoil is relatively low and that only simple carbohydrates could be utilised readily by the resident microorganisms.     

Elevated CO2 concentrations increase leaf nitrate reduction by strengthening sink activity in soybean plants

An experiment was conducted to examine the effect of CO₂ enrichment on the nitrate uptake, nitrate reduction activity, and translocation of assimilated-N from leaves at varying levels of nitrogen nutrition in soybean using ¹⁵N tracer technique. CO₂ enrichment significantly increased the plant biomass, apparent leaf photosynthesis, sugar and starch contents of leaves, and reduced-N contents of the plant organs only when the plants were grown at high levels of nitrogen. A high supply of nitrogen enhanced plant growth and increased the reduced-N content of the plant organs, but its effect on the carbohydrate contents and photosynthetic rate were not significant. However, the combination of high CO₂ and high nitrogen levels led to an additive effect on all these parameters. The nitrate reductase activity increased temporarily for a short period of time by CO₂ enrichment and high nitrogen levels. ¹⁵N tracer studies indicated that the increase in the amount of reduced-N by CO₂ enrichment was derived from nitrate-N and not from fixed-N of the plant. To examine the translocation of reduced-N from the leaf in more detail, another experiment was conducted by feeding the plants with ¹⁵NO₃-N through a terminal leaflet of an upper trifoliated leaf under depodding and/or CO₂ enrichment conditions. The export rate of ¹⁵N from the terminal leaflet to other plant parts decreased by depodding, but it increased by CO₂ enrichment. CO₂ enrichment increased the percentage of plant ¹⁵N in the stem and / or pods. Depodding increased the percentage of plant ¹⁵N in the leaf and stem. The results suggested that the increase in the leaf nitrate reduction activity by CO₂ enrichment was due to the increase of the translocation of reduced-N from leaves through the strengthening of the sink activity of pods and / or stem for reduced-N.     

The counteracting effects of elevated atmospheric CO2 concentrations and drought episodes: Studies of enchytraeid communities in a dry heathland

The potential impacts of interactions of multiple climate change factors in soil ecosystems have received little attention. Most studies have addressed effects of single factors such as increased temperature or atmospheric CO₂ but little is known about how such environmental factors will interact. In the present study we investigate the effects of in situ exposure to elevated atmospheric CO₂ concentration, increased temperatures and prolonged drought episodes on field communities of Enchytraeidae (Oligochaeta) in a dry heathland (Brandbjerg, Denmark). Increased CO₂ had a positive effect on enchytraeid biomass, whereas drought significantly reduced it. Elevated temperature did not result in any detectable effects. No interactions between the three factors were observed. Interestingly, the positive effect of increased CO₂ and the negative effect of drought were cancelled out when applied in combination. Thus, in the combined drought and CO₂ treatment, and when additionally combined with increased temperature, the total biomass of enchytraeids was similar to those in the ambient plots. The positive effect of increased CO₂ seemed to be influenced by season, as the response was most pronounced during summer, and less so in autumn. The impact of the drought was more consistent, with enchytraeids reduced at all sampling occasions. Moreover, the negative effect of drought seemed to depend on the inter-annual variability of precipitation. The year with a dry summer and autumn (2006) showed a stronger impact of drought on the enchytraeids, compared to the year with a wet summer and autumn (2007). Our study emphasises the importance of multi-factorial experimental design as a means to investigate effects of climatic changes.     

Influence of water depth and soil amelioration on greenhouse gas emissions from peat soil columns

Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO₂ emissions. No significant difference was observed in the CH₄ emissions in response to water depth and amelioration. The ameliorations influenced the CO₂ and N₂O emissions from the peat soil. The application of biochar+compost enhanced the CO₂ and N₂O emissions but reduced the CH₄ emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO₂ and N₂O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO₂, CH₄ and N₂O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.