Grading Woodland Soil Water Productivity and Soil Bioavailability in the Semi-Arid Loess Plateau of China

摘要

In the semi-arid region of the Loess Plateau in China, a portable photosynthesis system (Li-6400) and a portable steady porometer (Li-1600) were used to study the quantitative relation between the soil water content (SWC) and trees' physiological parameters including net photosynthesis rate (P_n), carboxylation efficiency (CE), transpiration rate (T_r), water use efficiency of leaf (WUE_L), stomatic conductivity (G_s), stomatal resistance (R_s), intercellular CO_2 (C_i), and stomatal limitation (L_s). These are criteria for grading and evaluating soil water productivity and availability in forests of Black Locust (Robinia pseudoacacia) and Oriental Arborvitae (Platycladus orientalis). The results indicated: To the photosynthesis of Locust and Arborvitae, the SWC of less than 4.5 and 4.0% (relative water content (RWC) 21.5 and 19.0%) belong to "non-productivity and non-efficiency water"; the SWC of 4.5-10.0% (RWC 21.5-47.5%) and 4.0-8.5% (RWC 19.0-40.5%) belong to "low productivity and low efficiency water"; the SWC of 10.0-13.5% (RWC 47.5-64.0%) and 8.5-11.0% (RWC 40.5-52.0%) belong to "middle productivity and high efficiency water"; the SWC of 13.5-17.0% (RWC 64.0-81.0%) and 11.0-16.0% (RWC 52.0-76.0%) belong to "high productivity and middle efficiency water"; the SWC of 17.0-19.0% (RWC 81.0-90.5%) and 16.0-19.0% (RWC 76.0-90.5%) belong to "middle productivity and low efficiency water"; the SWC of more than 19.0% (RWC 90.5%) belongs to "low productivity and low efficiency water". The SWC of about 13.5 and 11.0% (RWC 64.0 and 52.0%) are called "high productivity and high efficiency water", which provides the further evidence for Locust and Arborvitae to get both higher productivity (P_n and CE) and the highest WUE_L and adaptation to the local environment, respectively.