Effects of elevated CO2, warming and precipitation change on plant growth, photosynthesis and peroxidation in dominant species from North China grassland.

Warming, watering and elevated atmospheric CO2-concentration effects have been extensively studied separately; however, their combined impact on plants is not well understood. In the current research, we examined plant growth and physiological responses of three dominant species from the Eurasian Steppe with different functional traits to a combination of elevated CO2, high temperature, and four simulated precipitation patterns. Elevated CO2 stimulated plant growth by 10.8-41.7 % for a C3 leguminous shrub, Caragana microphylla, and by 33.2-52.3 % for a C3 grass, Stipa grandis, across all temperature and watering treatments. Elevated CO2, however, did not affect plant biomass of a C4 grass, Cleistogenes squarrosa, under normal or increased precipitation, whereas a 20.0-69.7 % stimulation of growth occurred with elevated CO2 under drought conditions. Plant growth was enhanced in the C3 shrub and the C4 grass by warming under normal precipitation, but declined drastically with severe drought. The effects of elevated CO2 on leaf traits, biomass allocation and photosynthetic potential were remarkably species-dependent. Suppression of photosynthetic activity, and enhancement of cell peroxidation by a combination of warming and severe drought, were partly alleviated by elevated CO2. The relationships between plant functional traits and physiological activities and their responses to climate change were discussed. The present results suggested that the response to CO2 enrichment may strongly depend on the response of specific species under varying patterns of precipitation, with or without warming, highlighting that individual species and multifactor dependencies must be considered in a projection of terrestrial ecosystem response to climatic change.

Intraspecific variation of a desert shrub species in phenotypic plasticity in response to sand burial.

Shoot elongation is one of the main plastic responses of plants to burial, a ubiquitous stress factor in dry ecosystems. Yet, intraspecific variation in this response to burial and the extent to which this variation is functionally coordinated with variation in other trait responses are largely unknown. We subjected seedlings of the shrub Caragana intermedia from 18 maternal parents (i.e. different half-sib families) to repeated partial burial to investigate how burial affects shoot growth, stem mechanical traits and associated plasticity. Burial increased both stem elongation and diameter growth of plants, but decreased biomass production. Half-sib families had different rates of shoot elongation, and differed in their response to burial with respect to biomechanical stem properties. Across half-sib families, the magnitude of these responses in mechanical traits was positively correlated with the magnitude of the stem elongation response. These results indicate that plasticity in different stem traits in response to sand burial and intraspecific variation therein are functionally coordinated with respect to mechanical stability. The results emphasize the importance of considering functionally coordinated traits when analyzing phenotypic plasticity in plants.

Different water use strategies of juvenile and adult Caragana intermedia plantations in the Gonghe Basin, Tibet Plateau.

BACKGROUND: In a semi-arid ecosystem, water is one of the most important factors that affect vegetation dynamics, such as shrub plantation. A water use strategy, including the main water source that a plant species utilizes and water use efficiency (WUE), plays an important role in plant survival and growth. The water use strategy of a shrub is one of the key factors in the evaluation of stability and sustainability of a plantation. METHODOLOGY/PRINCIPAL FINDINGS: Caragana intermedia is a dominant shrub of sand-binding plantations on sand dunes in the Gonghe Basin in northeastern Tibet Plateau. Understanding the water use strategy of a shrub plantation can be used to evaluate its sustainability and long-term stability. We hypothesized that C. intermedia uses mainly deep soil water and its WUE increases with plantation age. Stable isotopes of hydrogen and oxygen were used to determine the main water source and leaf carbon isotope discrimination was used to estimate long-term WUE. The root system was investigated to determine the depth of the main distribution. The results showed that a 5-year-old C. intermedia plantation used soil water mainly at a depth of 0-30 cm, which was coincident with the distribution of its fine roots. However, 9- or 25-year-old C. intermedia plantations used mainly 0-50 cm soil depth water and the fine root system was distributed primarily at soil depths of 0-50 cm and 0-60 cm, respectively. These sources of soil water are recharged directly by rainfall. Moreover, the long-term WUE of adult plantations was greater than that of juvenile plantations. CONCLUSIONS: The C. intermedia plantation can change its water use strategy over time as an adaptation to a semi-arid environment, including increasing the depth of soil water used for root growth, and increasing long-term WUE.

Responses to air temperature and soil moisture of growth of four dominant species on sand dunes of central Inner Mongolia.

Little attention has been paid to how four dominant shrub species distributed in semi-arid areas respond to the combined effects of temperature and water supply. Seedlings of four species were grown in a glasshouse for eight weeks at air temperatures of 12.5/22.5, 15/25, 17.5/27.5, and 20/30 degrees C (night/day) and with water supplies of 37.5, 75, 112.5, and 150 mm per month. When temperatures were 17.5/27.5 and 20/30 degrees C relative growth rate (RGR) decreased for Artemisia ordosica, A. sphaerocephala, and Hedysarum laeve but not for Caragana korshinskii. RGR increased with increasing water availability for all four species and most treatments. In response to changing water availability, the RGR tended to correlate mainly with the physiological trait (net assimilation rate, NAR) and with dry matter allocation traits (below-ground to above-ground dry matter and leaf mass ratio). A higher ratio of below to above-ground dry matter for all four species under most treatments (0.3-1.7) and water-use efficiency (1.4-9.2 g kg(-1)) may explain how all four species survive drought. Higher temperatures may be harmful to A. ordosica and A. sphaerocephala, under current precipitation levels (average 75 mm per month from mid-June to mid-August). These findings support the proposal that A. ordosica mixed with C. korshinskii will prove optimal for re-vegetation of degraded areas of the Ordos plateau.