1. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL By Wang Songliang,adapted from Dr Miller’s lecture 2005-3-22 THE SOIL CARBON CYCLE NUTRIENT CYCLING IN SOIL

2. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL THE SOIL CARBON CYCLE Learning objectives 1.What is the relationship between photosynthesis & cellular respiration? 2.Sketch a diagram illustrating the soil carbon cycle, including the major processes that drive this cycle and the inputs and outputs of carbon, energy and oxygen into/out of the cycle. 3.Identify the ecological classes of soil organisms, based on their role in the carbon cycle. 4.Explain the special role played by decomposers.

3. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL 生态系统（ ecosystem ） 1935 年英国生态学家坦斯列（ A.G.Tansley ） 于提出生态系统的概念，认为 “ 只有我们从根本上 认识有机体不能与它们的环境分开，而与它们的 环境形成一个自然生态系统，它们才会引起我们 的重视 ” 。 生态系统是指由生境（ habitat ）和占据该生境 并联结在一起的生命有机体所构成的动态整体。 ( 美 )E.P.Odum

4. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL = + 生态系统 = 生物群落（生命系统） + 生境（环境系统）

5. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL 生态系统的组成 生产者 （绿色植物） 消费者 （动物） 分解者 （微生物） 环 境（光、温、水、气、营养）

6. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL （ 1 ） 生产者（ producers ），又称初级生产者 （ primary producers ），指自养生物，主要指 绿色植物，也包括一些化能合成细菌。这些 生物能利用无机物合成有机物，并把环境中 的太阳能以生物化学能的形式第一次固定到 生物有机体中。初级生产者也是自然界生命 系统中唯一能将太阳能转化为生物化学能的 媒介。 生物组分

7. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL

8. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL 生物圈中的绿色植物 绿色植物是生物圈中作用最大的一类生 物，它对生物圈的存在和发展起着决定性作用。 绿色植物通过它的生命活动直接或间接地为其 它生物提供食物和能量，并对维持生物圈中的 碳氧平衡和水循环发挥着重要作用。 光合作用

9. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Autotroph: 自养生物

10. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL （ 2 ）大型消费者（ macro-consumers ）， 指以初级生产的产物为食物的大型异养生 物，主要是动物。

11. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL （ 3 ）分解者（ composers ），指利用动植 物残体及其它有机物为食的小型异养生 物，主要有真菌、细菌、放线菌等微生 物。小型消费者使构成有机成分的元素 和贮备的能量通过分解作用又释放到无 机环境中去。

12. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL  The basis of the C cycle Energy Capture: Sunlight is the source of energy for nearly all life on earth. This radiant energy is converted to chemical energy by "photosynthesis". Photosynthesis produces carbohydrates from carbon dioxide (CO2) and water. Carbon is said to be the "currency" of energy, because it is used in the transfer of energy to living cells. The biochemical processes of photosynthesis are summarized in the following reaction equation.

13. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Photosynthesis: Sunlight + H 2 O + CO 2 -> carbohydrates + O 2 Energy Utilization: Chemical energy is converted into life energy by chemical oxidation of carbohydrates within living cells, a process known as “respiration“( 呼吸 ). The biochemical processes of cellular 细胞的 respiration are summarized in the following reaction equation.

14. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Cellular Respiration: Carbohydrates + O2 -> Life energy + H2O + CO2 A Chemical Cycle: Note that these 2 processes are almost exact opposites. In fact, neither could exist without the other - the products of one form the reactants 反应物 of the other. Together, these processes transform CO 2 into carbohydrates and back to CO 2 in a continuous chemical cycle. They have evolved together and the balance between them ensures that earth's atmosphere remains in an equilibrium state suitable for continuation of life.

15. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL

16. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Ecological classes of soil organisms: producers, consumers, & decomposers Producers ("autotrophs") convert CO2 to carbohydrates, by photosynthesis and other processes. The most important producers are plants. There are some single-celled photosynthetic organisms and some primitive organisms that use inorganic substances, like ammonium and methane, as an energy source. Consumers ("heterotrophs") cannot produce their own carbohydrates, but consume the carbohydrates of other organisms. Consumers are categorized based on whether they consume the producers directly (primary [1°] consumers), or by consuming other consumers (secondary [2°] consumers, tertiary [3°], quaternary [4°],... consumers). Individually each class of organisms is not very efficient at converting carbohydrates to life energy. Most of the carbohydrates are left behind, mainly as soil organic matter. If this waste carbohydrate accumulated, it would eventually build up to mountainous levels. At the same time, oxygen would accumulate in our atmosphere.

17. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL It is the third main ecological class of organisms that close the carbon cycle - the decomposers (“saprophytes” 腐生物 ) use this waste as their food supply, converting it to CO2 while consuming the O2 produced by photosynthesis.

18. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL comments The carbon cycle involves the capture and utilization of energy for the soil ecosystem (and for all life on earth). Photosynthesis and respiration are the processes that drive this cycle. These 2 processes are in balance (think of the consequences of them not being balanced) - the amount of O2 and CO2 produced and consumed is equal, and has been for, perhaps 100's of millions of years (but not for all of earth's history). The soil ecosystem is of particular importance for the carbon cycle, because it is home to the process of decomposition, without which there would not be a balance between photosynthesis and respiration.

19. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL  Soil organisms in the C cycle.. The soil ecoystem is a world in itself. The discussion and illustrations offered below examine some examples of the immense variety of organisms and relationships that drive the soil carbon cycle.

20. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 1: Plants & Algae 藻类 Plants are responsible for most of the carbohydrate production on earth; however, plants are latecomers to the carbon cycle. The original producers were algae. The green color on the soil in this photo is from the chlorophyll 叶绿素 of single-celled algae, an ancient photosynthesizer.

21. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 2: Algae A microscopic view of blue-green algae grown in a laboratory. They form long chains of individual cells. Prior to their emergence there was no free oxygen in our atmosphere.

22. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 3: Lichens n.[ 植 ] 青苔, 地衣, 苔藓 Some algae have a special relationship with certain fungi. They form a close, mutually beneficial partnership, termed “symbiosis” 共生. This example of lichens is commonly called "redcoats". Algae, the photosynthetic partner in lichens, produce carbohydrates, which they share with the fungus, while the fungus extracts the necessary nutrients from the environment. (Prof.C.Miller, NSAC)

23. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 4: Lichens growing on granite 花岗岩 In this photo, the yellowish scale on a granite boulder is lichens. The fungus is extracting nutrients from the rock. Technically the fungus is a consumer, since it gets its carbohydrates from the algae. If we regard lichens as a single organism, then it would be classed as a producer.

24. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 5: Beetle grub ( 幼虫 ) This beetle grub is a subterranean 地下的 grazer. It burrows 挖洞 through the soil, just below the surface, and consumes plant roots. It is one of the larger and more identifiable of the soil 1° consumers

25. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 6: Nematode 线 虫 A microscopic photo of a nematode. Parasites 寄生虫 and diseases of plants are primary consumers. Some nematodes parasitize plant roots and stems. (Nematodes are tiny round worms, barely visible to the naked eye.)

26. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 7: Slime mould 黏虫 Slime mould growing on a blade of grass. This fungus disease consumes plant carbohydrates

27. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 8: Legume root-nodule bacteria Not all 1° consumers are harmful to plants. These soybean root nodules house bacteria which "fix" atmospheric nitrogen for the use of the plant. In return, the plant provides the bacteria with carbohydrates. This is another example of symbiosis.

28. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 9: Mgt. of legume nodule bacteria This field contains soybeans which have had seeds treated with root nodule bacteria (2 rows on the right hand side), alongside 2 rows which lack effective bacteria. The bacteria have provided the crop on the right with sufficient nitrogen for a good crop yield. The non- bacterial plants are smaller & paler, and will produce a poor yield of beans.

29. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 10: Centipede 蜈蚣 Centipedes prey on other soil insects. They consume the tissue of their prey as carbohydrate source. Merciless to their prey, but beneficial to mankind, they help keep crop pests under control. Secondary (2°) ConsumersConsumers which feed on primary consumers are called secondary consumers.

30. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 11: Amoeba 变 形虫 Amoebas are microscopic single-celled soil organisms which lack a definite shape.

31. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 12: Amoeba attacking a bacterium This amoeba (upper right corner) is ingesting a soil bacterial cell. The amoeba simply flows around the bacterium and then assimilates bacterial carbohydrates.

32. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 13: Fungus trapping a nematode We have seen fungi which are 1° consumers, but other fungi are 2° consumers. This fungus sets snares along its hyphae. A nematode has had the misfortune of swimming into a snare. The nematode will thrash about, using up its strength & eventually succumbing to the fungus. The end is shown in the next slide. (

33. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 14: Continuation of slide 13 The fungus grows its hyphae into the dead tissue of the nematode, consuming its carbohydrates.

34. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 15: Benefits of 2° consumers This white mould growing on a bean plant is a 1° consumer, a common economic disease of farm and garden vegetables. (Prof.B.Gray, NSAC)

35. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 16: Fungus versus fungus This microscopic photo shows 2 fungi: the white area running horizontally through the photo is a white mould hyphae (same species as shown in previous slide). The other fungus (dark area along bottom of photo has penetrated the cell wall of the white mould and is growing inside its fungal host. It will weaken or kill the white mould. 2° consumers are important allies to farmers, because they help keep crop diseases and pests under control.

36. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 17: The benefit of soil 2° consumers are apparent in this photo. Pot 3 contains citrus plants infected with a soil-borne parasite. Pot 4 has the same parasite, along with another soil organism which feeds on the parasite. Pot 2 contains plants growing in sterilized soil (no parasites). It can be inferred that the 2° consumer in pot 4 has reduced the damage caused by the plant parasite (as seen in pot 3). Growth of plants in pot 4 is almost as good as in the pot with no parasites (#2). (S.S.S.A.)

37. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Higher Order Consumers "1° consumers have 2° consumers Upon their backs to bite 'em, & 2° consumers have 3° consumers, & so on, ad infinitum." (paraphrased from Jonathan Swift) Consumers which feed on 2° consumers are sometimes called tertiary (3°) consumers. Some classifications also identify quaternary (4°) consumers. It is not necessary for us to further classify consumers - you can regard all consumers that feed on other consumers as 2°. The next 2 examples are higher order consumers.

38. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 18: fungus attacking amoeba This amoeba is in the deadly embrace of a predatory 食肉的 fungus. The fungus will infect the amoeba and feed on its carbohydrates.

39. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 19: bacteria attacking fungus Fungi, in turn, are attacked by other consumers. These spherical bacterial cells have attached themselves to a fungal hyphae which they are in the process of parasitizing.

40. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Decomposers Consumers use only part of the carbohydrates they consume. The carbohydrates which are left over add to soil organic matter. If this "waste" carbohydrate accumulated it would eventually create mountains of organic matter. Decomposers, the third main class of soil organisms, consume this extra carbohydrate material, as well as the oxygen produced by photosynthesis. The decomposers close the carbon cycle and balance the production of CO 2 and O 2.

41. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 20: Earthworms Earthworms are readily identifiable decomposers. They burrow through the soil, ingest organic matter along with mineral particles, and excrete castings. The organic matter excreted in the castings is a carbohydrate source for other decomposers.

42. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 21: Isopods Isopods, commonly called "sow bugs", help to decompose woody material. You can usually find them in rotting trees stumps or under rotting lumber.

43. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 22: Leaf mould Many fungi are decomposers. They are important colonizers of freshly deposited organic matter, like this forest litter, because of their extensive network of hyphae which allows them to extract nutrients remotely from their carbohydrate source.

44. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 23: Bacteria This microscopic photo depicts the biologically active zone around a growing root tip. The dots are bacterial cells, which feed on the carbohydrates sloughed off the root as it grows through the soil. These decomposers release the nutrients in the dead plant tissue, allowing them to be reused by the plant.

45. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Slide # 24: Fungus growing on grass clippings This photo shows fungal hyphae (hair-like structures) growing on a fresh grass clipping. The leaf is still functioning, so it is not clear whether this fungus should be called a consumer or a decomposer - the soil ecosystem is complex and does not always conform to our classification system.

46. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL LO 1.Sketch a diagram of the soil nutrient cycle and identify the 3 distinct stores of nutrients, transformations between stores, and all potential losses, and inputs of nutrients from/to the soil ecosystem. 2.Explain the differences in nutrient cycling between harvested (agricultural) & unharvested soil ecosystems. 3.Identify the problems of management of the soil nutrient cycle associated with specialization of production (cash cropping and concentrated livestock).

47. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Comparison: C-Cycle vs. Nutrient Cycle Nutrients,like carbon, are cycled within the soil ecosystem, but nutrients are not used up. A nutrient atom can be reused over & over again. An ecosystem can function with no additions of nutrients almost indefinitely, unless there is some loss of nutrients from the system.

48. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Nutrient Stores:Forms / stores of nutrients in soil Nutrients in soil can be distinguished by their biological or chemical form: Inorganic - original rocks & minerals, dissolved or adsorbed ions. Biomass - living tissue of plants & soil organisms (especially microbes). Organic - dead tissue in various stages of decay, including soil humus.

49. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Nutrient Transformations: Nutrients are not locked up in one store - natural processes constantly change them from one form to another. It is this continual process of biological-geological-chemical transformations, that we call the Soil Nutrient Cycle, as depicted in the diagram, below:

50. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL The soil nutrient cycle : nutrient forms (stores) & transformations.

51. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Absorption: Plant roots and soil organisms extract nutrients as simple inorganic ions released by decay of rocks & minerals and soil organic matter. Plants in particular, can only take up nutrients as simple inorganic ions.

52. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Death,excretion, cell leakage: When organisms die their tissue is added to the soil organic matter store. In addition, some material is excreted as waste organic matter and some is released accidentally by damaged cells. All of this material immediately starts to decay. Some of the more resistant material forms soil "humus" which decays very slowly.

53. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Mineralization: Organic residues provide food for other soil organisms. This carbohydrate material is utilized by decomposing organisms (especially microbes) in the process known as "mineralization", which releases simple inorganic ions from decaying organic matter.

54. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Losses: The soil nutrient cycle is not a closed system. There is always some "leakage". erosion - water & wind can carry away nutrients in eroding soil particles. leaching - percolating water can carry dissolved nutrients downward beyond the reach of plant roots. gaseous losses - volatile forms of nutrients such as nitrogen & sulfur can escape into the air.

55. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Inputs: At the same time, nutrients are added to soil by: Natural precipitation carrying dust particles and dissolved gases. Acid rain depositing nitrogen and sulfur from industrial pollution. Nitrogen fixation by certain microbes (notably the legume root-nodule bacteria) converting N 2 gas in the air to ammonium (NH 4 +) ions which can be used by plants and other soil organisms.

56. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Unharvested soils: Most natural soil ecosystems tend toward an equilibrium state wherein the losses are balanced by natural inputs. The diagram below shows data from nutrient cycling studies in an unharvested forest soil ecosystem.

57. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Calcium cycling in a New Hampshire hardwood forest soil. Numbers in brackets represent yearly flux, in kg Ca / ha. (Data from Borman & Likens, 1970)

58. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Farm soils: Harvested vs Unharvested Soils: Farms soils differ from unharvested soils in that nutrients are removed with the harvested crops. In addition, some farm management practices increase the amount of nutrients lost by other mechanisms, such as erosion, leaching and gaseous loss.

59. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Nutrient cycling in farm soils. (Adapted from the Phosphate & Potash Inst.)

60. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Farm soil management: The additional losses from harvested soils require special management in order to maintain soil fertility for crop production. Farmers seek to reduce or replace the losses by good soil husbandry, by recycling crop residues in the form of unharvested plant material and livestock manure, and by taking advantage of natural inputs.

61. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL N Fixation: Use of legumes in crop rotations increases the nitrogen fixation input

62. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Supplemental nutrient inputs: In North American agriculture, continuing harvests require that some additional supplemental nutrients inputs be applied to maintain high crop yields. Such nutrient inputs include fertilizers and lime, as well as off-farm livestock manure, sewage and food-processing wastes.

63. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL NUTRIENT CYLING IN DIFFERENT FARMING SYSTEMS Mixed Farms:The traditional method of farming in this region involves production of forages which are fed to livestock on-farm. Most of the nutrients in the feed are excreted by the animals. Mixed farms have an important supply of nutrients for the next year's crop stored in the manure. Combined with the nitrogen fixed by legume forages, manure nutrients may provide most of the crop requirements

64. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Specialized agriculture: Cash Cropping In many areas crops are raised to be sold. There is no manure nutrient supply. This type of production relies on off-farm supplies of nutrients for next year's crops. Most often these nutrients are purchased in the form of commercial fertilizers, which are highly concentrated and highly soluble forms of nutrients.Concentrated Livestock Production Other agricultural production systems raise animals exclusively. Their feed is provided by purchased crops. These systems have little or no land base and end up with a surplus of nutrients in the manure from the livestock. In this type of system, manure nutrients are a disposal problem, rather than a resource for soil fertlity replenishment.

65. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Production problems: Separating the production of crops from the production of livestock has produced twin problems - nutrient deficiencies for crop production and nutrient surplusses from animal production. There are also serious environmental issues associated with heavy use of fertizers on the one hand, and disposal of manure on the other. The solution would appear to be to use the manure from livestock production to supply the nutrients for cash cropping. However, manure is a bulky commodity and presents many transportation problems. Often the different production systems are distant from each other.

66. Wang College of Sciences, FAFU NUTRIENT CYCLING IN SOIL Thank you