西南喀斯特地区两种草本对干湿交替和N添加的生长响应

喀斯特地区的"岩溶干旱"和频繁的变水环境成为喀斯特地区植被生长和分布的重要选择压力,是该地区植被恢复重建的主要障碍因子。N沉降也会对喀斯特地区的生态系统造成难以预测的影响。为了探究喀斯特地区草本植物对干湿交替和N添加的生长响应,以苍耳(Xanthium sibiricum)和三叶鬼针草(Bidens pilosa)为研究对象,通过盆栽水分受控实验,研究了5种不同水分处理对照组(CK)、干旱组(D)、1周干湿交替处理组(DW-1)、2周干湿交替处理组(DW-2)和3周干湿交替处理组(DW-3)]与N添加(N+、N-)对两种草本植物生长和生物量的影响。结果表明,干旱胁迫抑制了植物生长和生物量的积累,株高、叶面积、总根长和根体积等生长指标和地上生物量均显著降低,根冠比增大。不同程度的干湿交替对植物的生长和生物量的积累均表现出一定程度的补偿效应,但这种补偿效应的大小随着干旱持续时间的延长而减弱。N添加对植物的生长和生物量积累有显著地促进作用,株高、根表面积、根体积和根生物量较对照组显著增加,但这种促进作用随着干旱历时的增加而减弱,可能与土壤水分状况有关。同时,N添加还影响着植物生物量的分配,在促进两种植物地上和地下生长的同时,还促进了植物根冠比的增加。

Growth response of two annual herb species to alternating drying-wetting and nitrogen addition in the karst area of Southwest China

Plants growing in the subtropical karst region of China are frequently subjected to periodical drought stress within a growing season. The available soil water is sufficient for plant transpiration needs for only 7-14 days following heavy rainfall exceeding soil field capacity, because of the shallow soils and highly porous limestone in this region. However, frequent precipitation in the form of extreme rainfall events allows the soils to remain wet before or after drought. Therefore, "karst drought" and strong fluctuations in water availability are becoming important selection pressure for vegetation growth and distribution in the karst region. In recent years, the concentration of atmospheric nitrogen compounds has been increasing sharply owing to human activities. Nitrogen deposition in a global context also has unpredictable impact on the ecological system in karst region. Thus,simultaneously exploring the response of plants to frequent alternation of drying and wetting and nitrogen deposition and their interaction in vulnerable karst vegetation is necessary; we used two Asteraceae annual herbs, Xanthium sibiricum and Bidens pilosa as the experimental materials. These two species were selected since they are native species,are widely distributed in the southwest karst area of China, and have a strong ability to adapt to the abiotic environment and to tolerate dry and barren conditions. We manipulated three factors (species, water treatment and nitrogen addition) in a factorial randomized design to determine how the two species respond to the different water treatments and nitrogen addition in terms of above- and belowground growth and biomass accumulation. The following results were obtained.Plant growth was markedly restrained by drought stress. Stem length, leaf area, total root length, root volume and aboveground biomass in both the species were significantly lower than thoes of the control whose soil water content was kept in 80%-90% of field capacity. However, the root to shoot ratio of both the species increased significantly. Re-watering after different periods of drought somewhat compensated for the decrease in the growth and biomass accumulation of the plants. However,the compensation effect was related to the drought period, and decreased with prolongation of drought. Nitrogen addition promoted plant growth and singnificantly increased the total and above- and belowground biomass. However, the stimulatory effect of nitrogen addition was weakened with increasing drought duration, which was probably related to the decreased soil moisture. Nitrogen addition also significantly affected the biomass allocation:it increased the root to shoot ratio and stimultaneously stimulated the above- and belowground growth of plants.