Department of Biology and Environment, University of Haifa-Oranim, Tivon 36006, Israel.
Ann Bot. 2011 Jul;108(1):197-206. doi: 10.1093/aob/mcr104. Epub 2011 May 17.
Sex allocation has been studied mainly in small herbaceous plants but much less in monoecious wind-pollinated trees. The aim of this study was to explore changes in gender segregation and sex allocation by Pinus halepensis, a Mediterranean lowland pine tree, within tree crowns and between trees differing in their size or crown shape.
The production of new male and female cones and sex allocation of biomass, nitrogen and phosphorus were studied. The relationship between branch location, its reproductive status and proxies of branch vigour was also studied.
Small trees produced only female cones, but, as trees grew, they produced both male and female cones. Female cones were produced mainly in the upper part of the crown, and male cones in its middle and lower parts. Lateral branch density was correlated with the number of male but not female cones; lateral branches were more dense in large than in small trees and even denser in hemispherical trees. Apical branches grew faster, were thicker and their phosphorus concentration was higher than in lateral shoots. Nitrogen concentration was higher in cone-bearing apical branches than in apical vegetative branches and in lateral branches with or without cones. Allocation to male relative to female function increased with tree size as predicted by sex allocation theory.
The adaptive values of sex allocation and gender segregation patterns in P. halepensis, in relation to its unique life history, are demonstrated and discussed. Small trees produce only female cones that have a higher probability of being pollinated than the probability of male cones pollinating; the female-first strategy enhances population spread. Hemispherical old trees are loaded with serotinous cones that supply enough seeds for post-fire germination; thus, allocation to males is more beneficial than to females.
性分配主要在小型草本植物中进行研究，但在雌雄同体风授粉的树木中研究较少。本研究旨在探索地中海低地松树地中海松（Pinus halepensis）在树冠内和树冠大小或形状不同的树木之间的性别隔离和性分配的变化。
研究了新的雄球果和雌球果的产生以及生物量、氮和磷的性分配。还研究了枝条位置与其生殖状态及其代表的枝条活力之间的关系。
小树只产生雌球果，但随着树木的生长，它们也产生雄球果和雌球果。雌球果主要产生在树冠的上部，而雄球果则产生在树冠的中部和下部。侧枝密度与雄球果的数量相关，但与雌球果无关；侧枝在大树上比在小树密度更大，甚至在半球形树上更密集。顶枝生长更快，更粗，其磷浓度高于侧枝。与具有或不具有球果的侧枝相比，具有球果的顶枝的氮浓度更高。性分配理论预测，性分配的大小和性别隔离模式与树木大小的关系表明，性分配的大小和性别隔离模式具有适应性价值。
展示并讨论了地中海松性分配和性别隔离模式与独特的生活史相关的适应价值。小树只产生雌性球果，其被授粉的可能性高于雄性球果授粉的可能性；雌先策略增强了种群的传播。半球形老树载有结实的球果，可提供足够的种子用于火灾后萌发；因此，分配给雄性比分配给雌性更有利。
