Perennial vegetables: A neglected resource for biodiversity, carbon sequestration, and nutrition

line with estimates of the growth needed to provide all of humanity with sufficient nutrients [16]. Adoption rates are set based on historical data from [6] for the global production area of artichoke, asparagus, avocado, and olive from 1967–2017. In the absence of similar data for the other PVs, only the sum of these four PVs is considered in projecting the future adoption between 2020–2050. Both linear and exponential trends are modeled. Twelve scenarios were developed, using the variables adoption rate (linear and exponen- tial), percent of woody PVs out of total PVs adopted (25%, 50%, and 75%), and total global vegetable production area (58.2 Mha and 174.5 Mha). In scenarios 1 and 2, the current world vegetable production area is used, while in scenarios 3 and 4, world vegetable production area is tripled to meet nutritional needs. In scenarios 1 and 3, a linear adoption rate is used, while in scenarios 2 and 4 an exponential rate is used. For each scenario, woody PVs are assumed to occupy 25%, 50%, and 75% of new adoption. Nutrition Determining the potential of PVs to address nutrient deficiencies is a core goal of this study. To this end, it aims to compare PVs to globally-traded vegetables in several ways. Individual species with “superabundant” levels of single key nutrients are identified, as are “multi-nutri- ent” species with high levels of multiple key nutrients. Subclasses of PVs, based on form and part used, are also compared to globally-traded vegetables. Nutrients assessed were those identified as priorities for addressing deficiencies in the liter-

ature (fiber, Ca, Fe, Zn, folate, and antioxidants). In the case of antioxidants, vitamins A, C, and E were selected as data are more available for these than other antioxidants. Note that ter- restrial plants do not contain significant iodine, so this nutrient was not assessed despite the importance of addressing iodine deficiency. Following an extensive literature review, we conducted a meta-analysis on nutrient content using data from [17, 28, 32, 36, 40, 41, 49–50, 53, 65–109]. Our analysis produced mean nutri- ent values for 240 species of perennial vegetables, including 31 species that are frequently grown as annuals despite having a perennial lifecycle. As the international standard for vegetable nutrient testing is a fresh weight sample of 100 grams, this was used as the basis of data collection and comparison for this study. In several cases values were converted from dry weight to fresh weight. As vegetables are usually con- sumed fresh (rather than dried), and this study compares vegetables to vegetables, values were not converted to dry weight, though dry weight comparison would offer some advantages. For several reasons, the direct ability of these crops to meet daily requirements was not cal- culated. The first reason is that for all vegetables, limited bioavailability means that less than 100% of nutrients are actually digested. Bioavailability is variable, for example increasing if small amounts of animal protein are consumed, and this makes calculating the precise dietary

impact of vegetable consumption difficult. Nevertheless there is consensus that vegetables are an essential source of nutrients [110]. The second reason is that the daily requirement for each nutrient varies widely between ages, genders, and pregnancy and lactation status [111]. It was therefore determined that the data should be compared to vegetables which are widely grown and marketed. To this end, we selected 22 vegetable species tracked by the FAO Statistical Service [16] as a reference set and nutritional benchmark. These reference crops, both annual and perennial, include okra (Abelmoschus esculentus), leek (Allium ampeloprasum), scallion (Allium fistulo- sum), asparagus (Asparagus officinalis), broccoli (Brassica oleracea Italica group), cabbage (Brassica oleracea Capitata group), cauliflower (Brassica oleracea Botrytis group), kale and PLOS ONE Perennial vegetables: A neglected resource for biodiversity, carbon sequestration, and nutrition PLOS ONE | https://doi.org/10.1371/journal.pone.0234611 July 10, 2020 6 / 19