Natvik and Henry_Differential effects of the grasses Festuca rubra, Andropogon gerardii, and Elymus virginicus on the growth of Eurasian versus North American oak seedlings

OVERVIEW OF RESEARCH: Research was conducted to compare how the origin of grass cover effects the growth of oak seedlings. Our hypothesis was that that grass species origin may influence oak recruitment. The experiment included 3 grasses species consisting of 2 species native to North America (Andropogon gerardii and Elymus virginicus) and 1 species native to Eurasia (Festuca rubra var. rubra). Comparisons were made between 6 oak species consisting of 3 species native to North America (Quercus alba, Q. macrocarpa, and Q. rubra) and 3 species native to Eurasia (Quercus acutissima, Q. cerris, and Q. robur). We predicted that oak seedlings would demonstrate greater growth when growing in grasses that they share a co-evolutionary history with. EXPERIMENTAL DESIGN: The 3 grass species were seeded into single-species plots measuring 6 x 7 metres. There were 8 plots seeded for each of the grass species (for a total of 24 grass plots). All 6 oak species were seeded into the plots as acorns. Each of the 24 plots contained 1 oak seedling of each species, with a total of 144 oak seedlings in the entire experiment (6 seedlings x 24 plots). DESCRIPTION OF DATA: 1. OAK SEEDLING MEASURMENTS: After 2 growing seasons, all oak seedlings were harvested. Measurements of each oak seedling were taken including stem height, stem diameter, total biomass (separated into stem biomass and root biomass), and root-to-shoot ratios. This data was analysed to compare the growth of all 6 oak species between the 3 species of grasses. 2. LIGHT READINGS: Photosynthetically Active Radiation (PAR) was measured from all of the grass plots at 15 cm above the soil surface during spring summer, and fall. These measurements indicate how much exposure to light the oak seedlings received across the growing season within the 3 different species of grasses. 3. SOIL TESTS: A range of soil parameters were measured from all grass plots at the end of the experiment (3 years after the grass plots were established). The purpose of the soil tests was to see if soil parameters were impacted in any way by the 3 different species of grasses. SUMMARY OF RESULTS: Our results demonstrate that grass cover has a significant but species-specific impact on the growth of two-year-old native and non-native oak seedlings. The variation in seedling growth in response to variation in grass cover was, in part, consistent with the hypothesis that grass species origin may influence oak recruitment, but there were nevertheless exceptions that could be explained in part by shading effects.研究概述：本研究旨在对比草本覆盖层的起源对栎属幼苗生长的影响。我们提出的假说为：草本物种的起源可能会影响栎属的自然更新。本实验共选用3种草本植物，其中2种为北美本土物种（须芒草（Andropogon gerardii）和纤毛鹅观草（Elymus virginicus）），1种为欧亚本土物种（紫羊茅（Festuca rubra var. rubra））；同时选用6种栎属植物，其中3种为北美本土物种（白栎（Quercus alba）、大果栎（Q. macrocarpa）以及红栎（Q. rubra）），另外3种为欧亚本土物种（麻栎（Quercus acutissima）、土耳其栎（Q. cerris）以及夏栎（Q. robur））。我们预测，当栎属幼苗与其存在协同进化历史的草本植物伴生生长时，其生长表现会更佳。 实验设计：将3种草本植物分别播种于单物种样地，样地规格为6×7米。每种草本植物对应设置8个样地，总计24个草本样地。将6种栎属植物的橡实播种于上述样地中。24个样地中的每一个均栽植各1株对应栎属物种的幼苗，整个实验共计144株栎属幼苗（6株幼苗×24个样地）。 数据说明： 1. 栎属幼苗测量指标：经过2个生长季后，收获所有栎属幼苗并测定多项指标，包括茎高、茎粗、总生物量（分为茎生物量与根生物量）以及根冠比。本数据集用于对比6种栎属幼苗在3种草本植物样地中的生长差异。 2. 光照读数：在春、夏、秋三季，于土壤表面上方15厘米处对所有草本样地开展光合有效辐射（Photosynthetically Active Radiation, PAR）测量。此类测量可反映不同草本物种样地内栎属幼苗在整个生长季所接收的光照暴露量。 3. 土壤测试：于实验结束时（即草本样地定植3年后），对所有草本样地开展多项土壤参数测定，以探究3种不同草本植物是否会对土壤参数产生影响。 结果概述：本研究结果表明，草本覆盖层对2年生本土及非本土栎属幼苗的生长具有显著且物种特异性的影响。幼苗生长随草本覆盖层差异产生的变化，部分符合“草本物种起源可影响栎属自然更新”的假说，但同时也存在部分例外情况，此类例外可部分通过遮荫效应加以解释。