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1.
Coffee (Coffea canephora var robusta) is grown in Southwestern Togo under shade of native Albizia adianthifolia as a low input cropping system. However, there is no information on carbon and nutrient cycling in these shaded coffee systems. Hence, a study was conducted in a mature coffee plantation in Southwestern Togo to determine carbon and nutrient stocks in shaded versus open-grown coffee systems. Biomass of Albizia trees was predicted by allometry, whereas biomass of coffee bushes was estimated through destructive sampling. Above- and belowground biomass estimates were respectively, 140 Mg ha−1 and 32 Mg ha−1 in the coffee–Albizia association, and 29.7 Mg ha−1 and 18.7 Mg ha−1 in the open-grown system. Albizia trees contributed 87% of total aboveground biomass and 55% of total root biomass in the shaded coffee system. Individual coffee bushes consistently had higher biomass in the open-grown than in the shaded coffee system. Total C stock was 81 Mg ha−1 in the shaded coffee system and only 22.9 Mg ha−1 for coffee grown in the open. Apart from P and Mg, considerable amounts of major nutrients were stored in the shade tree biomass in non-easily recyclable fractions. Plant tissues in the shaded coffee system had higher N concentration, suggesting possible N fixation. Given the potential for competition between the shade trees and coffee for nutrients, particularly in low soil fertility conditions, it is suggested that the shade trees be periodically pruned in order to increase organic matter addition and nutrient return to the soil. An erratum to this article can be found at  相似文献   

2.
Tree based land use systems make a valuable contribution to sequester carbon and improve productivity and nutrient cycling within the systems. This study was conducted to determine biomass production, C-sequestration and nitrogen allocation in Gmelina arborea planted as sole and agrisilviculture system on abandoned agricultural land. At 5 years, total stand biomass in agrisilviculture system was 14.1 Mg ha−1. Plantations had 35% higher biomass than agrisilviculture system. At 5 years, leaves, stem, branches and roots contributed 4.1, 65.2, 10.0 and 20.7%, respectively to total standing biomass (17.9 Mg ha−1). Over the 5 years of study, trees had 3.5 Mg ha−1 more C and 36 kg ha−1 more N in plantation than agrisilviculture system. Biomass and C storage followed differential allocation. Relatively more C was allocated in above ground components in plantations compared to agrisilviculture system. C:N ratios for tree components were higher in stem wood (135–142) followed by roots (134–139), branches (123–128) and leaves (20–21). In agrisilviculture system crops recommended are: soybean and cowpea in rainy season; wheat and mustard in winter season. After 5 years, soil organic C increased by 51.2 and 15.1% and N by 38.4 and 9.3% in plantation and agrisilviculture system, respectively. Total C storage in abandoned agricultural land before planting was 26.3 Mg ha−1, which increased to 33.7 and 45.8 Mg ha−1 after 5 years in plantation and agrisilviculture system, respectively. Net C storage (soil + tree) was 7.4 Mg ha−1 in agrisilviculture system compared to 19.5 Mg ha−1 in G. arborea monoculture stands. The studies suggest that competitive interactions played a significant role in agrisilviculture system. Plantations were more efficient in accreting C than agrisilviculture system on abandoned agricultural land.  相似文献   

3.
Biomass of a mature man-made forest in West Java, Indonesia, was estimated to evaluate the carbon sequestration potential of plantation forest in the humid tropics. Twenty plots, each 0.25 ha in area and containing one to six planted species over 40 years of age and with closed canopies, were selected. Trunk dry mass was estimated from trunk diameter, tree height, and bulk density. Maximum trunk diameter (122 cm) was observed in a 46-year-old Khaya grandifoliola C. DC. tree, and the tallest tree (51 m) was a 46-year-old Shorea selanica (DC.) Blume. The largest trunk biomass (911 Mg ha−1) was achieved in the plot composed of two Khaya spp. Among the plots composed of indigeneous Dipterocarpaceae species, the largest trunk biomass was 635 Mg ha−1. These trunk biomasses were larger than those reported from primary rainforests in Southeast Asia (e.g., 403 Mg ha−1 in East Kalimantan, 522 and 368 Mg ha−1 in Peninsular Malaysia). The large biomass in this forest suggests that, given favorable conditions, man-made forests can accumulate the quantities of atmospheric carbon that were lost by the logging of primary forests in the humid tropics.  相似文献   

4.
Generic or default values to account for biomass and carbon accumulation in tropical forest ecosystems are generally recognized as a major source of errors, making site and species specific data the best way to achieve precise and reliable estimates. The objective of our study was to determine carbon in various components (leaves, branches, stems, structural roots and soil) of single-species plantations of Vochysia guatemalensis and Hieronyma alchorneoides from 0 to 16 years of age. Carbon fraction in the biomass, mean (±standard deviation), for the different pools varied between 38.5 and 49.7% (±3 and 3.8). Accumulated carbon in the biomass increased with the plantation age, with mean annual increments of 7.1 and 5.3 Mg ha−1 year−1 for forest plantations of V. guatemalensis and H. alchorneoides, respectively. At all ages, 66.3% (±10.6) of total biomass was found within the aboveground tree components, while 18.6% (±20.9) was found in structural roots. The soil (0–30 cm) contained 62.2 (±13) and 71.5% (±17.1) of the total carbon (biomass plus soil) under V. guatemalensis and H. alchorneoides, respectively. Mean annual increment for carbon in the soil was 1.7 and 1.3 Mg ha−1 year−1 in V. guatemalensis and H. alchorneoides. Allometric equations were constructed to estimate total biomass and carbon in the biomass which had an R 2aj (adjusted R square) greater than 94.5%. Finally, we compare our results to those that could have resulted from the use of default values, showing how site and species specific data contribute to the overall goal of improving carbon estimates and providing a more reliable account of the mitigation potential of forestry activities on climate change.  相似文献   

5.
Community forests of developing countries are eligible to participate in the Reducing Emissions from Deforestation and Forest Degradation (REDD+) scheme. For this, estimation of carbon stock and the sequestration is essential. The carbon stock in the living biomass of nine community managed Shorea robusta forests of the mid hill regions of central Nepal (managed for 4–29 yr) were estimated. The carbon stock of trees and shrubs was estimated using an allometric equation while the biomass of herbaceous vegetation was estimated by the harvest method. The carbon stock in the living biomass of the studied forests ranged from 70–183 Mg ha?1(mean: 120 Mg ha?1) and it increased with increasing soil organic carbon. However, the carbon stock did not vary significantly with species richness and litter cover. The biomass and carbon stock in the forests managed for >20 yr were significantly higher than in the forests managed for < 20 yr. The carbon stock increased with the management duration (p < .05) with sequestration rate of 2.6 Mg C ha?1 yr?1. The local management has had positive effects on the carbon stock of the forests and thus the community forests have been acting as a sink of the atmospheric CO2. Therefore, the community managed forests of Nepal are eligible to participate in the REDD+ scheme.  相似文献   

6.
杉木纯林、混交林土壤微生物特性和土壤养分的比较研究   总被引：6，自引：0，他引：6  
王清奎  汪思龙 《林业研究》2008,19(2):131-135
本文于2005年5月份,在中国科学院会同森林生态实验站选择了一块15年生的杉木纯林和两块15年生杉阔混交林作为研究对象,调查了林地土壤有机碳、全氮、全磷、硝态氮、有效磷和土壤微生物碳、氮、磷、基础呼吸以及呼吸熵,比较了纯林和混交林土壤微生物特性和土壤养分.结果表明,杉阔混交林的土壤有机碳、全氮、全磷硝态氮和有效磷含量高于杉木纯林;在混交林中,土壤微生物学特性得到改善.在0(10 cm和10(20 cm两层土壤中,杉阔混交林土壤微生物氮含量分别比杉木纯林高69%和61%.在0(10 cm土层,杉阔混交林土壤微生物碳、磷和基础呼吸分别比杉木纯林高11%、14%和4%;在10(20 cm土层,分别高6%、3%和3%.但是,杉阔混交林土壤微生物碳:氮比和呼吸熵较杉木纯林低34%和4%.另外,土壤微生物与土壤养分的相关性高于土壤呼吸、微生物碳:氮比和呼吸熵与土壤养分的相关性.由此可知,在针叶纯林中引入阔叶树后,土壤肥力得以改善,并有利于退化森林土壤的恢复.  相似文献   

7.
The importance of agroforestry systems in CO2 mitigation has become recognized worldwide in recent years. However, little is known about carbon (C) sequestered in poplar intercropping systems. The main objective of this study is to compare the effects of three poplar intercropping designs (configuration A: 250 trees ha−1; configuration B: 167 trees ha−1 and configuration C: 94 trees ha−1) and two intercropping systems (wheat–corn cropping system and wheat–soybean cropping system) on biomass production and C stocks in poplar intercropping systems. The experiment was conducted at Suqian Ecological Demonstration Garden of fast-growing poplar plantations in northwestern Jiangsu. A significant difference in C concentration was observed among the poplar biomass components investigated (P ≤ 0.05), with the highest value in stemwood and the lowest in fine roots, ranging from 459.9 to 526.7 g kg−1. There was also a significant difference in C concentration among the different crop components (P ≤ 0.05), and the highest concentration was observed in the corn ear. Over the 5-year period, the total poplar biomass increased with increasing tree density, ranging from 8.77 to 15.12 t ha−1, while annual biomass production among the crops ranged from 4.69 to 16.58 t ha−1 in the three configurations. Overall, total C stock in the poplar intercropping system was affected by configurations and cropping systems, and configuration A obtained the largest total C stock, reaching 16.7 t C ha−1 for the wheat–soybean cropping system and 18.9 t C ha−1 for the wheat–corn cropping system. Results from this case study suggest that configuration A was a relative optimum poplar intercropping system both for economic benefits and for C sequestration.  相似文献   

8.
The conversion of forests to agroecosystems or agroforests comes with many changes in biological and chemical processes. Agroforestry, a tree based agroecosystem, has shown promise with respect to enhanced system nutrient accumulation after land conversion as compared to sole cropping systems. Previous research on tropical agroforestry systems has revealed increases in soil organic matter and total organic nitrogen in the short term. However, research is lacking on long-term system level sustainability of nutrient cycles and storage, specifically in traditional multi-strata agroforestry systems, as data on both the scope and duration of nutrient instability are inconclusive and often conflicting. This study, conducted in Ghana, West Africa, focused on carbon and nitrogen dynamics in a twenty-five year chronosequence of cacao (Theobroma cacao Linn.) plantations. Three treatments were selected as on-farm research sites: 2, 15 and 25-year-old plantations. Soil carbon (C, to a depth of 15 cm) varied between treatments (2 years: 22.6 Mg C ha−1; 15 years: 17.6 Mg C ha−1; 25 years: 18.2 Mg C ha−1) with a significant difference between the 2- and 15- and the 2- and 25-year-old treatments (p < 0.05). Total soil nitrogen in the top 15 cm varied between 1.09 and 1.25 Mg N ha−1 but no significant differences were noted between treatments. Soil nitrification rates and litter fall increased significantly with treatment age. However, photosynthetically active radiation (PAR) and soil temperature showed a significant decrease with age. No difference was found between decay rates of litter at each treatment age. By 25 years, system carbon sequestration rates were 3 Mg C ha−1 y−1, although results suggest that even by 15 years, system-level attributes were progressing towards those of a natural system.  相似文献   

9.
A number of multipurpose tree species are conserved as scattered trees in settled farms on terraced slopes by the traditional farmers in Central Himalaya, India. Knowledge on growth rates and ecological impacts of these tree species is limited. Ten locally valued multipurpose tree species, viz., Albizzia lebbek, Alnus nepalensis, Boehmeria rugulosa, Celtis australis, Dalbergia sissoo, Ficus glomerata, Grewia optiva, Prunus cerasoides, Pyrus pashia and Sapium sebiferum, were established as mixed plantations at a degraded community forest land site and an abandoned agricultural land site in a village at 1200 m altitude in District Chamoli, India. At the abandoned agricultural land site, annual food crops were grown, along with planted trees, providing supplemental irrigation and organic manure following traditional farming practices. Survival, height, stem circumference, crown depth and width, number of branches, above-ground biomass and soil physico-chemical characteristics were monitored up to five years of plantation growth. Above-ground tree biomass accumulation at the abandoned agricultural land site was 3.9 t ha−1 yr−1 compared with 1.1 t ha−1 yr−1at the degraded forest land site. B. rugulosa, C. australis, F. glomerata, G. optiva, P. cerasoides and S. sebiferum showed more prominent differences in growth at the two sites compared with A. lebbek, A. nepalensis, D. sissoo and P. pashia. A. nepalensis and D. sissoo showed best growth performance at both the sites. A significant improvement in soil physico-chemical characteristics was observed after five years at both of the sites. Carbon sequestration in soil was higher than that in bole biomass. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

10.
Further study is needed on loblolly pine (Pinus taeda L.) growth in a systematic array of plantation designs or stocking rates commonly used in temperate forestry and agroforestry practices. Our objective was to determine loblolly pine growth responses and agroforestry implications of 13 plantation designs (i.e., stocking rates in trees ha−1 [TPH]) at mid-rotation (14 years old). Survival, diameter at 1.3 m above soil surface (dbh), height, basal area (BA), and volume (V) were measured in unthinned plantations ranging from 490 to 2,300 TPH. Stocking rate was positively correlated with BA (r ≥ 0.67) and V (r ≥ 0.55) and negatively correlated with survival (r ≤ −0.83) and dbh (r ≤ −0.83). Plantations with ≥2,000 TPH had closed canopies and excessively high BA and V at mid-rotation. The 4- and 5-row plantations (≥12 m alley spacing) had small dbh (≤17.5 cm). Single-row plantations with ≥3.6 m within row spacing and ≤700 TPH, and the 3-row multiple-row plantations (1,200 TPH), had acceptable BA (29.4–33.2 m2 ha−1) and V (127–136 m3 ha−1). Basal area was ≥30 m2 ha−1 in most plantations indicating thinning is needed to optimize individual tree growth. Besides timber, an array of design-dependent agroforestry and forestry products should drive the selection of any one of these plantation designs: pine straw or biomass production at ≥1,800 TPH, and alley cropping or silvopasture in single-row (≤1,000 TPH) and multiple-row plantations (<1,400 TPH).  相似文献   

11.
A study was conducted to assess carbon stocks in various forms and land-use types and reliably estimate the impact of land use on C stocks in the Nam Yao sub-watershed (19°05'10"N, 100°37'02"E), Thailand. The carbon stocks of aboveground, soil organic and fine root within primary forest, reforestation and agricultural land were estimated through field data collection. Results revealed that the amount of total carbon stock of forests (357.62 ± 28.51 Mg·ha-1, simplified expression of Mg (carbon)·ha-1) was significantly greater (P＜ 0.05) than the reforestation (195.25 ±14.38 Mg·ha-1) and the agricultural land (103.10±18.24 Mg·ha-1). Soil organic carbon in the forests (196.24 ±22.81 Mg·ha-1) was also significantly greater (P＜ 0.05) than the reforestation (146.83± 7.22 Mg·ha-1) and the agricultural land (95.09 ± 14.18 Mg·ha-1). The differences in carbon stocks across land-use types are the primary consequence of variations in the vegetation biomass and the soil organic matter. Fine root carbon was a small fraction of carbon stocks in all land-use types. Most of the soil organic carbon and fine root carbon content was found in the upper 40-cm layer and decreased with soil depth. The aboveground carbon(soil organic carbon: fine root carbon ratios (ABGC: SOC: FRC), was 5:8:1, 2:8:1, and 3:50:1 for the forest, reforestation and agricultural land, respectively. These results indicate that a relatively large proportion of the C loss is due to forest conversion to agricultural land. However, the C can be effectively recaptured through reforestation where high levels of C are stored in biomass as carbon sinks, facilitating carbon dioxide mitigation.  相似文献   

12.
Subtropical evergreen broad-leaved forest is the most widely distributed land-cover type in eastern China. As the rate of land-use change accelerates worldwide, it is becoming increasingly important to quantify ecosystem biomass and carbon (C) and nitrogen (N) pools. Above and below-ground biomass and ecosystem pools of N and C in a subtropical secondary forest were investigated at Laoshan Mountain Natural Reserve, eastern China. Total biomass was 142.9 Mg ha−1 for a young stand (18 years) and 421.9 Mg ha−1 for a premature stand (ca. 60 years); of this, root biomass was from 26.9 (18.8% of the total) to 100.3 Mg ha−1 (23.8%). Total biomass C and N pools were, respectively, 71.4 Mg ha−1 and 641.6 kg ha−1 in the young stand, and 217.0 Mg ha−1 and 1387.4 kg ha−1 in the premature stand. The tree layer comprised 91.8 and 89.4% of the total biomass C and N pools in the young stand, and 98.0 and 95.6% in the premature stand. Total ecosystem C and N pools were, respectively, 101.4 and 4.6 Mg ha−1 for the young stand, and 260.2 and 6.6 Mg ha−1 for the premature stand. Soil C comprised 23.8–29.6% of total ecosystem C whereas soil N comprised 76.9–84.4% of the total. Our results suggest that a very high percentage of N in this subtropical forest ecosystem is stored in the mineral soil, whereas the proportion of organic C in the soil pool is more variable. The subtropical forest in eastern China seems to rapidly accumulate biomass during secondary succession, which makes it a potentially rapid accumulator of, and large sink for, atmospheric C.  相似文献   

13.
The effect of six plantation species in comparison to natural forest (NF) on soil organic carbon (SOC) and total nitrogen (TN) stocks, depth-wise distribution, biomass carbon (C), and N was investigated on plantations and cultivated lands on an Andic paleudalf soil in Southern Ethiopia. The SOC, N, and bulk density were determined from samples taken in 4 replicates from 10-, 20-, 40-, 60-, and 100-cm depth under each site. Similarly, the biomass C and N of the plantation species and understory vegetation were also determined. The SOC and N were concentrated in the 0- to 10-cm depth and decreased progressively to the 1-m depth. Next to the NF, Juniperous procera accrued higher SOC and N in all depths than the corresponding plantations. No evidence of significant difference on SOC and N distribution among plantations was observed below the 10-cm depth with minor exceptions. The plantations accrue from 133.62 to 213.73 Mg ha–1 or 59.1 to 94.5% SOC, 230.4 to 497.3 Mg ha–1 or 6.9 to 14.9% TBC and 420.37 to 672.80 Mg ha–1 or 12.5 to 20% total C-pool of that under the NF. The N stock under Juniperous procera was the highest, while the lowest was under Eucalyptus globulus and Cupressus lusitanica. We suggest that SOC and N sequestration can be enhanced through mixed cropping and because the performance of the native species Juniperous procera is encouraging, it should be planted to restock its habitat.  相似文献   

14.
We measured the aboveground biomass, biomass increment and litterfall production of a 140-year-old, abandoned Cryptomeria japonica plantation in order to infer the effects of topography on biomass production. The plantation was unsuccessful and the naturally regenerated broad-leaved trees contributed 93.4% (374.2 Mg ha−1) of the total aboveground biomass (400.2 Mg ha−1). Comparing between different slope positions, aboveground biomass decreased downslope corresponding to the decrease in broad-leaved tree biomass. The biomass of C. japonica did not vary with slope position. Biomass increment and litterfall production of the broad-leaved trees also decreased downslope. However, litterfall production per unit biomass and aboveground net primary production per unit biomass increased downslope. Results of a path analysis showed that biomass increment of C. japonica decreased with increasing topographical convexity, whereas biomass and litterfall production of broad-leaved tree increased. Litterfall production of broad-leaved tree decreased with increasing biomass of C. japonica, suggesting that, despite their small biomass, the presence of residual C. japonica may have negative effects on the distribution and productivity of the broad-leaved trees. Our results indicated that total aboveground biomass of the study site was comparable to that of old-growth C. japonica plantations. We inferred that the variation in aboveground biomass of the broad-leaved trees was largely determined by the topography, while their productivity was affected by interactions with planted C. japonica.  相似文献   

15.
Doubts exist about the effectiveness of establishing trees near saline discharge areas on farmland to manage dryland salinity. These centre on low rates of water uptake from saline water tables, salt accumulation in tree root zones and the consequent poor growth and survival of trees. Despite this, trees still survive in many plantations established adjacent to saline discharge areas and land-holders often favour such locations, as they do not compete for arable land such as that occurs with plantings in recharge areas. Tree performance and salt accumulation were assessed in three experimental plantations established adjacent to saline discharge areas 20–25 years ago. These were all in the 400–600 mm rainfall zone of south-western Australia. Mean soil salinity, within 1 m of the surface, ranged from 220 to 630 mS m−1, while permanent ground-waters occurred within 2–5 m of the surface and had electrical conductivities ranging from 175 to 4150 mS m−1. The study confirmed the low growth rates expected for trees established over shallow, saline water tables in a relatively low rainfall environment, with estimated wood volumes in Eucalyptus cladocalyx, E. spathulata, E. sargentii, E. occidentalis and E. wandoo of between 0.5 and 1.5 m3 ha−1 yr−1. Values of up to 3 m3 ha−1 yr−1 were obtained on soils with low salinity (<200 mS m−1). The excellent survival (>70%) of several Eucalyptus species confirms that discharge plantations species can persist, despite increasing soil salinity. However, the long-term sustainability of such plantings (50–100 years) without broader landscape treatment of the present hydrological imbalance must be questioned.  相似文献   

16.
Agroforestry systems based on poplar (Populus deltoides) are becoming popular in eastern and northern parts of India. Therefore studies on the structure and function of the systems are important. The investigations included allometric equations for above- and belowground tree components, crop and plantation floor biomass and litter fall estimation at Pusa, Bihar, India. Biomass, floor litter mass, litter fall and net primary productivity (NPP) of plantations increased with an increase in age of trees whereas, crop biomass for any specific crop interplanted with poplar decreased with the age of the plantation. The total plantation biomass increased from 12.08 to 90.59 Mg ha−1 and NPP varied from 5.69 to 27.9 Mg ha−1 year−1. The biomass accumulation ratio ranged from 2.1 to 3.2. Total annual litter fall was in between 1.95 and 10.00 Mg ha−1 year−1, of which 92–94% was contributed by leaf litter. Compartmental models were developed for dry matter distribution in agroforestry systems involving young (3-year-old) and mature (9-year-old) poplar trees interplanted with various crops, the crops being grown in two rotations maize (Zea mays) – wheat (Triticum aestivum) – turmeric (Curcuma domestica) and pigeonpea (Cajanus cajan) – turmeric. This study substantiates the potential of Populus deltoides G3 under agroforestry combinations.  相似文献   

17.
Striga hermonthica (striga) weed is a major threat to crop production in sub-Saharan Africa, and short duration improved fallow species have recently been found to reduce the effects of this weed because of their ability to replenish soil nitrogen. The objective of this study was to compare the efficacy and profitability of coppicing improved fallow species (Gliricidia sepium [gliricidia], Leucaena trichandra [leucaena] and Calliandra calothyrsus [calliandra]) and non-coppicing species (Sesbania sesban [sesbania], Mucuna pruriens [mucuna], and Tephrosia vogelii [tephrosia]), in controlling striga. Natural fallow and a sole maize crop were included as control treatments. The fallow treatments were split into two and either fertilized with N or unfertilized. The results showed that coppicing fallows produced higher biomass than non-coppicing fallows. For example, Callindra (coppicing fallow species) produced 19.5 and 41.4 Mg ha−1 of leafy and woody biomass, respectively after four cumulative harvests as compared with Sesbania (non-coppicing species), which produced only 2.3 and 5.9 Mg ha−1 leaf and woody biomass, respectively. Improved fallows reduced striga population in proportion to the amount of leafy biomass incorporated into the soil (r = 0.87). N application increased cumulative maize yield by between 15–28% in improved fallow systems and by as much as 51–83% in the control treatments. Added total costs of the coppicing fallows did not differ significantly from those of the non-coppicing fallows and control treatments. However, the added net benefits of the coppicing fallows were significantly higher (US$ 527 for +N and 428 for −N subplots; P < 0.01) than those of the non-coppicing fallows (US$ 374 for +N and 278 for −N), and the least for the control treatments. The most profitable fallow system was Tephrosia with net added benefits of US$ 453.5 ha−1 season−1 without N, and US$ 586.7 ha−1 season−1 with added N.  相似文献   

18.
A Review of Fine Root Dynamics in Populus Plantations   总被引：1，自引：0，他引：1  
Production of native and hybridized varieties of Populus has received considerable interest in temperate regions as an alternative to agricultural crops and an additional wood source, while acting as a potential carbon (C) sink to offset emissions of fossil fuel-based greenhouse gases. Research of root system dynamics in Populus species is expanding, however, our understanding of the nature and role of fine roots (FR) is incomplete. The study objective, therefore, was to review the literature regarding FR production, mortality and longevity in Populus, and evaluate the magnitude and significance of the FR fraction to C sequestration. FRs, conventionally defined as less than 2 mm in diameter and responsible for water and nutrient uptake, are an essential component of the tree. Populus FRs are relatively short-lived, with reported lifespans ranging from 30 to 300 days, depending on root diameter, tree species and age, and soil environmental factors. Standing FR biomass fluctuates throughout the growing season. Fine root production generally peaks in mid-summer, and ranges between 1.0 and 5.0 mg ha−1 yr−1, while FR mortality has less seasonal amplitude. Production and mortality dynamics in Populus are highly plastic in response to soil environmental conditions, and although opposing conclusions have been proposed, research suggests soil moisture and nitrogen to be most important. Results from the literature indicate annual FR turnover to the soil C pool may be small (0.2–1.6 mg C ha−1 yr−1), but substantial in maintaining or enhancing C levels in natural and managed stands of Populus.  相似文献   

19.
选择4种人工林,包括3个乡土树种(阔叶合欢(Albizia lebbeck)、黄豆树(A.procera)、柚木(Tectona grandis))和一个乡土草种(印度实竹(Dendrocalamus strictus))的高密度人工幼林,研究了人工林发育早期阶段对印度Singrauli煤矿废弃地土壤养分的影响。在4种人工林4年生和5年生阶段,采集0-10、10-20cm层土壤,分析其总有机碳、全氮和全磷含量。结果表明,林龄、树种和土层对土壤总有机碳、全氮和全磷含量的影响存在显著差异;各林分10-20cm土层中的全总有机碳、全氮和全磷含量较低;4个不同林分对土壤养分的改良效果表现为:阔叶合欢>印度实竹>黄豆树>柚木。说明人工林对煤矿废弃地土壤的改良效果因树种而异。  相似文献   

20.
Interest in planted fallow systems has focused on soil fertility improvement, neglecting other potential benefits of such systems. It is important to quantify other processes responsible for crop yield increases under planted fallows, such as weed control. The suppressive potential on weeds of Flemingia macrophylla [(Willd.) Merrill] and Pueraria phaseoloides (Roxb.) Benth, planted fallows was evaluated in field trials in three villages in southern Cameroon. In each village, experiments were set up in 4–5 year-old bush fallow dominated by Chromolaena odorata (L.) R. M. King & H. Rob. and 20 year-old secondary forest. Total aboveground biomass production of P. phaseoloides was 7.45 Mg ha−1, 4.2 times higher than F. macrophylla (1.78 Mg ha−1 ; P < 0.05). The high biomass of P. phaseoloides resulted in a significantly greater reduction in total weed biomass compared to Flemingia macrophylla in both wet and dry seasons. In the wet season (11 and 18 MAP), there were significant fallow system × land use and fallow system × village interactions for total weeds and broadleaf weeds. P. phaseoloides in bush (0.55 Mg ha−1), and P. phaseoloides at Ngoumou (0.09 Mg ha−1) had the lowest total weeds in the wet seasons. After the dry season, the lowest total weed mass was consistently recorded in P. phaseoloides while the highest was in the natural regrowth. The population of grasses was always higher in the F. macrophylla system than in P. phaseoloides system throughout the wet and dry seasons. Grass biomass in the P. phaseoloides-forest LUS was the least (0.01 Mg ha−1), 58 times lower than in F. macrophylla-bush (0.58 Mg ha−1). Biomass production of P. phaseoloides was highly significantly correlated with total weed biomass (r = −0.64; P = 0.004) while no relationship was found between biomass production of F. macrophylla and total weed biomass (r = −0.08, P = 0.747). It was concluded that P. phaseoloides was a suitable leguminous species for weed control. But for F. macrophylla, its low biomass production coupled with a compact plant architecture compromised it as an appropriate species for weed control in a planted fallow system.  相似文献   

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