Light absorption and photosynthesis of a benthic moss community: importance of spectral quality of light and implications of changing light attenuation in the water column

1. The underwater light climate and benthic moss communities of Grane Langsø were investigated in May 1997 to determine the potential effects on benthic production of changing water column attenuation and spectral quality of light.
2. A reduction in water clarity in the lake since the 1960s was manifested as a marked increase in the attenuation of blue light, relative to red light, which can be attributed to increased dissolved organic carbon.
3. The biomass of the benthic moss community ranged from a maximum of 195 gDW m⁻² at a depth of 4 m to 39 g DW m⁻² at a depth of 10 m and Drepanocladus exannulatus contributed 70% of the biomass at all depths.
4. Absorption of PAR by D. exannulatus was maximal in the highly pigmented youngest parts of the plant and these correspondingly showed the highest rates of net photosynthesis. The absolute amount of chlorophyll- a per g dry weight was greater at 10 m than 2 m, but the ratio of accessory pigments to chlorophyll- a did not change. Deep growing plants did not show adaptation to changed light quality.
5. Increased attenuation of blue light and the resultant overall decrease in water clarity is likely to impact negatively on net annual production of benthic macrophytes of Grane Langsø. Any further increase in dissolved organic carbon concentration has the potential to markedly decrease the depth to which mosses grow by reducing the length of time in a year during which net photosynthesis occurs.     

土壤水分亏缺对春小麦根系干物质累积和分配的影响

在人工气候室中进行实验,实施光、温自动控制,研究了土壤水分对春小麦根系干物质积累和分配的影响,３个处理是春小科整个生长发育期内土壤水分分别控制在田间持水量的３０％,６０％,９０％,实验结果表明,在四叶一心－抽穗开花期间,３个处理气孔阻力逐渐降低,光合速率蒸腾速度逐渐上升,其中,中等水分条件下蒸腾速率明显低于充分供水,而光合速率则接近或显著高于是。抽一开花期,下层以根长,根竽中等水分处理显著高于其余     

青藏高原主要植被类型生物生产量的比较研究

以１８种群落类型的实测为数据和１０１３块森林测树样地的估算数据为基础,首次系统地分析和比较了青藏高原主要植被类型生物生产量的构成规律及分布格局。亚高山暗针叶 生物量一般在３００ｔ／ｈｍ＾２以上,最高可达约１６００ｔ／ｈｍ＾２,叶生物量８～３９ｔ／ｈｍ＾２,根茎比０．１～０．２,生产量８～１３ｔ／ｈｍ＾２．ａ;高山灌丛类型生物量２０～４０ｔ／ｈｍ＾２,叶生物量３～６ｔ／ｈｍ＾２,根茎比０．４～０．８     

麦角固醇高产菌株的构建及其培养优化条件的研究

通过初筛、单倍体分离、诱变及酵母菌种间原生质体融合技术构建了2株麦角固醇产量明显提高的优良菌株YEF-21和YEF-29。并对YEF-21的培养优化条件进行了研究。结果表明在优化的实验条件下YEF-21的生物量及麦角固醇含量的综合值分别为原始亲株YE227和YE180的1.54和1.55倍。经遗传稳定性分析,没有发现标记基因的分离现象,从而证明获得的融合菌株是遗传稳定的,是具有一定实际应用价值的麦角固醇高产菌株。     

Changes in the canopy structure of the Mediterranean shrub Lavandula stoechas after disturbance

Abstract. This study attempts to show the dynamics of the canopy structure of the Mediterranean pioneer shrub Lavandula stoechas after man-made perturbation (i.e. grazing). The development of the vertical structure of the shrub was studied by harvesting the canopy of plants of 2–6 yr old in horizontal layers. The supportive biomass of the canopy was concentrated near the base at all ages. Leaf biomass was evenly distributed all over the vertical profile in 2- and 3-yr old plants. In 4-yr old plants it presented a maximum near the top of the canopy. For 5-yr old plants a structural transition started with leaf profiles showing a bimodal distribution. Leaf biomass predominated near the base in 6-yr old plants, suggesting that the transition was completed. Three canopy stages in the growth processes of the plant were recognized after the first year of growth: in the first one (from 2 to 3 yr old) both leaf and supportive biomass increased; in the second one (from 3 to 4 yr) leaf biomass remained stable and there was an increase in supportive biomass until the plants reached a ‘mature stage’, in 4-yr old plants; finally, in 5- and 6-yr old plants there was a decrease both in leaf and supportive biomass and plant structure showed evidence of senescence. Early transitions from seedling to 1-yr old plant and from this to 2- to 3-yr old plants were less obvious. The leaf/supportive biomass ratio always decreased with plant age, from 1.88 in seedlings to 0.01 in 6-yr old plants. Biomass density followed the pattern of supportive biomass, with an increase from 1.7 g/dm³ (2-yr old plants) to 2.4 g/dm³ (4-yr old plants). Thereafter, biomass density decreased to 0.6 g/dm³ (6-yr old plants).     

Elevated CO2 increases nitrogen fixation and decreases soil nitrogen mineralization in Florida scrub oak

We report changes in nitrogen cycling in Florida scrub oak in response to elevated atmospheric CO₂ during the first 14 months of experimental treatment. Elevated CO₂ stimulated above-ground growth, nitrogen mass, and root nodule production of the nitrogen-fixing vine, Galactia elliottii Nuttall. During this period, elevated CO₂ reduced rates of gross nitrogen mineralization in soil, and resulted in lower recovery of nitrate on resin lysimeters. Elevated CO₂ did not alter nitrogen in the soil microbial biomass, but increased the specific rate of ammonium immobilization (NH₄⁺ immobilized per unit microbial N) measured over a 24-h period. Increased carbon input to soil through greater root growth combined with a decrease in the quality of that carbon in elevated CO₂ best explains these changes. These results demonstrate that atmospheric CO₂ concentration influences both the internal cycling of nitrogen (mineralization, immobilization, and nitrification) as well as the processes that regulate total ecosystem nitrogen mass (nitrogen fixation and nitrate leaching) in Florida coastal scrub oak. If these changes in nitrogen cycling are sustained, they could cause long-term feedbacks to the growth responses of plants to elevated CO₂. Greater nitrogen fixation and reduced leaching could stimulate nitrogen-limited plant growth by increasing the mass of labile nitrogen in the ecosystem. By contrast, reduced nitrogen mineralization and increased immobilization will restrict the supply rate of plant-available nitrogen, potentially reducing plant growth. Thus, the net feedback to plant growth will depend on the balance of these effects through time.     

小叶章种群地上生物量生长量及其时间序列分析

本文通过对三江平原典型草甸、沼泽化草甸及沼泽群落的优势种群-小叶章种群地上生物量生长量及其时间序列的分析表明:典型草甸小叶章种群地上生物量生长量季节动态呈"W"型。另两个类型呈双峰型。其累积生长量均呈单峰型,且在整个生长季,干物质均有一定程度的积累,时间序列分析也验证了上述变化趋势。     

Effects of drainage and soil organic content on growth of Spartina alterniflora (Poaceae) in an artificial salt marsh mesocosm

An artificial salt marsh mesocosm was constructed using 680-L polypropylene tanks to determine the effect of soil drainage depth and organic content on growth and rhizome proliferation of the salt marsh smooth cordgrass Spartina alterniflora. Soil drainage depth had no effect on accumulation of aerial or subsurface plant tissue, but tanks that had 2.5% soil organic content supported enhanced aerial tissue and rhizome growth compared to tanks that contained sand alone. We propose a mathematical model for predicting the mass of photosynthetically significant leaf tissue without cutting and drying leaves. Implications of these findings for salt marsh creation projects are discussed.     

KIRA指标的拓展及其在中国植被与气候关系研究中的应用

根据Kira以月平均气温5℃为界的热量指数和干湿度指数概念,提出了以月平均气温10℃为界的生物热量指数,包括生物温暖指数(BWI)和生物寒冷指数(BCI),并修正其干湿度指数为生物干湿度指数(BK).利用中国689个标准气象台站的资料,分析我国主要植被类型分布与热量因子和干湿度因子的关系,得出两者之间较好的相关性,生物温暖指数、寒冷指数和干湿度指数的散点图较好地表现了中国各植被类型与气候指标的关系和格局.以10℃为界的生物温暖指数不仅对我国森林植被的地理分布和温度气候带的划分具有较好的指示作用,而且对西南部高山、亚高山地区的植被与气候关系指示性较强;生物寒冷指数则对亚热带和热带的指示性很好,能够较好区分亚热带南部及热带地区;由热量指数和降水量综合得出的生物干湿度指数,对中国西北部干旱、半干旱区以至全国的植被分布与水分、热量因子的关系分析有较好的应用价值.     

缙云山马尾松种群数量动态初步研究

马尾松(Pinus massoniana)种群是我国亚热带森林植被演替的先锋种群之—。研究其数量动态对亚热带森林群落和生态系统的研究有着重要意义。“样地编年序列”的应用为长命多年生植物种群数量动态的研究提供了一条捷径。缙云山马尾松种群,约在7龄前,其密度随时间而增长,其后降低。其间关系可用下式近似表达：(07), 式中,D是种群密度估计值,A是种群年龄。缙云山马尾松种群生物量在灌草从到松阔混交林初期的演替中呈现Logistic增长。符合公式：式中,Bp是种群生物量的估计值,A,e是自然对数的底。在从混交林到常绿阔叶林的演替中,其生物量表现出随时间下降的趋势。在自疏过程中,马尾松种群平均植株生物量与种群密度服从-3/2稀疏定律。符合公式：式中,Bi是平均植株生物量,D是种群密度。导致缙云山马尾松种群数量动态变化的动力,主要是种内光资源竞争引起的自疏和种间光资源竞争引起的他疏。