Influence of alternated drying and wetting on the characteristics of soil preferential flow formation in Honghe Arid Valley.

To clarify the effects of alternation of drying and wetting on the formation of soil preferential flow in arid valley, taking the wasteland in the arid valley of Honghe River as the research object, we analyzed the soil preferential flow characteristics before and after the simulation of drying and wetting alternation based on dyeing tracer method, water breakthrough curve, and image processing technology. The results showed that, under the simulated alternation of drying and wetting, the matrix flow occurred in the 0-10 cm soil layer, the dyeing depth reached 35 cm, the horizontal width of the preferred path was only 3-10 cm, and the dyeing area curve fluctuated little. Simulated alternation of drying and wetting led to significant increases in the steady effluent, macropores number, and macroporosity. In the 0-20 cm soil layer, the steady effluent after alternation of drying and wetting was about 0.27 cm3·s-1 higher than that non-alternation of drying and wetting, macropores number in dyeing area was about 1.4 times higher, and the macroporosity was 13.4% higher. The macropores number was positively correlated with stable flow rate. After simulated alternation of drying and wetting, the number of macropores from large to small was 0.6-0.8 mm＞0.8-1.0 mm＞1.0-1.5 mm＞1.5-2.0 mm＞2.0-3.7 mm, while under non-alternation of drying and wetting, it was 0.8-1.0 mm＞0.6-0.8 mm＞1.0-1.5 mm＞2.0-3.7 mm＞1.5-2.0 mm. The macropores number in each pore size range was significantly correlated with the dyeing area ratio. After simulated alternation of drying and wetting, the correlation increased, and the dominant factor affecting the occurrence of preferential flow changed from the macropores number in the pore size range of 1.5-2.0 mm to that of 0.8-1.0 mm. Therefore, the alternation of drying and wetting would affect the characteristics of macropores, which caused the soil to be more prone to preferential flow and with higher magnitude.

[Effects of plant roots on soil preferential flow in typical forest and grassland in the dry-hot valley of Jinsha River, China]. / é‡‘æ²™æ±Ÿå¹²çƒ­æ²³è°·å ¸åž‹æž—è‰åœ°æ¤ç‰©æ ¹ç³»å¯¹åœŸå£¤ä¼˜å ˆæµçš„å½±å“.

To clarify the morphological characteristics of soil preferential flow and the effect of plant roots on its formation, plants from the typical vegetation types of an artificial woodland (Leucaena acacia) and a dry watershed grassland (Heteropogon contortus) of Yuanmou County, Jinsha River were selected as the experimental objects. Based on the staining and tracing method combined with Photoshop CS5 and the Image-Pro Plus 6.0 image processing technology, we analyzed the morphological and distribution characteristics of soil preferential flow under the two planting types and examined the effects of plant roots. We found significant difference in soil preferential flow dyeing area between the woodland and grassland species, and the overall variation trend of the forestland dyeing area ratio decreased with increasing soil depth. The dyeing area of the grassland decreased monotonously with the increases of soil depth. The occurrence degree of soil preferential flow in forest was higher than that of grassland. Root systemaffected the formation of soil preferential flow. At the root diameter ranges of 0≤d≤5 mm and d>10 mm, root length density of the woodland showed a monotonous decreasing trend with increasing soil depth, while in the root diameter range of 5 mm5 mm. The overall change trend of soil preferential flow dyeing area of two vegetation types in the study area decreased with increasing soil depth. Plant root system was closely related to the formation of soil preferential flow. Fine roots could promote while coarse roots may retard the formation of preferential flows.

[Responses of tree growth to artificial intervention on micro-topography in degraded woodland on hillslope]. / 山坡退化林地林木生长对微地形人工干预的响应.

We explored the effects of microtopography changes from artificial intervention of soil and water conservation (contour reverse-slope terrace, CRT) on tree growth in a degraded woodland on hillslope in water resource area of Songhua dam in Kunming City. The differences of the diameter at breast height (DBH), tree height, new branch increment, and leaf area index (LAI) of dominant tree species in different plots were compared through dynamic monitoring. Then, the causes of differences were analyzed by combining the soil water availability. The results showed that the maximum and mean values of DBH and height of Pinus yunnanensis (dominant species) in contour reverse-slope terrace plot were larger than those in control plot (CK), and the proportion of small-sized and low-dwarf trees in degraded forest community was higher, which indicated that the growth potential of new and seriously degraded forest was stimulated. The annual variation rate of the ave-rage new branch length and diameter of P. yunnanensis in different plots reached 72.4% and 39.1%, respectively. The changes of new branch growth of P. yunnanensis, LAI of plots, and the new branch growth rate were greater in CRT than those in CK. Soil water content was significantly correlated with both the new branch growth and LAI. The ratio of available water in plot (64.2%) was higher than that in CK (54.7%). During the rainy season (from May to September), the available water in CRT existed longer, which was conducive to tree growth and the improvement of plant community structure in degraded woodland.