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71.
72.
Bareroot jack pine (Pinus banksiana Lamb.) and white spruce (Picea glauca (Moench) Voss) were planted near Elliot Lake, Ontario, on a boreal reforestation site. Site preparation treatments were mixed, mineral and undisturbed (i.e., control) soil. Seedling water relations and growth were examined during the first field season. During the first 28 days after planting, jack pine base (i.e., predawn) and minimum xylem water potential readings were more negative in the control site preparation treatment. White spruce, during the first 10 days, in all site preparation treatments had base and minimum xylem water potential readings more negative than –1.7 MPa. By day 28 base xylem water potentials of white spruce had increased to approximately –1.0 MPa in all site preparation treatments. As the growing season progressed, white spruce minimum xylem water potential readings ceased exceeding the measured turgor loss point first in the mixed followed by the mineral and then control site preparation treatment. Jack pine minimum xylem water potential readings, in all site preparation treatments, almost never exceeded the measured turgor loss point. Water stress and stomatal optimization integrals, day 28 and 125, for both species showed least water stress and greater stomatal optimization in the mixed, mineral and control site preparation treatments, respectively. Both species had less new root growth in the field during the first 28 days after planting compared to seedlings grown for 28 days in a greenhouse for root growth capacity testing. Root growth at 28 days and both shoot and root development at the end of the growing season, were greatest to least in mixed, mineral, and control site preparation treatments, respectively. 相似文献
73.
74.
75.
Xu Jun-liang Ma Lv-yi 《中国林学(英文版)》2007,9(4):251-255
In order to explore the relationship between the time processes of solar radiation and sap flow, sap flow velocity (SFV) of Platycladus orientalis and Pinus tabulaeformis, effective solar radiation (ESR) and other environmental factors were synchronously monitored for one year in the Beijing Western Mountains by using a thermal dissipation probe (TDP) system and an automatic weather station. Results showed significant differences between changes in diurnal characteristics of ESR and sap flow in sunny days during three seasons. Starting times of sap flow occurred generally 1.5–3 hours later than those of solar radiation and there were small differences between Platycladus orientalis and Pinus tabulaeformis. But peak times and stopping times of sap flow varied con-siderably with large contrasts in ESR. The duration of sap flow showed clear differences among the seasons owing to the variable rhythms of climate factors in Beijing. Fluctuation amplitude in the duration of sap flow remained relatively stable during the autumn but changed greatly during spring and summer. Changes in diurnal sap flow velocity of both Platycladus orientalis and Pinus tabu-laeformis were about 0–3 hours later than those of ESR but with the same configuration. The start of sap flow was mainly induced by the sudden intensification of ESR (sunrise effect). Seasonal models of SFV indicated that a cubic equation had the best fit. It was more practical to simulate seasonal water consumption models of trees with ESR. In further investigations, these models should be optimized. 相似文献
76.
Nitrification is the biological conversion of organic or inorganic nitrogen compounds from a reduced to a more oxidized state.
Denitrification is generally referred to as the microbial reduction of nitrate to nitrite and further gaseous forms of nitric
oxide, nitrous oxide and molecular nitrogen. They are functionally interconnected processes in the soil nitrogen cycle that
are involved in the control of long-term nitrogen losses in ecosystems through nitrate leaching and gaseous N losses. In order
to better understand how nitrification and denitrification change during the process of ecosystem restoration and how they
are affected by various controlling factors, gross nitrification rates and denitrification rates were determined using the
barometric process separation (BaPS) technique in subalpine coniferous forests of different restoration stages. The results
showed that forest restoration stage had no significant effects on gross nitrification rates or denitrification rates (One-way
ANOVA (analysis of variance), p < 0.05). There was no significant difference in the temperature coefficient (Q
10) for gross nitrification rate among all the forest sites (One-way ANOVA, p < 0.05). Gross nitrification rates were positively correlated with water content (p < 0.05), but not with soil pH, organic matter, total nitrogen, or C/N ratios. Denitrification rates in all the forest soils
were low and not closely correlated with water content, soil pH, organic matter, or total nitrogen. Nevertheless, we found
that C/N ratios obviously affected denitrification rates (p < 0.05). Results from this research suggest that gross nitrification is more responsible for the nitrogen loss from soils
compared with denitrification.
Translated from Journal of Plant Ecology, 2006, 30(1): 90–96 [译自: 植物生态学报] 相似文献
78.
观光木播种苗生长规律及育苗技术研究 总被引:3,自引:1,他引:3
用有序样本聚类分析法将观光木1年生播种苗生长过程划分为4个时期:出苗期(2月26日-5月20日)、幼苗期(5月21日-7月20日)、速生期(7月21日-10月20日)和生长后期(10月21日-11月20日)。不同播种期的试验表明:冬播观光木比春播提早16 d萌发,苗高、地径生长量和总生物量分别比春播提高13.3%、15.1%和18.8%。采用沙藏可促进种子提早萌发和提高场圃发芽率。不同密度试验表明,观光木育苗采用60株.m-2的密度较好。 相似文献
79.
在充分考虑数控车床加工表面特征的基础上,对以往仿真模型的不足进行了分析,提出了基于螺旋曲面的加工表面模型。该模型充分考虑了数控程序中主轴转速和进给速率两个重要参数,并提出了数控车床动态加工过程仿真的时间驱动机制。 相似文献
80.
The soil structure was expressed with fractal dimensions of particle size distribution (PSD), aggregate size distribution
(ASD), and soil pore size distribution (SPD). The effect of soil fractal features on soil infiltration velocity and process
was studied. The result of the fractal feature shows that fractal dimensions of PSD are obviously greater than those of ASD
and SPD, and in different soil genetic horizons, the fractal dimension of ASD has the greatest variability, and shows a downtrend
on the top-to-bottom genetic horizon. According to the soil infiltration process curve, the infiltration process was divided
into three phases: (1) the initial phase (0–5 min), (2) the transition phase (5–30 min), and (3) the stable phase (30–180
min). In the initial phase of infiltration, the soil structure of soil genetic horizon A was the major influencing factor;
in the transition phase of infiltration, the pore distribution of soil horizon AB and soil structure of horizon B were the
major influencing factors; in the stable phase of infiltration, the soil structure of horizon C was the major influencing
factor to the infiltration velocity. Soil infiltration process is influenced comprehensively by soil PSD, ASD, and SPD. In
the overall soil water infiltration, the infiltration in shrub forest land was much faster than that in other land uses, and
in the initial infiltration phase, arable land soil infiltration was much faster than that in forest land, and in the stable
infiltration phase, the infiltration velocity in forest land was faster than that in arable land.
__________
Translated from Journal of Beijing Forestry University, 2006, 28(3): 73–78 [译自: 北京林业大学学报] 相似文献