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1.
Effects of enhanced nitrogen deposition on nutrient foliar concentrations and net photosynthesis of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh) and red spruce (Picea rubens Sarg.) were evaluated at the Bear Brook Watershed in Maine (BBWM). The BBWM is a paired-watershed forest ecosystem study with one watershed treated since 1989 with bimonthly dry ammonium sulfate ((NH4)2SO4) additions at a rate of 25.2 kg N ha−1 year−1, while the other watershed serves as a reference. The (NH4)2SO4 treatment resulted in significant increases in foliar N concentrations for all three species and significant reductions in foliar Ca, Mg and Zn concentrations for American beech and red spruce. Treatment effects on foliar concentrations of other nutrients were not significant in any species. Despite higher N concentrations in all species, only treated sugar maple showed significantly higher photosynthetic rates. The non-response in net photosynthesis to higher foliar N in American beech and red spruce might be attributed to their low foliar Ca and/or Mg concentrations. Higher net photosynthetic rates in sugar maple might be explained by the higher foliar N and by the ability of this species to maintain an adequate Ca and Mg supply. Results suggested that nutrient imbalances due to inadequate supply of Ca and Mg might have counteracted a potential increase in net photosynthesis induced by higher N concentrations in American beech and red spruce.  相似文献   

2.
Above ground dry mass production and N accumulation on an areal basis in stems, branches and needles as well as in litterfall in a Norway spruce stand in south Sweden treated with unlimited availability of water and nutrients (fertilisation with irrigation) or of water (irrigation) during a 6 year experimental period are presented. Fertilisation was made in liquid form on a weekly basis during the vegetation period with 100 kg N ha−1 year−1 during each year. The fertiliser also included a balanced composition of P, K, Ca, Mg and S as well as of micronutrients. Irrigation was carried out as soon as a 20 mm water storage deficit developed. It is concluded that there is a large potential to improve Norway spruce production through liquid fertilisation with irrigation. Stem and branch production of Norway spruce was almost doubled due to this treatment. Also, stand needle dry mass and litterfall were markedly increased in comparison with the control. Water and N availability were the two most limiting growth factors. During the experimental period, irrigation had a greater effect on growth than N addition. The gross N uptake increased by 450 kg ha−1 as a result of 600 kg ha−1 fertiliser addition. Needle retention was increased for irrigated trees but needle litterfall remained unchanged. Changing the forest management of Norway spruce to intensive cultivatation results in transitional carbon sequestration in both stand and soil compared with an untreated ecosystem. The largest long-term environmental value is, however, achieved if this cultivated renewable biomass is used as a substitute for fossil fuels. Wood utilisation options of intensively cultivated Norway spruce are discussed.  相似文献   

3.
Rehabilitated forests established about 100 years ago on denuded lands in a hilly granitic area are widespread in the Kyoto–Osaka area, the second largest megalopolis in Japan. From 2001 to 2003, we monitored the annual nitrogen (N) budget of a rehabilitated forest watershed dominated by Quercus serrata and Ilex pedunculosa. The ion concentrations of bulk rain in the watershed were similar to those of other watersheds in Japan. The annual bulk rain input of N ranged from 5.1 to 6.3 kg N ha−1 year−1, and the N deposition from throughfall and stem-flow ranged from 7.5 to 8.2 kg N ha−1 year−1. Estimated annual outputs of N from the stream ranged from 3.3 to 10.6 kg N ha−1 year−1. These results indicate that the amount of N deposition in this area is less than that in urban Tokyo (>10 kg N ha−1 year−1), but the N output of the watershed is comparable with that of the Tokyo area. We discuss the characteristics of N dynamics in rehabilitated forests, focusing on the biogeochemical processes of this watershed.  相似文献   

4.
The effects of fertilizer treatment on nutrient transfers to the forest floor were examined in regrowth Eucalyptus diversicolor F. Muell. forest. Dry weight and nutrient content of leaf litterfall and total litterfall were measured for 3 years in a stand to which two levels of N (0, 200 kg ha-1 year-1) were applied each year at each of three levels of a single initial application of P (0, 30, 200 kg ha-1). Annual accessions of litter to the forest floor were significantly increased by additions of both N (by 17%, 18% and 21% in the 3 years) and 200 kg P ha-1 (by 8%, 8% and 4% in the 3 years) but there was no interaction between effects of N and P treatments. Fertilizer application also had a significant effect on the nutrient content of leaf litterfall and total litterfall. Concentration of N in leaf litterfall was 9% to 23% greater on plots treated with N fertilizer compared to untreated plots. The amounts of N in litterfall were about 30% greater on N-treated compared to untreated plots. On plots treated with 200 kg P ha-1, P concentrations in leaf litter were 50% to 100% greater than in litter from plots receiving no P. Application of 200 kg P ha-1 increased the amounts of P in annual litterfall by 32% to 87%. The greatest increase in P accessions occurred soon after fertilizer treatment. The amounts of Ca, K, and Na in litterfall were also significantly increased by fertilizer application. For Ca and K this was due partly to increases in element concentrations in litterfall following application of treatments. The effect of fertilizers on internal recycling of plant nutrients and on litter accumulation and nutrient dynamics in forest floor litter is discussed.  相似文献   

5.
Because both natural and anthropogenic disturbances affect biogeochemical cycles in forest ecosystems, monitoring is needed to separate their influences. Chronosequence is very useful for such studies. In our study area, plantation through forest rotation on a watershed basis resulted in more than 40 adjacent watersheds of between 0 and 87 years of stand age, kind of chronosequence. Here, we examined the biological similarity of the watersheds and the long-term effects of clear-cutting on stream water chemistry. The stream water NO3−–stand age relationship was similar between the two observation years; stream water NO3− concentrations increased dramatically in the watersheds after clear-cutting and decreased in 7–10-year-old replanted watersheds. The slope of stream water NO3− concentrations between the different watersheds covered by same age stand was significant, at 1:1. Additionally, stream water NO3− concentrations were more strongly correlated between the different watersheds covered by same aged stand than between the observations at 4 years intervals within a watershed. These findings indicate that stream water NO3− concentration is mainly regulated by stand age, i.e., by vegetation regrowth, rather than watershed-specific characteristics. Hence, adjacent watersheds are biologically similar apart from stand age and can be regarded as a chronosequence. While there was a clear relationship between stream water NO3− concentration and stand age, there was significant correlation with stream water SO42−, Ca2+, Mg2+, Cl− or Na+ between two observations in the same watershed. This indicates that watershed-specific characteristics, rather than vegetation regrowth, control stream SO42−, Ca2+, Mg2+, Cl−, and Na+ concentrations. After 25 years of clear-cutting Ca2+, Mg2+ and Na+ concentrations significantly increased. It is likely the contribution of forest floor accumulation with stand development. Based on these results, clear-cutting influences stream chemistry, not only NO3−, but also the major cation and the influence of clear-cutting continues for several decades at this study site.  相似文献   

6.
Wastewater bioremediation has been practised successfully in several forests without significant adverse effect on water quality of adjacent aquatic systems. However, long-term success of wastewater irrigation systems depends on an overall positive response of the forest ecosystem to substantial amounts of added water and nutrients over time. Municipal wastewater irrigation effects on the fate of added nitrogen in a mature Appalachian hardwood forest were investigated during the first 2 years of irrigation. Wastewater was secondarily treated, chlorinated, and sprayed on the study site at five rates. Forest litter N decreased on irrigated sites due to increased litter decomposition rates. Nitrogen mineralization potential (N0) decreased greatly in soils irrigated at a rate of 140 cm year−1 for 2 years. Net nitrification and relative nitrification (the amount of NO3−-N as a proportion of the total mineral N) increased proportionally with irrigation rate. The highest irrigation rates increased denitrification activity and contributed significantly to the bioremediation process by removing nitrate that otherwise would have been subject to leaching. The increase in NO3− production in the soil and limited N sequestration by the forest system nevertheless resulted in a net loss of N via leaching. Nitrate concentrations of soil water increased owing to irrigation, with the highest rate at 11 mg 1−1 on sites receiving 70 cm year−1. During the 2-year period, the forest ecosystem experienced a net leaching loss of N that ranged from 14.8 to 105 kg N ha−1 year−1, depending on the application rate. It is likely that this mature hardwood forest will continue to lose N, and that little or no additional N will be sequestered.  相似文献   

7.
The effects of wax myrtle (Myrica cerifera L.) on the nitrogen cycle were examined in a 23-year-old slash pine (Pinus elliottii Engelm. var. elliottii) plantation located near Gainesville, FL. These shrubs occurred naturally as an understory and had a crown cover of 8% of the study area. The potential rate of nitrogen fixation by wax myrtle was estimated to be 13 g N m?2 year?1, or 10.6 kg N ha?1 year?1 on a stand wide basis. Wax myrtle fixed substantial amounts of nitrogen throughout the year although winter rates were significantly less due to the greatly reduced activity of old nodules during that season. The average accumulation rate of nitrogen beneath wax myrtle was 1.5 g N m?2 year?1 in the soil and 0.9 g N m?2 year?1 in the forest floor. On a stand wide basis this amounted to an accretion of 1.9 kg N ha?1 year?1 in the soil and forest floor.  相似文献   

8.
During the period 1976–1991, a combined experiment of acidification, liming and nitrogen addition in a mature spruce stand was conducted at Farabol in south-east Sweden. The aim of this study was to investigate the effects of these treatments on the ground vegetation 0, 1, 5 and 15 years after experimental establishment. The treatment regimes were nitrogen (200 kg N ha−1, repeated three times at 4–5-year intervals, totally 600 kg N ha−1), sulphur powder (50 and 100 kg S ha−1 a−1, totally 600 and 1200 kg ha−1), sulphur plus nitrogen (600+600 kg ha−1) and limestone (500 kg ha−1 a−1, i.e. totally 6000 kg ha−1). The results showed that nitrogen addition and liming promoted the abundance of the grass Deschampsia flexuosa, while acidification had a negative effect on D. flexuosa and herbs in the field layer. There was a negative reaction giving immediate damage to the bryophytes in connection with additions of nitrogen, sulphur powder and lime. The magnitude of damage and the capacity to recover varied among species as well as among treatments. The recovery from immediate damage after liming was much faster than after the treatments with sulphur powder and/or nitrogen. A negative interaction between sulphur powder and nitrogen was found for herbs and mosses where the combined effects were stronger than the effects of a single treatment alone. Acidification also had a negative effect on the total number of species. The results of this study showed that acidification and nitrogen deposition could negatively influence forest vegetation by changing the nutrient availability in the soils. Liming led to an improved growth of the forest ground vegetation and the flora changed towards a more nitrophilic species composition.  相似文献   

9.
High elevation ecosystems are particularly sensitive to environmental change. Mountain agriculture is extending to areas at high elevations in Taiwan but the effects on nutrient cycling of the surrounding ecosystems are largely unknown. We examined precipitation chemistry at Piluchi Experimental Forest in central Taiwan to evaluate the contributions of local air pollution and long-range transport of air pollutants on nutrient cycling at this seemingly remote forest. Sea-salt aerosols and anthropogenic pollutants resulting from long-range transport of air pollutants and mountain agriculture activities are the key factors affecting precipitation chemistry at Piluchi Experimental Forest. Precipitation chemistry was dominated by ions of oceanic origin in the summer and by anthropogenic pollutants SO4 2−, NO3 − and NH4 + in the winter and spring, the northeast monsoon season. The much higher concentrations of S and N in the northeast monsoon season than the summer suggest a substantial contribution from long-range transport as the prevailing air masses moved from inland China and passed over the industrialized east coast of China before arriving in Taiwan. The very high concentration of NH4 + (22 μeq L−1) in the spring, when the local application of N-containing fertilizers was high, signifies the influences of mountain agriculture. Despite very low concentrations relative to other sites in Taiwan, annual input of NH4 + (3.6 kg ha−1 year−1), NO3 − (7.2 kg ha−1 year−1) and SO4 2− (10 kg ha−1 year−1) via precipitation was substantial suggesting that high elevation ecosystems of Taiwan are not free from the threat of atmospheric deposition of pollutants.  相似文献   

10.
Nitrogen biogeochemistry of 24 forested sites in Japan was used in evaluating the status of ‘nitrogen saturation’ for this region. Bulk deposition of inorganic N ranged from 3.5 to 10.5 kg N ha−1 yr−1 and losses in drainage waters ranged from 0.6 to 28 kg N ha−1 yr−1. Concentrations of NO3− in drainage waters during the growing season either remained fairly constant or increased during periods of high precipitation inputs. This pattern is markedly different than that exhibited for most forested watersheds in Europe and North America where during the growing season nitrate concentrations often reach their lowest values. These Japanese sites had high rates of N mineralization as a function of abundant moisture and warm temperatures. Nevertheless, most sites, except those with elevated atmospheric inputs of N, had high levels of nitrogen retention. The general absence of seasonal patterns of NO3− concentrations also suggests that this condition cannot be used to evaluate nitrogen saturation in Japanese forests as has been done for some watersheds in North America and Europe.  相似文献   

11.
To investigate the potential effects of nitrogen (N) deposition on Japanese forests, a chronic N-addition experiment that included three treatments (HNO3, NH4NO3, and control) was carried out in a 20-year-old Japanese cedar (Cryptomeria japonica D. Don) stand in eastern Japan over 7 years. The amount of N applied was 168 kg N ha−1 year−1 on the HNO3 plots and 336 kg N ha−1 year−1 on the NH4NO3 plots. Tree growth, current needle N concentration, and soil solution chemistry were measured. Nitrogen application decreased the pH and increased NO3 −, Ca2+, Mg2+, and Al concentrations in the soil solution. The needle N concentration increased in both of the N plots during the first 3 years. Nevertheless, the annual increments in height and in the diameter at breast height of the Japanese cedars were not affected by N application, and no visible signs of stress were detected in the crowns. Our results suggest that young Japanese cedar trees are not deleteriously affected by an excess N load.  相似文献   

12.
Intensification of coffee (Coffea arabica) production is associated with increases in inorganic fertilizer application and decreases in species diversity. Both the use of organic fertilizers and the incorporation of trees on farms can, in theory, reduce nutrient loss in comparison with intensified practices. To test this, we measured nutrient concentrations in leachate at 15 and 100 cm depths on working farms. We examined (1) organically managed coffee agroforests (38 kg N ha?1 year?1; n = 4), (2) conventionally managed coffee agroforests (96 kg N ha?1 year?1; n = 4), and (3) one conventionally managed monoculture coffee farm in Costa Rica (300 kg N ha?1 year?1). Concentrations of nitrate (NO3 ?-N) and phosphate (PO4 3?-P) were higher in the monoculture compared to agroforests at both depths. Nitrate concentrations were higher in conventional than organic agroforests at 15 cm only. Soil solutions collected under nitrogen (N)-fixing Erythrina poeppigiana had elevated NO3 ?-N concentrations at 15 cm compared to Musa acuminata (banana) or Coffea. Total soil N and carbon (C) were also higher under Erythrina. This research shows that both fertilizer type and species affect concentrations of N and P in leachate in coffee agroecosystems.  相似文献   

13.
Wood volume yield and stand structure were investigated for Norway spruce understorey growing at 1500 trees ha−1 under birch shelters of two different densities, 300 and 600 trees ha−1, and Norway spruce growing without shelter, in a field trial in the boreal coniferous forest, 56 years after the establishment of the stand and 19 years after establishment of the trial.Wood volume yield in sheltered spruce (mean annual increments of 1.87 and 1.78 m3 ha−1 year−1 under the dense and sparse shelterwoods, respectively) was significantly lower than that of unsheltered spruce (mean annual increment 2.43 m3 ha−1 year−1). The loss in wood volume yield for sheltered spruce was more than compensated for by the additional wood volume yield in the shelterwoods (mean annual increments 3.26 and 1.88 m3 ha−1 year−1 for the dense and sparse shelterwood respectively).Shelterwood density did not produce any significant differences in inequality of the understorey stands, measured as skewness and the Gini coefficient for the wood volume distributions. This implies that two-sided competition for nutrients and water was more significant than competition for light.Immediately after trial establishment, trees in the no shelterwood treatment (i.e. where all overstory trees had been removed) showed a marked increase in diameter growth. Over time, the growth rate of unsheltered Norway spruce was reduced to a level comparable to that of sheltered spruce. The difference in average diameter has persisted during the trial period. There was no similar effect on height growth, resulting in an increased slenderness index (h/d) with increased shelterwood density for the understorey trees.  相似文献   

14.
The magnitude of nitrogen storage and its temporal change in forest ecosystems are important when analysing global change. For example, the accelerated growth of European forests has been linked to increased nitrogen deposition, but the changes in the N inputs that cause long-term changes in ecosystems have not yet been identified. We used two Swedish forest optimum nutrition experiments with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) to study the long-term fate of N applied to these forest ecosystems. In the pine experiment, in addition to fertiliser (NPK) application, soil acidity was manipulated by application of lime and dilute sulphuric acid. From the spruce experiment, we selected treatments with similar fertiliser doses as in the pine experiment and with and without lime addition.We quantified various terms in the N budget 12 years (pine) and 7 years (spruce) after the last N addition. In the pine stand the NPK-treatment was the only treatment to produce a significant increase in N in the tree biomass (97% above control), whereas in the spruce stand the N additions increased tree N in all treatment combinations (207% above control). In the pine stand the relative distribution of nitrogen between trees and soil did not vary across treatments, with trees containing around 12% of ecosystem N and humus containing around 44% of soil N. The increases in N stocks in the pine stands were mainly in the soil. In contrast, in the spruce ecosystem trees accumulated most of the added N and the increase in the soil was restricted to the humus layer.In the pine ecosystem, large losses of added N (between 254 and 738 kg ha−1 out of 1040 kg ha−1 added as fertiliser) occurred, whereas in the spruce ecosystem we recovered more N than could be accounted for by inputs (between 250 and 591 kg ha−1). There was no clear pattern in the interaction between acidification/liming and N additions.  相似文献   

15.
Hydrochemical studies were conducted in three forested catchments in central Sweden during a 12-year period (1977–1989). During this period, 50% and 95% of the surface of two of the areas were clear - felled. The third area was left untouched as a control for reference. A qualitative analysis of clear-cut effects was conducted to investigate changes in streamwater quality by use of Principal Component and SIMCA analyses. During the 8 years of clear-cutting, with reference to the control period, the average runoff increased by 85% and 110% (220 mm and 274 mm year−1), respectively, in the two areas felled to 50% and 95%. Significant changes in the status of the streamwater were detected for the two clear-felled catchments, whereas the changes detected in the control catchment were not significant, and within the limits of natural variation.In relation to the reference period, the changes in the clear-felled catchments were identified as dependent mainly on increased concentrations of K+, NH4+, NO3−, org-N, and tot-N. Concentrations of H+ decreased, while changes in concentrations of Ca2+, Mg2+, Na+, SO42−, and Cl− were less distinct. At the end of the 8 year investigation period, run-off and chemical composition of the streamwater successively returned to pre-cut conditions.  相似文献   

16.
The retention of applied 35S was studied in a lysimeter experiment, in which the lysimeters, consisting of soil columns with intact field and groundlayer vegetation, had previously been treated with either sulphuric acid, NPK or a combination of sulphuric acid and NPK.35S was applied as Na235SO4 to all lysimeters in an amount corresponding to 2 kg S ha?1, 3 months before the termination of the experiment. Of the applied 35S, 4.7 ± 1.6% (the error term showing the standard error of the mean) was leached from the lysimeters; 35SO42?, was preferentially sorbed in the upper part of the B horizon, >61% being sorbed in the B horizon as a whole. The influence of previous treatments was seen in SO42? content in the B horizon and also in the SO42? concentrations in the leachates from the lysimeters. Sorption of 35SO42? was enhanced by the acid treatment in the A0 and A1/A2 horizons. Ratios between water-extractable SO42? and KCl-extractable SO42? varied from 0.88 in the A1/A2 horizon to 0.46 in the lower part of the B horizon, indicating a preferential sorption of less available SO42? fractions in that part of the soil.Significant positive correlations between soil organic carbon and various sulphur fractions, both labelled and unlabelled, indicated the importance of biological S transformations in the A0 and A1/A2 horizons.Positive correlations between KCl-extractable Al and KCl-extractable SO42? were found in the B horizon. Equilibrium calculations suggested that the SO42? activity and Al3+ activity in leachates from control and acidified lysimeters were within the stability fields of basaluminite (Al4(OH)10SO4), activities in leachates from the latter group of lysimeters, also being close to jurbanite (Al(OH)SO4).  相似文献   

17.
In most temperate forest, nitrogen (N) is considered a limiting factor. This becomes important in extreme environments, as Nothofagus antarctica forests, where the antecedents are scarce. Thinning practices in N. antarctica forests for silvopastoral uses may modify the soil N dynamics. Therefore, the objective of this work was to evaluate the temporal variation of soil N in these ecosystems. The mineral extractable soil N, net nitrification and net N mineralization were evaluated under different crown cover and two site quality stands. The mineral N extractable (NH4 +–N + NO3 ?–N) was measured periodically. Net nitrification and net N mineralization were estimated through the technique of incubation of intact samples with tubes. The total mineral extractable N concentration varied between crown cover and dates, with no differences among site classes. The lowest and highest values were found in the minimal and intermediate crown cover, respectively. In the higher site quality stand, the annual net N mineralization was lower in the minimal crown cover reaching 11 kg N ha?1 year?1, and higher in the maximal crown cover (54 kg N ha?1 year?1). In the lower site quality stand there was no differences among crown cover. The same pattern was found for net nitrification. Thinning practices for silvopastoral use of these forests, keeping intermediate crown cover values, did not affect both N mineralization and nitrification. However, the results suggest that total trees removal from the ecosystem may decrease N mineralization and nitrification.  相似文献   

18.
Mineral fertilizers were applied to adjacent plantations of 2, 4-year old, hybrid poplars: clone 27 (Northwest, P. deltoides × P. balsamifera) and 794 (Brooks, P. deltoides × P. × petrowskyana), in north eastern Alberta. Fertilization was done in May 2003 to see whether growth rates could be increased and rotations shortened. Three fertilizers (N, NP and NPKS + Cu + Zn) were applied at each of three rates (supplying N at 0, 100 and 200 kg ha−1) in a factorial randomized block design to the two separate plantations. Fertilization with 200 kg ha−1 N and 100 kg ha−1 P increased volume growth of clone 27 by 1 m3 ha−1 year−1 over 2 years. Clone 794 showed no volume response to fertilization, but produced 8.7 m3 ha−1 more than clone 27. Leaf area, dry mass and nutrient concentrations of both clones increased in the first year after fertilization, showing that fertilizer uptake occurred. Decrease in leaf size between 2003 and 2004 was affected by fertilizer level in clone 794. There were differences between some nutrient concentrations in the soils occupied by the two clones, and clone 794 had higher leaf concentrations of N, K, Ca, S, Mn, Zn, B and Mo than clone 27. Fertilization of 4-year old plantations of either clone was unwarranted, and planting clone 794 would be likely to provide greater yield than planting and fertilizing clone 27.  相似文献   

19.
In the Northern and Baltic countries, grey alder is a prospective tree species for short-rotation forestry. Hence, knowledge about the functioning of such forest ecosystems is critical in order to manage them in a sustainable and environmentally sound way. The 17-year-long continuous time series study is conducted in a grey alder plantation growing on abandoned agricultural land. The results of above- and below-ground biomass and production of the 17-year-old stand are compared to the earlier published respective data from the same stand at the ages of 5 and 10 years. The objectives of the current study were to assess (1) above-ground biomass (AGB) and production; (2) below-ground biomass: coarse root biomass (CRB), fine root biomass (FRB) and fine root production (FRP); (3) carbon (C) and nitrogen (N) accumulation dynamics in grey alder stand growing on former arable land. The main results of the 17-year-old stand were as follows: AGB 120.8 t ha?1; current annual increment of the stem mass 5.7 t ha year?1; calculated CRB 22.3 t ha?1; FRB 81 ± 10 g m?2; nodule biomass 31 ± 19 g m?2; fine root necromass 11 ± 2 g m?2; FRP 53 g DM m?2 year?1; fine root turnover rate 0.54 year?1; and fine root longevity 1.9 years. FRB was strongly correlated with the stand basal area and stem mass. Fine root efficiency was the highest at the age of 10 years; at the age of 17 years, it had slightly reduced. Grey alder stand significantly increased N and Corg content in topsoil. The role of fine roots for the sequestration of C is quite modest compared to leaf litter C flux.  相似文献   

20.
Nitrogen (N)-fixing tree and crop intercropping systems can be a sustainable agricultural practice in sub-Saharan Africa and can also contribute to resolving climate change through enhancing soil carbon (C) sequestration. A study conducted by Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) on the N-fixing tree gliricidia and maize intercropping system in southern Malawi provides a rare dataset of both sequestered soil C and C loss as soil carbon dioxide (CO2) emissions. However, no soil C gain and loss estimates were made so the study failed to show the net gain of soil C. Also absent from this study was potential benefit or negative impact related to the other greenhouse gas, nitrous oxide (N2O) and methane (CH4) emissions from the intercropping system. Using the data provided in Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) a C loss as soil CO2 emissions (51.2?±?0.4?Mg?C?ha?1) was estimated, amounting to 67.4% of the sequestered soil C (76?±?8.6?Mg?C?ha?1 in 0?C2?m soil depth) for the first 7?years in the intercropping system. An annual net gain of soil C of 3.5?Mg?C?ha?1?year?1 was estimated from soil C sequestered and lost. Inclusion of the potential for N2O mitigation [0.12?C1.97?kg?N2O?CN?ha?1?year?1, 0.036?C0.59?Mg CO2 equivalents (eq.) ha?1?year?1] within this intercropping system mitigation as CO2 eq. basis was estimated to be 3.5?C4.1?Mg CO2 eq.?ha?1?year?1. These results suggest that reducing N2O emission can significantly increase the overall mitigation benefit from the intercropping system. However, significant uncertainties are associated with estimating the effect of intercropping on soil N2O and CH4 emissions. These results stress the importance of including consideration of quantifying soil CO2, N2O and CH4 emissions when quantifying the C sequestration potential in intercropping system.  相似文献   

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