Growth and reproduction of Sophora moorcroftiana responding to altitude and sand burial in the middle Tibet

Abstract

Sophora moorcroftiana, an endemic leguminous shrub in Tibet, is found in valleys, slopes, terraces from 3,000 to 3,900 m above sea level along the middle reaches of the Yarlung Zangbo River. S. moorcroftiana is more tolerant of sand burial than other species in the valleys and is regarded as an ideal species for studying acclimatization to climatic factors. Stem basal diameter showed decline as altitude increased from 3,039 to 3,928 m in the Yarlung Zangbo River valley. Population density increased with the rise of altitude. However, seed bank density, seed germination and seed weight of S. moorcroftiana did not change with changing elevation. Plants responded to altitude variances with remarkable sensitivities. Stem basal diameter size declined along the vertical gradient between plateau and mountainside. Both in alpine and plateau areas, plants similarly adapted growth to altitude, but displayed different responses with respect to reproductive parameters, such as seed bank density, dry weight of seed, seed germination, seedling density and sapling density. Sand accretion remarkably reduced seed bank density and seedling density of the total population of S. moorcroftiana, but could promote shoot sprouting and shoot growing on the individual scale that stimulated the overall development of the population. The results suggested that this particular foredune species did not merely tolerate sand burial, but actually responded positively to sand accumulation.