Non-rainfall Water Research Articles

Non-rainfall water sources in the topsoil and their changes during formation of man-made algal crusts at the eastern edge of Qubqi Desert, Inner Mongolia

In arid and semiarid areas, water uptake (non-rainfall water) serves as an important water source for plants, biological soil crusts, insects and small animals. In this study, a measurement program was undertaken to investigate water uptake and its changes during formation of man-made algal crusts in the Qubqi Desert. In the study region, water uptake from the atmosphere accounted for 25.07%-39.83% of the total water uptake, and was mainly taken up by a water vapor adsorption mechanism; the proportion of water uptake from the soil substrate was much higher (60.17%-74.93%). The formation of crusts promoted water uptake, but the increased uptake did not occur immediately after inoculation or crusts formation. The water taken up from the atmosphere increased significantly from day 15 after inoculation, and the soil water content was markedly enhanced from day 20 after inoculation. It is considered that the growth of algal filaments and their secretions were the main factors increasing the amount of water uptake and water content in the crusts, and these variables increased even during dry periods when some algae are likely to have died.

Linking population density and habitat structure to ecophysiological responses in semiarid Spanish steppes

We have studied the underlying factors responsible for the heterogeneous ecophysiological status of a semiarid Stipa tenacissima L. steppe in a subcatchment of SE Spain by assessing population composition and habitat structure of S. tenacissima stands. To do this, we measured and estimated 18 variables (11 biotic and seven abiotic) in 15 plots randomly distributed in the subcatchment, and then zoned this area by plot affinity using PCA. This analysis produced three sectors determined mainly by S. tenacissima cover and soil depth variables. The linear relationship fitted between S. tenacissima tussock biomass and tussock density in monospecific stands (both logarithmic) indicated a curve close to −1, suggesting that the system is close to the maximum constant yield state. Ecophysiological measurements (gas exchange, fluorescence and individual leaf area index) were taken in two periods with different water availability in a representative plot in each sector. The intraspecific competition (inferred from the density dependence of green biomass) and rock outcrops were the main factors influencing the ecophysiological status in the study area. While, in the wet season, intraspecific competition regulated water consumption in zones where S. tenacissima tussocks (monospecific stands) are dominant, during the dry season, stands in zones with extensive rock outcrops and stone cover (tussocks in “soil pockets”) had no access to non-rainfall water gains because of the adjacent bare soil, and so in these stands, gas exchange was lower and photoinhibition higher. This article stresses the importance of considering the connection between tussocks and bare-ground interspace in the functional and structural analysis of semiarid steppes.

Can water responses in Stipa tenacissima L. during the summer season be promoted by non-rainfall water gains in soil?

This article reports on quantified soil water gains and their possible effects on summer water relationships in a semiarid Stipa tenacissima L. grasslands located in SE Spain. We believe that the net soil water gains detected using minilysimeters could be from soil water vapour adsorption (WVA). Our study of high water-stress showed stomatal conductance (21.8–43.1 mmol H2O m−2 s−1) in S. tenacissima leaves unusual for the summer season, and the evapotranspiration from S. tenacissima grassland, estimated by a multi-source sparse evapotranspiration model, closely corresponding to total WVA. This highlights the importance of summer soil WVA to stomatal conductance and vital transpiration in S. tenacissima. This study measured pre-dawn leaf water potential (ψ) response to sporadic light rainfall, finding that a light summer rainfall (1.59 mm day−1) was sufficient to vary ψ in S. tenacissima from −3.8 (close to the turgour loss point) to −2.7 MPa. We hypothesize that soil WVA can supply vegetation with water vital to its survival in seasons with a severe water deficit, giving rise to a close relationship between soil water dynamics and plant water response.