可获得种子量和种子出苗对草地裸沙斑植被恢复的相对制约

以科尔沁沙化草地的裸斑为研究对象,布设种子捕捉器监测生长季传播到裸斑的种子数量、物种组成,并人工播种监测裸斑中出苗情况,研究可获得种子数量和出苗对裸斑植被恢复的制约.结果表明:沙生植物3种,种子数为71 ～623粒·m-2,非沙生植物9种,种子数为73 ～410粒·m-2;裸斑中沙生植物的出苗数(9.3 ～22.3株·m-2)高于非沙生植物(0 ～3.4株·m-2);沙生植物在裸斑的出苗率最高为沙蓬(12.2％ ～34.1％),其次是乌丹蒿(4.5％ ～10.3％),小叶锦鸡儿(0～0.5％),非沙生植物狗尾草出苗率为0～6％,蒲公英为0 ～0.4％,其余植物种出苗率为0;沙生植物裸斑出苗数(9.3 ～22.3株·m-2)高于植被区(7.7株·m-2),而非沙生植物在裸斑的出苗数(0～3.4株·m-2)低于植被区(4.5株·m-2).可见,裸斑植被恢复中,沙生植物的可获得种子量制约高于出苗制约;非沙生植物的可获得种子量制约与出苗制约相当.     

Effect of season of burning and removal of herbaceous cover on seedling emergence in a eucalypt savanna of north‐eastern Australia

Abstract Seedling emergence in a eucalypt savanna of north‐eastern Australia was documented over a 12‐month period, between May 1999 and May 2000. Seedling emergence for grasses, forbs and subshrubs was found to mainly occur in a brief pulse at the start of the wet season following fire or the removal of grass biomass. Only a minor number of tree and shrub seedlings were detected overall. Burning, or cutting away the grass layer in unburnt savanna, in both the early (i.e. May) and the late (i.e. October) dry seasons significantly increased seedling emergence over undisturbed savanna that had been unburnt for 3 years. Removing the grass layer in unburnt savanna, during either the early or the late dry season, triggered similar seedling densities to savanna burnt in the early dry season. Late dry season fires promoted the greatest seedling density. We attribute this to the higher intensity, late dry season fires releasing a greater proportion of seed from dormancy, coupled with the higher density of soil seed reserves present in the late dry season.     

Effects of watering regime and depth of burial on seedling emergence of four dominant psammophytes in the Mu Us sandy land, Inner Mongolia, China, and relevance to revegetation of a desertified region

Four dominant psammophyte species are air-seeded in attempts to revegetate the Mu Us sandy land in Inner Mongolia, but seedling emergence is low. This study sought to clarify the behaviour of seedling emergence under different water supply and sand burial regimes to improve the technology of air seeding. Seeds were buried in sand at depths of 0, 0.5, 1, 1.5, 2, 3 and 5 cm and supplied one time with 2.5, 5, 7.5, 10, 15, 20, 30 or 40 mm of water or with 2.5 mm once every 3 days for 30 days. Our study showed that a 0.5-cm burial depth and under 10- to 20-mm single-watering regimes resulted in highest seedling emergence percentage and rate of these four species. All emerged seedlings of Caragana korshinskii , Hedysarum laeve and Artemisia ordosica died under 2.5, 5 and 7.5 mm of watering, respectively, but seedling mortality was <50% when the single-watering regime was >10 mm. In the field, germination of the four species increased from the top of the dune to the middle of the leeward side and then to the bottom. Based on precipitation pattern in the Mu Us sandy land, our study indicates that 0.5-cm burial depth and a single-watering regime of >7.5 mm is the threshold condition for seedling emergence.