Effect of annual weeds on the growth of perennial grass mixtures in the alpine region of the Qinghai-Tibetan Plateau

In the alpine region of the Tibetan Plateau, five perennial grass cultivars, Bromus inermis (B), Elymus nutans (E), Clinelymus nutans (C), Agropyron cristatum (A), and Poa crymophila (P) were combined into nine communities with different compositions and ratios, B+C, E+A, B+E+A, E+B+C,C+E+A,B+E+C+A,B+C+A+P,B+E+A+P and E+C+A+P. Each combination was sown in six 10 X 10 m plots with three hand-weeded plots and three natural-growing plots in a completely randomised design in 1998. A field experiment studied the performance of these perennial grass combinations under the competitive interference of annual weeds in 3 consecutive years from 1998 to 2000. The results showed that annual weeds occupied more space and suppressed the growth of the grasses due to earlier germination and quicker growth in the establishment year, but this pattern changed in the second and third years. Leaf area indexes (LAIs) of grasses were greatly decreased by the competitive interference of weeds, and the negative effect of weeds on LAIs of grasses declined and stabilised in the second and third years. E+B+C, B+E+C+A, and B+E+A+P possessed relatively higher LAIs (P < 0.05) among all grass combinations and their LAIs were close to five when the competitive interference of weeds was removed. Grasses were competitively inferior to weeds in the establishment year, although their competitive ability (aggressivities) increased throughout the growing season. In the second and third years, grasses were competitively superior to weeds, and their competitive ability decreased from May until August and increased in September. Dry matter (DM) yields of grasses were reduced by 29.8-74.1% in the establishment year, 11.0-64.9% in the second year, and 16.0-55.8% in the third year by the competitive interference of weeds. B+E+C+A and B+E+A+P can produce around 14 t/ha of DM yields, significantly higher (P < 0.05) than the production of the other grass combinations in the second and third years after the competitive interference of weeds was removed. It was preliminarily concluded that removal of competitive interference of weeds increased the LAIs of all grass swards and improved the light interception of grasses, thus promoting the production of perennial grass pastures. The germination stage of the grasses in the establishment year was the critical period for weeding and suppression of weeds should occur at an early stage of plant growth. The grass combinations of B+E+C+A and B+E+A+P were productive and can be extensively established in the alpine regions of the Tibetan Plateau. Two or three growing seasons will be needed before determining success of establishment of grass mixtures under the alpine conditions of the Tibetan Plateau.

Influence of lanthanum on the uptake of trace elements in cucumber plant

The effects of La3+ on the uptake of trace elements (Se, Co, V, and Tc) in cucumber plants were studied by a radioactive multitracer technique. It was observed that the uptake and distribution of these trace elements in roots, stems, and leaves are different under different La3+, treatments. Furthermore, in the control, the plant accumulates Se-75, Co-56, and V-48 all in the order roots>leaves>stems, whereas Tc-95m was in the order leaves>stems>roots. The accumulations of Se-75 and Tc-95m in plants treated with different La3+ concentration were in the same order as those in the control, but the uptakes percentages of other kinds of element changed differently. The results indicate that lanthanum treatments to a growing cucumber lead to the change of uptake of trace elements, which suggest that a rare earth element is directly or indirectly involved in the ion transport of the plant and affects plant growth by regulating the uptake and distribution of elements that influence the plant cell physiology and biochemistry.

德国鸢尾快速分株繁殖的研究

本实验用喷施6-BA和茎切生根的方法建立了一套德国鸢尾快速分株繁殖的体系。用3 000 mg/L 或5 000 mg/L 的6-BA 对德国鸢尾（Iris germanica）‘lovely again’进行单次喷施可以促进根茎芽的萌发和根状茎的形成。在喷施后的30 天到90 天内，BA的促进作用在具有2个或4个起始根状茎的植株上表现得很显著，但对于只有一个起始根状茎的植株不显著。在喷施后的150 天以及第二年，具有2个或4个起始根状茎的母株总体上比只具有1个起始根状茎的母株产生了更多的根状茎。而6-BA的喷施对母株的叶面积和叶片数变化没有显著影响。在早春时，把处于不同发育阶段的侧芽或小根茎从母株上取下，并且用不同浓度的IBA处理。总体上，处于较高发育阶段的茎切（芽切）在生根率、初级根和次级根的数目，总根长、根干重以及植株高度等测量指标方面的表现较好。IBA对德国鸢尾的茎切（芽切）的生根作用不显著。多次喷施6-BA 对德国鸢尾根茎芽的生出的促进作用显著，并且使生物量重新分配。连续喷施6-BA后，对内源生长素和细胞分裂素的连续测定结果表明，6-BA的作用主要是解除了顶端优势对侧芽的萌发和生长的抑制，从而形成新的根茎。