滴灌下新疆北部棉田杂草土壤种子库的时空变化

Spatiotemporal variation of weed seed banks under drip irrigation in cotton fields of Northern Xinjiang

以天山北坡绿洲至沙漠边缘垂直分布的3个试验点,对比分析了漫灌和1a至4、8a的不同滴灌时间的棉田,以及不同试验点和土层深度等不同空间的杂草土壤种子库变化。结果表明,滴灌对棉田杂草种子库影响大,物种数和单位面积的种子库密度的年际间波动明显。连续滴灌改变了杂草土壤种子库的结构和组成,物种数由漫灌27种下降到1a滴灌的20种,滴灌8a后下降到15种,Shannon-Wiener多样性指数达到最低,单位面积的种子密度明显降低。随着滴灌年限的增长,狗尾草、藜、龙葵、反枝苋和凹头苋等喜旱性杂草占总种子库的比例逐渐增加,为滴灌棉田的优势杂草。狗尾草、藜、灰绿藜、龙葵、马齿苋、凹头苋、刺儿菜、黄花蒿、苦苣菜、小蓬草、荠菜、小藜、扁蓄、苘麻、田旋花、野薄荷等物种时间生态位宽度和空间生态位宽度均较大,适应较好,而虎尾草、百脉根、播娘蒿、酸模叶蓼、滨藜、野胡麻等物种生存受到明显影响。受耕作方式影响,杂草种子库主要分布于耕作层,耕作层以下46～50cm种子数最少。水平分布格局分析发现,3个地点杂草种子库的物种相似性较高,滴灌与漫灌之间种子库的物种差异要大于地理位置间的差异。

Three cotton fields located on the northern slope of Tianshan Mountains, along the gradient from the oasis to the edges of desert, were selected as our experimental sites. We analyzed the effects of flood irrigation and drip irrigation on the spatiotemporal variation of soil seed banks for the first 4 years and the 8^th year. The results showed that drip irrigation had a larger effect on the seed banks of weeds in cotton fields, as the species number and seed density per unit area fluctuated significantly between the years. Continuous drip irrigations changed the structure and the composition of soil seed banks; number of species decreased from 27 species by flood irrigations to 20 and 15 species after 1 and 8 years of drip irrigation respectively. The Shannon-Wiener diversity index reached the lowest for the 8th year drip irrigation and seed density per unit area dropped substantially. With the increase of drip irrigation duration, the species-Chloris virgata, Lotus corniculatus, Descurainia sophia, Polygonum lapathifolium, Atriplex centralasiatica and Dodartia orientalis etc, were found to be affected considerably, while species, such as Setaria viridis, Chenopodium album, Chenopodium glaucum, Solanum nigrum, Portlulaca oleracea, Amaranthus lividus, Cirsium setosuum, Artemisia annua, Sonchus oleraceus, Conyza canadensis, Capsella bursapastoris, C. serotinum, Polygonum aviculare, Abutilon theophrasti, Convolvulus arvensis and Mentha haplocalyx adapted well owing to their wide time niche breadth and spatial niche breadth, especially the Setaria viridis, Chenopodium album, Solanum nigrum, A.retroflexus and Amaranthus lividus, which were found in dryer conditions. The ratio of these species in all seed banks increased gradually and they were the dominant weeds in the cotton fields. Affected by tillage methods, the seed banks of weeds were mainly distributed in the farming layer. The seed number was the lowest beyond the farming layer from 46cm to 50cm. Analysis of horizontal distribution patterns revealed that species at the three sites were very similar. The irrigation methods, flood irrigation and drip irrigation, appeared to have greater impact on the species variation than the difference of geographical locations.