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Plant phenotypic plasticity is a common feature that is crucial for explaining interspecific competition, dynamics and biological evolution of plant communities. In this study, we tested the effects of soil CaCO3 (calcium carbonate) on the phenotypic plasticity of a psammophyte, Artemisia ordosica, an important plant species on sandy lands in arid and semi-arid areas of China, by performing pot experiments under different CaCO3 contents with a two-factor randomized block design and two orthogonal designs. We analyzed the growth responses (including plant height, root length, shoot-leaf biomass and root biomass) of A. ordosica seedlings to different soil CaCO3 contents. The results revealed that, with a greater soil CaCO3 content, A. ordosica seedlings gradually grew more slowly, with their relative growth rates of plant height, root length, shoot-leaf biomass and root biomass all decreasing significantly. Root N/P ratios showed significant negative correlations with the relative growth rates of plant height, shoot-leaf biomass and root length of A. ordosica seedlings; however, the relative growth rate of root length increased significantly with the root P concentration increased, showing a positive correlation. These results demonstrate that soil CaCO3 reduces the local P availability in soil, which produces a non-adaptive phenotypic plasticity to A. ordosica seedlings. This study should prove useful for planning and promoting the restoration of damaged/degraded vegetation in arid and semi-arid areas of China.

A dominant species of steppe in northern China, Stipa grandis, is gradually being replaced by S. krylovii due to climate change events. The aim of this study was to explore how conditioned soil, nitrogen (N) resource, and competitor influenced the responses of S. grandis and S. krylovii. We planted S. grandis and S. krylovii monoculture and mixture in each of four conditioned soils with two N treatments and analyzed which factor(s) significantly influenced the plant–soil feedbacks (PSFs), competitiveness, and N-addition effects of each species by general linear model univariate analysis. Competitor but not nitrogen significantly influenced PSFs of both S. grandis and S. krylovii. Compared with PSFs in monoculture, the negative PSFs of S. grandis were suppressed and PSFs of S. krylovii shifted from positive to negative in mixture. Competitor only significantly influenced the N-addition effects on S. krylovii; nitrogen only significantly influenced the competitiveness of S. krylovii. The highest competitiveness of S. krylovii was obtained in S. grandis conditioning soil with high N treatment. Compared with any of the other growth conditions, soil conditioned by S. grandis with high N treatment could increase S. krylovii’s competition superiority by increasing its competitiveness and N-addition effect.

Whether plants are able to adapt to environmental changes depends on their genetic characteristics and phenotypic plastic responses. We investigated the phenotypic responses of 7 populations of an important dominant species in semi-arid steppe of China - Stipa grandis, and then distinguished which adaptive mechanism(s), phenotypic plasticity or local adaptation, was/were involved in this species to adapt to environmental changes. (1) All traits were significantly influenced by the interaction of population and growth condition and by population in each condition, and inter-population variability (CVinter) was larger in the field than in the common garden for 8/9 traits, indicating that both phenotypic plasticity and genetic differentiation controlled the phenotypic differences of S. grandis. (2) From a functional standpoint, the significant relationships between the values of traits in the common garden and the environmental variables in their original habitats couldn’t support local habitat adaptation of these traits. (3) Low CVintra, low quantitative differentiation among populations (Q ST ), and low plasticity shown in the western populations indicated the very low adaptive potential of S. grandis to environmental changes. (4) From the original habitats to the common garden which is far away from S. grandis distribution region, positive phenotypic responses were found in several populations, indicating that some original habitats have become unfavorable for S. grandis.

Switching expansion reduction (SER) uses a switch valve instead of the throttle valve to realize electronically controlled pressure reduction for high pressure pneumatics. A comprehensive and interactive pneumatic simulation model according to the experimental setup of SER has been built. The mathematical model considers heat exchanges, source air pressure and temperature, environmental temperatures and heat transfer coefficients variations. In addition, the compensation for real gas effect is used in the model building. The comparison between experiments and simulations of SER indicates that, to compensate the real gas effect in high pressure discharging process, the thermal capacity of air supply container in simulation should be less than the actual value. The higher the pressure range, the greater the deviation. Simulated and experimental results are highly consistent within pressure reduction ratios ranging from 1.4 to 20 and output air mass flow rates ranging from 3.5 to 132 g/s, which verifies the high adaptability of SER and the validity of the mathematic model and the compensation method.

The effect of infection by the fungal endophyte Neotyphodium, host genotype, and their interaction on growth and physiology, as well as photosynthesis, was investigated in the native grass Achnatherum sibiricum. We artificially inoculated the endophyte into mature tillers of endophyte-free A. sibiricum. Plants were clipped to 5 cm height after recording growth traits, and analyzed for total nonstructural carbohydrates (TNC %), the percentage of nitrogen (N %), and carbon (C %) in leaves before and after clipping. In our study, the prominent host genotype–endophyte infection interactions detected in A. sibiricum indicates that, for many growth and storage traits, endophyte infection can impact a little change. However, there is no overriding consistently positive effect of the endophyte on growth or storage in A. sibiricum before or after clipping. Our study showed that the interaction between endophyte and host grasses was highly contingent on plant genotypes. We found host genotype overrode fungal endophyte infection in influencing tiller number and photosynthetic properties of A. sibiricum before clipping. After clipping, host genotype accounted for more of the variation in regrowth and above-ground biomass of A. sibiricum than endophyte infection. Our study showed that host genotype affected the total nonstructural carbohydrates of A. sibiricum before and after clipping, whereas endophyte infection increased the carbon content after clipping. Genotype by infection interactions for plant height, leaf mass, total nonstructural carbohydrates, and photosynthetic characteristics indicated genotype-specific effects of endophytes on A. sibiricum physiology and photosynthetic capacity. The host genotype–endophyte infection interactions detected in A. sibiricum suggest that host genotype overrides fungal endophyte infection on growth, physiology, and nutrient content of this native grass. In contrast, endophyte effects did not appear to positively affect growth, physiology, or photosynthetic capacity before or after clipping.

Disturbance can affect biomass allocation of plants, but can it influence plant reproductive behavior? To address this issue, we performed field plant community investigations and explored the reproductive behaviors of Stipa grandis and Stipa krylovii in response to grazing and mowing treatments at Maodeng pasture of Xilinguole League of Inner Mongolia, China during 2007–2009. The results showed that, with a similar niche width for the two plant species under mowing and grazing treatments, mowing significantly increased the ratio of ramet to genet number of S. krylovii and the carbon to nitrogen ratio of S. grandis, and grazing significantly decreased the ratio of vegetative to reproductive tiller biomass of S. grandis and increased the ratio of vegetative to reproductive tiller number of S. krylovii. Regression analysis showed that the significantly positive effect of root to shoot biomass ratio was stronger on the ratio of vegetative to reproductive tiller number of S. grandis than on that of S. krylovii. These results indicated that grazing and mowing influenced the reproductive manner and the process of sexual reproduction of S. grandis and S. krylovii.

There has been a dramatic shift in dominance from Stipa grandis communities to S. krylovii communities in the Inner Mongolia steppe of China, in recent decades due to climate change and human activity. We examined the growth and carbohydrate allocation pattern of S. grandis and S. krylovii under controlled conditions. The experimental approach involved a drought stress treatment and a simulated defoliation (clipping) treatment of both species. Growth (above ground biomass and root biomass) and carbon allocation (concentration of leaf total phenolics and pool of total non-structural carbohydrate) variables were evaluated at the end of the experiment. Responses to drought stress differed significantly between S. grandis and S. krylovii. For S. krylovii, growth and the pool of total non-structural carbohydrate were more negatively affected by drought stress, whereas concentration of total phenolics was positively affected. Drought stress reinforced responses to defoliation, and drought stress × defoliation interaction was significant for all of the variables. There was a distinct defoliation response level for growth after drought stress between the two species. For aboveground biomass, both species responded positively to drought stress, which changed from responses equivalence to S. krylovii being superior; for root biomass, the two species responded oppositely to drought stress, which changed from S. grandis being superior to S. krylovii being superior. There was a weak and reverse defoliation response level for the carbon allocation pattern after drought stress between the two species, with S. krylovii changing from superior in defense to superior in storage. These results suggested that S. grandis utilized an avoidance strategy (investment in defense compounds) and S. krylovii utilized a tolerance strategy (investment in storage for regrowth) in response to defoliation under drought stress, supporting the idea that stress-tolerant species may become the new dominant species because of their ability to re-grow after disturbance. This provided a possible explanation for the replacement of S. grandis communities from the view point of adaptive strategy.

Nutrient nitrogen and water availability are co-limiting factors for grassland productivity in the Inner Mongolian steppe. The objective of this study was to evaluate the interactive effects of water and nitrogen (N) addition on soil abiotic factors and soil nematode community composition. A 3-year experiment with addition of water (with and without irrigation simulating wet year precipitation) and nitrogen (0, 25, and 50 kg N ha−1) was conducted at two sites in Inner Mongolia with histories of heavy grazing (HG) and moderate grazing (MG). The results showed that HG had several lower nematode ecological indicators; namely, the Simpson index (P

Symbiotic relationships with microbes may influence how plants respond to environmental change. Here, we investigated how fungal endophyte infection affected the growth of a native grass under altered water and nutrient availability. In a two-month field experiment, we compared the performance of endophyte-infected (EI) and endophyte-free (EF) Achnatherum sibiricum subjected to four treatments comprised of a factorial combination of two levels of water availability and two levels of fertilization. The greatest benefits of endophyte infection occurred in the well-watered fertilized treatment. With reduced water and/or nutrient availability, the benefits declined. EI plants subjected to drought and fertilization had higher root:shoot ratios and allocated more nitrogen to photosynthetic machinery and thus had a higher net photosynthetic rate than EF counterparts. In the well-watered unfertilized treatment, EF plants allocated more nutrients to photosynthetic machinery, while EI plants allocated more resources to defense. Thus EI plants were superior to EF plants in terms of nutrient conservation. In the drought unfertilized treatment, no significant difference occurred between EI and EF plants. Our results support the idea that the endophyte-grass interactions are dependent on available resources. However, we did not find a clear cost of endophyte infection. For A. sibiricum, fertilizer addition resulted in greater benefits of the symbiosis for plant growth, but this advantage decreased under drought.