Genetic diversity, stand structure and sex ratio of Populus euphratica floodplain forests at the Tarim River, Xinjiang, NW China

在中国新疆省极度干旱的塔里木盆地，所谓的土盖森林由周围山脉冰川流出的河流灌溉，主要由一种树种组成，即雌雄异株的胡杨。虽然成年树只在高洪水后的河岸发芽，但它们可以在地下10米深的地方存活，并在离母树30米远的地方产生吸根器。该项目旨在调查这些森林的空间和遗传结构，解决以下问题：曲曲折折的河流上有树苗，也有垂死的老树。林分发展的时间尺度是什么？连片森林是如何从萌芽行发展而来的？树木及其性别的空间映射是否允许对克隆大小的估计（通过分子分析进行校准）？我们是否可以在景观尺度上利用这种方法来识别森林中具有高遗传多样性的区域？土改林的大规模遗传结构如何依赖于过去的河流运动，我们能否从景观特征中预测土改林的遗传多样性？干旱胁迫下的森林似乎有男性偏向的性别比例。这其中的原因是什么？两性比例的平衡是否意味着更适宜的生长环境？

Watered by rivers draining glaciers of the surrounding mountain ranges, the so-called Tugai forests in the extremely arid Tarim basin of Chinas Xinjiang province are made up mainly by a single tree species, the dioecious Populus euphratica. Although germinating exclusively at riverbanks after high floods, adult trees can survive up 10 m ground water depth and produce root suckers up to 30 m apart from the mother tree. The proposed project aims to investigate the spatial and genetic structure of these forests, addressing the following questions:1. Meandering rivers have stands ranging from seedlings to dying old trees. What is the time scale of stand development; how can a contiguous forest develop from germination rows?2. Does spatial mapping of trees and their sexes allow an estimation of clone size (to be calibrated by molecular analyses)? Can we identify pockets of high genetic diversity in the forests by using this method at a landscape scale?3. How depends the large-scale genetic structure of Tugai forests from past river movements, and can we predict the genetic diversity of the forests from landscape features?4. Forests under drought stress seem to have a male-biased sex ratio. What are the reasons, and does an even sex ratio indicate more suitable growth conditions?