Carbon isotope discrimination in Quercus ilex resprouts after fire and tree-fell

Ecophysiological differences related to photosynthesis were compared in holm oak Quercus ilex leaves from undisturbed holm-oak vegetation, resprouts after fire and resprouts after tree-fell. No significant differences in any parameter measured were observed between the two kinds of resprout throughout the first growing season following disturbance. Resprouting leaves showed lower carbon isotope discrimination () and intercellular CO₂ concentration (p _i), and higher photosynthesis, leaf conductance and transpiration rates than leaves from undisturbed stands. Nitrogen, soluble protein content and ribulose bisphosphate carboxylase (RuBPCase) activity were 88%, 96% and 45% higher respectively, in both kinds of resprout. The results indicate that photosynthetic capacity, rather than stomatal conductance, is the limiting factor in photosynthesis in resprouts, Chlorophyll content and chlorophyll a/b ratio did not differ between resprouts and undisturbed leaves, indicating that the observed differences were not a result of differences in light environment during leaf development. Leaf mass per area (LMA), was 80% higher in the resprouts, and was negatively related (r=–0.86) to and positively related (r=0.87) to N content. Enhanced carbon assimilation after disturbances resulted in higher water use efficiency, as indicated by lower values in the resprouts. We conclude that the cause of defoliation was not relevant in the physiology of the resprouts, suggesting the importance of underground organs.     

冰雪灾害后木荷倒木萌枝光合特性研究

采用Li-6400型便携式光合测定仪,对冰雪灾害后夏季木荷倒木萌枝和未受损木荷枝条的叶片进行光合特性研究。结果表明:倒木萌枝和未受损木荷枝条的Pn、Tr和Gs日变化均呈双峰曲线,具有典型的光合"午休"现象,中午Pn降低均为气孔限制;未受损木荷Pn中午午休时间(10:00～15:00)长于倒木的午休时间(11:00～15:00),其自我保护能力强于倒木,且对光适应的生态辐较宽;环境因子对Pn的直接作用由大到小为倒木:PAR>Ca>Ta>RH,未受损木荷:Ta>PAR>Ca>RH。倒木和未受损木荷的RH与Pn分别呈极显著(P<0.01)和显著(P<0.05)负相关,高温高湿、高湿分别是制约倒木、未受损木荷Pn进一步升高的主要环境因子。     

Effects of bicarbonate and high pH on growth of Zn-efficient and Zn-inefficient genotypes of rice,wheat and rye

We studied the source of the nitrogen used for the growth and resprouting of holm-oak (Quercus ilexL.), and the contribution of nitrogen and carbohydrate root reserves to these processes. Three-year-old plants were grown in a greenhouse with either a sufficient or restricted nitrogen supply for one year. Half the individuals were subjected to shoot excision to provoke resprouting, and a ¹⁵N solution was given to these plants and to controls for two months. Nitrogen, Total Non-structural Carbohydrate (TNC), Total Soluble Protein content, and ¹⁵N and ¹³C composition were determined, and histological analyses of woody tissue were performed. Our results show that N-deprived plants used nitrogen from root reserves to support a growth rate similar to that of non-deprived plants. However, deprived plants lost their resprouting capacity in spite of the high TNC accumulation and nitrogen resupply to the soil. After the supply of nitrogen was restored to N-deprived plants, this nutrient mainly accumulated in under-ground organs, which limited the above-ground growth. Resprouting plants first remobilized the nitrogen stored in roots, and thereafter took it up from the solution. The root-crown region did not behave as a specialised reserve organ in three-year-old Quercus ilex L. plants.     

Within‐plant variation in defences in response to simulated herbivory in a semi‐arid southern African savannah

Within‐plant spatial variation in herbivore pressure can induce localized antiherbivory defence responses. We tested this hypothesis by studying branch‐specific responses of Acacia robusta, Dichrostachys cinerea and Ziziphus mucronata to simulated mammalian herbivory. Herbivory was simulated by clipping the terminal shoots (3 cm from tip) of tree branchlets, allowing them one year of regrowth and then comparing their spine length and density and condensed tannins with those of adjacent unclipped branchlets. Condensed tannins concentrations were higher in clipped branchlets than in unclipped branchlets in all three woody species (P < 0.05). Spine length was higher in clipped branchlets than in unclipped branchlets in A. robusta (P < 0.05) but was similar in both D. cinerea and Z. mucronata (P > 0.05). Spine density was double in clipped branchlets as compared to the unclipped branchlets in Z. mucronata (P < 0.05) but was similar in both A. robusta and D. cinerea (P > 0.05). We found evidence of within‐plant variation in condensed tannins concentration and spine length and density in response to simulated herbivory in the three woody species.     

冰灾后受害木荷萌枝光合生理响应和叶绿素荧光特性

以2008年南方冰雪灾害中受到严重损害的木荷为对象,在浙江江郎山设置5个400m2样地,通过Li-6400光合仪人工控制光强和CO2浓度测定相关光合参数,采用指数方程对不同受害类型木荷(倒木和断木)的光合生理响应曲线进行拟合,并结合叶绿素荧光参数分析了不同部位萌枝叶片的光合能力。结果表明:(1)光响应曲线中,木荷断木不同部位萌枝叶片在初始阶段(光照强度0～200μmol.mol-1)较陡,随着光强的增大,断木相对于倒木较早达到光饱和点,但其最大净光合速率较倒木低;CO2响应曲线中,倒木和断木在起始阶段(CO2浓度在0～200μmol.mol-1)的斜率较接近,随着CO2浓度增加,各条拟合曲线趋势相似。(2)不同受害类型木荷之间比较,倒木的光饱和最大净光合速率(PLmax)、CO2饱和最大净光合速率(PCmax)、光补偿点(LCP)、光饱和点(LSP)、有效光化学效率(Fv′/Fm′)分别比断木高22.03%、5.22%、13.73%、52.48%、22.53%,且二者间的PLmax、LSP、Fv′/Fm′均差异显著。(3)相同受害类型木荷的不同部位之间比较,倒木不同部位的PLmax、PCmax、PSⅡ最大光化学效率(Fv/Fm)、Fv′/Fm′、PSⅡ潜在活性(Fv/F0)、电子传递速率(ETR)均表现为底部>中部>顶部,而断木不同部位则表现为顶部和中部大于底部,但未达到显著水平。研究发现,遭受冰雪灾害的木荷倒木的光合作用能力高于断木,且倒木底部和断木顶部的光合作用能力高于其它部位。