Edwards G, Clark H, Newton P
AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand.
TH Huxley School, Imperial College at Wye, Wye, Ashford, Kent, TN25 5AH, UK.
Oecologia. 2001 May;127(3):383-394. doi: 10.1007/s004420000602. Epub 2001 May 1.
Seed production and seedling recruitment were measured over 2 years under ambient (360 ppm) and elevated (475 ppm) atmospheric CO in a free air carbon dioxide enrichment (FACE) experiment, carried out in a sheep-grazed pasture on dry, sandy soil in New Zealand. In both years elevated CO led to more dispersed seeds of the grasses Anthoxanthum odoratum, Lolium perenne and Poa pratensis, the legumes Trifolium repens and T. subterraneum and the herbs Hypochaeris radicata and Leontodon saxatilis. The increased seed dispersal in A. odoratum, H. radicata, Leontodon saxatilis and T. repens reflected both more inflorescences per unit area and more seeds per inflorescence under elevated CO. The increased seed dispersal in Lolium perenne, P. pratensis and T. subterraneum was due solely to more inflorescences per unit area. The number of seedlings that emerged and survived to at least 7 months of age was increased by elevated CO for H. radicata, Leontodon saxatilis, T. repens and T. subterraneum in both years and for A. odoratum and Lolium perenne in the first year. For species where increased seedling recruitment was noted, there was a significant positive correlation between seed production in summer and seedling emergence in the following autumn and winter, and sowing 200 extra seeds per species m resulted in more seedlings compared to unsown controls. Elevated CO did not affect seedling survival in any species. There was no measurable effect of elevated CO on canopy and soil surface conditions or soil moisture at the time of seedling emergence. The results suggest the dominant effect of elevated CO on seedling recruitment in this pasture was an indirect one, reflecting effects on the number of seeds produced. The biomass of H. radicata, Leontodon saxatilis, T. repens and T. subterraneum in the above-ground vegetation was greater under elevated than ambient CO. However, the size of individual seedlings and mature plants of these four species was unaffected by elevated CO. The results indicate an important way elevated CO influenced plant species composition in this pasture was through changes in the pattern of seedling recruitment.
在新西兰一片绵羊放牧的干燥沙质土壤牧场上进行的自由空气二氧化碳富集（FACE）实验中，在2年时间里对环境大气二氧化碳浓度（360 ppm）和高浓度大气二氧化碳（475 ppm）条件下的种子产量和幼苗补充情况进行了测定。在这两年中，高浓度二氧化碳导致禾本科的香茅、多年生黑麦草和草地早熟禾、豆科的白三叶草和 subterraneum 三叶草以及草本植物的长叶车前和岩生蒲公英的种子分布更为分散。香茅、长叶车前、岩生蒲公英和白三叶草种子传播的增加反映了在高浓度二氧化碳条件下单位面积上更多的花序以及每个花序上更多的种子。多年生黑麦草、草地早熟禾和 subterraneum 三叶草种子传播的增加仅仅是由于单位面积上更多的花序。在这两年中，高浓度二氧化碳使长叶车前、岩生蒲公英、白三叶草和 subterraneum 三叶草至少存活到7个月大的幼苗数量增加，在第一年中，香茅和多年生黑麦草的幼苗数量也增加。对于观察到幼苗补充增加的物种，夏季种子产量与次年秋冬幼苗出土之间存在显著正相关，与未播种的对照相比，每个物种每平方米多播种200粒种子会产生更多的幼苗。高浓度二氧化碳对任何物种的幼苗存活均无影响。在幼苗出土时，高浓度二氧化碳对冠层和土壤表面条件或土壤湿度没有可测量的影响。结果表明，高浓度二氧化碳对该牧场幼苗补充的主要影响是间接的，反映了对种子产量的影响。在高浓度二氧化碳条件下，地上植被中长叶车前、岩生蒲公英、白三叶草和 subterraneum 三叶草的生物量比环境二氧化碳条件下更大。然而，这四个物种的单个幼苗和成熟植株的大小不受高浓度二氧化碳的影响。结果表明，高浓度二氧化碳影响该牧场植物物种组成的一个重要方式是通过改变幼苗补充模式。
