Latitude, seed predation and seed mass

Aim We set out to test the hypothesis that rates of pre‐ and post‐dispersal seed predation would be higher towards the tropics, across a broad range of species from around the world. We also aimed to quantify the slope and predictive power of the relationship between seed mass and latitude both within and across species. Methods Seed mass, pre‐dispersal seed predation and post‐dispersal seed removal data were compiled from the literature. Wherever possible, these data were combined with information regarding the latitude at which the data were collected. Analyses were performed using both cross‐species and phylogenetic regressions. Results Contrary to expectations, we found no significant relationship between seed predation and latitude (log₁₀ proportion of seeds surviving predispersal seed predation vs. latitude, P = 0.63; R² = 0.02; n = 122 species: log₁₀ proportion of seeds remaining after postdispersal seed removal vs. latitude, P = 0.54; R² = 0.02; n = 205 species). These relationships remained non‐significant after variation because of seed mass was accounted for. We also found a very substantial (R² = 0.21) relationship between seed mass and latitude across 2706 species, with seed mass being significantly higher towards the tropics. Within‐species seed mass decline with latitude was significant, but only about two‐sevenths, as rapid as the cross‐species decline with latitude. Results of phylogenetic analyses were very similar to cross‐species analyses. We also demonstrated a positive relationship between seed mass and development time across ten species from dry sclerophyll woodland in Sydney (P < 0.001; R² = 0.77; Standardized Major Axis slope = 0.14). These data lend support to the hypothesis that growing period might affect the maximum attainable seed mass in a given environment. Main conclusions There was no evidence that seed predation is higher towards the tropics. The strong relationship between seed mass and latitude shown here had been observed in previous studies, but had not previously been quantified at a global scale. There was a tenfold reduction in mean seed mass for every c. 23° moved towards the poles, despite a wide range of seed mass within each latitude.     

Long-term variation in seed mass and seed production in populations of Paris quadrifolia

Seed production of the perennial herb Paris quadrifolia L. (Liliaceae) was investigated in five populations in northern Poland. The long-term seed production per square metre differed significantly among populations and years. Moreover, throughout the 7-year study period, 30% of both whole ripe fruits and seeds alone were predated. Variation in seed mass per fruit in both space and time was significant. Throughout the 7-year study, nearly all the marked individuals produced fruits once every 2 years. The most frequent break between fruiting was 2 years and the longest was 5 years. Only the mean seed mass in fruits of the same individual varied significantly over subsequent years. In the five populations, the number of ovules, number of seeds in the fruit and seed mass varied significantly between populations. However seed/ovule ratio did not differ in fruits in the five populations. The seed mass/number trade-off in fruits was strongly partially correlated when the effect of total seed mass was considered. Breeding experiments suggest that P. quadrifolia has a substantial capacity for both inbreeding and outbreeding. There were no significant differences in the seed/ovule ratio, seed number or seed mass in fruits produced from bagged or control flowers. However, both seed/ovule ratio and number of seeds were significantly lower in fruits from emasculated flowers.     

Geographical and environmental gradients of lianas and vines in China

Aim Climbing plants are characterized by long, wide vessel elements, which may be vulnerable to cold‐ or drought‐induced embolism. However, the difference in vulnerability between lianas (woody climbing plants) and vines (herbaceous climbing plants) has not yet been reported. Here we hypothesize that both lianas and vines are more sensitive to variations in water and temperature than are self‐supporting plants. Consequently, the proportions of lianas and vines in flora are expected to decline significantly along geographical and environmental gradients. Location China. Methods A unique dataset describing 82 floras in China was examined. The proportion of lianas in the flora (LPF) and the proportion of vines in the flora (VPF) were calculated independently. The proportion of the climbing plants in total spermatophyte flora (CPF) was also calculated. LPF and VPF were compared along latitudinal, mean annual rainfall (Rain), and mean January temperature (T₁) gradients. Local linear regression analyses showed the changing tendencies of LPF and VPF. Prediction models of LPF using geographical and environmental factors were studied in some subranges. Results (1) LPF was highest in the tropics (13.8% on average), decreased linearly with increasing latitude within the latitude < 42 °N subrange, and reached < 1% north of 42 °N in China. VPF fluctuated slightly from tropical (4.7%), to subtropical (4.2%) to warm temperate (4.5%) regions, but declined significantly in temperate (3.2%) and dry (1.5%) zones in China. (2) LPF decreased significantly with decreasing rainfall, and decreased significantly with decreasing T₁ in areas where T₁ > −10 °C. In contrast, VPF tended to be constant in areas where T₁ > −5 °C or Rain > 1000 mm, and declined under extreme water or temperature stresses. (3) Predictions of LPF using Rain and T₁ in areas where T₁ > −10 °C, and using latitude and altitude within the latitude < 42 °N subrange were both reliable. According to the geographical model for LPF and a constant VPF, tropical Asian forests would have a LPF as high as 25.4% and the highest CPF would be c. 30%. Conclusions We conclude that liana diversity is more sensitive to temperature and water availability than that of vines and other plants. Geographical and environmental gradients affected LPF but not VPF. Shorter life spans and underground nutrient storage may be effective strategies adopted by vines to avoid drought and cold stresses.     

中国人身体质量指数的地理性分布

2009-2013年测量了中国11个汉语方言族群26954例汉族人的身高、体重值,计算了身体质量指数(I_(bm)),将汉族人的I_(bm)与经度、纬度进行相关分析。研究结果表明:总的说来,随年龄增长,11个方言族群I_(bm)值均呈线性增大,并且年龄组间差异均具有统计学意义。11个族群中,北方话族群I_(bm)值明显大于南方各族群。乡村男性(r=0.671; p0.05)、城市女性(r=0.043; p=0.820>0.05)I_(bm)与经度无相关。按照I_(bm)均数大于24.0、I_(bm)均数在23.1～24.0之间、I_(bm)均数小于23.0,可以将中国方言族群分成3个层次,中国北方话族群均分布在第1、2层次,南方族群主要分布在第2、3层次,也就是说11个族群大致按照纬度高低顺序依次分布在第1、2、3层次。遗传、环境、饮食、劳作强度等因素都不同程度影响身高、体重,也影响中国人的I_(bm)值。     

种子地理学研究的新进展

在已发表的“种子地理学”基本理论框架和内涵的基础上, 该文对种子地理学理论进行了补充和修订, 在以前提出的7个方面的研究内容基础上, 补充了土壤种子库的地理学、种子雨的地理学、种子散布方式的地理学三个方面的研究内容, 提出了“土壤种子库的三向(纬度、经度和海拔)梯度变化假说”和“种子散布模式的三向梯度变化假说”。还对以前提出的6个方面的研究内容进行了增补, 在“种子化学性状地理学”方面添加了种子稳定性同位素性状, 在“种子重量的地理学”方面添加了油质体性状, 在“种子形态性状的地理学”方面补充了种子长、种子宽、种子长宽比、种子的附属结构(如果翅的有无以及种子附属物种翅长、种翅宽、种翅长宽比)等性状, 在“花和果实的地理学”方面增添了一些新的关注对象, 如花瓣的长和宽、花萼长和宽, 还有果实的长、宽、高及其比值, 夏季成熟的果实及秋天成熟的果实比例等, 在“种子遗传学性状的地理学”方面添加了DNA含量这个性状, 在“种子细胞性状的地理学”方面增添了淀粉粒。     

Seed germination responses to seasonal temperature and drought stress are species‐specific but not related to seed size in a desert steppe: Implications for effect of climate change on community structure

Investigating how seed germination of multiple species in an ecosystem responds to environmental conditions is crucial for understanding the mechanisms for community structure and biodiversity maintenance. However, knowledge of seed germination response of species to environmental conditions is still scarce at the community level. We hypothesized that responses of seed germination to environmental conditions differ among species at the community level, and that germination response is not correlated with seed size. To test this hypothesis, we determined the response of seed germination of 20 common species in the Siziwang Desert Steppe, China, to seasonal temperature regimes (representing April, May, June, and July) and drought stress (0, ?0.003, ?0.027, ?0.155, and ?0.87 MPa). Seed germination percentage increased with increasing temperature regime, but Allium ramosum, Allium tenuissimum, Artemisia annua, Artemisia mongolica, Artemisia scoparia, Artemisia sieversiana, Bassia dasyphylla, Kochia prastrata, and Neopallasia pectinata germinated to >60% in the lowest temperature regime (April). Germination decreased with increasing water stress, but Allium ramosum, Artemisia annua, Artemisia scoparia, Bassia dasyphylla, Heteropappus altaicus, Kochia prastrata, Neopallasia pectinata, and Potentilla tanacetifolia germinated to near 60% at ?0.87 MPa. Among these eight species, germination of six was tolerant to both temperature and water stress. Mean germination percentage in the four temperature regimes and the five water potentials was not significantly correlated with seed mass or seed area, which were highly correlated. Our results suggest that the species‐specific germination responses to environmental conditions are important in structuring the desert steppe community and have implications for predicting community structure under climate change. Thus, the predicted warmer and dryer climate will favor germination of drought‐tolerant species, resulting in altered proportions of germinants of different species and subsequently change in community composition of the desert steppe.     

The effect of seed mass and gap size on seed fate of tropical rain forest tree species in guyana

Abstract: For eleven tree species, differing in seed mass, germination success (emergence success for two small-seeded species) and the causes of failure to germinate were studied in the forest understorey and in logging gaps in the tropical rain forests of Guyana. In the forest understorey, germination success increased with seed mass. However, as gap size increased the difference between smaller and larger seeded species diminished because germination success of smaller-seeded species increased slightly, while that of larger-seeded species decreased dramatically. The negative effect of gap size on germination success of larger-seeded species was caused by an increased risk of desiccation with gap size, which was a far more important seed mortality agent for larger than for smaller-seeded species. Generally, seeds of smaller-seeded species suffered more from insect predation and were removed at higher rates than larger-seeded species. On the other hand, larger-seeded species were eaten more by mammals than smaller-seeded species. It is concluded that logging can result in shifts in the species composition in the tropical rain forests of Guyana which are dominated by species with large seeds, since germination success of larger-seeded species is dramatically reduced in large logging gaps.     

Correlated evolution of genome size and seed mass

Previous investigators have identified strong positive relationships between genome size and seed mass within species, and across species from the same genus and family. Here, we make the first broad-scale quantification of this relationship, using data for 1222 species, from 139 families and 48 orders. We analyzed the relationship between genome size and seed mass using a statistical framework that included four different tests. A quadratic relationship between genome size and seed mass appeared to be driven by the large genome/seed mass gymnosperms and the many small genome size/large seed mass angiosperms. Very small seeds were never associated with very large genomes, possibly indicating a developmental constraint. Independent contrast results showed that divergences in genome size were positively correlated with divergences in seed mass. Divergences in seed mass have been more closely correlated with divergences in genome size than with divergences in other morphological and ecological variables. Plant growth form is the only variable examined thus far that explains a greater proportion of variation in seed mass than does genome size.     

Seed dormancy in relation to seed storage behaviour in Acer

Dormancy in seeds of Acer opalus is shown to be mainly caused by the seed coats, although a slight embryo dormancy exists in fresh seeds. The ability to germinate after drying indicates that seed storage behaviour is orthodox. Recalcitrant seeds were heavier than orthodox seeds not only within section Acer but also within the whole genus after statistical control of phylogeny, through a phylogenetic ANOVA with data from two different Acer phylogenies. An evolutionary change from orthodox to recalcitrant behaviour is postulated for genus Acer , but this change appears not to have been accompanied by a change in seed dormancy, at least in the taxonomic section in which Acer opalus belongs.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 203–208.     

土壤种子库的分类系统和种子在土壤中的持久性

对国际上已经发表的10个土壤种子库分类系统的内容进行了总结和阐述,并对土壤种子库分类系统进行了评述,其中Thompson ＆ Grime在1979年提出的把土壤种子库分为短暂土壤种子库（Transient soil seed bank）和持久土壤种子库（Persistent seed bank）的二元分类系统以及Thompson等人提出的把土壤种子库分为（1）短暂土壤种子库,（2）短期持久土壤种子库（Short term persistent seed bank）,（3）长期土壤种子库（Long termp ersistent seed bank）的三元分类系统在生态学文献中已被广泛采用。在此分类的基础上产生了植物种子在土壤中的持久性（Persistence）概念,持久性是指植物的一种特性,是指植物的种子在土壤中能够存活超过1a的特性;植物种子的持久性被认为是一种对环境的进化适应,它可以在多个生长季节萌发从而分担环境震荡的风险,持久土壤种子库不仅在不稳定的环境里占有优势;即使在稳定的环境里,也被认为能够减少种内和种间的竞争;造成持久性的原因可分为环境因子和种子本身的特性比如休眠等两个方面,持久土壤种子库的出现使得土壤种子库的研究与进化生物学结合起来,使得土壤种子库的研究进入一个新的领域,更易激发人们的兴趣。关于种子的大小、形状及持久性的关系问题已经引起了相当的争论,基本上有4种格局：一是种子大小和形状与种子在土壤中的持久性有关,小而圆或扁的种子在土壤易存活持久;二是种子大小与种子在土壤中的持久性有关,小种子在土壤中易存活持久,但种子形状与持久性无关;三是种子大小、形状与种子在土壤中的持久性无关;四为较大的种子在土壤易存活持久,而种子形状与种子在土壤中的持久性无关。影响种子在土壤中的持久性因子比较复杂,总结过去的文献发现主要有以下几个因子：①种子的散布方式,②捕食,③植被的物种组成,④风,⑤土壤基质,⑥火,⑦干扰等。通过比较分析和研究,提出影响种子大小和在土壤中的持久性关系格局的关键因子是气候,特别是生态系统所在地的雨量;湿润气候下容易产生前两种格局,而干旱环境下的生境容易产生后两种格局。     

珍稀植物连香树(Cercidiphyllum japonicum)的种子萌发特性

连香树（Cercidiphyllum japonicum Sieb.et Zucc.）属第三纪孑遗植物,被列为国家二级保护植物,种群的自然更新困难。在实验室条件下研究了连香树种子萌发的生物学特性,以了解该种自然种群更新困难的原因和机制,为其有效保护提供理论依据。经测定,连香树种子千粒重为（0.5821&#177;0.0166）g,种子重量极轻且产量大。四唑染色法对种子生活力的测定表明有活力种子比率仅为19.8%&#177;1.3%。种子吸胀时吸水量达种子干重的482.13%&#177;8.54%。将种子划分为6种表面形态类型进行萌发实验,发现不同形态种子萌发率显著不同,大小适中的黄褐色饱满种子萌发率最高,可达91.25%&#177;2.36%。仅用饱满种子进行萌发实验,验证主要环境因子对种子萌发过程的影响,结果表明,以滤纸置床时萌发率高且有利于种子萌发整齐;种子表面可能存在促进种子萌发的物质;种子萌发对于湿度的响应最为明显,适宜的萌发湿度是20%～25%;萌发具有广泛的温度和光照适应性,除5℃萌发率降低外,10～30℃之间的萌发率无显著差异,随温度升高,萌发开始时间提前,萌发速率加快,幼苗活力指数增加;过弱光照不利于幼苗生长。种子萌发特性导致连香树种群自然更新困难的原因可能是：（1）虽然占有更多安全位,但小种子在竞争中处劣势;（2）生境片断化减少了种子产量也降低了种子质量;（3）较低温度条件下启动萌发有利于幼苗的物质积累,但增大了种群的风险;（4）林下光照不足使幼苗根茎生长严重失衡;（5）湿度依赖易造成爆发型萌发。     

Geographical distribution of myxomycetes living on Cryptomeria japonica bark in Japan

There is little available data on the biogeography of myxomycetes at the regional scale within any given climate zone. To investigate the geographical distribution of these protozoans, we focused on corticolous myxomycetes associated with the bark of Cryptomeria japonica trees, which we sampled extensively throughout Japan. Myxomycete sporophores developed in 73% of 2244 moist-chamber cultures of 188 bark samples from 24 regions, including 31 species. The most abundant species were Paradiacheopsis rigida and Cribraria confusa, which accounted for over 20% of all myxomycetes sampled. Non-metric multidimensional scaling was used to analyze the distribution of myxomycetes in relation to geographical variables and bark pH. The distribution of myxomycetes was influenced by altitude, temperature and bark pH. Temperature gradients and relative abundance of species were negatively correlated in P. rigida and Comatricha laxa and positively correlated in C. confusa, Macbrideora cornea, and Diderma chondrioderma. Bark pH was also positively correlated with the relative abundance of C. confusa, D. chondrioderma, and Physarum nutans and negatively correlated with that of P. rigida, P. cribrata, Enerthnema papillatum, and E. melanospermum. Geographical distribution of corticolous myxomycete communities was determined based on temperature and bark pH, which acted as local barriers in our study area.     

Parental effects on seed mass: seed coat but not embryo/endosperm effects

Many biologists studying environmentally induced parental effects have indirectly suggested that the parental environment alters seed mass by altering the amount of endosperm or embryo tissue in the seed. We tested this hypothesis by measuring the effects of parental temperature on total seed mass, seed coat mass, and embryo/endosperm mass in offspring of Plantago lanceolata. Parental temperature significantly affected total seed and coat mass but not endosperm/embryo mass. Thus, larger seeds do not contain more resources in the embryo or endosperm than do small seeds. Rather they have more coat mass, which probably strongly influences germination. These results suggest caution when making assumptions about the pathways by which environmentally induced parental effects are transmitted in plant species. We also observed that controlled crosses differed significantly in their response to parental temperature, which provides evidence for genetic variation in environmentally induced parental effects, i.e., intergenerational phenotypic plasticity, in natural populations of P. lanceolata.     

Potential effects of climate change on DOC release from three different soil types on the Northern Pennines UK: examination using field manipulation experiments

Three field manipulation experiments were carried out during 1993–1995 on the Northern Pennines to investigate the influences of temperature, solar radiation and rainfall on the release of dissolved organic carbon (DOC) from vegetated soil cores using zero‐tension lysimeters. The cores were manipulated by being translocated to four sites down a climatic gradient, by artificial soil heating or being exposed to double normal rainfall. In each experiment three soil types, a brown earth, a micropodzol and a peaty gley, with differing organic matter content and distribution within the profile, were studied. DOC data, expressed as mg C m^?2 day^?1, were analysed following log₁₀ transformation, by a repeated measures analysis of variance procedure, using climatic variables measured concurrently with sampling, and 1 and 2 months before sampling. DOC release was dominated by rainfall but was also associated with solar radiation and temperature. With each of the three climatic variables, rainfall, solar radiation and temperature, both positive and negative effects on DOC release have been found significant, indicating that the concurrent and delayed effects of the same variable may be different. DOC release was positively related with all three soils to concurrent rainfall, indicating rainfall's primary leaching action. DOC release was also negatively related to rainfall of the previous month indicating that its action depletes the leachable pool of DOC in the soil. DOC release was positively associated with solar radiation 2 months earlier, indicating that DOC's main source is that of primary production; DOC peaks closely followed peaks of annual primary production. DOC release was linked with temperature, the strongest association being with temperature 2 months earlier, indicating that temperature effects both primary production and DOC regeneration via organic matter decomposition. A conceptual model, relating our findings to those processes known to govern DOC release from soils, has been presented.