摘要:在农业可持续发展的背景下，稻田杂草防控需要兼顾生物多样性的保护。为了解浮萍覆盖对稻田杂草群落组成及物种多样性的影响，运用群落生态学的方法，研究了多根紫萍覆盖（SP）、少根紫萍覆盖（LP）和不投放浮萍（CK）3种处理下稻田杂草发生量和群落多样性在水稻4个生育期（分蘖期、孕穗期、扬花期和成熟期）的动态变化，并对水稻产量进行分析。结果表明：SP和LP处理在前两生育期分别比CK显著降低杂草密度60.3%~75.8%和81.1%~90.4%，在整个水稻生育期能分别降低杂草鲜重生物量48.0%以上和81.3%以上，杂草群落中阔叶类杂草比例明显下降。不同处理下，稻田最主要杂草类别均是莎草科杂草；不同处理的杂草群落中重要杂草的种类和相对重要程度都有较大差异，SP和LP处理重要值较高的杂草均为莎草科的萤蔺和碎米莎草，CK处理重要值较高的杂草则为阔叶类的鸭舌草；在多数生育期，两种浮萍覆盖下的杂草群落的Margalef丰富度指数、Shannon-Wiener多样性指数和Simpson优势度指数均与CK无显著差异。SP和LP处理水稻的每穗粒数和穗重均有不同程度显著提高，SP处理的水稻产量显著提高28.0%。综合上述分析，稻田投放初始覆盖面积70.0%的多根紫萍和少根紫萍都能在降低稻田杂草密度和生物量的同时维持杂草群落的多样性，且多根紫萍覆盖能促进水稻产量增长，对保护稻田生物多样性和促进农业可持续发展有重要意义。
关键词:可持续农业/
稻田/
浮萍覆盖/
杂草防控/
群落结构/
生物多样性
Abstract:Weed control and biodiversity conservation are both required for sustainable agricultural production. As duckweeds are capable of colonizing open water surfaces in several days on account of their extremely rapid growth rate, introduction of duckweeds to paddy field is considered to inhibit weed growth as a result of shading. To acquire evidence for the utility of duckweed to control weeds and the impact on weed community composition in paddy fields, a field experiment was conducted for a rice-growing seasons. Using community ecology methods, we investigated dynamic changes of weed quantity and community diversity at 4 rice growth stages (tillering stage, booting stage, flowering stage, and maturing stage) and rice grain traits at maturing stage under three treatments: rice grown with Spirodela polyrrhiza mulching (SP), rice grown with Landoltia punctata mulching (LP), and rice grown without duckweed mulching (CK). (Landoltia punctata and Spirodela polyrrhiza were introduced into the respective plots with about 70% floodwater coverage on the day of rice transplantation.) The results showed that: ten species from seven families were recorded in weed surveys. Both duckweed species significantly suppressed weed emergence. SP and LP significantly reduced weed density by 60.3%-75.8% and 81.1%-90.4%, respectively, in the first two stages; and reduced weed biomass by more than 48.0% and 81.3%, respectively, throughout the rice-growing season. Both duckweed species changed the composition of weed communities. Cyperaceae weeds were predominant in the weed communities of the SP and LP treatments. Biomass proportions of Cyperaceae weeds were more than 62.9% and 60.2% in the weed communities of the SP and LP treatments, respectively; while the proportions of broadleaf weeds decreased significantly. Cyperaceae weeds Scirpus juncoides and Cyperus iria showed higher important values in the weed communities of the SP and LP treatments. In the weed communities of the CK, broadleaf weeds Monochoria vaginalis showed the highest important values. The Bray-Curtis similarity indice between weed communities of CK and duckweed mulching treatments was less than 0.25. Correspondingly, the weed communities of CK were separated from the weed communities of duckweed mulching treatments in UPGMA clustering. Duckweed mulching showed no negative impact on plant diversity and rice grain yields. In most rice growth stages, the Margalef index, Shannon-Wiener index, and Simpson index of weed communities under three treatments were not different significantly. Due to the mitigation of weed competition and the potential nutrients supplied by decomposition of duckweed, SP and LP significantly improved grain number per panicle by 33.7% and 15.8%, respectively, and panicle weight by 28.2% and 17.0%, respectively. Rice grain yield in the SP treatment significantly increased by 28.0%. In summary, duckweed mulching reduced weed density and biomass and altered weed community composition while maintained weed diversity in paddy fields, and Spirodela polyrrhiza mulching improved rice yield. The results demonstrated that duckweed introduction to paddy fields is an effective and eco-friendly weed management strategy which is conducive to biodiversity conservation and sustainable agricultural development.
Key words:Sustainable agriculture/
Paddy field/
Duckweed mulching/
Weed control/
Community structure/
Biodiversity
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