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1.
A 27-year-old stand of flooded gum (Eucalyptus grandis Hill ex Maiden) in the North Coast Region of N.S.W. was assessed in relation to aboveground distribution and turnover of organic matter, nitrogen, phosphorus, calcium, magnesium and potassium. Of the 453 t ha?1 of aboveground organic matter present, 394 t was in the tree, 42 t in the understorey and 28 t in the forest floor. The total nitrogen, phosphorus, calcium, magnesium and potassium contents of the stand were 739, 44, 1254 and 658 kg ha?1, respectively, and the understorey contained 35%, 35%, 16%, 24% and 49% of the above-ground distribution of these nutrients respectively. Although the developing rainforest understorey comprised a relatively small portion (9.3%) of the total aboveground biomass, it played a disproportionate role in nutrient accumulation and uptake, and had an annual net accumulation of 14%, 55%, 59%, 30%, 44% and 69% of the aboveground organic matter, nitrogen, phosphorus, calcium, magnesium and potassium respectively. The net annual removal from the soil was 30, 1, 38, 5 and 31 kg ha?1 year?1 for nitrogen, phosphorus, calcium, magnesium and potassium, respectively. Flooded gum had very high accumulations of calcium in the bark and the effect of this in nutrient cycling is discussed. An idealised management system, to exploit and optimise the nutrient cycle of flooded gum, has been hypothesided.  相似文献   

2.
ABSTRACT

Grey alder (Alnus incana) is a highly productive indigenous tree species, potential for short-rotation forestry in the Baltic and Nordic countries. The aim of the study was to investigate the development of a new forest generation, as well as the nitrogen (N) and carbon (C) storages and fluxes in a grey alder regenerating coppice (COP) after clear-cut and in an adjacent unharvested 21-year-old stand (MAT), which had reached its bulk maturity. The regeneration of COP was rapid and 5 years after clear-cut, stem mass was 6.4?t?ha?1. The nitrogen demand of the aboveground part of the 5-year-old COP trees was estimated to be roughly half of the corresponding value for MAT, depending mostly on leaf production. The annual N leaching flux in MAT was in the range of 16–29?kg?ha?1, the corresponding values for COP were roughly half of that. Net nitrogen mineralization did not differ significantly between MAT (117?kg?ha?1) and COP (129?kg?ha?1). For the soil respiration study, a 32-year-old grey alder stand growing at a similar site was included; soil respiration was significantly higher in MAT compared to COP in all study years in both studied stands.  相似文献   

3.
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   

4.
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   

5.
Liu  Guancheng  Yan  Guoyong  Chang  Mengyu  Huang  Binbin  Sun  Xingyu  Han  Shijie  Xing  Yajuan  Wang  Qinggui 《European Journal of Forest Research》2021,140(5):1113-1126

In recent decades, global warming and nitrogen (N) deposition have been increasing obviously, which have led to some strong responses in terrestrial ecosystems, especially the carbon (C) cycle. The boreal forest occupies an important position in the global C cycle with its huge C storage. However, the impact of global change such as N deposition on boreal forest ecosystem C cycle has been not very clear. In order to solve this problem, the field experiment of N addition in a boreal forest has been built in the Greater Khingan Mountains of Northeast China since 2011. Four N addition gradients (0, 25, 50, 75 kg N ha?1 year?1) were set up to study the response of above- and belowground C pool to N addition. The results showed that the total forest C sequestration of low-, medium- and high-N treatments was 104.4?±?5.9, 20.2?±?2.7 and 5.3?±?0.4 g C/g N, respectively. Aboveground trees were the largest C pool, followed by soil, roots and floor C pool. Low-N increased the input of C by promoting photosynthesis. Trees of Larix gmelini increased the investment in the belowground root system and increased the belowground C pool. High-N reduced the inter-annual litter biomass and decreased litter C:N that accelerated the decomposition of litter, resulting in a reduction in the floor C pool. Low-N increased total soil respiration, while medium- and high-N inhibited heterotrophic respiration and then increased soil C sequestration. The estimation of forest C pool provides valuable data for improving the C dynamic characteristics of boreal forest ecosystem and is of great significance for us to understand the impact of climate change on the global C cycle.

  相似文献   

6.
The impacts of wood harvest, biomass removal and inter-rotation site management practices on productivity of Acacia mangium in South Sumatra were studied over 12 years across successive rotations. The productivity measured as MAI increased from 29.4 m3 ha?1 year?1 in the first to 48.0 m3 ha?1 year?1 in the second rotation. Whole tree harvesting (total stem, branches and leaves) caused a 21 % reduction in volume compared to harvesting merchantable wood alone in the next rotation. The rates of nutrients accumulation in trees were highest during the first year of growth, and declined from age 2 years. Significant amounts of nutrients were recycled through litter fall from 1 year after planting. Results highlight the importance of management which promotes nutrient supply on stand growth. Removal of slash and litter lowered soil pH, by about 0.1 unit. A small reduction was also found in soil organic carbon and nitrogen in the top soil during the first 3–4 years but values returned to pre-harvest levels by the end of the rotation. Extractable soil phosphorus and exchangeable cations decreased by the end of second rotation but these measures underestimate the nutrient pools available for A. mangium. These findings along with results from other studies have helped to implement operations which promote conservation of site resources for sustainable production in the region.  相似文献   

7.
To examine the effects of elevated N and S inputs on a central hardwood forest, a whole-watershed acidification experiment was initiated in 1989 on the Fernow Experimental Forest, West Virginia. Annual experimental additions of 40 kg S ha−1 year−1 and 35 kg N ha−1 year−1 as ammonium sulfate fertilizer were applied to a 34 ha watershed with a 25-year-old stand of central Appalachian hardwoods. An adjacent watershed served as the control. After 5 years of treatment (total additions of 275 kg S ha−1 and 220 kg N ha−1), stream water NO3−, Ca2+, Mg2+ concentrations and export increased. Soil solution concentrations provide evidence that the treatment watershed is nitrogen-saturated, which was unexpected for such a young stand. No statistically significant changes in annual SO42− export were observed, but peak stream water concentrations of SO42− did increase during the treatment period. Changes in soil solution chemistry suggest that the treated watershed also may be approaching SO42− saturation.  相似文献   

8.
This study was conducted to determine carbon (C) dynamics following forest tending works (FTW) which are one of the most important forest management activities conducted by Korean forest police and managers. We measured organic C storage (above- and below-ground biomass C, forest floor C, and soil C at 50 cm depth), soil environmental factors (soil CO2 efflux, soil temperature, soil water content, soil pH, and soil organic C concentration), and organic C input and output (litterfall and litter decomposition rates) for one year in FTW and non-FTW (control) stands of approximately 40-year-old red pine (Pinus densiflora S. et Z.) forests in the Hwangmaesan Soopkakkugi model forest in Sancheonggun, Gyeongsangnam-do, Korea. This forest was thinned in 2005 as a representative FTW practice. The total C stored in tree biomass was significantly lower (P < 0.05) in the FTW stand (40.17 Mg C ha−1) than in the control stand (64.52 Mg C ha−1). However, C storage of forest floor and soil layers measured at four different depths was not changed by FTW, except for that at the surface soil depth (0–10 cm). The organic C input due to litterfall and output due to needle litter decomposition were both significantly lower in the FTW stand than in the control stand (2.02 Mg C ha−1 year−1 vs. 2.80 Mg C ha−1 year−1 and 308 g C kg−1 year−1 vs. 364 g C kg−1 year−1, respectively, both P < 0.05). Soil environmental factors were significantly affected (P < 0.05) by FTW, except for soil CO2 efflux rates and organic C concentration at soil depth of 0–20 cm. The mean annual soil CO2 efflux rates were the same in the FTW (0.24 g CO2 m−2 h−1) and control (0.24 g CO2 m−2 h−1) stands despite monthly variations of soil CO2 efflux over the one-year study period. The mean soil organic C concentration at a soil depth of 0–20 cm was lower in the FTW stand (81.3 g kg−1) than in the control stand (86.4 g kg−1) but the difference was not significant (P > 0.05). In contrast, the mean soil temperature was significantly higher, the mean soil water content was significantly lower, and the soil pH was significantly higher in the FTW stand than in the control stand (10.34 °C vs. 8.98 °C, 48.2% vs. 56.4%, and pH 4.83 vs. pH 4.60, respectively, all P < 0.05). These results indicated that FTW can influence tree biomass C dynamics, organic C input and output, and soil environmental factors such as soil temperature, soil water content and soil pH, while soil C dynamics such as soil CO2 efflux rates and soil organic C concentration were little affected by FTW in a red pine stand.  相似文献   

9.
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   

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.
Some land-use systems in Saskatchewan, Canada include the nitrogen-fixing trees buffaloberry (Shepherdia argentea Nutt.), caragana (Caragana arborescens Lam.) and sea buckthorn (Hippophae rhamnoides L.). These species provide various ecological functions such as ameliorating soil moisture, light and temperature but little work has been done quantifying biological nitrogen fixation by these species. Greenhouse experiments were conducted to quantify N2-fixation using the 15N natural abundance and the 15N dilution methods. Buffaloberry failed to form nodules in all but one of the four replicates in the natural abundance experiment. Using the 15N dilution method, the percentage of N derived from atmosphere (%Ndfa) in the shoot of buffaloberry averaged 64 %. For caragana, the mean  %Ndfa was 59 and 65 % and seabuckthorn was 70 and 73 % measured using the natural abundance and dilution methods, respectively. Because of large variability in biomass production between plants grown in the natural abundance experiment and the dilution experiment, the amounts of N2 fixed also were very variable. Buffaloberry fixed an average of 0.89 g N m?2; the average for caragana ranged from 1.14 to 4.12 g N m?2 and seabuckthorn ranged from 0.85 to 3.77 g N m?2 in the natural abundance and dilution experiments, respectively. This corresponds to 16 kg N ha?1 year?1 for buffaloberry; an average of 15–73 kg N ha?1 year?1 in caragana and 11–67 kg N ha?1 year?1 in seabuckthorn. The substantial amounts of N2 fixed by these species indicate that they have the potential to contribute to the overall N balance in land-use systems in which they are included.  相似文献   

12.
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   

13.
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   

14.
In order to find a nitrogen fertilization regime that is economically feasible in commercial short‐rotation forest stands of basket willow (Salix viminalis L.), a field trial was established on a clay soil near Västerås, central Sweden, in early 1990. A response surface design was used in which three levels of treatment were chosen for each single year: year 1—0, 30, 60, kg N ha?1; year 2—0, 60, 120, kg N ha?1; year 3—0, 90, 180, kg N ha?1; year 4—0, 60, 120, kg N ha?1. Thirty‐two combinations of these levels, out of 81 possible, were chosen and divided into four blocks. Thus, eight unique treatments were randomized to the plots within each block, providing no replicates at the end of the experimental period. This gave us a more flexible and informative experiment than many of those used earlier with rather few treatments, although they were replicated. After 4 years the willow stand was harvested and the accumulated stem production of each treatment was assessed. The effect of nitrogen fertilization on accumulated stem growth over the experimental period was found to be significant only for nitrogen applied in years 2 and 3, with a somewhat (statistically significant) larger effect in year 2. Growth response to nitrogen fertilization was best approximated with a function including terms with applied amount of nitrogen in years 2 and 3 and, furthermore, a term of interaction with negative coefficient between these years. The interaction between these years was interpreted as the system's ability to recycle nitrogen from one year to another.  相似文献   

15.
The objective of this study was to quantify the effects of high nitrogen (N) inputs on N cycling in a 35–45-yr-old Scots pine (Pinus sylvestris L.) forest. Nitrogen was added annually (single doses) as NH4NO3 in doses of 0 (N0), 30 (N1) and 90 (N2) kg N ha?1 yr?1. The only N input to the N0 plots was atmospheric deposition of 10 kg N ha?1 yr?1. The N cycle in these plots was tight, with almost complete retention of the incoming N. In the N1 plots the N retention was 83% after 9 yrs of N addition. The trees were the major sink, but the soil also contributed to the N retention. In the N2 plots the N retention was 63%, being mainly accounted for by accumulation in the soil. The leaching of N from the N2 stands was as high as 35 kg N ha?1 yr?1. The N2 system was N saturated.  相似文献   

16.
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   

17.
Large amounts of plant litter deposited in cacao agroforestry systems play a key role in nutrient cycling. Organic matter, nitrogen and phosphorus cycling and microbial biomass were investigated in cacao agroforestry systems on Latosols and Cambisols in Bahia, Brazil. The objective of this study was to characterize the microbial C and N, mineralizable N and organic P in two soil orders under three types of cacao agroforestry systems and an adjacent natural forest in Bahia, Brazil and also to evaluate the relationship between P fractions, microbial biomass and mineralized N with other soil attributes. Overall, the average stocks of organic C, total N and total organic P across all systems for 0?C50?cm soil depth were 89,072, 8,838 and 790?kg?ha?1, respectively. At this soil depth the average stock of labile organic P was 55.5?kg?ha?1. For 0?C10?cm soil depth, there were large amounts of microbial biomass C (mean of 286?kg?ha?1), microbial biomass N (mean of 168?kg?ha?1) and mineralizable N (mean of 79?kg?ha?1). Organic P (total and labile) was negatively related to organic C, reflecting that the dynamics of organic P in these cacao agroforestry systems are not directly associated with organic C dynamics in soils, in contrast to the dynamics of N. Furthermore, the amounts of soil microbial biomass, mineralizable N, and organic P could be relevant for cacao nutrition, considering the low amount of N and P exported in cacao seeds.  相似文献   

18.
The decomposition of harvest residues (brash) in managed forests has an important influence on the carbon (C) and nitrogen (N) stocks of these ecosystems. The brash input from thinning events in a 25-year-old Sitka spruce plantation was determined. A litter-bag method was used to determine the mass loss and decomposition rate of brash left on the forest floor. The changes in C and N concentrations and the C:N ratio of the needles and branches were also monitored as decomposition progressed for 2.5 years. Using the decomposition rate (k b) and estimated brash inputs, we then determined the total cumulative stock of C that the brash could supply to the deadwood pool over a 41-year rotation period. The three thinning events resulted in the addition of 37.99 t C ha?1 and 0.61 t N ha?1 to the forest floor. A significant mass loss of 44 % was recorded from brash decomposition bags after 2.5 years, with a rapid loss of 35 % in the first year, after which the rate of decomposition slowed. The k b-value and residence time (95 % decomposition) were 0.311 year?1 and 9.6 years, respectively. There was a 69 % increase in the N concentration of needles after 1.5 years, while an increase of 185 % in the N concentration of branches was recorded after 2.5 years. The C concentration (48.55 ± 0.20 %) did not differ significantly between the needles and branches over time. The accumulated C stock from decomposing brash at clearfell was estimated at 18.51 t C ha?1.  相似文献   

19.
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   

20.
Abstract

The National Forest Inventory (NFI) is an important resource for estimating the national carbon (C) balance. Based on the volume, biomass, annual biomass increment and litterfall of different forest types and the 6th NFI in China, the hyperbolic relationships between them were established and net primary production (NPP) and net ecosystem production (NEP) were estimated accordingly. The results showed that the total biomass, NPP and NEP of China's forests were 5.06 Pg C, 0.68 Pg C year?1 and 0.21 Pg C year?1, respectively. The area-weighted mean biomass, NPP and NEP were 35.43 Mg C ha?1, 4.76 Mg C ha?1 year?1 and 1.47 Mg C ha?1 year?1 and varied from 13.36 to 79.89 Mg C ha?1, from 2.13 to 9.15 Mg C ha?1 year?1 and from ?0.16 to 5.80 Mg C ha?1 year?1, respectively. The carbon sequestration was composed mainly of Betula and Populus forest, subtropical evergreen broadleaved forest and subtropical mixed evergreen–deciduous broadleaved forest, whereas Pinus massoniana forest and P. tabulaeformis forest were carbon sources. This study provides a method to calculate the biomass, NPP and NEP of forest ecosystems using the NFI, and may be useful for evaluating terrestrial carbon balance at regional and global levels.  相似文献   

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