Daily precipitation at Gonghe Station from May 1 to September 13, 2014.

<p>Daily precipitation at Gonghe Station from May 1 to September 13, 2014.</p

Root mass density of <i>Salix psammophila</i> and <i>S</i>. <i>cheilophila</i> at different soil depth.

<p>Different lower case letters indicate significant difference in root mass density at different soil depths according to Duncan’s test (<i>P</i> < 0.05).</p

Seasonal Dynamics of Water Use Strategy of Two <i>Salix</i> Shrubs in Alpine Sandy Land, Tibetan Plateau

<div><p>Water is a limiting factor for plant growth and vegetation dynamics in alpine sandy land of the Tibetan Plateau, especially with the increasing frequency of extreme precipitation events and drought caused by climate change. Therefore, a relatively stable water source from either deeper soil profiles or ground water is necessary for plant growth. Understanding the water use strategy of dominant species in the alpine sandy land ecosystem is important for vegetative rehabilitation and ecological restoration. The stable isotope methodology of δD, δ¹⁸O, and δ¹³C was used to determine main water source and long-term water use efficiency of <i>Salix psammophila</i> and <i>S</i>. <i>cheilophila</i>, two dominant shrubs on interdune of alpine sandy land in northeastern Tibetan Plateau. The root systems of two <i>Salix</i> shrubs were investigated to determine their distribution pattern. The results showed that <i>S</i>. <i>psammophila</i> and <i>S</i>. <i>cheilophila</i> absorbed soil water at different soil depths or ground water in different seasons, depending on water availability and water use strategy. <i>Salix psammophila</i> used ground water during the growing season and relied on shallow soil water recharged by rain in summer. <i>Salix cheilophila</i> used ground water in spring and summer, but relied on shallow soil water recharged by rain in spring and deep soil water recharged by ground water in fall. The two shrubs had dimorphic root systems, which is coincident with their water use strategy. Higher biomass of fine roots in <i>S</i>. <i>psammophila</i> and longer fine roots in <i>S</i>. <i>cheilophila</i> facilitated to absorb water in deeper soil layers. The long-term water use efficiency of two <i>Salix</i> shrubs increased during the dry season in spring. The long-term water use efficiency was higher in <i>S</i>. <i>psammophila</i> than in <i>S</i>. <i>cheilophila</i>, as the former species is better adapted to semiarid climate of alpine sandy land.</p></div

Soil water content at different soil depth for <i>Salix psammophila</i> and <i>S</i>. <i>cheilophila</i>.

<p>Different lower case letters indicate significant difference in soil water content at different depths and at different time according to Duncan’s test (<i>P</i> < 0.05).</p

Water use ratio (%) of <i>Salix psammophila</i> for different sources (n = 4, mean ± SD).

<p>Water use ratio (%) of <i>Salix psammophila</i> for different sources (n = 4, mean ± SD).</p

The ratio value of δD and δ¹⁸O in xylem water of <i>Salix cheilophila</i>, soil water, and ground water.

<p>Full line is ground water. Dotted line is the precipitation of 6.4 mm that occurred on July 8. Hollow symbols are xylem water. Solid symbols are soil water.</p

Water use ratio (%) of <i>Salix cheilophila</i> for different sources (n = 4, mean ± SD).

<p>Water use ratio (%) of <i>Salix cheilophila</i> for different sources (n = 4, mean ± SD).</p

The value of δD and δ¹⁸O in xylem water of <i>Salix psammophila</i>, soil water, and ground water.

<p>Full line is ground water. Dotted line is the precipitation of 6.4 mm that occurred on July 8. Hollow symbols are xylem water. Solid symbols are soil water.</p

Root length density of <i>Salix psammophila</i> and <i>S</i>. <i>cheilophila</i> at different soil depth.

<p>Different lower case letters indicate significant difference in root length density at different soil depths according to Duncan’s test (<i>P</i> < 0.05).</p

Selective Release of Hydrophobic and Hydrophilic Cargos from Multi-Stimuli-Responsive Nanogels

Highly stable multi-stimuli-responsive nanogels for selective release of simultaneously encapsulated hydrophobic and hydrophilic cargos in a spatiotemporally controlled manner are demonstrated here. The nanogel is composed of hydrophilic pH- and thermoresponsive poly­(2-(dimethylamino)­ethyl methacrylate) (PDMAEMA) and hydrophobic photocleavable <i>o</i>-nitrobenzyl (ONB) linkage. The hydrophobic cargos were noncovalently encapsulated into lipophilic interiors of the nanogels, while the hydrophilic cargos were chemically linked to the nanogel precursor polymer PDMAEMA through a redox-cleavable disulfide junction. For these dual-loaded nanogels, hydrophobic cargos can be released in response to temperature, pH, and UV light, while the hydrophilic cargos can be released in response to redox reagent. The stimuli-selective release of hydrophobic and hydrophilic cargos affords the system with great potential applications in combination chemotherapy, tissue engineering, anticorrosion, and smart nanoreactors