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At present, our understanding of the dynamics of microbial biomass and soil N in silvopastoral systems is very limited. In
this paper, the effects of understorey management on soil microbial C and N, net N mineralization, and net nitrification were
studied in two seven-year-old radiata pine (Pinus radiata D. Don) – pasture systems, consisting of plots with and without ryegrass (Lolium perenne) as an understorey. Mini-plots (1 × 1 m) with animals excluded and herbage repeatedly clipped and removed were used for soil
sampling. Three mini-plots formed a transect at each of two positions: 0.9 and 3.5 m north of the tree rows. Measurements
were taken from July 1997 to June 1998 about once every 40 days. One composite sample was collected from each of two sampling
depths (0–10 and 10–20 cm) at each transect position on each sampling date. Temporal and spatial variability of N mineralization
rates and microbial biomass C and N was large. Net mineralization and nitrification rates were higher in the bare ground than
in the ryegrass plots for a major part of the year, particularly from late spring to early fall. Net N mineralization and
nitrification rates were higher in the 0–10 than in the 10–20 cm soil layers in both the ryegrass and bare ground treatments;
however, the depth effect on microbial biomass C and N was only significant in the ryegrass treatment. In the surface soil
layer, microbial biomass C and N were substantially greater in the ryegrass than in the bare ground plots. Soil microbial
properties and activities were closely linked to pasture root activities, soil depth, and site biophysical conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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Zhaohua Dai Carl C. Trettin Changsheng Li Harbin Li Ge Sun Devendra M. Amatya 《Water, air, and soil pollution》2012,223(1):253-265
Emissions of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) from a forested watershed (160 ha) in South Carolina, USA, were estimated with a spatially explicit watershed-scale modeling
framework that utilizes the spatial variations in physical and biogeochemical characteristics across watersheds. The target
watershed (WS80) consisting of wetland (23%) and upland (77%) was divided into 675 grid cells, and each of the cells had unique
combination of vegetation, hydrology, soil properties, and topography. Driven by local climate, topography, soil, and vegetation
conditions, MIKE SHE was used to generate daily flows as well as water table depth for each grid cell across the watershed.
Forest-DNDC was then run for each cell to calculate its biogeochemistry including daily fluxes of the three greenhouse gases
(GHGs). The simulated daily average CH4, CO2 and N2O flux from the watershed were 17.9 mg C, 1.3 g C and 0.7 mg N m−2, respectively, during the period from 2003–2007. The average contributions of the wetlands to the CH4, CO2 and N2O emissions were about 95%, 20% and 18%, respectively. The spatial and temporal variation in the modeled CH4, CO2 and N2O fluxes were large, and closely related to hydrological conditions. To understand the impact of spatial heterogeneity in
physical and biogeochemical characteristics of the target watershed on GHG emissions, we used Forest-DNDC in a coarse mode
(field scale), in which the entire watershed was set as a single simulated unit, where all hydrological, biogeochemical, and
biophysical conditions were considered uniform. The results from the field-scale model differed from those modeled with the
watershed-scale model which considered the spatial differences in physical and biogeochemical characteristics of the catchment.
This contrast demonstrates that the spatially averaged topographic or biophysical conditions which are inherent with field-scale
simulations could mask “hot spots” or small source areas with inherently high GHGs flux rates. The spatial resolution in conjunction
with coupled hydrological and biogeochemical models could play a crucial role in reducing uncertainty of modeled GHG emissions
from wetland-involved watersheds. 相似文献
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Agroforestry in Nepal: research and practice 总被引：1，自引：0，他引：1
Agroforestry research and practice in Nepal is reviewed. The social and ecological complexity of the country is outlined along with some of the methodological problems. The central importance of trees for fodder and areas that they can be planted on farms are discussed. The role of adjacent forest for compost, firewood and tree seedlings is also highlighted. A system containing Nepalese Alder is outlined and assessed as an agroforestry system that is increasingly being adapted in the middle hills of eastern Nepal. 相似文献
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Understanding the changes in soil properties in silvopastoral systems is important in regulating the interactions between
tree and understorey pastures. In this study, the effects of understorey management on soil mineral N and moisture availability,
soil temperature, soil C, and tree growth were investigated in a seven-year-old silvopastoral agroforestry experiment in Canterbury,
New Zealand. The systems included understorey treatments of bare ground and ryegrass (Lolium perenne) pasture. Soil mineral N, moisture content, and temperature were monitored from July 1997 to July 1998 in two positions (0.9
and 3.5 m north of tree rows) and two soil depths (0–10 and 10–20 cm). Soil C and N in the 0–10 cm depth were higher in the
ryegrass than in the bare ground plots, reflecting the organic C and N input in the ryegrass plots, as well as greater N loss
from the bare ground plots in the form of nitrate leaching and/or denitrification. Soil C was higher in the position 0.9 m
than 3.5 m away from the tree rows, possibly caused by the greater C input from decomposing fine tree roots and needle litterfall
at the 0.9 m position. Soil moisture availability was greater in the bare ground than in the ryegrass plots in the summer.
No effect of understorey management on soil temperature was found. Soil nitrate levels were lower in the ryegrass plots and
may be limiting when soil moisture supply was adequate. Tree volume growth from winter 1997 to 1998 was significantly greater
in the bare ground treatment, reflecting better soil moisture and N supply conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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G. Sun A. Noormets M.J. Gavazzi S.G. McNulty J. Chen J.-C. Domec J.S. King D.M. Amatya R.W. Skaggs 《Forest Ecology and Management》2010
During 2005–2007, we used the eddy covariance and associated hydrometric methods to construct energy and water budgets along a chronosequence of loblolly pine (Pinus taeda) plantations that included a mid-rotation stand (LP) (i.e., 13–15 years old) and a recently established stand on a clearcut site (CC) (i.e., 4–6 years old) in Eastern North Carolina. Our central objective was to quantify the differences in both energy and water balances between the two contrasting stands and understand the underlining mechanisms of environmental controls. We found that the LP site received about 20% more net radiation (Rn) due to its lower averaged albedo (α) of 0.25, compared with that at the CC (α = 0.34). The mean monthly averaged Bowen ratios (β) at the LP site were 0.89 ± 0.7, significantly (p = 0.02) lower than at the CC site (1.45 ± 1.2). Higher net radiation resulted in a 28% higher (p = 0.02) latent heat flux (LE) for ecosystem evapotranspiration at the LP site, but there was no difference in sensible heat flux (H) between the two contrasting sites. The annual total evapotranspiration (ET) at the LP site and CC site was estimated as 1011–1226 and 755–855 mm year−1, respectively. The differences in ET rates between the two contrasting sites occurred mostly during the non-growing seasons and/or dry periods, and they were small during peak growing seasons or wet periods. Higher net radiation and biomass in LP were believed to be responsible to the higher ET. The monthly ET/Grass Reference ET ratios differed significantly across site and season. The annual ET/P ratio for the LP and CC were estimated as 0.70–1.13 and 0.60–0.88, respectively, indicating higher runoff production from the CC site than the LP site. This study implied that reforestation practices reduced surface albedos and thus increased available energy, but they did not necessarily increase energy for warming the atmosphere in the coastal plain region where soil water was generally not limited. This study showed the highly variable response of energy and water balances to forest management due to climatic variability. 相似文献
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