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1、免费查阅精品论文Analysis of root fractal character in the hinterland ofTaklimakan desert, ChinaYang Xiaolin a, b*，Zhang Ximinga，Li Yiling a,b，Xie Tingtinga,b，Wang Weihua a,b，Ma Jianbinga,baXinjiang Institute of Ecology and Geography，Chinese Academic of Science，Urumqi(830011)bGraduate University of the Chine
2、se Academy of Science，Beijing（100039)E-mail：AbstractFractal geometry is a potential new approach to the analysis of root architecture which may offerimproved ways to quantify and summarize root system complexity as well as yield ecological and physiological insights into the functional relevance of
3、specific architectural patterns. Otherwise, fractal analysis is a sensitive measure of root branching intensity and fractal dimension expresses the space filling properties of a structure. The objective of this study was to find out the fractal characteristics of root system in the hinterland of Tak
4、limakan desert in China. The whole root system of two naturally species was excavated and exposed with shovels in 2007.These species includes: Tamarix taklamakanensis, alligonum roborovskii.A one-factorial ANOVA with species as factor showed a highly significant effect on fractal dimension, the diff
5、erence of fractal dimension indicates the otherness of root branching pattern.The regression between link diameter and q, a were not significant for either species .So the ratio of the sum of root cross-sectional areas after a bifurcation to the cross-sectional area before bifurcation, a and the dis
6、tribution of the cross-sectional areas after bifurcation ,q are the ubiquitous characters of root system. In this paper ,we find the significant linear relationships between the diameter after branching and root length, biomass respectively, because root branching is self-similar and branchingrules
7、are the same for roots of all sizes, root lengths，root biomass for the root systems of whole treescan then be estimated by measuring the diameter of each root at the base of the trunk or diameter after branching. The study showed that diameter of each root at the base of the trunk or diameter after
8、branching are effective indexes which can measured easily to estimate the root lengths, biomass and other parameters of root architecture.Keywords: Taklimakan desert，root system，root architecture，fractal dimension，root length，rootbiomassPlant root systems are a major carbon sink as uptake organs for
9、 water and nutrients, and the interface between plants and the soil system, roots govern many competitive interactions (Fitter, 1987, 1991; Casper and Jackson, 1997). At a larger scale, roots influence processes important at the ecosystem level, such as soil erosion and carbon cycling (Andrew D. Ric
10、hardson and Heinrich Zu Dohna, 2003). The size, structure, and extent of root systems control many of these functions, so it became a hotspot in underground ecology research (J S Huo, 2004).However, root systems of plants in general and trees in particular are notoriously difficult to measure becaus
11、e of the difficulty in excavating large volumes of soil (Bhm W., 1979). Estimation of root lengths and root biomass for tree root systems using conventional methods is invariably a difficult and laborious task (Smith, D.M., 2001). How to research the root architecture by relating easily measurable p
12、arameters were attended in recent literatures (Andrew D. Richardson, 2003; Armin L. Oppelt, 2001; Eduardo Salas, 2004)The root architecture reflects the plants adaptive ability to make best use of unevenly distributed soil resources (Fitter, 1994). There are various means for determining the size of
13、 root systems (A. Eshel,1998; Box, 1996) and the principles of fractal geometry seem appropriate for the description of rootsystems because the repetitive branching of roots leads to a certain degree of self-symmetry. Such*Corresponding author: Xinjiang Institute of Ecology and Geography, Chinese Ac
14、ademy of Sciences, No. 40-3South Beijing Road, Urumqi 830011, China.- 9 -self-similarity is a fundamental characteristic of fractal objects (A. Eshel, 1998).The self-similarity principle defines an object that maintains similar form over a range of scales. This principle applied to a tree root syste
15、m predicts that roots follow the same bifurcation pattern from proximal roots to the smallest transport roots. The basic parameters of fractal root models describe the ratio of the sum of root cross-sectional areas after a bifurcation to the cross-sectional area before bifurcation, , and the distrib
16、ution of the cross-sectional areas after bifurcation, q (Van Noordwijk et al., 1994; Louise Y. Spek, 1994).Fractal dimension is an important parameter which reflects the difference of root branching status and extension of root system. P L Yang (1994) proposed that the fractal dimension changes with
17、 age and environment condition, and fractal dimension increased with development degree, Reversely, simpler the root branching, lower the fractal dimension. D.M. Smith (2001) concludes that the obvious relationship between fractal dimension and root length indicated the significant correlation betwe
18、en fractal dimension and the ability of exploration in the soil (Thomas C. Walk, 2004).The application of fractal dimension exist some shortcomings because its calculation need the whole root system excavation, an alternative method is needed, therefore, to enable routine estimation of the size of t
19、ree root systems. Based on the hypothesis of self-similarity, Van Noordwijk et al. (1994; 1995) attempted to overcome the previous constraint by relating easily measurable parameters for instance, trunk diameters and diameters of proximal roots to predict the whole structure of the root system. Link
20、ed with the pipe model theory (Mkel, 1986), Spek and Van Noordwijk (1994) hypothesized that this approach may be well suited to predict the distribution of dry matter, and total root length within a tree root system.If this can be established, the length and biomass of a root can be estimated from e
21、asily-determined information the initial diameter of the root. Root lengths and total biomass for the root systems of whole trees can then be estimated by measuring the diameter of each root at the base of the trunk and estimation for each root by each root collar diameter.The objective of our work
22、is to research the application of fractal theory and the fractal root model as formulated by Van Noordwijk et al. (1994; 1995) for predicting root biomass and length. We applied the model to two desert trees in the hinterland of Taklimakan desert in Xinjiang: Tamarixtaklamakanensis, Calligonum robor
23、ovskii. The objective of this work was () to find the relationshipbetween fractal dimension and branching pattern, root length respectively () to test the assumption of self-similarity () to test the suitability of self-similarity and pipe model assumptions for the prediction of root biomass, root l
24、ength.1. MATERIALS AND METHODS1.1. Study area and test sitesThe Taklimakan desert is in the Northwest of China and the location of the study area is in the hinterland of desert which is closed to Tazhong desert arboretum, E8339，N3857 (Figure 1), Thenatural plant community structure is simple in stud
25、y area and the natural plants include: Phragmites australis, Apocynum venetum,Cistanche tubulosa, Hexinia polydichotoma, Tamarix.taklamakanensis, Calligonum roborovskii. Because of restriction of the features of environment and water-salt conditions in desert, vegetation type is simple and vegetativ
26、e coverness is low. According to the data from Tazhong Meteorological Station and the Auto-Meteorological Station, the annual average temperatureis 12.4. The recorded highest temperature is 45.6 and the lowest temperature on record is 22.2.The mean annual precipitation is 36.6 mm. The potential evap
27、otranspiration rate is 3638.6mm. The wind speed there is 2.5 m/s on average and the highest instantaneous speed is 24.0 m/s. The salinity content is 1.26-1.63 g/kg. The ground water is about 1.2 m.Fig.1 The location of study area in the hinterland of Taklimakan desert1.2 The fractal root modelsThe b
28、ox-counting method (Y Q Wang, 1999) was applied to determine the fractal dimension, and then based on fractal dimension to analysis the difference of root branching pattern and the relationship between root length and fractal dimension. The specific methods are as follow: the top view images of root
29、 system were first covered with a frame (34cm34cm). The frame was divided into a grid in five steps, each box having a side length r=34/2n (n=0-5). The numbers of intersected boxes N(r), found in the root images at each scale were counted. Plotting number of boxes N(r) against side length (r) on a l
30、oglog scale gave a straight line. Their linear regression equation is: logNr=-FDlogr+logK (FD is fractal dimension and logK is has been associated with fractal abundance)Van Noordwijk et al. (1994) proposed that fractal geometry combined with parameter estimation based on the pipe model theory (MacD
31、onald. N., 1983) could be applied for describing tree root architecture. The basic parameters of fractal root models describe the ratio of the sum of root cross-sectional areas after a bifurcation to the cross-sectional area before bifurcation, a , and thedistribution of the cross-sectional areas af
32、ter bifurcation , q .The equations as follow: = D 2beforeD 2 afterq = max(D 2before )D 2 after（ Dbeforeis diameter before bifurcation， Dafteris diameter after bifurcation）1.3 The method of root excavationFrom August to September in 2007, five plants of Tamarix.taklamakanensis,Calligonumroborovskii r
33、espectively were selected for the architectural description of root systems in the hinterland of Taklimakan desert. All the root systems were excavated by hand. In this study, we take more attention with coarse root. Coarse roots were defined as roots that exceed a threshold diameter of3 mm. A recon
34、struction of root architecture below that value was not possible (Armin L.Oppelta, 2000, 2005). To maintain the spatial orientation and position of root as sufficient as possible. The root location of each exposed root was determined by 50 cm 50cm Grid and we accurately mapped the top view designs i
35、n the 3525cm paper in accordance with the ratio of 1:50.Fig.2 Schematic representation of root branching. The dbefore is diameter before bifurcation; d1 and d2 are diameters after bifurcation1.4 The measurement of root parameterThe variables measured in exposed root systems were similar for Tamarix
36、taklamakanensis,alligonum roborovskii( ) root diameters before bifurcation and after bifurcation (see Figure 2); ()the root diameter at the point of bifurcation (see figure 3); () the root length and dry matter forwhole root system and some main root segments (such as segment 1and segment 2 in figur
37、e 3); () to draw top view design of root system.2 RESULTS2.1 Fractal dimension and root lengthTable 1 shows the results of the calculation of FD forTamarix.taklamakanensis,Calligonum roborovskii, it ranged from 1.1449 to 1.3679 and the average FD of Tamarix.taklamakanensis, Calligonumroborovskiiis1.
38、31260.049,1.21720.0583respectively.Aone-factorial ANOVA with species as factor showed a highly significant effect on FD (F=7.835, P=0.0230.05). Thereby, FD is closely correlated with species. It was found that there is remarkable exponential correlation relationship between FD and the rootFig.3 Sche
39、matic representation of the fractal model was presented by Van Noordwijk et al. (1994). Base on this hypothesis, root lengths and dry matters could be estimated by using basal diameter or the diameter after bifurcation, so we can estimated the whole root length and dry matter by basal diameter (Db)
40、and forecastedthe root length and biomass for root segments of S1 andS2 by the diameters after bifurcation DS1 and DS2respectively.180length (see Figure 4): L=0.0097e7.061D, (R2=0.9596,root length(cm)L is root length, D is FD). This is closed to the result proposed by P L Yang (1994) for the relatio
41、nship between root length and fractal dimension: with the root length increasing or decreasing, the FD was increased or decreased. But also the minimal difference of FD will lead to160140120100806040200y = 0.0097e7.061xR2 = 0.9596maximal difference of root length and rootbranching pattern.1.1 1.21.3
42、1.4 fractal dimensionFig.4 The relationship between fractal dimensions and root lengthTab.1.The fractal dimensions of two difference speciesTamarixFDRootCalligonumFDRoot0011.34241230011.306785.20021.289980.030021.210347.660031.3679162.130031.223549.60041.2414680041.200845.50051.3213130.320051.144934
43、.8Mean1.31256108.696Mean1.2172452.5522.2 Root diameter and root length, root dry matterFractal geometry combined with parameter180root length L(cm)160140120100806040200y = 28.694x - 22.093R2 = 0.97240 2 4 68 root diameter d(cm)estimation based on the pipe model theory (Van Noordwijk et al., 1994; Ma
44、cDonald.N., 1983) could be applied for describing tree root architecture. Linked with the pipe model theory (Mkel, 1986), and using a recursive model, Spek and Van Noordwijk (1994) hypothesized that this approach may be well suited to predict the distribution of dry matter, root length within a tree
45、 root system by relating easily measured1800root biomass B(g)160014001200100080060040020002.52lg(L)1.510.50-0.5y = 280.64x - 229.5R2 = 0.94070 2 4 68 root diameter d(cm)y = 1.9235x + 0.8123R2 = 0.9595parameters. The obvious linear relationshipbetween basal diameter or the diameter after bifurcationa
46、ndrootlength,drymatter respectively are showed in Figure 5 for Tamarix. taklamakanensis, Calligonum roborovskii. The linear relationship can be reflected by the regression equation as follow: L= 28.694d -22.903(R2 = 0.9724, L is root length, d is basaldiameter or the diameter after bifurcation), B=2
47、80.64d- 229.5(R2 = 0.9407, B is dry matter, d is basal diameter or the diameter after bifurcation). West, et al. (1997) claimed to have found “a general model for the origin of allometric scaling laws in biology,” and the allometric exponent is closed 2 for the relationship between base diameter and total length (Van Noordwijk, et al.1994). In our study for the root system ofTamarixtaklama