Land-based drip-irrigated culture of Ulva compressa: The effect of culture platform design and nutrient concentration on biomass production and protein content

This work developed a laboratory prototype methodology for cost-effective, water-sparing drip-irrigation of seaweeds, as a model for larger-scale, on-land commercial units, which we envision as semi-automated, inexpensive polyethylene sheet-covered bow-framed greenhouses with sloping plastic covered floors, water-collecting sumps, and pumped recycling of culture media into overhead low-pressure drip emitters. Water droplets form on the continually wetted interior plastic surfaces of these types of greenhouses scattering incoming solar radiation to illuminate around and within the vertically-stacked culture platforms. Concentrated media formulations applied through foliar application optimize nutrient uptake by the seaweeds to improve growth and protein content of the cultured biomass. An additional attribute is that seaweed growth can be accelerated by addition of anthropogenic CO2-containing industrial flue gases piped into the head-space of the greenhouse to reuse and recycle CO2 into useful algal biomass. This demonstration tested three different drip culture platform designs (horizontal, vertical and slanted) and four increasing fertilizer media concentrations (in seawater) for growth, areal productivity, and thallus protein content of wild-collected Ulva compressa biomass, against fully-submerged controls. Cool White fluorescent lights provided 150–200 μmol photon m-2 s-1 illumination on a 12/12 hr day/night cycle. Interactive effects we tested using a four-level single factorial randomized block framework (p-1 and 5–18 g m-2 day-1 (d.w.) respectively, whereas the fully-submerged control group grew better at 8–11% per day with of 20–30 g m-2 day-1, indicating further optimization of the drip irrigation methodology is needed to improve growth and biomass production. Results demonstrated that protein content of Ulva biomass grown using the vertically-oriented drip culture platform and 2x fertilizer concentrations (42:16:36 N:P:K) was 27% d.w., approximating the similarly-fertilized control group. The drip methodology was found to significantly improve gas and nutrient mass transfer through the seaweed thalli, and overall, the labor- and-energy-saving methodology would use a calculated 20% of the seawater required for conventional on-land tank-based tumble culture.本研究开发了一种经济高效、节水的海藻滴灌（drip-irrigation）实验室原型方法，作为大规模陆地商业养殖单元的示范模型。我们设想该商业单元采用半自动化、低成本的聚乙烯膜（polyethylene sheet）覆盖弓形框架温室，配套倾斜塑料覆盖地面、集水集液坑（water-collecting sumps），以及将培养液泵送至顶部低压滴灌喷头（drip emitters）的循环系统。此类温室的内壁塑料表面会持续凝结水滴，散射入射太阳光，为垂直堆叠的养殖平台及其周边提供光照。通过叶面喷施的浓缩培养液配方可优化海藻对养分的吸收，提升养殖海藻的生长速率与藻体蛋白质含量。该体系的另一优势在于，可将含人为排放二氧化碳的工业烟道气通过管道通入温室顶空，以此加速海藻生长，将二氧化碳回收转化为具有利用价值的藻类生物质。本示范实验以野外采集的条浒苔（Ulva compressa）为研究对象，设置三种滴灌养殖平台设计（水平、垂直与倾斜式）与四个梯度递增的（以海水配制的）肥料培养液浓度，以全浸没对照组（fully-submerged controls）为对照，考察其生长情况、单位面积生产力以及藻体蛋白质含量。实验采用冷白色荧光灯提供150–200 μmol光子·m⁻²·s⁻¹的光照强度，设置12小时光照/12小时黑暗的昼夜循环周期。本研究采用四水平单因子随机区组设计考察交互效应，结果显示滴灌组的日干重（d.w.）产量分别为1–5 g·m⁻²·d⁻¹与5–18 g·m⁻²·d⁻¹，而全浸没对照组的日增长率可达8%–11%，日干重产量为20–30 g·m⁻²·d⁻¹，生长表现更优。这表明仍需进一步优化滴灌方法以提升海藻生长与生物质生产效率。实验结果显示，采用垂直式滴灌养殖平台与2倍浓度肥料（氮磷钾配比42:16:36，N:P:K）培养的条浒苔藻体蛋白质含量可达干重的27%，与同施肥水平的对照组相当。研究表明，该滴灌方法可显著提升海藻藻体对气体与养分的传质效率；总体而言，经测算，这种节省人力与能源的养殖方法的海水消耗量仅为传统陆地储罐式翻滚养殖所需海水的20%。