Data from: Native grass ground covers provide multiple ecosystem services in Californian vineyards

1. The mechanisms responsible for the success or failure of agricultural diversification are often unknown. Most studies of arthropod pest management focus on enhancing the effectiveness of natural enemies, but non-crop plants can also improve or hamper pest suppression by changing the host quality of crop plants by reducing or adding available soil nutrients or water. Native perennial ground covers may provide resources and long-term habitat to resident natural enemies and be more compatible than exotic annuals for crop management in terms of competition for soil nutrients or water. 2. A three-year study was conducted in a California vineyard to examine the impacts of native perennial grasses on pests, natural enemies, crop plant condition and soil properties. Three ground cover treatments were included: bare soil with a grower standard drip irrigation, native grasses with the drip irrigation, or native grasses with the drip irrigation and an additional flood irrigation to keep the grasses green and growing during the season. 3. Numbers of leafhopper pests (Erythroneura spp.) decreased in both native grass treatments, where parasitism rates and spider densities were higher. 4. Nitrate levels in vine leaf petioles were lower in grass treatments, indicating competition with vines for soil nitrogen, which is most often considered to be detrimental. Berry weight was higher in the irrigated treatment but did not differ between the bare soil and non-irrigated native grass treatments. Grape quality (brix) was similar in the bare soil and native grass treatments, suggesting that increased soil moisture in the presence of native grasses did not compromise grape quality. In fact, leaf water stress was lower and available soil moisture higher not only in the irrigated native grass treatment but, at times, in the non-irrigated native grass treatment, in comparison to the no ground cover treatment. 5. We conclude that native grasses contributed to a reduction in leafhopper density by reducing host quality through competition with vines for soil nitrogen and providing food resources and/or habitat for natural enemies. Native grasses also improved soil water content and may be part of a water conservation program for perennial crops in dry climate regions.1. 农业多样化成败背后的作用机制往往尚不明确。当前多数节肢动物害虫治理（arthropod pest management）研究均聚焦于提升天敌（natural enemies）的控害效能，但非作物植物可通过改变作物寄主质量（host quality），即增减土壤有效养分或水分，对害虫抑制效果产生正向或负向影响。本土多年生地被植物（native perennial ground covers）可为常驻天敌提供资源与长期栖息环境，且相较于外来一年生植物（exotic annuals），在土壤养分与水分竞争层面更适配作物种植管理需求。 2. 本研究在加利福尼亚州某葡萄园开展了为期三年的定位试验，旨在探究本土多年生草本植物对害虫、天敌、作物生长状况及土壤性状（soil properties）的影响。试验共设置三种地表覆盖处理：① 采用种植者标准滴灌（drip irrigation）的裸地处理；② 采用滴灌的本土草本覆盖处理；③ 采用滴灌+额外漫灌（flood irrigation）的本土草本覆盖处理，以维持草本植物在生长季保持青绿状态。 3. 两种本土草本覆盖处理下，叶蝉（Erythroneura spp.）的种群数量均有所下降，此时寄生率（parasitism rates）与蜘蛛密度（spider densities）均显著提升。 4. 草本覆盖处理的葡萄叶柄（vine leaf petioles）硝酸盐（nitrate）含量更低，表明本土草本与葡萄藤竞争土壤氮素，而这通常被认为是不利因素。采用漫灌的草本覆盖处理的葡萄单果重（berry weight）更高，但裸地处理与非漫灌的本土草本覆盖处理间无显著差异。裸地处理与本土草本覆盖处理的葡萄品质（糖度brix）无明显差异，说明本土草本存在下土壤水分增加并未损害葡萄品质。事实上，相较于无地表覆盖处理组，不仅采用漫灌的本土草本覆盖组的叶片水分胁迫程度更低、有效土壤水分更高，在部分时段非漫灌的本土草本覆盖组亦呈现相同表现。 5. 综上，本土草本植物通过与葡萄藤竞争土壤氮素以降低作物寄主质量，并为天敌提供食物资源与栖息环境，从而降低了叶蝉种群密度。此外，本土草本植物还可提升土壤含水量，有望成为干旱气候区多年生作物节水保育计划（water conservation program）的组成部分。