Schimd College of Science and Technology, Chapman University. One University Drive, Orange, CA, 92866, USA.
Centro de Investigaciones Biológicas del Noroeste, Av. Instituto Politécnico Nacional 195, Col. Playa Palo de Santa Rita Sur, La Paz, B.C.S., 23096, México.
Am J Bot. 2021 Feb;108(2):334-345. doi: 10.1002/ajb2.1572. Epub 2020 Dec 6.
Woody plants with photosynthetic stems are common in the drylands of the world; however, we know little about the origin(s) and geographical distribution of photosynthetic stems. Therefore, we set to answer the following questions: (1) Is stem photosynthesis phylogenetically conserved? (2) Do green-stemmed and fleshy-stemmed species have identifiable climatic niches?
We mapped the photosynthetic stem trait onto a phylogeny of 228 mediterranean and desert species and calculated indices of phylogenetic signal and created climatic niche models of 28 species belonging to three groups: green, fleshy, and green-and-fleshy stemmed species.
We found phylogenetic signal in the fleshy stem trait, but not in the green stem trait. Fleshy-stemmed species occupy areas associated with high isothermality, high precipitation seasonality, and high mean temperature of the wettest quarter, whereas green-stemmed species occupy areas associated with high precipitation of driest month, high precipitation of coldest quarter, high mean diurnal temperature range and high maximum temperature of the warmest month.
Despite the fact that both photosynthetic stem types help cope with water shortage, having fleshy stems allows plants to cope with greater precipitation seasonality than is possible with green stems. Green stems require a lot of water to be stored in the soil to maintain net photosynthesis during the dry season, so they inhabit areas with higher and more predictable precipitation.
具有光合作用茎的木本植物在世界干旱地区很常见；然而，我们对光合作用茎的起源和地理分布知之甚少。因此，我们着手回答以下问题：(1) 茎的光合作用在系统发育上是否保守？(2) 绿色茎和肉质茎的物种是否具有可识别的气候生态位？
我们将光合作用茎的特征映射到 228 种地中海和沙漠物种的系统发育树上，并计算了系统发育信号指数，并为属于三个组的 28 个物种创建了气候生态位模型：绿色、肉质和绿色和肉质茎的物种。
我们发现肉质茎特征在系统发育上具有信号，但绿色茎特征则没有。肉质茎物种占据与等温和性高、降水季节性高、最湿润季度平均温度高相关的区域，而绿色茎物种则占据与最干燥月份降水高、最寒冷季度降水高、最大日温差高和最温暖月份最高温度高相关的区域。
尽管两种光合作用茎类型都有助于应对水分短缺，但具有肉质茎的植物比绿色茎植物更能适应更大的降水季节性。绿色茎需要在土壤中储存大量水分，以在旱季维持净光合作用，因此它们栖息在降水更高、更可预测的地区。
