Weed Seed Bank in an Agroforestry System With Eucalyptus in Subtropical Brazil

ABSTRACT : Trees can modify the weed seed bank composition and distribution in the cropped area of an agroforestry system. This study aimed at analyzing the eucalyptus (Eucalyptus dunnii) effect on spatial distribution, functional traits abundance and weed seed bank botanic composition in an agroforestry system under no-tillage in Subtropical Brazil. The experiment was conducted in a randomized block design with five replications, and five positions between 4.5-year-old eucalyptus double rows [(4x3) x 20 m] as treatments. Soil sampling was performed at 0-20 cm and the method to quantify and identify seeds was the seedling emergence in trays, inside a greenhouse. Weed phytosociological indices (relative density, frequency and importance), functional traits abundance (life cycle, shade tolerance, reproduction, spread and seed form) and seed densities (m-2) of families and species were evaluated; 17 weed families and 49 species were found. The indices that contributed to the relative importance of families and species differed among the positions between rows. Eucalyptus grown as an intercrop changed the composition and size of the weed seed bank, in a different way for functional traits, families and species depeding on the distance from trees.

摘要：林木可改变农林业系统种植区内杂草种子库的组成与分布格局。本研究旨在分析巴西亚热带地区免耕农林业系统中，桉树（Eucalyptus dunnii）对杂草种子库空间分布、功能性状丰度及物种组成的影响。本试验采用随机区组设计，设置5次重复，以4.5年生桉树双行带[(4×3)×20 m]间的5个位置作为处理组。土壤采样深度为0~20 cm，种子定量与鉴定方法采用温室内托盘育苗法。本研究评估了杂草的植物社会学指标（相对密度、频度及重要值）、功能性状丰度（生活周期、耐荫性、繁殖方式、扩散特性与种子形态）以及各科、各物种的种子密度（单位：粒·m⁻²）；共记录到17个杂草科、49个杂草物种。影响杂草科与物种相对重要性的指标，在桉树双行带的不同位置间存在差异。作为间作作物的桉树，会改变杂草种子库的组成与规模，且其对功能性状、杂草科及物种的影响模式，会随与林木的距离不同而发生变化。