亚热带生态公益林冠层结构与林下辐射动态

冠层结构动态是林冠生长动态的一个表现,冠层结构对森林群落生产力、生态系统功能、群落更新与演替等具有重要作用。准确量化森林群落冠层结构和林下辐射特征可以为研究森林生态系统功能提供基础。以亚热带山地的红花荷林、密花树次生林、樟树人工林、杉木林、杉木-红锥混交林和毛竹林为对象,利用半球面影像技术探讨不同林型冠层结构与林下辐射动态,揭示冠层结构与林下辐射之间的相关性。结果表明,不同的森林群落类型有比较固定的冠层结构和林下辐射特征,且不同林型的冠层结构与林下辐射存在极显著差异(P<0.01)。樟树林的林冠开度最小(16.47%),其次是杉木林(17.12%)、杉木-红锥混交林(17.45%)、红花荷林(20.21%)以及密花树次生林(20.93%),毛竹林的林冠开度最大(21.32%)。而叶面积指数则呈相反的变化趋势,樟树林的叶面积指数最大(2.04),毛竹林的叶面积指数最小(1.78)。另外,樟树人工林的林下直射光(4.34 mol·m^-2·d^-1)、林下散射光(3.52 mol·m^-2·d^-1)和林下总光照(7.86 mol·m^-2·d^-1)均小于其他林型;而杉木林由于其冠幅较窄,林下直射光最强(5.22 mol·m^-2·d^-1)。不同林型林下直射光、林下散射光和林下总光照的月际动态变化极显著(P<0.0001),生长季的林下辐射强度最大。不同林型冠层结构与林下辐射相关性存在差异,越简单的群落结构,林冠开度与林下光照的相关性越强,叶面积指数与林下光照的相关性越强。研究冠层结构与林下辐射异质性为营造最适的冠层、充分发挥生态系统效能,以及森林生态系统可持续发展提供理论依据。

林下太阳辐射环境对人参生长发育影响的初步研究

[目的]探究林下太阳辐射环境对人参生长发育的影响。[方法]选取吉林省梅河口市吉乐林场内10个试验单位,测定其内的太阳直射辐射、散射辐射、光合有效辐射(PAR)及光谱辐射指标,以8年生林下参为试验材料,测定其形态指标及净光合速率(Pn)。[结果]林下散射辐射日累计值在109.45～202.27 W/m2时,人参地上部分的生长与散射辐射呈显著负相关;林下参株高仅取决于PAR的大小,茎高、叶宽和叶面积与散射辐射呈显著负相关,而与PAR相关性不显著;茎粗与散射辐射和PAR均呈显著负相关;当PAR值接近时,红橙光和绿光含量高的试验单位,林下参Pn较大。[结论]林下太阳辐射环境对人参的形态特征及光合生理特性均有较大影响。

Phosphorus fertilizer induced changes in the soil available P,the P nutrition and the growth of Pinus radiata seedlings grown in association with understory

A study was carried out to investigate changes in the soil plant-available P,the P nutrition and the growth of Pinus radiata seedlings grown in association with understory,broom（Cytisus scoparius L.） or ryegrass（Lolium multiflorum） on Orthic Allophanic Soil,following the application of three rates of triple superphosphate（TSP）（0,50,and 100 mg·kg^-1P） under a glasshouse condition.The application of P fertilizer enhanced P availability in the rhizospheric of radiata seedlings and the bulk soils in a P-deficient site.P availability in the rhizospheric soils of ryegrass and broom,grown in association with radiata,were also increased by the presence of radiata roots.P concentrations in new shoot needles,old shoot needles,stem and roots of radiata pine increased with increase rates of TSP application,but the effects of ryegrass and broom on P nutrition of radiata seedlings depended on the soil P status.In the absence of P fertilizer addition（control treatment）,P concentrations in new shoot needles,old shoot needles,stem,and roots of radiata grown in association with broom were higher than those with ryegrass,whereas,when P fertilizer was added（50 and 100 mg·kg^-1） the P concentration was lower.This is probably related to the growth of broom that may have removed much of the plant-available P in the soil as indicated by the consistently lower Bray-2 P concentration in the rhizosphere soil of radiata in association with broom than that in the rhizosphere soil of radiata in association with grass at the two high P rates.Furthermore,in the high P fertile soil（application rate of 100 mg·kg^-1）,the dry matter yield of radiata was lower when it was grown with broom than with ryegrass.This result suggests that in moderate to high P fertile soils,P.radiata seedlings grow better with ryegrass than with broom,because broom grows vigorously in high P fertile soil and competes with P.radiata for P and perhaps for other nutrients as well.

Observations and Modeling of Incoming Longwave Radiation to Snow Beneath Forest Canopies in the West Tianshan Mountains, China

Forest canopy reduces shortwave radiation and increases the incoming longwave radiation to snowpacks beneath forest canopies. Furthermore, the effect of forest canopy may be changed by complex topography. In this paper, we measured and simulated the incoming longwave radiation to snow beneath forest at different canopy openness in the west Tianshan Mountains, China(43°16'N, 84°24'E) during spring 2013. A sensitivity study was conducted to explore the way that terrain influenced the incoming longwave radiation to snow beneath forest canopies. In the simulation model, measurement datasets, including air temperature, incoming shortwave radiation above canopy, and longwave radiation enhanced by adjacent terrain, were applied to calculate the incoming longwave radiation to snow beneath forest canopy. The simulation results were consistent with the measurements on hourly scale and daily scale. The effect of longwave radiation enhanced by terrain was important than that of shortwave radiation above forest canopy with different openness except the 20% canopy openness. The longwave radiation enhanced due to adjacent terrain increases with the slope increase and temperature rise. When air temperature(or slope) is relatively low, thelongwave radiation enhanced by adjacent terrain is not sensitive to slope(or air temperature), but the sensitivity increases with the decrease of snow cover area on sunny slope. The effect of longwave radiation is especially sensitive when the snow cover on sunny slope melts completely. The effect of incoming shortwave radiation reflected by adjacent terrain on incoming longwave radiation to snow beneath forest canopies is more slight than that of the enhanced longwave radiation.