Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, D-85350 Freising-Weihenstephan, Germany.
Ecology. 2012 Jan;93(1):169-79. doi: 10.1890/11-1166.1.
Measurements of resource capture by individuals, species, or functional groups coexisting in field stands improve our ability to investigate the ecophysiological basis of plant competition. But methodological and technical difficulties have limited the use of such measurements. Carbon capture, in particular, is difficult to asses in heterogeneous, dense field stands. Here we present a new approach to measure in situ daily gross carbon gain of individuals. It is based on measuring the 13C content of shoots after a few hours of continuous labeling of all assimilated CO2. The technique is simple and has few assumptions. A new, fully mobile facility was developed, capable of providing a labeling environment with a CO2 concentration close to atmospheric air and known, constant 13C-enrichment, while maintaining temperature and relative humidity within ambient values. This facility was used in seminatural grasslands of Germany and Argentina to explore the relationship between size and carbon gain of individuals of coexisting species growing in contrasting hierarchical positions, and to analyze the carbon gain of functional groups. In general, carbon gain per unit shoot mass increased with increasing size among small individuals, but it became independent of size among the largest ones. In consequence, competition appeared to be size asymmetric between subordinate individuals but size symmetric between dominant individuals. When comparing functional groups, the carbon gain per unit shoot mass of rosette dicots vs. grasses reflected not their relative contribution to stand biomass, but their hierarchical position: irrespectively of mass or growth form, being taller than neighbors was most important in determining carbon gain per unit shoot mass. We believe these results show that in situ measurements of carbon gain can provide valuable insight in field studies of plant competition.
对个体、物种或共存于野外林分中的功能群的资源捕获的测量，提高了我们研究植物竞争的生理生态学基础的能力。但是，方法和技术上的困难限制了这些测量的应用。特别是，在异质、密集的野外林分中，很难评估碳捕获。在这里，我们提出了一种新的方法来测量个体的现场日总碳增益。它基于在连续标记所有同化的 CO2 几个小时后测量新梢的 13C 含量。该技术简单，假设少。开发了一种新的、完全移动的设备，能够提供接近大气 CO2 浓度和已知恒定 13C 富集的标记环境，同时将温度和相对湿度保持在环境值内。该设备在德国和阿根廷的半自然草地中使用，以探讨共存物种个体在不同层次位置的大小与碳增益之间的关系，并分析功能群的碳增益。一般来说，在小个体中，单位新梢质量的碳增益随个体大小的增加而增加，但在最大个体中，碳增益与个体大小无关。因此，在从属个体之间，竞争似乎是大小不对称的，而在优势个体之间，竞争是大小对称的。当比较功能群时，与禾本科植物相比，头状二倍体植物的单位新梢质量的碳增益并不反映它们对林分生物量的相对贡献，而是反映它们的层次位置：无论质量或生长形式如何，比邻居长得高是决定单位新梢质量碳增益的最重要因素。我们认为这些结果表明，现场碳增益测量可以为植物竞争的野外研究提供有价值的见解。
