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1.
The current expansion of the oil palm (Elaeis guineensis Jacq.) in the Brazilian Amazon has mainly occurred within smallholder agricultural and degraded areas. Under the social and environmental scenarios associated with these areas, oil palm-based agroforestry systems represent a potentially sustainable method of expanding the crop. The capacity of such systems to store carbon (C) in the soil is an important ecosystem service that is currently not well understood. Here, we quantified the spatial variation of soil C stocks in young (2.5-year-old) oil palm-based agroforestry systems with contrasting species diversity (high vs. low); both systems were compared with a ~10-year-old forest regrowth site and a 9-year-old traditional agroforestry system. The oil palm-based agroforestry system consisted of series of double rows of oil palm and strips of various herbaceous, shrub, and tree species. The mean (±standard error) soil C stocks at 0–50 cm depth were significantly higher in the low (91.8 ± 3.1 Mg C ha?1) and high (87.6 ± 3.3 Mg C ha?1) species diversity oil palm-based agroforestry systems than in the forest regrowth (71.0 ± 2.4 Mg C ha?1) and traditional agroforestry (68.4 ± 4.9 Mg C ha?1) sites. In general, no clear spatial pattern of soil C stocks could be identified in the oil palm-based agroforestry systems. The significant difference in soil carbon between the oil palm area (under oil palm: 12.7 ± 2.3 Mg C ha?1 and between oil palm: 10.6 ± 0.5 Mg C ha?1) and the strip area (17.0 ± 1.4 Mg C ha?1) at 0–5 cm depth very likely reflects the high input of organic fertilizer in the strip area of the high species diversity oil palm-based agroforestry system treatment. Overall, our results indicate a high level of early net accumulation of soil C in the oil palm-based agroforestry systems (6.6–8.3 Mg C ha?1 year?1) that likely reflects the combination of fire-free land preparation, organic fertilization, and the input of plant residues from pruning and weeding.  相似文献   

2.
Macro- (C, N, P, K, Ca and Mg) and micronutrient (Fe, Mn, Cu and Zn) reservoirs were estimated in the O (Oi+Oe+Oa) and in the A (0–10 cm depth) soil horizons of four stands of Nothofagus pumilio (lenga) from Tierra del Fuego which differ in their forestry characteristics. The type of soil layer (O and A) and the forest structure, as related to above-ground biomass storage, were assessed as a factor of variation in the nutrient reservoirs of both soils layers. Nutrient reservoirs showed similar ranges in both soil layers for total organic C (34–65 Mg ha?1), total N (1.5–3.5 Mg ha?1), rapidly available Ca (1.3–2.7 Mg ha?1) and Mg (0.18–0.36 Mg ha?1). Rapidly available K, available P, and medium-term available Fe and Cu were accumulated preferentially in A the horizons, whereas medium-term available Mn and Zn were mainly stored in the O horizons. The forest structure was not a statistically significant factor of variation on the nutrient reservoirs in the O horizons, although a legacy effect of the accumulated above-ground biomass on nutrient reservoirs in this soil layer can not be discarded. On the contrary, the pools of total organic C, total N, rapidly available K and medium-term available Cu and Zn in the A horizons varied significantly with the different forest structure. In terms of lenga forests sustainability, uppermost soils layers should be preserved as they accumulate most of the soil fertility which is essential for lenga regeneration after logging. The inclusion of the assessment of soil fertility in the management plans of the lenga forests in the ecotone of the Argentinean Tierra del Fuego is strongly recommended, as it will contribute to ensure a successful regeneration of lenga in logged areas.  相似文献   

3.
Agroforestry is an ancient practice widespread throughout Africa. However, the influence of Sahelian agroforestry systems on carbon storage in soil and biomass remains poorly understood. We evaluated the carbon storage potential of three agroforestry systems (fallow, parkland and rangeland) and five tree species (Faidherbia albida, Acacia raddiana, Neocarya macrophylla, Balanites aegyptiaca and Euphorbia balsamifera) growing on three different soils (clay, sandy loam and sandy) in the Niayes zone, Senegal. We calculated tree biomass carbon stocks using allometric equations and measured soil organic carbon (SOC) stocks at four depths (0–20, 20–50, 50–80 and 80–100 cm). F. albida and A. raddiana stored the highest amount of carbon in their biomass. Total biomass carbon stocks were greater in the fallow (40 Mg C ha?1) than in parkland (36 Mg C ha?1) and rangeland (29 Mg C ha?1). More SOC was stored in the clay soil than in the sandy loam and sandy soils. On average across soil texture, SOC stocks were greater in fallow (59 Mg C ha?1) than in rangeland (30 Mg C ha?1) and parkland (15 Mg C ha?1). Overall, the total amount of carbon stored in the soil + plant compartments was the highest in fallow (103 Mg C ha?1) followed by rangeland (68 Mg C ha?1) and parkland (52 Mg C ha?1). We conclude that in the Niayes zones of Senegal, fallow establishment should be encouraged and implemented on degraded lands to increase carbon storage and restore soil fertility.  相似文献   

4.
Replantation of degraded forest using rapidgrowth trees can play a significant role in global carbon budget by storing large quantities of carbon in live biomass,forest floor,and soil organic matter.We assessed the potential of 20-year old stands of three rapid-growth tree species,including Alnus subcordata,Populus deltoides and Taxodium distichum,for carbon(C) storage at ecosystem level.In September 2013,48 replicate plots(16 m × 16 m) in 8 stands of three plantations were established.36 trees were felled down and fresh biomass of different components was weighed in the field.Biomass equations were fitted using data based on the 36 felled trees.The biomass of understory vegetation and litter were measured by harvesting all the components.The C fraction of understory,litter,and soil were measured.The ecosystem C storage was as follows: A.subcordata(626.5 Mg ha~(-1)) [ P.deltoides(542.9Mg ha~(-1)) [ T.distichum(486.8 Mg ha~(-1))(P \ 0.001),of which78.1–87.4% was in the soil.P.deltoides plantation reached the highest tree biomass(206.6 Mg ha~(-1)),followed by A.subcordata(134.5 Mg ha~(-1)) and T.distichum(123.3 Mg ha~(-1)).The highest soil C was stored in theplantation of A.subcordata(555.5 Mg ha~(-1)).The C storage and sequestration of the plantations after 20 years were considerable(25–30 Mg ha~(-1) year~(-1)) and broadleaves species had higher potential.Native species had a higher soil C storage while the potential of introduced species for live biomass production was higher.  相似文献   

5.
Downed and standing deadwood (DW) is a key resource for maintaining forest biodiversity. Although extreme events such as windthrow and fires produce large quantities of DW, this substrate is often drastically reduced by logging activities. To elucidate the respecting consequences of salvage-logging, we assessed both quantity and quality of storm-derived DW (storms Vivian 1990 and Lothar 1999) in Swiss forests using a sample of 90 windthrow sites with ≥3 ha complete windthrow and at elevations ranging from 350 to 1,800 m a.s.l. The majority had been salvage-logged (SL) a few years after the windthrow. On each site, we recorded DW amount and quality on six circular sample plots 20 or 50 m2 in size. DW volume on SL sites was surprisingly high, with 76.4 m3 ha?1 on average 20 years after Vivian and 73.8 m3 ha?1 10 years after Lothar. In comparison, DW volumes on unsalvaged sites, that is, with no post-windthrow intervention (NI), amounted to 270 m3 ha?1. A wide variety of wood decay stages and diameter classes (10 to ≥70 cm) was found on both NI and SL sites, suggesting considerable habitat diversity for DW-associated species irrespective of the treatment. The considerable amounts of DW left after salvage-logging distinctly exceed the minimum DW volumes in forest stands proposed by Müller and Bütler (Eur J For Res 129: 981–992, 2010) in a conservation context, which demonstrates the importance of wind disturbance for biodiversity. Further studies should quantify DW of individual tree species, since habitat requirements are species-specific.  相似文献   

6.
Tropical forests store a large part of the terrestrial carbon and play a key role in the global carbon (C) cycle. In parts of Southeast Asia, conversion of natural forest to cacao agroforestry systems is an important driver of deforestation, resulting in C losses from biomass and soil to the atmosphere. This case study from Sulawesi, Indonesia, compares natural forest with nearby shaded cacao agroforests for all major above and belowground biomass C pools (n = 6 plots) and net primary production (n = 3 plots). Total biomass (above- and belowground to 250 cm soil depth) in the forest (approx. 150 Mg C ha?1) was more than eight times higher than in the agroforest (19 Mg C ha?1). Total net primary production (NPP, above- and belowground) was larger in the forest than in the agroforest (approx. 29 vs. 20 Mg dry matter (DM) ha?1 year?1), while wood increment was twice as high in the forest (approx. 6 vs. 3 Mg DM ha?1 year?1). The SOC pools to 250 cm depth amounted to 134 and 78 Mg C ha?1 in the forest and agroforest stands, respectively. Replacement of tropical moist forest by cacao agroforest reduces the biomass C pool by approximately 130 Mg C ha?1; another 50 Mg C ha?1 may be released from the soil. Further, the replacement of forest by cacao agroforest also results in a 70–80 % decrease of the annual C sequestration potential due to a significantly smaller stem increment.  相似文献   

7.
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   

8.
Afforestation and ecological restoration have often been carried out with fast-growing exotic tree species because of their high apparent growth and yield. Moreover, fast-growing forest plantations have become an important component of mitigation measures to offset greenhouse gas emissions. However, information on the long-term performance of exotic and fast-growing species is often lacking especially with respect to their vulnerability to disturbance compared to native species. We compared carbon (C) storage and C accumulation rates in vegetation (above- and belowground) and soil in 21-year-old exotic slash pine (Pinus elliottii Engelm.) and native Masson pine (Pinus massoniana Lamb.) plantations, as well as their responses to a severe ice storm in 2008. Our results showed that mean C storage was 116.77 ± 7.49 t C ha?1 in slash pine plantation and 117.89 ± 8.27 t C ha?1 in Masson pine plantation. The aboveground C increased at a rate of 2.18 t C ha?1 year?1 in Masson pine and 2.23 t C ha?1 year?1 in slash pine plantation, and there was no significant difference in C storage accumulation between the two plantation types. However, we observed significant differences in ice storm damage with nearly 7.5 % of aboveground biomass loss in slash pine plantation compared with only 0.3 % loss in Masson pine plantation. Our findings indicated that the native pine species was more resistant to ice storm because of their adaptive biological traits (tree shape, crown structure, and leaf surface area). Overall, the native pine species might be a safer choice for both afforestation and ecological restoration in our study region.  相似文献   

9.
This study analyses the trade-off between bioenergy production and soil conservation through thinning operations in Norway spruce (Picea abies L. Karst) plantations in Denmark. Thinning operations were evaluated under different regimes and intensities for a complete rotation period of sixty years and for different site qualities (site-classes I–VI). Applying a dynamic forest growth modeling tool, evolution of forest structure was predicted to observe the potentials for biomass production and inevitable soil degradation. Results showed thinning from below, with a higher utilization (maintenance of a minimum basal area of 25 m2 ha?1) could produce more bioenergy. However, these operations require simultaneous severe forest soil degradation. Therefore, the optimum thinning for bioenergy production under preservation constraints was thinning from above with a lower intensity (maintenance of a minimum basal area of 45 m2 ha?1). The ratio of bioenergy win (kWh) to soil-loss (m3 ha?1) was calculated for this regime varying between 74,894 kWh m?3 in a high quality site (site-class I) and 6,516 kWh m?3 in a low quality site (site-class VI) with an average of 44,282 kWh m?3. However, this could not always preserve the highest amount of growing stock essential for natural dynamics of forest ecosystem with an exception of the low quality sites (site-class VI). Thus, when aiming at bioenergy production through thinning operations, trade-offs with soil conservation and growing stock preservation should be regarded to prevent environmental degradation.  相似文献   

10.
The effect of different planting densities (100,000 and 167,000 plants ha?1) and levels of nitrogen fertilization (0, 261, 521, and 782 kg N ha?1 year?1) on biomass production and chemical composition of Moringa oleifera was studied in a split-plot design with four randomized complete blocks over 2 years with eight cuts year?1 at the National Agrarian University farm in Managua, Nicaragua (12°09′30.65″N, 86°10′06.32″W, altitude 50 m above sea level). Density 167,000 plants ha?1 produced significantly higher total dry matter yield (TDMY) and fine fraction yield (FFDM), 21.2 and 19.2 ton ha?1 respectively, compared with 11.6 and 11 ton ha?1 for 100,000 plants ha?1. Growth rate in 167,000 plants ha?1 was higher than in 100,000 plants ha?1 (0.06 compared with 0.03 ton ha?1 day?1). Average plant height was 119 cm irrespective of planting density. Fertilization at the 521 and 782 kg N ha?1 year?1 levels produced the highest TDMY and FFDM in both years of the study and along all cuts. The interaction between cut and year was significant, with the highest TDMY and FFDM during the rainy season in the second year. Chemical composition of fractions showed no significant differences between planting densities. Significantly higher crude protein content was found in the coarse fraction at fertilizer levels 521 and 782 kg N ha?1 year?1 (87.9 and 93.7 g kg?1 DM) compared with lower levels. The results indicate that Moringa can maintain up to 27 ton ha?1 dry matter yield under dry tropical forest conditions over time at a planting density of 167,000 plants ha?1 if the soil is regularly supplied with N at a level of approximately 521 kg ha year?1 in conditions where phosphorus and potassium are not limiting.  相似文献   

11.
Grewia optiva Drummond is one of important agroforestry tree species grown by the farmers in the lower and mid-hills of western Himalaya. Different models viz., monomolicular, logistic, gompetz, allometric, rechards, chapman and linear were fitted to the relationship between total biomass and diameter at breast height (DBH) as independent variable. The adjusted R2 values were more than 0.924 for all the seven models implying that all models are apparently equally efficient. Out of the six non-linear models, allometric model (Y = a × DBH b ) fulfils the validation criterion to the best possible extent and is thus considered as best performing. Biomass in different tree components was fitted to allometric models using DBH as explanatory variable, the adjusted R2 for fitted functions varied from 0.872 to 0.965 for different biomass components. The t values for all the components were found non-significant (p > 0.05), thereby indicating that model is valid. Using the developed model, the estimated total biomass varied from 6.62 Mg ha?1 in 4 year to 46.64 Mg ha?1 in 23 year old plantation. MAI in biomass varied from 1.66–2.05 Mg ha?1 yr?1. The total biomass carbon stocks varied from 1.99 Mg ha?1 in 4 year to 15.27 Mg ha?1 in 23 year old plantation. Rate of carbon sequestration varied from 0.63–0.81 Mg ha?1 yr?1. Carbon storage in the soil up to 30 cm soil depth varied from 25.4 to 33.6 Mg ha?1.  相似文献   

12.
The present study was an effort to understand the amount of litter fall and its subsequent decomposition and quantify the release of available nutrients and soil physicochemical characteristics in plantations of four forest tree species(Lagerstroemia parviflora, Tectona grandis, Shorea robusta and Michelia champaca) in the Chilapatta Reserve Forest of the Cooch Behar Wildlife Division in the Terai zone of West Bengal, India. The most litter(5.61 Mg ha~(-1))was produced by T. grandis plantation and the least(4.72 Mg ha~(-1)) by L. parviflora. The material turnover rate to the soil through decomposition from total litter was fastest during the first quarter of the year and subsequently decreased during the next two quarters. The material turnover rate was only 1 year, which indicates that more than90% of the total litter produced decomposed within a year.The available primary nutrient content in litter varied across the four plantations over the year. The plantations generally did not significantly influence the soil physical characteristics but did significantly influence the availability of primary nutrients and organic carbon at two depths(1–15 and16–30 cm) over the year. The availability of soil primary nutrients in the four plantations also increased gradually from the first quarter of the year to the third quarter and then decreased during the last quarter to the same level as in the first quarter of the year at both depths. The availability for soil organic carbon in the plantations followed a similar trend. The amount of litter produced and the material turnover in the soil in the different plantations differed, influencing the nutrient availability and organic carbon at the plantations. The amount of soil organic carbon was highest for T. grandis(2.52 Mg ha~(-1)) and lowest for L. parviflora(2.12 Mg ha~(-1)). Litter is the source of soil organic matter,and more the litter that is produced by the plantations, the higher will be the content and amount of soil organic carbon in the plantation.  相似文献   

13.
Recent re-measurements of silvicultural trials in conifer plantations on nutrient-poor cedar-hemlock (CH) cutovers on northern Vancouver Island have confirmed co-limitation by nitrogen and phosphorus. Repeated fertilization increased volumes of both cedar and hemlock on CH sites (at 2,500 stems ha?1) by about 100 m3 ha?1 relative to unfertilized plots 22 years following initial fertilization, and increased the productivity of regenerating conifers to a level approximating that of neighbouring hemlock-amabilis fir (HA) sites. More surprising was the response to fertilization on the more-productive HA sites. After 22 years, cedar in fertilized HA plots had produced an extra 180 m3 ha?1 compared to unfertilized HA plots, while hemlock had produced an extra 250 m3 ha?1 in fertilized plots (at 2,500 stems ha?1). Thus, contrary to expectations, the greatest volume responses of both hemlock and cedar to fertilization occurred on the good (HA) sites rather than on the poor (CH) sites. Ecological studies of CH and HA sites supported the hypothesis that the poor nutrient supply and productivity of CH sites is a long-term consequence of excessive moisture, and that the two site types bracket a critical ecological threshold of moisture, aeration and redox.  相似文献   

14.
Abstract

The present study was aimed to anticipate how forest composition, regeneration, biomass production, and carbon storage vary in the ridge top forests of the high mountains of Garhwal Himalaya. For this purpose five major forest types—(a) Pinus wallichiana, (b) Quercus semecarpifolia, (c) Cedrus deodara, (d) Abies spectabilis, and (e) Betula utilis mixed forests—were selected on different ridge tops in the Bhagirathi Catchment Area of the Uttarkashi District of Garhwal Himalaya. The highest species richness (10 species) and stand density (804 ± 184.5 stems ha?1) were recorded in Abies spectabilis forests, whereas lowest species richness (4 species) and species density (428 ± 144.7 stems ha?1) were found in Quercus semecarpifolia forests. The total basal cover (TBC) values were maximum (91.1 ± 24.4 m2 ha?1) in Cedrus deodara forests and minimum (26.5 ± 11.7 m2 ha?1) in Pinus wallichiana forests. The highest total biomass density (TBD) (464.2 ± 152.5 Mg ha?1) and total carbon density (TCD; 208.9 ± 68.6 Mg C ha?1) values were recorded for Cedrus deodara forests; however, lowest TBD (283.4 ± 74.8 Mg ha?1) and TCD (127.5 ± 33.7 Mg C ha?1) values for Quercus semecarpifolia forests. Our study suggests that Abies spectabilis-dominated forests should be encouraged for biodiversity enrichment and reducing carbon emissions on ridge top forests of high mountains.  相似文献   

15.
Carbon (C) sequestration potential was quantified for five tree species, commonly used in tree-based intercropping (TBI) and for conventional agricultural systems in southern Ontario, Canada. In the 25-year-old TBI system, hybrid poplar (Populus deltoides × Populus nigra clone DN-177), Norway spruce (Picae abies), red oak (Quercus rubra), black walnut (Juglans nigra), and white cedar (Thuja occidentalis) were intercropped with soybean (Glycine max). In the conventional agricultural system, soybean was grown as a sole crop. Above- and belowground tree C Content, soil organic C, soil respiration, litterfall and litter decomposition were quantified for each tree species in each system. Total C pools for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and a soybean sole-cropping system were 113.4, 99.4, 99.2, 91.5, 91.3, and 71.1 t C ha?1, respectively at a tree density of 111 trees ha?1, including mean tree C content and soil organic C stocks. Net C flux for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and soybean sole-crop were 2.1, 1.4, 0.8, 1.8, 1.6 and ?1.2 t C ha?1 year?1, respectively. Results presented suggest greater atmospheric CO2 sequestration potential for all five tree species when compared to a conventional agricultural system.  相似文献   

16.
Ecosystem-level assessments of carbon (C) stocks of agroforestry systems are scarce. We quantified the ecosystem-level C stocks of one agroforestry-based oil palm production system (AFSP) and one agroforestry-based oil palm and cacao production system (AFSP+C) in eastern Amazonia. We quantified the stocks of C in four pools: aboveground live biomass, litter, roots, and soil. We evaluated the distribution of litter, roots, and soil C stocks in the oil palm management zones and in the area planted with cacao and other agroforestry species. The ecosystem-C stock was higher in AFSP+C (116.7 ± 1.5 Mg C ha?1) than in AFSP (99.1 ± 3.1 Mg C ha?1). The total litter-C stock was higher in AFSP+C (3.27 ± 0.01 Mg C ha?1) than in AFSP (2.26 ± 0.06 Mg C ha?1). Total root and soil C stocks (0–30 cm) did not differ between agroforestry systems. Ecosystem-C stocks varied between agroforestry systems due to differences in both aboveground and belowground stocks. In general, the belowground-C stocks varied spatially in response to the management in the oil palm and non-oil palm strips; these results have important implications for the monitoring of ecosystem-level C dynamics and the refinement of soil management.  相似文献   

17.
High population density and unscientific land use practices have induced severe land degradation in the fragile Lower Himalayan ecosystem of India. Land cover management has been an effective strategy in managing land degradation through the reduction of water, soil and nutrient losses and improvement in soil fertility and quality. Acacia nilotica (Acacia)-based silvipastoral systems with five intercrops, viz., Eulaliopsis binata (bhabbar), Saccharum munja (munj), Vetiveria zizanioides (vetiver), natural grasses and no grass, were evaluated in a long-term study in degraded bouldery lands in Haryana state of India. All grasses resulted in a reduction of soil, water and nutrient losses and improved microbial properties. However, their association adversely affected the growth of Acacia, and the decline varied with grass species. After 11 years of establishment, sole Acacia plantation had the maximum height (7.58 m), diameter at breast height (dbh) (21.32 cm) and crown spread (7.41 m). Munj produced the highest biomass under Acacia, but most adversely affected its growth, resulting in minimum survival (48 %), height (7.07 m), dbh (16.23 cm) and crown spread (6.57 m). Yield of all the grasses increased during the initial 5–6 years, but declined sharply thereafter, with the maximum decline in bhabbar. Detailed investigations established that the sharp decline in survival and growth of bhabbar was due to shade and not because of nutrient competition or allelopathy. Acacia + V. zizanioides proved the most effective silvipastoral system for resource conservation and biomass production. It also provided the highest NPV (Rs 1.88 lakhs ha?1), B:C (2.37) and IRR (24.70 %) as compared to Rs 6,998 ha?1, 1.05 and 8.76 % under pure Acacia plantation, respectively.  相似文献   

18.
In the context of global carbon cycle management, accurate knowledge of carbon content in forests is a relevant issue in contemporary forest ecology. We measured the above-ground and soil carbon pools in the darkconiferous boreal taiga. We compared measured carbon pools to those calculated from the forest inventory records containing volume stock and species composition data. The inventory data heavily underestimated the pools in the study area(Stolby State Nature Reserve, central Krasnoyarsk Territory, Russian Federation). The carbon pool estimated from the forest inventory data varied from 25(t ha-1)(low-density stands) to 73(t ha-1)(highly stocked stands). Our estimates ranged from 59(t ha-1)(lowdensity stands) to 147(t ha-1)(highly stocked stands). Our values included living trees, standing deadwood, living cover, brushwood and litter. We found that the proportion of biomass carbon(living trees): soil carbon varied from99:1 to 8:2 for fully stocked and low-density forest stands,respectively. This contradicts the common understanding that the biomass in the boreal forests represents only16–20 % of the total carbon pool, with the balance being the soil carbon pool.  相似文献   

19.
Afforestation of degraded croplands by planting N2-fixing trees in arid regions is highly recognized. However, fixation of atmospheric nitrogen gas (N2) by woody perennials is often limited on phosphorus (P) poor soils, while any factor limiting N nutrition inhibits tree growth. In a two-factorial field experiment, the effect of three P amendments was examined during 2006–2008 on N2 fixation, biomass production, and foliage feed quality of actinorhizal Elaeagnus angustifolia L. and leguminous Robinia pseudoacacia L. With the 15N natural abundance method, N2 fixation was quantified based on foliar and whole-tree sampling against three non-N2-fixing reference species: Gleditsia triacanthos L., Populus euphratica Oliv., and Ulmus pumila L. The P applications, in March 2006 and April 2007 only, included (i) high-P (90 kg P ha?1), (ii) low-P (45 kg P ha?1), and (iii) 0-P. After 3 years, the average proportion of N derived from atmosphere (Ndfa, %) increased from 78 % with 0-P to 87 % with high P when confounded over both N2-fixing species. With the used density of 5,714 trees ha?1, the total amount of N2 fixed (Ndfa, kg N ha?1) with high-P increased from 64 kg N ha?1 (year 1) to 807 kg N ha?1 (year 3) in E. angustifolia and from 9 kg N ha?1 (year 1) to 155 kg N ha?1 (year 3) in R. pseudoacacia. Total above-ground biomass increases were too variable to be significant. Leaf N content and therewith also leaf crude protein content, which is an indicator for feed quality, increased significantly (24 %) with high-P when compared to 0-P for E. angustifolia. Overall findings indicated the suitability of the two N2-fixing species for afforestating salt-affected croplands, low in soil P. With P-applications as low as 90 kg P ha?1, the production potential of E. angustifolia and R. pseudoacacia, including the supply of protein-rich feed, could be increased on salt-affected croplands.  相似文献   

20.
The effects of silvicultural treatments on carbon sequestration are poorly understood, particularly in areas like the Mediterranean where soil fertility is low and climatic conditions can be harsh. In order to improve our understanding of these effects, a long-term thinning experiment in a stand of Mediterranean maritime pine (Pinus pinaster Ait.) was studied to identify the effects of thinning on soil carbon (forest floor and mineral soil), above and belowground biomass and fine and coarse woody debris. The study site was a 59-year-old pinewood, where three thinnings of differing intensities were applied: unthinned (control), moderate thinning and heavy thinning. The three thinning interventions (for the managed plots) involved whole-tree harvesting. The results revealed no differences between the different thinning treatments as regards the total soil carbon pool (forest floor + mineral soil). However, differences were detected in the case of living aboveground biomass and total dead wood debris between unthinned and thinned plots; the former containing larger amounts of carbon. The total carbon present in the unthinned plots was 317 Mg ha?1; in the moderately thinned plots, it was 256 Mg ha?1 and in the case of heavily thinned plots, 234 Mg ha?1. Quantification of these carbon compartments can be used as an indicator of total carbon stocks under different forest management regimes and thus identify the most appropriate to mitigate the effects of global change. Our results indicated that thinning do not alter the total soil carbon content at medium term, suggesting the sustainability of these silvicultural treatments.  相似文献   

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