Background
Caragana intermedia Kuanget H.C. Fu is a deciduous shrub of semi-arid northern China that occurs primarily in the country's Maowusu sandland, as well as parts of Inner Mongolia. The authors say it "is used by local people as feed for livestock, and as shelter for protection of soils (Zhang, 1994)." Specifically, they say "it is one of the dominant shrubs that fix soil and reduce wind speed, thus actively mitigating desertification."

What was done
Xiao et al. grew seedlings of C. intermedia for 3.5 months in 10-cm-diameter by 10-cm-deep pots filled with sand and maintained at three different water regimes - well-watered (60-70% field capacity), moderate-watered (45-55% field capacity) and drought-stressed (30-40% field capacity) - in greenhouse compartments maintained at atmospheric CO2 concentrations of either 350 or 700 ppm. Near the end of this period, they measured leaf water potentials and a number of different plant growth parameters.

What was learned
The five Chinese researchers report that "elevated CO2 significantly increased leaf water potential [so it became less negative, characteristic of a less-water-stressed condition, "especially at midday"], decreased specific leaf area [leaf area per leaf mass] and leaf area ratio [leaf area per total biomass] of drought-stressed seedlings, and increased tree height, basal diameter, shoot biomass, root biomass as well as total biomass ["by 79% under the well-watered condition, by 61% under moderate-watered condition, and by 53% under drought-stressed condition"] under all the three water regimes." In addition, they say that the Canopy Productivity Index (CPI, or total growth per unit leaf area) "was significantly increased by elevated CO2, and the increase in CPI became stronger as the level of drought stress increased."

What it means
Xiao et al. concluded that the results of their study "confirmed the beneficial effects of elevated CO2 on C. intermedia seedlings exposed to drought-stressed conditions," and that these findings "suggest that elevated CO2 may enhance drought avoidance and improved water relations, thus weakening the effect of drought stress on growth of C. intermedia seedlings," all of which phenomena should help to fight desertification in the Maowusu sandland of China and parts of Inner Mongolia as the air's CO2 content continues to rise.

Reference
Zhang, X.S. 1994. The ecological background of the Maowusu sandland: the principles and optimal models for grass land management. Acta Photoecologica Sinica 18: 1-6.