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Shou-Li Li(124) Marinus J. A. Werger(2) Pieter A. Zuidema(2) Fei-Hai Yu(31) Ming Dong(1)
1.State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093 China 2.Ecology and Biodiversity Group, Institute of Environmental Biology, Utrecht University, PO Box 80084, 3508 Utrecht, The Netherlands 3.College of Nature Conservation, Beijing Forestry University, Beijing, 100083 China 4.Graduate University of Chinese Academy of Sciences, Beijing, 100049 China
Sand movement is a common stress for plants in dune ecosystems. Seedlings in such an environment often experience various degrees of denudation or burial. A field experiment was conducted withArtemisia ordosica, a dominant semi-shrub species in Mu Us sandland, China, to test seedling survival and growth under different degrees of denudation and burial. Seedlings from two cohorts with height of 5.0 ± 0.02 cm (S1) and 9.3 ± 0.09 cm (S2) were selected and randomly subjected to three denudation treatments (2.5, 5, and 10 cm), five burial treatments (2.5, 5, 7.5, 10, and 15 cm), or a control.S2 seedlings had a higher survivorship thanS1 seedlings, especially under severe denudation (10 cm) and complete burial (5 cm inS1; 10 cm inS2). Seedling survivorship was unaffected by moderate burial (<5 cm inS1;<10 cm inS2) or denudation (<10 cm), but it was significantly reduced under complete burial or severe denudation. Seedling growth in leaf area, height, and biomass only declined in severe denudation or complete burial. Seedling burial led to higher biomass investment in shoots, while the reverse was the case in denudation. The results indicateA. ordosica is highly tolerant to moderate burial and denudation, showing adaptive responses that likely increase survival. Differences in responses between seedling cohorts suggest that large seedling size is beneficial for successful establishment in sandy environments and measures to prevent severe denudation and burial of recently germinated seedlings are necessary in attempts to restore steppe vegetations.
Responses to mechanical stress(such as wind)should be suppressed in dense vegetation since the resultant shorter stature would lead to low fitness.However,this point has been debated,i.e.it has been argued that in dense vegetations a sensitivity to mechanical stress might provide an additional cue to shade avoidance.For 10 different genotypes of the clonal plant Potentilla reptans,the effects of shade(15% of daylight with a red:far red ratio,R/FR of 0.3 vs.50% daylight and R/FR of 1.2)and wind(0 or 40 daily brushes with a duster)on the mother leaf properties were investigated.All genotypes exhibited typical'shade avoidance' responses under shade,such as the production of fewer leaves with longer petioles,reductions in petiole diameter,and the production of more rigid petiole tissue(petioles with a higherYoung'modulus).Wind-treated plants produced more leaves with shorter and thicker petioles made of nlore flexible tissue (lower Young's modulus).All responses to wind are different from responses to shade.Interestingly the responses to wind in leaf of Potentilla reptans were opposite in nature to the responses to light.
1.Dipartimento di Scienze e Tecnologie per l′Ambiente ed il Territorio Università degli Studi del Molise Via Mazzini 8 86170 Isernia Italy 2.Laboratoire de Rhéologie du Bois de Bordeaux Unit: CNRS/INRA/Université Bordeaux I Domaine de l′Hermitage, 69, Route d’Arcachon 33612 Cestas Cedex France 3.CIRAD Unité de Modélisation des Plantes Laboratoire de Rhéologie du Bois de Bordeaux Domaine de l′Hermitage, 69, Route d’Arcachon 33612 Cestas Cedex France 4.INRA Ephyse, Recherches Forestières 69, route d’Arcachon 33612 Cestas Cedex France 5.Dipartimento di Scienze Chimiche ed Ambientali Università degli Studi dell’Insubria Via Valleggio 11 22100 Como Italy 6.Forest Research Northern Research Station Roslin Midlothian EH25, 9SY UK
The effect of wind loading on seedlings of English oak (Quercus robur L.) was investigated. Instead of using a traditional wind tunnel, an innovative ventilation system was designed. This device was set up in the field and composed of a rotating arm supporting an electrical fan, which emitted an air current similar to that of wind loading. Oaks were sown from seed in a circle around the device. A block of control plants was situated nearby, and was not subjected to artificial wind loading. After 7 months, 16 plants from each treatment were excavated, and root architecture and morphological characteristics measured using a 3D digitiser. The resulting geometrical and topological data were then analysed using AMAPmod software. Results showed that total lateral root number and length in wind stressed plants were over two times greater than that in control trees. However, total lateral root volume did not differ significantly between treatments. In comparing lateral root characters between the two populations, it was found that mean root length, diameter and volume were similar between the two treatments. In trees subjected to wind loading, an accentuated asymmetry of root distribution and mean root length was found between the windward and leeward sides of the root system, with windward roots being significantly more numerous and longer than leeward roots. However, no differences were found when the two sectors perpendicular to the wind direction were compared. Mean tap root length was significantly higher in control samples compared to wind stressed plants, whilst mean diameter was greater in the latter. Wind loading appears to result in increased growth of lateral roots at the expense of the tap root. Development of the lateral root system may therefore ensure better anchorage of young trees subjected to wind loading under certain conditions.
1.Université Bordeaux I, INRA, CNRS, UMR US2B Talence 33405 France 2.INRA, LIAMA-CASIA P.O. Box 2728 Haidian District 100080 Beijing China 3.INRA, Botanique et Bioinformatique de l’Architecture des Plantes (AMAP) TA A-51/PS2, Boulevard de la Lironde Montpellier Cedex 5 34398 France 4.INRA, UR1263 EPHYSE 69 route d’Arcachon F-33612 Cestas France 5.NAGREF, Forest Research Institute Vassilika, Thessaloniki 57006 Greece
The optimal root system architecture for increased tree anchorage has not yet been determined and in particular, the role of the tap root remains elusive. In Maritime pine (Pinus pinaster Ait.), tap roots may play an important role in anchoring young trees, but in adult trees, their growth is often impeded by the presence of a hard pan layer in the soil and the tap root becomes a minor component of tree anchorage. To understand better the role of the tap root in young trees, we grew cuttings (no tap root present) and seedlings where the tap root had (−) or had not ( ) been pruned, in the field for 7 years. The force (F) necessary to deflect the stem sideways was then measured and divided by stem cross-sectional area (CSA), giving a parameter analogous to stress during bending. Root systems were extracted and root architecture and wood mechanical properties (density and longitudinal modulus of elasticity,EL) determined. In seedlings (−) tap roots, new roots had regenerated where the tap root had been pruned, whereas in cuttings, one or two lateral roots had grown downwards and acted as tap roots. Cuttings had significantly less lateral roots than the other treatments, but those near the soil surface were 14% and 23% thicker than plants ( ) and (−) tap roots, respectively. Cuttings were smaller than seedlings, but were not relatively less resistant to stem deflection, probably because the thicker lateral roots compensated for their lower number. Apart from stem volume which was greater in trees ( ) tap roots, no significant differences with regard to size or any root system variable were found in plants (−) or ( ) tap roots. In all treatments, lateral roots were structurally reinforced through extra growth along the direction of the prevailing wind, which also improved tap root anchorage. Predictors of log F/CSA differed depending on treatment: in trees (−) tap roots, a combination of the predictors stem taper and %volume allocated to deep roots was highly regressed with log F/CSA (R2 = 0.83), unlike plants ( ) tap roots where the combined predictors of lateral root number and root depth were best regressed with log F/CSA (R2 = 0.80). In cuttings, no clear relationships between log F/CSA and any parameter could be found. Wood density andEL did not differ between roots, but did diminish with increasing distance from the stem in lateral roots.EL was significantly lower in lateral roots from cuttings. Results showed that nursery techniques influence plant development but that the architectural pattern of Maritime pine root systems is stable, developing a sinker root system even when grown from cuttings. Anchorage is affected but the consequences for the long-term are still not known. Numerical modelling may be the only viable method to investigate the function that each root plays in adult tree anchorage.
YU Yun-Jiang, SHI Pei-Jun, LU Chun-Xia and LIU Jia-Qiong
于云江,史培军,鲁春霞,刘家琼
Blown sand is very common in nature. In areas with frequent blown sand, especially arid and semi-arid areas, blown sand not only buries highways and railways but also poses a threat to the sustainable use and development of plant resources. In the past, researchers have conducted many studies of sand-burying and wind erosion, but there are few studies on the effect of blown sand on plant eco-physiology. The nature of the influence of blown sand on the eco-physiological characteristics of plants is an important question. Though scientists have observed and studied some effects of wind on morphological characters and transpiration ratios the effects of blown sand on the net photosynthetic rate, water use efficiency etc. of plants are unknown. In this paper, based on experimental methods we showed relations between different blown sand conditions and some ecophysiological characteristics in plants, and revealed adaptability of experimental plants to blown sand by observing the change of hotosynthesis and water use efficiency in plants. In this paper, using a field wind tunnel, the effects of blown sand on the growth characteristics of some sand-fixing plants (Eragrostis poaeoides Beauv.,Agriophyllum squarrosum, Bassia dasyphylla Kuntze,Caragana korshinskii Kom., Artemisia ordosica Krasch,Reaumuria soongorica Maxim, Ammopiptanthus mongolicus Cheng f., Hedysarum scoparium L.,Robinia pseudoacacia L.) were studied under different wind conditions including different wind velocities (5.9, 7.9, 9.9, 14 m·s-1 etc.) and blowing intervals (2 d, 4 d, 9 d), and some eco-physiological parameters were measured. The results showed: 1) Both wind and wind-sand current made net photosynthetic ratio (Pn) decrease and transpiration ratio (E) rise, and thus made water use efficiency (WUE) decrease. 2) The larger the wind velocity was or the shorter the blowing interval by wind-sand was, the larger the reduction in Pn; the effect of wind-sand current on the above index was greater than the effect of pure wind. The more fierce the wind-sand menace to the plants was, the less the substance accumulation was, and thus the more slowly the plant grew in height; 3) Wind-sand current aggravated desiccation of plants, due to the reduction in WUE. Meanwhile sand-fixing plants have adaptability to wind-sand current. The shrubs showed more adaptability to wind-sand current than the grasses. According to the change of WUE in experimental plants under blown sand conditions, the adaptability of experimental shrubs to blown sand ranks as follows: Reaumuria soongorica >Ammopiptanthus mongolicus > Caragana korshinskii>Artemisia ordosica >Hedysarum scoparium > Robinia pseudoacacia. This ranking corresponds with the order in their capability of resisting drought. (4) The affecting capability of the blown sand on different plants is different. In this experiment, the change in Pn and WUE for grasses is more than shrubs, and the change for Artemisia ordosica is less than for Agriophyllum squarrosum under higher velocity.
QU Hao1,2, ZHAO Xue-yong1, YUE Guang-yang1,2, WANG Shao-kun1,2
曲 浩1,2, 赵学勇1, 岳广阳1,2, 王少昆1,2
1.Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China; 2.Graduate School of Chinese Academy of Sciences, Beijing 100049, China
Wind exerts influence on plant, especially in arid and semiarid regions. In the portable wind tunnel, the net photosynthetic ratio(Pn), stomata conductance(Gs) and transpiration ratio(Ts) of four kinds common plants (Agriophyllum squarrosum, Corispermum macrocarpum, Lespedeza davurica and Digitaria cilliaris) in Horqin Sand Land were measured with a Li-6400 under different air velocities (4 and 8 m·s-1) and blowing duration (20 to 120 min). The results showed that wind made Pn, Gs and Ts decreased significantly with elevated wind levels and blowing duration. At the air velocity of 4 m·s-1, the Pn, Gs and Ts of plants inside the wind tunnel were 47.2%~89.3%, 49.4%~90.1% and 45.7%~86.5% lower than the beginning, respectively. Similarly, Pn, Gs and Ts remained lower as a result of 8 m·s-1 air current, and the decreasing extent was 59.2%~91.3%, 47.3%~93.5% and 69.5%~91.8% respectively. All the indices measured at the air velocity of 8 m·s-1 decreased more than that at the air velocity of 4 m·s-1 except the Gs of Lespedeza davurica. Furthermore, the water use efficiency (WUE) presented evident uptrend at the beginning of wind treatment, suggesting that sand-fixing plants have adaptability to the wind current in short time. However, continuous strong wind current more than 60 min would cause the WUE turning to drop.
1Cold and Arid Regions Environment and Engineering Institute, Chinese Aca demy of Sciences, Lanzhou 730000, China|2Faculty of Life Sciences, Ludong University, Yantai 264025, Shandong, China
Aimed to understand the effects of wind blow and sand burial on the ph ysiological and ecological properties of desert plants, a field experiment with Caragana microphilla was conducted in Horqin Sand Land in 2006 and 2007. The wind blow experiment had five treatments, i.e., 0, 2, 4, 6, and 8 m·s-1 of wind velocity, and the sand burial experiment also had five treatments, i.e., 〖JP2〗 none, light, moderate, heavy, and severe sand burial, with 0, 33%, 66%, 100%, a nd 133% of plant height sandburied. A continuous wind blow with a velocity of 2 m·s-1 resulted in a slight decrease of photosynthetic rate and transpir ation rate, that of 6〖KG-*2〗-〖KG-*7〗8 m·s-1 increased the two rates o bviously, while a continuous wind blow with a velocity of 4 m·s-1 had no obvious effects on the photosynthetic and transpiration rates. Light sand burial promoted the stem, leaf, and root growth, and increased the biomass of C. mic rophilla, moderate sand burial only promoted the root growth and increased the biomass but restrained the height growth, while heavy and severe sand burial in jured the plant growth seriously, even resulted in plant death. As a dominant sa ndfixing plant, C. microphilla could adapt the wi nd blow and sand burial to a certain degree through regulating its growth rhythm and physiological characteristics, and thus, had strong capability to adapt w indsand environment. However, severe wind blow and sand burial could result in a severe injury to the plant, even in plant death. Therefore, C. microphilla sh ould be planted in the place without strong windsand activity when used for fi xing mobile sand.