California Ag Network

Tag: SSSA

  • How Young Soil Supports Plant Life with Naturally Occurring Fungus

    In order to grow well, plants need a place to grow, access to nutrients, and in most cases sunlight. A rich soil provides that home and a good supply of nutrients. But young soils have less to offer – yes, soils can have different ages ranging from hundreds, to thousands, to millions of years old. According to soil scientist and Soil Science Society of America’s (SSSA) blogger Madhav Dhakal, soil is being made and lost all the time, with various dynamic processes.

    The process of soil formation is often given the acronym ClORPT for: climate, organisms, relief, parent material and time. Soils in warmer climates tend to be older than ones in colder climates. Many organisms, like microbes or insects, help aid soil formation. The term “relief” refers to the topography area. So, usually soil at the bottom of a mountain range – exposed to less erosion and warmer weather, will be older than soil at the top of a mountain.

    The major parent material for soils are rocks. Soil formation takes place after a gradual exposure of rocks to the elements and activity of organism – called weathering.

    One important thing to consider during this whole transformation is time. Time is relatively long for the formation of soil. It happens over geologic time – or millions of years. Over these long periods, landscapes and soils are continuously transforming from one form to another. With time, soil forms different horizons or layers, parallel to the earth’s surface.

    However, soils of recent origin may not contain a distinct horizons or formations. For example, Entisol and Inceptisol are among the 12 soil orders in the U.S. Soil Taxonomy that contain no or very weak horizons or layers of soil.

    In addition to the variety and ages of soils as a home for plants, plants themselves have different types of adaptability. For millions of years, the plant kingdom endured several catastrophic events, geological changes, and climatic extremes. Plants were able to adopt to incredibly different types of surfaces or soil, where the soil itself is highly dynamic and changeable.

    The versatility of plant species may have allowed them to survive in extreme conditions such as hostile climate, rocky, acidic, and salty surfaces.

    There are nearly 435,000 unique land-dwelling species of plants in the world. Some of them grow with very little ingredients or even without sufficient water. For example, some cactus species thrive in the desert. Similarly, lithophytes can grow either on the surface of rocks or in crevices.

    What is it about some plants that allows them to grow in unfavorable conditions? There are a few things. Rock felt ferns, orchids, and liverworts can grow on a rocky substrate, with different tactics or physiological adaptation. They are even capable of feeding off the nutrients from rainwater and nearby decomposed plants, including their own dead cells.

    Lithophytes are a type of plant that grows well on rock surfaces. For most of the lithophytes, the nutrient nitrogen is available from the atmosphere in the form of ammonia. Lithophytes have a smaller number of root hairs and larger root diameters compared to common plant species. This makes them able to efficiently absorb nutrients.

    Lithophytes are a type of plant that grows well on rock surfaces. For most of the lithophytes, the nutrient nitrogen is available from the atmosphere in the form of ammonia. Lithophytes have a smaller number of root hairs and larger root diameters compared to common plant species. Provided by Madhav Dhakal

    Other plants have developed cooperative relationships with soil microbes, which may help them survive in younger soils. Cacti can metabolize a type of acid that helps them with photosynthesis. Plants like peas are legumes – and can work with a bacterium in the category of Rhizobium, and this helps them acquire nitrogen.

    Newly formed soils, such as Entisols and Inceptisols can support plant that have these built-in strategies to supplement their essential nutrients. Depending on the parent material, these soils can provide mineral nutrients such as nitrogen, phosphorus, potassium, as well as micronutrients like calcium, iron, zinc, boron, etc.

    Indeed, as adaptable plants colonize these soils, they also start to help build more soil, in conjunction with microbial and insect activity. Their dead roots and waste products become organic matter, building up the soil bit by bit. One example of how plants can improve soils is the plant lupine (Lupinus Lepidus). Lupine’s metabolites can neutralize acids produced by volcanic emanations. This makes the soil more habitable by other types of plants that cannot survive in acidic soils. There are hundreds of plant species that can survive on and improve young soils over time.

    The Soil Science Society of America (SSSA) is a progressive international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, and founded in 1936, SSSA is the professional home for 6,000+ members and 1,000+ certified professionals dedicated to advancing the field of soil science. The Society provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

  • How do Nematodes Help Plants and Soils?

    Nematodes normally get a bad reputation. Yes, some of these miniscule creatures can cause harm in plants and animals. But little is known about the non-parasitic nematodes, which have many beneficial roles. Ashley Shaw from the University of Oregon explores this topic in this Soils Matter blog:

    It might be hard to believe, but you may never have seen the most abundant animal on Earth: soil nematodes! They represent eighty percent of animal life by number and live in nearly every habitat. They are hard-working and important organisms.

    Soil-dwelling nematodes, which I research, are tiny – usually between 1/500th to 1/20th of an inch! (But there is a nematode that lives inside sperm whales that is nearly thirty feet long.)

    Indeed, some of the best-known nematodes are parasites. There are different nematode parasites of plants and animals. That means they live in or on the plant or animal, cannot survive without them, and sometimes kill their host (and then move on). But many more nematodes are free-living. In soils, nematodes live in water films that surround soil particles. Both plant root parasitic and free-living nematodes play an important role in plant health and plant feedback to soil carbon.

    Photo of a predatory nematode. Predatory nematodes attack and devour other nematodes. Through their feeding, they keep populations of plant parasites and microbial feeding nematodes in check, optimizing plant growth (Credit: Ashley Shaw).

    An incredible variety of soil nematodes exist at all levels of the soil food web. At the base of the food web, some feed on plants and algae, others graze on microbes (bacteria and fungi). At higher levels in the food web, nematodes that are predators and omnivores eat other invertebrates, protists, and even other nematodes. In some cases, “predatory” nematodes are the “good guys,” keeping populations of parasitic nematodes in check.

    This food web is important to plant health and soil carbon storage. For example, by feeding on bacteria and fungi, microbial grazing nematodes help return nitrogen to the soil through their waste. This makes the nitrogen available again for plant use, improving plant growth.

    Nematodes bring other species into the soil food web, too. Some bacteria survive the nematode gut and are deposited along with nematodes’ waste products. Still more hitch a ride on the outside of nematodes’ bodies. As nematodes move around in soil, they deposit bacteria in new places, spreading them around. The bacteria can contribute to and speed the process of decomposition, returning carbon to the soil for storage.

    But most good things have a limit: at very high populations, nematodes that feed on bacteria and fungi can reduce their populations. This can lead to lower decomposition and nutrient turnover rates by bacteria and fungi, even lowering plant growth.

    Plant parasitic nematodes attack roots using a piercing tool in their mouth. This “stylet” punctures plant cells so it can suck its carbon-rich juices. Some nematodes release chemicals that cause lesions or tumor-like growths on roots. They drain the plant’s strength above- and belowground.

    In small populations, plant parasitic nematodes can stimulate root growth, but in high numbers they destroy roots, stunt aboveground growth, and cause disease. Lower plant growth (of both roots and shoots) leads to lower return of organic material to soil and eventually, lower soil carbon.

    While the nematode species responsible for plant diseases have received a lot of attention, far less is known about the non-parasitic part of the soil nematode community, which plays mostly beneficial roles in soil. Ensuring a balance between beneficial and plant parasitic nematode groups is important for plant health and its contributions to soil carbon.

    Generally, plant-root parasitic nematodes harm plant growth and microbial-feeding nematodes improve it, but other nematodes are also important. For example, predatory nematodes play an important role in regulating populations of plant-parasitic and microbial-feeding nematodes. Through their feeding, they keep populations of plant parasites and microbial feeding nematodes in check, optimizing plant growth.

    However, predatory nematodes are also highly sensitive to environmental changes. Their populations often decline with soil disturbances such as pesticide use, fertilization, tilling, or soil compaction. Situations where soil is heavily managed often leads to very low predator populations and higher populations of harmful groups. Predators are also sensitive to changes in rain and temperature, which can also cause an imbalance toward harmful groups.

    Shaw is studying compost additions to rangelands to determine the effects on soil carbon and plant growth. Compost also changes the soil food web – including the numbers and diversity of nematodes.

    My current research is examining how active land management practices can help boost beneficial nematode groups in soil by improving soil habitat. We are studying compost additions to rangelands and whether they can improve soil carbon storage and plant growth.

    Compost directly provides nutrients and increases soil water retention, improving plant growth. Compost is also changing the soil food web in ways not seen in some of the other treatments in our study plots. We think that the soil organic matter in the compost improves soil habitat for predators, supporting the long and complex soil food webs with abundant predatory nematodes that help keep root parasitic nematode populations in check. The result is that plant disease and root parasitism has declined, leading to greater plant growth and root carbon inputs under compost treatments, which benefits soil carbon storage.

    Photo: After collecting soil samples, Shaw and her research group inspect nematodes by extracting them into water and examining them in a dish using a microscope. Shown: a diverse grouping of nematodes (longer, worm-like structures) along with a tardigrade and some small soil debris that made it through the extraction process. Credit: Ashley Shaw 

    The Soil Science Society of America (SSSA) is a progressive, international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, SSSA is the professional home for 6,000+ members dedicated to advancing the field of soil science. It provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

    Follow SSSA on Facebook at SSSA.soils, and Twitter at SSSA_Soils. SSSA has soils information on www.soils.org/about-soils, for teachers at www.soils4teachers.org, and for students through 12th grade, www.soils4kids.org.