Soil moisture control of sap-flow response to biophysical factors in a desert-shrub species, <i>Artemisia ordosica</i>

Abstract

Abstract. The current understanding of acclimation processes in desert-shrub species to drought stress in dryland ecosystems is still incomplete. In this study, we measured sap flow in Artemisia ordosica and associated environmental variables throughout the growing seasons of 2013 and 2014 (May-September period of each year) to better understand the environmental controls on the temporal dynamics of sap flow. We found that the occurrence of drought in the dry year of 2013 during the leaf-expansion and leaf-expanded periods caused sap flow per leaf area (J s ) to decline significantly, resulting in transpiration being 34 % lower in 2013 than in 2014. Sap flow per leaf area correlated positively with radiation (R s ), air temperature (T ), and water vapor pressure deficit (VPD) when volumetric soil water content (VWC) was greater than 0.10 m 3 m −3 . Diurnal J s was generally ahead of R s by as much as 6 hours. This time lag, however, decreased with increasing VWC. The relative response of J s to the environmental variables (i.e., R s , T , and VPD) varied with VWC, J s being more strongly controlled by plant-physiological processes during periods of dryness indicated by a low decoupling coefficient and low sensitivity to the environmental variables. According to this study, soil moisture is shown to control sap-flow (and, therefore, plant-transpiration) response in Artemisia ordosica to diurnal variations in biophysical factors. This species escaped (acclimated to) water limitations by invoking a water-conservation strategy with the regulation of stomatal conductance and advancement of J s peaking time, manifesting in a hysteresis effect. The findings of this study add to the knowledge of acclimation processes in desert-shrub species under droughtassociated stress. This knowledge is essential in modeling desert-shrub-ecosystem functioning under changing climatic conditions.

Dynamic Changes in Plant Resource Use Efficiencies and Their Primary Influence Mechanisms in a Typical Desert Shrub Community

“…Plants in drylands generally experience more environmental stress, especially as severity and duration of droughts continue to increase under a warming climatic regime [7][8][9]. Consequently, it is expected that there will be changes in the supply of available plant resources, such as water (W), light (L), and nitrogen (N) for photosynthetic assimilation, as well as for the maintenance of functional plant structures.…”

Scaling Up Sap Flow Measurements from the Stem Scale to the Individual Scale for Multibranched Caragana Korshinskii on the Chinese Loess Plateau

“…Several studies have reported a close relationship between SWC and SF for a variety of tree species [16,19,40]. The results of regression analysis between SWC and SF are shown in Figure A1.…”

“…In our study, we observed that the stem-scale SF differed notably with the SBD despite sharing the same diurnal variation ( Figure A4). Summarizing the different categories of plant morphological variables (Figure 6), the stem-scale SFs were significantly largest (p < 0.05) in the largest levels of PBN (18)(19)(20)(21)(22)(23)(24)(25), SL (230-270 cm), SBD (17-21 mm), and W (350-550 g), followed by those in the middle levels of PBN (11)(12)(13)(14)(15)(16)(17)(18), SL (190-230 cm), SBD (13-17 mm), and W (200-350 g), and lastly followed by those in the smallest levels of PBN (4-11), SL (150-190 cm), SBD (9-11 mm), and W (50-200 g). The regression analysis further indicated that the stem-scale SF of C. korshinskii had significantly positive linear correlations with PBN (Figure 7a), SL (Figure 7b), SBD (Figure 7c), and W ( Figure 7d)…”

“…The SF value predicted in our study (1.10-1.91 mm•d −1 ) is comparable to that in previous studies. Estimating transpiration water use for individual trees is usually achieved by multiplying the average stand SF by the total sapwood area of the stand [13,[17][18][19]. Shrubs, however, typically have many branches, and their basal diameter is small.…”

“…Shrubs, however, typically have many branches, and their basal diameter is small. Zha et al [19] estimated stem-scale SF for A. ordosica by measuring the SF per leaf area, total leaf area per stem, and the number of stems. The authors then determined the transpiration amount per stand by the stem-scale SF and the leaf area index of shrubs.…”