Hideyuki Shimizu

Plant responses to drought and rewatering

Plants would be more vulnerable to water stress and thereafter rewatering or a cycled water environmental change, which occur more frequently under climatic change conditions in terms of the prediction scenarios. Effects of water stress on plants alone have been well-documented in many reports. However, the combined responses to drought and rewatering and its mechanism are relatively scant. As we known, plant growth, photosynthesis and stomatal aperture may be limited under water deficit, which would be regulated by physical and chemical signals. Under severe drought, while peroxidation may be provoked, the relevant antioxidant metabolism would be involved to annihilate the damage of reactive oxygen species. As rewatering, the recoveries of plant growth and photosynthesis would appear immediately through growing new plant parts, re-opening the stomata, and decreasing peroxidation; the recovery extents (reversely: pre-drought limitation) due to rewatering strongly depend on pre-drought intensity, duration and species. Understanding how plants response to episodic drought and watering pulse and the underlying mechanism is remarkably helpful to implement vegetation management practices in climatic changing.

Are plant growth and photosynthesis limited by pre-drought following rewatering in grass?

Although the relationship between grassland productivity and soil water status has been extensively researched, the responses of plant growth and photosynthetic physiological processes to long-term drought and rewatering are not fully understood. Here, the perennial grass (Leymus chinensis), predominantly distributed in the Euro-Asia steppe, was used as an experimental plant for an irrigation manipulation experiment involving five soil moisture levels [75–80, 60–75, 50–60, 35–50, and 25–35% of soil relative water content (SRWC), i.e. the ratio between present soil moisture and field capacity] to examine the effects of soil drought and rewatering on plant biomass, relative growth rate (RGR), and photosynthetic potential. The recovery of plant biomass following rewatering was lower for the plants that had experienced previous drought compared with the controls; the extent of recovery was proportional to the intensity of soil drought. However, the plant RGR, leaf photosynthesis, and light use potential were markedly stimulated by the previous drought, depending on drought intensity, whereas stomatal conductance (gs) achieved only partial recovery. The results indicated that gs may be responsible for regulating actual photosynthetic efficiency. It is assumed that the new plant growth and photosynthetic potential enhanced by pre-drought following rewatering may try to overcompensate the great loss of the plants net primary production due to the pre-drought effect. The present results highlight the episodic effects of drought on grass growth and photosynthesis. This study will assist in understanding how degraded ecosystems can potentially cope with climate change.

Interactive effects of elevated CO2, Drought, and warming on plants

Adverse climate change attributed to elevated atmospheric carbon dioxide concentration (CO2) and increased temperature components of global warming has been a central issue affecting economic and social development. Climate change, particularly global warming, imposes a severe impact on the terrestrial ecosystem. Elevated CO2, drought, and high temperature have been extensively documented individually; however, relatively little is known about how plants respond to the interaction of these factors. To summarize current knowledge on the response of plants to global change factors, we focus on the interactive effects of CO2 enrichment, warming, and drought on plant growth, carbon allocation, and photosynthesis. Stimulation due to elevated CO2 might be suppressed under other negative climatic/environmental stresses such as drought, high temperature, and their combination. However, elevated CO2 could alleviate deleterious effects of moderate drought via reducing stomatal conductance, altering leaf surface, and regulating gene expression. High CO2 levels and rising temperatures may result in opposite responses in plant water use efficiency. Stimulation of plant growth due to elevated CO2 for C3 species occurs regardless of water conditions, but only under a water deficit for C4 species. The positive effect of elevated CO2 on C4 species is derived mainly from the improved water status. Plant adaptive or maladaptive responses to multivariate environments are interactive; thus, researchers need to explore the ecological underpinnings involved in such responses to the multiple factors involved in climate change.

Germination responses of Caragana korshinskii Kom. to light, temperature and water stress

Caragana korshinskii Kom. is a very important shrub species for vegetation rehabilitation in northern China for its high ecological and economic values. Experiments were conducted to determine its germination responses to (i) different temperature regimes under light and/or dark conditions, (ii) different light intensities, and (iii) different water potentials combined with varied constant temperatures. Under alternating temperatures (from 5:15 to 25:35°C), final percent germinations of Caragana korshinskii were quite similar. In dark conditions, constant temperatures resulted in lower final percent germinations than alternating temperatures. At a controlled temperature regime of 10:20°C, neither final percent germinations nor germination rates showed significant differences among varied light intensities. As water potentials were reduced from 0 (distilled water) to −0.6 MPa, final percent germinations increased slightly and reached the peak at approximately −0.6 MPa, however, the increment was not significant. Beyond −0.6 MPa, further water potential reduction led to decreased final percent germinations and few seeds could germinate at −1.4 MPa. Water stress also strongly inhibited germination at very high or low temperatures. The experimental results suggested that middle May might be a suitable time for aerial seeding for this species.

Strong light inhibits germination of Artemisia sphaerocephala and A. ordosica at low temperature and its relevance to revegetation in sandy lands of Inner Mongolia, China

Artemisia sphaerocephala and A. ordosica are two dominant shrub species in Mu Us sandy land (Inner Mongolia, China) and are widely used for vegetation restoration. However, there are two different conclusions about the effect of light on their germination: light promotes germination versus light inhibits germination. The aim of this study was to evaluate these two conclusions and relate the results to instances of failure of these two species to germinate well when air-dispersed in revegetation projects. The effects of fluctuating temperature, light/dark, source (population), position on mother plant, storage condition, and storage time were tested on germination of achenes of these two species. At low temperature, final percent germination (FPG) of achenes in dark and nearly dark conditions was significantly higher than those in light. At 10:20°C, achenes of both A. sphaerocephala and A. ordosica had higher FPG in dark than in light regardless of source, position on mother plants or storage condition. At suboptimum (5:15°C) and supraoptimal (25:35°C) temperatures, germination of A. sphaerocephala and A. ordosica achenes was inhibited in both light and darkness. It was concluded that light inhibits germination of A. sphaerocephala and A. ordosica achenes at low (10:20°C) temperature but not at high (15:25°C) temperature. Since the temperature in Mu Us sandy land is around 10:20°C in early June, when air sowing is done, achenes should germinate best when they are covered by a thin layer of sand.

Major activities of acid deposition monitoring network in East Asia (EANET) and related studies

In order to act against acid deposition problems in East Asian regions, the Acid Deposition Monitoring Network in East Asia (EANET) was established on the decision at the First Intergovernmental Meeting in 1998 among participating countries including China, Indonesia, Japan, Malaysia, Mongolia, Philippines, Republic of Korea, Russia, Thailand and Viet Nam. Based on the decision, the preparatory phase activities of EANET were started from 1998, and finished successfully in 2000. From January 2001, the regular phase activities were started. Major activities of EANET are, 1) to implement the national monitoring of acid deposition, 2) to develop and implement the QA/QC (quality assurance/quality control) programs, 3) to develop and implement training programs, etc. The acid deposition monitoring covers four environmental media; wet deposition, dry deposition, soil and vegetation, and inland aquatic environment.

A recipe for sustainable agriculture in drylands.

About 47% of the earth’s land area is classified as dryland, wherein the farming system is characterized by an annual rainfall of approximately 300 – 500mm, with much of the rainfall in the spring and early summer. The low rainfall, which is not only insufficient but irregular, constitutes a major challenge to profitable farming in dry areas. Meeting this challenge in the years ahead will require a more sustainable product per unit area of land, conservation and rational use of natural resources, protection of the environment, improved management practices, cost-effective technologies, and favorable government policies and incentives for farmers to increase their productivity. In this review, we discuss the major ingredients essential for sustainable dryland agriculture which include: efficient use of water, seeding at rates corresponding to the soil water supply, management practices that minimize water loss and soil erosion, managing soil fertility and organic matter, selection of suitable crop species and management of pests. We conclude that an approach integrating scientific technologies with indigenous farming methods offers the best hope for sustainable agriculture in the drylands of the world.

A model system to study the effect of SO2 on plant cells. II: Effect of sulfite on fern spore germination and rhizoid development

Fumigation with 0.05 μl/l SO2 decreased the germination rate of fern spores ofAdiantum capillus-veneris L. and influenced greatly the rhizoid development for abnormities such as apical swelling. Even 10 μM sulfite derived from SO2 fumigation was influential. These SO2 effects on germination and following rhizoid development were proved to be independent of each other, and could be induced separately by pulse treatment with K2SO3 solution given at different timings. According to the analysis using a time-lapse video recorder, growth retardation and apical swelling of rhizoid occurred just after the application of sulfite. It became clear that the fern gametophytes are very sensitive to SO2, (that is sulfite) as compared with other plants used for air pollutant experiments so far.

Persistence of four dominant psammophyte species in central Inner Mongolia of China under continual drought

Clarifying the persistence time of seedlings of dominant species under continual drought will help us understand responses of ecosystems to global climate change and improve revegetation efforts. Drought tolerance of four dominant psammophytic shrub species occurring in different environments was studied in the semi-arid areas of Inner Mongolian grasslands. Seedlings of Hedysarum laeve, Caragana korshinskii, Artemisia sphaerocephala and Artemisia ordosica were grown under four air temperature regimes (night/day: 12.5/22.5°C, 15/25°C, 17.5/27.5°C and 20/30°C) within climate (air temperature and humidity) controlled, naturally lit glasshouses with a night/day relative humidity of 70%/50%. Pots were watered to field capacity for each temperature treatment. Soil water condition was monitored by weighting each pot every day using an electronic balance. Date of seedling death for each treatment was recorded and the dead plants were harvested. Plant dry weights were determined after oven drying at 80°C for 3 days. Two Artemisia species had higher growth rates than H. laeve and C. korshinskii, and the growth of all four species increased with increasing temperatures. The two Artemisia species had the highest leaf biomass increment, followed by C. korshinskii, and then H. laeve. Shoot biomass increment was higher for A. ordosica and C. korshinskii, intermediate for A. sphaerocephala and lowest for H. laeve. C. korshinskii had the highest root biomass increment. The final soil water content at death for all four species varied from 1% to 2%. C. korshinskii, A. sphaerocephala, H. laeve and A. ordosica survived for 25–43, 24–41, 26–41, and 24–37 days without watering, respectively. C. korshinskii, A. sphaerocephala, H. Laeve, and A. ordosica seedlings survived longer at the lowest temperatures (12.5/22.5°C) than at the highest temperatures (20/30°C) by 18, 17, 15 and 13 days, respectively. Increased climatic temperatures induce the death of seedlings in years with long intervals between rainfall events. The adaptation of seedlings to droughts should be emphasized in revegetation efforts in the Ordos Plateau, Inner Mongolia.

Land degradation and blown-sand disaster in China

China is a country with severe land degradation and blown sand disasters. The arid and semi-arid regions, in which land desiccation, vegetation degeneration, wind erosion, sandification, Gobi-pebblization and salinization occur, take up one third of China’s total land area. Vegetation degradation is most serious in lower flood plains of the inland rivers and the semi-arid Agro-pastoral Ecotone due to excessive use of water resources, grassland reclamation, overgrazing and collection of firewood and herbal medicines. Wind erosion features are common around terminal dry lakes, in inland-river fluvial plains, and the semi-arid dry grasslands. Studies by the methods of aeolian sand transport, soil texture analysis, 137Cs tracing and archaeology confirmed that the rate of wind erosion is normally between 1000 to 2000 ton km−1 a−1. The gravel Gobi on Mongolian Plateau has been formed to a large degree by wind erosion. The severity of sandification has been manifested by the twelve sandy deserts and lands occupying 710, 000 km2, and the enlargement of sandy land at increasing spreading rates in the past three decades. Salinization has not received enough public attention yet, but soil salinization in Ningxia and Hetao Plains and dry lake basins is unfavorable for crop growth and natural vegetation. Salinization of surface water and ground water in the lower reaches of most inland rivers restricts utilization of insufficient water resources. The exacerbation of sand and dust storms disasters is the ultimate outcome of desertification in China.