Rainfall and flowering synchrony in a tropical shrub: Variable selection on the flowering time ofErythroxylum havanense

Summary We tested the adaptive significance of flowering synchrony by means of a quantitative analysis of selection and by flowering induction experiments with the deciduous shrubErythroxylum havanense. Temporal schedules of flower and fruit production were determined for a local population (in three sites) in a Mexican seasonal forest for 2 years (1987–1988). The consequences of natural variation in flowering time (flowering initiation day) on maternal reproductive success (fecundity) were evaluated. We observed high levels of inter- and intraindividual flowering synchrony in 1987, but not in 1988 and this contrast was related to differences in rainfall patterns between the two years. A significant proportion (15.4%) of the phenotypic variation in flowering initiation day was accounted for by environmental variance. The expression of phenotypic variance of flowering time and, consequently, the opportunity for selection to act, are controlled by annual variation in rainfall. Despite the between-year difference in flowering synchrony, we detected a relatively intense directional selection on flowering initiation day in both years, but selection coefficients were of opposite sign (standardized directional gradients were –0.326 and 0.333 for 1987 and 1988, respectively). For both years there was a significant relationship between individual relative fitness and the number of neighbouring flowering plants in a given day, suggesting positive frequency-dependent selection.     

刈割、施肥和浇水对矮嵩草补偿生长的影响

通过对青海海北高寒矮嵩草(Kobresia humilis)草甸进行为期3年的野外控制试验, 研究了刈割(留茬1 cm、3 cm及不刈割)、施肥(2.5 g·m^-2尿素+ 0.6 g·m^-2磷酸二胺、不施肥)和浇水(20.1 kg·m^-2、不浇水)处理对矮嵩草补偿生长(包括分株密度、株高和分株地上生物量)的影响, 及其比叶面积、叶片净光合速率和相对增长率的变化, 探讨矮嵩草补偿生长的机制。研究结果表明: 刈割后, 矮嵩草的补偿生长高度和比叶面积显著降低; 分株密度有增加的趋势, 但会随刈割强度的增加而下降; 株高和生物量的相对增长率随刈割强度的增加而呈上升趋势; 补偿地上生物量在重度刈割处理下最高。施肥能显著增加矮嵩草的补偿高度、分株密度、补偿地上生物量、株高相对增长率、生物量相对增长率、比叶面积和净光合速率; 与不浇水处理相比, 浇水处理对重度刈割处理下的分株地上生物量、密度相对增长率、比叶面积和净光合速率无影响, 而显著降低了中度刈割处理下的补偿高度和株高相对增长率, 提高了不刈割处理下的分株密度和重度刈割处理下的生物量相对增长率。刈割、施肥和浇水处理的交互作用也显示出刈割与施肥对矮嵩草补偿生长具有拮抗效应, 而刈割与浇水具有协同效应。上述结果说明, 矮嵩草在刈割后可通过增加分株密度和相对增长率等途径来提高补偿能力, 弥补在生长高度上出现的低补偿, 而施肥可显著抵消刈割的不利影响, 提高矮嵩草的补偿能力。     

Hydraulic conductance, stomatal conductance, and maximal photosynthetic rate in bean leaves

A positive correlation was found between steady state values of hydraulic (L _pA) and stomatal conductance (g _s) of French bean leaves: both were lower in the dark than in the light and lower in water-deficient plants than in the well-watered ones. The relative rate of stomatal opening after a pressure rise in the xylem was also positively related to L _pA. The L _pA and g _s were both related to the maximal photosynthetic rate at saturating CO2 concentrations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Species Identity and Water Availability Determine Establishment Success Under the Canopy of Retama sphaerocarpa Shrubs in a Dry Environment

Seedling establishment in harsh environments is often enhanced by the proximity of adult shrubs. This information has been used in restoration work by placing seedlings of species being restored under the canopy of some shrubs. However, monitoring this process is often restricted to a single species, and comparisons with practices that protect planted seedlings against harsh conditions are scant. Similarly, few studies have supplied seedlings with water in the summer to observe the effects of water availability on the interaction. We compared sapling survival of three woody species (Olea europaea, Pistacia lentiscus, and Ziziphus lotus) under the leguminous shrub Retama sphaerocarpa and in gaps covered with piled branches that mimicked a shrub canopy. After 3 years, survival of saplings planted under Retama differed depending on species identity and water supply. Survival of Olea saplings placed under Retama shrubs was twice that under piled branches if not watered (35 ± 8 vs. 17 ± 2 %, respectively), whereas survival of saplings under Retama, if watered, was less (48 ± 11 vs. 68 ± 8%, respectively). Retama shrubs had a negative effect on Ziziphus; most saplings died under its canopy, whereas survival in piled branches ranged 10–54%. Pistacia was neither facilitated nor outcompeted by Retama. Facilitation of Olea by Retama shrubs was more apparent under dry conditions where watering increased competition and decreased facilitation. Overall, we conclude that Retama shrubs can help dry land restoration to a greater extent than artificial shade for Olea when not watered. The critical role played by water supply in determining nursing success rates warrants further study.     

Effect of restricted watering and its combination with root pruning on root growth capacity,water status and food reserves ofPinus caribaea var.hondurensis seedlings

Summary Six-month oldPinus caribaea var.hondurensis seedling were subjected to various regimes of restricted watering and their combinations with root pruning to determine a suitable technique of producing seedlings with optimum physiological condition for successful bare-root planting.From the range of treatments tested, plants subjected to watering once every 9 days (D9) were found to be the hardest in terms of highest root growth capacity, leaf water content, root starch content and in having a moderately low transpiration rate.P. caribaea seedlings subjected to this preconditioning treatment may be more able to survive bare-root planting.     

Modification of soil aggregation by watering regime and roots growing through beds of large aggregates

The influence of root growth and soil watering regime on aggregation was studied under controlled conditions. The study examined the influence of pea (Pisum sativum cv Greenfeast), ryegrass (Lolium rigidum cv Wimmera) and wheat (Triticum aestivum cv Kite) roots on changes in aggregation and on the properties of the aggregates. The soil was a non swelling red-brown earth which was either kept wet or was allowed to wet and dry during the experiment. Root growth increased the percentage of small sized aggregates (<18 mm diameter), organic carbon, tensile strength and stability of aggregates in comparison with a non planted soil. Changes in aggregate size distribution and properties of the aggregates were related to root length density of the species and also to the soil watering regime. Root length density was in the order ryegrass>pea>wheat. Wetting and drying of soil increased the strength and stability of aggregates. Incubating aggregates allowed some roots to decompose but did not increase the strength or stability of aggregates compared with unincubated soil. The results of this experiment are of practical significance in soil structural management, and in studies of soil aggregation dynamics. It may be possible to use plant roots to alter the size and properties of aggregates.     

A new species of watering pot shell (Bivalvia: Anomalodesmata: Clavagelloidea) from the Miocene of the Murray Basin,South Australia

Abstract: A new species of penicillid watering pot shell, Kendrickiana coquinacola sp. nov., is described from the middle Miocene (Balcombian) Bryant Creek Formation of the Murray Basin, South Australia. The new species differs from the extant K. veitchi in its smaller size, much shorter posterior tube, fewer tubules in the anterior watering pot structure, absence of the pedal slit, discontinuous dorsolateral bands of pitted muscle scars on the internal surface of the anterior bulb and habit of cementing itself to the shells in its surrounding environment. The fossil record of Kendrickiana is reviewed. The record from the Dry Creek Sands is discounted, while a record for the extant K. veitchi from the earliest Pleistocene of York Peninsula is added. K. coquinacola indicates the highly derived anatomy of the genus evolved over a 10‐Ma period from the late Oligocene through the early Miocene.     

高寒矮嵩草草甸两种主要植物耐牧性的比较

通过野外控制实验,研究了刈割(留茬3 cm、留茬1 cm及不刈割)、施肥(施肥、不施肥)和浇水(浇水、不浇水)处理对高寒草甸矮嵩草(Kobresia humilis)和垂穗披碱草(Elymus nutans)补偿高度、株高相对生长率、比叶面积、叶片净光合速率和地上总生物量的影响.结果表明:2物种的株高和地上总生物量在刈割后均为低补偿响应,但其株高相对生长率显著提高,并均随年份而增加;垂穗披碱草比叶面积、叶片净光合速率和地上总生物量对刈割损伤更加敏感;尽管施肥能显著提高2物种上述各项指标,但在不同处理条件下矮嵩草的耐牧性指数均小于垂穗披碱草;浇水的作用不显著.说明2物种的耐牧性依赖于土壤养分资源获得性,矮嵩草的耐牧性强于垂穗披碱草.