1 Nutrient Cycling and Retention Chapter 19

2 Outline Nutrient Cycles  Phosphorus  Nitrogen  Carbon Rates of Decomposition  Terrestrial  Aquatic Organisms and Nutrients Disturbance and Nutrients

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4 Nutrient pool is the amount of a particular nutrient stored in a portion, or compartment, of an ecosystem. ( 養分庫 ) Nutrient flux ( 養分通量 ): moving nutrients between the pools of an ecosystem Nutrient sink is a part of the biosphere where a particular nutrient is absorbed faster than it release. ( 養分沉匯 ) Nutrient source is a portion of the biosphere where a particular nutrient is released faster than it is absorbed. ( 養分來 源 )

5 Phosphorus Cycle Mycorrhizae generally play a key role in the uptake of phosphorus by plants in terrestrial ecosystems. Global phosphorus cycle does not include substantial atmospheric pool.  Largest quantities found in mineral deposits and marine sediments.  Much of this in forms not directly available to plants.  Slowly released in terrestrial and aquatic ecosystems via weathering of rocks.

6 Phosphorus Cycle

7 Nitrogen Cycle Includes major atmospheric pool - N 2.  Only nitrogen fixers can use atmospheric supply directly.  Energy-demanding process.  N 2 reduced to ammonia (NH 3 ).  Once N is fixed it is available to organisms.  Upon death of an organism, N can be released by fungi and bacteria during decomposition.

8 Nitrogen Cycle

9 Carbon Cycle Moves between organisms and atmosphere as a consequence of photosynthesis and respiration.  In aquatic ecosystems, CO 2 must first dissolve into water before being used by primary producers.  Although some C cycles rapidly, some remains sequestered in unavailable forms for long periods of time. ( 隱蔽的 )

10 Carbon Cycle

11 Rates of Decomposition Nutrient conversion from organic to inorganic form is called mineralization. ( 礦化作用 ) Mineralization takes place principally during decomposition, which is the breakdown of organic matter accompanies by the release of CO 2. ( 分解作用 ) Rate at which nutrients are made available to primary producers is determined largely by rate of mineralization.  Occurs primarily during decomposition.  Rate in terrestrial systems is significantly influenced by temperature, moisture, and chemical compositions.

12 Decomposition in Temperate Woodland Ecosystems Gallardo and Merino found differences in mass loss by the target species reflected differences in the physical and chemical characteristics of their leaves. Fraxinus angustifpolia

13 Figure 19.5 Decomposition of Fraxinus angustifpolia leaves at drier and wetter sites. Dry Wet

14 Decomposition in Temperate Woodland Ecosystems Mass = 545[toughness / %N] -0.38

15 Decomposition in Temperate Forest Ecosystems Melillo et al. used litter bags to study decomposition in temperate forests. The litter bags had a mesh size of 1 mm—small enough to reduce the loss of small leaves, yet large enough to permit aerobic microbial activity and entry of soil invertebrates. ( 落葉袋 )  Found leaves with higher lignin:nitrogen ratios lost less mass.  Suggested higher N availability in soil might have contributed to higher decomposition rates.  Higher environmental temperatures may have also played a role.

16 白蠟樹 賓州櫟 紙樺 山茱萖 Figure 19.7 Influence of lignin and nitrogen content of leaves on decomposition.

17 Figure 19_08 Figure 19.7 Relationship between actual evapotranspiration and decomposition. AET 地區蒸發散速率 vs. 分解速率

18 Figure 19.9 Decomposition in tropical and temperate forests.

19 Decomposition in Temperate Forest Ecosystems The average annual mass loss in tropical forests shown in figure 19.9 is 120%, or three times the average rate measured in temperate forests. The higher rate s probably reflect the effects of higher AET ( actual evapotranspiration ) in tropical forests and indicate complete decomposition in less than a year.

20 Figure 19_10 第四紀 第三紀 超基性岩 婆羅洲

21 Decomposition in Aquatic Ecosystems Gessner and Chauvet found leaves with a higher lignin content decomposed at a slower rate.  Higher lignin inhibits fungi colonization of leaves. Suberkropp and Chauvet found leaves degraded faster in streams with higher nitrate concentrations.

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23 Figure 19_11 梧桐 榛 赤楊 光臘樹

24 Figure 19_12 鵝掌秋葉

25 Figure 19_13 熱帶溪流 光滑榕葉

26 Nutrient Cycling in Streams and Lakes Webster pointed out nutrients in streams are subject to downstream transport.  Little nutrient cycling in one place.  Nutrient Spiraling ( 營養渦旋 )  Spiraling Length is the length of a stream required for a nutrient atom to complete a cycle. ( 渦旋長度 )  Related to rate of nutrient cycling and velocity of downstream nutrient movement.

27 屑食的

28 Nutrient Cycling in Streams Spiraling Length: S = VT S = Spiraling Length V = Average velocity of a nutrient atom. T = Average time to complete a cycle. 若速度 (V) 慢而養分完成一個循環的時間 (T) 短，則渦旋長度短， 某特定養分原子被洗出溪流生態系前，可能已被利用過許多次。  Nutrient retentiveness ( 養分留存 )  Short lengths = high  Long lengths = low  溪流生態系中，養分留存度與渦旋長度呈負相關。

29 Stream Invertebrates and Spiraling Length Grimm showed aquatic invertebrates significantly increase rate of N cycling, because the invertebrate population densities were estimated as high as 110,000 individuals/m 2 and dry biomass as high as 9.62 g/m 2. More than 80% of macroinvertebrate biomass in Sycamore Creek was made up of species that feed on small organic particles, a feeding group that stream ecologists call collector- gatherers.

30 Stream Invertebrates and Spiraling Length Suggested rapid recycling of N by macroinvertebrates may increase primary production. The macroinvertebrates excreted and recycled 15-70% of nitrogen pool as ammonia. By their high rates of feeding on the particulate N pool and their high rates of excretion of ammonia, they reduce the T in the equation for spiral length. This effect coupled with the 10% of N tied up in their biomass, which reduces V, reduces the N spiral length and increases the nutrient retentiveness of Sycamore Creek.

31 The Effect of Vertebrate Species on Nutrient Cycling in Aquatic Ecosystems 鯰魚 2 species 26 species

32 產卵 The Effect of Vertebrate Species on Nutrient Cycling in Aquatic Ecosystems

33 The Effect of Vertebrate Species on Nutrient Cycling in Aquatic Ecosystems The life cycle of Pacific salmon, is a dramatic example of how animals can affect nutrient cycling across ecosystem boundaries. Annual spawning of Oncorhynchus spp. provides an important seasonal food resource for mammals and birds, and the marine-derived nutrients from salmon carcasses are utilized by multiple trophic levels in both freshwater and terrestrial ecosystems. ( 屍體 )

34 Animals and Nutrient Cycling in Terrestrial Ecosystems Huntley and Inouye found pocket gophers altered N cycle by bringing N-poor subsoil to the surface. ( 囊鼠 ) Their mounds may cover as much as 25% to 30% of the ground surface. Estimates of the amount of soil deposited in mounds by gophers range from 10,000 to 85,000 kg/ha/yr.

35 Animals and Nutrient Cycling in Terrestrial Ecosystems

36 Animals and Nutrient Cycling in Terrestrial Ecosystems Prairie dogs consume or waste 60% to 80% of the net annual production from the grass-dominated area around their colonies. One result of this heavy grazing is that aboveground biomass is reduced by 33% to 67% and the young grass tissue that remains is higher in nitrogen content. ( 草原犬鼠 ) This higher nitrogen content may influence the behavior of bison, which spend a disproportionate amount of their time grazing near prairie dog colonies. ( 不均衡的 )

37 草原犬鼠

38 Animals and Nutrient Cycling in Terrestrial Ecosystems MacNaughton found a positive relationship between grazing intensity and rate of turnover in plant biomass in Serengeti Plain. ( 轉化速率 )  Without grazing, nutrient cycling occurs more slowly through decomposition and feeding of small herbivores.

39 Figure 19_19

40 Plants and Ecosystem Nutrient Dynamics In general, plants in low-nutrient ecosystems tend to grow more slowly to decrease their nutrient demand and allocate more resources to roots to access nutrients in soil. Plants in these ecosystems produce litter with high-lignin and low-nutrient content that decomposes slowly and deter herbivory. ( 威 嚇 )

41 Myrica faya ( 楊梅 )

42 Introduced Tree and Hawaiian Ecosystem Vitousek and Walker found invading N-fixing tree Myrica faya is altering N dynamics of Hawaiian ecosystems.  Introduced in late 1800’s as ornamental or medicinal plant, and later used for watershed reclamation. ( 觀賞用 )  Nitrogen fixation by Myrica large N input.  Leaves contain high N content. – High decomposition rate.

43 Introduced Tree and Hawaiian Ecosystem The higher N content of the leaves is associated with a higher rate of decomposition and greater N release during decomposition. The result of these processes is increased nitrogen content in the soils associated with Myrica.

44 Figure 19_21

45 Figure 19_22 原生種 外來種

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47 Disturbance and Nutrient Loss From Forest Vitousek studied effects of disturbance and environmental conditions on N loss. Figure shows the highly significant increases in nitrate losses following deforestation, which were 40X to 50X higher than those in the forested basin.  Nitrate losses are generally greatest at sites with rapid decomposition.  Uptake by vegetation is most important in ecosystems with fertile soils and warm, moist conditions.

48 Figure 19_23

49 Flooding and Nutrient Export by Streams P inputs into to Bear Brook were almost evenly divided between dissolved (28%), fine particulate (37%), and coarse particulate (35%). However, 62% of exports were fine particulates. Meyer and Likens found P exports in Bear Brook were highly episodic and associated with periods of high flow. ( 不連貫的 )  Annual peak in P input associated with spring snowmelt.  Most export was irregular because it was driven by flooding caused by intense periodic storms.

50 Figure 19_24

51 Flooding and Nutrient Export by Streams

52 Altering Aquatic and Terrestrial Ecosystems Wet deposition 濕沉降 Dry deposition 乾沉降 Eutrophication 優養化

53 Figure 19_26

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55 Review Nutrient Cycles  Phosphorus  Nitrogen  Carbon Rates of Decomposition  Terrestrial  Aquatic Organisms and Nutrients Disturbance and Nutrients

56 Plants and Ecosystem Nutrient Dynamics Fynbos is a temperate shrub/woodland known for high plant diversity and low soil fertility. ( 南非地名 )  Two species of Acacia used to stabilize shifting sand dunes. ( 金合歡 ) Witkowski compared nutrient dynamics under canopy of native shrub and introduced acacia.  Amount of litter was similar, but nutrient content was significantly different.  Acacia - N fixer