wood density and anatomy of water limitted eucalyptus.ptx

Presentation for wood properties

1. THE WOOD DENSITY AND ANATOMY OF WATER-LIMITED EUCALYPTS

2. GROUP 3 MEMBERS BRIGHT CHAKALE 220100714 PRAISE BEULANI 220100712 MOJA ZALIMBA 220100755 FUNNY CHITINI 200100679 DESIRE JACKSON 210100739 GIBSON MILANZI 220100739 PRECIOUS CHICHITIKE 210100724 PETER KUMBANGA 210100749 BESTER MSONTHI 210100770 CHIKONDI MAIKO 220100737

3. INTRODUCTION The term wood density is defined as a ratio of the mass of wood to its volume and is measured in kg/m3, (Matthew et al , 2004). The wood density is determined by the proportion of the wood volume taken up by the cell lumens. T he smaller the cell lumens or the thick cells result in an increase in wood density and vice verse.

4. INTRODUCTION CONTI…… Xylem vessels are responsible for water transportation in trees, and their diameter and frequency impact hydraulic conductivity. According to Hagen- Poiseuille law (Tyree and Ewers 1991), the xylem vessels are smaller and less frequent in the denser woods. N arrower xylem vessels , reduce water flow that decrease the hydraulic conductivity of the wood, because more wood volume is taken up by cell wall material, hence increasing wood density.

5. INTRODUCTION CONTI….. However, several studies have attempted to relate the effects of water stress or osmotic stress to wood density in the genus Eucalyptus. An increase in wood density has been associated with decreased soil water supply in Eucalyptus globulus , ( Wimmer et al . 2002).

6. INTRODUCTION CONTI….. In contrast, Macfarlane and Adams (1998) and Catchpoole et a l. (2000) found no relationship between wood density and the severity of water stress or soil salinity, respectively, in E. globulus . This finding was associated with site factors such as temperature or nutrient supply, but it may also be related to extractives (i.e ., those components that can be removed by solvent).

7. INTRODUCTION CONTI….. An experiment was set to test the hypotheses that waterlimited greenhouse-grown Eucalyptus seedlings have greater stem wood density than well-watered seedlings once the extractives are removed.  

8. MATERIALS AND METHODOLOGY Plant culture Each tree species was obtained from their provenances as follows E.grandis from coffs harbor region of northern new south wales, E. occidentalis from mallee physiographic region of south west while E. sideroxylon from drier region of mid westen .

9. MATERIALS & METHODOLOGY CONTI….. Seedlings germinated in trays for 7 weeks & transported in pots Potted seedlings were grown under well watered condition for 6 weeks before commencement of watering treatments

10. EXPERIMENTAL AND GROWTH CONDITIONS A 13-week experiment was conducted in a climate-controlled greenhouse at the University of Western Sydney, with controlled temperature 25/20 degree celcius and humidity level (55%) levels, using a randomized block design to test plant growth. A factorial experiment tested the effects of watering treatments(well-watered versus water-limited) on three Eucalyptus species, replicated five times .

11. CONTI…… Watering schedules were based on soil field capacity, with drought cycles occurring four times during the 13-week experiment. The design allowed for two harvests ( at 4 and 13 weeks) and an initial preliminary harvest at week 0, to assess seedling growth and response to water treatments

12. WATER POTENTIAL During week 13, when soil water content was lowest in the water-limited treatment, diurnal leaf water potential was measured using a pressure chamber. Measurements were taken on the youngest fully expanded leaf of each replicate at three times: before dawn, midday and early afternoon. The diurnal variation in leaf water potential was calculated by subtracting the most negatively afternoon value from predawn value, to assess daily changes in leaf water status.

13. HARVESTS Three harvests were done which incudes Preliminary (week 0) where species were measured for stem diameter and wood density At week 4,plant dry mass was determined and week 13 where there was extensive measurents Roots and shoots were separated and dried up to 70 degrees celcius in 48hrs and measured at week 4

14. CONTI….. At week 13,Plant and diameter were measured where 6cm stem sample was taken for wood density measurement. Leaf area was measured and roots washed and dried up to 70 degrees celcius for 48hrs then dry mass was measured for all plant parts Lastly relative growth rate was calculated using dry matter increment between weeks 4 & 13 harvests ( Atwell et a l 1999).

15. WOOD DENSITY Wood density can be measured with or without extractives which can be used to compare total density ( Dt ) and residual density ( Dr ) Total density ( Dt ) can be measured with extractives as follows Remove the periderm from stem segments then measure fresh wood volume ( Vfs ) using Archimedes principles and freeze-dry sample and measure dry mass ( Wds )

16. CONTI….. Then calculate Total density as Dt = Wds / Vfs But if Wds is composed of extractives ( Wdse ) embedded within the non-extractible cell wall matrix ( Wdsne ) ,this can be included as: Dt = Wds / Vfs = ( Wdse ) + ( Wdsne ) / Vfs  

17. CONTI….. Without the extractives Soak freeze-dried samples in 100% ethanol for 5 days then replace with 50% ethanol solution for 2 days and replace with distilled water for 5 days and measure residual density ( Dr ) Residual density ( Dr ) can be measured as follows Measure fresh wood volume ( Vfs ) again after extractive removal then Freeze-dry sample and measure dry mass ( Wdsne )

18. WOOD ANATOMY Wood anatomy samples were prepared by fixing, dehydrating, and embedding stem segments, then sectioning and staining them. Digital images were taken at 10x magnification and analyzed using image Pro Plus software to: Measure pith area, Detect and measure xylem vessels(number, dimensions, frequency, and lumen area ),

19. ANATOMY CONTI….. Calculate conduit efficiency value(CEV), an estimate of stem hydraulic conductivity, and to Create a transect of vessel diameters from pith to cambium

20. RESULTS Preliminary harvests (week 0) Mean stem diameter and wood density ( Dt ) by species were as follows : E. grandis had 1.73mm diameter, and 390kg/m3 E. sideroxylon 1.22mm diameter, and 280kg/m3 E.occidentalis 1.26mm diameter, and 320kg/m3 It was found that E. grandis had signicantly larger stem diameter than othe species and wood density did not differ significantly between species.

21. WATER POTENTIAL AND GROWTH Key Findings: Predawn Ψleaf (water potential): No difference between species under water stress. Lower predawn Ψleaf in water-limited plants compared to well-watered plants. Seedling height Reduced 17-37% by water limitation in all species .   Stem diameter

22. CONTI….. Reduced by water limitation in all species. Greatest reduction in E. grandis (39%) and E. sideroxylon (38 %). Smallest reduction in E. occidentalis (10%). Seedling dry mass: Significantly reduced by water limitation, ranging from 51-70%.

23. RELATIVE GROWTH RATE No significant effect of watering treatment or species. Trend for lower RGR in water-limited plants. Interpretantion Water stress has a significant impact on plant growth, reducing height, stem diameter, and dry mass .

24. TOTAL AND RESIDUAL WOOD DENSITY Water-limited seedlings of Eucalyptus grandis and E. sideroxylon had higher wood density ( Dt ) than well-watered seedlings, but not E. occidentalis . E. sideroxylon had the highest wood density overall. When soluble extracts were removed, water limitation only affected the residual wood density ( Dr ) of E. grandis , not E. sideroxylon .

25. CONTI….. The decrease in the Dr was due to a 10-20% decrease in dry mass, with no change in volume. All in all, E. sideroxylon had higher wood density than the other two species.

26. WOOD ANATOMY E.grandis and E.occidentalis have more wood area compared to E.siderixylon . This is because E.occidentalis have more vessels per unit area where as E. grandis has larger vessel sizes Reduced mean vessels lumen area by 7 to 30% Did not change the overall proportion of wood taken up by the vessels due to the increase in vessel frequencies. Did not show clear pattern of vessel diameter changes with drought cycles

27. DICUSSION Water limited eucalypts seedling can have higher wood density than well watered seedlings Wood density was unaffected by water limitation in E. sideroxylon but E. grandis produced hinger wood density in response to water limitation which in tells that water limitation can increase wood density in some eucalyptus species

28. CONCLUSION It was therefore noted that: Water limitation did not significantly increase wood density in eucalyptus species Vessel diameter and frequency change but vessel area remained stable Pith dominance or short drought duration may have masked potential effects.

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