Phenological change in a spring ephemeral: implications for pollination and plant reproduction

Climate change has had numerous ecological effects, including species range shifts and altered phenology. Altering flowering phenology often affects plant reproduction, but the mechanisms behind these changes are not well‐understood. To investigate why altering flowering phenology affects plant reproduction, we manipulated flowering phenology of the spring herb Claytonia lanceolata (Portulacaceae) using two methods: in 2011–2013 by altering snow pack (snow‐removal vs. control treatments), and in 2013 by inducing flowering in a greenhouse before placing plants in experimental outdoor arrays (early, control, and late treatments). We measured flowering phenology, pollinator visitation, plant reproduction (fruit and seed set), and pollen limitation. Flowering occurred approx. 10 days earlier in snow‐removal than control plots during all years of snow manipulation. Pollinator visitation patterns and strength of pollen limitation varied with snow treatments, and among years. Plants in the snow removal treatment were more likely to experience frost damage, and frost‐damaged plants suffered low reproduction despite lack of pollen limitation. Plants in the snow removal treatment that escaped frost damage had higher pollinator visitation rates and reproduction than controls. The results of the array experiment supported the results of the snow manipulations. Plants in the early and late treatments suffered very low reproduction due either to severe frost damage (early treatment) or low pollinator visitation (late treatment) relative to control plants. Thus, plants face tradeoffs with advanced flowering time. While early‐flowering plants can reap the benefits of enhanced pollination services, they do so at the cost of increased susceptibility to frost damage that can overwhelm any benefit of flowering early. In contrast, delayed flowering results in dramatic reductions in plant reproduction through reduced pollination. Our results suggest that climate change may constrain the success of early‐flowering plants not through plant‐pollinator mismatch but through the direct impacts of extreme environmental conditions.     

Potential Autonomous Selfing in Gesneria citrina （Gesneriaceae）, a Specialized Hummingbird Pollinated Species with Variable Expression of Herkogamy

Species with mixed mating systems often demonstrate variable expression of breeding system characteristics and thus represent the opportunity to understand the factors and mechanisms that promote both outcrossed and selfed seed production. Here, we investigate variation in levels of herkogamy （variation in stigma-anther separation distance） in a Puerto Rican population of hummingbird pollinated Gesneria citrina Urban. There is significant variation in herkogamy levels among individuals of this species and stigma-anther separation is negatively associated with the ability to set fruits and seeds in the absence of pollinators. The variation in levels of herkogamy may represent a mechanism to ensure the production of some self-fertilized progeny in the absence of hummingbird pollinators. We also describe a novel breeding system in G. citrina, where stamens elongate over time to reach stigma height, but stamen elongation is accelerated by pollination. These results suggest that once the flowers are pollinated, stamen elongation may favor increased pollen removal and siring success, while the reduction in stigma-anther distance no longer imposes the risk of interference between male and female functions. We discuss our findings of breeding system variation in the context of pollination system evolution in an island setting （Antillean islands）.     

The Planktonic Index of Biotic Integrity (P-IBI): An approach for assessing lake ecosystem health

Using historical (1970) and more recent (1996) Lake Erie plankton and trophic status data, we developed a Planktonic Index of Biotic Integrity (P-IBI) to measure changes in lake ecosystem health. We used discriminant analysis to determine phytoplankton and zooplankton community characteristics (metrics) that distinguished among levels of impairment. Traditional measures of lake trophic status classes (i.e., oligotrophic, mesotrophic, eutrophic), such as chlorophyll a and total phosphorus concentrations, were used to classify sites on a gradient of impairment. We then judged the ability of plankton metrics to distinguish among trophic status classes. Because of the temporal variability found in plankton communities, we conducted analyses on a monthly basis (May–September). For June, July and August we found five unique metrics that could distinguish among trophic status classes. The P-IBI showed an increase in water quality in Lake Erie between 1970 (<3 = eutrophic) and the mid-1990s (1996 and 1997) (3–4 = mesotrophic) (which reflected mean (±standard error) total phosphorus concentrations (μg/L) 1970 > 1996; western basin (41.53 ± 2.68 > 29.75 ± 1.39), eastern basin (14.84 ± 0.82 > 7.74 ± 0.28) and mean (±standard error) chlorophyll a concentrations (μg/L) uncorrected for pheophytin 1970 > 1996; western basin (12.58 ± 1.82 > 5.40 ± 0.22), central basin (5.90 ± 0.36 > 3.17 ± 0.54), and eastern basin (5.17 ± 0.38 > 1.67 ± 0.18)), with declining water quality in the late 1990s (1998 and 1999) (3) and 2002 (<3). We recommend that the techniques used in creating the P-IBI be investigated for determining ecosystem health of other lakes.     

营养盐初始组合浓度对类波氏真眼点藻生长和油脂积累的影响

为了研究培养基中主要营养元素氮、磷、硫初始组合浓度对类波氏真眼点藻(Eustigmatos cf.polyphem D.J.Hibberd)生长、油脂积累和脂肪酸组成的影响,分别以NaNO_3、K_2HPO_4、MgSO_4为氮、磷、硫源,设置不同的营养盐初始组合浓度对其进行培养,采用干重法、重量法、气相色谱分析法、元素分析仪等依次对生物量、总脂、脂肪酸组成和细胞内元素含量进行测定。结果显示,氮、磷、硫三者的初始组合浓度变化对类波氏真眼点藻的生长和油脂积累具有明显的影响,9 mmol/L NaNO_3、0.92 mmol/L K_2HPO_4、0.3 mmol/L MgSO_4营养条件下其生物量达到最大值,为9.19 g/L;低氮、低磷胁迫或二者共同胁迫均促进其油脂积累,但低硫胁迫对油脂的积累影响不大,最大油脂含量出现在3 mmol/L NaNO_3、0.029 mmol/L K_2HPO_4、0.3 mmol/L MgSO_4条件下,为68.7%(DW)。此外,类波氏真眼点藻富含棕榈油酸,占总脂肪酸含量的最大值达60.88%。选择合理的氮、磷、硫初始组合浓度能够有效促进其生长或油脂及棕榈油酸的积累。     

白浆土植物系统营养物质转化机制及其有效性研究Ⅴ.有机物对磷根际有效性的影响

采用根盒试验研究了施用紫花苜蓿腐解物对白浆土小麦根际Ｐ 素形态转化、有效性及小麦植株Ｐ 素吸收的影响．结果表明,施用有机物料使土壤有效磷显著上升,铝磷、铁磷含量也显著升高,且培养时间越长,效果越明显．小麦植株含Ｐ 量明显上升,且与非根际土壤铝磷、铁磷的变化显著相关     

太行山北段地区荆条灌丛和三裂绣线菊灌丛群落谱系结构

灌丛是太行山地区最重要的生态系统类型之一, 灌丛群落生物多样性的维持及其生态系统服务功能对京津冀地区的生态安全具有重要作用。本研究选择太行山最具代表性的两种灌木群落——荆条(Vitex negundo var. heterophylla)灌丛和三裂绣线菊(Spiraea trilobata)灌丛为研究对象, 利用净亲缘关系指数(net relatedness index, NRI)和多元回归等方法探究了两种灌丛群落构建机制的异同及主要的环境影响因子, 同时还利用谱系结构主坐标分析(principal coordinates of phylogenetic structure, PCPS)对决定群落谱系结构的关键系统发育节点进行了探究。结果表明: 两种灌丛群落内灌木植物的物种多样性没有显著差异, 但谱系结构差异显著。三裂绣线菊群落表现出显著的谱系发散趋势, 而荆条群落谱系聚集程度高于三裂绣线菊群落, 但未表现出显著的谱系结构。三裂绣线菊灌丛群落构建的驱动机制是生态位分化, 荆条灌丛中生境过滤作用有所增加, 与生态位分化共同驱动其群落构建过程。与干旱胁迫相关的生境过滤因素增加是荆条灌丛群落谱系聚集程度增加的重要原因。PCPS二维排序结果表明: 荆条灌丛群落谱系趋向聚集与其群落内缺乏蔷薇目、壳斗目等亲缘关系较远的类群有关, 而三裂绣线菊灌丛群落内物种则包含较多的演化分支。总体而言, 环境过滤不是决定太行山地区灌丛群落构建的主要驱动因素, 但水分条件仍然是影响区域群落谱系结构的重要因素。     

磷对土壤中砷吸附的影响

在黄壤、红壤和褐土中进行As的等温吸附实验表明,在不添加P的情况下,3种土壤对As的吸附能力随土壤pH的升高而降低,随土壤粘粒含量的降低而减弱,3种土壤吸附能力为黄壤>红壤>褐土,As在土壤中的吸附受P存在的影响,60mg·kg^-1的P可以降低黄壤和红壤对As最大吸附量．吸附质中P：As的比例不同,P对土壤吸附As的影响差异很大：吸附质中P：As=1：2时,土壤对As的吸附能力均强于P：As=1：1和P：As=2：1,后两者差异不显著,表明土壤中的吸附点位对As和P的亲和性具有一定的差异,Languir方程能很好地拟合所测得的土壤平衡溶液中As浓度。     

洱海螺旋鱼腥藻生长生理特性的初步研究

近年来,洱海正处于中营养水平向富营养湖泊的过渡阶段,蓝藻水华也频繁发生。本文作者在洱海大规模水华暴发期间,分离、纯化了水华优势种螺旋鱼腥藻,并对其生长生理特性进行了初步研究,以期为探讨洱海鱼腥藻水华发生的环境影响因素提供基础的参考资料。实验结果表明,氮含量1.5mmol/L、磷含量12µmol/L、光照强度30E/ m·s、pH值8－10及温度25℃时,螺旋鱼腥藻生长状况最好,生物量及相对生长速率较高。不同氮、磷浓度下的氮磷代谢活性表明：氮浓度在0－0.36mmol/L时,硝酸还原酶活性随着氮浓度的增加而增强;氮浓度在0.36－6 mmol/L时,酶活性由其生长状况决定,生长越好,酶活性越高。碱性磷酸酶受磷影响较大,随着磷浓度的增加其活性逐渐减弱,磷充足时,氮对其活性并无显著影响。此外,洱海螺旋鱼腥藻可在低的氮、磷浓度下生长,这与其氮磷代谢活性的调节作用有关。     

Characterisation of Phosphate Solubilising Bacteria in Sandy Loam Soil Under Chickpea Cropping System

With the aim to explore the possible role of phosphate-solubilizing bacteria (PSB) in phosphorus (P) cycling in agricultural soils, we isolated PSB inhabiting naturally in the sandy loam soils under chickpea cropping of Patiala (Punjab State). A total of 31 bacterial isolates showing solubilizing activities were isolated on Pikovskaya agar plates. The potent phosphate solubilizers were selected for further characterization. These isolates were shown to belong to the genera Pseudomonas and Serratia by partial sequencing analysis of their respective 16S rDNA genes. ERIC-PCR based fingerprinting was done for tracking the survival of introduced populations of the PSB during mass inoculation of these strains under chickpea plots. The results showed positive correlation (r² = 0.853) among soil phosphatase activity and phosphate solubilizers population, which was also positively correlated (r² = 0.730) to available phosphorus. Identification and characterization of soil PSB for the effective plant growth-promotion broadens the spectrum of phosphate solubilizers available for field application.     

Effects of long-term exposure to elevated UV-B radiation on the photosynthetic performance of five broad-leaved tree species

As part of an ongoing investigation into the effects of long-term UV-B radiation exposure on the growth and morphology of woody perennials, the gas exchange and photosynthesis of five common deciduous tree species were measured. All five tree species had been exposed to UV-B radiation for 5 years, in the field, at an enhancement level equivalent to an 18% ozone depletion. Measurements made during the fifth year of UV-B irradiation recorded reductions in light-saturated photosynthesis, transpiration and water use efficiencies. These changes were accompanied by marked reductions in individual leaf areas, stomatal density, stomatal conductance and carboxylation efficiency. There were no significant changes in the maximum variable fluorescence ratio, the quantum requirement of oxygen evolution, or light-saturated O₂ production. Analysis of the response of net carbon assimilation to changing intercellular CO₂ concentration (A/c_i response) demonstrated no significant change in stomatal limitation. Reductions in photosynthesis were consistent with decreased carboxylation efficiency. Although all five tree species were similarly affected by UV-B radiation treatment, the magnitude of the responses was species-specific. These findings demonstrate the need for more long-term experimentation and also suggest that changes in water use efficiency may be a significant factor in plants' responses to UV-B radiation. This revised version was published online in June 2006 with corrections to the Cover Date.