Response of Anatomical Features of Broadlesf Tree Root in Karst Area to Soil Erosion

Available online at www.sciencedirect.com Procedia Engineering Procedia EngineeringProcedia Engineering 00 (2011 )18 000 (2011)–000 232 – 239 www.elsevier.com/locate/procedia

The Second SREE Conference on Chemical Engineering Response of Anatomical Features of Broadlesf Tree Root in Karst Area to Soil Erosion

Luo Mei a, Zhou yunchao a a*, Wang Ke Ke b

a Forestry College of Guizhou University, Guiyang and 550025, China b Forest Bureau of Xinren County, Guizhou and 562300, China

Abstract

Karst rocky desertification occurred in the southwest part of China was a seriously environmental problem, it is very important that expressing, dating, and reconstructing karst soil erosion process and history for understanding geomorphology of karst rocky desertification. Whereas accurately understanding karst soil erosion met a great obstacle of measuring problem for karst soil erosion from underground due to the dualistic systems of overground and underground. This was first time using exposed root anatomical features to imply karst soil erosion in China. Exposed and unexposed root samples in Puding, Guizhou, China were collected, and anatomical features were compared, parameters were measured, so as to obtain indicated information of soil erosion. Annual ring width could be appropriately applied to study the relationship of tree growth with environmental factors for the average sensitivity was larger than 0.2 for annual ring responding to soil layer. Tree root anatomical features were compared between exposed and unexposed root. The annual ring of unexposed root was smoothly increased from pith and decreased slowly when closed to bark, vessel size was the same and evenly distributed in each ring. Annual ring, pattern of vessel, and vessel size of exposed root was the same as unexposed root in prophase but an obviously mutation followed, annual ring narrowed, vessel lumen area reduced, vessel number decreased. After this mutation, a regular trend was shown but annual ring was narrower than unexposed root. From the anatomical changes of exposed root, the exact time of root exposure can be identified and the beginning of soil erosion happening. The response of anatomical features of tree root to soil erosion can offered a new method for the study of karst soil erosion and soil erosion historical record.

Keywords: Exposed root; Broadleaf tree; Anatomical features; Karst; Soil erosion.

* Corresponding author. Tel.: +86-851-3851335; fax: +86-851-3851335. E-mail address: [email protected].

1. Introduction

Karst rocky desertification is a process of land degradation [1]. But the formation mechanism, which implied less understood about karst soil erosion process, was also discussed owing to the unclear history of karst rocky desertification which could be divided into geological rocky desertification, ecosystem rocky desertification and artificial accelerated rocky desertification [2]. Some researchers have reported that karst soil erosion didn’t happen while rainfall less than 80 mm [3], and the way of soil lose was mainly from underground [4], which lead difficultly to measure karst soil erosion for the way of karst soil lost from underground. Less understanding karst soil erosion process and history (three main aspects about longer time scale recording, soil lost from underground, accurately quantifying and dating soil erosion) constrained clarify karst rocky desertification, although karst soil erosion was studied by using remote sensing [5~8], radio isotopic tracing [9], lake sediment, monitoring bury stake [10], artificial simulation, runoff square and sand-sinking pool [11,12], naked rock variance eroding, stalagmite analysis [13], and so on, all methods involve certain characteristics and a series of biases. New method was needed to reveal karst soil erosion. A new accurate technique of studying soil erosion within temporal and spatial change is dendrogeomorphology [14~16], which was applied to exactly identify soil erosion speed [15, 17~19], longer time scale soil erosion history [14, 16, 20, 21] karst rocky desertification history [22], landslide [23], mudslide [24]. Research in Dendrogeomorphology mainly concentrated on analyzing growth reactions in the stem of disturbed trees, but more attentions had focused on the root recently [25]. Erosion rate was connected exposed root age with measuring the height between the centre axis of exposed root and the actual soil surface [16, 19], erosion process was related to a sequence exposed roots which were dated [19, 26], gully erosion, sheet erosion can be precisely studied [14, 26]. Dendrochronology is the most accurate dating technique in geosciences within a time span of several hundreds to thousands of years [19, 27], it can be dated by using dead root, scars, and wood cell changed [19, 26], especially analysis of anatomical changes that take place in the roots as a response to exposure provides a powerful tool for geoscientists to quantify rates of soil erosion in areas where no measurements of past processes are available [15, 23, 28], nevertheless, not all the species allow dendrogeomorphological analyses, conifers show easily observable growth rings, but it is not for broad- leaved trees [14], meanwhile, the opposite result was also exist [15]. Dendrogeomophological technique could be used to research karst soil erosion for exposure roots can be seen in karst rocky desertification area [29,30], but most of karst area was covered by broad-leaved trees, which means that the most difficulty and fundamentality is to accurately identify the year of root exposure during the research [29]. Therefore, the objectives of this paper are: first, to understand karst broad-leaved tree roots anatomical feature; second, to compare difference of exposed and unexposed root of karst trees; and third, to accurately identify the year of root exposure. This work represents the first attempt in karst area to study soil erosion using dendrogeomophological technique through anatomical indicators.

2. Study area conditions

The study area is located at Chenqi village of Puding County in the middle of Guizhou province, China (1385~1520m, 105°42'~105°46'E, 26°14'~26°16' N) (Fig. 1) . Puding is a 100% karst rocky desertification county. The naked rocks are composed of dolomite and argillaceous dolomite inter- limestone of mid-Triassic period. The topography is composed of outside karst hill and karst valley flat. The subtropical monsoon climate is warm and humid with an average annual temperature of 15.1°C and average annual precipitation of 1,314.6 mm. More than 81% precipitation (about 1,064.8mm) occurs from 234 AuthorLuo name Mei et / Procediaal. / Procedia Engineering Engineering00 (2011 18 (2011)) 000– 232000 – 239 3

April to September. Sampling area, villages and arable lands were all around, was mainly covered by shrub, only some hill tops growing secondary forest.

Fig. 1 Location of the Study Area

3. Materials and Methods

3.1. Sampling

It is difficult to identify root origin of tree for the diversity of species [31], heterogenety of soil distribution and diversity of microhabitats [32] owing to karst rocky desertification. Exposed and buried root of 24 shrub roots were sampled after documented the position of exposed as well as undisturbed roots regarding the soil surface. The samples were then dried; polished; immerged; and sliced; microscopic sections were prepared from these samples in order to show the wood structure of the roots. Slices of wood 20 μm thick were cut by means of a microtome, measurement and of anatomic feature analysis were under the electron microscope and image analysis instrument.

3.2. Methods

Slices (about 2 cm) were taken at selected root of the exposed and buried, dried and polished. Tree-ring features were observed under anatomical lens for the purpose of preliminarily identifying tree-ring, and samples were cut off a 1 cm block crossing the whole slice, softened, and cut into 8 mm ×16 mm sequence wood blocks. 20 μm thin cross sections of these blocks were taken using a sledge microtome. The thin section was dyed in a solution of 1% water solvable Safranin. For dehydration the sample is to be rinsed with alcohol (50%; 96%; 100%) and immersed in Xylol. Finally the sample is put to a slide, imbedded in Canada-Balsam, and dried at 50°-60° C in an oven for 24 hours. Growth ring boundaries were identified according to terminal parenchyma cell under microscope. The thin sections were taken photos, saved and measured width of growth ring, earlywood, and latewood, vessel lumen size, vessel lumen area of, and fibre area.

4. Results

4.1. Response of width of tree root growth ring to soil thickness

Sensitivity, implied the relative quantity variance of one by one root ring, is an index of climate information [33]. Tree root absorbed water and nutrient from soil to support tree growth. In karst rocky desertification area, soil was thin and incontinuous, so it contained less water and nutrient to support tree growth, which caused soil cover to become important factor of root exposure. The sensitivity of root ring variance was correlated with soil covering thickness, meanwhile, with climate which controlled soil water content. The thinner the soil covering, the more water containing. Thinner soil covering means soil water 4 LuoAuthor Mei name et al. / /Procedia Procedia Engineering Engineering00 18 ( (2011)2011) 000 232– 000– 239 235 content be less, sensitivity of tree growth enhanced. Tab. 1 shows the sensitivity of root ring was all more than 0.2 in the studying area, just in the range of sensitivity from 0 to 2 [33], implied tree root growth was extremely sensitive to its growing environment; root could be used to study the relation between tree growth and environmental factors.

Table 1. Mean Sensitivity of Ring Width

Sample trees 1 2 3 4 5 6 7 8 9 10 11 12 Mean Sensitivity 0.3 0.5 0.6 0.2 0.4 0.4 0.3 0.4 0.5 0.2 0.2 0.6

4.2. Anatomical features of exposed root and buried root

Anatomical features of exposed and buried from same root were compared (Fig. 2). Tree ring width of buried root was changed smoothly from pith to bark, at first increased slowly and then decreased slowly. The vessel changed less and distributed uniformly in the earlywood and latewood. Root growth rings showed eccentric pattern in 12 slices of exposed root. Vessel change and distribution was the same as buried root in early time, afterwards, a significant mutation happened. The mutation included growth ring narrowed down, vessel size increased and number decreased in earlywood, but size decreased in latewood. Followed that, showed a relatively stabilized trend but growth ring width was more narrow after mutation than buried root. The sharp increase in ring width probably corresponds with the time when the root exposed, as root growth accelerates to produce callused tissue and/or anatomical variations (transition from root to stem anatomical structure) [34]. An increase of up to 10 times the average value of the ring’s width due to exposure at a point corresponded to the traumatic disappearance of the secondary meristem (cambium) [14].

Fig.2 Micro-sections of exposed root (top) and buried root (bottom) 236 AuthorLuo name Mei / etProcedia al. / Procedia Engineering Engineering00 (2011 18) (2011) 000–000 232 – 239 5

4.3. Vessel feature of exposed root

The vessel lumen area of exposed root was shown in Fig.3, at first, the curve of vessel lumen area was increased to the peak in 1994 but decreased to a concave in 1996, the vessel lumen area nearly decreased 50% and the number was also reduced. From 1996 to 2004, vessel lumen area kept tranquility, till 2005, vessel lumen area downed to the bottom. This root anatomical feature changed pattern implied soil gradually denuded. The root cell sharply changed indicated intensely erosion. Former study has shown that continuous erosion causes a continuous lowering of soil surface and with this a continuous reduction of cell sizes over many years, until a reduction of about 50% is reached once a large part of the root is exposed [28].

Fig. 3. Mean annual values vessel Fig. 4. Mean annual values fibre

4.4 Fibre feature of exposed root

Fibre lumen area has shown nearly the same curve pattern with vessel lumen area (Fig. 4). The highest fibre lumen area was 229μm2 in 1994, gradually decreased to a concave of 156μm2 in 1996, then climbed up to 206μm2 in 2001 and down to the bottom of 71μm2 in 2005, after that displayed minor fluctuation. Because soil erosion was a gradually process, root lost soil covering was the same step with erosion and also fibre area. But during soil erosion process, incomplete exposure root could absorbed enough water while weather condition was better in some years and the fibre and vessel lumen area would be improved till soil covering was denuded. Root exposed completely and fibre lumen area decreased gradually.

5. Discusses

Exactly to understand karst soil erosion will meet 3 big problems, the first is difficult to get much longer time scale karst soil erosion historical records, owing to absence of long time monitoring data of karst soil erosion. The second is difficult to get any information of karst soil erosion about the quantity and process from underground for lack of monitoring method because karst soil lost mainly from underground [4]. The third is still unknown karst soil erosion quantity and process for the reasons of the first and second. Tree roots of karst area were always uncovered by soil, which implied soil erosion and that of soil erosion from surface and underground, nevertheless, an important factor controlled to understand karst soil erosion that is to identify exact soil erosion happening time. Nutrient and water of tree growth comes from root absorbing from soil, as soon as root exposed in the air, anatomical structure of tree ring changed evidently, such as cell sizes, cell pattern, width of tree ring, earlywood and latewood, which could be used to identify the exact time of root exposure and erosion episodes [35]. Nevertheless, 6 LuoAuthor Mei name et al. / /Procedia Procedia Engineering Engineering00 18 ( (2011)2011) 000 232– 000– 239 237 tree ring changed unconspicuous for broadleaf trees [28], few data reported clear [15] and opposite also reported [14]. To exactly identify soil erosion episodes time was a key controlling factor in using dendrogeomorphology in karst area for mainly species were broadleaves [36]. The pattern of exposed tree root ring was eccentric in karst areas which coincide with other researchers’ work [19]. Vessel disposal ways and size of exposed root from pith to bark was the same as unexposed root in prophase, but evidently mutation behind, which include annual ring narrowed, vessel diameter of earlywood largened and number reduced; vessel diameter of latewood diminished and number reduced, and continuously steady since then. Trend of annual ring width in exposed root was narrower than in unexposed root, and transformed trend of vessel area was similar with vessel lumen area in exposed root. The results was disagreed with others, Gärtner found the cell number of earlywood was 50% of unexposed [15, 25]. Whereas Ireneusz Malik et al. discovered annual ring wider in exposed root than in unexposed root during studied soil erosion by root exposure in the shore, annual ring was becoming wider after root lost of soil covering and soil mechanical stress, root could be supported by adequate nutrition and water from soil [35]. Annual ring was narrower after root exposure in karst area because soil erosion reduced nutrient ions and water supply as rock naked, discontinuously soil distribution, and thinner soil layer. Anatomical annual ring pattern of exposed root in non-karst area was coincided with the study of Malik [35] that exposed root ring was wider in prophase, but narrower as soil continuously eroded and exposed time longer (unpublished data), which appropriately annotated soil layer was the key factor of controlling tree and root growing in karst area. From above anatomical mutation, soil erosion episodes time could be exactly identified and also eroded soil quantity. In all conscience, the decrease of vessel lumen area and fibre area was not persistently, an increase would happen behind it, afterwards, gradually decrease. The explanation was that root absorbed nutrition and water from soil to maintain tree and root growth, moreover, root growth was controlled by temperature and moisture for adequate climate and plenty rainfall in special years, that soil layer was not the key factor before root exposed because soil erosion was gradually process. The trend of root cell decreased continuously only after root exposed thoroughly.

6. Summary

Anatomical features were compared between exposed and unexposed root in Puding County, P. R. China. The pattern of exposed tree root ring was eccentric in karst areas, Vessel disposal ways and size of exposed root from pith to bark was the same as unexposed root in prophase, but evidently mutation behind, nnual ring narrowed, vessel diameter of earlywood largened and number reduced; vessel diameter of latewood diminished and number reduced and continuously steady since then. Trend of annual ring width in exposed root was narrower than in unexposed root, and transformed trend of vessel area was similar with vessel lumen area in exposed root. These changes implied the exactly time of soil erosion could be identified which illustrated that it is possible to obtain karst soil erosion historical record by using dedrogeomophological method.

Acknowledgements

This work was jointly funded by the National Key Basic Research Development Program (Grant No. 2006CB403201), Chinese-Hungary intergovernmental Scientific Cooperation Project of The Ministry of Science-Technology of the Peoples’ Republic of China (No. 2008-333-4-16), International Scientific Project of Guizhou (QKHWGZ-2010-7009), and Scientific Fund of Back from Abroad in Guizhou (Grant No.Qian-Ren 2009-3). 238 AuthorLuo name Mei / etProcedia al. / Procedia Engineering Engineering00 (2011 18) (2011) 000–000 232 – 239 7

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