Tzialla C E, Veresoglou D S, Papakosta D, Mamolos A P
National agricultural Research Foundation, Agricultural Research Station of Ioannina, Katsikas, 45500 Ioannina, Greece.
J Environ Manage. 2006 Jul;80(1):90-8. doi: 10.1016/j.jenvman.2005.08.017. Epub 2005 Dec 9.
Soil physicochemical characteristics, total aboveground biomass, number of species and relative abundance of groups and individual species were measured along a moisture gradient in a pasture, flooded in part during winter through early summer, adjacent to Pamvotis lake in Ioannina, Greece. Soil and vegetation measurements were conducted in 39 quadrats arranged in four zones perpendicular to the moisture gradient. The zone closest to the lake, recently separated from the lake, became part of the pasture and its soil texture was quite different from that of the other zones with a substrate containing 91% sand. Except for pH, this zone had the lowest values in the other five soil physicochemical characteristics measured (organic matter, total and extracted inorganic nitrogen, Olsen extracted phosphorus and extractable potassium); in the other zones organic matter, total nitrogen, phosphorus and potassium tended to increase from the driest to the wettest zone. Total aboveground biomass, ranging from 280 to 840 gm-2, is high for herbaceous pastures in the conditions of Mediterranean climate and it was not related to distance from the lake's shoreline, although the highest values were measured at intermediate distances, or to any of the various soil characteristics measured. Also, the number of species/0.25 m2 was not related to any of the various soil characteristics, but it was highest at the intermediate distances from the lake's shoreline. Species composition varied along the moisture gradient. Forbs as well as annual grasses and legumes declined in abundance from the driest to the wettest places; the reverse was the case for sedges and perennial grasses and legumes. These results indicate that the soil moisture gradient was the principal factor affecting soil characteristics and plant species composition. Since most species were recorded in all the four zones of the pasture, indicating that these can tolerate all variations in abiotic conditions of pasture, the vegetation zonation seems to be influenced by competition. Each functional group of species tends to dominate in a particular range of the soil moisture gradient where it is better suited and tends to exclude competitively other species. Management practices (mowing and grazing) affect the kinds of processes which maintain the observed community structure either by preventing the establishment of later successional species, like reeds and woody species, or by moderating the shoot competition, especially in the wetter zones, and thus permitting the creeping species to grow successfully.
在希腊约阿尼纳的潘沃蒂斯湖附近的一片牧场中，沿着湿度梯度测量了土壤理化特性、地上总生物量、物种数量以及各植物类群和单个物种的相对丰度。该牧场在冬季至初夏期间部分被水淹没。土壤和植被测量在39个样方中进行，这些样方分布在与湿度梯度垂直的四个区域。最靠近湖泊的区域最近与湖泊分离，成为牧场的一部分，其土壤质地与其他区域有很大不同，含有91%的沙子。除了pH值外，该区域在测量的其他五个土壤理化特性（有机质、总无机氮和速效无机氮、有效磷和速效钾）方面的值最低；在其他区域，有机质、总氮、磷和钾含量往往从最干燥的区域到最湿润的区域呈增加趋势。地上总生物量在280至840克/平方米之间，在地中海气候条件下，对于草本牧场来说是较高的，并且它与距湖岸线的距离无关，尽管在中间距离处测量到的值最高，也与测量的任何土壤特性无关。此外，物种数量/0.25平方米与任何土壤特性均无关，但在距湖岸线的中间距离处最高。物种组成沿湿度梯度变化。从最干燥的地方到最湿润的地方，草本植物以及一年生禾本科植物和豆科植物的丰度下降；莎草科植物、多年生禾本科植物和豆科植物则相反。这些结果表明，土壤湿度梯度是影响土壤特性和植物物种组成 的主要因素。由于大多数物种在牧场的所有四个区域都有记录，这表明它们能够耐受牧场非生物条件的所有变化，植被分区似乎受竞争影响。每个物种功能群往往在土壤湿度梯度的特定范围内占主导地位，在这个范围内它更适合生长，并倾向于竞争性地排除其他物种。管理措施（割草和放牧）会影响维持观察到的群落结构的过程类型，要么通过阻止芦苇和木本植物等后期演替物种的建立，要么通过缓和地上部分的竞争，特别是在较湿润的区域，从而使匍匐植物能够成功生长。
