Effect of fruiting and drought or flooding on carbon balance of apple trees

The response of fruiting or deblossomed trees to water stress such as drought or flooding was investigated in six semi open-top cuvettes each containing one apple (Malus domestica Borkh. cv. Golden Delicious) tree. Xylem water potentials of leaves dropped from -1.2 to -4.1 MPa within 7 d of drought, the effect being enhanced by fruiting. Apple trees without fruits showed smaller reductions in net photosynthetic rate (P _N ) and dark respiration rate (R _D ) after 2 d of drought and hence more positive carbon balances relative to fruiting trees. Flooding for 4 d had a more pronounced effect on P _N than on transpiration, resulting in a reduced water use efficiency (WUE). This reduction in WUE was greater in the non-fruiting trees. Flooding reduced P _N of the whole apple canopies irrespective of fruiting; aple trees without fruits increased R _D resulting in a less positive carbon balance relative to fruiting trees. Fruiting increased the sensitivity to drought of apple trees (R _D and P _N ), but decreased their sensitivity to flooding (R _D and WUE), suggesting different adaptation mechanisms for the two forms of water stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Field observations on nitrogen catch crops. I. Potential and actual growth and nitrogen accumulation in relation to sowing date and crop species

In temperate climates with a precipitation surplus during autumn and winter, nitrogen catch crops can help to reduce nitrogen losses from cropping systems by absorbing nitrogen from the soil and transfer it to a following main crop. The actual and potential accumulation of dry matter and nitrogen in catch crops were studied in the field during four seasons with winter rye (Secale cereale) and forage rape (Brassica napus ssp. oleifera (Metzg.) Sinsk) or oil radish (Raphanus sativus spp. oleiferus (DC.) Metzg.). Sowing dates were end of August and three and six weeks later. Potential nitrogen accumulation, Y (g m^-2), could be summarized with Y = 96 –0.34 X, where X is the day number in the year of the sowing date (range: late August till end of September). Species were compared in their performance, looking at differences in specific leaf area, leaf weight ratio, leaf area ratio, light extinction and persistence during frost. The rate of dry matter accumulation in intervals of 14 days appeared to be determined primarily by the amount of radiation intercepted. A regression, forced through the origin, gave as a common slope 1.12 g dry matter accumulated per MJ intercepted global radiation, irrespective of season, species, sowing date or nitrogen treatment (period from ca. day 250 to day 310). From this result the inference is made that leaf expansion is a key process, determining the performance of catch crop species under varying environmental conditions.     

大气CO2浓度升高对植物的直接影响-国外十余年来模拟实验研究主要手段及基本结论

 本文针对国外近十几年来在CO2浓度升高对植物的直接影响方面所开展的生理生态学研究方法、动态、基本结论、存在问题等内容做了简要的介绍。大气CO2浓度在过去200年内已增加了80μmol·mol-1,生长在高CO2环境下的植物,其生理生态、形态及化学成分等方面将会发生相应的变化。表现在光合作用速率出现不同程度的提高;呼吸作用受抑制;气孔密度减少,水分利用效率增加;生物量及产量增加;一些关键蛋白质及酶、非结构性碳水化合物含量增加;组织中的氮、硫等元素含量降低;根系及花的发育也随CO2浓度的升高而提前等。不同光合途径(C3、C4及CAM)及不同植被类型(自然植被、栽培植被)的植物随CO2浓度发生的上述指标的变化在长期反应与短期反应方面具有很大的差异。另外,实验控制条件如温度、光照、水分、养分甚至实验装置(如花盆)的大小对预测结果也有很大的影响。     

沈阳市东部土地利用格局变化

以沈阳市东部１９７６～１９８９年的历史航空像片为基础,以地理信息系统（ＧＩＳ）技 术为手段,分析土地利用的空间格局及其变化．结果表明,针叶林、水田平均嵌块体大小增 加,旱地、落叶林、灌丛平均嵌块体大小减少;分数维值略有增加．预示嵌块体形状逐步复 杂化;多样性指数、均匀性指数增加．优势度和蔓延度指数由原来的１．６３２７和８９．２０２２分 别减少到１．３２２６和８８．２７４４,说明景观嵌块体的空间分布趋于均匀,嵌块体的聚集分布状 况将随时间的推移逐步分散化．此外．本文对沈阳东部土地利用格局变化的原因进行了剖 析．     

春小麦水分利用效率日变化及其生理生态基础的研究

采用光合速率和蒸腾速率之比 (Pn/Tr)表示植物水分利用效率 (WUE) ,发现在两种不同水分处理下春小麦拔节期 .WUE日变化中都有上午高于下午值 ,且 8∶0 0～ 1 0∶0 0为明显峰值的特征 ,这种特征与Pn、Tr日变化存在的上、下午值不对称性和反向性 (Pn为上午高于下午 ,Tr相反 )紧密相关 ,水分胁迫处理中 ,Pn、Tr值均有降低 ,但不同品种的WUE反应不一 .研究表明 ,叶水势 ( ψw)、气孔阻力 (Rs)等生理因素和空气相对湿度 (RH)、光照 (Q)及冠层温度 (Tc)等生态因子 ,通过对Tr和Pn的不同影响而同WUE显著相关 ,40 %RH是WUE变化的一个重要阈值 .     

田间不同条件下玉米叶片的气孔阻力及与光合,蒸腾作用的关系

以玉米 1 7个自交系和 1 0个杂交种为试材 ,在田间条件下研究了不同光强、不同叶位、不同生育期、不同源库比例和株间差异状态下的气孔阻力及其与光合 (PH)、蒸腾(TR)和叶片水分利用效率 (WUE)的关系 ,结果表明 ,不同自交系之间RS具有显著的差异 ,相差最大可达 2 .3倍以上 ;光照条件变弱、穗叶位差增加、生育期推延和源 /库比例改变等均可引起RS值的增加 ;在各种情况下导致RS变化的同时也引起TR和PH产生相应的变化 ,RS与TR、PH表现出显著或极显著的负相关 ,且相关系数rRS TR>rRS PH;RS与WUE的相关关系在不同的条件下表现出不稳定性     

Sex ratio in populations of Silene otites in relation to vegetation cover,population size and fungal infection

Abstract. In contrast to populations of most dioecious Silene species (which usually are female-biased), populations of Silene otites have been frequently reported to be male-biased. We describe sex ratio variation in 34 natural S. otites populations in Central Germany in relation to vegetation cover, population size and fungal infection. The overall sex ratio was unbiased in 1994 and only slightly male-biased in 1995. Sex ratio varied among the populations from 26.6 % to 72.6 % females. The sex ratio of small populations varied strongly due to stochastic processes. Furthermore, we found that populations in habitats with high vegetation cover contained a higher percentage of females. Hermaphroditic plants, theoretically, could increase male bias as they only produce male or hermaphroditic offspring. Their frequency in the populations, however, was far too low to affect sex ratio. In 1994 12.1 % and in 1995 17.0 % of the plants were infected by the smut fungus Ustilago major. Disease incidence in the population was not related to sex ratio, suggesting equal susceptibility of males and females. The sex ratio of partially infected plants did not deviate from the population sex ratio, both under field conditions and in a greenhouse laboratory experiment. The results suggest that the frequently reported male bias in Silene otites populations is not a general pattern, but is mainly caused by environmental conditions.     

Does diversity beget diversity? A case study of crops and weeds

Abstract. The ecological literature is ambiguous as to whether the initial diversity of a plant community facilitates or deters the diversity of colonizing species. We experimentally planted annual crop species in monoculture and polyculture, and examined the resulting weed communities. The species composition of weeds was similar among treatments, but the species richness of weeds was significantly higher in the polycultures than in the monocultures. This supports the ‘diversity begets diversity’ hypothesis. Environmental microheterogeneity, diversity promoters, and ecological equivalency do not seem able to explain the observed patterns.     

Using an ecosystem model linked to GCM-derived local weather scenarios to analyse effects of climate change and elevated CO2 on dry matter production and partitioning, and water use in temperate managed grasslands

Local effects of climate change (CC) and elevated CO₂ (2 × CO₂, 660 μmol mol^–1) on managed temperate grasslands were assessed by forcing a dynamic ecosystem model with weather scenarios. The aims of the study were to compare the relative importance of individual and combined effects of CC, 2 × CO₂, and photosynthetic acclimation, and to assess the importance of local site conditions. The model was driven by hourly means for temperature (T), precipitation (P), global radiation (G), vapour pressure (VP), and wind speed (U). Local climate scenarios were derived by statistical downscaling techniques from a 2 × CO₂ simulation with the General Circulation Model of the Canadian Climate Centre (CCC-GCMII). Simulations over 14 growing seasons to account for year-to-year variability of climate were carried out for a low, relatively dry site, and a high, more humid site. At both sites, shoot dry matter responded positively to 2 × CO₂ with the site at low elevation being more sensitive than the higher site. The effect of assumed changes in climate was negative at the lower, but positive at the higher site. Shoot dry matter was more sensitive to the effects of 2 × CO₂ than to CC. Both effects combined increased shoot dry matter by up to 20%. This was attributed to direct effects of 2 × CO₂ and increased T, and indirect stimulation via increased soil N availability. Biomass partitioning to roots increased with 2 × CO₂ but decreased with CC, while an intermediate response resulted from the combination. Leaf area index (LAI) increased under 2 × CO₂, but not enough to compensate fully for a decrease in leaf conductance. Under the 2 × CO₂ scenario evapotranspiration (ET) decreased, but increased under CC. Photosynthetic acclimation reduced the effect of 2 × CO₂ on shoot growth, but had little effect on ET. The seasonal water use efficiency (WUE) was improved under 2 × CO₂, and reduced under CC. With the combination of both factors, the change was small but still positive, especially at the high elevation site with more favourable soil water conditions. This reflects the stronger positive yield response in combination with a smaller increase in ET under cooler, more humid conditions. The results for the combination of factors suggest that except for shoot growth, effects of 2 × CO₂ and CC tend to offset each other. While CC determines the sign of the ET response, the sign of the biomass response is determined by 2 × CO₂. The results highlight the importance of a site-specific analysis of ecosystem responses by using a flexible approach based on a combination of state-of-the-art downscaling, spatially resolved data sets, and a mechanistic model to obtain quantitative and reproducible assessments of climate change impacts at the ecosystem level.