A field experiment was conducted to investigate the effect of supplementary irrigation on watermelon (Citullus lanatus) yield, water-use efficiency (WUE) and root distribution in gravel-mulched field in northwest Loess Plateau, China, during 2001 and 2002 growing seasons. The results showed that gravel mulch significantly improved seedling emergence, increased yield and WUE, and alleviated the influence of drought on plant growth. Regardless of gravel mulch application, supplementary irrigation increased watermelon yields, average fruit weight and number of fruit, especially yield increased as the amount of irrigation increased (P<0.05). Generally, WUE of irrigated treatments were higher than that of non-irrigation treatment in gravel-mulched field. The effect of water supply on root distribution was different in two years. In 2001, average root length density (RLD) and root weight density (RWD) whole the soil profile increased. In 2002, however, RLD and RWD decreased as water supply increased. The average RLD and RWD in 2001 were significantly higher than those in 2002. Maybe we can interpret the phenomenon with the theory that there is a need to optimize root distribution (in terms of water relations) and aboveground biomass for a given water supply.The yield may not depend as much on root growth as on the amount of water required at critical stages. A significant effect of soil depth on RLD and RWD were observed in both years, but did not rapidly decrease with depth.
Taking annual plant Eragrostis poaeides in the artificial vegetation-stabilized sand dune in the Shapotou Experimental Research Station as example, study has been done on the adaptation strategies of annual plants to random environment through fixed quadrat observations of population changes and fixed plant determinations of individual growth, seed germination,population dynamics, spatial distribution pattern of population, competition and regulation. During the growing season, the survival rate of annual plants depends on the precipitation intensity and precipitation duration which activate the germination of seeds. The optimal germination strategy of annual plants in this habitat during the growing season appears as continuous germination under suitable conditions. Such continuous germination is an adaptive characteristic of annual plants to random environment. In addition, the variation processes of population size and regulation mechanism of E. poaeoides are studied. Statistical results of natural population in four consecutive years show that water condition in the habitat is the leading factor affecting the population dynamics of E. poaeoides. During the establishment period E. poaeoides had a higher death rate, but in the middle to later period they could survive stably. Due to the limitation of soil moisture, the competition among individuals for water inevitably led to self-thinning phenomena. Under very arid condition, the survival curve of annual herbs entirely appears as Deevey Ⅲ type (C type), but under relatively adequate precipitation condition, the survival curve appears as intermediate type. The strategy of life history obviously appears as r-strategy. Plant species of r-strategy often occurs in the early succession stage of the communities. In the relatively adequate and evenly-distributed rainfall years, E. poaeoides population exhibited a density-dependent, i. e., survival rate increased with decrease in population density. The main pattern to regulate the population number for the intraspec
Study is made on a 45 km-long artificial ecosystem without irrigation in Tengger desert on the basis of long-term ecological monitoring and ecohydrological fundamentals.Changes in water allocation, utilization, cycle and balance patterns in more than 40-year evolution of the soil-plant system are analyzed. The formation of a drought horizon in shrub rhizosphere and its effect, ecohydrological function of the crust and its effect on the soil-plant system change are discussed. Driven by water self-regulation and water stress, the soil-plant system is going to develop towards the steppe desert to ensure more effective use and optimum collocation of water resource.
XIAO Honglang CHENG Guodong LI Xinrong SONG Yaoxuan WANG Xinping
