sustainability Review Soil Biodiversity Integrates Solutions for a Sustainable Future Elizabeth M. Bach 1,2,* , Kelly S. Ramirez 3,4, Tandra D. Fraser 5 and Diana H. Wall 1 1 School of Global Environmental Sustainability and Department of Biology, Colorado State University, Fort Collins, CO 80523, USA; [email protected] 2 The Nature Conservancy—Nachusa Grasslands, Franklin Grove, IL 61031, USA 3 Netherlands Institute of Ecology, 6708 PB Wageningen, The Netherlands; [email protected] 4 Department of Biological Sciences, University of Texas at El Paso, El Paso, TX 79968, USA 5 Charlottetown Research and Development Centre, Agriculture and Agri-Food Canada, Charlottetown, PE C1A4N6, Canada; [email protected] * Correspondence: [email protected] Received: 26 February 2020; Accepted: 25 March 2020; Published: 27 March 2020 Abstract: Soils are home to more than 25% of the earth’s total biodiversity and supports life on land and water, nutrient cycling and retention, food production, pollution remediation, and climate regulation. Accumulating evidence demonstrates that multiple sustainability goals can be simultaneously addressed when soil biota are put at the center of land management assessments; this is because the activity and interactions of soil organisms are intimately tied to multiple processes that ecosystems and society rely on. With soil biodiversity at the center of multiple globally relevant sustainability programs, we will be able to more efficiently and holistically achieve the Sustainable Development Goals and Aichi Biodiversity Targets. Here we review scenarios where soil biota can clearly support global sustainability targets, global changes and pressures that threaten soil biodiversity, and actions to conserve soil biodiversity and advance sustainability goals. This synthesis shows how the latest empirical evidence from soil biological research can shape tangible actions around the world for a sustainable future. Keywords: belowground; diversity; microbes; worm; mite; insect; Sustainable Development Goals; Aichi Targets; land-use; climate change 1. Introduction As the world’s human population continues to rise and is expected to reach 8.6 billion by 2030 (UN 2017), it is paramount to respect and protect natural resources, including soil, water, air, minerals, and biodiversity that support life on Earth, including humanity. Current rates of consumption and inadequate management of resources are putting unprecedented pressure on global systems and it is estimated that one to six billion hectares (up to 30%) of land has been degraded globally [1]. Land degradation negatively affects 3.2 billion people, threatens sustained human well-being and is a major contributor to climate change and biodiversity loss [2]. Global initiatives to meet these challenges include the UN 2030 Agenda for Sustainable Development (Figure1) and the UN Convention on Biodiversity’s Strategic Plan for 2020 (Table1). Broadly, these agendas address areas to improve human life and environmental sustainability, rely on the participation of all countries and stakeholders, and will require innovative, timely, and interdisciplinary approaches [3]. Sustainability 2020, 12, 2662; doi:10.3390/su12072662 www.mdpi.com/journal/sustainability Sustainability 2020, 12, x FOR PEER REVIEW 2 of 19 Sustainability 2020, 12, 2662 2 of 20 Figure 1. The UN 2030 Agenda for Sustainable Development centers around 17 Sustainable Development Goals (SDGs). These goals broadly address areas to improve human life and environmental sustainability and include 169 specific targets supported by member nations. Figure 1. The UN 2030 Agenda for Sustainable Development centers around 17 Sustainable DevelopmentTable 1. The Aichi Goals Biodiversity (SDGs). These Targets goals are centralbroadly to theaddress UN Convention areas to improve on Biodiversity’s human Strategiclife and environmentalPlan for 2020 and sustainability result from yearsand include of discussion 169 spec andific consensus targets supported building among by member more thannations. 190 member nations. The targets are divided into strategic goals to be implemented by 2020. Table 1. The Aichi Biodiversity TargetsStrategic are central Goal to the UN Convention on Biodiversity’s Strategic Targets AddressPlan the for underlying 2020 and causes result of biodiversity from years loss byof mainstreamingdiscussion and biodiversity consensus across buildin governmentg among and society. more than1, 2,190 3, 4 member nations.Reduce The the targets direct pressures are divided on biodiversity into strategi and promotec goals sustainable to be implemented use. by 2020. 5, 6, 7, 8, 9, 10 Improve the status of biodiversity by safeguarding ecosystems, species, and genetic diversity. 11, 12, 13 Enhance the benefits to allStrategic from biodiversity Goal and ecosystem services. 14,Targets 15, 16 AddressEnhance the implementation underlying through causes participatory of biodiversity planning, loss knowledge by mainstreaming management, biodiversity and capacity building.across 17, 18, 19, 20 1, 2, 3, 4 government and society. SoilsReduce are central the direct to supporting pressures on natural biodiversity systems and andpromote human sustainable well-being use. [4] (Figure25,), yet6, 7, to8, date9, 10 Improve the status of biodiversity by safeguarding ecosystems, species, and genetic soil biodiversity—the diversity of life in soil which drives ecosystems, sustains life aboveground,11, 12, 13 and maintains healthy landscapes—hasdiversity. remained largely overlooked in global agendas. For example, Enhance the benefits to all from biodiversity and ecosystem services. 14, 15, 16 the term ‘soil biodiversity’ does not appear in any UN documentation while forests, wetlands, rivers, Enhance implementation through participatory planning, knowledge management, and 17, 18, 19, 20 and drylands have received specificcapacity attention building. to their benefit. Soil-dwelling organisms, including bacteria, fungi, nematodes, earthworms, moles, and even plant roots, contribute the majority of living biomass on Earth [5] and represent more than 25% of all described species [6,7], not to mention the Soils are central to supporting natural systems and human well-being [4] (Figure 2), yet to date genetic diversity represented within these species. The activity and complex interactions of soil soil biodiversity—the diversity of life in soil which drives ecosystems, sustains life aboveground, and organisms provides the backbone for many ecosystem functions, including nutrient cycling, pathogen maintains healthy landscapes—has remained largely overlooked in global agendas. For example, the control, water infiltration, foundations to food webs, and supporting agroecosystems (Figure2). term ‘soil biodiversity’ does not appear in any UN documentation while forests, wetlands, rivers, and Our understanding of the critical connections between soil biodiversity and sustainability are rapidly drylands have received specific attention to their benefit. Soil-dwelling organisms, including bacteria, progressing [8–10]. The time has come to incorporate this knowledge to bolster global actions and fungi, nematodes, earthworms, moles, and even plant roots, contribute the majority of living biomass create a more holistic sustainability agenda that can simultaneously address biodiversity loss, climate on Earth [5] and represent more than 25% of all described species [6,7], not to mention the genetic change, and land degradation. diversity represented within these species. The activity and complex interactions of soil organisms provides the backbone for many ecosystem functions, including nutrient cycling, pathogen control, water infiltration, foundations to food webs, and supporting agroecosystems (Figure 2). Our understanding of the critical connections between soil biodiversity and sustainability are rapidly progressing [8–10]. The time has come to incorporate this knowledge to bolster global actions and create a more holistic sustainability agenda that can simultaneously address biodiversity loss, climate change, and land degradation. Sustainability 2020, 12, 2662 3 of 20 Sustainability 2020, 12, x FOR PEER REVIEW 3 of 19 Figure 2. Soil organisms support multiple ecosystem services, which underpin global sustainability agendas.Figure The 2. colored Soil organisms circles next support to each organismmultiple ecosystem type represent services, which which of the underpin four overarching global sustainability parts of sustainableagendas. development The colored the circles organism next contributes to each organism to directly. type Image represent credit: which K. Pintauro, of the four E. Bach.overarching Photo parts creditsof (top sustainable to bottom): development E. Saunders, the S.organism Axford, M.contributes J. I. Briones, to directly. D. Robson, Image K. credit: Markarov, K. Pintauro, A. Murray, E. Bach. M. P. Veldhuis,Photo credits G. Faulkner. (top to bottom): E. Saunders, S. Axford, M. J. I. Briones, D. Robson, K. Markarov, A. Murray, M. P. Veldhuis, G. Faulkner. Like most of the resources humans rely on, soils and soil biodiversity are under threat by land degradation,Like most climate of the change,resources pollution, humans urbanization,rely on, soils and and soil over-use biodiversity and misuse are under [11]. threat Soils areby land a finite,degradation, non-renewable climate resource change, because pollution, they urbanization, cannot be replenished and over-use within and misuse a human [11]. lifespan Soils are [12 a].