Effects of monsoon precipitation variability on the physiological response of two dominant C₄ grasses across a semiarid ecotone

Life history response of Echinops gmelinii Turcz. to variation in the rainfall pattern in a temperate desert

BACKGROUND

Current and future changes in rainfall amount and frequency may particularly impact annual plants in desert ecosystems. The winter annual Echinops gmelinii Turcz. is widely distributed in the desert habitats of northern China and is a dominant pioneer annual plant following sand stabilization in the Tengger Desert. This species plays a vital role in dune stabilization during spring and early summer, when wind erosion is the most severe and frequent. However, seedling emergence and regeneration in sandy soil are mainly determined by rainfall patterns. Therefore, understanding the life history response of this species to rainfall variation is necessary for understanding the change of population dynamics under the future climate change.

METHODS

A field simulation rainfall pot experiment using rainout shelter was conducted that included five amounts and five frequencies of rainfall based on historical and predicted values to monitor the life history responses of E. gmelinii in a near-natural habitat.

RESULTS

We found that rainfall amount and frequency significantly affected seedling survival, growth and reproduction. The plant height, biomass, capitula number, seed number, seed mass and reproductive effort, but not the root/shoot ratio, significantly increased with increasing rainfall. Further, these traits exhibited the greatest response to low-frequency and larger rainfall events, especially the optimal rainfall frequency of 10-day intervals. Offspring seed germination showed increasing trends with decreasing rainfall, suggesting that the maternal effects may have occurred.

CONCLUSIONS

Our study shows that the plasticity in growth and reproduction of E. gmelinii in response to rainfall variations may help it to gain dominance in the harsh and unpredictable desert environment. Furthermore, population development of this winter annual species should be promoted under the likely future scenarios of large rainfall events and increasing cool-season precipitation in temperate desert.

Growth and Physiology of Two Psammophytes to Precipitation Manipulation in Horqin Sandy Land, Eastern China

The availability of water is the critical factor driving plant growth, physiological responses, population and community succession in arid and semiarid regions, thus a precipitation addition-reduction platform with five experimental treatments, was established to explore the growth and physiology of two psammophytes (also known as psammophiles) to precipitation manipulation in Horqin Sandy Land. Changes in coverage and density were measured, and antioxidant enzymes and osmoregulatory substances in both of the studied species were determined. Investigation results showed that the average vegetation coverage increased with an increasing precipitation, and reached a maximum in July. Under the −60% precipitation treatment, Tribulus terrestris accounted for a large proportion of the area, but Bassia dasyphylla was the dominant species in the +60% treatment. T. terrestris was found to have higher a drought stress resistance than B. dasyphylla. From days 4 to 7 after rainfall, B. dasyphylla under precipitation reduction showed obvious water stress. The malondialdehyde (MDA) content of B. dasyphylla was higher than that of T. terrestris, but that of B. dasyphylla had the lower relative water content (RWC). The MDA content in the precipitation reduction treatments of the two studied species was higher than that in the precipitation addition treatments from days 4 to 10. Peroxidase (POD) and superoxide dismutase (SOD) activity and the soluble proteins and free proline content of T. terrestris were higher than those of B. dasyphylla. The free proline content of T. terrestris and B. dasyphylla increased with increasing drought stress. Our data illustrated that T. terrestris had a higher drought stress resistance than B. dasyphylla, which was correlated with the augmentation of some antioxidant enzymes and osmoregulatory substance. The adaptive mechanism provides solid physiological support for an understanding of psammophyte adaptation to drought stress, and of community succession or species manipulation for desertified land restoration.

Small rainfall pulses affected leaf photosynthesis rather than biomass production of dominant species in semiarid grassland community on Loess Plateau of China

In the semiarid region Loess Plateau of China, rainfall events, typically characterised as pulses, affect photosynthesis and plant community characteristics. The response of dominant species and grassland community to rainfall pulses was evaluated through a simulation experiment with five pulse sizes (0, 5, 10, 20 and 30mm) in the semiarid Loess Plateau of China in June and August of 2013. The study was conducted in a natural grassland community dominated by Bothrichloa ischaemum (L.)Keng and Lespedeza davurica (Lax.) Schindl. In June, the leaf photosynthetic rate (Pn), transpiration rate, stomatal conductance, intercellular CO2 concentration of both species and soil water content increased rapidly after rainfall pulses. B. ischaemum was more sensitive to the pulses and responded significantly to 5mm rainfall, whereas L. davurica responded significantly only to rainfall events greater than 5mm. The magnitude and duration of the photosynthetic responses of the two species to rainfall pulse gradually increased with rainfall sizes. The maximum Pn of B. ischaemum appeared on the third day under 30mm rainfall, whereas for L. davurica it appeared on the second day under 20mm rainfall. Soil water storage (0-50cm) was significantly affected under 10, 20 and 30mm rainfall. Only large pulses (20, 30mm) increased community biomass production by 21.3 and 27.6% respectively. In August, the effect of rainfall on the maximum Pn and community characteristics was generally not significant. Rainfall pulses affected leaf photosynthesis because of a complex interplay between rainfall size, species and season, but might not induce a positive community-level feedback under changing rainfall patterns.

Eco-Physiological Responses of Dominant Species to Watering in a Natural Grassland Community on the Semi-Arid Loess Plateau of China

Altered precipitation regimes significantly affect ecosystem structure and function in arid and semi-arid regions. In order to investigate effects of precipitation changes on natural grassland community in the semi-arid Loess Plateau, the current research examined eco-physiological characteristics of two co-dominant species (i.e., Bothriochloa ischaemum and Lespedeza davurica) and community composition following two watering instances (i.e., precipitation pulses, July and August, 2011, respectively) in a natural grassland community. Results showed that the photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration rapidly increased on the first to third day following watering in both species, and both months. Under watering treatments, the maximum net photosynthetic rates appeared on the second to third day after watering, which increased 30-80% in B. ischaemum and 40-50% in L. davurica compared with non-watering treatments, respectively. Leaf water use efficiency kept stable or initially decreased in both species under watering treatments. Watering in July produced more promoting effects on grass photosynthesis than in August, particularly in B. ischaemum. Community above-ground biomass at the end of the growing season increased after watering, although no significant changes in species diversity were observed. Our results indicated that timing and magnitude of watering could significantly affect plant eco-physiological processes, and there were species-specific responses in B. ischaemum and L. davurica. Pulsed watering increased community productivity, while did not significantly alter community composition after one growing season. The outcomes of this study highlight eco-physiological traits in dominant species may playing important roles in reshaping community composition under altered precipitation regimes.