Stable carbon isotope analyses show dominance of C3 grasses in the feed selected by small herbivores at the alpine meadow at the Tibetan Plateau

Muscle samples were collected from small herbivorous mammals (Ochotona curzoniae, Microtus oecnomus, Myospalax fontanierii and Lepus oiostolus) at the alpine meadow ecosystem at the Tibetan Plateau in order to address variability in stable carbon isotope composition. Stable carbon isotope values of muscles remain steady and show no significant variations (-25.72 to -27.04 parts per thousand) among the four small mammal species. Based on the mass balance theory of stable isotopes, it is proposed that small herbivorous mammals mainly (or totally) rely on C3 grasses as food supply, and there is few or no distribution of C4 grasses at the ecosystem. The results reflect our previous study on the isotope patterns of plant species. Thus, stable carbon isotope analysis of muscles provides a method to address dietary selection and dietary variability in herbivores. In addition, stable carbon isotopic analyses can be used to address changes in vegetation distributions in ecosystem and paleovegetaion and paleoclimate.

Notes on grasses (Poaceae) for the Flora of China, VI. New combinations in Stipeae and Anthoxantham

When Oryzopsis is confined to the type species, Chinese species are placed in Achnatherum and Piptatherum. This necessitates the following new combinations: Piptatherum grandispiculum, Piptatherum aequiglume var. ligulatum, Piptatherum tibeticum var. psilolepis.. Piptatherum. munroi var. parviflorum, Achnatherum henryi. and Achnatherum henryi var. acutum. Achnatherum henryi is lectotypified. The new name Piptatherum kuoi replaces the illegitimate name Piptatherum obtusum, and this species is lectotypified. Hierochloe potaninii is transferred to Anthoxanthum as A. potaninii, as Hierochloe is regarded as a synonym of Anthoxanthum. All the grass taxa (Poaceae) listed are endemic to China.

毛乌素沙地两种固沙禾草种子萌发和幼苗生长与环境的关系

干旱区和半干旱区生长的植物具有复杂的生存机制，以确保其能够在特定的环境中生存和发展。植物在干旱的荒漠条件下的生存，与其特殊的种子萌发机制密切相关，这种机制能够确保植物在合适的时间与地点进行种子萌发与幼苗生长发育。在植物的生活史中，种子对极端环境具有最大的忍耐力，而萌发的幼苗对环境胁迫的忍耐程度最小。在干旱区生长的植物往往具有特殊的萌发机制使萌发出的幼苗能够度过对外界的敏感期，对于植物的生存具有重要意义。 毛乌素沙地是我国的四大沙地之一，该地区具有水分短缺，蒸发强烈，风沙剧烈和生境异质性高的特征。本文假设生长在这种极端环境中的植物也发展出了“适时适地”的种子萌发和幼苗生长的适应对策。为了验证以上的假设，本文选取毛乌素沙地不同生境中生长的两种优势固沙禾草——流动沙丘上生长的沙鞭(Psammochloa villosa)和固定沙丘上生长的赖草(Leymus secalinus)为研究材料，通过野外调查、温室控制实验和实验室控制实验的方法，从生理生态学的角度探讨这两种植物的种子萌发和幼苗生长过程对沙丘环境的适应对策，主要对比它们在种子休眠、萌发和幼苗早期生长过程中对沙丘生境适应性的异同点。研究结果表明： （1）新成熟的沙鞭和赖草的种子为适应冬季低温而发展出生理性的内生休眠——非深度生理休眠。沙鞭和赖草的种子分别需要经过4周和8周的低温层积处理(3－5ºC)来完全打破休眠。另外，划破种皮或者部分切除胚乳也能够促进种子的萌发，这进一步证明两种植物的种子具有非深度生理休眠。然而，切除胚乳在不同程度上影响它们的幼苗生长。由非深度生理休眠、温度和损伤种皮/胚乳调节的部分萌发机制能够确保两种植物的种子即使在条件适宜的情况下只有部分种子萌发，从而分散植物生存的风险性。 （2）毛乌素沙地的小量降水（无法触发萌发）使种子经常遭受湿润－干燥的交替胁迫过程。种子先在湿润条件下吸涨1d或者2d，然后在室温下干燥0-8天。尽管在经历反复吸涨和自然干燥脱水后仍能够保持萌发能力，沙鞭和赖草种子的萌发特性却发生了不同的变化：和各自的对照相比，沙鞭种子萌发率相同而萌发速率降低;赖草种子的萌发率和萌发速率都降低，部分种子进入休眠状态。沙鞭和赖草萌发出的幼苗可能由于没有后续降雨或者因沙蚀而遭受干燥胁迫，但是其幼苗在生长早期能够忍耐一定程度的干燥，再次湿润后部分幼苗能够恢复生长。沙鞭和赖草幼苗的耐干燥的“极限点”不同：当幼根长度为1 mm时，它们的幼苗忍耐干燥的时间分别是60d和30d;当幼根长度为4 mm时，它们的幼苗忍耐干燥的时间分别是14d和7d。沙鞭和赖草的种子和生长早期的幼苗的耐干燥性特性可能是它们对降雨量和降雨时间都不可预测的沙地生境的生存策略之一。 （3）不同的沙埋深度影响沙鞭和赖草的种子萌发和出苗。这两种植物的种子萌发和出苗都需1－2 cm的浅层沙埋。随着沙埋深度的增加，两种植物的种子萌发率和出苗率逐渐降低，强迫休眠率逐渐升高;萌发率与出苗率和沙埋深度呈负相关关系而休眠率和沙埋深度呈正相关关系。但是，沙鞭种子出苗的最大沙埋深度是8 cm，而赖草的则为4 cm。因强迫休眠而没有萌发的种子对维持一个长期的土壤种子库来说具有生态学优势，这些种子暴露在合适的萌发土壤深度时具有生长出幼苗的潜能。 （4）沙鞭和赖草的种子都具有大小的差异性，种子大小对沙鞭和赖草的种子在不同沙埋深度的出苗具有不同的影响。沙鞭的三种不同大小种子的平均质量分别为小，4.489 ± 0.012 mg (4 – 4.9 mg);中，5.457 ± 0.012 mg (5 – 5.9 mg)和大，6.415 ± 0.011 mg (6 – 6.9 mg)。赖草的两种不同大小种子的平均质量分别为小，3.083 ± 0.026 mg (3 – 3.5 mg)和大3.955 ± 0.028 mg (3.6 – 4.0 mg)。在相同的沙埋深度下，两种植物的大种子的出苗率都显著高于小种子。和小种子相比，两种植物的大种子由于贮藏更多的能量，所以在相同深度的沙埋中具有出苗率更高的生态优势，而大量小种子在沙埋中不能萌发，可以作为种子库保存在沙层中，这样就分散了一次性大量萌发给植物带来的冒险性。 （5）沙鞭和赖草的幼苗在生长过程中会遭受沙埋，其幼苗忍耐沙埋的能力与沙埋的相对深度（沙埋比例）和幼苗年龄有关。沙鞭和赖草幼苗的耐沙埋能力不同：沙鞭的2周龄幼苗可以忍耐达到株高100%的沙埋，而其1周龄幼苗只能忍耐75%的沙埋。赖草的1周龄和2周龄幼苗都只能忍耐75%的沙埋。沙埋之后，沙鞭和赖草幼苗的生物量，根/茎比以及根和茎的长度都受到不同程度的影响。赖草幼苗不能忍耐完全沙埋可能是限制它在流动沙丘上分布的一个原因。 （6）降雨量和降雨频率能够不同程度地影响沙鞭和赖草在不同沙层的萌发和出苗。这两种植物的种子萌发和出苗需要的最小降雨量不同：在一次浇水相当于5 mm降雨量后，沙鞭和赖草种子的萌发率都超过50%;但是使沙鞭和赖草的出苗率能够达到50%的降雨量分别为10 mm和15 mm。沙埋中的沙鞭和赖草种子的出苗对降雨的响应具有以下特征：两种植物种子的出苗随降雨量或者降雨频率的增加而增加;沙鞭的出苗率受到降雨量和降雨频率的显著影响，但是二者交互作用的影响不显著;赖草的出苗率受到降雨量、降雨频率以及二者交互作用的显著影响。 由非深度生理休眠，种子大小，干燥－湿润循环，沙埋和降雨调节的种子萌发和出苗机制确保了自然条件下沙鞭和赖草每次只有少量种子萌发和出苗，从而分散了两种植物在沙丘上的生存风险。 根据沙鞭和赖草在沙丘上的种子萌发和幼苗生长特性，本文为毛乌素沙地通过植物固沙恢复受损的沙地生态系统的种子飞播实践提出了几点建议。

The Genomes of Oryza sativa: A history of duplications

We report improved whole-genome shotgun sequences for the genomes of indica and japonica rice, both with multimegabase contiguity, or almost 1,000-fold improvement over the drafts of 2002. Tested against a nonredundant collection of 19,079 full-length cDNAs, 97.7% of the genes are aligned, without fragmentation, to the mapped superscaffolds of one or the other genome. We introduce a gene identification procedure for plants that does not rely on similarity to known genes to remove erroneous predictions resulting from transposable elements. Using the available EST data to adjust for residual errors in the predictions, the estimated gene count is at least 38,000 - 40,000. Only 2% - 3% of the genes are unique to any one subspecies, comparable to the amount of sequence that might still be missing. Despite this lack of variation in gene content, there is enormous variation in the intergenic regions. At least a quarter of the two sequences could not be aligned, and where they could be aligned, single nucleotide polymorphism ( SNP) rates varied from as little as 3.0 SNP/kb in the coding regions to 27.6 SNP/kb in the transposable elements. A more inclusive new approach for analyzing duplication history is introduced here. It reveals an ancient whole-genome duplication, a recent segmental duplication on Chromosomes 11 and 12, and massive ongoing individual gene duplications. We find 18 distinct pairs of duplicated segments that cover 65.7% of the genome; 17 of these pairs date back to a common time before the divergence of the grasses. More important, ongoing individual gene duplications provide a never-ending source of raw material for gene genesis and are major contributors to the differences between members of the grass family.