Exploring the causes and patterns of ring-formation in plants in an unknown diversity hotspot of the Namib Desert

全球旱地植物中的环形成引起了研究界的极大兴趣，特别是关于产生这些对称形状的机制。在这里，植物环包括由单个草袜植物的缓慢营养生长过程产生的“草袜环”，以及2021年在纳米布沙漠发现的一类新的植物环：“集体植物环”。集体植物年轮由几个一年生草本植物或一年生杂草或两者的混合体组成，它们在东部纳米布沙漠的降雨事件后自发出现。这些环的功能目前还没有解决，也不清楚它们的直径、形状、密度和空间模式如何从雨季到雨季变化。初步调查表明，一年生草本植物和杂草形成直径达1米的年轮，共同消耗年轮内的土壤水分。这些环可能是植被自组织的结果，环外围的单个植物相互促进，以增加自己的生物量。然而，要更好地了解这类新的植物年轮，有必要进行深入的研究。令人惊讶的是，2021年，在纳米布沙漠中，总共发现了10种不同的草和杂草正在形成年轮，使纳米布成为真正的植物年轮形成的“多样性热点”。这是一个重大的研究空白，没有关于该生态系统的生物地理多样性和植物年轮范围的信息。只有著名的仙女圈在纳米布得到了广泛的研究，但这些植被缝隙的直径比植物环大得多，是一个不同的现象。我们将研究非洲西南部干旱地区形成环状植物的巨大财富。我们的开创性研究将包括一整套实地考察方法。在雨季使用无人机重复监测，我们将绘制草袜环和集体植物年轮的地图。从无人机数据中，我们将得出数字地形模型，并将地形异质性的变量与环的大小、形状和空间模式联系起来。通过对入渗速率、土壤水分、株高和根长的现场测量，研究土壤与年轮扩大或年轮形状之间潜在的风沙反馈效应。将使用数据记录器连续测量土壤水分，以测试生物质水反馈和潜在的自组织过程。对集体植物年轮的操纵实验将调查环状的原因，并将分析所有类型的植物年轮的微生物病原体，这些微生物也可能有助于它们的形成。最终，我们的结果将阐明在水紧张的生态系统中植被生长的基本过程，这些生态系统在气候变化下越来越容易沙漠化。

Ring formation in plants of the global drylands has attracted great interest in the research community, particularly regarding the mechanisms that generate these symmetric shapes. Here, plant rings include “tussock rings”, which result from slow vegetative growth processes of single tussock plants, and a new class of plant rings: “collective plant rings”, which were discovered in 2021 in the Namib Desert. Collective plant rings are composed of several individuals of annual grasses or annual forbs or a mixture of both, and they pop up spontaneously after rainfall events in the eastern Namib Desert. The function of these rings is currently unsolved and it is also unclear how their diameters, shapes, density, and spatial patterns change from rainy season to rainy season. Preliminary investigations suggest that the annual grasses and forbs form rings up to 1 m in diameter to collectively deplete the soil moisture within the rings. These rings could potentially be a consequence of vegetation self-organization whereby the individual plants on the ring periphery facilitate each other to increase their own biomass. However, in-depth research is necessary to better understand this new class of plant rings. Surprisingly, in 2021, altogether 10 different grass and forb species in the Namib desert were discovered to be ring-forming, making the Namib a genuine “diversity hotspot” of plant-ring formation. It is a major research gap that no information on the biogeographic diversity and range of plant rings exists for this ecosystem. Only the famous fairy circles have been widely studied in the Namib, but these vegetation gaps have much larger diameters than the plant rings, and are a different phenomenon. We will study the tremendous wealth of ring-forming plants in arid southwestern Africa. Our pioneering research will include a whole set of fieldwork methods. Using repeated drone monitoring during the rainy seasons, we will map both tussock rings and collective plant rings. From the drone data, we will derive digital terrain models and relate variables of topographical heterogeneity to the sizes, shapes, and spatial patterns of the rings. Potential aeolian feedback effects between soil and ring enlargement or ring shape will be investigated with in-situ measurements on infiltration rates, soil moisture, plant height and root length. Continuous soil-moisture measurements with data loggers will be used to test for biomass-water feedbacks and potential self-organization processes. Manipulative experiments on collective plant rings will investigate the cause of the rings, and all types of plant rings will be analyzed for microbial pathogens that may also contribute to their formation. Ultimately, our results will shed light on the basic processes of vegetation growth in water-stressed ecosystems that are increasingly prone to desertification under climate change.